Proton Transfer Dynamics at the Membrane/Water Interface: Dependence on the Fixed and Mobile pH Buffers, on the Size and Form of Membrane Particles, and on the Interfacial Potential Barrier

PubMed Central

Cherepanov, Dmitry A.; Junge, Wolfgang; Mulkidjanian, Armen Y.

2004-01-01

Crossing the membrane/water interface is an indispensable step in the transmembrane proton transfer. Elsewhere we have shown that the low dielectric permittivity of the surface water gives rise to a potential barrier for ions, so that the surface pH can deviate from that in the bulk water at steady operation of proton pumps. Here we addressed the retardation in the pulsed proton transfer across the interface as observed when light-triggered membrane proton pumps ejected or captured protons. By solving the system of diffusion equations we analyzed how the proton relaxation depends on the concentration of mobile pH buffers, on the surface buffer capacity, on the form and size of membrane particles, and on the height of the potential barrier. The fit of experimental data on proton relaxation in chromatophore vesicles from phototropic bacteria and in bacteriorhodopsin-containing membranes yielded estimates for the interfacial potential barrier for H+/OH− ions of ∼120 meV. We analyzed published data on the acceleration of proton equilibration by anionic pH buffers and found that the height of the interfacial barrier correlated with their electric charge ranging from 90 to 120 meV for the singly charged species to >360 meV for the tetra-charged pyranine. PMID:14747306

Surface-enhanced Raman spectroscopy study on the structure changes of 4-Mercaptophenylboronic Acid under different pH conditions

NASA Astrophysics Data System (ADS)

Su, Hongyang; Wang, Yue; Yu, Zhi; Liu, Yawen; Zhang, Xiaolei; Wang, Xiaolei; Sui, Huimin; Sun, Chengbin; Zhao, Bing

2017-10-01

4-Mercaptophenylboronic Acid (4-MPBA) plays pivotal role in various fields. The orientation and existing form of the 4-MPBA strongly depend on the pH value of the media. The general aim of this work is to obtain information about the structure changes of 4-MPBA absorbed on Ag nanoparticles in different pH environment. Surface-enhanced Raman spectroscopy (SERS) technique is a simple and rapid method to study adsorption phenomena at molecule level. The investigation is done by means of SERS. In order to interpret the experimental information, a series of SERS spectra is carried out. The relative intensities of the totally symmetric (a1 mode) and non-totally symmetric (b2 mode) bands in the SERS spectra of 4-MPBA change depend on the environmental pH values, which is a manifestation of charge transfer (CT) processes. The degree of charge transfer increases with the pH value of the media changing from acidity to alkalinity. The structure changes of MPBA had been carried out in different pH environment. We envision that this approach will be of great significance in related fields of 4-MPBA-involved detection.

Influence of surface charge on the rate, extent, and structure of adsorbed Bovine Serum Albumin to gold electrodes.

PubMed

Beykal, Burcu; Herzberg, Moshe; Oren, Yoram; Mauter, Meagan S

2015-12-15

The objective of this work is to investigate the rate, extent, and structure of amphoteric proteins with charged solid surfaces over a range of applied potentials and surface charges. We use Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring (E-QCM-D) to investigate the adsorption of amphoteric Bovine Serum Albumin (BSA) to a gold electrode while systematically varying the surface charge on the adsorbate and adsorbent by manipulating pH and applied potential, respectively. We also perform cyclic voltammetry-E-QCM-D on an adsorbed layer of BSA to elucidate conformational changes in response to varied applied potentials. We confirm previous results demonstrating that increasing magnitude of applied potential on the gold electrode is positively correlated with increasing mass adsorption when the protein and the surface are oppositely charged. On the other hand, we find that the rate of BSA adsorption is not governed by simple electrostatics, but instead depends on solution pH, an observation not well documented in the literature. Cyclic voltammetry with simultaneous E-QCM-D measurements suggest that BSA protein undergoes a conformational change as the surface potential varies. Copyright © 2015 Elsevier Inc. All rights reserved.

Measurements and theoretical interpretation of points of zero charge/potential of BSA protein.

PubMed

Salis, Andrea; Boström, Mathias; Medda, Luca; Cugia, Francesca; Barse, Brajesh; Parsons, Drew F; Ninham, Barry W; Monduzzi, Maura

2011-09-20

The points of zero charge/potential of proteins depend not only on pH but also on how they are measured. They depend also on background salt solution type and concentration. The protein isoelectric point (IEP) is determined by electrokinetical measurements, whereas the isoionic point (IIP) is determined by potentiometric titrations. Here we use potentiometric titration and zeta potential (ζ) measurements at different NaCl concentrations to study systematically the effect of ionic strength on the IEP and IIP of bovine serum albumin (BSA) aqueous solutions. It is found that high ionic strengths produce a shift of both points toward lower (IEP) and higher (IIP) pH values. This result was already reported more than 60 years ago. At that time, the only available theory was the purely electrostatic Debye-Hückel theory. It was not able to predict the opposite trends of IIP and IEP with ionic strength increase. Here, we extend that theory to admit both electrostatic and nonelectrostatic (NES) dispersion interactions. The use of a modified Poisson-Boltzmann equation for a simple model system (a charge regulated spherical colloidal particle in NaCl salt solutions), that includes these ion specific interactions, allows us to explain the opposite trends observed for isoelectric point (zero zeta potential) and isoionic point (zero protein charge) of BSA. At higher concentrations, an excess of the anion (with stronger NES interactions than the cation) is adsorbed at the surface due to an attractive ionic NES potential. This makes the potential relatively more negative. Consequently, the IEP is pushed toward lower pH. But the charge regulation condition means that the surface charge becomes relatively more positive as the surface potential becomes more negative. Consequently, the IIP (measuring charge) shifts toward higher pH as concentration increases, in the opposite direction from the IEP (measuring potential). © 2011 American Chemical Society

Probing the Surface Charge on the Basal Planes of Kaolinite Particles with High-Resolution Atomic Force Microscopy

PubMed Central

2017-01-01

High-resolution atomic force microscopy is used to map the surface charge on the basal planes of kaolinite nanoparticles in an ambient solution of variable pH and NaCl or CaCl2 concentration. Using DLVO theory with charge regulation, we determine from the measured force–distance curves the surface charge distribution on both the silica-like and the gibbsite-like basal plane of the kaolinite particles. We observe that both basal planes do carry charge that varies with pH and salt concentration. The silica facet was found to be negatively charged at pH 4 and above, whereas the gibbsite facet is positively charged at pH below 7 and negatively charged at pH above 7. Investigations in CaCl2 at pH 6 show that the surface charge on the gibbsite facet increases for concentration up to 10 mM CaCl2 and starts to decrease upon further increasing the salt concentration to 50 mM. The increase of surface charge at low concentration is explained by Ca2+ ion adsorption, while Cl– adsorption at higher CaCl2 concentrations partially neutralizes the surface charge. Atomic resolution imaging and density functional theory calculations corroborate these observations. They show that hydrated Ca2+ ions can spontaneously adsorb on the gibbsite facet of the kaolinite particle and form ordered surface structures, while at higher concentrations Cl– ions will co-adsorb, thereby changing the observed ordered surface structure. PMID:29140711

Probing the Surface Charge on the Basal Planes of Kaolinite Particles with High-Resolution Atomic Force Microscopy.

PubMed

Kumar, N; Andersson, M P; van den Ende, D; Mugele, F; Siretanu, I

2017-12-19

High-resolution atomic force microscopy is used to map the surface charge on the basal planes of kaolinite nanoparticles in an ambient solution of variable pH and NaCl or CaCl 2 concentration. Using DLVO theory with charge regulation, we determine from the measured force-distance curves the surface charge distribution on both the silica-like and the gibbsite-like basal plane of the kaolinite particles. We observe that both basal planes do carry charge that varies with pH and salt concentration. The silica facet was found to be negatively charged at pH 4 and above, whereas the gibbsite facet is positively charged at pH below 7 and negatively charged at pH above 7. Investigations in CaCl 2 at pH 6 show that the surface charge on the gibbsite facet increases for concentration up to 10 mM CaCl 2 and starts to decrease upon further increasing the salt concentration to 50 mM. The increase of surface charge at low concentration is explained by Ca 2+ ion adsorption, while Cl - adsorption at higher CaCl 2 concentrations partially neutralizes the surface charge. Atomic resolution imaging and density functional theory calculations corroborate these observations. They show that hydrated Ca 2+ ions can spontaneously adsorb on the gibbsite facet of the kaolinite particle and form ordered surface structures, while at higher concentrations Cl - ions will co-adsorb, thereby changing the observed ordered surface structure.

Charging Properties of Cassiterite (alpha-SnO2) Surfaces in NaCl and RbCl Ionic Media.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenqvist, Jorgen K; Machesky, Michael L.; Vlcek, Lukas

2009-01-01

The acid-base properties of cassiterite ({alpha}-SnO{sub 2}) surfaces at 10-50 C were studied using potentiometric titrations of powder suspensions in aqueous NaCl and RbCl media. The proton sorption isotherms exhibited common intersection points in the pH range of 4.0-4.5 under all conditions, and the magnitude of charging was similar but not identical in NaCl and RbCl. The hydrogen bonding configuration at the oxide-water interface, obtained from classical molecular dynamics (MD) simulations, was analyzed in detail, and the results were explicitly incorporated in calculations of protonation constants for the reactive surface sites using the revised MUSIC model. The calculations indicated thatmore » the terminal SnOH{sub 2} group is more acidic than the bridging Sn{sub 2}OH group, with protonation constants (log K{sub H}) of 3.60 and 5.13 at 25 C, respectively. This is contrary to the situation on the isostructural {alpha}-TiO{sub 2} (rutile), apparently because of the difference in electronegativity between Ti and Sn. MD simulations and speciation calculations indicated considerable differences in the speciation of Na{sup +} and Rb{sup +}, despite the similarities in overall charging. Adsorbed sodium ions are almost exclusively found in bidentate surface complexes, whereas adsorbed rubidium ions form comparable numbers of bidentate and tetradentate complexes. Also, the distribution of adsorbed Na{sup +} between the different complexes shows a considerable dependence on the surface charge density (pH), whereas the distribution of adsorbed Rb{sup +} is almost independent of pH. A surface complexation model (SCM) capable of accurately describing both the measured surface charge and the MD-predicted speciation of adsorbed Na{sup +}/Rb{sup +} was formulated. According to the SCM, the deprotonated terminal group (SnOH{sup -0.40}) and the protonated bridging group (Sn{sub 2}OH{sup +0.36}) dominate the surface speciation over the entire pH range of this study (2.7-10). The complexation of medium cations increases significantly with increasing negative surface charge, and at pH 10, roughly 40% of the terminal sites are predicted to form cation complexes, whereas anion complexation is minor throughout the studied pH range.« less

Quantification of surface charge density and its effect on boundary slip.

PubMed

Jing, Dalei; Bhushan, Bharat

2013-06-11

Reduction of fluid drag is important in the micro-/nanofluidic systems. Surface charge and boundary slip can affect the fluid drag, and surface charge is also believed to affect boundary slip. The quantification of surface charge and boundary slip at a solid-liquid interface has been widely studied, but there is a lack of understanding of the effect of surface charge on boundary slip. In this paper, the surface charge density of borosilicate glass and octadecyltrichlorosilane (OTS) surfaces immersed in saline solutions with two ionic concentrations and deionized (DI) water with different pH values and electric field values is quantified by fitting experimental atomic force microscopy (AFM) electrostatic force data using a theoretical model relating the surface charge density and electrostatic force. Results show that pH and electric field can affect the surface charge density of glass and OTS surfaces immersed in saline solutions and DI water. The mechanisms of the effect of pH and electric field on the surface charge density are discussed. The slip length of the OTS surface immersed in saline solutions with two ionic concentrations and DI water with different pH values and electric field values is measured, and their effects on the slip length are analyzed from the point of surface charge. Results show that a larger absolute value of surface charge density leads to a smaller slip length for the OTS surface.

Exploring the Relationship between Structural and Air-Water Interfacial Properties of Wheat (Triticum aestivum L.) Gluten Hydrolysates in a Food System Relevant pH Range.

PubMed

Wouters, Arno G B; Fierens, Ellen; Rombouts, Ine; Brijs, Kristof; Joye, Iris J; Delcour, Jan A

2017-02-15

The relationship between structural and foaming properties of two tryptic and two peptic wheat gluten hydrolysates was studied at different pH conditions. The impact of pH on foam stability (FS) of the samples heavily depended on the peptidase used and the degree of hydrolysis reached. Surface dilatational moduli were in most, but not all, instances related to FS, implying that, although the formation of a viscoelastic protein hydrolysate film is certainly important, this is not the only phenomenon that determines FS. In contrast to what might be expected, surface charge was not a major factor contributing to FS, except when close to the point-of-zero-charge. Surface hydrophobicity and intrinsic fluorescence measurements suggested that changes in protein conformation take place when the pH is varied, which can in turn influence foaming. Finally, hydrolyzed gluten proteins formed relatively large particles, suggesting that protein hydrolysate aggregation probably influences its foaming properties.

Electrochemical modelling of QD-phospholipid interactions.

PubMed

Zhang, Shengwen; Chen, Rongjun; Malhotra, Girish; Critchley, Kevin; Vakurov, Alexander; Nelson, Andrew

2014-04-15

The aggregation of quantum dots (QDs) and capping of individual QDs affects their activity towards biomembrane models. Electrochemical methods using a phospholipid layer on mercury (Hg) membrane model have been used to determine the phospholipid monolayer activity of thioglycollic acid (TGA) coated quantum dots (QDs) as an indicator of biomembrane activity. The particles were characterised for size and charge. The activity of the QDs towards dioleoyl phosphatidylcholine (DOPC) monolayers is pH dependent, and is most active at pH 8.2 within the pH range 8.2-6.5 examined in this work. This pH dependent activity is the result of increased particle aggregation coupled to decreasing surface charge emanating from the TGA carboxylic groups employed to stabilize the QD dispersion in aqueous media. Capping the QDs with CdS/ZnS lowers the particles' activity to phospholipid monolayers. Copyright © 2014 Elsevier Inc. All rights reserved.

Partial oxidation of step-bound water leads to anomalous pH effects on metal electrode step-edges

DOE PAGES

Schwarz, Kathleen; Xu, Bingjun; Yan, Yushan; ...

2016-05-26

The design of better heterogeneous catalysts for applications such as fuel cells and electrolyzers requires a mechanistic understanding of electrocatalytic reactions and the dependence of their activity on operating conditions such as pH. A satisfactory explanation for the unexpected pH dependence of electrochemical properties of platinum surfaces has so far remained elusive, with previous explanations resorting to complex co-adsorption of multiple species and resulting in limited predictive power. This knowledge gap suggests that the fundamental properties of these catalysts are not yet understood, limiting systematic improvement. In this paper, we analyze the change in charge and free energies upon adsorptionmore » using density-functional theory (DFT) to establish that water adsorbs on platinum step edges across a wide voltage range, including the double-layer region, with a loss of approximately 0.2 electrons upon adsorption. We show how this as-yet unreported change in net surface charge due to this water explains the anomalous pH variations of the hydrogen underpotential deposition (H upd) and the potentials of zero total charge (PZTC) observed in published experimental data. This partial oxidation of water is not limited to platinum metal step edges, and we report the charge of the water on metal step edges of commonly used catalytic metals, including copper, silver, iridium, and palladium, illustrating that this partial oxidation of water broadly influences the reactivity of metal electrodes.« less

Vibrational spectroscopic study of pH dependent solvation at a Ge(100)-water interface during an electrode potential triggered surface termination transition

NASA Astrophysics Data System (ADS)

Niu, Fang; Rabe, Martin; Nayak, Simantini; Erbe, Andreas

2018-06-01

The charge-dependent structure of interfacial water at the n-Ge(100)-aqueous perchlorate interface was studied by controlling the electrode potential. Specifically, a joint attenuated total reflection infrared spectroscopy and electrochemical experiment was used in 0.1M NaClO4 at pH ≈ 1-10. The germanium surface transformation to an H-terminated surface followed the thermodynamic Nernstian pH dependence and was observed throughout the entire pH range. A singular value decomposition-based spectra deconvolution technique coupled to a sigmoidal transition model for the potential dependence of the main components in the spectra shows the surface transformation to be a two-stage process. The first stage was observed together with the first appearance of Ge-H stretching modes in the spectra and is attributed to the formation of a mixed surface termination. This transition was reversible. The second stage occurs at potentials ≈0.1-0.3 V negative of the first one, shows a hysteresis in potential, and is attributed to the formation of a surface with maximum Ge-H coverage. During the surface transformation, the surface becomes hydrophobic, and an effective desolvation layer, a "hydrophobic gap," developed with a thickness ≈1-3 Å. The largest thickness was observed near neutral pH. Interfacial water IR spectra show a loss of strongly hydrogen-bound water molecules compared to bulk water after the surface transformation, and the appearance of "free," non-hydrogen bound OH groups, throughout the entire pH range. Near neutral pH at negative electrode potentials, large changes at wavenumbers below 1000 cm-1 were observed. Librational modes of water contribute to the observed changes, indicating large changes in the water structure.

Effect of surface charge density on the affinity of oxide nanoparticles for the vapor-water interface.

PubMed

Brown, Matthew A; Duyckaerts, Nicolas; Redondo, Amaia Beloqui; Jordan, Inga; Nolting, Frithjof; Kleibert, Armin; Ammann, Markus; Wörner, Hans Jakob; van Bokhoven, Jeroen A; Abbas, Zareen

2013-04-23

Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si-O(-)) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor-water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye-Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.

Zeta potentials in the flotation of oxide and silicate minerals.

PubMed

Fuerstenau, D W; Pradip

2005-06-30

Adsorption of collectors and modifying reagents in the flotation of oxide and silicate minerals is controlled by the electrical double layer at the mineral-water interface. In systems where the collector is physically adsorbed, flotation with anionic or cationic collectors depends on the mineral surface being charged oppositely. Adjusting the pH of the system can enhance or prevent the flotation of a mineral. Thus, the point of zero charge (PZC) of the mineral is the most important property of a mineral in such systems. The length of the hydrocarbon chain of the collector is important because of chain-chain association enhances the adsorption once the surfactant ions aggregate to form hemimicelles at the surface. Strongly chemisorbing collectors are able to induce flotation even when collector and the mineral surface are charged similarly, but raising the pH sufficiently above the PZC can repel chemisorbing collectors from the mineral surface. Zeta potentials can be used to delineate interfacial phenomena in these various systems.

Effects of Particle Hydrophobicity, Surface Charge, Media pH Value and Complexation with Human Serum Albumin on Drug Release Behavior of Mitoxantrone-Loaded Pullulan Nanoparticles

PubMed Central

Tao, Xiaojun; Jin, Shu; Wu, Dehong; Ling, Kai; Yuan, Liming; Lin, Pingfa; Xie, Yongchao; Yang, Xiaoping

2015-01-01

We prepared two types of cholesterol hydrophobically modified pullulan nanoparticles (CHP) and carboxyethyl hydrophobically modified pullulan nanoparticles (CHCP) substituted with various degrees of cholesterol, including 3.11, 6.03, 6.91 and 3.46 per polymer, and named CHP−3.11, CHP−6.03, CHP−6.91 and CHCP−3.46. Dynamic laser light scattering (DLS) showed that the pullulan nanoparticles were 80–120 nm depending on the degree of cholesterol substitution. The mean size of CHCP nanoparticles was about 160 nm, with zeta potential −19.9 mV, larger than CHP because of the carboxyethyl group. A greater degree of cholesterol substitution conferred greater nanoparticle hydrophobicity. Drug-loading efficiency depended on nanoparticle hydrophobicity, that is, nanoparticles with the greatest degree of cholesterol substitution (6.91) showed the most drug encapsulation efficiency (90.2%). The amount of drug loading increased and that of drug release decreased with enhanced nanoparticle hydrophobicity. Nanoparticle surface-negative charge disturbed the amount of drug loading and drug release, for an opposite effect relative to nanoparticle hydrophobicity. The drug release in pullulan nanoparticles was higher pH 4.0 than pH 6.8 media. However, the changed drug release amount was not larger for negative-surface nanoparticles than CHP nanoparticles in the acid release media. Drug release of pullulan nanoparticles was further slowed with human serum albumin complexation and was little affected by nanoparticle hydrophobicity and surface negative charge. PMID:28344259

Uranyl adsorption and surface speciation at the imogolite-water interface: Self-consistent spectroscopic and surface complexation models

USGS Publications Warehouse

Arai, Y.; McBeath, M.; Bargar, J.R.; Joye, J.; Davis, J.A.

2006-01-01

Macro- and molecular-scale knowledge of uranyl (U(VI)) partitioning reactions with soil/sediment mineral components is important in predicting U(VI) transport processes in the vadose zone and aquifers. In this study, U(VI) reactivity and surface speciation on a poorly crystalline aluminosilicate mineral, synthetic imogolite, were investigated using batch adsorption experiments, X-ray absorption spectroscopy (XAS), and surface complexation modeling. U(VI) uptake on imogolite surfaces was greatest at pH ???7-8 (I = 0.1 M NaNO3 solution, suspension density = 0.4 g/L [U(VI)]i = 0.01-30 ??M, equilibration with air). Uranyl uptake decreased with increasing sodium nitrate concentration in the range from 0.02 to 0.5 M. XAS analyses show that two U(VI) inner-sphere (bidentate mononuclear coordination on outer-wall aluminol groups) and one outer-sphere surface species are present on the imogolite surface, and the distribution of the surface species is pH dependent. At pH 8.8, bis-carbonato inner-sphere and tris-carbonato outer-sphere surface species are present. At pH 7, bis- and non-carbonato inner-sphere surface species co-exist, and the fraction of bis-carbonato species increases slightly with increasing I (0.1-0.5 M). At pH 5.3, U(VI) non-carbonato bidentate mononuclear surface species predominate (69%). A triple layer surface complexation model was developed with surface species that are consistent with the XAS analyses and macroscopic adsorption data. The proton stoichiometry of surface reactions was determined from both the pH dependence of U(VI) adsorption data in pH regions of surface species predominance and from bond-valence calculations. The bis-carbonato species required a distribution of surface charge between the surface and ?? charge planes in order to be consistent with both the spectroscopic and macroscopic adsorption data. This research indicates that U(VI)-carbonato ternary species on poorly crystalline aluminosilicate mineral surfaces may be important in controlling U(VI) mobility in low-temperature geochemical environments over a wide pH range (???5-9), even at the partial pressure of carbon dioxide of ambient air (pCO2 = 10-3.45 atm). ?? 2006 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwarz, Kathleen; Xu, Bingjun; Yan, Yushan

The design of better heterogeneous catalysts for applications such as fuel cells and electrolyzers requires a mechanistic understanding of electrocatalytic reactions and the dependence of their activity on operating conditions such as pH. A satisfactory explanation for the unexpected pH dependence of electrochemical properties of platinum surfaces has so far remained elusive, with previous explanations resorting to complex co-adsorption of multiple species and resulting in limited predictive power. This knowledge gap suggests that the fundamental properties of these catalysts are not yet understood, limiting systematic improvement. In this paper, we analyze the change in charge and free energies upon adsorptionmore » using density-functional theory (DFT) to establish that water adsorbs on platinum step edges across a wide voltage range, including the double-layer region, with a loss of approximately 0.2 electrons upon adsorption. We show how this as-yet unreported change in net surface charge due to this water explains the anomalous pH variations of the hydrogen underpotential deposition (H upd) and the potentials of zero total charge (PZTC) observed in published experimental data. This partial oxidation of water is not limited to platinum metal step edges, and we report the charge of the water on metal step edges of commonly used catalytic metals, including copper, silver, iridium, and palladium, illustrating that this partial oxidation of water broadly influences the reactivity of metal electrodes.« less

Gallium(III) adsorption on carbonates and oxides: X-ray absorption fine structure spectroscopy study and surface complexation modeling.

PubMed

Pokrovsky, O S; Pokrovski, G S; Schott, J

2004-11-15

Adsorption of Ga on calcite, magnesite, amorphous silica, and manganese oxide as a function of pH and gallium concentration in solution was studied using a batch adsorption technique. Adsorbed complexes of Ga on calcite, magnesite, and delta-MnO2 were further characterized using XAFS spectroscopy. At high surface loadings from supersaturated solutions, Ga is likely to form a polymeric network at the surface (edge- and corner-sharing octahedra). At low surface loadings, Ga presents as isolated octahedra, probably attached to the Me-O sites on the surface, and coordinated by water molecules and hydroxide groups at 1.90-1.94 A. At pH>6, Ga therefore changes its coordination from 4 to 6 when adsorbing from solution (Ga(OH)(-)4(aq)) onto metal surface sites (MeOGa(OH)n(H2O)2-n(5-n), Me = Ca, Mg, or Mn, and n=1 and 2 for carbonate minerals and MnO2, respectively). Because the EXAFS is not capable of seeing hydrogen atoms, the protonation of surface complexes was determined by fitting the experimental pH-dependent Ga adsorption edge. A surface complexation model which assumes the constant capacitance of the electric double layer (CCM) and postulates the formation of positively charged, neutral and negatively charged surface complexes for carbonates, manganese oxide and silica, respectively, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Ga concentration.

Anomalous mobility of highly charged particles in pores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiu, Yinghua; Yang, Crystal; Hinkle, Preston

2015-07-16

Single micropores in resistive-pulse technique were used to understand a complex dependence of particle mobility on its surface charge density. We show that the mobility of highly charged carboxylated particles decreases with the increase of the solution pH due to an interplay of three effects: (i) ion condensation, (ii) formation of an asymmetric electrical double layer around the particle, and (iii) electroosmotic flow induced by the charges on the pore walls and the particle surfaces. The results are important for applying resistive-pulse technique to determine surface charge density and zeta potential of the particles. As a result, the experiments alsomore » indicate the presence of condensed ions, which contribute to the measured current if a sufficiently high electric field is applied across the pore.« less

Dolomite surface speciation and reactivity in aquatic systems

NASA Astrophysics Data System (ADS)

Pokrovsky, Oleg S.; Schott, Jacques; Thomas, Fabien

1999-10-01

The surface charge of dolomite (CaMg(CO3)2) was measured as a function of pH (6.5-11.5), pCO2 (10-3.5, 0.01, and 0.96 atm) and ionic strength (0.01, 0.1, and 0.5 M NaCl) using potentiometric titrations in a limited residence time reactor. Dolomite zeta potential (ζ) was determined using streaming potential and electrophoresis techniques at pH 2 to 12 in solutions having ionic strengths from 0.001 to 0.1 M NaCl as a function of aqueous Ca2+, Mg2+, and CO32- concentrations. The point of zero charge (PZC) and isoelectric point (IEP) of dolomite are the same (pH ∼8 at pCO2 ∼10-3.5 atm) and very close to those of calcite and magnesite. On the basis of these results, a surface complexation model (SCM) is proposed that postulates the presence of three distinct primary hydration sites: >CO3H°, >CaOH°, and >MgOH°. The intrinsic stability constants of dolomite surface reactions were determined by fitting the pH dependence of the surface charge and taking into account the isoelectric points and ζ-potential values for a wide range of solution compositions. In most natural aquatic environments, dolomite surface speciation can be modeled using the following species: >CO3-, >CO3Me+, >MeOH2+, >MeHCO3o, and >MeCO3-, where Me = Ca, Mg. The speciation model presented in this study allows description of metal and ligand adsorption onto dolomite surface and provides new insights on the mechanisms that control dolomite dissolution/crystallization in aqueous solutions. In particular, it is shown that dolomite dissolution is controlled by the protonation of >CO3H° surface complexes at pH < 6 and by hydrolysis of >MeOH2+ groups at higher pH.

Novel silica surface charge density mediated control of the optical properties of embedded optically active materials and its application for fiber optic pH sensing at elevated temperatures.

PubMed

Wang, Congjun; Ohodnicki, Paul R; Su, Xin; Keller, Murphy; Brown, Thomas D; Baltrus, John P

2015-02-14

Silica and silica incorporated nanocomposite materials have been extensively studied for a wide range of applications. Here we demonstrate an intriguing optical effect of silica that, depending on the solution pH, amplifies or attenuates the optical absorption of a variety of embedded optically active materials with very distinct properties, such as plasmonic Au nanoparticles, non-plasmonic Pt nanoparticles, and the organic dye rhodamine B (not a pH indicator), coated on an optical fiber. Interestingly, the observed optical response to varying pH appears to follow the surface charge density of the silica matrix for all the three different optically active materials. To the best of our knowledge, this optical effect has not been previously reported and it appears universal in that it is likely that any optically active material can be incorporated into the silica matrix to respond to solution pH or surface charge density variations. A direct application of this effect is for optical pH sensing which has very attractive features that can enable minimally invasive, remote, real time and continuous distributed pH monitoring. Particularly, as demonstrated here, using highly stable metal nanoparticles embedded in an inorganic silica matrix can significantly improve the capability of pH sensing in extremely harsh environments which is of increasing importance for applications in unconventional oil and gas resource recovery, carbon sequestration, water quality monitoring, etc. Our approach opens a pathway towards possible future development of robust optical pH sensors for the most demanding environmental conditions. The newly discovered optical effect of silica also offers the potential for control of the optical properties of optically active materials for a range of other potential applications such as electrochromic devices.

Biosorption of metal ions from aqueous solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jiaping; Yiacoumi, Sotira

1997-01-01

Copper biosorption from aqueous solutions by calcium alginate is reported in this paper. The experimental section includes potentiometric titrations of biosorbents, batch equilibrium and kinetic studies of copper biosorption, as well as fixed-bed biosorption experiments. The potentiometric titration results show that the surface charge increases with decreasing pH. The biosorption of copper strongly depends on solution pH; the metal ion binding increases from 0 to 90 percent in pH ranging from 1.5 to 5.0. In addition, a decrease in ionic strength results in an increase of copper ion removal. Kinetic studies indicate that mass transfer plays an important role inmore » the biosorption rate. Furthermore, a fixed-bed biosorption experiment shows that calcium alginate has a significant capacity for copper ion removal. The two-pK Basic Stem model successfully represents the surface charge and equilibrium biosorption experimental data. The calculation results demonstrate that the copper removal may result from the binding of free copper and its hydroxide with surface functional groups of the biosorbents.« less

Charging properties of cassiterite (alfa-SnO2) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenqvist, Jorgen K; Machesky, Michael L.; Vlcek, L.

The acid-base properties of cassiterite (alfa-SnO2) surfaces at 10 50 C were studied using potentiometric titrations of powder suspensions in aqueous NaCl and RbCl media. The proton sorption isotherms exhibited common intersection points in the pH-range 4.0 to 4.5 at all conditions and the magnitude of charging was similar but not identical in NaCl and RbCl. The hydrogen bonding configuration at the oxide-water interface, obtained from classical Molecular Dynamics (MD) simulations, was analyzed in detail and the results were explicitly incorporated in calculations of protonation constants for the reactive surface sites using the revised MUSIC model. The calculations indicated thatmore » the terminal SnOH2 group is more acidic than the bridging Sn2OH group, with protonation constants (log KH) of 3.60 and 5.13 at 25 C, respectively. This is contrary to the situation on the isostructural alfa-TiO2 (rutile), apparently due to the difference in electronegativity between Ti and Sn. MD simulations and speciation calculations indicated considerable differences in the speciation of Na+ and Rb+, despite the similarities in overall charging. Adsorbed sodium ions are almost exclusively found in bidentate surface complexes, while adsorbed rubidium ions form comparable amounts of bidentate and tetradentate complexes. Also, the distribution of adsorbed Na+ between the different complexes shows a considerable dependence on surface charge density (pH), while the distribution of adsorbed Rb+ is almost independent of pH. A Surface Complexation Model (SCM) capable of accurately describing both the measured surface charge and the MD predicted speciation of adsorbed Na+/Rb+ was formulated. According to the SCM, the deprotonated terminal group (SnOH-0.40) and the protonated bridging group (Sn2OH+0.36) dominate the surface speciation over the entire pH-range (2.7 10), illustrating the ability of positively and negatively charged surface groups to coexist. Complexation of the medium cations increases significantly with increasing negative surface charge and at pH 10 roughly 40 percent of the terminal sites are predicted to form cation complexes, while anion complexation is minor throughout the studied pH-range.« less

pH-Dependent Surface Chemistry from First Principles: Application to the BiVO4(010)-Water Interface.

PubMed

Ambrosio, Francesco; Wiktor, Julia; Pasquarello, Alfredo

2018-03-28

We present a theoretical formulation for studying the pH-dependent interfacial coverage of semiconductor-water interfaces through ab initio electronic structure calculations, molecular dynamics simulations, and the thermodynamic integration method. This general methodology allows one to calculate the acidity of the individual adsorption sites on the surface and consequently the pH at the point of zero charge, pH PZC , and the preferential adsorption mode of water molecules, either molecular or dissociative, at the semiconductor-water interface. The proposed method is applied to study the BiVO 4 (010)-water interface, yields a pH PZC in excellent agreement with the experimental characterization. Furthermore, from the calculated p K a values of the individual adsorption sites, we construct an ab initio concentration diagram of all adsorbed species at the interface as a function of the pH of the aqueous solution. The diagram clearly illustrates the pH-dependent coverage of the surface and indicates that protons are found to be significantly adsorbed (∼1% of available sites) only in highly acidic conditions. The surface is found to be mostly covered by molecularly adsorbed water molecules in a wide interval of pH values ranging from 2 to 8. Hydroxyl ions are identified as the dominant adsorbed species at pH larger than 8.2.

Experimental study of brucite dissolution and precipitation in aqueous solutions: surface speciation and chemical affinity control

NASA Astrophysics Data System (ADS)

Pokrovsky, Oleg S.; Schott, Jacques

2004-01-01

Dissolution and precipitation rates of brucite (Mg(OH) 2) were measured at 25°C in a mixed-flow reactor as a function of pH (2.5 to 12), ionic strength (10 -4 to 3 M), saturation index (-12 < log Ω < 0.4) and aqueous magnesium concentrations (10 -6 to 5·10 -4 M). Brucite surface charge and isoelectric point (pH IEP) were determined by surface titrations in a limited residence time reactor and electrophoretic measurements, respectively. The pH of zero charge and pH IEP were close to 11. A two-pK, one site surface speciation model which assumes a constant capacitance of the electric double layer (5 F/m 2) and lack of dependence on ionic strength predicts the dominance of >MgOH 2+ species at pH < 8 and their progressive replacement by >MgOH° and >MgO - as pH increases to 10-12. Rates are proportional to the square of >MgOH 2+ surface concentration at pH from 2.5 to 12. In accord with surface speciation predictions, dissolution rates do not depend on ionic strength at pH 6.5 to 11. Brucite dissolution and precipitation rates at close to equilibrium conditions obeyed TST-derived rate laws. At constant saturation indices, brucite precipitation rates were proportional to the square of >MgOH 2+ concentration. The following rate equation, consistent with transition state theory, describes brucite dissolution and precipitation kinetics over a wide range of solution composition and chemical affinity: R=k Mg+ · {>MgOH 2+} 2 · (1-Ω 2) where kMg+ is the dissolution rate constant, {> i} is surface species concentration (mol/m 2), and Ω is the solution saturation index with respect to brucite. Measurements of nonsteady state brucite dissolution rates, in response to cycling the pH from 12 to 2 (pH-jump experiments), indicate the important role of surface hydroxylation — that leads to the formation of Mg oxo or -hydroxo complexes — in the formation of dissolution-active sites. Replacement of water molecules by these oxygen donor complexes in the Mg coordination sphere has a labilizing effect on the dynamics of the remaining water molecules and thus increases reaction rates.

The surface properties of Shewanella putrefaciens 200 and S. oneidensis MR-1: the effect of pH and terminal electron acceptors.

PubMed

Furukawa, Yoko; Dale, Jason R

2013-04-08

We investigated the surface characteristics of two strains of Shewanella sp., S. oneidensis MR-1 and S. putrefaciens 200, that were grown under aerobic conditions as well as under anaerobic conditions with trimethylamine oxide (TMAO) as the electron acceptor. The investigation focused on the experimental determination of electrophoretic mobility (EPM) under a range of pH and ionic strength, as well as by subsequent modeling in which Shewanella cells were considered to be soft particles with water- and ion-permeable outermost layers. The soft layer of p200 is significantly more highly charged (i.e., more negative) than that of MR-1. The effect of electron acceptor on the soft particle characteristics of Shewanella sp. is complex. The fixed charge density, which is a measure of the deionized and deprotonated functional groups in the soft layer polymers, is slightly greater (i.e., more negative) for aerobically grown p200 than for p200 grown with TMAO. On the other hand, the fixed charge density of aerobically grown MR1 is slightly less than that of p200 grown with TMAO. The effect of pH on the soft particle characteristics is also complex, and does not exhibit a clear pH-dependent trend. The Shewanella surface characteristics were attributed to the nature of the outermost soft layer, the extracellular polymeric substances (EPS) in case of p200 and lypopolysaccharides (LPS) in case of MR1 which generally lacks EPS. The growth conditions (i.e., aerobic vs. anaerobic TMAO) have an influence on the soft layer characteristics of Shewanella sp. cells. Meanwhile, the clear pH dependency of the mechanical and morphological characteristics of EPS and LPS layers, observed in previous studies through atomic force microscopy, adhesion tests and spectroscopies, cannot be corroborated by the electrohydrodynamics-based soft particle characteristics which does not exhibited a clear pH dependency in this study. While the electrohydrodynamics-based soft-particle model is a useful tool in understanding bacteria's surface properties, it needs to be supplemented with other characterization methods and models (e.g., chemical and micromechanical) in order to comprehensively address all of the surface-related characteristics important in environmental and other aqueous processes.

Negative differential electrolyte resistance in a solid-state nanopore resulting from electroosmotic flow bistability.

PubMed

Luo, Long; Holden, Deric A; White, Henry S

2014-03-25

A solid-state nanopore separating two aqueous solutions containing different concentrations of KCl is demonstrated to exhibit negative differential resistance (NDR) when a constant pressure is applied across the nanopore. NDR refers to a decrease in electrical current when the voltage applied across the nanopore is increased. NDR results from the interdependence of solution flow (electroosmotic and pressure-engendered) with the distributions of K+ and Cl- within the nanopore. A switch from a high-conductivity state to a low-conductivity state occurs over a very narrow voltage window (<2 mV) that depends on the nanopore geometry, electrolyte concentration, and nanopore surface charge density. Finite element simulations based on a simultaneous solution of the Navier-Stokes, Poisson, and Nernst-Planck equations demonstrate that NDR results from a positive feedback mechanism between the ion distributions and electroosmotic flow, yielding a true bistability in fluid flow and electrical current at a critical applied voltage, i.e., the NDR "switching potential". Solution pH and Ca2+ were separately employed as chemical stimuli to investigate the dependence of the NDR on the surface charge density. The NDR switching potential is remarkably sensitive to the surface charge density, and thus to pH and the presence of Ca2+, suggesting possible applications in chemical sensing.

On the Applicability of DLVO Theory to the Prediction of Clay Colloids Stability.

PubMed

Missana; Adell

2000-10-01

The stability behavior of Na-montmorillonite colloids has been studied by combining the analysis of their surface charge properties and time-resolved dynamic light scattering experiments. The chemical surface model for several types of clays, including montmorillonite, has to take into account the double surface charge contribution due to their permanent structural charge and to their pH-dependent charge, which is developed at the edge sites, therefore, these stability studies were carried out as a function of both ionic strength and pH. DLVO theory is largely applied for the prediction of the stability of many colloidal systems, including the natural ones. This work shows that the stability behavior of Na-montmorillonite colloids cannot be satisfactorily reproduced by DLVO theory, using the surface parameters experimentally obtained. Particularly, this theory is unable to explain their pH-dependent stability behavior caused by the small charge at the edge sites. Based on these results, a literature review of DLVO stability prediction of clay colloids was performed. It confirmed that this theory is not capable of taking into account the double contribution to the total surface charge and, at the same time, pointed out the main uncertainties related to the appropriate use of the input parameters for the calculation as, for example, the Hamaker constant or the surface potential. Copyright 2000 Academic Press.

Modification by protons of frog skeletal muscle KATP channels: effects on ion conduction and nucleotide inhibition.

PubMed Central

Vivaudou, M; Forestier, C

1995-01-01

1. The molecular mechanisms underlying pH regulation of skeletal muscle ATP-sensitive K+ (KATP) channels were studied using the patch clamp technique in the inside-out configuration. Two effects of intracellular protons were studied in detail: the decrease in magnitude of single-channel currents and the increase in open probability (Po) of nucleotide-inhibited channels. 2. The pH dependence of inward unit currents under different ionic conditions was in poor agreement with either a direct block of the pore by protons or an indirect proton-induced conformational change, but was compatible with the protonation of surface charges located near the cytoplasmic entrance of the pore. This latter electrostatic mechanism was modelled using Gouy-Chapman-Stern theory, which predicted the data accurately with a surface charge density of about 0.1 negative elementary charges per square nanometre and a pK (pH value for 50% effect) value for protonation of these charges of 6.25. The same mechanism, i.e. neutralization of negative surface charges by cation binding, could also account for the previously reported reduction of inward unit currents by Mg2+. 3. Intracellular alkalization did not affect Po of the KATP channels. Acidification increased Po. In the presence of 0.1 mM ATP (no Mg2+), the channel activation vs. pH relationship could be fitted with a sigmoid curve with a Hill coefficient slightly above 2 and a pK value of 6. This latter value was dependent on the ATP concentration, decreasing from 6.3 in 30 microM ATP to 5.3 in 1 microM ATP. 4. Conversely, the channel inhibition vs. ATP concentration curve was shifted to the right when the pH was lowered. At pH 7.1, the ATP concentration causing half-maximal inhibition was about 10 microM. At pH 5.4, it was about 400 microM. The Hill coefficient values remained slightly below 2. Similar effects were observed when ADP was used as the inhibitory nucleotide. 5. These results confirm that a reciprocal competitive link exists between proton and nucleotide binding sites. Quantitatively, they are in full agreement with a steady-state model of a KATP channel possessing four identical protonation sites (microscopic pK, 6) allosterically connected to the channel open state and two identical nucleotide sites (microscopic ATP dissociation constant, approximately 30 microM) connected to the closed state. Images Figure 13 PMID:7473225

Transport of colloidal silica in unsaturated sand: Effect of charging properties of sand and silica particles.

PubMed

Fujita, Yosuke; Kobayashi, Motoyoshi

2016-07-01

We have studied the transport of colloidal silica in various degrees of a water-saturated Toyoura sand column, because silica particles are widely used as catalyst carriers and abrasive agents, and their toxicity is reported recently. Since water-silica, water-sand, and air-water interfaces have pH-dependent negative charges, the magnitude of surface charge was controlled by changing the solution pH. The results show that, at high pH conditions (pH 7.4), the deposition of colloidal silica to the sand surface is interrupted and the silica concentration at the column outlet immediately reaches the input concentration in saturated conditions. In addition, the relative concentration of silica at the column outlet only slightly decreases to 0.9 with decreasing degrees of water saturation to 38%, because silica particles are trapped in straining regions in the soil pore and air-water interface. On the other hand, at pH 5 conditions (low pH), where sand and colloid have less charge, reduced repulsive forces result in colloidal silica attaching onto the sand in saturated conditions. The deposition amount of silica particles remarkably increases with decreasing degrees of water saturation to 37%, which is explained by more particles being retained in the sand column associated with the air-water interface. In conclusion, at higher pH, the mobility of silica particles is high, and the air-water interface is inactive for the deposition of silica. On the other hand, at low pH, the deposition amount increases with decreasing water saturation, and the particle transport is inhibited. Copyright © 2016 Elsevier Ltd. All rights reserved.

pH-dependent electron-transport properties of carbon nanotubes.

PubMed

Back, Ju Hee; Shim, Moonsub

2006-11-30

Carbon nanotube electrochemical transistors integrated with microfluidic channels are utilized to examine the effects of aqueous electrolyte solutions on the electron-transport properties of single isolated carbon nanotubes. In particular, pH and concentration of supporting inert electrolytes are examined. A systematic threshold voltage shift with pH is observed while the transconductance and subthreshold swing remain independent of pH and concentration. Decreasing pH leads to a negative shift of the threshold voltage, indicating that protonation does not lead to hole doping. Changing the type of contact metal does not alter the observed pH response. The pH-dependent charging of SiO2 substrate is ruled out as the origin based on measurements with suspended nanotube transistors. Increasing the ionic strength leads to reduced pH response. Contributions from possible surface chargeable chemical groups are considered.

Surface charge features of kaolinite particles and their interactions

NASA Astrophysics Data System (ADS)

Gupta, Vishal

Kaolinite is both a blessing and a curse. As an important industrial mineral commodity, kaolinite clays are extensively used in the paper, ceramic, paint, plastic and rubber industries. In all these applications the wettability, aggregation, dispersion, flotation and thickening of kaolinite particles are affected by its crystal structure and surface properties. It is therefore the objective of this research to investigate selected physical and surface chemical properties of kaolinite, specifically the surface charge of kaolinite particles. A pool of advanced analytical techniques such as XRD, XRF, SEM, AFM, FTIR and ISS were utilized to investigate the morphological and surface chemistry features of kaolinite. Surface force measurements revealed that the silica tetrahedral face of kaolinite is negatively charged at pH>4, whereas the alumina octahedral face of kaolinite is positively charged at pH<6, and negatively charged at pH>8. Based on electrophoresis measurements, the apparent iso-electric point for kaolinite particles was determined to be less than pH 3. In contrast, the point of zero charge was determined to be pH 4.5 by titration techniques, which corresponds to the iso-electric point of between pH 4 and 5 as determined by surface force measurements. Results from kaolinite particle interactions indicate that the silica face--alumina face interaction is dominant for kaolinite particle aggregation at low and intermediate pH values, which explains the maximum shear yield stress at pH 5-5.5. Lattice resolution images reveal the hexagonal lattice structure of these two face surfaces of kaolinite. Analysis of the silica face of kaolinite showed that the center of the hexagonal ring of oxygen atoms is vacant, whereas the alumina face showed that the hexagonal surface lattice ring of hydroxyls surround another hydroxyl in the center of the ring. High resolution transmission electron microscopy investigation of kaolinite has indicated that kaolinite is indeed composed of silica/alumina bilayers with a c-spacing of 7.2 A. The surface charge densities of the silica face, the alumina face and the edge surface of kaolinite all influence particle interactions, and thereby affect the mechanical properties of kaolinite suspensions. The improved knowledge of kaolinite surface chemistry from this dissertation research provides a foundation for the development of improved process strategies for both the use and disposal of clay particles such as kaolinite.

Non-monotonic swelling of surface grafted hydrogels induced by pH and/or salt concentration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Longo, Gabriel S.; Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208; Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois 60208

2014-09-28

We use a molecular theory to study the thermodynamics of a weak-polyacid hydrogel film that is chemically grafted to a solid surface. We investigate the response of the material to changes in the pH and salt concentration of the buffer solution. Our results show that the pH-triggered swelling of the hydrogel film has a non-monotonic dependence on the acidity of the bath solution. At most salt concentrations, the thickness of the hydrogel film presents a maximum when the pH of the solution is increased from acidic values. The quantitative details of such swelling behavior, which is not observed when themore » film is physically deposited on the surface, depend on the molecular architecture of the polymer network. This swelling-deswelling transition is the consequence of the complex interplay between the chemical free energy (acid-base equilibrium), the electrostatic repulsions between charged monomers, which are both modulated by the absorption of ions, and the ability of the polymer network to regulate charge and control its volume (molecular organization). In the absence of such competition, for example, for high salt concentrations, the film swells monotonically with increasing pH. A deswelling-swelling transition is similarly predicted as a function of the salt concentration at intermediate pH values. This reentrant behavior, which is due to the coupling between charge regulation and the two opposing effects triggered by salt concentration (screening electrostatic interactions and charging/discharging the acid groups), is similar to that found in end-grafted weak polyelectrolyte layers. Understanding how to control the response of the material to different stimuli, in terms of its molecular structure and local chemical composition, can help the targeted design of applications with extended functionality. We describe the response of the material to an applied pressure and an electric potential. We present profiles that outline the local chemical composition of the hydrogel, which can be useful information when designing applications that pursue or require the absorption of biomolecules or pH-sensitive molecules within different regions of the film.« less

Polymerized PolyHEMA photonic crystals: pH and ethanol sensor materials.

PubMed

Xu, Xiangling; Goponenko, Alexander V; Asher, Sanford A

2008-03-12

The surface of monodisperse silica particles synthesized using the Stober process were coated with a thin layer of polystyrene. Surface charge groups were attached by a grafting polymerization of styrene sulfonate. The resulting highly charged monodisperse silica particles self-assemble into crystalline colloidal arrays (CCA) in deionized water. We polymerized hydroxyethyl methacrylate (HEMA) around the CCA to form a HEMA-polymerized crystalline colloidal array (PCCA). Hydrofluoric acid was utilized to etch out the silica particles to produce a three-dimensional periodic array of voids in the HEMA PCCA. The diffraction from the embedded CCA sensitively monitors the concentration of ethanol in water because the HEMA PCCA shows a large volume dependence on ethanol due to a decreased Flory-Huggins mixing parameter. Between pure water and 40% ethanol the diffraction shifts across the entire visible spectral region. We accurately modeled the dependence of the diffraction wavelength on ethanol concentration using Flory theory. We also fabricated a PCCA (which responds to pH changes in both low and high ionic strength solutions) by utilizing a second polymerization to incorporate carboxyl groups into the HEMA PCCA. We were also able to model the pH dependence of diffraction of the HEMA PCCA by using Flory theory. An unusual feature of the pH response is a hysteresis in response to titration to higher and lower pH. This hysteresis results from the formation of a Donnan potential at high pH which shifts the ionic equilibrium. The kinetics of equilibration is very slow due to the ultralow diffusion constant of protons in the carboxylated PCCA as predicted earlier by the Tanaka group.

Use of anionic surfactants for selective polishing of silicon dioxide over silicon nitride films using colloidal silica-based slurries

NASA Astrophysics Data System (ADS)

Penta, Naresh K.; Amanapu, H. P.; Peethala, B. C.; Babu, S. V.

2013-10-01

Four different anionic surfactants, sodium dodecyl sulfate, dodecyl benzene sulfonic acid (DBSA), dodecyl phosphate and Sodium lauroyl sarcosine, selected from the sulfate, phosphate, and carboxylic family, were investigated as additives in silica dispersions for selective polishing of silicon dioxide over silicon nitride films. We found that all these anionic surfactants suppress the nitride removal rates (RR) for pH ≤4 while more or less maintaining the oxide RRs, resulting in high oxide-to-nitride RR selectivity. The RR data obtained as a function of pH were explained based on pH dependent distributions of surfactant species, change in the zeta potentials of oxide and nitride surfaces, and thermogravimetric data. It appears that the negatively charged surfactant species preferentially adsorb on the positively charged nitride surface below IEP through its electrostatic interactions and form a bilayer adsorption, resulting in the suppression of nitride RRs. In contrast to the surfactants, K2SO4 interacts only weakly with the nitride surface and hence cannot suppress its RR.

Electrokinetic Properties of Fullerene nC60 Nanoparticles: Role of Co-ions and pH

EPA Science Inventory

Environmental exposure, bioavailability, and mobility of nanoparticles (NPs) in part depend on their aggregated state and their surface charge. These fundamental characteristics are functions of the aqueous media in which the particles are suspended. For example, inorganic ions p...

Solution pH change in non-uniform alternating current electric fields at frequencies above the electrode charging frequency

PubMed Central

An, Ran; Massa, Katherine

2014-01-01

AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (fc), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above fc. In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H+] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5fc). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H+] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 Vpp potential, and voltage dependency was explored from 3.5 to 7.5 Vpp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position. PMID:25553200

TiO2 nanoparticles aggregation and disaggregation in presence of alginate and Suwannee River humic acids. pH and concentration effects on nanoparticle stability.

PubMed

Loosli, Frédéric; Le Coustumer, Philippe; Stoll, Serge

2013-10-15

The behavior of manufactured TiO2 nanoparticles is studied in a systematic way in presence of alginate and Suwannee River humic acids at variable concentrations. TiO2 nanoparticles aggregation, disaggregation and stabilization are investigated using dynamic light scattering and electrophoretic experiments allowing the measurement of z-average hydrodynamic diameters and zeta potential values. Stability of the TiO2 nanoparticles is discussed by considering three pH-dependent electrostatic scenarios. In the first scenario, when pH is below the TiO2 nanoparticle point of zero charge, nanoparticles exhibit a positively charged surface whereas alginate and Suwannee River humic acids are negatively charged. Fast adsorption at the TiO2 nanoparticles occurs, promotes surface charge neutralization and aggregation. By increasing further alginate and Suwannee River humic acids concentrations charge inversion and stabilization of TiO2 nanoparticles are obtained. In the second electrostatic scenario, at the surface charge neutralization pH, TiO2 nanoparticles are rapidly forming aggregates. Adsorption of alginate and Suwannee River humic acids on aggregates leads to their partial fragmentation. In the third electrostatic scenario, when nanoparticles, alginate and Suwannee River humic acids are negatively charged, only a small amount of Suwannee River humic acids is adsorbed on TiO2 nanoparticles surface. It is found that the fate and behavior of individual and aggregated TiO2 nanoparticles in presence of environmental compounds are mainly driven by the complex interplay between electrostatic attractive and repulsive interactions, steric and van der Waals interactions, as well as concentration ratio. Results also suggest that environmental aquatic concentration ranges of humic acids and biopolymers largely modify the stability of aggregated or dispersed TiO2 nanoparticles. Copyright © 2013 Elsevier Ltd. All rights reserved.

Isoelectric points of viruses.

PubMed

Michen, B; Graule, T

2010-08-01

Viruses as well as other (bio-)colloids possess a pH-dependent surface charge in polar media such as water. This electrostatic charge determines the mobility of the soft particle in an electric field and thus governs its colloidal behaviour which plays a major role in virus sorption processes. The pH value at which the net surface charge switches its sign is referred to as the isoelectric point (abbreviations: pI or IEP) and is a characteristic parameter of the virion in equilibrium with its environmental water chemistry. Here, we review the IEP measurements of viruses that replicate in hosts of kingdom plantae, bacteria and animalia. IEPs of viruses are found in pH range from 1.9 to 8.4; most frequently, they are measured in a band of 3.5 < IEP < 7. However, the data appear to be scattered widely within single virus species. This discrepancy is discussed and should be considered when IEP values are used to account for virus sorption processes.

pH effects on the hyaluronan hydrolysis catalysed by hyaluronidase in the presence of proteins: Part I. Dual aspect of the pH-dependence.

PubMed

Lenormand, Hélène; Deschrevel, Brigitte; Vincent, Jean-Claude

2010-05-01

Hyaluronan (HA) hydrolysis catalysed by hyaluronidase (HAase) is strongly inhibited when performed at a low ratio of HAase to HA concentrations and at low ionic strength. This is because long HA chains can form non-active complexes with HAase. Bovine serum albumin (BSA) is able to compete with HAase to form electrostatic complexes with HA so freeing HAase which then recovers its catalytic activity. This BSA-dependence is characterised by two main domains separated by the optimal BSA concentration: below this concentration the HAase activity increases when the BSA concentration is increased, above this concentration the HAase activity decreases. This occurs provided that HA is negatively charged and BSA is positively charged, i.e. in a pH range from 3 to 5.25. The higher the pH value the higher the optimal BSA concentration. Other proteins can also modulate HAase activity. Lysozyme, which has a pI higher than that of BSA, is also able to compete with HAase to form electrostatic complexes with HA and liberate HAase. This occurs over a wider pH range that extends from 3 to 9. These results mean that HAase can form complexes with HA and recover its enzymatic activity at pH as high as 9, consistent with HAase having either a high pI value or positively charged patches on its surface at high pH. Finally, the pH-dependence of HAase activity, which results from the influence of pH on both the intrinsic HAase activity and the formation of complexes between HAase and HA, shows a maximum at pH 4 and a significant activity up to pH 9. Copyright 2009 International Society of Matrix Biology. Published by Elsevier B.V. All rights reserved.

The pH dependent surface charging and points of zero charge. VII. Update.

PubMed

Kosmulski, Marek

2018-01-01

The pristine points of zero charge (PZC) and isoelectric points (IEP) of metal oxides and IEP of other materials from the recent literature, and a few older results (overlooked in previous searches) are summarized. This study is an update of the previous compilations by the same author [Surface Charging and Points of Zero Charge, CRC, Boca Raton, 2009; J. Colloid Interface Sci. 337 (2009) 439; 353 (2011) 1; 426 (2014) 209]. The field has been very active, but most PZC and IEP are reported for materials, which are very well-documented already (silica, alumina, titania, iron oxides). IEP of (nominally) Gd 2 O 3 , NaTaO 3 , and SrTiO 3 have been reported in the recent literature. Their IEP were not reported in older studies. Copyright © 2017 Elsevier B.V. All rights reserved.

The effect of high ionic strength on neptunium (V) adsorption to a halophilic bacterium

NASA Astrophysics Data System (ADS)

Ams, David A.; Swanson, Juliet S.; Szymanowski, Jennifer E. S.; Fein, Jeremy B.; Richmann, Michael; Reed, Donald T.

2013-06-01

The mobility of neptunium (V) in subsurface high ionic strength aqueous systems may be strongly influenced by adsorption to the cell wall of the halophilic bacteria Chromohalobacter sp. This study is the first to evaluate the adsorption of neptunium (V) to the surface of a halophilic bacterium as a function of pH from approximately 2 to 10 and at ionic strengths of 2 and 4 M. This is also the first study to evaluate the effects of carbonate complexation with neptunium (V) on adsorption to whole bacterial cells under high pH conditions. A thermodynamically-based surface complexation model was adapted to describe experimental adsorption data under high ionic strength conditions where traditional corrections for aqueous ion activity are invalid. Adsorption of neptunium (V) was rapid and reversible under the conditions of the study. Adsorption was significant over the entire pH range evaluated for both ionic strength conditions and was shown to be dependent on the speciation of the sites on the bacterial surface and neptunium (V) in solution. Adsorption behavior was controlled by the relatively strong electrostatic attraction of the positively charged neptunyl ion to the negatively charged bacterial surface at pH below circum-neutral. At pH above circum-neutral, the adsorption behavior was controlled by the presence of negatively charged neptunium (V) carbonate complexes resulting in decreased adsorption, although adsorption was still significant due to the adsorption of negatively charged neptunyl-carbonate species. Adsorption in 4 M NaClO4 was enhanced relative to adsorption in 2 M NaClO4 over the majority of the pH range evaluated, likely due to the effect of increasing aqueous ion activity at high ionic strength. The protonation/deprotonation characteristics of the cell wall of Chromohalobacter sp. were evaluated by potentiometric titrations in 2 and 4 M NaClO4. Bacterial titration results indicated that Chromohalobacter sp. exhibits similar proton buffering capacity to previously studied non-halophilic bacteria. The titration data were used to determine the number of types, concentrations, and associated deprotonation constants of functional groups on the bacterial surface; the neptunium adsorption measurements were used to constrain binding constant values for the important neptunium (V)-bacterial surface species. Together, these results can be incorporated into geochemical speciation models to aid in the prediction of neptunium (V) mobility in complex bacteria-bearing geochemical systems.

Adsorption of charged protein residues on an inorganic nanosheet: Computer simulation of LDH interaction with ion channel

NASA Astrophysics Data System (ADS)

Tsukanov, Alexey A.; Psakhie, Sergey G.

2016-08-01

Quasi-two-dimensional and hybrid nanomaterials based on layered double hydroxides (LDH), cationic clays, layered oxyhydroxides and hydroxides of metals possess large specific surface area and strong electrostatic properties with permanent or pH-dependent electric charge. Such nanomaterials may impact cellular electrostatics, changing the ion balance, pH and membrane potential. Selective ion adsorption/exchange may alter the transmembrane electrochemical gradient, disrupting potential-dependent cellular processes. Cellular proteins as a rule have charged residues which can be effectively adsorbed on the surface of layered hydroxide based nanomaterials. The aim of this study is to attempt to shed some light on the possibility and mechanisms of protein "adhesion" an LDH nanosheet and to propose a new direction in anticancer medicine, based on physical impact and strong electrostatics. An unbiased molecular dynamics simulation was performed and the combined process free energy estimation (COPFEE) approach was used.

Cooperative effect of pH-dependent ion transport within two symmetric-structured nanochannels.

PubMed

Meng, Zheyi; Chen, Yang; Li, Xiulin; Xu, Yanglei; Zhai, Jin

2015-04-15

A novel and simple design is introduced to construct bichannel nanofluid diodes by combining two poly(ethylene terephthalate) (PET) films with columnar nanochannel arrays varying in size or in surface charge. This type of bichannel device performs obvious ion current rectification, and the pH-dependent tunability and degree of rectification can be improved by histidine modification. The origin of the ion current rectification and its pH-dependent tunability are attributed to the cooperative effect of the two columnar half-channels and the applied bias on the mobile ions. As a result of surface groups on the bichannel being charged with different polarities or degrees at different pH values, the function of the bichannel device can be converted from a nanofluid diode to a normal nanochannel or to a reverse diode.

Mobile colloid generation induced by a cementitious plume: mineral surface-charge controls on mobilization.

PubMed

Li, Dien; Kaplan, Daniel I; Roberts, Kimberly A; Seaman, John C

2012-03-06

Cementitious materials are increasingly used as engineered barriers and waste forms for radiological waste disposal. Yet their potential effect on mobile colloid generation is not well-known, especially as it may influence colloid-facilitated contaminant transport. Whereas previous papers have studied the introduction of cement colloids into sediments, this study examined the influence of cement leachate chemistry on the mobilization of colloids from a subsurface sediment collected from the Savannah River Site, USA. A sharp mobile colloid plume formed with the introduction of a cement leachate simulant. Colloid concentrations decreased to background concentrations even though the aqueous chemical conditions (pH and ionic strength) remained unchanged. Mobile colloids were mainly goethite and to a lesser extent kaolinite. The released colloids had negative surface charges and the mean particle sizes ranged primarily from 200 to 470 nm. Inherent mineralogical electrostatic forces appeared to be the controlling colloid removal mechanism in this system. In the background pH of ~6.0, goethite had a positive surface charge, whereas quartz (the dominant mineral in the immobile sediment) and kaolinite had negative surface charges. Goethite acted as a cementing agent, holding kaolinite and itself onto the quartz surfaces due to the electrostatic attraction. Once the pH of the system was elevated, as in the cementitious high pH plume front, the goethite reversed to a negative charge, along with quartz and kaolinite, then goethite and kaolinite colloids were mobilized and a sharp spike in turbidity was observed. Simulating conditions away from the cementitious source, essentially no colloids were mobilized at 1:1000 dilution of the cement leachate or when the leachate pH was ≤ 8. Extreme alkaline pH environments of cementitious leachate may change mineral surface charges, temporarily promoting the formation of mobile colloids.

Experimental demonstration of scaling behavior for ionic transport and its fluctuations in individual carbon nanotube

NASA Astrophysics Data System (ADS)

Bocquet, Lyderic; Secchi, Eleonora; Nigues, Antoine; Siria, Alessandro

2015-11-01

We perform an experimental study of ionic transport and current fluctuations inside individual Carbon Nanotubes (CNT) with a size ranging from 40 down to 7 nanometers in radius. The conductance exhibits a power law behavior dependence on the salinity, with an exponent close to 1/3. This is in contrast to Boron-Nitride nanotubes which exhibits a constant surface conductance. This scaling behavior is rationalized in terms of a model accounting for hydroxide adsorption at the (hydrophobic) carbon surface. This predicts a density dependent surface charge with a exponent 1/3 in full agreement with the experimental observations. Then we measure the low frequency noise of the ionic current in single CNTs. The noise exhibits a robust 1/f characteristic, with an amplitude which scales proportionaly to the surface charge measured independently. Data for the various CNT at a given pH do collapse on a master curve. This behavior is rationalized in terms of the fluctuations of the surface charge based on the adsorption behavior. This suggests that the low frequency noise takes its origin in the process occuring at the surface of the carbon nanotube.

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

NASA Astrophysics Data System (ADS)

Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

2011-07-01

The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Charge-based characterization of nanometric cationic bifunctional maghemite/silica core/shell particles by capillary zone electrophoresis.

PubMed

d'Orlyé, Fanny; Varenne, Anne; Georgelin, Thomas; Siaugue, Jean-Michel; Teste, Bruno; Descroix, Stéphanie; Gareil, Pierre

2009-07-01

In view of employing functionalized nanoparticles (NPs) in the context of an immunodiagnostic, aminated maghemite/silica core/shell particles were synthesized so as to be further coated with an antibody or an antigen via the amino groups at their surface. Different functionalization rates were obtained by coating these maghemite/silica core/shell particles with 3-(aminopropyl)triethoxysilane and 2-[methoxy(polyethyleneoxy)propyl]-trimethoxysilane at different molar ratios. Adequate analytical performances with CE coupled with UV-visible detection were obtained through semi-permanent capillary coating with didodecyldimethyl-ammonium bromide, thus preventing particle adsorption. First, the influence of experimental conditions such as electric field strength, injected particle amount as well as electrolyte ionic strength and pH, was evaluated. A charge-dependent electrophoretic mobility was evidenced and the separation selectivity was tuned according to electrolyte ionic strength and pH. The best resolutions were obtained at pH 8.0, high ionic strength (ca. 100 mM), and low total particle volume fraction (ca. 0.055%), thus eliminating interference effects between different particle populations in mixtures. A protocol derived from Kaiser's original description was performed for quantitation of the primary amino groups attached onto the NP surface. Thereafter a correlation between particle electrophoretic mobility and the density of amino groups at their surface was established. Eventually, CE proved to be an easy, fast, and reliable method for the determination of NP effective surface charge density.

Differential effects of DEAE negative mode chromatography and gel-filtration chromatography on the charge status of Helicobacter pylori neutrophil-activating protein

PubMed Central

Pan, Timothy; Tzeng, Huey-Fen

2017-01-01

Helicobacter pylori neutrophil-activating protein (HP-NAP) is involved in H. pylori-associated gastric inflammation. HP-NAP is also a vaccine candidate, a possible drug target, and a potential diagnostic marker for H. pylori-associated diseases. Previously, we purified recombinant HP-NAP by one-step diethylaminoethyl (DEAE) negative mode chromatography by collecting the unbound fraction at pH 8.0 at 4°C. It remains unclear why HP-NAP does not bind to DEAE resins at the pH above its isoelectric point during the purification. To investigate how pH affects the surface net charge of HP-NAP and its binding to DEAE resins during the purification, recombinant HP-NAP expressed in Escherichia coli was subjected to DEAE negative mode chromatography at pH ranging from 7.0 to 9.0 at 25°C and the surface charge of purified HP-NAP was determined by capillary electrophoresis. A minimal amount of HP-NAP was detected in the elution fraction of DEAE Sepharose resin at pH 8.5, whereas recombinant HP-NAP was detected in the elution fraction of DEAE Sephadex resin only at pH 7.0 and 8.0. The purified recombinant HP-NAP obtained from the unbound fractions was not able to bind to DEAE resins at pH 7.0 to 9.0. In addition, the surface charge of the purified HP-NAP was neutral at pH 7.0 to 8.0 and was either neutral or slightly negative at pH 8.5 and 9.0. However, recombinant HP-NAP purified from gel-filtration chromatography was able to bind to DEAE Sepharose resin at pH 7.0 to 9.0 and DEAE Sephadex resin at pH 7.0. At pH 8.5 and 9.0, only the negatively charged species of HP-NAP were found. Thus, recombinant HP-NAP with different charge status can be differentially purified by DEAE negative mode chromatography and gel-filtration chromatography. Furthermore, the charge distribution on the surface of HP-NAP, the presence of impure proteins, and the overall net charge of the resins all affect the binding of HP-NAP to DEAE resins during the negative purification. PMID:28328957

Differential effects of DEAE negative mode chromatography and gel-filtration chromatography on the charge status of Helicobacter pylori neutrophil-activating protein.

PubMed

Hong, Zhi-Wei; Yang, Yu-Chi; Pan, Timothy; Tzeng, Huey-Fen; Fu, Hua-Wen

2017-01-01

Helicobacter pylori neutrophil-activating protein (HP-NAP) is involved in H. pylori-associated gastric inflammation. HP-NAP is also a vaccine candidate, a possible drug target, and a potential diagnostic marker for H. pylori-associated diseases. Previously, we purified recombinant HP-NAP by one-step diethylaminoethyl (DEAE) negative mode chromatography by collecting the unbound fraction at pH 8.0 at 4°C. It remains unclear why HP-NAP does not bind to DEAE resins at the pH above its isoelectric point during the purification. To investigate how pH affects the surface net charge of HP-NAP and its binding to DEAE resins during the purification, recombinant HP-NAP expressed in Escherichia coli was subjected to DEAE negative mode chromatography at pH ranging from 7.0 to 9.0 at 25°C and the surface charge of purified HP-NAP was determined by capillary electrophoresis. A minimal amount of HP-NAP was detected in the elution fraction of DEAE Sepharose resin at pH 8.5, whereas recombinant HP-NAP was detected in the elution fraction of DEAE Sephadex resin only at pH 7.0 and 8.0. The purified recombinant HP-NAP obtained from the unbound fractions was not able to bind to DEAE resins at pH 7.0 to 9.0. In addition, the surface charge of the purified HP-NAP was neutral at pH 7.0 to 8.0 and was either neutral or slightly negative at pH 8.5 and 9.0. However, recombinant HP-NAP purified from gel-filtration chromatography was able to bind to DEAE Sepharose resin at pH 7.0 to 9.0 and DEAE Sephadex resin at pH 7.0. At pH 8.5 and 9.0, only the negatively charged species of HP-NAP were found. Thus, recombinant HP-NAP with different charge status can be differentially purified by DEAE negative mode chromatography and gel-filtration chromatography. Furthermore, the charge distribution on the surface of HP-NAP, the presence of impure proteins, and the overall net charge of the resins all affect the binding of HP-NAP to DEAE resins during the negative purification.

pH-activatable nanoparticles for tumor-specific drug delivery

NASA Astrophysics Data System (ADS)

Liu, Karen C.

To address the need for a tumor-specific drug delivery system that can achieve both prolonged circulation and cellular retention at the tumor site, nanocomplexes of Zwitterionic Chitosan (ZWC) and Polyamidoamine (PAMAM) generation 5 were designed. Polyamidoamine (PAMAM) dendrimers have been widely explored as carriers of therapeutics and imaging agents, however, amine-terminated PAMAM dendrimers are rarely utilized in systemic applications due to its cytotoxicity and risk of opsonization, caused by its cationic charge. Such undesirable effects may be mitigated by shielding the PAMAM dendrimer surface with polymers that reduce the charges. However, this shielding may also interfere with PAMAM dendrimers' ability to interact with target cells, thus reducing cellular uptake and overall efficacy of the delivery system. ZWC, a new chitosan derivative, has a unique pH-sensitive charge profile and can shield the cationic surface of PAMAM dendrimers and block adsorption of serum proteins to allow for prolonged circulation. The hypothesis of this approach is that ZWC is anionic and able to coat PAMAM in neutral pH but becomes positive in the acidic tumor microenvironment, revealing the polycationic drug carrier. We expect that ZWC will provide (i) stealth coating for PAMAM drug carrier during circulation (pH 7.4) and (ii) be removed from the PAMAM drug carrier at acidic pH (pH ~6.3), allowing for cellular interaction. The cationic charge of PAMAM has been demonstrated to facilitate uptake and drug delivery to tumor cells via interactions with the negatively charged cell surface. Stable electrostatic complexes of ZWC and PAMAM dendrimers were formed at pH 7.4, as demonstrated by fluorescence spectroscopy and transmission electron microscopy. The presence of ZWC coating protected red blood cells and fibroblast cells from hemolytic and cytotoxic activities of PAMAM dendrimers, respectively. Confocal microscopy showed that the protective effect of ZWC disappeared at low pH as the complex dissociated due to the charge conversion of ZWC, allowing PAMAM dendrimers to enter cells. These results demonstrate that ZWC is able to provide a surface coverage of PAMAM dendrimers in a pH-dependent manner and, thus, enhance the utility of PAMAM dendrimers as a drug carrier to solid tumors with acidifying microenvironment. Paclitaxel, curcumin, and camptothecin were evaluated as model drugs for use in ZWC(PAMAM) drug carrier based on bioactivity against SKOV-3 ovarian cancer cells and drug loading and release. Stability of nanocarriers in circulation is a requirement for successful tumor-specific drug release. Strategies to improve the stability of ZWC(PAMAM) NPs were also explored and evaluated.

Surface charge engineering of a Bacillus gibsonii subtilisin protease.

PubMed

Jakob, Felix; Martinez, Ronny; Mandawe, John; Hellmuth, Hendrik; Siegert, Petra; Maurer, Karl-Heinz; Schwaneberg, Ulrich

2013-08-01

In proteins, a posttranslational deamidation process converts asparagine (Asn) and glutamine (Gln) residues into negatively charged aspartic (Asp) and glutamic acid (Glu), respectively. This process changes the protein net charge affecting enzyme activity, pH optimum, and stability. Understanding the principles which affect these enzyme properties would be valuable for protein engineering in general. In this work, three criteria for selecting amino acid substitutions of the deamidation type in the Bacillus gibsonii alkaline protease (BgAP) are proposed and systematically studied in their influence on pH-dependent activity and thermal resistance. Out of 113 possible surface amino acids, 18 (11 Asn and 7 Gln) residues of BgAP were selected and evaluated based on three proposed criteria: (1) The Asn or Gln residues should not be conserved, (2) should be surface exposed, and (3) neighbored by glycine. "Deamidation" in five (N97, N253, Q37, Q200, and Q256) out of eight (N97, N154, N250, N253, Q37, Q107, Q200, and Q256) amino acids meeting all criteria resulted in increased proteolytic activity. In addition, pH activity profiles of the variants N253D and Q256E and the combined variant N253DQ256E were dramatically shifted towards higher activity at lower pH (range of 8.5-10). Variant N253DQ256E showed twice the specific activity of wild-type BgAP and its thermal resistance increased by 2.4 °C at pH 8.5. These property changes suggest that mimicking surface deamidation by substituting Gln by Glu and/or Asn by Asp might be a simple and fast protein reengineering approach for modulating enzyme properties such as activity, pH optimum, and thermal resistance.

Sorption Mechanisms of Antibiotic Cephapirin onto Quartz and Feldspar by Raman Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peterson, Jonathan; Wang, Wei; Gu, Baohua

2009-01-01

Raman spectroscopy was used to investigate the sorption mechanisms of cephapirin (CHP), a veterinary antibiotic, onto quartz (SiO2) and feldspar (KAlSi3O8) at different pH values. Depending on the charge and surface properties of the mineral, different reaction mechanisms including electrostatic attraction, monodentate and bidentate complexation were found to be responsible for CHP sorption. The zwitterion (CHPo) adsorbs to a quartz(+) surface by electrostatic attraction of the carboxylate anion group ( COO-) at a low pH, but adsorbs to a quartz(-) surface through electrostatic attraction of the pyridinium cation and possibly COO- bridge complexes at relatively higher pH conditions. CHP- bondsmore » to a quartz(-) surface by bidentate complexation between one oxygen of COO- and oxygen from the carbonyl (C=O) of the acetoxymethyl group. On a feldspar surface of mixed charge, CHPo forms monodentate complexes between C=O as well as COO- bridging complexes or electrostatically attached to localized edge (hydr)oxy-Al surfaces. CHP- adsorbs to feldspar(-) through monodentate C=O complexation, and similar mechanisms may operate for the sorption of other cephalosporins. This research demonstrates, for the first time, that Raman spectroscopic techniques can be effective for evaluating the sorption processes and mechanisms of cephalosporin antibiotics even at relatively low sorbed concentrations (97-120 μmol/kg).« less

Modelling charge interactions in the prion protein: predictions for pathogenesis.

PubMed

Warwicker, J

1999-04-30

Calculations are presented for the pH-dependence of stability and membrane charge complementarity of prion protein fragments. The theoretical results are compared with reported characterisations of prion protein folding in vitro. Discussion of models for conformational change and pathogenesis in vivo leads to the prediction of amino acids that could mediate sensitivity to the endosomal pH and to a design strategy for recombinant prion proteins with an increased susceptibility to prion proteinSc-like properties in vitro. In this model, the protective effect of certain basic polymorphisms can be interpreted in terms of oligomerisation on a negatively-charged surface.

Surface charge control for zwitterionic polymer brushes: Tailoring surface properties to antifouling applications.

PubMed

Guo, Shanshan; Jańczewski, Dominik; Zhu, Xiaoying; Quintana, Robert; He, Tao; Neoh, Koon Gee

2015-08-15

Electrostatic interactions play an important role in adhesion phenomena particularly for biomacromolecules and microorganisms. Zero charge valence of zwitterions has been claimed as the key to their antifouling properties. However, due to the differences in the relative strength of their acid and base components, zwitterionic materials may not be charge neutral in aqueous environments. Thus, their charge on surfaces should be further adjusted for a specific pH environment, e.g. physiological pH typical in biomedical applications. Surface zeta potential for thin polymeric films composed of polysulfobetaine methacrylate (pSBMA) brushes is controlled through copolymerizing zwitterionic SBMA and cationic methacryloyloxyethyltrimethyl ammonium chloride (METAC) via surface-initiated atom transfer polymerization. Surface properties including zeta potential, roughness, free energy and thickness are measured and the antifouling performance of these surfaces is assessed. The zeta potential of pSBMA brushes is -40 mV across a broad pH range. By adding 2% METAC, the zeta potential of pSBMA can be tuned to zero at physiological pH while minimally affecting other physicochemical properties including dry brush thickness, surface free energy and surface roughness. Surfaces with zero and negative zeta potential best resist fouling by bovine serum albumin, Escherichia coli and Staphylococcus aureus. Surfaces with zero zeta potential also reduce fouling by lysozyme more effectively than surfaces with negative and positive zeta potential. Copyright © 2015 Elsevier Inc. All rights reserved.

Surface speciation of yttrium and neodymium sorbed on rutile: Interpretations using the charge distribution model

NASA Astrophysics Data System (ADS)

Ridley, Moira K.; Hiemstra, Tjisse; Machesky, Michael L.; Wesolowski, David J.; van Riemsdijk, Willem H.

2012-10-01

The adsorption of Y3+ and Nd3+ onto rutile has been evaluated over a wide range of pH (3-11) and surface loading conditions, as well as at two ionic strengths (0.03 and 0.3 m), and temperatures (25 and 50 °C). The experimental results reveal the same adsorption behavior for the two trivalent ions onto the rutile surface, with Nd3+ first adsorbing at slightly lower pH values. The adsorption of both Y3+ and Nd3+ commences at pH values below the pHznpc of rutile. The experimental results were evaluated using a charge distribution (CD) and multisite complexation (MUSIC) model, and Basic Stern layer description of the electric double layer (EDL). The coordination geometry of possible surface complexes were constrained by molecular-level information obtained from X-ray standing wave measurements and molecular dynamic (MD) simulation studies. X-ray standing wave measurements showed an inner-sphere tetradentate complex for Y3+ adsorption onto the (1 1 0) rutile surface (Zhang et al., 2004b). The MD simulation studies suggest additional bidentate complexes may form. The CD values for all surface species were calculated based on a bond valence interpretation of the surface complexes identified by X-ray and MD. The calculated CD values were corrected for the effect of dipole orientation of interfacial water. At low pH, the tetradentate complex provided excellent fits to the Y3+ and Nd3+ experimental data. The experimental and surface complexation modeling results show a strong pH dependence, and suggest that the tetradentate surface species hydrolyze with increasing pH. Furthermore, with increased surface loading of Y3+ on rutile the tetradentate binding mode was augmented by a hydrolyzed-bidentate Y3+ surface complex. Collectively, the experimental and surface complexation modeling results demonstrate that solution chemistry and surface loading impacts Y3+ surface speciation. The approach taken of incorporating molecular-scale information into surface complexation models (SCMs) should aid in elucidating a fundamental understating of ion-adsorption reactions.

Influence of surface charge, binding site residues and glycosylation on Thielavia terrestris cutinase biochemical characteristics

PubMed Central

Shirke, Abhijit N.; Basore, Danielle; Holton, Samantha; Su, An; Baugh, Evan; Butterfoss, Glenn L.; Makhatadze, George

2016-01-01

Cutinases are esterases of industrial importance for applications in recycling and surface modification of polyesters. The cutinase from Thielavia terrestris (TtC) is distinct in terms of its ability to retain its stability and activity in acidic pH. Stability and activity in acidic pHs are desirable for esterases as the pH of the reaction tends to go down with the generation of acid. The pH stability and activity are governed by the charged state of the residues involved in catalysis or in substrate binding. In this study, we performed the detailed structural and biochemical characterization of TtC coupled with surface charge analysis to understand its acidic tolerance. The stability of TtC in acidic pH was rationalized by evaluating the contribution of charge interactions to the Gibbs free energy of unfolding at varying pHs. The activity of TtC was found to be limited by substrate binding affinity, which is a function of the surface charge. Additionally, the presence of glycosylation affects the biochemical characteristics of TtC owing to steric interactions with residues involved in substrate binding. PMID:26758295

Monitoring the degrafting of polyelectrolyte brushes by using surface gradients

NASA Astrophysics Data System (ADS)

Ko, Yeongun; Genzer, Jan

Polymer brushes comprise densely grafted polymer chains on surfaces, which possess high stability and high concentration of reactive centers per unit area compared to physisorbed polymer film. Polymer brushes are employed in many applications, including anti-fouling surfaces, cell adhesive surfaces, responsive surfaces, low-friction surfaces, etc. Recently, researchers reported that charged (or chargeable) polymer brushes can be degrafted from substrate while incubated in buffer solutions. Based on previous experiments conducted in our group and by others, we assume that chain degrafting results from the hydrolysis of Si-O groups in head-group of the initiator and/or the ester groups in main body of the initiator. The kinetic of hydrolysis is affected by mechanical forces acting on the initiator. Those forces depend on the molecular weight and the grafting density of the brush, and the concentration and distribution of charges along the macromolecule (tuned by pH - for weak electrolytes - and concentration of external salt). In this work, we study the stability of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes in two solvents (ethanol and water) at various pH values in water and under different levels of external salt concentration. National Science Foundation.

Impact of Environmental Conditions (pH, Ionic Strength, And Electrolyte Type) On The Surface Charge And Aggregation Of Silver Nanoparticles Suspensions

EPA Science Inventory

The impact of capping agents and environmental conditions (pH, ionic strength, and background electrolytes) on surface charge and aggregation potential of silver nanoparticles (AgNPs) suspensions were investigated. Capping agents are chemicals used in the synthesis of nanopartic...

Destabilization and Treatment of Emulsified Oils in Wastewaters by Electrocoagulation.

PubMed

Genc, Ayten; Bakirci, Busra

2016-11-01

  In this study, the optimum operating conditions for the treatment of emulsified oils by electrocoagulation were determined depending on droplet stability analysis. Zeta potential measurements were used as the indication of oil droplet charges. In addition, the effects of pH and ionic conductivity on the droplet sizes and surface charges were investigated. The studied emulsified oil droplet sizes were more sensitive to changes in pH rather than salt concentration. The droplets became larger and unstable in alkaline conditions. As the initial pH of wastewaters increased, the oil removal efficiency increased during the electrocoagulation experiments as well. The use of iron or aluminum electrodes resulted in higher removal efficiencies in comparison to stainless steel electrodes. In addition, the energy consumption for aluminum electrodes was much lower than iron electrodes. To obtain 98% oil removal efficiency, distance between the electrodes was recommended to be less than or equal to 1 cm.

Scaling Behavior for Ionic Transport and its Fluctuations in Individual Carbon Nanotubes.

PubMed

Secchi, Eleonora; Niguès, Antoine; Jubin, Laetitia; Siria, Alessandro; Bocquet, Lydéric

2016-04-15

In this Letter, we perform an experimental study of ionic transport and current fluctuations inside individual carbon nanotubes (CNTs). The conductance exhibits a power law behavior at low salinity, with an exponent close to 1/3 versus the salt concentration in this regime. This behavior is rationalized in terms of a salinity dependent surface charge, which is accounted for on the basis of a model for hydroxide adsorption at the (hydrophobic) carbon surface. This is in contrast to boron nitride nanotubes which exhibit a constant surface conductance. Further, we measure the low frequency noise of the ionic current in CNTs and show that the amplitude of the noise scales with the surface charge, with data collapsing on a master curve for the various studied CNTs at a given pH.

Model for screened, charge-regulated electrostatics of an eye lens protein: Bovine gammaB-crystallin

PubMed Central

Wahle, Christopher W.; Martini, K. Michael; Hollenbeck, Dawn M.; Langner, Andreas; Ross, David S.; Hamilton, John F.; Thurston, George M.

2018-01-01

We model screened, site-specific charge regulation of the eye lens protein bovine gammaB-crystallin (γ B) and study the probability distributions of its proton occupancy patterns. Using a simplified dielectric model, we solve the linearized Poisson-Boltzmann equation to calculate a 54 × 54 work-of-charging matrix, each entry being the modeled voltage at a given titratable site, due to an elementary charge at another site. The matrix quantifies interactions within patches of sites, including γB charge pairs. We model intrinsic pK values that would occur hypothetically in the absence of other charges, with use of experimental data on the dependence of pK values on aqueous solution conditions, the dielectric model, and literature values. We use Monte Carlo simulations to calculate a model grand-canonical partition function that incorporates both the work-of-charging and the intrinsic pK values for isolated γB molecules and we calculate the probabilities of leading proton occupancy configurations, for 4 < pH < 8 and Debye screening lengths from 6 to 20 Å. We select the interior dielectric value to model γB titration data. At pH 7.1 and Debye length 6.0 Å, on a given γB molecule the predicted top occupancy pattern is present nearly 20% of the time, and 90% of the time one or another of the first 100 patterns will be present. Many of these occupancy patterns differ in net charge sign as well as in surface voltage profile. We illustrate how charge pattern probabilities deviate from the multinomial distribution that would result from use of effective pK values alone and estimate the extents to which γB charge pattern distributions broaden at lower pH and narrow as ionic strength is lowered. These results suggest that for accurate modeling of orientation-dependent γB-γB interactions, consideration of numerous pairs of proton occupancy patterns will be needed. PMID:29346981

Model for screened, charge-regulated electrostatics of an eye lens protein: Bovine gammaB-crystallin.

PubMed

Wahle, Christopher W; Martini, K Michael; Hollenbeck, Dawn M; Langner, Andreas; Ross, David S; Hamilton, John F; Thurston, George M

2017-09-01

We model screened, site-specific charge regulation of the eye lens protein bovine gammaB-crystallin (γB) and study the probability distributions of its proton occupancy patterns. Using a simplified dielectric model, we solve the linearized Poisson-Boltzmann equation to calculate a 54×54 work-of-charging matrix, each entry being the modeled voltage at a given titratable site, due to an elementary charge at another site. The matrix quantifies interactions within patches of sites, including γB charge pairs. We model intrinsic pK values that would occur hypothetically in the absence of other charges, with use of experimental data on the dependence of pK values on aqueous solution conditions, the dielectric model, and literature values. We use Monte Carlo simulations to calculate a model grand-canonical partition function that incorporates both the work-of-charging and the intrinsic pK values for isolated γB molecules and we calculate the probabilities of leading proton occupancy configurations, for 4

Derivatizing weak polyelectrolytes--solution properties, self-aggregation, and association with anionic surfaces of hydrophobically modified poly(ethylene imine).

PubMed

Griffiths, Peter C; Paul, Alison; Fallis, Ian A; Wellappili, Champa; Murphy, Damien M; Jenkins, Robert; Waters, Sarah J; Nilmini, Renuka; Heenan, Richard K; King, Stephen M

2007-10-15

The physical properties of weak polyelectrolytes may be tailored via hydrophobic modification to exhibit useful properties under appropriate pH and ionic strength conditions as a consequence of the often inherently competing effects of electrostatics and hydrophobicity. Pulsed-gradient spin-echo NMR (PGSE-NMR), electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS) surface tension, fluorescence, and pH titration have been used to examine the solution conformation and aggregation behavior of a series of hydrophobically modified hyperbranched poly(ethylene imine) (PEI) polymers in aqueous solution, and their interaction with sodium dodecylsulfate (SDS). PGSE-NMR gave a particularly insightful picture of the apparent molecular weight distribution. The presence of the hydrophobes led to a lower effective charge on the polymer at any given pH, compared to the (parent) nonmodified samples. Analysis of the SANS data showed that the propensity to form highly elliptical or rod-like aggregates at higher pHs, reflecting both the changes in protonation behavior induced by the hydrophobic modification and an hydrophobic interaction, but that these structures were disrupted with decreasing pH (increasing charge). The parent samples were not surface active yet the hydrophobically modified samples show pronounced surface activity and the presence of small hydrophobic domains. The surface activity increased with an increase in the degree of modification. On addition of SDS, the onset of the formation of polymer/surfactant complexes was insensitive to the degree of modification with the resultant PEI/SDS complexes resembling the size and shape of simple SDS micelles. Indeed, the presence of the SDS effectively nullifies the effects of the hydrophobe. Hydrophobic modification is therefore a viable option to tailor pH dependent properties, whose effects may be removed by the presence of surfactant.

Polyelectrolyte coating on superparamagnetic iron oxide nanoparticles as interface between magnetic core and biorelevant media

PubMed Central

Farkas, Katalin; Földesi, Imre; Szekeres, Márta; Illés, Erzsébet; Tóth, Ildikó Y.; Nesztor, Daniel; Szabó, Tamás

2016-01-01

Nanoparticles do not exist in thermodynamical equilibrium because of high surface free energy, thus they have only kinetic stability. Spontaneous changes can be delayed by designed surface coating. In biomedical applications, superparamagnetic iron oxide nanoparticles (SPIONs) require an optimized coating in order to fulfil the expectation of medicine regulatory agencies and ultimately that of biocompatibility. In this work, we show the high surface reactivity of naked SPIONs due to ≡Fe–OH sites, which can react with H+/OH− to form pH- and ionic strength-dependent charges. We explain the post-coating of naked SPIONs with organic polyacids via multi-site complex bonds formed spontaneously. The excess polyacids can be removed from the medium. The free COOH groups in coating are prone to react with active biomolecules like proteins. Charging and pH- and salt-dependent behaviour of carboxylated SPIONs were characterized quantitatively. The interrelation between the coating quality and colloidal stability measured under biorelevant conditions is discussed. Our coagulation kinetics results allow us to predict colloidal stability both on storage and in use; however, a simpler method would be required to test SPION preparations. Haemocompatibility tests (smears) support our qualification for good and bad SPION manufacturing; the latter ‘promises’ fatal outcome in vivo. PMID:27920900

Ion transport in a pH-regulated nanopore.

PubMed

Yeh, Li-Hsien; Zhang, Mingkan; Qian, Shizhi

2013-08-06

Fundamental understanding of ion transport phenomena in nanopores is crucial for designing the next-generation nanofluidic devices. Due to surface reactions of dissociable functional groups on the nanopore wall, the surface charge density highly depends upon the proton concentration on the nanopore wall, which in turn affects the electrokinetic transport of ions, fluid, and particles within the nanopore. Electrokinetic ion transport in a pH-regulated nanopore, taking into account both multiple ionic species and charge regulation on the nanopore wall, is theoretically investigated for the first time. The model is verified by the experimental data of nanopore conductance available in the literature. The results demonstrate that the spatial distribution of the surface charge density at the nanopore wall and the resulting ion transport phenomena, such as ion concentration polarization (ICP), ion selectivity, and conductance, are significantly affected by the background solution properties, such as the pH and salt concentration.

Adsorption behaviour of methylene blue onto Jordanian diatomite: a kinetic study.

PubMed

Al-Ghouti, Mohammad A; Khraisheh, Majeda A M; Ahmad, Mohammad N M; Allen, Stephen

2009-06-15

The effect of initial concentration, particle size, mass of the adsorbent, pH and agitation speed on adsorption behaviour of methylene blue (MB) onto Jordanian diatomite has been investigated. The maximum adsorption capacity, q, increased from 75 to 105 mg/g when pH of the dye solution increased from 4 to 11. It is clear that the ionisable charge sites on the diatomite surface increased when pH increased from 4 to 11. When the solution pH was above the pH(ZPC), the diatomite surface had a negative charge, while at low pH (pH<5.4) it has a positive charge. The adsorption capacity increased from 88.6 to 143.3mg/g as the initial MB concentrations increased from 89.6 to 225.2mg/dm(3). The experimental results were also applied to the pseudo-first and -second order kinetic models. It is noticed that the whole experimental data of MB adsorption onto diatomite did not follow the pseudo-first order model and had low correlation coefficients (R(2)<0.3). The calculated adsorption capacity, q(e,cal), values obtained from pseudo-first order kinetic model did not give acceptable values, q(e,exp.) The maximum uptake capacity seems to be independent of the particle size of the diatomite when the particle size distribution is less than 250-500 microm. While at larger particle size 250-500 microm, the maximum uptake capacity was dependent on the particle size. It would imply that the MB adsorption is limited by the external surface and that intraparticle diffusion is reduced. The effect of the agitation speeds on the removal of MB from aqueous solution using the diatomite is quite low. The MB removal increased from 43 to 100% when mass of the diatomite increased from 0.3 to 1.7 g.

Dendrimer-protein interactions versus dendrimer-based nanomedicine.

PubMed

Shcharbin, Dzmitry; Shcharbina, Natallia; Dzmitruk, Volha; Pedziwiatr-Werbicka, Elzbieta; Ionov, Maksim; Mignani, Serge; de la Mata, F Javier; Gómez, Rafael; Muñoz-Fernández, Maria Angeles; Majoral, Jean-Pierre; Bryszewska, Maria

2017-04-01

Dendrimers are hyperbranched polymers belonging to the huge class of nanomedical devices. Their wide application in biology and medicine requires understanding of the fundamental mechanisms of their interactions with biological systems. Summarizing, electrostatic force plays the predominant role in dendrimer-protein interactions, especially with charged dendrimers. Other kinds of interactions have been proven, such as H-bonding, van der Waals forces, and even hydrophobic interactions. These interactions depend on the characteristics of both participants: flexibility and surface charge of a dendrimer, rigidity of protein structure and the localization of charged amino acids at its surface. pH and ionic strength of solutions can significantly modulate interactions. Ligands and cofactors attached to a protein can also change dendrimer-protein interactions. Binding of dendrimers to a protein can change its secondary structure, conformation, intramolecular mobility and functional activity. However, this strongly depends on rigidity versus flexibility of a protein's structure. In addition, the potential applications of dendrimers to nanomedicine are reviwed related to dendrimer-protein interactions. Copyright © 2017 Elsevier B.V. All rights reserved.

pH-Dependence of Binding Constants and Desorption Rates of Phosphonate- and Hydroxamate-Anchored [Ru(bpy)3]2+ on TiO2 and WO3.

PubMed

Esarey, Samuel L; Bartlett, Bart M

2018-04-17

The binding constants and rate constants for desorption of the modified molecular dye [Ru(bpy) 3 ] 2+ anchored by either phosphonate or hydroxamate on the bipyridine ligand to anatase TiO 2 and WO 3 have been measured. In aqueous media at pH 1-10, repulsive electrostatic interactions between the negatively charged anchor and the negatively charged surface govern phosphonate desorption under neutral and basic conditions for TiO 2 anatase due to the high acidity of phosphonic acid (p K a,4 = 5.1). In contrast, the lower acidity of hydroxamate (p K a,1 = 6.5, p K a,2 = 9.1) leads to little change in adsorption/desorption properties as a function of pH from 1 to 7. The binding constant for hydroxamate is 10 3 in water, independent of pH in this range. These results are true for WO 3 as well, but are not reported at pH > 4 due to its Arrhenius acidity. Kinetics for desorption as a function of pH are reported, with a proposed mechanism for phosphonate desorption at high pH being the electrostatic repulsion of negative charges between the surface and the anionic anchor. Further, the hydroxamic acid anchor itself is likely the site of quasi-reversible redox activity in [Ru(bpy) 2 (2,2'-bpy-4,4'-(C(O)N(OH)) 2 )] 2+ , which does not lead to any measurable deterioration of the complex within 2 h of dark cyclic voltammogram scans in aqueous media. These results posit phosphonate as the preferred anchoring group under acidic conditions and hydroxamate for neutral/basic conditions.

Single Nanoparticle Translocation Through Chemically Modified Solid Nanopore

NASA Astrophysics Data System (ADS)

Tan, Shengwei; Wang, Lei; Liu, Hang; Wu, Hongwen; Liu, Quanjun

2016-02-01

The nanopore sensor as a high-throughput and low-cost technology can detect single nanoparticle in solution. In the present study, the silicon nitride nanopores were fabricated by focused Ga ion beam (FIB), and the surface was functionalized with 3-aminopropyltriethoxysilane to change its surface charge density. The positively charged nanopore surface attracted negatively charged nanoparticles when they were in the vicinity of the nanopore. And, nanoparticle translocation speed was slowed down to obtain a clear and deterministic signal. Compared with previous studied small nanoparticles, the electrophoretic translocation of negatively charged polystyrene (PS) nanoparticles (diameter ~100 nm) was investigated in solution using the Coulter counter principle in which the time-dependent nanopore current was recorded as the nanoparticles were driven across the nanopore. A linear dependence was found between current drop and biased voltage. An exponentially decaying function ( t d ~ e -v/v0 ) was found between the duration time and biased voltage. The interaction between the amine-functionalized nanopore wall and PS microspheres was discussed while translating PS microspheres. We explored also translocations of PS microspheres through amine-functionalized solid-state nanopores by varying the solution pH (5.4, 7.0, and 10.0) with 0.02 M potassium chloride (KCl). Surface functionalization showed to provide a useful step to fine-tune the surface property, which can selectively transport molecules or particles. This approach is likely to be applied to gene sequencing.

Ionic strength effects on silicic acid (H4SiO4) sorption and oligomerization on an iron oxide surface: an interesting interplay between electrostatic and chemical forces.

PubMed

Hamid, Rossuriati Dol; Swedlund, Peter J; Song, Yantao; Miskelly, Gordon M

2011-11-01

The effect of ionic strength on reactions at aqueous interfaces can provide insights into the nature of the chemistry involved. The adsorption of H(4)SiO(4) on iron oxides at low surface silicate concentration (Γ(Si)) forms monomeric silicate complexes with Fe-O-Si linkages, but as Γ(Si) increases silicate oligomers with Si-O-Si linkages become increasingly prevalent. In this paper, the effect of ionic strength (I) on both Γ(Si) and the extent of silicate oligomerization on the ferrihydrite surface is determined at pH 4, 7, and 10, where the surface is, respectively, positive, nearly neutral, and negatively charged. At pH 4, an increase in ionic strength causes Γ(Si) to decrease at a given H(4)SiO(4) solution concentration, while the proportion of oligomers on the surface at a given Γ(Si) increases. At pH 10, the opposite is observed; Γ(Si) increases as I increases, while the proportion of surface oligomers at a given Γ(Si) decreases. Ionic strength has only a small effect on the surface chemistry of H(4)SiO(4) at pH 7, but at low Γ(Si) this effect is in the direction observed at pH 4 while at high Γ(Si) the effect is in the direction observed at pH 10. The pH where the surface has zero charge decreases from ≈8 to 6 as Γ(Si) increases so that the surface potential (Ψ) is positive at pH 4 for all Γ(Si) and at pH 7 with low Γ(Si). Likewise, Ψ < 0 at pH 10 for all Γ(Si) and at pH 7 with high Γ(Si). The diffuse layer model is used to unravel the complex and subtle interactions between surface potential (Ψ) and chemical parameters that influence interfacial silicate chemistry. This analysis reveals that the decrease in the absolute value of Ψ as I increases causes Γ(Si) to decrease or increase where Ψ is, respectively, positive or negative. Therefore, at a given Γ(Si), the solution H(4)SiO(4) concentration changes with I, and because oligomerization has a higher H(4)SiO(4) stoichiometry coefficient than monomer adsorption, this results in the observed dependence of the extent of silicate oligomerization on I.

Macroion induced dehydration of weak polyelectrolyte brushes

NASA Astrophysics Data System (ADS)

Zheng, Zhongli; Zhu, Y. Elaine

2014-03-01

The interaction of macroions, including polyelectrolytes, DNAs, and proteins, with polymer and cellular surfaces is critically related to many biomolecular activities, such as protein adsorption and DNA hybridization at probe surfaces. In an experimental approach to examine the macroion electrostatic interaction with a polymer surface while minimizing the long-debated hydrophobic interaction, we study the interaction of molybdenum-based inorganic polyoxometalate (POM) nanoclusters carrying 42 negative charges as model hydrophilic macroions with surface-tethered poly-2-vinylpyridine (P2VP) brushes immersed in aqueous solutions. By AFM, QCM, and contact goniometer, we have observed the collapse of P2VP chains by adding POM macroions at a constant pH. Surprisingly, added POM macroions can cause the shift of swollen-to-collapse transition pH to a lower value, in contrast to the shift to high pH value by adding simple monovalent salts. At sufficiently high POM concentration, a stable POM-P2VP composite layer, showing little dependence on solution pH and additional salts, can be formed, suggesting a simple route to construct meso-porous polymer membranes.

Observation of Iron Specific Interaction with a Charge Neutral Phospholipid

NASA Astrophysics Data System (ADS)

Wang, Wenjie; Zhang, Honghu; Feng, Shuren; San Emeterio, Josue; Kuzmenko, Ivan; Nilsen-Hamilton, Marit; Mallapragada, Surya; Vaknin, David

2015-03-01

Using surface sensitive X-ray scattering and spectroscopic techniques we show that phosphatidyl choline (PC) head groups attract positively charged iron ions and complexes even at pH values that are lower than 3. DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) is a zwitterionic lipid typically used as a model system for cell membranes. Within a large pH range (3 -11), it carries a negative charge on the phosphate group and a positive charge on the quaternary ammonium cation, thus appears charge neutral. Further lowering the pH, i.e. adding a proton to the phosphate group, results in a positively charged headgroup. Surprisingly, we detect significant enrichment of iron at the interface of the DPPC monolayer and the aqueous subphase with the pH maintained at 3 or even lower. With a supposedly charge neutral or even positive surface, the observation of surface bound, charge positive iron ions or iron hydroxides is counter-intuitive and suggests iron-specific interaction with the phospholipid headgroup, which is not governed by electrostatic interaction. The effect of the integration of Mms6, a membrane protein that promotes the formation of magnetic nanocrystals, into the DPPC monolayer will also be discussed. Research supported by the U.S. Department of Energy under Contract No. DE-AC02-07CH11358 and DE-AC02-06CH11357.

Simulating the thermodynamics of charging in weak polyelectrolytes: the Debye-Hückel limit

NASA Astrophysics Data System (ADS)

Rathee, Vikramjit S.; Sikora, Benjamin J.; Sidky, Hythem; Whitmer, Jonathan K.

2018-01-01

The coil-globule transition in weak (annealed) polyelectrolytes involves a subtle balance of pH, charge strength, and solvation forces. In this work, we utilize a coarse-grained hybrid grand-canonical Monte Carlo and molecular dynamics approach to explore the swelling behavior of weak linear and star polyelectrolytes under different ionic screening conditions and pH. Importantly, we are able to quantify topology-dependent effects in charging which arise at the core of star polymers. Our results are suggestive of suppression of charging in star weak polyelectrolytes in comparison to linear weak polyelectrolytes. Furthermore, we characterize the coil-globule transition in linear and star weak polyelectrolyte through expanded ensemble density-of-states simulations which suggest a change from a first order to second order phase transition moving from linear to star polyelectrolytes. Lastly, we characterize the inhomogeneous charging across the weak star polyelectrolyte through observed shifts in {{Δ }}{{{pK}}}{{o}}, and compare with experimental work. We discuss these results in relation to surfaces functionalized by weak polyelectrolyte brushes and weak polyelectrolyte-based drug delivery applications.

Solution pH and oligoamine molecular weight dependence of the transition from monolayer to multilayer adsorption at the air-water interface from sodium dodecyl sulfate/oligoamine mixtures.

PubMed

Halacheva, S S; Penfold, J; Thomas, R K; Webster, J R P

2013-05-14

Neutron reflectivity and surface tension have been used to investigate the solution pH and oligoamine molecular weight dependence of the adsorption of sodium dodecyl sulfate (SDS)/oligoamine mixtures at the air-water interface. For diethylenetriamine, triamine, or triethylenetetramine, tetramine mixed with SDS, there is monolayer adsorption at pH 7 and 10, and multilayer adsorption at pH 3. For the slightly higher molecular weight tetraethylenepentamine, pentamine, and pentaethylenehexamine, hexamine, the adsorption is in the form of a monolayer at pH 3 and multilayers at pH 7 and 10. Hence, there is a pH driven transition from monolayer to multilayer adsorption, which shifts from low pH to higher pH as the oligoamine molecular weight increases from tetramine to pentamine. This results from the relative balance between the electrostatic attraction between the SDS and amine nitrogen group which decreases as the charge density decreases with increasing pH, the ion-dipole interaction between the amine nitrogen and SDS sulfate group which is dominant at higher pH, and the hydrophobic interalkyl chain interaction between bound SDS molecules which changes with oligoamine molecular weight.

Adsorptive Removal of Nitrate from Aqueous Solution Using Nitrogen Doped Activated Carbon.

PubMed

Machida, Motoi; Goto, Tatsuru; Amano, Yoshimasa; Iida, Tatsuya

2016-01-01

Activated carbon (AC) has been widely applied for adsorptive removal of organic contaminants from aqueous phase, but not for ionic pollutants. In this study, nitrogen doped AC was prepared to increase the adsorption capacity of nitrate from water. AC was oxidized with (NH 4 ) 2 S 2 O 8 solution to maximize oxygen content for the first step, and then NH 3 gas treatment was carried out at 950°C to aim at forming quaternary nitrogen (N-Q) species on AC surface (Ox-9.5AG). Influence of solution pH was examined so as to elucidate the relationship between surface charge and adsorption amounts of nitrate. The results showed that Ox-9.5AG exhibited about twice higher adsorption capacity than non-treatment AC at any initial nitrate concentration and any equilibrium solution pH (pH e ) investigated. The more decrease in pH e value, the more adsorption amount of negatively charged nitrate ion, because the surface charge of AC and Ox-9.5AG could become more positive in acidic solution. The oxidation and consecutive ammonia treatments lead to increase in nitrogen content from 0.35 to 6.4% and decrease in the pH of the point of zero charge (pH pzc ) from 7.1 to 4.0 implying that positively charged N-Q of a Lewis acid was created on the surface of Ox-9.5AG. Based on a Langmuir data analysis, maximum adsorption capacity attained 0.5-0.6 mmol/g of nitrate and adsorption affinity was 3.5-4.0 L/mmol at pH e 2.5 for Ox-9.5AG.

pH-Switchable Interaction of a Carboxybetaine Ester-Based SAM with DNA and Gold Nanoparticles.

PubMed

Filip, Jaroslav; Popelka, Anton; Bertok, Tomas; Holazova, Alena; Osicka, Josef; Kollar, Jozef; Ilcikova, Marketa; Tkac, Jan; Kasak, Peter

2017-07-11

We describe a self-assembled monolayer (SAM) on a gold surface with a carboxybetaine ester functionality to control the interaction between DNA and gold nanoparticles via pH. The negatively charged phosphate backbone of DNA interacts with and adsorbs to the positively charged carboxybetaine esters on the SAM. DNA release can be achieved by the hydrolysis of carboxybetaine ester (CBE) to a zwitterionic carboxybetaine state. Furthermore, the adsorption of negatively charged citrate-capped gold nanoparticles to a SAM-modified plain gold surface can be controlled by the pH. The SAM based on carboxybetaine ester allows for the homogeneous adsorption of particles, whereas the SAM after hydrolysis at high pH repels AuNP adsorption. The antifouling surface properties of the surface modified with carboxybetaine were investigated with protein samples.

Comparison of calculation and experiment implicates significant electrostatic contributions to the binding stability of barnase and barstar.

PubMed

Dong, Feng; Vijayakumar, M; Zhou, Huan-Xiang

2003-07-01

The contributions of electrostatic interactions to the binding stability of barnase and barstar were studied by the Poisson-Boltzmann model with three different protocols: a), the dielectric boundary specified as the van der Waals (vdW) surface of the protein along with a protein dielectric constant (epsilon (p)) of 4; b), the dielectric boundary specified as the molecular (i.e., solvent-exclusion (SE)) surface along with epsilon (p) = 4; and c), "SE + epsilon (p) = 20." The "vdW + epsilon (p) = 4" and "SE + epsilon (p) = 20" protocols predicted an overall electrostatic stabilization whereas the "SE + epsilon (p) = 4" protocol predicted an overall electrostatic destabilization. The "vdW + epsilon (p) = 4" protocol was most consistent with experiment. It quantitatively reproduced the observed effects of 17 mutations neutralizing charged residues lining the binding interface and the measured coupling energies of six charge pairs across the interface and reasonably rationalized the experimental ionic strength and pH dependences of the binding constant. In contrast, the "SE + epsilon (p) = 4" protocol predicted significantly larger coupling energies of charge pairs whereas the "SE + epsilon (p) = 20" protocol did not predict any pH dependence. This study calls for further scrutiny of the different Poisson-Boltzmann protocols and demonstrates potential danger in drawing conclusions on electrostatic contributions based on a particular calculation protocol.

A semi-grand canonical Monte Carlo simulation model for ion binding to ionizable surfaces: proton binding of carboxylated latex particles as a case study.

PubMed

Madurga, Sergio; Rey-Castro, Carlos; Pastor, Isabel; Vilaseca, Eudald; David, Calin; Garcés, Josep Lluís; Puy, Jaume; Mas, Francesc

2011-11-14

In this paper, we present a computer simulation study of the ion binding process at an ionizable surface using a semi-grand canonical Monte Carlo method that models the surface as a discrete distribution of charged and neutral functional groups in equilibrium with explicit ions modelled in the context of the primitive model. The parameters of the simulation model were tuned and checked by comparison with experimental titrations of carboxylated latex particles in the presence of different ionic strengths of monovalent ions. The titration of these particles was analysed by calculating the degree of dissociation of the latex functional groups vs. pH curves at different background salt concentrations. As the charge of the titrated surface changes during the simulation, a procedure to keep the electroneutrality of the system is required. Here, two approaches are used with the choice depending on the ion selected to maintain electroneutrality: counterion or coion procedures. We compare and discuss the difference between the procedures. The simulations also provided a microscopic description of the electrostatic double layer (EDL) structure as a function of pH and ionic strength. The results allow us to quantify the effect of the size of the background salt ions and of the surface functional groups on the degree of dissociation. The non-homogeneous structure of the EDL was revealed by plotting the counterion density profiles around charged and neutral surface functional groups. © 2011 American Institute of Physics

Decreasing DOC trends in soil solution along the hillslopes at two IM sites in southern Sweden--geochemical modeling of organic matter solubility during acidification recovery.

PubMed

Löfgren, Stefan; Gustafsson, Jon Petter; Bringmark, Lage

2010-12-01

Numerous studies report increased concentrations of dissolved organic carbon (DOC) during the last two decades in boreal lakes and streams in Europe and North America. Recently, a hypothesis was presented on how various spatial and temporal factors affect the DOC dynamics. It was concluded that declining sulphur deposition and thereby increased DOC solubility, is the most important driver for the long-term DOC concentration trends in surface waters. If this recovery hypothesis is correct, the DOC levels should increase both in the soil solution as well as in the surrounding surface waters as soil pH rises and the ionic strength declines due to the reduced input of SO(4)(2-) ions. In this project a geochemical model was set up to calculate the net humic charge and DOC solubility trends in soils during the period 1996-2007 at two integrated monitoring sites in southern Sweden, showing clear signs of acidification recovery. The Stockholm Humic Model was used to investigate whether the observed DOC solubility is related to the humic charge and to examine how pH and ionic strength influence it. Soil water data from recharge and discharge areas, covering both podzols and riparian soils, were used. The model exercise showed that the increased net charge following the pH increase was in many cases counteracted by a decreased ionic strength, which acted to decrease the net charge and hence the DOC solubility. Thus, the recovery from acidification does not necessarily have to generate increasing DOC trends in soil solution. Depending on changes in pH, ionic strength and soil Al pools, the trends might be positive, negative or indifferent. Due to the high hydraulic connectivity with the streams, the explanations to the DOC trends in surface waters should be searched for in discharge areas and peat lands. Copyright © 2010 Elsevier B.V. All rights reserved.

The Strength of Disease: Molecular Bonds Between Asbestos and Human Cells

NASA Astrophysics Data System (ADS)

Taylor, E. S.; Lower, S. K.; Wylie, A. G.; Mossman, B. T.

2008-12-01

Occupational exposure to asbestos has been linked to the development of life-threatening cancers (i.e., mesothelioma) and diseases (i.e., asbestosis), which can sometimes take decades to appear after initial exposure. There is increasing evidence that environmental exposure to asbestos is a significant public health concern in some regions of the United States, and this type of asbestos contamination could lead to an epidemic of mesothelioma for at least the next two decades. Although mines and regions nearby should be safer with stricter protocols for processing asbestos, the long latent period for asbestos-related diseases makes understanding them an ever-present concern. In addition to the many epidemiological studies, laboratory in vitro and in vivo studies on the biochemical effect of asbestos show that the most trusted predictor for disease is the dosage of longer, thinner chrysotile and amphibole asbestos fibers. However, many scientists agree that incorporating the many physical and chemical properties of the mineral fibers is needed to properly assess their influence. The study of asbestos-related disease is essentially a multidisciplinary task, requiring knowledge from medicine, biochemistry and mineralogy. To bridge the gap between these disciplines, attention needs to be placed on the molecular communication between the asbestos fibers and the biological environments in which they can be deposited. Our work focused on determining the surface chemical response of riebeckite and crocidolite-its asbestiform counterpart-to changes in salinity and pH. As expected, studies on the mineral surface charge using atomic force microscopy (AFM) yielded a slight dependence on pH, as measured by the adhesion force acting on the probe, but not on ionic strength, except at near zero salt concentration. A transition was found for the surface charge of crocidolite above pH 7, where forces at the mineral surface increased. In contrast, the surface charge on riebeckite was not dependent on pH or ionic strength. Since the AFM probe was coated with a short chain polymer film, the application of our data should naturally proceed to comparison with protein-functionalized probes as they interact with crocidolite asbestos and riebeckite amphibole for a more detailed understanding of the response of biomolecules to asbestos and non-asbestos fragments.

The effect of net charge on the solubility, activity, and stability of ribonuclease Sa.

PubMed

Shaw, K L; Grimsley, G R; Yakovlev, G I; Makarov, A A; Pace, C N

2001-06-01

The net charge and isoelectric pH (pI) of a protein depend on the content of ionizable groups and their pK values. Ribonuclease Sa (RNase Sa) is an acidic protein with a pI = 3.5 that contains no Lys residues. By replacing Asp and Glu residues on the surface of RNase Sa with Lys residues, we have created a 3K variant (D1K, D17K, E41K) with a pI = 6.4 and a 5K variant (3K + D25K, E74K) with a pI = 10.2. We show that pI values estimated using pK values based on model compound data can be in error by >1 pH unit, and suggest how the estimation can be improved. For RNase Sa and the 3K and 5K variants, the solubility, activity, and stability have been measured as a function of pH. We find that the pH of minimum solubility varies with the pI of the protein, but that the pH of maximum activity and the pH of maximum stability do not.

Scaling Behavior for Ionic Transport and its Fluctuations in Individual Carbon Nanotubes

PubMed Central

Secchi, Eleonora; Niguès, Antoine; Jubin, Laetitia; Siria, Alessandro; Bocquet, Lydéric

2016-01-01

In this Letter, we perform an experimental study of ionic transport and current fluctuations inside individual carbon nanotubes (CNTs). The conductance exhibits a power law behavior at low salinity, with an exponent close to 1/3 versus the salt concentration in this regime. This behavior is rationalized in terms of a salinity dependent surface charge, which is accounted for on the basis of a model for hydroxide adsorption at the (hydrophobic) carbon surface. This is in contrast to boron nitride nanotubes which exhibit a constant surface conductance. Further, we measure the low frequency noise of the ionic current in CNTs and show that the amplitude of the noise scales with the surface charge, with data collapsing on a master curve for the various studied CNTs at a given pH. PMID:27127970

External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba

PubMed Central

1994-01-01

Previous studies reveal that the pH of the apoplastic solution in the guard cell walls may vary between 7.2 and 5.1 in closed and open stomata, respectively. During these aperture and pH changes, massive K+ fluxes cross the cellular plasma membrane driving the osmotic turgor and volume changes of guard cells. Therefore, we examined the effect of extracellular pH on the depolarization-activated K channels (KD channels), which constitute the K+ efflux pathway, in the plasma membrane of Vicia faba guard cell protoplasts. We used patch clamp, both in whole cells as well as in excised outside-out membrane patches. Approximately 500 KD channels, at least, could be activated by depolarization in one protoplast (density: approximately 0.6 micron-2). Acidification from ph 8.1 to 4.4 decreased markedly the whole-cell conductance, GK, of the KD channels, shifted its voltage dependence, GK- EM, to the right on the voltage axis, slowed the rate of activation and increased the rate of deactivation, whereas the single channel conductance was not affected significantly. Based on the GK-EM shifts, the estimated average negative surface charge spacing near the KD channel is 39 A. To quantify the effects of protons on the rates of transitions between the hypothesized conformational states of the channels, we fitted the experimental macroscopic steady state conductance-voltage relationship and the voltage dependence of time constants of activation and deactivation, simultaneously, with a sequential three-state model CCO. In terms of this model, protonation affects the voltage-dependent properties via a decrease in localized, rather than homogeneous, surface charge sensed by the gating moieties. In terms of either the CO or CCO model, the protonation of a site with a pKa of 4.8 decreases the voltage-independent number of channels, N, that are available for activation by depolarization. PMID:8035163

Chitosan based atorvastatin nanocrystals: effect of cationic charge on particle size, formulation stability, and in-vivo efficacy

PubMed Central

Kurakula, Mallesh; El-Helw, AM; Sobahi, Tariq R; Abdelaal, Magdy Y

2015-01-01

Cationic charged chitosan as stabilizer was evaluated in preparation of nanocrystals using probe sonication method. The influence of cationic charge densities of chitosan (low CSL, medium CSM, high CSH molecular weights) and Labrasol® in solubility enhancement and modifying the release was investigated, using atorvastatin (ATR) as poorly soluble model drug. Compared to CSM and CSH; low cationic charge of CSL acted as both electrostatic and steric stabilizer by significant size reduction to 394 nm with charge of 21.5 meV. Solubility of ATR-CSL increased to 60-fold relative to pure ATR and ATR-L. Nanocrystals were characterized for physiochemical properties. Scanning electron microscopy revealed scaffold-like structures with high surface area. X-ray powder diffractometry and differential scanning calorimetry revealed crystalline to slight amorphous state changes after cationic charge size reduction. Fourier transform-infrared spectra indicated no potent drug-excipient interactions. The enhanced dissolution profile of ATR-CSL indicates that sustained release was achieved compared with ATR-L and Lipitor®. Anti-hyperlipidemic performance was pH dependent where ATR-CSL exhibited 2.5-fold higher efficacy at pH 5 compared to pH 6 and Lipitor®. Stability studies indicated marked changes in size and charge for ATR-L compared to ATR-CSL exemplifying importance of the stabilizer. Therefore, nanocrystals developed with CSL as a stabilizer is a promising choice to enhance dissolution, stability, and in-vivo efficacy of major Biopharmaceutical Classification System II/IV drugs. PMID:25609947

Colloidal behavior of aluminum oxide nanoparticles as affected by pH and natural organic matter.

PubMed

Ghosh, Saikat; Mashayekhi, Hamid; Pan, Bo; Bhowmik, Prasanta; Xing, Baoshan

2008-11-04

The colloidal behavior of aluminum oxide nanoparticles (NPs) was investigated as a function of pH and in the presence of two structurally different humic acids (HAs), Aldrich HA (AHA) and the seventh HA fraction extracted from Amherst peat soil (HA7). Dynamic light scattering (DLS) and atomic force microscopy (AFM) were employed to determine the colloidal behavior of the NPs. Influence of pH and HAs on the surface charges of the NPs was determined. zeta-Potential data clearly showed that the surface charge of the NPs decreased with increasing pH and reached the point of zero charge (ZPC) at pH 7.9. Surface charge of the NPs also decreased with the addition of HAs. The NPs tend to aggregate as the pH of the suspension approaches ZPC, where van der Waals attraction forces dominate over electrostatic repulsion. However, the NP colloidal suspension was stable in the pHs far from ZPC. Colloidal stability was strongly enhanced in the presence of HAs at the pH of ZPC or above it, but in acidic conditions NPs showed strong aggregation in the presence of HAs. AFM imaging revealed the presence of long-chain fractions in HA7, which entangled with the NPs to form large aggregates. The association of HA with the NP surface can be assumed to follow a two-step process, possibly the polar fractions of the HA7 sorbed on the NP surface followed by entanglement with the long-chain fractions. Thus, our study demonstrated that the hydrophobic nature of the HA molecules strongly influenced the aggregation of colloidal NPs, possibly through their conformational behavior in a particular solution condition. Therefore, various organic matter samples will result in different colloidal behavior of NPs, subsequently their environmental fate and transport.

Characterization of the Adsorption of Nucleic Acid Bases onto Ferrihydrite via Fourier Transform Infrared and Surface-Enhanced Raman Spectroscopy and X-ray Diffractometry.

PubMed

Canhisares-Filho, José E; Carneiro, Cristine E A; de Santana, Henrique; Urbano, Alexandre; da Costa, Antonio C S; Zaia, Cássia T B V; Zaia, Dimas A M

2015-09-01

Minerals could have played an important role in concentration, protection, and polymerization of biomolecules. Although iron is the fourth most abundant element in Earth's crust, there are few works in the literature that describe the use of iron oxide-hydroxide in prebiotic chemistry experiments. In the present work, the interaction of adenine, thymine, and uracil with ferrihydrite was studied under conditions that resemble those of prebiotic Earth. At acidic pH, anions in artificial seawater decreased the pH at the point of zero charge (pHpzc) of ferrihydrite; and at basic pH, cations increased the pHpzc. The adsorption of nucleic acid bases onto ferrihydrite followed the order adenine > uracil > thymine. Adenine adsorption peaked at neutral pH; however, for thymine and uracil, adsorption increased with increasing pH. Electrostatic interactions did not appear to play an important role on the adsorption of nucleic acid bases onto ferrihydrite. Adenine adsorption onto ferrihydrite was higher in distilled water compared to artificial seawater. After ferrihydrite was mixed with artificial seawaters or nucleic acid bases, X-ray diffractograms and Fourier transform infrared spectra did not show any change. Surface-enhanced Raman spectroscopy showed that the interaction of adenine with ferrihydrite was not pH-dependent. In contrast, the interactions of thymine and uracil with ferrihydrite were pH-dependent such that, at basic pH, thymine and uracil lay flat on the surface of ferrihydrite, and at acidic pH, thymine and uracil were perpendicular to the surface. Ferrihydrite adsorbed much more adenine than thymine; thus adenine would have been better protected against degradation by hydrolysis or UV radiation on prebiotic Earth.

Adsorption of weak polyelectrolytes on charged nanoparticles. Impact of salt valency, pH, and nanoparticle charge density. Monte Carlo simulations.

PubMed

Carnal, Fabrice; Stoll, Serge

2011-10-27

Complex formation between a weak flexible polyelectrolyte chain and one positively charged nanoparticle in presence of explicit counterions and salt particles is investigated using Monte Carlo simulations. The influence of parameters such as the nanoparticle surface charge density, salt valency, and solution property such as the pH on the chain protonation/deprotonation process and monomer adsorption at the nanoparticle surface are systematically investigated. It is shown that the nanoparticle presence significantly modifies chain acid/base and polyelectrolyte conformational properties. The importance of the attractive electrostatic interactions between the chain and the nanoparticle clearly promotes the chain deprotonation leading, at high pH and nanoparticle charge density, to fully wrapped polyelectrolyte at the nanoparticle surface. When the nanoparticle bare charge is overcompensated by the polyelectrolyte charges, counterions and salt particles condense at the surface of the polyelectrolyte-nanoparticle complex to compensate for the excess of charges providing from the adsorbed polyelectrolyte chain. It is also shown that the complex formation is significantly affected by the salt valency. Indeed, with the presence of trivalent salt cations, competition is observed between the nanoparticle and the trivalent cations. As a result, the amount of adsorbed monomers is less important than in the monovalent and divalent case and chain conformations are different due to the collapse of polyelectrolyte segments around trivalent cations out of the nanoparticle adsorption layer.

Adsorption of Dyes in Studying the Surface Chemistry of Ultradispersed Diamond

NASA Astrophysics Data System (ADS)

Khokhlova, T. D.; Yunusova, G. R.; Lanin, S. N.

2018-05-01

The effect the surface chemistry of ultradispersed diamond (UDD) has on the adsorption of watersoluble dyes is considered. A comparison is made to adsorption on graphitized thermal carbon black (GTCB), which has a homogeneous and nonporous surface. The adsorption isotherms of dyes and the dependence of the adsorption on the pH of solutions are measured. It is found that UDD adsorbs acid (anionic) dyes—acid orange (AO) and acid anthraquinone blue (AAB)—but barely adsorbs a basic (cationic) dye, methylene blue (MB), because of the predominance of positively charged basic groups on the surface of UDD. The maximum adsorption of AO is much lower on UDD than on GTCB, while the maximum adsorption of AAB is similar for both surfaces. The adsorption of AO on UDD depends strongly on the pH of the solution, while the adsorption of AAB is independent of this parameter. It is suggested that the adsorption of AAB is determined not only by ionic and hydrophobic interactions but also by coordination interactions with impurity metal ions on a UDD surface. It is concluded that the adsorption of dyes characterizes the chemistry of a UDD surface with high sensitivity.

Adsorption of a cationic dye molecule on polystyrene microspheres in colloids: effect of surface charge and composition probed by second harmonic generation.

PubMed

Eckenrode, Heather M; Jen, Shih-Hui; Han, Jun; Yeh, An-Gong; Dai, Hai-Lung

2005-03-17

Nonlinear optical probe, second harmonic generation (SHG), of the adsorption of the dye molecule malachite green (MG), in cationic form at pH < or = 5, on polystyrene microspheres in aqueous solution is used to study the effect of surface charge and composition on molecular adsorption. Three types of polystyrene microspheres with different surface composition are investigated: (1) a sulfate terminated, anionic surface, (2) a neutral surface without any functional group termination, and (3) an amine terminated, cationic surface. The cationic dye was found to adsorb at all three surfaces, regardless of surface charge. The adsorption free energies, DeltaG's, measured for the three surfaces are -12.67, -12.39, and -10.46 kcal/mol, respectively, with the trend as expected from the charge interactions. The adsorption density on the anionic surface, where attractive charge-charge interaction dominates, is determined by the surface negative charge density. The adsorption densities on the neutral and cationic surfaces are on the other hand higher, perhaps as a result of a balance between minimizing repulsive charge interaction and maximizing attractive molecule-substrate and intermolecular interactions. The relative strength of the SH intensity per molecule, in combination of a model calculation, reveals that the C(2) axis of the MG molecule is nearly perpendicular to the surface on the anionic surface and tilts away from the surface norm when the surface is neutral and further away when cationic. Changing the pH of the solution may alter the surface charge and subsequently affect the adsorption configuration and SH intensity.

Macroscopic and spectroscopic investigations on Eu(III) and Cm(III) sorption onto bayerite (β-Al(OH)3) and corundum (α-Al2O3).

PubMed

Kupcik, Tomas; Rabung, Thomas; Lützenkirchen, Johannes; Finck, Nicolas; Geckeis, Horst; Fanghänel, Thomas

2016-01-01

The interaction of trivalent Cm and Eu with the aluminum hydroxide bayerite (β-Al(OH)3) and the aluminum oxide corundum (α-Al2O3) was investigated by batch sorption experiments and time resolved laser fluorescence spectroscopy (TRLFS). The experimental methods for both polymorphs show similar pH dependent sorption behavior at trace metal ion concentrations (∼10(-7) M), i.e. similar Eu sorption edges and nearly identical Cm speciation between pH=3 and 13. In this pH range the Cm aquo ion as well as the Cm(III) surface species surface⋯Cm(OH)x(H2O)(5-x) (x=0, 1, 2) can be distinguished by TRLFS. The similar sorption data point to a (surface) transformation of the thermodynamically unstable Al2O3 surface into bayerite, in agreement with the similar isoelectric points obtained for both minerals (pH(IEP)=8.6-8.8). The pH dependent surface charge is most likely due to the protonation/deprotonation of singly coordinated Al-OH surface groups, prevailing on the edge planes of the rod-like bayerite crystals and the surface of the colloidal Al2O3 particles. These surface groups are also believed to act as ligands for lanthanide/actinide(III) surface complexation. In contrast to the similar sorption behavior at trace metal ion concentrations, discrepancies are observed at higher Eu levels. While similar sorption edges occur up to 7×10(-7) M Eu for corundum, the pH edge on bayerite is gradually shifted to higher pH values in this Eu concentration range. The latter behavior may be related either to the existence of multiple sorption sites with different sorption affinities, or to the influence of an additional amorphous Al-phase, forming in the course of the bayerite synthesis. Copyright © 2015 Elsevier Inc. All rights reserved.

Cell surface characteristics of Lactobacillus casei subsp. casei, Lactobacillus paracasei subsp. paracasei, and Lactobacillus rhamnosus strains.

PubMed Central

Pelletier, C; Bouley, C; Cayuela, C; Bouttier, S; Bourlioux, P; Bellon-Fontaine, M N

1997-01-01

Hydrophilic and electrostatic cell surface properties of eight Lactobacillus strains were characterized by using the microbial adhesion to solvents method and microelectrophoresis, respectively. All strains appeared relatively hydrophilic. The strong microbial adhesion to chloroform, an acidic solvent, in comparison with microbial adhesion to hexadecane, an apolar n-alkane, demonstrated the particularity of lactobacilli to have an important electron donor and basic character and consequently their potential ability to generate Lewis acid-base interactions with a support. Regardless of their electrophoretic mobility (EM), strains were in general slightly negatively charged at alkaline pH. A pH-dependent behavior concerning cell surface charges was observed. The EM decreased progressively with more acidic pHs for the L. casei subsp. casei and L. paracasei subsp. paracasei strains until the isoelectric point (IEP), i.e., the pH value for which the EM is zero. On the other hand, the EM for the L. rhamnosus strains was stable from pH 8 to pH 3 to 4, at which point there was a shift near the IEP. Both L. casei subsp. casei and L. paracasei subsp. paracasei strains were characterized by an IEP of around 4, whereas L. rhamnosus strains possessed a markedly lower IEP of 2. The present study showed that the cell surface physicochemical properties of lactobacilli seem to be, at least in part and under certain experimental conditions, particular to the bacterial species. Such differences detected between species are likely to be accompanied by some particular changes in cell wall chemical composition. PMID:9143109

Sorption and transport of acetaminophen, 17alpha-ethynyl estradiol, nalidixic acid with low organic content aquifer sand.

PubMed

Lorphensri, Oranuj; Sabatini, David A; Kibbey, Tohren C G; Osathaphan, Khemarath; Saiwan, Chintana

2007-05-01

The sorption and transport of three pharmaceutical compounds (acetaminophen, an analgesic; nalidixic acid, an antibiotic; and 17alpha-ethynyl estradiol, a synthetic hormone) were examined by batch sorption experiments and solute displacement in columns of silica, alumina, and low organic carbon aquifer sand at neutral pH. Silica and alumina were used to represent negatively-charged and positively-charged fractions of subsurface media. Column transport experiments were also conducted at pH values of 4.3, 6.2, and 8.2 for the ionizable nalidixic acid. The computer program UFBTC was used to fit the breakthrough data under equilibrium and nonequilibrium conditions with linear/nonlinear sorption. Good agreement was observed between the retardation factors derived from column model studies and estimated from equilibrium batch sorption studies. The sorption and transport of nalidixic acid was observed to be highly pH dependent, especially when the pH was near the pK(a) of nalidixic acid (5.95). Thus, near a compound's pK(a) it is especially important that the batch studies be performed at the same pH as the column experiment. While for ionic pharmaceuticals, ion exchange to oppositely-charged surfaces, appears to be the dominant adsorption mechanism, for neutral pharmaceuticals (i.e., acetaminophen, 17alpha-ethynyl estradiol) the sorption correlated well with the K(ow) of the pharmaceuticals, suggesting hydrophobically motivated sorption as the dominant mechanism.

pH Reversible Encapsulation of Oppositely Charged Colloids Mediated by Polyelectrolytes

PubMed Central

2017-01-01

We report the first example of reversible encapsulation of micron-sized particles by oppositely charged submicron smaller colloids. The reversibility of this encapsulation process is regulated by pH-responsive poly(acrylic acid) (PAA) present in solution. The competitive adsorption between the small colloids and the poly(acrylic acid) on the surface of the large colloids plays a key role in the encapsulation behavior of the system. pH offers an experimental knob to tune the electrostatic interactions between the two oppositely charged particle species via regulation of the charge density of the poly(acrylic acid). This results in an increased surface coverage of the large colloids by the smaller colloids when decreasing pH. Furthermore, the poly(acrylic acid) also acts as a steric barrier limiting the strength of the attractive forces between the oppositely charged particle species, thereby enabling detachment of the smaller colloids. Finally, based on the pH tunability of the encapsulation behavior and the ability of the small colloids to detach, reversible encapsulation is achieved by cycling pH in the presence of the PAA polyelectrolytes. The role of polyelectrolytes revealed in this work provides a new and facile strategy to control heteroaggregation behavior between oppositely charged colloids, paving the way to prepare sophisticated hierarchical assemblies. PMID:28419800

Chemical equilibrium modeling of organic acids, pH, aluminum, and iron in Swedish surface waters.

PubMed

Sjöstedt, Carin S; Gustafsson, Jon Petter; Köhler, Stephan J

2010-11-15

A consistent chemical equilibrium model that calculates pH from charge balance constraints and aluminum and iron speciation in the presence of natural organic matter is presented. The model requires input data for total aluminum, iron, organic carbon, fluoride, sulfate, and charge balance ANC. The model is calibrated to pH measurements (n = 322) by adjusting the fraction of active organic matter only, which results in an error of pH prediction on average below 0.2 pH units. The small systematic discrepancy between the analytical results for the monomeric aluminum fractionation and the model results is corrected for separately for two different fractionation techniques (n = 499) and validated on a large number (n = 3419) of geographically widely spread samples all over Sweden. The resulting average error for inorganic monomeric aluminum is around 1 µM. In its present form the model is the first internally consistent modeling approach for Sweden and may now be used as a tool for environmental quality management. Soil gibbsite with a log *Ks of 8.29 at 25°C together with a pH dependent loading function that uses molar Al/C ratios describes the amount of aluminum in solution in the presence of organic matter if the pH is roughly above 6.0.

Adsorption of bovine serum albumin on silicon dioxide nanoparticles: Impact of pH on nanoparticle-protein interactions.

PubMed

Givens, Brittany E; Diklich, Nina D; Fiegel, Jennifer; Grassian, Vicki H

2017-05-03

Bovine serum albumin (BSA) adsorbed on amorphous silicon dioxide (SiO 2 ) nanoparticles was studied as a function of pH across the range of 2 to 8. Aggregation, surface charge, surface coverage, and protein structure were investigated over this entire pH range. SiO 2 nanoparticle aggregation is found to depend upon pH and differs in the presence of adsorbed BSA. For SiO 2 nanoparticles truncated with hydroxyl groups, the largest aggregates were observed at pH 3, close to the isoelectric point of SiO 2 nanoparticles, whereas for SiO 2 nanoparticles with adsorbed BSA, the aggregate size was the greatest at pH 3.7, close to the isoelectric point of the BSA-SiO 2 complex. Surface coverage of BSA was also the greatest at the isoelectric point of the BSA-SiO 2 complex with a value of ca. 3 ±   1 × 10 11 molecules cm -2 . Furthermore, the secondary protein structure was modified when compared to the solution phase at all pH values, but the most significant differences were seen at pH 7.4 and below. It is concluded that protein-nanoparticle interactions vary with solution pH, which may have implications for nanoparticles in different biological fluids (e.g., blood, stomach, and lungs).

Influence of the pH value of a colloidal gold solution on the absorption spectra of an LSPR-assisted sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Jin; Li, Wenbin; Zhu, Mao

2014-03-15

The localized surface plasmon resonances (LSPRs) of gold particles assembled on a crystal plate are a powerful tool for biological sensors. Here, we prepare gold colloids in different pH solutions. We monitor the effects of the particle radius and particle coverage on the absorption spectra of AT-cut (r-face dihedral angle of about 3°) crystal plates supporting gold nanoparticles. The surface morphologies were monitored on silicon dioxide substrates using ultraviolet and visible (UV-vis) spectroscopy, and atomic force microscopy (AFM). The results showed that the gold particle coverage decreases with increasing pH value of the gold colloid solution. This phenomenon demonstrates thatmore » self-assembled gold surfaces were formed via the electrostatic adsorption of gold particles on the positively charged, ionized amino groups on the crystal plates in the acidic solution. The spectrum of gold nanoparticles with different coverage degree on the crystal plates showed that the LSPR properties are highly dependent on pH.« less

Electrostatic Interactions Influence Protein Adsorption (but Not Desorption) at the Silica-Aqueous Interface.

PubMed

McUmber, Aaron C; Randolph, Theodore W; Schwartz, Daniel K

2015-07-02

High-throughput single-molecule total internal reflection fluorescence microscopy was used to investigate the effects of pH and ionic strength on bovine serum albumin (BSA) adsorption, desorption, and interfacial diffusion at the aqueous-fused silica interface. At high pH and low ionic strength, negatively charged BSA adsorbed slowly to the negatively charged fused silica surface. At low pH and low ionic strength, where BSA was positively charged, or in solutions at higher ionic strength, adsorption was approximately 1000 times faster. Interestingly, neither surface residence times nor the interfacial diffusion coefficients of BSA were influenced by pH or ionic strength. These findings suggested that adsorption kinetics were dominated by energy barriers associated with electrostatic interactions, but once adsorbed, protein-surface interactions were dominated by short-range nonelectrostatic interactions. These results highlight the ability of single-molecule techniques to isolate elementary processes (e.g., adsorption and desorption) under steady-state conditions, which would be impossible to measure using ensemble-averaging methods.

Soil pH on mobility of imazaquin in oxisols with positive balance of charges.

PubMed

Regitano, Jussara B; da Rocha, Wadson S D; Alleoni, Luís R F

2005-05-18

The influence of soil pH on the leaching potential of the ionizable herbicide imazaquin was assessed on the profile of two highly weathered soils having a net positive charge in the B horizon, in contrast to a soil having a net negative charge in the whole profile, using packed soil column experiments. Imazaquin leached to a large extent and faster at Kd values lower than 1.0 L kg(-1), a much more lenient limit than usually proposed for pesticides in the literature (Kd < 5.0 L kg(-1)). The amount of imazaquin leached increased with soil pH. As the soil pH increased, the percentage of imazaquin in the anionic forms, the negative surface potential of the soils, as well as imazaquin water solubility also increased, thus reducing sorption because of repulsive electrostatic forces (hydrophilic interactions). For all surface samples (0-0.2 m), imazaquin did not leach at soil pH values lower than pKa (3.8) and more than 80% of the applied amount was leached at pH values higher than 5.5. For subsurface samples from the acric soils, imazaquin only began to leach at soil pH values > zero point of salt effects (ZPSE > 5.7). In conclusion, the use of surface K(oc) values to predict the amount of imazaquin leached within soil profiles having a positive balance of charges may greatly overestimate its actual leaching potential.

Hydroxy-Al and cell-surface negativity are responsible for the enhanced sensitivity of Rhodotorula taiwanensis to aluminum by increased medium pH.

PubMed

Zhao, Xue Qiang; Bao, Xue Min; Wang, Chao; Xiao, Zuo Yi; Hu, Zhen Min; Zheng, Chun Li; Shen, Ren Fang

2017-10-01

Aluminum (Al) is ubiquitous and toxic to microbes. High Al 3+ concentration and low pH are two key factors responsible for Al toxicity, but our present results contradict this idea. Here, an Al-tolerant yeast strain Rhodotorula taiwanensis RS1 was incubated in glucose media containing Al with a continuous pH gradient from pH 3.1-4.2. The cells became more sensitive to Al and accumulated more Al when pH increased. Calculations using an electrostatic model Speciation Gouy Chapman Stern indicated that, the increased Al sensitivity of cells was associated with AlOH 2+ and Al(OH) 2 + rather than Al 3+ . The alcian blue (a positively charged dye) adsorption and zeta potential determination of cell surface indicated that, higher pH than 3.1 increased the negative charge and Al adsorption at the cell surface. Taken together, the enhanced sensitivity of R. taiwanensis RS1 to Al from pH 3.1-4.2 was associated with increased hydroxy-Al and cell-surface negativity.

Increasing binding density of yeast cells by control of surface charge with allylamine grafting to ion modified polymer surfaces.

PubMed

Tran, Clara T H; Kondyurin, Alexey; Chrzanowski, Wojciech; Bilek, Marcela M M; McKenzie, David R

2014-10-01

Plasma immersion ion implantation (PIII) treatment of polymers creates a biointerface capable of direct covalent immobilization of biomolecules. The immobilization of protein molecules is achieved by covalent bonds formed between embedded radicals on the treated surface and amino acid side chains and cells can be immobilized through cell-wall proteins. The attachment density of negatively charged entities on a PIII treated surface is inhibited by its negative surface charge at neutral pH. To reduce the negative charge of PIII treated surfaces in phosphate buffer (pH 7.4, 11mM), we develop an effective approach of grafting allylamine monomers onto the treated surface. The results reveal reactions between allylamine and radicals on the PIII treated surface. One of these triggers polymerization, increasing the number of amine groups grafted. As a consequence, the PIII treated polystyrene surface after allylamine exposure becomes more hydrophobic and less negatively charged in phosphate buffer. Using yeast cells as an example, we have shown a significant improvement (6-15 times) of cell density immobilized on the PIII treated surface after exposure to allylamine. Copyright © 2014 Elsevier B.V. All rights reserved.

Charge reversible gold nanoparticles for high efficient absorption and desorption of DNA

NASA Astrophysics Data System (ADS)

Wang, Can; Zhuang, Jiaqi; Jiang, Shan; Li, Jun; Yang, Wensheng

2012-10-01

Mercaptoundecylamine and mercaptoundecanoic acid co-modified Au nanoparticles were prepared by two-step ligand exchange of 6-mercaptohexanoic acid modified gold nanoparticles. Such particles terminated by appropriate ratios of the amine and carboxyl groups ( R N/C) were identified to show reversible charge on their surface, which were switchable by pH of the solution. The isoelectric point (IEP) of the particles is tunable by changing the ratios of the amine and carboxyl groups on the particle surfaces. The particles can absorb DNA effectively at pH lower than the IEP driven by the direct electrostatic interactions between DNA and the particle surface. When pH of the solutions was elevated to be higher than the IEP, the absorbed DNA can be released almost completely due to the electrostatic repulsion between the particle surface and DNA. With appropriate R N/C ratios of 0.8, the absorption and desorption efficiencies of DNA were 97 and 98 %, respectively, corresponding an extraction efficiency of 95 %. Such particles with reversible surface charges allow the high efficient extraction of DNA by simply changing pH instead of by changing salt concentration in the conventional salt bridge method.

Adsorption of dissolved aluminum on sapphire-c and kaolinite: implications for points of zero charge of clay minerals

PubMed Central

2014-01-01

We have studied the impact of dissolved aluminum on interfacial properties of two aluminum bearing minerals, corundum and kaolinite. The effect of intentionally adding dissolved aluminum on electrokinetic potential of basal plane surfaces of sapphire was studied by streaming potential measurements as a function of pH and was complemented by a second harmonic generation (SHG) study at pH 6. The electrokinetic data show a similar trend as the SHG data, suggesting that the SHG electric field correlates to zeta-potential. A comparable study was carried out on kaolinite particles. In this case electrophoretic mobility was measured as a function of pH. In both systems the addition of dissolved aluminum caused significant changes in the charging behavior. The isoelectric point consistently shifted to higher pH values, the extent of the shift depending on the amount of aluminum present or added. The experimental results imply that published isoelectric points of clay minerals may have been affected by this phenomenon. The presence of dissolved aluminum in experimental studies may be caused by particular pre-treatment methods (such as washing in acids and subsequent adsorption of dissolved aluminum) or even simply by starting a series of measurements from extreme pH (causing dissolution), and subsequently varying the pH in the very same batch. This results in interactions of dissolved aluminum with the target surface. A possible interpretation of the experimental results could be that at low aluminum concentrations adatoms of aluminum (we will refer to adsorbed mineral constituents as adatoms) can form at the sapphire basal plane, which can be rather easily removed. Simultaneously, once the surface has been exposed to sufficiently high aluminum concentration, a visible change of the surface is seen by AFM which is attributed to a surface precipitate that cannot be removed under the conditions employed in the current study. In conclusion, whenever pre-treatment or the starting point of an experiment favor the dissolution of aluminum, dissolved Al may remain in the experimental system and interact with the target surfaces. The systems are then no longer pristine and points of zero charge or sorption data are those of aluminum-bearing systems. PMID:25045321

Adsorption of charged albumin subdomains on a graphite surface.

PubMed

Raffaini, Giuseppina; Ganazzoli, Fabio

2006-03-01

We report some new molecular dynamics simulation results about the adsorption on a hydrophobic graphite surface of two albumin subdomains, each formed by three different alpha-helices, considering the correctly charged side groups at pH = 7 instead of the neutral ones as done in our previous exploratory paper (Raffaini and Ganazzoli, Langmuir 2003;19:3403-3412). We find that the presence of charges affects somewhat the initial adsorption stage on the electrostatically neutral surface, but not the final one. Thus, we recover the result that a monolayer of aminoacids is eventually formed, with a rough parallelism of distant strands to optimize both the intramolecular and the surface interactions. This feature is consistent with the adsorption on the hydrophobic surface being driven by dispersion forces only, and with the "soft" nature of albumin. Additional optimizations of the final monolayer carried out at pH = 3 and 11 do not modify appreciably this picture, suggesting that adsorption on graphite is basically independent of pH. The enhanced hydration of the final adsorption state due to the (delocalized) charges of the side groups is also discussed in comparison with similar results of the neutralized subdomains. (c) 2005 Wiley Periodicals, Inc.

Comparison of Calculation and Experiment Implicates Significant Electrostatic Contributions to the Binding Stability of Barnase and Barstar

PubMed Central

Dong, Feng; Vijayakumar, M.; Zhou, Huan-Xiang

2003-01-01

The contributions of electrostatic interactions to the binding stability of barnase and barstar were studied by the Poisson-Boltzmann model with three different protocols: a), the dielectric boundary specified as the van der Waals (vdW) surface of the protein along with a protein dielectric constant (ɛp) of 4; b), the dielectric boundary specified as the molecular (i.e., solvent-exclusion (SE)) surface along with ɛp = 4; and c), “SE + ɛp = 20.” The “vdW + ɛp = 4” and “SE + ɛp = 20” protocols predicted an overall electrostatic stabilization whereas the “SE + ɛp = 4” protocol predicted an overall electrostatic destabilization. The “vdW + ɛp = 4” protocol was most consistent with experiment. It quantitatively reproduced the observed effects of 17 mutations neutralizing charged residues lining the binding interface and the measured coupling energies of six charge pairs across the interface and reasonably rationalized the experimental ionic strength and pH dependences of the binding constant. In contrast, the “SE + ɛp = 4” protocol predicted significantly larger coupling energies of charge pairs whereas the “SE + ɛp = 20” protocol did not predict any pH dependence. This study calls for further scrutiny of the different Poisson-Boltzmann protocols and demonstrates potential danger in drawing conclusions on electrostatic contributions based on a particular calculation protocol. PMID:12829463

Surface Oxide Net Charge of a Titanium Alloy; Comparison Between Effects of Treatment With Heat or Radiofrequency Plasma Glow Discharge

PubMed Central

MacDonald, Daniel E.; Rapuano, Bruce E.; Schniepp, Hannes C.

2010-01-01

In the current study, we have compared the effects of heat and radiofrequency plasma glow discharge (RFGD) treatment of a Ti6Al4V alloy on the physico-chemical properties of the alloy’s surface oxide. Titanium alloy (Ti6Al4V) disks were passivated alone, heated to 600 °C, or RFGD plasma treated in pure oxygen. RFGD treatment did not alter the roughness, topography, elemental composition or thickness of the alloy’s surface oxide layer. In contrast, heat treatment altered oxide topography by creating a pattern of oxide elevations approximately 50–100 nm in diameter. These nanostructures exhibited a three-fold increase in roughness compared to untreated surfaces when RMS roughness was calculated after applying a spatial high-pass filter with a 200 nm cutoff wavelength. Heat treatment also produced a surface enrichment in aluminum and vanadium oxides. Both RFGD and heat treatment produced similar increases in oxide wettability. Atomic force microscopy (AFM) measurements of metal surface oxide net charge signified by a long range force of attraction to or repulsion from a (negatively charged) silicon nitride AFM probe were also obtained for all three experimental groups. Force measurements showed that the RFGD-treated Ti6Al4V samples demonstrated a higher net positive surface charge at pH values below 6 and a higher net negative surface charge at physiological pH (pH values between 7 and 8) compared to control and heat-treated samples These findings suggest that RFGD treatment of metallic implant materials can be used to study the role of negatively charged surface oxide functional groups in protein bioactivity, osteogenic cell behavior and osseointegration independently of oxide topography. PMID:20880672

Effect of amino acid sequence and pH on nanofiber formation of self-assembling peptides EAK16-II and EAK16-IV.

PubMed

Hong, Yooseong; Legge, Raymond L; Zhang, S; Chen, P

2003-01-01

Atomic force microscopy (AFM) and axisymmetric drop shape analysis-profile (ASDA-P) were used to investigate the mechanism of self-assembly of peptides. The peptides chosen consisted of 16 alternating hydrophobic and hydrophilic amino acids, where the hydrophilic residues possess alternating negative and positive charges. Two types of peptides, AEAEAKAKAEAEAKAK (EAK16-II) and AEAEAEAEAKAKAKAK (EAK16-IV), were investigated in terms of nanostructure formation through self-assembly. The experimental results, which focused on the effects of the amino acid sequence and pH, show that the nanostructures formed by the peptides are dependent on the amino acid sequence and the pH of the solution. For pH conditions around neutrality, one of the peptides used in this study, EAK16-IV, forms globular assemblies and has lower surface tension at air-water interfaces than another peptide, EAK16-II, which forms fibrillar assemblies at the same pH. When the pH is lowered below 6.5 or raised above 7.5, there is a transition from globular to fibrillar structures for EAK16-IV, but EAK16-II does not show any structural transition. Surface tension measurements using ADSA-P showed different surface activities of peptides at air-water interfaces. EAK16-II does not show a significant difference in surface tension for the pH range between 4 and 9. However, EAK16-IV shows a noticeable decrease in surface tension at pH around neutrality, indicating that the formation of globular assemblies is related to the molecular hydrophobicity.

Sorption of imazaquin in soils with positive balance of charges.

PubMed

Rocha, Wadson S D; Regitano, Jussara B; Alleoni, Luis R F; Tornisielo, Valdemar L

2002-10-01

The herbicide imazaquin has both an acid and a basic ionizable groups, and its sorption depends upon the pH, the electric potential (psi0), and the oxide and the organic carbon (OC) contents of the soil. Sorption and extraction experiments using 14C-imazaquin were performed in surface and subsurface samples of two acric oxisols (an anionic "rhodic" acrudox and an anionic "xanthic" acrudox) and one non-acric alfisol (a rhodic kandiudalf), treated at four different pH values. Imazaquin showed low to moderate sorption to the soils. Sorption decreased and aqueous extraction increased as pH increased. Up to pH 5.8, sorption was higher in subsurface than in surface layers of the acric soils, due to the positive balance of charges resulted from the high Fe and Al oxide and the low OC contents. It favored electrostatic interactions with anionic molecules of imazaquin. For the subsurface samples of these highly weathered soils, where psi0 was positive and OC was low, it was not possible to predict sorption just by considering imazaquin speciation and its hydrophobic partition to the organic domains of the soil. Moreover, if Koc measured for thesurface samples were assumed to represent the whole profile in predictive models for leaching potential, then it would result in underestimation of sorption potential in subsurface, and consequently result in overestimation of the leaching potential.

Cell-secreted flavins bound to membrane cytochromes dictate electron transfer reactions to surfaces with diverse charge and pH.

PubMed

Okamoto, Akihiro; Kalathil, Shafeer; Deng, Xiao; Hashimoto, Kazuhito; Nakamura, Ryuhei; Nealson, Kenneth H

2014-07-11

The variety of solid surfaces to and from which microbes can deliver electrons by extracellular electron transport (EET) processes via outer-membrane c-type cytochromes (OM c-Cyts) expands the importance of microbial respiration in natural environments and industrial applications. Here, we demonstrate that the bifurcated EET pathway of OM c-Cyts sustains the diversity of the EET surface in Shewanella oneidensis MR-1 via specific binding with cell-secreted flavin mononucleotide (FMN) and riboflavin (RF). Microbial current production and whole-cell differential pulse voltammetry revealed that RF and FMN enhance EET as bound cofactors in a similar manner. Conversely, FMN and RF were clearly differentiated in the EET enhancement by gene-deletion of OM c-Cyts and the dependency of the electrode potential and pH. These results indicate that RF and FMN have specific binding sites in OM c-Cyts and highlight the potential roles of these flavin-cytochrome complexes in controlling the rate of electron transfer to surfaces with diverse potential and pH.

Initiating fibro-proliferation through interfacial interactions of myoglobin colloids with collagen in solution.

PubMed

Dhanasekaran, Madhumitha; Dhathathreyan, Aruna

2017-08-01

This work examines fibro-proliferation through interaction of myoglobin (Mb), a globular protein with collagen, an extracellular matrix fibrous protein. Designed colloids of Mb at pH 4.5 and 7.5 have been mixed with collagen solution at pH 7.5 and 4.5 in different concentrations altering their surface charges. For the Mb colloids, 100-200nm sizes have been measured from Transmission electron micrographs and zeta sizer. CD spectra shows a shift to beta sheet like structure for the protein in the colloids. Interaction at Mb/Collagen interface studied using Dilational rheology, Quartz crystal microbalance with dissipation and Differential Scanning calorimetry show that the perturbation is not only by the charge compensation arising from the difference in pH of the colloids and collagen, but also by the organized assembly of collagen at that particular pH. Results demonstrate that positive Mb colloids at pH 4.5, having more% of entrained water stabilize the collagen fibrils (pH 7.5) around them. Ensuing dehydration leads to effective cross-linking and inherently anisotropic growth of fibrils/fibres of collagen. In the case of Mb colloids at pH 7.5, the fibril formation seems to supersede the clustering of Mb suggesting that the fibro-proliferation is both pH and hydrophilic-hydrophobic balance dependent at the interface. Copyright © 2017 Elsevier B.V. All rights reserved.

Physicochemical Study of Viral Nanoparticles at the Air/Water Interface.

PubMed

Torres-Salgado, Jose F; Comas-Garcia, Mauricio; Villagrana-Escareño, Maria V; Durán-Meza, Ana L; Ruiz-García, Jaime; Cadena-Nava, Ruben D

2016-07-07

The assembly of most single-stranded RNA (ssRNA) viruses into icosahedral nucleocapsids is a spontaneous process driven by protein-protein and RNA-protein interactions. The precise nature of these interactions results in the assembly of extremely monodisperse and structurally indistinguishable nucleocapsids. In this work, by using a ssRNA plant virus (cowpea chlorotic mottle virus [CCMV]) as a charged nanoparticle we show that the diffusion of these nanoparticles from the bulk solution to the air/water interface is an irreversible adsorption process. By using the Langmuir technique, we measured the diffusion and adsorption of viral nucleocapsids at the air/water interface at different pH conditions. The pH changes, and therefore in the net surface charge of the virions, have a great influence in the diffusion rate from the bulk solution to the air/water interface. Moreover, assembly of mesoscopic and microscopic viral aggregates at this interface depends on the net surface charge of the virions and the surface pressure. By using Brewster's angle microscopy we characterized these structures at the interface. Most common structures observed were clusters of virions and soap-frothlike micron-size structures. Furthermore, the CCMV films were compressed to form monolayers and multilayers from moderate to high surface pressures, respectively. After transferring the films from the air/water interface onto mica by using the Langmuir-Blodgett technique, their morphology was characterized by atomic force microscopy. These viral monolayers showed closed-packing nano- and microscopic arrangements.

An extended model based on the modified Nernst-Planck equation for describing transdermal iontophoresis of weak electrolytes.

PubMed

Imanidis, Georgios; Luetolf, Peter

2006-07-01

An extended model for iontophoretic enhancement of transdermal drug permeation under constant voltage is described based on the previously modified Nernst-Planck equation, which included the effect of convective solvent flow. This model resulted in an analytical expression for the enhancement factor as a function of applied voltage, convective flow velocity due to electroosmosis, ratio of lipid to aqueous pathway passive permeability, and weighted average net ionic valence of the permeant in the aqueous epidermis domain. The shift of pH in the epidermis compared to bulk caused by the electrical double layer at the lipid-aqueous domain interface was evaluated using the Poisson-Boltzmann equation. This was solved numerically for representative surface charge densities and yielded pH differences between bulk and epidermal aqueous domain between 0.05 and 0.4 pH units. The developed model was used to analyze the experimental enhancement of an amphoteric weak electrolyte measured in vitro using human cadaver epidermis and a voltage of 250 mV at different pH values. Parameter values characterizing the involved factors were determined that yielded the experimental enhancement factors and passive permeability coefficients at all pH values. The model provided a very good agreement between experimental and calculated enhancement and passive permeability. The deduced parameters showed (i) that the pH shift in the aqueous permeation pathway had a notable effect on the ionic valence and the partitioning of the drug in this domain for a high surface charge density and depending on the pK(a) and pI of the drug in relation to the bulk pH; (ii) the magnitude and the direction of convective transport due to electroosmosis typically reflected the density and sign, respectively, of surface charge of the tissue and its effect on enhancement was substantial for bulk pH values differing from the pI of epidermal tissue; (iii) the aqueous pathway predominantly determined passive permeability of the studied compound despite its measurable lipophilicity and therefore the lipid pathway did not notably affect enhancement. Hence, the proposed model can provide a good quantitative insight into the interplay between different phenomena and permeant properties influencing iontophoresis and can potentially be used as a predictive tool of the process.

Adsorption of 6-mercaptopurine and 6-mercaptopurine riboside on silver colloid: a pH dependent surface enhanced Raman spectroscopy and density functional theory study. Part I. 6-Mercaptopurine

NASA Astrophysics Data System (ADS)

Szeghalmi, A. V.; Leopold, L.; Pînzaru, S.; Chis, V.; Silaghi-Dumitrescu, I.; Schmitt, M.; Popp, J.; Kiefer, W.

2005-02-01

Surface enhanced Raman spectroscopy (SERS) on silver colloid has been applied to characterize the interaction of 6-mercaptopurine (6MP), an active drug used in chemotherapy of acute lymphoblastic leukemia, with a model biological substrate at therapeutical concentrations and as function of the pH value. The adsorption active sites and molecular orientation on the metal surface have been determined on the basis of SERS 'surface selection rules' subsequent to a detailed vibrational analysis of the 6MP tautomeric forms. Therefore, DFT calculations (vibrational wavenumbers, Raman scattering activities, partial atomic charges) of the optimized tautomers and potential energy distribution calculations have been performed. Around neutral pH value reorientation of the molecule has been observed. Under basic conditions the 6MP molecule is probably adsorbed on the silver colloid through the N1 atom of the purine ring and possibly the S atom, and adopts a tilted orientation to the surface. A reduction in the number of adsorbed molecules under basic conditions is proposed, since the SERS spectrum recorded at 10-6 M concentration at neutral pH value resembles the SERS spectra obtained under basic conditions at 10-5 M concentration. At acidic pH values a stronger interaction through the N9 and N3 atoms is suggested with an end-on orientation.

Charge tunable thin-film composite membranes by gamma-ray triggered surface polymerization.

PubMed

Reis, Rackel; Duke, Mikel C; Tardy, Blaise L; Oldfield, Daniel; Dagastine, Raymond R; Orbell, John D; Dumée, Ludovic F

2017-06-30

Thin-film composite poly(amide) (PA) membranes have greatly diversified water supplies and food products. However, users would benefit from a control of the electrostatic interactions between the liquid and the net surface charge interface in order to benefit wider application. The ionic selectivity of the 100 nm PA semi-permeable layer is significantly affected by the pH of the solution. In this work, for the first time, a convenient route is presented to configure the surface charge of PA membranes by gamma ray induced surface grafting. This rapid and up-scalable method offers a versatile route for surface grafting by adjusting the irradiation total dose and the monomer concentration. Specifically, thin coatings obtained at low irradiation doses between 1 and 10 kGy and at low monomer concentration of 1 v/v% in methanol/water (1:1) solutions, dramatically altered the net surface charge of the pristine membranes from -25 mV to +45 mV, whilst the isoelectric point of the materials shifted from pH 3 to pH 7. This modification resulted in an improved water flux by over 55%, from 45.9 to up 70 L.m -2 .h -1 , whilst NaCl rejection was found to drop by only 1% compared to pristine membranes.

Surface modification of poly(L-lactic acid) to improve its cytocompatibility via assembly of polyelectrolytes and gelatin.

PubMed

Lin, Yuan; Wang, Luling; Zhang, Peibiao; Wang, Xin; Chen, Xuesi; Jing, Xiabin; Su, Zhaohui

2006-03-01

Poly(L-lactide) (PLLA) surface was modified via aminolysis by poly(allylamine hydrochloride) (PAH) at high pH and subsequent electrostatic self-assembly of poly(sodium styrenesulfonate) (PSS) and PAH, and the process was monitored by X-ray photoelectron spectroscopy (XPS) and contact angle measurement. These modified PLLAs were then used as charged substrates for further incorporation of gelatin to improve their cytocompatibility. The amphoteric nature of the gelatin was exploited and the gelatin was adsorbed to the negatively charged PLLA/PSS and positively charged PLLA/PAH at pH=3.4 and 7.4, respectively. XPS and water contact angle data indicated that the gelatin adsorption at pH=3.4 resulted in much higher surface coverage by gelatin than at pH=7.4. All the modified PLLA surfaces became more hydrophilic than the virgin PLLA. Chondrocyte culture was used to test the cell attachment, cell morphology and cell viability on the modified PLLA substrates. The results showed that the PAH and PSS modified PLLA exhibited better cytocompatibility than virgin PLLA, and the incorporation of the gelatin on these modified PLLA substrates further improved their cytocompatibility, with the PLLA/PSS substrate treated with the gelatin at pH=3.4 being the best, exceeding the chondrocyte compatibility of the tissue culture polystyrene.

Adsorption of cellular peptides of Microcystis aeruginosa and two herbicides onto activated carbon: effect of surface charge and interactions.

PubMed

Hnatukova, Petra; Kopecka, Ivana; Pivokonsky, Martin

2011-05-01

In this research, the adsorption of two herbicides, alachlor (ALA) and terbuthylazine (TBA), on granular activated carbon (GAC) in the presence of well-characterized peptide fraction of cellular organic matter (COM) produced by cyanobacterium Microcystis aeruginosa was studied. Two commercially available GACs were characterized using nitrogen gas adsorption and surface charge titrations. The COM peptides of molecular weight (MW) < 10 kDa were isolated and characterized using MW fractionation technique and high-performance size exclusion chromatography (HPSEC). The effect of surface charge on the adsorption of COM peptides was studied by means of equilibrium adsorption experiments at pH 5 and pH 8.5. Electrostatic interactions and hydrogen bonding proved to be important mechanisms of COM peptides adsorption. The adsorption of ALA and TBA on granular activated carbon preloaded with COM peptides was influenced by solution pH. The reduction in adsorption was significantly greater at pH 5 compared to pH 8.5, which corresponded to the increased adsorption of COM peptides at pH 5. The majority of the competition between COM peptides and both herbicides was attributed to low molecular weight COM peptides with MW of 700, 900, 1300 and 1700 Da. Copyright © 2011 Elsevier Ltd. All rights reserved.

Development of a model to predict the adsorption of lead from solution on a natural streambed sediment

USGS Publications Warehouse

Brown, David Wayne; Hem, John David

1984-01-01

Adsorption of solutes by solid mineral surfaces commonly influences the dissolved ionic composition of natural waters. A model based on electrical double-layer theory has been developed which appears to be capable of characterizing the surface chemical behavior of a natural fine-grained sediment containing mostly quartz and feldspar. This variable surface charge-variable surface potential (VSC-VSP) model differs from others in being capable of evaluating more closely the effect of total metal ion activity on the pH-dependent change in electrical potential at the solid surface. The model was tested using 10-4 molar solutions of lead and a silt-size fraction of sediment from the bed of Colma Creek, a small stream in urban northern San Mateo County, California. The average deviation of measured percent adsorption and values calculated from the model was 6.6 adsorption percent from pH 2.0 to pH 7.0.

Adsorption of aliphatic polyhydroxy carboxylic acids on gibbsite: pH dependency and importance of adsorbate structure.

PubMed

Schneckenburger, Tatjana; Riefstahl, Jens; Fischer, Klaus

2018-01-01

Aliphatic (poly)hydroxy carboxylic acids [(P)HCA] occur in natural, e.g. soils, and in technical (waste disposal sites, nuclear waste repositories) compartments . Their distribution, mobility and chemical reactivity, e.g. complex formation with metal ions and radionuclides, depend, among others, on their adsorption onto mineral surfaces. Aluminium hydroxides, e.g. gibbsite [α-Al(OH) 3 ], are common constituents of related solid materials and mimic the molecular surface properties of clay minerals. Thus, the study was pursued to characterize the adsorption of glycolic, threonic, tartaric, gluconic, and glucaric acids onto gibbsite over a wide pH and (P)HCA concentration range. To consider specific conditions occurring in radioactive wastes, adsorption applying an artificial cement pore water (pH 13.3) as solution phase was investigated additionally. The sorption of gluconic acid at pH 4, 7, 9, and 12 was best described by the "two-site" Langmuir isotherm, combining "high affinity" sorption sites (adsorption affinity constants [Formula: see text] > 1 L mmol -1 , adsorption capacities < 6.5 mmol kg -1 ) with "low affinity" sites ([Formula: see text] < 0.1 L mmol -1 , adsorption capacities ≥ 19 mmol kg -1 ). The total adsorption capacities at pH 9 and 12 were roughly tenfold of that at pH 4 and 7. The S-shaped pH sorption edge of gluconic acid was modelled applying a constant capacitance model, considering electrostatic interactions, hydrogen bonding, surface complex formation, and formation of solved polynuclear complexes between Al 3+ ions and gluconic acid. A Pearson and Spearman rank correlation between (P)HCA molecular properties and adsorption parameters revealed the high importance of the size and the charge of the adsorbates. The adsorption behaviour of (P)HCAs is best described by a combination of adsorption properties of carboxylic acids at acidic pH and of polyols at alkaline pH. Depending on the molecular properties of the adsorbates and on pH, electrostatic interactions, hydrogen bonding, and ternary surface complexation contribute in varying degrees to the adsorption process. Linear distribution coefficients K d between 8.7 and 60.5 L kg -1 (1 mmol L -1 initial PHCA concentration) indicate a considerable mineral surface affinity at very high pH, thus lowering the PHCA fraction available for the complexation of metal ions including radionuclides in solution and their subsequent mobilization.

Cell surface characteristics enable encrustation-free survival of neutrophilic iron-oxidizing bacteria

NASA Astrophysics Data System (ADS)

Saini, G.; Chan, C. S.

2011-12-01

Microbial growth in mineralizing environments depends on the cells' ability to evade surface precipitation. Cell-mineral interactions may be required for metabolism, but if unmoderated, cells could become encrusted, which would limit diffusion of nutrients and waste across cell walls. A combination of cell surface charge and hydrophobicity could enable the survival of microbes in such environments by inhibiting mineral attachment. To investigate this mechanism, we characterized the surfaces of two neutrophilic iron-oxidizing bacteria (FeOB): Mariprofundus ferrooxydans, a Zetaproteobacterium from Fe(II)-rich submarine hydrothermal vents and a Betaproteobacterium Gallionellales strain R-1, recently isolated from a ferrous groundwater seep. Both bacteria produce iron oxyhydroxides, yet successfully escape surface encrustation while inhabiting milieu where iron minerals are also produced by abiotic processes. SEM-EDX and TEM-EELS analyses of cultured bacteria revealed no iron on the cell surfaces. Zeta potential measurements showed that these bacteria have very small negative surface charge (0 to -4 mV) over a pH range of 4-9, indicating near-neutrally charged surfaces. Water contact angle measurements and thermodynamic calculations demonstrate that both bacteria and abiotically-formed Fe oxhydroxides are hydrophilic. Extended-DLVO calculations showed that hydrophilic repulsion between cells and minerals dominates over electrostatic and Lifshitz-van der Waals interactions. This leads to overall repulsion between microbes and minerals, thus preventing surface encrustation. Low surface charge and hydrophilicity (determined by microbial adhesion to hydrocarbon assay) were common features for both live and azide-inhibited cells, which shows that surface characteristics do not depend on active metabolism. It is remarkable that these two phylogenetically-distant bacteria from different environments employ similar adaptations to prevent surface mineralization. Our results confirm that surface characteristics can be a mechanism for survival in mineralizing environments. We predict that biotechnological applications such as bioremediation and microbial mineral carbon sequestration will benefit from microbes that can similarly avoid encrustation.

VARIABLE CHARGE SOILS: MINERALOGY AND CHEMISTRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Ranst, Eric; Qafoku, Nikolla; Noble, Andrew

2016-09-19

Soils rich in particles with amphoteric surface properties in the Oxisols, Ultisols, Alfisols, Spodosols and Andisols orders (1) are considered to be variable charge soils (2) (Table 1). The term “variable charge” is used to describe organic and inorganic soil constituents with reactive surface groups whose charge varies with pH and ionic concentration and composition of the soil solution. Such groups are the surface carboxyl, phenolic and amino functional groups of organic materials in soils, and surface hydroxyl groups of Fe and Al oxides, allophane and imogolite. The hydroxyl surface groups are also present on edges of some phyllosilicate mineralsmore » such as kaolinite, mica, and hydroxyl-interlayered vermiculite. The variable charge is developed on the surface groups as a result of adsorption or desorption of ions that are constituents of the solid phase, i.e., H+, and the adsorption or desorption of solid-unlike ions that are not constituents of the solid phase. Highly weathered soils and subsoils (e.g., Oxisols and some Ultisols, Alfisols and Andisols) may undergo isoelectric weathering and reach a “zero net charge” stage during their development. They usually have a slightly acidic to acidic soil solution pH, which is close to either the point of zero net charge (PZNC) (3) or the point of zero salt effect (PZSE) (3). They are characterized by high abundances of minerals with a point of zero net proton charge (PZNPC) (3) at neutral and slightly basic pHs; the most important being Fe and Al oxides and allophane. Under acidic conditions, the surfaces of these minerals are net positively charged. In contrast, the surfaces of permanent charge phyllosilicates are negatively charged regardless of ambient conditions. Variable charge soils therefore, are heterogeneous charge systems.« less

Coarse-graining, Electrostatics and pH effects in phospholipid systems

NASA Astrophysics Data System (ADS)

Travesset, Alex; Vangaveti, Sweta

2010-03-01

We introduce a minimal free energy describing the interaction of charged groups and counterions including both classical electrostatic and specific interactions. The predictions of the model are compared against the standard model for describing ions next to charged interfaces, consisting of Poisson-Boltzmann theory with additional constants describing ion binding, which are specific to the counterion and the interfacial charge (``chemical binding''). It is shown that the ``chemical'' model can be appropriately described by an underlying ``physical'' model over several decades in concentration, but the extracted binding constants are not uniquely defined, as they differ depending on the particular observable quantity being studied. It is also shown that electrostatic correlations for divalent (or higher valence) ions enhance the surface charge by increasing deprotonation, an effect not properly accounted within chemical models. The model is applied to the charged phospholipids phosphatidylserine, Phosphatidc acid and Phosphoinositides and implications for different biological processes are discussed.

Forsterite surface composition in aqueous solutions: a combined potentiometric, electrokinetic, and spectroscopic approach

NASA Astrophysics Data System (ADS)

Pokrovsky, Oleg S.; Schott, Jacques

2000-10-01

Surfaces of natural and synthetic forsterite (Fo 91 and Fo 100) in aqueous solutions at 25°C were investigated using surface titrations in batch and limited residence time reactors, column filtration experiments, electrokinetic measurements (streaming potential and electrophoresis techniques), Diffuse Reflectance Infrared Spectroscopy (DRIFT), and X-ray Photoelectron Spectroscopy (XPS). At pH < 9, a Mg-depleted, Si-rich layer (<20 Å thick) is formed on the forsterite surface due to a Mg 2+ ↔ H + exchange reaction. Electrokinetic measurements yield a pH IEP value of 4.5 corresponding to the dominance of SiO 2 in the surface layer at pH < 9. In contrast, surface titrations of fresh powders give an apparent pH PZC of about 10 with the development of a large positive charge (up to 10 -4 mol/m 2 or 10 C/m 2) in the acid pH region. This may be explained by penetration of H + into the first unit cells of forsterite surface. The surface charge of acid-reacted forsterite is one or two orders of magnitude lower than that of unreacted forsterite with an apparent pH PZC at around 6.5 and a pH IEP value of 2.1 which is close to that for amorphous silica and reflects the formation of a silica-rich layer on the surface. XPS analyses indicate the penetration of hydrogen into the surface and the polymerization of silica tetrahedra in this leached layer. At pH > 10, a Si-deficient, Mg-rich surface layer is formed as shown by XPS analyses and the preferential Si release from the surface during column filtration experiments.

Role of electrostatic interactions in the toxicity of titanium dioxide nanoparticles toward Escherichia coli.

PubMed

Pagnout, Christophe; Jomini, Stéphane; Dadhwal, Mandeep; Caillet, Céline; Thomas, Fabien; Bauda, Pascale

2012-04-01

The increasing production and use of titanium dioxide nanoparticles (NP-TiO(2)) has led to concerns about their possible impact on the environment. Bacteria play crucial roles in ecosystem processes and may be subject to the toxicity of these nanoparticles. In this study, we showed that at low ionic strength, the cell viability of Escherichia coli was more severely affected at pH 5.5 than at pH 7.0 and pH 9.5. At pH 5.5, nanoparticles (positively charged) strongly interacted with the bacterial cells (negatively charged) and accumulated on their surfaces. This phenomenon was observed in a much lower degree at pH 7.0 (NP-TiO(2) neutrally charged and cells negatively charged) and pH 9.5 (both NP-TiO(2) and cells negatively charged). It was also shown that the addition of electrolytes (NaCl, CaCl(2), Na(2)SO(4)) resulted in a gradual reduction of the NP-TiO(2) toxicity at pH 5.5 and an increase in this toxicity at pH 9.5, which was closely related to the reduction of the NP-TiO(2) and bacterial cell electrostatic charges. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

Integrated titanium dioxide (TiO2) nanoparticles on interdigitated device electrodes (IDEs) for pH analysis

NASA Astrophysics Data System (ADS)

Azizah, N.; Hashim, U.; Arshad, M. K. Md.; Gopinath, Subash C. B.; Nadzirah, Sh.; Farehanim, M. A.; Fatin, M. F.; Ruslinda, A. R.; Ayub, R. M.

2016-07-01

Titanium dioxide (TiO2) nanoparticles based Interdigitated Device Electrodes (IDEs) Nanobiosensor device was developed for intracellular biochemical detection. Fabrication and characterization of pH sensors using IDE nanocoated with TiO2 was studied in this paper. In this paper, a preliminary assessment of this intracellular sensor with electrical measurement under different pH levels. 3-aminopropyltriethoxysilane (APTES) was used to enhance the sensitivity of titanium dioxide layer as well as able to provide surface modification by undergoing protonation and deprotonation process. Different types of pH solution provide different resistivity and conductivity towards the surface. Base solution has the higher current compared to an acid solution. Amine and oxide functionalized TiO2 based IDE exhibit pH-dependent could be understood in terms of the change in surface charge during protonation and deprotonation. The simple fabrication process, high sensitivity, and fast response of the TiO2 based IDEs facilitate their applications in a wide range of areas. The small size of semiconductor TiO2 based IDE for sensitive, label-free, real time detection of a wide range of biological species could be explored in vivo diagnostics and array-based screening.

Humic acid protein complexation

NASA Astrophysics Data System (ADS)

Tan, W. F.; Koopal, L. K.; Weng, L. P.; van Riemsdijk, W. H.; Norde, W.

2008-04-01

Interactions of purified Aldrich humic acid (PAHA) with lysozyme (LSZ) are investigated. In solution LSZ is moderately positively and PAHA negatively charged at the investigated pH values. The proton binding of PAHA and of LSZ is determined by potentiometric proton titrations at various KCl concentrations. It is also measured for two mixtures of PAHA-LSZ and compared with theoretically calculated proton binding assuming no mutual interaction. The charge adaptation due to PAHA-LSZ interaction is relatively small and only significant at low and high pH. Next to the proton binding, the mass ratio PAHA/LSZ at the iso-electric point (IEP) of the complex at given solution conditions is measured together with the pH using the Mütek particle charge detector. From the pH changes the charge adaptation due to the interaction can be found. Also these measurements show that the net charge adaptation is weak for PAHA-LSZ complexes at their IEP. PAHA/LSZ mass ratios in the complexes at the IEP are measured at pH 5 and 7. At pH 5 and 50 mmol/L KCl the charge of the complex is compensated for 30-40% by K +; at pH 7, where LSZ has a rather low positive charge, this is 45-55%. At pH 5 and 5 mmol/L KCl the PAHA/LSZ mass ratio at the IEP of the complex depends on the order of addition. When LSZ is added to PAHA about 25% K + is included in the complex, but no K + is incorporated when PAHA is added to LSZ. The flocculation behavior of the complexes is also different. After LSZ addition to PAHA slow precipitation occurs (6-24 h) in the IEP, but after addition of PAHA to LSZ no precipitation can be seen after 12 h. Clearly, PAHA/LSZ complexation and the colloidal stability of PAHA-LSZ aggregates depend on the order of addition. Some implications of the observed behavior are discussed.

Functional Layer-by-Layer Thin Films of Inducible Nitric Oxide (NO) Synthase Oxygenase and Polyethylenimine: Modulation of Enzyme Loading and NO-Release Activity.

PubMed

Gunasekera, Bhagya; Abou Diwan, Charbel; Altawallbeh, Ghaith; Kalil, Haitham; Maher, Shaimaa; Xu, Song; Bayachou, Mekki

2018-03-07

Nitric oxide (NO) release counteracts platelet aggregation and prevents the thrombosis cascade in the inner walls of blood vessels. NO-release coatings also prevent thrombus formation on the surface of blood-contacting medical devices. Our previous work has shown that inducible nitric oxide synthase (iNOS) films release NO fluxes upon enzymatic conversion of the substrate l-arginine. In this work, we report on the modulation of enzyme loading in layer-by-layer (LbL) thin films of inducible nitric oxide synthase oxygenase (iNOSoxy) on polyethylenimine (PEI). The layer of iNOSoxy is electrostatically adsorbed onto the PEI layer. The pH of the iNOSoxy solution affects the amount of enzyme adsorbed. The overall negative surface charge of iNOSoxy in solution depends on the pH and hence determines the density of adsorbed protein on the positively charged PEI layer. We used buffered iNOSoxy solutions adjusted to pHs 8.6 and 7.0, while saline PEI solution was used at pH 7.0. Atomic force microscopy imaging of the outermost layer shows higher protein adsorption with iNOSoxy at pH 8.6 than with a solution of iNOSoxy at pH 7.0. Graphite electrodes with PEI/iNOSoxy films show higher catalytic currents for nitric oxide reduction mediated by iNOSoxy. The higher enzyme loading translates into higher NO flux when the enzyme-modified surface is exposed to a solution containing the substrate and a source of electrons. Spectrophotometric assays showed higher NO fluxes with iNOSoxy/PEI films built at pH 8.6 than with films built at pH 7.0. Fourier transform infrared analysis of iNOSoxy adsorbed on PEI at pH 8.6 and 7.0 shows structural differences of iNOSoxy in films, which explains the observed changes in enzymatic activity. Our findings show that pH provides a strategy to optimize the NOS loading and enzyme activity in NOS-based LbL thin films, which enables improved NO release with minimum layers of PEI/NOS.

Novel computational approach for studying ph effects, excluded volume and ion-ion correlations in electrical double layers around polyelectrolytes and nanoparticles

NASA Astrophysics Data System (ADS)

Ovanesyan, Zaven

Highly charged cylindrical and spherical objects (macroions) are probably the simplest structures for modeling nucleic acids, proteins and nanoparticles. Their ubiquitous presence within biophysical systems ensures that Coulomb forces are among the most important interactions that regulate the behavior of these systems. In these systems, ions position themselves in a strongly correlated manner near the surface of a macroion and form electrical double layers (EDLs). These EDLs play an important role in many biophysical and biochemical processes. For instance, the macroion's net charge can change due to the binding of many multivalent ions to its surface. Thus, proper description of EDLs near the surface of a macroion may reveal a counter-intuitive charge inversion behavior, which can generate attraction between like-charged objects. This is relevant for the variety of fields such as self-assembly of DNA and RNA folding, as well as for protein aggregation and neurodegenerative diseases. Certainly, the key factors that contribute to these phenomena cannot be properly understood without an accurate solvation model. With recent advancements in computer technologies, the possibility to use computational tools for fundamental understanding of the role of EDLs around biomolecules and nanoparticles on their physical and chemical properties is becoming more feasible. Establishing the impact of the excluded volume and ion-ion correlations, ionic strength and pH of the electrolyte on the EDL around biomolecules and nanoparticles, and how changes in these properties consequently affect the Zeta potential and surface charge density are still not well understood. Thus, modeling and understanding the role of these properties on EDLs will provide more insights on the stability, adsorption, binding and function of biomolecules and nanoparticles. Existing mean-field theories such as Poisson Boltzmann (PB) often neglect the ion-ion correlations, solvent and ion excluded volume effects, which are important details for proper description of EDL properties. In this thesis, we implement an efficient and accurate classical solvation density functional theory (CDSFT) for EDLs of spherical macroions and cylindrical polyelectrolytes embedded in aqueous electrolytes. This approach extends the capabilities of mean field approximations by taking into account electrostatic ion-ion correlations, size asymmetry and excluded volume effects without compromising the computational cost. We apply the computational tool to study the structural and thermodynamic properties of the ionic atmosphere around B-DNA and spherical nanoparticles. We demonstrate that the presence of solvent molecules at experimental concentration and size values has a significant impact on the layering of ions. This layering directly influences the integrated charge and mean electrostatic potential in the diffuse region of the spherical electrical double layer (SEDL) and have a noticeable impact on the behavior of zeta potential (ZP). Recently, we have extended the aforementioned CSDFT to account for the charge-regulated mechanisms of the macroion surface on the structural and thermodynamic properties of spherical EDLs. In the approach, the CSDFT is combined with a surface complexation model to account for ion correlation and excluded volume effects on the surface titration of spherical macroions. We apply the proposed computational approach to describe the role that the ion size and solvent excluded volume play on the surface titration properties of silica nanoparticles. We analyze the effects of the nanoparticle size, pH and salt concentration of the aqueous solution on the nanoparticle's surface charge and zeta potential. The results reveal that surface charge density and zeta potential significantly depend on excluded volume and ion-ion correlation effects as well as on pH for monovalent ion species at high salt concentrations. Overall, our results are in good agreement with Monte Carlo simulations and available experimental data. We discuss future directions of this work, which includes extension of the solvation model for studying the flexibility properties of rigid peptides and globular proteins, and describes benefits that this research can potentially bring to scientific and non scientific communities.

pH-dependence of single-protein adsorption and diffusion at a liquid chromatographic interface.

PubMed

Kisley, Lydia; Poongavanam, Mohan-Vivekanandan; Kourentzi, Katerina; Willson, Richard C; Landes, Christy F

2016-02-01

pH is a common mobile phase variable used to control protein separations due to the tunable nature of amino acid and adsorbent charge. Like other column variables such as column density and ligand loading density, pH is usually optimized empirically. Single-molecule spectroscopy extracts molecular-scale data to provide a framework for mechanistic optimization of pH. The adsorption and diffusion of a model globular protein, α-lactalbumin, was studied by single-molecule microscopy at a silica-aqueous interface analogous to aqueous normal phase and hydrophilic interaction chromatography and capillary electrophoresis interfaces at varied pH. Electrostatic repulsion resulting in free diffusion was observed at pH above the isoelectric point of the protein. In contrast, at low pH strong adsorption and surface diffusion with either no (D ∼ 0.01 μm(2) /s) or translational (D ∼ 0.3 μm(2) /s) motion was observed where the protein likely interacted with the surface through electrostatic, hydrophobic, and hydrogen bonding forces. The fraction of proteins immobilized could be increased by lowering the pH. These results show that retention of proteins at the silica interface cannot be viewed solely as an adsorption/desorption process and that the type of surface diffusion, which ultimately leads to ensemble chromatographic separations, can be controlled by tuning long-range electrostatic and short-range hydrophobic and hydrogen bonding forces with pH. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface charge effects in protein adsorption on nanodiamonds

NASA Astrophysics Data System (ADS)

Aramesh, M.; Shimoni, O.; Ostrikov, K.; Prawer, S.; Cervenka, J.

2015-03-01

Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins (bovine serum albumin and lysozyme) of different properties (charge, molecular weight and rigidity), the main driving mechanism responsible for the protein binding to the charged nanoparticles was identified. Electrostatic interactions were found to dominate the protein adsorption dynamics, attachment and conformation. We developed a simple electrostatic model that can qualitatively explain the observed adsorption behaviour based on charge-induced pH modifications near the charged nanoparticle surfaces. Under neutral conditions, the local pH around the positively and negatively charged nanodiamonds becomes very high (11-12) and low (1-3) respectively, which has a profound impact on the protein charge, hydration and affinity to the nanodiamonds. Small proteins (lysozyme) were found to form multilayers with significant conformational changes to screen the surface charge, while larger proteins (albumin) formed monolayers with minor conformational changes. The findings of this study provide a step forward toward understanding and eventually predicting nanoparticle interactions with biofluids.Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins (bovine serum albumin and lysozyme) of different properties (charge, molecular weight and rigidity), the main driving mechanism responsible for the protein binding to the charged nanoparticles was identified. Electrostatic interactions were found to dominate the protein adsorption dynamics, attachment and conformation. We developed a simple electrostatic model that can qualitatively explain the observed adsorption behaviour based on charge-induced pH modifications near the charged nanoparticle surfaces. Under neutral conditions, the local pH around the positively and negatively charged nanodiamonds becomes very high (11-12) and low (1-3) respectively, which has a profound impact on the protein charge, hydration and affinity to the nanodiamonds. Small proteins (lysozyme) were found to form multilayers with significant conformational changes to screen the surface charge, while larger proteins (albumin) formed monolayers with minor conformational changes. The findings of this study provide a step forward toward understanding and eventually predicting nanoparticle interactions with biofluids. Electronic supplementary information (ESI) available: The FTIR spectrum of nanodiamonds, QCM-D profiles of 50 nm nanodiamond adsorption on silica surfaces, QCM-D profiles of protein desorption after rinsing with water (rinsing experiment) and the full FTIR spectrum of proteins before and after adsorption on ND particles. See DOI: 10.1039/c5nr00250h

Elucidating the role of surface passivating ligand structural parameters in hole wave function delocalization in semiconductor cluster molecules.

PubMed

Teunis, Meghan B; Nagaraju, Mulpuri; Dutta, Poulami; Pu, Jingzhi; Muhoberac, Barry B; Sardar, Rajesh; Agarwal, Mangilal

2017-09-28

This article describes the mechanisms underlying electronic interactions between surface passivating ligands and (CdSe) 34 semiconductor cluster molecules (SCMs) that facilitate band-gap engineering through the delocalization of hole wave functions without altering their inorganic core. We show here both experimentally and through density functional theory calculations that the expansion of the hole wave function beyond the SCM boundary into the ligand monolayer depends not only on the pre-binding energetic alignment of interfacial orbitals between the SCM and surface passivating ligands but is also strongly influenced by definable ligand structural parameters such as the extent of their π-conjugation [π-delocalization energy; pyrene (Py), anthracene (Anth), naphthalene (Naph), and phenyl (Ph)], binding mode [dithiocarbamate (DTC, -NH-CS 2 - ), carboxylate (-COO - ), and amine (-NH 2 )], and binding head group [-SH, -SeH, and -TeH]. We observe an unprecedentedly large ∼650 meV red-shift in the lowest energy optical absorption band of (CdSe) 34 SCMs upon passivating their surface with Py-DTC ligands and the trend is found to be Ph- < Naph- < Anth- < Py-DTC. This shift is reversible upon removal of Py-DTC by triethylphosphine gold(i) chloride treatment at room temperature. Furthermore, we performed temperature-dependent (80-300 K) photoluminescence lifetime measurements, which show longer lifetime at lower temperature, suggesting a strong influence of hole wave function delocalization rather than carrier trapping and/or phonon-mediated relaxation. Taken together, knowledge of how ligands electronically interact with the SCM surface is crucial to semiconductor nanomaterial research in general because it allows the tuning of electronic properties of nanomaterials for better charge separation and enhanced charge transfer, which in turn will increase optoelectronic device and photocatalytic efficiencies.

Investigation of the polyvinyl alcohol stabilization mechanism and adsorption properties on the surface of ternary mixed nanooxide AST 50 (Al2O3-SiO2-TiO2)

NASA Astrophysics Data System (ADS)

Wiśniewska, Małgorzata; Ostolska, Iwona; Szewczuk-Karpisz, Katarzyna; Chibowski, Stanisław; Terpiłowski, Konrad; Gun'ko, Vladimir Moiseevich; Zarko, Vladimir Iljich

2015-01-01

A new adsorbent consisting of fumed, mixed alumina, silica, and titania in various proportions (AST 50) was investigated. The studied material was prepared by chemical vapor deposition method. The diameter of AST 50 primary particles was equal to about 51 nm which denotes that it can be classified as a nanomaterial. In the presented paper, the adsorption properties of polyvinyl alcohol on the ternary oxide were investigated. The polymer macromolecules were characterized by two different molecular weights and degree of hydrolysis. The polymer adsorption reaches the maximum at pH 3 and decreases with the solution pH rise. The reduction of the adsorbed PVA macromolecules is related to the electrostatic repulsion forces occurring in the studied system. The AST 50 point of zero charge (pHpzc) obtained from the potentiometric titration is equal to 4.7. Due to the nonionic character of the analyzed macromolecular compound, the polymer attendance has an insignificant effect on the AST 50 surface charge density. In the case of the adsorbent particles zeta potential, the obtained dependencies are different in the absence and presence of PVA. The shift of the slipping plane and displacement of the counter-ions from Stern layer by the adsorbed polymer chains have the greatest effect on the ζ potential value. The stability measurements indicate that the AST 50 suspensions in the presence of the background electrolyte at pH 3 and 6 are unstable. In turn, in an alkaline medium the mixed oxide suspensions exhibit the highest durability, which is a result of a large number of the negative charges on the AST 50 surface. The addition of PVA 100 significantly improves the suspension stability at pH 3 and 6; at higher pH value, the polymer presence does not influence the system durability. It is related to the steric and electrosteric stabilization of the colloidal particles by the adsorbed polyvinyl alcohol macromolecules.

Efficiency Improvement of Some Agricultural Residue Modified Materials for Textile Dyes Absorption

NASA Astrophysics Data System (ADS)

Boonsong, P.; Paksamut, J.

2018-03-01

In this work, the adsorption efficiency was investigated of some agricultural residue modified materials as natural bio-adsorbents which were rice straw (Oryza sativa L.) and pineapple leaves (Ananas comosus (L.) Merr.) for the removal of textile dyes. Reactive dyes were used in this research. The improvement procedure of agricultural residue materials properties were alkali-acid modification with sodium hydroxide solution and hydrochloric acid solution. Adsorption performance has been investigated using batch experiments. Investigated adsorption factors consisted of adsorbent dose, contact time, adsorbent materials and pH of solution. The results were found that rice straw had higher adsorption capacity than pineapple leaves. The increasing of adsorption capacity depends on adsorbent dose and contact time. Moreover, the optimum pH for dye adsorption was acidic range because lowering pH increased the positively charges on the adsorbent surface which could be attacked by negatively charge of acid dyes. The agricultural residue modified materials had significant dye removal efficiency which these adsorbents could be used for the treatment of textile effluent in industries.

Second-harmonic generation and theoretical studies of protonation at the water/α-TiO 2 (1 1 0) interface

NASA Astrophysics Data System (ADS)

Fitts, Jeffrey P.; Machesky, Michael L.; Wesolowski, David J.; Shang, Xiaoming; Kubicki, James D.; Flynn, George W.; Heinz, Tony F.; Eisenthal, Kenneth B.

2005-08-01

The pH of zero net surface charge (pH pzc) of the α-TiO 2 (1 1 0) surface was characterized using second-harmonic generation (SHG) spectroscopy. The SHG response was monitored during a series of pH titrations conducted at three NaNO 3 concentrations. The measured pH pzc is compared with a pH pzc value calculated using the revised MUltiSIte Complexation (MUSIC) model of surface oxygen protonation. MUSIC model input parameters were independently derived from ab initio calculations of relaxed surface bond lengths for a hydrated surface. Model (pH pzc 4.76) and experiment (pH pzc 4.8 ± 0.3) agreement establishes the incorporation of independently derived structural parameters into predictive models of oxide surface reactivity.

Charge heterogeneity: Basic antibody charge variants with increased binding to Fc receptors.

PubMed

Hintersteiner, Beate; Lingg, Nico; Zhang, Peiqing; Woen, Susanto; Hoi, Kong Meng; Stranner, Stefan; Wiederkum, Susanne; Mutschlechner, Oliver; Schuster, Manfred; Loibner, Hans; Jungbauer, Alois

We identified active isoforms of the chimeric anti-GD2 antibody, ch14.18, a recombinant antibody produced in Chinese hamster ovary cells, which is already used in clinical trials. 1,2,3 We separated the antibody by high resolution ion-exchange chromatography with linear pH gradient elution into acidic, main and basic charge variants on a preparative scale yielding enough material for an in-depth study of the sources and the effects of microheterogeneity. The binding affinity of the charge variants toward the antigen and various cell surface receptors was studied by Biacore. Effector functions were evaluated using cellular assays for antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity. Basic charge variants showed increased binding to cell surface receptor FcγRIIIa, which plays a major role in regulating effector functions. Furthermore, increased binding of the basic fractions to the neonatal receptor was observed. As this receptor mediates the prolonged half-life of IgG in human serum, this data may well hint at an increased serum half-life of these basic variants compared to their more acidic counterparts. Different glycoform patterns, C-terminal lysine clipping and N-terminal pyroglutamate formation were identified as the main structural sources for the observed isoform pattern. Potential differences in structural stability between individual charge variant fractions by nano differential scanning calorimetry could not been detected. Our in-vitro data suggests that the connection between microheterogeneity and the biological activity of recombinant antibody therapeutics deserves more attention than commonly accepted.

Regulation of arsenic mobility on basaltic glass surfaces by speciation and pH.

PubMed

Sigfusson, Bergur; Meharg, Andrew A; Gislason, Sigurdur R

2008-12-01

The importance of geothermal energy as a source for electricity generation and district heating has increased over recent decades. Arsenic can be a significant constituent of the geothermal fluids pumped to the surface during power generation. Dissolved As exists in different oxidation states, mainly as As(III) and As(V), and the charge of individual species varies with pH. Basaltic glass is one of the most important rock types in many high-temperature geothermal fields. Static batch and dynamic column experiments were combined to generate and validate sorption coefficients for As(III) and As(V) in contact with basaltic glass at pH 3-10. Validation was carried out by two empirical kinetic models and a surface complexation model (SCM). The SCM provided a better fit to the experimental column data than kinetic models at high pH values. However, in certain circumstances, an adequate estimation of As transport in the column could not be attained without incorporation of kinetic reactions. The varying mobility with pH was due to the combined effects of the variable charge of the basaltic glass with the pH point of zero charge at 6.8 and the individual As species as pH shifted, respectively. The mobility of As(III) decreased with increasing pH. The opposite was true for As(V), being nearly immobile at pH 3 to being highly mobile at pH 10. Incorporation of appropriate sorption constants, based on the measured pH and Eh of geothermal fluids, into regional groundwater-flow models should allow prediction of the As(III) and As(V) transport from geothermal systems to adjacent drinking water sources and ecosystems.

Surface charge-specific interactions between polymer nanoparticles and ABC transporters in Caco-2 cells

NASA Astrophysics Data System (ADS)

Bhattacharjee, Sourav; van Opstal, Edward J.; Alink, Gerrit M.; Marcelis, Antonius T. M.; Zuilhof, Han; Rietjens, Ivonne M. C. M.

2013-06-01

The surface charge-dependent transport of polymeric nanoparticles (PNPs) across Caco-2 monolayers grown on transwell culture systems as an in vitro model for intestinal transport was tested. The transport of well-characterized, monodisperse, and fluorescent tri-block copolymer nanoparticles (TCNPs/size 45 nm) and polystyrene nanoparticles (PSNPs/size 50 nm), with different surface charges (positive and negative), was quantified. The positive PNPs showed a higher intracellular uptake and flux across the Caco-2 monolayers than the negative PNPs. Multidrug resistance/P-glycoprotein (MDR1/P-gp), a specific ATP-binding cassette (ABC) transporter, was found to play a major role in the cellular efflux of positive PNPs, whereas the multidrug resistance protein 1 took part in the efflux of negative PNPs from Caco-2 cells. The positive PNPs also caused an increased cellular uptake and apical to basolateral transport of the carcinogen PhIP across the Caco-2 monolayer. The flavonoid quercetin, which is known to interact with ABC transporters, promoted the intracellular uptake of different PNPs and interfered with the normal distribution patterns of PNPs in the transwell system. These results indicate that PNPs display surface charge-specific interactions with ABC transporters and can even affect the bioavailability of toxic food-borne compounds (like pro-carcinogens).

Effect of pH and Pressure on Uranium Removal from Drinking Water Using NF/RO Membranes.

PubMed

Schulte-Herbrüggen, Helfrid M A; Semião, Andrea J C; Chaurand, Perrine; Graham, Margaret C

2016-06-07

Groundwater is becoming an increasingly important drinking water source. However, the use of groundwater for potable purposes can lead to chronic human exposure to geogenic contaminants, for example, uranium. Nanofiltration (NF) and reverse osmosis (RO) processes are used for drinking water purification, and it is important to understand how contaminants interact with membranes since accumulation of contaminants to the membrane surface can lead to fouling, performance decline and possible breakthrough of contaminants. During the current study laboratory experiments were conducted using NF (TFC-SR2) and RO (BW30) membranes to establish the behavior of uranium across pH (3-10) and pressure (5-15 bar) ranges. The results showed that important determinants of uranium-membrane sorption interactions were (i) the uranium speciation (uranium species valence and size in relation to membrane surface charge and pore size) and (ii) concentration polarization, depending on the pH values. The results show that it is important to monitor sorption of uranium to membranes, which is controlled by pH and concentration polarization, and, if necessary, adjust those parameters controlling uranium sorption.

Color removal from dye-containing wastewater by magnesium chloride.

PubMed

Gao, Bao-Yu; Yue, Qin-Yan; Wang, Yan; Zhou, Wei-Zhi

2007-01-01

Color removal by MgCl(2) when treating synthetic waste containing pure dyes was studied. The color removal efficiency of MgCl(2)/Ca(OH)(2) was compared with that of Al(2)(SO(4))(3), polyaluminum chloride (PAC) and FeSO(4)/Ca(OH)(2). The mechanism of color removal by MgCl(2) was also investigated. The experimental results show that the color removal efficiency of MgCl(2) is related to the type of dye and depends on the pH of the waste and the dosage of the coagulants used. Treatment of waste containing reactive dye or dispersed dye with MgCl(2) yielded an optimum color removal ratio when the pH of the solution was equal to or above 12.0. For both the reactive and dispersed dye waste, MgCl(2)/Ca(OH)(2) was shown to be superior to MgCl(2)/NaOH, Al(2)(SO(4))(3), PAC and FeSO(4)/Ca(OH)(2) for color removal. A magnesium hydroxide precipitate formed at pH values greater than 12.0, which provided a large adsorptive surface area and a positive electrostatic surface charge, enabling it to remove the dyes through charge neutralization and an adsorptive coagulating mechanism. So, the MgCl(2)/Ca(OH)(2) system is a viable alternative to some of the more conventional forms of chemical treatment, especially for treating actual textile waste with high natural pH.

Hydrophilic crosslinked-polymeric surface capable of effective suppression of protein adsorption

NASA Astrophysics Data System (ADS)

Kamon, Yuri; Inoue, Naoko; Mihara, Erika; Kitayama, Yukiya; Ooya, Tooru; Takeuchi, Toshifumi

2016-08-01

We investigated the nonspecific adsorption of proteins towards three hydrophilic crosslinked-polymeric thin layers prepared by surface-initiated atom transfer radical polymerization using N,N‧-methylenebisacrylamide, 2-(methacryloyloxy)ethyl-[N-(2-methacryloyloxy)ethyl]phosphorylcholine (MMPC), or 6,6‧-diacryloyl-trehalose crosslinkers. Protein binding experiments were performed by surface plasmon resonance with six proteins of different pI values including α-lactalbumin, bovine serum albumin (BSA), myoglobin, ribonuclease A, cytochrome C, and lysozyme in buffer solution at pH 7.4. All of the obtained crosslinked-polymeric thin layers showed low nonspecific adsorption of negatively charged proteins at pH 7.4 such as α-lactalbumin, BSA, and myoglobin. Nonspecific adsorption of positively charged proteins including ribonuclease A, cytochrome C, and lysozyme was the lowest for poly(MMPC). These results suggest poly(MMPC) can effectively reduce nonspecific adsorption of a wide range of proteins that are negatively or positively charged at pH 7.4. MMPC is a promising crosslinker for a wide range of polymeric materials requiring low nonspecific protein binding.

The titration of carboxyl-terminated monolayers revisited: in situ calibrated fourier transform infrared study of well-defined monolayers on silicon.

PubMed

Aureau, D; Ozanam, F; Allongue, P; Chazalviel, J-N

2008-09-02

The acid-base equilibrium at the surface of well-defined mixed carboxyl-terminated/methyl-terminated monolayers grafted on silicon (111) has been investigated using in situ calibrated infrared spectroscopy (attenuated total reflectance (ATR)) in the range of 900-4000 cm (-1). Spectra of surfaces in contact with electrolytes of various pH provide a direct observation of the COOH <--> COO (-) conversion process. Quantitative analysis of the spectra shows that ionization of the carboxyl groups starts around pH 6 and extends over more than 6 pH units: approximately 85% ionization is measured at pH 11 (at higher pH, the layers become damaged). Observations are consistently accounted for by a single acid-base equilibrium and discussed in terms of change in ion solvation at the surface and electrostatic interactions between surface charges. The latter effect, which appears to be the main limitation, is qualitatively accounted for by a simple model taking into account the change in the Helmholtz potential associated with the surface charge. Furthermore, comparison of calculated curves with experimental titration curves of mixed monolayers suggests that acid and alkyl chains are segregated in the monolayer.

Calculation of the acid-base equilibrium constants at the alumina/electrolyte interface from the ph dependence of the adsorption of singly charged ions (Na+, Cl-)

NASA Astrophysics Data System (ADS)

Gololobova, E. G.; Gorichev, I. G.; Lainer, Yu. A.; Skvortsova, I. V.

2011-05-01

A procedure was proposed for the calculation of the acid-base equilibrium constants at an alumina/electrolyte interface from experimental data on the adsorption of singly charged ions (Na+, Cl-) at various pH values. The calculated constants (p K {1/0}= 4.1, p K {2/0}= 11.9, p K {3/0}= 8.3, and p K {4/0}= 7.7) are shown to agree with the values obtained from an experimental pH dependence of the electrokinetic potential and the results of potentiometric titration of Al2O3 suspensions.

Stability of nTiO2 particles and their attachment to sand: Effects of humic acid at different pH.

PubMed

Wu, Yang; Cheng, Tao

2016-01-15

The fate and transport of nano-scale or micro-scale titanium dioxide particles (nTiO2) in subsurface environments are strongly influenced by the stability of nTiO2 and their attachment to sediment grains. nTiO2 may carry either positive or negative charges in natural water, therefore, environmental factors such as pH, humic substances, and Fe oxyhydroxide coatings on sediment grains, which are known to control the stability and transport of negatively-charged colloids, may influence nTiO2 in different manners. The objective of this study is to investigate the effects of pH and humic acid (HA) on the stability and attachment of nTiO2 to sand at HA concentrations that are relevant to typical groundwater conditions, so that mechanisms that control nTiO2 immobilization and transport in natural systems can be elucidated. Stability and attachment of nTiO2 to quartz sand and Fe oxyhydroxide coated quartz sand are experimentally measured under a range of HA concentrations at pH5 and 9. Results show that at pH5, negatively-charged HA strongly adsorbs to positively-charged nTiO2 and Fe oxyhydroxide, which, at low HA concentrations, partially neutralizes the positive charges on nTiO2 and Fe oxyhydroxide, and therefore decreases the repulsive electrostatic forces between the surfaces, resulting in nTiO2 aggregation and attachment. At high HA concentrations, adsorbed HA reverses the surface charges of nTiO2 and Fe oxyhydroxide, and makes nTiO2 and Fe oxyhydroxide strongly negatively charged, resulting in stable nTiO2 suspension and low nTiO2 attachment. At pH9, HA, nTiO2, and Fe oxyhydroxide are all negatively charged, and HA adsorption is low and does not have a strong impact on the stability and attachment of nTiO2. Overall, this study shows that changes in surface charges of nTiO2 and Fe oxyhydroxide coating caused by HA adsorption is a key factor that influences the stability and attachment of nTiO2. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of Salt Concentration on the pH Responses of Strong and Weak Polyelectrolyte Brushes.

PubMed

Zhang, Jian; Kou, Ran; Liu, Guangming

2017-07-11

Strong polyelectrolyte brushes (SPB) and weak polyelectrolyte brushes (WPB) have different origins with response to pH, which makes their pH-responsive properties sensitive to salt concentration in different ways. Herein, we have employed poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC) and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes as model systems for SPB and WPB, respectively, to investigate the effect of salt concentration on the pH responses of SPB and WPB using several surface-sensitive techniques. The pH-responsive properties of the PMETAC brushes are governed by the reorganization of the interchain hydrogen bonds between the grafted chains, whereas the pH response of the PDMAEMA brushes is controlled by the charge of the grafted chains. The response of the properties of the PMETAC brushes including hydration, conformation, and surface wettability becomes weaker with increasing salt concentration induced by the competitive adsorption of counterions to the brushes between OH - and Cl - . The weakening of the pH response of the PMETAC brushes is more remarkable at the relatively high pH values. The pH response of the PDMAEMA brushes also exhibits a salt-concentration dependence. As the salt concentration increases, the weakening of the pH response of the PDMAEMA brushes is attributed to the decrease in osmotic pressure within the brushes at relatively low pH values.

Stoichiometry and pH dependence of the rabbit proton-dependent oligopeptide transporter PepT1.

PubMed

Steel, A; Nussberger, S; Romero, M F; Boron, W F; Boyd, C A; Hediger, M A

1997-02-01

1. The intestinal H(+)-coupled peptide transporter PepT1, displays a broad substrate specificity and accepts most charged and neutral di- and tripeptides. To study the proton-to-peptide stoichiometry and the dependence of the kinetic parameters on extracellular pH (pHo), rabbit PepT1 was expressed in Xenopus laevis oocytes and used for uptake studies of radiolabelled neutral and charged dipeptides, voltage-clamp analysis and intracellular pH measurements. 2. PepT1 did not display the substrate-gated anion conductances that have been found to be characteristic of members of the Na(+)- and H(+)-coupled high-affinity glutamate transporter family. In conjunction with previous data on the ion dependence of PepT1, it can therefore be concluded that peptide-evoked charge fluxes of PepT1 are entirely due to H+ movement. 3. Neutral, acidic and basic dipeptides induced intracellular acidification. The rate of acidification, the initial rates of the uptake of radiolabelled peptides and the associated charge fluxes gave proton-substrate coupling ratios of 1:1, 2:1 and 1:1 for neutral, acidic and basic dipeptides, respectively. 4. Maximal transport of the neutral and charged dipeptides Gly-Leu, Gly-Glu, Gly-Lys and Ala-Lys occurred at pHo 5.5, 5.2, 6.2 and 5.8, respectively. The Imax values were relatively pHo independent but the apparent affinity (Km(app) values for these peptides were shown to be highly pHo dependent. 5. Our data show that at physiological pH (pHo 5.5-6.0) PepT1 prefers neutral and acidic peptides. The shift in transport maximum for the acidic peptide Gly-Glu to a lower pH value suggests that acidic dipeptides are transported in the protonated form. The shift in the transport maxima of the basic dipeptides to higher pH values may involve titration of a side-chain on the transporter molecule (e.g. protonation of a histidine group). These considerations have led us to propose a model for coupled transport of neutral, acidic and basic dipeptides.

Measuring the isoelectric point of the edges of clay mineral particles: the case of montmorillonite.

PubMed

Pecini, Eliana M; Avena, Marcelo J

2013-12-03

The isoelectric point (IEP) of the edge surface of a montmorillonite sample was determined by using electrophoretic mobility measurements. This parameter, which is fundamental for the understanding of the charging behavior of clay mineral surfaces, was never measured so far because of the presence of permanent negative charges within the montmorillonite structure, charges that mask the electrokinetic behavior of the edges. The strategy was to block or neutralize the structural charges with two different cations, methylene blue (MB(+)) and tetraethylenepentaminecopper(II) ([Cu(tetren)](2+)), so that the charging behavior of the particles becomes that of the edge surfaces. Adsorption isotherms of MB(+) and [Cu(tetren)](2+) at different ionic strengths (NaCl) were performed to establish the uptakes that neutralize the cation exchange capacity (CEC, 0.96 meq g(-1)) of the sample. At high adsorptive concentrations, there was a superequivalent adsorption of MB(+) (adsorption exceeding the CEC) and an equivalent adsorption of [Cu(tetren)](2+) (adsorption reaching the CEC). In both cases, structural charges were neutralized at uptakes very close to the CEC. Zeta potential (ζ) vs pH data at different ionic strengths of montmorillonite with adsorbed MB(+) allowed to estimate an upper limit of the edge's IEP, 5.3 ± 0.2. The same kind of data obtained with adsorbed [Cu(tetren)](2+) provided a lower limit of the IEP, 4.0 ± 0.2. These values are in agreement with previously informed IEP and point of zero charge of pyrophyllite, which is structurally analogous to montmorillonite but carries no permanent charges. The importance of knowing the IEP of the edge surface of clay minerals is discussed. This value characterizes the intrinsic reactivity of edges, that is, the protonating capacity of edge groups in absence of any electric field generated by structural charges. It also allows us to correct relative edge charge vs pH curves obtained by potentiometric titrations and to obtain the true edge charge vs pH curves at different electrolyte concentrations.

Multilayering of Calcium Aerosol-OT at the Mica/Water Interface Studied with Neutron Reflection: Formation of a Condensed Lamellar Phase at the CMC.

PubMed

Griffin, L R; Browning, K L; Lee, S Y; Skoda, M W A; Rogers, S; Clarke, S M

2016-12-13

Using specular neutron reflection, the adsorption of sodium and calcium salts of the surfactant bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT or AOT) has been studied at the mica/water interface at concentrations between 0.1 and 2 CMC. The pH dependence of the adsorption was also probed. No evidence of the adsorption of Na(AOT) was found even at the critical micelle concentration (CMC) while the calcium salt was found to adsorb significantly at concentrations of 0.5 CMC and above. This interesting and somewhat unexpected finding demonstrates that counterion identity may be used to tune the adsorption of anionic surfactants on anionic surfaces. At the CMC, three condensed bilayers of Ca(AOT) 2 were adsorbed at pH 7 and 9 and four bilayers adsorbed at pH 4. Multilayering at the CMC of Ca(AOT) 2 on the mica surface is an unusual feature of this surfactant/surface combination. Only single bilayer adsorption has been observed at other surfaces at the CMC. We suggest this arises from the high charge density of mica which must provide an excellent template for the surfactant.

BSA adsorption onto nanospheres: Influence of surface curvature as probed by electrophoretic light scattering and UV/vis spectroscopy

NASA Astrophysics Data System (ADS)

Sánchez-Pérez, Julio A.; Gallardo-Moreno, Amparo M.; González-Martín, M. Luisa; Vadillo-Rodríguez, Virginia

2015-10-01

The influence of surface curvature on the adsorption of bovine serum albumin (BSA) was evaluated through the combination of two fairly simple techniques: electrophoretic light scattering and UV/vis spectroscopy. Measurements were carried out for a range of protein concentrations (0-320 μg/ml) at pH 3.5, 4.5 and 7 using hydrophobic polystyrene nanospheres of 38.8, 82 and 220 nm in diameter. The results obtained demonstrate that the charge of the BSA molecules in solution dictates the pH-dependent behavior of the protein-coated nanospheres, indicating in all cases a significant adsorption of BSA molecules. At a fixed pH, however, it is the zeta potential that characterizes the uncoated nanospheres normalized by their surface area that primarily controls protein adsorption. In particular, it is found that the rate at which BSA interact with the different nanospheres increases as their negative zeta potential per unit area (or diameter) increases (decreases) regardless of the pH. Moreover, provided that adsorption occurs away from the isoelectric point of the protein, highly curved surfaces are found to stabilize the native-like conformation of BSA upon adsorption by likely reducing lateral interactions between adsorbed molecules.

Dynamic electrophoretic fingerprinting of the HIV-1 envelope glycoprotein

PubMed Central

2013-01-01

Background Interactions between the HIV-1 envelope glycoprotein (Env) and its primary receptor CD4 are influenced by the physiological setting in which these events take place. In this study, we explored the surface chemistry of HIV-1 Env constructs at a range of pH and salinities relevant to mucosal and systemic compartments through electrophoretic mobility (EM) measurements. Sexual transmission events provide a more acidic environment for HIV-1 compared to dissemination and spread of infection occurring in blood or lymph node. We hypothesize functional, trimeric Env behaves differently than monomeric forms. Results The dynamic electrophoretic fingerprint of trimeric gp140 revealed a change in EM from strongly negative to strongly positive as pH increased from that of the lower female genital tract (pHx) to that of the blood (pHy). Similar findings were observed using a trimeric influenza Haemagglutinin (HA) glycoprotein, indicating that this may be a general attribute of trimeric viral envelope glycoproteins. These findings were supported by computationally modeling the surface charge of various gp120 and HA crystal structures. To identify the behavior of the infectious agent and its target cells, EM measurements were made on purified whole HIV-1 virions and primary T-lymphocytes. Viral particles had a largely negative surface charge, and lacked the regions of positivity near neutral pH that were observed with trimeric Env. T cells changed their surface chemistry as a function of activation state, becoming more negative over a wider range of pH after activation. Soluble recombinant CD4 (sCD4) was found to be positively charged under a wide range of conditions. Binding studies between sCD4 and gp140 show that the affinity of CD4-gp140 interactions depends on pH. Conclusions Taken together, these findings allow a more complete model of the electrochemical forces involved in HIV-1 Env functionality. These results indicate that the influence of the localized environment on the interactions of HIV with target cells are more pronounced than previously appreciated. There is differential chemistry of trimeric, but not monomeric, Env under conditions which mimic the mucosa compared to those found systemically. This should be taken into consideration during design of immunogens which targets virus at mucosal portals of entry. PMID:23514633

Formulation design space for stable, pH sensitive crystalline nifedipine nanoparticles.

PubMed

Jog, Rajan; Unachukwu, Kenechi; Burgess, Diane J

2016-11-30

Enteric coated formulations protect drugs from degrading in the harsh environment of the stomach (acidic pH and enzymes), and promotes drug delivery to and absorption into the duodenum and/or later parts of the intestine. Four DoE models were applied to optimize formulation parameters for the preparation of pH sensitive nifedipine nanoparticles. Stability studies were performed on the optimized formulations to monitor any possible variation in particle size distribution, homogeneity index, surface charge and drug release (pH 1.2 and pH 6.8). Stability studies were performed for 3 months at 4°C, 25°C and 40°C. A combination of Eudragit ® L 100-55 and polyvinyl alcohol was determined to be the most effective in stabilizing the nanoparticle suspension. The average particle size distribution, polydispersity index and surface charge of the optimized pH sensitive nifedipine nanoparticles were determined to be 131.86±8.21nm, 0.135±0.008 and -7.631±0.146mV, respectively. Following three months storage, it was observed that the formulations stored at 4°C were stable in terms of particle size distribution, polydispersity index, surface charge, drug loading and drug release, whereas those stored at 25°C and 40°C were relatively unstable. A predictive model to prepare stable pH sensitive nifedipine nanoparticles, was successfully developed using multiple linear regression analysis. Copyright © 2016 Elsevier B.V. All rights reserved.

Dispersion of nano-silicon carbide (SiC) powder in aqueous suspensions

NASA Astrophysics Data System (ADS)

Singh, Bimal P.; Jena, Jayadev; Besra, Laxmidhar; Bhattacharjee, Sarama

2007-10-01

The dispersion characteristics of nanosize silicon carbide (SiC) suspension were investigated in terms of surface charge, particle size, rheological measurement and adsorption study. Ammonium polycarboxylate has been used as dispersant to stabilize the suspension. It was found that the isoelectric point (iep) of SiC powder was pHiep (4.9). The surface charge of powder changed significantly in presence of the ammonium polycarboxylate dispersant and iep shifted significantly towards lower acidic pH (3.6). The shift in iep has been quantified in terms of Δ G 0 SP, the specific free energy of adsorption between the surface sites and the adsorbing polyelectrolyte (APC). The values of Δ G 0 SP (-10.85 RT unit) estimated by the electro kinetic data compare well with those obtained from adsorption isotherms (-9.521 RT unit). The experimentally determined optimum concentration of dispersant required for maximizing the dispersion was found to be 2.4 mg/g of SiC (corresponding to an adsorbed amount of 1.10 mg/g), at pH 7.5. This is much below the full monolayer coverage (corresponding to adsorbed amount of 1.75 mg/g) of the particles surface by the dispersant. The surface charge quantity, rheological, pH, electro kinetic and adsorption isotherm results were used to explain and correlate the stability of the nanosize silicon carbide in aqueous media. At pH 7.5, where both SiC surface and APC are negatively charged, the adsorption of APC was low because of limited availability of favourable adsorption sites. In addition, the brush-like configuration of the adsorbed polymer prevented close approach of any additional dispersant; hence stabilization of the slurry happens at a comparatively lower concentration than the monolayer coverage.

Mineralogical and hydrochemical effects on adsorption removal of cesium-137 and strontium-90 by kaolinite.

PubMed

Jeong, C H

2001-01-01

Adsorption characteristics of the nuclides onto kaolinite were investigated by batch experiment under various pH conditions and concentrations of groundwater cations (Ca2+, Mg2+, K+ and Na+) and anions (HCO3-, CO3(2-) and SO4(2-). Adsorption removal of 137Cs and 90Sr by kaolinite greatly increased as the concentration of groundwater cations increased from 10(-5) to 10(-1) M. In contrast, the pH exerted a small effect on the adsorption of 137Cs and 90Sr onto kaolinite. The zeta potential of kaolinite particles showed a negative increase of amphoteric surface charge with increasing pH. The adsorption behavior of 90Sr was also highly dependent on the concentration of bicarbonate. The thermodynamic saturation index indicated that bicarbonate exerts great effect on strontium adsorption by the precipitation of a strontianite (SrCO3) and a change in pH.

Surface charge effects in protein adsorption on nanodiamonds.

PubMed

Aramesh, M; Shimoni, O; Ostrikov, K; Prawer, S; Cervenka, J

2015-03-19

Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins (bovine serum albumin and lysozyme) of different properties (charge, molecular weight and rigidity), the main driving mechanism responsible for the protein binding to the charged nanoparticles was identified. Electrostatic interactions were found to dominate the protein adsorption dynamics, attachment and conformation. We developed a simple electrostatic model that can qualitatively explain the observed adsorption behaviour based on charge-induced pH modifications near the charged nanoparticle surfaces. Under neutral conditions, the local pH around the positively and negatively charged nanodiamonds becomes very high (11-12) and low (1-3) respectively, which has a profound impact on the protein charge, hydration and affinity to the nanodiamonds. Small proteins (lysozyme) were found to form multilayers with significant conformational changes to screen the surface charge, while larger proteins (albumin) formed monolayers with minor conformational changes. The findings of this study provide a step forward toward understanding and eventually predicting nanoparticle interactions with biofluids.

BioFET-SIM web interface: implementation and two applications.

PubMed

Hediger, Martin R; Jensen, Jan H; De Vico, Luca

2012-01-01

We present a web interface which allows us to conveniently set up calculations based on the BioFET-SIM model. With the interface, the signal of a BioFET sensor can be calculated depending on its parameters, as well as the signal dependence on pH. As an illustration, two case studies are presented. In the first case, a generic peptide with opposite charges on both ends is inverted in orientation on a semiconducting nanowire surface leading to a corresponding change in sign of the computed sensitivity of the device. In the second case, the binding of an antibody/antigen complex on the nanowire surface is studied in terms of orientation and analyte/nanowire surface distance. We demonstrate how the BioFET-SIM web interface can aid in the understanding of experimental data and postulate alternative ways of antibody/antigen orientation on the nanowire surface.

Multifunctional nanoparticulate polyelectrolyte complexes.

PubMed

Hartig, Sean M; Greene, Rachel R; DasGupta, Jayasri; Carlesso, Gianluca; Dikov, Mikhail M; Prokop, Ales; Davidson, Jeffrey M

2007-12-01

Water-soluble, biodegradable, polymeric, polyelectrolyte complex dispersions (PECs) have evolved because of the limitations, in terms of toxicity, of the currently available systems. These aqueous nanoparticulate architectures offer a significant advantage for products that may be used as drug delivery systems in humans. PECs are created by mixing oppositely charged polyions. Their hydrodynamic diameter, surface charge, and polydispersity are highly dependent on concentration, ionic strength, pH, and molecular parameters of the polymers that are used. In particular, the complexation between polyelectrolytes with significantly different molecular weights leads to the formation of water-insoluble aggregates. Several PEC characteristics are favorable for cellular uptake and colloidal stability, including hydrodynamic diameter less than 200 nm, surface charge of >30 mV or <-30 mV, spherical morphology, and polydispersity index (PDI) indicative of a homogeneous distribution. Maintenance of these properties is critical for a successful delivery vehicle. This review focuses on the development and potential applications of PECs as multi-functional, site-specific nanoparticulate drug/gene delivery and imaging devices.

Defining reactive sites on hydrated mineral surfaces: Rhombohedral carbonate minerals

NASA Astrophysics Data System (ADS)

Villegas-Jiménez, Adrián; Mucci, Alfonso; Pokrovsky, Oleg S.; Schott, Jacques

2009-08-01

Despite the success of surface complexation models (SCMs) to interpret the adsorptive properties of mineral surfaces, their construct is sometimes incompatible with fundamental chemical and/or physical constraints, and thus, casts doubts on the physical-chemical significance of the derived model parameters. In this paper, we address the definition of primary surface sites (i.e., adsorption units) at hydrated carbonate mineral surfaces and discuss its implications to the formulation and calibration of surface equilibria for these minerals. Given the abundance of experimental and theoretical information on the structural properties of the hydrated (10.4) cleavage calcite surface, this mineral was chosen for a detailed theoretical analysis of critical issues relevant to the definition of primary surface sites. Accordingly, a single, generic charge-neutral surface site ( tbnd CaCO 3·H 2O 0) is defined for this mineral whereupon mass-action expressions describing adsorption equilibria were formulated. The one-site scheme, analogous to previously postulated descriptions of metal oxide surfaces, allows for a simple, yet realistic, molecular representation of surface reactions and provides a generalized reference state suitable for the calculation of sorption equilibria for rhombohedral carbonate minerals via Law of Mass Action (LMA) and Gibbs Energy Minimization (GEM) approaches. The one-site scheme is extended to other rhombohedral carbonate minerals and tested against published experimental data for magnesite and dolomite in aqueous solutions. A simplified SCM based on this scheme can successfully reproduce surface charge, reasonably simulate the electrokinetic behavior of these minerals, and predict surface speciation agreeing with available spectroscopic data. According to this model, a truly amphoteric behavior is displayed by these surfaces across the pH scale but at circum-neutral pH (5.8-8.2) and relatively high ΣCO 2 (⩾1 mM), proton/bicarbonate co-adsorption becomes important and leads to the formation of a charge-neutral H 2CO 3-like surface species which may largely account for the surface charge-buffering behavior and the relatively wide range of pH values of isoelectric points (pH iep) reported in the literature for these minerals.

Developing a Small-scale De-fluoridation Filter for use in Rural Northern Ghana with Activated Alumina as the Sorbent

NASA Astrophysics Data System (ADS)

Craig, L.; Stillings, L. L.; Decker, D.; Thomas, J.

2013-12-01

In northern Ghana, groundwater is the main source of household water and is generally considered a safe and economical source of drinking water. However in some areas it contains fluoride (F-) concentrations above the 1.5 ppm limit recommended by the World Health Organization, putting the users at risk of fluorosis. The study area in the Upper East Region of northern Ghana has pockets of groundwater F- up to 4.6 ppm and, as a result, also has a high percentage of residents with dental fluorosis. They have no alternative water source and, because of the poverty and limited access to technology, the affected community lacks the capacity to set up advanced treatment systems. One proposed solution is to attach F- adsorption filters to the wells, since adsorption is considered a simple and cost effective approach for treating high F- drinking water. This study evaluates activated alumina as a sorbent for use in de-fluoridation filters in the study area. We evaluated the long-term adsorption capacity of activated alumina, as well as potential changes in F- adsorption rate and capacity with grain size. We measured differences in positive surface charge (as C m-2) via slow acid titration, as well as F- loading with varied prior hydration time. Experimental results from this research show no notable change in F- adsorption or positive surface charge when the activated alumina surface was pre-equilibrated in distilled water from 24 hours up to 30 weeks before the experiment. The results of F- loading show a maximum of ~3.4 mg F- sorbed per gm activated alumina (at initial pH ~6.9, initial F- 1 to 60 ppm, and 20 hr reaction time). The pH dependent surface charge shows a maximum of ~0.14 C m-2 at pH of ~4.4 and zero surface charge at pH ~8.5. F- loading experiments were conducted with grain size ranges 0.125 to 0.250 mm and 0.5 to 1.0 mm to evaluate changes in F- adsorption rate (initial pH ~6.9, initial F- 10 ppm) and F- loading (initial pH ~6.9, initial F- 1 to 60 ppm, 20 hr reaction time). The F- loading onto activated alumina did not change with grain size. However time to equilibrium increased dramatically with a decrease in grain size - after one hour of reaction time, the larger grain size adsorbed only 59% of F-, while at the finer grain size 90% was adsorbed. Future work will determine the volume of high F- water that can be treated before activated alumina needs to be regenerated or changed. These data will be incorporated into the design of a small-scale F-1 adsorption filter in the study area, and will predict the longevity of activated alumina as the sorbent.

Variable Charge Soils: Mineralogy and Chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qafoku, Nik; Van Ranst, Eric; Noble, Andrew

2003-11-01

Soils rich in particles with amphoteric surface properties in the Oxisols, Ultisols, Alfisols, Spodosols and Andisols orders (1) are considered variable charge soils (2). The term “variable charge” is used to describe organic and inorganic soil constituents with reactive surface groups whose charge varies with pH, ionic concentration and composition of the soil solution. Such groups are the surface carboxyl, phenolic and amino functional groups of organic materials in soils, and surface hydroxyl groups of Fe and Al oxides, allophane and imogolite. The hydroxyl surface groups are also present on edges of some phyllosilicate minerals such as kaolinite, mica, andmore » hydroxyl-interlayered vermiculite. The variable charge is developed on the surface groups as a result of adsorption or desorption of ions that are constituents of the solid phase, i.e., H+, and the adsorption or desorption of solid-unlike ions that are not constituents of the solid. Highly weathered soils usually undergo isoeletric weathering and reach a “zero net charge” stage during their development. They have a slightly acidic to acidic soil solution pH, which is close to either point of zero net charge (PZNC) (3) or point of zero salt effect (PZSE) (3). They are characterized by high abundances of minerals with a point of zero net proton charge (PZNPC) (3) at neutral and slightly basic pHs; the most important being Fe and Al oxides and allophane. Under acidic conditions, the surfaces of these minerals are net positively charged. In contrast, the surfaces of permanent charge phyllosilicates are negatively charged regardless of ambient conditions. Variable charge soils therefore, are heterogeneous charge systems. The coexistence and interactions of oppositely charged surfaces or particles confers a different pattern of physical and chemical behavior on the soil, relatively to a homogeneously charged system of temperate regions. In some variable charge soils (Oxisols and some Ultisols developed on ferromagnesian-rich parent materials) the surfaces of phyllosilicates are coated to a lesser or greater extent by amorphous or crystalline, oppositely charged nanoparticles of Fe and Al oxides. These coatings exhibit a high reactive surface area and help cementing larger particles with one another. As a result of these electrostatic interactions, stable microaggregates that are difficult to disperse are formed in variable charge soils. Most of highly weathered soils have reached the “advanced stage” of Jackson-Sherman weathering sequence that is characterized by the removal of Na, K, Ca, Mg, and Fe(II), the presence of Fe and Al polymers, and very dilute soil solutions with an ionic strength (IS) of less than 1 mmol L-1. The inter-penetration or overlapping of the diffuse double layers on oppositely charged surfaces may occur in these dilute systems. These diffuse layer interactions may affect the magnitude of the effective charge, i.e., the counter-ion charge (4). In addition, salt adsorption, which is defined as the simultaneous adsorption in equivalent amounts of the cation and anion of an electrolyte with no net release of other ions into the soil solution, appears to be a common phenomenon in these soils. They act as cation- and anion-exchangers and as salt-sorbers. The magnitude of salt adsorption depends strongly on initial IS in the soil solution and the presence in appreciable amounts of oppositely charged surfaces. Among the authors that have made illustrious contributions towards a better understanding of these fascinating soil systems are S. Matson, R.K. Schofield, van Olphen, M.E. Sumner, G.W. Thomas, G.P. Gillman, G. Uehara, B.K.G. Theng, K. Wada, N.J. Barrow, J.W. Bowden, R.J. Hunter and G. Sposito. This entry is mainly based on publications by these authors.« less

Modeling the adsorption of metal ions (Cu 2+, Ni 2+, Pb 2+) onto ACCs using surface complexation models

NASA Astrophysics Data System (ADS)

Faur-Brasquet, Catherine; Reddad, Zacaria; Kadirvelu, Krishna; Le Cloirec, Pierre

2002-08-01

Activated carbon cloths (ACCs), whose efficiency has been demonstrated for microorganics adsorption from water, were here studied in the removal of metal ions from aqueous solution. Two ACCs are investigated, they are characterized in terms of porosity parameters (BET specific surface area, percentage of microporosity) and chemical characteristics (acidic surface groups, acidity constants, point of zero charge). A first part consists in the experimental study of three metal ions removal (Cu 2+, Ni 2+ and Pb 2+) in a batch reactor. Isotherms modeling by Freundlich and Brunauer-Emmett-Teller (BET) equations enables the following adsorption order: Cu 2+>Ni 2+>Pb 2+ to be determined for adsorption capacities on a molar basis. It may be related to adsorbates characteristics in terms of electronegativity and ionic radius. The influence of adsorbent's microporosity is also shown. Adsorption experiments carried out for pH values ranging from 2 to 10 demonstrate: (i) an adsorption occurring below the precipitation pH; (ii) the strong influence of pH, with a decrease of electrostatic repulsion due to the formation of less charged hydrolyzed species coupled with a decrease of activated carbon surface charge as pH increases. The second part focuses on the modeling of adsorption versus the pH experimental data by the diffuse layer model (DLM) using Fiteql software. The model is efficient to describe the system behavior in the pH range considered. Regarding complexation constants, they show the following affinity for ACC: Pb 2+>Cu 2+>Ni 2+. They are related to initial concentrations used for the three metal ions.

The electrokinetic behavior of calcium oxalate monohydrate in macromolecular solutions

NASA Technical Reports Server (NTRS)

Curreri, P. A.; Onoda, G. Y., Jr.; Finlayson, B.

1988-01-01

Electrophoretic mobilities were measured for calcium oxalate monohydrate (COM) in solutions containing macromolecules. Two mucopolysaccharides (sodium heparin and chrondroitin sulfate) and two proteins (positively charged lysozyme and negatively charged bovine serum albumin) were studied as adsorbates. The effects of pH, calcium oxalate surface charge (varied by calcium or oxalate ion activity), and citrate concentration were investigated. All four macromolecules showed evidence for chemical adsorption. The macromolecule concentrations needed for reversing the surface charge indicated that the mucopopolysacchrides have greater affinity for the COM surface than the proteins. The amount of proteins that can chemically adsorb appears to be limited to approximately one monomolecular layer. When the surface charge is high, an insufficient number of proteins can chemically adsorb to neutralize or reverse the surface charge. The remaining surface charge is balanced by proteins held near the surface by longer range electrostatic forces only. Citrate ions at high concentrations appear to compete effectively with the negative protein for surface sites but show no evidence for competing with the positively charged protein.

Photo-inducible Crosslinked Nanoassemblies for pH-Controlled Drug Release

PubMed Central

Dickerson, Matthew; Winquist, Nickolas; Bae, Younsoo

2014-01-01

Purpose To control drug release from block copolymer nanoassemblies by variation in the degree of photo-crosslinking and inclusion of acid sensitive linkers. Methods Poly(ethylene glycol)-poly(aspartate-hydrazide-cinnamate) (PEG-CNM) block copolymers were prepared and conjugated with a model drug, doxorubicin (DOX), through acid sensitive hydrazone linkers. The block copolymers formed photo-inducible, self-assembled nanoassemblies (piSNAs), which were used to produce photo-inducible crosslinked nanoassemblies (piCNAs) through UV crosslinking. The nanoassemblies were characterized to determine particle size, surface charge, pH- and crosslinking-dependent DOX release, in vitro cytotoxicity, and intracellular uptake as a function of photo-crosslinking degree. Results Nanoassemblies with varying photo-crosslinking degrees were successfully prepared while retaining particle size and surface charge. Photo-crosslinking caused no noticeable change in DOX release from the nanoassemblies at pH 7.4, but the DOX-loaded nanoassemblies modulated drug release as a function of crosslinking at pH 6.0. The nanoassemblies showed similar cytotoxicity regardless of crosslinking degrees, presumably due to the low cellular uptake and cell nucleus drug accumulation. Conclusion Photo-crosslinking is useful to control drug release from pH-sensitive block copolymer nanoassemblies as a function of crosslinking without altering the particle properties, and thus providing unique tools to investigate the pharmaceutical effects of drug release on cellular response. PMID:24254196

Polysaccharide/Surfactant complexes at the air-water interface - effect of the charge density on interfacial and foaming behaviors.

PubMed

Ropers, M H; Novales, B; Boué, F; Axelos, M A V

2008-11-18

The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide. Besides classical methods to investigate polymer/surfactant systems, we applied, for the first time concerning these systems, the analogy between the small angle neutron scattering by foams and the neutron reflectivity of films to measure in situ film thicknesses of foams. CTAB/pectin foam films are much thicker than the pure surfactant foam film but similar for high- and low-charged pectin/CTAB systems despite the difference in structure of complexes at interfaces. The improvement of the foam properties of CTAB bound to pectin is shown to be directly related to the formation of pectin-CTAB complexes at the air-water interface. However, in opposition to surface activity, there is no specific behavior for the highly charged pectin: foam properties depend mainly upon the bulk charge concentration, while the interfacial behavior is mainly governed by the charge density of pectin. For the highly charged pectin, specific cooperative effects between neighboring charged sites along the chain are thought to be involved in the higher surface activity of pectin/CTAB complexes. A more general behavior can be obtained at lower charge density either by using a low-charged pectin or by neutralizing the highly charged pectin in decreasing pH.

Cation Exchange in the Presence of Oil in Porous Media

PubMed Central

2017-01-01

Cation exchange is an interfacial process during which cations on a clay surface are replaced by other cations. This study investigates the effect of oil type and composition on cation exchange on rock surfaces, relevant for a variety of oil-recovery processes. We perform experiments in which brine with a different composition than that of the in situ brine is injected into cores with and without remaining oil saturation. The cation-exchange capacity (CEC) of the rocks was calculated using PHREEQC software (coupled to a multipurpose transport simulator) with the ionic composition of the effluent histories as input parameters. We observe that in the presence of crude oil, ion exchange is a kinetically controlled process and its rate depends on residence time of the oil in the pore, the temperature, and kinetic rate of adsorption of the polar groups on the rock surface. The cation-exchange process occurs in two stages during two phase flow in porous media. Initially, the charged sites of the internal surface of the clays establish a new equilibrium by exchanging cations with the aqueous phase. At later stages, the components of the aqueous and oleic phases compete for the charged sites on the external surface or edges of the clays. When there is sufficient time for crude oil to interact with the rock (i.e., when the core is aged with crude oil), a fraction of the charged sites are neutralized by the charged components stemming from crude oil. Moreover, the positively charged calcite and dolomite surfaces (at the prevailing pH environment of our experiments) are covered with the negatively charged components of the crude oil and therefore less mineral dissolution takes place when oil is present in porous media. PMID:28580442

Competitive Adsorption of Metals onto Magnetic Graphene Oxide: Comparison with Other Carbonaceous Adsorbents

PubMed Central

Hur, Jin; Shin, Jaewon; Yoo, Jeseung; Seo, Young-Soo

2015-01-01

Competitive adsorption isotherms of Cu(II), Pb(II), and Cd(II) were examined on a magnetic graphene oxide (GO), multiwalled carbon nanotubes (MWCNTs), and powered activated carbon (PAC). A series of analyses confirmed the successful synthesis of the magnetic GO based on a simple ultrasonification method. Irrespective of the adsorbents, the adsorption was highly dependent on pH, and the adsorption was well described by the Langmuir isotherm model. The maximum adsorption capacities of the adsorbents were generally higher in the order of Pb(II) > Cu(II) > Cd(II), which is the same as the degree of the electronegativity and the hydrated radius of the metals, suggesting that the metal adsorption may be governed by an ion exchange between positively charged metals and negatively charged surfaces, as well as diffusion of metals into the surface layer. The adsorption of each metal was mostly lower for multi- versus single-metal systems. The antagonistic effects were influenced by solution pH as well as the type of metals, and they were higher in the order of the magnetic GO > MWCNT > PAC. Dissolved HS played a greater role than HS adsorbed onto the adsorbents, competing with the adsorption sites for metal complexation. PMID:25861683

Microelectrophoretic study of calcium oxalate monohydrate in macromolecular solutions

NASA Technical Reports Server (NTRS)

Curreri, P. A.; Onoda, G. Y., Jr.; Finlayson, B.

1987-01-01

Electrophoretic mobilities were measured for calcium oxalate monohydrate (COM) in solutions containing macromolecules. Two mucopolysaccharides (sodium heparin and chondroitin sulfate) and two proteins (positively charged lysozyme and negatively charged bovine serum albumin) were studied as adsorbates. The effects of pH, calcium oxalate surface charge (varied by calcium or oxalate ion activity), and citrate concentration were investigated. All four macromolecules showed evidence for adsorption. The macromolecule concentrations needed for reversing the surface charge indicated that the mucopolysaccharides have greater affinity for the COM surface than the proteins. Citrate ions at high concentrations appear to compete effectively with the negative protein for surface sites but show no evidence for competing with the positively charged protein.

Electrofluidic gating of a chemically reactive surface.

PubMed

Jiang, Zhijun; Stein, Derek

2010-06-01

We consider the influence of an electric field applied normal to the electric double layer at a chemically reactive surface. Our goal is to elucidate how surface chemistry affects the potential for field-effect control over micro- and nanofluidic systems, which we call electrofluidic gating. The charging of a metal-oxide-electrolyte (MOE) capacitor is first modeled analytically. We apply the Poisson-Boltzmann description of the double layer and impose chemical equilibrium between the ionizable surface groups and the solution at the solid-liquid interface. The chemically reactive surface is predicted to behave as a buffer, regulating the charge in the double layer by either protonating or deprotonating in response to the applied field. We present the dependence of the charge density and the electrochemical potential of the double layer on the applied field, the density, and the dissociation constants of ionizable surface groups and the ionic strength and the pH of the electrolyte. We simulate the responses of SiO(2) and Al(2)O(3), two widely used oxide insulators with different surface chemistries. We also consider the limits to electrofluidic gating imposed by the nonlinear behavior of the double layer and the dielectric strength of oxide materials, which were measured for SiO(2) and Al(2)O(3) films in MOE configurations. Our results clarify the response of chemically reactive surfaces to applied fields, which is crucial to understanding electrofluidic effects in real devices.

Dimerization of Organic Dyes on Luminescent Gold Nanoparticles for Ratiometric pH Sensing.

PubMed

Sun, Shasha; Ning, Xuhui; Zhang, Greg; Wang, Yen-Chung; Peng, Chuanqi; Zheng, Jie

2016-02-12

Synergistic effects arising from the conjugation of organic dyes onto non-luminescent metal nanoparticles (NPs) have greatly broadened their applications in both imaging and sensing. Herein, we report that conjugation of a well-known pH-insensitive dye, tetramethyl-rhodamine (TAMRA), to pH-insensitive luminescent gold nanoparticles (AuNPs) can lead to an ultrasmall nanoindicator that can fluorescently report local pH in a ratiometric way. Such synergy originated from the dimerization of TAMRA on AuNPs, of which geometry was very sensitive to surface charges of the AuNPs and can be reversely modulated through protonation of surrounding glutathione ligands. Not limited to pH-insensitive dyes, this pH-dependent dimerization can also enhance the pH sensitivity of fluorescein, a well-known pH-sensitive dye, within a larger pH range, opening up a new pathway to design ultrasmall fluorescent ratiometric nanoindicators with tunable wavelengths and pH response ranges. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hiemstra, T.; Riemsdijk, W.H. van

1999-02-01

An important challenge in surface complexation models (SCM) is to connect the molecular microscopic reality to macroscopic adsorption phenomena. This study elucidates the primary factor controlling the adsorption process by analyzing the adsorption and competition of PO{sub 4}, AsO{sub 4}, and SeO{sub 3}. The authors show that the structure of the surface-complex acting in the dominant electrostatic field can be ascertained as the primary controlling adsorption factor. The surface species of arsenate are identical with those of phosphate and the adsorption behavior is very similar. On the basis of the selenite adsorption, The authors show that the commonly used 1pKmore » models are incapable to incorporate in the adsorption modeling the correct bidentate binding mechanism found by spectroscopy. The use of the bidentate mechanism leads to a proton-oxyanion ratio and corresponding pH dependence that are too large. The inappropriate intrinsic charge attribution to the primary surface groups and the condensation of the inner sphere surface complex to a point charge are responsible for this behavior of commonly used 2pK models. Both key factors are differently defined in the charge distributed multi-site complexation (CD-MUSIC) model and are based in this model on a surface structural approach. The CD-MUSIC model can successfully describe the macroscopic adsorption phenomena using the surface speciation and binding mechanisms as found by spectroscopy. The model is also able to predict the anion competition well. The charge distribution in the interface is in agreement with the observed structure of surface complexes.« less

Surface properties of magnetite in high temperature aqueous electrolyte solutions: A review.

PubMed

Vidojkovic, Sonja M; Rakin, Marko P

2017-07-01

Deposits and scales formed on heat transfer surfaces in power plant water/steam circuits have a significant negative impact on plant reliability, availability and performance, causing tremendous economic consequences and subsequent increases in electricity cost. Consequently, the improvement of the understanding of deposition mechanisms on power generating surfaces is defined as a high priority in the power industry. The deposits consist principally of iron oxides, which are steel corrosion products and usually present in colloidal form. Magnetite (Fe 3 O 4 ) is the predominant and most abundant compound found in water/steam cycles of all types of power plants. The crucial factor that governs the deposition process and influences the deposition rate of magnetite is the electrostatic interaction between the metal wall surfaces and the suspended colloidal particles. However, there is scarcity of data on magnetite surface properties at elevated temperatures due to difficulties in their experimental measurement. In this paper a generalized overview of existing experimental data on surface characteristics of magnetite at high temperatures is presented with particular emphasis on possible application in the power industry. A thorough analysis of experimental techniques, mathematical models and results has been performed and directions for future investigations have been considered. The state-of-the-art assessment showed that for the characterization of magnetite/aqueous electrolyte solution interface at high temperatures acid-base potentiometric titrations and electrophoresis were the most beneficial and dependable techniques which yielded results up to 290 and 200°C, respectively. Mass titrations provided data on magnetite surface charge up to 320°C, however, this technique is highly sensitive to the minor concentrations of impurities present on the surface of particle. Generally, fairly good correlation between the isoelectric point (pH iep ) and point of zero charge (pH pzc ) values has been obtained. All obtained results showed that the surface of magnetite particles is negatively charged in typical high temperature thermal power plant water, which indicates the low probability of aggregation and deposition on plant metal surfaces. The results also gave strong evidence on decline of pH iep and pH pzc with temperature in the same manner as neutral pH of water. The thermodynamic parameters of magnetite surface protonation reactions were in good agreement with each other and obtained using one site/two pK and mainly one site/one pK model. All collected data provided evidences for interaction between particles, probability of deposition and eventual attachment to the steel surface at various pH and temperatures and can serve as a foundation for future surface studies aimed at optimizing plant performances and reducing of magnetite deposition. In future works it would be indispensable to provide the surface experimental data for extended temperature ranges, typical solution chemistries and metal surfaces of power plant structural components and thus obtain entire set of results useful in modeling the surface behavior and control of deposition process in power reactors and thermal plant circuits. Moreover, the acquired results will be applicable and greatly valuable to all other types of power plants, industrial facilities and technological processes using the high temperature water medium. Copyright © 2016 Elsevier B.V. All rights reserved.

Influence of molecular weight and pH on adsorption of chitosan at the surface of large and giant vesicles.

PubMed

Quemeneur, Francois; Rinaudo, Marguerite; Pépin-Donat, Brigitte

2008-01-01

This paper describes the mechanisms of adsorption of chitosan, a positively charged polyelectrolyte, on the DOPC lipid membrane of large and giant unilamellar vesicles (respectively, LUVs and GUVs). We observe that the variation of the zeta potential of LUVs as a function of chitosan concentration is independent on the chitosan molecular weight (Mw). This result is interpreted in terms of electrostatic interactions, which induce a flat adsorption of the chitosan on the surface of the membrane. The role of electrostatic interactions is further studied by observing the variation of the zeta potential as a function of the chitosan concentration for two different charge densities tuned by the pH. Results show a stronger chitosan-membrane affinity at pH 6 (lipids are negatively charged, and 40% chitosan amino groups are protonated) than at pH 3.4 (100% of protonated amino groups but zwitterionic lipids are positively charged) which confirms that adsorption is of electrostatic origin. Then, we investigate the stability of decorated LUVs and GUVs in a large range of pH (6.0 < pH < 12.0) in order to complete a previous study made in acidic conditions [Quemeneur et al. Biomacromolecules 2007, 8, 2512-2519]. A comparative study of the variation of the zeta potential as a function of the pH (2.0 < pH < 12.0) reveals a difference in behavior between naked and chitosan-decorated LUVs. This result is further confirmed by a comparative observation by optical microscopy of naked and chitosan-decorated GUVs in basic conditions (6.0 < pH < 12.0): at pH > 10.0, in the absence of chitosan, the vesicles present complex shapes, contrary to the chitosan-decorated vesicles which remain spherical, confirming thus that chitosan remains adsorbed on vesicles in basic conditions up to pH = 12.0. These results, in addition with our previous data, show that the chitosan-decorated vesicles are stable over a very broad range of pH (2.0 < pH < 12.0), which holds promise for their in vivo applications. Finally, the quantification of the chitosan adsorption on a LUV membrane is performed by zeta potential and fluorescence measurements. The fraction of membrane surface covered by chitosan is estimated to be lower than 40 %, which corresponds to the formation of a flat layer of chitosan on the membrane surface on an electrostatic basis.

Lysozyme adsorption in pH-responsive hydrogel thin-films: the non-trivial role of acid-base equilibrium.

PubMed

Narambuena, Claudio F; Longo, Gabriel S; Szleifer, Igal

2015-09-07

We develop and apply a molecular theory to study the adsorption of lysozyme on weak polyacid hydrogel films. The theory explicitly accounts for the conformation of the network, the structure of the proteins, the size and shape of all the molecular species, their interactions as well as the chemical equilibrium of each titratable unit of both the protein and the polymer network. The driving forces for adsorption are the electrostatic attractions between the negatively charged network and the positively charged protein. The adsorption is a non-monotonic function of the solution pH, with a maximum in the region between pH 8 and 9 depending on the salt concentration of the solution. The non-monotonic adsorption is the result of increasing negative charge of the network with pH, while the positive charge of the protein decreases. At low pH the network is roughly electroneutral, while at sufficiently high pH the protein is negatively charged. Upon adsorption, the acid-base equilibrium of the different amino acids of the protein shifts in a nontrivial fashion that depends critically on the particular kind of residue and solution composition. Thus, the proteins regulate their charge and enhance adsorption under a wide range of conditions. In particular, adsorption is predicted above the protein isoelectric point where both the solution lysozyme and the polymer network are negatively charged. This behavior occurs because the pH in the interior of the gel is significantly lower than that in the bulk solution and it is also regulated by the adsorption of the protein in order to optimize protein-gel interactions. Under high pH conditions we predict that the protein changes its charge from negative in the solution to positive within the gel. The change occurs within a few nanometers at the interface of the hydrogel film. Our predictions show the non-trivial interplay between acid-base equilibrium, physical interactions and molecular organization under nanoconfined conditions, which leads to non-trivial adsorption behavior that is qualitatively different from what would be predicted from the state of the proteins in the bulk solution.

Silica nanoparticle phytotoxicity to Arabidopsis thaliana.

PubMed

Slomberg, Danielle L; Schoenfisch, Mark H

2012-09-18

The phytotoxicity of silica nanoparticles (SiNPs) was evaluated as a function of particle size (14, 50, and 200 nm), concentration (250 and 1000 mg L(-1)), and surface composition toward Arabidopsis thaliana plants grown hydroponically for 3 and 6 weeks. Reduced development and chlorosis were observed for plants exposed to highly negative SiNPs (-20.3 and -31.9 mV for the 50 and 200 nm SiNPs, respectively) regardless of particle concentration when not controlling pH of the hydroponic medium, which resulted in increased alkalinity (~pH 8). Particles were no longer toxic to the plants at either concentration upon calcination or removal of surface silanols from the SiNP surface, or adjusting the pH of the growth medium to pH 5.8. The phytotoxic effects observed for the negatively charged 50 and 200 nm SiNPs were attributed to pH effects and the adsorption of macro- and micro-nutrients to the silica surface. Size-dependent uptake of the nanoparticles by the plants was confirmed using transmission electron microscopy (TEM) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) with plant roots containing 32.0, 1.85, and 7.00 × 10(-3) mg Si·kg tissue(-1)/nm(3) (normalized for SiNP volume) for the 14, 50, and 200 nm SiNPs respectively, after 6 weeks exposure at 1000 ppm (pH 5.8). This study demonstrates that the silica scaffolds are not phytotoxic up to 1000 ppm despite significant uptake of the SiNPs (14, 50, and 200 nm) into the root system of A. thaliana.

Modeling of salt and pH gradient elution in ion-exchange chromatography.

PubMed

Schmidt, Michael; Hafner, Mathias; Frech, Christian

2014-01-01

The separation of proteins by internally and externally generated pH gradients in chromatofocusing on ion-exchange columns is a well-established analytical method with a large number of applications. In this work, a stoichiometric displacement model was used to describe the retention behavior of lysozyme on SP Sepharose FF and a monoclonal antibody on Fractogel SO3 (S) in linear salt and pH gradient elution. The pH dependence of the binding charge B in the linear gradient elution model is introduced using a protein net charge model, while the pH dependence of the equilibrium constant is based on a thermodynamic approach. The model parameter and pH dependences are calculated from linear salt gradient elutions at different pH values as well as from linear pH gradient elutions at different fixed salt concentrations. The application of the model for the well-characterized protein lysozyme resulted in almost identical model parameters based on either linear salt or pH gradient elution data. For the antibody, only the approach based on linear pH gradients is feasible because of the limited pH range useful for salt gradient elution. The application of the model for the separation of an acid variant of the antibody from the major monomeric form is discussed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

pH-dependent interaction and resultant structures of silica nanoparticles and lysozyme protein.

PubMed

Kumar, Sugam; Aswal, Vinod K; Callow, P

2014-02-18

Small-angle neutron scattering (SANS) and UV-visible spectroscopy studies have been carried out to examine pH-dependent interactions and resultant structures of oppositely charged silica nanoparticles and lysozyme protein in aqueous solution. The measurements were carried out at fixed concentration (1 wt %) of three differently sized silica nanoparticles (8, 16, and 26 nm) over a wide concentration range of protein (0-10 wt %) at three different pH values (5, 7, and 9). The adsorption curve as obtained by UV-visible spectroscopy shows exponential behavior of protein adsorption on nanoparticles. The electrostatic interaction enhanced by the decrease in the pH between the nanoparticle and protein (isoelectric point ∼11.4) increases the adsorption coefficient on nanoparticles but decreases the overall amount protein adsorbed whereas the opposite behavior is observed with increasing nanoparticle size. The adsorption of protein leads to the protein-mediated aggregation of nanoparticles. These aggregates are found to be surface fractals at pH 5 and change to mass fractals with increasing pH and/or decreasing nanoparticle size. Two different concentration regimes of interaction of nanoparticles with protein have been observed: (i) unaggregated nanoparticles coexisting with aggregated nanoparticles at low protein concentrations and (ii) free protein coexisting with aggregated nanoparticles at higher protein concentrations. These concentration regimes are found to be strongly dependent on both the pH and nanoparticle size.

Charge heterogeneity: Basic antibody charge variants with increased binding to Fc receptors

PubMed Central

Hintersteiner, Beate; Lingg, Nico; Zhang, Peiqing; Woen, Susanto; Hoi, Kong Meng; Stranner, Stefan; Wiederkum, Susanne; Mutschlechner, Oliver; Schuster, Manfred; Loibner, Hans; Jungbauer, Alois

2016-01-01

ABSTRACT We identified active isoforms of the chimeric anti-GD2 antibody, ch14.18, a recombinant antibody produced in Chinese hamster ovary cells, which is already used in clinical trials.1,2,3 We separated the antibody by high resolution ion-exchange chromatography with linear pH gradient elution into acidic, main and basic charge variants on a preparative scale yielding enough material for an in-depth study of the sources and the effects of microheterogeneity. The binding affinity of the charge variants toward the antigen and various cell surface receptors was studied by Biacore. Effector functions were evaluated using cellular assays for antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity. Basic charge variants showed increased binding to cell surface receptor FcγRIIIa, which plays a major role in regulating effector functions. Furthermore, increased binding of the basic fractions to the neonatal receptor was observed. As this receptor mediates the prolonged half-life of IgG in human serum, this data may well hint at an increased serum half-life of these basic variants compared to their more acidic counterparts. Different glycoform patterns, C-terminal lysine clipping and N-terminal pyroglutamate formation were identified as the main structural sources for the observed isoform pattern. Potential differences in structural stability between individual charge variant fractions by nano differential scanning calorimetry could not been detected. Our in-vitro data suggests that the connection between microheterogeneity and the biological activity of recombinant antibody therapeutics deserves more attention than commonly accepted. PMID:27559765

Isoelectric point is an inadequate descriptor of MS2, Phi X 174 and PRD1 phages adhesion on abiotic surfaces.

PubMed

Dika, Christelle; Duval, Jérôme F L; Francius, Gregory; Perrin, Aline; Gantzer, Christophe

2015-05-15

MS2, Phi X 174 and PRD1 bacteriophages are commonly used as surrogates to evaluate pathogenic virus behavior in natural aquatic media. The interfacial properties of these model soft bioparticles are herein discussed in connection with their propensities to adhere onto abiotic surfaces that differ in terms of surface charges and hydrophobicities. The phages considered in this work exhibit distinct multilayered surface structures and their electrostatic charges are evaluated from the dependence of their electrophoretic mobilities on electrolyte concentration at neutral pH on the basis of electrokinetic theory for soft (bio)particles. The charges of the viruses probed by electrokinetics vary according to the sequence Phi X 174⩽PRD1≪MS2, where '<' stands for 'less charged than'. The hydrophobic/hydrophilic balances of the phages are further derived from their adhesions onto model hydrophobic and hydrophilic self-assembled mono-layers. The corresponding results lead to the following hydrophobicity sequence Phi X 174≪MS2

pH regulation of the kinetic stability of the lipase from Thermomyces lanuginosus.

PubMed

Wang, H; Andersen, K K; Sehgal, P; Hagedorn, J; Westh, P; Borch, K; Otzen, D E

2013-01-08

Thermomyces lanuginosus lipase (TlL) is a kinetically stable protein, resistant toward both denaturation and refolding in the presence of the ionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant decyl maltoside (DecM). We investigate the pH dependence of this kinetic stability. At pH 8, TlL remains folded and enzymatically active at multimillimolar surfactant concentrations but fails to refold from the acid urea-denatured state at submillimolar concentrations of SDS and DecM, indicating a broad concentration range of kinetic trapping or hysteresis. At pH 8, very few SDS molecules bind to TlL. The hysteresis SDS concentration range shrinks when moving to pH 4-6; in this pH range, SDS binds as micellelike clusters. Although hysteresis can be eliminated by reducing disulfide bonds, destabilizing the native state, and lowering the unfolding activation barrier, SDS sensitivity is not directly linked to intrinsic kinetic stability [its resistance to the general chemical denaturant guanidinium chloride (GdmCl)], because TlL unfolds more slowly in GdmCl at pH 6.0 than at pH 8.0. However, the estimated net charge drops from approximately -12 to approximately -5 between pH 8 and 6. SDS denatures TlL at pH 6.0 by nucleating via a critical number of bound SDS molecules on the surface of native TlL to form clusters. These results imply that SDS sensitivity is connected to the availability of appropriately charged regions on the protein. We suggest that conformational rigidity is a necessary but not sufficient feature of SDS resistance, because this has to be combined with sufficient negative electrostatic potential to avoid extensive SDS binding.

Regulation of the Electric Charge in Phosphatidic Acid Domains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wenjie; Anderson, Nathaniel A.; Travesset, Alex

Although a minor component of the lipidome, phosphatidic acid (PA) plays a crucial role in nearly all signaling pathways involving cell membranes, in part because of its variable electrical charge in response to environmental conditions. To investigate how charge is regulated in domains of PA, we applied surface-sensitive X-ray reflectivity and fluorescence near-totalreflection techniques to determine the binding of divalent ions (Ca2+ at various pH values) to 1,2-dimyristoyl-sn-glycero-3-phosphate (DMPA) and to the simpler lipid dihexadecyl phosphate (DHDP) spread as monolayers at the air/water interface. We found that the protonation state of PA is controlled not only by the pKa andmore » local pH but also by the strong affinity to PA driven by electrostatic correlations from divalent ions and the cooperative effect of the two dissociable protons, which dramatically enhance the surface charge. A precise theoretical model is presented providing a general framework to predict the protonation state of PA. Implications for recent experiments on charge regulation by hydrogen bonding and the role of pH in PA signaling are discussed in detail.« less

Complexation between sodium dodecyl sulfate and amphoteric polyurethane nanoparticles.

PubMed

Qiao, Yong; Zhang, Shifeng; Lin, Ouya; Deng, Liandong; Dong, Anjie

2007-09-27

The complexation between negatively charged sodium dodecyl sulfate (SDS) and positively charged amphoteric polyurethane (APU) self-assembled nanoparticles (NPs) containing nonionic hydrophobic segments is studied by dynamic light scattering, pyrene fluorescent probing, zeta-potential, and transmission electron microscopy (TEM) in the present paper. With increasing the mol ratio of SDS to the positive charges on the surface of APU NPs, the aqueous solution of APU NPs presents precipitation at pH 2, around stoichiometric SDS concentration, and then the precipitate dissociates with excess SDS to form more stable nanoparticles of ionomer complexes. Three stages of the complexation process are clearly shown by the pyrene I1/I3 variation of the complex systems, which only depends on the ratio of SDS/APU, and demonstrate that the process is dominated by electrostatic attraction and hydrophobic aggregation.

Protein adsorption at the electrified air-water interface: implications on foam stability.

PubMed

Engelhardt, Kathrin; Rumpel, Armin; Walter, Johannes; Dombrowski, Jannika; Kulozik, Ulrich; Braunschweig, Björn; Peukert, Wolfgang

2012-05-22

The surface chemistry of ions, water molecules, and proteins as well as their ability to form stable networks in foams can influence and control macroscopic properties such as taste and texture of dairy products considerably. Despite the significant relevance of protein adsorption at liquid interfaces, a molecular level understanding on the arrangement of proteins at interfaces and their interactions has been elusive. Therefore, we have addressed the adsorption of the model protein bovine serum albumin (BSA) at the air-water interface with vibrational sum-frequency generation (SFG) and ellipsometry. SFG provides specific information on the composition and average orientation of molecules at interfaces, while complementary information on the thickness of the adsorbed layer can be obtained with ellipsometry. Adsorption of charged BSA proteins at the water surface leads to an electrified interface, pH dependent charging, and electric field-induced polar ordering of interfacial H(2)O and BSA. Varying the bulk pH of protein solutions changes the intensities of the protein related vibrational bands substantially, while dramatic changes in vibrational bands of interfacial H(2)O are simultaneously observed. These observations have allowed us to determine the isoelectric point of BSA directly at the electrolyte-air interface for the first time. BSA covered air-water interfaces with a pH near the isoelectric point form an amorphous network of possibly agglomerated BSA proteins. Finally, we provide a direct correlation of the molecular structure of BSA interfaces with foam stability and new information on the link between microscopic properties of BSA at water surfaces and macroscopic properties such as the stability of protein foams.

Biochemical enhancement of transdermal delivery with magainin peptide: modification of electrostatic interactions by changing pH.

PubMed

Kim, Yeu-Chun; Late, Sameer; Banga, Ajay K; Ludovice, Peter J; Prausnitz, Mark R

2008-10-01

Magainin is a naturally occurring, pore-forming peptide that has recently been shown to increase skin permeability. This study tested the hypothesis that electrostatic forces between magainin peptides and drugs mediate drug transport across the skin. Electrostatic interaction between positively charged magainin and a negatively charged model drug, fluorescein, was attractive at pH 7.4 and resulted in a 35-fold increase in delivery across human epidermis in vitro when formulated with 2% N-lauroylsarcosine in 50% ethanol. Increasing to pH 10 or 11 largely neutralized magainin's charge, which eliminated enhancement due to magainin. Shielding electrostatic interactions with 1-2M NaCl solution similarly eliminated enhancement. Showing the opposite dependence on pH, electrostatic interaction between magainin and a positively charged anti-nausea drug, granisetron, was largely neutralized at pH 10 and resulted in a 92-fold increase in transdermal delivery. Decreasing to pH 5 increased magainin's positive charge, which repelled granisetron and progressively decreased transdermal flux. Circular dichroism analysis, multi-photon microscopy, and FTIR spectroscopy showed no significant pH effect on magainin secondary structure, magainin deposition in stratum corneum, or stratum corneum lipid order, respectively. We conclude that magainin increases transdermal delivery by a mechanism involving electrostatic interaction between magainin peptides and drugs.

Biochemical enhancement of transdermal delivery with magainin peptide: Modification of electrostatic interactions by changing pH

PubMed Central

Kim, Yeu-Chun; Late, Sameer; Banga, Ajay K.; Ludovice, Peter J.; Prausnitz, Mark R.

2008-01-01

Magainin is a naturally occurring, pore-forming peptide that has recently been shown to increase skin permeability. This study tested the hypothesis that electrostatic forces between magainin peptides and drugs mediate drug transport across the skin. Electrostatic interaction between positively charged magainin and a negatively charged model drug, fluorescein, was attractive at pH 7.4 and resulted in a 35 fold increase in delivery across human epidermis in vitro when formulated with 2% N-lauroylsarcosine in 50% ethanol. Increasing to pH 10 or 11 largely neutralized magainin’s charge, which eliminated enhancement due to magainin. Shielding electrostatic interactions with 1–2 M NaCl solution similarly eliminated enhancement. Showing the opposite dependence on pH, electrostatic interaction between magainin and a positively charged anti-nausea drug, granisetron, was largely neutralized at pH 10 and resulted in a 59 fold increase in transdermal delivery. Decreasing to pH 5 increased magainin’s positive charge, which repelled granisetron and progressively decreased transdermal flux. Circular dichroism analysis, multi-photon microscopy, and FTIR spectroscopy showed no significant pH effect on magainin secondary structure, magainin deposition in stratum corneum, or stratum corneum lipid order, respectively. We conclude that magainin increases transdermal delivery by a mechanism involving electrostatic interaction between magainin peptides and drugs. PMID:18601987

pH-Induced Changes in the Surface Viscosity of Unsaturated Phospholipids Monitored Using Active Interfacial Microrheology.

PubMed

Ghazvini, Saba; Alonso, Ryan; Alhakamy, Nabil; Dhar, Prajnaparamita

2018-01-23

Lipid membranes, a major component of cells, are subjected to significant changes in pH depending on their location in the cell: the outer leaflet of the cell membrane is exposed to a pH of 7.4 whereas lipid membranes that make up late endosomes and lysosomes are exposed to a pH of as low as 4.4. The purpose of this study is to evaluate how changes in the environmental pH within cells alter the fluidity of phospholipid membranes. Specifically, we studied pH-induced alterations in the surface arrangement of monounsaturated lipids with zwitterionic headgroups (phosphoethanolamine (PE) and phosphocholine (PC)) that are abundant in plasma membranes as well as anionic lipids (phosphatidylserine (PS) and phosphatidylglycerol (PG)) that are abundant in inner membranes using a combination of techniques including surface tension vs area measurements, interfacial microrheology, and fluorescence/atomic force microscopy. Using an active interfacial microrheology technique, we find that phospholipids with zwitterionic headgroups show a significant increase in their surface viscosity at acidic pH. This increase in surface viscosity is also found to depend on the size of the lipid headgroup, with a smaller headgroup showing a greater increase in viscosity. The observed pH-induced increase in viscosity is also accompanied by an increase in the cohesion pressure between zwitterionic molecules at acidic pH and a decrease in the average molecular area of the lipids, as measured by fitting the surface pressure isotherms to well-established equations of state. Because fluorescent images show no change in the phase of the lipids, we attribute this change in surface viscosity to the pH-induced reorientation of the P - -N + dipoles that form part of the polar lipid headgroup, resulting in increased lipid-lipid interactions. Anionic PG headgroups do not demonstrate this pH-induced change in viscosity, suggesting that the presence of a net negative charge on the headgroup causes electrostatic repulsion between the headgroups. Our results also show that active interfacial microrheology is a sensitive technique for detecting minute changes in the lipid headgroup orientation induced by changes in the local membrane environment, even in unsaturated phospholipids where the surface viscosity is close to the experimental detection limit.

Carbodiimide-mediated immobilization of acidic biomolecules on reversed-charge zwitterionic sensor chip surfaces.

PubMed

Risse, Fabian; Gedig, Erk T; Gutmann, Jochen S

2018-04-30

The carbodiimide-mediated amine coupling of protein ligands to sensor chips coated with anionic polycarboxylate hydrogels, such as carboxymethyl dextran, is the predominant covalent immobilization procedure utilized in optical biosensors, namely surface plasmon resonance (SPR) biosensors. Usually, electrostatic interactions at a slightly acidic pH and low ionic strength are employed to efficiently accumulate neutral and basic ligands on the chip surface, which are then covalently coupled by surface-bound active N-hydroxysuccinimide (NHS) esters. Unfortunately, this approach is not suitable for acidic proteins or other ligands with low isoelectric points (IEPs), such as nucleic acids, because the charge density of the polycarboxylates is greatly reduced at acidic pH or because electrostatic attraction cannot be achieved. To overcome these drawbacks, we have established a charge-reversal approach that allows the preconcentration of acidic proteins above their IEPs. A precisely controlled amount of tertiary amines is applied to reverse the previous anionic surface charge while maintaining carbodiimide compatibility with future protein immobilization. The mechanism of this reversed-charge immobilization approach was demonstrated employing protein A as a model protein and using attenuated total reflectance Fourier transform infrared spectroscopy, dynamic contact angle measurements, colorimetric quantification, and SPR analysis to characterize surface derivatization. Furthermore, even though it had previously proven impossible to preconcentrate DNA electrostatically and to covalently couple it to polyanionic chip surfaces, we demonstrated that our approach allowed DNA to be preconcentrated and immobilized in good yields. Graphical abstract Principle of the covalent immobilization of acidic ligands on reversed-charge zwitterionic sensor chip surfaces.

Reversibly extracellular pH controlled cellular uptake and photothermal therapy by PEGylated mixed-charge gold nanostars.

PubMed

Wang, Shouju; Teng, Zhaogang; Huang, Peng; Liu, Dingbin; Liu, Ying; Tian, Ying; Sun, Jing; Li, Yanjun; Ju, Huangxian; Chen, Xiaoyuan; Lu, Guangming

2015-04-17

Shielding nanoparticles from nonspecific interactions with normal cells/tissues before they reach and after they leave tumors is crucial for the selective delivery of NPs into tumor cells. By utilizing the reversible protonation of weak electrolytic groups to pH changes, long-chain amine/carboxyl-terminated polyethylene glycol (PEG) decorated gold nanostars (GNSs) are designed, exhibiting reversible, significant, and sensitive response in cell affinity and therapeutic efficacy to the extracellular pH (pHe) gradient between normal tissues and tumors. This smart nanosystem shows good dispersity and unimpaired photothermal efficacy in complex bioenvironment at pH 6.4 and 7.4 even when their surface charge is neutral. One PEGylated mixed-charge GNSs with certain surface composition, GNS-N/C 4, exhibits high cell affinity and therapeutic efficacy at pH 6.4, and low affinity and almost "zero" damage to cells at pH 7.4. Remarkably, this significant and sensitive response in cell affinity and therapeutic efficacy is reversible as local pH alternated. In vivo, GNS-N/C 4 shows higher accumulation in tumors and improved photothermal therapeutic efficacy than pH-insensitive GNSs. This newly developed smart nanosystem, whose cell affinity reversibly transforms in response to pHe gradient with unimpaired biostability, provides a novel effective means of tumor-selective therapy. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rb + adsorption at the quartz(101)-aqueous interface: comparison of resonant anomalous x-ray reflectivity with ab initio calculations

DOE PAGES

Bellucci, Francesco; Lee, Sang Soo; Kubicki, James D.; ...

2015-01-29

We study adsorption of Rb + to the quartz(101)–aqueous interface at room temperature with specular X-ray reflectivity, resonant anomalous X-ray reflectivity, and density functional theory. The interfacial water structures observed in deionized water and 10 mM RbCl solution at pH 9.8 were similar, having a first water layer at height of 1.7 ± 0.1 Å above the quartz surface and a second layer at 4.8 ± 0.1 Å and 3.9 ± 0.8 Å for the water and RbCl solutions, respectively. The adsorbed Rb + distribution is broad and consists of presumed inner-sphere (IS) and outer-sphere (OS) complexes at heights ofmore » 1.8 ± 0.1 and 6.4 ± 1.0 Å, respectively. Projector-augmented planewave density functional theory (DFT) calculations of potential configurations for neutral and negatively charged quartz(101) surfaces at pH 7 and 12, respectively, reveal a water structure in agreement with experimental results. These DFT calculations also show differences in adsorbed speciation of Rb + between these two conditions. At pH 7, the lowest energy structure shows that Rb + adsorbs dominantly as an IS complex, whereas at pH 12 IS and OS complexes have equivalent energies. The DFT results at pH 12 are generally consistent with the two site Rb distribution observed from the X-ray data at pH 9.8, albeit with some differences that are discussed. In conclusion, surface charge estimated on the basis of the measured total Rb + coverage was -0.11 C/m 2, in good agreement with the range of the surface charge magnitudes reported in the literature.« less

Interactions of microbicide nanoparticles with a simulated vaginal fluid.

PubMed

das Neves, José; Rocha, Cristina M R; Gonçalves, Maria Pilar; Carrier, Rebecca L; Amiji, Mansoor; Bahia, Maria Fernanda; Sarmento, Bruno

2012-11-05

The interaction with cervicovaginal mucus presents the potential to impact the performance of drug nanocarriers. These systems must migrate through this biological fluid in order to deliver their drug payload to the underlying mucosal surface. We studied the ability of dapivirine-loaded polycaprolactone (PCL)-based nanoparticles (NPs) to interact with a simulated vaginal fluid (SVF) incorporating mucin. Different surface modifiers were used to produce NPs with either negative (poloxamer 338 NF and sodium lauryl sulfate) or positive (cetyltrimethylammonium bromide) surface charge. Studies were performed using the mucin particle method, rheological measurements, and real-time multiple particle tracking. Results showed that SVF presented rheological properties similar to those of human cervicovaginal mucus. Analysis of NP transport indicated mild interactions with mucin and low adhesive potential. In general, negatively charged NPs underwent subdiffusive transport in SVF, i.e., hindered as compared to their diffusion in water, but faster than for positively charged NPs. These differences were increased when the pH of SVF was changed from 4.2 to 7.0. Diffusivity was 50- and 172-fold lower in SVF at pH 4.2 than in water for negatively charged and positively charged NPs, respectively. At pH 7.0, this decrease was around 20- and 385-fold, respectively. The estimated times required to cross a layer of SVF were equal to or lower than 1.7 h for negatively charged NPs, while for positively charged NPs these values were equal to or higher than 7 h. Overall, our results suggest that negatively charged PCL NPs may be suitable to be used as carriers in order to deliver dapivirine and potentially other antiretroviral drugs to the cervicovaginal mucosal lining. Also, they further reinforce the importance in characterizing the interactions of nanosystems with mucus fluids or surrogates when considering mucosal drug delivery.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Azizah, N., E-mail: norazizahparmin84@gmail.com; Gopinath, Subash C. B.; Nadzirah, Sh.

Titanium dioxide (TiO{sub 2}) nanoparticles based Interdigitated Device Electrodes (IDEs) Nanobiosensor device was developed for intracellular biochemical detection. Fabrication and characterization of pH sensors using IDE nanocoated with TiO{sub 2} was studied in this paper. In this paper, a preliminary assessment of this intracellular sensor with electrical measurement under different pH levels. 3-aminopropyltriethoxysilane (APTES) was used to enhance the sensitivity of titanium dioxide layer as well as able to provide surface modification by undergoing protonation and deprotonation process. Different types of pH solution provide different resistivity and conductivity towards the surface. Base solution has the higher current compared to anmore » acid solution. Amine and oxide functionalized TiO{sub 2} based IDE exhibit pH-dependent could be understood in terms of the change in surface charge during protonation and deprotonation. The simple fabrication process, high sensitivity, and fast response of the TiO{sub 2} based IDEs facilitate their applications in a wide range of areas. The small size of semiconductor TiO{sub 2} based IDE for sensitive, label-free, real time detection of a wide range of biological species could be explored in vivo diagnostics and array-based screening.« less

Surface speciation of yttrium and neodymium sorbed on rutile: Interpretations using the change distribution model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ridley, Mora K.; Hiemstra, T; Machesky, Michael L.

2012-01-01

The adsorption of Y3+ and Nd3+ onto rutile has been evaluated over a wide range of pH (3 11) and surface loading conditions, as well as at two ionic strengths (0.03 and 0.3 m), and temperatures (25 and 50 C). The experimental results reveal the same adsorption behavior for the two trivalent ions onto the rutile surface, with Nd3+ first adsorbing at slightly lower pH values. The adsorption of both Y3+ and Nd3+ commences at pH values below the pHznpc of rutile. The experimental results were evaluated using a charge distribution (CD) and multisite complexation (MUSIC) model, and Basic Sternmore » layer description of the electric double layer (EDL). The coordination geometry of possible surface complexes were constrained by molecular-level information obtained from X-ray standing wave measurements and molecular dynamic (MD) simulation studies. X-ray standing wave measurements showed an inner-sphere tetradentate complex for Y3+ adsorption onto the (110) rutile surface (Zhang et al., 2004b). TheMDsimulation studies suggest additional bidentate complexes may form. The CD values for all surface species were calculated based on a bond valence interpretation of the surface complexes identified by X-ray and MD. The calculated CD values were corrected for the effect of dipole orientation of interfacial water. At low pH, the tetradentate complex provided excellent fits to the Y3+ and Nd3+ experimental data. The experimental and surface complexation modeling results show a strong pH dependence, and suggest that the tetradentate surface species hydrolyze with increasing pH. Furthermore, with increased surface loading of Y3+ on rutile the tetradentate binding mode was augmented by a hydrolyzed-bidentate Y3+ surface complex. Collectively, the experimental and surface complexation modeling results demonstrate that solution chemistry and surface loading impacts Y3+ surface speciation. The approach taken of incorporating molecular-scale information into surface complexation models (SCMs) should aid in elucidating a fundamental understating of ion-adsorption reactions.« less

An experimental study of Au removal from solution by non-metabolizing bacterial cells and their exudates

NASA Astrophysics Data System (ADS)

Kenney, Janice P. L.; Song, Zhen; Bunker, Bruce A.; Fein, Jeremy B.

2012-06-01

In this study, we examine the initial interactions between aqueous Au(III)-hydroxide-chloride aqueous complexes and bacteria by measuring the effects of non-metabolizing cells on the speciation and distribution of Au. We conducted batch Au(III) removal experiments, measuring the kinetics and pH dependence of Au removal, and tracking valence state transformations and binding environments using XANES spectroscopy. These experiments were conducted using non-metabolizing cells of Bacillus subtilis or Pseudomonas putida suspended in a 5 ppm Au(III)-(hydroxide)-chloride starting solution of 0.1 M NaClO4 to buffer ionic strength. Both bacterial species removed greater than 85% of the Au from solution after 2 h of exposure time below approximately pH 5. Above pH 5, the extent of Au removed from solution decreased with increasing pH, with less than approximately 10% removal of Au from solution above pH 7.5. Kinetics experiments indicated that the Au removal with both bacterial species was rapid at pH 3, and slowed with increasing pH. Reversibility experiments demonstrated that (1) once the Au was removed from solution, adjusting 35 the pH alone did not remobilize the Au into solution and (2) the presence of cysteine in solution in the reversibility experiments caused Au to desorb, suggesting that the Au was not internalized within the bacterial cells. Our results suggest that Au removal occurs as a two-step pH-dependent adsorption reduction process. The speciation of the aqueous Au and the bacterial surface appears to control the rate of Au removal from solution. Under low pH conditions, the cell walls are only weakly negatively charged and aqueous Au complexes adsorb readily and rapidly. With increasing pH, the cell wall becomes more negatively charged, slowing adsorption significantly. The XANES data demonstrate that the reduction of Au(III) by bacterial exudates is slower and less extensive than the reduction observed in the bacteria-bearing systems, and we conclude that Au reduction occurs most rapidly and extensively upon interaction with cell wall functional groups.

Preliminary investigation of phosphorus adsorption onto two types of iron oxide-organic matter complexes.

PubMed

Yan, Jinlong; Jiang, Tao; Yao, Ying; Lu, Song; Wang, Qilei; Wei, Shiqiang

2016-04-01

Iron oxide (FeO) coated by natural organic matter (NOM) is ubiquitous. The associations of minerals with organic matter (OM) significantly changes their surface properties and reactivity, and thus affect the environmental fate of pollutants, including nutrients (e.g., phosphorus (P)). In this study, ferrihydrite/goethite-humic acid (FH/GE-HA) complexes were prepared and their adsorption characteristics on P at various pH and ionic strength were investigated. The results indicated that the FeO-OM complexes showed a decreased P adsorption capacity in comparison with bare FeO. The maximum adsorption capacity (Qmax) decreased in the order of FH (22.17 mg/g)>FH-HA (5.43 mg/g)>GE (4.67 mg/g)>GE-HA (3.27 mg/g). After coating with HA, the amorphous FH-HA complex still showed higher P adsorption than the crystalline GE-HA complex. The decreased P adsorption observed might be attributed to changes of the FeO surface charges caused by OM association. The dependence of P adsorption on the specific surface area of adsorbents suggests that the FeO component in the complexes is still the main contributor for the adsorption surfaces. The P adsorptions on FeO-HA complexes decreased with increasing initial pH or decreasing initial ionic strength. A strong dependence of P adsorption on ionic strength and pH may demonstrate that outer-sphere complexes between the OM component on the surface and P possibly coexist with inner-sphere surface complexes between the FeO component and P. Therefore, previous over-emphasis on the contributions of original minerals to P immobilization possibly over-estimates the P loading capacity of soils, especially in humic-rich areas. Copyright © 2015. Published by Elsevier B.V.

Unfolding of a model protein on ion exchange and mixed mode chromatography surfaces.

PubMed

Gospodarek, Adrian M; Hiser, Diana E; O'Connell, John P; Fernandez, Erik J

2014-08-15

Recent studies with proteins indicate that conformational changes and aggregation can occur during ion exchange chromatography (IEC). Such behavior is not usually expected, but could lead to decreased yield and product degradation from both IEC and multi mode chromatography (MMC) that has ligands of both hydrophobic and charged functionalities. In this study, we used hydrogen exchange mass spectrometry to investigate unfolding of the model protein BSA on IEC and MMC surfaces under different solution conditions at 25°C. Increased solvent exposure, indicating greater unfolding relative to that in solution, was found for protein adsorbed on cationic IEC and MMC surfaces in the pH range of 3.0 to 4.5, where BSA has decreased stability in solution. There was no effect of anionic surfaces at pH values in the range from 6.0 to 9.0. Differences of solvent exposure of whole molecules when adsorbed and in solution suggest that adsorbed BSA unfolds at lower pH values and may show aggregation, depending upon pH and the surface type. Measurements on digested peptides showed that classifications of stability can be made for various regions; these are generally retained as pH is changed. When salt was added to MMC systems, where electrostatic interactions would be minimized, less solvent exposure was seen, implying that it is the cationic moieties, rather than the hydrophobic ligands, which cause greater surface unfolding at low salt concentrations. These results suggest that proteins of lower stability may exhibit unfolding and aggregation during IEC and MMC separations, as they can with hydrophobic interaction chromatography. Copyright © 2014 Elsevier B.V. All rights reserved.

Interfacial Electron Transfer at Sensitized Nanocrystalline TiO2 Electrolyte Interfaces: Influence of Surface Electric Fields and Lewis-Acidic Cations

NASA Astrophysics Data System (ADS)

Barr, Timothy J.

Interfacial electron transfer reactions facilitate charge separation and recombination in dye-sensitized solar cells (DSSCs). Understanding what controls these electron transfer reactions is necessary to develop efficient DSSCs. Gerischer proposed a theory for interfacial electron transfer where the rate constant was related to the energetic overlap between the donor and acceptor states. The present work focuses on understanding how the composition of the CH3CN electrolyte influenced this overlap. It was found that the identity of the electrolyte cation tuned the energetic position of TiO2 electron acceptor states, similar to how pH influences the flatband potential of bulk semiconductors in aqueous electrolytes. For example, the onset for absorption changes, that were attributed to electrons in the TiO2 thin film, were 0.5 V more positive in Mg2+ containing electrolyte than TBA+, where TBA+ is tetrabutylammonium. Similar studies performed on mesoporous, nanocrystalline SnO2 thin films reported a similar cation dependence, but also found evidence for electrons that did not absorb in the visible region that were termed ‘phantom electrons.’. Electron injection is known to generate surface electric fields on the order of 2 MV/cm. The rearrangement of cations in response to surface electric fields, termed screening, was investigated. It was found that magnitude of the electric field and the screening dynamics were dependent on the identity of the electrolyte cation. The rate of charge recombination to the anionic iodide/triiodide redox mediator correlated with the screening ability of the cation, and was initially thought to control charge recombination. However, it was difficult to determine whether electron diffusion or driving force were also cation dependent. Therefore, a in-lab built apparatus, termed STRiVE, was constructed that could disentangle the influence electron diffusion, driving force, and electric fields had on charge recombination. It was found that electron diffusion was independent of the electrolyte cation. Furthermore, charge recombination displayed the same cation-sensitivity using both anionic and cationic redox mediators, indicating electric fields did not cause the cation-dependence of charge recombination. Instead, it was found that the electrolyte cation tuned the energetic position of the TiO2 acceptor states and modulated the driving force for charge recombination.

Effect of dissolved oxygen on two bacterial pathogens examined using ATR-FTIR spectroscopy, microelectrophoresis, and potentiometric titration.

PubMed

Castro, Felipe D; Sedman, Jacqueline; Ismail, Ashraf A; Asadishad, Bahareh; Tufenkji, Nathalie

2010-06-01

The effects of dissolved oxygen tension during bacterial growth and acclimation on the cell surface properties and biochemical composition of the bacterial pathogens Escherichia coli O157:H7 and Yersinia enterocolitica are characterized. Three experimental techniques are used in an effort to understand the influence of bacterial growth and acclimation conditions on cell surface charge and the composition of the bacterial cell: (i) electrophoretic mobility measurements; (ii) potentiometric titration; and (iii) ATR-FTIR spectroscopy. Potentiometric titration data analyzed using chemical speciation software are related to measured electrophoretic mobilities at the pH of interest. Titration of bacterial cells is used to identify the major proton-active functional groups and the overall concentration of these cell surface ligands at the cell membrane. Analysis of titration data shows notable differences between strains and conditions, confirming the appropriateness of this tool for an overall charge characterization. ATR-FTIR spectroscopy of whole cells is used to further characterize the bacterial biochemical composition and macromolecular structures that might be involved in the development of the net surficial charge of the organisms examined. The evaluation of the integrated intensities of HPO(2)(-) and carbohydrate absorption bands in the IR spectra reveals clear differences between growth protocols. Taken together, the three techniques seem to indicate that the dissolved oxygen tension during cell growth or acclimation can noticeably influence the expression of cell surface molecules and the measurable cell surface charge, though in a strain-dependent fashion.

Influence of humic acid concentration on nTiO2 attachment to quartz sand and Fe-coated quartz sand

NASA Astrophysics Data System (ADS)

Cheng, T.; Wu, Y.

2016-12-01

The transport of nano-scale or micro-scale titanium dioxide particles (nTiO2) in subsurface environments are strongly influenced by nTiO2 attachment to sediment grains. The objective of this study is to investigate the role of humic acid (HA) in the attachment of nTiO2 to sand at low HA concentrations that are relevant to typical groundwater conditions, so that mechanisms that control nTiO2 immobilization and transport in groundwater can be elucidated. nTiO2 may carry either positive or negative charges in natural water, therefore, environmental factors such as pH, humic substances, and Fe oxyhydroxide coatings on sediment grains, which are known to control the transport of negatively-charged colloids, may influence nTiO2 in different manners. Attachment of nTiO2 to quartz sand and Fe oxyhydroxide coated quartz sand are experimentally measured under a range of HA concentrations at fixed pH. Experimental results show that at pH 5, negatively-charged HA strongly adsorbs to positively-charged nTiO2 and Fe oxyhydroxide, which, at low HA concentrations, partially neutralizes the positive charges on nTiO2 and Fe oxyhydroxide, and therefore decreases the repulsive electrostatic forces between the surfaces, resulting in relatively high nTiO2 attachment. At high HA concentrations, adsorbed HA reverses the surface charges of nTiO2 and Fe oxyhydroxide, and makes nTiO2 and Fe oxyhydroxide strongly negatively charged, resulting in low nTiO2 attachment. At pH 9, HA, nTiO2, and Fe oxyhydroxide are all negatively charged, and HA adsorption is low and does not have a strong impact on the attachment of nTiO2. This study demonstrates that the changes in surface charges of nTiO2 and Fe oxyhydroxide coating caused by HA adsorption could be a key factor that controls the attachment of nTiO2 to sediment grains.

Spectroscopic Methodologies for Characterizing the Adsorption Behavior and Distribution of Silver Nanoparticles to Hydrated Mineral Surfaces

NASA Astrophysics Data System (ADS)

Brittle, S. W.; O'Neil, K. A.; Foose, D. P.; Stahler, A. C.; Johnson, J. K.; Higgins, S. R.; Sizemore, I. E.; Sikon, J.

2016-12-01

The expansive incorporation of silver nanoparticles (AgNPs) into over 400 consumer products has raised considerable concern about their eventual release into the environment. Although minerals make up a large component of soils, there has been limited research on their interactions with AgNPs. In this study, a representative nonsilicate mineral, corundum (α-Al2O3), was used in fused beaded form (specific surface area of 6-8 m2 g-1) as a model to study the interaction between minerals and negatively-charged, Creighton AgNPs. A concentration of 1 mg L-1 of AgNPs was selected in order to ensure sub-monolayer surface coverage and to surpass the maximum contaminant level (MCL) set by the U.S. Environmental Agency (EPA) for Ag+ in drinking water (0.1 mg L-1). Raman maps collected on the corundum particles exposed to AgNPs at environmentally relevant pH values (6-11) demonstrated AgNP adsorption onto the hydrated mineral surface through OH- moieties regardless of surface charge (i.e. no pH dependence). In addition, two other well-established analytical techniques were employed for supportive purposes. Namely, the AgNP-corundum interaction was also confirmed by inductively coupled plasma optical emission spectroscopy (ICP-OES) through the quantification of the total amount of AgNPs adsorbed onto α-Al2O3. It was found that approximately 75% of the available AgNPs had adsorbed to the mineral surface at all pH values. Atomic force microscopy (AFM), in intermittent contact mode, was also performed to map AgNPs surface distribution on polished and annealed flatter corundum windows. To further demonstrate the Raman analysis, the corundum were also imaged to observe AgNPs adsorption with less surface area and onto other minerals through the occurrence of molecular Ag- vibrations and/or the enhancement of a tracer compound dispensed on mineral surfaces with adsorbed AgNPs (i.e., Surface Enhanced Raman Spectroscopy hot-spots). Overall, this spectroscopic-based analysis promotes extrapolation to other studies as an effective way to observe the interactions between mineral surfaces and nanomaterials.

Sulfur geochemistry of hydrothermal waters in Yellowstone National Park: IV Acid-sulfate waters

USGS Publications Warehouse

Nordstrom, D. Kirk; McCleskey, R. Blaine; Ball, J.W.

2009-01-01

Many waters sampled in Yellowstone National Park, both high-temperature (30-94 ??C) and low-temperature (0-30 ??C), are acid-sulfate type with pH values of 1-5. Sulfuric acid is the dominant component, especially as pH values decrease below 3, and it forms from the oxidation of elemental S whose origin is H2S in hot gases derived from boiling of hydrothermal waters at depth. Four determinations of pH were obtained: (1) field pH at field temperature, (2) laboratory pH at laboratory temperature, (3) pH based on acidity titration, and (4) pH based on charge imbalance (at both laboratory and field temperatures). Laboratory pH, charge imbalance pH (at laboratory temperature), and acidity pH were in close agreement for pH ??10%, a selection process was used to compare acidity, laboratory, and charge balance pH to arrive at the best estimate. Differences between laboratory and field pH can be explained based on Fe oxidation, H2S or S2O3 oxidation, CO2 degassing, and the temperature-dependence of pK2 for H2SO4. Charge imbalances are shown to be dependent on a speciation model for pH values 350 mg/L Cl) decrease as the Cl- concentration increases from boiling which appears inconsistent with the hypothesis of H2S oxidation as a source of hydrothermal SO4. This trend is consistent with the alternate hypothesis of anhydrite solubility equilibrium. Acid-sulfate water analyses are occasionally high in As, Hg, and NH3 concentrations but in contrast to acid mine waters they are low to below detection in Cu, Zn, Cd, and Pb concentrations. Even concentrations of SO4, Fe, and Al are much lower in thermal waters than acid mine waters of the same pH. This difference in water chemistry may explain why certain species of fly larvae live comfortably in Yellowstone's acid waters but have not been observed in acid rock drainage of the same pH.

Nanoparticle/Polymer assembled microcapsules with pH sensing property.

PubMed

Zhang, Pan; Song, Xiaoxue; Tong, Weijun; Gao, Changyou

2014-10-01

The dual-labeled microcapsules via nanoparticle/polymer assembly based on polyamine-salt aggregates can be fabricated for the ratiometric intracellular pH sensing. After deposition of SiO2 nanoparticles on the poly(allylamine hydrochloride)/multivalent anionic salt aggregates followed by silicic acid treatment, the generated microcapsules are stable in a wide pH range (3.0 ∼ 8.0). pH sensitive dye and pH insensitive dye are simultaneously labeled on the capsules, which enable the ratiometric pH sensing. Due to the rough and positively charged surface, the microcapsules can be internalized by several kinds of cells naturally. Real-time measurement of intracellular pH in several living cells shows that the capsules are all located in acidic organelles after being taken up. Furthermore, the negatively charged DNA and dyes can be easily encapsulated into the capsules via charge interaction. The microcapsules with combination of localized pH sensing and drug loading abilities have many advantages, such as following the real-time transportation and processing of the carriers in cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acid-base behavior of the gaspeite (NiCO3(s)) surface in NaCl solutions.

PubMed

Villegas-Jiménez, Adrián; Mucci, Alfonso; Pokrovsky, Oleg S; Schott, Jacques

2010-08-03

Gaspeite is a low reactivity, rhombohedral carbonate mineral and a suitable surrogate to investigate the surface properties of other more ubiquitous carbonate minerals, such as calcite, in aqueous solutions. In this study, the acid-base properties of the gaspeite surface were investigated over a pH range of 5 to 10 in NaCl solutions (0.001, 0.01, and 0.1 M) at near ambient conditions (25 +/- 3 degrees C and 1 atm) by means of conventional acidimetric and alkalimetric titration techniques and microelectrophoresis. Over the entire experimental pH range, surface protonation and electrokinetic mobility are strongly affected by the background electrolyte, leading to a significant decrease of the pH of zero net proton charge (PZNPC) and the pH of isoelectric point (pH(iep)) at increasing NaCl concentrations. This challenges the conventional idea that carbonate mineral surfaces are chemically inert to background electrolyte ions. Multiple sets of surface complexation reactions (i.e., ionization and ion adsorption) were formulated within the framework of three electrostatic models (CCM, BSM, and TLM) and their ability to simulate proton adsorption and electrokinetic data was evaluated. A one-site, 3-pK, constant capacitance surface complexation model (SCM) reproduces the proton adsorption data at all ionic strengths and qualitatively predicts the electrokinetic behavior of gaspeite suspensions. Nevertheless, the strong ionic strength dependence exhibited by the optimized SCM parameters reveals that the influence of the background electrolyte on the surface reactivity of gaspeite is not fully accounted for by conventional electrostatic and surface complexation models and suggests that future refinements to the underlying theories are warranted.

Label-free specific detection of femtomolar cardiac troponin using an integrated nanoslit array fluidic diode.

PubMed

Liu, Yifan; Yobas, Levent

2014-12-10

We demonstrate here for the first time the utility of an integrated nanofluidic diode for detecting and quantifying physiologically relevant macromolecules. Troponin T, a key human cardiac protein biomarker, was selectively and rapidly detected free of labels for concentrations down to 10 fg/mL (∼ 0.3 fM) in buffer as well as 10 pg/mL (∼ 300 fM) in untreated human serum. This ultrasensitive detection arises from monolithic integration of a unique nanofluidic diode structure that is highly robust and amenable to site-specific surface modification. The structure features a planar nanoslit array where each nanoslit is defined at a nominal width of 70 nm over a micrometer-scale silicon trench without the use of high-resolution patterning techniques. Through vapor deposition, a glass layer is placed at a nonuniform thickness, tapering the trench profile upward and contributing to the triangular nanoslit structure. This asymmetric profile is essential for ionic current rectification noted here at various pH values, ionic strengths, and captured target species, which modulate the surface-charge density within the sensitive region of the nanoslit. The nanoslit, unlike nanopores, offers only 1D confinement, which appears to be adequate for reasonable rectification. The measurements are found in quantitative agreement with the diode simulations for the first time based on a pH- and salt-dependent surface-charge model.

Dispersion stability of a ceramic glaze achieved through ionic surfactant adsorption.

PubMed

Panya, Preecha; Arquero, Orn-anong; Franks, George V; Wanless, Erica J

2004-11-01

The adsorption of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) onto a ceramic glaze mixture composed of limestone, feldspar, quartz, and kaolin has been investigated. Both adsorption isotherms and the average particle zeta potential have been studied in order to understand the suspension stability as a function of pH, ionic strength, and surfactant concentration. The adsorption of small amounts of cationic CPC onto the primarily negatively charged surfaces of the particles at pH 7 and 9 results in strong attraction and flocculation due to hydrophobic interactions. At higher surfactant concentrations a zeta potential of more than +60 mV results from the bilayered adsorbed surfactant, providing stability at salt concentrations < or = 0.01 M. At 0.1 M salt poor stability results despite substantial zeta potential values. Three mechanisms for SDBS adsorption have been identified. When anionic SDBS monomers either adsorb by electrostatic interactions with the few positive surface sites at high pH or adsorb onto like charged negative surface sites due to dispersion or hydrophobic interactions, the magnitude of the negative zeta potential increases slightly. At pH 9 this increase is enough to promote stability with an average zeta potential of more than -55 mV, whereas at pH 7 the zeta potential is lower at about -45 mV. The stability of suspensions at pH 7 is additionally due to steric repulsion caused by the adsorption of thick layers of neutrally charged Ca(DBS)2 complexes created when the surfactant interacts with dissolved calcium ions from the calcium carbonate component.

Molecular adsorption at electrolyte/α-Al2O3 interface of aluminum electrolytic capacitor revealed by sum frequency vibrational spectroscopy.

PubMed

Jia, Ming; Hu, Xiaoyu; Liu, Jin; Liu, Yexiang; Ai, Liang

2017-05-21

The operating voltage of an aluminum electrolytic capacitor is determined by the breakdown voltage (U b ) of the Al 2 O 3 anode. U b is related to the molecular adsorption at the Al 2 O 3 /electrolyte interface. Therefore, we have employed sum-frequency vibrational spectroscopy (SFVS) to study the adsorption states of a simple electrolyte, ethylene glycol (EG) solution with ammonium adipate, on an α-Al 2 O 3 surface. In an acidic electrolyte (pH < 6), the Al 2 O 3 surface is positively charged. The observed SFVS spectra show that long chain molecules poly ethylene glycol and ethylene glycol adipate adopt a "lying" orientation at the interface. In an alkaline electrolyte (pH > 8), the Al 2 O 3 surface is negatively charged and the short chain EG molecules adopt a "tilting" orientation. The U b results exhibit a much higher value at pH < 6 compared with that at pH > 8. Since the "lying" long chain molecules cover and protect the Al 2 O 3 surface, U b increases with a decrease of pH. These findings provide new insights to study the breakdown mechanisms and to develop new electrolytes for high operating voltage capacitors.

Influence of pH, layer charge location and crystal thickness distribution on U(VI) sorption onto heterogeneous dioctahedral smectite.

PubMed

Guimarães, Vanessa; Rodríguez-Castellón, Enrique; Algarra, Manuel; Rocha, Fernando; Bobos, Iuliu

2016-11-05

The UO2(2+) adsorption on smectite (samples BA1, PS2 and PS3) with a heterogeneous structure was investigated at pH 4 (I=0.02M) and pH 6 (I=0.2M) in batch experiments, with the aim to evaluate the influence of pH, layer charge location and crystal thickness distribution. Mean crystal thickness distribution of smectite crystallite used in sorption experiments range from 4.8nm (sample PS2), to 5.1nm (sample PS3) and, to 7.4nm (sample BA1). Smaller crystallites have higher total surface area and sorption capacity. Octahedral charge location favor higher sorption capacity. The sorption isotherms of Freundlich, Langmuir and SIPS were used to model the sorption experiments. The surface complexation and cation exchange reactions were modeled using PHREEQC-code to describe the UO2(2+) sorption on smectite. The amount of UO2(2+) adsorbed on smectite samples decreased significantly at pH 6 and higher ionic strength, where the sorption mechanism was restricted to the edge sites of smectite. Two binding energy components at 380.8±0.3 and 382.2±0.3eV, assigned to hydrated UO2(2+) adsorbed by cation exchange and by inner-sphere complexation on the external sites at pH 4, were identified after the U4f7/2 peak deconvolution by X-photoelectron spectroscopy. Also, two new binding energy components at 380.3±0.3 and 381.8±0.3eV assigned to AlOUO2(+) and SiOUO2(+) surface species were observed at pH 6. Copyright © 2016 Elsevier B.V. All rights reserved.

pH-Responsive Mercaptoundecanoic Acid Functionalized Gold Nanoparticles and Applications in Catalysis

PubMed Central

Ansar, Siyam M.; Chakraborty, Saptarshi

2018-01-01

Mercaptoundecanoic acid (MUA) functionalized gold nanoparticles (AuNP-MUA) were synthesized and demonstrated to possess pH-triggered aggregation and re-dispersion, as well as the capability of phase transfer between aqueous and organic phases in response to changes in pH. The pH of aggregation for AuNP-MUA is consistent with the pKa of MUA (pH ~4) in solution, while AuNP-MUA phase transition between aqueous and organic phases occurs at pH ~9. The ion pair formation between the amine group in octadecylamine (ODA), the carboxylate group in MUA, and the hydrophobic alkyl chain of ODA facilitates the phase transfer of AuNP-MUA into an organic medium. The AuNP-MUA were investigated as a reusable catalyst in the catalytic reduction of 4-nitrophenol by borohydride—a model reaction for AuNPs. It was determined that 100% MUA surface coverage completely inhibits the catalytic activity of AuNPs. Decreasing the surface coverage was shown to increase catalytic activity, but this decrease also leads to decreased colloidal stability, recoverability, and reusability in subsequent reactions. At 60% MUA surface coverage, colloidal stability and catalytic activity were achieved, but the surface coverage was insufficient to enable redispersion following pH-induced recovery. A balance between AuNP colloidal stability, recoverability, and catalytic activity with reusability was achieved at 90% MUA surface coverage. The AuNP-MUA catalyst can also be recovered at different pH ranges depending on the recovery method employed. At pH ~4, protonation of the MUA results in reduced surface charge and aggregation. At pH ~9, ODA will form an ion-pair with the MUA and induce phase transfer into an immiscible organic phase. Both the pH-triggered aggregation/re-dispersion and aqueous/organic phase transfer methods were employed for catalyst recovery and reuse in subsequent reactions. The ability to recover and reuse the AuNP-MUA catalyst by two different methods and different pH regimes is significant, based on the fact that nanoparticle-catalyzed reactions may occur under different pH conditions. PMID:29772775

The amphoteric effect on friction between the bovine cartilage/cartilage surfaces under slightly sheared hydration lubrication mode.

PubMed

Pawlak, Zenon; Gadomski, Adam; Sojka, Michal; Urbaniak, Wieslaw; Bełdowski, Piotr

2016-10-01

The amphoteric effect on the friction between the bovine cartilage/cartilage contacts has been found to be highly sensitive to the pH of an aqueous solution. The cartilage surface was characterized using a combination of the pH, wettability, as well as the interfacial energy and friction coefficient testing methods to support lamellar-repulsive mechanism of hydration lubrication. It has been confirmed experimentally that phospholipidic multi-bilayers are essentially described as lamellar frictionless lubricants protecting the surface of the joints against wear. At the hydrophilicity limit, the low friction would then be due to (a) lamellar slippage of bilayers and (b) a short-range (nanometer-scale) repulsion between the interfaces of negatively charged (PO4(-)) cartilage surfaces, and in addition, contribution of the extracellular matrix (ECM) collagen fibers, hyaluronate, proteoglycans aggregates (PGs), glycoprotein termed lubricin and finally, lamellar PLs phases. In this paper we demonstrate experimentally that the pH sensitivity of cartilage to friction provides a novel concept in joint lubrication on charged surfaces. Copyright © 2016 Elsevier B.V. All rights reserved.

Adsorption of transgenic insecticidal Cry1Ab protein to silica particles. Effects on transport and bioactivity.

PubMed

Madliger, Michael; Gasser, Christoph A; Schwarzenbach, René P; Sander, Michael

2011-05-15

Bt crops are genetically modified to be resistant against insect pests by expressing insecticidal Cry proteins. The processes governing the fate and bioavailability of the expressed transgenic Cry proteins in soils are poorly understood. We studied adsorption of Cry1Ab to negatively charged silica (SiO(2)) particles, a major soil constituent and a model for negatively charged mineral surfaces, at pH 5 to 10 and ionic strengths I = 10 mM to 250 mM, both in solution depletion and saturated column transport experiments. Cry1Ab-SiO(2) interactions were dominated by patch-controlled electrostatic attraction (PCEA), as evident from increasing Cry1Ab attraction to SiO(2) with decreasing I at pH at which both Cry1Ab and SiO(2) were net negatively charged. Experimental and modeling evidence is provided that the surface heterogeneity of SiO(2) particles modulated PCEA, leading to a fraction of adsorption sites with slow Cry1Ab desorption kinetics. Desorption rates from these sites increased upon increasing the solution pH. In toxicity bioassays, we demonstrated that Cry1Ab retained insecticidal activity when adsorbed to SiO(2), suggesting high protein conformational stability during adsorption-desorption cycles. Models predicting Cry1A protein adsorption in soils therefore need to account for combined effects of the nonuniform protein surface charge distribution and of sorbent surface heterogeneity.

Improvement of calcium mineral separation contrast using anionic reagents: electrokinetics properties and flotation

NASA Astrophysics Data System (ADS)

Lafhaj, Z.; Filippov, L. O.; Filippova, I. V.

2017-07-01

The flotation separation of salt type calcium minerals is problematic, due to the similarities in their same active Ca2+ related site for interaction with anionic collectors and similar physicochemical characteristics such as solubility, zero-point charge, surface speciation and Ca-site density. The work was performed to achieve effective and selective separation of the calcium-minerals using pure minerals samples: orange calcite with Mg impurities, optic calcite with impurities level and an apatite. The pure samples surface was examined using techniques sensitive near-surface like infrared spectroscopy (FTIR) and chemical composition was obtained by ICPMS. The isoelectric point (IEP) and point of zero charge (PZC) in electrolyte were recorded using electrophoresis method at different ionic strengths of the solution. Mechanisms of charge development at the mineral-water interface are discussed. The time of contact as important parameter for the charge equilibrium was deduced from kinetics study and fixed to 30 minutes. The difference in the values obtained between IEP and PZSE can be explained by the presence of a specific adsorption of cations and anions on the surface. The effect of pure anionic collectors such as oleic and linoleic acid were studied. At low pH, both collectors lead to a good recovery for the calcites. The flotation recovery of optic calcite at pH 9 with sodium oleate is higher than with sodium linoleate. At alkaline pH, apatite showed a better recovery with sodium linoleate.

Investigation of adsorptive fractionation of humic acid on graphene oxide using fluorescence EEM-PARAFAC.

PubMed

Lee, Bo-Mi; Seo, Young-Soo; Hur, Jin

2015-04-15

In this study, the adsorptive fractionation of a humic acid (HA, Elliott soil humic acid) on graphene oxide (GO) was examined at pH 4 and 6 using absorption spectroscopy and fluorescence excitation-emission matrix (EEM)-parallel factor analysis (PARAFAC). The extent of the adsorption was greater at pH 4.0 than at pH 6.0. Aromatic molecules within the HA were preferentially adsorbed onto the GO surface, and the preferential adsorption was more pronounced at pH 6, which is above the zero point of charge of GO. A relative ratio of two PARAFAC humic-like components (ex/em maxima at 270/510 nm and at (250, 265)/440 nm) presented an increasing trend with larger sizes of ultrafiltered humic acid fractions, suggesting the potential for using fluorescence EEM-PARAFAC for tracking the changes in molecular sizes of aromatic HA molecules. The individual adsorption behaviors of the two humic-like components revealed that larger sized aromatic components within HA had a higher adsorption affinity and more nonlinear isotherms compared to smaller sized fractions. Our results demonstrated that adsorptive fractionation of HA occurred on the GO surface with respect to their aromaticity and the sizes, but the degree was highly dependent on solution pH as well as the amount of adsorbed HS (or available surface sites). The observed adsorption behaviors were reasonably explained by a combination of different mechanisms previously suggested. Copyright © 2015 Elsevier Ltd. All rights reserved.

Determination of Surface Charge of Titanium Dioxide (Anatase) at High Ionic Strength

NASA Astrophysics Data System (ADS)

Schoonen, M. A.; Strongin, D. R.

2014-12-01

Charge development on mineral surfaces is an important control on the fate of minor and trace elements in a wide range of environments, including in possible radioactive waste repositories. Formation waters have often a high ionic strength. In this study, we determined the zeta potential (ζ) of anatase in potassium chloride solutions with concentrations up to 3M (25°C). The zeta potential is the potential at the hydrodynamic shear plane. In this study, we made use of the electro-acoustic effect. This effect is based on the development of a measureable potential/current when the electrical double layer outside the shearplane is separated from a charged particle through rapid oscillation induced by a sound wave. The advantage of this type of measurement is that the particles are not subjected to a high electric field (common to typical zeta potential measurements), which leads to electrode reactions and a shift of solution pH. Measurements were collected by subtracting the ion vibration current (IVI) due to the presence of potassium and chloride ions from the CVI. The correction is necessary for measurements in solutions with I > 0.25 M. This subtraction was done at each of the measurement conditions by centrifuging the slurrly, measuring the IVI of the supernatant, reconstituting the slurry, and then measuring CVI of the slurry. Subtraction of IVI at each condition is critical because IVI changes with pH and accounts for most of raw signal. The results show that the anatase isoelectric point shifts from a pH ~6.5 to a value of ~4.5 at 1M KCl. At ionic strength in excess of 1 M KCl, the surface appears to be slightly negatively charged accross the pH range accessible by this technique (pH 2.5-10). The loss of an isoelectric point suggests that KCl is no longer an indifferent electrolyte at 1 M KCl and higher. The results are in disagreement with earlier measurements in which anatase was shown to have a positive charge at high ionic strength across the pH scale. The difference between the current and earlier work is likely a result of the IVI correction. While anatase is unlikely to be of importance in a waste environment, the work provides a method to determine charge on more relevant mineral surfaces. This can then lead to a better representation of the fate for radionuclides in the subsurface.

Influence of polymer size, liposomal composition, surface charge, and temperature on the permeability of pH-sensitive liposomes containing lipid-anchored poly(2-ethylacrylic acid).

PubMed

Lu, Tingli; Wang, Zhao; Ma, Yufan; Zhang, Yang; Chen, Tao

2012-01-01

Liposomes containing pH-sensitive polymers are promising candidates for the treatment of tumors and localized infection. This study aimed to identify parameters influencing the extent of contents release from poly(ethylacrylic acid) (PEAA) vesicles, focusing on the effects of polymer size, lipid composition, vesicle surface charge, and temperature. Anchored lipid pH-sensitive PEAA was synthesized using PEAA with a molecular weight of 8.4 kDa. PEAA vesicles were prepared by insertion of the lipid-anchored PEAA into preformed large unilamellar vesicles. The preformed liposomes were manipulated by varying the phosphocholine and cholesterol content, and by adding negative or positive charges to the liposomes. A calcein release assay was used to evaluate the effects of polymer size, liposome composition, surface charge, and temperature on liposomal permeability. The release efficiency of the calcein-entrapped vesicles was found to be dependent on the PEAA polymer size. PEAA vesicles containing a phosphatidylcholine to cholesterol ratio of 60:40 (mol/mol) released more than 80% of their calcein content when the molecular weight of PEAA was larger than 8.4 kDa. Therefore, the same-sized polymer of 8.4 kDa was used for the rest of study. The calcein release potential was found to decrease as the percentage of cholesterol increased and with an increase in the phosphocholine acyl chain length (DMPC DPPC DSPC). Negatively charged and neutral vesicles released similar amounts of calcein, whereas positively charged liposomes released a significant amount of their contents. pH-sensitive release was dependent on temperature. Dramatic content release was observed at higher temperatures. The observed synergistic effect of pH and temperature on release of the contents of PEAA vesicles suggests that this pH-sensitive liposome might be a good candidate for intracellular drug delivery in the treatment of tumors or localized infection.

Influence of polymer size, liposomal composition, surface charge, and temperature on the permeability of pH-sensitive liposomes containing lipid-anchored poly(2-ethylacrylic acid)

PubMed Central

Lu, Tingli; Wang, Zhao; Ma, Yufan; Zhang, Yang; Chen, Tao

2012-01-01

Background Liposomes containing pH-sensitive polymers are promising candidates for the treatment of tumors and localized infection. This study aimed to identify parameters influencing the extent of contents release from poly(ethylacrylic acid) (PEAA) vesicles, focusing on the effects of polymer size, lipid composition, vesicle surface charge, and temperature. Methods Anchored lipid pH-sensitive PEAA was synthesized using PEAA with a molecular weight of 8.4 kDa. PEAA vesicles were prepared by insertion of the lipid-anchored PEAA into preformed large unilamellar vesicles. The preformed liposomes were manipulated by varying the phosphocholine and cholesterol content, and by adding negative or positive charges to the liposomes. A calcein release assay was used to evaluate the effects of polymer size, liposome composition, surface charge, and temperature on liposomal permeability. Results The release efficiency of the calcein-entrapped vesicles was found to be dependent on the PEAA polymer size. PEAA vesicles containing a phosphatidylcholine to cholesterol ratio of 60:40 (mol/mol) released more than 80% of their calcein content when the molecular weight of PEAA was larger than 8.4 kDa. Therefore, the same-sized polymer of 8.4 kDa was used for the rest of study. The calcein release potential was found to decrease as the percentage of cholesterol increased and with an increase in the phosphocholine acyl chain length (DMPC DPPC DSPC). Negatively charged and neutral vesicles released similar amounts of calcein, whereas positively charged liposomes released a significant amount of their contents. pH-sensitive release was dependent on temperature. Dramatic content release was observed at higher temperatures. Conclusion The observed synergistic effect of pH and temperature on release of the contents of PEAA vesicles suggests that this pH-sensitive liposome might be a good candidate for intracellular drug delivery in the treatment of tumors or localized infection. PMID:23028220

Developing a Small-Scale De-Fluoridation Filter for Use in Rural Northern Ghana with Activated Alumina As the Sorbent

NASA Astrophysics Data System (ADS)

Craig, L.; Stillings, L. L.

2014-12-01

In northern Ghana, groundwater is the main source of household water and is generally considered safe to drink. However in some areas it contains fluoride (F-) concentrations above the 1.5 ppm limit recommended by the World Health Organization, putting the users at risk of fluorosis. The study area in the Upper East Region of Ghana has pockets of groundwater F- up to 4.6 ppm and, as a result, also has a high percentage of residents with dental fluorosis. They have no alternative water source and, because of poverty and limited access to technology, lack the capacity to set up advanced treatment systems. One proposed solution is to attach F- adsorption filters to the wells, since adsorption is considered a simple and cost effective approach for treating high F-drinking water. This study evaluates activated alumina as a sorbent for use in de-fluoridation filters in the study area. We evaluated the long-term adsorption capacity of activated alumina, and changes in F- adsorption rate and capacity with grain size. We measured differences in positive surface charge (C m-2) via slow acid titration, as well as F- loading with varied prior hydration time. Results from this research show no notable change in F- adsorption or positive surface charge when the activated alumina surface was pre-equilibrated in distilled water from 24 hours to 30 weeks. The results of F- loading show a maximum of ~3.4 mg F- sorbed per gm activated alumina (initial pH ~6.9, initial F- 1 to 60 ppm, 20 hr reaction time). The pH dependent surface charge is ~0.14 C m-2 at pH of ~4.4 and is zero at pH ~8.6. F- loading experiments were conducted with grain size 0.125 to 0.250 mm and 0.5 to 1.0 mm to evaluate changes in F- adsorption rate (initial pH ~6.9, initial F- 10 ppm) and F- loading (initial pH ~6.9, initial F- 1 to 60 ppm, 20 hr reaction time). The F- loading did not change with grain size. However time to equilibrium increased dramatically with a decrease in grain size - after one hour of reaction time, the larger grain size adsorbed only 59% of F-, while at the finer grain size 90% was adsorbed. Future work will determine the volume of high F- water that can be treated before activated alumina needs to be regenerated or changed. These data will aid in the design of a small-scale F- adsorption filter in the study area, and will predict the longevity of activated alumina as the sorbent.

PH-dependence of detergent-induced hemolysis and vesiculation of erythrocytes.

PubMed

Chernitsky, E A; Rozin, V V; Senkovich, O A

2001-01-01

The influence of pH of the medium on the parameters of detergent-induced fast hemolysis and vesiculation of human erythrocytes was studied. In the range of pH 6.3-7.2 neither the extent nor the rate of the vesiculation induced by 25 microM sodium dodecyl sulfate (SDS) changed. However, a decrease of pH from 8.0 to 5.8 strongly modified both the extent and the rate of the hemolysis induced by SDS. Within the range of pH 8.0-6.4, the effect can be ascribed to the increase of the positive charge of the membrane. This could lead to the accumulation of the membrane-bound anion detergent and, hence, to the change of the hemolysis parameters. Non-charged detergent Triton X-100 did not display any pH-dependence. At pH between 6.4 and 5.8 the extent and rate of hemolysis changed in a complicated manner. The kinetic curves of hemolysis could be approximated by a single exponential within the pH range between 8.0 and 7.2. Upon further reduction of pH, a second exponential component, with a larger time constant, appeared in the kinetic curves. At 5.8 < pH < 7.2, the contribution of the "fast" hemolysis dropped virtually to zero, with pK about 6.0. This points to a structural transition of the membrane, possibly involving histidine. We suggest that the parameters of the detergent-induced hemolysis are sensitive to the changes of the charge and structural state of erythrocyte membrane.

Ion-ion correlation, solvent excluded volume and pH effects on physicochemical properties of spherical oxide nanoparticles.

PubMed

Ovanesyan, Zaven; Aljzmi, Amal; Almusaynid, Manal; Khan, Asrar; Valderrama, Esteban; Nash, Kelly L; Marucho, Marcelo

2016-01-15

One major source of complexity in the implementation of nanoparticles in aqueous electrolytes arises from the strong influence that biological environments has on their physicochemical properties. A key parameter for understanding the molecular mechanisms governing the physicochemical properties of nanoparticles is the formation of the surface charge density. In this article, we present an efficient and accurate approach that combines a recently introduced classical solvation density functional theory for spherical electrical double layers with a surface complexation model to account for ion-ion correlation and excluded volume effects on the surface titration of spherical nanoparticles. We apply the proposed computational approach to account for the charge-regulated mechanisms on the surface chemistry of spherical silica (SiO2) nanoparticles. We analyze the effects of the nanoparticle size, as well as pH level and electrolyte concentration of the aqueous solution on the nanoparticle's surface charge density and Zeta potential. We validate our predictions for 580Å and 200Å nanoparticles immersed in acid, neutral and alkaline mono-valent aqueous electrolyte solutions against experimental data. Our results on mono-valent electrolyte show that the excluded volume and ion-ion correlations contribute significantly to the surface charge density and Zeta potential of the nanoparticle at high electrolyte concentration and pH levels, where the solvent crowding effects and electrostatic screening have shown a profound influence on the protonation/deprotonation reactions at the liquid/solute interface. The success of this approach in describing physicochemical properties of silica nanoparticles supports its broader application to study other spherical metal oxide nanoparticles. Copyright © 2015 Elsevier Inc. All rights reserved.

Fluorescent Nanocrystals Reveal Regulated Portals of Entry into and Between the Cells of Hydra

PubMed Central

Tortiglione, Claudia; Quarta, Alessandra; Malvindi, Maria Ada; Tino, Angela; Pellegrino, Teresa

2009-01-01

Initially viewed as innovative carriers for biomedical applications, with unique photophysical properties and great versatility to be decorated at their surface with suitable molecules, nanoparticles can also play active roles in mediating biological effects, suggesting the need to deeply investigate the mechanisms underlying cell-nanoparticle interaction and to identify the molecular players. Here we show that the cell uptake of fluorescent CdSe/CdS quantum rods (QRs) by Hydra vulgaris, a simple model organism at the base of metazoan evolution, can be tuned by modifying nanoparticle surface charge. At acidic pH, amino-PEG coated QRs, showing positive surface charge, are actively internalized by tentacle and body ectodermal cells, while negatively charged nanoparticles are not uptaken. In order to identify the molecular factors underlying QR uptake at acidic pH, we provide functional evidence of annexins involvement and explain the QR uptake as the combined result of QR positive charge and annexin membrane insertion. Moreover, tracking QR labelled cells during development and regeneration allowed us to uncover novel intercellular trafficking and cell dynamics underlying the remarkable plasticity of this ancient organism. PMID:19888325

Polyethylenimine-modified fungal biomass as a high-capacity biosorbent for Cr(VI) anions: sorption capacity and uptake mechanisms.

PubMed

Deng, Shubo; Ting, Yen Peng

2005-11-01

Heavy metal pollution in the aqueous environment is a problem of global concern. Biosorption has been considered as a promising technology for the removal of low levels of toxic metals from industrial effluents and natural waters. A modified fungal biomass of Penicillium chrysogenum with positive surface charges was prepared by grafting polyethylenimine (PEI) onto the biomass surface in a two-step reaction. The presence of PEI on the biomass surface was verified by FTIR and X-ray photoelectron spectroscopy (XPS) analyses. Due to the high density of amine groups in the long chains of PEI molecules on the surface, the modified biomass was found to possess positive zeta potential at pH below 10.4 as well as high sorption capacity for anionic Cr(VI). Using the Langmuir adsorption isotherm, the maximum sorption capacity for Cr(VI) at a pH range of 4.3-5.5 was 5.37 mmol/g of biomass dry weight, the highest sorption capacity for Cr(VI) compared to other sorbents reported in the literature. Scanning electronic microscopy (SEM) provided evidence of chromium aggregates formed on the biomass surface. XPS results verified the presence of Cr(III) on the biomass surface in the pH range 2.5-10.5, suggesting that some Cr(VI) anions were reduced to Cr(III) during the sorption. The sorption kinetics indicated that redox reaction occurred on the biomass surface, and whether the converted Cr(III) ions were released to solution or adsorbed on the biomass depended on the solution pH. Sorption mechanisms including electrostatic interaction, chelation, and precipitation were found to be involved in the complex sorption of chromium on the PEI-modified biomass.

Aging and behavior of functional TiO2 nanoparticles in aqueous environment.

PubMed

Lu, Huiting; Dong, Haifeng; Fan, Wenhong; Zuo, Jinxing; Li, Xiaomin

2017-03-05

Nanoparticles are usually functionalized with various surface capping moieties in practical applications. Understand the behavior and fate of them is critical to evaluate or even predict their risk to environment. However, little attention has been denoted on this issue until now. Using three commercial TiO 2 nanoparticles with different capping moieties, their aging procedures and corresponding change as well as their byproducts were systematically studied. Comprehensive microscopic and spectrometric measurements demonstrated a capping agent-dependent with the aging procedure. All the aging agents exhibited sharp change in morphologies compared to the fresh counterparts. The degraded degree and surface properties including surface charge and hydrophobicity of the functional TiO 2 nanoparticles were varied depended on the capping moieties. Furthermore, the behaviors of these byproducts in various background media had also been investigated. Contrastively, environment factors such as pH, electrolyte valence, and humic acid regardless of capping moieties govern the behavior of these byproducts, despite of the capping moieties slightly affect the point of zero charge. This study highlights the influence of the capping moieties and environmental factors to the transformation progress of functional nanomaterials in environment exposure, which contributes to design and assess the environmental risk of other analogous functional nanoparticles in practical application. Copyright © 2016 Elsevier B.V. All rights reserved.

Simultaneous detection of refractive index and surface charges in nanolaser biosensors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, Keisuke; Kishi, Yoji; Hachuda, Shoji

2015-01-12

The emission intensity of a GaInAsP photonic crystal nanolaser is affected by the pH of the solution, in which the nanolaser is immersed. This phenomenon can be explained by the change in the redox potential, which modifies the filling of electrons at surface states of the semiconductor and hence the nonradiative surface recombination. This phenomenon allows the nanolaser to simultaneously and independently detect the refractive index and electric charges near the surface on the basis of the variation in emission wavelength and intensity, respectively. This paper demonstrates this function through alternate deposition of charged polyelectrolytes and hybridization of deoxyribonucleic acids.

Development of Functional Thin Polymer Films Using a Layer-by-Layer Deposition Technique.

PubMed

Yoshida, Kentaro

2017-01-01

Functional thin films containing insulin were prepared using layer-by-layer (LbL) deposition of insulin and negatively- or positively-charged polymers on the surface of solid substrates. LbL films composed of insulin and negatively-charged polymers such as poly(acrylic acid) (PAA), poly(vinylsulfate) (PVS), and dextran sulfate (DS) were prepared through electrostatic affinity between the materials. The insulin/PAA, insulin/PVS, and insulin/DS films were stable in acidic solutions, whereas they decomposed under physiological conditions as a result of a change in the net electric charge of insulin from positive to negative. Interestingly, the insulin-containing LbL films were stable even in the presence of a digestive-enzyme (pepcin) at pH 1.4 (stomach pH). In contrast, LbL films consisting of insulin and positively-charged polymers such as poly(allylamine hydrochloride) (PAH) decomposed in acidic solutions due to the positive charges of insulin generated in acidic media. The insulin-containing LbL films can be prepared not only on the surface of flat substrates, such as quartz slides, but also on the surface of microparticles, such as poly(lactic acid) (PLA) microbeads. Thus, insulin-containing LbL film-coated PLA microbeads can be handled as a powder. In addition, insulin-containing microcapsules were prepared by coating LbL films on the surface of insulin-doped calcium carbonate (CaCO 3 ) microparticles, followed by dissolution of the CaCO 3 core. The release of insulin from the microcapsules was accelerated at pH 7.4, whereas it was suppressed in acidic solutions. These results suggest the potential use of insulin-containing microcapsules in the development of oral formulations of insulin.

Probing Anisotropic Surface Properties of Molybdenite by Direct Force Measurements.

PubMed

Lu, Zhenzhen; Liu, Qingxia; Xu, Zhenghe; Zeng, Hongbo

2015-10-27

Probing anisotropic surface properties of layer-type mineral is fundamentally important in understanding its surface charge and wettability for a variety of applications. In this study, the surface properties of the face and the edge surfaces of natural molybdenite (MoS2) were investigated by direct surface force measurements using atomic force microscope (AFM). The interaction forces between the AFM tip (Si3N4) and face or edge surface of molybdenite were measured in 10 mM NaCl solutions at various pHs. The force profiles were well-fitted with classical DLVO (Derjaguin-Landau-Verwey-Overbeek) theory to determine the surface potentials of the face and the edge surfaces of molybdenite. The surface potentials of both the face and edge surfaces become more negative with increasing pH. At neutral and alkaline conditions, the edge surface exhibits more negative surface potential than the face surface, which is possibly due to molybdate and hydromolybdate ions on the edge surface. The point of zero charge (PZC) of the edge surface was determined around pH 3 while PZC of the face surface was not observed in the range of pH 3-11. The interaction forces between octadecyltrichlorosilane-treated AFM tip (OTS-tip) and face or edge surface of molybdenite were also measured at various pHs to study the wettability of molybdenite surfaces. An attractive force between the OTS-tip and the face surface was detected. The force profiles were well-fitted by considering DLVO forces and additional hydrophobic force. Our results suggest the hydrophobic feature of the face surface of molybdenite. In contrast, no attractive force between the OTS-tip and the edge surface was detected. This is the first study in directly measuring surface charge and wettability of the pristine face and edge surfaces of molybdenite through surface force measurements.

Influence of charge and flexibility on smectic phase formation in filamentous virus suspensions

NASA Astrophysics Data System (ADS)

Purdy, Kirstin R.; Fraden, Seth

2007-07-01

We present experimental measurements of the cholesteric-smectic phase transition of suspensions of charged semiflexible rods as a function of rod flexibility and surface charge. The rod particles consist of the bacteriophage M13 and closely related mutants, which are structurally identical to M13, but vary either in contour length and therefore ratio of persistence length to contour length, or surface charge. Surface charge is altered in two ways; by changing solution pH and by comparing M13 with fd virus, a virus which differs from M13 only by the substitution of a single charged amino acid for a neutral one per viral coat protein. Phase diagrams are measured as a function of particle length, particle charge, and ionic strength. The experimental results are compared with existing theoretical predictions for the phase behavior of flexible rods and charged rods.

Surface functionalization of dopamine coated iron oxide nanoparticles for various surface functionalities

NASA Astrophysics Data System (ADS)

Sherwood, Jennifer; Xu, Yaolin; Lovas, Kira; Qin, Ying; Bao, Yuping

2017-04-01

We present effective conjugation of four small molecules (glutathione, cysteine, lysine, and Tris(hydroxymethyl)aminomethane) onto dopamine-coated iron oxide nanoparticles. Conjugation of these molecules could improve the surface functionality of nanoparticles for more neutral surface charge at physiological pH and potentially reduce non-specific adsorption of proteins to nanoparticles surfaces. The success of conjugation was evaluated with dynamic light scattering by measuring the surface charge changes and Fourier transform infrared spectroscopy for surface chemistry analysis. The stability of dopamine-coated nanoparticles and the ability of conjugated nanoparticles to reduce the formation of protein corona were evaluated by measuring the size and charge of the nanoparticles in biological medium. This facile conjugation method opens up possibilities for attaching various surface functionalities onto iron oxide nanoparticle surfaces for biomedical applications.

Surface Oxide Net Charge of a Titanium Alloy ; Modulation of Fibronectin-Activated Attachment and Spreading of Osteogenic Cells

PubMed Central

Rapuano, Bruce E.; MacDonald, Daniel E.

2010-01-01

In the current study, we have altered the surface oxide properties of a Ti6Al4V alloy using heat treatment or radiofrequency glow discharge (RFGD) in order to evaluate the relationship between the physico-chemical and biological properties of the alloy's surface oxide. The effects of surface pretreatments on the attachment of cells from two osteogenic cell lines (MG63 and MC3T3) and a mesenchymal stem cell line (C3H10T1/2) to fibronectin adsorbed to the alloy were measured. Both heat and RFGD pretreatments produced a several-fold increase in the number of cells that attached to fibronectin adsorbed to the alloy (0.001 and 10 nM FN) for each cell line tested. An antibody (HFN7.1) directed against the central integrin binding domain of fibronectin produced a 65-70% inhibition of cell attachment to fibronectin-coated disks, incdicating that cell attachment to the metal discs was dependent on fibronectin binding to cell integrin receptors. Both treatments also accelerated the cell spreading response manifested by extensive flattening and an increase in mean cellular area. The treatment-induced increases in the cell attachment activity of adsorbed fibronectin were correlated with previously demonstrated increases in Ti6Al4V oxide negative net surface charge at physiological pH produced by both heat and RFGD pretreatments. Since neither treatment increased the adsorption mass of fibronectin, these findings suggest that negatively charged surface oxide functional groups in Ti6Al4V can modulate fibronectin's integrin receptor activity by altering the adsorbed protein's conformation. Our results further suggest that negatively charged functional groups in the surface oxide can play a prominent role in the osseointegration of metallic implant materials. PMID:20884181

A mathematical model of the influence of salivary urea on the pH of fasted dental plaque and on the changes occurring during a cariogenic challenge.

PubMed

Dibdin, G H; Dawes, C

1998-01-01

Urea diffusing from saliva into dental plaque is converted to ammonia and carbon dioxide by bacterial ureases. The influence of normal salivary urea levels on the pH of fasted plaque and on the depth and duration of a Stephan curve is uncertain. A numerical model which simulates a cariogenic challenge (a 10% sucrose rinse alone or one followed by use of chewing-gum with or without sugar) was modified to include salivary urea levels from 0 to 30 mmol/l. It incorporated: site-dependent exchange between bulk saliva and plaque surfaces via a salivary film; sugar and urea diffusion into plaque; pH-dependent rates of acid formation and urea breakdown; diffusion and dissociation of end-products and other buffers (acetate, lactate, phosphate, ammonia and carbonate); diffusion of protons and other ions; equilibration with fixed and mobile buffers; and charge-coupling between ionic flows. The Km (2.12 mmol/l) and Vmax (0.11 micromol urea/min/mg dry weight) values for urease activity and the pH dependence of Vmax were taken from the literature. From the results, it is predicted that urea concentrations normally present in saliva (3-5 mmol/l) will increase the pH at the base of a 0.5-mm-thick fasted plaque by up to 1 pH unit, and raise the pH minimum after a sucrose rinse or sugar-containing chewing-gum by at least half a pH unit. The results suggest that plaque cariogenicity may be inversely related to salivary urea concentrations, not only when the latter are elevated because of disease, but even when they are in the normal range.

Examination and Manipulation of Protein Surface Charge in Solution with Electrospray Ionization Mass Spectrometry

ERIC Educational Resources Information Center

Gross, Deborah S.; Van Ryswyk, Hal

2014-01-01

Electrospray ionization mass spectrometry (ESI-MS) is a powerful tool for examining the charge of proteins in solution. The charge can be manipulated through choice of solvent and pH. Furthermore, solution-accessible, protonated lysine side chains can be specifically tagged with 18-crown-6 ether to form noncovalent adducts. Chemical derivatization…

Variation in bacterial ATP concentration during rapid changes in extracellular pH and implications for the activity of attached bacteria.

PubMed

Albert, Lynal S; Brown, Derick G

2015-08-01

In this study we investigated the relationship between a rapid change in extracellular pH and the alteration of bacterial ATP concentration. This relationship is a key component of a hypothesis indicating that bacterial bioenergetics - the creation of ATP from ADP via a proton gradient across the cytoplasmic membrane - can be altered by the physiochemical charge-regulation effect, which results in a pH shift at the bacteria's surface upon adhesion to another surface. The bacterial ATP concentration was measured during a rapid change in extracellular pH from a baseline pH of 7.2 to pH values between 3.5 and 10.5. Experiments were conducted with four neutrophilic bacterial strains, including the Gram-negative Escherichia coli and Pseudomonas putida and the Gram-positive Bacillus subtilis and Staphylococcus epidermidis. A change in bulk pH produced an immediate response in bacterial ATP, demonstrating a direct link between changes in extracellular pH and cellular bioenergetics. In general, the shifts in ATP were similar across the four bacterial strains, with results following an exponential relationship between the extracellular pH and cellular ATP concentration. One exception occurred with S. epidermidis, where there was no variation in cellular ATP at acidic pH values, and this finding is consistent with this species' ability to thrive under acidic conditions. These results provide insight into obtaining a desired bioenergetic response in bacteria through (i) the application of chemical treatments to vary the local pH and (ii) the selection and design of surfaces resulting in local pH modification of attached bacteria via the charge-regulation effect. Copyright © 2015 Elsevier B.V. All rights reserved.

Removal of aniline and phenol from water using raw and aluminum hydroxide-modified diatomite.

PubMed

Wu, C D; Zhang, J Y; Wang, L; He, M H

2013-01-01

The feasibility of using raw diatomite and aluminum hydroxide-modified diatomite (Al-diatomite) for removal of aniline and phenol from water was investigated. Their physicochemical characteristics such as pHsolution, point of zero charge (pHPZC), surface area, Fourier transform infrared (FT-IR) and scanning electron microscopy was determined. After the raw diatomite was modified, the surface area of Al-diatomite increases from 26.67 to 82.65 m(2) g(-1). The pHPZC and pHsolution (10%) occurred around pH 5.2 and pH 8.6, respectively. The removal rates of aniline and phenol on diatomite and Al-diatomite decreased with increasing solution pH, while surface charge density decreased. The adsorption of aniline and phenol on diatomite presented a good fit to the Langmuir and Freundlich models, but the models are not fit to forecast the adsorption of aniline and phenol on Al-diatomite. The study indicated that electrostatic interaction was a dominating mechanism of aniline and phenol sorption onto Al-diatomite.

Albumin adsorption on CoCrMo alloy surfaces

NASA Astrophysics Data System (ADS)

Yan, Yu; Yang, Hongjuan; Su, Yanjing; Qiao, Lijie

2015-12-01

Proteins can adsorb on the surface of artificial joints immediately after being implanted. Although research studying protein adsorption on medical material surfaces has been carried out, the mechanism of the proteins’ adsorption which affects the corrosion behaviour of such materials still lacks in situ observation at the micro level. The adsorption of bovine serum albumin (BSA) on CoCrMo alloy surfaces was studied in situ by AFM and SKPFM as a function of pH and the charge of CoCrMo alloy surfaces. Results showed that when the specimens were uncharged, hydrophobic interaction could govern the process of the adsorption rather than electrostatic interaction, and BSA molecules tended to adsorb on the surfaces forming a monolayer in the side-on model. Results also showed that adsorbed BSA molecules could promote the corrosion process for CoCrMo alloys. When the surface was positively charged, the electrostatic interaction played a leading role in the adsorption process. The maximum adsorption occurred at the isoelectric point (pH 4.7) of BSA.

Structure-charge relationship - the case of hematite (001)

DOE PAGES

Lutzenkirchen, Johannes; Heberling, Frank; Supljika, Filip; ...

2015-01-16

We present a multidisciplinary study on the hematite (001)–aqueous solution interface, in particular the relationship between surface structure (studied via surface diffraction in a humid atmosphere) and the macroscopic charging (studied via surface- and zeta-potential measurements in electrolyte solutions as a function of pH). Upon aging in water changes in the surface structure are observed, that are accompanied by drastic changes in the zeta-potential. Surprisingly the surface potential is not accordingly affected. We interpret our results by increasing hydration of the surface with time and enhanced reactivity of singly-coordinated hydroxyl groups that cause the isoelectric point of the surface tomore » shift to values that are reminiscent of those typically reported for hematite particles. In its initial stages after preparation the hematite surface is very flat and only weakly hydrated. Our model links the entailing weak water structure with the observed low isoelectric point reminiscent of hydrophobic surfaces. The absence of an aging effect on the surface potential vs. pH curves is interpreted as domination of the surface potential by the doubly coordinated hydroxyls, which are present on both surfaces.« less

Interdomain electron transfer in cellobiose dehydrogenase is governed by surface electrostatics.

PubMed

Kadek, Alan; Kavan, Daniel; Marcoux, Julien; Stojko, Johann; Felice, Alfons K G; Cianférani, Sarah; Ludwig, Roland; Halada, Petr; Man, Petr

2017-02-01

Cellobiose dehydrogenase (CDH) is a fungal extracellular oxidoreductase which fuels lytic polysaccharide monooxygenase with electrons during cellulose degradation. Interdomain electron transfer between the flavin and cytochrome domain in CDH, preceding the electron flow to lytic polysaccharide monooxygenase, is known to be pH dependent, but the exact mechanism of this regulation has not been experimentally proven so far. To investigate the structural aspects underlying the domain interaction in CDH, hydrogen/deuterium exchange (HDX-MS) with improved proteolytic setup (combination of nepenthesin-1 with rhizopuspepsin), native mass spectrometry with ion mobility and electrostatics calculations were used. HDX-MS revealed pH-dependent changes in solvent accessibility and hydrogen bonding at the interdomain interface. Electrostatics calculations identified these differences to result from charge neutralization by protonation and together with ion mobility pointed at higher electrostatic repulsion between CDH domains at neutral pH. In addition, we uncovered extensive O-glycosylation in the linker region and identified the long-unknown exact cleavage point in papain-mediated domain separation. Transition of CDH between its inactive (open) and interdomain electron transfer-capable (closed) state is shown to be governed by changes in the protein surface electrostatics at the domain interface. Our study confirms that the interdomain electrostatic repulsion is the key factor modulating the functioning of CDH. The results presented in this paper provide experimental evidence for the role of charge repulsion in the interdomain electron transfer in cellobiose dehydrogenases, which is relevant for exploiting their biotechnological potential in biosensors and biofuel cells. Copyright © 2016 Elsevier B.V. All rights reserved.

High-Sensitivity Surface-Enhanced Raman Scattering (SERS) Substrate Based on a Gold Colloid Solution with a pH Change for Detection of Trace-Level Polycyclic Aromatic Hydrocarbons in Aqueous Solution.

PubMed

Shi, Xiaofeng; Liu, Shu; Han, Xiaohong; Ma, Jun; Jiang, Yongchao; Yu, Guifeng

2015-05-01

In this study, a gold colloid solution whose parameters were optimized, and without any surfactants, was developed as a surface-enhanced Raman scattering (SERS) substrate for the detection of trace-level polycyclic aromatic hydrocarbons (PAHs). A gold colloid solution with 57 nm gold particles and pH 13 was prepared to be the SERS substrate. It had impressive enhancement that was two orders of magnitude higher than that of a gold colloid solution with 57 nm gold particles and without pH change (pH 6). Even with a compact field-based Raman spectrometer, naphthalene, phenanthrene, anthracene, fluoranthene, and pyrene were detected, with limits of detection at 6.8 nM, 3.4 nM, 1.8 nM, 0.68 nM (680 pM), and 0.44 nM (440 pM), respectively. The significant enhancement was ascribed to an electromagnetic mechanism and a charge-transfer mechanism. Quantitative analyses for these five PAHs in water were also performed. The SERS intensities of PAHs were found to have good linear dependence relations with the concentrations in low concentration. This high-sensitivity, easily prepared substrate offers a promising technology for the quantitative detection of trace-level PAHs.

On the pH Dependence of the Potential of Maximum Entropy of Ir(111) Electrodes.

PubMed

Ganassin, Alberto; Sebastián, Paula; Climent, Víctor; Schuhmann, Wolfgang; Bandarenka, Aliaksandr S; Feliu, Juan

2017-04-28

Studies over the entropy of components forming the electrode/electrolyte interface can give fundamental insights into the properties of electrified interphases. In particular, the potential where the entropy of formation of the double layer is maximal (potential of maximum entropy, PME) is an important parameter for the characterization of electrochemical systems. Indeed, this parameter determines the majority of electrode processes. In this work, we determine PMEs for Ir(111) electrodes. The latter currently play an important role to understand electrocatalysis for energy provision; and at the same time, iridium is one of the most stable metals against corrosion. For the experiments, we used a combination of the laser induced potential transient to determine the PME, and CO charge-displacement to determine the potentials of zero total charge, (E PZTC ). Both PME and E PZTC were assessed for perchlorate solutions in the pH range from 1 to 4. Surprisingly, we found that those are located in the potential region where the adsorption of hydrogen and hydroxyl species takes place, respectively. The PMEs demonstrated a shift by ~30 mV per a pH unit (in the RHE scale). Connections between the PME and electrocatalytic properties of the electrode surface are discussed.

Influence of environmental factors on pesticide adsorption by black carbon: pH and model dissolved organic matter.

PubMed

Qiu, Yuping; Xiao, Xiaoyu; Cheng, Haiyan; Zhou, Zunlong; Sheng, G Daniel

2009-07-01

Loading two organic acids of known molecular structures onto a black carbon was conducted to study the influence of pH and dissolved organic matter on the adsorption of pesticides. Tannic acid at the loading rates of 100 and 300 micromol/g reduced the surface area of black carbon by 18 and 63%, respectively. This was due principally to the blockage of micropores, as verified by measured pore volumes and pore-size distributions. With a comparatively much smaller molecular structure, gallic acid did not apparently influence these properties. The intrinsic acidities of the two acids increased the surface acidity from 1.88 mmol/g of black carbon to 1.93-2.02 mmol/g after DOM loading, resulting in a reduction in isoelectric point pH from 1.93 to 1.66-1.82. The adsorption of propanil, 2,4-D and prometon by black carbon free and loaded of DOM was dependent on pH because major adsorptive forces were the interactions between neutral pesticide molecules and uncharged carbon surfaces. The adsorption was diminished considerably by the deprotonation of 2,4-D and protonation of prometon, as well as the surface charge change of black carbon. Tannic acid of 100 and 300 micromol/g on black carbon reduced the pesticide adsorption at the equilibrium concentration of 10 mg/L by an average of 46 and 81%, respectively, consistent with the reductions of 42 and 81% in micropore volume. At the equilibrium concentration of 30 mg/L, the mesopore surface became the additional adsorptive domain for propanil. Loading tannic acid made the mesopore surface less accessible, due presumably to the enhanced obstruction by tannic acid.

Application of the method of images on electrostatic phenomena in aqueous Al2O3 and ZrO2 suspensions.

PubMed

Cordelair, Jens; Greil, Peter

2003-09-15

A new solution for the Poisson equation for the diffuse part of the double layer around spherical particles will be presented. The numerical results are compared with the solution of the well-known DLVO theory. The range of the diffuse layer differs considerably in the two theories. Also, the inconsistent representation of the surface and diffuse layer charge in the DLVO theory do not occur in the new theory. Experimental zeta potential measurements were used to determine the charge of colloidal Al2O3 and ZrO2 particles. It is shown that the calculated charge can be interpreted as a superposition of independent H+ and OH- adsorption isotherms. The corresponding Langmuir adsorption isotherms are taken to model the zeta potential dependence on pH. In the vicinity of the isoelectric point the model fits well with the experimental data, but at higher ion concentrations considerable deviations occur. The deviations are discussed. Furthermore, the numerical results for the run of the potential in the diffuse part of the double layer were used to determine the electrostatic interaction potential between the particles in correlation with the zeta potential measurements. The corresponding total interaction potentials, including the van der Waals attraction, were taken to calculate the coagulation half-life for a suspension with a particle loading of 2 vol%. It is shown that stability against coagulation is maintained for Al2O3 particles in the pH region between 3.3 and 7 and for ZrO2 only around pH 5. Stability against flocculation can be achieved in the pH regime between 4.5 and 7 for Al2O3, while the examined ZrO2 particles are not stable against flocculation in aqueous suspensions.

Facile Synthesis of Nitrogen Doped Graphene Oxide from Graphite Flakes and Powders: A Comparison of Their Surface Chemistry.

PubMed

Yokwana, Kholiswa; Ray, Sekhar C; Khenfouch, Mohammad; Kuvarega, Alex T; Mamba, Bhekie B; Mhlanga, Sabelo D; Nxumalo, Edward N

2018-08-01

Nitrogen-doped graphene oxide (NGO) nanosheets were prepared via a facile one-pot modified Hummer's approach at low temperatures using graphite powder and flakes as starting materials in the presence of a nitrogen precursor. It was found that the morphology, structure, composition and surface chemistry of the NGO nanosheets depended on the nature of the graphite precursor used. GO nanosheets doped with nitrogen atoms exhibited a unique structure with few thin layers and wrinkled sheets, high porosity and structural defects. NGO sheets made from graphite powder (NGOp) exhibited excellent thermal stability and remarkably high surface area (up to 240.53 m2 ·g-1) compared to NGO sheets made from graphite flakes (NGOf) which degraded at low temperatures and had an average surface area of 24.70 m2 ·g-1. NGOf sheets had a size range of 850 to 2200 nm while NGOp sheets demonstrated obviously small sizes (460-1600 nm) even when exposed to different pH conditions. The NGO nanosheets exhibited negatively charged surfaces in a wide pH range (1 to 12) and were found to be stable above pH 6. In addition, graphite flakes were found to be more suitable for the production of NGO as they produced high N-doping levels (0.65 to 1.29 at.%) compared to graphite powders (0.30 to 0.35 at.%). This study further demonstrates that by adjusting the amount of N source in the host GO, one can tailor its thermal stability, surface morphology, surface chemistry and surface area.

Measurement of clay surface areas by polyvinylpyrrolidone (PVP) sorption and its use for quantifying illite and smectite abundance

USGS Publications Warehouse

Blum, A.E.; Eberl, D.D.

2004-01-01

A new method has been developed for quantifying smectite abundance by sorbing polyvinylpyrrolidone (PVP) on smectite particles dispersed in aqueous solution. The sorption density of PVP-55K on a wide range of smectites, illites and kaolinites is ~0.99 mg/m2, which corresponds to ~0.72 g of PVP-55K per gram of montmorillonite. Polyvinylpyrrolidone sorption on smectites is independent of layer charge and solution pH. PVP sorption on SiO2, Fe2O3 and ZnO normalized to the BET surface area is similar to the sorption densities on smectites. γ-Al2O3, amorphous Al(OH)3 and gibbsite have no PVP sorption over a wide range of pH, and sorption of PVP by organics is minimal. The insensitivity of PVP sorption densities to mineral layer charge, solution pH and mineral surface charge indicates that PVP sorption is not localized at charged sites, but is controlled by more broadly distributed sorption mechanisms such as Van der Waals’ interactions and/or hydrogen bonding. Smectites have very large surface areas when dispersed as single unit-cell-thick particles (~725 m2/g) and usually dominate the total surface areas of natural samples in which smectites are present. In this case, smectite abundance is directly proportional to PVP sorption. In some cases, however, the accurate quantification of smectite abundance by PVP sorption may require minor corrections for PVP uptake by other phases, principally illite and kaolinite. Quantitative XRD can be combined with PVP uptake measurements to uniquely determine the smectite concentration in such samples.

Electrodynamics of Lipid Membrane Interactions in the Presence of Zwitterionic Buffers

PubMed Central

Koerner, Megan M.; Palacio, Luis A.; Wright, Johnnie W.; Schweitzer, Kelly S.; Ray, Bruce D.; Petrache, Horia I.

2011-01-01

Due to thermal motion and molecular polarizability, electrical interactions in biological systems have a dynamic character. Zwitterions are dipolar molecules that typically are highly polarizable and exhibit both a positive and a negative charge depending on the pH of the solution. We use multilamellar structures of common lipids to identify and quantify the effects of zwitterionic buffers that go beyond the control of pH. We use the fact that the repeat spacing of multilamellar lipid bilayers is a sensitive and accurate indicator of the force balance between membranes. We show that common buffers can in fact charge up neutral membranes. However, this electrostatic effect is not immediately recognized because of the concomitant modification of dispersion (van der Waals) forces. We show that although surface charging can be weak, electrostatic forces are significant even at large distances because of reduced ionic screening and reduced van der Waals attraction. The zwitterionic interactions that we identify are expected to be relevant for interfacial biological processes involving lipid bilayers, and for a wide range of biomaterials, including amino acids, detergents, and pharmaceutical drugs. An appreciation of zwitterionic electrodynamic character can lead to a better understanding of molecular interactions in biological systems and in soft materials in general. PMID:21767488

Designing carboxymethyl cellulose based layer-by-layer capsules as a carrier for protein delivery.

PubMed

Tripathy, Jasaswini; Raichur, Ashok M

2013-01-01

Stable hollow microcapsules composed of sodium carboxymethyl cellulose (CMC) and poly (allylamine hydrochloride) (PAH) were produced by layer-by-layer adsorption of polyelectrolytes onto CaCO(3) microparticles. Subsequently the core was removed by addition of chelating agents for calcium ions. Zeta potential studies showed charge reversal with deposition of successive polyelectrolyte layers, indicating that the alternate electrostatic adsorption of polyelectrolytes of opposite charge was successfully achieved. The size and surface morphology of the capsules was characterized by various microscopy techniques. The pH responsive loading behavior was elucidated by confocal laser scanning microscopy (CLSM) studies using fluorescence labeled dextran (FITC-dextran) and labeled BSA (FITC-BSA). CLSM images confirmed the open (pH≤6) and closed state (pH≥7) of the capsules. A model drug bovine serum albumin (BSA) was spontaneously loaded below its isoelectric point into hollow microcapsules, where BSA is positively charged. The loading of the BSA into the microcapsules was found to be dependent on the feeding concentration and pH of the medium. 65% of the loaded BSA was released over 7h of which about 34% was released in the first hour. These findings demonstrate that (CMC/PAH)(2) hollow capsules can be further exploited as a potential drug delivery system. Copyright © 2012 Elsevier B.V. All rights reserved.

Interaction of two overlapped synthetic peptides from GB virus C with charged mono and bilayers.

PubMed

Alay, M; Haro, I; Alsina, M A; Girona, V; Prat, J; Busquets, M A

2013-05-01

The physical chemistry properties and interactions of E2 (125-139) and E2 (120-139) peptide sequences from GB virus C with model cell membranes were investigated by means of several biophysical techniques in order to gain better understanding of the effect of peptide length and lipid charge on membrane binding. The peptides, having one net negative charge at the pH of the assays, interacted with monolayers of all the phospholipids regardless of the charge but with more extent with the cationic DPTAP thus indicating that the interaction had both a hydrophobic and an electrostatic component as has been observed for other peptides of the same family. The peptides were able to leakage contents of liposomes and showed fluorescence energy transfer in vesicles depending on the vesicles lipid composition. On another hand, circular dichroism has shown that the peptides exist mainly as a mixture of disordered structure and β-type conformations in aqueous solution but diminished its unstructured content, folding preferentially into α-helical conformation upon interaction with hydrophobic solvents or positively charged lipid surfaces. Altogether, results of this work indicate that the peptides interact at a surface level, penetrate into bilayers composed of fluid lipids and that conformational changes could be responsible for this effect. Copyright © 2012 Elsevier B.V. All rights reserved.

Electrochromatographic retention of peptides on strong cation-exchange stationary phases.

PubMed

Nischang, Ivo; Höltzel, Alexandra; Tallarek, Ulrich

2010-03-01

We analyze the systematic and substantial electrical field-dependence of electrochromatographic retention for four counterionic peptides ([Met5]enkephalin, oxytocin, [Arg8]vasopressin, and luteinizing hormone releasing hormone (LHRH) ) on a strong cation-exchange (SCX) stationary phase. Our experiments show that retention behavior in the studied system depends on the charge-selectivity of the stationary phase particles, the applied voltage, and the peptides' net charge. Retention factors of twice positively charged peptides ([Arg8]vasopressin and LHRH at pH 2.7) decrease with increasing applied voltage, whereas lower charged peptides (oxytocin and [Met5]enkephalin at pH 2.7, [Arg8]vasopressin and LHRH at pH 7.0) show a concomitant increase in their retention factors. The observed behavior is explained on the basis of electrical field-induced concentration polarization (CP) that develops around the SCX particles of the packing. The intraparticle concentration of charged species (buffer ions, peptides) increases with increasing applied voltage due to diffusive backflux from the enriched CP zone associated with each SCX particle. For twice charged and on the SCX phase strongly retained peptides the local increase in mobile phase ionic strength reduces the electrostatic interactions with the stationary phase, which explains the decrease of retention factors with increasing applied voltage and CP intensity. Lower charged and weaker retained peptides experience a much stronger relative intraparticle enrichment than the twice-charged peptides, which results in a net increase of retention factors with increasing applied voltage. The CP-related contribution to electrochromatographic retention of peptides on the SCX stationary phase is modulated by the applied voltage, the mobile phase ionic strength, and the peptides' net charge and could be used for selectivity tuning in difficult separations.

AFM Study of Charge Transfer Between Metals Due to the Oxygen Redox Couple in Water

NASA Astrophysics Data System (ADS)

Trombley, Jeremy; Panthani, Tessie; Sankaran, Mohan; Angus, John; Kash, Kathleen

2010-03-01

The oxygen redox couple in an adsorbed water film can pin the Fermi level at the surfaces of diamond, GaN and ZnO.footnotetextV. Chakrapani, C. Pendyala, K. Kash, A. B. Anderson, M. K. Sunkara and J. C. Angus, J. Am. Chem. Soc. 130 (2008) 12944-12952, and ref. 6 therein. We report here preliminary observations of the same phenomenon at metal surfaces. A Pt-coated atomic force microscope (AFM) tip was used to take force-distance measurements on Au, Ag, and Pt surfaces placed in pH-controlled water. The work functions of these surfaces vary over ˜2eV and span the electrochemical potential range of the oxygen redox couple, which varies with pH according to the Nernst equation. Adjusting the pH of the water from 4 to 12 allowed us to change the redox potential energy from -5.42eV to -4.95eV, changing the surface charge and the associated screening charge and modulating the pull-off force. This work has relevance to AFM of many materials in air, and to contact electrification, mechanical friction, and nanoscale corona discharges.

Pedogenic formation of montmorillonite from a 2:1-2:2 intergrade clay mineral

USGS Publications Warehouse

Malcolm, R.L.; Nettleton, W.D.; McCracken, R.J.

1968-01-01

Montmorillonite was found to be the dominant clay mineral in surface horizons of certain soils of the North Carolina Coastal Plain whereas a 2:1-2:2 intergrade clay mineral was dominant in subjacent horizons. In all soils where this clay mineral sequence was found, the surface horizon was low in pH (below 4⋅5) and high in organic matter content. In contrast, data from studies of other soils of this region (Weed and Nelson, 1962) show that: (1) montmorillonite occurs infrequently; (2) maximum accumulation of the 2:1-2:2 intergrade normally occurs in the surface horizon and decreases with depth in the profile; (3) organic matter contents are low; and (4) pH values are only moderately acid (pH 5-6).It is theorized that the montmorillonite in the surface horizon of the soils studied originated by pedogenic weathering of the 2:1-2:2 intergrade clay mineral. The combined effects of low pH (below 4⋅5) and high organic matter content in surface horizons are believed to be the agents responsible for this mineral transformation. The protonation and solubilization (reverse of hydrolysis) of Al-polymers in the interlayer of expansible clay minerals will occur at or below pH 4⋅5 depending on the charge and steric effects of the interlayer. A low pH alone may cause this solubilization and thus mineral transformation, but in the soils studied the organic matter is believed to facilitate and accelerage the transformation. The intermediates of organic matter decomposition provide an acid environment, a source of protons, and a source of watersoluble mobile organic substances (principally fulvic acids) which have the ability to complex the solubilized aluminum and move it down the profile. This continuous removal of solubilized aluminum would provide for a favorable gradient for aluminum solubilization.The drainage class or position in a catena is believed to be less important than the chemical factors in formation of montmorillonite from 2:1-2:2 intergrade, because montmorillonite is present in all drainage classes if the surface horizon is low in pH and high in organic matter.

pH and generation dependent morphologies of PAMAM dendrimers on a graphene substrate.

PubMed

Gosika, Mounika; Maiti, Prabal K

2018-03-07

The adsorption of PAMAM dendrimers at solid/water interfaces has been extensively studied, and is mainly driven by electrostatic and van der Waals interactions between the substrate and the dendrimers. However, the pH dependence of the adsorption driven predominantly by the van der Waals interactions is poorly explored, although it is crucial for investigating the potentiality of these dendrimers in supercapacitors and surface patterning. Motivated by this aspect, we have studied the adsorption behavior of PAMAM dendrimers of generations 2 (G2) to 5 (G5) with pH and salt concentration variation, on a charge neutral graphene substrate, using fully atomistic molecular dynamics simulations. The instantaneous snapshots from our simulations illustrate that the dendrimers deform significantly from their bulk structures. Based on various structural property calculations, we classify the adsorbed dendrimer morphologies into five categories and map them to a phase diagram. Interestingly, the morphologies we report here have striking analogies with those reported in star-polymer adsorption studies. From the fractional contacts and other structural property analyses we find that the deformations are more pronounced at neutral pH as compared to high and low pH. Higher generation dendrimers resist deformation following the deformation trend, G2 > G3 > G4 > G5 at any given pH level. As the adsorption here is mainly driven by van der Waals interactions, we observe no desorption of the dendrimers as the salt molarity is increased, unlike that reported in the electrostatically driven adsorption studies.

Rheological behavior of clay-nanoparticle hybrid-added bentonite suspensions: specific role of hybrid additives on the gelation of clay-based fluids.

PubMed

Jung, Youngsoo; Son, You-Hwan; Lee, Jung-Kun; Phuoc, Tran X; Soong, Yee; Chyu, Minking K

2011-09-01

Two different types of clay nanoparticle hybrid, iron oxide nanoparticle clay hybrid (ICH) and Al(2)O(3)-SiO(2) nanoparticle clay hybrid (ASCH), were synthesized and their effects on the rheological properties of aqueous bentonite fluids in steady state and dynamic state were explored. When ICH particles were added, bentonite particles in the fluid cross-link to form relatively well-oriented porous structure. This is attributed to the development of positively charged edge surfaces in ICH that leads to strengthening of the gel structure of the bentonite susensions. The role of ASCH particles on the interparticle association of the bentonite fluids is different from that of ICH and sensitive to pH. As pH of ASCH-added bentonite suspensions increased, the viscosity, yield stress, storage modulus, and flow stress decreased. In contrast, at low pH, the clay suspensions containing ASCH additives were coagulated and their rheological properties become close to those of ICH added bentonite fluids. A correlation between the net surface charge of the hybrid additives and the rheological properties of the fluids indicates that the embedded nanoparticles within the interlayer space control the variable charge of the edge surfaces of the platelets and determine the particles association behavior of the clay fluids.

Sorption of the organic cation metoprolol on silica gel from its aqueous solution considering the competition of inorganic cations.

PubMed

Kutzner, Susann; Schaffer, Mario; Börnick, Hilmar; Licha, Tobias; Worch, Eckhard

2014-05-01

Systematic batch experiments with the organic monovalent cation metoprolol as sorbate and the synthetic material silica gel as sorbent were conducted with the aim of characterizing the sorption of organic cations onto charged surfaces. Sorption isotherms for metoprolol (>99% protonated in the tested pH of around 6) in competition with mono- and divalent inorganic cations (Na(+), NH4(+), Ca(2+), and Mg(2+)) were determined in order to assess their influence on cation exchange processes and to identify the role of further sorptive interactions. The obtained sorption isotherms could be described well by an exponential function (Freundlich isotherm model) with consistent exponents (about 0.8). In general, a decreasing sorption of metoprolol with increasing concentrations in inorganic cations was observed. Competing ions of the same valence showed similar effects. A significant sorption affinity of metoprolol with ion type dependent Freundlich coefficients KF,0.77 between 234.42 and 426.58 (L/kg)(0.77) could still be observed even at very high concentrations of competing inorganic cations. Additional column experiments confirm this behavior, which suggests the existence of further relevant interactions beside cation exchange. In subsequent batch experiments, the influence of mixtures with more than one competing ion and the effect of a reduced negative surface charge at a pH below the point of zero charge (pHPZC ≈ 2.5) were also investigated. Finally, the study demonstrates that cation exchange is the most relevant but not the sole mechanism for the sorption of metoprolol on silica gel. Copyright © 2014 Elsevier Ltd. All rights reserved.

Humic acid facilitates the transport of ARS-labeled hydroxyapatite nanoparticles in iron oxyhydroxide-coated sand.

PubMed

Wang, Dengjun; Bradford, Scott A; Harvey, Ronald W; Gao, Bin; Cang, Long; Zhou, Dongmei

2012-03-06

Hydroxyapatite nanoparticles (nHAP) have been widely used to remediate soil and wastewater contaminated with metals and radionuclides. However, our understanding of nHAP transport and fate is limited in natural environments that exhibit significant variability in solid and solution chemistry. The transport and retention kinetics of Alizarin red S (ARS)-labeled nHAP were investigated in water-saturated packed columns that encompassed a range of humic acid concentrations (HA, 0-10 mg L(-1)), fractional surface coverage of iron oxyhydroxide coatings on sand grains (λ, 0-0.75), and pH (6.0-10.5). HA was found to have a marked effect on the electrokinetic properties of ARS-nHAP, and on the transport and retention of ARS-nHAP in granular media. The transport of ARS-nHAP was found to increase with increasing HA concentration because of enhanced colloidal stability and the reduced aggregate size. When HA = 10 mg L(-1), greater ARS-nHAP attachment occurred with increasing λ because of increased electrostatic attraction between negatively charged nanoparticles and positively charged iron oxyhydroxides, although alkaline conditions (pH 8.0 and 10.5) reversed the surface charge of the iron oxyhydroxides and therefore decreased deposition. The retention profiles of ARS-nHAP exhibited a hyperexponential shape for all test conditions, suggesting some unfavorable attachment conditions. Retarded breakthrough curves occurred in sands with iron oxyhydroxide coatings because of time-dependent occupation of favorable deposition sites. Consideration of the above effects is necessary to improve remediation efficiency of nHAP for metals and actinides in soils and subsurface environments.

Atomistic and molecular effects in electric double layers at high surface charges

DOE PAGES

Templeton, Jeremy Alan; Lee, Jonathan; Mani, Ali

2015-06-16

Here, the Poisson–Boltzmann theory for electrolytes near a charged surface is known to be invalid due to unaccounted physics associated with high ion concentration regimes. In order to investigate this regime, fluids density functional theory (f-DFT) and molecular dynamics (MD) simulations were used to determine electric surface potential as a function of surface charge. Based on these detailed computations, for electrolytes with nonpolar solvent, the surface potential is shown to depend quadratically on the surface charge in the high charge limit. We demonstrate that modified Poisson–Boltzmann theories can model this limit if they are augmented with atomic packing densities providedmore » by MD. However, when the solvent is a highly polar molecule water an intermediate regime is identified in which a constant capacitance is realized. Simulation results demonstrate the mechanism underlying this regime, and for the salt water system studied here, it persists throughout the range of physically realistic surface charge densities so the potential’s quadratic surface charge dependence is not obtained.« less

Prediction of purification of biopharmeceuticals with molecular dynamics

NASA Astrophysics Data System (ADS)

Ustach, Vincent; Faller, Roland

Purification of biopharmeceuticals remains the most expensive part of protein-based drug production. In ion exchange chromatography (IEX), prediction of the elution ionic strength of host cell and target proteins has the potential to reduce the parameter space for scale-up of protein production. The complex shape and charge distribution of proteins and pores complicates predictions of the interactions in these systems. All-atom molecular dynamics methods are beyond the scope of computational limits for mass transport regimes. We present a coarse-grained model for proteins for prediction of elution pH and ionic strength. By extending the raspberry model for colloid particles to surface shapes and charge distributions of proteins, we can reproduce the behavior of proteins in IEX. The average charge states of titratatable amino acid residues at relevant pH values are determined by extrapolation from all-atom molecular dynamics at pH 7. The pH specific all-atom electrostatic field is then mapped onto the coarse-grained surface beads of the raspberry particle. The hydrodynamics are reproduced with the lattice-Boltzmann scheme. This combination of methods allows very long simulation times. The model is being validated for known elution procedures by comparing the data with experiments. Defense Threat Reduction Agency (Grant Number HDTRA1-15-1-0054).

Morphological driven photocatalytic activity of ZnO nanostructures

NASA Astrophysics Data System (ADS)

Abbas, Khaldoon N.; Bidin, Noriah

2017-02-01

Using a simple combination of pulse laser ablation in liquid and hydrothermal (PLAL-H) approaches, we control the morphology of ZnO nanostructures (ZNSs) to determine the feasibility of their photocatalytic efficacy. These ZNSs are deposited on Si (100) substrates and two different morphologies are achieved. In this synergistic approach, PLAL synthesized NSs are used as a nutrient solution with different pH for further hydrothermal treatment at 110 °C under varying growth time (5, 30 and 60 min). Surface morphology, structure, composition, and optical characteristics of the prepared ZNSs are determined using FESEM, XRD, FTIR and Photoluminescence (PL) and UV-vis absorption measurements. The morphology revealed remarkable transformation from nanorods (NRs)/nanoflowers (NFs) (at pH 7.6) to nanoparticles (NPs)-like (at pH 10.5) structure. XRD patterns showed better polycrystallinity for NPs with enlarged band gap than NR/NF-like structures. Both PL and UV-vis spectral analysis of ZNPs exhibited higher surface area and deep level defects density dependent morphology, where the nutrient pH and growth time variation are found to play a significant role towards structural evolution. Furthermore, the photocatalytic activities of, such ZNSs are evaluated via sunlight driven photo-degradation of methylene blue (MB) dye. The photocatalytic efficiency of ZNPs is demonstrated to be much superior (97.4%) than ZNRs/ZNFs-like morphology (86%). Such enhanced photocatalytic activities of as-synthesized ZNPs is attributed to the synergism of the improved surface area and defects density, which is useful for promoting the adsorption of the MB dye and suppressed surface recombination of photo-generated charge carriers.

Zeta Potential and Aggregation of Virus-Like Particle of Human Norovirus and Feline Calicivirus Under Different Physicochemical Conditions.

PubMed

Samandoulgou, Idrissa; Fliss, Ismaïl; Jean, Julie

2015-09-01

Although the spread of human norovirus reportedly depends on its ability to bind to food materials, the mechanism of the phenomenon remains unknown. Since protein size and electrical charge are reportedly important parameters in their adsorption, the current work is focused on determining human noroviruses isoelectric point (IEP), electrical charge and aggregate size at different pH, ionic strength (IS), and temperature. Using the baculovirus expression vector system, we produced and purified virus-like particles (VLPs) of GI.1 and GII.4 noroviruses and feline calicivirus, determined their IEP, and examined their size and electrical charge using a Zetasizer Nano ZS apparatus. Shape and size were also visualized using transmission electron microscopy. IEPs were found close to pH 4. Net charge increased as the pH deviated from the IEP. VLPs were negatively charged at all IS tested and showed a gradual decrease in charge with increasing IS. At low temperature, VLPs were 20-45 nm in diameter at pH far from their IEP and under almost all IS conditions, while aggregates appeared at or near the IEP. At increased temperatures, aggregates appeared at or near the IEP and at high IS. Aggregation at the IEP was also confirmed by microscopy. This suggests that electrostatic interactions would be the predominant factor in VLPs adhesion at pH far from 4 and at low ionic strength. In contrast, non-electrostatic interactions would prevail at around pH 4 and would be reinforced by aggregates, since size generally favors multiple bonding with sorbents.

CO2 controlled flocculation of microalgae using pH responsive cellulose nanocrystals

NASA Astrophysics Data System (ADS)

Eyley, Samuel; Vandamme, Dries; Lama, Sanjaya; van den Mooter, Guy; Muylaert, Koenraad; Thielemans, Wim

2015-08-01

Cellulose nanocrystals were grafted with imidazole functionalities up to DS 0.06 using a one-pot functionalization strategy. The resulting nanocrystals were shown to have a pH responsive surface charge which was found to be positive below pH 6 and negative above pH 7. These imidazolyl cellulose nanocrystals were tested for flocculation of Chlorella vulgaris using CO2 to induce flocculation. Up to 90% flocculation efficiency was achieved with 200 mg L-1 dose. Furthermore, the modified cellulose nanocrystals showed good compatibility with the microalgae during cultivation, giving potential for the production of reversible flocculation systems.Cellulose nanocrystals were grafted with imidazole functionalities up to DS 0.06 using a one-pot functionalization strategy. The resulting nanocrystals were shown to have a pH responsive surface charge which was found to be positive below pH 6 and negative above pH 7. These imidazolyl cellulose nanocrystals were tested for flocculation of Chlorella vulgaris using CO2 to induce flocculation. Up to 90% flocculation efficiency was achieved with 200 mg L-1 dose. Furthermore, the modified cellulose nanocrystals showed good compatibility with the microalgae during cultivation, giving potential for the production of reversible flocculation systems. Electronic supplementary information (ESI) available: Spectra for all products. See DOI: 10.1039/C5NR03853G

Interfacial charging phenomena of aluminum (hydr)oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hiemstra, T.; Yong, H.; Van Riemsdijk, W.H.

1999-08-31

The interfacial charging of Al(OH){sub 3} (gibbsite and bayerite) and Al{sub 2}O{sub 3} has been studied. For Al(OH){sub 3} it can be shown that the very strong variation in charging behavior for different preparations is related to the relative presence of differently reacting crystal planes. The edge faces of the hexagonal gibbsite crystals are proton reactive over the whole pH range, in contrast to the 001 plane, which is mainly uncharged below pH = 10. On this 001 face only doubly coordinated surface groups are found, in contrast to the edges which also have singly coordinated surface groups. The resultsmore » are fully in agreement with the predictions of the Multi site complexation (MUSIC) model. The proton adsorption, electrolyte ion adsorption, and shift of the IEP of gibbsite and aluminum oxide have been modeled simultaneously. For gibbsite, the ion pair formation of Na is larger than that of Cl, as is evidenced by modeling the experimentally observed upward shift on the IEP and charge reversal at high electrolyte concentrations. All these experimental results can be satisfactorily modeled with the MUSIC model, including the experimental surface potential of aluminum oxide (ISFET).« less

Spherical LDH-Ag°-montmorillonite heterocoagulated system with a pH-dependent sol-gel structure for controlled accessibility of AgNPs immobilized on the clay lamellae.

PubMed

Deák, Ágota; Janovák, László; Tallósy, Szabolcs Péter; Bitó, Tamás; Sebők, Dániel; Buzás, Norbert; Pálinkó, István; Dékány, Imre

2015-02-17

Aqueous suspensions of spherical ZnMgAl-layered double hydroxides [LDH(sph)] and antibacterial silver nanoparticles (AgNPs) deposited on the lamellae of montmorillonite were used for the synthesis of composites, which behave like coherent gels at low pH (≲4.5) and incoherent sols at higher pH (≳4.5). The composition of the composite was chosen as LDH(sph)/Ag°-montm. = 25:75 wt % in order to ensure a sol-gel transition that can also be characterized by viscometry. This pH-sensitive heterocoagulated system consisting of oppositely charged colloid particles was suitable for the release of antimicrobial AgNPs immobilized on the clay lamellae via a pH-controlled gel-sol transition. The heterocoagulation process was also characterized by surface charge titration measurements. Spherical LDH/Ag°-montmorillonite composite samples were identified by X-ray diffraction (XRD) measurements. The morphological properties of the composites were studied, and the presence of the heterocoagulated structure was confirmed by scanning electron microscopy (SEM). The nanoscale structure of the LDH(sph)-Ag°-montmorillonite composite obtained was also verified by small-angle X-ray scattering (SAXS), and the rheological characteristics were studied at various pH values. The viscosity and yield value of the composite decreased by an order of magnitude upon increasing the pH from 3.0 to 5.5. The sol-gel transition of the composite suspension was reversible in the previously mentioned pH range.

Zeta Potential Measurements on Solid Surfaces for in Vitro Biomaterials Testing: Surface Charge, Reactivity Upon Contact With Fluids and Protein Absorption

PubMed Central

Ferraris, Sara; Cazzola, Martina; Peretti, Veronica; Stella, Barbara; Spriano, Silvia

2018-01-01

Surface properties of biomaterials (e.g., roughness, chemical composition, charge, wettability, and hydroxylation degree) are key features to understand and control the complex interface phenomena that happens upon contact with physiological fluids. Numerous physico-chemical techniques can be used in order to investigate in depth these crucial material features. Among them, zeta potential measurements are widely used for the characterization of colloidal suspensions, but actually poorly explored in the study of solid surfaces, even if they can give significant information about surface charge in function of pH and indirectly about surface functional groups and reactivity. The aim of the present research is application of zeta potential measurements of solid surfaces for the in vitro testing of biomaterials. In particular, bare and surface modified Ti6Al4V samples have been compared in order to evaluate their isoelectric points (IEPs), surface charge at physiological pH, in vitro bioactivity [in simulated body fluid (SBF)] and protein absorption. Zeta potential titration was demonstrated as a suitable technique for the surface characterization of surface treated Ti6Al4V substrates. Significant shift of the isoelectric point was recorded after a chemical surface treatment (because of the exposition of hydroxyl groups), SBF soaking (because of apatite precipitation IEP moves close to apatite one) and protein absorption (IEP moves close to protein ones). Moreover, the shape of the curve gives information about exposed functional groups (e.g., a plateau in the basic range appears due to the exposition of acidic OH groups and in the acidic range due to exposition of basic NH2 groups). PMID:29868575

Probing the influence of cell surface polysaccharides on nanodendrimer binding to Gram-negative and Gram-positive bacteria using single-nanoparticle force spectroscopy.

PubMed

Beaussart, Audrey; Beloin, Christophe; Ghigo, Jean-Marc; Chapot-Chartier, Marie-Pierre; Kulakauskas, Saulius; Duval, Jérôme F L

2018-06-27

The safe use and design of nanoparticles (NPs) ask for a comprehensive interpretation of their potentially adverse effects on (micro)organisms. In this respect, the prior assessment of the interactions experienced by NPs in the vicinity of - and in contact with - complex biological surfaces is mandatory. It requires the development of suitable techniques for deciphering the processes that govern nano-bio interactions when a single organism is exposed to an extremely low dose of NPs. Here, we used atomic force spectroscopy (AFM)-based force measurements to investigate at the nanoscale the interactions between carboxylate-terminated polyamidoamine (PAMAM) nanodendrimers (radius ca. 4.5 nm) and two bacteria with very distinct surface properties, Escherichia coli and Lactococcus lactis. The zwitterionic nanodendrimers exhibit a negative peripheral surface charge and/or a positive intraparticulate core depending on the solution pH and salt concentration. Following an original strategy according to which a single dendrimer NP is grafted at the very apex of the AFM tip, the density and localization of NP binding sites are probed at the surface of E. coli and L. lactis mutants expressing different cell surface structures (presence/absence of the O-antigen of the lipopolysaccharides (LPS) or of a polysaccharide pellicle). In line with electrokinetic analysis, AFM force measurements evidence that adhesion of NPs onto pellicle-decorated L. lactis is governed by their underlying electrostatic interactions as controlled by the pH-dependent charge of the peripheral and internal NP components, and the negatively-charged cell surface. In contrast, the presence of the O-antigen on E. coli systematically suppresses the adhesion of nanodendrimers onto cells, may the apparent NP surface charge be determined by the peripheral carboxylate groups or by the internal amine functions. Altogether, this work highlights the differentiated roles played by surface polysaccharides in mediating NP attachment to Gram-positive and Gram-negative bacteria. It further demonstrates that the assessment of NP bioadhesion features requires a critical analysis of the electrostatic contributions stemming from the various structures composing the stratified cell envelope, and those originating from the bulk and surface NP components. The joint use of electrokinetics and AFM provides a valuable option for rapidly addressing the binding propensity of NPs to microorganisms, as urgently needed in NP risk assessments.

Gypsum (CaSO4·2H2O) Scaling on Polybenzimidazole and Cellulose Acetate Hollow Fiber Membranes under Forward Osmosis

PubMed Central

Chen, Si Cong; Su, Jincai; Fu, Feng-Jiang; Mi, Baoxia; Chung, Tai-Shung

2013-01-01

We have examined the gypsum (CaSO4·2H2O) scaling phenomena on membranes with different physicochemical properties in forward osmosis (FO) processes. Three hollow fiber membranes made of (1) cellulose acetate (CA), (2) polybenzimidazole (PBI)/polyethersulfone (PES) and (3) PBI-polyhedral oligomeric silsesquioxane (POSS)/polyacrylonitrile (PAN) were studied. For the first time in FO processes, we have found that surface ionic interactions dominate gypsum scaling on the membrane surface. A 70% flux reduction was observed on negatively charged CA and PBI membrane surfaces, due to strong attractive forces. The PBI membrane surface also showed a slightly positive charge at a low pH value of 3 and exhibited a 30% flux reduction. The atomic force microscopy (AFM) force measurements confirmed a strong repulsive force between gypsum and PBI at a pH value of 3. The newly developed PBI-POSS/PAN membrane had ridge morphology and a contact angle of 51.42° ± 14.85° after the addition of hydrophilic POSS nanoparticles and 3 min thermal treatment at 95 °C. Minimal scaling and an only 1.3% flux reduction were observed at a pH value of 3. Such a ridge structure may reduce scaling by not providing a locally flat surface to the crystallite at a pH value of 3; thus, gypsum would be easily washed away from the surface. PMID:24957062

The interplay between pH sensitivity and label-free protein detection in immunologically modified nano-scaled field-effect transistor.

PubMed

Shalev, Gil; Rosenwaks, Yossi; Levy, Ilan

2012-01-15

We present experimental results in order to establish a correlation between pH sensitivity of immunologically modified nano-scaled field-effect transistor (NS-ImmunoFET) with their sensing capacity for label-free detection. The NS-ImmunoFETs are fabricated from silicon-on-insulator (SOI) wafers and are fully-depleted with thickness of ~20 nm. The data shows that higher sensitivity to pH entails enhanced sensitivity to analyte detection. This suggests that the mechanism of analyte detection as pure electrostatic perturbation induced by antibody-analyte interaction is over simplified. The fundamental assumption, in existing models for field-effect sensing mechanism assumes that the analyte molecules do not directly interact with the surface but rather stand 'deep' in the solution and away from the dielectric surface. Recent studies clearly provide contradicting evidence demonstrating that antibodies lie down flat on the surface. These observations led us to propose that the proteins that cover the gate area intimately interact with active sites on the surface thus forming a network of interacting sites. Since sensitivity to pH is directly correlated with the amount of amphoteric sites, we witness a direct correlation between sensitivity to pH and analyte detection. The highest and lowest threshold voltage shift for a label-free and specific detection of 6.5 nM IgG were 40 mV and 2.3 mV for NS-ImmunoFETs with pH sensitivity of 35 mV/decade and 15 mV/decade, respectively. Finally, physical modeling of the NS-ImmunoFET is presented and charge of a single IgG protein at pH 6 is calculated. The obtained value is consistent with charge of IgG protein cited in literature. Copyright © 2011 Elsevier B.V. All rights reserved.

A multifunctional nanocarrier based on nanogated mesoporous silica for enhanced tumor-specific uptake and intracellular delivery.

PubMed

Gao, Yaohua; Yang, Cuihong; Liu, Xue; Ma, Rujiang; Kong, Deling; Shi, Linqi

2012-02-01

A multifunctional drug delivery system based on MCM-41-type mesoporous silica nanoparticles is described that behaves as if nanogates were covalently attached to the outlets of the mesopores through a highly acid-sensitive benzoic-imine linker. Tumor-specific uptake and intracellular delivery results from the pH-dependent progressive hydrolysis of the benzoic-imine linkage that starts at tumor extracellular pH = 6.8 and increases with decreasing pH. The cleavage of the benzoic-imine bond leads to the removal of the polypseudorotaxane caps and subsequent release of the payload drugs at tumor sites. At the same time, the carrier surface becomes positively charged, which further facilitates cellular uptake of the nanocarriers, thus offering a tremendous potential for targeted tumor therapy. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Role of Solution Conditions in the Bacteriophage PP7 Capsid Charge Regulation

DOE PAGES

Nap, Rikkert J.; Bozic, Anze Losdorfer; Szleifer, Igal; ...

2014-10-21

Here, we investigate and quantify the effects of pH and salt concentration on the charge regulation of the bacteriophage PP7 capsid. These effects are found to be extremely important and substantial, introducing qualitative changes in the charge state of the capsid such as a transition from net-positive to net-negative charge depending on the solution pH. The overall charge of the virus capsid arises as a consequence of a complicated balance with the chemical dissociation equilibrium of the amino acids and the electrostatic interaction between them, and the translational entropy of the mobile solution ions, i.e., counterion release. We show thatmore » to properly describe and predict the charging equilibrium of viral capsids in general, one needs to include molecular details as exemplified by the acid-base equilibrium of the detailed distribution of amino acids in the proteinaceous capsid shell.« less

Effects of inorganic electrolyte anions on enrichment of Cu(II) ions with aminated Fe3O4/graphene oxide: Cu(II) speciation prediction and surface charge measurement.

PubMed

Hu, Xin-jiang; Liu, Yun-guo; Zeng, Guang-ming; Wang, Hui; You, Shao-hong; Hu, Xi; Tan, Xiao-fei; Chen, An-wei; Guo, Fang-ying

2015-05-01

The present work evaluated the effects of six inorganic electrolyte anions on Cu(II) removal using aminated Fe3O4/graphene oxide (AMGO) in single- and multi-ion systems. A 2(6-2) fractional factorial design (FFD) was employed for assessing the effects of multiple anions on the adsorption process. The results indicated that the Cu(II) adsorption was strongly dependent on pH and could be significantly affected by inorganic electrolyte anions due to the changes in Cu(II) speciation and surface charge of AMGO. In the single-ion systems, the presence of monovalent anions (Cl(-), ClO4(-), and NO3(-)) slightly increased the Cu(II) adsorption onto AMGO at low pH, while the Cu(II) adsorption was largely enhanced by the presence of SO4(2-), CO3(2-), and HPO4(2-). Based on the estimates of major effects and interactions from FFD, the factorial effects of the six selected species on Cu(II) adsorption in multi-ion system were in the following sequence: HPO4(2-)>CO3(2-)>Cl(-)>SO4(2-)>NO3(-)=ClO4(-), and the combined factors of AD (Cl(-)×SO4(2-)) and EF (Cl(-)×SO4(2-)) had significant effects on Cu(II) removal. Copyright © 2015 Elsevier Ltd. All rights reserved.

In vitro cytotoxicity of iron oxide nanoparticles: effects of chitosan and polyvinyl alcohol as stabilizing agents

NASA Astrophysics Data System (ADS)

Tran, Phong A.; Nguyen, Hiep T.; Fox, Kate; Tran, Nhiem

2018-03-01

Iron oxide magnetic nanoparticles have significant potential in biomedical applications such as in diagnosis, imaging and therapeutic agent delivery. The choice of stabilizers and surface functionalization is important as it is known to strongly influence the cytotoxicity of the nanoparticles. The present study aimed at investigating the effects of surface charges on the cytotoxicity of iron oxide nanoparticles. We used a co-precipitation method to synthesize iron oxide nanoparticles which were then stabilized with either chitosan (CS) or polyvinyl alcohol (PVA) which have net positive charge and zero charge at physiological pH, respectively. The nanoparticles were characterized in terms of size, charges and chemical oxidation state. Cytotoxicity of the nanoparticles was assessed using mouse fibroblast cells and was correlated with surface charges of the nanoparticles and their aggregation.

Molecular interactions in self-assembled nano-structures of chitosan-sodium alginate based polyelectrolyte complexes.

PubMed

Wasupalli, Geeta Kumari; Verma, Devendra

2018-03-16

We report here the self-assembled structures of polyelectrolyte complexes (PECs) of polyanionic sodium alginate with the polycationic chitosan at room temperature. The PECs prepared at different pH values exhibited two distinct morphologies. The chitosan-alginate PECs self-assembled into the fibrous structure in a low pH range of pH3 to 7. The PECs obtained at high pH series around pH8 and above resulted in the formation of colloidal nanoparticles in the range of 120±9.48nm to 46.02±16.66nm. The zeta potential measurement showed that PECs prepared at lower pH (pH<6) exhibited nearly neutral surface charge, whereas PECs prepared at higher pH than 6 exhibited highly negative surface charge. The molecular interactions in nano-colloids and fibers were evaluated using FTIR analysis. The results attest that the ionic state of the chitosan and alginate plays an important role controlling the morphologies of the PECS. The present study has identified the enormous potential of the polyelectrolytes complexes to exploit shape by the alteration of ionic strength. These findings might be useful in the development of novel biomaterial. The produced fibers and nanocolloids could be applied as a biomaterial for tissue engineering and drug delivery. Copyright © 2017. Published by Elsevier B.V.

Drinking water obtaining by nanofiltration from waters contaminated with glyphosate formulations: process evaluation by means of toxicity tests and studies on operating parameters.

PubMed

Saitúa, Hugo; Giannini, Fernando; Padilla, Antonio Perez

2012-08-15

Glyphosate formulations toxicity depends on all its components but commercial products only specify the active principle in their label. To treat contaminated waters and to verify if the unknown components which add toxicity have been removed represent a challenge. Nanofiltration and permeate analysis by toxicity tests with fish are an interesting alternative to evaluate the process. Permeates of solutions with concentrations five times above the lethal doses (48 mg/l) did not present toxicity, pointing that all toxic compounds were removed at the same time. Glyphosate rejection over an 80% despite its molecular weight is lower than membrane MWCO, this could be associated to a predominant Donnan exclusion mechanism, combined with dielectric exclusion due to the solute high charge density. Glyphosate concentration did not show any effect over rejection. It increased when pressure was incremented from 2.5 to 4 bar and then remained constant in a 4-10 bar range. Because of dissociation of the glyphosate and the surface charged of the membrane depend on pH value, the rejection increase from 72.5 to 92.5% when pH increase from 4 to 8.5. Studies with river water showed the same behavior with a slight decrease in rejection. Copyright © 2012 Elsevier B.V. All rights reserved.

Ultrafiltration and nanofiltration membrane fouling by natural organic matter: Mechanisms and mitigation by pre-ozonation and pH.

PubMed

Yu, Wenzheng; Liu, Teng; Crawshaw, John; Liu, Ting; Graham, Nigel

2018-08-01

The fouling of ultrafiltration (UF) and nanofiltration (NF) membranes during the treatment of surface waters continues to be of concern and the particular role of natural organic matter (NOM) requires further investigation. In this study the effect of pH and surface charge on membrane fouling during the treatment of samples of a representative surface water (Hyde Park recreational lake) were evaluated, together with the impact of pre-ozonation. While biopolymers in the surface water could be removed by the UF membrane, smaller molecular weight (MW) fractions of NOM were poorly removed, confirming the importance of membrane pore size. For NF membranes the removal of smaller MW fractions (800 Da-10 kDa) was less than expected from their pore size; however, nearly all of the hydrophobic, humic-type substances could be removed by the hydrophilic NF membranes for all MW distributions (greater than 90%). The results indicated the importance of the charge and hydrophilic nature of the NOM. Thus, the hydrophilic NF membrane could remove the hydrophobic organic matter, but not the hydrophilic substances. Increasing charge effects (more negative zeta potentials) with increasing solution pH were found to enhance organics removal and reduce fouling (flux decline), most likely through greater membrane surface repulsion. Pre-ozonation of the surface water increased the hydrophilic fraction and anionic charge of NOM and altered their size distributions. This resulted in a decreased fouling (less flux decline) for the UF and smaller pore NF, but a slight increase in fouling for the larger pore NF. The differences in the NF behavior are believed to relate to the relative sizes of ozonated organic fractions and the NF pores; a similar size of ozonated organic fractions and the NF pores causes significant membrane fouling. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Heavy metals alter the electrokinetic properties of bacteria, yeasts, and clay minerals.

PubMed Central

Collins, Y E; Stotzky, G

1992-01-01

The electrokinetic patterns of four bacterial species (Bacillus subtilis, Bacillus megaterium, Pseudomonas aeruginosa, and Agrobacterium radiobacter), two yeasts (Saccharomyces cerevisiae and Candida albicans), and two clay minerals (montmorillonite and kaolinite) in the presence of the chloride salts of the heavy metals, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, and of Na and Mg were determined by microelectrophoresis. The cells and kaolinite were net negatively charged at pH values above their isoelectric points (pI) in the presence of Na, Mg, Hg, and Pb at an ionic strength (mu) of 3 x 10(-4); montmorillonite has no pI and was net negatively charged at all pH values in the presence of these metals. However, the charge of some bacteria, S. cerevisiae, and kaolinite changed to a net positive charge (charge reversal) in the presence of Cd, Cr, Cu, Ni, and Zn at pH values above 5.0 (the pH at which charge reversal occurred differed with the metal) and then, at higher pH values, again became negative. The charge of the bacteria and S. cerevisiae also reversed in solutions of Cu and Ni with a mu of greater than 3 x 10(-4), whereas there was no reversal in solutions with a mu of less than 3 x 10(-4). The clays became net positively charged when the mu of Cu was greater than 3 x 10(-4) and that of Ni was greater than 1.5 x 10(-4). The charge of the cells and clays also reversed in solutions containing both Mg and Ni or both Cu and Ni (except montmorillonite) but not in solutions containing both Mg and Cu (except kaolinite) (mu = 3 x 10(-4)). The pIs of the cells in the presence of the heavy metals were at either higher or lower pH values than in the presence of Na and Mg. Exposure of the cells to the various metals at pH values from 2 to 9 for the short times (ca. 10 min) required to measure the electrophoretic mobility did not affect their viability. The specific adsorption on the cells and clays of the hydrolyzed species of some of the heavy metals that formed at higher pH values was probably responsible for the charge reversal. These results suggest that the toxicity of some heavy metals to microorganisms varies with pH because the hydrolyzed speciation forms of these metals, which occur at higher pH values, bind on the cell surface and alter the net charge of the cell.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1622229

Systematic Approach to Electrostatically Induced 2D Crystallization of Nanoparticles at Liquid Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukuto, M.; Kewalramani, S.; Wang, S.

2011-02-07

We report an experimental demonstration of a strategy for inducing two-dimensional (2D) crystallization of charged nanoparticles on oppositely charged fluid interfaces. This strategy aims to maximize the interfacial adsorption of nanoparticles, and hence their lateral packing density, by utilizing a combination of weakly charged particles and a high surface charge density on the planar interface. In order to test this approach, we investigated the assembly of cowpea mosaic virus (CPMV) on positively charged lipid monolayers at the aqueous solution surface, by means of in situ X-ray scattering measurements at the liquid-vapor interface. The assembly was studied as a function ofmore » the solution pH, which was used to vary the charge on CPMV, and of the mole fraction of the cationic lipid in the binary lipid monolayer, which set the interface charge density. The 2D crystallization of CPMV occurred in a narrow pH range just above the particle's isoelectric point, where the particle charge was weakly negative, and only when the cationic-lipid fraction in the monolayer exceeded a threshold. The observed 2D crystals exhibited nearly the same packing density as the densest lattice plane within the known 3D crystals of CPMV. The above electrostatic approach of maximizing interfacial adsorption may provide an efficient route to the crystallization of nanoparticles at aqueous interfaces.« less

Voltammetric studies of hemoglobin-coated polystyrene latex bead films on pyrolytic graphite electrodes.

PubMed

Sun, Hong; Hu, Naifei

2004-08-01

A novel hemoglobin (Hb)-coated polystyrene (PS) latex bead film was deposited on pyrolytic graphite (PG) electrode surface. In the first step, positively charged Hb molecules in pH 5.0 buffers were adsorbed on the surface of negatively charged, 500 nm diameter PS latex beads bearing sulfate groups by electrostatic interaction. The aqueous dispersion of Hb-coated PS particles was then deposited on the surface of PG electrodes and, after evaporation of the solvent, Hb-PS films were formed. The Hb-PS film electrodes exhibited a pair of well-defined, quasi-reversible cyclic voltammetric (CV) peaks at about -0.36 V vs. SCE in pH 7.0 buffers, characteristic of Hb heme Fe(III)/Fe(II) redox couples. Positions of Soret absorption band of Hb-PS films suggest that Hb retains its near-native structure in the films in its dry form and in solution at medium pH. The Hb in PS films was also acted as a catalyst to catalyze electrochemical reduction of various substrates such as trichloroacetic acid (TCA), nitrite, oxygen and hydrogen peroxide.

Formation of polyelectrolyte complexes with diethylaminoethyl dextran: charge ratio and molar mass effect.

PubMed

Le Cerf, Didier; Pepin, Anne Sophie; Niang, Pape Momar; Cristea, Mariana; Karakasyan-Dia, Carole; Picton, Luc

2014-11-26

The formation of polyelectrolyte complexes (PECs) between carboxymethyl pullulan and DEAE Dextran, was investigated, in dilute solution, with emphasis on the effect of charge density (molar ratio or pH) and molar masses. Electrophoretic mobility measurements have evidenced that insoluble PECs (neutral electrophoretic mobility) occurs for charge ratio between 0.6 (excess of polycation) and 1 (stoichiometry usual value) according to the pH. This atypical result is explained by the inaccessibility of some permanent cationic charge when screened by pH dependant cationic ones (due to the Hoffman alkylation). Isothermal titration calorimetry (ITC) indicates an endothermic formation of PEC with a binding constant around 10(5) L mol(-1). Finally asymmetrical flow field flow fractionation coupled on line with static multi angle light scattering (AF4/MALS) evidences soluble PECs with very large average molar masses and size around 100 nm, in agreement with scrambled eggs multi-association between various polyelectrolyte chains. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effect of pH and leucine concentration on aerosolization properties of carrier-free formulations of levofloxacin.

PubMed

Barazesh, Ahmadreza; Gilani, Kambiz; Rouini, Mohammadreza; Barghi, Mohammad Ali

2018-06-15

The aim of this study was to evaluate the effect of leucine at different pH values preferred for inhalation on particle characteristics and aerosolization performance of spray dried carrier-free formulations of levofloxacin. A full factorial design was applied to optimize the formulation containing levofloxacin with or without leucine in different pH values and the optimum condition was determined. Particle size and morphology, crystallinity state, electrostatic charge and surface composition of the particles were determined. Aerodynamic properties of the powders were also assessed by an Andersen cascade impactor after aerosolization through an Aerolizer® at an air flow rate of 60 L/min. The pH of initial solution affected various physical properties of the drug containing particles and hence their in vitro deposition. The profound effect of pH was on water content, electrostatic charge and surface composition of the particles. The negative effect of water content on in vitro deposition of the drug was covered by preferred surface accumulation of leucine at pH 6. Optimum formulation which obtained by co-spray drying of the drug with 21.79% leucine at pH 5.98 presented a fine particle fraction equal to 54.38. In conclusion, changing pH of the initial solution influenced the effect of leucine on aerosolization of levofloxacine spray dried particles by modification of their physical properties. Copyright © 2018 Elsevier B.V. All rights reserved.

Characterization of charged polymer self-assemblies by multidetector thermal field-flow fractionation in aqueous mobile phases.

PubMed

Greyling, Guilaume; Pasch, Harald

2018-01-12

Charged block copolymer self-assemblies, such as charged micelles, have attracted much attention as versatile drug delivery systems due to their readily tunable characteristics such as size and surface charge. However, current column-based analytical techniques are not suitable to fractionate and comprehensively characterize charged micelles in terms of size, molar mass, chemical composition and morphology. Multidetector thermal field-flow fractionation (ThFFF) is shown to be a unique characterization platform that can be used to characterize charged micelles in terms of size, molar mass, chemical composition and morphology in aqueous mobile phases with various ionic strengths and pH. This is demonstrated by the characterization of poly(methacrylic acid)-b-poly(methyl methacrylate) self-assemblies in high pH buffers as well as the characterization of cationic poly(2-vinyl pyridine)-b-polystyrene and poly(4-vinyl pyridine)-b-polystyrene self-assemblies in low pH buffers. Moreover, it is shown that ThFFF is capable of separating charged micelles according to the corona composition. These investigations prove convincingly that ThFFF is broadly applicable to the comprehensive characterization of amphiphilic self-assemblies even when aqueous mobile phases are used. Copyright © 2017 Elsevier B.V. All rights reserved.

Interactions between cells and ionized dendritic biomaterials: Flow cytometry and fluorescence spectroscopic studies

NASA Astrophysics Data System (ADS)

Kannan, R. M.; Kolhe, Parag; Khandare, Jayant; Kannan, Sujatha; Lieh-Lai, Mary

2004-03-01

Dendrimers and hyperbranched polymers are a new class of macromolecules characterized by large density of "tunable" peripheral functional groups. Therefore dendrimers can serve as a model macromolecular system to study the influence of molecular geometry and charge density on transport across biological barriers, especially cellular interfaces. The effect of size, end-functionality, surface charge (pH), and the nature of the cell surface are expected to play an important role in transport, and are investigated using flow cytometry, fluorescene microscopy and UV/Vis spectroscopy. Our results suggest that at physiological pH, cationic polyamidoamine (PAMAM) dendrimers can enter the A549 cancer lung epithelial cells within 5 minutes, perhaps due to the favorable interaction between anionic surface receptors of cells and cationic PAMAM dendrimer, through adsorptive endocytosis. On the other hand, hyperbranched polyol, which is a neutral polymer at physiological pH, enters cells at a much slower rate. The entry of hyperbranched polyol may be because of fluid-phase pinocytosis. Our results also indicate that the dendritic polymers enter the cell surface much more rapidly than linear polymers, and some small drugs, suggesting that the high density of functional groups plays a key role in the interaction with the cell surface, and the subsequent transport inside.

Performance of colloidal silica and ceria based slurries on CMP of Si-face 6H-SiC substrates

NASA Astrophysics Data System (ADS)

Chen, Guomei; Ni, Zifeng; Xu, Laijun; Li, Qingzhong; Zhao, Yongwu

2015-12-01

Colloidal silica and ceria based slurries, both using KMnO4 as an oxidizer, for chemical mechanical polishing (CMP) of Si-face (0 0 0 1) 6H-SiC substrate, were investigated to obtain higher material removal rate (MRR) and ultra-smooth surface. The results indicate that there was a significant difference in the CMP performance of 6H-SiC between silica and ceria based slurries. For the ceria based slurries, a higher MRR was obtained, especially in strong acid KMnO4 environment, and the maximum MRR (1089 nm/h) and a smoother surface with an average roughness Ra of 0.11 nm was achieved using slurries containing 2 wt% colloidal ceria, 0.05 M KMnO4 at pH 2. In contrast, due to the attraction between negative charged silica particles and positive charged SiC surface below pH 5, the maximum MRR of silica based slurry was only 185 nm/h with surface roughness Ra of 0.254 nm using slurries containing 6 wt% colloidal silica, 0.05 M KMnO4 at pH 6. The polishing mechanism was discussed based on the zeta potential measurements of the abrasives and the X-ray photoelectron spectroscopy (XPS) analysis of the polished SiC surfaces.

Electric double layer at metal oxide surfaces:static properties of the cassiterite-water interface.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlcek, L.; Zhang, Z.; Machesky, M .L.

2007-03-24

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively chargedmore » variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).« less

Electric double layer at metal oxide surfaces: Static properties of the cassiterite - Water Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlcek, Lukas; Zhang, Zhan; Machesky, Michael L.

2007-01-01

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively chargedmore » variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).« less

Varieties of charge distributions in coat proteins of ssRNA+  viruses

NASA Astrophysics Data System (ADS)

Lošdorfer Božič, Anže; Podgornik, Rudolf

2018-01-01

A major part of the interactions involved in the assembly and stability of icosahedral, positive-sense single-stranded RNA (ssRNA+) viruses is electrostatic in nature, as can be inferred from the strong pH- and salt-dependence of their assembly phase diagrams. Electrostatic interactions do not act only between the capsid coat proteins (CPs), but just as often provide a significant contribution to the interactions of the CPs with the genomic RNA, mediated to a large extent by positively charged, flexible N-terminal tails of the CPs. In this work, we provide two clear and complementary definitions of an N-terminal tail of a protein, and use them to extract the tail sequences of a large number of CPs of ssRNA+  viruses. We examine the pH-dependent interplay of charge on both tails and CPs alike, and show that—in contrast to the charge on the CPs—the net positive charge on the N-tails persists even to very basic pH values. In addition, we note a limit to the length of the wild-type genomes of those viruses which utilize positively charged tails, when compared to viruses without charged tails and similar capsid size. At the same time, we observe no clear connection between the charge on the N-tails and the genome lengths of the viruses included in our study.

Chitosan-carboxymethylcellulose based microcapsules formulation for controlled release of active ingredients from cosmeto textile

NASA Astrophysics Data System (ADS)

Roy, J. C.; Ferri, A.; Salaün, F.; Giraud, S.; Chen, G.; Jinping, G.

2017-10-01

Chitosan-based emulsions were prepared at pH from 4.0 to 6.0. The zeta potential and droplet size were monitored at different pH. Double emulsions (wateroil- water) were observed due to the stiff conformation of chitosan at pH 4.0. At pH 5.0, the emulsion droplets were the smallest (2.9 μm) of the experimental pH range. The emulsion droplets were well dispersed due to high surface charge of chitosan (for example, +50 mV at pH 5.5) in entire pH range. The emulsion was treated with carboxymethyl cellulose (CMC) for neutralizing the charged chitosan on the surface of emulsion droplets. Above 10×10-2 mg/ml of CMC, no change in zeta potential was observed indicating no more free chitosan existed after neutralization with CMC. The emulsion was then crosslinked with different amount of glutaraldehyde. Upon increasing the amount of glutaraldehyde, the amount of core content inside the microcapsule and encapsulation efficiency of shell materials decreased gradually. The Dynamic Scanning Calorimetry data confirmed no interaction between core and shell material in the microencapsulation process. The thermal degradation of the microcapsules was examined by thermogravimetric analysis and a gradual decrease in the degradation temperature upon increasing glutaraldehyde concentration was found. The tuning of CMC concentration can provide valuable information regarding stable emulsion and efficient microcapsule formulation via coacervation.

Zeta potential orientation dependence of sapphire substrates.

PubMed

Kershner, Ryan J; Bullard, Joseph W; Cima, Michael J

2004-05-11

The zeta potential of planar sapphire substrates for three different crystallographic orientations was measured by a streaming potential technique in the presence of KCl and (CH3)4NCl electrolytes. The streaming potential was measured for large single crystalline C-plane (0001), A-plane (1120), and R-plane (1102) wafers over a full pH range at three or more ionic strengths ranging from 1 to 100 mM. The roughness of the epi-polished wafers was verified using atomic force microscopy to be on the order of atomic scale, and X-ray photoelectron spectroscopy (XPS) was used to ensure that the samples were free of silica and other contaminants. The results reveal a shift in the isoelectric point (iep) of the three samples by as much as two pH units, with the R-plane surface exhibiting the most acidic behavior and the C-plane samples having the highest iep. The iep at all ionic strengths was tightly centered around a single pH for each wafer. These values of iep are substantially different from the range of pH 8-10 consistently reported in the literature for alpha-Al2O3 particles. Particle zeta potential measurements were performed on a model powder using phase analysis light scattering, and the iep was confirmed to occur at pH 8. Modified Auger parameters (MAP) were calculated from XPS spectra of a monolayer of iridium metal deposited on the sapphire by electron beam deposition. A shift in MAP consistent with the observed differences in iep of the surfaces confirms the effect of surface structure on the transfer of charge between the Ir and sapphire, hence accounting for the changes in acidity as a function of crystallographic orientation.

A Mussel-Derived One-Component Adhesive Coacervate

PubMed Central

Wei, Wei; Tan, Yerpeng; Rodriguez, N. Martinez; Yu, Jing; Israelachvili, Jacob N.; Waite, J. Herbert

2013-01-01

Marine organisms process and deliver many of their underwater coatings and adhesives as complex fluids. In marine mussels, one such fluid, secreted during the formation of adhesive plaques, consists of a concentrated colloidal suspension of a mussel foot protein (mfp) known as Mfp-3S. Results of this study suggest that Mfp-3S becomes a complex fluid by a liquid-liquid phase separation from equilibrium solution at a pH and ionic strength reminiscent of conditions created by the mussel foot during plaque formation. The pH dependence of phase separation and its sensitivity indicate that inter/intra-molecular electrostatic interactions are partially responsible for driving the phase separation. Hydrophobic interactions between the nonpolar Mfp-3S proteins provide another important driving force for coacervation. As complex coacervation typically results from charge-charge interactions between polyanions and polycations, Mfp-3S is thus unique in being the only known protein that coacervates with itself. The Mfp-3S coacervate was shown to have an effective interfacial energy of ≤ 1 mJ/m2 which explains its tendency to spread over or engulf most surfaces. Of particular interest to biomedical applications is the extremely high adsorption capacity of coacervated Mfp-3S on hydroxyapatite. PMID:24060881

The isoelectric point/point-of zero-charge of interfaces formed by aqueous solutions and nonpolar solids, liquids, and gases.

PubMed

Healy, Thomas W; Fuerstenau, Douglas W

2007-05-01

From our previous work on the role of the electrostatic field strength in controlling the pH of the iso-electric point (iep)/point-of-zero-charge (pzc) of polar solids we have extended the analysis to predict that the pH of the iep/pzc of a nonpolar solid, liquid or gas-aqueous interface should occur at pH 1.0-3.0, dependent on the value assigned to water molecules or clusters at the interface. Consideration of a wide range of experimental results covering nonpolar solids such as molybdenite, stibnite, paraffin, etc. as well as hydrocarbon liquids such as xylene, decalin, and long chain (>C8) alkane oils, as well as nitrogen and hydrogen gases, all in various simple 1:1 electrolyte solutions confirm the general validity of the result. We further consider various models of the origin of the charge on nonpolar material-water interfaces.

pH-Dependent Optical Properties of Synthetic Fluorescent Imidazoles

PubMed Central

Berezin, Mikhail Y.; Kao, Jeff; Achilefu, Samuel

2010-01-01

An imidazole moiety is often found as an integral part of fluorophores in a variety of fluorescent proteins and many such proteins possess pH dependent light emission. In contrast, synthetic fluorescent compounds with incorporated imidazoles are rare and have not been studied as pH probes. In this report, the richness of imidazole optical properties, including pH sensitivity, was demonstrated via a novel imidazole-based fluorophore 1H-imidazol-5-yl-vinyl-benz[e]indolium. Three species corresponding to protonated, neutral and deprotonated imidazoles were identified in the broad range of pH 1-12. The absorption and emission bands of each species were assigned by comparative spectral analysis with synthesized mono- and di-N-methylated fluorescent imidazole analogues. pKa analysis in the ground and the excited states showed photoacidic properties of the fluorescent imidazoles due to the excited state proton transfer (ESPT). This effect was negligible for substituted imidazoles. The assessment of a pH sensitive center in the imidazole ring revealed the switching of the pH sensitive centers from 1-N in the ground state to 3-N in the excited state. The effect was attributed to the unique kind of the excited state charge transfer (ESCT) resulting in a positive charge swapping between two nitrogens. PMID:19212987

Preparation of poly(β-L-malic acid)-based charge-conversional nanoconjugates for tumor-specific uptake and cellular delivery.

PubMed

Zhou, Qing; Yang, Tiehong; Qiao, Youbei; Guo, Songyan; Zhu, Lin; Wu, Hong

2015-01-01

In this study, a multifunctional poly(β-L-malic acid)-based nanoconjugate with a pH-dependent charge conversional characteristic was developed for tumor-specific drug delivery. The short branched polyethylenimine-modified poly(β-L-malic acid) (PEPM) was first synthesized. Then, the fragment HAb18 F(ab')2 and 2,3-dimethylmaleic anhydride were covalently attached to the PEPM to form the nanoconjugate, HDPEPM. In this nanoconjugate, the 2,3-dimethylmaleic anhydride, the shielding group, could shield the positive charge of the conjugate at pH 7.4, while it was selectively hydrolyzed in the tumor extracellular space (pH 6.8) to expose the previously-shielded positive charge. To study the anticancer activity, the anticancer drug, doxorubicin, was covalently attached to the nanoconjugate. The doxorubicin-loaded HDPEPM nanoconjugate was able to efficiently undergo a quick charge conversion from -11.62 mV to 9.04 mV in response to the tumor extracellular pH. The electrostatic interaction between the positively charged HDPEPM nanoconjugates and the negatively charged cell membrane significantly enhanced their cellular uptake, resulting in the enhanced anticancer activity. Also, the tumor targetability of the nanoconjugates could be further improved via the fragment HAb18 F(ab')2 ligand-receptor-mediated tumor cell-specific endocytosis.

DNA assisted self-assembly of PAMAM dendrimers.

PubMed

Mandal, Taraknath; Kumar, Mattaparthi Venkata Satish; Maiti, Prabal K

2014-10-09

We report DNA assisted self-assembly of polyamidoamine (PAMAM) dendrimers using all atom Molecular Dynamics (MD) simulations and present a molecular level picture of a DNA-linked PAMAM dendrimer nanocluster, which was first experimentally reported by Choi et al. (Nano Lett., 2004, 4, 391-397). We have used single stranded DNA (ssDNA) to direct the self-assembly process. To explore the effect of pH on this mechanism, we have used both the protonated (low pH) and nonprotonated (high pH) dendrimers. In all cases studied here, we observe that the DNA strand on one dendrimer unit drives self-assembly as it binds to the complementary DNA strand present on the other dendrimer unit, leading to the formation of a DNA-linked dendrimer dimeric complex. However, this binding process strongly depends on the charge of the dendrimer and length of the ssDNA. We observe that the complex with a nonprotonated dendrimer can maintain a DNA length dependent inter-dendrimer distance. In contrast, for complexes with a protonated dendrimer, the inter-dendrimer distance is independent of the DNA length. We attribute this observation to the electrostatic complexation of a negatively charged DNA strand with the positively charged protonated dendrimer.

``Smart'' Surfaces of Polymer Brushes

NASA Astrophysics Data System (ADS)

Wang, Qiang; Meng, Dong

2009-03-01

``Smart'' surfaces, also known as stimuli-responsive surfaces, can change their properties (e.g., wettability, adhesion, friction, elasticity, and biocompatibility) in response to external stimuli (e.g., temperature, pressure, light, solvent selectivity, ionic strength, type of salt, pH, applied electric field, etc.). In this work, we use numerical self-consistent field calculations to study in detail the structure and stimuli- responses of various polymer brushes, including (1) the thermo- response of PNIPAM brushes in water, (2) solvent-response of uncharged diblock copolymer brushes, and (3) the stimuli- response of charged two-component polymer brushes (including both the binary A/B brushes and diblock copolymer A-B brushes) to ionic strength, pH, and applied electric field. Among the many design parameters (e.g., chain lengths, grafting densities, A-B incompatibility, degree of ionization of charged polymers, etc.) we identify those that strongly affect the surface switchability. Such knowledge is useful to the experimental design of these smart polymer brushes for their applications.

Aging of Nanocrystalline Mackinawite (FeS): Mineralogical and Physicochemical Properties

NASA Astrophysics Data System (ADS)

Jeong, H. Y.; Lee, H.

2011-12-01

Due to the extraordinary physical properties and high surface areas, nanocrystalline minerals have been widely investigated for their potential uses in treating contaminated groundwaters and surface waters. Most previous studies in this field have focused on either preparation of nanocrystalline minerals or measurement of their reactivity with environmental contaminants. Nanocrystalline minerals, due to the inherent thermodynamic instability, tend to change the physicochemical and mineralogical properties over time, usually resulting in the decreased reactivity. Thus, to better assess the long-term effectiveness of nanocrystalline minerals in field applications, such "aging" effects should be clearly delineated. In the present work, we have investigated the aging impact on nanocrystalline mackinawite (FeS), the ubiquitous Fe-bearing mineral in anoxic sulfidic sediments. Mackinawite (FeS) is known to be an effective scavenger for metal pollutants and a strong reducing reagent for chromate and chlorinated organic compounds. Our preliminary results indicate that nanocrystalline FeS ages via Ostwald ripening, particle aggregation, or mineralogical transformation. By X-ray diffraction (XRD) analysis, aging of nanocrystalline FeS via Ostwald ripening is found to be dominant at acidic pH. Cryogenic transmission electron microscopy (TEM) shows that particle aggregation is most evident at neutral pH. Transformation of nanosized FeS into a more thermodynamically stable greigite (Fe3S4) is observed in the presence of folic acid at acidic pH. The pH-dependent aging process may be linked with changes in the apparent solubility and surface charge of FeS with pH. The Ostwald ripening or particle aggregation of nanocrystalline FeS leads to the decrease surface area, thus causing the decreased reactivity. Given the less reactivity of greigite, the transformation of nanocrystalline FeS to greigite is also expected to result in the decreased reactivity.

Humic acid facilitates the transport of ARS-labeled hydroxyapatite nanoparticles in iron oxyhydroxide-coated sand

USGS Publications Warehouse

Wang, Dengjun; Bradford, Scott A.; Harvey, Ronald W.; Gao, Bin; Cang, Long; Zhou, Dongmei

2012-01-01

Hydroxyapatite nanoparticles (nHAP) have been widely used to remediate soil and wastewater contaminated with metals and radionuclides. However, our understanding of nHAP transport and fate is limited in natural environments that exhibit significant variability in solid and solution chemistry. The transport and retention kinetics of Alizarin red S (ARS)-labeled nHAP were investigated in water-saturated packed columns that encompassed a range of humic acid concentrations (HA, 0–10 mg L–1), fractional surface coverage of iron oxyhydroxide coatings on sand grains (λ, 0–0.75), and pH (6.0–10.5). HA was found to have a marked effect on the electrokinetic properties of ARS-nHAP, and on the transport and retention of ARS-nHAP in granular media. The transport of ARS-nHAP was found to increase with increasing HA concentration because of enhanced colloidal stability and the reduced aggregate size. When HA = 10 mg L–1, greater ARS-nHAP attachment occurred with increasing λ because of increased electrostatic attraction between negatively charged nanoparticles and positively charged iron oxyhydroxides, although alkaline conditions (pH 8.0 and 10.5) reversed the surface charge of the iron oxyhydroxides and therefore decreased deposition. The retention profiles of ARS-nHAP exhibited a hyperexponential shape for all test conditions, suggesting some unfavorable attachment conditions. Retarded breakthrough curves occurred in sands with iron oxyhydroxide coatings because of time-dependent occupation of favorable deposition sites. Consideration of the above effects is necessary to improve remediation efficiency of nHAP for metals and actinides in soils and subsurface environments.

Structural origins of pH and ionic strength effects on protein stability. Acid denaturation of sperm whale apomyoglobin.

PubMed

Yang, A S; Honig, B

1994-04-15

A recently developed approach to calculate the pH dependence of protein stability from three-dimensional structure information is applied to the analysis of acid denaturation of sperm whale apomyoglobin. The finite difference Poisson-Boltzmann method is used to calculate pKa values and these are used to obtain titration curves for the folded protein as well as for compact intermediates. The total electrostatic free energy change involved in apomyoglobin unfolding is then evaluated. Calculations are carried out of the unfolding free energy of the native (N) and the compact intermediate (I) of apomyoglobin relative to the unfolded state (U) over a range of pH at various ionic strengths. The contributions from key ionizable groups to the unfolding process are discussed. For the acid-induced partial unfolding of apomyoglobin near pH 5, the transition from N to I is found to be driven by three histidines that are exposed when the B, C, D and E helices unfold. Similarly, the unfolding of the compact intermediate I consisting of the A, G and H helices is driven primarily by a few carboxylic acids with low pKa values in the compact state. This picture is in contrast to the view which attributes acid denaturation to electrostatic repulsion resulting from the build up of positive charge. In fact, charge-charge interactions in myoglobin are found to be attractive at all pH values where the protein unfolds. pH-dependent changes in these interactions contribute to acid denaturation but other electrostatic effects, such as hydrogen bonding and solvation, are important as well. The effect of increasing ionic strength on unfolding is attributed to the decrease of attractive charge-charge interactions which destabilize the N state relative to I, but stabilize the I state relative to U by reducing the pKa shifts of a few critical carboxylic acids. The I state is found to be more stable than U at neutral pH thus accounting for its presence as an intermediate on the protein folding pathway. Our results have implications for the origins of compact intermediates or "molten globule" states.

Contribution of Electrostatics in the Fibril Stability of a Model Ionic-Complementary Peptide.

PubMed

Owczarz, Marta; Casalini, Tommaso; Motta, Anna C; Morbidelli, Massimo; Arosio, Paolo

2015-12-14

In this work we quantified the role of electrostatic interactions in the self-assembly of a model amphiphilic peptide (RADA 16-I) into fibrillar structures by a combination of size exclusion chromatography and molecular simulations. For the peptide under investigation, it is found that a net charge of +0.75 represents the ideal condition to promote the formation of regular amyloid fibrils. Lower net charges favor the formation of amorphous precipitates, while larger net charges destabilize the fibrillar aggregates and promote a reversible dissociation of monomers from the ends of the fibrils. By quantifying the dependence of the equilibrium constant of this reversible reaction on the pH value and the peptide net charge, we show that electrostatic interactions contribute largely to the free energy of fibril formation. The addition of both salt and a charged destabilizer (guanidinium hydrochloride) at moderate concentration (0.3-1 M) shifts the monomer-fibril equilibrium toward the fibrillar state. Whereas the first effect can be explained by charge screening of electrostatic repulsion only, the promotion of fibril formation in the presence of guanidinium hydrochloride is also attributed to modifications of the peptide conformation. The results of this work indicate that the global peptide net charge is a key property that correlates well with the fibril stability, although the peptide conformation and the surface charge distribution also contribute to the aggregation propensity.

Effects of pH on transport properties of articular cartilages.

PubMed

Loret, Benjamin; Simões, Fernando M F

2010-02-01

Articular cartilages swell and shrink depending on the ionic strength of the electrolyte they are in contact with. This electro-chemo-mechanical coupling is due to the presence of fixed electrical charges on proteoglycans (PGs). In addition, at nonphysiological pH, collagen fibers become charged. Therefore, variation of the pH of the electrolyte has strong implications on the electrical charge of cartilages and, by the same token, on their transport and mechanical properties. Articular cartilages are viewed as three-phase multi-species porous media. The constitutive framework is phrased in the theory of thermodynamics of porous media. Acid-base reactions, as well as calcium binding, are embedded in this framework. Although macroscopic in nature, the model accounts for a number of biochemical details defining collagen and PGs. The change of the electrical charge is due to the binding of hydrogen ions on specific sites of PGs and collagen. Simulations are performed mimicking laboratory experiments where either the ionic strength or the pH of the bath, the cartilage piece is in contact with, is varied. They provide the evolutions of the chemical compositions of mobile ions, of the sites of acid-base reactions and calcium binding, and of the charges of collagen and glycosaminoglycans, at constant volume fraction of water. Emphasis is laid on the effects of pH, ionic strength and calcium binding on the transport properties of cartilages, and, in particular, on the electrical conductivity and electro-osmotic coefficient.

The role of surface charge in the desolvation process of gelatin: implications in nanoparticle synthesis and modulation of drug release

PubMed Central

Ahsan, Saad M; Rao, Chintalagiri Mohan

2017-01-01

The process of moving hydrophobic amino acids into the core of a protein by desolvation is important in protein folding. However, a rapid and forced desolvation can lead to precipitation of proteins. Desolvation of proteins under controlled conditions generates nanoparticles – homogeneous aggregates with a narrow size distribution. The protein nanoparticles, under physiological conditions, undergo surface erosion due to the action of proteases, releasing the entrapped drug/gene. The packing density of protein nanoparticles significantly influences the release kinetics. We have investigated the desolvation process of gelatin, exploring the role of pH and desolvating agent in nanoparticle synthesis. Our results show that the desolvation process, initiated by the addition of acetone, follows distinct pathways for gelatin incubated at different pH values and results in the generation of nanoparticles with varying matrix densities. The nanoparticles synthesized with varying matrix densities show variations in drug loading and protease-dependent extra- and intracellular drug release. These results will be useful in fine-tuning the synthesis of nanoparticles with desirable drug release profiles. PMID:28182126

Determination of the surface charge density and temperature dependence of purple membrane by electric force microscopy.

PubMed

Du, Huiwen; Li, Denghua; Wang, Yibing; Wang, Chenxuan; Zhang, Dongdong; Yang, Yan-lian; Wang, Chen

2013-08-29

We report here the measurement of the temperature-dependent surface charge density of purple membrane (PM) by using electrostatic force microscopy (EFM). The surface charge density was measured to be 3.4 × 10(5) e/cm(2) at room temperature and reaches the minimum at around 52 °C. The initial decrease of the surface charge density could be attributed to the reduced dipole alignment because of the thermally induced protein mobility in PM. The increase of charge density at higher temperature could be ascribed to the weakened interaction between proteins and the lipids, which leads to the exposure of the charged amino acids. This work could be a benefit to the direct assessment of the structural stability and electric properties of biological membranes at the nanoscale.

pH-Induced interfacial properties of Chaplin E from Streptomyces coelicolor.

PubMed

Dokouhaki, Mina; Hung, Andrew; Prime, Emma L; Qiao, Greg G; Day, Li; Gras, Sally L

2017-12-01

Chaplin E, or Chp E, is a surface active peptide secreted by Streptomyces coelicolor that adopts different structures depending on solution pH but the effect of these structures on the interfacial properties of Chp E is not known. In experiments paired with simulations, Chp E was found to display pH-dependent interfacial assembly and surface activity. At pH 3.0, Chp E formed an ordered non-amyloidal interfacial film with high surface activity; while at pH 10.0, Chp E self-assembled into a heterogeneous film containing randomly arranged fibrils at the interface that was less surface active compared to the film formed at pH 3.0. In simulations at pH 10.0, Chp E molecules showed a higher propensity for dimerization within the solution phase, lower rate of adsorption to the interface and tighter inter-molecular associations at the interface, consistent with the lower surface activity and smaller interfacial area coverage per molecule measured at this pH compared to at pH 3.0. A model is presented for the role of Chp E in the developmental differentiation of Streptomyces coelicolor, where Chp E contributes to changes in surface tension at low pH and the formation of fibrils on the surface of aerial hyphae at high pH. Our data also suggest Chp E could be a promising surface active agent with functional activity that can be controlled by pH. Copyright © 2017 Elsevier B.V. All rights reserved.

Change of physical and chemical parameters of fulvic acids at different pH of the system

NASA Astrophysics Data System (ADS)

Dinu, Marina; Kremleva, Tatyana

2017-04-01

Organic substances of humic nature significantly change physicochemical properties at different pH of natural waters. As a consequence, a large number of consecutive and parallel reactions in the structure of organic polymers, and reacting with inorganic anions. The main indicators of changes in the properties of organic acids in natural systems are changes in their IR spectra, changes in the colloid stability (the zeta potential) as well as in the molecular weight and emission spectra (fluorescence emission spectra). The aim of our study was to evaluate of changing in physical and chemical properties of the fulvic acid from soil/water samples in the natural areas of European Russia and Western Siberia (the steppe and the northern taiga zones) at different pH (from 8 to 1.5). Changes in absorption bands of fulvic acid caused by both COOH groups and amino groups with varying degrees of protonation were found. Consequently, we can assume that in an electric field fulvic acid change the sign of their charge at depending on pH. During the lowering of the pH intensity of C-O bands generally decreases, while in the region 1590 cm-1 disappears. In turn, the band at 1700 cm-1 is the most intense; it could mean a complete protonation of the carboxyl groups. According to our data, the values of zeta potential changes depending on pH of the system. The zeta potential becomes more negative with increasing pH and it may be due to ionization of oxygen groups of fulvic acid. For the colloidal polymer systems the value of the zeta potential is strongly negative (less than -20 mV) and strongly positive (over 20 mV) characterize the system as the most stable. Our experimental data for the study of the zeta potential of fulvic acids extracted from the soils and waters of different climatic zones show zonal influence of the qualitative characteristics of organic substances on the surface charge of the high-molecular micelle of fulvic acids. It was found that fulvic acids extracted from objects of the steppes zone have greater stability that soil fulvic the same territory. In turn, the fulvic acids isolated from the northern boreal forest sites have a large size and the saturated positive charge; that can be attributed to their high content of hard Pearson acids ions - sodium, potassium, aluminum, iron, etc. In external influence on the mesomeric energy of the boundary functional groups (change in pH and the influence of transition metal ions) is not only the redistribution of the charge (zeta potential variation), but also changes in the size of the molecule. In the process of acidification of fulvic acid of samples extracted there was a decrease the size an average of 20-25%, due to the formation of a larger number of individual fragments increasingly capable to the elimination of a proton. The work was performed as part of the Grant of the President of the Russian Federation for young scientists № MK-7485.2016.5

Influence of chitosan structure on the formation and stability of DNA-chitosan polyelectrolyte complexes.

PubMed

Strand, Sabina P; Danielsen, Signe; Christensen, Bjørn E; Vårum, Kjell M

2005-01-01

The interactions between DNA and chitosans varying in fractional content of acetylated units (FA), degree of polymerization (DP), and degree of ionization were investigated by several techniques, including an ethidium bromide (EtBr) fluorescence assay, gel retardation, atomic force microscopy, and dynamic and electrophoretic light scattering. The charge density of the chitosan and the number of charges per chain were found to be the dominating factors for the structure and stability of DNA-chitosan complexes. All high molecular weight chitosans condensed DNA into physically stable polyplexes; however, the properties of the complexes were strongly dependent on FA, and thereby the charge density of chitosan. By employing fully charged oligomers of constant charge density, it was shown that the complexation of DNA and stability of the polyplexes is governed by the number of cationic residues per chain. A minimum of 6-9 positive charges appeared necessary to provide interaction strength comparable to that of polycations. In contrast, further increase in the number of charges above 9 did not increase the apparent binding affinity as judged from the EtBr displacement assay. The chitosan oligomers exhibited a pH-dependent interaction with DNA, reflecting the number of ionized amino groups. The complexation of DNA and the stability of oligomer-based polyplexes became reduced above pH 7.4. Such pH-dependent dissociation of polyplexes around the physiological pH is highly relevant in gene delivery applications and might be one of the reasons for the high transfection activity of oligomer-based polyplexes observed.

Natural and synthetic polymers in fabric and home care applications

NASA Astrophysics Data System (ADS)

Paderes, Monissa; Ahirwal, Deepak; Fernández Prieto, Susana

2017-07-01

Polymers can be tailored to provide different benefits in Fabric & Home Care formulations depending on the monomers and modifications used, such as avoiding dye transfer inhibition in the wash, modifying the surface of tiles or increasing the viscosity and providing suspension properties to consumer products. Specifically, the rheology modification properties of synthetic and natural polymers are discussed in this chapter. The choice of a polymeric rheology modifier will depend on the formulation ingredients (charges, functional groups), the type and the amount of surfactants, the pH and the desired rheology modification. Natural polymeric rheology modifiers have been traditionally used in the food industry, being xanthan gum one of the most well-known ones. On the contrary, synthetic rheology modifiers are preferably used in paints & coats, textile printing and cleaning products.

Charge composition of high energy heavy primary cosmic ray nuclei. Ph.D. Thesis - Catholic Univ. of Am.

NASA Technical Reports Server (NTRS)

Price, R. D.

1974-01-01

A detailed study of the charge composition of primary cosmic radiation for about 5000 charged nuclei from neon to iron with energies greater than 1.16 GeV/nucleon is presented. Values are obtained after corrections were made for detector dependences, atmospheric attenuation, and solar modulation. New values of 38.5, 32.4, 23.7, and 16.8 g/sq cm for the attenuation mean free paths in air for the same charge groups are presented.

Formation of positively charged gold nanoparticle monolayers on silica sensors.

PubMed

Oćwieja, Magdalena; Maciejewska-Prończuk, Julia; Adamczyk, Zbigniew; Roman, Maciej

2017-09-01

Formation of positively charged gold nanoparticle monolayers on the Si/SiO 2 was studied under in situ conditions using quartz microbalance (QCM). The gold nanoparticles were synthesized in a chemical reduction method using sodium borohydride as reducing agent. Cysteamine hydrochloride was applied to generate a positive surface charge of nanoparticles. The micrographs obtained from transmission electron microscopy (TEM) revealed that the average size of nanoparticles was equal to 12±3nm. The stability of nanoparticle suspensions under controlled pH and ionic strength was determined by dynamic light scattering (DLS). The electrophoretic mobility measurements showed that the zeta potential of nanoparticles was positive, decreasing with ionic strength and pH from 56mV at pH 4.2 and I=10 -4 M to 22mV at pH 8.3 and I=3×10 -3 M. The surface enhanced Raman spectroscopy (SERS) confirmed chemisorption of cysteamine on nanoparticles and the contribution of amine moieties in the generation of nanoparticle charge. The influence of suspension concentration, ionic strength and flow rate on the kinetics of nanoparticle deposition on the sensors was quantitatively determined. It was confirmed that the deposition for the low coverage regime is governed by the bulk mass transfer that results in a linear increase of the coverage with time. The significant increase in the maximum coverage of gold monolayers with ionic strength was interpreted as due to the decreasing range of the electrostatic interactions among deposited particles. Moreover, the hydratation of formed monolayers, their structure and the stability were determined by the comparison of the QCM results with those obtained by AFM and SEM. The experimental data were adequately interpreted in terms of the extended random sequential adsorption (eRSA) model that considers the bulk and surface transfer steps in a rigorous way. The obtained results are useful for a facile fabrication of gold nanoparticle-based biosensors capable to bind target molecules via available amine moieties. Copyright © 2017 Elsevier Inc. All rights reserved.

Utilization of turkey manure as granular activated carbon: physical, chemical and adsorptive properties.

PubMed

Lima, Isabel; Marshall, Wayne E

2005-01-01

The high availability of large quantities of turkey manure generated from turkey production makes it an attractive feedstock for carbon production. Pelletized samples of turkey litter and cake were converted to granular activated carbons (GACs) by steam activation. Water flow rate and activation time were changed to produce a range of activation conditions. The GACs were characterized for select physical (yield, surface area, bulk density, attrition), chemical (pH, surface charge) and adsorptive properties (copper ion uptake). Carbon physical and adsorptive properties were dependent on activation time and quantity of steam used as activant. Yields varied from 23% to 37%, surface area varied from 248 to 472 m(2)/g and copper ion adsorption varied from 0.72 to 1.86 mmol Cu(2+)/g carbon. Copper ion adsorption greatly exceeded the values for two commercial GACs. GACs from turkey litter and cake show considerable potential to remove metal ions from water.

An alkaline active xylanase: insights into mechanisms of high pH catalytic adaptation.

PubMed

Mamo, Gashaw; Thunnissen, Marjolein; Hatti-Kaul, Rajni; Mattiasson, Bo

2009-09-01

The alkaliphilic bacterium, Bacillus halodurans S7, produces an alkaline active xylanase (EC 3.2.1.8), which differs from many other xylanases in being operationally stable under alkaline conditions as well as at elevated temperature. Compared to non-alkaline active xylanases, this enzyme has a high percent composition of acidic amino acids which results in high ratio of negatively to positively charged residues. A positive correlation was observed between the charge ratio and the pH optima of xylanases. The recombinant xylanase was crystallized using a hanging drop diffusion method. The crystals belong to the space group P2(1)2(1)2(1) and the structure was determined at a resolution of 2.1 A. The enzyme has the common eight-fold TIM-barrel structure of family 10 xylanases; however, unlike non-alkaline active xylanases, it has a highly negatively charged surface and a deeper active site cleft. Mutational analysis of non-conserved amino acids which are close to the acid/base residue has shown that Val169, Ile170 and Asp171 are important to hydrolyze xylan at high pH. Unlike the wild type xylanase which has optimum pH at 9-9.5, the triple mutant xylanase (V169A, I170F and D171N), which was constructed using sequence information of alkaline sensitive xylanses was optimally active around pH 7. Compared to non-alkaline active xylanases, the alkaline active xylanases have highly acidic surfaces and fewer solvent exposed alkali labile residues. Based on these results obtained from sequence, structural and mutational analysis, the possible mechanisms of high pH stability and catalysis are discussed. This will provide useful information to understand the mechanism of high pH adaptation and engineering of enzymes that can be operationally stable at high pH.

Profiling charge complementarity and selectivity for binding at the protein surface.

PubMed

Sulea, Traian; Purisima, Enrico O

2003-05-01

A novel analysis and representation of the protein surface in terms of electrostatic binding complementarity and selectivity is presented. The charge optimization methodology is applied in a probe-based approach that simulates the binding process to the target protein. The molecular surface is color coded according to calculated optimal charge or according to charge selectivity, i.e., the binding cost of deviating from the optimal charge. The optimal charge profile depends on both the protein shape and charge distribution whereas the charge selectivity profile depends only on protein shape. High selectivity is concentrated in well-shaped concave pockets, whereas solvent-exposed convex regions are not charge selective. This suggests the synergy of charge and shape selectivity hot spots toward molecular selection and recognition, as well as the asymmetry of charge selectivity at the binding interface of biomolecular systems. The charge complementarity and selectivity profiles map relevant electrostatic properties in a readily interpretable way and encode information that is quite different from that visualized in the standard electrostatic potential map of unbound proteins.

Effect of preconditioning on silver leaching and bromide removal properties of silver-impregnated activated carbon (SIAC).

PubMed

Rajaeian, Babak; Allard, Sébastien; Joll, Cynthia; Heitz, Anna

2018-07-01

Silver impregnated activated carbon (SIAC) has been found to be effective in mitigating the formation of brominated-disinfection by products during drinking water treatment. However, there are still uncertainties regarding its silver leaching properties, and strategies for the prevention of silver leaching have remained elusive. This study focused on the evaluation of one type of commercially available SIAC for its ability to remove bromide while minimising silver leaching from the material. Both synthetic and real water matrices were tested. Depending on solution pH, it was found that changing the surface charge properties of SIAC, as measured by the point of zero charge pH, can result in additional bromide removal while minimising the extent of silver leaching. To better understand the mechanism of silver leaching from the SIAC, eight preconditioning environments, i.e. variable pH and ionic strength were tested for a fixed amount of SIAC and two preconditioning environments were selected for a more detailed investigation. Experiments carried out in synthetic water showed that preconditioning at pH 10.4 did not deteriorate the capacity of SIAC to remove bromide, but significantly decreased the release of silver in the form of ionic silver (Ag + ), silver bromide (AgBr) and silver chloride (AgCl) from 40% for the pristine to 3% for the treated SIAC. This was confirmed using a groundwater sample. These results suggest that preconditioned SIAC has the potential to be an effective method for bromide removal with minimised silver leaching in a long-term field application for drinking water production. Copyright © 2018 Elsevier Ltd. All rights reserved.

Analysis of new charge-neutral DNA/RNA analogues phosphoryl guanidine oligonucleotides (PGO) by gel electrophoresis.

PubMed

Fokina, Alesya; Wang, Meiling; Ilyina, Anna; Klabenkova, Kristina; Burakova, Ekaterina; Chelobanov, Boris; Stetsenko, Dmitry

2018-06-02

Analysis and isolation of new charge-neutral phosphoryl guanidine oligonucleotides (PGO) by vertical slab electrophoresis were tested at different pH values (3-11) or in the presence of SDS as a micelle-forming agent. The most convenient way to analyze and purify phosphoryl guanidine oligonucleotides was by denaturing PAGE (8 M urea) at pH 3. The mobility of PGO is dependent on their A + C content. To analyze PGO containing only G, T or U, denaturing PAGE at pH 11 can be used, although the conditions need to be optimized. Bands were visualized by UV shadowing or Coomassie Brilliant Blue staining. Copyright © 2018. Published by Elsevier Inc.

The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

DOE PAGES

Kweon, Hyojin; Yiacoumi, Sotira Z.; Tsouris, Costas

2015-06-19

In this study, the influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorptionmore » on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.« less

Human fibrinogen adsorption on positively charged latex particles.

PubMed

Zeliszewska, Paulina; Bratek-Skicki, Anna; Adamczyk, Zbigniew; Cieśla, Michał

2014-09-23

Fibrinogen (Fb) adsorption on positively charged latex particles (average diameter of 800 nm) was studied using the microelectrophoretic and the concentration depletion methods based on AFM imaging. Monolayers on latex were adsorbed from diluted bulk solutions at pH 7.4 and an ionic strength in the range of 10(-3) to 0.15 M where fibrinogen molecules exhibited an average negative charge. The electrophoretic mobility of the latex after controlled fibrinogen adsorption was systematically measured. A monotonic decrease in the electrophoretic mobility of fibrinogen-covered latex was observed for all ionic strengths. The results of these experiments were interpreted according to the three-dimensional electrokinetic model. It was also determined using the concentration depletion method that fibrinogen adsorption was irreversible and the maximum coverage was equal to 0.6 mg m(-2) for ionic strength 10(-3) M and 1.3 mg m(-2) for ionic strength 0.15 M. The increase of the maximum coverage was confirmed by theoretical modeling based on the random sequential adsorption approach. Paradoxically, the maximum coverage of fibrinogen on positively charged latex particles was more than two times lower than the maximum coverage obtained for negative latex particles (3.2 mg m(-2)) at pH 7.4 and ionic strength of 0.15 M. This was interpreted as a result of the side-on adsorption of fibrinogen molecules with their negatively charged core attached to the positively charged latex surface. The stability and acid base properties of fibrinogen monolayers on latex were also determined in pH cycling experiments where it was observed that there were no irreversible conformational changes in the fibrinogen monolayers. Additionally, the zeta potential of monolayers was more positive than the zeta potential of fibrinogen in the bulk, which proves a heterogeneous charge distribution. These experimental data reveal a new, side-on adsorption mechanism of fibrinogen on positively charged surfaces and confirmed the decisive role of electrostatic interactions in this process.

Adsorption of organic ligands on low surface charge clay minerals: the composition in the aqueous interface region.

PubMed

Jelavić, S; Stipp, S L S; Bovet, N

2018-06-27

An understanding of the mechanisms that control the adsorption of organic molecules on clay minerals is of interest in several branches of science and industry. Oil production using low salinity injection fluids can increase yields by as much as 40% over standard injection with seawater or formation water. The mechanism responsible for the low salinity response is still debated, but one hypothesis is a change in pore surface wettability. Organic contamination in soil and drinking water aquifers is a challenge for municipal water suppliers and for agriculture. A better understanding is needed for how mineral species, solution composition and pH affect the desorption of low molecular weight organic ligands from clay minerals and consequently their wettability. We used X-ray photoelectron spectroscopy under cryogenic conditions to investigate the in situ composition in the mineral-solution interface region in a series of experiments with a range of pH and ion concentrations. We demonstrate that both chlorite and kaolinite release organic molecules under conditions relevant for low salinity water flooding. This release increases with a higher solution pH but is only slightly affected by the character of the organic ligand. This is consistent with the observation that low salinity enhanced oil recovery correlates with the presence of chlorite and kaolinite. Our results indicate that the pore surface charge and salinity of formation water and injection fluids are key parameters in determining the low salinity response. In general, our results imply that clay mineral surface charge influences the composition in the interface through an affinity for organic molecules.

Collisional charging of individual submillimeter particles: Using ultrasonic levitation to initiate and track charge transfer

NASA Astrophysics Data System (ADS)

Lee, Victor; James, Nicole M.; Waitukaitis, Scott R.; Jaeger, Heinrich M.

2018-03-01

Electrostatic charging of insulating fine particles can be responsible for numerous phenomena ranging from lightning in volcanic plumes to dust explosions. However, even basic aspects of how fine particles become charged are still unclear. Studying particle charging is challenging because it usually involves the complexities associated with many-particle collisions. To address these issues, we introduce a method based on acoustic levitation, which makes it possible to initiate sequences of repeated collisions of a single submillimeter particle with a flat plate, and to precisely measure the particle charge in situ after each collision. We show that collisional charge transfer between insulators is dependent on the hydrophobicity of the contacting surfaces. We use glass, which we modify by attaching nonpolar molecules to the particle, the plate, or both. We find that hydrophilic surfaces develop significant positive charges after contacting hydrophobic surfaces. Moreover, we demonstrate that charging between a hydrophilic and a hydrophobic surface is suppressed in an acidic environment and enhanced in a basic one. Application of an electric field during each collision is found to modify the charge transfer, again depending on surface hydrophobicity. We discuss these results within the context of contact charging due to ion transfer, and we show that they lend strong support to O H- ions as the charge carriers.

Emulsions Stabilized by Chitosan-Modified Silica Nanoparticles: pH Control of Structure-Property Relations.

PubMed

Alison, Lauriane; Demirörs, Ahmet F; Tervoort, Elena; Teleki, Alexandra; Vermant, Jan; Studart, Andre R

2018-05-29

In food-grade emulsions, particles with an appropriate surface modification can be used to replace surfactants and potentially enhance the stability of emulsions. During the life cycle of products based on such emulsions, they can be exposed to a broad range of pH conditions and hence it is crucial to understand how pH changes affect stability of emulsions stabilized by particles. Here, we report on a comprehensive study of the stability, microstructure, and macroscopic behavior of pH-controlled oil-in-water emulsions containing silica nanoparticles modified with chitosan, a food-grade polycation. We found that the modified colloidal particles used as stabilizers behave differently depending on the pH, resulting in unique emulsion structures at multiple length scales. Our findings are rationalized in terms of the different emulsion stabilization mechanisms involved, which are determined by the pH-dependent charges and interactions between the colloidal building blocks of the system. At pH 4, the silica particles are partially hydrophobized through chitosan modification, favoring their adsorption at the oil-water interface and the formation of Pickering emulsions. At pH 5.5, the particles become attractive and the emulsion is stabilized by a network of agglomerated particles formed between the droplets. Finally, chitosan aggregates form at pH 9 and these act as the emulsion stabilizers under alkaline conditions. These insights have important implications for the processing and use of particle-stabilized emulsions. On one hand, changes in pH can lead to undesired macroscopic phase separation or coalescence of oil droplets. On the other hand, the pH effect on emulsion behavior can be harnessed in industrial processing, either to tune their flow response by altering the pH between processing stages or to produce pH-responsive emulsions that enhance the functionality of the emulsified end products.

The Role of Ionic Interactions in the Adherence of the S. epidermidis Adhesin SdrF to Prosthetic Material

PubMed Central

Toba, Faustino A.; Visai, Livia; Trivedi, Sheetal; Lowy, Franklin D.

2012-01-01

Staphylococcus epidermidis infections are common complications of prosthetic device implantation. SdrF, a surface protein, appears to play a critical role in the initial colonization step by adhering to type I collagen and Dacron™. The role of ionic interactions in S. epidermidis adherence to prosthetic material was examined. SdrF was cloned and expressed in Lactococcus lactis. The effect of pH, cation concentration and detergents on adherence to different types of plastic surfaces was assessed by crystal violet staining and bacterial cell counting. SdrF, in contrast with controls and other S. epidermidis surface proteins, bound to hydrophobic materials such as polystyrene. Binding was an ionic interaction and was affected by surface charge of the plastic, pH and cation concentration. Adherence of the SdrF construct was increased to positively charged plastics and was reduced by increasing concentrations of Ca2+ and Na+. Binding was optimal at pH 7.4. Kinetic studies demonstrated that the SdrF B domain, as well as one of the B subdomains was sufficient to mediate binding. The SdrF construct also bound more avidly to Goretex™ than the lacotococcal control. SdrF is a multifunctional protein that contributes to prosthetic devices infections by ionic, as well as specific receptor-ligand interactions. PMID:23039791

Attractive non-DLVO forces induced by adsorption of monovalent organic ions.

PubMed

Smith, Alexander M; Maroni, Plinio; Borkovec, Michal

2017-12-20

Direct force measurements between negatively charged colloidal particles were carried out using an atomic force microscope (AFM) in aqueous solutions containing monovalent organic cations, namely tetraphenylarsonium (Ph 4 As + ), 1-hexyl-3-methylimidazolium (HMIM + ), and 1-octyl-3-methylimidazolium (OMIM + ). These ions adsorb to the particle surface, and induce a charge reversal. The forces become attractive at the charge neutralization point, but they are stronger than van der Waals forces. This additional and unexpected attraction decays exponentially with a decay length of a few nanometers, and is strikingly similar to the one previously observed in the presence of multivalent ions. This attractive force probably originates from coupled spontaneous charge fluctuations on the respective surfaces as initially suggested by Kirkwood and Shumaker.

Adsorption of Cr(III) on ozonised activated carbon. Importance of Cpi-cation interactions.

PubMed

Rivera-Utrilla, J; Sánchez-Polo, M

2003-08-01

The adsorption of Cr(III) in aqueous solution was investigated on a series of ozonised activated carbons, analysing the effect of oxygenated surface groups on the adsorption process. A study was carried out to determine the adsorption isotherms and the influence of the pH on the adsorption of this metal. The adsorption capacity and affinity of the adsorbent for Cr(III) increased with the increase in oxygenated acid groups on the surface of the activated carbon. These findings imply that electrostatic-type interactions predominate in the adsorption process, although the adsorption of Cr(III) on the original (basic) carbon indicates that other forces also participate in the adsorption process. Thus, the ionic exchange of protons in the -Cpi-H3O(+) interaction for Cr(III) accounts for the adsorption of cationic species in basic carbons with positive charge density. Study of the influence of pH on the adsorption of Cr(III) showed that, in each system, the maximum adsorption occurred when the charge of the carbon surface was opposite that of the species of Cr(III) present at the pH of the experiment. These results confirmed that electrostatic interactions predominate in the adsorption process.

Clay minerals behaviour in thin sandy clay-rich lacustrine turbidites (Lake Hazar, Turkey)

NASA Astrophysics Data System (ADS)

El Ouahabi, Meriam; Hubert-Ferrari, Aurelia; Lamair, Laura; Hage, Sophie

2017-04-01

Turbidites have been extensively studied in many different areas using cores or outcrop, which represent only an integrated snapshot of a dynamic evolving flow. Laboratory experiments provide the missing relationships between the flow characteristics and their deposits. In particular, flume experiments emphasize that the presence of clay plays a key role in turbidity current dynamics. Clay fraction, in small amount, provides cohesive strength to sediment mixtures and can damp turbulence. However, the degree of flocculation is dependent on factors such as the amount and size of clay particles, the surface of clay particles, chemistry and pH conditions in which the clay particles are dispersed. The present study focuses on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in stacked thin beds. Depositional processes and sources have been previously studied and three types were deciphered, including laminar flows dominated by cohesion, transitional, and turbulence flow regimes (Hage et al., in revision). For the purpose of determine the clay behavior in the three flow regimes, clay mineralogical, geochemical measurements on the cores allow characterising the turbidites. SEM observations provide further information regarding the morphology of clay minerals and other clasts. The study is particularly relevant given the highly alkaline and saline water of the Hazar Lake. Clay minerals in Hazar Lake sediments include kaolinite (1:1-type), illite and chlorite (2:1-type). Hazar lake water is alkaline having pH around 9.3, in such alkaline environment, a cation-exchange reaction takes place. Furthermore, in saline water (16‰), salts can act as a shield and decrease the repulsive forces between clay particle surfaces. So, pH and salt content jointly impact the behaviour of clays differently. Since the Al-faces of clay structures have a negative charge in basic solutions. At high pH, all kaolinite surfaces become negative-charged, and then kaolinite particles are dispersed, and the suspension is stabilized supported by our SEM observations. In alkaline water, kaolinite reveals a lower degree of consolidation. While, alkaline water has no measurable effect on illite and chlorite surface properties due to the absence of modifications in charge. Illite and chlorite form with other clasts clusters or aggregate structures in suspension when the particle interactions are dominated by attractive energies were formed. The aggregate structure plays a major part in the flow behavior of clay suspensions. Flocs will immobilize the suspending medium, and give rise to increasing viscosity and yield strength of the suspension. S. Hage, A. Hubert-Ferrari, L. Lamair, U. Avşar, M. El Ouahabi, M. Van Daele, F. Boulvain, M.A. Bahri, A. Seret, Al. Plenevaux. Flow dynamics at the origin of thin sandy clay-rich lacustrine turbidites: Examples from Lake Hazar, Turkey, submitted to Sedimentology, in revision.

Contributions of depth filter components to protein adsorption in bioprocessing.

PubMed

Khanal, Ohnmar; Singh, Nripen; Traylor, Steven J; Xu, Xuankuo; Ghose, Sanchayita; Li, Zheng J; Lenhoff, Abraham M

2018-04-16

Depth filtration is widely used in downstream bioprocessing to remove particulate contaminants via depth straining and is therefore applied to harvest clarification and other processing steps. However, depth filtration also removes proteins via adsorption, which can contribute variously to impurity clearance and to reduction in product yield. The adsorption may occur on the different components of the depth filter, that is, filter aid, binder, and cellulose filter. We measured adsorption of several model proteins and therapeutic proteins onto filter aids, cellulose, and commercial depth filters at pH 5-8 and ionic strengths <50 mM and correlated the adsorption data to bulk measured properties such as surface area, morphology, surface charge density, and composition. We also explored the role of each depth filter component in the adsorption of proteins with different net charges, using confocal microscopy. Our findings show that a complete depth filter's maximum adsorptive capacity for proteins can be estimated by its protein monolayer coverage values, which are of order mg/m 2 , depending on the protein size. Furthermore, the extent of adsorption of different proteins appears to depend on the nature of the resin binder and its extent of coating over the depth filter surface, particularly in masking the cation-exchanger-like capacity of the siliceous filter aids. In addition to guiding improved depth filter selection, the findings can be leveraged in inspiring a more intentional selection of components and design of depth filter construction for particular impurity removal targets. © 2018 Wiley Periodicals, Inc.

Impact of the interaction with the positive charge in adsorption of benzene and other organic compounds from aqueous solutions on carbons

NASA Astrophysics Data System (ADS)

Terzyk, Artur P.; Ćwiertnia, Magdalena S.; Wiśniewski, Marek; Gauden, Piotr A.; Rychlicki, Gerhard; Szymański, Grzegorz S.

2007-02-01

We present the results of benzene adsorption at the acidic pH level determined on the series of chemically modified activated carbons and at three temperatures. The influence of carbon surface chemical composition on benzene adsorption is discussed. It is shown that the decrease in the pH level from 7 up to 1.5 increases benzene adsorption and the only exception is carbon modified with gaseous ammonia. Basing on the results of current work and those published previously (for phenol, paracetamol, acetanilide and aniline) and using the results of quantum chemistry calculations (DFT, Gaussian 98) we show, that the value of the energy of interaction with unit positive charge is crucial during the analysis of the influence of pH level on adsorption. Obtained results allow to predict the changes in adsorption of aromatics on carbons with the decrease in the pH level.

Fibronectin module FN(III)9 adsorption at contrasting solid model surfaces studied by atomistic molecular dynamics.

PubMed

Kubiak-Ossowska, Karina; Mulheran, Paul A; Nowak, Wieslaw

2014-08-21

The mechanism of human fibronectin adhesion synergy region (known as integrin binding region) in repeat 9 (FN(III)9) domain adsorption at pH 7 onto various and contrasting model surfaces has been studied using atomistic molecular dynamics simulations. We use an ionic model to mimic mica surface charge density but without a long-range electric field above the surface, a silica model with a long-range electric field similar to that found experimentally, and an Au {111} model with no partial charges or electric field. A detailed description of the adsorption processes and the contrasts between the various model surfaces is provided. In the case of our model silica surface with a long-range electrostatic field, the adsorption is rapid and primarily driven by electrostatics. Because it is negatively charged (-1e), FN(III)9 readily adsorbs to a positively charged surface. However, due to its partial charge distribution, FN(III)9 can also adsorb to the negatively charged mica model because of the absence of a long-range repulsive electric field. The protein dipole moment dictates its contrasting orientation at these surfaces, and the anchoring residues have opposite charges to the surface. Adsorption on the model Au {111} surface is possible, but less specific, and various protein regions might be involved in the interactions with the surface. Despite strongly influencing the protein mobility, adsorption at these model surfaces does not require wholesale FN(III)9 conformational changes, which suggests that the biological activity of the adsorbed protein might be preserved.

Electrokinetic Response of Charge-Selective Nanostructured Polymeric Membranes

NASA Astrophysics Data System (ADS)

Schiffbauer, Jarrod; Li, Diya; Gao, Feng; Phillip, William; Chang, Hsueh-Chia

2017-11-01

Nanostructured polymeric membranes, with a tunable pore size and ease of surface molecular functionalization, are a promising material for separations, filtration, and sensing applications. Recently, such membranes have been fabricated wherein the ion selectivity is imparted by self-assembled functional groups through a two-step process. Amine groups are used to provide a positive surface charge and acid groups are used to yield a negative charge. The membranes can be fabricated as either singly-charged or patterned/mosaic membranes, where there are alternating regions of amine- lined or acid-lined pores. We demonstrate that such membranes, in addition to having many features in common with other charge selective membranes (i.e. AMX or Nafion), display a unique single-membrane rectification behavior. This is due to the asymmetric distribution of charged functional groups during the fabrication process. We demonstrate this rectification effect using both dc current-voltage characteristics as well as dc-biased electrical impedance spectroscopy. Furthermore, surface charge changes due to dc concentration polarization and generation of localized pH shifts are monitored using electrical impedance spectroscopy. (formerly at University of Notre Dame).

Improving the enzymatic hydrolysis of dilute acid pretreated wheat straw by metal ion blocking of non-productive cellulase adsorption on lignin.

PubMed

Akimkulova, Ardak; Zhou, Yan; Zhao, Xuebing; Liu, Dehua

2016-05-01

Eleven salts were selected to screen the possible metal ions for blocking the non-productive adsorption of cellulase onto the lignin of dilute acid pretreated wheat straw. Mg(2+) was screened finally as the promising candidate. The optimal concentration of MgCl2 was 1 mM, but the beneficial action was also dependent on pH, hydrolysis time and cellulase loading. Significant improvement of glucan conversion (19.3%) was observed at low cellulase loading (5 FPU/g solid). Addition of isolated lignins, tannic acid and lignin model compounds to pure cellulose hydrolysis demonstrated that phenolic hydroxyl group (Ph-OH) was the main active site blocked by Mg(2+). The interaction between Mg(2+) and Ph-OH of lignin monomeric moieties followed an order of p-hydroxyphenyl (H)>guaiacyl (G)>syringyl (S). Mg(2+) blocking made the lignin surface less negatively charged, which might weaken the hydrogen bonding and electrostatically attractive interaction between lignin and cellulase enzymes. Copyright © 2016 Elsevier Ltd. All rights reserved.

Physical Stability Studies of Semi-Solid Formulations from Natural Compounds Loaded with Chitosan Microspheres

PubMed Central

Acosta, Niuris; Sánchez, Elisa; Calderón, Laura; Cordoba-Diaz, Manuel; Cordoba-Diaz, Damián; Dom, Senne; Heras, Ángeles

2015-01-01

A chitosan-based hydrophilic system containing an olive leaf extract was designed and its antioxidant capacity was evaluated. Encapsulation of olive leaf extract in chitosan microspheres was carried out by a spray-drying process. The particles obtained with this technique were found to be spherical and had a positive surface charge, which is an indicator of mucoadhesiveness. FTIR and X-ray diffraction results showed that there are not specific interactions of polyphenolic compounds in olive leaf extract with the chitosan matrix. Stability and release studies of chitosan microspheres loaded with olive leaf extract before and after the incorporation into a moisturizer base were performed. The resulting data showed that the developed formulations were stable up to three months. The encapsulation efficiency was around 44% and the release properties of polyphenols from the microspheres were found to be pH dependent. At pH 7.4, polyphenols release was complete after 6 h; whereas the amount of polyphenols released was 40% after the same time at pH 5.5. PMID:26389926

Methotrexate loading in chitosan nanoparticles at a novel pH: Response surface modeling, optimization and characterization.

PubMed

Hashad, Rania A; Ishak, Rania A H; Geneidi, Ahmed S; Mansour, Samar

2016-10-01

The aim of this study was to assess the feasibility of employing a novel but critical formulation pH (6.2) to encapsulate an anionic model drug (methotrexate, MTX) into chitosan(Cs)-tripolyphosphate nanoparticles(NPs). A response surface methodology using a three-level full factorial design was applied studying the effects of two independent variables namely; Cs concentration and MTX concentration. The responses investigated were the entrapment efficiency (EE%), mean hydrodynamic particle size (PS), polydispersity index (PDI) and zeta potential (ZP). In order to simultaneously optimize the series of models obtained, the desirability function approach was applied with a goal to produce high percent of MTX encapsulated into highly charged Cs-TPP NPs of homogenous optimum PS. MTX-loaded CsNPs were successfully prepared at the novel pH applied. The suggested significant models were found quadratic for EE, PS and ZP responses, while 2-factor interaction model for PDI. The optimization overlay graph showed that the maximum global desirability, D=0.856, was reached when the conditions were set at high Cs and MTX concentration. Thus, the use of such optimized conditions, at this novel pH, achieved a maximum drug EE% (73.38%) into NPs characterized by optimum PS (232.6nm), small PDI value (0.195) and highly surface charged (+18.4mV). Copyright © 2016 Elsevier B.V. All rights reserved.

Sensors and regulators of intracellular pH.

PubMed

Casey, Joseph R; Grinstein, Sergio; Orlowski, John

2010-01-01

Protons dictate the charge and structure of macromolecules and are used as energy currency by eukaryotic cells. The unique function of individual organelles therefore depends on the establishment and stringent maintenance of a distinct pH. This, in turn, requires a means to sense the prevailing pH and to respond to deviations from the norm with effective mechanisms to transport, produce or consume proton equivalents. A dynamic, finely tuned balance between proton-extruding and proton-importing processes underlies pH homeostasis not only in the cytosol, but in other cellular compartments as well.

Aqueous speciation is likely to control the stable isotopic fractionation of cerium at varying pH

NASA Astrophysics Data System (ADS)

Nakada, Ryoichi; Tanaka, Masato; Tanimizu, Masaharu; Takahashi, Yoshio

2017-12-01

Cerium (Ce) can be used as a plaeoredox proxy as shown by a recent study of stable isotopic fractionation of Ce during adsorption and precipitation. However, the experiments in that study were performed at pH conditions lower than that of natural seawater. In the current study, adsorption and precipitation experiments were performed at pH 6.80, 8.20, and 11.00 with 2.25 mM dissolved carbonate to simulate Ce isotopic fractionation in the natural environment and examine the relationship between isotopic fractionation and Ce speciation in the liquid phase. Mean isotopic fractionation factors between liquid and solid phases (αLq-So) of Ce adsorbed on ferrihydrite did not depend on pH conditions or dissolved Ce species. In the Ce/δ-MnO2 system,αLq-So values decreased from 1.000411 (±0.000079) to 1.000194 (±0.000067) with increasing pH or number of carbonate ions, from Ce3+ to Ce(CO3)2-. In the Ce/precipitation system at pH 8.20 and 11.00 where Ce(CO3)2- is present in solution, the αLq-So values were 0.999821 (±0.000071) and 0.999589 (±0.000074), respectively, meaning that lighter isotope enrichment was observed in the liquid phase, which is the contrary to those of the other systems. Extended X-ray absorption fine structure (EXAFS) analyses were also performed to investigate the coordination structure of the adsorbed or precipitated Ce species that control the isotopic fractionation during adsorption. Even at higher pH, where Ce(CO3)+ or Ce(CO3)2- are the dominant dissolved species, the first coordination sphere of Ce in the solid phase in the Ce/ferrihydrite and Ce/precipitation systems was similar to that observed at pH 5.00 where Ce3+ was the main species in solution. A slight elongation in the Cesbnd O bond length in the solid phase at pH 11.00, where negatively charged dissolved species are dominant in the liquid phase, may cause a decrease in isotopic fractionation in the Ce/δ-MnO2 system. The coordination environment of Ce may not change significantly during the adsorption onto ferrihydrite, because Ce binds to the neutral surface OH group on ferrihydrite at pH below 8.5-8.8 (i.e. the pH of the point of zero charge (PZC) for ferrihydrite), similar to other cations when the metal-O distance was similar in hydrated and adsorbed species. At pH above PZC, Ce bonds to the negatively charged surface OH group, while Ce also bonds with CO32- in dissolved species. The reduced partition functions (ln β) for dissolved species (ln βLq) and adsorbed species (ln βSo) with the same trends canceled each other, because ln β of hydrated cation was reduced by the binding anion, resulting in small isotope fractionations. Thus, isotope fractionations for Ce/ferrihydrite may be quite small at the entire pH conditions in this study. The direction of the isotopic fractionation was estimated based on density functional theory (DFT) calculations, which confirmed that lighter Ce is enriched in the liquid phase when Ce forms a complex with carbonate ions. Therefore, this study indicates that the dissolved species can control stable Ce isotopic fractionation during precipitation reactions.

A Closer Look at Solar Wind Sputtering of Lunar Surface Materials

NASA Technical Reports Server (NTRS)

Barghouty, A. F.; Adams, J. H., Jr.; Meyer, F.; Mansur, L.; Reinhold, C.

2008-01-01

Solar-wind induced potential sputtering of the lunar surface may be a more efficient erosive mechanism than the "standard" kinetic (or physical) sputtering. This is partly based on new but limited laboratory measurements which show marked enhancements in the sputter yields of slow-moving, highly-charged ions impacting oxides. The enhancements seen in the laboratory can be orders of magnitude for some surfaces and highly charged incident ions, but seem to depend very sensitively on the properties of the impacted surface in addition to the fluence, energy and charge of the impacting ion. For oxides, potential sputtering yields are markedly enhanced and sputtered species, especially hydrogen and light ions, show marked dependence on both charge and dose.

Time and voltage dependences of nanoscale dielectric constant modulation on indium tin oxide films

NASA Astrophysics Data System (ADS)

Li, Liang; Hao, Haoyue; Zhao, Hua

2017-01-01

The modulation of indium tin oxide (ITO) films through surface charge accumulation plays an important role in many different applications. In order to elaborately study the modulation, we measured the dielectric constant of the modulated layer through examining the excitation of surface plasmon polaritons. Charges were pumped on the surfaces of ITO films through applying high voltage in appropriate directions. Experiments unveiled that the dielectric constant of the modulated layer had large variation along with the nanoscale charge accumulation. Corresponding numerical results were worked out through combining Drude model and Mayadas-Shatzkes model. Based on the above results, we deduced the time and voltage dependences of accumulated charge density, which revealed a long-time charge accumulation process.

Aggregation and charge behavior of metallic and nonmetallic nanoparticles in the presence of competing similarly-charged inorganic ions.

PubMed

Mukherjee, Biplab; Weaver, James W

2010-05-01

The influence of competing, similarly charged, inorganic ions on the size and charge behavior of suspended titanium-dioxide (nTiO(2)), silver (nAg) and fullerene (nC(60)) nanoparticles (NPs) was investigated. Under pH and ionic conditions similar to natural water bodies, Ca(2+) induced aggregation of nTiO(2) and nAg NPs more strongly than K(+) and Na(+). Although K(+) and Na(+) had a similar effect on aggregation, K(+) provided better screening of the particle surface charge presumably because of its small hydrated radius. These effects were decidedly more prominent for TiO(2) than Ag. Anions (co-ions), SO(4)(2-) and Cl(-), affected the surface charge behavior of nTiO(2) but not of nAg NPs. The zeta potential (ZP) of nTiO(2) NPs was more negative at higher SO(4)(2-)/Cl(-) ratios than lower. When Mg(2+) was the counterion, charge inversion and rapid aggregation of nC(60) NPs occurred under alkaline conditions, with a more pronounced effect for Cl(-) than SO(4)(2-). Response dissimilarities suggest fundamental differences in the interfacial-interaction characteristics of these NPs in the aquatic environment with corresponding differences in transport of these particles. Our study also shows the important role played by the iso-electric point pH (pH(iep)) of the NPs in determining their aggregation kinetics in the environment.

pH Sensing Properties of Flexible, Bias-Free Graphene Microelectrodes in Complex Fluids: From Phosphate Buffer Solution to Human Serum.

PubMed

Ping, Jinglei; Blum, Jacquelyn E; Vishnubhotla, Ramya; Vrudhula, Amey; Naylor, Carl H; Gao, Zhaoli; Saven, Jeffery G; Johnson, Alan T Charlie

2017-08-01

Advances in techniques for monitoring pH in complex fluids can have a significant impact on analytical and biomedical applications. This study develops flexible graphene microelectrodes (GEs) for rapid (<5 s), very-low-power (femtowatt) detection of the pH of complex biofluids by measuring real-time Faradaic charge transfer between the GE and a solution at zero electrical bias. For an idealized sample of phosphate buffer solution (PBS), the Faradaic current is varied monotonically and systematically with the pH, with a resolution of ≈0.2 pH unit. The current-pH dependence is well described by a hybrid analytical-computational model, where the electric double layer derives from an intrinsic, pH-independent (positive) charge associated with the graphene-water interface and ionizable (negative) charged groups. For ferritin solution, the relative Faradaic current, defined as the difference between the measured current response and a baseline response due to PBS, shows a strong signal associated with ferritin disassembly and the release of ferric ions at pH ≈2.0. For samples of human serum, the Faradaic current shows a reproducible rapid (<20 s) response to pH. By combining the Faradaic current and real-time current variation, the methodology is potentially suitable for use to detect tumor-induced changes in extracellular pH. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Application of Iron Oxide as a pH-dependent Indicator for Improving the Nutritional Quality

PubMed Central

2016-01-01

Acid food indicators can be used as pH indicators for evaluating the quality and freshness of fermented products during the full course of distribution. Iron oxide particles are hardly suspended in water, but partially or completely agglomerated. The agglomeration degree of the iron oxide particles depends on the pH. The pH-dependent particle agglomeration or dispersion can be useful for monitoring the acidity of food. The zeta potential of iron oxide showed a decreasing trend as the pH increased from 2 to 8, while the point of zero charge (PZC) was observed around at pH 6.0-7.0. These results suggested that the size of the iron oxide particles was affected by the change in pH levels. As a result, the particle sizes of iron oxide were smaller at lower pH than at neutral pH. In addition, agglomeration of the iron oxide particles increased as the pH increased from 2 to 7. In the time-dependent aggregation test, the average particle size was 730.4 nm and 1,340.3 nm at pH 2 and 7, respectively. These properties of iron oxide particles can be used to develop an ideal acid indicator for food pH and to monitor food quality, besides a colorant or nutrient for nutrition enhancement and sensory promotion in food industry. PMID:27482521

Profiling Charge Complementarity and Selectivity for Binding at the Protein Surface

PubMed Central

Sulea, Traian; Purisima, Enrico O.

2003-01-01

A novel analysis and representation of the protein surface in terms of electrostatic binding complementarity and selectivity is presented. The charge optimization methodology is applied in a probe-based approach that simulates the binding process to the target protein. The molecular surface is color coded according to calculated optimal charge or according to charge selectivity, i.e., the binding cost of deviating from the optimal charge. The optimal charge profile depends on both the protein shape and charge distribution whereas the charge selectivity profile depends only on protein shape. High selectivity is concentrated in well-shaped concave pockets, whereas solvent-exposed convex regions are not charge selective. This suggests the synergy of charge and shape selectivity hot spots toward molecular selection and recognition, as well as the asymmetry of charge selectivity at the binding interface of biomolecular systems. The charge complementarity and selectivity profiles map relevant electrostatic properties in a readily interpretable way and encode information that is quite different from that visualized in the standard electrostatic potential map of unbound proteins. PMID:12719221

Removal of binary dyes mixtures with opposite and similar charges by adsorption, coagulation/flocculation and catalytic oxidation in the presence of CeO2/H2O2 Fenton-like system.

PubMed

Issa Hamoud, Houeida; Finqueneisel, Gisèle; Azambre, Bruno

2017-06-15

In this study, the removal of binary mixtures of dyes with similar (Orange II/Acid Green 25) or opposite charges (Orange II/Malachite Green) was investigated either by simple adsorption on ceria or by the heterogeneous Fenton reaction in presence of H 2 O 2 . First, the CeO 2 nanocatalyst with high specific surface area (269 m 2 /g) and small crystal size (5 nm) was characterized using XRD, Raman spectroscopy and N 2 physisorption at 77 K. The adsorption of single dyes was studied either from thermodynamic and kinetic viewpoints. It is shown that the adsorption of dyes on ceria surface is highly pH-dependent and followed a pseudo-second order kinetic model. Adsorption isotherms fit well the Langmuir model with a complete monolayer coverage and higher affinity towards Orange II at pH 3, compared to other dyes. For the (Orange II/Acid Green 25) mixture, both the amounts of dyes adsorbed on ceria surface and discoloration rates measured from Fenton experiments were decreased by comparison with single dyes. This is due to the adsorption competition existing onto the same surface Ce x+ sites and the reaction competition with hydroxyl radicals, respectively. The behavior of the (Orange II/Malachite Green) mixture is markedly different. Dyes with opposite charges undergo paired adsorption on ceria as well as homogeneous and heterogeneous coagulation/flocculation processes, but can also be removed by heterogeneous Fenton process. Copyright © 2016 Elsevier Ltd. All rights reserved.

Stability and in vitro digestibility of emulsions containing lecithin and whey proteins.

PubMed

Mantovani, Raphaela Araujo; Cavallieri, Ângelo Luiz Fazani; Netto, Flavia Maria; Cunha, Rosiane Lopes

2013-09-01

The effect of pH and high-pressure homogenization on the properties of oil-in-water (O/W) emulsions stabilized by lecithin and/or whey proteins (WPI) was evaluated. For this purpose, emulsions were characterized by visual analysis, droplet size distribution, zeta potential, electrophoresis, rheological measurements and their response to in vitro digestion. Lecithin emulsions were stable even after 7 days of storage and WPI emulsions were unstable only at pH values close to the isoelectric point (pI) of proteins. Systems containing the mixture of lecithin and WPI showed high kinetic instability at pH 3, which was attributed to the electrostatic interaction between the emulsifiers oppositely charged at this pH value. At pH 5.5 and 7, the mixture led to reduction of the droplet size with enhanced emulsion stability compared to the systems with WPI or lecithin. The stability of WPI emulsions after the addition of lecithin, especially at pH 5.5, was associated with the increase of droplet surface charge density. The in vitro digestion evaluation showed that WPI emulsion was more stable against gastrointestinal conditions.

Adsorption effectiveness of β-lactoglobulin onto gold surface determined by quartz crystal microbalance.

PubMed

Jachimska, B; Świątek, S; Loch, J I; Lewiński, K; Luxbacher, T

2018-06-01

Bovine β-lactoglobulin (LGB) is a transport protein that can bind to its structure hydrophobic bioactive molecules. Due to the lack of toxicity, high stability and pH-dependent molecular binding mechanism, lactoglobulin can be used as a carrier of sparingly soluble drugs. Dynamic light scattering has confirmed LGB's tendency to create oligomeric forms. The hydrodynamic diameter of LGB molecules varies from 4 nm to 6 nm in the pH range of 2-10 and ionic strength I = 0.001-0.15 M, which corresponds to the presence of mono or dimeric LGB forms. The LGB zeta potential varies from 26.5 mV to -33.3 mV for I = 0.01 M and from 13.3 mV to -16 mV for I = 0.15 M in the pH range of 2-10. The isoelectric point is at pH 4.8. As a result of strong surface charge compensation, the maximum effective ionization degree of the LGB molecule is 35% for ionic strength I = 0.01 M and 22% for I = 0.15 M. The effectiveness of adsorption is linked with the properties of the protein, as well as those of the adsorption surface. The functionalization of gold surfaces with β-lactoglobulin (LGB) was studied using a quartz crystal microbalance with energy dissipation monitoring (QCM-D). The effectiveness of LGB adsorption correlates strongly with a charge of gold surface and the zeta potential of the molecule. The greatest value of the adsorbed mass was observed in the pH range in which LGB has a positive zeta potential values, below pH 4.8. This observation shows that electrostatic interactions play a dominant role in LGB adsorption on gold surfaces. Based on the adsorbed mass, protein orientation on gold surfaces was determined. The preferential side-on orientation of LGB molecules observed in the adsorption layer is consistent with the direction of the molecule dipole momentum determined by molecular dynamics simulations of the protein (MD). The use of the QCM-D method also allowed us to determine the effectiveness of adsorption of LGB on gold surface. Knowing the mechanism of LGB adsorption is significant importance for determining the optimum conditions for immobilizing this protein on solid surfaces. As β-lactoglobulin is a protein that binds various ligands, the binding properties of immobilized β-lactoglobulin can be used to design controlled protein structures for biomedical applications. Copyright © 2018 Elsevier B.V. All rights reserved.

Lentil and chickpea protein-stabilized emulsions: optimization of emulsion formulation.

PubMed

Can Karaca, Asli; Nickerson, Michael T; Low, Nicholas H

2011-12-28

Chickpea and lentil protein-stabilized emulsions were optimized with regard to pH (3.0-8.0), protein concentration (1.1-4.1% w/w), and oil content (20-40%) for their ability to form and stabilize oil-in-water emulsions using response surface methodology. Specifically, creaming stability, droplet size, and droplet charge were assessed. Optimum conditions for minimal creaming (no serum separation after 24 h), small droplet size (<2 μm), and high net droplet charge (absolute value of ZP > 40 mV) were identified as 4.1% protein, 40% oil, and pH 3.0 or 8.0, regardless of the plant protein used for emulsion preparation.

On the origin of the halo stabilization.

PubMed

Trulsson, Martin; Jönsson, Bo; Labbez, Christophe

2013-01-14

Monte Carlo simulations show that charge-regulation alone can cause highly charged zirconium nanoparticles to adsorb to a similarly charged or neutral silica particle and thereby stabilizing the latter. This mechanism, referred to as halo stabilization, is quite general and applicable in a range of systems provided that pH, van der Waals forces, and dissociation constants of the charge-regulating particles are properly chosen. In our modeling we see an overall attraction at low volume fractions of nanoparticles, while at higher a repulsive barrier is created, stabilizing the microparticles and protecting them from aggregation. The charge-regulation mechanism also turns the silica surface from positively charged, without nanoparticles, to negatively charged in the presence of nanoparticles.

Effects of Discrete Charge Clustering in Simulations of Charged Interfaces.

PubMed

Grime, John M A; Khan, Malek O

2010-10-12

A system of counterions between charged surfaces is investigated, with the surfaces represented by uniform charged planes and three different arrangements of discrete surface charges - an equispaced grid and two different clustered arrangements. The behaviors of a series of systems with identical net surface charge density are examined, with particular emphasis placed on the long ranged corrections via the method of "charged slabs" and the effects of the simulation cell size. Marked differences are observed in counterion distributions and the osmotic pressure dependent on the particular representation of the charged surfaces; the uniformly charged surfaces and equispaced grids of discrete charge behave in a broadly similar manner, but the clustered systems display a pronounced decrease in osmotic pressure as the simulation size is increased. The influence of the long ranged correction is shown to be minimal for all but the very smallest of system sizes.

Electroreduction of carbon monoxide over a copper nanocube catalyst: Surface structure and pH dependence on selectivity

DOE PAGES

Roberts, F. Sloan; Kuhl, Kendra P.; Nilsson, Anders

2016-02-16

The activity and selectivity for CO 2/CO reduction over copper electrodes is strongly dependent on the local surface structure of the catalyst and the pH of the electrolyte. Here we investigate a unique, copper nanocube surface (CuCube) as a CO reduction electrode under neutral and basic pH, using online electrochemical mass spectroscopy (OLEMS) to determine the onset potentials and relative intensities of methane and ethylene production. To relate the unique selectivity to the surface structure, the CuCube surface reactivity is compared to polycrystalline copper and three single crystals under the same reaction conditions. Here, we find that the high selectivitymore » for ethylene over the CuCube surface is most comparable to the Cu(100) surface, which has the cubic unit cell. However, the suppression of methane production over CuCube is unique to that particular surface. Basic pH is also shown to enhance ethylene selectivity on all surfaces, again with the CuCube surface being unique.« less

Colloidal approach to dispersion and enhanced deaggregation of aqueous ferrite suspensions

NASA Astrophysics Data System (ADS)

Mandanas, Michael Patrick M.

The role of solution and surface chemistry on deaggregation of calcined ferrites during attrition (stirred-media) milling of aqueous suspensions were investigated. Suspensions of commercially calcined Fe2O 3 powder (d50 ˜ 5.0 mum) were milled at different solid loadings and suspension pH. The drift of suspension pH, from pH 2.5 to pH 7.0, during solid loading experiments accounted for the observed reagglomeration with milling time. The observed deaggregation rates during pH stat milling, in the acidic region, can be related to (i) elevated solubility and (ii) enhanced dispersion via surface charge. Proton adsorption density during pH stat milling at different pH values is also comparable to existing potentiometric titration plots and can be related to deaggregation rates. A passivation-dispersion approach for dispersing manganese zinc ferrite (MnxZn(1 - x)Fe2O4) powder is presented. Addition of oxalic acid can help control dissolution reactions from particle surfaces and is subsequently dispersed with polyethyleneimine (PEI). Fully dissociated oxalic acid (pK1 = 1.2, pK2 = 4.3) solutions reacted with MnxZn(1 - x)Fe 2O4 leads to the formation of a uniform negative charge on the particle surface, resulting from the sparingly soluble salt formed on the surface. The resulting rheological data for passivation/dispersion of relatively high solid MnxZn(1 - x)Fe2O 4 suspensions (˜80 w/o, (˜40 v/o)) demonstrate improved colloid stability with improved rheological properties. Using the passivation dispersion scheme developed, deaggregation of commercially calcined MnxZn(1 - x)Fe2O4 powders during attrition milling was investigated. Reagglomeration is apparent when using a typical treatment, 2 w/w of a sulfonated based naphthalene condensate, during deaggregation of the calcined MnxZn(1 - x)Fe 2O4. However, is not observed for select oxalate/PEI treatments. The determined ideal treatment is 2 w/w oxalate and 3 w/w PEI based on the particle size and rheological characteristics of the suspensions during milling. (Abstract shortened by UMI.)

Surface-charge-dependent cell localization and cytotoxicity of cerium oxide nanoparticles.

PubMed

Asati, Atul; Santra, Santimukul; Kaittanis, Charalambos; Perez, J Manuel

2010-09-28

Cerium oxide nanoparticles (nanoceria) have shown great potential as antioxidant and radioprotective agents for applications in cancer therapy. Recently, various polymer-coated nanoceria preparations have been developed to improve their aqueous solubility and allow for surface functionalization of these nanoparticles. However, the interaction of polymer-coated nanoceria with cells, their uptake mechanism, and subcellular localization are poorly understood. Herein, we engineered polymer-coated cerium oxide nanoparticles with different surface charges (positive, negative, and neutral) and studied their internalization and toxicity in normal and cancer cell lines. The results showed that nanoceria with a positive or neutral charge enters most of the cell lines studied, while nanoceria with a negative charge internalizes mostly in the cancer cell lines. Moreover, upon entry into the cells, nanoceria is localized to different cell compartments (e.g., cytoplasm and lysosomes) depending on the nanoparticle's surface charge. The internalization and subcellular localization of nanoceria plays a key role in the nanoparticles' cytotoxicity profile, exhibiting significant toxicity when they localize in the lysosomes of the cancer cells. In contrast, minimal toxicity is observed when they localize into the cytoplasm or do not enter the cells. Taken together, these results indicate that the differential surface-charge-dependent localization of nanoceria in normal and cancer cells plays a critical role in the nanoparticles' toxicity profile.

Structural Insight into and Mutational Analysis of Family 11 Xylanases: Implications for Mechanisms of Higher pH Catalytic Adaptation.

PubMed

Bai, Wenqin; Zhou, Cheng; Zhao, Yueju; Wang, Qinhong; Ma, Yanhe

2015-01-01

To understand the molecular basis of higher pH catalytic adaptation of family 11 xylanases, we compared the structures of alkaline, neutral, and acidic active xylanases and analyzed mutants of xylanase Xyn11A-LC from alkalophilic Bacillus sp. SN5. It was revealed that alkaline active xylanases have increased charged residue content, an increased ratio of negatively to positively charged residues, and decreased Ser, Thr, and Tyr residue content relative to non-alkaline active counterparts. Between strands β6 and β7, alkaline xylanases substitute an α-helix for a coil or turn found in their non-alkaline counterparts. Compared with non-alkaline xylanases, alkaline active enzymes have an inserted stretch of seven amino acids rich in charged residues, which may be beneficial for xylanase function in alkaline conditions. Positively charged residues on the molecular surface and ionic bonds may play important roles in higher pH catalytic adaptation of family 11 xylanases. By structure comparison, sequence alignment and mutational analysis, six amino acids (Glu16, Trp18, Asn44, Leu46, Arg48, and Ser187, numbering based on Xyn11A-LC) adjacent to the acid/base catalyst were found to be responsible for xylanase function in higher pH conditions. Our results will contribute to understanding the molecular mechanisms of higher pH catalytic adaptation in family 11 xylanases and engineering xylanases to suit industrial applications.

Structural Insight into and Mutational Analysis of Family 11 Xylanases: Implications for Mechanisms of Higher pH Catalytic Adaptation

PubMed Central

Bai, Wenqin; Zhou, Cheng; Zhao, Yueju; Wang, Qinhong; Ma, Yanhe

2015-01-01

To understand the molecular basis of higher pH catalytic adaptation of family 11 xylanases, we compared the structures of alkaline, neutral, and acidic active xylanases and analyzed mutants of xylanase Xyn11A-LC from alkalophilic Bacillus sp. SN5. It was revealed that alkaline active xylanases have increased charged residue content, an increased ratio of negatively to positively charged residues, and decreased Ser, Thr, and Tyr residue content relative to non-alkaline active counterparts. Between strands β6 and β7, alkaline xylanases substitute an α-helix for a coil or turn found in their non-alkaline counterparts. Compared with non-alkaline xylanases, alkaline active enzymes have an inserted stretch of seven amino acids rich in charged residues, which may be beneficial for xylanase function in alkaline conditions. Positively charged residues on the molecular surface and ionic bonds may play important roles in higher pH catalytic adaptation of family 11 xylanases. By structure comparison, sequence alignment and mutational analysis, six amino acids (Glu16, Trp18, Asn44, Leu46, Arg48, and Ser187, numbering based on Xyn11A-LC) adjacent to the acid/base catalyst were found to be responsible for xylanase function in higher pH conditions. Our results will contribute to understanding the molecular mechanisms of higher pH catalytic adaptation in family 11 xylanases and engineering xylanases to suit industrial applications. PMID:26161643

The effects of surface chemistry of mesoporous silica materials and solution pH on kinetics of molsidomine adsorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolinina, E.S.; Parfenyuk, E.V., E-mail: terrakott37@mail.ru

2014-01-15

Adsorption kinetics of molsidomine on mesoporous silica material (UMS), the phenyl- (PhMS) and mercaptopropyl-functionalized (MMS) derivatives from solution with different pH and 298 K was studied. The adsorption kinetics was found to follow the pseudo-second-order kinetic model for all studied silica materials and pH. Effects of surface functional groups and pH on adsorption efficiency and kinetic adsorption parameters were investigated. At all studied pH, the highest molsidomine amount is adsorbed on PhMS due to π–π interactions and hydrogen bonding between surface groups of PhMS and molsidomine molecules. An increase of pH results in a decrease of the amounts of adsorbedmore » molsidomine onto the silica materials. Furthermore, the highest adsorption rate kinetically evaluated using a pseudo-second-order model, is observed onto UMS and it strongly depends on pH. The mechanism of the adsorption process was determined from the intraparticle diffusion and Boyd kinetic film–diffusion models. The results showed that the molsidomine adsorption on the silica materials is controlled by film diffusion. Effect of pH on the diffusion parameters is discussed. - Graphical abstract: The kinetic study showed that the k{sub 2} value, the rate constant of pseudo-second order kinetic model, is the highest for molsidomine adsorption on UMS and strongly depends on pH because it is determined by availability and accessibility of the reaction sites of the adsorbents molsidomine binding. Display Omitted - Highlights: • The adsorption capacities of UMS, PhMS and MMS were dependent on the pH. • At all studied pH, the highest molsidomine amount is adsorbed on PhMS. • The highest adsorption rate, k{sub 2}, is observed onto UMS and strongly depends on pH. • Film diffusion was the likely rate-limiting step in the adsorption process.« less

Polarized Neutron Reflectometry of Nickel Corrosion Inhibitors.

PubMed

Wood, Mary H; Welbourn, Rebecca J L; Zarbakhsh, Ali; Gutfreund, Philipp; Clarke, Stuart M

2015-06-30

Polarized neutron reflectometry has been used to investigate the detailed adsorption behavior and corrosion inhibition mechanism of two surfactants on a nickel surface under acidic conditions. Both the corrosion of the nickel surface and the structure of the adsorbed surfactant layer could be monitored in situ by the use of different solvent contrasts. Layer thicknesses and roughnesses were evaluated over a range of pH values, showing distinctly the superior corrosion inhibition of one negatively charged surfactant (sodium dodecyl sulfate) compared to a positively charged example (dodecyl trimethylammonium bromide) due to its stronger binding interaction with the surface. It was found that adequate corrosion inhibition occurs at significantly less than full surface coverage.

Anions adsorption onto nanoparticles: effects on colloid stability and mobility in the environment

NASA Astrophysics Data System (ADS)

Missana, Tiziana; Benedicto, Ana; Mayordomo, Natalia; Alonso, Ursula

2013-04-01

Nanoparticles and colloids can enhance the contaminant transport in groundwater, if the contaminant is irreversibly adsorbed onto their surface; additionally colloids must be stable and mobile under the chemical conditions of the environment of interest. Colloid stability and mobility are factors directly related to the chemistry of the water, which determines the charge and size of the particles, but these colloidal properties can also be affected by the contaminant adsorption. This last point, which is potentially very relevant on the overall colloid-driven transport, is scarcely investigated. The evaluation of the stability of a colloidal system is generally carried out by measuring the aggregation kinetic after the change of a specific chemical condition, mainly pH or ionic strength of the aqueous solution. The effect of anion adsorption onto the stability of colloidal systems is mostly neglected. Parameters of the nanoparticles,as the point of zero charge (pH PCZ) or the isoelectric point (pH IEP) are determined with "inert" electrolytes and this might not be representative of their real behavior in natural systems. In this work, the effects of the Se(IV) (selenite) adsorption on alumina (Al2O3) nanoparticles have been analyzed. Selenite adsorption was studied in a wide range of pH (2-12) and ionic strengths (0.0005 - 0.1 M in NaClO4) and the effect of the adsorption on the main properties of the colloids (size and charge) were analyzed. Se adsorption on Al2O3 is almost independent of the ionic strength and decreases with increasing pH; sorption data were successfully fit by surface complexation modeling. Selenite adsorption (at medium-high surface occupancies) clearly affected the stability of Al2O3 colloids, with a clear shift of the isoelectric point towards more acid pH and enhancing colloid aggregation when the ionic strength increases. Considering the obtained results, the effect of anions in the chemical composition of natural water, frequently not accounted for in stability studies, will be discussed, as well as their implications on possible colloid-driven selenite transport in the environment.

Increasing surface enhanced Raman spectroscopy effect of RNA and DNA components by changing the pH of silver colloidal suspensions.

PubMed

Primera-Pedrozo, Oliva M; Rodríguez, Gabriela Del Mar; Castellanos, Jorge; Felix-Rivera, Hilsamar; Resto, Oscar; Hernández-Rivera, Samuel P

2012-02-15

This work focused on establishing the parameters for enhancing the Raman signals of DNA and RNA constituents: nitrogenous bases, nucleosides and nucleotides, using metallic nanoparticles as surface enhanced Raman scattering substrates. Silver nanospheres were synthesized using sodium borohydride as a reducing agent and sodium citrate as a capping agent. The prepared nanoparticles had a surface plasmon band at ∼384nm and an average size of 12±3nm. The nanoparticles' surface charge was manipulated by changing the pH of the Ag colloidal suspensions in the range of 1-13. Low concentrations as 0.7μM were detected under the experimental conditions. The optimum pH values were: 7 for adenine, 9 for AMP, 5 for adenosine, 7 for dAMP and 11 for deoxyadenosine. Copyright © 2011 Elsevier B.V. All rights reserved.

Film Self-Assembly of Oppositely Charged Macromolecules Triggered by Electrochemistry through a Morphogenic Approach.

PubMed

Dochter, Alexandre; Garnier, Tony; Pardieu, Elodie; Chau, Nguyet Trang Thanh; Maerten, Clément; Senger, Bernard; Schaaf, Pierre; Jierry, Loïc; Boulmedais, Fouzia

2015-09-22

The development of new surface functionalization methods that are easy to use, versatile, and allow local deposition represents a real scientific challenge. Overcoming this challenge, we present here a one-pot process that consists in self-assembling, by electrochemistry on an electrode, films made of oppositely charged macromolecules. This method relies on a charge-shifting polyanion, dimethylmaleic-modified poly(allylamine) (PAHd), that undergoes hydrolysis at acidic pH, leading to an overall switching of its charge. When a mixture of the two polyanions, PAHd and poly(styrenesulfonate) (PSS), is placed in contact with an electrode, where the pH is decreased locally by electrochemistry, the transformation of PAHd into a polycation (PAH) leads to the continuous self-assembly of a nanometric PAH/PSS film by electrostatic interactions. The pH decrease is obtained by the electrochemical oxidation of hydroquinone, which produces protons locally over nanometric distances. Using a negatively charged enzyme, alkaline phosphatase (AP), instead of PSS, this one-pot process allows the creation of enzymatically active films. Under mild conditions, self-assembled PAH/AP films have an enzymatic activity which is adjustable simply by controlling the self-assembly time. The selective functionalization of microelectrode arrays by PAH/AP was achieved, opening the route toward miniaturized biosensors.

Effect of strong acids on red mud structural and fluoride adsorption properties.

PubMed

Liang, Wentao; Couperthwaite, Sara J; Kaur, Gurkiran; Yan, Cheng; Johnstone, Dean W; Millar, Graeme J

2014-06-01

The removal of fluoride using red mud has been improved by acidifying red mud with hydrochloric, nitric and sulphuric acid. The acidification of red mud causes sodalite and cancrinite phases to dissociate, confirmed by the release of sodium and aluminium into solution as well as the disappearance of sodalite bands and peaks in infrared and X-ray diffraction data. The dissolution of these mineral phases increases the amount of available iron and aluminium oxide/hydroxide sites that are accessible for the adsorption of fluoride. However, concentrated acids have a negative effect on adsorption due to the dissolution of these iron and aluminium oxide/hydroxide sites. The removal of fluoride is dependent on the charge of iron and aluminium oxide/hydroxides on the surface of red mud. Acidifying red mud with hydrochloric, nitric and sulphuric acid resulted in surface sites of the form ≡SOH2(+) and ≡SOH. Optimum removal is obtained when the majority of surface sites are in the form ≡SOH2(+) as the substitution of a fluoride ion does not cause a significant increase in pH. This investigation shows the importance of having a low and consistent pH for the removal of fluoride from aqueous solutions using red mud. Copyright © 2014 Elsevier Inc. All rights reserved.

Block ionomer complexes as prospective nanocontainers for drug delivery.

PubMed

Oh, Kyung T; Bronich, Tatiana K; Bromberg, Lev; Hatton, T Alan; Kabanov, Alexander V

2006-09-28

Nanosized environmentally responsive materials are of special interest for various applications, including drug delivery. Block ionomer complexes (BIC) composed of graft-comb copolymers of Pluronic and poly(acrylic acid) (Pluronic-PAA) and a model cationic surfactant, hexadecyltrimethylammonium bromide (HTAB), were synthesized by mixing the polymer and surfactant in aqueous media. According to TEM, the resulting BIC represented spherical particles of nanoscale size (50 to 100 nm). The stability of the BIC in the aqueous dispersion depended on the lengths of the hydrophilic poly(ethylene oxide) and hydrophobic poly(propylene oxide) chains in Pluronic molecules as well as on the surface charge of the resulting complexes. The latter was controlled by changing the ratio of the Pluronic-PAA and HTAB in the BIC and by changing the pH due to reversible ionization of the PAA chains. The acidification of the media below pH 6.0 resulted in the appearance of a strong positive charge on the BIC, which in the intracellular environment can trigger interaction of such BIC with the cell membranes. An efficient solubilization of a model hydrophobic molecule, Sudan III, and a drug, Etoposide, in such BIC was demonstrated with the loading capacities of about 6 to 15% by weight of the dispersed complex. Overall, these BIC wield a promise as environmentally responsive nanocarriers for pharmaceuticals.

The pH-dependent release of platinum group elements (PGEs) from gasoline and diesel fuel catalysts: Implication for weathering in soils.

PubMed

Suchá, Veronika; Mihaljevič, Martin; Ettler, Vojtěch; Strnad, Ladislav

2016-04-15

Powdered samples of new and old gasoline catalysts (Pt, Pd, Rh) and new and old diesel (Pt) catalysts were subjected to a pH-static leaching procedure (pH 2-9) coupled with thermodynamic modeling using PHREEQC-3 to verify the release and mobility of PGEs (platinum group elements). PGEs were released under acidic conditions, mostly exhibiting L-shaped leaching patterns: diesel old: 5.47, 0.005, 0.02; diesel new: 68.5, 0.23, 0.11; gasoline old: 0.1, 11.8, 4.79; gasoline new 2.6, 25.2, 35.9 in mg kg(-1) for Pt, Pd and Rh, respectively. Only the new diesel catalyst had a strikingly different leaching pattern with elevated concentrations at pH 4, probably influenced by the dissolution of the catalyst carrier and washcoat. The pH-static experiment coupled with thermodynamic modeling was found to be an effective instrument for understanding the leaching behavior of PGEs under various environmental conditions, and indicated that charged Pt and Rh species may be adsorbed on the negatively charged surface of kaolinite or Mn oxides in the soil system, whereas uncharged Pd and Rh species may remain mobile in soil solutions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Diffusion of flexible, charged, nanoscopic molecules in solution: Size and pH dependence for PAMAM dendrimer

NASA Astrophysics Data System (ADS)

Maiti, Prabal K.; Bagchi, Biman

2009-12-01

In order to understand self-diffusion (D) of a charged, flexible, and porous nanoscopic molecule in water, we carry out very long, fully atomistic molecular dynamics simulation of PAMAM dendrimer up to eight generations in explicit salt water under varying pH. We find that while the radius of gyration (Rg) varies as N1/3, the self-diffusion constant (D ) scales, surprisingly, as N-α, with α =0.39 at high pH and 0.5 at neutral pH, indicating a dramatic breakdown of Stokes-Einstein relation for diffusion of charged nanoscopic molecules. The variation in D as a function of radius of gyration demonstrates the importance of treating water and ions explicitly in the diffusion process of a flexible nanoscopic molecule. In agreement with recent experiments, the self-diffusion constant increases with pH, revealing the importance of dielectric friction in the diffusion process. The shape of a dendrimer is found to fluctuate on a nanosecond time scale. We argue that this flexibility (and also the porosity) of the dendrimer may play an important role in determining the mean square displacement of the dendrimer and the breakdown of the Stokes-Einstein relation between diffusion constant and the radius.

Electroacoustic isoelectric point determinations of bauxite refinery residues: different neutralization techniques and minor mineral effects.

PubMed

Freire, Tiago S S; Clark, Malcolm W; Comarmond, M Josick; Payne, Timothy E; Reichelt-Brushett, Amanda J; Thorogood, Gordon J

2012-08-14

Bauxite refinery residue (BRR) is a highly caustic, iron hydroxide-rich byproduct from alumina production. Some chemical treatments of BRR reduce soluble alkalinity and lower residue pH (to values <10) and generate a modified BRR (MBRR). MBRR has excellent acid neutralizing (ANC) and trace-metal adsorption capacities, making it particularly useful in environmental remediation. However, soluble ANC makes standard acid-base isoelectric point (IEP) determination difficult. Consequently, the IEP of a BRR and five MBRR derivatives (sulfuric acid-, carbon dioxide-, seawater-, a hybrid neutralization, i.e, partial CO(2) neutralization followed by seawater, and an activated-seawater-neutralized MBRR) were determined using electroacoustic techniques. Residues showed three significantly different groups of IEPs (p < 0.05) based around the neutralization used. Where the primary mineral assemblage is effectively unchanged, the IEPs were not significantly different from BRR (pH 6.6-6.9). However, neutralizations generating neoformational minerals (alkalinity precipitation) significantly increased the IEP to pH 8.1, whereas activation (a removal of some primary mineralogy) significantly lowered the IEP to pH 6.2. Moreover, surface charging curves show that surfaces remain in the ±30 mV surface charge instability range, which provides an explanation as to why MBRRs remove trace metals and oxyanions over a broad pH range, often simultaneously. Importantly, this work shows that minor mineral components in complex mineral systems may have a disproportionate effect on the observable bulk IEP. Furthermore, this work shows the appropriateness of electroacoustic techniques in investigating samples with significant soluble mineral components (e.g., ANC).

Boosting water oxidation layer-by-layer.

PubMed

Hidalgo-Acosta, Jonnathan C; Scanlon, Micheál D; Méndez, Manuel A; Amstutz, Véronique; Vrubel, Heron; Opallo, Marcin; Girault, Hubert H

2016-04-07

Electrocatalysis of water oxidation was achieved using fluorinated tin oxide (FTO) electrodes modified with layer-by-layer deposited films consisting of bilayers of negatively charged citrate-stabilized IrO2 NPs and positively charged poly(diallyldimethylammonium chloride) (PDDA) polymer. The IrO2 NP surface coverage can be fine-tuned by controlling the number of bilayers. The IrO2 NP films were amorphous, with the NPs therein being well-dispersed and retaining their as-synthesized shape and sizes. UV/vis spectroscopic and spectro-electrochemical studies confirmed that the total surface coverage and electrochemically addressable surface coverage of IrO2 NPs increased linearly with the number of bilayers up to 10 bilayers. The voltammetry of the modified electrode was that of hydrous iridium oxide films (HIROFs) with an observed super-Nernstian pH response of the Ir(III)/Ir(IV) and Ir(IV)-Ir(IV)/Ir(IV)-Ir(V) redox transitions and Nernstian shift of the oxygen evolution onset potential. The overpotential of the oxygen evolution reaction (OER) was essentially pH independent, varying only from 0.22 V to 0.28 V (at a current density of 0.1 mA cm(-2)), moving from acidic to alkaline conditions. Bulk electrolysis experiments revealed that the IrO2/PDDA films were stable and adherent under acidic and neutral conditions but degraded in alkaline solutions. Oxygen was evolved with Faradaic efficiencies approaching 100% under acidic (pH 1) and neutral (pH 7) conditions, and 88% in alkaline solutions (pH 13). This layer-by-layer approach forms the basis of future large-scale OER electrode development using ink-jet printing technology.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avazbaeva, Zaure; Sung, Woongmo; Lee, Jonggwan

In this paper, it has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284–285, 166–174). However, by lowering the pH further, ODA molecules reoccupy the surface, and a full monolayer is recovered at pH 2.5. Using surface sum-frequency spectroscopy and pressure–area isotherms, it is found that the recovered monolayer at very low pH has a larger area per molecule with many gauche defects in the ODA molecules as comparedmore » to that at high pH values. This structural change suggests that the reappearance of the monolayer is due to the adsorbed Cl– counterions to the protonated amine groups, leading to partial charge neutralization. This proposition is confirmed by intentionally adding monovalent salts (i.e., NaCl, NaBr, or NaI) to the subphase to recover the monolayer at pH 3.5, in which the detailed structure of the monolayer is confirmed by sum frequency spectra and the adsorbed anions by X-ray reflectivity.« less

The study of the dynamics of erythrocytes under the influence of an external electric field

NASA Astrophysics Data System (ADS)

Mamaeva, Sargylana N.; Maksimov, Georgy V.; Antonov, Stepan R.

2017-11-01

A mathematical model is considered for the determination of the surface charge of an erythrocyte with its shape approximated by a surface of revolution of the second order, and the investigation of the dynamics of erythrocytes under the influence of an external electric field. In the first part of this work, the electrical surface charge of the erythrocyte of the patient was calculated with the assumption that the change in the shape and size of the red blood cells leads to stabilization of the electric field, providing a normal electrostatic repulsion. In the second part of the work, the research results of dynamics of changes in the morphology of erythrocytes under the influence of an external electric field depending on the values of their surface charge and resistance of blood plasma is presented. In the course of the work, the dependence of the surface charge of red blood cells from their shape and size is presented. The determination of the relationship between the value of the charge field and the surface of erythrocytes in norm and in pathology is shown. The dependence of the velocity of the erythrocytes on the characteristics of the external electric field, surface charge of the erythrocyte and properties of the medium is obtained. The results of this study can be applied indirectly to diagnose diseases and to develop recommendations for experimental studies of hemodynamics under the influence of various external physical factors.

Structure and Interaction in the pH-Dependent Phase Behavior of Nanoparticle-Protein Systems.

PubMed

Yadav, Indresh; Kumar, Sugam; Aswal, Vinod K; Kohlbrecher, Joachim

2017-02-07

The pH-dependent structure and interaction of anionic silica nanoparticles (diameter 18 nm) with two globular model proteins, lysozyme and bovine serum albumin (BSA), have been studied. Cationic lysozyme adsorbs strongly on the nanoparticles, and the adsorption follows exponential growth as a function of lysozyme concentration, where the saturation value increases as pH approaches the isoelectric point (IEP) of lysozyme. By contrast, irrespective of pH, anionic BSA does not show any adsorption. Despite having a different nature of interactions, both proteins render a similar phase behavior where nanoparticle-protein systems transform from being one-phase (clear) to two-phase (turbid) above a critical protein concentration (CPC). The measurements have been carried out for a fixed concentration of silica nanoparticles (1 wt %) with varying protein concentrations (0-5 wt %). The CPC is found to be much higher for BSA than for lysozyme and increases for lysozyme but decreases for BSA as pH approaches their respective IEPs. The structure and interaction in these systems have been examined using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The effective hydrodynamic size of the nanoparticles measured using DLS increases with protein concentration and is related to the aggregation of the nanoparticles above the CPC. The propensity of the nanoparticles to aggregate is suppressed for lysozyme and enhanced for BSA as pH approached their respective IEPs. This behavior is understood from SANS data through the interaction potential determined by the interplay of electrostatic repulsion with a short-range attraction for lysozyme and long-range attraction for BSA. The nanoparticle aggregation is caused by charge neutralization by the oppositely charged lysozyme and through depletion for similarly charged BSA. Lysozyme-mediated attractive interaction decreases as pH approaches the IEP because of a decrease in the charge on the protein. In the case of BSA, a decrease in the BSA-BSA repulsion enhances the depletion attraction between the nanoparticles as pH is shifted toward the IEP. The morphology of the nanoparticle aggregates is found to be mass fractal.

An assessment of strontium sorption onto bentonite buffer material in waste repository.

PubMed

Pathak, Pankaj

2017-03-01

In the present study, changes occurring in sorption characteristics of a representative bentonite (WIn-BT) exposed to SrCl 2 (0.001-0.1 M) under the pH range of 1-13 were investigated. Such interaction revealed a significant variation in surface charge density and binding energy of ions with respect to bentonite, and alteration in their physicochemical properties viz., specific surface area, cation exchange capacity, thermal and mechanical behaviour were observed. The distribution coefficients (k d ) calculated for sorption onto virgin (UCBT) and contaminated bentonite (CBT) indicated a greater influence of mineralogical changes occurred with variance of pH and strontium concentration. Notably, the sorption mechanism clearly elucidates the effect of structural negative charge and existence of anionic metal species onto CBT, and depicted the reason behind significant k d values at highly acidic and alkaline pH. The maximum k d of UCBT and CBT (0.001M SrCl2) were 8.99 and 2.92 L/kg, respectively, at the soil pH 8.5; whereas it was 2.37 and 1.23 L/kg at pH 1 for the CBT (0.1M SrCl2) and CBT (0.01M SrCl2) , respectively. The findings of this study can be useful to identify the physicochemical parameters of candidate buffer material and sorption reversibility in waste repository.

[Sorption of microorganisms by fiber materials].

PubMed

Nikovskaia, G N; Gordienko, A S; Globa, L I

1986-01-01

Candida guilliermondii and Escherichia coli cells were adsorbed on glass and basalt fibres with a similar specific surface, but with a different charge. The quantity of adsorbed microorganisms did not depend on the type and charge of a fibre surface. However, cells were adsorbed faster and more firmly on positively charged and uncharged fibres than on negatively charged fibres.

Surface active complexes formed between keratin polypeptides and ionic surfactants.

PubMed

Pan, Fang; Lu, Zhiming; Tucker, Ian; Hosking, Sarah; Petkov, Jordan; Lu, Jian R

2016-12-15

Keratins are a group of important proteins in skin and hair and as biomaterials they can provide desirable properties such as strength, biocompatibility, and moisture regaining and retaining. The aim of this work is to develop water-soluble keratin polypeptides from sheep wool and then explore how their surface adsorption behaves with and without surfactants. Successful preparation of keratin samples was demonstrated by identification of the key components from gel electrophoresis and the reproducible production of gram scale samples with and without SDS (sodium dodecylsulphate) during wool fibre dissolution. SDS micelles could reduce the formation of disulphide bonds between keratins during extraction, reducing inter-molecular crosslinking and improving keratin polypeptide solubility. However, Zeta potential measurements of the two polypeptide batches demonstrated almost identical pH dependent surface charge distributions with isoelectric points around pH 3.5, showing complete removal of SDS during purification by dialysis. In spite of different solubility from the two batches of keratin samples prepared, very similar adsorption and aggregation behavior was revealed from surface tension measurements and dynamic light scattering. Mixing of keratin polypeptides with SDS and C 12 TAB (dodecyltrimethylammonium bromide) led to the formation of keratin-surfactant complexes that were substantially more effective at reducing surface tension than the polypeptides alone, showing great promise in the delivery of keratin polypeptides via the surface active complexes. Neutron reflection measurements revealed the coexistence of surfactant and keratin polypeptides at the interface, thus providing the structural support to the observed surface tension changes associated with the formation of the surface active complexes. Copyright © 2016. Published by Elsevier Inc.

Surface Properties and Photocatalytic Activities of the Colloidal ZnS:Mn Nanocrystals Prepared at Various pH Conditions

PubMed Central

Heo, Jungho; Hwang, Cheong-Soo

2015-01-01

Water-dispersible ZnS:Mn nanocrystals (NC) were synthesized by capping the surface with mercaptoacetic acid (MAA) molecules at three different pH conditions. The obtained ZnS:Mn-MAA NC products were physically and optically characterized by corresponding spectroscopic methods. The UV-Visible absorption spectra and PL emission spectra showed broad peaks at 310 and 590 nm, respectively. The average particle sizes measured from the HR-TEM images were 5 nm, which were also supported by the Debye-Scherrer calculations using the X-ray diffraction (XRD) data. Moreover, the surface charges and the degrees of aggregation of the ZnS:Mn-MAA NCs were determined by electrophoretic and hydrodynamic light scattering methods, indicating formation of agglomerates in water with various sizes (50–440 nm) and different surface charge values accordingly the preparation conditions of the NCs (−7.59 to −24.98 mV). Finally, the relative photocatalytic activities of the ZnS:Mn-MAA NCs were evaluated by measuring the degradation rate of methylene blue (MB) molecule in a pseudo first-order reaction condition under the UV-visible light irradiation. As a result, the ZnS:Mn-MAA NC prepared at the pH 7 showed the best photo-degradation efficiency of the MB molecule with the first-order rate constant (kobs) of 2.0 × 10−3·min−1. PMID:28347105

Polypeptide multilayer films on colloidal particles: an in situ electro-optical study.

PubMed

Radeva, Tsetska; Kamburova, Kamelia

2007-04-15

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on beta-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse "in" and "out" of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.

Sorption of Lincomycin by Manure-Derived Biochars from Water

PubMed Central

Liu, Cheng-Hua; Chuang, Ya-Hui; Li, Hui; Teppen, Brian J.; Boyd, Stephen A.; Gonzalez, Javier M.; Johnston, Cliff T.; Lehmann, Johannes; Zhang, Wei

2018-01-01

The presence of antibiotics in agroecosystems raises concerns about the proliferation of antibiotic-resistant bacteria and adverse effects to human health. Soil amendment with biochars pyrolized from manures may be a win-win strategy for novel manure management and antibiotics abatement. In this study, lincomycin sorption by manure-derived biochars was examined using batch sorption experiments. Lincomycin sorption was characterized by two-stage kinetics with fast sorption reaching quasi-equilibrium in the first 2 d, followed by slow sorption over 180 d. The fast sorption was primarily attributed to surface adsorption, whereas the long-term slow sorption was controlled by slow diffusion of lincomycin into biochar pore structures. Two-day sorption experiments were performed to explore effects of biochar particle size, solid/water ratio, solution pH, and ionic strength. Lincomycin sorption to biochars was greater at solution pH 6.0 to 7.5 below the dissociation constant of lincomycin (7.6) than at pH 9.9 to 10.4 above its dissociation constant. The enhanced lincomycin sorption at lower pH likely resulted from electrostatic attraction between the positively charged lincomycin and the negatively charged biochar surfaces. This was corroborated by the observation that lincomycin sorption decreased with increasing ionic strength at lower pH (6.7) but remained constant at higher pH (10). The long-term lincomycin sequestration by biochars was largely due to pore diffusion plausibly independent of solution pH and ionic composition. Therefore, manure-derived biochars had lasting lincomycin sequestration capacity, implying that biochar soil amendment could significantly affect the distribution, transport, and bioavailability of lincomycin in agroecosystems. PMID:27065399

Model for thickness dependence of radiation charging in MOS structures

NASA Technical Reports Server (NTRS)

Viswanathan, C. R.; Maserjian, J.

1976-01-01

The model considers charge buildup in MOS structures due to hole trapping in the oxide and the creation of sheet charge at the silicon interface. The contribution of hole trapping causes the flatband voltage to increase with thickness in a manner in which square and cube dependences are limiting cases. Experimental measurements on samples covering a 200 - 1000 A range of oxide thickness are consistent with the model, using independently obtained values of hole-trapping parameters. An important finding of our experimental results is that a negative interface charge contribution due to surface states created during irradiation compensates most of the positive charge in the oxide at flatband. The tendency of the surface states to 'track' the positive charge buildup in the oxide, for all thicknesses, applies both in creation during irradiation and in annihilation during annealing. An explanation is proposed based on the common defect origin of hole traps and potential surface states.

Inner-Helmholtz potential development at the hematite (α-Fe 2O 3) (0 0 1) surface

NASA Astrophysics Data System (ADS)

Boily, Jean-François; Chatman, Shawn; Rosso, Kevin M.

2011-08-01

Electric potentials of the (0 0 1) surface of hematite were measured as a function of pH and ionic strength in solutions of sodium nitrate and oxalic acid using the single-crystal electrode approach. The surface is predominantly charge-neutral in the pH 4-14 range, and develops a positive surface potential below pH 4 due to protonation of μ-OH 0 sites (p K1,1,0,int = -1.32). This site is resilient to deprotonation up to at least pH 14 (-p K-1,1,0,int ≫ 19). The associated Stern layer capacitance of 0.31-0.73 F/m 2 is smaller than typical values of powders, and possibly arises from a lower degree of surface solvation. Acid-promoted dissolution under elevated concentrations of HNO 3 etches the (0 0 1) surface, yielding a convoluted surface populated by -OH20.5+ sites. The resulting surface potential was therefore larger under these conditions than in the absence of dissolution. Oxalate ions also promoted (0 0 1) dissolution. Associated electric potentials were strongly negative, with values as large as -0.5 V, possibly from metal-bonded interactions with oxalate. The hematite surface can also acquire negative potentials in the pH 7-11 range due to surface complexation and/or precipitation of iron species (0.0038 Fe/nm 2) produced from acidic conditions. Oxalate-bearing systems also result in negative potentials in the same pH range, and may include ferric-oxalate surface complexes and/or surface precipitates. All measurements can be modeled by a thermodynamic model that can be used to predict inner-Helmholtz potentials of hematite surfaces.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth.

PubMed

Jarisz, Tasha A; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K

2018-06-14

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth

NASA Astrophysics Data System (ADS)

Jarisz, Tasha A.; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K.

2018-06-01

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Role of Surface Charge Density in Nanoparticle-templated Assembly of Bromovirus Protein Cages

PubMed Central

Daniel, Marie-Christine; Tsvetkova, Irina B.; Quinkert, Zachary T.; Murali, Ayaluru; De, Mrinmoy; Rotello, Vincent M.; Kao, C. Cheng; Dragnea, Bogdan

2010-01-01

Self-assembling icosahedral protein cages have potencially useful physical and chemical characteristics for a variety of nanotechnology applications, ranging from therapeutic or diagnostic vectors to building blocks for hierarchical materials. For application-specific functional control of protein cage assemblies, a deeper understanding of the interaction between the protein cage and its payload is necessary. Protein-cage encapsulated nanoparticles, with their well-defined surface chemistry, allow for systematic control over key parameters of encapsulation such as the surface charge, hydrophobicity, and size. Independent control over these variables allows experimental testing of different assembly mechanism models. Previous studies done with Brome mosaic virus capsids and negatively-charged gold nanoparticles indicated that the result of the self-assembly process depends on the diameter of the particle. However, in these experiments, the surface-ligand density was maintained at saturation levels, while the total charge and the radius of curvature remained coupled variables, making the interpretation of the observed dependence on the core size difficult. The current work furnishes evidence of a critical surface charge density for assembly through an analysis aimed at decoupling the surface charge the core size. PMID:20575505

Nanoparticle modification by weak polyelectrolytes for pH-sensitive pickering emulsions.

PubMed

Haase, Martin F; Grigoriev, Dmitry; Moehwald, Helmuth; Tiersch, Brigitte; Shchukin, Dmitry G

2011-01-04

The affinity of weak polyelectrolyte coated oxide particles to the oil-water interface can be controlled by the degree of dissociation and the thickness of the weak polyelectrolyte layer. Thereby the oil in water (o/w) emulsification ability of the particles can be enabled. We selected the weak polyacid poly(methacrylic acid sodium salt) and the weak polybase poly(allylamine hydrochloride) for the surface modification of oppositely charged alumina and silica colloids, respectively. The isoelectric point and the pH range of colloidal stability of both particle-polyelectrolyte composites depend on the thickness of the weak polyelectrolyte layer. The pH-dependent wettability of a weak polyelectrolyte-coated oxide surface is characterized by contact angle measurements. The o/w emulsification properties of both particles for the nonpolar oil dodecane and the more polar oil diethylphthalate are investigated by measurements of the droplet size distributions. Highly stable emulsions can be obtained when the degree of dissociation of the weak polyelectrolyte is below 80%. Here the average droplet size depends on the degree of dissociation, and a minimum can be found when 15 to 45% of the monomer units are dissociated. The thickness of the adsorbed polyelectrolyte layer strongly influences the droplet size of dodecane/water emulsion droplets but has a less pronounced impact on the diethylphthalate/water droplets. We explain the dependency of the droplet size on the emulsion pH value and the polyelectrolyte coating thickness with arguments based on the particle-wetting properties, the particle aggregation state, and the oil phase polarity. Cryo-SEM visualization shows that the regularity of the densely packed particles on the oil-water interface correlates with the degree of dissociation of the corresponding polyelectrolyte.

Tuning structure of oppositely charged nanoparticle and protein complexes

NASA Astrophysics Data System (ADS)

Kumar, Sugam; Aswal, V. K.; Callow, P.

2014-04-01

Small-angle neutron scattering (SANS) has been used to probe the structures of anionic silica nanoparticles (LS30) and cationic lyszyme protein (M.W. 14.7kD, I.P. ˜ 11.4) by tuning their interaction through the pH variation. The protein adsorption on nanoparticles is found to be increasing with pH and determined by the electrostatic attraction between two components as well as repulsion between protein molecules. We show the strong electrostatic attraction between nanoparticles and protein molecules leads to protein-mediated aggregation of nanoparticles which are characterized by fractal structures. At pH 5, the protein adsorption gives rise to nanoparticle aggregation having surface fractal morphology with close packing of nanoparticles. The surface fractals transform to open structures of mass fractal morphology at higher pH (7 and 9) on approaching isoelectric point (I.P.).

Influence of alumina coating on characteristics and effects of SiO2 nanoparticles in algal growth inhibition assays at various pH and organic matter contents.

PubMed

Van Hoecke, Karen; De Schamphelaere, Karel A C; Ramirez-Garcia, Sonia; Van der Meeren, Paul; Smagghe, Guy; Janssen, Colin R

2011-08-01

Silica nanoparticles (NPs) belong to the industrially most important NP types. In a previous study it was shown that amorphous SiO(2) NPs of 12.5 and 27.0 nm are stable in algal growth inhibition assays and that their ecotoxic effects are related to NP surface area. Here, it was hypothesized and demonstrated that an alumina coating completely alters the particle-particle, particle-test medium and particle-algae interactions of SiO(2) NPs. Therefore, stability and surface characteristics, dissolution, nutrient adsorption and effects on algal growth rate of both alumina coated SiO(2) NPs and bare SiO(2) NPs in OECD algal test medium as a function of pH (6.0-8.6) and natural organic matter (NOM) contents (0-12 mg C/l) were investigated. Alumina coated SiO(2) NPs aggregated in all media and adsorbed phosphate depending on pH and NOM concentration. On the other hand, no aggregation or nutrient adsorption was observed for the bare SiO(2) NPs. Due to their positive surface charge, alumina coated SiO(2) NPs agglomerated with Pseudokirchneriella subcapitata. Consequently, algal cell density measurements based on cell counts were unreliable and hence fluorescent detection of extracted chlorophyll was the preferred method. Alumina coated SiO(2) NPs showed lower toxicity than bare SiO(2) NPs at concentrations ≥46 mg/l, except at pH 6.0. At low concentrations, no clear pH effect was observed for alumina coated SiO(2) NPs, while at higher concentrations phosphate deficiency could have contributed to the higher toxicity of those particles at pH 6.0-6.8 compared to higher pH values. Bare SiO(2) NPs were not toxic at pH 6.0 up to 220 mg/l. Addition of NOM decreased toxicity of both particles. For SiO(2) NPs the 48 h 20% effect concentration of 21.8 mg/l increased 2.6-21 fold and a linear relationship was observed between NOM concentration and effective concentrations. No effect was observed for alumina coated SiO(2) NPs in presence of NOM up to 1000 mg/l. All experiments point out that the alumina coating completely altered NP interactions. Due to the difference in surface composition the SiO(2) NPs, which had the smallest surface area, were more toxic to the alga than the alumina coated SiO(2) NPs. Hence, surface modification can dominate the effect of surface area on toxicity. Copyright © 2011 Elsevier Ltd. All rights reserved.

Structural and denaturation studies of two mutants of a cold adapted superoxide dismutase point to the importance of electrostatic interactions in protein stability.

PubMed

Merlino, Antonello; Russo Krauss, Irene; Castellano, Immacolata; Ruocco, Maria Rosaria; Capasso, Alessandra; De Vendittis, Emmanuele; Rossi, Bianca; Sica, Filomena

2014-03-01

A peculiar feature of the psychrophilic iron superoxide dismutase from Pseudoalteromonas haloplanktis (PhSOD) is the presence in its amino acid sequence of a reactive cysteine (Cys57). To define the role of this residue, a structural characterization of the effect of two PhSOD mutations, C57S and C57R, was performed. Thermal and denaturant-induced unfolding of wild type and mutant PhSOD followed by circular dichroism and fluorescence studies revealed that C→R substitution alters the thermal stability and the resistance against denaturants of the enzyme, whereas C57S only alters the stability of the protein against urea. The crystallographic data on the C57R mutation suggest an involvement of the Arg side chain in the formation of salt bridges on protein surface. These findings support the hypothesis that the thermal resistance of PhSOD relies on optimization of charge-charge interactions on its surface. Our study contributes to a deeper understanding of the denaturation mechanism of superoxide dismutases, suggesting the presence of a structural dimeric intermediate between the native state and the unfolded state. This hypothesis is supported by the crystalline and solution data on the reduced form of the enzyme. Copyright © 2014 Elsevier B.V. All rights reserved.

Specific Inhibition of Bacterial β-Glucuronidase by Pyrazolo[4,3-c]quinoline Derivatives via a pH-Dependent Manner To Suppress Chemotherapy-Induced Intestinal Toxicity.

PubMed

Cheng, Kai-Wen; Tseng, Chih-Hua; Yang, Chia-Ning; Tzeng, Cherng-Chyi; Cheng, Ta-Chun; Leu, Yu-Lin; Chuang, Yu-Chung; Wang, Jaw-Yuan; Lu, Yun-Chi; Chen, Yeh-Long; Cheng, Tian-Lu

2017-11-22

The direct inhibition of bacterial β-glucuronidase (βG) activity is expected to reduce the reactivation of glucuronide-conjugated drugs in the intestine, thereby reducing drug toxicity. In this study, we report on the effects of pyrazolo[4,3-c]quinolines acting as a new class of bacterial βG-specific inhibitors in a pH-dependent manner. Refinement of this chemotype for establishing structure-activity relationship resulted in the identification of potential leads. Notably, the oral administration of 3-amino-4-(4-fluorophenylamino)-1H-pyrazolo[4,3-c]quinoline (42) combined with chemotherapeutic CPT-11 treatment prevented CPT-11-induced serious diarrhea while maintaining the antitumor efficacy in tumor-bearing mice. Importantly, the inhibitory effects of 42 to E. coli βG was reduced as the pH decreased due to the various surface charges of the active pocket of the enzyme, which may make their combination more favorable at neutral pH. These results demonstrate novel insights into the potent bacterial βG-specific inhibitor that would allow this inhibitor to be used for the purpose of reducing drug toxicity.

Directional flow induced by synchronized longitudinal and zeta-potential controlling AC-electrical fields.

PubMed

van der Wouden, E J; Hermes, D C; Gardeniers, J G E; van den Berg, A

2006-10-01

Electroosmotic flow (EOF) in a microchannel can be controlled by electronic control of the surface charge using an electrode embedded in the wall of the channel. By setting a voltage to the electrode, the zeta-potential at the wall can be changed locally. Thus, the electrode acts as a "gate" for liquid flow, in analogy with a gate in a field-effect transistor. In this paper we will show three aspects of a Field Effect Flow Control (FEFC) structure. We demonstrate the induction of directional flow by the synchronized switching of the gate potential with the channel axial potential. The advantage of this procedure is that potential gas formation by electrolysis at the electrodes that provide the axial electric field is suppressed at sufficiently large switching frequencies, while the direction and magnitude of the EOF can be maintained. Furthermore we will give an analysis of the time constants involved in the charging of the insulator, and thus the switching of the zeta potential, in order to predict the maximum operating frequency. For this purpose an equivalent electrical circuit is presented and analyzed. It is shown that in order to accurately describe the charging dynamics and pH dependency the traditionally used three capacitor model should be expanded with an element describing the buffer capacitance of the silica wall surface.

Effect of Gold on the Corrosion Behavior of an Electroless Nickel/Immersion Gold Surface Finish

NASA Astrophysics Data System (ADS)

Bui, Q. V.; Nam, N. D.; Yoon, J. W.; Choi, D. H.; Kar, A.; Kim, J. G.; Jung, S. B.

2011-09-01

The performance of surface finishes as a function of the pH of the utilized plating solution was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. In addition, the surface finishes were examined by x-ray diffraction (XRD), and the contact angle of the liquid/solid interface was recorded. NiP films on copper substrates with gold coatings exhibited their highest coating performance at pH 5. This was attributed to the films having the highest protective efficiency and charge transfer resistance, lowest porosity value, and highest contact angle among those examined as a result of the strongly preferred Au(111) orientation and the improved surface wettability.

Origin of the instability of octadecylamine Langmuir monolayer at low pH

DOE PAGES

Avazbaeva, Zaure; Sung, Woongmo; Lee, Jonggwan; ...

2015-11-30

In this paper, it has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284–285, 166–174). However, by lowering the pH further, ODA molecules reoccupy the surface, and a full monolayer is recovered at pH 2.5. Using surface sum-frequency spectroscopy and pressure–area isotherms, it is found that the recovered monolayer at very low pH has a larger area per molecule with many gauche defects in the ODA molecules as comparedmore » to that at high pH values. This structural change suggests that the reappearance of the monolayer is due to the adsorbed Cl– counterions to the protonated amine groups, leading to partial charge neutralization. This proposition is confirmed by intentionally adding monovalent salts (i.e., NaCl, NaBr, or NaI) to the subphase to recover the monolayer at pH 3.5, in which the detailed structure of the monolayer is confirmed by sum frequency spectra and the adsorbed anions by X-ray reflectivity.« less

Protofit: A program for determining surface protonation constants from titration data

NASA Astrophysics Data System (ADS)

Turner, Benjamin F.; Fein, Jeremy B.

2006-11-01

Determining the surface protonation behavior of natural adsorbents is essential to understand how they interact with their environments. ProtoFit is a tool for analysis of acid-base titration data and optimization of surface protonation models. The program offers a number of useful features including: (1) enables visualization of adsorbent buffering behavior; (2) uses an optimization approach independent of starting titration conditions or initial surface charge; (3) does not require an initial surface charge to be defined or to be treated as an optimizable parameter; (4) includes an error analysis intrinsically as part of the computational methods; and (5) generates simulated titration curves for comparison with observation. ProtoFit will typically be run through ProtoFit-GUI, a graphical user interface providing user-friendly control of model optimization, simulation, and data visualization. ProtoFit calculates an adsorbent proton buffering value as a function of pH from raw titration data (including pH and volume of acid or base added). The data is reduced to a form where the protons required to change the pH of the solution are subtracted out, leaving protons exchanged between solution and surface per unit mass of adsorbent as a function of pH. The buffering intensity function Qads* is calculated as the instantaneous slope of this reduced titration curve. Parameters for a surface complexation model are obtained by minimizing the sum of squares between the modeled (i.e. simulated) buffering intensity curve and the experimental data. The variance in the slope estimate, intrinsically produced as part of the Qads* calculation, can be used to weight the sum of squares calculation between the measured buffering intensity and a simulated curve. Effects of analytical error on data visualization and model optimization are discussed. Examples are provided of using ProtoFit for data visualization, model optimization, and model evaluation.

Adsorption of a reactive dye on chemically modified activated carbons--influence of pH.

PubMed

Orfão, J J M; Silva, A I M; Pereira, J C V; Barata, S A; Fonseca, I M; Faria, P C C; Pereira, M F R

2006-04-15

The surface chemistry of a commercial activated carbon with a slightly basic nature was modified by appropriate treatments in order to obtain two additional samples, respectively with acidic and basic properties, without changing its textural parameters significantly. Different techniques (N2 adsorption at 77 K, temperature programmed desorption, and determination of acidity, basicity, and pH at the point of zero charge) were used to characterize the adsorbents. Kinetic and equilibrium adsorption data of a selected textile reactive dye (Rifafix Red 3BN, C.I. reactive red 241) on the mentioned materials were obtained at the pH values of 2, 7, and 12. The kinetic curves are fitted using the second-order model. The respective rate constants seem to diminish progressively with the initial concentration for the more diluted solutions tested, reaching a constant value at higher concentrations, which depends on the experimental system under consideration (adsorbent and pH). In general, the Langmuir model provides the best fit for the equilibrium data. The different uptakes obtained are discussed in relation to the surface chemical properties of the adsorbents. It is shown that the adsorption of the reactive (anionic) dye on the basic sample (prepared by thermal treatment under H2 flow at 700 degrees C) is favored. This conclusion is explained on the basis of the dispersive and electrostatic interactions involved. Moreover, it is also shown that the optimal adsorption condition for all the activated carbons tested corresponds to solution pH values not higher than the pH(pzc) of the adsorbents, which may be interpreted by taking into account the electrostatic forces present.

Phenothiazinium based photosensitisers--photodynamic agents with a multiplicity of cellular targets and clinical applications.

PubMed

Harris, F; Chatfield, L K; Phoenix, D A

2005-08-01

PhBPs show selectivity for tumour and microbial cells, which appears to be based on electrostatic interactions between the positive charge generally carried by these molecules and the negative charge found on the outer surface of these target cells. In some cases, a site of action for photoactivated PhBPs is the outer membrane/envelope of the target cell. Such action can involve the modification of membrane lipid and/or lipopolysaccharide, and the inactivation of essential proteins and enzymes, with these effects usually leading to cell lysis and death. However, more often, PhBPs are internalised by target cells, promoted by a variety of factors, including low pH and enzymatic reduction, and upon photoactivation, internalised, PhBPs are able to inflict damage on a number of intracellular targets. In tumour cells, PhBPs can photodamage DNA and the membranes of organelles, thereby inducing necrosis and/or apoptosis. In bacterial cells, whilst DNA is generally a primary target of PhBPs, these compounds can exhibit multiple sites of action within a given cell and show different sites of action between different bacterial species. This variable targeting makes PhBPs attractive propositions as alternatives to conventional antibiotics in that the emergence of bacterial strains with acquired resistance to these compounds appears to be highly unlikely.

Effect of pH value on structural and photoluminescence properties of Tb3+ -doped Lu2O3 nanopowders synthesized by sol-gel route

NASA Astrophysics Data System (ADS)

Mendoud, A.; Guerbous, L.; Boukerika, A.; Boudine, B.; Benrekaa, N.

2018-01-01

Tb3+-doped Lu2O3 nanophosphors were prepared via simple sol-gel method, at different pH value of solution (2, 5, 8 and 11), using diethanolamine (DEA) as polymerization agent. The nanopowder samples were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, room temperature steady and time resolved photoluminescence spectroscopy. The structural analysis reveals that all samples mainely crystallized in the cubic bixbyite structure with Ia3 space group. Also, it was found that the pH value of solution strongly influences the crystallite size, the vibrational frequency modes and the surface morphology of Lu2O3:Tb3+ nanocrystals. All samples show blue-greenish emissions, corresponding to 5D4 → 7FJ (J = 3, 4, 5 and 6) intraconfigurationnelles transitions. The intense green emission peak situated at 542 nm is assigned to 5D4 → 7F5 transition. The 4f8 → 4f75d1 spin-allowed and forbidden transitions, the charge transfer band (CTB) O2- → Tb3+ and the host absorption bands were observed and their dependence on pH value is discussed.

Stability and electrostatics of mercaptoundecanoic acid-capped gold nanoparticles with varying counterion size.

PubMed

Laaksonen, Timo; Ahonen, Päivi; Johans, Christoffer; Kontturi, Kyösti

2006-10-13

The solubility of charged nanoparticles is critically dependent on pH. However, the concentration range available with bases such as NaOH is quite narrow, since the particles precipitate due to compression of the electric double layer when the ionic strength is increased. The stability of mercaptoundecanoic acid-capped Au nanoparticles is studied at a set pH using the hydroxide as base and different cations of various sizes. The counterions used are sodium (Na(+)), tetramethylammonium (TMA(+)), tetraethylammonium (TEA(+)), and tetrabutylammonium (TBA(+)). The particles precipitate in the 70-90 mM range with Na(+) as the counterion, but with quaternary ammonium hydroxides the particles are stable even in concentrations exceeding 1 M. The change in solubility is linked to a strongly adsorbed layer on the surface of the ligand shell of the nanoparticles. The increased concentration range obtained with TEAOH is further used to facilitate thiol exchange which occurs at a greater extent than would be achieved in NaOH solution.

X-Ray Crystallographic Studies of Electrostatic Effects in Cubic Insulin

NASA Astrophysics Data System (ADS)

Gursky, Olga

1992-09-01

Cubic crystals of bovine insulin were obtained at pH 9 from sodium phosphate buffer. Pathway dependence of crystallization was analysed and crystallization using controlled nucleation was developed. Crystal stability and solubility were surveyed by dialysing the crystals against salt solutions varying in salt composition and ionic strength. Crystals dialysed in 0.1-0.2M Li, Na, K, Rb, NH(4) or Tl salt solutions at pH 9 diffracted to beyond 2.8A, while crystals dialysed in Cs, Mg, Ca or La rapidly lost lattice order. Change in the solvent anion did not affect crystal stability. Electron density maps calculated from X-ray data to 2.8A resolution showed two specific cation binding sites which may be occupied by monovalent cations with ionic radii <1.5A. One site lies between insulin dimers near crystallographic two-fold axis without the close involvement of protein charged groups. Cation binding at this site is important for crystal stability. The other site is alternatively occupied by B10 His in one of its two conformations. At pH 7, the Tl occupancy at both sites was decreased, at pH 9.5 the Tl occupancy of the site near B10 His was increased. The structure was refined using the refined model of cubic porcine insulin and the X-ray data collected to 2A resolution from a bovine insulin crystal at pH 9, to R = 16.1% for the data extending from 10A to 2A. High -resolution data from crystals at pH 7 and pH 10 were collected and analysed. The weights of the two B10 His conformers and the cation occupancy near B10 vary in the pH range from 7 to 10, indicating histidine titration. Shifts in the positions of B1-B4 at pH 7 suggest titration of the B-chain terminal amino groups. Co-operative conformational changes in the surface charged residues A1, A4, B21, B29, B30 at pH 10.2 suggest titration of the A-chain terminal amino groups. In several crystals treated with dichloroethane, the syn-dichloroethane was bound in the niche across the two-fold axis connecting insulin monomers. Dichloroethane binding does not perturb the site geometry and probably leads to cubic insulin preparations of increased stability.

In situ measurement of surface potential developed on MgO thin film surface under ion irradiation using ion scattering spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nagatomi, T.; Kuwayama, T.; Takai, Y.

2009-11-15

The application of ion scattering spectroscopy (ISS) to the in situ measurement of the surface potential developed on an insulator surface under positive ion irradiation was investigated. The ISS spectra measured for a MgO film of 600 nm thickness on a Si substrate by the irradiation of 950 eV He{sup +} ions revealed that the surface is positively charged by approximately 180 V. For accurate measurement of the surface potential, a correction to take into account the angular deflection of primary ions induced by the high surface potential is required. The dependence of the surface potential on the sample temperaturemore » revealed that no charging is induced above 700 deg. C, indicating that accumulated charges can be removed by heating to 700 deg. C. From the measurement of the ion-induced secondary electron yield using a collector electrode located in front of the sample surface, the surface potential and ion-induced secondary electron yield were found to be strongly affected by the experimental setup. Secondary electrons produced by the impact of slow positive secondary ions, the maximum energy of which corresponds to the surface potential, play an important role when the bias voltage applied to the collector electrode is positively high for the present experimental setup. The surface potential developed on the surface of MgO films of 600 and 200 nm thickness was measured in situ, revealing that the amount of accumulated charges and the time required to attain the steady state of charging are slightly dependent on the beam current of primary ions and strongly dependent on the thickness of the MgO film. The present results confirmed that the application of ISS has high potential for investigating charging phenomena and the secondary electron emission from insulator surfaces under positive ion irradiation.« less

PHEPS: web-based pH-dependent Protein Electrostatics Server

PubMed Central

Kantardjiev, Alexander A.; Atanasov, Boris P.

2006-01-01

PHEPS (pH-dependent Protein Electrostatics Server) is a web service for fast prediction and experiment planning support, as well as for correlation and analysis of experimentally obtained results, reflecting charge-dependent phenomena in globular proteins. Its implementation is based on long-term experience (PHEI package) and the need to explain measured physicochemical characteristics at the level of protein atomic structure. The approach is semi-empirical and based on a mean field scheme for description and evaluation of global and local pH-dependent electrostatic properties: protein proton binding; ionic sites proton population; free energy electrostatic term; ionic groups proton affinities (pKa,i) and their Coulomb interaction with whole charge multipole; electrostatic potential of whole molecule at fixed pH and pH-dependent local electrostatic potentials at user-defined set of points. The speed of calculation is based on fast determination of distance-dependent pair charge-charge interactions as empirical three exponential function that covers charge–charge, charge–dipole and dipole–dipole contributions. After atomic coordinates input, all standard parameters are used as defaults to facilitate non-experienced users. Special attention was given to interactive addition of non-polypeptide charges, extra ionizable groups with intrinsic pKas or fixed ions. The output information is given as plain-text, readable by ‘RasMol’, ‘Origin’ and the like. The PHEPS server is accessible at . PMID:16845042

Development and characterization of ferrihydrite-modified diatomite as a phosphorus adsorbent.

PubMed

Xiong, Wenhui; Peng, Jian

2008-12-01

A novel phosphorus adsorbent, ferrihydrite-modified diatomite was developed and characterized in this study. The ferrihydrite-modified diatomite was made through surface modification treatments including NaOH treatment and ferrihydrite deposition on raw diatomite. In the NaOH treatment, surface SiO(2) of diatomite was partially dissolved in the NaOH solution. The dissolved Si contributed to form the stable 2-line ferrihydrite which deposited into the macropores and mesopores of diatomite. Blocking macropores and larger mesopores of diatomite with 0.24g Fe/g of 2-line ferrihydrite resulted in a specific surface area of 211.1m(2)/g for the ferrihydrite-modified diatomite, which is 8.5-fold increase than the raw diatomite (24.77m(2)/g). The surface modification also increased the point of zero charge (pH(PZC)) values to 10 for the ferrihydrite-modified diatomite from 5.8 for the raw diatomite. Because of the increased surface area and surface charge, the maximum adsorption capacity of ferrihydrite-modified diatomite at pH 4 and pH 8.5 was increased from 10.2mgP/g and 1.7mgP/g of raw diatomite to 37.3mgP/g and 13.6mgP/g, respectively.

Analysis of the improvement of selenite retention in smectite by adding alumina nanoparticles.

PubMed

Mayordomo, Natalia; Alonso, Ursula; Missana, Tiziana

2016-12-01

Smectite clay is used as barrier for hazardous waste retention and confinement. It is a powerful material to retain cations, but less effective for retaining anionic species like selenite. This study shows that the addition of a small percentage of γ-Al 2 O 3 nanoparticles to smectite significantly improves selenite sorption. γ-Al 2 O 3 nanoparticles provide high surface area and positively charged surface sites within a wide range of pH, since their point of zero charge is at pH8-9. An addition of 20wt% of γ-Al 2 O 3 to smectite is sufficient to approach the sorption capacity of pure alumina. To analyze the sorption behavior of the smectite/oxide mixtures, a nonelectrostatic surface complexation model was considered, accounting for the surface complexation of HSeO 3 - and SeO 3 2- , the anion competition, and the formation of surface ternary complexes with major cations present in the solution. Selenite sorption in mixtures was satisfactorily described with the surface parameters and complexation constants defined for the pure systems, accounting only for the mixture weight fractions. Sorption in mixtures was additive despite the particle heteroaggregation observed in previous stability studies carried out on smectite/γ-Al 2 O 3 mixtures. Copyright © 2016 Elsevier B.V. All rights reserved.

Fabrication of pH sensitive nanovalves using smart surface coated nanopores

NASA Astrophysics Data System (ADS)

Nieto-Soto, A. M.; Diaz-Maldonado, D. K.; Rios Angarita, F. A.

2017-01-01

A pH sensitive nanovalve was fabricated using different smart surfaces covalently attached to an anodized aluminium oxide membrane (AAO). The smart surfaces were synthesized using a mixture of aliphatic and aminated silanes. Effect on the contact angle of the aliphatic silane chain length was evaluated. The smart surface, in conjunction with a nanoporous membrane, allowed the formation of a hydrophobic plug which controlled the transport of the molecule safranine depending on the pH of the solution. It was demonstrated that mixtures of butyl and methyl-trimethoxysilane with aminopropyl-trimethoxysilane were able to perform as effective nanovalves creating a plug that remained closed at pH>7 and opened up at pH<5.

Polyelectrolyte multilayer capsules as vehicles with tunable permeability.

PubMed

Antipov, Alexei A; Sukhorukov, Gleb B

2004-11-29

This review is devoted to a novel type of polymer micro- and nanocapsules. The shell of the capsule is fabricated by alternate adsorption of oppositely charged polyelectrolytes (PEs) onto the surface of colloidal particles. Cores of different nature (organic or inorganic) with size varied from 0.1 to 10 mum can be used for templating such PE capsules. The shell thickness can be tuned in nanometer range by assembling of defined number of PE layers. The permeability of capsules depends on the pH, ionic strength, solvent, polymer composition, and shell thickness; it can be controlled and varied over wide range of substances regarding their molecular weight and charge. Including functional polymers into capsule wall, such as weak PEs or thermosensitive polymers, makes the capsule permeability sensitive to correspondent external stimuli. Permeability of the capsules is of essential interest in diverse areas related to exploitation of systems with controlled and sustained release properties. The envisaged applications of such capsules/vesicles cover biotechnology, medicine, catalysis, food industry, etc.

Modeling the binding of fulvic acid by goethite: the speciation of adsorbed FA molecules

NASA Astrophysics Data System (ADS)

Filius, Jeroen D.; Meeussen, Johannes C. L.; Lumsdon, David G.; Hiemstra, Tjisse; van Riemsdijk, Willem H.

2003-04-01

Under natural conditions, the adsorption of ions at the solid-water interface may be strongly influenced by the adsorption of organic matter. In this paper, we describe the adsorption of fulvic acid (FA) by metal(hydr)oxide surfaces with a heterogeneous surface complexation model, the ligand and charge distribution (LCD) model. The model is a self-consistent combination of the nonideal competitive adsorption (NICA) equation and the CD-MUSIC model. The LCD model can describe simultaneously the concentration, pH, and salt dependency of the adsorption with a minimum of only three adjustable parameters. Furthermore, the model predicts the coadsorption of protons accurately for an extended range of conditions. Surface speciation calculations show that almost all hydroxyl groups of the adsorbed FA molecules are involved in outer sphere complexation reactions. The carboxylic groups of the adsorbed FA molecule form inner and outer sphere complexes. Furthermore, part of the carboxylate groups remain noncoordinated and deprotonated.

Quantifying Interfacial pH Variation at Molecular Length Scales Using a Concurrent Non-Faradaic Reaction.

PubMed

Ryu, Jaeyune; Wuttig, Anna; Surendranath, Yogesh

2018-05-15

We quantify changes in the interfacial pH local to the electrochemical double layer during electrocatalysis, using a concurrent non-faradaic probe reaction. In the absence of electrocatalysis, nanostructured Pt/C surfaces mediate the reaction of H2 with cis-2-butene-1,4-diol to form a mixture of 1,4-butanediol and n-butanol with a selectivity that is linearly dependent on the bulk solution pH. We show that kinetic branching occurs from a common surface-bound intermediate, ensuring that this probe reaction is uniquely sensitive to the interfacial pH within molecular length scales of the surface. We use the pH-dependent selectivity of this reaction to track changes in interfacial pH during concurrent hydrogen oxidation electrocatalysis and find that the local pH can vary dramatically, > 3 units, relative to the bulk value even at modest current densities in well-buffered electrolytes. This work highlights the key role that interfacial pH variation plays in modulating inner-sphere electrocatalysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Binding Interactions of Keratin-Based Hair Fiber Extract to Gold, Keratin, and BMP-2

PubMed Central

de Guzman, Roche C.; Tsuda, Shanel M.; Ton, Minh-Thi N.; Zhang, Xiao; Esker, Alan R.; Van Dyke, Mark E.

2015-01-01

Hair-derived keratin biomaterials composed mostly of reduced keratin proteins (kerateines) have demonstrated their utility as carriers of biologics and drugs for tissue engineering. Electrostatic forces between negatively-charged keratins and biologic macromolecules allow for effective drug retention; attraction to positively-charged growth factors like bone morphogenetic protein 2 (BMP-2) has been used as a strategy for osteoinduction. In this study, the intermolecular surface and bulk interaction properties of kerateines were investigated. Thiol-rich kerateines were chemisorbed onto gold substrates to form an irreversible 2-nm rigid layer for surface plasmon resonance analysis. Kerateine-to-kerateine cohesion was observed in pH-neutral water with an equilibrium dissociation constant (KD) of 1.8 × 10−4 M, indicating that non-coulombic attractive forces (i.e. hydrophobic and van der Waals) were at work. The association of BMP-2 to kerateine was found to be greater (KD = 1.1 × 10−7 M), within the range of specific binding. Addition of salts (phosphate-buffered saline; PBS) shortened the Debye length or the electrostatic field influence which weakened the kerateine-BMP-2 binding (KD = 3.2 × 10−5 M). BMP-2 in bulk kerateine gels provided a limited release in PBS (~ 10% dissociation in 4 weeks), suggesting that electrostatic intermolecular attraction was significant to retain BMP-2 within the keratin matrix. Complete dissociation between kerateine and BMP-2 occurred when the PBS pH was lowered (to 4.5), below the keratin isoelectric point of 5.3. This phenomenon can be attributed to the protonation of keratin at a lower pH, leading to positive-positive repulsion. Therefore, the dynamics of kerateine-BMP-2 binding is highly dependent on pH and salt concentration, as well as on BMP-2 solubility at different pH and molarity. The study findings may contribute to our understanding of the release kinetics of drugs from keratin biomaterials and allow for the development of better, more clinically relevant BMP-2-conjugated systems for bone repair and regeneration. PMID:26317522

FAMBE-pH: A Fast and Accurate Method to Compute the Total Solvation Free Energies of Proteins

PubMed Central

Vorobjev, Yury N.; Vila, Jorge A.

2009-01-01

A fast and accurate method to compute the total solvation free energies of proteins as a function of pH is presented. The method makes use of a combination of approaches, some of which have already appeared in the literature; (i) the Poisson equation is solved with an optimized fast adaptive multigrid boundary element (FAMBE) method; (ii) the electrostatic free energies of the ionizable sites are calculated for their neutral and charged states by using a detailed model of atomic charges; (iii) a set of optimal atomic radii is used to define a precise dielectric surface interface; (iv) a multilevel adaptive tessellation of this dielectric surface interface is achieved by using multisized boundary elements; and (v) 1:1 salt effects are included. The equilibrium proton binding/release is calculated with the Tanford–Schellman integral if the proteins contain more than ∼20–25 ionizable groups; for a smaller number of ionizable groups, the ionization partition function is calculated directly. The FAMBE method is tested as a function of pH (FAMBE-pH) with three proteins, namely, bovine pancreatic trypsin inhibitor (BPTI), hen egg white lysozyme (HEWL), and bovine pancreatic ribonuclease A (RNaseA). The results are (a) the FAMBE-pH method reproduces the observed pKa's of the ionizable groups of these proteins within an average absolute value of 0.4 pK units and a maximum error of 1.2 pK units and (b) comparison of the calculated total pH-dependent solvation free energy for BPTI, between the exact calculation of the ionization partition function and the Tanford–Schellman integral method, shows agreement within 1.2 kcal/mol. These results indicate that calculation of total solvation free energies with the FAMBE-pH method can provide an accurate prediction of protein conformational stability at a given fixed pH and, if coupled with molecular mechanics or molecular dynamics methods, can also be used for more realistic studies of protein folding, unfolding, and dynamics, as a function of pH. PMID:18683966

Nanomechanics of layer-by-layer polyelectrolyte complexes: a manifestation of ionic cross-links and fixed charges.

PubMed

Han, Biao; Chery, Daphney R; Yin, Jie; Lu, X Lucas; Lee, Daeyeon; Han, Lin

2016-01-28

This study investigates the roles of two distinct features of ionically cross-linked polyelectrolyte networks - ionic cross-links and fixed charges - in determining their nanomechanical properties. The layer-by-layer assembled poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) network is used as the model material. The densities of ionic cross-links and fixed charges are modulated through solution pH and ionic strength (IS), and the swelling ratio, elastic and viscoelastic properties are quantified via an array of atomic force microscopy (AFM)-based nanomechanical tools. The roles of ionic cross-links are underscored by the distinctive elastic and viscoelastic nanomechanical characters observed here. First, as ionic cross-links are highly sensitive to solution conditions, the instantaneous modulus, E0, exhibits orders-of-magnitude changes upon pH- and IS-governed swelling, distinctive from the rubber elasticity prediction based on permanent covalent cross-links. Second, ionic cross-links can break and self-re-form, and this mechanism dominates force relaxation of PAH/PAA under a constant indentation depth. In most states, the degree of relaxation is >90%, independent of ionic cross-link density. The importance of fixed charges is highlighted by the unexpectedly more elastic nature of the network despite low ionic cross-link density at pH 2.0, IS 0.01 M. Here, the complex is a net charged, loosely cross-linked, where the degree of relaxation is attenuated to ≈50% due to increased elastic contribution arising from fixed charge-induced Donnan osmotic pressure. In addition, this study develops a new method for quantifying the thickness of highly swollen polymer hydrogel films. It also underscores important technical considerations when performing nanomechanical tests on highly rate-dependent polymer hydrogel networks. These results provide new insights into the nanomechanical characters of ionic polyelectrolyte complexes, and lay the ground for further investigation of their unique time-dependent properties.

Surface reaction of SnII on goethite (α-FeOOH): surface complexation, redox reaction, reductive dissolution, and phase transformation.

PubMed

Dulnee, Siriwan; Scheinost, Andreas C

2014-08-19

To elucidate the potential risk of (126)Sn migration from nuclear waste repositories, we investigated the surface reactions of Sn(II) on goethite as a function of pH and Sn(II) loading under anoxic condition with O2 level < 2 ppmv. Tin redox state and surface structure were investigated by Sn K edge X-ray absorption spectroscopy (XAS), goethite phase transformations were investigated by high-resolution transmission electron microscopy and selected area electron diffraction. The results demonstrate the rapid and complete oxidation of Sn(II) by goethite and formation of Sn(IV) (1)E and (2)C surface complexes. The contribution of (2)C complexes increases with Sn loading. The Sn(II) oxidation leads to a quantitative release of Fe(II) from goethite at low pH, and to the precipitation of magnetite at higher pH. To predict Sn sorption, we applied surface complexation modeling using the charge distribution multisite complexation approach and the XAS-derived surface complexes. Log K values of 15.5 ± 1.4 for the (1)E complex and 19.2 ± 0.6 for the (2)C complex consistently predict Sn sorption across pH 2-12 and for two different Sn loadings and confirm the strong retention of Sn(II) even under anoxic conditions.

SPM observation of nano-dots induced by slow highly charged ions

NASA Astrophysics Data System (ADS)

Nakamura, Nobuyuki; Terada, Masashi; Nakai, Yoichi; Kanai, Yasuyuki; Ohtani, Shunsuke; Komaki, Ken-ichiro; Yamazaki, Yasunori

2005-05-01

We have observed nano-dots on a highly oriented pyrolytic graphite (HOPG) surface produced by highly charged ion impacts with a scanning probe microscope. In order to clarify the role of potential and kinetic energies in surface modification, we have measured the kinetic energy and incident ion charge dependences of the dot size. The results showed that the potential energy or the incident ion charge has strong influence on the surface modification rather than the kinetic energy.

Microbead-based immunoassay using the outer membrane layer of Escherichia coli combined with autodisplayed Z-domains

NASA Astrophysics Data System (ADS)

Kim, Do-Hoon; Bong, Ji-Hong; Yoo, Gu; Chang, Seo-Yoon; Park, Min; Chang, Young Wook; Kang, Min-Jung; Jose, Joachim; Pyun, Jae-Chul

2016-01-01

The Z-domain has the potential to control the orientation of immobilized antibodies because of its binding affinity to the Fc regions of antibodies (IgGs). In this work, Z-domains were autodisplayed on the outer membrane (OM) of Escherichia coli. OM particles were isolated and coated onto microbeads with positive, neutral, or negative surface charges. Other conditions such as incubation time and initial OM concentration were also optimized for the OM coating to obtain maximum antibody-binding. Using three kinds of model proteins with different isoelectric points (pI), streptavidin (pI = 5, negative charge at pH 7), horseradish peroxidase (pI = 7, neutral charge at pH 7), and avidin (pI = 10, positive charge at pH 7), protein immobilization onto the microbeads was carried out through physical adsorption and electrostatic interactions. Using fluorescently labeled antibodies and fluorescence-activated cell sorting, it was determined that the neutral and the positively charged microbeads effectively bound antibodies while minimizing non-specific protein binding. The OM-coated microbeads with autodisplayed Z-domains were applied to C-reactive protein immunoassay. This immunoassay achieved 5-fold improved sensitivity compared to conventional immunoassay based on physical adsorption of antibodies at the cutoff concentration of medical diagnosis of inflammatory diseases (1000 ng/ml) and cardiovascular diseases (200 ng/ml).

Thermodynamics, electrostatics, and ionic current in nanochannels grafted with pH-responsive end-charged polyelectrolyte brushes.

PubMed

Chen, Guang; Das, Siddhartha

2017-03-01

In this paper, we study the thermodynamics, electrostatics, and an external electric field driven ionic current in a pH-responsive, end-charged polyelectrolyte (PE) brush grafted nanochannel. By employing a mean field theory, we unravel a highly nonintuitive interplay of pH and electrolyte salt concentration in dictating the height of the end-charged PE brush. Larger pH or weak hydrogen ion concentration leads to maximum ionization of the charge-producing group-as a consequence, the resulting the electric double layer (EDL) energy get maximized causing a maximum deviation of the brush height from the value (d 0 ) of the uncharged brush. This deviation may result in enhancement or lowering of the brush height as compared to d 0 depending on whether the PE end locates lower or higher than h/2 (h is the nanochannel half height) and the salt concentration. Subsequently, we use this combined PE-brush-configuration-EDL-electrostatics framework to compute the ionic current in the nanochannel. We witness that the ionic current for smaller pH is much larger despite the corresponding magnitude of the EDL electrostatic potential being much smaller-this stems from the presence of a much larger concentration of H+ ions at small pH and the fact that H+ ions have very large mobilities. In fact, this ionic current shows a steep variation with pH that can be useful in exploring new designs for applications involving quantification and characterization of ionic current in PE-brush-grafted nanochannels. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Large area graphene ion sensitive field effect transistors with tantalum pentoxide sensing layers for pH measurement at the Nernstian limit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fakih, Ibrahim, E-mail: ibrahim.fakih@mail.mcgill.ca; Sabri, Shadi; Szkopek, Thomas, E-mail: thomas.szkopek@mcgill.ca

2014-08-25

We have fabricated and characterized large area graphene ion sensitive field effect transistors (ISFETs) with tantalum pentoxide sensing layers and demonstrated pH sensitivities approaching the Nernstian limit. Low temperature atomic layer deposition was used to deposit tantalum pentoxide atop large area graphene ISFETs. The charge neutrality point of graphene, inferred from quantum capacitance or channel conductance, was used to monitor surface potential in the presence of an electrolyte with varying pH. Bare graphene ISFETs exhibit negligible response, while graphene ISFETs with tantalum pentoxide sensing layers show increased sensitivity reaching up to 55 mV/pH over pH 3 through pH 8. Applying themore » Bergveld model, which accounts for site binding and a Guoy-Chapman-Stern picture of the surface-electrolyte interface, the increased pH sensitivity can be attributed to an increased buffer capacity reaching up to 10{sup 14} sites/cm{sup 2}. ISFET response was found to be stable to better than 0.05 pH units over the course of two weeks.« less

Large area graphene ion sensitive field effect transistors with tantalum pentoxide sensing layers for pH measurement at the Nernstian limit

NASA Astrophysics Data System (ADS)

Fakih, Ibrahim; Sabri, Shadi; Mahvash, Farzaneh; Nannini, Matthieu; Siaj, Mohamed; Szkopek, Thomas

2014-08-01

We have fabricated and characterized large area graphene ion sensitive field effect transistors (ISFETs) with tantalum pentoxide sensing layers and demonstrated pH sensitivities approaching the Nernstian limit. Low temperature atomic layer deposition was used to deposit tantalum pentoxide atop large area graphene ISFETs. The charge neutrality point of graphene, inferred from quantum capacitance or channel conductance, was used to monitor surface potential in the presence of an electrolyte with varying pH. Bare graphene ISFETs exhibit negligible response, while graphene ISFETs with tantalum pentoxide sensing layers show increased sensitivity reaching up to 55 mV/pH over pH 3 through pH 8. Applying the Bergveld model, which accounts for site binding and a Guoy-Chapman-Stern picture of the surface-electrolyte interface, the increased pH sensitivity can be attributed to an increased buffer capacity reaching up to 1014 sites/cm2. ISFET response was found to be stable to better than 0.05 pH units over the course of two weeks.

Gold Nanoparticle-Quantum Dot Fluorescent Nanohybrid: Application for Localized Surface Plasmon Resonance-induced Molecular Beacon Ultrasensitive DNA Detection

NASA Astrophysics Data System (ADS)

Adegoke, Oluwasesan; Park, Enoch Y.

2016-11-01

In biosensor design, localized surface plasmon resonance (LSPR)-induced signal from gold nanoparticle (AuNP)-conjugated reporter can produce highly sensitive nanohybrid systems. In order to retain the physicochemical properties of AuNPs upon conjugation, high colloidal stability in aqueous solution is needed. In this work, the colloidal stability with respect to the zeta potential (ZP) of four negatively charged thiol-functionalized AuNPs, thioglycolic (TGA)-AuNPs, 3-mercaptopropionic acid (MPA)-AuNPs, l-cysteine-AuNPs and l-glutathione (GSH)-AuNPs, and a cationic cyteamine-capped AuNPs was studied at various pHs, ionic strength, and NP concentration. A strong dependence of the ZP charge on the nanoparticle (NP) concentration was observed. High colloidal stability was exhibited between pH 3 and 9 for the negatively charged AuNPs and between pH 3 and 7 for the cationic AuNPs. With respect to the ionic strength, high colloidal stability was exhibited at ≤104 μM for TGA-AuNPs, l-cysteine-AuNPs, and GSH-AuNPs, whereas ≤103 μM is recommended for MPA-AuNPs. For the cationic AuNPs, very low ionic strength of ≤10 μM is recommended due to deprotonation at higher concentration. GSH-AuNPs were thereafter bonded to SiO2-functionalized alloyed CdZnSeS/ZnSe1.0S1.3 quantum dots (SiO2-Qdots) to form a plasmon-enhanced AuNP-SiO2-Qdots fluorescent nanohybrid. The AuNP-SiO2-Qdots conjugate was afterward conjugated to a molecular beacon (MB), thus forming an ultrasensitive LSPR-induced SiO2-Qdots-MB biosensor probe that detected a perfect nucleotide DNA sequence at a concentration as low as 10 fg/mL. The limit of detection was 11 fg/mL (1.4 fM) while the biosensor probe efficiently distinguished between single-base mismatch and noncomplementary sequence target.

Preparation of pH-sensitive zwitterionic nano micelles and drug controlled release for enhancing cellular uptake.

PubMed

Wu, Luyan; Ni, Caihua; Zhang, Liping; Shi, Gang

2016-01-01

Zwitterionic copolymers have exhibited high resistance to nonspecific protein adsorption and have wide applications in drug delivery systems. Herein, a pH-responsive poly(Lysine-alt-N,N'-bis(acryloyl) diaminohexane) was synthesized through the Michael addition polymerization between N, N'-bis(acryloyl) diaminohexane and lysine. Subsequently, nano micelles (NMs) were formed by self-assembly of the copolymer in an aqueous solution. The NMs showed a slightly negative charge in blood environment, but a positively charged surface in extracellular pH of tumor. This feature could be used to enhance permeability and retention effect, and reinforce tumor cell uptake. Vitro release studies revealed that the release of DOX from the DOX-loaded NMs was evidently faster at pH 5.0 than at pH 7.4. MTT assays revealed that NMs were nontoxic. Thus, these smart NMs were feasible candidates and could be potentially used in cancer chemotherapy.

Charge-reversal nanoparticles: novel targeted drug delivery carriers.

PubMed

Chen, Xinli; Liu, Lisha; Jiang, Chen

2016-07-01

Spurred by significant progress in materials chemistry and drug delivery, charge-reversal nanocarriers are being developed to deliver anticancer formulations in spatial-, temporal- and dosage-controlled approaches. Charge-reversal nanoparticles can release their drug payload in response to specific stimuli that alter the charge on their surface. They can elude clearance from the circulation and be activated by protonation, enzymatic cleavage, or a molecular conformational change. In this review, we discuss the physiological basis for, and recent advances in the design of charge-reversal nanoparticles that are able to control drug biodistribution in response to specific stimuli, endogenous factors (changes in pH, redox gradients, or enzyme concentration) or exogenous factors (light or thermos-stimulation).

Use of a chemical equilibrium model to describe surface properties and uptake of cadmium, strontium, and lead by Chlorella (UTEX 252)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassett, J.M.

1988-01-01

Metal-aquatic biota interactions are important in both natural and engineered systems. In this study, the uptake of cadmium, strontium and lead by the unicellular green alga Chlorella (UTEX 252) was investigated. Variables included metal concentration, pH, and ionic strength. Data gathered included dry weights (mg/l), cell counts (cells/ml), electrophoretic mobilities (EPMs, {mu}m/sec/V/cm) of metal-free and metal-exposed cells, and metal uptake - difference in concentration in filtrate of cell-metal and cell-free metal solutions. Derived data included cell volumes and surface area, uptake on a {mu}M/m{sup 2} basis, {zeta}-potentials, diffuse layer potentials and charge densities. Typical uptake values were 1.1, 5.2, andmore » 6 {mu}M/m{sup 2} for Cd, Pb, and Sr, respectively, from solutions of pH 6, ionic strength 0.02M, and metal concentration 10{sup {minus}4} M. Cell EPMs were insensitive to metal; under certain conditions, however, (pM > 4, pH > 8), cadmium exposed cells exhibited a reversal in surface charge from negative to positive. The chemical equilibrium model MINEQL1 + STANFORD was used to model algal surface properties and metal uptake. Input data included site pK, density, and {Delta}pK, estimated from EPM-pH data. The model described surface properties of Chlorella (UTEX 252) as judged by a close fit of {zeta}-potentials and model-derived diffuse layer potentials. Metal uptake was modelled by adjusting site density and/or metal-surface site equilibrium constants. Attempts to model surface properties and metal uptake simultaneously were not successful.« less

Defect Generation for a Hydrated Layer and Thermal Stability Based on Ba0.7Sr0.3TiO3/SiO2 as H+ Sensitive Layer in Ion-Sensitive Field-Effect Transistor Devices

NASA Astrophysics Data System (ADS)

Chen, Chun-Yuan; Chou, Jung-Chuan; Chou, Hsueh-Tao

2009-04-01

In this paper, we present a novel sensitive ion-sensitive field-effect transistor (ISFET) membrane based on Ba0.7Sr0.3TiO3 (BST)/SiO2 fabricated by sputtering deposition. The proposed device exhibits a linear shift in acidic solutions in the pH range from 1 to 10. The device sensitivity was about 50-55 mV/pH for different deposition times. We also examined the trapping behavior of the surface hydrated layer using the metal-insulator-semiconductor (MIS) structure. Results show that the hydration layer gives rise to stress polarity dependence of electron injection when immersed in pH buffer solutions. Injection from the gate electrode produces larger positive charges and interface state densities in contrast to the substrate injection, which causes simultaneous positive and negative charge trapping. A physical model that quantitatively describes the asymmetry associated with the hydrated diffusion layer is presented, and the temperature effects of BST/SiO2 ISFET devices in the range from 25 to 65 °C were examined. We observed that pH sensitivity increases with increasing temperature. The temperature coefficient of sensitivity (TCS) can be divided into two different ranges: 0.08 mV/pH °C between 25 and 45 °C, and 0.57 mV/pH °C between 45 and 65 °C. A better thermal stability is produced in the 25 and 45 °C range in comparison with other sensitive layers.

A Surfactant-Free Synthesis Technique of Coral-Like Zno Hierarchical Structures for Photocatalytic Degradation of Resorcinol under UV Irradiation

NASA Astrophysics Data System (ADS)

Sin, Jin-Chung; Lam, Sze-Mun; Chin, Ying-Hui

2018-01-01

Hierarchical coral-like ZnO structures were successfully prepared by a surfactant-free wet chemical method. Various characterization tests were carried out to analyze the as-prepared ZnO samples. The coral-like ZnO was used to degrade resorcinol at three different solution pH values (pH 5.0, pH 8.0 and pH 11.0). It was observed that the resorcinol adsorption onto the ZnO was strongly dependent on the electrical charge properties of both photocatalyst and resorcinol. Photocatalytic degradation of resorcinol reached the highest at pH 11.0 due to high concentration of hydroxyl ions for hydroxyl radicals generation.

Octanol-water distribution of engineered nanomaterials.

PubMed

Hristovski, Kiril D; Westerhoff, Paul K; Posner, Jonathan D

2011-01-01

The goal of this study was to examine the effects of pH and ionic strength on octanol-water distribution of five model engineered nanomaterials. Distribution experiments resulted in a spectrum of three broadly classified scenarios: distribution in the aqueous phase, distribution in the octanol, and distribution into the octanol-water interface. Two distribution coefficients were derived to describe the distribution of nanoparticles among octanol, water and their interface. The results show that particle surface charge, surface functionalization, and composition, as well as the solvent ionic strength and presence of natural organic matter, dramatically impact this distribution. Distributions of nanoparticles into the interface were significant for nanomaterials that exhibit low surface charge in natural pH ranges. Increased ionic strengths also contributed to increased distributions of nanoparticle into the interface. Similarly to the octanol-water distribution coefficients, which represent a starting point in predicting the environmental fate, bioavailability and transport of organic pollutants, distribution coefficients such as the ones described in this study could help to easily predict the fate, bioavailability, and transport of engineered nanomaterials in the environment.

Biophysics and Structure of the Patch and the Gigaseal

PubMed Central

Suchyna, Thomas M.; Markin, Vladislav S.; Sachs, Frederick

2009-01-01

Abstract Interpreting channel behavior in patches requires an understanding of patch structure and dynamics, especially in studies of mechanosensitive channels. High resolution optical studies show that patch formation occurs via blebbing that disrupts normal membrane structure and redistributes in situ components including ion channels. There is a 1–2 μm region of the seal below the patch where proteins are excluded and this may consist of extracted lipids that form the gigaseal. Patch domes often have complex geometries with inhomogeneous stresses due to the membrane-glass adhesion energy (Ea), cytoskeletal forces, and possible lipid subdomains. The resting tension in the patch dome ranges from 1–4 mN/m, a significant fraction of the lytic tension of a bilayer (∼10 mN/m). Thus, all patch experiments are conducted under substantial, and uneven, resting tension that may alter the kinetics of many channels. Ea seems dominated by van der Waals attraction overlaid with a normally repulsive Coulombic force. High ionic strength pipette saline increased Ea and, surprisingly, increased cytoskeletal rigidity in cell-attached patches. Low pH pipette saline also increased Ea and reduced the seal selectivity for cations, presumably by neutralizing the membrane surface charge. The seal is a negatively charged, cation selective, space with a resistance of ∼7 gigohm/μm in 100 mM KCl, and the high resistivity of the space may result from the presence of high viscosity glycoproteins. Patches creep up the pipette over time with voltage independent and voltage dependent components. Voltage-independent creep is expected from the capillary attraction of Ea and the flow of fresh lipids from the cell. Voltage-dependent creep seems to arise from electroosmosis in the seal. Neutralization of negative charges on the seal membrane with low pH decreased the creep rate and reversed the direction of creep at positive pipette potentials. PMID:19651032

Chitosan capped nanoscale Fe-MIL-88B-NH2 metal-organic framework as drug carrier material for the pH responsive delivery of doxorubicin

NASA Astrophysics Data System (ADS)

Sivakumar, P.; Priyatharshni, S.; Nagashanmugam, K. B.; Thanigaivelan, A.; Kumar, K.

2017-08-01

In recent years nanoscale metal-organic frameworks (NMOFs) are contributing as an effective material for use in drug delivery and imaging applications due to their porous surfaces and easy surface modifications. In this work, Fe-MIL-88B-NH2 NMOFs were successfully synthesized on facile hydrothermal route and 2-aminoterephthalic acid (NH2-BDC) was employed as a bridging ligand to activate amine functional groups on the surface. Amine functional groups not only serve as a structure stabilizing agent but also enhance the loading efficiency of the doxorubicin (DOX) anticancer drug. A pH responsive DOX release was realized by introducing a positively charged chitosan (Chi) capping layer. Upon Chi-coating, cleavage was observed in the Fe-MIL-88B-NH2 structure at acidic pH, while gel-like insoluble structure was formed at basic pH. By utilizing this phenomenon, a pH responsive DOX release system was developed by using Chi capped Fe-MIL-88B-NH2 NMOFs under the designed pH (4.0-8.0). The results suggest the Chi capped Fe-MIL-88B-NH2 can be a promising candidate for future pH responsive drug delivery systems.

Positively charged and bipolar layered poly(ether imide) nanofiltration membranes for water softening applications

NASA Astrophysics Data System (ADS)

Gassara, S.; Abdelkafi, A.; Quémener, D.; Amar, R. Ben; Deratani, A.

2015-07-01

Poly(ether imide) (PEI) ultrafiltration membranes were chemically modified with branched poly(ethyleneimine) to obtain nanofiltration (NF) membrane Cat PEI with a positive charge in the pH range below 9. An oppositely charged polyelectrolyte layer was deposited on the resulting membrane surface by using sodium polystyrene sulfonate (PSSNa) and sodium polyvinyl sulfonate (PVSNa) to prepare a bipolar layered membrane NF Cat PEI_PSS and Cat PEI_PVS having a negatively charged surface and positively charged pores. Cat PEI exhibited good performance to remove multivalent cations (more than 90% of Ca2+) from single salt solutions except in presence of sulfate ions. Adding an anionic polyelectrolyte layer onto the positively charged surface resulted in a significant enhancement of rejection performance even in presence of sulfate anions. Application of the prepared membranes in water softening of natural complex mixtures was successful for the different studied membranes and a large decrease of hardness was obtained. Moreover, Cat PEI_PSS showed a good selectivity for nitrate removal. Fouling experiments were carried out with bovine serum albumin, as model protein foulant. Cat PEI_PSS showed much better fouling resistance than Cat PEI with a quantitative flux recovery ratio.

Impact of water chemistry on surface charge and aggregation of polystyrene microspheres suspensions.

PubMed

Lu, Songhua; Zhu, Kairuo; Song, Wencheng; Song, Gang; Chen, Diyun; Hayat, Tasawar; Alharbi, Njud S; Chen, Changlun; Sun, Yubing

2018-07-15

The discharge of microplastics into aquatic environment poses the potential threat to the hydrocoles and human health. The fate and transport of microplastics in aqueous solutions are significantly influenced by water chemistry. In this study, the effect of water chemistry (i.e., pH, foreign salts and humic acid) on the surface charge and aggregation of polystyrene microsphere in aqueous solutions was conducted by batch, zeta potentials, hydrodynamic diameters, FT-IR and XPS analysis. Compared to Na + and K + , the lower negative zeta potentials and larger hydrodynamic diameters of polystyrene microspheres after introduction of Mg 2+ were observed within a wide range of pH (2.0-11.0) and ionic strength (IS, 0.01-500mmol/L). No effect of Cl - , HCO 3 - and SO 4 2- on the zeta potentials and hydrodynamic diameters of polystyrene microspheres was observed at low IS concentrations (<5mmol/L), whereas the zeta potentials and hydrodynamic diameters of polystyrene microspheres after addition of SO 4 2- were higher than that of Cl - and HCO 3 - at high IS concentrations (>10mmol/L). The zeta potentials of polystyrene microspheres after HA addition were decreased at pH2.0-11.0, whereas the lower hydrodynamic diameters were observed at pH<4.0. According to FT-IR and XPS analysis, the change in surface properties of polystyrene microspheres after addition of hydrated Mg 2+ and HA was attributed to surface electrostatic and/or steric repulsions. These investigations are crucial for understanding the effect of water chemistry on colloidal stability of microplastics in aquatic environment. Copyright © 2018 Elsevier B.V. All rights reserved.

Analysis of the sorption properties of different soils using water vapour adsorption and potentiometric titration methods

NASA Astrophysics Data System (ADS)

Skic, Kamil; Boguta, Patrycja; Sokołowska, Zofia

2016-07-01

Parameters of specific surface area as well as surface charge were used to determine and compare sorption properties of soils with different physicochemical characteristics. The gravimetric method was used to obtain water vapour isotherms and then specific surface areas, whereas surface charge was estimated from potentiometric titration curves. The specific surface area varied from 12.55 to 132.69 m2 g-1 for Haplic Cambisol and Mollic Gleysol soil, respectively, and generally decreased with pH (R=0.835; α = 0.05) and when bulk density (R=-0.736; α = 0.05) as well as ash content (R=-0.751; α = 0.05) increased. In the case of surface charge, the values ranged from 63.00 to 844.67 μmol g-1 Haplic Fluvisol and Mollic Gleysol, respecively. Organic matter gave significant contributions to the specific surface area and cation exchange capacity due to the large surface area and numerous surface functional groups, containing adsorption sites for water vapour molecules and for ions. The values of cation exchange capacity and specific surface area correlated linearly at the level of R=0.985; α = 0.05.

Montmorillonite-lipid hybrid carriers for ionizable and neutral poorly water-soluble drugs: Formulation, characterization and in vitro lipolysis studies.

PubMed

Dening, Tahnee J; Rao, Shasha; Thomas, Nicky; Prestidge, Clive A

2017-06-30

Lipid-based formulations (LBFs) are a popular strategy for enhancing the gastrointestinal solubilization and absorption of poorly water-soluble drugs. In light of this, montmorillonite-lipid hybrid (MLH) particles, composed of medium-chain triglycerides, lecithin and montmorillonite clay platelets, have been developed as a novel solid-state LBF. Owing to the unique charge properties of montmorillonite, whereby the clay platelet surfaces carry a permanent negative charge and the platelet edges carry a pH-dependent charge, three model poorly water-soluble drugs with different charge properties; blonanserin (weak base, pKa 7.7), ibuprofen (weak acid, pKa 4.5) and fenofibrate (neutral), were formulated as MLH particles and their performance during biorelevant in vitro lipolysis at pH 7.5 was investigated. For blonanserin, drug solubilization during in vitro lipolysis was significantly reduced 3.4-fold and 3.2-fold for MLH particles in comparison to a control lipid solution and silica-lipid hybrid (SLH) particles, respectively. It was hypothesized that strong electrostatic interactions between the anionic montmorillonite platelet surfaces and cationic blonanserin molecules were responsible for the inferior performance of MLH particles. In contrast, no significant influence on drug solubilization was observed for ibuprofen- and fenofibrate-loaded MLH particles. The results of the current study indicate that whilst MLH particles are a promising novel formulation strategy for poorly water-soluble drugs, drug ionization tendency and the potential for drug-clay interactions must be taken into consideration to ensure an appropriate performance. Copyright © 2017 Elsevier B.V. All rights reserved.

Acid-base properties of the alumina surface: influence of the titration procedures on the microcalorimetric results.

PubMed

Morel, Jean-Pierre; Marmier, Nicolas; Hurel, Charlotte; Morel-Desrosiers, Nicole

2009-10-01

The enthalpy changes associated with the protonation and deprotonation of an alumina surface have been determined on the basis of microcalorimetry experiments and acid-base potentiometric titrations at 25 degrees C. It has been shown that the results may vary significantly according to the experimental procedure. In order to do so, the potentiometric and microcalorimetric titrations have been carried out first from an acidic pH to basic pH and second from a pH near the pH(zpc) of alumina to acidic or basic pH. It has been demonstrated that the pK(a) values deduced from the potentiometric titrations are the same whatever the experimental protocol whereas the only way to obtain meaningful enthalpies of proton exchange is to carry out microcalorimetric titrations by starting around the point of zero charge.

Effect of softening precipitate composition and surface characteristics on natural organic matter adsorption.

PubMed

Russell, Caroline G; Lawler, Desmond F; Speitel, Gerald E; Katz, Lynn E

2009-10-15

Natural organic matter (NOM) removal during water softening is thought to occur through adsorption onto or coprecipitation with calcium and magnesium solids. However, details of precipitate composition and surface chemistry and subsequent interactions with NOM are relatively unknown. In this study, zeta potentiometry analyses of precipitates formed from inorganic solutions under varying conditions (e.g., Ca-only, Mg-only, Ca + Mg, increasing lime or NaOH dose) indicated that both CaCO3 and Mg(OH)2 were positively charged at higher lime (Ca(OH)2) and NaOH doses (associated with pH values above 11.5), potentially yielding a greater affinity for adsorbing negatively charged organic molecules. Environmental scanning electron microscopy (ESEM) images of CaCO3 solids illustrated the rhombohedral shape characteristic of calcite. In the presence of increasing concentrations of magnesium, the CaCO3 rhombs shifted to more elongated crystals. The CaCO3 solids also exhibited increasingly positive surface charge from Mg incorporation into the crystal lattice, potentially creating more favorable conditions for adsorption of organic matter. NOM adsorption experiments using humic substances extracted from Lake Austin and Missouri River water elucidated the role of surface charge and surface area on adsorption.

Study of the electrostatic effects of mutations on the surface of dehaloperoxidase-hemoglobin A.

PubMed

Zhao, Junjie; Rowe, Jennifer; Franzen, Jocelyn; He, Chi; Franzen, Stefan

2012-04-20

Point mutations of dehaloperoxidase-hemoglobin A (DHP A) that affect the surface charge have been prepared to study the interaction between DHP A with its substrate 2,4,6-trichlorophenol (TCP). Kinetic studies of these surface mutations showed a correlation, in which the more positively charged mutants have increased catalytic efficiency compared with wild type DHP A. As a result, the hypothesis of this study is that there is a global electrostatic interaction between DHP A and TCP. The electrostatic nature of substrate binding was further confirmed by the result that kinetic assays of DHP A were affected by ionic strength. Furthermore, isoelectric focusing (IEF) gel study showed that the pI-6.8 for DHP A, which indicates that DHP A has a slight negative charge pH 7, consistent with the kinetic observations. Copyright © 2012 Elsevier Inc. All rights reserved.

Lipids and topological rules of membrane protein assembly: balance between long and short range lipid-protein interactions.

PubMed

Vitrac, Heidi; Bogdanov, Mikhail; Heacock, Phil; Dowhan, William

2011-04-29

The N-terminal six-transmembrane domain (TM) bundle of lactose permease of Escherichia coli is uniformly inverted when assembled in membranes lacking phosphatidylethanolamine (PE). Inversion is dependent on the net charge of cytoplasmically exposed protein domains containing positive and negative residues, net charge of the membrane surface, and low hydrophobicity of TM VII acting as a molecular hinge between the two halves of lactose permease (Bogdanov, M., Xie, J., Heacock, P., and Dowhan, W. (2008) J. Cell Biol. 182, 925-935). Net neutral lipids suppress the membrane translocation potential of negatively charged amino acids, thus increasing the cytoplasmic retention potential of positively charged amino acids. Herein, TM organization of sucrose permease (CscB) and phenylalanine permease (PheP) as a function of membrane lipid composition was investigated to extend these principles to other proteins. For CscB, topological dependence on PE only becomes evident after a significant increase in the net negative charge of the cytoplasmic surface of the N-terminal TM bundle. High negative charge is required to overcome the thermodynamic block to inversion due to the high hydrophobicity of TM VII. Increasing the positive charge of the cytoplasmic surface of the N-terminal TM hairpin of PheP, which is misoriented in PE-lacking cells, favors native orientation in the absence of PE. PheP and CscB also display co-existing dual topologies dependent on changes in the charge balance between protein domains and the membrane lipids. Therefore, the topology of both permeases is dependent on PE. However, CscB topology is governed by thermodynamic balance between opposing lipid-dependent electrostatic and hydrophobic interactions.

Effect of polycarboxylate ether comb-type polymer on viscosity and interfacial properties of kaolinite clay suspensions.

PubMed

Zhang, Ling; Lu, Qingye; Xu, Zhenghe; Liu, Qingxia; Zeng, Hongbo

2012-07-15

The interactions between kaolinite clay particles and a comb-type polymer (polycarboxylate ether or PCE), so-called PCE super-plasticizer, were investigated through viscosity and surface forces measurements by a rheometer and a Surface Forces Apparatus (SFA). The addition of PCE shows a strong impact on the viscosity of concentrated kaolinite suspensions in alkaline solutions (pH=8.3) but a weak effect under acidic conditions (pH=3.4). In acidic solutions, the high viscosity measured is attributed to the strong electrostatic interaction between negatively charged basal planes and positively charged edge surfaces of clay particles. Under the alkaline condition, the suspension viscosity was found to first increase significantly and then decrease with increasing PCE dosages. The results from surface forces measurement show that PCE molecules at low dosages can bridge the kaolinite particles in the concentrated suspensions via hydrogen bonding, leading to the formation of a kaolinite-PCE "network" and hence an increased suspension viscosity. At high PCE dosages, clay particles are fully covered by PCE molecules, leading to a more dispersed kaolinite suspensions and hence lower suspension viscosity due to steric repulsion between the adsorbed PCE molecules. The insights derived from measuring viscosity and interfacial properties of kaolinite suspensions containing varying amount of comb-type super-plasticizer PCE at different pH provide the foundation for many engineering applications and optimizing industrial processes. Copyright © 2012 Elsevier Inc. All rights reserved.

Apparent electric charge of protein molecules. Human thyroxine - binding proteins.

PubMed

Hocman, G; Sadlon, J

1977-01-01

1. By comparison of electrophoretic mobilities of two different charged particles under the same conditions the net elementary electrostatic charge of one particle could be calculated when the charge of the other is known. 2. The electrophoretic mobility of human thyroxine - binding globulin does not depend upon the concentration of Tris - HCl buffer in the range 0.05 to 0.20 molar. The value of this mobility is 0.078 and 0.083 cm2 vol(-1) hour(-1) at pH 7.0 and 8.6, respectively. 3. The net elementary electrostatic charge of the human thyroxine - binding globulin appears to be approximately 22 negative elementary electrostatic units in mild alkaline solutions.

Adsorption properties of the nanozirconia/anionic polyacrylamide system-Effects of surfactant presence, solution pH and polymer carboxyl groups content

NASA Astrophysics Data System (ADS)

Wiśniewska, Małgorzata; Chibowski, Stanisław; Urban, Teresa

2016-05-01

The adsorption mechanism of anionic polyacrylamide (PAM) on the nanozirconia surface was examined. The effects of solution pH, carboxyl groups content in macromolecules and anionic surfactant (sodium dodecyl sulfate-SDS) addition were determined. The more probable structure of polymer adsorption layer was characterized based on the data obtained from spectrophotometry, viscosimetry and potentiometric titration methods. The adsorbed amount of polymer, size of macromolecules in the solution and surface charge density of ZrO2 particles in the absence and presence of PAM were assessed, respectively. Analysis of these results indicated that the increase of solution pH and content of carboxyl groups in the polymeric chains lead to more expanded conformations of adsorbing macromolecules. As a result, the adsorption of anionic polyacrylamide decreased. The SDS presence caused the significant increase of PAM adsorbed amount at pH 3, whereas at pH 6 and 9 the surfactant addition resulted in reduction of polymer adsorption level.

Nanoparticle Stabilized Liposomes for Acne Therapy

NASA Astrophysics Data System (ADS)

Fu, Victoria

Acne vulgaris is a common skin disease that affects over 40 million people in the United States alone. The main cause of acne vulgaris is Propionibacterium acnes (P. acnes), resides deep in the pores and follicles of the skin in order to feed on oil produced by the sebaceous glands. The liposome is a lipid based nanoparticle with numerous advantages over free drug molecules as an acne treatment alternative. Bare liposomes loaded with lauric acid (LipoLA) were found to show strong antimicrobial activity against P. acnes while generating minimal toxicity. However, the platform is limited by the spontaneous tendency of liposomes to fuse with each other. Attaching nanoparticles to the surface of liposomes can overcome this challenge by providing steric repulsion and reduce surface tension. Thus, carboxyl-functionalized gold nanoparticles (AuC) were attached to the surface of liposomes (AuC-liposomes) loaded with doxycycline, a general tetracycline antibiotic. These particles were found to have a diameter of 120 nm and a zeta potential of 20.0 mV. Both fluorescent and antimicrobial studies demonstrated that based on electrostatic interaction, negatively charged AuC attached to the liposome's positively charged surface and stabilized liposomes in a neutral pH environment (pH = 7.4). Upon entering the skin's acidic environment (pH = 4), AuC detached from the liposome's surface and liposomes could fuse with P. acnes residing in the pores. Furthermore, toxicity studies showed that AuC-liposomes did not induce any significant toxicity, while two of the leading over-the-counter therapies, benzoyl peroxide and salicylic acid, generated substantial skin irritation.

Adsorption of Ions on Zirconium Oxide Surfaces from Aqueous Solutions at High Temperatures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmer, Donald; Machesky, Michael L.; Benezeth, Pascale

2009-07-01

Surface titrations were carried out on suspensions of monoclinic ZrO{sub 2} from 25 to 290 C slightly above saturation vapor pressure at ionic strengths of 0.03, 0.1 and 1.0 mol {center_dot} kg{sup -1}(NaCl). A typical increase in surface charge was observed with increasing temperature. There was no correlation between the radius of the cations, Li{sup +}, Na{sup +}, K{sup +} and (CH{sub 3}){sub 4}N{sup +}, and the magnitude of their association with the surface. The combined results were treated with a 1-pK{sub a} MUSIC model, which yielded association constants for the cations (and chloride ion at low pH) at eachmore » temperature. The pH of zero-point-charge, pH{sub zpc}, decreased with increasing temperature as found for other metal oxides, reaching an apparent minimum value of 4.1 by 250 C. Batch experiments were performed to monitor the concentration of LiOH in solutions containing suspended ZrO{sub 2} particles from 200 to 360 C. At 350 and 360 C, Li{sup +} and OH{sup -} ions were almost totally adsorbed when the pressure was lowered to near saturation vapor pressure. This reversible trend has implications not only to pressure-water reactor, PWR, operations, but is also of general scientific and other applied interest. Additional experiments probed the feasibility that boric acid/borate ions adsorb reversibly onto ZrO{sub 2} surfaces at near-neutral pH conditions as indicated in earlier publications.« less

Nuclear Magnetic Resonance Structures of GCN4p Are Largely Conserved When Ion Pairs Are Disrupted at Acidic pH but Show a Relaxation of the Coiled Coil Superhelix.

PubMed

Kaplan, Anne R; Brady, Megan R; Maciejewski, Mark W; Kammerer, Richard A; Alexandrescu, Andrei T

2017-03-21

To understand the roles ion pairs play in stabilizing coiled coils, we determined nuclear magnetic resonance structures of GCN4p at three pH values. At pH 6.6, all acidic residues are fully charged; at pH 4.4, they are half-charged, and at pH 1.5, they are protonated and uncharged. The α-helix monomer and coiled coil structures of GCN4p are largely conserved, except for a loosening of the coiled coil quaternary structure with a decrease in pH. Differences going from neutral to acidic pH include (i) an unwinding of the coiled coil superhelix caused by the loss of interchain ion pair contacts, (ii) a small increase in the separation of the monomers in the dimer, (iii) a loosening of the knobs-into-holes packing motifs, and (iv) an increased separation between oppositely charged residues that participate in ion pairs at neutral pH. Chemical shifts (HN, N, C', Cα, and Cβ) of GCN4p display a seven-residue periodicity that is consistent with α-helical structure and is invariant with pH. By contrast, periodicity in hydrogen exchange rates at neutral pH is lost at acidic pH as the exchange mechanism moves into the EX1 regime. On the basis of 1 H- 15 N nuclear Overhauser effect relaxation measurements, the α-helix monomers experience only small increases in picosecond to nanosecond backbone dynamics at acidic pH. By contrast, 13 C rotating frame T 1 relaxation (T 1ρ ) data evince an increase in picosecond to nanosecond side-chain dynamics at lower pH, particularly for residues that stabilize the coiled coil dimerization interface through ion pairs. The results on the structure and dynamics of GCNp4 over a range of pH values help rationalize why a single structure at neutral pH poorly predicts the pH dependence of the unfolding stability of the coiled coil.

Response of the Shockley surface state on Cu(111) to an external electrical field: A density-functional theory study

NASA Astrophysics Data System (ADS)

Berland, Kristian; Hyldgaard, Per; Einstein, T. L.

2011-03-01

We study the response of the Cu(111) Shockley surface state to an external electrical field E by combining a density-functional theory calculation for a finite slab geometry with an analysis of the Kohn-Sham wavefunctions to obtain a well-converged characterization. We find that the surface state displays isotropic dispersion, quadratic until the Fermi wave vector but with a significant quartic contribution beyond. We find that the shift in band minimum and effective mass depend linearly on E. Most change in electrostatic potential profile, and charge transfer occurs outside the outermost copper atoms, and most of the screening is due to bulk electrons. Our analysis is facilitated by a method used to decouple the Kohn-Sham states due to the finite slab geometry, using a rotation in Hilbert space. We discuss applications to tuning the Fermi wavelength and so the many patterns attributed to metallic surface states. Supported by (KB and PH) Swedish Vetenskapsrådet VR 621-2008-4346 and (TLE) NSF CHE 07-50334 & UMD MRSEC DMR 05-20471.

On the dependence of charge density on surface curvature of an isolated conductor

NASA Astrophysics Data System (ADS)

Bhattacharya, Kolahal

2016-03-01

A study of the relation between the electrostatic charge density at a point on a conducting surface and the curvature of the surface (at that point) is presented. Two major papers in the scientific literature on this topic are reviewed and the apparent discrepancy between them is resolved. Hence, a step is taken towards obtaining a general analytic formula for relating the charge density with surface curvature of conductors. The merit of this formula and its limitations are discussed.

Mechanisms of antimony adsorption onto soybean stover-derived biochar in aqueous solutions.

PubMed

Vithanage, Meththika; Rajapaksha, Anushka Upamali; Ahmad, Mahtab; Uchimiya, Minori; Dou, Xiaomin; Alessi, Daniel S; Ok, Yong Sik

2015-03-15

Limited mechanistic knowledge is available on the interaction of biochar with trace elements (Sb and As) that exist predominantly as oxoanions. Soybean stover biochars were produced at 300 °C (SBC300) and 700 °C (SBC700), and characterized by BET, Boehm titration, FT-IR, NMR and Raman spectroscopy. Bound protons were quantified by potentiometric titration, and two acidic sites were used to model biochar by the surface complexation modeling based on Boehm titration and NMR observations. The zero point of charge was observed at pH 7.20 and 7.75 for SBC300 and SBC700, respectively. Neither antimonate (Sb(V)) nor antimonite (Sb(III)) showed ionic strength dependency (0.1, 0.01 and 0.001 M NaNO3), indicating inner sphere complexation. Greater adsorption of Sb(III) and Sb(V) was observed for SBC300 having higher -OH content than SBC700. Sb(III) removal (85%) was greater than Sb(V) removal (68%). Maximum adsorption density for Sb(III) was calculated as 1.88 × 10(-6) mol m(-2). The Triple Layer Model (TLM) successfully described surface complexation of Sb onto soybean stover-derived biochar at pH 4-9, and suggested the formation of monodentate mononuclear and binuclear complexes. Spectroscopic investigations by Raman, FT-IR and XPS further confirmed strong chemisorptive binding of Sb to biochar surfaces. Copyright © 2014 Elsevier Ltd. All rights reserved.

Investigating the Role of Phosphorylation in the Binding of Silaffin Peptide R5 to Silica with Molecular Dynamics Simulations.

PubMed

Sprenger, K G; Prakash, Arushi; Drobny, Gary; Pfaendtner, Jim

2018-01-23

Biomimetic silica formation, a process that is largely driven by proteins, has garnered considerable interest in recent years due to its role in the development of new biotechnologies. However, much remains unknown of the molecular-scale mechanisms underlying the binding of proteins to biomineral surfaces such as silica, or even of the key residue-level interactions between such proteins and surfaces. In this study, we employ molecular dynamics (MD) simulations to study the binding of R5-a 19-residue segment of a native silaffin peptide used for in vitro silica formation-to a silica surface. The metadynamics enhanced sampling method is used to converge the binding behavior of R5 on silica at both neutral (pH 7.5) and acidic (pH 5) conditions. The results show fundamental differences in the mechanism of binding between the two cases, providing unique insight into the pH-dependent ability of R5 and native silaffin to precipitate silica. We also study the effect of phosphorylation of serine residues in R5 on both the binding free energy to silica and the interfacial conformation of the peptide. Results indicate that phosphorylation drastically decreases the binding free energy and changes the structure of silica-adsorbed R5 through the introduction of charge and steric repulsion. New mechanistic insights from this work could inform rational design of new biomaterials and biotechnologies.

A surface-enhanced infrared absorption spectroscopic study of pH dependent water adsorption on Au

NASA Astrophysics Data System (ADS)

Dunwell, Marco; Yan, Yushan; Xu, Bingjun

2016-08-01

The potential dependent behavior of near-surface water on Au film electrodes in acidic and alkaline solutions is studied using a combination of attenuated total reflectance surface enhanced infrared spectroscopy and chronoamperometry. In acid, sharp νOH peaks appear at 3583 cm- 1 at high potentials attributed to non-H-bonded water coadsorbed in the hydration sphere of perchlorate near the electrode surface. Adsorbed hydronium bending mode at near 1680 cm- 1 is observed at low potentials in low pH solutions (1.4, 4.0, 6.8). At high pH (10.0, 12.3), a potential-dependent OH stretching band assigned to adsorbed hydroxide emerges from 3400-3506 cm- 1. The observation of adsorbed hydroxide, even on a weakly oxophilic metal such as Au, provides the framework for further studies of hydroxide adsorption on other electrodes to determine the role of adsorbed hydroxide on important reactions such as the hydrogen oxidation reaction.

Transport of Cryptosporidium parvum Oocysts in Charge Heterogeneous Porous Media: Microfluidics Experiment and Numerical Simulation

NASA Astrophysics Data System (ADS)

Liu, Y.; Meng, X.; Guo, Z.; Zhang, C.; Nguyen, T. H.; Hu, D.; Ji, J.; Yang, X.

2017-12-01

Colloidal attachment on charge heterogeneous grains has significant environmental implications for transport of hazardous colloids, such as pathogens, in the aquifer, where iron, manganese, and aluminium oxide minerals are the major source of surface charge heterogeneity of the aquifer grains. A patchwise surface charge model is often used to describe the surface charge heterogeneity of the grains. In the patchwise model, the colloidal attachment efficiency is linearly correlated with the fraction of the favorable patches (θ=λ(θf - θu)+θu). However, our previous microfluidic study showed that the attachment efficiency of oocysts of Cryptosporidium parvum, a waterborne protozoan parasite, was not linear correlated with the fraction of the favorable patches (λ). In this study, we developed a pore scale model to simulate colloidal transport and attachment on charge heterogeneous grains. The flow field was simulated using the LBM method and colloidal transport and attachment were simulated using the Lagrange particle tracking method. The pore scale model was calibrated with experimental results of colloidal and oocyst transport in microfluidic devices and was then used to simulate oocyst transport in charge heterogeneous porous media under a variety of environmental relative conditions, i.e. the fraction of favorable patchwise, ionic strength, and pH. The results of the pore scale simulations were used to evaluate the effect of surface charge heterogeneity on upscaling of oocyst transport from pore to continuum scale and to develop an applicable correlation between colloidal attachment efficiency and the fraction of the favorable patches.

IEP as a parameter characterizing the pH-dependent surface charging of materials other than metal oxides.

PubMed

Kosmulski, Marek

2012-01-01

The numerical values of points of zero charge (PZC, obtained by potentiometric titration) and of isoelectric points (IEP) of various materials reported in the literature have been analyzed. In sets of results reported for the same chemical compound (corresponding to certain chemical formula and crystallographic structure), the IEP are relatively consistent. In contrast, in materials other than metal oxides, the sets of PZC are inconsistent. In view of the inconsistence in the sets of PZC and of the discrepancies between PZC and IEP reported for the same material, it seems that IEP is more suitable than PZC as the unique number characterizing the pH-dependent surface charging of materials other than metal oxides. The present approach is opposite to the usual approach, in which the PZC and IEP are considered as two equally important parameters characterizing the pH-dependent surface charging of materials other than metal oxides. Copyright © 2012 Elsevier B.V. All rights reserved.

Cellulose nanocrystals with tunable surface charge for nanomedicine

NASA Astrophysics Data System (ADS)

Hosseinidoust, Zeinab; Alam, Md Nur; Sim, Goeun; Tufenkji, Nathalie; van de Ven, Theo G. M.

2015-10-01

Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For applications in imaging and drug delivery, surface charge is one of the most important factors affecting the performance of nanocarriers. However, current methods of preparation offer little flexibility for controlling the surface charge of cellulose nanocrystals, leading to compromised colloidal stability under physiological conditions. We report a synthesis method that results in nanocrystals with remarkably high carboxyl content (6.6 mmol g-1) and offers continuous control over surface charge without any adjustment to the reaction conditions. Six fractions of nanocrystals with various surface carboxyl contents were synthesized from a single sample of softwood pulp with carboxyl contents varying from 6.6 to 1.7 mmol g-1 and were fully characterized. The proposed method resulted in highly stable colloidal nanocrystals that did not aggregate when exposed to high salt concentrations or serum-containing media. Interactions of these fractions with four different tissue cell lines were investigated over a wide range of concentrations (50-300 μg mL-1). Darkfield hyperspectral imaging and confocal microscopy confirmed the uptake of nanocrystals by selected cell lines without any evidence of membrane damage or change in cell density; however a charge-dependent decrease in mitochondrial activity was observed for charge contents higher than 3.9 mmol g-1. A high surface carboxyl content allowed for facile conjugation of fluorophores to the nanocrystals without compromising colloidal stability. The cellular uptake of fluoresceinamine-conjugated nanocrystals exhibited a time-dose dependent relationship and increased significantly with doubling of the surface charge.Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For applications in imaging and drug delivery, surface charge is one of the most important factors affecting the performance of nanocarriers. However, current methods of preparation offer little flexibility for controlling the surface charge of cellulose nanocrystals, leading to compromised colloidal stability under physiological conditions. We report a synthesis method that results in nanocrystals with remarkably high carboxyl content (6.6 mmol g-1) and offers continuous control over surface charge without any adjustment to the reaction conditions. Six fractions of nanocrystals with various surface carboxyl contents were synthesized from a single sample of softwood pulp with carboxyl contents varying from 6.6 to 1.7 mmol g-1 and were fully characterized. The proposed method resulted in highly stable colloidal nanocrystals that did not aggregate when exposed to high salt concentrations or serum-containing media. Interactions of these fractions with four different tissue cell lines were investigated over a wide range of concentrations (50-300 μg mL-1). Darkfield hyperspectral imaging and confocal microscopy confirmed the uptake of nanocrystals by selected cell lines without any evidence of membrane damage or change in cell density; however a charge-dependent decrease in mitochondrial activity was observed for charge contents higher than 3.9 mmol g-1. A high surface carboxyl content allowed for facile conjugation of fluorophores to the nanocrystals without compromising colloidal stability. The cellular uptake of fluoresceinamine-conjugated nanocrystals exhibited a time-dose dependent relationship and increased significantly with doubling of the surface charge. Electronic supplementary information (ESI) available: Additional results are presented in the ESI in Fig. S1 through S4. See DOI: 10.1039/c5nr02506k

Comparison of the surface charge behavior of commercial silicon nitride and silicon carbide powders

NASA Technical Reports Server (NTRS)

Whitman, Pamela K.; Feke, Donald L.

1988-01-01

The adsorption and desorption of protons from aqueous solution onto the surfaces of a variety of commercial silicon carbide and silicon nitride powders has been examined using a surface titration methodology. This method provides information on some colloidal characteristics, such as the point of zero charge (pzc) and the variation of proton adsorption with dispersion pH, useful for the prediction of optimal ceramic-processing conditions. Qualitatively, the magnitude of the proton adsorption from solution reveals small differences among all of the materials studied. However, the results show that the pzc for the various silicon nitride powders is affected by the powder synthesis route. Complementary investigations have shown that milling can also act to shift the pzc exhibited by silicon nitride powder. Also, studies of the role of the electrolyte in the development of surface charge have indicated no evidence of specific adsorption of ammonium ion on either silicon nitride or silicon carbide powders.

Application of nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, UV-Visible spectroscopy and kinetic modeling for elucidation of adsorption chemistry in uptake of tetracycline by zeolite beta.

PubMed

Kang, Jin; Liu, Huijuan; Zheng, Yu-Ming; Qu, Jiuhui; Chen, J Paul

2011-02-01

Extensive usage of tetracycline has resulted in its contamination in surface water and groundwater. The adsorption of tetracycline on zeolite beta was systematically investigated for the decontamination of the antibiotic polluted water in this study. Ninety percent of uptake by the zeolite beta occured in 0.25h, and the adsorption equilibrium was obtained within 3h, which was well described by an intraparticle diffusion model. The adsorption generally increased when pH was increased from 4.0 to 5.0, and then decreased significantly as the pH was further increased, which was caused by the pH-dependent speciation of tetracycline and surface charge of zeolite beta. Both Freundlich and Langmuir equations well described the adsorption isotherm. A thermodynamic analysis showed that the sorption process was spontaneous and endothermic. Aluminum atoms in the zeolite played a crucial role in the uptake; the adsorption increased with the increasing aluminum content in zeolite. The UV-Visible spectroscopy study showed that the spectra of tetracycline changed upon the interaction with zeolite beta, which could be ascribed to the formation of complexes of tetracycline and aluminum atoms in the zeolite surface. Nuclear magnetic resonance spectroscopy study further confirmed the participation of Al in the tetracycline adsorption. Fourier transform infrared spectroscopy studies showed that the amino functional groups in tetracycline were involved in the complexation with the zeolite surface. Copyright © 2010 Elsevier Inc. All rights reserved.

Application of linear pH gradients for the modeling of ion exchange chromatography: Separation of monoclonal antibody monomer from aggregates.

PubMed

Kluters, Simon; Wittkopp, Felix; Jöhnck, Matthias; Frech, Christian

2016-02-01

The mobile phase pH is a key parameter of every ion exchange chromatography process. However, mechanistic insights into the pH influence on the ion exchange chromatography equilibrium are rare. This work describes a mechanistic model capturing salt and pH influence in ion exchange chromatography. The pH dependence of the characteristic protein charge and the equilibrium constant is introduced to the steric mass action model based on a protein net charge model considering the number of amino acids interacting with the stationary phase. This allows the description of the adsorption equilibrium of the chromatographed proteins as a function of pH. The model parameters were determined for a monoclonal antibody monomer, dimer, and a higher aggregated species based on a manageable set of pH gradient experiments. Without further modification of the model parameters the transfer to salt gradient elution at fixed pH is demonstrated. A lumped rate model was used to predict the separation of the monoclonal antibody monomer/aggregate mixture in pH gradient elution and for a pH step elution procedure-also at increased protein loadings up to 48 g/L packed resin. The presented model combines both salt and pH influence and may be useful for the development and deeper understanding of an ion exchange chromatography separation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acid base activity of live bacteria: Implications for quantifying cell wall charge

NASA Astrophysics Data System (ADS)

Claessens, Jacqueline; van Lith, Yvonne; Laverman, Anniet M.; Van Cappellen, Philippe

2006-01-01

To distinguish the buffering capacity associated with functional groups in the cell wall from that resulting from metabolic processes, base or acid consumption by live and dead cells of the Gram-negative bacterium Shewanella putrefaciens was measured in a pH stat system. Live cells exhibited fast consumption of acid (pH 4) or base (pH 7, 8, 9, and 10) during the first few minutes of the experiments. At pH 5.5, no acid or base was required to maintain the initial pH constant. The initial amounts of acid or base consumed by the live cells at pH 4, 8, and 10 were of comparable magnitudes as those neutralized at the same pHs by intact cells killed by exposure to gamma radiation or ethanol. Cells disrupted in a French press required higher amounts of acid or base, due to additional buffering by intracellular constituents. At pH 4, acid neutralization by suspensions of live cells stopped after 50 min, because of loss of viability. In contrast, under neutral and alkaline conditions, base consumption continued for the entire duration of the experiments (5 h). This long-term base neutralization was, at least partly, due to active respiration by the cells, as indicated by the build-up of succinate in solution. Qualitatively, the acid-base activity of live cells of the Gram-positive bacterium Bacillus subtilis resembled that of S. putrefaciens. The pH-dependent charging of ionizable functional groups in the cell walls of the live bacteria was estimated from the initial amounts of acid or base consumed in the pH stat experiments. From pH 4 to 10, the cell wall charge increased from near-zero values to about -4 × 10 -16 mol cell -1 and -6.5 × 10 -16 mol cell -1 for S. putrefaciens and B. subtilis, respectively. The similar cell wall charging of the two bacterial strains is consistent with the inferred low contribution of lipopolysaccharides to the buffering capacity of the Gram-negative cell wall (of the order of 10%).

Controlling silk fibroin particle features for drug delivery

PubMed Central

Lammel, Andreas; Hu, Xiao; Park, Sang-Hyug; Kaplan, David L.; Scheibel, Thomas

2010-01-01

Silk proteins are a promising material for drug delivery due to their aqueous processability, biocompatibility, and biodegradability. A simple aqueous preparation method for silk fibroin particles with controllable size, secondary structure and zeta potential is reported. The particles were produced by salting out a silk fibroin solution with potassium phosphate. The effect of ionic strength and pH of potassium phosphate solution on the yield and morphology of the particles was determined. Secondary structure and zeta potential of the silk particles could be controlled by pH. Particles produced by salting out with 1.25 M potassium phosphate pH 6 showed a dominating silk II (crystalline) structure whereas particles produced at pH 9 were mainly composed of silk I (less crystalline). The results show that silk I rich particles possess chemical and physical stability and secondary structure which remained unchanged during post treatments even upon exposure to 100% ethanol or methanol. A model is presented to explain the process of particle formation based on intra- and intermolecular interactions of the silk domains, influenced by pH and kosmotrope salts. The reported silk fibroin particles can be loaded with small molecule model drugs, such as alcian blue, rhodamine B, and crystal violet, by simple absorption based on electrostatic interactions. In vitro release of these compounds from the silk particles depends on charge – charge interactions between the compounds and the silk. With crystal violet we demonstrated that the release kinetics are dependent on the secondary structure of the particles. PMID:20219241

Adsorption/Desorption Transition of Recombinant Human Neurotrophin 4: Physicochemical Characterization.

PubMed

Dąbkowska, Maria; Adamczak, Małgorzata; Barbasz, Jakub; Cieśla, Michał; Machaliński, Bogusław

2017-09-26

Bulk physicochemical properties of neurotrophin 4 (NT-4) in electrolyte solutions and its adsorption/desorption on/from mica surfaces have been studied using dynamic light scattering (DLS), microelectrophoresis, a solution depletion technique (enzyme-linked immunosorbent assay, ELISA), and AFM imaging. Our study presents a determination of the diffusion coefficient, hydrodynamic diameters, electrophoretic mobility, and isoelectric point of the NT-4 under various ionic strength and pH conditions. The size of the NT-4 homodimer for an ionic strength of 0.015 M was substantially independent of pH and equal to 5.1 nm. It has been found that the number of electrokinetic charges per NT-4 molecule was equal to zero for all studied ionic strengths at pH 8.1, which was identified as the isoelectric point (iep). The protein adsorption/desorption on/from mica surfaces was examined as a function of ionic strength and pH. The kinetics of neurotrophin adsorption/desorption were evaluated at pH 3.5, 7.4, and 11 by direct AFM imaging and the ELISA technique. A monotonic increase in the maximum coverage of adsorbed NT-4 molecules with ionic strength (up to 5.5 mg/m 2 ) was observed at pH 3.5. These results were interpreted in terms of the theoretical model postulating an irreversible adsorption of the protein governed by the random sequential adsorption (RSA). Our measurements revealed a significant role of ionic strength, pH, and electrolyte composition in the lateral electrostatic interactions among differently charged NT-4 molecules. The transition between adsorption/desorption processes is found for the region of high pH and low surface concentration of adsorbed neurotrophin molecules at constant ionic strength. Additionally, results presented in this work show that the adsorption behavior of neurotrophin molecules may be governed by intrasolvent electrostatic interactions yielding an aggregation process. Understanding polyvalent neurotrophin interactions may have an impact on the reversibility/irreversibility of adsorption, and hence they might be useful for obtaining well-ordered protein layers, targeting the future development of drug delivery systems for treating neurodegenerative diseases.

Wheat germ agglutinin-conjugated chitosan-Ca-alginate microparticles for local colon delivery of 5-FU: development and in vitro characterization.

PubMed

Glavas Dodov, M; Calis, S; Crcarevska, M S; Geskovski, N; Petrovska, V; Goracinova, K

2009-11-03

The aim of this work was to prepare lectin-conjugated chitosan-Ca-alginate microparticles (MPs) loaded with acid-resistant particles of 5-fluorouracil (5-FU) for efficient local treatment of colon cancer. MPs were prepared by a novel one-step spray-drying technique and after wheat germ agglutinin (WGA) conjugation, they were characterized for size, swelling behavior, surface charge, entrapment efficiency and in vitro drug release. Prepared particles were spherical, with 6.73 microg/mg of WGA conjugated onto their surface. The size and zeta potential increased after conjugation, from 6.6 to 14.7 microm and from 9.6 to 15.3 mV, while drug encapsulation was 75.6 and 72.8%, respectively after conjugation. The swelling behavior of beads was mainly determined by properties of the cross-linked chitosan-alginate network. In vitro drug release studies carried out in simulated in vivo conditions with respect to pH, confirmed the potential of the particles to release the drug in a controlled manner. Also, the drug release was not significantly affected by WGA conjugation. The retention of biorecognitive activity of WGA after covalent coupling to MPs was confirmed by haemagglutination test. Functionalized MPs showed excessive mucoadhesiveness in vitro, due to the positive surface charge, pH-dependent swelling of the matrix and lectin-sugar recognition.

Control of electroosmosis in coated quartz capillaries

NASA Technical Reports Server (NTRS)

Herren, Blair J.; Van Alstine, James; Snyder, Robert S.; Shafer, Steven G.; Harris, J. Milton

1987-01-01

The effectiveness of various coatings for controlling the electroosmotic fluid flow that hinders electrophoretic processes is studied using analytical particle microelectrophoresis. The mobilities of 2-micron diameter glass and polystyrene latex spheres (exhibiting both negative and zero effective surface charge) were measured in 2-mm diameter quartz capillaries filled with NaCl solutions within the 3.5-7.8 pH range. It is found that capillary inner surface coatings using 5000 molecular weight (or higher) poly(ethylene glycol): significantly reduced electroosmosis within the selected pH range, were stable for long time periods, and appeared to be more effective than dextran, methylcellulose, or silane coatings.

IgG1 adsorption to siliconized glass vials-influence of pH, ionic strength, and nonionic surfactants.

PubMed

Höger, Kerstin; Mathes, Johannes; Frieß, Wolfgang

2015-01-01

In this study, the adsorption of an IgG1 antibody to siliconized vials was investigated with focus on the formulation parameters pH, ionic strength, and nonionic surfactants. Electrophoretic mobility measurements were performed to investigate the charge characteristics of protein and siliconized glass particles at different pH values. Calculation of the electrokinetic charge density allowed further insight into the energetic conditions in the protein-sorbent interface. Maximum adsorption of IgG1 was found at acidic pH values and could be correlated with energetically favorable minimal ion incorporation into the interface. The importance of electrostatic interactions for IgG1 adsorption at acidic pH values was also confirmed by the efficient adsorption reduction at decreased solution ionic strength. A second adsorption maximum around the pI of the protein was assigned to hydrophobic interactions with the siliconized surface. Addition of the nonionic surfactants poloxamer 188 or polysorbate 80 resulted in almost complete suppression of adsorption at pH 7.2, and a strong but less efficient effect at pH 4 on siliconized glass vials. This adsorption suppression was much less pronounced on borosilicate glass vials. From these results, it can be concluded that electrostatic interactions contribute substantially to IgG1 adsorption to siliconized glass vials especially at acidic formulation pH. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Perchlorate adsorption and desorption on activated carbon and anion exchange resin.

PubMed

Yoon, In-Ho; Meng, Xiaoguang; Wang, Chao; Kim, Kyoung-Woong; Bang, Sunbaek; Choe, Eunyoung; Lippincott, Lee

2009-05-15

The mechanisms of perchlorate adsorption on activated carbon (AC) and anion exchange resin (SR-7 resin) were investigated using Raman, FTIR, and zeta potential analyses. Batch adsorption and desorption results demonstrated that the adsorption of perchlorate by AC and SR-7 resin was reversible. The reversibility of perchlorate adsorption by the resin was also proved by column regeneration test. Solution pH significantly affected perchlorate adsorption and the zeta potential of AC, while it did not influence perchlorate adsorption and the zeta potential of resin. Zeta potential measurements showed that perchlorate was adsorbed on the negatively charged AC surface. Raman spectra indicated the adsorption resulted in an obvious position shift of the perchlorate peak, suggesting that perchlorate was associated with functional groups on AC at neutral pH through interactions stronger than electrostatic interaction. The adsorbed perchlorate on the resin exhibited a Raman peak at similar position as the aqueous perchlorate, indicating that perchlorate was adsorbed on the resin through electrostatic attraction between the anion and positively charged surface sites.

Time-dependent density functional theory for the charging kinetics of electric double layer containing room-temperature ionic liquids

DOE PAGES

Lian, Cheng; Univ. of California, Riverside, CA; Zhao, Shuangliang; ...

2016-11-29

Understanding the charging kinetics of electric double layers is of fundamental importance for the design and development of novel electrochemical devices such as supercapacitors and field-effect transistors. In this paper, we study the dynamic behavior of room-temperature ionic liquids using a classical time-dependent density functional theory that accounts for the molecular excluded volume effects, the electrostatic correlations, and the dispersion forces. While the conventional models predict a monotonic increase of the surface charge with time upon application of an electrode voltage, our results show that dispersion between ions results in a non-monotonic increase of the surface charge with the durationmore » of charging. Finally and furthermore, we investigate the effects of van der Waals attraction between electrode/ionic-liquid interactions on the charging processes.« less

LUNAR SURFACE AND DUST GRAIN POTENTIALS DURING THE EARTH’S MAGNETOSPHERE CROSSING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vaverka, J.; Richterová, I.; Pavlu, J.

2016-07-10

Interaction between the lunar surface and the solar UV radiation and surrounding plasma environment leads to its charging by different processes like photoemission, collection of charged particles, or secondary electron emission (SEE). Whereas the photoemission depends only on the angle between the surface and direction to the Sun and varies only slowly, plasma parameters can change rapidly as the Moon orbits around the Earth. This paper presents numerical simulations of one Moon pass through the magnetospheric tail including the real plasma parameters measured by THEMIS as an input. The calculations are concentrated on different charges of the lunar surface itselfmore » and a dust grain lifted above this surface. Our estimations show that (1) the SEE leads to a positive charging of parts of the lunar surface even in the magnetosphere, where a high negative potential is expected; (2) the SEE is generally more important for isolated dust grains than for the lunar surface covered by these grains; and (3) the time constant of charging of dust grains depends on their diameter being of the order of hours for sub-micrometer grains. In view of these results, we discuss the conditions under which and the areas where a levitation of the lifted dust grains could be observed.« less

Influence of Protamine Functionalization on the Colloidal Stability of 1D and 2D Titanium Oxide Nanostructures.

PubMed

Rouster, Paul; Pavlovic, Marko; Horváth, Endre; Forró, László; Dey, Sandwip K; Szilagyi, Istvan

2017-09-26

The colloidal stability of titanium oxide nanosheets (TNS) and nanowires (TiONW) was studied in the presence of protamine (natural polyelectrolyte) in aqueous dispersions, where the nanostructures possessed negative net charge, and the protamine was positively charged. Regardless of their shape, similar charging and aggregation behaviors were observed for both TNS and TiONW. Electrophoretic experiments performed at different protamine loadings revealed that the adsorption of protamine led to charge neutralization and charge inversion depending on the polyelectrolyte dose applied. Light scattering measurements indicated unstable dispersions once the surface charge was close to zero or slow aggregation below and above the charge neutralization point with negatively or positively charged nanostructures, respectively. These stability regimes were confirmed by the electron microscopy images taken at different polyelectrolyte loadings. The protamine dose and salt-dependent colloidal stability confirmed the presence of DLVO-type interparticle forces, and no experimental evidence was found for additional interactions (e.g., patch-charge, hydrophobic, or steric forces), which are usually present in similar polyelectrolyte-particle systems. These findings indicate that the polyelectrolyte adsorbs on the TNS and TiONW surfaces in a flat and extended conformation giving rise to the absence of surface heterogeneities. Therefore, protamine is an excellent biocompatible candidate to form smooth surfaces, for instance in multilayers composed of polyelectrolytes and particles to be used in biomedical applications.

Adsorption mechanism of mixed cationic/anionic collectors in feldspar-quartz flotation system.

PubMed

Vidyadhar, A; Hanumantha Rao, K

2007-02-15

The adsorption mechanism of mixed cationic alkyl diamine and anionic sulfonate/oleate collectors at acidic pH values was investigated on microcline and quartz minerals through Hallimond flotation, electrokinetic and diffuse reflectance FTIR studies. In the presence of anionic collectors, neither of the minerals responded to flotation but the diamine flotation of the minerals was observed to be pH and concentration dependent. The presence of sulfonate enhanced the diamine flotation of the minerals by its co-adsorption. The difference in surface charge between the minerals at pH 2 was found to be the basis for preferential feldspar flotation from quartz in mixed diamine/sulfonate collectors. The infrared spectra revealed no adsorption of sulfonate collector when used alone but displayed its co-adsorption as diamine-sulfonate complex when used with diamine. The presence of sulfonate increased the diamine adsorption due to a decrease in the electrostatic head-head repulsion between the adjacent surface ammonium ions and thereby increasing the lateral tail-tail hydrophobic bonds. The mole ratio of diamine/sulfonate was found to be an important factor in the orientation of alkyl chains and thus the flotation response of minerals. The increase in sulfonate concentration beyond diamine concentration leads to the formation of soluble 1:2 diamine-sulfonate complex or precipitate and the adsorption of these species decreased the flotation since the alkyl chains are in chaotical orientation with a conceivable number of head groups directing towards the solution phase.

pH-sensitive optrode

DOEpatents

Hirschfeld, Tomas B.; Wang, Francis T.

1989-01-01

An apparatus is provided for remotely monitoring pH. A support material is provided on which organic dye molecules are covalently attached at a surface density falling within a predetermined range. The pH dependent fluorescence response of the bound organic dye molecules depends critically on surface density of the organic dye molecules bound to the support material and the nature of the covalent linkage betwen the organic dye molecules and the support material. The invention is operated by contacting the support material on which the organic dye is attached with the fluid whose pH is to be determined. When in contact, the organic dye on the support material is illuminated so that it is caused to fluoresce. The intensity of organic dye fluorescence is then related to pH.

Neutron Reflection Study of Surface Adsorption of Fc, Fab, and the Whole mAb.

PubMed

Li, Zongyi; Li, Ruiheng; Smith, Charles; Pan, Fang; Campana, Mario; Webster, John R P; van der Walle, Christopher F; Uddin, Shahid; Bishop, Steve M; Narwal, Rojaramani; Warwicker, Jim; Lu, Jian Ren

2017-07-12

Characterizing the influence of fragment crystallization (Fc) and antigen-binding fragment (Fab) on monoclonal antibody (mAb) adsorption at the air/water interface is an important step to understanding liquid mAb drug product stability during manufacture, shipping, and storage. Here, neutron reflection is used to study the air/water adsorption of a mAb and its Fc and Fab fragments. By varying the isotopic contrast, the adsorbed amount, thickness, orientation, and immersion of the adsorbed layers could be determined unambiguously. While Fc adsorption reached saturation within the hour, its surface adsorbed amount showed little variation with bulk concentration. In contrast, Fab adsorption was slower and the adsorbed amount was concentration dependent. The much higher Fc adsorption, as compared to Fab, was linked to its lower surface charge. Time and concentration dependence of mAb adsorption was dominated by Fab behavior, although both Fab and Fc behaviors contributed to the amount of mAb adsorbed. Changing the pH from 5.5 to 8.8 did not much perturb the adsorbed amount of Fc, Fab, or mAb. However, a small decrease in adsorption was observed for the Fc over pH 8-8.8 and vice versa for the Fab and mAb, consistent with a dominant Fab behavior. As bulk concentration increased from 5 to 50 ppm, the thicknesses of the Fc layers were almost constant at 40 Å, while Fab and mAb layers increased from 45 to 50 Å. These results imply that the adsorbed mAb, Fc, and Fab all retained their globular structures and were oriented with their short axial lengths perpendicular to the interface.

Pulsed laser deposited metal oxide thin films mediated controlled adsorption of proteins

NASA Astrophysics Data System (ADS)

Kim, Se Jin

Several metal oxide thin films were grown on Si substrate by pulsed laser deposition for controlling adsorption of proteins. No intentional heating of substrate and introduction of oxygen gas during growth were employed. Additionally, fibrinogen, bovine serum albumin (BSA), and lysozyme were used as model protein in this study. The film properties such as cyratllinity, surface roughness, surface electrical charge and chemistry were investigated by many techniques in order to obtain the relationship with protein adsorption. Firstly, as grown Ta2O5 and ZnO thin film were used to study the effects of surface charge on the behaviors of BSA and lysozyme adsorption. The protein thickness results by ellipsometry showed that negatively charged Ta2O5 had a stronger affinity to positively charged lysozyme, while positively charged ZnO had a stronger affinity to negatively charged BSA. The results confirmed electrostatic interaction due to surface charge is one of main factors for determining adsorption of proteins. Furthermore, annealing studies were performed by heat treatment of as grown Ta2O5 and ZnO at 800°C in air ambience. Annealed Ta2O5 thin film had almost wetting property (from 10.02° to less than 1˜2°) and the change of cystallinity (from amorphous to cyrsalline) while annealed ZnO thin film had a reduced contact angle (from 75.65° to 39.41°) and remained to crystalline structure. The fibrinogen thickness on annealed Ta2O5 film was increased compared with as grown sample, while heat treated ZnO film showed much reduction of fibrinogen adsorption. Binary Ta-Zn oxide thin films (TZ) were grown by preparing PLD target composed of 50 wt% Ta2O5 and 50 wt% ZnO. This binary film had IEP pH 7.1 indicating nearly neutral charge in pH 7.4 PBS solution, and hydrophilic property. Ellipsometrical results showed that TZ film had the lowest fibrinogen, BSA and lysozyme thickness after 120 min adsorption compared with Ta2O5 and ZnO. Other samples, bilayer oxide films in which Ta2O5 and ZnO coexist were also employed to study adsorption behaviors. Especially, Ta2O 5-based bilayer films revealed zero adsorption of lysozyme.

Mechanism of the free charge carrier generation in the dielectric breakdown

NASA Astrophysics Data System (ADS)

Rahim, N. A. A.; Ranom, R.; Zainuddin, H.

2017-12-01

Many studies have been conducted to investigate the effect of environmental, mechanical and electrical stresses on insulator. However, studies on physical process of discharge phenomenon, leading to the breakdown of the insulator surface are lacking and difficult to comprehend. Therefore, this paper analysed charge carrier generation mechanism that can cause free charge carrier generation, leading toward surface discharge development. Besides, this paper developed a model of surface discharge based on the charge generation mechanism on the outdoor insulator. Nernst’s Planck theory was used in order to model the behaviour of the charge carriers while Poisson’s equation was used to determine the distribution of electric field on insulator surface. In the modelling of surface discharge on the outdoor insulator, electric field dependent molecular ionization was used as the charge generation mechanism. A mathematical model of the surface discharge was solved using method of line technique (MOL). The result from the mathematical model showed that the behaviour of net space charge density was correlated with the electric field distribution.

Controlling effective aspect ratio and packing of clay with pH for improved gas barrier in nanobrick wall thin films.

PubMed

Hagen, David A; Saucier, Lauren; Grunlan, Jaime C

2014-12-24

Polymer-clay thin films constructed via layer-by-layer (LbL) assembly, with a nanobrick wall structure (i.e., clay nanoplatelets as bricks surrounded by a polyelectrolyte mortar), are known to exhibit a high oxygen barrier. Further barrier improvement can be achieved by lowering the pH of the clay suspension in the polyethylenimine (PEI) and montmorillonite (MMT) system. In this case, the charge of the deposited PEI layer is increased in the clay suspension environment, which causes more clay to be deposited. At pH 4, MMT platelets deposit with near perfect ordering, observed with transmission electron microscopy, enabling a 5× improvement in the gas barrier for a 10 PEI/MMT bilayer thin film (85 nm) relative to the same film made with pH 10 MMT. This improved gas barrier approaches that achieved with much higher aspect ratio vermiculite clay. In essence, lower pH is generating a higher effective aspect ratio for MMT due to greater induced surface charge in the PEI layers, which causes heavier clay deposition. These flexible, transparent nanocoatings have a wide range of possible applications, from food and electronics packaging to pressurized bladders.

Surface Charge Effects on the Electro-Orientation of Insulating Nanotubes in Aqueous Electrolytes

NASA Astrophysics Data System (ADS)

Cetindag, Semih; Tiwari, Bishnu; Zhang, Dongyan; Yap, Yoke Khin; Kim, Sangil; Shan, Jerry W.

2017-11-01

While the alignment of electrically conductive nanowires and nanotubes by electric fields in liquid solution has been well studied, much less is known about the electro-orientation of insulating 1D particles, such as boron-nitride nanotubes (BNNTs). Here, we demonstrate for the first time the electro-orientation of individual insulating BNNTs in aqueous KCl solutions under AC fields. Comparison to theory indicates that the observed frequency response is not related to the crossover for Maxwell-Wagner interfacial polarization. Instead, the cross-over frequency in the low-frequency regime scales as the square root of solution conductivity, indicating that alignment is associated with the formation and motion of an electrical double layer (EDL), much like induced-charge electro-osmosis for a conducting particle. However, the mechanism for the formation of the EDL is presumably different for insulating particles like BNNTs as compared to conductors. By varying the surface charge of the particle by changing pH, we show that the alignment rate increases with increasing surface charge, and is likely a result of counter-ion migration and EDL polarization under the influence of applied electric field. Thus, particle surface charge (large Dukhin number) is believed to play a vital role in the electro-orientation of insulating particles in aqueous solutions. NSF CBET-1604931 and NSF DMR-1261910.

Surface Assisted Transient Displacement Charge Technique. II. Effect of Gases on Photoinduced Charge Transfer in Self-Assembled Monolayers

PubMed Central

Krasnoslobodtsev, Alexey V.; Smirnov, Sergei N.

2008-01-01

Surface assisted photoinduced transient displacement charge (SPTDC) technique was used to study charge transfer in self-assembled monolayers of 7-diethylaminocoumarin covalently linked to oxide surface in atmosphere of different gases. The dipole signal was found to be opposite to that in solution and dependent on the nature of gas and its pressure. The results were explained by collision-induced relaxation that impedes uninhibited tilting of molecules onto the surface. Collisions with paramagnetic oxygen induce intersystem crossing to long-lived triplet dipolar states of coumarin with the rate close to the half of that for the collision rate. PMID:16956285

Dual-pH Sensitive Charge-reversal Nanocomplex for Tumor-targeted Drug Delivery with Enhanced Anticancer Activity.

PubMed

Zhou, Qing; Hou, Yilin; Zhang, Li; Wang, Jianlin; Qiao, Youbei; Guo, Songyan; Fan, Li; Yang, Tiehong; Zhu, Lin; Wu, Hong

2017-01-01

Poly(β-L-malic acid) (PMLA), a natural aliphatic polyester, has been proven to be a promising carrier for anti-cancer drugs. In spite of excellent bio-compatibility, the application of PMLA as the drug carrier for cancer therapy is limited by its low cellular uptake efficiency. The strong negative charge of PMLA impedes its uptake by cancer cells because of the electrostatic repulsion. In this study, a dual pH-sensitive charge-reversal PMLA-based nanocomplex (PMLA-PEI-DOX-TAT@PEG-DMMA) was developed for effective tumor-targeted drug delivery, enhanced cellular uptake, and intracellular drug release. The prepared nanocomplex showed a negative surface charge at the physiological pH, which could protect the nanocomplex from the attack of plasma proteins and recognition by the reticuloendothelial system, so as to prolong its circulation time. While at the tumor extracellular pH 6.8, the DMMA was hydrolyzed, leading to the charge reversal and exposure of the TAT on the polymeric micelles, thus enhancing the cellular internalization. Then, the polymeric micelles underwent dissociation and drug release in response to the acidic pH in the lyso/endosomal compartments of the tumor cell. Both in vitro and in vivo efficacy studies indicated that the nanocomplex significantly inhibited the tumor growth while the treatment showed negligible systemic toxicity, suggesting that the developed dual pH-sensitive PMLA-based nanocomplex would be a promising drug delivery system for tumor-targeted drug delivery with enhanced anticancer activity.

Dual-pH Sensitive Charge-reversal Nanocomplex for Tumor-targeted Drug Delivery with Enhanced Anticancer Activity

PubMed Central

Zhou, Qing; Hou, Yilin; Zhang, Li; Wang, Jianlin; Qiao, Youbei; Guo, Songyan; Fan, Li; Yang, Tiehong; Zhu, Lin; Wu, Hong

2017-01-01

Poly(β-L-malic acid) (PMLA), a natural aliphatic polyester, has been proven to be a promising carrier for anti-cancer drugs. In spite of excellent bio-compatibility, the application of PMLA as the drug carrier for cancer therapy is limited by its low cellular uptake efficiency. The strong negative charge of PMLA impedes its uptake by cancer cells because of the electrostatic repulsion. In this study, a dual pH-sensitive charge-reversal PMLA-based nanocomplex (PMLA-PEI-DOX-TAT@PEG-DMMA) was developed for effective tumor-targeted drug delivery, enhanced cellular uptake, and intracellular drug release. The prepared nanocomplex showed a negative surface charge at the physiological pH, which could protect the nanocomplex from the attack of plasma proteins and recognition by the reticuloendothelial system, so as to prolong its circulation time. While at the tumor extracellular pH 6.8, the DMMA was hydrolyzed, leading to the charge reversal and exposure of the TAT on the polymeric micelles, thus enhancing the cellular internalization. Then, the polymeric micelles underwent dissociation and drug release in response to the acidic pH in the lyso/endosomal compartments of the tumor cell. Both in vitro and in vivo efficacy studies indicated that the nanocomplex significantly inhibited the tumor growth while the treatment showed negligible systemic toxicity, suggesting that the developed dual pH-sensitive PMLA-based nanocomplex would be a promising drug delivery system for tumor-targeted drug delivery with enhanced anticancer activity. PMID:28638469

Method for Estimating the Charge Density Distribution on a Dielectric Surface.

PubMed

Nakashima, Takuya; Suhara, Hiroyuki; Murata, Hidekazu; Shimoyama, Hiroshi

2017-06-01

High-quality color output from digital photocopiers and laser printers is in strong demand, motivating attempts to achieve fine dot reproducibility and stability. The resolution of a digital photocopier depends on the charge density distribution on the organic photoconductor surface; however, directly measuring the charge density distribution is impossible. In this study, we propose a new electron optical instrument that can rapidly measure the electrostatic latent image on an organic photoconductor surface, which is a dielectric surface, as well as a novel method to quantitatively estimate the charge density distribution on a dielectric surface by combining experimental data obtained from the apparatus via a computer simulation. In the computer simulation, an improved three-dimensional boundary charge density method (BCM) is used for electric field analysis in the vicinity of the dielectric material with a charge density distribution. This method enables us to estimate the profile and quantity of the charge density distribution on a dielectric surface with a resolution of the order of microns. Furthermore, the surface potential on the dielectric surface can be immediately calculated using the obtained charge density. This method enables the relation between the charge pattern on the organic photoconductor surface and toner particle behavior to be studied; an understanding regarding the same may lead to the development of a new generation of higher resolution photocopiers.

Use of drinking water treatment solids for arsenate removal from desalination concentrate.

PubMed

Xu, Xuesong; Lin, Lu; Papelis, Charalambos; Myint, Maung; Cath, Tzahi Y; Xu, Pei

2015-05-01

Desalination of impaired water can be hindered by the limited options for concentrate disposal. Selective removal of specific contaminants using inexpensive adsorbents is an attractive option to address the challenges of concentrate management. In this study, two types of ferric-based drinking water treatment solids (DWTS) were examined for arsenate removal from reverse osmosis concentrate during continuous-flow once-through column experiments. Arsenate sorption was investigated under different operating conditions including pH, arsenate concentration, hydraulic retention time, loading rate, temperature, and moisture content of the DWTS. Arsenate removal by the DWTS was affected primarily by surface complexation, electrostatic interactions, and arsenate speciation. Results indicated that arsenate sorption was highly dependent on initial pH and initial arsenate concentration. Acidic conditions enhanced arsenate sorption as a result of weaker electrostatic repulsion between predominantly monovalent H2AsO4(-) and negatively charged particles in the DWTS. High initial arsenate concentration increased the driving force for arsenate sorption to the DWTS surface. Tests revealed that the potential risks associated with the use of DWTS include the leaching of organic contaminants and ammonia, which can be alleviated by using wet DWTS or discarding the initially treated effluent that contains high organic concentration. Copyright © 2015 Elsevier Inc. All rights reserved.

Photocatalytic hydrogen production from biomass-derived compounds: a case study of citric acid.

PubMed

Alkaim, Ayad F; Kandiel, Tarek A; Dillert, Ralf; Bahnemann, Detlef W

2016-11-01

Highly crystalline anatase TiO2 nanoparticles with high BET surface area have been synthesized by thermal hydrolysis of titanium(IV) bis(ammoniumlactato) dihydroxide aqueous solutions. The photocatalytic H2 production from aqueous citric acid (CA) solutions over Pt-loaded TiO2 has been investigated under different experimental conditions, that is, different CA concentration, temperature, light intensity, and pH of Pt/TiO2 suspension. For comparison, the photocatalytic dehydrogenation of triethanolamine (TEA) has also been investigated. The highest H2 production rates were obtained at pH 3 and 9 for CA and TEA, respectively. This behavior is readily explained by the adsorption characteristic of the employed reagent on the surface of the charged TiO2. The effect of the photocatalyst loading and the light intensity on the H2 production rate showed the same behavior in the case of CA and TEA evincing that these parameters are catalyst dependent. The apparent activation energies have been determined to be 13.5 ± 1.8 and 14.7 ± 1.6 kJ mol(-1) for CA and TEA, respectively, indicating the existence of an activation energy barrier in a photocatalytic process which can be attributed to the desorption of adsorbed products.

Effects of organic silicon compounds as additives on charge-discharge cycling efficiencies of lithium in nonaqueous electrolytes for rechargeable lithium cells

NASA Astrophysics Data System (ADS)

Yanagisawa, Ryota; Endo, Hisayuki; Unno, Masafumi; Morimoto, Hideyuki; Tobishima, Shin-ichi

2014-11-01

Influence of mixing organic silicon compounds into 1 M (M: mol L-1) LiPF6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio = 3:7) mixed solvent electrolytes on charge-discharge cycling efficiencies of lithium metal negative electrodes is examined. As organic silicon compounds, polyether-modified siloxanes with polyethylene oxide chains, chlorotrimethylsilane, tetraethoxysilane, cis-tetra [isobutyl (dimethylsiloxy)] cyclotetrasiloxane and cage-type silsesquioxane are investigated. Charge-discharge cycling tests of lithium are galvanostatically carried out using stainless steel working electrodes. Charge-discharge cycling efficiencies of lithium tend to improve by mixing organic silicon compounds. A cage-type silsesquioxane, octaphenyloctasilsesquioxane (Ph8T8) exhibits the highest cycling efficiency of approximately 80% with small mixing amount of 0.02 M Ph8T8. Mechanism of enhancement of lithium cycling efficiencies by mixing organic silicon compounds is considered to be due to the suppression of excess reduction of LiPF6-EC/EMC by lithium and the growth of surface film on lithium.

Dependence of Lunar Surface Charging on Solar Wind Plasma Conditions and Solar Irradiation

NASA Technical Reports Server (NTRS)

Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.; Burchill, J. K.; Collier, M. R.; Zimmerman, M. I.; Vondrak, R. R.; Delory, G. T.; Pfaff, R. F.

2014-01-01

The surface of the Moon is electrically charged by exposure to solar radiation on its dayside, as well as by the continuous flux of charged particles from the various plasma environments that surround it. An electric potential develops between the lunar surface and ambient plasma, which manifests itself in a near-surface plasma sheath with a scale height of order the Debye length. This study investigates surface charging on the lunar dayside and near-terminator regions in the solar wind, for which the dominant current sources are usually from the pohotoemission of electrons, J(sub p), and the collection of plasma electrons J(sub e) and ions J(sub i). These currents are dependent on the following six parameters: plasma concentration n(sub 0), electron temperature T(sub e), ion temperature T(sub i), bulk flow velocity V, photoemission current at normal incidence J(sub P0), and photo electron temperature T(sub p). Using a numerical model, derived from a set of eleven basic assumptions, the influence of these six parameters on surface charging - characterized by the equilibrium surface potential, Debye length, and surface electric field - is investigated as a function of solar zenith angle. Overall, T(sub e) is the most important parameter, especially near the terminator, while J(sub P0) and T(sub p) dominate over most of the dayside.

Charge Behaviors around Oxide Device/Pseudo-Physiological Solution Interface with Molecular Dynamic Simulations

NASA Astrophysics Data System (ADS)

Maekawa, Yuki; Shibuta, Yasushi; Sakata, Toshiya

2013-12-01

In this study, we investigated the charge behaviors of ions and water molecules at the oxide device/pseudo-physiological solution interface by use of molecular dynamics (MD) simulations because the detection principle of semiconductor-based biosensors is based on the detection of charge density changes at the oxide sensing surface in physiological environments. In particular, we designed an alpha-quartz (100) surface with some charges corresponding to pH=5.5 so that the ionic behaviors for 500 mM each of Na+ and Cl- around the interface were calculated under the surface condition with charges, considering a real system. As a result of the simulation, we defined the region of Debye length from the calculated potential distribution, in which some parameters such as diffusion coefficient and the vibration of water molecules around the interface differed from those of the bulk solution. The elucidation of the solid/liquid interfacial behaviors by the simulation technique should deepen our understanding of the detection principle of semiconductor-based biosensors and will give guidelines for the design of a bio-interface in the field of biosensing technology, because they cannot be demonstrated experimentally.

Mechanistic understanding of crystal violet dye sorption by woody biochar: implications for wastewater treatment.

PubMed

Wathukarage, Awanthi; Herath, Indika; Iqbal, M C M; Vithanage, Meththika

2017-08-17

Dye-based industries, particularly small and medium scale, discharge their effluents into waterways without treatment due to cost considerations. We investigated the use of biochars produced from the woody tree Gliricidia sepium at 300 °C (GBC300) and 500 °C (GBC500) in the laboratory and at 700 °C from a dendro bioenergy industry (GBC700), to evaluate their potential for sorption of crystal violet (CV) dye. Experiments were conducted to assess the effect of pH reaction time and CV loading on the adsorption process. The equilibrium adsorption capacity was higher with GBC700 (7.9 mg g -1 ) than GBC500 (4.9 mg g -1 ) and GBC300 (4.4 mg g -1 ), at pH 8. The CV sorption process was dependent on the pH, surface area and pore volume of biochar (GBC). Both Freundlich and Hill isotherm models fitted best to the equilibrium isotherm data suggesting cooperative interactions via physisorption and chemisorption mechanisms for CV sorption. The highest Hill sorption capacity of 125.5 mg g -1 was given by GBC700 at pH 8. Kinetic data followed the pseudo-second-order model, suggesting that the sorption process is more inclined toward the chemisorption mechanism. Pore diffusion, π-π electron donor-acceptor interaction and H-bonding were postulated to be involved in physisorption, whereas electrostatic interactions of protonated amine group of CV and negatively charged GBC surface led to a chemisorption type of adsorption. Overall, GBC produced as a by-product of the dendro industry could be a promising remedy for CV removal from an aqueous environment.

Glutamate Induced Thermal Equilibrium Intermediate and Counteracting Effect on Chemical Denaturation of Proteins.

PubMed

Anumalla, Bramhini; Prabhu, N Prakash

2018-01-25

When organisms are subjected to stress conditions, one of their adaptive responses is accumulation of small organic molecules called osmolytes. These osmolytes affect the structure and stability of the biological macromolecules including proteins. The present study examines the effect of a negatively charged amino acid osmolyte, glutamate (Glu), on two model proteins, ribonuclease A (RNase A) and α-lactalbumin (α-LA), which have positive and negative surface charges at pH 7, respectively. These proteins follow two-state unfolding transitions during both heat and chemical induced denaturation processes. The addition of Glu stabilizes the proteins against temperature and induces an early equilibrium intermediate during unfolding. The stability is found to be enthalpy-driven, and the free energy of stabilization is more for α-LA compared to RNase A. The decrease in the partial molar volume and compressibility of both of the proteins in the presence of Glu suggests that the proteins attain a more compact state through surface hydration which could provide a more stable conformation. This is also supported by molecule dynamic simulation studies which demonstrate that the water density around the proteins is increased upon the addition of Glu. Further, the intermediates could be completely destabilized by lower concentrations (∼0.5 M) of guanidinium chloride and salt. However, urea subverts the Glu-induced intermediate formed by α-LA, whereas it only slightly destabilizes in the case of RNase A which has a positive surface charge and could possess charge-charge interactions with Glu. This suggests that, apart from hydration, columbic interactions might also contribute to the stability of the intermediate. Gdm-induced denaturation of RNase A and α-LA in the absence and the presence of Glu at different temperatures was carried out. These results also show the Glu-induced stabilization of both of the proteins; however, all of the unfolding transitions followed two-state transitions during chemical denaturation. The extent of stability exerted by Glu is higher for RNase A at higher temperature, whereas it provides more stability for α-LA at lower temperature. Thus, the experiments indicate that Glu induces a thermal equilibrium intermediate and increases the thermodynamic stability of proteins irrespective of their surface charges. The extent of stability varies between the proteins in a temperature-dependent manner.

The effect of surface charge of glycerol monooleate-based nanoparticles on the round window membrane permeability and cochlear distribution.

PubMed

Liu, Hongzhuo; Chen, Shichao; Zhou, Yanyan; Che, Xin; Bao, Zhihong; Li, Sanming; Xu, Jinghua

2013-11-01

The aim of this study is to elucidate the impact of surface charge of glycerol monooleate-based nanoparticles (NPs) on the cellular uptake and its distribution in the cochlea. These NPs are modified using varied concentration of anionic or cationic lipid. Upon dilution, these lipid mixtures self-assemble to form a series of cubic NPs with various surface charges, but with similar particle size. Positively charged NPs exhibited dose-dependent cytotoxicities against L929 cells proportional to the concentration of cationic lipid; whereas negatively charged NPs did not show obvious cytotoxic properties as compared to unmodified NPs. Meanwhile, confocal microscopy and flow cytometry results suggested that NPs with high positive surface charge were taken up more efficiently by L929 cells. The permeability of round window membrane (RWM) was high for highly positively charged NPs, which is likely due to their highly cellular uptake efficiency and consequently high concentration gradient between RWM and cochlear fluid. More importantly, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) modified NPs greatly facilitated broadly distribution in cochlea, favoring the treatment of hearing loss of low frequencies. Taken together, these findings about charge-dependent of NPs on RWM permeability and cochlear distribution could serve as guideline in the rational design of NP for drug and gene delivery to inner ear.

Sorption of Sr, Co and Zn on illite: Batch experiments and modelling including Co in-diffusion measurements on compacted samples

NASA Astrophysics Data System (ADS)

Montoya, V.; Baeyens, B.; Glaus, M. A.; Kupcik, T.; Marques Fernandes, M.; Van Laer, L.; Bruggeman, C.; Maes, N.; Schäfer, T.

2018-02-01

Experimental investigations on the uptake of divalent cations (Sr, Co and Zn) onto illite (Illite du Puy, Le-Puy-en-Velay, France) were carried out by three different international research groups (Institute for Nuclear Waste Disposal, KIT (Germany), Group Waste & Disposal, SCK-CEN, (Belgium) and Laboratory for Waste Management, PSI (Switzerland)) in the framework of the European FP7 CatClay project. The dependence of solid-liquid distribution ratios (Rd values) on pH at trace metal conditions (sorption edges) and on the metal ion concentration (sorption isotherms) was determined in dilute suspensions of homo-ionic Na-illite (Na-IdP) under controlled N2 atmosphere. The experimental results were modelled using the 2 Site Protolysis Non Electrostatic Surface Complexation and Cation Exchange (2SPNE SC/CE) sorption model. The sorption of Sr depends strongly on ionic strength, while a rather weak pH dependence is observed in a pH range between 3 and 11. The data were modelled with cation exchange reactions, taking into account competition with H, K, Ca, Mg and Al, and surface complexation on weak amphotheric edge sites at higher pH values. The sorption of Co on Na-IdP, however, is strongly pH dependent. Cation exchange on the planar sites and surface complexation on strong and weak amphoteric edge sites were used to describe the Co sorption data. Rd values for Co derived from in-diffusion measurements on compacted Na-IdP samples (bulk-dry density of 1700 kg m-3) between pH 5.0 and 9.0 are in good agreement with the batch sorption data. The equivalence of both approaches to measure sorption was thus confirmed for the present test system. In addition, the results highlight the importance of both major and minor surface species for the diffusive transport behaviour of strongly sorbing metal cations. While surface complexes at the edge sites determine largely the Rd value, the diffusive flux may be governed by those species bound to the planar sites, even at low fractional occupancies. The pH dependent sorption determined for trace Zn concentrations showed large Rd values across the entire pH range with almost no dependence on the background electrolyte concentration. Additional sorption experiments carried out at substantial fractional Zn loadings demonstrated that the selectivity for the exchange of Na+ for Zn2+ at the planar sites could not explain the large Rd values measured at low pH and trace Zn concentrations. This suggests that another mechanism is ruling Zn uptake under these conditions.

Fate of chromium in soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prokisch, J.; Gyori, Z.; Kovacs, B.

The chromium cycle in soil was studied with speciation of chromium. The aim was to look for the possibilities the mobilization of chromium(III) and to measure the rate of chromate reduction in nature and pot and field experiments in Hungarian soils. The authors developed a sensitive and simple method for chromium speciation with a microcolumn connected an inductively coupled plasma atomic emission spectrometer. Detection limits are convenient to measure chromium forms in a 0.01 M CaCl{sub 2} extract of a contaminated soil, but it is not enough to measure that of the uncontaminated soils. CR(VI) as chromate anion is notmore » adsorbed on pH dependent temporary charges of clays but in strongly acidic soil. Therefore CR(VI) can be leached out easily from the top layer of soil and can be transported into the ground water. Chromate ion can be reduced to CR(III) by organic matter of soil in acidic medium. CR(VI) is more stable at higher pH and lower humus content. Thus the reduction much quicker in the upper, weakly acidic top layer. CR(VI) oxidizes the organic matter of soil. The rate of this reaction depends on pH values, the humus content of the soil and temperature. CR(III) leaching in different uncontaminated soils was studied too. There are 3 pathways of mobilization of Cr(III). When pH decreases in soil the CR(III) becomes more soluble, similarly to the aluminium(III) ion. When the soil contains large quantity of water soluble organic ligands, Cr makes complexes with them and complexes formed can be leached out from the top layer. The third possibility is the oxidation of CR(III) to Cr(VI). It could happen on surface of manganese dioxide in the well-aired top layer.« less

Effect of concentration and pH on the surface-enhanced Raman scattering of captopril on nano-colloidal silver surface

NASA Astrophysics Data System (ADS)

Gao, Junxiang; Gu, Huaimin; Liu, Fangfang; Dong, Xiao; Xie, Min; Hu, Yongjun

2011-07-01

In this report, Raman and surface-enhanced Raman scattering (SERS) spectra of captopril are studied in detail. Herein, the Raman bands are assigned by the density functional theory (DFT) calculations and potential energy distributions (PED) based on internal coordinates of the molecule, which are found to be in good agree with the experimental values. Furthermore, the concentration and pH dependence of the SERS intensity of the molecule is discussed. By analyzing the intensities variation of SERS bands of the different concentrations of captopril solution, it can be concluded that the molecules orientation adsorbed on the silver nanoparticles surface change with the change of the concentrations. The variation of SERS spectra of captopril with the change of pH suggests that the interaction among the adsorbates with Ag cluster depend on the protonated state of the adsorbate and the aggregation of silver nanoparticles.

Chemically grafted polymeric filters for chemical sensors: Hyperbranched poly(acrylic acid) films incorporating {Beta}-cyclodextrin receptors and amine-functionalized filter layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dermody, D.L.; Peez, R.F.; Bergbreiter, D.E.

1999-02-02

The authors report a new molecular-filter approach for enhancing the selectivity of chemical sensors. Specifically, they describe electrochemical sensors prepared from Au electrodes coated with {beta}-cyclodextrin-functionalized, hyperbranched poly(acrylic acid)(PAA) films capped with a chemically grafted, ultrathin polyamine layer. The hyperbranched PAA film is a highly functionalized framework for covalently binding the {beta}-cyclodextrin molecular receptors. The thin, grafted polyamine overlayer acts as a pH-sensitive molecular filter that selectively passes suitably charged analytes. Poly(amidoamine) dendrimers or poly-D-lysine is used as 10--15-nm-thick filter layers. The results show that at low pH, when the polyamines are fully protonated, positively charged redox probe molecules, suchmore » as benzyl viologen (BV), do not permeate the filter layer. However, at high pH, when the filter layer is uncharged, BV penetrates the filter layer and is reduced at the electrode. The opposite pH dependence is observed for negatively charged redox molecules such as anthraquinone-2-sulfonate (AQS). Both BV and AQS specifically interact with the {beta}-cyclodextrin receptors underlying the polyamine filter layers.« less

Charge-patterning phase transition on a surface lattice of titratable sites adjacent to an electrolyte solution

NASA Astrophysics Data System (ADS)

Shore, Joel; Thurston, George

We discuss a model for a charge-patterning phase transition on a two-dimensional square lattice of titratable sites, here regarded as protonation sites, placed on a square lattice in a dielectric medium just below the planar interface between this medium and an aqueous salt solution. Within Debye-Huckel theory, the analytical form of the electrostatic repulsion between protonated sites exhibits an approximate inverse cubic power-law decrease beyond short distances. The problem can thus be mapped onto the two-dimensional antiferromagnetic Ising model with this longer-range interaction, which we study with Monte Carlo simulations. As we increase pH, the occupation probability of a site decreases from 1 at low pH to 0 at high pH. For sufficiently-strong interaction strengths, a phase transition occurs as the occupation probability of 1/2 is approached: the charges arrange themselves into a checkerboard pattern. This ordered phase persists over a range of pH until a transition occurs back to a disordered state. This state is the analogue of the Neel state in the antiferromagnetic Ising spin model. More complicated ordered phases are expected for sufficiently strong interactions (with occupation probabilities of 1/4 and 3/4) and if the lattice is triangular rather than square. This work was supported by NIH EY018249 (GMT).

Phenylboronate chromatography selectively separates glycoproteins through the manipulation of electrostatic, charge transfer, and cis-diol interactions.

PubMed

Carvalho, Rimenys J; Woo, James; Aires-Barros, M Raquel; Cramer, Steven M; Azevedo, Ana M

2014-10-01

Phenylboronate chromatography (PBC) has been applied for several years, however details regarding the mechanisms of interactions between the ligand and biomolecules are still scarce. The goal of this work is to investigate the various chemical interactions between proteins and their ligands, using a protein library containing both glycosylated and nonglycosylated proteins. Differences in the adsorption of these proteins over a pH range from 4 to 9 were related to two main properties: charge and presence of glycans. Acidic or neutral proteins were strongly adsorbed below pH 8 although the uncharged trigonal form of phenylboronate (PB) is less susceptible to forming electrostatic and cis-diol interactions with proteins. The glycosylated proteins were only adsorbed above pH 8 when the electrostatic repulsion between the boronate anion and the protein surface was mitigated (at 200 mM NaCl). All basic proteins were highly adsorbed above pH 8 with PB also acting as a cation-exchanger with binding occurring through electrostatic interactions. Batch adsorption performed at acidic conditions in the presence of Lewis base showed that charge-transfer interactions are critical for protein retention. This study demonstrates the multimodal interaction of PBC, which can be a selective tool for separation of different classes of proteins. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Identification of key amino acid residues responsible for internal and external pH sensitivity of Orai1/STIM1 channels.

PubMed

Tsujikawa, Hiroto; Yu, Albert S; Xie, Jia; Yue, Zhichao; Yang, Wenzhong; He, Yanlin; Yue, Lixia

2015-11-18

Changes of intracellular and extracellular pH are involved in a variety of physiological and pathological processes, in which regulation of the Ca(2+) release activated Ca(2+) channel (I CRAC) by pH has been implicated. Ca(2+) entry mediated by I CRAC has been shown to be regulated by acidic or alkaline pH. Whereas several amino acid residues have been shown to contribute to extracellular pH (pHo) sensitivity, the molecular mechanism for intracellular pH (pHi) sensitivity of Orai1/STIM1 is not fully understood. By investigating a series of mutations, we find that the previously identified residue E106 is responsible for pHo sensitivity when Ca(2+) is the charge carrier. Unexpectedly, we identify that the residue E190 is responsible for pHo sensitivity when Na(+) is the charge carrier. Furthermore, the intracellular mutant H155F markedly diminishes the response to acidic and alkaline pHi, suggesting that H155 is responsible for pHi sensitivity of Orai1/STIM1. Our results indicate that, whereas H155 is the intracellular pH sensor of Orai1/STIM1, the molecular mechanism of external pH sensitivity varies depending on the permeant cations. As changes of pH are involved in various physiological/pathological functions, Orai/STIM channels may be an important mediator for various physiological and pathological processes associated with acidosis and alkalinization.

The PH domain of phosphoinositide-dependent kinase-1 exhibits a novel, phospho-regulated monomer-dimer equilibrium with important implications for kinase domain activation: single-molecule and ensemble studies.

PubMed

Ziemba, Brian P; Pilling, Carissa; Calleja, Véronique; Larijani, Banafshé; Falke, Joseph J

2013-07-16

Phosphoinositide-dependent kinase-1 (PDK1) is an essential master kinase recruited to the plasma membrane by the binding of its C-terminal PH domain to the signaling lipid phosphatidylinositol-3,4,5-trisphosphate (PIP3). Membrane binding leads to PDK1 phospho-activation, but despite the central role of PDK1 in signaling and cancer biology, this activation mechanism remains poorly understood. PDK1 has been shown to exist as a dimer in cells, and one crystal structure of its isolated PH domain exhibits a putative dimer interface. It has been proposed that phosphorylation of PH domain residue T513 (or the phospho-mimetic T513E mutation) may regulate a novel PH domain dimer-monomer equilibrium, thereby converting an inactive PDK1 dimer to an active monomer. However, the oligomeric states of the PH domain on the membrane have not yet been determined, nor whether a negative charge at position 513 is sufficient to regulate its oligomeric state. This study investigates the binding of purified wild-type (WT) and T513E PDK1 PH domains to lipid bilayers containing the PIP3 target lipid, using both single-molecule and ensemble measurements. Single-molecule analysis of the brightness of the fluorescent PH domain shows that the PIP3-bound WT PH domain on membranes is predominantly dimeric while the PIP3-bound T513E PH domain is monomeric, demonstrating that negative charge at the T513 position is sufficient to dissociate the PH domain dimer and is thus likely to play a central role in PDK1 monomerization and activation. Single-molecule analysis of two-dimensional (2D) diffusion of PH domain-PIP3 complexes reveals that the dimeric WT PH domain diffuses at the same rate as a single lipid molecule, indicating that only one of its two PIP3 binding sites is occupied and there is little penetration of the protein into the bilayer as observed for other PH domains. The 2D diffusion of T513E PH domain is slower, suggesting the negative charge disrupts local structure in a way that allows deeper insertion of the protein into the viscous bilayer, thereby increasing the diffusional friction. Ensemble measurements of PH domain affinity for PIP3 on plasma membrane-like bilayers reveal that the dimeric WT PH domain possesses a one order of magnitude higher target membrane affinity than the previously characterized monomeric PH domains, consistent with a dimerization-triggered, allosterically enhanced affinity for one PIP3 molecule (a much larger affinity enhancement would be expected for dimerization-triggered binding to two PIP3 molecules). The monomeric T513E PDK1 PH domain, like other monomeric PH domains, exhibits a PIP3 affinity and bound state lifetime that are each 1 order of magnitude lower than those of the dimeric WT PH domain, which is predicted to facilitate release of activated, monomeric PDK1 to the cytoplasm. Overall, the study yields the first molecular picture of PH domain regulation via electrostatic control of dimer-monomer conversion.

Anionic pH-Sensitive Lipoplexes.

PubMed

Mignet, Nathalie; Scherman, Daniel

2017-01-01

To provide long circulating nanoparticles able to carry a gene to tumors, we have designed anionic pegylated lipoplexes which are pH sensitive. Anionic pegylated lipoplexes have been prepared from the combined formulation of cationic lipoplexes and pegylated anionic liposomes. The neutralization of the particle surface charge as a function of the pH was monitored by light scattering in order to determine the ratio between anionic and cationic lipids that would give pH sensitive complexes. This ratio has been optimized to form particles sensitive to pH change in the range 5.5-6.5. Compaction of DNA into these newly formed anionic complexes is checked by DNA accessibility to picogreen. The transfection efficiency and pH sensitive property of these formulations has been shown in vitro using bafilomycin, a vacuolar H + -ATPase inhibitor.

pH-sensitive optrode

DOEpatents

Hirschfeld, T.B.; Wang, F.T.

1989-02-07

An apparatus is provided for remotely monitoring pH. A support material is provided on which organic dye molecules are covalently attached at a surface density falling within a predetermined range. The pH dependent fluorescence response of the bound organic dye molecules depends critically on surface density of the organic dye molecules bound to the support material and the nature of the covalent linkage between the organic dye molecules and the support material. The invention is operated by contacting the support material on which the organic dye is attached with the fluid whose pH is to be determined. When in contact, the organic dye on the support material is illuminated so that it is caused to fluoresce. The intensity of organic dye fluorescence is then related to pH. 4 figs.

Full-Length Trimeric Influenza Virus Hemagglutinin II Membrane Fusion Protein and Shorter Constructs Lacking the Fusion Peptide or Transmembrane Domain: Hyperthermostability of the Full-Length Protein and the Soluble Ectodomain and Fusion Peptide Make Significant Contributions to Fusion of Membrane Vesicles†

PubMed Central

Ratnayake, Punsisi U.; Ekanayaka, E. A. Prabodha; Komanduru, Sweta S.; Weliky, David P.

2015-01-01

Influenza virus is a Class I enveloped virus which is initially endocytosed into a host respiratory epithelial cell. Subsequent reduction of the pH to the 5–6 range triggers a structural change of the viral hemagglutinin II (HA2) protein, fusion of the viral and endosomal membranes, and release of the viral nucleocapsid into the cytoplasm. HA2 contains fusion peptide (FP), soluble ectodomain (SE), transmembrane (TM), and intraviral domains with respective lengths of ~25, ~160, ~25, and ~10 residues. The present work provides a straightforward protocol for producing and purifying mg quantities of full-length HA2 from expression in bacteria. Biophysical and structural comparisons are made between full-length HA2 and shorter constructs including SHA2 ≡ SE, FHA2 ≡ FP + SE, and SHA2-TM ≡ SE + TM constructs. The constructs are helical in detergent at pH 7.4 and the dominant trimer species. The proteins are highly thermostable in decylmaltoside detergent with Tm > 90 °C for HA2 with stabilization provided by the SE, FP, and TM domains. The proteins are likely in a trimer-of-hairpins structure, the final protein state during fusion. All constructs induce fusion of negatively-charged vesicles at pH 5.0 with much less fusion at pH 7.4. Attractive protein/vesicle electrostatics play a role in fusion, as the proteins are positively-charged at pH 5.0 and negatively-charged at pH 7.4 and the pH-dependence of fusion is reversed for positively-charged vesicles. Comparison of fusion between constructs supports significant contributions to fusion from the SE and the FP with little effect from the TM. PMID:26297995

Full-length trimeric influenza virus hemagglutinin II membrane fusion protein and shorter constructs lacking the fusion peptide or transmembrane domain: Hyperthermostability of the full-length protein and the soluble ectodomain and fusion peptide make significant contributions to fusion of membrane vesicles.

PubMed

Ratnayake, Punsisi U; Prabodha Ekanayaka, E A; Komanduru, Sweta S; Weliky, David P

2016-01-01

Influenza virus is a class I enveloped virus which is initially endocytosed into a host respiratory epithelial cell. Subsequent reduction of the pH to the 5-6 range triggers a structural change of the viral hemagglutinin II (HA2) protein, fusion of the viral and endosomal membranes, and release of the viral nucleocapsid into the cytoplasm. HA2 contains fusion peptide (FP), soluble ectodomain (SE), transmembrane (TM), and intraviral domains with respective lengths of ∼ 25, ∼ 160, ∼ 25, and ∼ 10 residues. The present work provides a straightforward protocol for producing and purifying mg quantities of full-length HA2 from expression in bacteria. Biophysical and structural comparisons are made between full-length HA2 and shorter constructs including SHA2 ≡ SE, FHA2 ≡ FP+SE, and SHA2-TM ≡ SE+TM constructs. The constructs are helical in detergent at pH 7.4 and the dominant trimer species. The proteins are highly thermostable in decylmaltoside detergent with Tm>90 °C for HA2 with stabilization provided by the SE, FP, and TM domains. The proteins are likely in a trimer-of-hairpins structure, the final protein state during fusion. All constructs induce fusion of negatively-charged vesicles at pH 5.0 with much less fusion at pH 7.4. Attractive protein/vesicle electrostatics play a role in fusion, as the proteins are positively-charged at pH 5.0 and negatively-charged at pH 7.4 and the pH-dependence of fusion is reversed for positively-charged vesicles. Comparison of fusion between constructs supports significant contributions to fusion from the SE and the FP with little effect from the TM. Copyright © 2015 Elsevier Inc. All rights reserved.

Endogenous minerals have influences on surface electrochemistry and ion exchange properties of biochar.

PubMed

Zhao, Ling; Cao, Xinde; Zheng, Wei; Wang, Qun; Yang, Fan

2015-10-01

The feedstocks for biochar production are diverse and many of them contain various minerals in addition to being rich in carbon. Twelve types of biomass classified into 2 categories: plant-based and municipal waste, were employed to produce biochars under 350 °C and 500 °C. Their pH, point of zero net charge (PZNC), zeta potential, cation and anion exchange capacity (CEC and AEC) were analyzed. The municipal waste-based biochars (MW-BC) had higher mineral levels than the plant-based biochars (PB-BC). However, the water soluble mineral levels were lower in the MW-BCs due to the dominant presence of less soluble minerals, such as CaCO3 and (Ca,Mg)3(PO4)2. The higher total minerals in MW-BCs accounted for the higher PZNC (5.47-9.95) than in PB-BCs (1.91-8.18), though the PZNCs of the PB-BCs increased more than that of the MW-BCs as the production temperature rose. The minerals had influence on the zeta potentials via affecting the negative charges of biochars and the ionic strength of solution. The organic functional groups in PB-BCs such as -COOH and -OH had a greater effect on the CEC and AEC, while the minerals had a greater effect on that of MW-BCs. The measured CEC and AEC values had a strong positive correlation with the total amount of soluble cations and anions, respectively. Results indicated that biochar surface charges depend not only on the organic functional groups, but also on the minerals present and to some extent, minerals have more influences on the surface electrochemistry and ion exchange properties of biochar. Copyright © 2015 Elsevier Ltd. All rights reserved.

Phenol adsorption on surface-functionalized iron oxide nanoparticles: modeling of the kinetics, isotherm, and mechanism

NASA Astrophysics Data System (ADS)

Yoon, Soon Uk; Mahanty, Biswanath; Ha, Hun Moon; Kim, Chang Gyun

2016-06-01

Phenol adsorption from aqueous solution was carried out using uncoated and methyl acrylic acid (MAA)-coated iron oxide nanoparticles (NPs), having size <10 nm, as adsorbents. Batch adsorption studies revealed that the phenol removal efficiency of MAA-coated NPs (950 mg g-1) is significantly higher than that of uncoated NPs (550 mg g-1) under neutral to acidic conditions. However, this improvement disappears above pH 9. The adsorption data under optimized conditions (pH 7) were modeled with pseudo-first- and pseudo-second-order kinetics and subjected to Freundlich and Langmuir isotherms. The analysis determined that pseudo-second-order kinetics and the Freundlich model are appropriate for both uncoated and MAA-coated NPs (all R 2 > 0.98). X-ray photoelectron spectroscopy analysis of pristine and phenol-adsorbed NPs revealed core-level binding energy and charge for Fe(2 s) and O(1 s) on the NP surfaces. The calculations suggest that phenol adsorption onto MAA-coated NPs is a charge transfer process, where the adsorbate (phenol) acts as an electron donor and the NP surface (Fe, O) as an electron acceptor. However, a physisorption process appears to be the relevant mechanism for uncoated NPs.

Extraction, characterization and application of malva nut gum in water treatment.

PubMed

Ho, Y C; Norli, I; Alkarkhi, Abbas F M; Morad, N

2015-06-01

In view of green developments in water treatment, plant-based flocculants have become the focus due to their safety, degradation and renewable properties. In addition, cost and energy-saving processes are preferable. In this study, malva nut gum (MNG), a new plant-based flocculant, and its composite with Fe in water treatment using single mode mixing are demonstrated. The result presents a simplified extraction of the MNG process. MNG has a high molecular weight of 2.3 × 10⁵ kDa and a high negative charge of -58.7 mV. From the results, it is a strong anionic flocculant. Moreover, it is observed to have a branch-like surface structure. Therefore, it conforms to the surface of particles well and exhibits good performance in water treatment. In water treatment, the Fe-MNG composite treats water at pH 3.01 and requires a low concentration of Fe and MNG of 0.08 and 0.06 mg/L, respectively, when added to the system. It is concluded that for a single-stage flocculation process, physico-chemical properties such as molecular weight, charge of polymer, surface morphology, pH, concentration of cation and concentration of biopolymeric flocculant affect the flocculating performance.

Structural characteristics of mixed oxides MOx/SiO2 affecting photocatalytic decomposition of methylene blue

NASA Astrophysics Data System (ADS)

Gun'ko, V. M.; Blitz, J. P.; Bandaranayake, B.; Pakhlov, E. M.; Zarko, V. I.; Sulym, I. Ya.; Kulyk, K. S.; Galaburda, M. V.; Bogatyrev, V. M.; Oranska, O. I.; Borysenko, M. V.; Leboda, R.; Skubiszewska-Zięba, J.; Janush, W.

2012-06-01

A series of photocatalysts based on silica (nanoparticulate) supported titania, ceria, and ceria/zirconia were synthesized and characterized by a variety of techniques including surface area measurements, X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential, surface charge density, and photocatalytic behavior toward methylene blue decomposition. Thermal treatment at 600 °C increases the anatase content of the titania based catalysts detected by XRD. Changes in the infrared spectra before and after thermal treatment indicate that at low temperature there are more tbnd Sisbnd Osbnd Titbnd bonds than at high temperature. As these bonds break upon heating the SiO2 and TiO2 separate, allowing the TiO2 anatase phase to form. This results in an increased catalytic activity for the thermally treated samples. Nearly all titania based samples exhibit a negative surface charge density at pH 7 (initial pH of photocatalytic studies) which aids adsorption of methylene blue. The crystallinity of ceria and ceria/zirconia based catalysts are in some cases limited, and in others non-existent. Even though the energy band gap (Eg) can be lower for these catalysts than for the titania based catalysts, their photocatalytic properties are inferior.

Oil Contact Angles in a Water-Decane-Silicon Dioxide System: Effects of Surface Charge

NASA Astrophysics Data System (ADS)

Xu, Shijing; Wang, Jingyao; Wu, Jiazhong; Liu, Qingjie; Sun, Chengzhen; Bai, Bofeng

2018-04-01

Oil wettability in the water-oil-rock systems is very sensitive to the evolution of surface charges on the rock surfaces induced by the adsorption of ions and other chemical agents in water flooding. Through a set of large-scale molecular dynamics simulations, we reveal the effects of surface charge on the oil contact angles in an ideal water-decane-silicon dioxide system. The results show that the contact angles of oil nano-droplets have a great dependence on the surface charges. As the surface charge density exceeds a critical value of 0.992 e/nm2, the contact angle reaches up to 78.8° and the water-wet state is very apparent. The variation of contact angles can be confirmed from the number density distributions of oil molecules. With increasing the surface charge density, the adsorption of oil molecules weakens and the contact areas between nano-droplets and silicon dioxide surface are reduced. In addition, the number density distributions, RDF distributions, and molecular orientations indicate that the oil molecules are adsorbed on the silicon dioxide surface layer-by-layer with an orientation parallel to the surface. However, the layered structure of oil molecules near the silicon dioxide surface becomes more and more obscure at higher surface charge densities.

Oil Contact Angles in a Water-Decane-Silicon Dioxide System: Effects of Surface Charge.

PubMed

Xu, Shijing; Wang, Jingyao; Wu, Jiazhong; Liu, Qingjie; Sun, Chengzhen; Bai, Bofeng

2018-04-19

Oil wettability in the water-oil-rock systems is very sensitive to the evolution of surface charges on the rock surfaces induced by the adsorption of ions and other chemical agents in water flooding. Through a set of large-scale molecular dynamics simulations, we reveal the effects of surface charge on the oil contact angles in an ideal water-decane-silicon dioxide system. The results show that the contact angles of oil nano-droplets have a great dependence on the surface charges. As the surface charge density exceeds a critical value of 0.992 e/nm 2 , the contact angle reaches up to 78.8° and the water-wet state is very apparent. The variation of contact angles can be confirmed from the number density distributions of oil molecules. With increasing the surface charge density, the adsorption of oil molecules weakens and the contact areas between nano-droplets and silicon dioxide surface are reduced. In addition, the number density distributions, RDF distributions, and molecular orientations indicate that the oil molecules are adsorbed on the silicon dioxide surface layer-by-layer with an orientation parallel to the surface. However, the layered structure of oil molecules near the silicon dioxide surface becomes more and more obscure at higher surface charge densities.

Defining the property space for chromatographic ligands from a homologous series of mixed-mode ligands.

PubMed

Woo, James A; Chen, Hong; Snyder, Mark A; Chai, Yiming; Frost, Russell G; Cramer, Steven M

2015-08-14

A homologous ligand library based on the commercially-available Nuvia cPrime ligand was generated to systematically explore various features of a multimodal cation-exchange ligand and to identify structural variants that had significantly altered chromatographic selectivity. Substitution of the polar amide bond with more hydrophobic chemistries was found to enhance retention while remaining hydrophobically-selective for aromatic residues. In contrast, increasing the solvent exposure of the aromatic ring was observed to strengthen the ligand affinity for both types of hydrophobic residues. An optimal linker length between the charged and hydrophobic moieties was also observed to enhance retention, balancing the steric accessibility of the hydrophobic moiety with its ability to interact independently of the charged group. The weak pKa of the carboxylate charge group was found to have a notable impact on protein retention on Nuvia cPrime at lower pH, increasing hydrophobic interactions with the protein. Substituting the charged group with a sulfonic acid allowed this strong MM ligand to retain its electrostatic-dominant character in this lower pH range. pH gradient experiments were also carried out to further elucidate this pH dependent behavior. A single QSAR model was generated using this accumulated experimental data to predict protein retention across a range of multimodal and ion exchange systems. This model could correctly predict the retention of proteins on resins that were not included in the original model and could prove quite powerful as an in silico approach toward designing more effective and differentiated multimodal ligands. Copyright © 2015. Published by Elsevier B.V.

Stepwise pH-responsive nanoparticles for enhanced cellular uptake and on-demand intracellular release of doxorubicin.

PubMed

Chen, Wei-Liang; Li, Fang; Tang, Yan; Yang, Shu-di; Li, Ji-Zhao; Yuan, Zhi-Qiang; Liu, Yang; Zhou, Xiao-Feng; Liu, Chun; Zhang, Xue-Nong

2017-01-01

Physicochemical properties, including particle size, zeta potential, and drug release behavior, affect targeting efficiency, cellular uptake, and antitumor effect of nanocarriers in a formulated drug-delivery system. In this study, a novel stepwise pH-responsive nanodrug delivery system was developed to efficiently deliver and significantly promote the therapeutic effect of doxorubicin (DOX). The system comprised dimethylmaleic acid-chitosan-urocanic acid and elicited stepwise responses to extracellular and intracellular pH. The nanoparticles (NPs), which possessed negative surface charge under physiological conditions and an appropriate nanosize, exhibited advantageous stability during blood circulation and enhanced accumulation in tumor sites via enhanced permeability and retention effect. The tumor cellular uptake of DOX-loaded NPs was significantly promoted by the first-step pH response, wherein surface charge reversion of NPs from negative to positive was triggered by the slightly acidic tumor extracellular environment. After internalization into tumor cells, the second-step pH response in endo/lysosome acidic environment elicited the on-demand intracellular release of DOX from NPs, thereby increasing cytotoxicity against tumor cells. Furthermore, stepwise pH-responsive NPs showed enhanced antiproliferation effect and reduced systemic side effect in vivo. Hence, the stepwise pH-responsive NPs provide a promising strategy for efficient delivery of antitumor agents.

Modeling the adsorption of hydrogen, sodium, chloride and phthalate on goethite using a strict charge-neutral ion-exchange theory.

PubMed

Schulthess, Cristian P; Ndu, Udonna

2017-01-01

Simultaneous adsorption modeling of four ions was predicted with a strict net charge-neutral ion-exchange theory and its corresponding equilibrium and mass balance equations. An important key to the success of this approach was the proper collection of all the data, particularly the proton adsorption data, and the inclusion of variable concentrations of conjugate ions from the experimental pH adjustments. Using IExFit software, the ion-exchange model used here predicted the competitive retention of several ions on goethite by assuming that the co-adsorption or desorption of all ions occurred in the correct stoichiometries needed to maintain electroneutrality. This approach also revealed that the retention strength of Cl- ions on goethite increases in the presence of phthalate ions. That is, an anion-anion enhancement effect was observed. The retention of Cl- ions was much weaker than phthalate ions, and this also resulted in a higher sensitivity of the Cl- ions toward minor variations in the surface reactivity. The proposed model uses four goethite surface sites. The drop in retention of phthalate ions at low pH was fully described here as resulting from competitive Cl- reactions, which were introduced in increasing concentrations into the matrix as the conjugate base to the acid added to lower the pH.

Stepwise pH-responsive nanoparticles for enhanced cellular uptake and on-demand intracellular release of doxorubicin

PubMed Central

Chen, Wei-liang; Li, Fang; Tang, Yan; Yang, Shu-di; Li, Ji-zhao; Yuan, Zhi-qiang; Liu, Yang; Zhou, Xiao-feng; Liu, Chun; Zhang, Xue-nong

2017-01-01

Physicochemical properties, including particle size, zeta potential, and drug release behavior, affect targeting efficiency, cellular uptake, and antitumor effect of nanocarriers in a formulated drug-delivery system. In this study, a novel stepwise pH-responsive nanodrug delivery system was developed to efficiently deliver and significantly promote the therapeutic effect of doxorubicin (DOX). The system comprised dimethylmaleic acid-chitosan-urocanic acid and elicited stepwise responses to extracellular and intracellular pH. The nanoparticles (NPs), which possessed negative surface charge under physiological conditions and an appropriate nanosize, exhibited advantageous stability during blood circulation and enhanced accumulation in tumor sites via enhanced permeability and retention effect. The tumor cellular uptake of DOX-loaded NPs was significantly promoted by the first-step pH response, wherein surface charge reversion of NPs from negative to positive was triggered by the slightly acidic tumor extracellular environment. After internalization into tumor cells, the second-step pH response in endo/lysosome acidic environment elicited the on-demand intracellular release of DOX from NPs, thereby increasing cytotoxicity against tumor cells. Furthermore, stepwise pH-responsive NPs showed enhanced antiproliferation effect and reduced systemic side effect in vivo. Hence, the stepwise pH-responsive NPs provide a promising strategy for efficient delivery of antitumor agents. PMID:28652730

Properties of an αs-casein-rich casein fraction: influence of dialysis on surface properties, miscibility, and micelle formation.

PubMed

Kessler, Anne; Menéndez-Aguirre, Orquidéa; Hinrichs, Jörg; Stubenrauch, Cosima; Weiss, Jochen

2013-09-01

In this study, the surface tension, miscibility, and particle size distribution of a solution containing an αs-casein (CN)-rich CN fraction (54 wt % αs-CN, 32 wt % β-CN, and 15 wt % κ-CN) were determined at pH 6.6. The nondialyzed CN fraction was compared with a dialyzed one. In the nondialyzed sample, every charge on the protein was compensated by 0.3 charges coming from counterions, whereas in the dialyzed sample, only 0.2 charges could be assigned to each charge on the protein. This relation was determined by calculating the charges at the proteins, taking the measured mineral content into account. The surface tension was measured as a function of the protein concentration by the du Noüy ring method at room temperature. Results indicated alterations in the surface properties after reduction of counterions. The equilibrium surface tension above the critical micelle concentration increased from 40.1×10(-3) to 45×10(-3) N/m, the critical micelle concentration increased from 0.9×10(-4) to 2×10(-3) mol/L, and the minimal area occupied per molecule at the surface increased from 2.4×10(-18) to 4.6×10(-18) m(2). Cloud points were determined by measuring the absorbance of CN solutions as a function of the temperature. The cloud points were found to be concentration dependent and had a minimum at 0.2 wt % at 34°C for nondialyzed CN and at 0.25 wt % at 28°C for dialyzed CN, again demonstrating the influence of counterion reduction. Below the cloud point, a micellar phase was found to exist. The hydrodynamic diameter of the micelles were characterized by dynamic light scattering in both auto- and cross-correlation mode. However, no influence of reduction in counterions could be observed, possibly due to the fact that dynamic light scattering is not a suitable method for this type of system. The presence of self-assembled structures was verified by freeze-fracture electron microscopy. The observed differences between dialyzed and nondialyzed samples were explained by changes in the counterion cloud surrounding the proteins. Consequently, the electrostatic interactions between as well as within the CN are altered by dialysis, which, in turn, affects the behavior at the surface as well as the properties in the solution. Copyright © 2013 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Effect of pH buffer molecules on the light-induced currents from oriented purple membrane.

PubMed Central

Liu, S Y; Kono, M; Ebrey, T G

1991-01-01

The effect of pH buffers on the microsecond photocurrent component, B2, of oriented purple membranes has been studied. We found that under low salt conditions (less than 10 mM monovalent cationic salt) pH buffers can dramatically alter the waveform of the B2 component. The effect is induced by the protonation process of the buffer molecules by protons expelled from the membrane. These effects can be classified according to the charge transition upon protonation of the buffer. Buffers that carry two positive charges in their protonated form add a negative current component (N component) to B2. Almost all of the other buffers add a positive current component (P component) to B2, which is essentially a mirror image of the N component. Buffers with a pK less than 5.5 have only a small positive buffer component. The pH dependence of the buffer effect is closely related to the pK of the buffer; it requires that the buffer be in its unprotonated form. The rise time of the buffer component increases with the concentration of the buffer molecules. All the buffer effects can be inhibited by the addition of 5 mM of a divalent cation such as Ca2+. Reducing the surface potential slows down the N component but accelerates the P component without affecting the amplitude of the buffer effect significantly. Many of the buffer effects can be explained if we assume that upon protonation of the buffer by a proton expelled from the membrane by light, the buffer molecules move toward the membrane. This backward movement of buffer molecules forms a counter current very similar to that due to cations discussed in Liu, S. Y., R. Govindjee, and T. G. Ebrey. (1990. Biophys. J. 57:951-963). PMID:1883939

Subunit assembly of hemoglobin: an important determinant of hematologic phenotype.

PubMed

Bunn, H F

1987-01-01

Hemoglobin's physiologic properties depend on the orderly assembly of its subunits in erythropoietic cells. The biosynthesis of alpha- and beta-globin polypeptide chains is normally balanced. Heme rapidly binds to the globin subunit, either during translation or shortly thereafter. The formation of the alpha beta-dimer is facilitated by electrostatic attraction of a positively charged alpha-subunit to a negatively charged beta-subunit. The alpha beta-dimer dissociates extremely slowly. The difference between the rate of dissociation of alpha beta- and alpha gamma-dimers with increasing pH explains the well-known alkaline resistance of Hb F. Two dimers combine to form the functioning alpha 2 beta 2-tetramer. This model of hemoglobin assembly explains the different levels of positively charged and negatively charged mutant hemoglobins that are encountered in heterozygotes and the effect of alpha-thalassemia and heme deficiency states in modifying the level of the variant hemoglobin as well as Hb A2. Electrostatic interactions also affect the binding of hemoglobin to the cytoplasmic surface of the red cell membrane and may underlie the formation of target cells. Enhanced binding of positively charged variants such as S and C trigger a normally dormant pathway for potassium and water loss. Thus, the positive charge on beta c is responsible for the two major contributors to the pathogenesis of Hb SC disease: increased proportion of Hb S and increased intracellular hemoglobin concentration. It is likely that electrostatic interactions play an important role in the assembly of a number of other multisubunit macromolecules, including membrane receptors, cytoskeletal proteins, and DNA binding proteins.

On the theoretical description of weakly charged surfaces.

PubMed

Wang, Rui; Wang, Zhen-Gang

2015-03-14

It is widely accepted that the Poisson-Boltzmann (PB) theory provides a valid description for charged surfaces in the so-called weak coupling limit. Here, we show that the image charge repulsion creates a depletion boundary layer that cannot be captured by a regular perturbation approach. The correct weak-coupling theory must include the self-energy of the ion due to the image charge interaction. The image force qualitatively alters the double layer structure and properties, and gives rise to many non-PB effects, such as nonmonotonic dependence of the surface energy on concentration and charge inversion. In the presence of dielectric discontinuity, there is no limiting condition for which the PB theory is valid.