Selective synthesis and characterization of single-crystal silver molybdate/tungstate nanowires by a hydrothermal process.

PubMed

Cui, Xianjin; Yu, Shu-Hong; Li, Lingling; Biao, Liu; Li, Huabin; Mo, Maosong; Liu, Xian-Ming

2004-01-05

Selective synthesis of uniform single crystalline silver molybdate/tungstate nanorods/nanowires in large scale can be easily realized by a facile hydrothermal recrystallization technique. The synthesis is strongly dependent on the pH conditions, temperature, and reaction time. The phase transformation was examined in details. Pure Ag(2)MoO(4) and Ag(6)Mo(10)O(33) can be easily obtained under neutral condition and pH 2, respectively, whereas other mixed phases of Mo(17)O(47), Ag(2)Mo(2)O(7,) Ag(6)Mo(10)O(33) were observed under different pH conditions. Ag(6)Mo(10)O(33) nanowires with uniform diameter 50-60 nm and length up to several hundred micrometers were synthesized in large scale for the first time at 140 degrees C. The melting point of Ag(6)Mo(10)O(33) nanowires were found to be about 238 degrees C. Similarly, Ag(2)WO(4), and Ag(2)W(2)O(7) nanorods/nanowires can be selectively synthesized by controlling pH value. The results demonstrated that this route could be a potential mild way to selectively synthesize various molybdate nanowires with various phases in large scale.

Solubility of polyvalent cations in fogwater at an urban site in Strasbourg (France)

NASA Astrophysics Data System (ADS)

Millet, M.; Wortham, H.; Mirabel, Ph.

The concentrations in the soluble and total (soluble + insoluble) fractions of Mg, Ca, Fe, Mn, Zn, Al, Cd and Pb have been analysed by "inductively coupled plasma (ICP)" in 14 fog events collected in 1992 at an urban site in France (Strasbourg). For each fog event, two droplet size categories (2-6 μm and 5-8 μm) have been collected separately. For the analysis of the polyvalent cations in the soluble and total fractions, an analytical procedure using ICP and filtration on cellulose/PVC filters has been developed. The study of the solubility of some polyvalent cations has shown that two of the most important factors controlling the partitioning between the soluble and insoluble fraction are the nature of the particles and the pH of the fogwater. The influence of pH depended on the element. The solubility of Pb, Cd, Al, Fe, Mg, and Ca were pH dependent whereas, Zn and Mn solubility varied but no relationship with pH existed, ranging between 25 and 100% and 10 and 100%, respectively. On the other hand, Mg, Pb and Ca were predominantly present in the soluble phase, whereas Al was prevalent in the insoluble fraction. In the case of Cd and Fe., the presence in the soluble or insoluble phase depended largely on the fogwater pH.

Computational scheme for pH-dependent binding free energy calculation with explicit solvent.

PubMed

Lee, Juyong; Miller, Benjamin T; Brooks, Bernard R

2016-01-01

We present a computational scheme to compute the pH-dependence of binding free energy with explicit solvent. Despite the importance of pH, the effect of pH has been generally neglected in binding free energy calculations because of a lack of accurate methods to model it. To address this limitation, we use a constant-pH methodology to obtain a true ensemble of multiple protonation states of a titratable system at a given pH and analyze the ensemble using the Bennett acceptance ratio (BAR) method. The constant pH method is based on the combination of enveloping distribution sampling (EDS) with the Hamiltonian replica exchange method (HREM), which yields an accurate semi-grand canonical ensemble of a titratable system. By considering the free energy change of constraining multiple protonation states to a single state or releasing a single protonation state to multiple states, the pH dependent binding free energy profile can be obtained. We perform benchmark simulations of a host-guest system: cucurbit[7]uril (CB[7]) and benzimidazole (BZ). BZ experiences a large pKa shift upon complex formation. The pH-dependent binding free energy profiles of the benchmark system are obtained with three different long-range interaction calculation schemes: a cutoff, the particle mesh Ewald (PME), and the isotropic periodic sum (IPS) method. Our scheme captures the pH-dependent behavior of binding free energy successfully. Absolute binding free energy values obtained with the PME and IPS methods are consistent, while cutoff method results are off by 2 kcal mol(-1) . We also discuss the characteristics of three long-range interaction calculation methods for constant-pH simulations. © 2015 The Protein Society.

Protocols Utilizing Constant pH Molecular Dynamics to Compute pH-Dependent Binding Free Energies

PubMed Central

2015-01-01

In protein–ligand binding, the electrostatic environments of the two binding partners may vary significantly in bound and unbound states, which may lead to protonation changes upon binding. In cases where ligand binding results in a net uptake or release of protons, the free energy of binding is pH-dependent. Nevertheless, conventional free energy calculations and molecular docking protocols typically do not rigorously account for changes in protonation that may occur upon ligand binding. To address these shortcomings, we present a simple methodology based on Wyman’s binding polynomial formalism to account for the pH dependence of binding free energies and demonstrate its use on cucurbit[7]uril (CB[7]) host–guest systems. Using constant pH molecular dynamics and a reference binding free energy that is taken either from experiment or from thermodynamic integration computations, the pH-dependent binding free energy is determined. This computational protocol accurately captures the large pKa shifts observed experimentally upon CB[7]:guest association and reproduces experimental binding free energies at different levels of pH. We show that incorrect assignment of fixed protonation states in free energy computations can give errors of >2 kcal/mol in these host–guest systems. Use of the methods presented here avoids such errors, thus suggesting their utility in computing proton-linked binding free energies for protein–ligand complexes. PMID:25134690

pH and heat-dependent behaviour of glucose oxidase down to single molecule level by combined fluorescence spectroscopy and molecular modelling.

PubMed

Dumitraşcu, Loredana; Stănciuc, Nicoleta; Bahrim, Gabriela Elena; Ciumac, Alexandrina; Aprodu, Iuliana

2016-04-01

In the food industry, glucose oxidase (GOX) is used to improve the shelf life of food materials. The pH- and heat-induced conformational changes of glucose oxidase from Aspergillus niger were quantified by means of fluorescence spectroscopy and molecular dynamics simulations. The phase diagram showed an all-or-none transition process, indicating that pH and temperature largely influence the conformational state of GOX. Shifts in maximum wavelength of Trp, Tyr were registered as the protein encounters a lower pH (pH 4.0), suggesting significant changes of the polarity around the chromophore molecule. Quenching experiments using KI showed higher quenching constants of Trp and flavin adenine dinucleotide upon heating or by changing pH value, and were mainly correlated with the conformational changes upon protein matrix. Finally, valuable insights into the thermal behaviour of GOX were obtained from molecular modelling results. The conformation and structure of GOX protein is dependent upon the pH and heat treatment applied. Molecular dynamics simulation indicated significant changes in the substrate binding region at temperatures over 60 °C that might affect enzyme activity. Moreover, an important alteration of the small pocket hosting the positively charged His(516) residue responsible for oxygen activation appears evident at high temperatures. © 2015 Society of Chemical Industry.

The gene ICS3 from the yeast Saccharomyces cerevisiae is involved in copper homeostasis dependent on extracellular pH.

PubMed

Alesso, C A; Discola, K F; Monteiro, G

2015-09-01

In the yeast Saccharomyces cerevisiae, many genes are involved in the uptake, transport, storage and detoxification of copper. Large scale studies have noted that deletion of the gene ICS3 increases sensitivity to copper, Sortin 2 and acid exposure. Here, we report a study on the Δics3 strain, in which ICS3 is related to copper homeostasis, affecting the intracellular accumulation of this metal. This strain is sensitive to hydrogen peroxide and copper exposure, but not to other tested transition metals. At pH 6.0, the Δics3 strain accumulates a larger amount of intracellular copper than the wild-type strain, explaining the sensitivity to oxidants in this condition. Unexpectedly, sensitivity to copper exposure only occurs in acidic conditions. This can be explained by the fact that the exposure of Δics3 cells to high copper concentrations at pH 4.0 results in over-accumulation of copper and iron. Moreover, the expression of ICS3 increases in acidic pH, and this is correlated with CCC2 gene expression, since both genes are regulated by Rim101 from the pH regulon. CCC2 is also upregulated in Δics3 in acidic pH. Together, these data indicate that ICS3 is involved in copper homeostasis and is dependent on extracellular pH. Copyright © 2015 Elsevier Inc. All rights reserved.

Probing pH difference between micellar solution and nanoscale water within common black film by fluorescent dye

NASA Astrophysics Data System (ADS)

Fu, Jingni; Zhang, Luning

2018-03-01

The protonation/deprotonation equilibrium of a fluorescent pH probe (carboxy-seminaphthorhodafluor-1, SNARF-1) within the nanoscale water layer confined in common black films (CBFs) has been studied. We find that SNARF-1 molecules feel a more acidic environment in CBFs than when they are in the bulk micellar solution, using the base/acid peak area ratio of the dye to indicate its microenvironment pH. Three surfactants are used to study the dependence of the pH drop versus charge: cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium dodecylsulphate, SDS) and nonionic (Triton X-100) species. The decrease of CBFs pH versus the pH of the micellar solution is the following: ΔpH ≈ 1.5 for CTAB (pH: 7.0-9.0), ΔpH ≈ 0.8 for SDS, and ΔpH ≈ 0.4 for Triton X-100. With the addition of electrolyte in CBFs, we observe large decrease the amplitude of the pH anomaly, thus suggesting an electrostatic origin of the pH change at nanoscale environment.

Functional characterization of a ClC transporter by solid-supported membrane electrophysiology

PubMed Central

Garcia-Celma, Juan; Szydelko, Adrian

2013-01-01

EcClC, a prokaryotic member of the ClC family of chloride channels and transporters, works as coupled H+/Cl− exchanger. With a known structure and the possibility of investigating its behavior with different biochemical and biophysical techniques, the protein has become an important model system for the family. Although many aspects of its function have been previously characterized, it was difficult to measure transport on the same sample under different environmental conditions. To overcome this experimental limitation, we have studied EcClC by solid-supported membrane electrophysiology. The large transport-related transient currents and a simple way of relating transport rates to the measured signal have allowed a thorough investigation of ion selectivity, inhibition, and the dependence of transport on changes in ion concentration and pH. Our results confirm that the protein transports larger anions with about similar rates, whereas the smaller fluoride is not a substrate. We also show that 4,4′-diisothiocyano-2,2’-stilbenedisulfonic acid (DIDS), a known inhibitor of other anion transport protein, irreversibly inhibits EcClC from the intracellular side. The chloride dependence shows an apparent saturation at millimolar concentrations that resembles a similar behavior in eukaryotic ClC channels. Our experiments have also allowed us to quantify the pH dependence of transport. EcClC shows a strong activation at low pH with an apparent pKa of 4.6. The pronounced pH dependence is lost by the mutation of a conserved glutamate facing the extracellular solution that was previously shown to be an acceptor for transported protons, whereas it is largely retained by the mutation of an equivalent residue at the intracellular side. Our results have provided a quantitative basis for the transport behavior of EcClC, and they will serve as a reference for future investigations of novel electrogenic transporters with still-uncharacterized properties. PMID:23478993

A pH-responsive molecular switch with tricolor luminescence.

PubMed

Ahn, Hyungmin; Hong, Jaewan; Kim, Sung Yeon; Choi, Ilyoung; Park, Moon Jeong

2015-01-14

We developed a new ratiometric pH sensor based on poly(N-phenylmaleimide) (PPMI)-containing block copolymer that emits three different fluorescent colors depending on the pH. The strong solvatochromism and tautomerism of the PPMI derivatives enabled precise pH sensing for almost the entire range of the pH scale. Theoretical calculations have predicted largely dissimilar band gaps for the keto, enol, and enolate tautomers of PPMI owing to low-dimensional conjugation effects. The tunable emission wavelength and intensity of our sensors, as well as the reversible color switching with high-luminescent contrast, were achieved using rational molecular design of PPMI analogues as an innovative platform for accurate H(+) detection. The self-assembly of block copolymers on the nanometer length scale was particularly highlighted as a novel prospective means of regulating fluorescence properties while avoiding the self-quenching phenomenon, and this system can be used as a fast responsive pH sensor in versatile device forms.

A novel ''donor-π-acceptor'' type fluorescence probe for sensing pH: mechanism and application in vivo.

PubMed

Chao, Jianbin; Wang, Huijuan; Zhang, Yongbin; Yin, Caixia; Huo, Fangjun; Song, Kailun; Li, Zhiqing; Zhang, Ting; Zhao, Yaqin

2017-11-01

A novel pH fluorescent probe 1-(pyren-1-yl)-3-(6-methoxypridin-3-yl)-acrylketone, (PMPA), which had a pyrene structure attached to methoxypyridine, was synthesized for monitoring extremely acidic and alkaline pH. The pH titrations indicated that PMPA displayed a remarkable emission enhancement with a pK a of 2.70 and responded linearly to minor pH fluctuations within the extremely acidic range of 1.26-3.97. Interestingly, PMPA also exhibited strong pH-dependent characteristics with pK a 9.32 and linear response to extreme-alkalinity range of 8.54-10.36. In addition, PMPA displayed a good selectivity, excellent photostability and large Stokes shift (167nm). Furthermore, the probe PMPA had excellent cell membrane permeability and was applied successfully to rapidly detect pH in living cells. pH value in these organs was closely related to many diseases, so these findings suggested that the probe had potential application in pH detecting for disease diagnosis. Copyright © 2017 Elsevier B.V. All rights reserved.

Fluorophotometric measurement of the buffering action of human tears in vivo.

PubMed

Yamada, M; Kawai, M; Mochizuki, H; Hata, Y; Mashima, Y

1998-10-01

The buffering action of human tears is thought to be important to keep its pH constant. We measured the change in pH in the precorneal tear film in vivo when the acidic solution is challenged, using a fluorophotometric technique. Twelve eyes from 6 healthy subjects were entered in this study. Each subject was pretreated with either one drop of 0.4% oxybuprocaine for once (light anesthesia), three times (deep anesthesia), or none (controls). The measurement was initiated by instilling 20 microl of 0.067 M phosphate buffer at pH 5.5 containing 2 mM bis-carboxyethyl-carboxyfluorescein free acid, a pH sensitive dye, into the subject's eye. The pH was determined by the ratio of fluorescent intensities at two excitation wavelengths (490 and 430 nm). pH recovery time (PHRT) as defined by the time required for pH to reach 95% of pH at equilibrium was used for the marker of tear buffering action. Tear turnover rate was also determined using the fluorescent decay curve at 430 nm, which was independent of pH, but dependent on dye concentration. Immediately after the instillation, the pH value in the tear film was around 6.0-6.5 in all cases. The tear film rapidly became more alkaline, reaching its normal value in 2.3 +/- 0.5 min in untreated eyes. The pretreatment with 0.4% oxybuprocaine retarded the neutralization process. A single regression analysis revealed that the PHRT had a significant negative correlation with the tear turnover rate (r = -0.78). Our results suggest that the neutralization process of tears largely depends on the tear turnover rate. The buffering action of tears in vivo consists of the tear turnover as well as its chemical buffering capacity.

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

Qasim, Mohammad A., E-mail: qasimm@ipfw.edu; Song, Jikui; Markley, John L.

Research highlights: {yields} Large pK shifts in ionizable groups when buried in the protein interior. {yields} Substrate dependent shifts in pH optimum for serine proteases. {yields} Lys side chain is a stronger acid in serine protease S{sub 1} pocket than Asp side chain. -- Abstract: Enzymatic hydrolysis of the synthetic substrate succinyl-Ala-Ala-Pro-Xxx-pNA (where Xxx = Leu, Asp or Lys) catalyzed by bovine chymotrypsin (CHYM) or Streptomyces griseus protease B (SGPB) has been studied at different pH values in the pH range 3-11. The pH optima for substrates having Leu, Asp, and Lys have been found to be 7.5-8.0, 5.5-6.0, andmore » {approx}10, respectively. At the normally reported pH optimum (pH 7-8) of CHYM and SGPB, the substrate with Leu at the reactive site is more than 25,000-fold more reactive than that with Asp. However, when fully protonated, Asp is nearly as good a substrate as Leu. The pK values of the side chains of Asp and Lys in the hydrophobic S{sub 1} pocket of CHYM and SGPB have been calculated from pH-dependent hydrolysis data and have been found to be about 9 for Asp and 7.4 and 9.7 for Lys for CHYM and SGPB, respectively. The results presented in this communication suggest a possible application of CHYM like enzymes in cleaving peptide bonds contributed by acidic amino acids between pH 5 and 6.« less

Beneficial reuse of fly ashes in geotechnical engineering with physicochemical and electron microscopic methods.

DOT National Transportation Integrated Search

2013-06-01

The sedimentation behavior of fine grained soil is largely dependent on its pore fluid chemistry. Physicochemical properties of the : pore fluid, such as ionic strength and pH, could greatly influence the micro structure of kaolinite which in turn in...

Acidic pH increases airway surface liquid viscosity in cystic fibrosis

PubMed Central

Tang, Xiao Xiao; Ostedgaard, Lynda S.; Hoegger, Mark J.; Moninger, Thomas O.; Karp, Philip H.; McMenimen, James D.; Choudhury, Biswa; Varki, Ajit; Stoltz, David A.; Welsh, Michael J.

2016-01-01

Cystic fibrosis (CF) disrupts respiratory host defenses, allowing bacterial infection, inflammation, and mucus accumulation to progressively destroy the lungs. Our previous studies revealed that mucus with abnormal behavior impaired mucociliary transport in newborn CF piglets prior to the onset of secondary manifestations. To further investigate mucus abnormalities, here we studied airway surface liquid (ASL) collected from newborn piglets and ASL on cultured airway epithelia. Fluorescence recovery after photobleaching revealed that the viscosity of CF ASL was increased relative to that of non-CF ASL. CF ASL had a reduced pH, which was necessary and sufficient for genotype-dependent viscosity differences. The increased viscosity of CF ASL was not explained by pH-independent changes in HCO3– concentration, altered glycosylation, additional pH-induced disulfide bond formation, increased percentage of nonvolatile material, or increased sulfation. Treating acidic ASL with hypertonic saline or heparin largely reversed the increased viscosity, suggesting that acidic pH influences mucin electrostatic interactions. These findings link loss of cystic fibrosis transmembrane conductance regulator–dependent alkalinization to abnormal CF ASL. In addition, we found that increasing Ca2+ concentrations elevated ASL viscosity, in part, independently of pH. The results suggest that increasing pH, reducing Ca2+ concentration, and/or altering electrostatic interactions in ASL might benefit early CF. PMID:26808501

An Electrochemistry Study of Cryoelectrolysis in Frozen Physiological Saline.

PubMed

Manuel, Thomas J; Munnangi, Pujita; Rubinsky, Boris

2017-07-01

Cryoelectrolysis is a new minimally invasive tissue ablation surgical technique that combines the processes of electrolysis and solid/liquid phase transformation (freezing). This study investigated this new technique by measuring the pH front propagation and the changes in resistance in a tissue simulant made of physiological saline gel with a pH dye as a function of the sample temperature in the high subzero range above the eutectic. Results demonstrated that effective electrolysis can occur in a high subzero freezing milieu and that the propagation of the pH front is only weakly dependent on temperature. These observations are consistent with a mechanism involving ionic movement through the concentrated saline solution channels between ice crystals at subfreezing temperatures above the eutectic. Moreover, results suggest that Joule heating in these microchannels may cause local microscopic melting, the observed weak dependence of pH front propagation on temperature, and the large changes in resistance with time. A final insight provided by the results is that the pH front propagation from the anode is more rapid than from the cathode, a feature indicative of the electro-osmotic flow from the cathode to the anode. The findings in this paper may be critical for designing future cryoelectrolytic ablation surgery protocols.

Effect of pH on the rheological properties of borate crosslinked hydroxypropyl guar gum hydrogel and hydroxypropyl guar gum.

PubMed

Wang, Shibin; Tang, Hongbiao; Guo, Jianchun; Wang, Kunjie

2016-08-20

pH is an important factor affecting the performance of polymer fluid. The rheological properties of hydroxypropyl guar gum (HPG) base fluid and the structural strength, rheological properties, viscoelastic properties and thixotropy properties of HPG gel depend largely on the pH values. For the base fluid, an apparent viscosity-increasing effect was observed over the pH range from 7 to 11, and the apparent viscosity gradually decreased at pH 11.5-14, exhibiting electrostatic repulsion behavior and steric effects. For the HPG gel, at pH 7-12.5, the gel possessed higher apparent viscosity, higher elastic modulus (G'), lower tanδ (the ratio of the viscous modulus to the elastic modulus) and an "8"-shaped hysteresis loop, indicating stronger gel structure strength and the elastic dominant property. At pH 13-13.5, the gel samples exhibited the transition from a pseudoplastic fluid to a Newtonian fluid, and their viscosity, elastic modulus decreased but tanδ increased with the increase in pH values, exhibiting gradually weakened elastic properties. When the pH was 14, the gel mainly exhibited viscous characteristics. Copyright © 2016 Elsevier Ltd. All rights reserved.

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.

Superstar of the Sloan Minority Ph.D. Program.

PubMed

Greenwood, Ted

2013-01-01

In AY 1994-95 the Alfred P. Sloan Foundation launched a program, later known as the Minority Ph.D. Program, to increase the number of underrepresented minority students earning Ph.D.s in natural sciences, engineering and mathematics (SEM). This program emerged from a recognition that African Americans, Hispanic Americans and American Indians were very underrepresented at all levels and in all aspects of SEM disciplines and that, although undergraduate education had received and continued to received much attention by universities, private funders and government agencies, there was still relatively little attention being paid to the graduate and especially the Ph.D. level. Because earning the Ph.D. is a necessary milestone along the pathway to a faculty position and the effort to diversify the graduates of SEM disciplines depends, in large part, on diversifying the faculty at American universities, this relative lack of attention to Ph.D. education was, in the opinion of the Sloan Foundation, a significant deficiency of national efforts. As a Program Director at the Sloan Foundation, I initiated this Minority Ph.D. Program and ran it until my retirement in June 2011.

A single pH fluorescent probe for biosensing and imaging of extreme acidity and extreme alkalinity.

PubMed

Chao, Jian-Bin; Wang, Hui-Juan; Zhang, Yong-Bin; Li, Zhi-Qing; Liu, Yu-Hong; Huo, Fang-Jun; Yin, Cai-Xia; Shi, Ya-Wei; Wang, Juan-Juan

2017-07-04

A simple tailor-made pH fluorescent probe 2-benzothiazole (N-ethylcarbazole-3-yl) hydrazone (Probe) is facilely synthesized by the condensation reaction of 2-hydrazinobenzothiazole with N-ethylcarbazole-3-formaldehyde, which is a useful fluorescent probe for monitoring extremely acidic and alkaline pH, quantitatively. The pH titrations indicate that Probe displays a remarkable emission enhancement with a pK a of 2.73 and responds linearly to minor pH fluctuations within the extremely acidic range of 2.21-3.30. Interestingly, Probe also exhibits strong pH-dependent characteristics with pK a 11.28 and linear response to extreme-alkalinity range of 10.41-12.43. In addition, Probe shows a large Stokes shift of 84 nm under extremely acidic and alkaline conditions, high selectivity, excellent sensitivity, good water-solubility and fine stability, all of which are favorable for intracellular pH imaging. The probe is further successfully applied to image extremely acidic and alkaline pH values fluctuations in E. coli cells. Copyright © 2017 Elsevier B.V. All rights reserved.

A novel fiber optic sensor for the measurement of pH of blood based on colorimetry

NASA Astrophysics Data System (ADS)

Chaudhari, A. L.; Patil, D. D.; Shaligram, Arvind D.

2005-04-01

Fiber optic sensors designed to the date are largely based on monitoring the absorption change of several immobilized indicators or change in fluorescence of fluorometric indicators. The present paper reports a new type of fiber optic sensor for the measurement of blood pH based on Colorimetric principle. The sensor consists of two multimode step index fibers, mirror as reflector and blood serum with universal indicator as medium. LED is used as source and photodiode as detector. The intensity of color produced due to addition of indicator to blood serum depends upon hydrogen ion concentration. The output intensity from receiving fiber is measured as a function of pH of blood. The developed sensor is calibrated against the standard pH meter. The design, construction and calibration details are presented in paper.

Investigation of the pH-dependence of dye-doped protein-protein interactions.

PubMed

Nudelman, Roman; Gloukhikh, Ekaterina; Rekun, Antonina; Richter, Shachar

2016-11-01

Proteins can dramatically change their conformation under environmental conditions such as temperature and pH. In this context, Glycoprotein's conformational determination is challenging. This is due to the variety of domains which contain rich chemical characters existing within this complex. Here we demonstrate a new, straightforward and efficient technique that uses the pH-dependent properties of dyes-doped Pig Gastric Mucin (PGM) for predicting and controlling protein-protein interaction and conformation. We utilize the PGM as natural host matrix which is capable of dynamically changing its conformational shape and adsorbing hydrophobic and hydrophilic dyes under different pH conditions and investigate and control the fluorescent properties of these composites in solution. It is shown at various pH conditions, a large variety of light emission from these complexes such as red, green and white is obtained. This phenomenon is explained by pH-dependent protein folding and protein-protein interactions that induce different emission spectra which are mediated and controlled by means of dye-dye interactions and surrounding environment. This process is used to form the technologically challenging white light-emitting liquid or solid coating for LED devices. © 2016 The Protein Society.

Fecal hydroxysteroid dehydrogenase activities in vegetarian Seventh-Day Adventists, control subjects, and bowel cancer patients.

PubMed

Macdonald, I A; Webb, G R; Mahony, D E

1978-10-01

Cell-free extracts were prepared from mixed fecal anaerobic bacteria grown from stools of 14 vegetarian Seventh-Day Adventists, 16 omnivorous control subjects, and eight patients recently diagnosed with cancer of the large bowel. Preparations were assayed for NAD- and NADP-dependent 3alpha-, 7alpha- and 12alpha-hydroxysteroid dehydrogenases with bile salts and androsterone as substrates (eight substrate-cofactor combinations were tested). A significant intergroup difference was observed in the amounts of NAD- and NADP-dependent 7alpha-hydroxysteroid dehydrogenase produced: bowel cancer patients exceeded controls, and controls exceeded Seventh-Day Adventists. Other enzyme activity comparisons were not significant. The pH values of the stools were significantly higher in cancer patients compared to Seventh-Day Adventists; values were 7.03 +/- 0.60 and 6.46 +/- 0.58 respectively. The pH value for controls was 6.66 +/- 0.62. A plot of pH value versus NADP-dependent 7alpha-hydroxysteroid dehydrogenase tended to separate the cancer patients from the other groups. Comparative data suggest that much of the 3alpha-hydroxysteroid dehydrogenase active against bile salt is also active against androsterone.

Analytical coupled-wave model for photonic crystal surface-emitting quantum cascade lasers.

PubMed

Wang, Zhixin; Liang, Yong; Yin, Xuefan; Peng, Chao; Hu, Weiwei; Faist, Jérôme

2017-05-15

An analytical coupled-wave model is developed for surface-emitting photonic-crystal quantum cascade lasers (PhC-QCLs). This model provides an accurate and efficient analysis of full three-dimensional device structure with large-area cavity size. Various laser properties of interest including the band structure, mode frequency, cavity loss, mode intensity profile, and far field pattern (FFP), as well as their dependence on PhC structures and cavity size, are investigated. Comparison with numerical simulations confirms the accuracy and validity of our model. The calculated FFP and polarization profile well explain the previously reported experimental results. In particular, we reveal the possibility of switching the lasing modes and generating single-lobed FFP by properly tuning PhC structures.

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.

Prediction of pH dependent absorption using in vitro, in silico, and in vivo rat models: Early liability assessment during lead optimization.

PubMed

Saxena, Ajay; Shah, Devang; Padmanabhan, Shweta; Gautam, Shashyendra Singh; Chowan, Gajendra Singh; Mandlekar, Sandhya; Desikan, Sridhar

2015-08-30

Weakly basic compounds which have pH dependent solubility are liable to exhibit pH dependent absorption. In some cases, a subtle change in gastric pH can significantly modulate the plasma concentration of the drug and can lead to sub-therapeutic exposure of the drug. Evaluating the risk of pH dependent absorption and potential drug-drug interaction with pH modulators are important aspects of drug discovery and development. In order to assess the risk around the extent of decrease in the systemic exposure of drugs co-administered with pH modulators in the clinic, a pH effect study is carried out, typically in higher species, mostly dog. The major limitation of a higher species pH effect study is the resource and material requirement to assess this risk. Hence, these studies are mostly restricted to promising or advanced leads. In our current work, we have used in vitro aqueous solubility, in silico simulations using GastroPlus™ and an in vivo rat pH effect model to provide a qualitative assessment of the pH dependent absorption liability. Here, we evaluate ketoconazole and atazanavir with different pH dependent solubility profiles and based on in vitro, in silico and in vivo results, a different extent of gastric pH effect on absorption is predicted. The prediction is in alignment with higher species and human pH effect study results. This in vitro, in silico and in vivo (IVISIV) correlation is then extended to assess pH absorption mitigation strategy. The IVISIV predicts pH dependent absorption for BMS-582949 whereas its solubility enhancing prodrug, BMS-751324 is predicted to mitigate this liability. Overall, the material requirement for this assessment is substantially low which makes this approach more practical to screen multiple compounds during lead optimization. Copyright © 2015 Elsevier B.V. All rights reserved.

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

Gu, Lina; He, Xiaomei; Wu, Zhenyu, E-mail: zhenyuwuhn@sina.com

Highlights: • Mesoporous Fe{sub 3}O{sub 4}/hydroxyapatite composite was synthesized by a simple, efficient and environmental friendly method. • The prepared material had a large surface area, high pore volume, and good magnetic separability. • DOX-loaded Fe{sub 3}O{sub 4}/hydroxyapatite composite exhibited surprising slow drug release behavior and pH-dependent behavior. - Abstract: In this contribution, we introduced a simple, efficient, and green method of preparing a mesoporous Fe{sub 3}O{sub 4}/hydroxyapatite (HA) composite. The as-prepared material had a large surface area, high pore volume, and good magnetic separability, which made it suitable for targeted drug delivery systems. The chemotherapeutic agent doxorubicin (DOX) wasmore » used to investigate the drug release behavior of Fe{sub 3}O{sub 4}/HA composite. The drug release profiles displayed a little burst effect and pH-dependent behavior. The release rate of DOX at pH 5.8 was larger than that at pH 7.4, which could be attributed to DOX protonation in acid medium. In addition, the released DOX concentrations remained at 0.83 and 1.39 μg/ml at pH 7.4 and 5.8, respectively, which indicated slow, steady, and safe release rates. Therefore, the as-prepared Fe{sub 3}O{sub 4}/hydroxyapatite composite could be an efficient platform for targeted anticancer drug delivery.« less

A petunia ethylene-responsive element binding factor, PhERF2, plays an important role in antiviral RNA silencing

USDA-ARS?s Scientific Manuscript database

Virus-induced gene silencing (VIGS) is a useful technique for functional characterization of plant genes. However, the silencing efficiency of the VIGS system is variable largely depending on compatibility between the host and the virus. Antiviral RNA silencing is involved in plant antiviral defense...

Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods

PubMed Central

Fulati, Alimujiang; Ali, Syed M.Usman; Riaz, Muhammad; Amin, Gul; Nur, Omer; Willander, Magnus

2009-01-01

ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells. PMID:22291545

Histidine168 is crucial for ΔpH-dependent gating of the human voltage-gated proton channel, hHV1.

PubMed

Cherny, Vladimir V; Morgan, Deri; Thomas, Sarah; Smith, Susan M E; DeCoursey, Thomas E

2018-05-09

We recently identified a voltage-gated proton channel gene in the snail Helisoma trivolvis , HtH V 1, and determined its electrophysiological properties. Consistent with early studies of proton currents in snail neurons, HtH V 1 opens rapidly, but it unexpectedly exhibits uniquely defective sensitivity to intracellular pH (pH i ). The H + conductance ( g H )- V relationship in the voltage-gated proton channel (H V 1) from other species shifts 40 mV when either pH i or pH o (extracellular pH) is changed by 1 unit. This property, called ΔpH-dependent gating, is crucial to the functions of H V 1 in many species and in numerous human tissues. The HtH V 1 channel exhibits normal pH o dependence but anomalously weak pH i dependence. In this study, we show that a single point mutation in human hH V 1-changing His 168 to Gln 168 , the corresponding residue in HtH V 1-compromises the pH i dependence of gating in the human channel so that it recapitulates the HtH V 1 response. This location was previously identified as a contributor to the rapid gating kinetics of H V 1 in Strongylocentrotus purpuratus His 168 mutation in human H V 1 accelerates activation but accounts for only a fraction of the species difference. H168Q, H168S, or H168T mutants exhibit normal pH o dependence, but changing pH i shifts the g H - V relationship on average by <20 mV/unit. Thus, His 168 is critical to pH i sensing in hH V 1. His 168 , located at the inner end of the pore on the S3 transmembrane helix, is the first residue identified in H V 1 that significantly impairs pH sensing when mutated. Because pH o dependence remains intact, the selective erosion of pH i dependence supports the idea that there are distinct internal and external pH sensors. Although His 168 may itself be a pH i sensor, the converse mutation, Q229H, does not normalize the pH i sensitivity of the HtH V 1 channel. We hypothesize that the imidazole group of His 168 interacts with nearby Phe 165 or other parts of hH V 1 to transduce pH i into shifts of voltage-dependent gating. © 2018 Cherny et al.

Aspartate-Histidine Interaction in the Retinal Schiff Base Counterion of the Light-Driven Proton Pump of Exiguobacterium sibiricum†

PubMed Central

Balashov, S.P.; Petrovskaya, L.E.; Lukashev, E.P.; Imasheva, E.S.; Dioumaev, A.K.; Wang, J.M.; Sychev, S.V.; Dolgikh, D.A.; Rubin, A.B.; Kirpichnikov, M.P.; Lanyi, J.K.

2012-01-01

One of the distinctive features of eubacterial retinal based proton pumps, proteorhodopsins, xanthorhodopsin and others, is hydrogen bonding of the key aspartate residue, the counterion to the retinal Schiff base, to a histidine. We describe properties of the recently found eubacterium proton pump from Exiguobacterium sibiricum (named ESR) expressed in E. coli, especially features that depend on Asp-His interaction, the protonation state of the key aspartate, Asp85, and its ability to accept proton from the Schiff base during the photocycle. Proton pumping by liposomes and E. coli cells containing ESR occurs in a broad pH range above pH 4.5. Large light-induced pH changes indicate that ESR is a potent proton pump. Replacement of His57 with methionine or asparagine strongly affects the pH dependent properties of ESR. In the H57M mutant a dramatic decrease in the quantum yield of chromophore fluorescence emission and a 45 nm blue shift of the absorption maximum upon raising the pH from 5 to 8 indicates deprotonation of the counterion with a pKa of 6.3, which is also the pKa at which the M intermediate is observed in the photocycle of the protein solubilized in detergent (DDM). This is in contrast with the wild type protein, in which the same experiments show that the major fraction of Asp85 is deprotonated at pH > 3 and that it protonates only at low pH, with a pKa of 2.3. The M intermediate in the wild type photocycle accumulates only at high pH, with an apparent pKa of 9 from deprotonation of a residue interacting with Asp85, presumably His57. In liposomes reconstituted with ESR the pKas for M formation and spectral shifts are 2–3 pH units lower than in DDM. The distinctively different pH dependencies of the protonation of Asp85 and the accumulation of the M intermediate in the wild type protein vs. the H57M mutant indicate that there is strong Asp-His interaction, which substantially lowers the pKa of Asp85 by stabilizing its deprotonated state. PMID:22738070

A histidine residue of the influenza virus hemagglutinin controls the pH dependence of the conformational change mediating membrane fusion.

PubMed

Mair, Caroline M; Meyer, Tim; Schneider, Katjana; Huang, Qiang; Veit, Michael; Herrmann, Andreas

2014-11-01

The conformational change of the influenza virus hemagglutinin (HA) protein mediating the fusion between the virus envelope and the endosomal membrane was hypothesized to be induced by protonation of specific histidine residues since their pKas match the pHs of late endosomes (pK(a) of ∼ 6.0). However, such critical key histidine residues remain to be identified. We investigated the highly conserved His184 at the HA1-HA1 interface and His110 at the HA1-HA2 interface of highly pathogenic H5N1 HA as potential pH sensors. By replacing both histidines with different amino acids and analyzing the effect of these mutations on conformational change and fusion, we found that His184, but not His110, plays an essential role in the pH dependence of the conformational change of HA. Computational modeling of the protonated His184 revealed that His184 is central in a conserved interaction network possibly regulating the pH dependence of conformational change via its pKa. As the propensity of histidine to get protonated largely depends on its local environment, mutation of residues in the vicinity of histidine may affect its pK(a). The HA of highly pathogenic H5N1 viruses carries a Glu-to-Arg mutation at position 216 close to His184. By mutation of residue 216 in the highly pathogenic as well as the low pathogenic H5 HA, we observed a significant influence on the pH dependence of conformational change and fusion. These results are in support of a pK(a)-modulating effect of neighboring residues. The main pathogenic determinant of influenza viruses, the hemagglutinin (HA) protein, triggers a key step of the infection process: the fusion of the virus envelope with the endosomal membrane releasing the viral genome. Whereas essential aspects of the fusion-inducing mechanism of HA at low pH are well understood, the molecular trigger of the pH-dependent conformational change inducing fusion has been unclear. We provide evidence that His184 regulates the pH dependence of the HA conformational change via its pK(a). Mutations of neighboring residues which may affect the pK(a) of His184 could play an important role in virus adaptation to a specific host. We suggest that mutation of neighboring residue 216, which is present in all highly pathogenic phenotypes of H5N1 influenza virus strains, contributed to the adaptation of these viruses to the human host via its effect on the pKa of His184. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

A petunia ethylene-responsive element binding factor, PhERF2, plays an important role in antiviral RNA silencing

PubMed Central

Sun, Daoyang; Nandety, Raja Sekhar; Zhang, Yanlong; Reid, Michael S.; Niu, Lixin; Jiang, Cai-Zhong

2016-01-01

Virus-induced RNA silencing is involved in plant antiviral defense and requires key enzyme components, including RNA-dependent RNA polymerases (RDRs), Dicer-like RNase III enzymes (DCLs), and Argonaute proteins (AGOs). However, the transcriptional regulation of these critical components is largely unknown. In petunia (Petunia hybrida), an ethylene-responsive element binding factor, PhERF2, is induced by Tobacco rattle virus (TRV) infection. Inclusion of a PhERF2 fragment in a TRV silencing construct containing reporter fragments of phytoene desaturase (PDS) or chalcone synthase (CHS) substantially impaired silencing efficiency of both the PDS and CHS reporters. Silencing was also impaired in PhERF2- RNAi lines, where TRV-PhPDS infection did not show the expected silencing phenotype (photobleaching). In contrast, photobleaching in response to infiltration with the TRV-PhPDS construct was enhanced in plants overexpressing PhERF2. Transcript abundance of the RNA silencing-related genes RDR2, RDR6, DCL2, and AGO2 was lower in PhERF2-silenced plants but higher in PhERF2-overexpressing plants. Moreover, PhERF2-silenced lines showed higher susceptibility to Cucumber mosaic virus (CMV) than wild-type (WT) plants, while plants overexpressing PhERF2 exhibited increased resistance. Interestingly, growth and development of PhERF2-RNAi lines were substantially slower, whereas the overexpressing lines were more vigorous than the controls. Taken together, our results indicate that PhERF2 functions as a positive regulator in antiviral RNA silencing. PMID:27099376

Balanced Electrostatic and Structural Forces Guide the Large Conformational Change Associated with Maturation of T = 4 Virus

PubMed Central

Matsui, Tsutomu; Tsuruta, Hiro; Johnson, John E.

2010-01-01

Nudaurelia capensis omega virus has a well-characterized T = 4 capsid that undergoes a pH-dependent large conformational changes (LCC) and associated auto-catalytic cleavage of the subunit. We examined previously the particle size at different pH values and showed that maturation occurred at pH 5.5. We now characterized the LCC with time-resolved small-angle x-ray scattering and showed that there were three kinetic stages initiated with an incremental drop in pH: 1), a rapid (<10 ms) collapse to an incrementally smaller particle; 2), a continuous size reduction over the next 5 s; and 3), a smaller final transition occurring in 2–3 min. Equilibrium measurements similar to those reported previously, but now more precise, showed that the particle dimension between pH 5.5 and 5 requires the autocatalytic cleavage to achieve its final compact size. A balance of electrostatic and structural forces shapes the energy landscape of the LCC with the latter requiring annealing of portions of the subunit. Equilibrium experiments showed that many intermediate states could be populated with a homogeneous ensemble of particles by carefully controlling the pH. A titration curve for the LCC was generated that showed that the virtual pKa (i.e., the composite of all titratable residues that contribute to the LCC) is 5.8. PMID:20371334

Validation of a triangular quantum well model for GaN-based HEMTs used in pH and dipole moment sensing

NASA Astrophysics Data System (ADS)

Rabbaa, S.; Stiens, J.

2012-11-01

Gallium nitride (GaN) is a relatively new semiconductor material that has the potential of replacing gallium arsenide (GaAs) in some of the more recent technological applications, for example chemical sensor applications. In this paper, we introduce a triangular quantum well model for an undoped AlGaN/GaN high electron mobility transistor (HEMT) structure used as a chemical and biological sensor for pH and dipole moment measurements of polar liquids. We have performed theoretical calculations related to the HEMT characteristics and we have compared them with experimental measurements carried out in many previous papers. These calculations include the current-voltage (I-V) characteristics of the device, the surface potential, the change in the drain current with the dipole moment and the drain current as a function of pH. The results exhibit good agreement with experimental measurements for different polar liquids and electrolyte solutions. It is also found that the drain current of the device exhibits a large linear variation with the dipole moment, and that the surface potential and the drain current depend strongly on the pH. Therefore, it can distinguish molecules with slightly different dipole moments and solutions with small variations in pH. The ability of the device to sense biomolecules (such as proteins) with very large dipole moments is investigated.

pH-dependent Differential Scanning Calorimetry and Dynamic Light Scattering Studies of 21:0 PC and 18:0 PS Lipid Binary System

NASA Astrophysics Data System (ADS)

Ali, Rejwan

2010-03-01

Large unilamallar vesicle has been a model system to study many membrane functions. High Tg lipid systems offer many potential biomedical applications in lipid-based delivery applications. While the optimized vesicle functionalities are achieved by Polyethylene Glycol (PEG) polymer, modified PEG and other functional molecule incorporation, however, the host binary lipid system plays the pivotal role in pH-dependent phase transition based lipid vehicular methods. We have investigated a lipid binary system composed of 21:0 PC (1,2-dihenarachidoyl-sn-glycero-3-phosphocholine) and 18:0 PS(1,2-distearoyl-sn-glycero-3-phospho-L-serine). Preliminary studies implementing differential scanning calorimetry shows pH plays key role in temperature shift and thermotropic phase behavior of the binary system. While dynamic light scattering study shows lipid vesicle size is almost independent of pH changes. We will also present pH-dependent thermodynamic parameters to correlate underlying molecular mechanism in relevant pH-range.

pH-Dependent Binding of Chloride to a Marine Alkaline Phosphatase Affects the Catalysis, Active Site Stability, and Dimer Equilibrium.

PubMed

Hjörleifsson, Jens G; Ásgeirsson, Bjarni

2017-09-26

The effect of ionic strength on enzyme activity and stability varies considerably between enzymes. Ionic strength is known to affect the catalytic activity of some alkaline phosphatases (APs), such as Escherichia coli AP, but how ions affect APs is debated. Here, we studied the effect of various ions on a cold-adapted AP from Vibrio splendidus (VAP). Previously, we have found that the active form of VAP is extremely unstable at low ionic strengths. Here we show that NaCl increased the activity and stability of VAP and that the effect was pH-dependent in the range of pH 7-10. The activity profile as a function of pH formed two maxima, indicating a possible conformational change. Bringing the pH from the neutral to the alkaline range was accompanied by a large increase in both the K i for inorganic phosphate (product inhibition) and the K M for p-nitrophenyl phosphate. The activity transitions observed as the pH was varied correlated with structural changes as monitored by tryptophan fluorescence. Thermal and urea-induced inactivation was shown to be accompanied by neither dissociation of the active site metal ions nor dimer dissociation. This would suggest that the inactivation involved subtle changes in active site conformation. Furthermore, the VAP dimer equilibrium was studied for the first time and shown to highly favor dimerization, which was dependent on pH and NaCl concentration. Taken together, the data support a model in which anions bind to some specific acceptor in the active site of VAP, resulting in great stabilization and catalytic rate enhancement, presumably through a different mechanism.

Effects of acidic pH on voltage-gated ion channels in rat trigeminal mesencephalic nucleus neurons.

PubMed

Han, Jin-Eon; Cho, Jin-Hwa; Choi, In-Sun; Kim, Do-Yeon; Jang, Il-Sung

2017-03-01

The effects of acidic pH on several voltage-dependent ion channels, such as voltage-dependent K + and Ca 2+ channels, and hyperpolarization-gated and cyclic nucleotide-activated cation (HCN) channels, were examined using a whole-cell patch clamp technique on mechanically isolated rat mesencephalic trigeminal nucleus neurons. The application of a pH 6.5 solution had no effect on the peak amplitude of voltage-dependent K + currents. A pH 6.0 solution slightly, but significantly inhibited the peak amplitude of voltage-dependent K + currents. The pH 6.0 also shifted both the current-voltage and conductance-voltage relationships to the depolarization range. The application of a pH 6.5 solution scarcely affected the peak amplitude of membrane currents mediated by HCN channels, which were profoundly inhibited by the general HCN channel blocker Cs + (1 mM). However, the pH 6.0 solution slightly, but significantly inhibited the peak amplitude of HCN-mediated currents. Although the pH 6.0 solution showed complex modulation of the current-voltage and conductance-voltage relationships, the midpoint voltages for the activation of HCN channels were not changed by acidic pH. On the other hand, voltage-dependent Ca 2+ channels were significantly inhibited by an acidic pH. The application of an acidic pH solution significantly shifted the current-voltage and conductance-voltage relationships to the depolarization range. The modulation of several voltage-dependent ion channels by an acidic pH might affect the excitability of mesencephalic trigeminal nucleus neurons, and thus physiological functions mediated by the mesencephalic trigeminal nucleus could be affected in acidic pH conditions.

Signaling alkaline pH stress in the yeast Saccharomyces cerevisiae through the Wsc1 cell surface sensor and the Slt2 MAPK pathway.

PubMed

Serrano, Raquel; Martín, Humberto; Casamayor, Antonio; Ariño, Joaquín

2006-12-29

Alkalinization of the external environment represents a stress situation for Saccharomyces cerevisiae. Adaptation to this circumstance involves the activation of diverse response mechanisms, the components of which are still largely unknown. We show here that mutation of members of the cell integrity Pkc1/Slt2 MAPK module, as well as upstream and downstream elements of the system, confers sensitivity to alkali. Alkalinization resulted in fast and transient activation of the Slt2 MAPK, which depended on the integrity of the kinase module and was largely abolished by sorbitol. Lack of Wsc1, removal of specific extracellular and intracellular domains, or substitution of Tyr(303) in this putative membrane stress sensor rendered cells sensitive to alkali and considerably decreased alkali-induced Slt2 activation. In contrast, constitutive activation of Slt2 by the bck1-20 allele increased pH tolerance in the wsc1 mutant. DNA microarray analysis revealed that several genes encoding cell wall proteins, such as GSC2/FKS2, DFG5, SKT5, and CRH1, were induced, at least in part, by high pH in an Slt2-dependent manner. We observed that dfg5, skt5, and particularly dfg5 skt5 cells were alkali-sensitive. Therefore, our results show that an alkaline environment imposes a stress condition on the yeast cell wall. We propose that the Slt2-mediated MAPK pathway plays an important role in the adaptive response to this insult and that Wsc1 participates as an essential cell-surface pH sensor. Moreover, these results provide a new example of the complexity of the response of budding yeast to the alkalinization of the environment.

An interfacial and comparative in vitro study of gastrointestinal lipases and Yarrowia lipolytica LIP2 lipase, a candidate for enzyme replacement therapy.

PubMed

Bénarouche, Anaïs; Point, Vanessa; Carrière, Frédéric; Cavalier, Jean-François

2014-07-01

Lipolytic activities of Yarrowia lipolytica LIP2 lipase (YLLIP2), human pancreatic (HPL) and dog gastric (DGL) lipases were first compared using lecithin-stabilized triacylglycerol (TAG) emulsions (Intralipid) at various pH and bile salt concentrations. Like DGL, YLLIP2 was able to hydrolyze TAG droplets covered by a lecithin monolayer, while HPL was not directly active on that substrate. These results were in good agreement with the respective kinetics of adsorption on phosphatidylcholine (PC) monomolecular films of the same three lipases, YLLIP2 being the most tensioactive lipase. YLLIP2 adsorption onto a PC monolayer spread at the air/water interface was influenced by pH-dependent changes in the enzyme/lipid interfacial association constant (KAds) which was optimum at pH 6.0 on long-chain egg PC monolayer, and at pH 5.0 on medium chain dilauroylphosphatidylcholine film. Using substrate monolayers (1,2-dicaprin, trioctanoin), YLLIP2 displayed the highest lipolytic activities on both substrates in the 25-35 mN m(-1) surface pressure range. YLLIP2 was active in a large pH range and displayed a pH-dependent activity profile combining DGL and HPL features at pH values found in the stomach (pH 3-5) and in the intestine (pH 6-7), respectively. The apparent maximum activity of YLLIP2 was observed at acidic pH 4-6 and was therefore well correlated with an efficient interfacial binding at these pH levels, whatever the type of interfaces (Intralipid emulsions, substrate or PC monolayers). All these findings support the use of YLLIP2 in enzyme replacement therapy for the treatment of pancreatic exocrine insufficiency, a pathological situation in which an acidification of intestinal contents occurs. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

Temporal differentiation of pH-dependent capacitive current from dopamine.

PubMed

Yoshimi, Kenji; Weitemier, Adam

2014-09-02

Voltammetric recording of dopamine (DA) with fast-scan cyclic voltammetry (FSCV) on carbon fiber microelectrodes have been widely used, because of its high sensitivity to dopamine. However, since an electric double layer on a carbon fiber surface in a physiological ionic solution behaves as a capacitor, fast voltage manipulation in FSCV induces large capacitive current. The faradic current from oxidation/reduction of target chemicals must be extracted from this large background current. It is known that ionic shifts, including H(+), influence this capacitance, and pH shift can cause confounding influences on the FSCV recordings within a wide range of voltage. Besides FSCV with a triangular waveform, we have been using rectangular pulse voltammetry (RPV) for dopamine detection in the brain. In this method, the onset of a single pulse causes a large capacitive current, but unlike FSCV, the capacitive current is restricted to a narrow temporal window of just after pulse onset (<5 ms). In contrast, the peak of faradic current from dopamine oxidation occurs after a delay of more than a few milliseconds. Taking advantage of the temporal difference, we show that RPV could distinguish dopamine from pH shifts clearly and easily. In addition, the early onset current was useful to evaluate pH shifts. The narrow voltage window of our RPV pulse allowed a clear differentiation of dopamine and serotonin (5-HT), as we have shown previously. Additional recording with RPV, alongside FSCV, would improve identification of chemicals such as dopamine, pH, and 5-HT.

Finite-size effects in the short-time height distribution of the Kardar-Parisi-Zhang equation

NASA Astrophysics Data System (ADS)

Smith, Naftali R.; Meerson, Baruch; Sasorov, Pavel

2018-02-01

We use the optimal fluctuation method to evaluate the short-time probability distribution P(H, L, t) of height at a single point, H=h(x=0, t) , of the evolving Kardar-Parisi-Zhang (KPZ) interface h(x, t) on a ring of length 2L. The process starts from a flat interface. At short times typical (small) height fluctuations are unaffected by the KPZ nonlinearity and belong to the Edwards-Wilkinson universality class. The nonlinearity, however, strongly affects the (asymmetric) tails of P(H) . At large L/\\sqrt{t} the faster-decaying tail has a double structure: it is L-independent, -\\lnP˜≤ft\\vert H\\right\\vert 5/2/t1/2 , at intermediately large \\vert H\\vert , and L-dependent, -\\lnP˜ ≤ft\\vert H\\right\\vert 2L/t , at very large \\vert H\\vert . The transition between these two regimes is sharp and, in the large L/\\sqrt{t} limit, behaves as a fractional-order phase transition. The transition point H=Hc+ depends on L/\\sqrt{t} . At small L/\\sqrt{t} , the double structure of the faster tail disappears, and only the very large-H tail, -\\lnP˜ ≤ft\\vert H\\right\\vert 2L/t , is observed. The slower-decaying tail does not show any L-dependence at large L/\\sqrt{t} , where it coincides with the slower tail of the GOE Tracy-Widom distribution. At small L/\\sqrt{t} this tail also has a double structure. The transition between the two regimes occurs at a value of height H=Hc- which depends on L/\\sqrt{t} . At L/\\sqrt{t} \\to 0 the transition behaves as a mean-field-like second-order phase transition. At \\vert H\\vert <\\vert H_c-\\vert the slower tail behaves as -\\lnP˜ ≤ft\\vert H\\right\\vert 2L/t , whereas at \\vert H\\vert >\\vert H_c-\\vert it coincides with the slower tail of the GOE Tracy-Widom distribution.

Exotic properties of a voltage-gated proton channel from the snail Helisoma trivolvis.

PubMed

Thomas, Sarah; Cherny, Vladimir V; Morgan, Deri; Artinian, Liana R; Rehder, Vincent; Smith, Susan M E; DeCoursey, Thomas E

2018-06-04

Voltage-gated proton channels, H V 1, were first reported in Helix aspersa snail neurons. These H + channels open very rapidly, two to three orders of magnitude faster than mammalian H V 1. Here we identify an H V 1 gene in the snail Helisoma trivolvis and verify protein level expression by Western blotting of H. trivolvis brain lysate. Expressed in mammalian cells, HtH V 1 currents in most respects resemble those described in other snails, including rapid activation, 476 times faster than hH V 1 (human) at pH o 7, between 50 and 90 mV. In contrast to most H V 1, activation of HtH V 1 is exponential, suggesting first-order kinetics. However, the large gating charge of ∼5.5 e 0 suggests that HtH V 1 functions as a dimer, evidently with highly cooperative gating. HtH V 1 opening is exquisitely sensitive to pH o , whereas closing is nearly independent of pH o Zn 2+ and Cd 2+ inhibit HtH V 1 currents in the micromolar range, slowing activation, shifting the proton conductance-voltage ( g H - V ) relationship to more positive potentials, and lowering the maximum conductance. This is consistent with HtH V 1 possessing three of the four amino acids that coordinate Zn 2+ in mammalian H V 1. All known H V 1 exhibit ΔpH-dependent gating that results in a 40-mV shift of the g H - V relationship for a unit change in either pH o or pH i This property is crucial for all the functions of H V 1 in many species and numerous human cells. The HtH V 1 channel exhibits normal or supernormal pH o dependence, but weak pH i dependence. Under favorable conditions, this might result in the HtH V 1 channel conducting inward currents and perhaps mediating a proton action potential. The anomalous ΔpH-dependent gating of HtH V 1 channels suggests a structural basis for this important property, which is further explored in this issue (Cherny et al. 2018. J. Gen. Physiol. https://doi.org/10.1085/jgp.201711968). © 2018 Thomas et al.

Surface Charge Development on Transition Metal Sulfides: An Electrokinetic Study

NASA Astrophysics Data System (ADS)

Bebie, Joakim; Schoonen, Martin A. A.; Fuhrmann, Mark; Strongin, Daniel R.

1998-02-01

The isoelectric points, pH i.e.p., of ZnS, PbS, CuFeS 2, FeS, FeS 2, NiS 2, CoS 2, and MnS 2 in NaCl supported electrolyte solutions are estimated to be between pH 3.3 and 0.6, with most of the isoelectric points below pH 2. The first electrokinetic measurements on NiS 2, CoS 2, and MnS 2 are reported here. Below pH i.e.p. the metal-sulfide surfaces are positively charged, above pH i.e.p. the surfaces are negatively charged. The addition of Me 2+ ions shifts the pH i.e.p. and changes the pH dependence considerably. The isoelectric points of the measured transition metal sulfides in the absence of metal ions or dissolved sulfide (H 2S or HS -) are in agreement with those found in earlier studies. The pH range of observed isoelectric points for metal sulfides (0.6-3.3) is compared to the considerably wider pH i.e.p. range (2-12) found for oxides. The correlation between pH i.e.p. and the electronegativities of the metal sulfides suggests that all metal sulfides will have an isoelectric point between pH 0.6 and 3.3. Compared to metal oxides, sulfides exhibit an isoelectric point that is largely independent of the nature of the metal cation in the solid.

pH-dependent and pH-independent self-assembling behavior of surfactant-like peptides

NASA Astrophysics Data System (ADS)

Gurevich, Leonid; Fojan, Peter

2012-02-01

Self-assembly of amphiphilic peptides designed during the last years by several research groups leads to a large variety of 3D-structures that already found applications in stabilization of large protein complexes, cell culturing systems etc. In this report, we present synthesis and characterization of two novel families of amphiphilic peptides KAn and KAnW (n=6,5,4) that exhibits clear charge separation controllable by pH of the environment. As the pH changes from acidic to basic, the charge on the ends of the peptide molecule varies eventually leading to reorganization of KAn micelles and even micellar inversion. On contrary, the bulky geometry of the tryptophan residue in KAnW limits the variation of the surfactant parameter and hence largely prevents assembly into spherical or cylindrical micelles while favouring flatter geometries. The studied short peptide families demonstrate formation of ordered aggregates with well-defined secondary structure from short unstructured peptides and provide a simple system where factors responsible for self-assembly can be singled out and studied one by one. The ability to control the shape and structure of peptide aggregates can provide basis for novel designer pH sensitive materials including drug delivery and controlled release systems.

Detection of Supernova Neutrinos on the Earth for Large θ13

NASA Astrophysics Data System (ADS)

Xu, Jing; Huang, Ming-Yang; Hu, Li-Jun; Guo, Xin-Heng; Young, Bing-Lin

2014-02-01

Supernova (SN) neutrinos detected on the Earth are subject to the shock wave effects, the Mikheyev—Smirnov—Wolfenstein (MSW) effects, the neutrino collective effects and the Earth matter effects. Considering the recent experimental result about the large mixing angle θ13 (≃ 8.8°) provided by the Daya Bay Collaboration and applying the available knowledge for the neutrino conversion probability in the high resonance region of SN, PH, which is in the form of hypergeometric function in the case of large θ13, we deduce the expression of PH taking into account the shock wave effects. It is found that PH is not zero in a certain range of time due to the shock wave effects. After considering all the four physical effects and scanning relevant parameters, we calculate the event numbers of SN neutrinos for the “Garching” distribution of neutrino energy spectrum. From the numerical results, it is found that the behaviors of neutrino event numbers detected on the Earth depend on the neutrino mass hierarchy and neutrino spectrum parameters including the dimensionless pinching parameter βα (where α refers to neutrino flavor), the average energy , and the SN neutrino luminosities Lα. Finally, we give the ranges of SN neutrino event numbers that will be detected at the Daya Bay experiment.

The pH dependence of the cathodic peak potential of the active sites in bilirubin oxidase.

PubMed

Filip, Jaroslav; Tkac, Jan

2014-04-01

This is the first study showing pH dependence of three distinct redox sites within bilirubin oxidase (BOD) adsorbed on a nanocomposite modified electrode. The 1st redox centre with the highest redox potential Ec(1st)=404 mV vs. Ag/AgCl (614 mV vs. NHE at pH7.0) exhibited pH dependence with a slope -dEc(1st)/dpH=66(±3) mV under a non-turnover process. The 2nd redox centre with a potential Ec(2nd)=228 mV vs. Ag/AgCl (438 mV vs. NHE at pH7.0) was not dependent on pH in the absence and presence of O2. Finally, the 3rd redox site with a redox potential Ec(3rd)=92 mV vs. Ag/AgCl (302 mV vs. NHE at pH7.0) exhibited pH dependence for a cathodic process with -dEc(3rd)/dpH=70(±6) mV and for anodic process with -dEa(3rd)/dpH=73(±2) mV, respectively. Moreover, two break points for dependence of Ec(1st) or Ec(3rd) on pH were observed for the 1st (T1) site and the 3rd site assigned to involvement of two acidic amino acids (Asp105 and Glu463). A diagram of a potential difference between cathodic peaks of BOD as a dependence on pH is shown. The results obtained can be of interest for construction of biofuel cells based on BOD such as for generation of a low level of electricity from body fluids. Copyright © 2013 Elsevier B.V. All rights reserved.

Coral calcification in a changing World and the interactive dynamics of pH and DIC upregulation.

PubMed

McCulloch, Malcolm T; D'Olivo, Juan Pablo; Falter, James; Holcomb, Michael; Trotter, Julie A

2017-05-30

Coral calcification is dependent on the mutualistic partnership between endosymbiotic zooxanthellae and the coral host. Here, using newly developed geochemical proxies (δ 11 B and B/Ca), we show that Porites corals from natural reef environments exhibit a close (r 2 ∼0.9) antithetic relationship between dissolved inorganic carbon (DIC) and pH of the corals' calcifying fluid (cf). The highest DIC cf (∼ × 3.2 seawater) is found during summer, consistent with thermal/light enhancement of metabolically (zooxanthellae) derived carbon, while the highest pH cf (∼8.5) occurs in winter during periods of low DIC cf (∼ × 2 seawater). These opposing changes in DIC cf and pH cf are shown to maintain oversaturated but stable levels of carbonate saturation (Ω cf ∼ × 5 seawater), the key parameter controlling coral calcification. These findings are in marked contrast to artificial experiments and show that pH cf upregulation occurs largely independent of changes in seawater carbonate chemistry, and hence ocean acidification, but is highly vulnerable to thermally induced stress from global warming.

A petunia ethylene-responsive element binding factor, PhERF2, plays an important role in antiviral RNA silencing.

PubMed

Sun, Daoyang; Nandety, Raja Sekhar; Zhang, Yanlong; Reid, Michael S; Niu, Lixin; Jiang, Cai-Zhong

2016-05-01

Virus-induced RNA silencing is involved in plant antiviral defense and requires key enzyme components, including RNA-dependent RNA polymerases (RDRs), Dicer-like RNase III enzymes (DCLs), and Argonaute proteins (AGOs). However, the transcriptional regulation of these critical components is largely unknown. In petunia (Petunia hybrida), an ethylene-responsive element binding factor, PhERF2, is induced by Tobacco rattle virus (TRV) infection. Inclusion of a PhERF2 fragment in a TRV silencing construct containing reporter fragments of phytoene desaturase (PDS) or chalcone synthase (CHS) substantially impaired silencing efficiency of both the PDS and CHS reporters. Silencing was also impaired in PhERF2- RNAi lines, where TRV-PhPDS infection did not show the expected silencing phenotype (photobleaching). In contrast, photobleaching in response to infiltration with the TRV-PhPDS construct was enhanced in plants overexpressing PhERF2 Transcript abundance of the RNA silencing-related genes RDR2, RDR6, DCL2, and AGO2 was lower in PhERF2-silenced plants but higher in PhERF2-overexpressing plants. Moreover, PhERF2-silenced lines showed higher susceptibility to Cucumber mosaic virus (CMV) than wild-type (WT) plants, while plants overexpressing PhERF2 exhibited increased resistance. Interestingly, growth and development of PhERF2-RNAi lines were substantially slower, whereas the overexpressing lines were more vigorous than the controls. Taken together, our results indicate that PhERF2 functions as a positive regulator in antiviral RNA silencing. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.

A gain-of-function mutation of plastidic invertase alters nuclear gene expression with sucrose treatment partially via GENOMES UNCOUPLED1-mediated signaling.

PubMed

Maruta, Takanori; Miyazaki, Nozomi; Nosaka, Ryota; Tanaka, Hiroyuki; Padilla-Chacon, Daniel; Otori, Kumi; Kimura, Ayako; Tanabe, Noriaki; Yoshimura, Kazuya; Tamoi, Masahiro; Shigeoka, Shigeru

2015-05-01

Plastid gene expression (PGE) is one of the signals that regulate the expression of photosynthesis-associated nuclear genes (PhANGs) via GENOMES UNCOUPLED1 (GUN1)-dependent retrograde signaling. We recently isolated Arabidopsis sugar-inducible cotyledon yellow-192 (sicy-192), a gain-of-function mutant of plastidic invertase, and showed that following the treatment of this mutant with sucrose, the expression of PhANGs as well as PGE decreased, suggesting that the sicy-192 mutation activates a PGE-evoked and GUN1-mediated retrograde pathway. To clarify the relationship between the sicy-192 mutation, PGE, and GUN1-mediated pathway, plastid and nuclear gene expression in a double mutant of sicy-192 and gun1-101, a null mutant of GUN1 was studied. Plastid-encoded RNA polymerase (PEP)-dependent PGE was markedly suppressed in the sicy-192 mutant by the sucrose treatment, but the suppression as well as cotyledon yellow phenotype was not mitigated by GUN1 disruption. Microarray analysis revealed that the altered expression of nuclear genes such as PhANG in the sucrose-treated sicy-192 mutant was largely dependent on GUN1. The present findings demonstrated that the sicy-192 mutation alters nuclear gene expression with sucrose treatment via GUN1, which is possibly followed by inhibiting PEP-dependent PGE, providing a new insight into the role of plastid sugar metabolism in nuclear gene expression. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Constant pH Molecular Dynamics of Proteins in Explicit Solvent with Proton Tautomerism

PubMed Central

Goh, Garrett B.; Hulbert, Benjamin S.; Zhou, Huiqing; Brooks, Charles L.

2015-01-01

pH is a ubiquitous regulator of biological activity, including protein-folding, protein-protein interactions and enzymatic activity. Existing constant pH molecular dynamics (CPHMD) models that were developed to address questions related to the pH-dependent properties of proteins are largely based on implicit solvent models. However, implicit solvent models are known to underestimate the desolvation energy of buried charged residues, increasing the error associated with predictions that involve internal ionizable residue that are important in processes like hydrogen transport and electron transfer. Furthermore, discrete water and ions cannot be modeled in implicit solvent, which are important in systems like membrane proteins and ion channels. We report on an explicit solvent constant pH molecular dynamics framework based on multi-site λ-dynamics (CPHMDMSλD). In the CPHMDMSλD framework, we performed seamless alchemical transitions between protonation and tautomeric states using multi-site λ-dynamics, and designed novel biasing potentials to ensure that the physical end-states are predominantly sampled. We show that explicit solvent CPHMDMSλD simulations model realistic pH-dependent properties of proteins such as the Hen-Egg White Lysozyme (HEWL), binding domain of 2-oxoglutarate dehydrogenase (BBL) and N-terminal domain of ribosomal L9 (NTL9), and the pKa predictions are in excellent agreement with experimental values, with a RMSE ranging from 0.72 to 0.84 pKa units. With the recent development of the explicit solvent CPHMDMSλD framework for nucleic acids, accurate modeling of pH-dependent properties of both major class of biomolecules – proteins and nucleic acids is now possible. PMID:24375620

Four base recognition by triplex-forming oligonucleotides at physiological pH

PubMed Central

Rusling, David A.; Powers, Vicki E. C.; Ranasinghe, Rohan T.; Wang, Yang; Osborne, Sadie D.; Brown, Tom; Fox, Keith R.

2005-01-01

We have achieved recognition of all 4 bp by triple helix formation at physiological pH, using triplex-forming oligonucleotides that contain four different synthetic nucleotides. BAU [2′-aminoethoxy-5-(3-aminoprop-1-ynyl)uridine] recognizes AT base pairs with high affinity, MeP (3-methyl-2 aminopyridine) binds to GC at higher pHs than cytosine, while APP (6-(3-aminopropyl)-7-methyl-3H-pyrrolo[2,3-d]pyrimidin-2(7H)-one) and S [N-(4-(3-acetamidophenyl)thiazol-2-yl-acetamide)] bind to CG and TA base pairs, respectively. Fluorescence melting and DNase I footprinting demonstrate successful triplex formation at a 19mer oligopurine sequence that contains two CG and two TA interruptions. The complexes are pH dependent, but are still stable at pH 7.0. BAU, MeP and APP retain considerable selectivity, and single base pair changes opposite these residues cause a large reduction in affinity. In contrast, S is less selective and tolerates CG pairs as well as TA. PMID:15911633

Anaerobic hydrogen production from unhydrolyzed mushroom farm waste by indigenous microbiota.

PubMed

Lin, Chiu-Yue; Lay, Chyi-How; Sung, I-Yuan; Sen, Biswarup; Chen, Chin-Chao

2017-10-01

The cultivation of mushrooms generates large amounts of waste polypropylene bags stuffed with wood flour and bacterial nutrients that makes the mushroom waste (MW) a potential feedstock for anaerobic bioH 2 fermentation. MW indigenous bacteria were enriched using thermophilic temperature (55°C) for use as the seed inoculum without any external seeding. The peak hydrogen production rate (6.84 mmol H 2 /L-d) was obtained with cultivation pH 8 and substrate concentration of 60 g MW/L in batch fermentation. Hydrogen production yield (HY) is pH and substrate concentration dependent with an HY decline occurring at pH and substrate concentration increasing from pH 8 to 10 and 60 to 80 g MW/L, respectively. The fermentation bioH 2 production from MW is in an acetate-type metabolic path. Copyright © 2017 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

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.

LHCSR1 induces a fast and reversible pH-dependent fluorescence quenching in LHCII in Chlamydomonas reinhardtii cells.

PubMed

Dinc, Emine; Tian, Lijin; Roy, Laura M; Roth, Robyn; Goodenough, Ursula; Croce, Roberta

2016-07-05

To avoid photodamage, photosynthetic organisms are able to thermally dissipate the energy absorbed in excess in a process known as nonphotochemical quenching (NPQ). Although NPQ has been studied extensively, the major players and the mechanism of quenching remain debated. This is a result of the difficulty in extracting molecular information from in vivo experiments and the absence of a validation system for in vitro experiments. Here, we have created a minimal cell of the green alga Chlamydomonas reinhardtii that is able to undergo NPQ. We show that LHCII, the main light harvesting complex of algae, cannot switch to a quenched conformation in response to pH changes by itself. Instead, a small amount of the protein LHCSR1 (light-harvesting complex stress related 1) is able to induce a large, fast, and reversible pH-dependent quenching in an LHCII-containing membrane. These results strongly suggest that LHCSR1 acts as pH sensor and that it modulates the excited state lifetimes of a large array of LHCII, also explaining the NPQ observed in the LHCSR3-less mutant. The possible quenching mechanisms are discussed.

Coordinated regulation of intracellular pH by two glucose-sensing pathways in yeast.

PubMed

Isom, Daniel G; Page, Stephani C; Collins, Leonard B; Kapolka, Nicholas J; Taghon, Geoffrey J; Dohlman, Henrik G

2018-02-16

The yeast Saccharomyces cerevisiae employs multiple pathways to coordinate sugar availability and metabolism. Glucose and other sugars are detected by a G protein-coupled receptor, Gpr1, as well as a pair of transporter-like proteins, Rgt2 and Snf3. When glucose is limiting, however, an ATP-driven proton pump (Pma1) is inactivated, leading to a marked decrease in cytoplasmic pH. Here we determine the relative contribution of the two sugar-sensing pathways to pH regulation. Whereas cytoplasmic pH is strongly dependent on glucose abundance and is regulated by both glucose-sensing pathways, ATP is largely unaffected and therefore cannot account for the changes in Pma1 activity. These data suggest that the pH is a second messenger of the glucose-sensing pathways. We show further that different sugars differ in their ability to control cellular acidification, in the manner of inverse agonists. We conclude that the sugar-sensing pathways act via Pma1 to invoke coordinated changes in cellular pH and metabolism. More broadly, our findings support the emerging view that cellular systems have evolved the use of pH signals as a means of adapting to environmental stresses such as those caused by hypoxia, ischemia, and diabetes. © 2018 by The American Society for Biochemistry and Molecular Biology, Inc.

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.

Facile Syntheses of Monodisperse Ultra-Small Au Clusters

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

Bertino, Massimo F.; Sun, Zhong-Ming; Zhang, Rui

2006-11-02

During our effort to synthesize the tetrahedral Au20 cluster, we found a facile synthetic route to prepare monodisperse suspensions of ultra-small Au clusters AuN (N<12) using diphosphine ligands. In our monophasic and single-pot synthesis, a Au precursor ClAu(I)PPh3 and a bidentate phosphine ligand P(Ph)2(CH2)MP(Ph)2 (Ph = phenyl) are dissolved in an organic solvent. Au(I) is reduced slowly by a borane-tert-butylamine complex to form Au clusters coordinated by the diphosphine ligand. The Au clusters are characterized by both high resolution mass spectrometry and UV-Vis absorption spectroscopy. We found that the mean cluster size obtained depends on the chain length M ofmore » the ligand. In particular, a single monodispersed Au11 cluster is obtained with the P(Ph)2(CH2)3P(Ph)2 ligand, whereas P(Ph)2(CH2)MP(Ph)2 ligands with M = 5 and 6 yield Au10 and Au8 clusters. The simplicity of our synthetic method makes it suitable for large-scale production of nearly monodisperse ultrasmall Au clusters. It is suggested that diphosphines provide a set of flexible ligands to allow size-controlled synthesis of Au nanoparticles.« less

Genetic and maternal effect influences on viability of common frog tadpoles under different environmental conditions.

PubMed

Pakkasmaa, S; Merilä, J; O'Hara, R B

2003-08-01

The influence of environmental stress on the expression of genetic and maternal effects on the viability traits has seldom been assessed in wild vertebrates. We have estimated genetic and maternal effects on the viability (viz probability of survival, probability of being deformed, and body size and shape) of common frog, Rana temporaria, tadpoles under stressful (low pH) and nonstressful (neutral pH) environmental conditions. A Bayesian analysis using generalized linear mixed models was applied to data from a factorial laboratory experiment. The expression of additive genetic variance was independent of pH treatments, and all traits were significantly heritable (survival: h2 approximately 0.08; deformities: h2 approximately 0.26; body size: h2 approximately 0.12; body shape: h2 approximately 0.14). Likewise, nonadditive genetic contributions to variation in all traits were significant, independent of pH treatments and typically of magnitude similar to the additive genetic effects. Maternal effects were large for all traits, especially for viability itself, and their expression was partly dependent on the environment. In the case of body size, the maternal effects were mediated largely through egg size. In general, the results give little evidence for the conjecture that environmental stress created by low pH would impact strongly on the genetic architecture of fitness-related traits in frogs, and hamper adaptation to stress caused by acidification. The low heritabilities and high dominance contributions conform to the pattern typical for traits subject to relatively strong directional selection.

Analysis of chemical equilibrium of silicon-substituted fluorescein and its application to develop a scaffold for red fluorescent probes.

PubMed

Hirabayashi, Kazuhisa; Hanaoka, Kenjiro; Takayanagi, Toshio; Toki, Yuko; Egawa, Takahiro; Kamiya, Mako; Komatsu, Toru; Ueno, Tasuku; Terai, Takuya; Yoshida, Kengo; Uchiyama, Masanobu; Nagano, Tetsuo; Urano, Yasuteru

2015-09-01

Fluorescein is a representative green fluorophore that has been widely used as a scaffold of practically useful green fluorescent probes. Here, we report synthesis and characterization of a silicon-substituted fluorescein, i.e., 2-COOH TokyoMagenta (2-COOH TM), which is a fluorescein analogue in which the O atom at the 10' position of the xanthene moiety of fluorescein is replaced with a Si atom. This fluorescein analogue forms a spirolactone ring via intramolecular nucleophilic attack of the carboxylic group in a pH-dependent manner. Consequently, 2-COOH TM exhibits characteristic large pH-dependent absorption and fluorescence spectral changes: (1) 2-COOH TM is colorless at acidic pH, whereas fluorescein retains observable absorption and fluorescence even at acidic pH, and the absorption maximum is also shifted; (2) the absorption spectral change occurs above pH 7.0 for 2-COOH TM and below pH 7.0 for fluorescein; (3) 2-COOH TM shows a much sharper pH response than fluorescein because of its pKa inversion, i.e., pKa1 > pKa2. These features are also different from those of a compound without the carboxylic group, 2-Me TokyoMagenta (2-Me TM). Analysis of the chemical equilibrium between pH 3.0 and 11.0 disclosed that 2-COOH TM favors the colorless and nonfluorescent lactone form, compared with fluorescein. Substitution of Cl atoms at the 4' and 5' positions of the xanthene moiety of 2-COOH TM to obtain 2-COOH DCTM shifted the equilibrium so that the new derivative exists predominantly in the strongly fluorescent open form at physiological pH (pH 7.4). To demonstrate the practical utility of 2-COOH DCTM as a novel scaffold for red fluorescent probes, we employed it to develop a probe for β-galactosidase.

Ab initio calculation of potential energy surfaces for the three lowest triplet states (1 3A'',1 3A,2 3A'') of PH(X,A)-He

NASA Astrophysics Data System (ADS)

Kolczewski, Ch.; Fink, K.; Staemmler, V.; Neitsch, L.

1997-05-01

Quantum chemical ab initio calculations at the complete active space SCF level and with inclusion of correlation effects have been performed for the potential energy surfaces of PH in its X 3Σ- ground state and its first excited triplet state, A 3Π, colliding with He atoms. The PH distance was fixed at its experimental value (of the A 3Π state), the PH-He distance and the HePH angle were varied. All three potential energy surfaces [1 3A'' for PH(X)-He and 1 3A,2 3A'' for the two components of PH(A)-He] are purely repulsive, except for very shallow van der Waals minima with well depths of about 15-40 cm-1. The interaction potentials decay approximately exponentially with increasing PH-He distance and show large angular anisotropies. Legendre expansions for the angular dependence of the potential surfaces converge slowly for V(1 3A'') and the sum potential 1/2[V(2 3A'')+V(1 3A)], but rapidly for the corresponding difference potential 1/2[V(2 3A'')-V(1 3A)]. The present PH(A)-He potentials have been used in the companion paper by Neitsch et al. [J. Chem. Phys. 106, 7642 (1997)], for the calculation of thermal state-to-state rate constants for inelastic PH(A)-He collisions.

pH Dependent Spin State Population and 19F NMR Chemical Shift via Remote Ligand Protonation in an Iron(II) Complex (Postprint)

DTIC Science & Technology

2017-12-11

AFRL-RX-WP-JA-2017-0501 pH- DEPENDENT SPIN STATE POPULATION AND 19F NMR CHEMICAL SHIFT VIA REMOTE LIGAND PROTONATION IN AN IRON(II...From - To) 16 November 2017 Interim 24 January 2014 – 16 October 2017 4. TITLE AND SUBTITLE PH- DEPENDENT SPIN STATE POPULATION AND 19F NMR CHEMICAL...dx.doi.org/10.1039/C7CC08099A 14. ABSTRACT (Maximum 200 words) An FeII complex that features a pH- dependent spin state population, by virtue of a

Indomethacin-Kollidon VA64 Extrudates: A Mechanistic Study of pH-Dependent Controlled Release.

PubMed

Tres, Francesco; Treacher, Kevin; Booth, Jonathan; Hughes, Leslie P; Wren, Stephen A C; Aylott, Jonathan W; Burley, Jonathan C

2016-03-07

Because of its weakly acidic nature (pKa of 4.5), indomethacin presents an aqueous solubility that significantly increases when changing from acidic to neutral/alkaline pH (1.5 μg/mL at pH 1.2 and 105.2 μg/mL at pH 7.4). We have therefore investigated the impact of the dissolution medium pH on the dissolution performance of indomethacin:Kollidon VA64 extrudates. The impact of the drug loading on the dissolution properties of these systems was also examined (5%, 15%, 30%, 50%, 70%, and 90% drug loading). Time-resolved Raman spectroscopy along with in-line UV-vis spectrophotometry was employed to directly relate changes in dissolution behavior to physicochemical changes that occur to the extrudate during the test. The dissolution tests were performed in pH 2 HCl (to mimic the stomach conditions), and this was then switched during the experiment to pH 6.8 phosphate buffer (to simulate the poststomach conditions). The rotating disc dissolution rate test was also used to simultaneously measure the dissolution rate of both the drug and the polymer. We found that in pH 2 HCl buffer, for the 15% or higher drug-loaded extrudates, Kollidon VA64 preferentially dissolves from the exterior of the compact leaving an amorphous drug-rich hydrophobic shell, which, similarly to an enteric coating, inhibits the drug release. The in situ formation of an enteric coating has been previously hypothesized, and this has been the first time that is directly observed in a pH-variable dissolution test. The dissolution medium switch to pH 6.8 phosphate buffer, due to the large increase of the aqueous solubility of indomethacin at this pH, leads to rapid dissolution of the material forming the coating and therefore total drug release. In contrast, the 5% extrudate is fully hydrated and quickly dissolves at low pH pointing to a dissolution performance dependent on highly water-soluble Kollidon VA64.

Characterization of glutamate decarboxylase from Lactobacillus plantarum and its C-terminal function for the pH dependence of activity.

PubMed

Shin, Sun-Mi; Kim, Hana; Joo, Yunhye; Lee, Sang-Jae; Lee, Yong-Jik; Lee, Sang Jun; Lee, Dong-Woo

2014-12-17

The gadB gene encoding glutamate decarboxylase (GAD) from Lactobacillus plantarum was cloned and expressed in Escherichia coli. The recombinant enzyme exhibited maximal activity at 40 °C and pH 5.0. The 3D model structure of L. plantarum GAD proposed that its C-terminal region (Ile454-Thr468) may play an important role in the pH dependence of catalysis. Accordingly, C-terminally truncated (Δ3 and Δ11 residues) mutants were generated and their enzyme activities compared with that of the wild-type enzyme at different pH values. Unlike the wild-type GAD, the mutants showed pronounced catalytic activity in a broad pH range of 4.0-8.0, suggesting that the C-terminal region is involved in the pH dependence of GAD activity. Therefore, this study may provide effective target regions for engineering pH dependence of GAD activity, thereby meeting industrial demands for the production of γ-aminobutyrate in a broad range of pH values.

Extracellular pH Regulates Zinc Signaling via an Asp Residue of the Zinc-sensing Receptor (ZnR/GPR39)*

PubMed Central

Cohen, Limor; Asraf, Hila; Sekler, Israel; Hershfinkel, Michal

2012-01-01

Zinc activates a specific Zn2+-sensing receptor, ZnR/GPR39, and thereby triggers cellular signaling leading to epithelial cell proliferation and survival. Epithelial cells that express ZnR, particularly colonocytes, face frequent changes in extracellular pH that are of physiological and pathological implication. Here we show that the ZnR/GPR39-dependent Ca2+ responses in HT29 colonocytes were maximal at pH 7.4 but were reduced by about 50% at pH 7.7 and by about 62% at pH 7.1 and were completely abolished at pH 6.5. Intracellular acidification did not attenuate ZnR/GPR39 activity, indicating that the pH sensor of this protein is located on an extracellular domain. ZnR/GPR39-dependent activation of extracellular-regulated kinase (ERK)1/2 or AKT pathways was abolished at acidic extracellular pH of 6.5. A similar inhibitory effect was monitored for the ZnR/GPR39-dependent up-regulation of Na+/H+ exchange activity at pH 6.5. Focusing on residues putatively facing the extracellular domain, we sought to identify the pH sensor of ZnR/GPR39. Replacing the histidine residues forming the Zn2+ binding site, His17 or His19, or other extracellular-facing histidines to alanine residues did not abolish the pH dependence of ZnR/GPR39. In contrast, replacing Asp313 with alanine resulted in similar Ca2+ responses triggered by ZnR/GPR39 at pH 7.4 or 6.5. This mutant also showed similar activation of ERK1/2 and AKT pathways, and ZnR-dependent up-regulation of Na+/H+ exchange at pH 7.4 and pH 6.5. Substitution of Asp313 to His or Glu residues restored pH sensitivity of the receptor. This indicates that Asp313, which was shown to modulate Zn2+ binding, is an essential residue of the pH sensor of GPR39. In conclusion, ZnR/GPR39 is tuned to sense physiologically relevant changes in extracellular pH that thus regulate ZnR-dependent signaling and ion transport activity. PMID:22879599

Extracellular pH regulates zinc signaling via an Asp residue of the zinc-sensing receptor (ZnR/GPR39).

PubMed

Cohen, Limor; Asraf, Hila; Sekler, Israel; Hershfinkel, Michal

2012-09-28

Zinc activates a specific Zn(2+)-sensing receptor, ZnR/GPR39, and thereby triggers cellular signaling leading to epithelial cell proliferation and survival. Epithelial cells that express ZnR, particularly colonocytes, face frequent changes in extracellular pH that are of physiological and pathological implication. Here we show that the ZnR/GPR39-dependent Ca(2+) responses in HT29 colonocytes were maximal at pH 7.4 but were reduced by about 50% at pH 7.7 and by about 62% at pH 7.1 and were completely abolished at pH 6.5. Intracellular acidification did not attenuate ZnR/GPR39 activity, indicating that the pH sensor of this protein is located on an extracellular domain. ZnR/GPR39-dependent activation of extracellular-regulated kinase (ERK)1/2 or AKT pathways was abolished at acidic extracellular pH of 6.5. A similar inhibitory effect was monitored for the ZnR/GPR39-dependent up-regulation of Na(+)/H(+) exchange activity at pH 6.5. Focusing on residues putatively facing the extracellular domain, we sought to identify the pH sensor of ZnR/GPR39. Replacing the histidine residues forming the Zn(2+) binding site, His(17) or His(19), or other extracellular-facing histidines to alanine residues did not abolish the pH dependence of ZnR/GPR39. In contrast, replacing Asp(313) with alanine resulted in similar Ca(2+) responses triggered by ZnR/GPR39 at pH 7.4 or 6.5. This mutant also showed similar activation of ERK1/2 and AKT pathways, and ZnR-dependent up-regulation of Na(+)/H(+) exchange at pH 7.4 and pH 6.5. Substitution of Asp(313) to His or Glu residues restored pH sensitivity of the receptor. This indicates that Asp(313), which was shown to modulate Zn(2+) binding, is an essential residue of the pH sensor of GPR39. In conclusion, ZnR/GPR39 is tuned to sense physiologically relevant changes in extracellular pH that thus regulate ZnR-dependent signaling and ion transport activity.

A calorimetric investigation of the interaction of the lac repressor with inducer.

PubMed

Donnér, J; Caruthers, M H; Gill, S J

1982-12-25

A calorimetric study has been made of the interaction between the lac repressor and isopropyl-1-thio-beta-D-galactopyranoside (IPTG). The buffer-corrected enthalpy of reaction at 25 degrees C was found to be -15.6, -24.7, -4.6 kJ/mol of bound IPTG at pH 7.0, pH 8.1, and pH 9.0, respectively. This large range of enthalpy values is in contrast to a maximum difference in the free energy of the reaction of only 1.5 kJ/mol of bound IPTG between these pH values. The reaction was found by calorimetric measurements in different buffers to be accompanied by an uptake of 0.29 mol of protons/mol of bound IPTG at pH 8.1. The pH dependency of the reaction enthalpy suggests differences in the extent of protonation of the binding site and the involvement of H bonding with IPTG. The lack of strong hydrophobic contributions in the IPTG binding process is revealed by the absence of any determinable heat capacity change for the reaction at pH 7.0. The presence of phosphate buffer significantly alters the enthalpy of IPTG binding at higher pH values, but has little effect upon the binding constant. This implies that highly negative phosphate species change the nature of the IPTG binding site without any displacement of phosphate upon IPTG binding.

pH-responsive drug delivery system based on AIE luminogen functionalized layered zirconium phosphate nano-platelets

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

Li, Dongdong, E-mail: lidongdong@jlu.edu.cn; Zhang, Yuping; Zhou, Bingbing

2015-05-15

Aggregation-induced emission (AIE) luminogen, quaternary tetraphenylethene cation (TPEN), was successfully incorporated into layered α-zirconium phosphate (α-ZrP) by using co-precipitation method to form inorganic–organic hybrid materials. The obtained materials show the characteristic hexagonal platelet shape with the interlayer distance did not reveal significant difference compared with pure α-ZrP. In addition, the obtained hybrid materials emit strong blue emission centered at 476 nm in aqueous media due to the electrostatic interactions of TPEN with the anionic framework of α-ZrP, which largely restrict their intramolecular rotation. More importantly, the materials provide a pH dependent release of doxorubicin (DOX), suggesting that AIE luminogen functionalizedmore » α-ZrP may be used as an imaging guided and pH-responsive delivery system for targeting therapy. - Graphical abstract: AIE luminogen was successfully incorporated into layered α-zirconium phosphate by a co-precipitation method to form inorganic–organic hybrid materials, showing a pH dependent release of DOX. - Highlights: • AIE luminogen cation was incorporated into layered α-ZrP by co-precipitation method. • The obtained material emits strong blue emission upon UV irradiation. • The material exhibits pH dependent release of DOX. • The AIE functionalized α-ZrP has potential applications in imaging guided therapy.« less

Control of Gastric H,K-ATPase Activity by Cations, Voltage and Intracellular pH Analyzed by Voltage Clamp Fluorometry in Xenopus Oocytes

PubMed Central

Dürr, Katharina L.; Tavraz, Neslihan N.; Friedrich, Thomas

2012-01-01

Whereas electrogenic partial reactions of the Na,K-ATPase have been studied in depth, much less is known about the influence of the membrane potential on the electroneutrally operating gastric H,K-ATPase. In this work, we investigated site-specifically fluorescence-labeled H,K-ATPase expressed in Xenopus oocytes by voltage clamp fluorometry to monitor the voltage-dependent distribution between E1P and E2P states and measured Rb+ uptake under various ionic and pH conditions. The steady-state E1P/E2P distribution, as indicated by the voltage-dependent fluorescence amplitudes and the Rb+ uptake activity were highly sensitive to small changes in intracellular pH, whereas even large extracellular pH changes affected neither the E1P/E2P distribution nor transport activity. Notably, intracellular acidification by approximately 0.5 pH units shifted V0.5, the voltage, at which the E1P/E2P ratio is 50∶50, by −100 mV. This was paralleled by an approximately two-fold acceleration of the forward rate constant of the E1P→E2P transition and a similar increase in the rate of steady-state cation transport. The temperature dependence of Rb+ uptake yielded an activation energy of ∼90 kJ/mol, suggesting that ion transport is rate-limited by a major conformational transition. The pronounced sensitivity towards intracellular pH suggests that proton uptake from the cytoplasmic side controls the level of phosphoenzyme entering the E1P→E2P conformational transition, thus limiting ion transport of the gastric H,K-ATPase. These findings highlight the significance of cellular mechanisms contributing to increased proton availability in the cytoplasm of gastric parietal cells. Furthermore, we show that extracellular Na+ profoundly alters the voltage-dependent E1P/E2P distribution indicating that Na+ ions can act as surrogates for protons regarding the E2P→E1P transition. The complexity of the intra- and extracellular cation effects can be rationalized by a kinetic model suggesting that cations reach the binding sites through a rather high-field intra- and a rather low-field extracellular access channel, with fractional electrical distances of ∼0.5 and ∼0.2, respectively. PMID:22448261

Reinvestigation of the Henry's law constant for hydrogen peroxide with temperature and acidity variation.

PubMed

Huang, Daoming; Chen, Zhongming

2010-01-01

Hydrogen peroxide is not only an important oxidant in itself; it also serves as both sink and temporary reservoir for other important oxidants including HOx (OH and HO2) radicals and O3 in the atmosphere. Its partitioning between gas and aqueous phases in the atmosphere, usually described by its Henry's law constant (K(H)), significantly influences its role in atmospheric processes. Large discrepancies between the K(H) values reported in previous work, however, have created uncertainty for atmospheric modelers. Based on our newly developed online instrumentation, we have re-determined the temperature and acidity dependence of K(H) for hydrogen peroxide at an air pressure of (0.960 +/- 0.013) atm (1 atm = 1.01325 x 10(5) Pa). The results indicated that the temperature dependence of K(H) for hydrogen peroxide fits to the Van't Hoff equation form, expressed as lnK(H) = a/T - b, and a = -deltaH/R, where K(H) is in M/atm (M is mol/L), T is in degrees Kelvin, R is the ideal gas constant, and deltaH is the standard heat of solution. For acidity dependence, results demonstrated that the K(H) value of hydrogen peroxide appeared to have no obvious dependence on decreasing pH level (from pH 7 to pH 1). Combining the dependence of both temperature and acidity, the obtained a and b were 7024 +/- 138 and 11.97 +/- 0.48, respectively, deltaH was (58.40 +/- 1.15) kJ/(K x mol), and the uncertainties represent sigma. Our determined K(H) values for hydrogen peroxide will therefore be of great use in atmospheric models.

PacC and pH–dependent transcriptome of the mycotrophic fungus Trichoderma virens

PubMed Central

2013-01-01

Background In fungi, environmental pH is an important signal for development, and successful host colonization depends on homeostasis. Surprisingly, little is known regarding the role of pH in fungal-fungal interactions. Species of Trichoderma grow as soil saprobes but many are primarily mycotrophic, using other fungi as hosts. Therefore, Trichoderma spp. are studied for their potential in biocontrol of plant diseases. Particularly in alkaline soil, pH is a critical limiting factor for these biofungicides, whose optimal growth pH is 4–6. Gaining an understanding of pH adaptability is an important step in broadening the activity spectrum of these economically important fungi. Results We studied the pH-responsive transcription factor PacC by gene knockout and by introduction of a constitutively active allele (pacCc). ΔpacC mutants exhibited reduced growth at alkaline pH, while pacCc strains grew poorly at acidic pH. In plate confrontation assays ΔpacC mutants showed decreased ability to compete with the plant pathogens Rhizoctonia solani and Sclerotium rolfsii. The pacCc strain exhibited an overgrowth of R. solani that was comparable to the wild type, but was unable to overgrow S. rolfsii. To identify genes whose expression is dependent on pH and pacC, we designed oligonucleotide microarrays from the transcript models of the T. virens genome, and compared the transcriptomes of wild type and mutant cultures exposed to high or low pH. Transcript levels from several functional classes were dependent on pacC, on pH, or on both. Furthermore, the expression of a set of pacC-dependent genes was increased in the constitutively-active pacCc strain, and was pH-independent in some, but not all cases. Conclusions PacC is important for biocontrol-related antagonism of other fungi by T. virens. As much as 5% of the transcriptome is pH-dependent, and of these genes, some 25% depend on pacC. Secondary metabolite biosynthesis and ion transport are among the relevant gene classes. We suggest that ΔpacC mutants may have lost their full biocontrol potential due to their inability to adapt to alkaline pH, to perceive ambient pH, or both. The results raise the novel possibility of genetically manipulating Trichoderma in order to improve adaptability and biocontrol at alkaline pH. PMID:23445374

The pH dependence of the allosteric response of human liver pyruvate kinase to fructose-1,6-bisphosphate, ATP, and alanine

PubMed Central

Fenton, Aron W.; Hutchinson, Myra

2009-01-01

The allosteric regulation of human liver pyruvate kinase (hL-PYK) by fructose-1,6-bisphosphate (Fru-1,6-BP; activator), ATP (inhibitor) and alanine (Ala; inhibitor) was monitored over a pH range from 6.5 to 8.0 at 37°C. As a function of increasing pH, hL-PYK's affinity for the substrate phosphoenolpyruvate (PEP), and for Fru-1,6-BP decreases, while affinities for ATP and Ala slightly increases. At pH 6.5, Fru-1,6-BP and ATP elicit only small allosteric impacts on PEP affinity. As pH increases, Fru-1,6-BP and ATP elicit greater allosteric responses, but the response to Ala is relatively constant. Since the magnitudes of the allosteric coupling for ATP and for Ala inhibition are different and the pH dependences of these magnitudes are not similar, these inhibitors likely elicit their responses using different molecular mechanisms. In addition, our results fail to support a general correlation between pH dependent changes in effector affinity and pH dependent changes in the corresponding allosteric response. PMID:19467627

Identification of critical amino acids in the proximal C-terminal of TREK-2 K+ channel for activation by acidic pHi and ATP-dependent inhibition.

PubMed

Woo, Joohan; Jun, Young Keul; Zhang, Yin-Hua; Nam, Joo Hyun; Shin, Dong Hoon; Kim, Sung Joon

2018-02-01

TWIK-related two-pore domain K + channels (TREKs) are regulated by intracellular pH (pH i ) and Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ). Previously, Glu 306 in proximal C-terminal (pCt) of mouse TREK-1 was identified as the pH i -sensing residue. The direction of PI(4,5)P 2 sensitivity is controversial, and we have recently shown that TREKs are inhibited by intracellular ATP via endogenous PI(4,5)P 2 formation. Here we investigate the anionic and cationic residues of pCt for the pH i and ATP-sensitivity in human TREK-2 (hTREK-2). In inside-out patch clamp recordings (I TREK-2,i-o ), acidic pH i -induced activation was absent in E332A and was partly attenuated in E335A. Neutralization of cationic Lys (K330A) also eliminated the acidic pH i sensitivity of I TREK-2,i-o . Unlike the inhibition of wild-type (WT) I TREK-2,i-o by intracellular ATP, neither E332A nor K330A was sensitive to ATP. Nevertheless, exogenous PI(4,5)P 2 (10 μM) abolished I TREK-2 i-o in all the above mutants as well as in WT, indicating unspecific inhibition by exogenous PI(4,5)P 2 . In whole-cell recordings of TREK-2 (I TREK-2,w-c ), K330A and E332A showed higher or fully active basal activity, showing attenuated or insignificant activation by 2-APB, arachidonic acid, or acidic pH e 6.9. I TREK-1,w-c of WT is largely suppressed by pH e 6.9, and the inhibition is slightly attenuated in K312A and E315A. The results show concerted roles of the oppositely charged Lys and Glu in pCt for the ATP-dependent low basal activity and pH i sensitivity.

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

Testing the limits of rational design by engineering pH sensitivity into membrane-active peptides.

PubMed

Wiedman, Gregory; Wimley, William C; Hristova, Kalina

2015-04-01

In this work, we sought to rationally design membrane-active peptides that are triggered by low pH to form macromolecular-sized pores in lipid bilayers. Such peptides could have broad utility in biotechnology and in nanomedicine as cancer therapeutics or drug delivery vehicles that promote release of macromolecules from endosomes. Our approach to rational design was to combine the properties of a pH-independent peptide, MelP5, which forms large pores allowing passage of macromolecules, with the properties of two pH-dependent membrane-active peptides, pHlip and GALA. We created two hybrid sequences, MelP5_Δ4 and MelP5_Δ6, by using the distribution of acidic residues on pHlip and GALA as a guide to insert acidic amino acids into the amphipathic helix of MelP5. We show that the new peptides bind to lipid bilayers and acquire secondary structure in a pH-dependent manner. The peptides also destabilize bilayers in a pH-dependent manner, such that lipid vesicles release the small molecules ANTS/DPX at low pH only. Thus, we were successful in designing pH-triggered pore-forming peptides. However, no macromolecular release was observed under any conditions. Therefore, we abolished the unique macromolecular poration properties of MelP5 by introducing pH sensitivity into its sequence. We conclude that the properties of pHlip, GALA, and MelP5 are additive, but only partially so. We propose that this lack of additivity is a limitation in the rational design of novel membrane-active peptides, and that high-throughput approaches to discovery will be critical for continued progress in the field. Copyright © 2015 Elsevier B.V. All rights reserved.

Constant pH molecular dynamics of proteins in explicit solvent with proton tautomerism.

PubMed

Goh, Garrett B; Hulbert, Benjamin S; Zhou, Huiqing; Brooks, Charles L

2014-07-01

pH is a ubiquitous regulator of biological activity, including protein-folding, protein-protein interactions, and enzymatic activity. Existing constant pH molecular dynamics (CPHMD) models that were developed to address questions related to the pH-dependent properties of proteins are largely based on implicit solvent models. However, implicit solvent models are known to underestimate the desolvation energy of buried charged residues, increasing the error associated with predictions that involve internal ionizable residue that are important in processes like hydrogen transport and electron transfer. Furthermore, discrete water and ions cannot be modeled in implicit solvent, which are important in systems like membrane proteins and ion channels. We report on an explicit solvent constant pH molecular dynamics framework based on multi-site λ-dynamics (CPHMD(MSλD)). In the CPHMD(MSλD) framework, we performed seamless alchemical transitions between protonation and tautomeric states using multi-site λ-dynamics, and designed novel biasing potentials to ensure that the physical end-states are predominantly sampled. We show that explicit solvent CPHMD(MSλD) simulations model realistic pH-dependent properties of proteins such as the Hen-Egg White Lysozyme (HEWL), binding domain of 2-oxoglutarate dehydrogenase (BBL) and N-terminal domain of ribosomal protein L9 (NTL9), and the pKa predictions are in excellent agreement with experimental values, with a RMSE ranging from 0.72 to 0.84 pKa units. With the recent development of the explicit solvent CPHMD(MSλD) framework for nucleic acids, accurate modeling of pH-dependent properties of both major class of biomolecules-proteins and nucleic acids is now possible. © 2013 Wiley Periodicals, Inc.

Biophysical characterization and conformational stability of Ebola and Marburg virus-like particles.

PubMed

Hu, Lei; Trefethen, Jared M; Zeng, Yuhong; Yee, Luisa; Ohtake, Satoshi; Lechuga-Ballesteros, David; Warfield, Kelly L; Aman, M Javad; Shulenin, Sergey; Unfer, Robert; Enterlein, Sven G; Truong-Le, Vu; Volkin, David B; Joshi, Sangeeta B; Middaugh, C Russell

2011-12-01

The filoviruses, Ebola virus and Marburg virus, cause severe hemorrhagic fever with up to 90% human mortality. Virus-like particles of EBOV (eVLPs) and MARV (mVLPs) are attractive vaccine candidates. For the development of stable vaccines, the conformational stability of these two enveloped VLPs produced in insect cells was characterized by various spectroscopic techniques over a wide pH and temperature range. Temperature-induced aggregation of the VLPs at various pH values was monitored by light scattering. Temperature/pH empirical phase diagrams (EPDs) of the two VLPs were constructed to summarize the large volume of data generated. The EPDs show that both VLPs lose their conformational integrity above about 50°C-60°C, depending on solution pH. The VLPs were maximally thermal stable in solution at pH 7-8, with a significant reduction in stability at pH 5 and 6. They were much less stable in solution at pH 3-4 due to increased susceptibility of the VLPs to aggregation. The characterization data and conformational stability profiles from these studies provide a basis for selection of optimized solution conditions for further vaccine formulation and long-term stability studies of eVLPs and mVLPs. Copyright © 2011 Wiley-Liss, Inc.

MS-2 and poliovirus transport in porous media: Hydrophobic effects and chemical perturbations

NASA Astrophysics Data System (ADS)

Bales, Roger C.; Li, Shimin; Maguire, Kimberly M.; Yahya, Moyasar T.; Gerba, Charles P.

1993-04-01

In a series of pH 7 continuous-flow column experiments, removal of the bacteriophage MS-2 by attachment to silica beads had a strong, systematic dependence on the amount of hydrophobic surface present on the beads. With no hydrophobic surface, removal of phage at pH 5 was much greater than at pH 7. Release of attached phage at both pH values did occur, but was slow; breakthrough curves exhibited tailing. Poliovirus attached to silica beads at pH 5.5 much more than at pH 7.0, and attachment was also slowly reversible. Time scales for phage and poliovinis attachment were of the order of hours. The sticking efficiency factor (α), reflecting microscaie physicochemical influences on virus attachment, was in the range of 0.0007-0.02. Phage release was small but measurable under steady state conditions. Release was enhanced by lowering ionic strength and by introducing beef extract, a high-ionic-strength protein solution. Results show that viruses experience reversible attachment/detachment (sometimes termed sorption), that large chemical perturbations are needed to induce rapid virus detachment, and that viruses should be quite mobile in sandy porous media. Even small amounts of hydrophobic organic material in the porous media (≥0.001%) can retard virus transport.

Interactions of flavonoids with iron and copper ions: a mechanism for their antioxidant activity.

PubMed

Mira, Lurdes; Fernandez, M Tereza; Santos, Marta; Rocha, Rui; Florêncio, M Helena; Jennings, Keith R

2002-11-01

The metal chelating properties of flavonoids suggest that they may play a role in metal-overload diseases and in all oxidative stress conditions involving a transition metal ion. A detailed study has been made of the ability of flavonoids to chelate iron (including Fe3+) and copper ions and its dependence of structure and pH. The acid medium may be important in some pathological conditions. In addition, the ability of flavonoids to reduce iron and copper ions and their activity-structure relationships were also investigated. To fulfill these objectives, flavones (apigenin, luteolin, kaempferol, quercetin, myricetin and rutin), isoflavones (daidzein and genistein), flavanones (taxifolin, naringenin and naringin) and a flavanol (catechin) were investigated. All flavonoids studied show higher reducing capacity for copper ions than for iron ions. The flavonoids with better Fe3+ reducing activity are those with a 2,3-double bond and possessing both the catechol group in the B-ring and the 3-hydroxyl group. The copper reducing activity seems to depend largely on the number of hydroxyl groups. The chelation studies were carried out by means of ultraviolet spectroscopy and electrospray ionisation mass spectrometry. Only flavones and the flavanol catechin interact with metal ions. At pH 7.4 and pH 5.5 all flavones studied appear to chelate Cu2+ at the same site, probably between the 5-hydroxyl and the 4-oxo groups. Myricetin and quercetin, however, at pH 7.4, appear to chelate Cu2+ additionally at the ortho-catechol group, the chelating site for catechin with Cu2+ at pH 7.4. Chelation studies of Fe3+ to flavonoids were investigated only at pH 5.5. Only myricetin and quercetin interact strongly with Fe3+, complexation probably occurring again between the 5-hydroxyl and the 4-oxo groups. Their behaviour can be explained by their ability to reduce Fe3+ at pH 5.5, suggesting that flavonoids reduce Fe3+ to Fe2+ before association.

Mechanism of energy coupling to entry and exit of neutral and branched chain amino acids in membrane vesicles of Streptococcus cremoris.

PubMed

Driessen, A J; Hellingwerf, K J; Konings, W N

1987-09-15

The energetics of neutral and branched chain amino acid transport by membrane vesicles from Streptococcus cremoris have been studied with a novel model system in which beef heart mitochondrial cytochrome c oxidase functions as a proton-motive force (delta p) generating system. In the presence of reduced cytochrome c, a large delta p was generated with a maximum value at pH 6.0. Apparent H+/amino acid stoichiometries (napp) have been determined at external pH values between 5.5 and 8.0 from the steady state levels of accumulation and the delta p. For L-leucine napp (0.8) was nearly independent of the pH. For L-alanine and L-serine napp decreased from 0.9-1.0 at pH 5.5 to 0-0.2 at pH 8.0. The napp for the different amino acids decreased with increasing external amino acid concentration. At pH 6.0, first order rate constants for amino acid exit (kex) under steady state conditions for L-leucine, L-alanine, and L-serine were 1.1-1.3, 0.084, and 0.053 min-1, respectively. From the pH dependence of kex it is concluded that amino acid exit in steady state is the sum of two processes, pH-dependent carrier-mediated amino acid exit and pH-independent passive diffusion (external leak). The first order rate constant for passive diffusion increased with increasing hydrophobicity of the side chain of the amino acids. As a result of these processes the kinetic steady state attained is less than the amino acid accumulation ratio predicted by thermodynamic equilibrium. The napp determined from the steady state accumulation represents, therefore, a lower limit. It is concluded that the mechanistic stoichiometry (n) for L-leucine, L-alanine, and L-serine transport most likely equals 1.

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

Impact of water quality on chlorine demand of corroding copper.

PubMed

Lytle, Darren A; Liggett, Jennifer

2016-04-01

Copper is widely used in drinking water premise plumbing system materials. In buildings such as hospitals, large and complicated plumbing networks make it difficult to maintain good water quality. Sustaining safe disinfectant residuals throughout a building to protect against waterborne pathogens such as Legionella is particularly challenging since copper and other reactive distribution system materials can exert considerable demands. The objective of this work was to evaluate the impact of pH and orthophosphate on the consumption of free chlorine associated with corroding copper pipes over time. A copper test-loop pilot system was used to control test conditions and systematically meet the study objectives. Chlorine consumption trends attributed to abiotic reactions with copper over time were different for each pH condition tested, and the total amount of chlorine consumed over the test runs increased with increasing pH. Orthophosphate eliminated chlorine consumption trends with elapsed time (i.e., chlorine demand was consistent across entire test runs). Orthophosphate also greatly reduced the total amount of chlorine consumed over the test runs. Interestingly, the total amount of chlorine consumed and the consumption rate were not pH dependent when orthophosphate was present. The findings reflect the complex and competing reactions at the copper pipe wall including corrosion, oxidation of Cu(I) minerals and ions, and possible oxidation of Cu(II) minerals, and the change in chlorine species all as a function of pH. The work has practical applications for maintaining chlorine residuals in premise plumbing drinking water systems including large buildings such as hospitals. Published by Elsevier Ltd.

Formation of metal-nicotianamine complexes as affected by pH, ligand exchange with citrate and metal exchange. A study by electrospray ionization time-of-flight mass spectrometry.

PubMed

Rellán-Alvarez, Rubén; Abadía, Javier; Alvarez-Fernández, Ana

2008-05-01

Nicotianamine (NA) is considered as a key element in plant metal homeostasis. This non-proteinogenic amino acid has an optimal structure for chelation of metal ions, with six functional groups that allow octahedral coordination. The ability to chelate metals by NA is largely dependent on the pK of the resulting complex and the pH of the solution, with most metals being chelated at neutral or basic pH values. In silico calculations using pKa and pK values have predicted the occurrence of metal-NA complexes in plant fluids, but the use of soft ionization techniques (e.g. electrospray), together with high-resolution mass spectrometers (e.g. time-of-flight mass detector), can offer direct and metal-specific information on the speciation of NA in solution. We have used direct infusion electrospray ionization mass spectrometry (time-of-flight) ESI-MS(TOF) to study the complexation of Mn, Fe(II), Fe(III), Ni, Cu by NA. The pH dependence of the metal-NA complexes in ESI-MS was compared to that predicted in silico. Possible exchange reactions that may occur between Fe-NA and other metal micronutrients as Zn and Cu, as well as between Fe-NA and citrate, another possible Fe ligand candidate in plants, were studied at pH 5.5 and 7.5, values typical of the plant xylem and phloem saps. Metal-NA complexes were generally observed in the ESI-MS experiments at a pH value approximately 1-2 units lower than that predicted in silico, and this difference could be only partially explained by the estimated error, approximately 0.3 pH units, associated with measuring pH in organic solvent-containing solutions. Iron-NA complexes are less likely to participate in ligand- and metal-exchange reactions at pH 7.5 than at pH 5.5. Results support that NA may be the ligand chelating Fe at pH values usually found in phloem sap, whereas in the xylem sap NA is not likely to be involved in Fe transport, conversely to what occurs with other metals such as Cu and Ni. Some considerations that need to be addressed when studying metal complexes in plant compartments by ESI-MS are also discussed.

Differential capacity of kaolinite and birnessite to protect surface associated proteins against thermal degradation [Fate of protein at mineral surfaces: influence of protein characteristics mineralogy, pH, and energy input

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

Chacon, Stephany S.; Garcia-Jaramillo, Manuel; Liu, Suet Yi

We report it is widely accepted that soil organic carbon cycling depends on the presence and catalytic functionality of extracellular enzymes. Recent reports suggest that combusted and autoclaved soils may have the capacity to degrade organic test substrates to a larger extent than the living, enzyme-bearing soils. In search of the underlying mechanisms, we adsorbed Beta-Glucosidase (BG) and Bovine Serum Albumin (BSA) on the phyllosilicate kaolinite and the manganese oxide birnessite at pH 5 and pH 7. The protein-mineral samples were then subjected to gradual energy inputs of a magnitude equivalent to naturally occurring wildfire events. The abundance and molecularmore » masses of desorbed organic compounds were recorded after ionization with tunable synchrotron vacuum ultraviolet radiation (VUV). The mechanisms controlling the fate of proteins varied with mineralogy. Kaolinite adsorbed protein largely through hydrophobic interactions and, even at large energy inputs, produced negligible amounts of desorption fragments compared to birnessite. Acid birnessite adsorbed protein through coulombic forces at low energy levels, became a hydrolyzing catalyst at low energies and low pH, and eventually turned into a reactant involving disintegration of both mineral and protein at higher energy inputs. Fragmentation of proteins was energy dependent and did not occur below an energy threshold of 0.20 MW cm -2 . Neither signal abundance nor signal intensity were a function of protein size. Above the energy threshold value, BG that had been adsorbed to birnessite at pH 7 showed an increase in signal abundance with increasing energy applications. Signal intensities differed with adsorption pH for BSA but only at the highest energy level applied. Our results indicate that proteins adsorbed to kaolinite may remain intact after exposure to such energy inputs as can be expected to occur in natural ecosystems. Protein fragmentation and concomitant loss of functionality must be expected in surface soils replete with pedogenic manganese oxides. Lastly, we conclude that minerals can do both: protect enzymes at high energy intensities in the case of kaolinite and, in the case of birnessite, substitute for and even exceed the oxidative functionality that may have been lost when unprotected oxidative enzymes were denatured at high energy inputs.« less

Time dependence of the pH of rain

Treesearch

John A. Kadlecek; Volkar A. Mohnen

1976-01-01

Standard procedures for determining the pH of rain samples usually involve substantial delays from the time of rainfall to the time of analysis. This assumes that no change in pH occurs during the storage period. We have found that this is not always true. We have determined that individual rain water samples possess a time dependent pH which can be correlated with the...

Molecular approaches to understand the regulation of N2O emission from denitrifying bacteria - model strains and soil communities (Invited)

NASA Astrophysics Data System (ADS)

Frostegard, A.; Bakken, L. R.

2010-12-01

Emissions of N2O from agricultural soils are largely caused by denitrifying bacteria. Field measurements of N2O fluxes show large variations and depend on several environmental factors, and possibly also on the composition of the denitrifying microbial community. The temporal and spatial variation of fluxes are not adequately captured by biogeochemical models, and few options for mitigations have been invented, which underscores the need to understand the mechanisms underlying the emissions of N2O. Analyses of denitrification genes and transcripts extracted from soils are important for describing the system, but may have limited value for prediction of N2O emissions. In contrast, phenotypic analyses are direct measures of the organisms’ responses to changing environmental conditions. Our approach is to combine phenotypic characterizations using high-resolution gas kinetics, with gene transcription analyses to study denitrification regulatory phenotypes (DRP) of bacterial strains or complex microbial communities. The rich data sets obtained provide a basis for refinement of biochemical and physiological research on this key process in the nitrogen cycle. The strength of this combined approach is illustrated by a series of experiments investigating effects of soil pH on denitrification. Soil pH emerges as a master variable determining the microbial community composition as well as its denitrification product ratio (N2O/N2), with higher ratio in acid than in alkaline soil. It is therefore likely that emissions of N2O from agro-ecosystems will increase in large parts of the world where soil pH is decreasing due to intensified management and increased use of chemical fertilizers. Considering its immense implications, surprisingly few attempts have been made to unravel the mechanisms involved in the pH-control of the product stoichiometry of denitrification. We investigated the kinetics of gas transformations (O2, NO, N2O and N2) and transcription of functional genes in intact soil samples from long-term liming experiments. Expression of nirS (encoding nitrite reductase) and nosZ (encoding N2OR) was generally lower at pH6 compared to pH8, but the nosZ/nirS transcript ratios were similar or even higher at pH6. These results were largely corroborated in refined experiments using extracted bacterial communities from the same soils, which allowed us to better control the pH levels experienced by the cells. The findings indicated that the higher N2O/N2 product ratios at pH6 were due to a post-transcriptional effect. Pure culture experiments using Paracoccus denitrificans demonstrated very low N2O/N2 ratios at pH7 while N2O reduction was severely inhibited by suboptimal pH, and that this inhibition occurred during protein synthesis/assembly rather than at the transcription level. The results are important for the understanding of main factors affecting N2O emissions from terrestrial ecosystems.

The Young's Modulus, Fracture Stress, and Fracture Strain of Gellan Hydrogels Filled with Whey Protein Microparticles.

PubMed

Lam, Cherry Wing Yu; Ikeda, Shinya

2017-05-01

Texture modifying abilities of whey protein microparticles are expected to be dependent on pH during heat-induced aggregation of whey protein in the microparticulation process. Therefore, whey protein microparticles were prepared at either pH 5.5 or 6.8 and their effects on small and large deformation properties of gellan gels containing whey protein microparticles as fillers were investigated. The majority of whey protein microparticles had diameters around 2 μm. Atomic force microscopy images showed that whey protein microparticles prepared at pH 6.8 partially collapsed and flatted by air-drying, while those prepared at pH 5.5 did not. The Young's modulus of filled gels adjusted to pH 5.5 decreased by the addition of whey protein microparticles, while those of filled gels adjusted to pH 6.8 increased with increasing volume fraction of filler particles. These results suggest that filler particles were weakly bonded to gel matrices at pH 5.5 but strongly at pH 6.8. Whey protein microparticles prepared at pH 5.5 showed more enhanced increases in the Young's modulus than those prepared at pH 6.8 at volume fractions between 0.2 and 0.4, indicating that microparticles prepared at pH 5.5 were mechanically stronger. The fracture stress of filled gels showed trends somewhat similar to those of the Young's modulus, while their fracture strains decreased by the addition of whey protein microparticles in all examined conditions, indicating that the primary effect of these filler particles was to enhance the brittleness of filled gels. © 2017 Institute of Food Technologists®.

Photodynamic Synergistic Effect of Pheophorbide a and Doxorubicin in Combined Treatment against Tumoral Cells.

PubMed

Ruiz-González, Rubén; Milán, Paula; Bresolí-Obach, Roger; Stockert, Juan Carlos; Villanueva, Angeles; Cañete, Magdalena; Nonell, Santi

2017-02-17

A combination of therapies to treat cancer malignancies is at the forefront of research with the aim to reduce drug doses (ultimately side effects) and diminish the possibility of resistance emergence given the multitarget strategy. With this goal in mind, in the present study, we report the combination between the chemotherapeutic drug doxorubicin (DOXO) and the photosensitizing agent pheophorbide a (PhA) to inactivate HeLa cells. Photophysical studies revealed that DOXO can quench the excited states of PhA, detracting from its photosensitizing ability. DOXO can itself photosensitize the production of singlet oxygen; however, this is largely suppressed when bound to DNA. Photodynamic treatments of cells incubated with DOXO and PhA led to different outcomes depending on the concentrations and administration protocols, ranging from antagonistic to synergic for the same concentrations. Taken together, the results indicate that an appropriate combination of DOXO with PhA and red light may produce improved cytotoxicity with a smaller dose of the chemotherapeutic drug, as a result of the different subcellular localization, targets and mode of action of the two agents.

Photodynamic Synergistic Effect of Pheophorbide a and Doxorubicin in Combined Treatment against Tumoral Cells

PubMed Central

Ruiz-González, Rubén; Milán, Paula; Bresolí-Obach, Roger; Stockert, Juan Carlos; Villanueva, Angeles; Cañete, Magdalena; Nonell, Santi

2017-01-01

A combination of therapies to treat cancer malignancies is at the forefront of research with the aim to reduce drug doses (ultimately side effects) and diminish the possibility of resistance emergence given the multitarget strategy. With this goal in mind, in the present study, we report the combination between the chemotherapeutic drug doxorubicin (DOXO) and the photosensitizing agent pheophorbide a (PhA) to inactivate HeLa cells. Photophysical studies revealed that DOXO can quench the excited states of PhA, detracting from its photosensitizing ability. DOXO can itself photosensitize the production of singlet oxygen; however, this is largely suppressed when bound to DNA. Photodynamic treatments of cells incubated with DOXO and PhA led to different outcomes depending on the concentrations and administration protocols, ranging from antagonistic to synergic for the same concentrations. Taken together, the results indicate that an appropriate combination of DOXO with PhA and red light may produce improved cytotoxicity with a smaller dose of the chemotherapeutic drug, as a result of the different subcellular localization, targets and mode of action of the two agents. PMID:28218672

PhAP protease from Pseudoalteromonas haloplanktis TAC125: Gene cloning, recombinant production in E. coli and enzyme characterization

NASA Astrophysics Data System (ADS)

de Pascale, D.; Giuliani, M.; De Santi, C.; Bergamasco, N.; Amoresano, A.; Carpentieri, A.; Parrilli, E.; Tutino, M. L.

2010-08-01

Cold-adapted proteases have been found to be the dominant activity throughout the cold marine environment, indicating their importance in bacterial acquisition of nitrogen-rich complex organic compounds. However, few extracellular proteases from marine organisms have been characterized so far, and the mechanisms that enable their activity in situ are still largely unknown. Aside from their ecological importance and use as model enzyme for structure/function investigations, cold-active proteolytic enzymes offer great potential for biotechnological applications. Our studies on cold adapted proteases were performed on exo-enzyme produced by the Antarctic marine bacterium Pseudoalteromonas haloplanktis TAC125. By applying a proteomic approach, we identified several proteolytic activities from its culture supernatant. PhAP protease was selected for further investigations. The encoding gene was cloned and the protein was recombinantly produced in E. coli cells. The homogeneous product was biochemically characterised and it turned out that the enzyme is a Zn-dependent aminopeptidase, with an activity dependence from assay temperature typical of psychrophilic enzymes.

Variability of pCO2 in surface waters and development of prediction model.

PubMed

Chung, Sewoong; Park, Hyungseok; Yoo, Jisu

2018-05-01

Inland waters are substantial sources of atmospheric carbon, but relevant data are rare in Asian monsoon regions including Korea. Emissions of CO 2 to the atmosphere depend largely on the partial pressure of CO 2 (pCO 2 ) in water; however, measured pCO 2 data are scarce and calculated pCO 2 can show large uncertainty. This study had three objectives: 1) to examine the spatial variability of pCO 2 in diverse surface water systems in Korea; 2) to compare pCO 2 calculated using pH-total alkalinity (Alk) and pH-dissolved inorganic carbon (DIC) with pCO 2 measured by an in situ submersible nondispersive infrared detector; and 3) to characterize the major environmental variables determining the variation of pCO 2 based on physical, chemical, and biological data collected concomitantly. Of 30 samples, 80% were found supersaturated in CO 2 with respect to the overlying atmosphere. Calculated pCO 2 using pH-Alk and pH-DIC showed weak prediction capability and large variations with respect to measured pCO 2 . Error analysis indicated that calculated pCO 2 is highly sensitive to the accuracy of pH measurements, particularly at low pH. Stepwise multiple linear regression (MLR) and random forest (RF) techniques were implemented to develop the most parsimonious model based on 10 potential predictor variables (pH, Alk, DIC, Uw, Cond, Turb, COD, DOC, TOC, Chla) by optimizing model performance. The RF model showed better performance than the MLR model, and the most parsimonious RF model (pH, Turb, Uw, Chla) improved pCO 2 prediction capability considerably compared with the simple calculation approach, reducing the RMSE from 527-544 to 105μatm at the study sites. Copyright © 2017 Elsevier B.V. All rights reserved.

An acid-loading chloride transport pathway in the intraerythrocytic malaria parasite, Plasmodium falciparum.

PubMed

Henry, Roselani I; Cobbold, Simon A; Allen, Richard J W; Khan, Asif; Hayward, Rhys; Lehane, Adele M; Bray, Patrick G; Howitt, Susan M; Biagini, Giancarlo A; Saliba, Kevin J; Kirk, Kiaran

2010-06-11

The intraerythrocytic malaria parasite exerts tight control over its ionic composition. In this study, a combination of fluorescent ion indicators and (36)Cl(-) flux measurements was used to investigate the transport of Cl(-) and the Cl(-)-dependent transport of "H(+)-equivalents" in mature (trophozoite stage) parasites, isolated from their host erythrocytes. Removal of extracellular Cl(-), resulting in an outward [Cl(-)] gradient, gave rise to a cytosolic alkalinization (i.e. a net efflux of H(+)-equivalents). This was reversed on restoration of extracellular Cl(-). The flux of H(+)-equivalents was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and, when measured in ATP-depleted parasites, showed a pronounced dependence on the pH of the parasite cytosol; the flux was low at cytosolic pH values < 7.2 but increased steeply with cytosolic pH at values > 7.2. (36)Cl(-) influx measurements revealed the presence of a Cl(-) uptake mechanism with characteristics similar to those of the Cl(-)-dependent H(+)-equivalent flux. The intracellular concentration of Cl(-) in the parasite was estimated to be approximately 48 mm in situ. The data are consistent with the intraerythrocytic parasite having in its plasma membrane a 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive transporter that, under physiological conditions, imports Cl(-) together with H(+)-equivalents, resulting in an intracellular Cl(-) concentration well above that which would occur if Cl(-) ions were distributed passively in accordance with the parasite's large, inwardly negative membrane potential.

Effect of pH and glucose on cultured human peritoneal mesothelial cells.

PubMed

Shao, J C; Yorioka, N; Nishida, Y; Yamakido, M

1999-08-01

We investigated the effects of various pH and glucose concentrations on the growth of human peritoneal mesothelial cells and on coagulation and fibrinolytic factors. Cells were cultured at various pH values in Ham's F-12 medium containing 1.0% foetal calf serum and supplemented with D-glucose or D-mannitol at various concentrations. After 4-48 h, cell proliferation and 3H-thymidine incorporation were determined. Coagulation and fibrinolytic factors were measured after 48 h. Glucose caused concentration-dependent inhibition of cell growth at all pH values, but the deleterious effect of low pH on cell proliferation was faster and stronger than that of high glucose. At a similar osmolality, mannitol caused less inhibition of cell proliferation than glucose. There was a glucose concentration-dependent increase of thrombin-antithrombin III complex production at all pH values. At pH 5.2, tissue-type plasminogen activator production was far lower than at higher pH values, and production of the plasminogen activator inhibitor showed a glucose concentration-dependent increase. At pH 6.5 or 7.3, however, the plasminogen activator inhibitor production decreased and tissue-type plasminogen activator production increased in a glucose concentration-dependent manner. Low pH and/or high glucose culture medium had an inhibitory effect on peritoneal mesothelial cells, with the effect of high glucose being partially related to hyperosmolality. These cells may modulate peritoneal coagulant and fibrinolytic activity, with the balance between coagulation and fibrinolysis being disturbed by low pH and/or high glucose.

Enhancement of bromate formation by pH depression during ozonation of bromide-containing water in the presence of hydroxylamine.

PubMed

Yang, Jingxin; Li, Ji; Dong, Wenyi; Ma, Jun; Yang, Yi; Li, Jiayin; Yang, Zhichao; Zhang, Xiaolei; Gu, Jia; Xie, Wanying; Cang, Yan

2017-02-01

This work investigated the fate of bromate formation during ozonation in the presence of hydroxylamine (HA). Results indicated that pH depression, as a commonly feasible control strategy for bromate formation during ozonation, unexpectedly enhanced the bromate formation during ozonation in the presence of HA. A dramatically high level of bromate was observed at acidic pH in the ozone/HA process. The scavenging experiments demonstrated the essential role of OH produced in the reaction of ozone with HA in bromate formation. In the process, OH mainly oxidizes bromide to Br, which is further oxidized by ozone and eventually converts to bromate. Further investigations suggested that the unexpected enhancement on bromate formation by pH depression can be mainly ascribed to the pH-dependent ozone decay, OH exposures and formation rate of Br. As pH decreased from 7 to 5, the reduced OH scavenging capacity of HA led to higher OH exposures, which contributed to the enhancement of bromate formation. As pH decreased from 5 to 3, the enhanced formation rate of Br largely augmented the formation of bromate. In addition, the ozone decay slowed down by pH depression provided more available ozone for the oxidation of the formed Br to bromate. The enhanced effect of pH depression on bromate formation was still observed in the real water samples in the ozone/HA process. Accordingly, pH depression might be avoided to control the bromate formation during ozonation in the presence of HA. Copyright © 2016 Elsevier Ltd. All rights reserved.

 De novo isolation of antibodies with pH-dependent binding properties.

PubMed

Bonvin, Pauline; Venet, Sophie; Fontaine, Gaëlle; Ravn, Ulla; Gueneau, Franck; Kosco-Vilbois, Marie; Proudfoot, Amanda Ei; Fischer, Nicolas

2015-01-01

pH-dependent antibodies are engineered to release their target at a slightly acidic pH, a property making them suitable for clinical as well as biotechnological applications. Such antibodies were previously obtained by histidine scanning of pre-existing antibodies, a labor-intensive strategy resulting in antibodies that displayed residual binding to their target at pH 6.0. We report here the de novo isolation of pH-dependent antibodies selected by phage display from libraries enriched in histidines. Strongly pH-dependent clones with various affinity profiles against CXCL10 were isolated by this method. Our best candidate has nanomolar affinity for CXCL10 at pH 7.2, but no residual binding was detected at pH 6.0. We therefore propose that this new process is an efficient strategy to generate pH-dependent antibodies.

RIM101-Dependent and -Independent Pathways Govern pH Responses in Candida albicans

PubMed Central

Davis, Dana; Wilson, R. Bryce; Mitchell, Aaron P.

2000-01-01

Growth and differentiation of Candida albicans over a broad pH range underlie its ability to infect an array of tissues in susceptible hosts. We identified C. albicans RIM101, RIM20, and RIM8 based on their homology to components of the one known fungal pH response pathway. PCR product-disruption mutations in each gene cause defects in three responses to alkaline pH: filamentation, induction of PRA1 and PHR1, and repression of PHR2. We find that RIM101 itself is an alkaline-induced gene that also depends on Rim20p and Rim8p for induction. Two observations indicate that a novel pH response pathway also exists. First, PHR2 becomes an alkaline-induced gene in the absence of Rim101p, Rim20p, or Rim8p. Second, we created strains in which Rim101p activity is independent of Rim20p and Rim8p; in these strains, filamentation remains pH dependent. Thus, pH governs gene expression and cellular differentiation in C. albicans through both RIM101-dependent and RIM101-independent pathways. PMID:10629054

Effects of pH on frog gustatory responses to chloride salts of alkali-metal and alkali-earth-metal.

PubMed

Kumai, T; Nomura, H

1980-01-01

The pH effects on frog gustatory responses to alkali-metal and alkali-earth-metal chloride salts were examined using single fungi-form papilla preparations. Responses to 0.1-0.5 M NaCl were clearly dependent upon the pH of the stimulating solutions. The responses increased as the pH decreased from 6.5 to 4.5 and were almost completely suppressed at pH's above 6.5. There was no significant difference in the pH dependency of the response among alkali-metal chlorides. HCl solutions elicited only a poor response under conditions in which the water response was suppressed by the simultaneous presence of a low NaCl concentration. Responses to alkali-earth-metal chlorides varied in their pH dependency. Response to CaCl2 was slightly affected by pH changes from 4.5 to 9.0, response to SrCl2 was considerably suppressed in the alkaline region, and responses to BaCl2 and MgCl2 were strongly suppressed at pH's above 6.5. BeCl2 solutions showed less marked stimulating effects over the pH range tested. The differences in pH dependency described above suggest the existence of two kinds of receptor sites, one being pH-insensitive sites responsible for the calcium response and the other pH-sensitive sites responsible for the sodium response. A cross-adaptation test appeared to support this possibility. Assuming that the pH effect mentioned is related to changes in the state of ionization of the receptor molecule, the pKa of the ionizable group responsible for the sodium response was determined to be approximately 5.5.

Treatment of severe pulmonary hypertension in the setting of the large patent ductus arteriosus.

PubMed

Niu, Mary C; Mallory, George B; Justino, Henri; Ruiz, Fadel E; Petit, Christopher J

2013-05-01

Treatment of the large patent ductus arteriosus (PDA) in the setting of pulmonary hypertension (PH) is challenging. Left patent, the large PDA can result in irreversible pulmonary vascular disease. Occlusion, however, may lead to right ventricular failure for certain patients with severe PH. Our center has adopted a staged management strategy using medical management, noninvasive imaging, and invasive cardiac catheterization to treat PH in the presence of a large PDA. This approach determines the safety of ductal closure but also leverages medical therapy to create an opportunity for safe PDA occlusion. We reviewed our experience with this approach. Patients with both severe PH and PDAs were studied. PH treatment history and hemodynamic data obtained during catheterizations were reviewed. Repeat catheterizations, echocardiograms, and clinical status at latest follow-up were also reviewed. Seven patients had both PH and large, unrestrictive PDAs. At baseline, all patients had near-systemic right ventricular pressures. Nine catheterizations were performed. Two patients underwent 2 catheterizations each due to poor initial response to balloon test occlusion. Six of 7 patients exhibited subsystemic pulmonary pressures during test occlusion and underwent successful PDA occlusion. One patient did not undergo PDA occlusion. In follow-up, 2 additional catheterizations were performed after successful PDA occlusion for subsequent hemodynamic assessment. At the latest follow-up, the 6 patients who underwent PDA occlusion are well, with continued improvement in PH. Five patients remain on PH treatment. A staged approach to PDA closure for patients with severe PH is an effective treatment paradigm. Aggressive treatment of PH creates a window of opportunity for PDA occlusion, echocardiography assists in identifying the timing for closure, and balloon test occlusion during cardiac catheterization is critical in determining safety of closure. By safely eliminating the large PDA, this treatment algorithm can halt the perilous combination of the large shunting from the PDA and PH in a population at high risk of morbidity and mortality.

A pH-dependent conformational ensemble mediates proton transport through the influenza A/M2 protein†

PubMed Central

Polishchuk, Alexei L.; Lear, James D.; Ma, Chunlong; Lamb, Robert A.; Pinto, Lawrence H.; DeGrado, William F.

2010-01-01

The influenza A M2 protein exhibits inwardly rectifying, pH-activated proton transport that saturates at low pH. A comparison of high-resolution structures of the transmembrane domain at high and low pH suggests that pH-dependent conformational changes may facilitate proton conduction by alternately changing the accessibility of the N-terminal and C-terminal regions of the channel as a proton transits through the transmembrane domain. Here, we show that M2 functionally reconstituted in liposomes populates at least three different conformational states over a physiologically relevant pH range, with transition midpoints that are consistent with previously reported His37 pKas. We then develop and test two similar, quantitative mechanistic models of proton transport, where protonation shifts the equilibrium between structural states having different proton affinities and solvent accessibilities. The models account well for a collection of experimental data sets over a wide range of pHs and voltages and require only a small number of adjustable parameters to accurately describe the data. While the kinetic models do not require any specific conformation for the protein, they nevertheless are consistent with a large body of structural information based on high-resolution NMR and crystallographic structures, optical spectroscopy, and MD calculations. PMID:20968306

Dual regulation of the native ClC-K2 chloride channel in the distal nephron by voltage and pH

PubMed Central

Pinelli, Laurent; Nissant, Antoine; Edwards, Aurélie; Paulais, Marc

2016-01-01

ClC-K2, a member of the ClC family of Cl− channels and transporters, forms the major basolateral Cl− conductance in distal nephron epithelial cells and therefore plays a central role in renal Cl− absorption. However, its regulation remains largely unknown because of the fact that recombinant ClC-K2 has not yet been studied at the single-channel level. In the present study, we investigate the effects of voltage, pH, Cl−, and Ca2+ on native ClC-K2 in the basolateral membrane of intercalated cells from the mouse connecting tubule. The ∼10-pS channel shows a steep voltage dependence such that channel activity increases with membrane depolarization. Intracellular pH (pHi) and extracellular pH (pHo) differentially modulate the voltage dependence curve: alkaline pHi flattens the curve by causing an increase in activity at negative voltages, whereas alkaline pHo shifts the curve toward negative voltages. In addition, pHi, pHo, and extracellular Ca2+ strongly increase activity, mainly because of an increase in the number of active channels with a comparatively minor effect on channel open probability. Furthermore, voltage alters both the number of active channels and their open probability, whereas intracellular Cl− has little influence. We propose that changes in the number of active channels correspond to them entering or leaving an inactivated state, whereas modulation of open probability corresponds to common gating by these channels. We suggest that pH, through the combined effects of pHi and pHo on ClC-K2, might be a key regulator of NaCl absorption and Cl−/HCO3− exchange in type B intercalated cells. PMID:27574292

Dual regulation of the native ClC-K2 chloride channel in the distal nephron by voltage and pH.

PubMed

Pinelli, Laurent; Nissant, Antoine; Edwards, Aurélie; Lourdel, Stéphane; Teulon, Jacques; Paulais, Marc

2016-09-01

ClC-K2, a member of the ClC family of Cl(-) channels and transporters, forms the major basolateral Cl(-) conductance in distal nephron epithelial cells and therefore plays a central role in renal Cl(-) absorption. However, its regulation remains largely unknown because of the fact that recombinant ClC-K2 has not yet been studied at the single-channel level. In the present study, we investigate the effects of voltage, pH, Cl(-), and Ca(2+) on native ClC-K2 in the basolateral membrane of intercalated cells from the mouse connecting tubule. The ∼10-pS channel shows a steep voltage dependence such that channel activity increases with membrane depolarization. Intracellular pH (pHi) and extracellular pH (pHo) differentially modulate the voltage dependence curve: alkaline pHi flattens the curve by causing an increase in activity at negative voltages, whereas alkaline pHo shifts the curve toward negative voltages. In addition, pHi, pHo, and extracellular Ca(2+) strongly increase activity, mainly because of an increase in the number of active channels with a comparatively minor effect on channel open probability. Furthermore, voltage alters both the number of active channels and their open probability, whereas intracellular Cl(-) has little influence. We propose that changes in the number of active channels correspond to them entering or leaving an inactivated state, whereas modulation of open probability corresponds to common gating by these channels. We suggest that pH, through the combined effects of pHi and pHo on ClC-K2, might be a key regulator of NaCl absorption and Cl(-)/HCO3 (-) exchange in type B intercalated cells. © 2016 Pinelli et al.

Constitutive expression of human gastric lipase in Pichia pastoris and site-directed mutagenesis of key lid-stabilizing residues.

PubMed

Sams, Laura; Amara, Sawsan; Chakroun, Almahdi; Coudre, Sébastien; Paume, Julie; Giallo, Jacqueline; Carrière, Frédéric

2017-10-01

The cDNA encoding human gastric lipase (HGL) was integrated into the genome of Pichia pastoris using the pGAPZα A transfer vector. The HGL signal peptide was replaced by the yeast α-factor to achieve an efficient secretion. Active rHGL was produced by the transformed yeast but its levels and stability were dependent on the pH. The highest activity was obtained upon buffering the culture medium at pH5, a condition that allowed preserving enzyme activity over time. A large fraction (72±2%) of secreted rHGL remained however bound to the yeast cells, and was released by washing the cell pellet with an acid glycine-HCl buffer (pH2.2). This procedure allowed establishing a first step of purification that was completed by size exclusion chromatography. N-terminal sequencing and MALDI-ToF mass spectrometry revealed that rHGL was produced in its mature form, with a global mass of 50,837±32Da corresponding to a N-glycosylated form of HGL polypeptide (43,193Da). rHGL activity was characterized as a function of pH, various substrates and in the presence of bile salts and pepsin, and was found similar to native HGL, except for slight changes in pH optima. We then studied by site-directed mutagenesis the role of three key residues (K4, E225, R229) involved in salt bridges stabilizing the lid domain that controls the access to the active site and is part of the interfacial recognition site. Their substitution has an impact on the pH-dependent activity of rHGL and its relative activities on medium and long chain triglycerides. Copyright © 2017 Elsevier B.V. All rights reserved.

Tailoring the structure of biphasic calcium phosphate via synthesis procedure

NASA Astrophysics Data System (ADS)

Mansour, S. F.; El-dek, S. I.; Ahmed, M. K.

2017-12-01

Nano calcium phosphate ceramics (CaPC) were synthesized using simple co-precipitation method at different preparation conditions. The selected Ca/P ratio with a variation of pH value lead to formation of dicalcium phosphate dihydrate (DCPD) at pH 5 and 6 while, hydroxyapatite (HAP) nano particles were formed at pH 9 and 12 at room temperature. The crystallite size was in the range of 15-55 nm depending on the obtained crystalline phase. The study displayed variation of decomposition depending on the annealing temperature. The significant note is the different transformation trend of each phase depending on the starting pH value. The HRTEM illustrated that the DCPD phase was formed as fibers with diameter around 4-6 nm, while HAP was formed in rod shape. The aspect ratio decreased from 6.6 at pH 9 to 4 at pH 12 which refer to the great influence of pH value on the morphology of calcium phosphates.

PhOBF1, a petunia ocs element binding factor, plays an important role in antiviral RNA silencing.

PubMed

Sun, Daoyang; Li, Shaohua; Niu, Lixin; Reid, Michael S; Zhang, Yanlong; Jiang, Cai-Zhong

2017-02-01

Virus-induced gene silencing (VIGS) is a common reverse genetics strategy for characterizing the function of genes in plants. The detailed mechanism governing RNA silencing efficiency triggered by viruses is largely unclear. Here, we reveal that a petunia (Petunia hybrida) ocs element binding factor, PhOBF1, one of the basic leucine zipper (bZIP) transcription factors, was up-regulated by Tobacco rattle virus (TRV) infection. Simultaneous silencing of PhOBF1 and a reporter gene, phytoene desaturase (PDS) or chalcone synthase (CHS), by TRV-based VIGS led to a failure of the development of leaf photobleaching or the white-corollas phenotype. PhOBF1 silencing caused down-regulation of RNA silencing-related genes, including RNA-dependent RNA polymerases (RDRs), Dicer-like RNase III enzymes (DCLs), and Argonautes (AGOs). After inoculation with the TRV-PhPDS, PhOBF1-RNAi lines exhibited a substantially impaired PDS silencing efficiency, whereas overexpression of PhOBF1 resulted in a recovery of the silencing phenotype (photobleaching) in systemic leaves. A compromised resistance to TRV and Tobacco mosaic virus was found in PhOBF1-RNAi lines, while PhOBF1-overexpressing lines displayed an enhanced resistance to their infections. Compared with wild-type plants, PhOBF1-silenced plants accumulated lower levels of free salicylic acid (SA), salicylic acid glucoside, and phenylalanine, contrarily to higher levels of those in plants overexpressing PhOBF1. Furthermore, transcripts of a number of genes associated with the shikimate and phenylpropanoid pathways were decreased or increased in PhOBF1-RNAi or PhOBF1-overexpressing lines, respectively. Taken together, the data suggest that PhOBF1 regulates TRV-induced RNA silencing efficiency through modulation of RDRs, DCLs, and AGOs mediated by the SA biosynthesis pathway. © The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Controlled sp(2) Functionalization of Boron Doped Diamond as a Route for the Fabrication of Robust and Nernstian pH Electrodes.

PubMed

Ayres, Zoë J; Borrill, Alexandra J; Newland, Jonathan C; Newton, Mark E; Macpherson, Julie V

2016-01-05

The development of a voltammetric boron doped diamond (BDD) pH sensor is described. To obtain pH sensitivity, laser micromachining (ablation) is utilized to introduce controlled regions of sp(2) carbon into a high quality polycrystalline BDD electrode. The resulting sp(2) carbon is activated to produce electrochemically reducible quinone groups using a high temperature acid treatment, followed by anodic polarization. Once activated, no further treatment is required. The quinone groups show a linear (R(2) = 0.999) and Nernstian (59 mV/(pH unit)) pH-dependent reductive current-voltage response over a large analyzable pH range, from pH 2 to pH 12. Using the laser approach, it is possible to optimize sp(2) coverage on the BDD surface, such that a measurable pH response is recorded, while minimizing background currents arising from oxygen reduction reactions on sp(2) carbon in the potential region of interest. This enables the sensor to be used in aerated solutions, boding well for in situ analysis. The voltammetric response of the electrode is not compromised by the presence of excess metal ions such as Pb(2+), Cd(2+), Cu(2+), and Zn(2+). Furthermore, the pH sensor is stable over a 3 month period (the current time period of testing), can be stored in air between measurements, requires no reactivation of the surface between measurements, and can be reproducibly fabricated using the proposed approach. The efficacy of this pH sensor in a real-world sample is demonstrated with pH measurements in U.K. seawater.

The Spinal Cord Has an Intrinsic System for the Control of pH.

PubMed

Jalalvand, Elham; Robertson, Brita; Tostivint, Hervé; Wallén, Peter; Grillner, Sten

2016-05-23

For survival of the organism, acid-base homeostasis is vital [1, 2]. The respiratory and renal systems are central to this control. Here we describe a novel mechanism, intrinsic to the spinal cord, with sensors that detect pH changes and act to restore pH to physiological levels by reducing motor activity. This pH sensor consists of somatostatin-expressing cerebrospinal fluid-contacting (CSF-c) neurons, which target the locomotor network. They have a low level of activity at pH 7.4. However, at both alkaline and acidic pH, the activity of the individual CSF-c neuron is markedly enhanced through the action of two separate channel subtypes. The alkaline response depends on PKD2L1 channels that have a large conductance and an equilibrium potential around 0 mV, both characteristics of mouse PKD2L1 channels [3-5]. The acidic response is due to an activation of ASIC3 [6]. The discharge pattern of the CSF-c neurons is U-shaped with a minimum frequency around pH 7.4 and a marked increase already at slightly lower and higher pH. During ongoing locomotor activity in the isolated spinal cord, both an increase and as a decrease of pH will reduce the locomotor burst rate. A somatostatin antagonist blocks these effects, suggesting that CSF-c neurons are responsible for the suppression of locomotor activity. CSF-c neurons thus represent a novel innate homeostatic mechanism, designed to sense any deviation from physiological pH and to respond by causing a depression of the motor activity. Because CSF-c neurons are found in all vertebrates, their pH-sensing function is most likely conserved. Copyright © 2016 Elsevier Ltd. All rights reserved.

Natural organic matter (NOM) adsorption to multi-walled carbon nanotubes: effect of NOM characteristics and water quality parameters.

PubMed

Hyung, Hoon; Kim, Jae-Hong

2008-06-15

The effect of natural organic matter (NOM) characteristics and water quality parameters on NOM adsorption to multiwalled carbon nanotubes (MWNT) was investigated. Isotherm experiment results were fitted well with a modified Freundlich isotherm model that took into account the heterogeneous nature of NOM. The preferential adsorption of the higher molecular weight fraction of NOM was observed by size exclusion chromatographic analysis. Experiments performed with various NOM samples suggested that the degree of NOM adsorption varied greatly depending on the type of NOM and was proportional to the aromatic carbon content of NOM. The NOM adsorption to MWNT was also dependent on water quality parameters: adsorption increased as pH decreased and ionic strength increased. As a result of NOM adsorption to MWNT, a fraction of MWNT formed a stable suspension in water and the concentration of MWNT suspension depended on the amount of NOM adsorbed per unit mass of MWNT. The amount of MWNT suspended in water was also affected by ionic strength and pH. The findings in this study suggested that the fate and transport of MWNT in natural systems would be largely influenced by NOM characteristics and water quality parameters.

Molecular interactions involved in proton-dependent gating in KcsA potassium channels

PubMed Central

Posson, David J.; Thompson, Ameer N.; McCoy, Jason G.

2013-01-01

The bacterial potassium channel KcsA is gated open by the binding of protons to amino acids on the intracellular side of the channel. We have identified, via channel mutagenesis and x-ray crystallography, two pH-sensing amino acids and a set of nearby residues involved in molecular interactions that influence gating. We found that the minimal mutation of one histidine (H25) and one glutamate (E118) near the cytoplasmic gate completely abolished pH-dependent gating. Mutation of nearby residues either alone or in pairs altered the channel’s response to pH. In addition, mutations of certain pairs of residues dramatically increased the energy barriers between the closed and open states. We proposed a Monod–Wyman–Changeux model for proton binding and pH-dependent gating in KcsA, where H25 is a “strong” sensor displaying a large shift in pKa between closed and open states, and E118 is a “weak” pH sensor. Modifying model parameters that are involved in either the intrinsic gating equilibrium or the pKa values of the pH-sensing residues was sufficient to capture the effects of all mutations. PMID:24218397

The effect of pH dependence of antibody-antigen interactions on subcellular trafficking dynamics.

PubMed

Devanaboyina, Siva Charan; Lynch, Sandra M; Ober, Raimund J; Ram, Sripad; Kim, Dongyoung; Puig-Canto, Alberto; Breen, Shannon; Kasturirangan, Srinath; Fowler, Susan; Peng, Li; Zhong, Haihong; Jermutus, Lutz; Wu, Herren; Webster, Carl; Ward, E Sally; Gao, Changshou

2013-01-01

A drawback of targeting soluble antigens such as cytokines or toxins with long-lived antibodies is that such antibodies can prolong the half-life of the target antigen by a "buffering" effect. This has motivated the design of antibodies that bind to target with higher affinity at near neutral pH relative to acidic endosomal pH (~pH 6.0). Such antibodies are expected to release antigen within endosomes following uptake into cells, whereas antibody will be recycled and exocytosed in FcRn-expressing cells. To understand how the pH dependence of antibody-antigen interactions affects intracellular trafficking, we generated three antibodies that bind IL-6 with different pH dependencies in the range pH 6.0-7.4. The behavior of antigen in the presence of these antibodies has been characterized using a combination of fixed and live cell fluorescence microscopy. As the affinity of the antibody:IL-6 interaction at pH 6.0 decreases, an increasing amount of antigen dissociates from FcRn-bound antibody in early and late endosomes, and then enters lysosomes. Segregation of antibody and FcRn from endosomes in tubulovesicular transport carriers (TCs) into the recycling pathway can also be observed in live cells, and the extent of IL-6 association with TCs correlates with increasing affinity of the antibody:IL-6 interaction at acidic pH. These analyses result in an understanding, in spatiotemporal terms, of the effect of pH dependence of antibody-antigen interactions on subcellular trafficking and inform the design of antibodies with optimized binding properties for antigen elimination.

The VCD pattern of the ν(C=O) bands in isoindolinones.

PubMed

Rode, Joanna Ewa; Lyczko, Krzysztof; Jawiczuk, Magdalena; Kawęcki, Robert; Stańczyk, Wojciech; Jaglińska, Agnieszka; Dobrowolski, Jan Cz

2018-05-18

The IR and VCD spectra of both enantiomers of Me, iPr, nBu, Ph and CH2Ph substituted isoindolinones in solution and KBr pellets were measured and interpreted with DFT calculations. The spectra in solution revealed no important differences in the C=O stretching vibration region while the interpretation of very distinct spectra taken in pellets required determining the crystal structures. The studied compounds crystallized in the P212121 (Me, iPr, CH2Ph), P31 (nBu), and P21 (Ph) space groups. We found that the quality of simulated spectra strongly depends on the substituent, the structure of the molecular cluster assumed, basis set, and use of the dispersion correction. The IR spectra can be reproduced well based on the simplest linear arrangement of hydrogen-bonded chains mimicking the molecular arrangement in the crystals. We found no common approach to reproduce all the registered VCD spectra in the crystal phase. For the Me and nBu isoindolinones, the VCD pattern was the best reproduced by full optimization of the selected large molecular clusters. For iPr, Ph and CH2Ph derivatives optimizing only the position of H-atoms in a fragment frozen as in the crystal provides the best results. Such an approach can reduce the computation time from months to one week. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Iodine-129 and iodine-127 speciation in groundwater at the Hanford site, US: iodate incorporation into calcite.

PubMed

Zhang, Saijin; Xu, Chen; Creeley, Danielle; Ho, Yi-Fang; Li, Hsiu-Ping; Grandbois, Russell; Schwehr, Kathleen A; Kaplan, Daniel I; Yeager, Chris M; Wellman, Dawn; Santschi, Peter H

2013-09-03

The geochemical transport and fate of radioiodine depends largely on its chemical speciation that is greatly affected by environmental factors. This study reports, for the first time, the speciation of stable and radioactive iodine in the groundwater from the Hanford Site. Iodate was the dominant species and accounted for up to 84% of the total iodine present. The alkaline pH (pH ∼ 8) and predominantly oxidizing environment may have prevented reduction of the iodate. In addition, groundwater samples were found to have large amounts of calcite precipitate which were likely formed as a result of CO2 degassing during removal from the deep subsurface (>70m depth). Further analyses indicated that between 7 and 40% of the dissolved (127)I and (129)I that was originally in the groundwater had coprecipitated in the calcite. Iodate was the main species incorporated into calcite and this incorporation process could be impeded by elevating the pH and decreasing ionic strength in groundwater. This study provides critical information for predicting the long-term fate and transport of (129)I. Furthermore, the common sampling artifact resulting in the precipitation of calcite by degassing CO2, had the unintended consequence of providing insight into a potential solution for the in situ remediation of groundwater (129)I.

Acid-inducible proton influx currents in the plasma membrane of murine osteoclast-like cells.

PubMed

Kuno, Miyuki; Li, Guangshuai; Moriura, Yoshie; Hino, Yoshiko; Kawawaki, Junko; Sakai, Hiromu

2016-05-01

Acidification of the resorption pits, which is essential for dissolving bone, is produced by secretion of protons through vacuolar H(+)-ATPases in the plasma membrane of bone-resorbing cells, osteoclasts. Consequently, osteoclasts face highly acidic extracellular environments, where the pH gradient across the plasma membrane could generate a force driving protons into the cells. Proton influx mechanisms during the acid exposure are largely unknown, however. In this study, we investigated extracellular-acid-inducible proton influx currents in osteoclast-like cells derived from a macrophage cell line (RAW264). Decreasing extracellular pH to <5.5 induced non-ohmic inward currents. The reversal potentials depended on the pH gradients across the membrane and were independent of concentrations of Na(+), Cl(-), and HCO3 (-), suggesting that they were carried largely by protons. The acid-inducible proton influx currents were not inhibited by amiloride, a widely used blocker for cation channels/transporters, or by 4,4'-diisothiocyanato-2,2'-stilbenesulfonate(DIDS) which blocks anion channels/transporters. Additionally, the currents were not significantly affected by V-ATPase inhibitors, bafilomycin A1 and N,N'-dicyclohexylcarbodiimide. Extracellular Ca(2+) (10 mM) did not affect the currents, but 1 mM ZnCl2 decreased the currents partially. The intracellular pH in the vicinity of the plasma membrane was dropped by the acid-inducible H(+) influx currents, which caused overshoot of the voltage-gated H(+) channels after removal of acids. The H(+) influx currents were smaller in undifferentiated, mononuclear RAW cells and were negligible in COS7 cells. These data suggest that the acid-inducible H(+) influx (H(+) leak) pathway may be an additional mechanism modifying the pH environments of osteoclasts upon exposure to strong acids.

A multimodal histamine ligand for chromatographic purification of plasmid DNA.

PubMed

Černigoj, Urh; Vidic, Urška; Barut, Miloš; Podgornik, Aleš; Peterka, Matjaž; Štrancar, Aleš

2013-03-15

To exploit different chromatographic modes for efficient plasmid DNA (pDNA) purification a novel monolithic chromatographic support bearing multimodal histamine (HISA) groups was developed and characterized. Electrostatic charge of HISA groups depends on the pH of the mobile phase, being neutral above pH 7 and becoming positively charged below. As a consequence, HISA groups exhibit predominantly ion-exchange character at low pH values, which decreases with titration of the HISA groups resulting in increased hydrophobicity. This feature enabled separation of supercoiled (sc) pDNA from other plasmid isoforms (and other process related impurities) by adjusting salt or pH gradient. The dynamic binding capacity (DBC) for a 5.1kbp large plasmid at pH 5 was 4.0 mg/ml under low salt binding conditions, remaining relatively high (3.0 mg/ml) even in the presence of 1.0 M NaCl due to the multimodal nature of HISA ligand. Only slightly lower DBC (2.7 mg/ml) was determined under preferentially hydrophobic conditions in 3.0 M (NH(4))(2)SO(4), pH 7.4. Open circular and sc pDNA isoforms were baseline separated in descending (NH(4))(2)SO(4) gradient. Furthermore, an efficient plasmid DNA separation was possible both on analytical as well as on preparative scale by applying the descending pH gradient at a constant concentration (above 3.0 M) of (NH(4))(2)SO(4). Copyright © 2013 Elsevier B.V. All rights reserved.

Study of the phosphine plasma decomposition and its formation by ablation of red phosphorus in hydrogen plasma

NASA Astrophysics Data System (ADS)

Bruno, G.; Losurdo, M.; Capezzuto, P.

1995-03-01

Mass spectrometry and optical emission spectroscopy have been used to study the chemistry of PH(sub 3) plasma decomposition as well as its formation by ablation of red phosphorus in hydrogen plasma. It has been shown that PH(sub 3) decomposition easily equilibrates at low levels of PH(sub 3) depletion (15%-30%), this depending mainly on the rf power. The ablation of red phosphorus in H(sub 2) plasma produces phosphine in significant amount, depending mainly on the total pressure but also on the rf power. It has also been found that H(sup *) and PH(sup *) emitting species originate not only by the dissociative excitation of H(sub 2) and PH(sub 3), respectively, but also by the direct excitation of the same species in the ground state. Considerations are developed on how to derive the H-atom and PH radical densities by actinometry, under specific experimental conditions. Besides, the linear dependence of PH(sub 3) formation rate, r(sub PH(3)), on H-atom density, (left bracket) H (right bracket), leads to the definition of the kinetic equation r(sub PH(3)) = k (left bracket) H (right bracket), and to the hypothesis that the formation of PH radical on the surface or its desorption is the dominant mechanism for PH(sub 3) production.

Regulation of intracellular pH in LLC-PK1 cells by Na+/H+ exchange.

PubMed

Montrose, M H; Murer, H

1986-01-01

Suspensions of LLC-PK1 cells (a continuous epitheliod cell line with renal characteristics) are examined for mechanisms of intracellular pH regulation using the fluorescent probe BCECF. Initial experiments determine suitable calibration procedures for use of the BCECF fluorescent signal. They also determine that the cell suspension contains cells which (after 4 hr in suspension) have Na+ and K+ gradients comparable to those of cells in monolayer culture. The steady-state intracellular pH (7.05 +/- 0.01, n = 5) of cells which have recovered in (pH 7.4) Na+-containing medium is not affected over several minutes by addition of 100 microM amiloride or removal of extracellular Na+ (Na+o less than 1 mM). In contrast, when the cells recover from an acid load (caused by NH4 preincubation and removal), the recovery is largely Na+ dependent and is sensitive to 100 microM amiloride. These results suggest that with resting pH near neutrality, both Na+o/H+i and Na+i/H+o exchange reactions are functionally inactive (compared to cellular buffering capacity). In contrast, Na+o/H+i exchange is activated by an increased cellular acid load. This activation may be observed directly either as a stimulation of net H+ efflux or net Na+ influx with decreasing intracellular pH. The extrapolation of this latter data suggests a "set point" of Na+/H+ exchange of approximately pH 7.0, consistent with the observed resting intracellular pH of approximately 7.05.

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.

Foaming and emulsifying properties of porcine red cell protein concentrate.

PubMed

Salvador, P; Saguer, E; Parés, D; Carretero, C; Toldrà, M

2010-08-01

This work focuses on studying the effects of pH (7.0 and 4.5) and protein concentration on the foaming and emulsifying properties of fresh (F) and spray-dried (SD) porcine red cell protein (RCP) concentrates in order to evaluate the proper use of this blood protein as a functional food ingredient. Also, protein solubility is measured through the pH range from 3.0 to 8.0. In each case, all concentrates show a high solubility, although this is significantly affected by pH. Spray drying slightly reduces the solubility at mild acid and neutral conditions. The foaming capacity is found to be dependent on pH as well as on the drying treatment. SD-RCP concentrates show better foaming capacity than F-RCP. The minimum protein concentration required to attain the highest foaming capacity is found under acid pH for the spray-dried concentrates. Although F-RCP shows low foam stability at acid and neutral pH, spray drying and protein content enhance the stability of foams. Emulsifying properties show dependence on pH as well as on protein content. Furthermore, spray drying affects the emulsifying properties but in different ways, depending on pH and protein concentration.

Gold Binding by Native and Chemically Modified Hops Biomasses

PubMed Central

López, M. Laura; Peralta-Videa, J. R.; de la Rosa, G.; Armendáriz, V.; Herrera, I.; Troiani, H.; Henning, J.

2005-01-01

Heavy metals from mining, smelting operations and other industrial processing facilities pollute wastewaters worldwide. Extraction of metals from industrial effluents has been widely studied due to the economic advantages and the relative ease of technical implementation. Consequently, the search for new and improved methodologies for the recovery of gold has increased. In this particular research, the use of cone hops biomass (Humulus lupulus) was investigated as a new option for gold recovery. The results showed that the gold binding to native hops biomass was pH dependent from pH 2 to pH 6, with a maximum percentage binding at pH 3. Time dependency studies demonstrated that Au(III) binding to native and modified cone hops biomasses was found to be time independent at pH 2 while at pH 5, it was time dependent. Capacity experiments demonstrated that at pH 2, esterified hops biomass bound 33.4 mg Au/g of biomass, while native and hydrolyzed hops biomasses bound 28.2 and 12.0 mg Au/g of biomass, respectively. However, at pH 5 the binding capacities were 38.9, 37.8 and 11.4 mg of Au per gram of native, esterified and hydrolyzed hops biomasses, respectively. PMID:18365087

Diversities and similarities in pH dependency among bacterial NhaB-like Na+/H+ antiporters.

PubMed

Kiriyama, Wakako; Honma, Kei; Hiratsuka, Tomoaki; Takahashi, Itsuka; Nomizu, Takahiro; Takashima, Yuta; Ohtsuka, Masataka; Takahashi, Daiki; Moriyama, Kazuya; Mori, Sayoko; Nishiyama, Shiho; Fukuhara, Masahiro; Nakamura, Tatsunosuke; Shigematsu, Toru; Yamaguchi, Toshio

2013-10-01

NhaB-like antiporters were the second described class of Na(+)/H(+) antiporters, identified in bacteria more than 20 years ago. While nhaB-like gene sequences have been found in a number of bacterial genomes, only a few of the NhaB-like antiporters have been functionally characterized to date. Although earlier studies have identified a few pH-sensitive and -insensitive NhaB-like antiporters, the mechanisms that determine their pH responses still remain elusive. In this study, we sought to investigate the diversities and similarities among bacterial NhaB-like antiporters, with particular emphasis on their pH responsiveness. Our phylogenetic analysis of NhaB-like antiporters, combined with pH profile analyses of activities for representative members of several phylogenetic groups, demonstrated that NhaB-like antiporters could be classified into three distinct types according to the degree of their pH dependencies. Interestingly, pH-insensitive NhaB-like antiporters were only found in a limited proportion of enterobacterial species, which constitute a subcluster that appears to have diverged relatively recently among enterobacterial NhaB-like antiporters. Furthermore, kinetic property analyses of NhaB-like antiporters at different pH values revealed that the degree of pH sensitivity of antiport activities was strongly correlated with the magnitude of pH-dependent change in apparent Km values, suggesting that the dramatic pH sensitivities observed for several NhaB-like antiporters might be mainly due to the significant increases of apparent Km at lower pH. These results strongly suggested the possibility that the loss of pH sensitivity of NhaB-like antiporters had occurred relatively recently, probably via accumulation of the mutations that impair pH-dependent change of Km in the course of molecular evolution.

Variations of thiaminase I activity pH dependencies among typical Great Lakes forage fish and Paenibacillus thiaminolyticus.

USGS Publications Warehouse

Zajicek, J.L.; Brown, L.; Brown, S.B.; Honeyfield, D.C.; Fitzsimons, J.D.; Tillitt, D.E.

2009-01-01

The source of thiaminase in the Great Lakes food web remains unknown. Biochemical characterization of the thiaminase I activities observed in forage fish was undertaken to provide insights into potential thiaminase sources and to optimize catalytic assay conditions. We measured the thiaminase I activities of crude extracts from five forage fish species and one strain of Paenibacillus thiaminolyticus over a range of pH values. The clupeids, alewife Alosa pseudoharengus and gizzard shad Dorosoma cepedianum, had very similar thiaminase I pH dependencies, with optimal activity ranges (> or = 90% of maximum activity) between pH 4.6 and 5.5. Rainbow smelt Osmerus mordax and spottail shiner Notropis hudsonius had optimal activity ranges between pH 5.5-6.6. The thiaminase I activity pH dependence profile of P. thiaminolyticus had an optimal activity range between pH 5.4 and 6.3, which was similar to the optimal range for rainbow smelt and spottail shiners. Incubation of P. thiaminolyticus extracts with extracts from bloater Coregonus hoyi (normally, bloaters have little or no detectable thiaminase I activity) did not significantly alter the pH dependence profile of P. thiaminolyticus-derived thiaminase I, such that it continued to resemble that of the rainbow smelt and spottail shiner, with an apparent optimal activity range between pH 5.7 and 6.6. These data are consistent with the hypothesis of a bacterial source for thiaminase I in the nonclupeid species of forage fish; however, the data also suggest different sources of thiaminase I enzymes in the clupeid species.

LRET Determination of Molecular Distances during pH Gating of the Mammalian Inward Rectifier Kir1.1b.

PubMed

Nanazashvili, Mikheil; Sánchez-Rodríguez, Jorge E; Fosque, Ben; Bezanilla, Francisco; Sackin, Henry

2018-01-09

Gating of the mammalian inward rectifier Kir1.1 at the helix bundle crossing (HBC) by intracellular pH is believed to be mediated by conformational changes in the C-terminal domain (CTD). However, the exact motion of the CTD during Kir gating remains controversial. Crystal structures and single-molecule fluorescence resonance energy transfer of KirBac channels have implied a rigid body rotation and/or a contraction of the CTD as possible triggers for opening of the HBC gate. In our study, we used lanthanide-based resonance energy transfer on single-Cys dimeric constructs of the mammalian renal inward rectifier, Kir1.1b, incorporated into anionic liposomes plus PIP 2 , to determine unambiguous, state-dependent distances between paired Cys residues on diagonally opposite subunits. Functionality and pH dependence of our proteoliposome channels were verified in separate electrophysiological experiments. The lanthanide-based resonance energy transfer distances measured in closed (pH 6) and open (pH 8) conditions indicated neither expansion nor contraction of the CTD during gating, whereas the HBC gate widened by 8.8 ± 4 Å, from 6.3 ± 2 to 15.1 ± 6 Å, during opening. These results are consistent with a Kir gating model in which rigid body rotation of the large CTD around the permeation axis is correlated with opening of the HBC hydrophobic gate, allowing permeation of a 7 Å hydrated K ion. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Hydrogeochemical processes governing the origin, transport and fate of major and trace elements from mine wastes and mineralized rock to surface waters

USGS Publications Warehouse

Nordstrom, D. Kirk

2011-01-01

Mobility of potential or actual contaminants from mining and mineral processing activities depends on (1) occurrence: is the mineral source of the contaminant actually present? (2) abundance: is the mineral present in sufficient quantity to make a difference? (3) reactivity: what are the energetics, rates, and mechanisms of sorption and mineral dissolution and precipitation relative to the flow rate of the water? and (4) hydrology: what are the main flow paths for contaminated water? Estimates of relative proportions of minerals dissolved and precipitated can be made with mass-balance calculations if minerals and water compositions along a flow path are known. Combined with discharge, these mass-balance estimates quantify the actual weathering rate of pyrite mineralization in the environment and compare reasonably well with laboratory rates of pyrite oxidation except when large quantities of soluble salts and evaporated mine waters have accumulated underground. Quantitative mineralogy with trace-element compositions can substantially improve the identification of source minerals for specific trace elements through mass balances. Post-dissolution sorption and precipitation (attenuation) reactions depend on the chemical behavior of each element, solution composition and pH, aqueous speciation, temperature, and contact-time with mineral surfaces. For example, little metal attenuation occurs in waters of low pH (2, and redox-sensitive oxyanions (As, Sb, Se, Mo, Cr, V). Once dissolved, metal and metalloid concentrations are strongly affected by redox conditions and pH. Iron is the most reactive because it is rapidly oxidized by bacteria and archaea and Fe(III) hydrolyzes and precipitates at low pH (1–3) which is related directly to its first hydrolysis constant, pK1 = 2.2. Several insoluble sulfate minerals precipitate at low pH including anglesite, barite, jarosite, alunite and basaluminite. Aluminum hydrolyzes near pH 5 (pK1 = 5.0) and provides buffering and removal of Al by mineral precipitation from pH 4–5.5. Dissolved sulfate behaves conservatively because the amount removed from solution by precipitation is usually too small relative to the high concentrations in the water column and relative to the flow rate of the water.

Effects of altered groundwater chemistry upon the pH-dependency and magnitude of bacterial attachment during transport within an organically contaminated sandy aquifer

USGS Publications Warehouse

Harvey, Ronald W.; Metge, David W.; Barber, Larry B.; Aiken, George R.

2010-01-01

The effects of a dilute (ionic strength = 5 ?? 10-3 M) plume of treated sewage, with elevated levels (3.9 mg/L) of dissolved organic carbon (DOC), upon the pH-dependency and magnitude of bacterial transport through an iron-laden, quartz sand aquifer (Cape Cod, MA) were evaluated using sets of replicate, static minicolumns. Compared with uncontaminated groundwater, the plume chemistry diminished bacterial attachment under mildly acidic (pH 5.0-6.5) in-situ conditions, in spite of the 5-fold increase in ionic strength and substantively enhanced attachment under more alkaline conditions. The effects of the hydrophobic neutral and total fractions of the plume DOC; modest concentrations of fulvic and humic acids (1.5 mg/L); linear alkyl benzene sulfonate (LAS) (25 mg/L); Imbentin (200 ??g/L), a model nonionic surfactant; sulfate (28 mg/L); and calcium (20 mg/L) varied sharply in response to relatively small changes in pH, although the plume constituents collectively decreased the pH-dependency of bacterial attachment. LAS and other hydrophobic neutrals (collectively representing only ???3% of the plume DOC) had a disproportionately large effect upon bacterial attachment, as did the elevated concentrations of sulfate within the plume. The findings further suggest that the roles of organic plume constituents in transport or bacteria through acidic aquifer sediments can be very different than would be predicted from column studies performed at circumneutral pH and that the inorganic constituents within the plume cannot be ignored.

Mechanisms of transient receptor potential vanilloid 1 activation and sensitization by allyl isothiocyanate.

PubMed

Gees, Maarten; Alpizar, Yeranddy A; Boonen, Brett; Sanchez, Alicia; Everaerts, Wouter; Segal, Andrei; Xue, Fenqin; Janssens, Annelies; Owsianik, Grzegorz; Nilius, Bernd; Voets, Thomas; Talavera, Karel

2013-09-01

Allyl isothiocyanate (AITC; aka, mustard oil) is a powerful irritant produced by Brassica plants as a defensive trait against herbivores and confers pungency to mustard and wasabi. AITC is widely used experimentally as an inducer of acute pain and neurogenic inflammation, which are largely mediated by the activation of nociceptive cation channels transient receptor potential ankyrin 1 and transient receptor potential vanilloid 1 (TRPV1). Although it is generally accepted that electrophilic agents activate these channels through covalent modification of cytosolic cysteine residues, the mechanism underlying TRPV1 activation by AITC remains unknown. Here we show that, surprisingly, AITC-induced activation of TRPV1 does not require interaction with cysteine residues, but is largely dependent on S513, a residue that is involved in capsaicin binding. Furthermore, AITC acts in a membrane-delimited manner and induces a shift of the voltage dependence of activation toward negative voltages, which is reminiscent of capsaicin effects. These data indicate that AITC acts through reversible interactions with the capsaicin binding site. In addition, we show that TRPV1 is a locus for cross-sensitization between AITC and acidosis in nociceptive neurons. Furthermore, we show that residue F660, which is known to determine the stimulation by low pH in human TRPV1, is also essential for the cross-sensitization of the effects of AITC and low pH. Taken together, these findings demonstrate that not all reactive electrophiles stimulate TRPV1 via cysteine modification and help understanding the molecular bases underlying the surprisingly large role of this channel as mediator of the algesic properties of AITC.

Nano-Nucleation Characteristic of Cu-Ag Alloy Directly Electrodeposited on W Diffusion Barrier for Microelectronic Device Interconnect.

PubMed

Kim, Kang O; Kim, Sunjung

2016-05-01

Cu-Ag alloy interconnect is promising for ultra-large-scale integration (ULSI) microelectronic system of which device dimension keeps shrinking. In this study, seedless electrodeposition of Cu-Ag alloy directly on W diffusion barrier as interconnect technology is presented in respect of nano-nucleation control. Chemical equilibrium state of electrolyte was fundamentally investigated according to the pH of electrolyte because direct nano-nucleation of Cu-Ag alloy on W surface is challenging. Chelation behavior of Cu2+ and Ag+ ions with citrate (Cit) and ammonia ligands was dependent on the pH of electrolyte. The amount and kind of Cu- and Ag-based complexes determine the deposition rate, size, elemental composition, and surface morphology of Cu-Ag alloy nano-nuclei formed on W surface.

Staying Alive: Cancer Cells Expressing Mutant KRas Depend on ERH for Survival | Center for Cancer Research

Cancer.gov

The small G-protein KRas acts like a molecular switch, turning on and off pro-growth signaling pathways within cells when appropriate. In a large number of cancers, KRas is permanently turned on by a variety of mutations and drives the constant growth of these tumor cells. KRas itself has proved to be a poor drug target so researchers in the laboratory of Ji Luo, Ph.D., in

pH-dependent electron transfer reaction and direct bioelectrocatalysis of the quinohemoprotein pyranose dehydrogenase

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

Takeda, Kouta; Matsumura, Hirotoshi; Ishida, Takuya

A pyranose dehydrogenase from Coprinopsis cinerea (CcPDH) is an extracellular quinohemoeprotein, which consists a b-type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of CcPDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c) reacted via the cytochrome domain of intact CcPDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of CcPDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron tomore » a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of L-fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of CcPDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. - Highlights: • pH dependencies of activity were different for the reduction of cyt c and DCPIP. • DET-based bioelectrocatalysis of CcPDH was observed. • The similar pH-dependent profile was found with cyt c and electrode. • The present results suggested that IET reaction of CcPDH shows pH dependence.« less

Dielectrophoresis-Assisted Integration of 1024 Carbon Nanotube Sensors into a CMOS Microsystem.

PubMed

Seichepine, Florent; Rothe, Jörg; Dudina, Alexandra; Hierlemann, Andreas; Frey, Urs

2017-05-01

Carbon-nanotube (CNT)-based sensors offer the potential to detect single-molecule events and picomolar analyte concentrations. An important step toward applications of such nanosensors is their integration in large arrays. The availability of large arrays would enable multiplexed and parallel sensing, and the simultaneously obtained sensor signals would facilitate statistical analysis. A reliable method to fabricate an array of 1024 CNT-based sensors on a fully processed complementary-metal-oxide-semiconductor microsystem is presented. A high-yield process for the deposition of CNTs from a suspension by means of liquid-coupled floating-electrode dielectrophoresis (DEP), which yielded 80% of the sensor devices featuring between one and five CNTs, is developed. The mechanism of floating-electrode DEP on full arrays and individual devices to understand its self-limiting behavior is studied. The resistance distributions across the array of CNT devices with respect to different DEP parameters are characterized. The CNT devices are then operated as liquid-gated CNT field-effect-transistors (LG-CNTFET) in liquid environment. Current dependency to the gate voltage of up to two orders of magnitude is recorded. Finally, the sensors are validated by studying the pH dependency of the LG-CNTFET conductance and it is demonstrated that 73% of the CNT sensors of a given microsystem show a resistance decrease upon increasing the pH value. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Escherichia coli YqjA, a Member of the Conserved DedA/Tvp38 Membrane Protein Family, Is a Putative Osmosensing Transporter Required for Growth at Alkaline pH

PubMed Central

Kumar, Sujeet

2015-01-01

ABSTRACT The ability to persist and grow under alkaline conditions is an important characteristic of many bacteria. In order to survive at alkaline pH, Escherichia coli must maintain a stable cytoplasmic pH of about 7.6. Membrane cation/proton antiporters play a major role in alkaline pH homeostasis by catalyzing active inward proton transport. The DedA/Tvp38 family is a highly conserved membrane protein family of unknown function present in most sequenced genomes. YqjA and YghB are members of the E. coli DedA family with 62% amino acid identity and partially redundant functions. We have shown that E. coli with ΔyqjA and ΔyghB mutations cannot properly maintain the proton motive force (PMF) and is compromised in PMF-dependent drug efflux and other PMF-dependent functions. Furthermore, the functions of YqjA and YghB are dependent upon membrane-embedded acidic amino acids, a hallmark of several families of proton-dependent transporters. Here, we show that the ΔyqjA mutant (but not ΔyghB) cannot grow under alkaline conditions (ranging from pH 8.5 to 9.5), unlike the parent E. coli. Overexpression of yqjA restores growth at alkaline pH, but only when more than ∼100 mM sodium or potassium is present in the growth medium. Increasing the osmotic pressure by the addition of sucrose enhances the ability of YqjA to support growth under alkaline conditions in the presence of low salt concentrations, consistent with YqjA functioning as an osmosensor. We suggest that YqjA possesses proton-dependent transport activity that is stimulated by osmolarity and that it plays a significant role in the survival of E. coli at alkaline pH. IMPORTANCE The ability to survive under alkaline conditions is important for many species of bacteria. Escherichia coli can grow at pH 5.5 to 9.5 while maintaining a constant cytoplasmic pH of about 7.6. Under alkaline conditions, bacteria rely upon proton-dependent transporters to maintain a constant cytoplasmic pH. The DedA/Tvp38 protein family is a highly conserved but poorly characterized family of membrane proteins. Here, we show that the DedA/Tvp38 protein YqjA is critical for E. coli to survive at pH 8.5 to 9.5. YqjA requires sodium and potassium for this function. At low cation concentrations, osmolytes, including sucrose, can facilitate rescue of E. coli growth by YqjA at high pH. These data are consistent with YqjA functioning as an osmosensing cation-dependent proton transporter. PMID:25917916

Influence of pH on hydrothermal treatment of swine manure: Impact on extraction of nitrogen and phosphorus in process water.

PubMed

Ekpo, U; Ross, A B; Camargo-Valero, M A; Fletcher, L A

2016-08-01

This study investigates the influence of pH on extraction of nitrogen and phosphorus from swine manure following hydrothermal treatment. Conditions include thermal hydrolysis (TH) at 120°C and 170°C, and hydrothermal carbonisation (HTC) at 200°C and 250°C in either water alone or in the presence of 0.1M NaOH, H2SO4, CH3COOH or HCOOH. Phosphorus extraction is pH and temperature dependent and is enhanced under acidic conditions. The highest level of phosphorus is extracted using H2SO4 reaching 94% at 170°C. The phosphorus is largely retained in the residue for all other conditions. The extraction of nitrogen is not as significantly influenced by pH, although the maximum N extraction is achieved using H2SO4. A significant level of organic-N is extracted into the process waters following hydrothermal treatment. The results indicate that operating hydrothermal treatment in the presence of acidic additives has benefits in terms of improving the extraction of phosphorus and nitrogen. Copyright © 2016. Published by Elsevier Ltd.

Oxidative versus Non-oxidative Decarboxylation of Amino Acids: Conditions for the Preferential Formation of Either Strecker Aldehydes or Amines in Amino Acid/Lipid-Derived Reactive Carbonyl Model Systems.

PubMed

Zamora, Rosario; León, M Mercedes; Hidalgo, Francisco J

2015-09-16

Comparative formation of both 2-phenylethylamine and phenylacetaldehyde as a consequence of phenylalanine degradation by carbonyl compounds was studied in an attempt to understand if the amine/aldehyde ratio can be changed as a function of reaction conditions. The assayed carbonyl compounds were selected because of the presence in the chain of both electron-donating and electron-withdrawing groups and included alkenals, alkadienals, epoxyalkenals, oxoalkenals, and hydroxyalkenals as well as lipid hydroperoxides. The obtained results showed that the 2-phenylethylamine/phenylacetaldehyde ratio depended upon both the carbonyls and the reaction conditions. Thus, it can be increased using electron-donating groups in the chain of the carbonyl compound, small amounts of carbonyl compound, low oxygen content, increasing the pH, or increasing the temperature at pH 6. Opposed conditions (use of electron-withdrawing groups in the chain of the carbonyl compound, large amounts of carbonyl compound, high oxygen contents, low pH values, and increasing temperatures at low pH values) would decrease the 2-phenylethylamine/phenylacetaldehyde ratio, and the formation of aldehydes over amines in amino acid degradations would be favored.

Stability of self-assembled polymer films investigated by optical laser reflectometry.

PubMed

Dejeu, Jérôme; Diziain, Séverine; Dange, Catherine; Membrey, François; Charraut, Daniel; Foissy, Alain

2008-04-01

We studied the influence of post-treatment rinsing after the formation of self-assembled polyelectrolyte films made with the weak base poly(allylamine hydrochloride) (PAH) and the strong acid poly(styrene sulfonate) (PSS). The stability of the film was studied using optical fixed-angle laser reflectometry to measure the release of polymeric material and AFM experiments to reveal the change of morphology and thickness. We found that the polymer films were stable upon rinsing when the pH was the same in the solution as that used in the buildup (pH 9). The films released most of the polymeric material when rinsed at higher pH values, but a layer remained that corresponded to a PAH monolayer directly bound with the silica surface. Films containing at least four bilayers were stable upon rinsing at lower pH values, but the stability of thinner films depended on the type of the last polymer deposited. They were stable in the case of PSS as an outermost deposit, but they released a large part of their material in the case of PAH. The stability results were determined using a simple model of the step-by-step assembly of the polymer film described formerly.

Differential capacity of kaolinite and birnessite to protect surface associated proteins against thermal degradation

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

Chacon, Stephany S.; Garcia-Jaramillo, Manuel; Liu, Suet Yi

2018-02-28

We report it is widely accepted that soil organic carbon cycling depends on the presence and catalytic functionality of extracellular enzymes. Recent reports suggest that combusted and autoclaved soils may have the capacity to degrade organic test substrates to a larger extent than the living, enzyme-bearing soils. In search of the underlying mechanisms, we adsorbed Beta-Glucosidase (BG) and Bovine Serum Albumin (BSA) on the phyllosilicate kaolinite and the manganese oxide birnessite at pH 5 and pH 7. The protein-mineral samples were then subjected to gradual energy inputs of a magnitude equivalent to naturally occurring wildfire events. The abundance and molecularmore » masses of desorbed organic compounds were recorded after ionization with tunable synchrotron vacuum ultraviolet radiation (VUV). The mechanisms controlling the fate of proteins varied with mineralogy. Kaolinite adsorbed protein largely through hydrophobic interactions and, even at large energy inputs, produced negligible amounts of desorption fragments compared to birnessite. Acid birnessite adsorbed protein through coulombic forces at low energy levels, became a hydrolyzing catalyst at low energies and low pH, and eventually turned into a reactant involving disintegration of both mineral and protein at higher energy inputs. Fragmentation of proteins was energy dependent and did not occur below an energy threshold of 0.20 MW cm -2 . Neither signal abundance nor signal intensity were a function of protein size. Above the energy threshold value, BG that had been adsorbed to birnessite at pH 7 showed an increase in signal abundance with increasing energy applications. Signal intensities differed with adsorption pH for BSA but only at the highest energy level applied. Our results indicate that proteins adsorbed to kaolinite may remain intact after exposure to such energy inputs as can be expected to occur in natural ecosystems. Protein fragmentation and concomitant loss of functionality must be expected in surface soils replete with pedogenic manganese oxides. Lastly, we conclude that minerals can do both: protect enzymes at high energy intensities in the case of kaolinite and, in the case of birnessite, substitute for and even exceed the oxidative functionality that may have been lost when unprotected oxidative enzymes were denatured at high energy inputs.« less

Cloud chemistry in eastern China: Observations from Mt. Tai

NASA Astrophysics Data System (ADS)

Collett, J. L.; Shen, X.; Lee, T.; Wang, X.; Li, Y.; Wang, W.; Wang, T.

2010-07-01

Until recently, studies of fog and cloud chemistry in China have been rare - even though the fate of China’s large sulfur dioxide emissions depends, in part, on the ability of regional clouds to support rapid aqueous oxidation to sulfate. Sulfur dioxide oxidized in regional clouds is more likely to be removed by wet deposition while sulfur dioxide that undergoes slower gas phase oxidation is expected to survive longer in the atmosphere and be transported over a much broader spatial scale. Two 2008 field campaigns conducted at Mt. Tai, an isolated peak on the NE China plain, provide insight into the chemical composition of regional clouds and the importance of various aqueous phase sulfur oxidation pathways. Single and two-stage Caltech Active Strand Cloudwater Collectors were used to collect bulk and drop size-resolved samples of cloudwater. Collected cloudwater was analyzed for key species that influence in-cloud sulfate production, including pH, S(IV), H2O2, Fe and Mn. Other major cloud solutes, including inorganic ions, total organic carbon (TOC), formaldehyde, and organic acids were also analyzed, as were gas phase concentrations of SO2, O3, and H2O2. A wide range of cloud pH was observed, from below 3 to above 6. High concentrations of cloudwater sulfate were consistent with abundant sulfur dioxide emissions in the region. Sampled clouds were also found to contain high concentrations of ammonium, nitrate, and organic carbon. Peak TOC concentrations reached approximately 200 ppmC, among the highest concentrations ever measured in cloudwater. Hydrogen peroxide was found to be the dominant aqueous phase S(IV) oxidant when cloud pH was less than approximately 5.4. Despite its fast reaction with sulfur dioxide in cloud droplets, high concentrations of residual hydrogen peroxide were measured in some clouds implying a substantial additional capacity for sulfate production. Ozone was found to be an important S(IV) oxidant when cloud pH was high. Oxidation of S(IV) by oxygen, catalyzed by Fe (III) and Mn(II) was generally the second or third fastest pathway for sulfate production. Differences between the pH and trace metal concentrations of small and large cloud droplets were observed, giving rise to aqueous phase sulfate production rates that were drop size-dependent for the ozone and metal-catalyzed pathways.

Control of continuous phase PH using visible light to activate PH-dependent fibers and gels in a controlled and reversible manner

NASA Astrophysics Data System (ADS)

Zirino, Albert

1994-08-01

A transparent polyelectrolyte fiber or gel, such as crosslinked polyacrylic acid, which contracts and expands upon the addition of an acid or base to an aqueous medium solution, is placed in the same solution with a pH dependent dye, a colored photochromatic indicator dye. The dye preferably has a pAa value that is the same as the pH at a null contraction point of the fiber. By irradiating the solution with light of a wavelength of the absorption band of either the acid or base form of the dye, the solution pH is made to change, and the fiber is made to expand or contract, depending upon the wavelength. Thus, light energy is readily converted to work energy and may be used to power a pump, for example or an artificial muscle can be powered via an optical fiber.

Two-dimensional pH distributions and dynamics in bioturbated marine sediments

NASA Astrophysics Data System (ADS)

Zhu, Qingzhi; Aller, Robert C.; Fan, Yanzhen

2006-10-01

The seafloor is the site of intense biogeochemical and mineral dissolution-precipitation reactions which generate strong gradients in pH near the sediment-overlying water interface. These gradients are usually measured in one-dimension vertically with depth. Two-dimensional pH distributions in marine sediments were examined at high resolution (65 × 65 μm pixel) and analytical precision over areas of ˜150 to 225 cm 2 using a newly developed pH planar fluorosensor. Dramatic three-dimensional gradients, complex heterogeneity, and dynamic changes of pH occur in the surficial zone of deposits inhabited by macrofauna. pH can vary by ±2 units horizontally as well as vertically over millimeter scales. pH minima zones often form in association with redoxclines within a few millimeters of inner burrow walls, and become more pronounced with time if burrows remain stable and irrigated for extended periods. Microenvironmental pH minima also form locally around decaying biomass and relict burrow tracks, and dissipate with time (˜5 d). H + concentrations and fluxes in sandy mud show complex acid-base reaction distributions with net H + fluxes around burrows up to ˜12 nmol cm -2 d -1 and maximum net reaction rates varying between -90 (consumption) to 120 (production) μM d -1 (˜90 nmol cm -1 d -1 burrow length). Acid producing zones that surround irrigated burrows are largely balanced by acid titration zones along inner burrow walls and outer radial boundaries. The geometry and scaling of pH microenvironments are functions of diagenetic reaction rates and three-dimensional transport patterns determined by sediment properties, such as diffusive tortuosity, and by benthic community characteristics such as the abundance, mobility, and size of infauna. Previously, undocumented biogeochemical phenomena such as low pH regions associated with in-filled relict biogenic structures and burrowing tracks are readily demonstrated by two-dimensional and time-dependent images of pH and sedimentary structure.

Enzyme Sorption onto Soil and Biocarbon Amendments Alters Catalytic Capacity and Depends on the Specific Protein and pH

NASA Astrophysics Data System (ADS)

Foster, E.; Fogle, E. J.; Cotrufo, M. F.

2017-12-01

Enzymes catalyze biogeochemical reactions in soils and play a key role in nutrient cycling in agricultural systems. Often, to increase soil nutrients, agricultural managers add organic amendments and have recently experimented with charcoal-like biocarbon products. These amendments can enhance soil water and nutrient holding capacity through increasing porosity. However, the large surface area of the biocarbon has the potential to sorb nutrients and other organic molecules. Does the biocarbon decrease nutrient cycling through sorption of enzymes? In a laboratory setting, we compared the interaction of two purified enzymes β-glucosidase and acid phosphatase with a sandy clay loam and two biocarbons. We quantified the sorbed enzymes at three different pHs using a Bradford protein assay and then measured the activity of the sorbed enzyme via high-throughput fluorometric analysis. Both sorption and activity depended upon the solid phase, pH, and specific enzyme. Overall the high surface area biocarbon impacted the catalytic capacity of the enzymes more than the loam soil, which may have implications for soil nutrient management with these organic amendments.

Impact of pH on Urine Chemistry Assayed on Roche Analyzers.

PubMed

Cohen, R; Alkouri, R; Tostivint, I; Djiavoudine, S; Mestari, F; Dever, S; Atlan, G; Devilliers, C; Imbert-Bismut, F; Bonnefont-Rousselot, D; Monneret, D

2017-10-01

The pH may impact the concentration of certain urinary parameters, making urine pre-treatment questionable. 1) Determining the impact of pH in vitro on the urinary concentration of chemistry parameters assayed on Roche Modular analyzers. 2) Evaluating whether concentrations depended on pH in non-pretreated urines from patients. 1) The optimal urinary pH values for each measurement were: 6.3 ± 0.8 (amylase), < 5.5 (calcium and magnesium), < 6.5 (phosphorus), > 6.5 (uric acid). Urinary creatinine, sodium and urea concentrations were not pH-dependent. 2) In urines from patients, the pH was negatively associated with the concentration of some urinary parameters. However, concentrations of all the parameters were strongly and positively correlated with urinary creatinine, and relationships with pH were no longer evidenced after creatinine-normalization. The need for urine pH adjustment does not seem necessary when considering renal function. However, from an analytical and accreditation standpoint, the relationship between urine pH and several parameters justifies its measurement.

A thermal and chemical degradation approach to decipher pristane and phytane precursors in sedimentary organic matter

USGS Publications Warehouse

Koopmans, M.P.; Rijpstra, W.I.C.; Klapwijk, M.M.; De Leeuw, J. W.; Lewan, M.D.; Sinninghe, Damste J.S.

1999-01-01

A thermal and chemical degradation approach was followed to determine the precursors of pristane (Pr) and phytane (Ph) in samples from the Gessoso-solfifera, Ghareb and Green River Formations. Hydrous pyrolysis of these samples yields large amounts of Pr and Ph carbon skeletons, indicating that their precursors are predominantly sequestered in high-molecular-weight fractions. However, chemical degradation of the polar fraction and the kerogen of the unheated samples generally does not release large amounts of Pr and Ph. Additional information on the precursors of Pr and Ph is obtained from flash pyrolysis analyses of kerogens and residues after hydrous pyrolysis and after chemical degradation. Multiple precursors for Pr and Ph are recognised in these three samples. The main increase of the Pr/Ph ratio with increasing maturation temperature, which is associated with strongly increasing amounts of Pr and Ph, is probably due to the higher amount of precursors of Pr compared to Ph, and not to the different timing of generation of Pr and Ph.A thermal and chemical degradation approach was followed to determine the precursors of pristane (Pr) and phytane (Ph) in samples from the Gessoso-solfifera, Ghareb and Green River Formations. Hydrous pyrolysis of these samples yields large amounts of Pr and Ph carbon skeletons, indicating that their precursors are predominantly sequestered in high-molecular-weight fractions. However, chemical degradation of the polar fraction and the kerogen of the unheated samples generally does not release large amounts of Pr and Ph. Additional information on the precursors of Pr and Ph is obtained from flash pyrolysis analyses of kerogens and residues after hydrous pyrolysis and after chemical degradation. Multiple precursors for Pr and Ph are recognised in these three samples. The main increase of the Pr/Ph ratio with increasing maturation temperature, which is associated with strongly increasing amounts of Pr and Ph, is probably due to the higher amount of precursors of Pr compared to Ph, and not to the different timing of generation of Pr and Ph.

Interaction of melanin with proteins--the importance of an acidic intramelanosomal pH.

PubMed

Mani, I; Sharma, V; Tamboli, I; Raman, G

2001-06-01

Melanin is a highly irregular heteropolymer consisting of monomeric units derived from the enzymatic oxidation of the amino acid tyrosine. The process of melanin formation takes place in specialized acidic organelles (melanosomes) in melanocytes. The process of melanin polymerization requires an alkaline pH in vitro, and therefore, the purpose of an acidic environment in vivo remains a mystery. It is known that melanin is always bound to protein in vivo. It is also seen that polymerization in vitro at an acidic pH necessarily requires the presence of proteins. The effect of various model proteins on melanin synthesis and their interaction with melanin was studied. It was seen that many proteins could increase melanin synthesis at an acidic pH, and that different proteins resulted in the formation of different states of melanin, i.e., a precipitate or a soluble, protein-bound form. We also present evidence to show that soluble protein-bound melanin is present in vivo (in B16 cells as well as in B16 melanoma tissue). An acidic pH appeared to be necessary to ensure the formation of a uniform, very high molecular weight melano-protein complex. The interaction between melanin and proteins appears to be largely charge-dependent as evidenced by zeta potential measurements, and this interaction is also increased in an acidic pH. Thus, it appears that an acidic intramelanosomal pH is essential to ensure maximum interaction between protein and melanin, and also to ensure that all the melanin formed is protein-bound.

Modeling the influence of variable pH on the transport of zinc in a contaminated aquifer using semiempirical surface complexation models

USGS Publications Warehouse

Kent, D.B.; Abrams, R.H.; Davis, J.A.; Coston, J.A.; LeBlanc, D.R.

2000-01-01

Land disposal of sewage effluent resulted in contamination of a sand and gravel aquifer (Cape Cod, Massachusetts) with zinc (Zn). The distribution of Zn was controlled by pH‐dependent adsorption; the Zn extended 15 m into the 30‐m‐thick sewage plume within approximately 100 m of the source but only 2–4 m into the plume between 100 and 400 m downgradient. A two‐dimensional vertical cross section model coupling groundwater flow with solute transport and equilibrium adsorption is used to simulate the influence of pH on Zn transport. Adsorption is described using semiempirical surface complexation models (SCM) by writing chemical reactions between dissolved Zn and mineral surface sites. SCM parameters were determined in independent laboratory experiments. A 59‐year simulation with a one‐site SCM describes the influence of pH on Zn transport well, with greater mobility at the low pH values near the upper sewage plume boundary than at the higher pH values deeper in the sewage‐contaminated zone. Simulation with a two‐site SCM describes both the sharpness and approximate location of the leading edge of the Zn‐contaminated region. Temporal variations in pH of incoming groundwater can result in large increases in Zn concentration and mobility. The influence of spatial and temporal variability in pH on adsorption and transport of Zn was accomplished much more easily with the semiempirical SCM approach than could be achieved with distribution coefficients or adsorption isotherms.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

PubMed Central

Malik, Erum; Dennison, Sarah R.; Harris, Frederick; Phoenix, David A.

2016-01-01

Antimicrobial peptides (AMPs) are potent antibiotics of the innate immune system that have been extensively investigated as a potential solution to the global problem of infectious diseases caused by pathogenic microbes. A group of AMPs that are increasingly being reported are those that utilise pH dependent antimicrobial mechanisms, and here we review research into this area. This review shows that these antimicrobial molecules are produced by a diverse spectrum of creatures, including vertebrates and invertebrates, and are primarily cationic, although a number of anionic examples are known. Some of these molecules exhibit high pH optima for their antimicrobial activity but in most cases, these AMPs show activity against microbes that present low pH optima, which reflects the acidic pH generally found at their sites of action, particularly the skin. The modes of action used by these molecules are based on a number of major structure/function relationships, which include metal ion binding, changes to net charge and conformational plasticity, and primarily involve the protonation of histidine, aspartic acid and glutamic acid residues at low pH. The pH dependent activity of pore forming antimicrobial proteins involves mechanisms that generally differ fundamentally to those used by pH dependent AMPs, which can be described by the carpet, toroidal pore and barrel-stave pore models of membrane interaction. A number of pH dependent AMPs and antimicrobial proteins have been developed for medical purposes and have successfully completed clinical trials, including kappacins, LL-37, histatins and lactoferrin, along with a number of their derivatives. Major examples of the therapeutic application of these antimicrobial molecules include wound healing as well as the treatment of multiple cancers and infections due to viruses, bacteria and fungi. In general, these applications involve topical administration, such as the use of mouth washes, cream formulations and hydrogel delivery systems. Nonetheless, many pH dependent AMPs and antimicrobial proteins have yet to be fully characterized and these molecules, as a whole, represent an untapped source of novel biologically active agents that could aid fulfillment of the urgent need for alternatives to conventional antibiotics, helping to avert a return to the pre-antibiotic era. PMID:27809281

pH imaging of mouse kidneys in vivo using a frequency-dependent paraCEST agent

PubMed Central

Wu, Yunkou; Zhang, Shanrong; Soesbe, Todd C.; Yu, Jing; Vinogradov, Elena; Lenkinski, Robert E.; Sherry, A. Dean

2015-01-01

Purpose This study explored the feasibility of using a pH responsive paraCEST agent to image the pH gradient in kidneys of healthy mice. Methods CEST signals were acquired on an Agilent 9.4 T small animal MRI system using a steady-state gradient echo pulse sequence after a bolus injection of agent. The magnetic field inhomogeneity across each kidney was corrected using the WASSR method and pH maps were calculated by measuring the frequency of water exchange signal arising from the agent. Results Dynamic CEST studies demonstrated that the agent was readily detectable in kidneys only between 4 to 12 min post-injection. The CEST images showed a higher signal intensity in the pelvis and calyx regions and lower signal intensity in the medulla and cortex regions. The pH maps reflected tissue pH values spanning from 6.0 to 7.5 in kidneys of healthy mice. Conclusion This study demonstrated that pH maps of the kidney can be imaged in vivo by measuring the pH-dependent chemical shift of a single water exchange CEST peak without prior knowledge of the agent concentration in vivo. The results demonstrate the potential of using a simple frequency-dependent paraCEST agent for mapping tissue pH in vivo. PMID:26173637

Gold Binding by Native and Chemically Modified Hops Biomasses

DOE PAGES

López, M. Laura; Gardea-Torresdey, J. L.; Peralta-Videa, J. R.; ...

2005-01-01

Heavy metals from mining, smelting operations and other industrial processing facilities pollute wastewaters worldwide. Extraction of metals from industrial effluents has been widely studied due to the economic advantages and the relative ease of technical implementation. Consequently, the search for new and improved methodologies for the recovery of gold has increased. In this particular research, the use of cone hops biomass ( Humulus lupulus ) was investigated as a new option for gold recovery. The results showed that the gold binding to native hops biomass was pH dependent from pH 2 to pH 6, with a maximum percentage binding atmore » pH 3. Time dependency studies demonstrated that Au(III) binding to native and modified cone hops biomasses was found to be time independent at pH 2 while at pH 5, it was time dependent. Capacity experiments demonstrated that at pH 2, esterified hops biomass bound 33.4 mg Au/g of biomass, while native and hydrolyzed hops biomasses bound 28.2 and 12.0 mg Au/g of biomass, respectively. However, at pH 5 the binding capacities were 38.9, 37.8 and 11.4 mg of Au per gram of native, esterified and hydrolyzed hops biomasses, respectively.« less

Arrestin-related proteins mediate pH signaling in fungi.

PubMed

Herranz, Silvia; Rodríguez, José M; Bussink, Henk-Jan; Sánchez-Ferrero, Juan C; Arst, Herbert N; Peñalva, Miguel A; Vincent, Olivier

2005-08-23

Metazoan arrestins bind to seven-transmembrane (7TM) receptors to regulate function. Aspergillus nidulans PalF, a protein involved in the fungal ambient pH signaling pathway, contains arrestin N-terminal and C-terminal domains and binds strongly to two different regions within the C-terminal cytoplasmic tail of the 7TM, putative pH sensor PalH. Upon exposure to alkaline ambient pH, PalF is phosphorylated and, like mammalian beta-arrestins, ubiquitinated in a signal-dependent and 7TM protein-dependent manner. Substitution in PalF of a highly conserved arrestin N-terminal domain Ser residue prevents PalF-PalH interaction and pH signaling in vivo. Thus, PalF is the first experimentally documented fungal arrestin-related protein, dispelling the notion that arrestins are restricted to animal proteomes. Epistasis analyses demonstrate that PalF posttranslational modification is partially dependent on the 4TM protein PalI but independent of the remaining pH signal transduction pathway proteins PalA, PalB, and PalC, yielding experimental evidence bearing on the order of participation of the six components of the pH signal transduction pathway. Our data strongly implicate PalH as an ambient pH sensor, possibly with the cooperation of PalI.

Chloride Fluxes in Isolated Dialyzed Barnacle Muscle Fibers

PubMed Central

DiPolo, R.

1972-01-01

Chloride outflux and influx has been studied in single isolated muscle fibers from the giant barnacle under constant internal composition by means of a dialysis perfusion technique. Membrane potential was continually recorded. The chloride outfluxes and influxes were 143 and 144 pmoles/cm2-sec (mean resting potential: 58 mv, temperature: 22°–24°C) with internal and external chloride concentrations of 30 and 541 mM, respectively. The chloride conductance calculated from tracer measurements using constant field assumptions is about fourfold greater than that calculated from published electrical data. Replacing 97% of the external chloride ions by propionate reduces the chloride efflux by 51%. Nitrate ions applied either to the internal or external surface of the membrane slows the chloride efflux. The external pH dependence of the chloride efflux follows the external pH dependence of the membrane conductance, in the range pH 3.9–4.7, increasing with decreasing pH. In the range pH 5–9, the chloride efflux increased with increasing pH, in a manner similar to that observed in frog muscle fibers. The titration curve for internal pH changes in the range 4.0–7.0 was quantitatively much different from that for external pH change, indicating significant asymmetry in the internal and external pH dependence of the chloride efflux. PMID:5074810

Extracellular pH Modulates Neuroendocrine Prostate Cancer Cell Metabolism and Susceptibility to the Mitochondrial Inhibitor Niclosamide

PubMed Central

Ippolito, Joseph E.; Brandenburg, Matthew W.; Ge, Xia; Crowley, Jan R.; Kirmess, Kristopher M.; Som, Avik; D’Avignon, D. Andre; Arbeit, Jeffrey M.; Achilefu, Samuel; Yarasheski, Kevin E.; Milbrandt, Jeffrey

2016-01-01

Neuroendocrine prostate cancer is a lethal variant of prostate cancer that is associated with castrate-resistant growth, metastasis, and mortality. The tumor environment of neuroendocrine prostate cancer is heterogeneous and characterized by hypoxia, necrosis, and numerous mitoses. Although acidic extracellular pH has been implicated in aggressive cancer features including metastasis and therapeutic resistance, its role in neuroendocrine prostate cancer physiology and metabolism has not yet been explored. We used the well-characterized PNEC cell line as a model to establish the effects of extracellular pH (pH 6.5, 7.4, and 8.5) on neuroendocrine prostate cancer cell metabolism. We discovered that alkalinization of extracellular pH converted cellular metabolism to a nutrient consumption-dependent state that was susceptible to glucose deprivation, glutamine deprivation, and 2-deoxyglucose (2-DG) mediated inhibition of glycolysis. Conversely, acidic pH shifted cellular metabolism toward an oxidative phosphorylation (OXPHOS)-dependent state that was susceptible to OXPHOS inhibition. Based upon this mechanistic knowledge of pH-dependent metabolism, we identified that the FDA-approved anti-helminthic niclosamide depolarized mitochondrial potential and depleted ATP levels in PNEC cells whose effects were enhanced in acidic pH. To further establish relevance of these findings, we tested the effects of extracellular pH on susceptibility to nutrient deprivation and OXPHOS inhibition in a cohort of castrate-resistant prostate cancer cell lines C4-2B, PC-3, and PC-3M. We discovered similar pH-dependent toxicity profiles among all cell lines with these treatments. These findings underscore a potential importance to acidic extracellular pH in the modulation of cell metabolism in tumors and development of an emerging paradigm that exploits the synergy of environment and therapeutic efficacy in cancer. PMID:27438712

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

Soileau, S.D.

Chlordecone (CHLO, 1-30 uM) and chlordecone alcohol (CHLO ALC, 1-23 uM) altered the permeability of isolated ovine erythrocytes (OE) as evidenced by a concentration- and time-dependent induction of K/sup +/ efflux and hemolysis. Hemolysis, but no K/sup +/ efflux, was markedly delayed when OE were suspended in isotonic sucrose. Low concentrations of both compounds (1-4 uM) protected OE against hypotonic hemolysis. Neither CHLO (30 uM) nor CHLO ALC (23 uM) induced the release of trapped K/sup +/ from KSCN-loaded, OE-lipid, unilamellar liposomes. CHLO- and CHLO ACL-induced hemolysis and K/sup +/ efflux were dependent upon the pH of the external media.more » CHLO ALC-induced K/sup +/ efflux and hemolysis showed a slight pH dependence, with increased potency of the compound detected over the pH range 8.3-9.4 CHLO ALC-induced protection against hypotonic hemolysis was pH independent. The potency of CHLO in all three assays decreased as the pH was raised from 6.4 to 9.4. (/sup 14/C)-CHLO and (/sup 14/C)-CHLO ALC binding to OE and OE membranes was pH independent. However, the binding of (/sup 14/C)-CHLO to polypropylene and glass was pH dependent. (/sup 14/C)-CHLO binding to polypropylene and glass decreased from pH 6.4 to pH 10.4. The pKa of CHLO was estimated to be 8.9. After the CHLO results were corrected for the fraction of CHLO present in the unionized form, it was estimated the ionized CHLO possessed 1/3 to 1/20 of the activity of the unionized species.« less

Dynamical electron-phonon coupling, G W self-consistency, and vertex effect on the electronic band gap of ice and liquid water

NASA Astrophysics Data System (ADS)

Ziaei, Vafa; Bredow, Thomas

2017-06-01

We study the impact of dynamical electron-phonon (el-ph) effects on the electronic band gap of ice and liquid water by accounting for frequency-dependent Fan contributions in the el-ph mediated self-energy within the many-body perturbation theory (MBPT). We find that the dynamical el-ph coupling effects greatly reduce the static el-ph band-gap correction of the hydrogen-rich molecular ice crystal from-2.46 to -0.23 eV in great contrast to the result of Monserrat et al. [Phys. Rev. B 92, 140302 (2015), 10.1103/PhysRevB.92.140302]. This is of particular importance as otherwise the static el-ph gap correction would considerably reduce the electronic band gap, leading to considerable underestimation of the intense peaks of optical absorption spectra of ice which would be in great disagreement to experimental references. By contrast, the static el-ph gap correction of liquid water is very moderate (-0.32 eV), and inclusion of dynamical effects slightly reduces the gap correction to -0.19 eV. Further, we determine the diverse sensitivity of ice and liquid water to the G W self-consistency and show that the energy-only self-consistent approach (GnWn ) exhibits large implicit vertex character in comparison to the quasiparticle self-consistent approach, for which an explicit calculation of vertex corrections is necessary for good agreement with experiment.

pH feedback and phenotypic diversity within bacterial functional groups of the human gut.

PubMed

Kettle, Helen; Donnelly, Ruairi; Flint, Harry J; Marion, Glenn

2014-02-07

Microbial diversity in the human colon is very high with apparently large functional redundancy such that within each bacterial functional group there are many coexisting strains. Modelling this mathematically is problematic since strains within a functional group are often competing for the same limited number of resources and therefore competitive exclusion theory predicts a loss of diversity over time. Here we investigate, through computer simulation, a fluctuation dependent mechanism for the promotion of diversity. A variable pH environment caused by acidic by-products of bacterial growth on a fluctuating substrate coupled with small differences in acid tolerance between strains promotes diversity under both equilibrium and far-from-equilibrium conditions. Under equilibrium conditions pH fluctuations and relative nonlinearity in pH limitation among strains combine to prevent complete competitive exclusion. Under far-from-equilibrium conditions, loss of diversity through extinctions is made more difficult because pH cycling leads to fluctuations in the competitive ranking of strains, thereby helping to equalise fitness. We assume a trade-off between acid tolerance and maximum growth rate so that our microbial system consists of strains ranging from specialists to generalists. By altering the magnitude of the effect of the system on its pH environment (e.g. the buffering capacity of the colon) and the pattern of incoming resource we explore the conditions that promote diversity. © 2013 Elsevier Ltd. Published by Elsevier Ltd. All rights reserved.

High concentrations of the carcinogen 2-amino-1-methyl-6-phenylimidazo- [4,5-b]pyridine (PhIP) occur in chicken but are dependent on the cooking method.

PubMed

Sinha, R; Rothman, N; Brown, E D; Salmon, C P; Knize, M G; Swanson, C A; Rossi, S C; Mark, S D; Levander, O A; Felton, J S

1995-10-15

Heterocyclic aromatic amines (HAAs) are mutagenic and carcinogenic compounds found in meats cooked at high temperatures. Although chicken is consumed in large quantities in the United States, there is little information on its HAA content. The objective of this study was to measure the five predominant HAAs (IQ, MeIQ, MeIQx, DiMeIQx, and PhIP) in chicken cooked by various methods to different degrees of doneness. Chicken breasts were panfried, oven-broiled, or grilled/barbecued. Whole chickens were roasted or stewed. Skinless, boneless chicken breasts were cooked to three degrees of doneness: just until done, well done, or very well done. High levels of PhIP (ranging from 12 to 480 ng/g cooked meat) were found in chicken breasts when panfried, oven-broiled, and grilled/barbecued but not in while roasted or stewed chicken. PhIP concentration increased in skinless, boneless chicken breast with longer cooking time, higher internal temperature, and greater degree of surface browning. PhIP concentration was also high in chicken breasts cooked with skin and bones. MeIQx and DiMeIQx levels increased with the degree of doneness, whereas IQ and MeIQ were not detectable in any of these chicken samples. Certain cooking methods produce PhIP, a known colon and breast carcinogen in rodents and possibly a human carcinogen, at substantially higher levels in chicken than has been reported previously in red meat.

The pH and ionic composition of stratiform cloud water

NASA Astrophysics Data System (ADS)

Castillo, Raymond A.; Jiusto, James E.; Mclaren, Eugene

Over 50 cloud water samples were collected during five comprehensive case studies of the water chemistry of stratiform clouds at Whiteface Mountain, New York. The water samples were analyzed for pH, conductivity and ions of sodium, potassium, magnesium, calcium, ammonium, sulfate, chloride and nitrate. Trajectory analyses and cloud condensation nucleus concentrations at 0.5 % confirmed that the air masses in all five of these cases represented continental air that was relatively clean (low aerosol concentration) for the northeystern United States. The major ions related to cloud water pH were found to be sulfate, nitrate, potassium, ammonium and calcium. The results revealed a mean hydrogen ion concentration [ H+] = 0.239 meq ℓ -1 ( σ = ± 0.21) which converts to a mean pH = 3.6 for all collected cloud samples. The low pH values are related to a normal background of nitrate ions found in the rural continental air masses plus sulfate ions largely from the industrial emissions of the midwestern United States. The [NO -3], in two of the three cases presented, demonstrates the importance of the nitrate ions' contribution to the pH of cloud water. A dependent means analysis of 40 events yielded a significant difference (0.04 level of significance), with the mean pH of precipitation (4.2) being greater than the mean pH of cloud water (4.0) for event samples. The ion concentrations indicated that the cloud rainout process contributed from 67 % to almost 100% of the total ion concentration of the precipitation. The washout process, i.e. precipitation scavenging below the cloud base, contributed considerably less than the cloud/rainout process of those total precipitation anions associated with air pollution.

In Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking Water.

PubMed

Ma, Xiangmeng; Armas, Stephanie M; Soliman, Mikhael; Lytle, Darren A; Chumbimuni-Torres, Karin; Tetard, Laurene; Lee, Woo Hyoung

2018-02-20

A novel method using a micro-ion-selective electrode (micro-ISE) technique was developed for in situ lead monitoring at the water-metal interface of a brass-leaded solder galvanic joint in a prepared chlorinated drinking water environment. The developed lead micro-ISE (100 μm tip diameter) showed excellent performance toward soluble lead (Pb 2+ ) with sensitivity of 22.2 ± 0.5 mV decade -1 and limit of detection (LOD) of 1.22 × 10 -6 M (0.25 mg L -1 ). The response time was less than 10 s with a working pH range of 2.0-7.0. Using the lead micro-ISE, lead concentration microprofiles were measured from the bulk to the metal surface (within 50 μm) over time. Combined with two-dimensional (2D) pH mapping, this work clearly demonstrated that Pb 2+ ions build-up across the lead anode surface was substantial, nonuniform, and dependent on local surface pH. A large pH gradient (ΔpH = 6.0) developed across the brass and leaded-tin solder joint coupon. Local pH decreases were observed above the leaded solder to a pH as low as 4.0, indicating it was anodic relative to the brass. The low pH above the leaded solder supported elevated lead levels where even small local pH differences of 0.6 units (ΔpH = 0.6) resulted in about four times higher surface lead concentrations (42.9 vs 11.6 mg L -1 ) and 5 times higher fluxes (18.5 × 10 -6 vs 3.5 × 10 -6 mg cm -2 s -1 ). Continuous surface lead leaching monitoring was also conducted for 16 h.

pH and Ion Homeostasis on Plant Endomembrane Dynamics: Insights from structural models and mutants of K+/H+ antiporters.

PubMed

Sze, Heven; Chanroj, Salil

2018-04-24

Plants remodel their cells through the dynamic endomembrane system. Intracellular pH is important for membrane trafficking, but the determinants of pH homeostasis are poorly defined in plants. Electrogenic proton (H+) pumps depend on counter-ion fluxes to establish transmembrane pH gradients at the plasma membrane and endomembranes. Vacuolar-type H+-ATPase-mediated acidification of the trans-Golgi network (TGN) is crucial for secretion and membrane recycling. Pump and counter-ion fluxes are unlikely to fine-tune pH; rather, alkali cation/H+ antiporters, which can alter pH and/or cation homeostasis locally and transiently, are prime candidates. Plants have a large family of predicted cation/H+ exchangers (CHX) of obscure function, in addition to the well-studied K+(Na+)/H+ exchangers (NHX). Here, we review the regulation of cytosolic and vacuolar pH, highlighting the similarities and distinctions of NHX and CHX members. In planta, alkalinization of the TGN or vacuole by NHXs promotes membrane trafficking, endocytosis, cell expansion, and growth. CHXs localize to endomembranes and/or the plasma membrane, contribute to male fertility, pollen tube guidance, pollen wall construction, stomatal opening, and in soybean (Glycine max), tolerance to salt stress. Three-dimensional structural models and mutagenesis of Arabidopsis thaliana genes have allowed us to infer that AtCHX17 and AtNHX1 share a global architecture and a translocation core like bacterial Na+/H+ antiporters. Yet the presence of distinct residues suggests some CHXs differ from NHXs in pH sensing and electrogenicity. How H+ pumps, counter-ion fluxes, and cation/H+ antiporters are linked with signaling and membrane trafficking to remodel membranes and cell walls awaits further investigation. {copyright, serif} 2018 American Society of Plant Biologists. All rights reserved.

Stabilization of milk proteins in acidic conditions by pectic polysaccharides extracted from soy flour.

PubMed

Cai, Y; Cai, B; Ikeda, S

2017-10-01

Pectic polysaccharides were extracted from soy flour at either room temperature (SPRT) or 121°C (SPH), and their abilities to stabilize milk proteins in acidic conditions were evaluated. Both SPRT and SPH were found to contain proteinaceous components that were difficult to dissociate from polysaccharide components using size exclusion chromatography, whereas the molar mass of the former was approximately twice that of the latter. Due to the higher molar mass, SPRT was expected to provide stronger steric effects to prevent aggregation between milk proteins in acidic conditions than SPH. Alkaline treatment of SPRT for breaking O-linkages between AA and monosaccharide residues decreased its molar mass by approximately 160 kDa, indicating that they contained naturally occurring conjugates of pectic and proteinaceous moieties. Particle size distributions in simulated acidified milk drink samples containing 0.2% SPRT or SPH showed monomodal distributions with median diameters of around 1.2 μm at pH 4. The presence of large protein aggregates (∼5 μm) was detected at 0.2% SPRT and pH 3.2, 0.6 to 0.8% SPRT and pH 4, or 0.2% SPH and pH 3.4. The presence of excess polysaccharide molecules unbound to proteins was detected at 0.2% SPRT and pH 3.2 to 3.4, 0.4 to 0.8% SPRT and pH 4, 0.2% SPH and pH 3.4 to 3.6, and 0.4 to 0.8% SPH and pH 4. The present results suggest that molecular characteristics of pectic polysaccharides vary depending on extraction conditions and hence their functional behavior. Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

A pH dependent Raman and surface enhanced Raman spectroscopic studies of citrazinic acid aided by theoretical calculations

NASA Astrophysics Data System (ADS)

Sarkar, Sougata; Chowdhury, Joydeep; Dutta, Soumen; Pal, Tarasankar

2016-12-01

A pH dependent normal Raman scattering (NRS) and surface enhanced Raman scattering (SERS) spectral patterns of citrazinic acid (CZA), a biologically important molecule, have been investigated. The acid, with different pKa values ( 4 and 11) for the two different functional groups (-COOH and -OH groups), shows interesting range of color changes (yellow at pH 14 and brown at pH 2) with the variation in solution pH. Thus, depending upon the pH of the medium, CZA molecule can exist in various protonated and/or deprotonated forms. Here we have prescribed the existence different possible forms of CZA at different pH (Forms ;C;, ;H; and ;Dprot; at pH 14 and Forms ;A;, ;D;, and ;P; at pH 2 respectively). The NRS spectra of these solutions and their respective SERS spectra over gold nanoparticles were recorded. The spectra clearly differ in their spectral profiles. For example the SERS spectra recorded with the CZA solution at pH 2 shows blue shift for different bands compared to its NRS window e.g. 406 to 450 cm- 1, 616 to 632 cm- 1, 1332 to 1343 cm- 1 etc. Again, the most enhanced peak at 1548 cm- 1 in NRS while in the SERS window this appears at 1580 cm- 1. Similar observation was also made for CZA at pH 14. For example, the 423 cm- 1 band in the NRS profile experience a blue shift and appears at 447 cm- 1 in the SERS spectrum as well as other bands at 850, 1067 and 1214 cm- 1 in the SERS window are markedly enhanced. It is also worth noting that the SERS spectra at the different pH also differ from each other. These spectral differences indicate the existence of various adsorptive forms of the CZA molecule depending upon the pH of the solution. Therefore based on the experimental findings we propose different possible molecular forms of CZA at different pH (acidic and alkaline) conditions. For example forms 'A', 'D' and 'P' existing in acidic pH (pH 2) and three other deprotonated forms 'C', 'H' and 'Dprot' in alkaline pH (pH 14). The DFT calculations for these prescribed model systems were also carried out to have a plausible understanding of their equilibrium geometries and the vibrational wavenumbers. An idea about the molecular orientation of the adsorbate over nanocolloidal gold substrate is also documented.

A pH dependent Raman and surface enhanced Raman spectroscopic studies of citrazinic acid aided by theoretical calculations.

PubMed

Sarkar, Sougata; Chowdhury, Joydeep; Dutta, Soumen; Pal, Tarasankar

2016-12-05

A pH dependent normal Raman scattering (NRS) and surface enhanced Raman scattering (SERS) spectral patterns of citrazinic acid (CZA), a biologically important molecule, have been investigated. The acid, with different pKa values (~4 and ~11) for the two different functional groups (-COOH and -OH groups), shows interesting range of color changes (yellow at pH~14 and brown at pH~2) with the variation in solution pH. Thus, depending upon the pH of the medium, CZA molecule can exist in various protonated and/or deprotonated forms. Here we have prescribed the existence different possible forms of CZA at different pH (Forms "C", "H" and "Dprot" at pH~14 and Forms "A", "D", and "P" at pH~2 respectively). The NRS spectra of these solutions and their respective SERS spectra over gold nanoparticles were recorded. The spectra clearly differ in their spectral profiles. For example the SERS spectra recorded with the CZA solution at pH~2 shows blue shift for different bands compared to its NRS window e.g. 406 to 450cm(-1), 616 to 632cm(-1), 1332 to 1343cm(-1) etc. Again, the most enhanced peak at ~1548cm(-1) in NRS while in the SERS window this appears at ~1580cm(-1). Similar observation was also made for CZA at pH~14. For example, the 423cm(-1) band in the NRS profile experience a blue shift and appears at ~447cm(-1) in the SERS spectrum as well as other bands at ~850, ~1067 and ~1214cm(-1) in the SERS window are markedly enhanced. It is also worth noting that the SERS spectra at the different pH also differ from each other. These spectral differences indicate the existence of various adsorptive forms of the CZA molecule depending upon the pH of the solution. Therefore based on the experimental findings we propose different possible molecular forms of CZA at different pH (acidic and alkaline) conditions. For example forms 'A', 'D' and 'P' existing in acidic pH (pH~2) and three other deprotonated forms 'C', 'H' and 'Dprot' in alkaline pH (pH~14). The DFT calculations for these prescribed model systems were also carried out to have a plausible understanding of their equilibrium geometries and the vibrational wavenumbers. An idea about the molecular orientation of the adsorbate over nanocolloidal gold substrate is also documented. Copyright © 2016 Elsevier B.V. All rights reserved.

Proton sensitivity of rat cerebellar granule cell GABAA receptors: dependence on neuronal development

PubMed Central

Krishek, Belinda J; Smart, Trevor G

2001-01-01

The effect of GABAA receptor development in culture on the modulation of GABA-induced currents by external H+ was examined in cerebellar granule cells using whole-cell and single-channel recording. Equilibrium concentration-response curves revealed a lower potency for GABA between 11 and 12 days in vitro (DIV) resulting in a shift of the EC50 from 10.7 to 2.4 μM. For granule cells before 11 DIV, the peak GABA-activated current was inhibited at low external pH and enhanced at high pH with a pKa of 6.65. For the steady-state response, low pH was inhibitory with a pKa of 5.56. After 11 DIV, the peak GABA-activated current was largely pH insensitive; however, the steady-state current was potentiated at low pH with a pKa of 6.84. Single GABA-activated ion channels were recorded from outside-out patches of granule cell bodies. At pH 5.4-9.4, single GABA channels exhibited multiple conductance states occurring at 22-26, 16-17 and 12-14 pS. The conductance levels were not significantly altered over the time period of study, nor by changing the external H+ concentration. Two exponential functions were required to fit the open-time frequency histograms at both early (< 11 DIV) and late (> 11 DIV) development times at each H+ concentration. The short and long open time constants were unaffected either by the extracellular H+ concentration or by neuronal development. The distribution of all shut times was fitted by the sum of three exponentials designated as short, intermediate and long. At acidic pH, the long shut time constant decreased with development as did the relative contribution of these components to the overall distribution. This was concurrent with an increase in the mean probability of channel opening. In conclusion, this study demonstrates in cerebellar granule cells that external pH can either reduce, have no effect on, or enhance GABA-activated responses depending on the stage of development, possibly related to the subunit composition of the GABAA receptors. The mode of interaction of H+ at the single-channel level and implications of such interactions at cerebellar granule cell GABAA receptors are discussed. PMID:11208970

Minimizing back exchange in the hydrogen exchange-mass spectrometry experiment.

PubMed

Walters, Benjamin T; Ricciuti, Alec; Mayne, Leland; Englander, S Walter

2012-12-01

The addition of mass spectrometry (MS) analysis to the hydrogen exchange (HX) proteolytic fragmentation experiment extends powerful HX methodology to the study of large biologically important proteins. A persistent problem is the degradation of HX information due to back exchange of deuterium label during the fragmentation-separation process needed to prepare samples for MS measurement. This paper reports a systematic analysis of the factors that influence back exchange (solution pH, ionic strength, desolvation temperature, LC column interaction, flow rates, system volume). The many peptides exhibit a range of back exchange due to intrinsic amino acid HX rate differences. Accordingly, large back exchange leads to large variability in D-recovery from one residue to another as well as one peptide to another that cannot be corrected for by reference to any single peptide-level measurement. The usual effort to limit back exchange by limiting LC time provides little gain. Shortening the LC elution gradient by 3-fold only reduced back exchange by ~2%, while sacrificing S/N and peptide count. An unexpected dependence of back exchange on ionic strength as well as pH suggests a strategy in which solution conditions are changed during sample preparation. Higher salt should be used in the first stage of sample preparation (proteolysis and trapping) and lower salt (<20 mM) and pH in the second stage before electrospray injection. Adjustment of these and other factors together with recent advances in peptide fragment detection yields hundreds of peptide fragments with D-label recovery of 90% ± 5%.

Minimizing Back Exchange in the Hydrogen Exchange-Mass Spectrometry Experiment

NASA Astrophysics Data System (ADS)

Walters, Benjamin T.; Ricciuti, Alec; Mayne, Leland; Englander, S. Walter

2012-12-01

The addition of mass spectrometry (MS) analysis to the hydrogen exchange (HX) proteolytic fragmentation experiment extends powerful HX methodology to the study of large biologically important proteins. A persistent problem is the degradation of HX information due to back exchange of deuterium label during the fragmentation-separation process needed to prepare samples for MS measurement. This paper reports a systematic analysis of the factors that influence back exchange (solution pH, ionic strength, desolvation temperature, LC column interaction, flow rates, system volume). The many peptides exhibit a range of back exchange due to intrinsic amino acid HX rate differences. Accordingly, large back exchange leads to large variability in D-recovery from one residue to another as well as one peptide to another that cannot be corrected for by reference to any single peptide-level measurement. The usual effort to limit back exchange by limiting LC time provides little gain. Shortening the LC elution gradient by 3-fold only reduced back exchange by ~2 %, while sacrificing S/N and peptide count. An unexpected dependence of back exchange on ionic strength as well as pH suggests a strategy in which solution conditions are changed during sample preparation. Higher salt should be used in the first stage of sample preparation (proteolysis and trapping) and lower salt (<20 mM) and pH in the second stage before electrospray injection. Adjustment of these and other factors together with recent advances in peptide fragment detection yields hundreds of peptide fragments with D-label recovery of 90 % ± 5 %.

PH DEPENDENT TOXICITY OF FIVE METALS TO THREE MARINE ORGANISMS

EPA Science Inventory

The pH of natural marine systems is relatively stable; this may explain why metal toxicity changes with pH have not been well documented. However, changes in metal toxicity with pH in marine waters are of concern in toxicity testing. During porewater toxicity testing pH can chang...

Kinetic characterization of Vibrio cholerae ApbE: Substrate specificity and regulatory mechanisms

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

Fang, Xuan; Liang, Pingdong; Raba, Daniel Alexander

ApbE is a member of a novel family of flavin transferases that incorporates flavin mononucleotide (FMN) to subunits of diverse respiratory complexes, which fulfill important homeostatic functions. In this work a detailed characterization of Vibrio cholerae ApbE physiologic activity, substrate specificity and pH dependency was carried out. The data obtained show novel characteristics of the regulation and function of this family. For instance, our experiments indicate that divalent cations are essential for ApbE function, and that the selectivity depends largely on size and the coordination sphere of the cation. Our data also show that ApbE regulation by pH, ADP andmore » potassium is an important mechanism that enhances the adaptation, survival and colonization of V. cholerae in the small intestine. Moreover, studies of the pH-dependency of the activity show that the reaction is favored under alkaline conditions, with a pKa of 8.4. These studies, together with sequence and structure analysis allowed us to identify His257, which is absolutely conserved in the family, as a candidate for the residue whose deprotonation controls the activity. Remarkably, the mutant H257G abolished the flavin transfer activity, strongly indicating that this residue plays an important role in the catalytic mechanism of ApbE.« less

Adsorption of Ten Microcystin Congeners to Common Laboratory-Ware Is Solvent and Surface Dependent.

PubMed

Altaner, Stefan; Puddick, Jonathan; Wood, Susanna A; Dietrich, Daniel R

2017-04-06

Cyanobacteria can produce heptapetides called microcystins (MC) which are harmful to humans due to their ability to inhibit cellular protein phosphatases. Quantitation of these toxins can be hampered by their adsorption to common laboratory-ware during sample processing and analysis. Because of their structural diversity (>100 congeners) and different physico-chemical properties, they vary in their adsorption to surfaces. In this study, the adsorption of ten different MC congeners (encompassing non-arginated to doubly-arginated congeners) to common laboratory-ware was assessed using different solvent combinations. Sample handling steps were mimicked with glass and polypropylene pipettes and vials with increasing methanol concentrations at two pH levels, before analysis by liquid chromatography-tandem mass spectrometry. We demonstrated that MC adsorb to polypropylene surfaces irrespective of pH. After eight successive pipet actions using polypropylene tips ca. 20% of the MC were lost to the surface material, which increased to 25%-40% when solutions were acidified. The observed loss was alleviated by changing the methanol (MeOH) concentration in the final solvent. The required MeOH concentration varied depending on which congener was present. Microcystins only adsorbed to glass pipettes (loss up to 30% after eight pipet actions) when in acidified aqueous solutions. The latter appeared largely dependent on the presence of ionizable groups, such as arginine residues.

Autophosphorylation-dependent inactivation of plant chimeric calcium/calmodulin-dependent protein kinase

NASA Technical Reports Server (NTRS)

Sathyanarayanan, P. V.; Poovaiah, B. W.

2002-01-01

Chimeric calcium/calmodulin dependent protein kinase (CCaMK) is characterized by the presence of a visinin-like Ca(2+)-binding domain unlike other known calmodulin- dependent kinases. Ca(2+)-Binding to the visinin-like domain leads to autophosphorylation and changes in the affinity for calmodulin [Sathyanarayanan P.V., Cremo C.R. & Poovaiah B.W. (2000) J. Biol. Chem. 275, 30417-30422]. Here, we report that the Ca(2+)-stimulated autophosphorylation of CCaMK results in time-dependent loss of enzyme activity. This time-dependent loss of activity or self-inactivation due to autophosphorylation is also dependent on reaction pH and ATP concentration. Inactivation of the enzyme resulted in the formation of a sedimentable enzyme due to self-association. Specifically, autophosphorylation in the presence of 200 microm ATP at pH 7.5 resulted in the formation of a sedimentable enzyme with a 33% loss in enzyme activity. Under similar conditions at pH 6.5, the enzyme lost 67% of its activity and at pH 8.5, 84% enzyme activity was lost. Furthermore, autophosphorylation at either acidic or alkaline reaction pH lead to the formation of a sedimentable enzyme. Transmission electron microscopic studies on autophosphorylated kinase revealed particles that clustered into branched complexes. The autophosphorylation of wild-type kinase in the presence of AMP-PNP (an unhydrolyzable ATP analog) or the autophosphorylation-site mutant, T267A, did not show formation of branched complexes under the electron microscope. Autophosphorylation- dependent self-inactivation may be a mechanism of modulating the signal transduction pathway mediated by CCaMK.

Tracing and separating plasma components causing matrix effects in hydrophilic interaction chromatography-electrospray ionization mass spectrometry.

PubMed

Ekdahl, Anja; Johansson, Maria C; Ahnoff, Martin

2013-04-01

Matrix effects on electrospray ionization were investigated for plasma samples analysed by hydrophilic interaction chromatography (HILIC) in gradient elution mode, and HILIC columns of different chemistries were tested for separation of plasma components and model analytes. By combining mass spectral data with post-column infusion traces, the following components of protein-precipitated plasma were identified and found to have significant effect on ionization: urea, creatinine, phosphocholine, lysophosphocholine, sphingomyelin, sodium ion, chloride ion, choline and proline betaine. The observed effect on ionization was both matrix-component and analyte dependent. The separation of identified plasma components and model analytes on eight columns was compared, using pair-wise linear correlation analysis and principal component analysis (PCA). Large changes in selectivity could be obtained by change of column, while smaller changes were seen when the mobile phase buffer was changed from ammonium formate pH 3.0 to ammonium acetate pH 4.5. While results from PCA and linear correlation analysis were largely in accord, linear correlation analysis was judged to be more straight-forward in terms of conduction and interpretation.

Directed evolution of enzymes using microfluidic chips

NASA Astrophysics Data System (ADS)

Pilát, Zdeněk.; Ježek, Jan; Šmatlo, Filip; Kaůka, Jan; Zemánek, Pavel

2016-12-01

Enzymes are highly versatile and ubiquitous biological catalysts. They can greatly accelerate large variety of reactions, while ensuring appropriate catalytic activity and high selectivity. These properties make enzymes attractive biocatalysts for a wide range of industrial and biomedical applications. Over the last two decades, directed evolution of enzymes has transformed the field of protein engineering. We have devised microfluidic systems for directed evolution of haloalkane dehalogenases in emulsion droplets. In such a device, individual bacterial cells producing mutated variants of the same enzyme are encapsulated in microdroplets and supplied with a substrate. The conversion of a substrate by the enzyme produced by a single bacterium changes the pH in the droplet which is signalized by pH dependent fluorescence probe. The droplets with the highest enzymatic activity can be separated directly on the chip by dielectrophoresis and the resultant cell lineage can be used for enzyme production or for further rounds of directed evolution. This platform is applicable for fast screening of large libraries in directed evolution experiments requiring mutagenesis at multiple sites of a protein structure.

Phytoplankton-Environmental Interactions in Reservoirs. Volume I. Papers Presented at Workshop, 10-12 April 1979, Monterey, California.

DTIC Science & Technology

1981-09-01

Antarctic waters. Symp. Antarctic Oceanography. Santiago , Chile . Eppley, R.W. 1972. Temperature and phytoplankton growth in the sea. Fish. Bull. 70:1063...photorespiration is largely dependent on the partial pressure of car- bon dioxide and oxygen concentrations . When CO2 limits photosynthesis and oxygen...hardness and alkalinity concentrations (> 200 mg/i as CaCO 3). As CO2 is removed from the alkalinity _ystem, pH increases and most alkalinity is

Kinetic modeling of the oxidative degradation of additive free PE in bleach disinfected water

NASA Astrophysics Data System (ADS)

Mikdam, Aïcha; Colin, Xavier; Billon, Noëlle; Minard, Gaëlle

2016-05-01

The chemical interactions between PE and bleach were studied at 60°C in immersion in bleach solutions kept at a free chlorine concentration of 100 ppm and a pH of 5 or 7.2. It was found that the polymer undergoes a severe oxidation from the earliest weeks of exposure, in a superficial layer whose thickness (of about 50-70 µm) is almost independent of the pH value, although the superficial oxidation rate is faster in acidic than in neutral medium. Oxidation leads to the formation and accumulation of a large variety of carbonyl products (mostly ketones and carboxylic acids) and, after a few weeks, to a decrease in the average molar mass due to the large predominance of chain scissions over crosslinking. A scenario was elaborated for explaining such unexpected results. According to this scenario, the non-ionic molecules (Cl2 and ClOH) formed from the disinfectant in the water phase, would migrate deeply into PE and dissociate into highly reactive radicals (Cl• and HO•) in order to initiate a radical chain oxidation. A kinetic model was derived from this scenario for predicting the general trends of the oxidation kinetics and its dependence on environmental factors such as temperature, free chlorine concentration and pH. The validity of this model was successfully checked by comparing the numerical simulations with experimental data.

Simultaneous in vitro and in vivo evaluation of both trimethoprim and sulfamethoxazole from certain dosage forms.

PubMed

Meshali, M; El-Sabbagh, H; Ghanem, A; Foda, A

1983-06-01

The dissolution rates of trimethoprim (T), and sulphamethoxazole (S), from different brands of tablets and suspensions were studied at pH = 1.1 and 7.2. The bioavailabilities of both drugs in humans were studied by the urine excretion method. The dissolution rates were dependent on the pH of the dissolution medium, the solubilities of the drugs at the pH involved, the dosage form and the brand studied. While the dissolution rates of T from all brands studied were consistent with their pH-dependent solubility, those of S were not. The dissolution rates of S from suspensions were found to be equal at pH = 7.2, but different at pH = 1.1. A correlation existed between the dissolution rate of T at pH = 1.1 from tablets and the excretion rate in humans. With S, however, no such correlation was observed at either pH.

Electronic Structure of Manganese Corroles Revisited: X-ray Structures, Optical and X-ray Absorption Spectroscopies, and Electrochemistry as Probes of Ligand Noninnocence

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

Ganguly, Sumit; MCormick, Laura J.; Conradie, Jeanet

Presented herein is a detailed multitechnique investigation of ligand noninnocence in S = 3/2 manganese corrole derivatives at the formal Mn IV oxidation state. The Soret maxima of Mn[T pXPC]Cl (T pXPC = meso-tris( p-X-phenyl)corrole, where X = CF 3, H, Me, and OMe) were found to red-shift over a range of 37 nm with increasing electron-donating character of X. For Mn[T pXPC]Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole •2–-like ligand for the MnCl complexes and an innocent corrole 3– ligand for the MnPh complexes. Single-crystalmore » X-ray structures of three Mn[T pXPC]Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn[T pOMePC]Ph. B3LYP density functional theory (DFT) calculations on Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities, consistent with an antiferromagnetically coupled Mn III-corrole •2– description. By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an essentially Mn IV-corrole 3– description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of 0.6 eV for the Mn K-pre-edge of Mn[T pCF 3PC]Ph and a striking enhancement of the pre-edge intensity, relative to Mn[T pCF 3PC]Cl, consistent with a more oxidized, i.e., Mn IV, center in Mn[T pCF 3PC]Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn[T pCF 3PC]Ph results from the extra 3d z2 hole, which mixes strongly with the Mn 4p z orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. As a result, cyclic voltammetry measurements revealed highly negative first reduction potentials for the Mn[T pXPC]Ph series (~–0.95 V) as well as large electrochemical HOMO-LUMO gaps of ~1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the Mn–Ph bond.« less

Electronic Structure of Manganese Corroles Revisited: X-ray Structures, Optical and X-ray Absorption Spectroscopies, and Electrochemistry as Probes of Ligand Noninnocence

DOE PAGES

Ganguly, Sumit; MCormick, Laura J.; Conradie, Jeanet; ...

2018-06-06

Presented herein is a detailed multitechnique investigation of ligand noninnocence in S = 3/2 manganese corrole derivatives at the formal Mn IV oxidation state. The Soret maxima of Mn[T pXPC]Cl (T pXPC = meso-tris( p-X-phenyl)corrole, where X = CF 3, H, Me, and OMe) were found to red-shift over a range of 37 nm with increasing electron-donating character of X. For Mn[T pXPC]Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole •2–-like ligand for the MnCl complexes and an innocent corrole 3– ligand for the MnPh complexes. Single-crystalmore » X-ray structures of three Mn[T pXPC]Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn[T pOMePC]Ph. B3LYP density functional theory (DFT) calculations on Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities, consistent with an antiferromagnetically coupled Mn III-corrole •2– description. By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an essentially Mn IV-corrole 3– description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of 0.6 eV for the Mn K-pre-edge of Mn[T pCF 3PC]Ph and a striking enhancement of the pre-edge intensity, relative to Mn[T pCF 3PC]Cl, consistent with a more oxidized, i.e., Mn IV, center in Mn[T pCF 3PC]Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn[T pCF 3PC]Ph results from the extra 3d z2 hole, which mixes strongly with the Mn 4p z orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. As a result, cyclic voltammetry measurements revealed highly negative first reduction potentials for the Mn[T pXPC]Ph series (~–0.95 V) as well as large electrochemical HOMO-LUMO gaps of ~1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the Mn–Ph bond.« less

Detection of low back pain using pH level-dependent imaging of the intervertebral disc using the ratio of R1ρ dispersion and -OH chemical exchange saturation transfer (RROC).

PubMed

Liu, Qi; Tawackoli, Wafa; Pelled, Gadi; Fan, Zhaoyang; Jin, Ning; Natsuaki, Yutaka; Bi, Xiaoming; Gart, Avrom; Bae, Hyun; Gazit, Dan; Li, Debiao

2015-03-01

Low pH is associated with intervertebral disc (IVD)-generated low back pain (LBP). The purpose of this work was to develop an in vivo pH level-dependent magnetic resonance imaging (MRI) method for detecting discogenic LBP, without using exogenous contrast agents. The ratio of R1ρ dispersion and chemical exchange saturation transfer (CEST) (RROC) was used for pH-level dependent imaging of the IVD while eliminating the effect of labile proton concentration. The technique was validated by numerical simulations and studies on phantoms and ex vivo porcine spines. Four male (ages 42.8 ± 18.3) and two female patients (ages 55.5 ± 2.1) with LBP and scheduled for discography were examined with the method on a 3.0 Tesla MR scanner. RROC measurements were compared with discography outcomes using paired t-test. Simulation and phantom results indicated RROC is a concentration independent and pH level-dependent technique. Porcine spine study results found higher RROC value was related to lower pH level. Painful discs based on discography had significant higher RROC values than those with negative diagnosis (P < 0.05). RROC imaging is a promising pH level dependent MRI technique that has the potential to be a noninvasive imaging tool to detect painful IVDs in vivo. © 2014 Wiley Periodicals, Inc.

Block of nicotinic acetylcholine receptors by philanthotoxins is strongly dependent on their subunit composition

PubMed Central

Kachel, Hamid S.; Patel, Rohit N.; Franzyk, Henrik; Mellor, Ian R.

2016-01-01

Philanthotoxin-433 (PhTX-433) is an active component of the venom from the Egyptian digger wasp, Philanthus triangulum. PhTX-433 inhibits several excitatory ligand-gated ion channels, and to improve selectivity two synthetic analogues, PhTX-343 and PhTX-12, were developed. Previous work showed a 22-fold selectivity of PhTX-12 over PhTX-343 for embryonic muscle-type nicotinic acetylcholine receptors (nAChRs) in TE671 cells. We investigated their inhibition of different neuronal nAChR subunit combinations as well as of embryonic muscle receptors expressed in Xenopus oocytes. Whole-cell currents in response to application of acetylcholine alone or co-applied with PhTX analogue were studied by using two-electrode voltage-clamp. α3β4 nAChRs were most sensitive to PhTX-343 (IC50 = 12 nM at −80 mV) with α4β4, α4β2, α3β2, α7 and α1β1γδ being 5, 26, 114, 422 and 992 times less sensitive. In contrast α1β1γδ was most sensitive to PhTX-12 along with α3β4 (IC50 values of 100 nM) with α4β4, α4β2, α3β2 and α7 being 3, 3, 26 and 49 times less sensitive. PhTX-343 inhibition was strongly voltage-dependent for all subunit combinations except α7, whereas this was not the case for PhTX-12 for which weak voltage dependence was observed. We conclude that PhTX-343 mainly acts as an open-channel blocker of nAChRs with strong subtype selectivity. PMID:27901080

Identification of Trans-4-Hydroxy-L-Proline as a Compatible Solute and Its Biosynthesis and Molecular Characterization in Halobacillus halophilus.

PubMed

Kim, Kyung Hyun; Jia, Baolei; Jeon, Che Ok

2017-01-01

Halobacillus halophilus , a moderately halophilic bacterium, accumulates a variety of compatible solutes including glycine betaine, glutamate, glutamine, proline, and ectoine to cope with osmotic stress. Non-targeted analysis of intracellular organic compounds using 1 H-NMR showed that a large amount of trans-4-hydroxy-L-proline (Hyp), which has not been reported as a compatible solute in H. halophilus , was accumulated in response to high NaCl salinity, suggesting that Hyp may be an important compatible solute in H. halophilus . Candidate genes encoding proline 4-hydroxylase (PH-4), which hydroxylates L-proline to generate Hyp, were retrieved from the genome of H. halophilus through domain searches based on the sequences of known PH-4 proteins. A gene, HBHAL_RS11735, which was annotated as a multidrug DMT transporter permease in GenBank, was identified as the PH-4 gene through protein expression analysis in Escherichia coli . The PH-4 gene constituted a transcriptional unit with a promoter and a rho-independent terminator, and it was distantly located from the proline biosynthetic gene cluster ( pro operon). Transcriptional analysis showed that PH-4 gene expression was NaCl concentration-dependent, and was specifically induced by chloride anion, similar to the pro operon. Accumulation of intracellular Hyp was also observed in other bacteria, suggesting that Hyp may be a widespread compatible solute in halophilic and halotolerant bacteria.

Identification of Trans-4-Hydroxy-L-Proline as a Compatible Solute and Its Biosynthesis and Molecular Characterization in Halobacillus halophilus

PubMed Central

Kim, Kyung Hyun; Jia, Baolei; Jeon, Che Ok

2017-01-01

Halobacillus halophilus, a moderately halophilic bacterium, accumulates a variety of compatible solutes including glycine betaine, glutamate, glutamine, proline, and ectoine to cope with osmotic stress. Non-targeted analysis of intracellular organic compounds using 1H-NMR showed that a large amount of trans-4-hydroxy-L-proline (Hyp), which has not been reported as a compatible solute in H. halophilus, was accumulated in response to high NaCl salinity, suggesting that Hyp may be an important compatible solute in H. halophilus. Candidate genes encoding proline 4-hydroxylase (PH-4), which hydroxylates L-proline to generate Hyp, were retrieved from the genome of H. halophilus through domain searches based on the sequences of known PH-4 proteins. A gene, HBHAL_RS11735, which was annotated as a multidrug DMT transporter permease in GenBank, was identified as the PH-4 gene through protein expression analysis in Escherichia coli. The PH-4 gene constituted a transcriptional unit with a promoter and a rho-independent terminator, and it was distantly located from the proline biosynthetic gene cluster (pro operon). Transcriptional analysis showed that PH-4 gene expression was NaCl concentration-dependent, and was specifically induced by chloride anion, similar to the pro operon. Accumulation of intracellular Hyp was also observed in other bacteria, suggesting that Hyp may be a widespread compatible solute in halophilic and halotolerant bacteria. PMID:29104571

Interaction of 8-anilinonaphthalene 1-sulphonate (ANS) and human matrix metalloproteinase 7 (MMP-7) as examined by MMP-7 activity and ANS fluorescence.

PubMed

Samukange, Vimbai; Yasukawa, Kiyoshi; Inouye, Kuniyo

2012-05-01

Human matrix metalloproteinase 7 (MMP-7) is the smallest matrix metalloproteinase. It plays important roles in tumour invasion and metastasis. 8-Anilinonaphthalene 1-sulphonate (ANS) is a fluorescent probe widely used for the analysis of proteins. It emits large fluorescence energy when its anilinonaphthalene group binds with hydrophobic regions of protein. In this study, we analysed the interaction of ANS and MMP-7. At pH 4.5-9.5, ANS inhibited MMP-7 activity in the hydrolysis of (7-methoxycoumarin-4-yl)acetyl-L-Pro-L-Leu-Gly-L-Leu-[N(3)-(2,4-dinitrophenyl)-L-2,3-diaminopropionyl]-L-Ala-L-Arg-NH(2). The inhibition was a non-competitive manner and depended on the time for pre-incubation of ANS and MMP-7. At pH 4.5-9.5, the fluorescence of ANS was not changed by the addition of MMP-7. At pH 3.5, MMP-7 lacked activity, and the fluorescence of ANS was increased by the addition of MMP-7. These results suggest that at pH 4.5-9.5, the sulphonic group of ANS binds with MMP-7 through electrostatic interaction, whereas at pH 3.5, the anilinonaphthalene group of ANS binds with MMP-7 through hydrophobic interaction.

A computational docking study on the pH dependence of peptide binding to HLA-B27 sub-types differentially associated with ankylosing spondylitis

NASA Astrophysics Data System (ADS)

Serçinoğlu, Onur; Özcan, Gülin; Kabaş, Zeynep Kutlu; Ozbek, Pemra

2016-07-01

A single amino acid difference (Asp116His), having a key role in a pathogenesis pathway, distinguishes HLA-B*27:05 and HLA-B*27:09 sub-types as associated and non-associated with ankylosing spondylitis, respectively. In this study, molecular docking simulations were carried out with the aim of comprehending the differences in the binding behavior of both alleles at varying pH conditions. A library of modeled peptides was formed upon single point mutations aiming to address the effect of 20 naturally occurring amino acids at the binding core peptide positions. For both alleles, computational docking was applied using Autodock 4.2. Obtained free energies of binding (FEB) were compared within the peptide library and between the alleles at varying pH conditions. The amino acid preferences of each position were studied enlightening the role of each on binding. The preferred amino acids for each position of pVIPR were found to be harmonious with experimental studies. Our results indicate that, as the pH is lowered, the capacity of HLA-B*27:05 to bind peptides in the library is largely lost. Hydrogen bonding analysis suggests that the interaction between the main anchor positions of pVIPR and their respective binding pocket residues are affected from the pH the most, causing an overall shift in the FEB profiles.

A computational docking study on the pH dependence of peptide binding to HLA-B27 sub-types differentially associated with ankylosing spondylitis.

PubMed

Serçinoğlu, Onur; Özcan, Gülin; Kabaş, Zeynep Kutlu; Ozbek, Pemra

2016-07-01

A single amino acid difference (Asp116His), having a key role in a pathogenesis pathway, distinguishes HLA-B*27:05 and HLA-B*27:09 sub-types as associated and non-associated with ankylosing spondylitis, respectively. In this study, molecular docking simulations were carried out with the aim of comprehending the differences in the binding behavior of both alleles at varying pH conditions. A library of modeled peptides was formed upon single point mutations aiming to address the effect of 20 naturally occurring amino acids at the binding core peptide positions. For both alleles, computational docking was applied using Autodock 4.2. Obtained free energies of binding (FEB) were compared within the peptide library and between the alleles at varying pH conditions. The amino acid preferences of each position were studied enlightening the role of each on binding. The preferred amino acids for each position of pVIPR were found to be harmonious with experimental studies. Our results indicate that, as the pH is lowered, the capacity of HLA-B*27:05 to bind peptides in the library is largely lost. Hydrogen bonding analysis suggests that the interaction between the main anchor positions of pVIPR and their respective binding pocket residues are affected from the pH the most, causing an overall shift in the FEB profiles.

Chlorination Revisited: Does Cl- Serve as a Catalyst in the Chlorination of Phenols?

PubMed

Lau, Stephanie S; Abraham, Sonali M; Roberts, A Lynn

2016-12-20

The aqueous chlorination of (chloro)phenols is one of the best-studied reactions in the environmental literature. Previous researchers have attributed these reactions to two chlorine species: HOCl (at circum-neutral and high pH) and H 2 OCl + (at low pH). In this study, we seek to examine the roles that two largely overlooked chlorine species, Cl 2 and Cl 2 O, may play in the chlorination of (chloro)phenols. Solution pH, chloride concentration, and chlorine dose were systematically varied in order to assess the importance of different chlorine species as chlorinating agents. Our findings indicate that chlorination rates at pH < 6 increase substantially when chloride is present, attributed to the formation of Cl 2 . At pH 6.0 and a chlorine dose representative of drinking water treatment, Cl 2 O is predicted to have at best a minor impact on chlorination reactions, whereas Cl 2 may contribute more than 80% to the overall chlorination rate depending on the (chloro)phenol identity and chloride concentration. While it is not possible to preclude H 2 OCl + as a chlorinating agent, we were able to model our low-pH data by considering Cl 2 only. Even traces of chloride can generate sufficient Cl 2 to influence chlorination kinetics, highlighting the role of chloride as a catalyst in chlorination reactions.

Escherichia coli YqjA, a Member of the Conserved DedA/Tvp38 Membrane Protein Family, Is a Putative Osmosensing Transporter Required for Growth at Alkaline pH.

PubMed

Kumar, Sujeet; Doerrler, William T

2015-07-01

The ability to persist and grow under alkaline conditions is an important characteristic of many bacteria. In order to survive at alkaline pH, Escherichia coli must maintain a stable cytoplasmic pH of about 7.6. Membrane cation/proton antiporters play a major role in alkaline pH homeostasis by catalyzing active inward proton transport. The DedA/Tvp38 family is a highly conserved membrane protein family of unknown function present in most sequenced genomes. YqjA and YghB are members of the E. coli DedA family with 62% amino acid identity and partially redundant functions. We have shown that E. coli with ΔyqjA and ΔyghB mutations cannot properly maintain the proton motive force (PMF) and is compromised in PMF-dependent drug efflux and other PMF-dependent functions. Furthermore, the functions of YqjA and YghB are dependent upon membrane-embedded acidic amino acids, a hallmark of several families of proton-dependent transporters. Here, we show that the ΔyqjA mutant (but not ΔyghB) cannot grow under alkaline conditions (ranging from pH 8.5 to 9.5), unlike the parent E. coli. Overexpression of yqjA restores growth at alkaline pH, but only when more than ∼100 mM sodium or potassium is present in the growth medium. Increasing the osmotic pressure by the addition of sucrose enhances the ability of YqjA to support growth under alkaline conditions in the presence of low salt concentrations, consistent with YqjA functioning as an osmosensor. We suggest that YqjA possesses proton-dependent transport activity that is stimulated by osmolarity and that it plays a significant role in the survival of E. coli at alkaline pH. The ability to survive under alkaline conditions is important for many species of bacteria. Escherichia coli can grow at pH 5.5 to 9.5 while maintaining a constant cytoplasmic pH of about 7.6. Under alkaline conditions, bacteria rely upon proton-dependent transporters to maintain a constant cytoplasmic pH. The DedA/Tvp38 protein family is a highly conserved but poorly characterized family of membrane proteins. Here, we show that the DedA/Tvp38 protein YqjA is critical for E. coli to survive at pH 8.5 to 9.5. YqjA requires sodium and potassium for this function. At low cation concentrations, osmolytes, including sucrose, can facilitate rescue of E. coli growth by YqjA at high pH. These data are consistent with YqjA functioning as an osmosensing cation-dependent proton transporter. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Surveillance of Nicotine and pH in Cigarette and Cigar Filler

PubMed Central

Lawler, Tameka S.; Stanfill, Stephen B.; deCastro, B. Rey; Lisko, Joseph G.; Duncan, Bryce W.; Richter, Patricia; Watson, Clifford H.

2017-01-01

Objective We examined differences between nicotine concentrations and pH in cigarette and cigar tobacco filler. Methods Nicotine and pH levels for 50 cigarette and 75 cigar brands were measured. Non-mentholated and mentholated cigarette products were included in the analysis along with several cigar types as identified by the manufacturer: large cigars, pipe tobacco cigars, cigarillos, mini cigarillos, and little cigars. Results There were significant differences found between pH and nicotine for cigarette and cigar tobacco products. Mean nicotine concentrations in cigarettes (19.2 mg/g) and large cigars (15.4 mg/g) were higher than the other cigars types, especially the pipe tobacco cigars (8.79 mg/g). The mean pH for cigarettes was pH 5.46. Large cigars had the highest mean pH value (pH 6.10) and pipe tobacco cigars had the lowest (pH 5.05). Conclusions Although cigarettes are the most common combustible tobacco product used worldwide, cigar use remains popular. Our research provides a means to investigate the possibility of distinguishing the 2 tobacco product types and offers information on nicotine and pH across a wide range of cigarette and cigar varieties that may be beneficial to help establish tobacco policies and regulations across product types. PMID:28989950

Complexation Key to a pH Locked Redox Reaction

ERIC Educational Resources Information Center

Rizvi, Masood Ahmad; Dangat, Yuvraj; Shams, Tahir; Khan, Khaliquz Zaman

2016-01-01

An unfavorable pH can block a feasible electron transfer for a pH dependent redox reaction. In this experiment, a series of potentiometric titrations demonstrate the sequential loss in feasibility of iron(II) dichromate redox reaction over a pH range of 0-4. The pH at which this reaction failed to occur was termed as a pH locked reaction. The…

Structure of bovine cytochrome c oxidase crystallized at a neutral pH using a fluorinated detergent.

PubMed

Luo, Fangjia; Shinzawa-Itoh, Kyoko; Hagimoto, Kaede; Shimada, Atsuhiro; Shimada, Satoru; Yamashita, Eiki; Yoshikawa, Shinya; Tsukihara, Tomitake

2017-07-01

Cytochrome c oxidase (CcO) couples proton pumping to O 2 reduction. Its enzymatic activity depends sensitively on pH over a wide range. However, owing to difficulty in crystallizing this protein, X-ray structure analyses of bovine CcO aimed at understanding its reaction mechanism have been conducted using crystals prepared at pH 5.7, which is significantly lower than that in the cell. Here, oxidized CcO at pH 7.3 was crystallized using a fluorinated octyl-maltoside derivative, and the structure was determined at 1.77 Å resolution. No structural differences between crystals obtained at the neutral pH and the acidic pH were detected within the molecules. On the other hand, some differences in intermolecular interactions were detected between the two types of crystal. The influence of pH on the molecular surface is likely to contribute to the pH dependency of the aerobic oxidation of ferrocytochrome c.

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.

Optimum Disinfection Properties and Commercially Available Disinfectants

DTIC Science & Technology

1989-07-01

organic constituents that display a chlorine demand.) d. Upon addition to water, the agent should dissolve quickly and release its active ingredient(s...trione pH dependence alkaline pH favored Temperature dependence high at low residual Palatability Taste and odor claimed to be lartgly absent Color...CryptosgortdLjM at various temperature and pH levels. 2. A field procedwu for masueing disinfectant residual is ".eded for chlorin dioaide. 3. Stability

Core sequence of PAPf39 amyloid fibrils and mechanism of pH-dependent fibril formation: the role of monomer conformation.

PubMed

French, Kinsley C; Makhatadze, George I

2012-12-21

PAPf39, a 39-residue peptide fragment from human prostatic acidic phosphatase, has been shown to form amyloid fibrils in semen (SEVI), which increase HIV infectivity by up to 5 orders of magnitude. The sequence of the PAPf39 fibrillar core was identified using hydrogen-deuterium exchange (HDX) mass spectrometry and protease protection assays. The central and C-terminal regions are highly protected from HDX and proteolytic cleavage and, thus, are part of the fibrillar core. Conversely, the N-terminal region is unprotected from HDX and proteolytic cleavage, suggesting that it is exposed and not part of the fibrillar core. This finding was tested using two N-terminal truncated variants, PAPf39Δ1-8 and PAPf39Δ1-13. Both variants formed amyloid fibrils at neutral pH. However, these variants showed a markedly different pH dependence of fibril formation versus that of PAPf39. PAPf39 fibrils can form at pH 7.7, but not at pH 5.5 or 2.5, while both N-terminally truncated variants can form fibrils at these pH values. Thus, the N-terminal region is not necessary for fibril formation but modulates the pH dependence of PAPf39 fibril formation. PAPf39Δ1-8 and PAPf39Δ1-13 are capable of seeding PAPf39 fibril formation at neutral pH, suggesting that these variants are structurally compatible with PAPf39, yet no mixed fibril formation occurs between the truncated variants and PAPf39 at low pH. This suggests that pH affects the PAPf39 monomer conformational ensemble, which is supported by far-UV circular dichroism spectroscopy. A conceptual model describing the pH dependence of PAPf39 aggregation is proposed and provides potential biological implications.

A thermostable trypsin inhibitor with antiproliferative activity from small pinto beans.

PubMed

Chan, Yau Sang; Zhang, Yanbo; Sze, Stephen Cho Wing; Ng, Tzi Bun

2014-08-01

Small pinto bean is a cultivar of Phaseolus vulgaris. It produces a 16-kDa trypsin inhibitor that could be purified using anion exchange and size chromatography. Q-Sepharose, Mono Q and Superdex 75 columns were employed for the isolation process. Small pinto bean trypsin inhibitor demonstrated moderate pH stability (pH 2-10) and marked heat stability, with its trypsin inhibitory activity largely retained after exposure to 100 °C for half an hour. The activity was abolished in the presence of dithiothreitol, in a dose-dependent manner, implying that disulfide bonds in small pinto bean trypsin inhibitor are crucial for the activity. The trypsin inhibitor showed a blocked N-terminus. The trypsin inhibitor only slightly inhibited the viability of breast cancer MCF7 and hepatoma HepG2 cells at 125 μM.

pH regulates genes for flagellar motility, catabolism, and oxidative stress in Escherichia coli K-12.

PubMed

Maurer, Lisa M; Yohannes, Elizabeth; Bondurant, Sandra S; Radmacher, Michael; Slonczewski, Joan L

2005-01-01

Gene expression profiles of Escherichia coli K-12 W3110 were compared as a function of steady-state external pH. Cultures were grown to an optical density at 600 nm of 0.3 in potassium-modified Luria-Bertani medium buffered at pH 5.0, 7.0, and 8.7. For each of the three pH conditions, cDNA from RNA of five independent cultures was hybridized to Affymetrix E. coli arrays. Analysis of variance with an alpha level of 0.001 resulted in 98% power to detect genes showing a twofold difference in expression. Normalized expression indices were calculated for each gene and intergenic region (IG). Differential expression among the three pH classes was observed for 763 genes and 353 IGs. Hierarchical clustering yielded six well-defined clusters of pH profiles, designated Acid High (highest expression at pH 5.0), Acid Low (lowest expression at pH 5.0), Base High (highest at pH 8.7), Base Low (lowest at pH 8.7), Neutral High (highest at pH 7.0, lower in acid or base), and Neutral Low (lowest at pH 7.0, higher at both pH extremes). Flagellar and chemotaxis genes were repressed at pH 8.7 (Base Low cluster), where the cell's transmembrane proton potential is diminished by the maintenance of an inverted pH gradient. High pH also repressed the proton pumps cytochrome o (cyo) and NADH dehydrogenases I and II. By contrast, the proton-importing ATP synthase F1Fo and the microaerophilic cytochrome d (cyd), which minimizes proton export, were induced at pH 8.7. These observations are consistent with a model in which high pH represses synthesis of flagella, which expend proton motive force, while stepping up electron transport and ATPase components that keep protons inside the cell. Acid-induced genes, on the other hand, were coinduced by conditions associated with increased metabolic rate, such as oxidative stress. All six pH-dependent clusters included envelope and periplasmic proteins, which directly experience external pH. Overall, this study showed that (i) low pH accelerates acid consumption and proton export, while coinducing oxidative stress and heat shock regulons; (ii) high pH accelerates proton import, while repressing the energy-expensive flagellar and chemotaxis regulons; and (iii) pH differentially regulates a large number of periplasmic and envelope proteins.

The Methodology Applied in DPPH, ABTS and Folin-Ciocalteau Assays Has a Large Influence on the Determined Antioxidant Potential.

PubMed

Abramovič, Helena; Grobin, Blaž; Poklar, Nataša; Cigić, Blaž

2017-06-01

Antioxidant potential (AOP) is not only the property of the matrix analyzed but also depends greatly on the methodology used. The chromogenic radicals 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+), 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and Folin-Ciocalteu (FC) assay were applied to estimate how the method and the composition of the assay solvent influence the AOP determined for coffee, tea, beer, apple juice and dietary supplements. Large differences between the AOP values depending on the reaction medium were observed, with the highest AOP determined mostly in the FC assay. In reactions with chromogenic radicals several fold higher values of AOP were obtained in buffer pH 7.4 than in water or methanol. The type of assay and solvent composition have similar influences on the reactivity of a particular antioxidant, either pure or as part of a complex matrix. The reaction kinetics of radicals with antioxidants in samples reveals that AOP depends strongly on incubation time, yet differently for each sample analyzed and the assay applied.

The influence of hydrous Mn–Zn oxides on diel cycling of Zn in an alkaline stream draining abandoned mine lands

USGS Publications Warehouse

Shope, Christopher L.; Xie, Ying; Gammons, Christopher H.

2006-01-01

Many mining-impacted streams in western Montana with pH near or above neutrality display large (up to 500%) diel cycles in dissolved Zn concentrations. The streams in question typically contain boulders coated with a thin biofilm, as well as black mineral crusts composed of hydrous Mn–Zn oxides. Laboratory mesocosm experiments simulating diel behavior in High Ore Creek (one of the Montana streams with particularly high Zn concentrations) show that the Zn cycles are not caused by 24-h changes in streamflow or hyporheic exchange, but rather to reversible in-stream processes that are driven by the solar cycle and its attendant influence on pH and water temperature (T). Laboratory experiments using natural Mn–Zn precipitates from the creek show that the mobilities of Zn and Mn increase nearly an order of magnitude for each unit decrease in pH, and decrease 2.4-fold for an increase in T from 5 to 20 °C. The response of dissolved metal concentration to small changes in either pH or T was rapid and reversible, and dissolved Zn concentrations were roughly an order of magnitude higher than Mn. These observations are best explained by sorption of Zn2+ and Mn2+ onto the secondary Mn–Zn oxide surfaces. From the T-dependence of residual metal concentrations in solution, approximate adsorption enthalpies of +50 kJ/mol (Zn) and +46 kJ/mol (Mn) were obtained, which are within the range of enthalpy values reported in the literature for sorption of divalent metal cations onto hydrous metal oxides. Using the derived pH- and T-dependencies from the experiments, good agreement is shown between predicted and observed diel Zn cycles for several historical data sets collected from High Ore Creek.

Particle size, charge and colloidal stability of humic acids coprecipitated with Ferrihydrite.

PubMed

Angelico, Ruggero; Ceglie, Andrea; He, Ji-Zheng; Liu, Yu-Rong; Palumbo, Giuseppe; Colombo, Claudio

2014-03-01

Humic acids (HA) have a colloidal character whose size and negative charge are strictly dependent on surface functional groups. They are able to complex large amount of poorly ordered iron (hydr)oxides in soil as a function of pH and other environmental conditions. Accordingly, with the present study we intend to assess the colloidal properties of Fe(II) coprecipitated with humic acids (HA) and their effect on Fe hydroxide crystallinity under abiotic oxidation and order of addition of both Fe(II) and HA. TEM, XRD and DRS experiments showed that Fe-HA consisted of Ferrihydrite with important structural variations. DLS data of Fe-HA at acidic pH showed a bimodal size distribution, while at very low pH a slow aggregation process was observed. Electrophoretic zeta-potential measurements revealed a negative surface charge for Fe-HA macromolecules, providing a strong electrostatic barrier against aggregation. Under alkaline conditions HA chains swelled, which resulted in an enhanced stabilization of the colloid particles. The increasing of zeta potential and size of the Fe-HA macromolecules, reflects a linear dependence of both with pH. The increase in the size and negative charge of the Fe-HA precipitate seems to be more affected by the ionization of the phenolic acid groups, than by the carboxylic acid groups. The main cause of negative charge generation of Fe/HA is due to increased dissociation of phenolic groups in more expanded structure. The increased net negative surface potential induced by coprecipitation with Ferrihydrite and the correspondent changes in configuration of the HA could trigger the inter-particle aggregation with the formation of new negative surface. The Fe-HA coprecipitation can reduce electrosteric repulsive forces, which in turn may inhibit the aggregation process at different pH. Therefore, coprecipitation of Ferrihydrite would be expected to play an important role in the carbon stabilization and persistence not only in organic soils, but also in waters containing dissolved organic matter. Copyright © 2013 Elsevier Ltd. All rights reserved.

Direct comparison of two different mesalamine formulations for the induction of remission in patients with ulcerative colitis: A double-blind, randomized study

PubMed Central

Ito, Hiroaki; Iida, Mitsuo; Matsumoto, Takayuki; Suzuki, Yasuo; Sasaki, Hidetaka; Yoshida, Toyomitsu; Takano, Yuichi; Hibi, Toshifumi

2010-01-01

Background: Mesalamine is the first-line drug for the treatment of ulcerative colitis (UC). We directly compared the efficacy and safety of two mesalamine formulations for the induction of remission in patients with UC. Methods: In a multicenter, double-blind, randomized study, 229 patients with mild-to-moderate active UC were assigned to 4 groups: 66 and 65 received a pH-dependent release formulation of 2.4 g/day (pH-2.4 g) or 3.6 g/day (pH-3.6 g), respectively; 65 received a time-dependent release formulation of 2.25 g/day (Time-2.25 g), and 33 received placebo (Placebo). The drugs were administered three times daily for eight weeks. The primary endpoint was a decrease in the UC disease activity index (UC-DAI). Results: In the full analysis set (n = 225) the decrease in UC-DAI in each group was 1.5 in pH-2.4 g, 2.9 in pH-3.6 g, 1.3 in Time-2.25 g and 0.3 in Placebo, respectively. These results demonstrate the superiority of pH-3.6 g over Time-2.25 g (P = 0.003) and the noninferiority of pH-2.4 g to Time-2.25 g. Among the patients with proctitis-type UC, a significant decrease in UC-DAI was observed in pH-2.4 g and pH-3.6 g as compared to Placebo, but not in Time-2.25 g. No differences were observed in the safety profiles. Conclusions: Higher dose of the pH-dependent release formulation was more effective for induction of remission in patients with mild-to-moderate active UC. Additionally, the pH-dependent release formulation was preferable to the time-dependent release formulation for patients with proctitis-type UC (UMIN Clinical Trials Registry, no. C000000288). (Inflamm Bowel Dis 2010) PMID:20049950

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

Protein removal from waste brines generated during ham salting through acidification and centrifugation.

PubMed

Gutiérrez-Martínez, Maria del Rosario; Muñoz-Guerrero, Hernán; Alcaína-Miranda, Maria Isabel; Barat, José Manuel

2014-03-01

The salting step in food processes implies the production of large quantities of waste brines, having high organic load, high conductivity, and other pollutants with high oxygen demand. Direct disposal of the residual brine implies salinization of soil and eutrophication of water. Since most of the organic load of the waste brines comes from proteins leaked from the salted product, precipitation of dissolved proteins by acidification and removal by centrifugation is an operation to be used in waste brine cleaning. The aim of this study is optimizing the conditions for carrying out the separation of proteins from waste brines generated in the pork ham salting operation, by studying the influence of pH, centrifugal force, and centrifugation time. Models for determining the removal of proteins depending on the pH, centrifugal force, and time were obtained. The results showed a high efficacy of the proposed treatment for removing proteins, suggesting that this method could be used for waste brine protein removal. The best pH value to be used in an industrial process seems to be 3, while the obtained results indicate that almost 90% of the proteins from the brine can be removed by acidification followed by centrifugation. A further protein removal from the brine should have to be achieved using filtrating techniques, which efficiency could be highly improved as a consequence of the previous treatment through acidification and centrifugation. Waste brines from meat salting have high organic load and electrical conductivity. Proteins can be removed from the waste brine by acidification and centrifugation. The total protein removal can be up to 90% of the initial content of the waste brine. Protein removal is highly dependent on pH, centrifugation rate, and time. © 2014 Institute of Food Technologists®

Avian Influenza Virus Infection of Immortalized Human Respiratory Epithelial Cells Depends upon a Delicate Balance between Hemagglutinin Acid Stability and Endosomal pH*

PubMed Central

Daidoji, Tomo; Watanabe, Yohei; Ibrahim, Madiha S.; Yasugi, Mayo; Maruyama, Hisataka; Masuda, Taisuke; Arai, Fumihito; Ohba, Tomoyuki; Honda, Ayae; Ikuta, Kazuyoshi; Nakaya, Takaaki

2015-01-01

The highly pathogenic avian influenza (AI) virus, H5N1, is a serious threat to public health worldwide. Both the currently circulating H5N1 and previously circulating AI viruses recognize avian-type receptors; however, only the H5N1 is highly infectious and virulent in humans. The mechanism(s) underlying this difference in infectivity remains unclear. The aim of this study was to clarify the mechanisms responsible for the difference in infectivity between the current and previously circulating strains. Primary human small airway epithelial cells (SAECs) were transformed with the SV40 large T-antigen to establish a series of clones (SAEC-Ts). These clones were then used to test the infectivity of AI strains. Human SAEC-Ts could be broadly categorized into two different types based on their susceptibility (high or low) to the viruses. SAEC-T clones were poorly susceptible to previously circulating AI but were completely susceptible to the currently circulating H5N1. The hemagglutinin (HA) of the current H5N1 virus showed greater membrane fusion activity at higher pH levels than that of previous AI viruses, resulting in broader cell tropism. Moreover, the endosomal pH was lower in high susceptibility SAEC-T clones than that in low susceptibility SAEC-T clones. Taken together, the results of this study suggest that the infectivity of AI viruses, including H5N1, depends upon a delicate balance between the acid sensitivity of the viral HA and the pH within the endosomes of the target cell. Thus, one of the mechanisms underlying H5N1 pathogenesis in humans relies on its ability to fuse efficiently with the endosomes in human airway epithelial cells. PMID:25673693

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.

Studies on the extraction of nitrogenous and phosphorus-containing materials from the seeds of kidney beans (Phaseolus vulgaris)

PubMed Central

Pusztai, A.

1965-01-01

1. The conditions of extracting nitrogenous, phosphorus-containing and glucosamine-containing components of the seeds of kidney bean have been studied. 2. The dispersing of proteins was incomplete below pH 7, and the exact amount of protein extracted depended on the pH and the ionic strength of the solvent. 3. The extraction of proteins was practically complete in the range pH 7–9, but the relative amounts of the individual proteins obtained still depended on the pH of the extracting media, indicating a pH-dependent association–dissociation reaction between the protein molecules present. 4. The extraction of phosphorus-containing material showed an optimum at pH 6–7, and only a part of this was removed on dialysis. The precipitates obtained with trichloroacetic acid, on the other hand, retained very little phosphorus-containing material. 5. The significance of these findings is discussed. PMID:14340051

The influence of drop size-dependent fog chemistry on aerosol processing by San Joaquin Valley fogs

NASA Astrophysics Data System (ADS)

Hoag, Katherine J.; Collett, Jeffrey L., Jr.; Pandis, Spyros N.

Drop size-resolved measurements of fog chemistry in California's San Joaquin Valley during the 1995 Integrated Monitoring Study reveal that fog composition varies with drop size. Small fog drops were less alkaline and typically contained higher major ion (nitrate, sulfate, ammonium) concentrations than large drops. Small drops often contained higher concentrations of Fe and Mn than large drops while H 2O 2 concentrations exhibited no strong drop size dependence. Simulation of an extended fog episode in Fresno, California revealed the capability of a drop size-resolved fog chemistry model to reproduce the measured (based on two drop size categories) drop size dependence of several key species. The model was also able to satisfactorily reproduce measured species-dependent deposition rates (ammonium>sulfate>nitrate) resulting from fog drop sedimentation. Both the model simulation and direct analysis of size-resolved fog composition observations and measured gas-phase oxidant concentrations indicate the importance of ozone as an aqueous-phase S(IV) oxidant in these high pH fogs. Due to the nonlinear dependence of the rate law for the ozone pathway on the hydrogen ion concentration, use of the average fog drop composition can lead to significant underprediction of aqueous phase sulfate production rates in these chemically heterogeneous fogs.

Preparation of dual-stimuli-responsive liposomes using methacrylate-based copolymers with pH and temperature sensitivities for precisely controlled release.

PubMed

Sugimoto, Takumi; Yamazaki, Naoko; Hayashi, Takaaki; Yuba, Eiji; Harada, Atsushi; Kotaka, Aki; Shinde, Chiharu; Kumei, Takayuki; Sumida, Yasushi; Fukushima, Mitsuhiro; Munekata, Yuki; Maruyama, Keiichi; Kono, Kenji

2017-07-01

Dual-signal-sensitive copolymers were synthesized by copolymerization of methoxy diethylene glycol methacrylate, methacrylic acid, and lauroxy tetraethylene glycol methacrylate, which respectively provide temperature sensitivity, pH sensitivity, and anchoring to liposome surfaces. These novel copolymers, with water solubility that differs depending on temperature and pH, are soluble in water under neutral pH and low-temperature conditions, but they become water-insoluble and form aggregates under acidic pH and high-temperature conditions. Liposomes modified with these copolymers exhibited enhanced content release at weakly acidic pH with increasing temperature, although no temperature-dependent content release was observed in neutral conditions. Interaction between the copolymers and the lipid monolayer at the air-water interface revealed that the copolymer chains penetrate more deeply into the monolayer with increasing temperature at acidic pH than at neutral pH, where the penetration of copolymer chains was moderate and temperature-independent at neutral pH. Interaction of the copolymer-modified liposomes with HeLa cells demonstrated that the copolymer-modified liposomes were adsorbed quickly and efficiently onto the cell surface and that they were internalized more gradually than the unmodified liposomes through endocytosis. Furthermore, the copolymer-modified liposomes enhanced the content release in endosomes with increasing temperature, but no such temperature-dependent enhancement of content release was observed for unmodified liposomes. Copyright © 2017 Elsevier B.V. All rights reserved.

pH dependent unfolding characteristics of DLC8 dimer: Residue level details from NMR.

PubMed

Mohan, P M Krishna; Hosur, Ramakrishna V

2008-11-01

Environment dependence of folding and unfolding of a protein is central to its function. In the same vein, knowledge of pH dependence of stability and folding/unfolding is crucial for many biophysical equilibrium and kinetic studies designed to understand protein folding mechanisms. In the present study we investigated the guanidine induced unfolding transition of dynein light chain protein (DLC8), a cargo adaptor of the dynein complex in the pH range 7-10. It is observed that while the protein remains a dimer in the entire pH range, its stability is somewhat reduced at alkaline pH. Global unfolding features monitored using fluorescence spectroscopy revealed that the unfolding transition of DLC8 at pH 7 is best described by a three-state model, whereas, that at pH 10 is best described by a two-state model. Chemical shift perturbations due to pH change provided insights into the corresponding residue level structural perturbations in the DLC8 dimer. Likewise, backbone (15)N relaxation measurements threw light on the corresponding motional changes in the dimeric protein. These observations have been rationalized on the basis of expected changes with increasing pH in the protonation states of the titratable residues on the structure of the protein. These, in turn provide an explanation for the change from three-state to two-state guanidine induced unfolding transition as the pH is increased from 7 to 10. All these results exemplify and highlight the role of environment vis-à-vis the sequence and structure of a given protein in dictating its folding/unfolding characteristics.

pH imaging of mouse kidneys in vivo using a frequency-dependent paraCEST agent.

PubMed

Wu, Yunkou; Zhang, Shanrong; Soesbe, Todd C; Yu, Jing; Vinogradov, Elena; Lenkinski, Robert E; Sherry, A Dean

2016-06-01

This study explored the feasibility of using a pH responsive paramagnetic chemical exchange saturation transfer (paraCEST) agent to image the pH gradient in kidneys of healthy mice. CEST signals were acquired on an Agilent 9.4 Tesla small animal MRI system using a steady-state gradient echo pulse sequence after a bolus injection of agent. The magnetic field inhomogeneity across each kidney was corrected using the WASSR method and pH maps were calculated by measuring the frequency of water exchange signal arising from the agent. Dynamic CEST studies demonstrated that the agent was readily detectable in kidneys only between 4 to 12 min postinjection. The CEST images showed a higher signal intensity in the pelvis and calyx regions and lower signal intensity in the medulla and cortex regions. The pH maps reflected tissue pH values spanning from 6.0 to 7.5 in kidneys of healthy mice. This study demonstrated that pH maps of the kidney can be imaged in vivo by measuring the pH-dependent chemical shift of a single water exchange CEST peak without prior knowledge of the agent concentration in vivo. The results demonstrate the potential of using a simple frequency-dependent paraCEST agent for mapping tissue pH in vivo. Magn Reson Med 75:2432-2441, 2016. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Ion transport and selectivity in biomimetic nanopores with pH-tunable zwitterionic polyelectrolyte brushes.

PubMed

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

2015-10-28

Inspired by nature, functionalized nanopores with biomimetic structures have attracted growing interests in using them as novel platforms for applications of regulating ion and nanoparticle transport. To improve these emerging applications, we study theoretically for the first time the ion transport and selectivity in short nanopores functionalized with pH tunable, zwitterionic polyelectrolyte (PE) brushes. In addition to background salt ions, the study takes into account the presence of H(+) and OH(-) ions along with the chemistry reactions between functional groups on PE chains and protons. Due to ion concentration polarization, the charge density of PE layers is not homogeneously distributed and depends significantly on the background salt concentration, pH, grafting density of PE chains, and applied voltage bias, thereby resulting in many interesting and unexpected ion transport phenomena in the nanopore. For example, the ion selectivity of the biomimetic nanopore can be regulated from anion-selective (cation-selective) to cation-selective (anion-selective) by diminishing (raising) the solution pH when a sufficiently small grafting density of PE chains, large voltage bias, and low background salt concentration are applied.

Physical and chemical stability of marine lipid-based liposomes under acid conditions.

PubMed

Nacka, F; Cansell, M; Gouygou, J P.; Gerbeaud, C; Méléard, P; Entressangles, B

2001-03-01

Liposomes made from a marine lipid extract containing a high polyunsaturated fatty lipid ratio were submitted to large pH variations, ranging from 1 to 8. Shape transformations were followed by video microscopy using giant liposomes and micromanipulation experiments. Acidification induced a decrease of the vesicle size simultaneous to the appearance of invaginations. These pH-dependent structural rearrangements were interpreted in terms of osmotic shocks and chemical modifications of the membranes. Liposomes produced by direct filtration were studied using turbidity measurements and optical microscopy observations. A low pH led to an instantaneous vesicle aggregation and to complex supramolecular and/or morphological changes as a function of time. The subsequent buffer neutralization of the liposome suspensions induced a partial reversion of the aggregation phenomenon while the structural membrane rearrangements were persisting. Furthermore, weak chemical degradations (oxidation and hydrolysis) were evidenced when the vesicles were incubated at low pH up to a 24-h incubation time. Thus, although acidification revealed liposome size and shape changes, the bilayer structure was maintained indicating that marine lipid-based liposomes could be used as oral administration vectors.

Influence of polymeric excipient properties on crystal hydrate formation kinetics of caffeine in aqueous slurries.

PubMed

Gift, Alan D; Southard, Leslie A; Riesberg, Amanda L

2012-05-01

The influence of polymeric excipients on the hydrate transformation of caffeine (CAF) was studied. Anhydrous CAF was added to aqueous solutions containing different additives and the transformation to the hydrate form was monitored using in-line Raman spectroscopy. Various properties of two known inhibitors of CAF hydrate formation, polyacrylic acid (PAA) and polyvinyl alcohol (PVA), were investigated. For inhibition by PAA, a pH dependence was observed: at low pH, the inhibition was greatest, whereas no inhibitory effects were observed at pH above 6.5. For PVA, grades with high percent hydrolysis were the most effective at inhibiting the transformation. In addition, PVA with higher molecular weight showed slightly more inhibition than the shorter chain PVA polymers. A variety of other hydroxyl containing compounds were examined but none inhibited the CAF anhydrate-to-hydrate transformation. The observed inhibitory effects of PAA and PVA are attributed to the large number of closely spaced hydrogen bond donating groups of the polymer molecule, which can interact with the CAF hydrate crystal. Copyright © 2012 Wiley Periodicals, Inc.

Removal of acid blue 062 on aqueous solution using calcinated colemanite ore waste.

PubMed

Atar, Necip; Olgun, Asim

2007-07-19

Colemanite ore waste (CW) has been employed as adsorbent for the removal of acid blue 062 anionic dye (AB 062) from aqueous solution. The adsorption of AB 062 onto CW was examined with respect to contact time, calcination temperature, particle size, pH, adsorbent dosage and temperature. The physical and chemical properties of the CW, such as particle sizes and calcinations temperature, play important roles in dye adsorption. The dye adsorption largely depends on the initial pH of the solution with maximum uptake occurring at pH 1. Three simplified kinetics models, namely, pseudo-first order, pseudo-second order, and intraparticle diffusion models were tested to investigate the adsorption mechanisms. The kinetic adsorption of AB 062 on CW follows a pseudo-second order equation. The adsorption data have been analyzed using Langmuir and Freundlich isotherms. The results indicate that the Langmuir model provides the best correlation of the experimental data. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy and entropy of the adsorption of dye onto CW.

Excitons emissions and Raman scattering of ZnO nanoparticles embedded in BaF2 matrices by reactive magnetron sputtering.

PubMed

Zang, C H; Su, J F; Liu, Y C; Tang, C J; Fang, S J; Zhang, D M; Zhang, Y S

2011-11-01

ZnO nanoparticles embedded in BaF2 matrix were fabricated by rf magnetic sputtering technology. The optical properties of high quality ZnO nanoparticles, thermally post treated in a N2 atmosphere, were investigated by temperature-dependence photoluminescence measurement. Free exciton and localized exciton were observed at the low temperature. Free exciton peak was at 3.374 eV and localized exciton peak was at 3.420 eV, dominating the PL spectrum at 77 K. Free exciton transition was observed at 3.310 eV at room temperature, whereas the localized exciton transition was at 3.378 eV. The multiple-phonon Raman scattering spectrum showed that ZnO nanoparticles embedded in BaF2 matrix had a large deformation energy originated from lattice mismatch between ZnO and BaF2 matrix. Analysis of the fitting results from the temperature dependence of FWHM of ZnO exciton illustrated that the large value of gamma(ph) was good qualitative agreement with the large deformation potential.

CdSe/ZnS quantum dots conjugated with a fluorescein derivative: a FRET-based pH sensor for physiological alkaline conditions.

PubMed

Kurabayashi, Tomokazu; Funaki, Nayuta; Fukuda, Takeshi; Akiyama, Shinnosuke; Suzuki, Miho

2014-01-01

Dual pH-dependent fluorescence peaks from a semiconductor quantum dot (QD) and a pH-dependent fluorescent dye can be measured by irradiating with a single wavelength light, and the pH can be estimated from the ratio of the fluorescent intensity of the two peaks. In this work, ratiometric pH sensing was achieved in an aqueous environment by a fluorescent CdSe/ZnS QD appended with a pH-sensitive organic dye, based on fluorescence resonance energy transfer (FRET). By functionalizing the CdSe/ZnS QD with 5-(and 6)-carboxynaphthofluorescein succinimidyl ester as a pH-dependent fluorescent dye, we succeeded in fabricating sensitive nanocomplexes with a linear response to a broad range of physiological pH levels (7.5-9.5) when excited at 450 nm. We found that a purification process is important for increasing the high-fluorescence intensity ratio of a ratiometric fluorescence pH-sensor, and the fluorescence intensity ratio was improved up to 1.0 at pH 8.0 after the purification process to remove unreacted CdSe/ZnS QDs even though the fluorescence of the dye could not be observed without the purification process. The fluorescence intensity ratio corresponds to the fluorescence intensity of the dye, and this fluorescent dye exhibited pH-dependent fluorescence intensity changes. These facts indicate that the fluorescence intensity ratio linearly increased with increasing pH value of the buffer solution containing the QD and the dye. The FRET efficiencies changed from 0.3 (pH 7.5) to 6.2 (pH 9.5).

Anomalous pH-Dependent Nanofluidic Salinity Gradient Power.

PubMed

Yeh, Li-Hsien; Chen, Fu; Chiou, Yu-Ting; Su, Yen-Shao

2017-12-01

Previous studies on nanofluidic salinity gradient power (NSGP), where energy associated with the salinity gradient can be harvested with ion-selective nanopores, all suggest that nanofluidic devices having higher surface charge density should have higher performance, including osmotic power and conversion efficiency. In this manuscript, this viewpoint is challenged and anomalous counterintuitive pH-dependent NSGP behaviors are reported. For example, with equal pH deviation from its isoelectric point (IEP), the nanopore at pH < IEP is shown to have smaller surface charge density but remarkably higher NSGP performance than that at pH > IEP. Moreover, for sufficiently low pH, the NSGP performance decreases with lowering pH (increasing nanopore charge density). As a result, a maximum osmotic power density as high as 5.85 kW m -2 can be generated along with a conversion efficiency of 26.3% achieved for a single alumina nanopore at pH 3.5 under a 1000-fold concentration ratio. Using the rigorous model with considering the surface equilibrium reactions on the pore wall, it is proved that these counterintuitive surface-charge-dependent NSGP behaviors result from the pH-dependent ion concentration polarization effect, which yields the degradation in effective concentration ratio across the nanopore. These findings provide significant insight for the design of next-generation, high-performance NSGP devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The role of groundwater chemistry in the transport of bacteria to water-supply wells

USGS Publications Warehouse

Harvey, R.W.; Metge, D.W.

1999-01-01

Static mini-columns and in situ injection and recovery tests were used to assess the effects of modest changes in groundwater chemistry upon the pH-dependence of bacterial attachment, a primary determinant of bacterial mobility in drinking water aquifers. In uncontaminated groundwater (<1 mg l-1 dissolved organic carbon, DOC), bacterial attachment to aquifer grain surfaces declined steadily from 93 to 20% in response to an increase in pH from 5.8 to 7.8. However, bacterial attachment in modestly-contaminated groundwater (4 mg l-1 DOC) was relatively insensitive to pH change from pH 3.5 to pH 8, as was bacterial attachment in uncontaminated groundwater amended with only ~3 mg l-1 of purified humic acid. Destruction by UV-oxidation of the DOC in contaminated groundwater partially restored the pH-dependence of bacterial attachment. Results from static column tests and from a small-scale (3.6 m) natural-gradient injection and recovery study suggest that low concentrations of surfactants can also substantively alter the attraction of groundwater bacteria for grain surfaces and, therefore can alter the transport of bacteria to water-supply wells. This phenomenon was pH-sensitive and dependent upon the nature of the surfactant. At pH 7.6, 200 mg l-1 of the non-ionic surfactant, Imbentin, caused a doubling of fractional bacterial attachment in aquifer-sediment columns, but had little effect under slightly acidic conditions (e.g. at pH 5.8). In contrast, 1 mg l-1 of linear alkylbenzene sulphonate (LAS) surfactant, a common sewage-derived contaminant, decreased the fractional bacterial attachment by more than 30% at pH 5.8, but had little effect at pH 7.3.Static mini-columns and in situ injection and recovery tests were used to assess the effects of modest changes in groundwater chemistry upon the pH-dependence of bacterial attachment, a primary determinant of bacterial mobility in drinking water aquifers. In uncontaminated groundwater (<1 mg l-1 dissolved organic carbon, DOC), bacterial attachment to aquifer grain surfaces declined steadily from 93 to 20% in response to an increase in pH from 5.8 to 7.8. However, bacterial attachment in modestly-contaminated groundwater (4 mg l-1 DOC) was relatively insensitive to pH change from pH 3.5 to pH 8, as was bacterial attachment in uncontaminated groundwater amended with only approx. 3 mg l-1 of purified humic acid. Destruction of UV-oxidation of the DOC in contaminated groundwater partially restored the pH-dependence of bacterial attachment. Results from the static column tests and from a small-scale (3.6 m) natural-gradient injection and recovery study suggest that low concentrations of surfactants can also substantively alter the attraction of groundwater bacteria for grain surfaces and, therefore can alter the transport of bacteria to water-supply wells. This phenomenon was pH-sensitive and dependent upon the nature of the surfactant. At pH 7.6, 200 mg l-1 of the non-ionic surfactant, Imbentin, caused a doubling of fractional bacterial attachment in aquifer-sediment columns, but had little effect under slightly acidic conditions (e.g. at pH 5.8). In contrast, 1 mg l-1 of linear alkylbenzene sulphonate (LAS) surfactant, a common sewage-derived contaminant, decreased the fractional bacterial attachment by more than 30% at pH 5.8, but had little effect at pH 7.3.

Hydrophobic interactions between polymethacrylic acid and sodium laureth sulfate in aqueous solutions

NASA Astrophysics Data System (ADS)

Yaremko, Z. M.; Fedushinskaya, L. B.; Burka, O. A.; Soltys, M. N.

2014-09-01

The role of hydrophobic interaction in the development of associative processes is demonstrated, based on the concentration dependences of the viscosity and pH of binary solutions of polymethacrylic acid as an anionic polyelectrolyte and sodium laureth sulfate as an anionic surfactant. It is found that the inflection point on the dependence of the difference between the pH values of binary solutions of polymethacrylic acid and sodium laureth sulfate on the polyelectrolyte concentration is a criterion for determining the predominant contribution from hydrophobic interaction, as is the inflection point on the dependence of pH of individual solutions of polymethacrylic acid on the polyelectrolyte concentration.

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.

Impact of water quality on chlorine demand of corroding copper

EPA Pesticide Factsheets

Copper is widely used in drinking water premise plumbing system materials. In buildings such ashospitals, large and complicated plumbing networks make it difficult to maintain good water quality.Sustaining safe disinfectant residuals throughout a building to protect against waterborne pathogenssuch as Legionella is particularly challenging since copper and other reactive distribution system materialscan exert considerable demands. The objective of this work was to evaluate the impact of pH andorthophosphate on the consumption of free chlorine associated with corroding copper pipes over time. Acopper test-loop pilot system was used to control test conditions and systematically meet the studyobjectives. Chlorine consumption trends attributed to abiotic reactions with copper over time weredifferent for each pH condition tested, and the total amount of chlorine consumed over the test runsincreased with increasing pH. Orthophosphate eliminated chlorine consumption trends with elapsedtime (i.e., chlorine demand was consistent across entire test runs). Orthophosphate also greatly reducedthe total amount of chlorine consumed over the test runs. Interestingly, the total amount of chlorineconsumed and the consumption rate were not pH dependent when orthophosphate was present. Thefindings reflect the complex and competing reactions at the copper pipe wall including corrosion,oxidation of Cu(I) minerals and ions, and possible oxidation of Cu(II) minerals, and the change in

Phosphate Removal by Anion Binding on Functionalized Nanoporous Sorbents

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

Chouyyok, Wilaiwan; Wiacek, Robert J.; Pattamakomsan, Kanda

2010-03-26

Phosphate was captured from aqueous solutions by cationic metal-EDA complexes anchored inside mesoporous silica MCM-41 supports (Cu(II)-EDA-SAMMS and Fe(III)-EDA-SAMMS). Fe-EDA-SAMMS was more effective at capturing phosphate than the Cu-EDA-SAMMS and was further studied for matrix effects (e.g., pH, ionic strength, and competing anions) and sorption performance (e.g., capacity and rate). The adsorption of phosphate was highly pH dependent; it increased with increasing pH from 1.0 to 6.5, and decreased above pH 6.5. The adsorption was affected by high ionic strength (0.1 M of NaCl). In the presence of 1000-fold molar excess of chloride and nitrate anions, phosphate removal by Fe-EDA-SAMMSmore » was not affected. Slight, moderate and large impacts were seen with bicarbonate, sulfate and citrate anions, respectively. The phosphate adsorption data on Fe-EDA-SAMMS agreed well with the Langmuir model with the estimated maximum capacity of 43.3 mg/g. The material displayed rapid sorption rate (99% of phosphate removal within 1 min) and lowering the phosphate content to ~ 10 µg/L of phosphorus, which is lower than the EPA’s established freshwater contaminant level for phosphorous (20 µg/L).« less

Computation of pH-Dependent Binding Free Energies

PubMed Central

Kim, M. Olivia; McCammon, J. Andrew

2015-01-01

Protein-ligand binding accompanies changes in the surrounding electrostatic environments of the two binding partners and may lead to changes in protonation upon binding. In cases where the complex formation results in a net transfer of protons, the binding process is pH-dependent. However, conventional free energy computations or molecular docking protocols typically employ fixed protonation states for the titratable groups in both binding partners set a priori, which are identical for the free and bound states. In this review, we draw attention to these important yet largely ignored binding-induced protonation changes in protein-ligand association by outlining physical origins and prevalence of the protonation changes upon binding. Following a summary of various theoretical methods for pKa prediction, we discuss the theoretical framework to examine the pH dependence of protein-ligand binding processes. PMID:26202905

Buffer capacity of biologics--from buffer salts to buffering by antibodies.

PubMed

Karow, Anne R; Bahrenburg, Sven; Garidel, Patrick

2013-01-01

Controlling pH is essential for a variety of biopharmaceutical process steps. The chemical stability of biologics such as monoclonal antibodies is pH-dependent and slightly acidic conditions are favorable for stability in a number of cases. Since control of pH is widely provided by added buffer salts, the current study summarizes the buffer characteristics of acetate, citrate, histidine, succinate, and phosphate buffers. Experimentally derived values largely coincide with values calculated from a model that had been proposed in 1922 by van Slyke. As high concentrated protein formulations become more and more prevalent for biologics, the self-buffering potential of proteins becomes of relevance. The current study provides information on buffer characteristics for pH ranges down to 4.0 and up to 8.0 and shows that a monoclonal antibody at 50 mg/mL exhibits similar buffer capacity as 6 mM citrate or 14 mM histidine (pH 5.0-6.0). Buffer capacity of antibody solutions scales linearly with protein concentration up to more than 200 mg/mL. At a protein concentration of 220 mg/mL, the buffer capacity resembles the buffer capacity of 30 mM citrate or 50 mM histidine (pH 5.0-6.0). The buffer capacity of monoclonal antibodies is practically identical at the process relevant temperatures 5, 25, and 40°C. Changes in ionic strength of ΔI=0.15, in contrast, can alter the buffer capacity up to 35%. In conclusion, due to efficient self-buffering by antibodies in the pH range of favored chemical stability, conventional buffer excipients could be dispensable for pH stabilization of high concentrated protein solutions. Copyright © 2013 American Institute of Chemical Engineers.

Acid-sensing ion channels contribute to chemosensitivity of breathing-related neurons of the nucleus of the solitary tract.

PubMed

Huda, Rafiq; Pollema-Mays, Sarah L; Chang, Zheng; Alheid, George F; McCrimmon, Donald R; Martina, Marco

2012-10-01

Cellular mechanisms of central pH chemosensitivity remain largely unknown. The nucleus of the solitary tract (NTS) integrates peripheral afferents with central pathways controlling breathing; NTS neurons function as central chemosensors, but only limited information exists concerning the ionic mechanisms involved. Acid-sensing ion channels (ASICs) mediate chemosensitivity in nociceptive terminals, where pH values ∼6.5 are not uncommon in inflammation, but are also abundantly expressed throughout the brain where pHi s tightly regulated and their role is less clear. Here we test the hypothesis that ASICs are expressed in NTS neurons and contribute to intrinsic chemosensitivity and control of breathing. In electrophysiological recordings from acute rat NTS slices, ∼40% of NTS neurons responded to physiological acidification (pH 7.0) with a transient depolarization. This response was also present in dissociated neurons suggesting an intrinsic mechanism. In voltage clamp recordings in slices, a pH drop from 7.4 to 7.0 induced ASIC-like inward currents (blocked by 100 μM amiloride) in ∼40% of NTS neurons, while at pH ≤ 6.5 these currents were detected in all neurons tested; RT-PCR revealed expression of ASIC1 and, less abundantly, ASIC2 in the NTS. Anatomical analysis of dye-filled neurons showed that ASIC-dependent chemosensitive cells (cells responding to pH 7.0) cluster dorsally in the NTS. Using in vivo retrograde labelling from the ventral respiratory column, 90% (9/10) of the labelled neurons showed an ASIC-like response to pH 7.0, suggesting that ASIC currents contribute to control of breathing. Accordingly, amiloride injection into the NTS reduced phrenic nerve activity of anaesthetized rats with an elevated arterial P(CO(2)) .

On-line focusing of flavin derivatives using Dynamic pH junction-sweeping capillary electrophoresis with laser-induced fluorescence detection.

PubMed

Britz-McKibbin, Philip; Otsuka, Koji; Terabe, Shigeru

2002-08-01

Simple yet effective methods to enhance concentration sensitivity is needed for capillary electrophoresis (CE) to become a practical method to analyze trace levels of analytes in real samples. In this report, the development of a novel on-line preconcentration technique combining dynamic pH junction and sweeping modes of focusing is applied to the sensitive and selective analysis of three flavin derivatives: riboflavin, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Picomolar (pM) detectability of flavins by CE with laser-induced fluorescence (LIF) detection is demonstrated through effective focusing of large sample volumes (up to 22% capillary length) using a dual pH junction-sweeping focusing mode. This results in greater than a 1,200-fold improvement in sensitivity relative to conventional injection methods, giving a limit of detection (S/N = 3) of approximately 4.0 pM for FAD and FMN. Flavin focusing is examined in terms of analyte mobility dependence on buffer pH, borate complexation and SDS interaction. Dynamic pH junction-sweeping extends on-line focusing to both neutral (hydrophobic) and weakly acidic (hydrophilic) species and is considered useful in cases when either conventional sweeping or dynamic pH junction techniques used alone are less effective for certain classes of analytes. Enhanced focusing performance by this hyphenated method was demonstrated by greater than a 4-fold reduction in flavin bandwidth, as compared to either sweeping or dynamic pH junction, reflected by analyte detector bandwidths <0.20 cm. Novel on-line focusing strategies are required to improve sensitivity in CE, which may be applied toward more effective biochemical analysis methods for diverse types of analytes.

Pilot study of Iopamidol-based quantitative pH imaging on a clinical 3T MR scanner.

PubMed

Müller-Lutz, Anja; Khalil, Nadia; Schmitt, Benjamin; Jellus, Vladimir; Pentang, Gael; Oeltzschner, Georg; Antoch, Gerald; Lanzman, Rotem S; Wittsack, Hans-Jörg

2014-12-01

The objective of this study was to show the feasibility to perform Iopamidol-based pH imaging via clinical 3T magnetic resonance imaging (MRI) using chemical exchange saturation transfer (CEST) imaging with pulse train presaturation. The pulse train presaturation scheme of a CEST sequence was investigated for Iopamidol-based pH measurements using a 3T magnetic resonance (MR) scanner. The CEST sequence was applied to eight tubes filled with 100-mM Iopamidol solutions with pH values ranging from 5.6 to 7.0. Calibration curves for pH quantification were determined. The dependence of pH values on the concentration of Iopamidol was investigated. An in vivo measurement was performed in one patient who had undergone a previous contrast-enhanced computed tomography (CT) scan with Iopamidol. The pH values of urine measured with CEST MRI and with a pH meter were compared. In the measured pH range, pH imaging using CEST imaging with pulse train presaturation was possible. Dependence between the pH value and the concentration of Iopamidol was not observed. In the in vivo investigation, the pH values in the human bladder measured by the Iopamidol CEST sequence and in urine were consistent. Our study shows the feasibility of using CEST imaging with Iopamidol for quantitative pH mapping in vitro and in vivo on a 3T MR scanner.

Fine-particle pH for Beijing winter haze as inferred from different thermodynamic equilibrium models

NASA Astrophysics Data System (ADS)

Song, Shaojie; Gao, Meng; Xu, Weiqi; Shao, Jingyuan; Shi, Guoliang; Wang, Shuxiao; Wang, Yuxuan; Sun, Yele; McElroy, Michael B.

2018-05-01

pH is an important property of aerosol particles but is difficult to measure directly. Several studies have estimated the pH values for fine particles in northern China winter haze using thermodynamic models (i.e., E-AIM and ISORROPIA) and ambient measurements. The reported pH values differ widely, ranging from close to 0 (highly acidic) to as high as 7 (neutral). In order to understand the reason for this discrepancy, we calculated pH values using these models with different assumptions with regard to model inputs and particle phase states. We find that the large discrepancy is due primarily to differences in the model assumptions adopted in previous studies. Calculations using only aerosol-phase composition as inputs (i.e., reverse mode) are sensitive to the measurement errors of ionic species, and inferred pH values exhibit a bimodal distribution, with peaks between -2 and 2 and between 7 and 10, depending on whether anions or cations are in excess. Calculations using total (gas plus aerosol phase) measurements as inputs (i.e., forward mode) are affected much less by these measurement errors. In future studies, the reverse mode should be avoided whereas the forward mode should be used. Forward-mode calculations in this and previous studies collectively indicate a moderately acidic condition (pH from about 4 to about 5) for fine particles in northern China winter haze, indicating further that ammonia plays an important role in determining this property. The assumed particle phase state, either stable (solid plus liquid) or metastable (only liquid), does not significantly impact pH predictions. The unrealistic pH values of about 7 in a few previous studies (using the standard ISORROPIA model and stable state assumption) resulted from coding errors in the model, which have been identified and fixed in this study.

Bicarbonate-regulated adenylyl cyclase (sAC) is a sensor that regulates pH-dependent V-ATPase recycling.

PubMed

Pastor-Soler, Nuria; Beaulieu, Valerie; Litvin, Tatiana N; Da Silva, Nicolas; Chen, Yanqiu; Brown, Dennis; Buck, Jochen; Levin, Lonny R; Breton, Sylvie

2003-12-05

Modulation of environmental pH is critical for the function of many biological systems. However, the molecular identity of the pH sensor and its interaction with downstream effector proteins remain poorly understood. Using the male reproductive tract as a model system in which luminal acidification is critical for sperm maturation and storage, we now report a novel pathway for pH regulation linking the bicarbonate activated soluble adenylyl cyclase (sAC) to the vacuolar H+ATPase (V-ATPase). Clear cells of the epididymis and vas deferens contain abundant V-ATPase in their apical pole and are responsible for acidifying the lumen. Proton secretion is regulated via active recycling of V-ATPase. Here we demonstrate that this recycling is regulated by luminal pH and bicarbonate. sAC is highly expressed in clear cells, and apical membrane accumulation of V-ATPase is triggered by a sAC-dependent rise in cAMP in response to alkaline luminal pH. As sAC is expressed in other acid/base transporting epithelia, including kidney and choroid plexus, this cAMP-dependent signal transduction pathway may be a widespread mechanism that allows cells to sense and modulate extracellular pH.

The effect of arginine glutamate on the stability of monoclonal antibodies in solution.

PubMed

Kheddo, Priscilla; Tracka, Malgorzata; Armer, Jonathan; Dearman, Rebecca J; Uddin, Shahid; van der Walle, Christopher F; Golovanov, Alexander P

2014-10-01

Finding excipients which mitigate protein self-association and aggregation is an important task during formulation. Here, the effect of an equimolar mixture of l-Arg and l-Glu (Arg·Glu) on colloidal and conformational stability of four monoclonal antibodies (mAb1-mAb4) at different pH is explored, with the temperatures of the on-set of aggregation (Tagg) and unfolding (Tm1) measured by static light scattering and intrinsic fluorescence, respectively. Arg·Glu increased the Tagg of all four mAbs in concentration-dependent manner, especially as pH increased to neutral. Arg·Glu also increased Tm1 of the least thermally stable mAb3, but without similar direct effect on the Tm1 of other mAbs. Raising pH itself from 5 to 7 increased Tm1 for all four mAbs. Selected mAb formulations were assessed under accelerated stability conditions for the monomer fraction remaining in solution after storage. The aggregation of mAb3 was suppressed to a greater extent by Arg·Glu than by Arg·HCl. Furthermore, Arg·Glu suppressed the aggregation of mAb1 at neutral pH such that the fraction monomer was near to that at the more typical formulation pH of 5.5. We conclude that Arg·Glu can suppress mAb aggregation with increasing temperature/pH and, importantly, under accelerated stability conditions at weakly acidic to neutral pH. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

Mechanistic Analysis of Cocrystal Dissolution as a Function of pH and Micellar Solubilization

PubMed Central

2016-01-01

The purpose of this work is to provide a mechanistic understanding of the dissolution behavior of cocrystals under the influence of ionization and micellar solubilization. Mass transport models were developed by applying Fick’s law of diffusion to dissolution with simultaneous chemical reactions in the hydrodynamic boundary layer adjacent to the dissolving cocrystal surface to predict the pH at the dissolving solid–liquid interface (i.e., interfacial pH) and the flux of cocrystals. To evaluate the predictive power of these models, dissolution studies of carbamazepine–saccharin (CBZ-SAC) and carbamazepine–salicylic acid (CBZ-SLC) cocrystals were performed at varied pH and surfactant concentrations above the critical stabilization concentration (CSC), where the cocrystals were thermodynamically stable. The findings in this work demonstrate that the pH dependent dissolution behavior of cocrystals with ionizable components is dependent on interfacial pH. This mass transport analysis demonstrates the importance of pH, cocrystal solubility, diffusivity, and micellar solubilization on the dissolution rates of cocrystals. PMID:26877267

Mechanistic Analysis of Cocrystal Dissolution as a Function of pH and Micellar Solubilization.

PubMed

Cao, Fengjuan; Amidon, Gordon L; Rodriguez-Hornedo, Nair; Amidon, Gregory E

2016-03-07

The purpose of this work is to provide a mechanistic understanding of the dissolution behavior of cocrystals under the influence of ionization and micellar solubilization. Mass transport models were developed by applying Fick's law of diffusion to dissolution with simultaneous chemical reactions in the hydrodynamic boundary layer adjacent to the dissolving cocrystal surface to predict the pH at the dissolving solid-liquid interface (i.e., interfacial pH) and the flux of cocrystals. To evaluate the predictive power of these models, dissolution studies of carbamazepine-saccharin (CBZ-SAC) and carbamazepine-salicylic acid (CBZ-SLC) cocrystals were performed at varied pH and surfactant concentrations above the critical stabilization concentration (CSC), where the cocrystals were thermodynamically stable. The findings in this work demonstrate that the pH dependent dissolution behavior of cocrystals with ionizable components is dependent on interfacial pH. This mass transport analysis demonstrates the importance of pH, cocrystal solubility, diffusivity, and micellar solubilization on the dissolution rates of cocrystals.

Bimodal MR-PET agent for quantitative pH imaging

PubMed Central

Frullano, Luca; Catana, Ciprian; Benner, Thomas; Sherry, A. Dean; Caravan, Peter

2010-01-01

Activatable or “smart” magnetic resonance contrast agents have relaxivities that depend on environmental factors such as pH or enzymatic activity, but the MR signal depends on relaxivity and agent concentration – two unknowns. A bimodal approach, incorporating a positron emitter, solves this problem. Simultaneous positron emission tomography (PET) and MR imaging with the biomodal, pH-responsive MR-PET agent GdDOTA-4AMP-F allows direct determination of both concentration (PET) and T1 (MRI), and hence pH. PMID:20191650

Modifying the Cold Gelation Properties of Quinoa Protein Isolate: Influence of Heat-Denaturation pH in the Alkaline Range.

PubMed

Mäkinen, Outi E; Zannini, Emanuele; Arendt, Elke K

2015-09-01

Heat-denaturation of quinoa protein isolate (QPI) at alkali pH and its influence on the physicochemical and cold gelation properties was investigated. Heating QPI at pH 8.5 led to increased surface hydrophobicity and decreases in free and bound sulfhydryl group contents. Heating at pH 10.5 caused a lesser degree of changes in sulfhydryl groups and surface hydrophobicity, and the resulting solutions showed drastically increased solubility. SDS PAGE revealed the presence of large aggregates only in the sample heated at pH 8.5, suggesting that any aggregates present in the sample heated at pH 10.5 were non-covalently bound and disintegrated in the presence of SDS. Reducing conditions partially dissolved the aggregates in the pH 8.5 heated sample indicating the occurrence of disulphide bonding, but caused no major alterations in the separation pattern of the pH 10.5 heated sample. Denaturation pH influenced the cold gelation properties greatly. Solutions heated at pH 8.5 formed a coarse coagulum with maximum G' of 5 Pa. Heat-denaturation at 10.5 enabled the proteins to form a finer and regularly structured gel with a maximum G' of 1140 Pa. Particle size analysis showed that the pH 10.5 heated sample contained a higher level of very small particles (0.1-2 μm), and these readily aggregated into large particles (30-200 μm) when pH was lowered to 5.5. Differences in the nature of aggregates formed during heating may explain the large variation in gelation properties.

Visible to near-IR fluorescence from single-digit detonation nanodiamonds: excitation wavelength and pH dependence.

PubMed

Reineck, Philipp; Lau, Desmond W M; Wilson, Emma R; Nunn, Nicholas; Shenderova, Olga A; Gibson, Brant C

2018-02-06

Detonation nanodiamonds are of vital significance to many areas of science and technology. However, their fluorescence properties have rarely been explored for applications and remain poorly understood. We demonstrate significant fluorescence from the visible to near-infrared spectral regions from deaggregated, single-digit detonation nanodiamonds dispersed in water produced via post-synthesis oxidation. The excitation wavelength dependence of this fluorescence is analyzed in the spectral region from 400 nm to 700 nm as well as the particles' absorption characteristics. We report a strong pH dependence of the fluorescence and compare our results to the pH dependent fluorescence of aromatic hydrocarbons. Our results significantly contribute to the current understanding of the fluorescence of carbon-based nanomaterials in general and detonation nanodiamonds in particular.

INFLUENCE OF PH AND REDOX CONDITIONS ON COPPER LEACHING

EPA Science Inventory

Leaching behavior of metals from a mineral processing waste at varying pH and redox conditions was studies. Effect of combinations of pH and Eh on leaching of copper is described. Leaching of copper was found to be dependent on both pH and Eh. Higher concentrations of Cu were ...

The effect of pH on chronic aquatic nickel toxicity is dependent on the pH itself: Extending the chronic nickel bioavailability models.

PubMed

Nys, Charlotte; Janssen, Colin R; Van Sprang, Patrick; De Schamphelaere, Karel A C

2016-05-01

The environmental quality standard for Ni in the European Commission's Water Framework Directive is bioavailability based. Although some of the available chronic Ni bioavailability models are validated only for pH ≤ 8.2, a considerable fraction of European surface waters has a pH > 8.2. Therefore, the authors investigated the effect of a change in pH from 8.2 to 8.7 on chronic Ni toxicity in 3 invertebrate (Daphnia magna, Lymnaea stagnalis, and Brachionus calyciflorus) and 2 plant species (Pseudokirchneriella subcapitata and Lemna minor). Nickel toxicity was almost always significantly higher at pH 8.7 than at pH 8.2. To test whether the existing chronic Ni bioavailability models developed for pH ≤ 8.2 can be used at higher pH levels, Ni toxicity at pH 8.7 was predicted based on Ni toxicity observed at pH 8.2. This resulted in a consistent underestimation of toxicity. The results suggest that the effect of pH on Ni(2+) toxicity is dependent on the pH itself: the slope of the pH effect is steeper above than below pH 8.2 for species for which a species-specific bioavailability model exists. Therefore, the existing chronic Ni bioavailability models were modified to allow predictions of chronic Ni toxicity to invertebrates and plants in the pH range of 8.2 to 8.7 by applying a pH slope (SpH ) dependent on the pH of the target water. These modified Ni bioavailability models resulted in more accurate predictions of Ni toxicity to all 5 species (within 2-fold error), without the bias observed using the bioavailability models developed for pH ≤ 8.2. The results of the present study can decrease the uncertainty in implementing the bioavailability-based environmental quality standard under the Water Framework Directive for high-pH regions in Europe. © 2015 SETAC.

Biological pH sensing based on the environmentally friendly Raman technique through a polyaniline probe.

PubMed

Li, Songyang; Liu, Zhiming; Su, Chengkang; Chen, Haolin; Fei, Xixi; Guo, Zhouyi

2017-02-01

The biological pH plays an important role in various cellular processes. In this work, a novel strategy is reported for biological pH sensing by using Raman spectroscopy and polyaniline nanoparticles (PANI NPs) as the pH-sensitive Raman probe. It is found that the Raman spectrum of PANI NPs is strongly dependent on the pH value. The intensities of Raman spectral bands at 1225 and 1454 cm -1 increase obviously with pH value varying from 5.5 to 8.0, which covers the range of regular biological pH variation. The pH-dependent Raman performance of PANI NPs, as well as their robust Raman signals and sensitivities to pH, was well retained after the nanoparticles incorporated into living 4T1 breast adenocarcinoma cells. The data indicate that such PANI NPs can be used as an effective biological pH sensor. Most interestingly, the PANI spherical nanostructures can be acquired by a low-cost, metal-free, and one-pot oxidative polymerization, which gives them excellent biocompatibility for further biological applications.

Genetically encoded proton sensors reveal activity-dependent pH changes in neurons.

PubMed

Raimondo, Joseph V; Irkle, Agnese; Wefelmeyer, Winnie; Newey, Sarah E; Akerman, Colin J

2012-01-01

The regulation of hydrogen ion concentration (pH) is fundamental to cell viability, metabolism, and enzymatic function. Within the nervous system, the control of pH is also involved in diverse and dynamic processes including development, synaptic transmission, and the control of network excitability. As pH affects neuronal activity, and can also itself be altered by neuronal activity, the existence of tools to accurately measure hydrogen ion fluctuations is important for understanding the role pH plays under physiological and pathological conditions. Outside of their use as a marker of synaptic release, genetically encoded pH sensors have not been utilized to study hydrogen ion fluxes associated with network activity. By combining whole-cell patch clamp with simultaneous two-photon or confocal imaging, we quantified the amplitude and time course of neuronal, intracellular, acidic transients evoked by epileptiform activity in two separate in vitro models of temporal lobe epilepsy. In doing so, we demonstrate the suitability of three genetically encoded pH sensors: deGFP4, E(2)GFP, and Cl-sensor for investigating activity-dependent pH changes at the level of single neurons.

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

Inhibition of DNA-Dependent Protein Kinase Activity for Breast Cancer Therapy

DTIC Science & Technology

2002-06-01

Dependent Protein Kinase Activity for Breast Cancer Therapy PRINCIPAL INVESTIGATOR: Chin-Rang Yang, Ph.D. CONTRACTING ORGANIZATION: University of Rochester...Activity for Breast Cancer Therapy 6. AUTHOR(S) Chin-Rang Yang, Ph.D. 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT...The formation of DNA double strand breaks (DSBs) correlates well with lethality of cancer cells following ionizing radiation (IR). The DNA-dependent

Neuroserpin Differentiates Between Forms of Tissue Type Plasminogen Activator via pH Dependent Deacylation

PubMed Central

Carlson, Karen-Sue B.; Nguyen, Lan; Schwartz, Kat; Lawrence, Daniel A.; Schwartz, Bradford S.

2016-01-01

Tissue-type plasminogen activator (t-PA), initially characterized for its critical role in fibrinolysis, also has key functions in both physiologic and pathologic processes in the CNS. Neuroserpin (NSP) is a t-PA specific serine protease inhibitor (serpin) found almost exclusively in the CNS that regulates t-PA’s proteolytic activity and protects against t-PA mediated seizure propagation and blood–brain barrier disruption. This report demonstrates that NSP inhibition of t-PA varies profoundly as a function of pH within the biologically relevant pH range for the CNS, and reflects the stability, rather than the formation of NSP: t-PA acyl-enzyme complexes. Moreover, NSP differentiates between the zymogen-like single chain form (single chain t-PA, sct-PA) and the mature protease form (two chain t-PA, tct-PA) of t-PA, demonstrating different pH profiles for protease inhibition, different pH ranges over which catalytic deacylation occurs, and different pH dependent profiles of deacylation rates for each form of t-PA. NSP’s pH dependent inhibition of t-PA is not accounted for by differential acylation, and is specific for the NSP-t-PA serpin-protease pair. These results demonstrate a novel mechanism for the differential regulation of the two forms of t-PA in the CNS, and suggest a potential specific regulatory role for CNS pH in controlling t-PA proteolytic activity. PMID:27378851

An EPR study of the pH dependence of formate effects on Photosystem II.

PubMed

Jajoo, Anjana; Katsuta, Nobuhiro; Kawamori, Asako

2006-04-01

Effects of formate on rates of O(2) evolution and electron paramagnetic resonance (EPR) signals were observed in the oxygen evolving PS II membranes as a function of pH. In formate treated PS II membranes, decrease in pH value resulted in the inhibition of the O(2) evolving activity, a decrease in the intensity of S(2) state multiline signal but an increase in the intensity of the Q(A)(-)Fe(2+) EPR signal. Time-resolved EPR study of the Y(Z)(*) decay kinetics showed that the light-induced intensity of Y(Z)(*) EPR signal was proportional to the formate concentration. The change in the pH affected both the light-induced intensities and the decay rates of Y(Z)(*), which was found to be faster at lower pH. At 253 K, t(1/e) value of Y(Z)(*) decay kinetics was found to be 8-10 s at pH 6.0 and 18-21 s at pH 5.0. The results presented here indicate that the extent of inhibition at the donor and the acceptor side of PS II due to formate is pH dependent, being more effective at lower pH.

Global Role of Cyclic AMP Signaling in pH-Dependent Responses in Candida albicans.

PubMed

Hollomon, Jeffrey M; Grahl, Nora; Willger, Sven D; Koeppen, Katja; Hogan, Deborah A

2016-01-01

Candida albicans behaviors are affected by pH, an important environmental variable. Filamentous growth is a pH-responsive behavior, where alkaline conditions favor hyphal growth and acid conditions favor growth as yeast. We employed filamentous growth as a tool to study the impact of pH on the hyphal growth regulator Cyr1, and we report that downregulation of cyclic AMP (cAMP) signaling by acidic pH contributes to the inhibition of hyphal growth in minimal medium with GlcNAc. Ras1 and Cyr1 are generally required for efficient hyphal growth, and the effects of low pH on Ras1 proteolysis and GTP binding are consistent with diminished cAMP output. Active alleles of ras1 do not suppress the hyphal growth defect at low pH, while dibutyryl cAMP partially rescues filamentous growth at low pH in a cyr1 mutant. These observations are consistent with Ras1-independent downregulation of Cyr1 by low pH. We also report that extracellular pH leads to rapid and prolonged decreases in intracellular pH, and these changes may contribute to reduced cAMP signaling by reducing intracellular bicarbonate pools. Transcriptomics analyses found that the loss of Cyr1 at either acidic or neutral pH leads to increases in transcripts involved in carbohydrate catabolism and protein translation and glycosylation and decreases in transcripts involved in oxidative metabolism, fluconazole transport, metal transport, and biofilm formation. Other pathways were modulated in pH-dependent ways. Our findings indicate that cAMP has a global role in pH-dependent responses, and this effect is mediated, at least in part, through Cyr1 in a Ras1-independent fashion. IMPORTANCE Candida albicans is a human commensal and the causative agent of candidiasis, a potentially invasive and life-threatening infection. C. albicans experiences wide changes in pH during both benign commensalism (a common condition) and pathogenesis, and its morphology changes in response to this stimulus. Neutral pH is considered an activator of hyphal growth through Rim101, but the effect of low pH on other morphology-related pathways has not been extensively studied. We sought to determine the role of cyclic AMP signaling, a central regulator of morphology, in the sensing of pH. In addition, we asked broadly what cellular processes were altered by pH in both the presence and absence of this important signal integration system. We concluded that cAMP signaling is impacted by pH and that cAMP broadly impacts C. albicans physiology in both pH-dependent and -independent ways.

Global Role of Cyclic AMP Signaling in pH-Dependent Responses in Candida albicans

PubMed Central

Hollomon, Jeffrey M.; Grahl, Nora; Willger, Sven D.; Koeppen, Katja

2016-01-01

ABSTRACT Candida albicans behaviors are affected by pH, an important environmental variable. Filamentous growth is a pH-responsive behavior, where alkaline conditions favor hyphal growth and acid conditions favor growth as yeast. We employed filamentous growth as a tool to study the impact of pH on the hyphal growth regulator Cyr1, and we report that downregulation of cyclic AMP (cAMP) signaling by acidic pH contributes to the inhibition of hyphal growth in minimal medium with GlcNAc. Ras1 and Cyr1 are generally required for efficient hyphal growth, and the effects of low pH on Ras1 proteolysis and GTP binding are consistent with diminished cAMP output. Active alleles of ras1 do not suppress the hyphal growth defect at low pH, while dibutyryl cAMP partially rescues filamentous growth at low pH in a cyr1 mutant. These observations are consistent with Ras1-independent downregulation of Cyr1 by low pH. We also report that extracellular pH leads to rapid and prolonged decreases in intracellular pH, and these changes may contribute to reduced cAMP signaling by reducing intracellular bicarbonate pools. Transcriptomics analyses found that the loss of Cyr1 at either acidic or neutral pH leads to increases in transcripts involved in carbohydrate catabolism and protein translation and glycosylation and decreases in transcripts involved in oxidative metabolism, fluconazole transport, metal transport, and biofilm formation. Other pathways were modulated in pH-dependent ways. Our findings indicate that cAMP has a global role in pH-dependent responses, and this effect is mediated, at least in part, through Cyr1 in a Ras1-independent fashion. IMPORTANCE Candida albicans is a human commensal and the causative agent of candidiasis, a potentially invasive and life-threatening infection. C. albicans experiences wide changes in pH during both benign commensalism (a common condition) and pathogenesis, and its morphology changes in response to this stimulus. Neutral pH is considered an activator of hyphal growth through Rim101, but the effect of low pH on other morphology-related pathways has not been extensively studied. We sought to determine the role of cyclic AMP signaling, a central regulator of morphology, in the sensing of pH. In addition, we asked broadly what cellular processes were altered by pH in both the presence and absence of this important signal integration system. We concluded that cAMP signaling is impacted by pH and that cAMP broadly impacts C. albicans physiology in both pH-dependent and -independent ways. PMID:27921082

The jumbo squid, Dosidicus gigas (Ommastrephidae), living in oxygen minimum zones II: Blood-oxygen binding

NASA Astrophysics Data System (ADS)

Seibel, Brad A.

2013-10-01

Dosidicus gigas is a large, metabolically active squid that migrates across a strong oxygen and temperature gradient in the Eastern Pacific. Here we analyze the oxygen-binding properties of the squid's respiratory protein (hemocyanin, Hc) that facilitate such activity. A high Hc-oxygen affinity, strong temperature dependence, and pronounced pH sensitivity (P50=0.009T2.03, pH 7.4; Bohr coefficient=ΔlogP50/ΔpH=-1.55+0.034T) of oxygen binding facilitate night-time foraging in the upper water column, and support suppressed oxygen demand in hypoxic waters at greater depths. Expanding hypoxia may act to alter the species habitable depth range. This analysis supports the contention that ocean acidification could limit oxygen carrying capacity in squids at warmer temperature leading to reduced activity levels or altered distribution.

The Role of Ru Redox in pH-Dependent Oxygen Evolution on Rutile Ruthenium Dioxide Surfaces

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

Stoerzinger, Kelsey A.; Rao, Reshma R.; Wang, Xiao Renshaw

Rutile RuO 2 is known to exhibit high catalytic activity for the oxygen evolution reaction (OER) and large pseudocapacitance associated with redox of surface Ru, however the mechanistic link between these properties and the role of pH is yet to be understood. Here we report that the OER activities of the (101), (001) and (111) RuO 2 surfaces were found to increase while the potential of a pseudocapacitive feature just prior to OER shifted to lower potentials (“super-Nernstian” shift) with increasing pH on the reversible hydrogen electrode (RHE) scale. This behavior is in contrast to the (100) and (110) surfacesmore » that have pH-independent Ru redox and OER activity. The link in catalytic and pseudocapacitive behavior illustrates the importance of this redox feature in generating active sites, building new mechanistic understanding of the OER.« less

Microenvironmental pH-modification to improve dissolution behavior and oral absorption for drugs with pH-dependent solubility.

PubMed

Taniguchi, Chika; Kawabata, Yohei; Wada, Koichi; Yamada, Shizuo; Onoue, Satomi

2014-04-01

Drug release and oral absorption of drugs with pH-dependent solubility are influenced by the conditions in the gastrointestinal tract. In some cases, poor oral absorption has been observed for these drugs, causing insufficient drug efficacy. The pH-modification of a formulation could be a promising approach to overcome the poor oral absorption of drugs with pH-dependent solubility. The present review aims to summarize the pH-modifier approach and strategic analyses of microenvironmental pH for formulation design and development. We also provide literature- and patent-based examples of the application of pH-modification technology to solid dosage forms. For the pH-modification approach, the microenvironmental pH at the diffusion area can be altered by dissolving pH-modifying excipients in the formulation. The modulation of the microenvironmental pH could improve dissolution behavior of drugs with pH-dependent solubility, possibly leading to better oral absorption. According to this concept, the modulated level of microenvironmental pH and its duration can be key factors for improvement in drug dissolution. The measurement of microenvironmental pH and release of pH-modifier would provide theoretical insight for the selection of an appropriate pH-modifier and optimization of the formulation.

In situ pH within particle beds of bioactive glasses.

PubMed

Zhang, Di; Hupa, Mikko; Hupa, Leena

2008-09-01

The in vitro behavior of three bioactive glasses with seven particle size distributions was studied by measuring the in situ pH inside the particle beds for 48h in simulated body fluid (SBF). After immersion, the surface of the particles was characterized with a field emission scanning electron microscope equipped with an energy-dispersive X-ray analyzer. In addition, the results were compared with the reactions of the same glasses formed as plates. A similar trend in pH as a function of immersion time was observed for all systems. However, the pH inside the particle beds was markedly higher than that in the bulk SBF of the plates. The pH decreased as power functions with increasing particle size, i.e. with decreasing surface area. The in vitro reactivity expressed as layer formation strongly depended on the particle size and glass composition. The average thickness of the total reaction layer decreased with the increase in sample surface area. Well-developed silica and calcium phosphate layers typically observed on glass plates could be detected only on some particles freely exposed to the solution. No distinct reaction layers were observed on the finest particles, possibly because the layers spread out on the large surface area. Differences in the properties of the bulk SBF and the solution inside the particle bed were negligible for particles larger than 800microm. The results enhance our understanding of the in vitro reactions of bioactive glasses in various product forms and sizes.

Evidence for a SN2-type pathway in the exchange of phosphines at a [PhSe]+ centre.

PubMed

Forfar, Laura C; Green, Michael; Haddow, Mairi F; Hussein, Sharifa; Lynam, Jason M; Slattery, John M; Russell, Christopher A

2015-01-07

A range of thio- and seleno-phosphonium cationic complexes [RE(PR'3)](+)[X](-) (R = Me, Ph; E = S, Se; X = GaCl4, SbF6) have been synthesised and structurally characterised. Reaction of [PhSPPh3][GaCl4] and [PhSePPh3][GaCl4] with P(t)Bu3 results in the ready transfer of the "RS(+)" and "RSe(+)" fragments from PPh3 to the stronger electron donor P(t)Bu3. NMR experiments combined with an Eyring analysis on the corresponding degenerate phosphine exchange reaction allowed the thermodynamic values for the phosphine exchange reaction of the sulfur cation (ΔH(‡) 18.7 ± 12.0 kJ mol(-1); ΔS(‡) -99.3 ± 36.3 J mol(-1) K(-1)) to be compared with the corresponding values (ΔH(‡) 2.4 ± 1.1 kJ mol(-1) and ΔS(‡) -58.1 ± 5.0 J mol(-1) K(-1)) for the [PhSePPh3](+) system. Importantly, the large negative entropy of activation and linear dependence on the rate of exchange are compatible with an SN2-type exchange process. This conclusion is supported by DFT calculations which confirm that the phosphine exchange process occurs via an associative mechanism. The rate of exchange was found to increase from sulfur to selenium and those with aryl substituents underwent exchange faster than those with alkyl substituents.

Cancer Survival Estimates Due to Non-Uniform Loss to Follow-Up and Non-Proportional Hazards

PubMed

K M, Jagathnath Krishna; Mathew, Aleyamma; Sara George, Preethi

2017-06-25

Background: Cancer survival depends on loss to follow-up (LFU) and non-proportional hazards (non-PH). If LFU is high, survival will be over-estimated. If hazard is non-PH, rank tests will provide biased inference and Cox-model will provide biased hazard-ratio. We assessed the bias due to LFU and non-PH factor in cancer survival and provided alternate methods for unbiased inference and hazard-ratio. Materials and Methods: Kaplan-Meier survival were plotted using a realistic breast cancer (BC) data-set, with >40%, 5-year LFU and compared it using another BC data-set with <15%, 5-year LFU to assess the bias in survival due to high LFU. Age at diagnosis of the latter data set was used to illustrate the bias due to a non-PH factor. Log-rank test was employed to assess the bias in p-value and Cox-model was used to assess the bias in hazard-ratio for the non-PH factor. Schoenfeld statistic was used to test the non-PH of age. For the non-PH factor, we employed Renyi statistic for inference and time dependent Cox-model for hazard-ratio. Results: Five-year BC survival was 69% (SE: 1.1%) vs. 90% (SE: 0.7%) for data with low vs. high LFU respectively. Age (<45, 46-54 & >54 years) was a non-PH factor (p-value: 0.036). However, survival by age was significant (log-rank p-value: 0.026), but not significant using Renyi statistic (p=0.067). Hazard ratio (HR) for age using Cox-model was 1.012 (95%CI: 1.004 -1.019) and the same using time-dependent Cox-model was in the other direction (HR: 0.997; 95% CI: 0.997- 0.998). Conclusion: Over-estimated survival was observed for cancer with high LFU. Log-rank statistic and Cox-model provided biased results for non-PH factor. For data with non-PH factors, Renyi statistic and time dependent Cox-model can be used as alternate methods to obtain unbiased inference and estimates. Creative Commons Attribution License

O(2)-dependent K(+) fluxes in trout red blood cells: the nature of O(2) sensing revealed by the O(2) affinity, cooperativity and pH dependence of transport.

PubMed

Berenbrink, M; Völkel, S; Heisler, N; Nikinmaa, M

2000-07-01

The effects of pH and O(2) tension on the isotonic ouabain-resistant K(+) (Rb+) flux pathway and on haemoglobin O2 binding were studied in trout red blood cells (RBCs) in order to test for a direct effect of haemoglobin O(2) saturation on K(+) transport across the RBC membrane. At pH values corresponding to in vivo control arterial plasma pH and higher, elevation of the O(2) partial pressure (PO(2)) from 7.8 to 157 mmHg increased unidirectional K(+) influx across the RBC membrane several-fold. At lower extracellular pH values, stimulation of K(+) influx by O(2) was depressed, exhibiting an apparent pK(a) (pK'(a)) for the process of 8.0. Under similar conditions the pK'(a) for acid-induced deoxygenation of haemoglobin (Hb) was 7.3. When trout RBCs were exposed to PO(2) values between 0 and 747 mmHg, O(2) equilibrium curves typical of Hb O(2) saturation were also obtained for K(+) influx and efflux. However, at pH 7.9, the PO(2) for half-maximal K(+) efflux and K(+) influx (P50) was about 8- to 12-fold higher than the P(50) for Hb-O(2) binding. While K(+) influx and efflux stimulation by O(2) was essentially non-cooperative, Hb-O(2) equilibrium curves were distinctly sigmoidal (Hill parameters close to 1 and 3, respectively). O(2)-stimulated K(+) influx and efflux were strongly pH dependent. When the definition of the Bohr factor for respiratory pigments (Phi = delta logP50 x delta pH(-1)) was extended to the effect of pH on O(2)-dependent K(+) influx and efflux, extracellular Bohr factors (Phi(o) of -2.00 and -2.06 were obtained, values much higher than that for Hb (Phi(o) = -0.49). The results of this study are consistent with an O(2) sensing mechanism differing markedly in affinity and cooperativity of O(2) binding, as well as in pH sensitivity, from bulk Hb.

Adsorption of Ten Microcystin Congeners to Common Laboratory-Ware Is Solvent and Surface Dependent

PubMed Central

Altaner, Stefan; Puddick, Jonathan; Wood, Susanna A.; Dietrich, Daniel R.

2017-01-01

Cyanobacteria can produce heptapetides called microcystins (MC) which are harmful to humans due to their ability to inhibit cellular protein phosphatases. Quantitation of these toxins can be hampered by their adsorption to common laboratory-ware during sample processing and analysis. Because of their structural diversity (>100 congeners) and different physico-chemical properties, they vary in their adsorption to surfaces. In this study, the adsorption of ten different MC congeners (encompassing non-arginated to doubly-arginated congeners) to common laboratory-ware was assessed using different solvent combinations. Sample handling steps were mimicked with glass and polypropylene pipettes and vials with increasing methanol concentrations at two pH levels, before analysis by liquid chromatography-tandem mass spectrometry. We demonstrated that MC adsorb to polypropylene surfaces irrespective of pH. After eight successive pipet actions using polypropylene tips ca. 20% of the MC were lost to the surface material, which increased to 25%–40% when solutions were acidified. The observed loss was alleviated by changing the methanol (MeOH) concentration in the final solvent. The required MeOH concentration varied depending on which congener was present. Microcystins only adsorbed to glass pipettes (loss up to 30% after eight pipet actions) when in acidified aqueous solutions. The latter appeared largely dependent on the presence of ionizable groups, such as arginine residues. PMID:28383495

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

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

Hirota, S.; Kawahara, T; Beltramini, M

2008-01-01

Flash photolysis and K-edge x-ray absorption spectroscopy (XAS) were used to investigate the functional and structural effects of pH on the oxygen affinity of three homologous arthropod hemocyanins (Hcs). Flash photolysis measurements showed that the well-characterized pH dependence of oxygen affinity (Bohr effect) is attributable to changes in the oxygen binding rate constant, kon, rather than changes in koff. In parallel, coordination geometry of copper in Hc was evaluated as a function of pH by XAS. It was found that the geometry of copper in the oxygenated protein is unchanged at all pH values investigated, while significant changes were observedmore » for the deoxygenated protein as a function of pH. The interpretation of these changes was based on previously described correlations between spectral lineshape and coordination geometry obtained for model compounds of known structure A pH-dependent change in the geometry of cuprous copper in the active site of deoxyHc, from pseudotetrahedral toward trigonal was assigned from the observed intensity dependence of the 1s ? 4pz transition in x-ray absorption near edge structure (XANES) spectra. The structural alteration correlated well with increase in oxygen affinity at alkaline pH determined in flash photolysis experiments. These results suggest that the oxygen binding rate in deoxyHc depends on the coordination geometry of Cu(I) and suggest a structural origin for the Bohr effect in arthropod Hcs.« less

L-lactic acid production by Aspergillus brasiliensis overexpressing the heterologous ldha gene from Rhizopus oryzae.

PubMed

Liaud, Nadège; Rosso, Marie-Noëlle; Fabre, Nicolas; Crapart, Sylvaine; Herpoël-Gimbert, Isabelle; Sigoillot, Jean-Claude; Raouche, Sana; Levasseur, Anthony

2015-05-03

Lactic acid is the building block of poly-lactic acid (PLA), a biopolymer that could be set to replace petroleum-based plastics. To make lactic acid production cost-effective, the production process should be carried out at low pH, in low-nutrient media, and with a low-cost carbon source. Yeasts have been engineered to produce high levels of lactic acid at low pH from glucose but not from carbohydrate polymers (e.g. cellulose, hemicellulose, starch). Aspergilli are versatile microbial cell factories able to naturally produce large amounts of organic acids at low pH and to metabolize cheap abundant carbon sources such as plant biomass. However, they have never been used for lactic acid production. To investigate the feasibility of lactic acid production with Aspergillus, the NAD-dependent lactate dehydrogenase (LDH) responsible for lactic acid production by Rhizopus oryzae was produced in Aspergillus brasiliensis BRFM103. Among transformants, the best lactic acid producer, A. brasiliensis BRFM1877, integrated 6 ldhA gene copies, and intracellular LDH activity was 9.2 × 10(-2) U/mg. At a final pH of 1.6, lactic acid titer reached 13.1 g/L (conversion yield: 26%, w/w) at 138 h in glucose-ammonium medium. This extreme pH drop was subsequently prevented by switching nitrogen source from ammonium sulfate to Na-nitrate, leading to a final pH of 3 and a lactic acid titer of 17.7 g/L (conversion yield: 47%, w/w) at 90 h of culture. Final titer was further improved to 32.2 g/L of lactic acid (conversion yield: 44%, w/w) by adding 20 g/L glucose to the culture medium at 96 h. This strain was ultimately able to produce lactic acid from xylose, arabinose, starch and xylan. We obtained the first Aspergillus strains able to produce large amounts of lactic acid by inserting recombinant ldhA genes from R. oryzae into a wild-type A. brasiliensis strain. pH regulation failed to significantly increase lactic acid production, but switching nitrogen source and changing culture feed enabled a 1.8-fold increase in conversion yields. The strain produced lactic acid from plant biomass. Our findings make A. brasiliensis a strong contender microorganism for low-pH acid production from various complex substrates, especially hemicellulose.

Regulation of neuronal pH by the metabotropic Zn(2+)-sensing Gq-coupled receptor, mZnR/GPR39.

PubMed

Ganay, Thibault; Asraf, Hila; Aizenman, Elias; Bogdanovic, Milos; Sekler, Israel; Hershfinkel, Michal

2015-12-01

Synaptically released Zn(2+) acts as a neurotransmitter, in part, by activating the postsynaptic metabotropic Zn(2+)-sensing Gq protein-coupled receptor (mZnR/GPR39). In previous work using epithelial cells, we described crosstalk between Zn(2+) signaling and changes in intracellular pH and/or extracellular pH (pHe). As pH changes accompany neuronal activity under physiological and pathological conditions, we tested whether Zn(2+) signaling is involved in regulation of neuronal pH. Here, we report that up-regulation of a major H(+) extrusion pathway, the Na(+)/H(+) exchanger (NHE), is induced by mZnR/GPR39 activation in an extracellular-regulated kinase 1/2-dependent manner in hippocampal neurons in vitro. We also observed that changes in pHe can modulate neuronal mZnR/GPR39-dependent signaling, resulting in reduced activity at pHe 8 or 6.5. Similarly, Zn(2+)-dependent extracellular-regulated kinase 1/2 phosphorylation and up-regulation of NHE activity were absent at acidic pHe. Thus, our results suggest that when pHe is maintained within the physiological range, mZnR/GPR39 activation can up-regulate NHE-dependent recovery from intracellular acidification. During acidosis, as pHe drops, mZnR/GPR39-dependent NHE activation is inhibited, thereby attenuating further H(+) extrusion. This mechanism may serve to protect neurons from excessive decreases in pHe. Thus, mZnR/GPR39 signaling provides a homeostatic adaptive process for regulation of intracellular and extracellular pH changes in the brain. We show that the postsynaptic metabotropic Zn(2+)-sensing Gq protein-coupled receptor (mZnR/GPR39) activation induces up-regulation of a major neuronal H(+) extrusion pathway, the Na(+)/H(+) exchanger (NHE), thereby enhancing neuronal recovery from intracellular acidification. Changes in extracellular pH (pHe), however, modulate neuronal mZnR/GPR39-dependent signaling, resulting in reduced activity at pHe 8 or 6.5. This mechanism may serve to protect neurons from excessive decreases in pHe during acidosis. Hence, mZnR/GPR39 signaling provides a homeostatic adaptive process for regulation of intracellular and extracellular pH changes in the brain. © 2015 International Society for Neurochemistry.

The impact of pH inhomogeneities on CHO cell physiology and fed-batch process performance - two-compartment scale-down modelling and intracellular pH excursion.

PubMed

Brunner, Matthias; Braun, Philipp; Doppler, Philipp; Posch, Christoph; Behrens, Dirk; Herwig, Christoph; Fricke, Jens

2017-07-01

Due to high mixing times and base addition from top of the vessel, pH inhomogeneities are most likely to occur during large-scale mammalian processes. The goal of this study was to set-up a scale-down model of a 10-12 m 3 stirred tank bioreactor and to investigate the effect of pH perturbations on CHO cell physiology and process performance. Short-term changes in extracellular pH are hypothesized to affect intracellular pH and thus cell physiology. Therefore, batch fermentations, including pH shifts to 9.0 and 7.8, in regular one-compartment systems are conducted. The short-term adaption of the cells intracellular pH are showed an immediate increase due to elevated extracellular pH. With this basis of fundamental knowledge, a two-compartment system is established which is capable of simulating defined pH inhomogeneities. In contrast to state-of-the-art literature, the scale-down model is included parameters (e.g. volume of the inhomogeneous zone) as they might occur during large-scale processes. pH inhomogeneity studies in the two-compartment system are performed with simulation of temporary pH zones of pH 9.0. The specific growth rate especially during the exponential growth phase is strongly affected resulting in a decreased maximum viable cell density and final product titer. The gathered results indicate that even short-term exposure of cells to elevated pH values during large-scale processes can affect cell physiology and overall process performance. In particular, it could be shown for the first time that pH perturbations, which might occur during the early process phase, have to be considered in scale-down models of mammalian processes. Copyright © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Role of individual histidines in the pH-dependent global stability of human chloride intracellular channel 1.

PubMed

Achilonu, Ikechukwu; Fanucchi, Sylvia; Cross, Megan; Fernandes, Manuel; Dirr, Heini W

2012-02-07

Chloride intracellular channel proteins exist in both a soluble cytosolic form and a membrane-bound form. The mechanism of conversion between the two forms is not properly understood, although one of the contributing factors is believed to be the variation in pH between the cytosol (~7.4) and the membrane (~5.5). We systematically mutated each of the three histidine residues in CLIC1 to an alanine at position 74 and a phenylalanine at positions 185 and 207. We examined the effect of the histidine-mediated pH dependence on the structure and global stability of CLIC1. None of the mutations were found to alter the global structure of the protein. However, the stability of H74A-CLIC1 and H185F-CLIC1, as calculated from the equilibrium unfolding data, is no longer dependent on pH because similar trends are observed at pH 7.0 and 5.5. The crystal structures show that the mutations result in changes in the local hydrogen bond coordination. Because the mutant total free energy change upon unfolding is not different from that of the wild type at pH 7.0, despite the presence of intermediates that are not seen in the wild type, we propose that it may be the stability of the intermediate state rather than the native state that is dependent on pH. On the basis of the lower stability of the intermediate in the H74A and H185F mutants compared to that of the wild type, we conclude that both His74 and His185 are involved in triggering the pH changes to the conformational stability of wild-type CLIC1 via their protonation, which stabilizes the intermediate state.

Hydrogen–Deuterium Exchange and Mass Spectrometry Reveal the pH-Dependent Conformational Changes of Diphtheria Toxin T Domain

PubMed Central

2015-01-01

The translocation (T) domain of diphtheria toxin plays a critical role in moving the catalytic domain across the endosomal membrane. Translocation/insertion is triggered by a decrease in pH in the endosome where conformational changes of T domain occur through several kinetic intermediates to yield a final trans-membrane form. High-resolution structural studies are only applicable to the static T-domain structure at physiological pH, and studies of the T-domain translocation pathway are hindered by the simultaneous presence of multiple conformations. Here, we report the application of hydrogen–deuterium exchange mass spectrometry (HDX-MS) for the study of the pH-dependent conformational changes of the T domain in solution. Effects of pH on intrinsic HDX rates were deconvolved by converting the on-exchange times at low pH into times under our “standard condition” (pH 7.5). pH-Dependent HDX kinetic analysis of T domain clearly reveals the conformational transition from the native state (W-state) to a membrane-competent state (W+-state). The initial transition occurs at pH 6 and includes the destabilization of N-terminal helices accompanied by the separation between N- and C-terminal segments. The structural rearrangements accompanying the formation of the membrane-competent state expose a hydrophobic hairpin (TH8–9) to solvent, prepare it to insert into the membrane. At pH 5.5, the transition is complete, and the protein further unfolds, resulting in the exposure of its C-terminal hydrophobic TH8–9, leading to subsequent aggregation in the absence of membranes. This solution-based study complements high resolution crystal structures and provides a detailed understanding of the pH-dependent structural rearrangement and acid-induced oligomerization of T domain. PMID:25290210

Hydrogen-deuterium exchange and mass spectrometry reveal the pH-dependent conformational changes of diphtheria toxin T domain.

PubMed

Li, Jing; Rodnin, Mykola V; Ladokhin, Alexey S; Gross, Michael L

2014-11-04

The translocation (T) domain of diphtheria toxin plays a critical role in moving the catalytic domain across the endosomal membrane. Translocation/insertion is triggered by a decrease in pH in the endosome where conformational changes of T domain occur through several kinetic intermediates to yield a final trans-membrane form. High-resolution structural studies are only applicable to the static T-domain structure at physiological pH, and studies of the T-domain translocation pathway are hindered by the simultaneous presence of multiple conformations. Here, we report the application of hydrogen-deuterium exchange mass spectrometry (HDX-MS) for the study of the pH-dependent conformational changes of the T domain in solution. Effects of pH on intrinsic HDX rates were deconvolved by converting the on-exchange times at low pH into times under our "standard condition" (pH 7.5). pH-Dependent HDX kinetic analysis of T domain clearly reveals the conformational transition from the native state (W-state) to a membrane-competent state (W(+)-state). The initial transition occurs at pH 6 and includes the destabilization of N-terminal helices accompanied by the separation between N- and C-terminal segments. The structural rearrangements accompanying the formation of the membrane-competent state expose a hydrophobic hairpin (TH8-9) to solvent, prepare it to insert into the membrane. At pH 5.5, the transition is complete, and the protein further unfolds, resulting in the exposure of its C-terminal hydrophobic TH8-9, leading to subsequent aggregation in the absence of membranes. This solution-based study complements high resolution crystal structures and provides a detailed understanding of the pH-dependent structural rearrangement and acid-induced oligomerization of T domain.

Dural stimulation in rats causes BDNF-dependent priming to subthreshold stimuli including a migraine trigger

PubMed Central

Burgos-Vega, Carolina C.; Quigley, Lilyana D.; Avona, Amanda; Price, Theodore; Dussor, Gregory

2016-01-01

Migraine is one of the most common and most disabling disorders. Between attacks, migraine patients are otherwise normal but are sensitized to non-noxious events known as triggers. The purpose of these studies was to investigate whether a headache-like event causes sensitization, or priming, to subsequent subthreshold events. Interleukin-6 (IL-6) was applied to the rat cranial dura mater which produced cutaneous facial and hindpaw allodynia that lasted 24 hours. At 72-hours, IL-6 treated rats developed allodynia in response to dural stimulation with either a pH 6.8 or pH 7.0 solution and to a systemic nitric oxide (NO) donor, a well-known migraine trigger. Vehicle-treated rats did not respond to either pH stimulus nor to the NO donor, demonstrating that IL-6 exposure primes rats to subthreshold stimuli. Inhibitors of brain-derived neurotrophic factor (BDNF) signaling given either systemically or intracisternally 24-hours after IL-6 eliminated responses to dural pH stimulation at 72 hours. Additionally, intracisternal administration of BDNF without prior dural stimulation produced allodynia and once resolved, animals were primed to dural pH 6.8/pH 7.0 and a systemic NO donor. Finally, hindpaw IL-6 produced paw allodynia but not priming to paw injection of pH 7.0 at 72 hours demonstrating differences in priming depending on location. These data indicate that afferent input from the meninges produces BDNF-dependent priming of the dural nociceptive system. This primed state mimics the interictal period of migraine where attacks can be triggered by normally non-noxious events and suggests that BDNF-dependent plasticity may contribute to migraine. PMID:27841839

Trichomonas vaginalis: identification of soluble and membrane-associated phospholipase A1 and A2 activities with direct and indirect hemolytic effects.

PubMed

Vargas-Villarreal, Javier; Mata-Cárdenas, Benito David; Palacios-Corona, Rebeca; González-Salazar, Francisco; Cortes-Gutierrez, Elva I; Martínez-Rodríguez, Herminia G; Said-Fernández, Salvador

2005-02-01

A direct hemolytic activity, dependent on phospholipase A (PLA) activity, was located in the particulate subcellular fraction (P30) of Trichomonas vaginalis. We identified soluble direct and indirect hemolytic activities in the spent medium and soluble fraction (S30) of T. vaginalis strain GT-13. Spent medium showed the highest specific indirect hemolytic activity (SIHA) at pH 6.0 (91 indirect hemolytic units [HU]/mg/hr). Spent medium and P30, but not S30, showed direct hemolytic activity. PLA activity was protein dose dependent and time dependent. The highest PLA activity was observed at pH 6.0. All trichomonad preparations showed phospholipase A1 (PLA A1) and phospholipase A2 (PLA A2) activities. Indirect and direct hemolytic activity and PLA A1 and PLA A2 diminished at pH 6.0 and 8.0 with increasing concentrations of Rosenthal's inhibitor. The greatest effect was observed with 80 microM at pH 6.0 on the SIHA of S30 (83% reduction) and the lowest at pH 8.0, also on the SIHA of S30 (26% reduction). In conclusion, T. vaginalis contains particulate and soluble acidic, and alkaline direct and indirect hemolytic activities, which are partially dependent on alkaline or acidic PLA A1 and PLA A2 enzymes. These could be responsible for the contact-dependent and -independent hemolytic and cytolytic activities of T. vaginalis.

Isolation of organic acids from large volumes of water by adsorption on macroporous resins

USGS Publications Warehouse

Aiken, George R.; Suffet, I.H.; Malaiyandi, Murugan

1987-01-01

Adsorption on synthetic macroporous resins, such as the Amberlite XAD series and Duolite A-7, is routinely used to isolate and concentrate organic acids from forge volumes of water. Samples as large as 24,500 L have been processed on site by using these resins. Two established extraction schemes using XAD-8 and Duolite A-7 resins are described. The choice of the appropriate resin and extraction scheme is dependent on the organic solutes of interest. The factors that affect resin performance, selectivity, and capacity for a particular solute are solution pH, resin surface area and pore size, and resin composition. The logistical problems of sample handling, filtration, and preservation are also discussed.

Photoswitchable red fluorescent protein with a large Stokes shift

PubMed Central

Piatkevich, Kiryl D.; English, Brian P.; Malashkevich, Vladimir N.; Xiao, Hui; Almo, Steven C.; Singer, Robert H.; Verkhusha, Vladislav V.

2014-01-01

SUMMARY Subclass of fluorescent proteins, large Stokes shift fluorescent proteins, is characterized by their increased spread between the excitation and emission maxima. Here we report a photoswitchable variant of a red fluorescent protein with a large Stokes shift, PSLSSmKate, which initially exhibits excitation/emission at 445/622 nm, but irradiation with violet light photoswitches PSLSSmKate into a common red form with excitation/emission at 573/621 nm. We characterize spectral, photophysical and biochemical properties of PSLSSmKate in vitro and in mammalian cells, and determine its crystal structure in the large Stokes shift form. Mass-spectrometry, mutagenesis and spectroscopic analysis of PSLSSmKate allow us to propose molecular mechanisms for the large Stokes shift, pH dependence and light-induced chromophore transformation. We demonstrate applicability of PSLSSmKate to superresolution PALM microscopy and protein dynamics in live cells. Given its promising properties, we expect that PSLSSmKate-like phenotype will be further used for photoactivatable imaging and tracking multiple populations of intracellular objects. PMID:25242289

The missing piece in the puzzle: Prediction of aggregation via the protein-protein interaction parameter A∗2.

PubMed

Koepf, Ellen; Schroeder, Rudolf; Brezesinski, Gerald; Friess, Wolfgang

2018-07-01

The tendency of protein pharmaceuticals to form aggregates is a major challenge during formulation development, as aggregation affects quality and safety of the product. In particular, the formation of large native-like particles in the context of liquid-air interfacial stress is a well-known but not fully understood problem. Focusing on the two most fundamental criteria of protein formulation affecting protein-protein interaction, the impact of pH and ionic strength on the interaction parameter A ∗ 2 and its link to aggregation upon mechanical stress was investigated. A ∗ 2 of two monoclonal antibodies (mABs) and a polyclonal IgG was determined using dynamic light scattering and was correlated to the number of particles formed upon shaking in vials analyzed by visual inspection, turbidity analysis, light obscuration and micro-flow imaging. A good correlation between aggregation induced by interfacial stress and formulation pH was given. It could be shown that A ∗ 2 was highest for mAB 1 and lowest for IgG, what was in good accordance with the number of particles formed. Shaking of IgG resulted in overall higher numbers of particles compared to the two mABs. A ∗ 2 decreased and particle numbers increased with increasing pH. Different to pH, ionic strength only slightly affected A ∗ 2 . Nevertheless, at high ionic (100 mM) strength the samples exhibited more pronounced particle formation, particularly of large particles >25 µm, which was most pronounced at high pH. Protein solutions were identified to form continuous films with an inhomogeneous protein distribution at the liquid-air interface. These areas of agglomerated, native-like protein material can be transferred into the bulk solution by compression-decompression of the interface. Whether or not those clusters lead to the appearance of large protein aggregates or fall apart depends on the attractive or repulsive forces between protein molecules. Thus, protein aggregation due to interfacial stress is correlated with the protein-protein interactions as determined by A ∗ 2 . This enables to differentiate different antibodies according to their propensity to form particles upon mechanical stress and to identify optimum formulation conditions. Copyright © 2018 Elsevier B.V. All rights reserved.

A comparative study on the effect of Curcumin and Chlorin-p6 on the transport of the LDS cation across a negatively charged POPG bilayer: Effect of pH

NASA Astrophysics Data System (ADS)

Varshney, G. K.; Kintali, S. R.; Gupta, P. K.; Das, K.

2017-02-01

We report the use of interface selective Second Harmonic generation technique to investigate the transport of the LDS cation across POPG liposomes in the pH range of 4.0 to 8.0 in the presence and absence of two amphiphilic drugs, Curcumin and Chlorin-p6 (Cp6). Our results show that bilayer permeability of liposomes is significantly affected by the presence of the drugs and pH of the medium as evidenced by significant changes in the transport kinetics of the LDS. Studies carried out in the pH range 4.0-8.0 show that while Cp6 significantly enhanced the transport of LDS at pH 4.0, the transport of the cation was seen to increase with increasing pH, with maximum effect at pH 7.4 for Curcumin. The pH dependent bilayer localization of both the drugs was investigated by conducting steady state FRET studies using DPH labeled lipids as donors. The FRET results and the relative population of the various ionic/nonionic species of the drugs at different pH suggest that distance dependent interaction between the various ionic species of the drugs and polar head groups of the lipid is responsible for the observed pH dependence enhancement of the drug induced membrane permeability. Another interesting observation was that the stability of Curcumin in presence of POPG liposomes was observed to degrade significantly near physiological pH (7.4 and 8.0). Although this degradation did not affect the liposome integrity, interestingly this was observed to enhance the transport of the LDS cation across the bilayer. That the degradation products of Curcumin are equally effective as the drug itself in enhancing the membrane permeability lends additional support to the current opinion that the bioactive degradation products of the drug may have a significant contribution to its observed pharmacological effects.

Intragastric pH and pressure profiles after intake of the high-caloric, high-fat meal as used for food effect studies.

PubMed

Koziolek, M; Schneider, F; Grimm, M; Modeβ, Chr; Seekamp, A; Roustom, T; Siegmund, W; Weitschies, W

2015-12-28

The intraluminal conditions of the fed stomach are critical for drug release from solid oral dosage forms and thus, often associated with the occurrence of food effects on oral bioavailability. In this study, intragastric pH and pressure profiles present after the ingestion of the high-caloric, high-fat (964 kcal) FDA standard breakfast were investigated in 19 healthy human subjects by using the telemetric SmartPill® capsule system (26 × 13 mm). Since the gastric emptying of such large non-digestible objects is typically accomplished by the migrating motor complex phase III activity, the time required for recurrence of fasted state motility determined the gastric emptying time (GET). Following the diet recommendations of the FDA guidance on food effect studies, the mean GET of the telemetric motility capsule was 15.3 ± 4.7 h. Thus, the high caloric value of the standard breakfast impeded gastric emptying before lunch in 18 out of 19 subjects. During its gastric transit, the capsule was exposed to highly dynamic conditions in terms of pH and pressure, which were mainly dependent on further meal and liquid intake, as well as the intragastric capsule deposition behavior. Maximum pH values in the stomach were measured immediately after capsule intake. The median pH value of the 5 min period after capsule ingestion ranged between pH 3.3 and 5.3. Subsequently, the pH decreased relatively constantly and reached minimum values of pH 0-1 after approximately 4 h. The maximum pressure within the stomach amounted to 293 ± 109 mbar and was clearly higher than the maximum pressure measured at the ileocaecal junction (60 ± 35 mbar). The physiological data on the intraluminal conditions within the fed stomach generated in this study will hopefully contribute to a better understanding of food effects on oral drug product performance.

An enzyme kinetics study of the pH dependence of chloride activation of oxygen evolution in photosystem II.

PubMed

Baranov, Sergei; Haddy, Alice

2017-03-01

Oxygen evolution by photosystem II (PSII) involves activation by Cl - ion, which is regulated by extrinsic subunits PsbQ and PsbP. In this study, the kinetics of chloride activation of oxygen evolution was studied in preparations of PSII depleted of the PsbQ and PsbP subunits (NaCl-washed and Na 2 SO 4 /pH 7.5-treated) over a pH range from 5.3 to 8.0. At low pH, activation by chloride was followed by inhibition at chloride concentrations >100 mM, whereas at high pH activation continued as the chloride concentration increased above 100 mM. Both activation and inhibition were more pronounced at lower pH, indicating that Cl - binding depended on protonation events in each case. The simplest kinetic model that could account for the complete data set included binding of Cl - at two sites, one for activation and one for inhibition, and four protonation steps. The intrinsic (pH-independent) dissociation constant for Cl - activation, K S , was found to be 0.9 ± 0.2 mM for both preparations, and three of the four pK a s were determined, with the fourth falling below the pH range studied. The intrinsic inhibition constant, K I , was found to be 64 ± 2 and 103 ± 7 mM for the NaCl-washed and Na 2 SO 4 /pH7.5-treated preparations, respectively, and is considered in terms of the conditions likely to be present in the thylakoid lumen. This enzyme kinetics analysis provides a more complete characterization of chloride and pH dependence of O 2 evolution activity than has been previously presented.

HNO and NO release from a primary amine-based diazeniumdiolate as a function of pH

PubMed Central

Salmon, Debra J.; Torres de Holding, Claudia L.; Thomas, Lynta; Peterson, Kyle V.; Goodman, Gens P.; Saavedra, Joseph E.; Srinivasan, Aloka; Davies, Keith M.; Keefer, Larry K.; Miranda, Katrina M.

2011-01-01

The growing evidence that nitroxyl (HNO) has a rich pharmacological potential that differs from that of nitric oxide (NO) has intensified interest in HNO donors. Recently, the diazeniumdiolate (NONOate) based on isopropylamine (IPA/NO; Na[(CH3)2CHNH(N(O)NO)]) was demonstrated to function under physiological conditions as an organic analogue to the commonly used HNO donor Angeli’s salt (Na2N2O3). The decomposition mechanism of Angeli’s salt is dependent on pH, with transition from an HNO to an NO donor occurring abruptly near pH 3. Here, pH is shown to also affect product formation from IPA/NO. Chemical analysis of HNO and NO production led to refinement of an earlier, quantum mechanically based prediction of the pH-dependent decomposition mechanisms of primary amine NONOates such as IPA/NO. Under basic conditions, the amine proton of IPA/NO is able to initiate decomposition to HNO by tautomerization to the nitroso nitrogen (N2). At lower pH, protonation activates a competing pathway to NO production. At pH 8, the donor properties of IPA/NO and Angeli’s salt are demonstrated to be comparable, suggesting that at or above this pH, IPA/NO is primarily an HNO donor. Below pH 5, NO is the major product, while IPA/NO functions as a dual donor of HNO and NO at intermediate pH. This pH-dependent variability in product formation may prove useful in examination of the chemistry of NO and HNO. Furthermore, primary amine NONOates may serve as a tunable class of nitrogen oxide donor. PMID:21405089

Silicate release from glass for pharmaceutical preparations.

PubMed

Bohrer, Denise; Bortoluzzi, Fabiana; Nascimento, Paulo Cícero; Carvalho, Leandro Machado; Ramirez, Adrian Gustavo

2008-05-01

Glass is made of polymeric silica and other minor components, which are necessary for turning the silica into a material more easily moldable and resistant to temperature changes. Glass containers for pharmaceutical usage are classified according to their resistance to a chemical attack, a test carried out in the presence of water and heat. The test is designed to show the released alkalinity, a variable dependent on the amount of sodium oxide, one of the minor components added to the glass mass. In this work, the release of silica from glass by action of constituents from pharmaceutical formulations was investigated. The study included products used in large volumes and usually stored in glass containers. Solutions of amino acids, electrolytes, glucose, oligoelements and others such as heparin and sodium bicarbonate were individually stored in glass containers and heated at 121 degrees C for 30min, as in the water attack test. The test was also carried out only with water, where the pH varied from 2 to 12. The released silicate was measured either by photometry or atomic absorption spectrometry, depending on the nature of the sample. The results showed that silicate is released during the heating cycle even if the contact is with pure water only. The pH exerts a considerable influence on the release, being that the higher the pH, the higher the silica dissolved. An elevated pH, however, is not the only factor responsible for silica dissolution. While in the solutions of NaCl, KCl, Mg Cl2 and ZnSO4 and in most of the amino acids, the concentration of silicate was as high as in pure water (0.1-1.0mg Si/L). In the solutions of sodium acetate, bicarbonate and gluconate, its concentration was much higher, over 30mg Si/L. These results were confirmed by the analysis of commercial products, where in solutions of amino acids the level of silicate ranged from 0.14 to 0.19mg Si/L. On the other hand, calcium gluconate, sodium bicarbonate and potassium phosphate presented silicate levels from 1 to 4mg/L. Although silica is not considered a toxic substance for humans, it is necessary to be aware of its presence in solutions for parenteral nutrition due to the direct introduction into the bloodstream and the large volume usually administrated, even to pre-term infants.

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.

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy

PubMed Central

Zheng, Jie; Sheng, Wenchao; Zhuang, Zhongbin; Xu, Bingjun; Yan, Yushan

2016-01-01

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER. PMID:27034988

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy.

PubMed

Zheng, Jie; Sheng, Wenchao; Zhuang, Zhongbin; Xu, Bingjun; Yan, Yushan

2016-03-01

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER.

Maximizing in vivo target clearance by design of pH-dependent target binding antibodies with altered affinity to FcRn.

PubMed

Yang, Danlin; Giragossian, Craig; Castellano, Steven; Lasaro, Marcio; Xiao, Haiguang; Saraf, Himanshu; Hess Kenny, Cynthia; Rybina, Irina; Huang, Zhong-Fu; Ahlberg, Jennifer; Bigwarfe, Tammy; Myzithras, Maria; Waltz, Erica; Roberts, Simon; Kroe-Barrett, Rachel; Singh, Sanjaya

2017-10-01

Antibodies with pH-dependent binding to both target antigens and neonatal Fc receptor (FcRn) provide an alternative tool to conventional neutralizing antibodies, particularly for therapies where reduction in antigen level is challenging due to high target burden. However, the requirements for optimal binding kinetic framework and extent of pH dependence for these antibodies to maximize target clearance from circulation are not well understood. We have identified a series of naturally-occurring high affinity antibodies with pH-dependent target binding properties. By in vivo studies in cynomolgus monkeys, we show that pH-dependent binding to the target alone is not sufficient for effective target removal from circulation, but requires Fc mutations that increase antibody binding to FcRn. Affinity-enhanced pH-dependent FcRn binding that is double-digit nM at pH 7.4 and single-digit nM at pH 6 achieved maximal target reduction when combined with similar target binding affinities in reverse pH directions. Sustained target clearance below the baseline level was achieved 3 weeks after single-dose administration at 1.5 mg/kg. Using the experimentally derived mechanistic model, we demonstrate the essential kinetic interplay between target turnover and antibody pH-dependent binding during the FcRn recycling, and identify the key components for achieving maximal target clearance. These results bridge the demand for improved patient dosing convenience with the "know-how" of therapeutic modality by design.

Preparing "Chameleon Balls" from Natural Plants: Simple Handmade pH Indicator and Teaching Material for Chemical Equilibrium

NASA Astrophysics Data System (ADS)

Kanda, Naoki; Asano, Takayuki; Itoh, Toshiyuki; Onoda, Makoto

1995-12-01

Anthocyanins are found in the flowers and fruits of natural plants. Since their color depends on pH, they are sometines used as a pH indicator. Since these sequences are reversible, they are also useful in demonstrating chemical equilibrium in the repetitive color changes of anthocyanins from flowers by controlling pH conditions. We prepared the polysaccharide beads conatining water extracts of red cabbage as calcium alginate. The beads showed a clear red color under acidic conditions, turned blue at neutral pH of 7, and orange-yellow at pH of 13. This color change could be demonstrated over and over. Because the color changes of these polysaccharide beads depended darmatically on pH, junior high students in science classes called them "chameleon balls" when we demonstrated this reaction for them. In this paper we describe how polysaccharide beads, which are made from calcium alginate with natural pigments, served as a teaching tool for the chemical equilibrium of anthocyanins under different pH conditions. Preparation of the chameleon ball is very easy. The most important thing is that making the chameleon ball is great fun. The ball should therefore be viewed not only as a handmade pH indicator but also an interesting teaching tool of the chemical equilibrium reaction.

In silico prediction of drug dissolution and absorption with variation in intestinal pH for BCS class II weak acid drugs: ibuprofen and ketoprofen.

PubMed

Tsume, Yasuhiro; Langguth, Peter; Garcia-Arieta, Alfredo; Amidon, Gordon L

2012-10-01

The FDA Biopharmaceutical Classification System guidance allows waivers for in vivo bioavailability and bioequivalence studies for immediate-release solid oral dosage forms only for BCS class I. Extensions of the in vivo biowaiver for a number of drugs in BCS class III and BCS class II have been proposed, in particular, BCS class II weak acids. However, a discrepancy between the in vivo BE results and in vitro dissolution results for BCS class II acids was recently observed. The objectives of this study were to determine the oral absorption of BCS class II weak acids via simulation software and to determine if the in vitro dissolution test with various dissolution media could be sufficient for in vitro bioequivalence studies of ibuprofen and ketoprofen as models of carboxylic acid drugs. The oral absorption of these BCS class II acids from the gastrointestinal tract was predicted by GastroPlus™. Ibuprofen did not satisfy the bioequivalence criteria at lower settings of intestinal pH of 6.0. Further the experimental dissolution of ibuprofen tablets in a low concentration phosphate buffer at pH 6.0 (the average buffer capacity 2.2 mmol l (-1) /pH) was dramatically reduced compared with the dissolution in SIF (the average buffer capacity 12.6 mmol l (-1) /pH). Thus these predictions for the oral absorption of BCS class II acids indicate that the absorption patterns depend largely on the intestinal pH and buffer strength and must be considered carefully for a bioequivalence test. Simulation software may be a very useful tool to aid the selection of dissolution media that may be useful in setting an in vitro bioequivalence dissolution standard. Copyright © 2012 John Wiley & Sons, Ltd.

In Silico Prediction of Drug Dissolution and Absorption with variation in Intestinal pH for BCS Class II Weak Acid Drugs: Ibuprofen and Ketoprofen§

PubMed Central

Tsume, Yasuhiro; Langguth, Peter; Garcia-Arieta, Alfredo; Amidon, Gordon L.

2012-01-01

The FDA Biopharmaceutical Classification System guidance allows waivers for in vivo bioavailability and bioequivalence studies for immediate-release solid oral dosage forms only for BCS class I. Extensions of the in vivo biowaiver for a number of drugs in BCS Class III and BCS class II have been proposed, particularly, BCS class II weak acids. However, a discrepancy between the in vivo- BE results and in vitro- dissolution results for a BCS class II acids was recently observed. The objectives of this study were to determine the oral absorption of BCS class II weak acids via simulation software and to determine if the in vitro dissolution test with various dissolution media could be sufficient for in vitro bioequivalence studies of ibuprofen and ketoprofen as models of carboxylic acid drugs. The oral absorption of these BCS class II acids from the gastrointestinal tract was predicted by GastroPlus™. Ibuprofen did not satisfy the bioequivalence criteria at lower settings of intestinal pH=6.0. Further the experimental dissolution of ibuprofen tablets in the low concentration phosphate buffer at pH 6.0 (the average buffer capacity 2.2 mmol L-1/pH) was dramatically reduced compared to the dissolution in SIF (the average buffer capacity 12.6 mmol L -1/pH). Thus these predictions for oral absorption of BCS class II acids indicate that the absorption patterns largely depend on the intestinal pH and buffer strength and must be carefully considered for a bioequivalence test. Simulation software may be very useful tool to aid the selection of dissolution media that may be useful in setting an in vitro bioequivalence dissolution standard. PMID:22815122

External pH changes affect NMDA-evoked and spontaneous release of cholecystokinin, somatostatin and noradrenaline from rat cerebrocortical nerve endings.

PubMed

Gemignani, Anita; Paudice, Paolo; Longordo, Fabio; Raiteri, Maurizio

2004-10-01

It was previously reported that the K+-evoked release of somatostatin-like immunoreactivity (SRIF-LI) and of cholecystokinin-like immunoreactivity (CCK-LI) from superfused rat cerebrocortical synaptosomes can be enhanced by NMDA or D-serine alone. We here studied the effects of extraterminal pH changes on SRIF-LI and CCK-LI release. Lowering pH from 7.4 to 6.9 or 6.4 abolished the effects of NMDA or D-serine on the K+-evoked peptide release. Identical results were obtained when external pH was raised to 8 or 8.7. Sudden alkalinization of the superfusion medium, in absence of K+-depolarization, induced SRIF-LI or CCK-LI release which was insensitive to NMDA. Based on experiments in Ca2+-free medium and with voltage-sensitive Ca2+ channel (VSCC) blockers, the pH 8.7-induced release of SRIF-LI and CCK-LI was only in part (30-50%) dependent on external Ca2+ and Ca2+ channel activation. In contrast, the alkalinization-evoked release of [3H]noradrenaline was highly sensitive to external Ca2+ removal and to blockade of Ca2+ channels with omega-conotoxins. The pH 8.7-evoked SRIF-LI and CCK-LI was about halved in synaptosomes intoxicated with botulinum toxin C1. The results suggest that the pH-sensitive NMDA receptors mediating somatostatin and cholecystokinin release contain NR1 subunits lacking the exon-5 cassette. Alkalinization represents a novel releasing stimulus which elicits neuropeptide release in part by conventional exocytosis and largely by an external Ca2+-independent mechanism. Differently, the release of noradrenaline provoked by alkalinization occurs entirely by conventional exocytosis.

Spectroscopic, Computational and Kinetic Studies of the μ4-Sulfide Bridged Tetranuclear CuZ Cluster in N2O Reductase: pH Effect on the Edge Ligand and its Contribution to Reactivity

PubMed Central

Ghosh, Somdatta; Gorelsky, Serge I.; George, Serena DeBeer; Chan, Jeannine M.; Cabrito, Inês; Dooley, David M.; Moura, José J. G.; Moura, Isabel; Solomon, Edward I.

2008-01-01

A combination of spectroscopy and DFT calculations has been used to evaluate the pH effect at the CuZ site in Pseudomonas nautica (Pn) N2OR and Achromobacter cycloclastes (Ac) N2OR and its relevance to catalysis. Absorption, MCD, EPR with sulfur K-edge XAS spectra of the enzymes at high and low pH show minor changes. However, resonance Raman (rR) spectroscopy of PnN2OR at high pH shows that the 415 cm−1 Cu-S vibration (observed at low pH) shifts to higher frequency, loses intensity and obtains a 9 cm−1 18O shift, implying significant Cu-O character, demonstrating the presence of a OH− ligand at the CuICuIV edge. From DFT calculations both protonation of the OH− to H2O or the μ4-S2− to μ4-SH− would produce large spectral changes which are not observed. Alternatively, DFT calculations including a lysine residue at an H-bonding distance from the CuICuIV edge ligand show that the position of the OH− ligand depends on the protonation state of the lysine. This would change the coupling of the Cu-(OH) stretch with the Cu-S stretch, as observed in the rR spectrum. Thus the observed pH effect (pKa ~9.2) likely reflects protonation equilibrium of the lysine residue which would both raise E0 and provide a proton for lowering the barrier for the N-O cleavage and for reduction of the [Cu4S(im)7OH]2+ to the fully reduced 4CuI active form for turnover. PMID:17352474

Dual pH durability studies of man-made vitreous fiber (MMVF).

PubMed Central

Bauer, J F; Law, B D; Hesterberg, T W

1994-01-01

Dissolution of fibers in the deep lung may involve both extracellular and intracellular mechanisms. This process was modeled in vitro for each environment using an experimental flow-through system to characterize both total dissolution and specific chemical changes for three representative MMVF's: a glasswool, a slagwool, and a refractory ceramic fiber (RCF). Synthetic physiological fluids at pH 4 and at pH 7.6 were used to simulate macrophage intraphagolysosomal, and extracellular environments, respectively. Actual commercial fiber, sized to rat-respirable dimension, having an average fiber diameter of 1 micron and an average length between 15 and 25 microns, was used in the experiments. Fiber dissolution was monitored through change in chemistry of the fluid collected after percolation at a constant rate through a thin bed of sample. There are great differences in total fiber dissolution rates for the different fibers. Slagwool and RCF dissolve more rapidly at pH 4 than at pH 7.6, while the reverse is true for glasswool. Dissolution is sometimes accompanied by a noticeable change in fiber morphology or dimension, and sometimes by no change. There is strong dependency on pH, which affects not only total fiber dissolution, but also the leaching of specific chemical components. This effect is different for each type of fiber, indicating that specific fiber chemistry largely controls whether a fiber dissolves or leaches more rapidly under acidic or neutral conditions. Both total dissolution rates and calculated fiber composition changes are valuable guides to interpreting in vivo behavior of man-made vitreous fibers, and demonstrate the usefulness of in vitro acellular experiments in understanding overall fiber persistence. Images Figure 3. A Figure 3. B Figure 4. A Figure 4. B Figure 4. C PMID:7882957

Fusion of small unilamellar vesicles induced by bovine serum albumin fragments.

PubMed

Garcia, L A; Schenkman, S; Araujo, P S; Chaimovich, H

1983-07-01

The limited pepsin proteolysis products of bovine serum albumin, fragment A (residues 307-586) and fragment B (residues 1-306), induced the fusion of small unilamellar vesicles of egg phosphatidyl choline at concentrations near 5 microM. Fusion was demonstrated and analyzed on the basis of: a) time-dependent changes in absorbance; b) dilution of the fluorescent label 2-(10-(1-pyrene)decanoyl) phosphatidyl choline, incorporated into a small percentage of the vesicles, as measured by the decrease in the excimer to monomer (E/M) ratio; c) increase of the average hydrodynamic radius of the liposomes, estimated by Sepharose 4B filtration, and d) the strict inverse relationship between the size of the liposomes and their E/M ratios. Albumin fragment B, like albumin, induced the formation of large aggregates in which rapid cooperative fusion produced vesicles having a large hydrodynamic radius. Fragment A did not produce large aggregates and the initial fusion products exhibited a hydrodynamic radius. Fragment A did not produce large aggregates and the initial fusion products exhibited a hydrodynamic radius smaller than those obtained with fragment B. Albumin and fragments A and B are fusogenic only at pH below 4.0. These data discussed in terms of a general model for a signal-dependent protein-induced membrane fusion.

Characterization of Polyelectrolyte Complex Formation Between Anionic and Cationic Poly(amino acids) and Their Potential Applications in pH-Dependent Drug Delivery.

PubMed

Folchman-Wagner, Zoë; Zaro, Jennica; Shen, Wei-Chiang

2017-06-30

Polyelectrolyte complexes (PECs) are self-assembling nano-sized constructs that offer several advantages over traditional nanoparticle carriers including controllable size, biodegradability, biocompatibility, and lack of toxicity, making them particularly appealing as tools for drug delivery. Here, we discuss potential application of PECs for drug delivery to the slightly acidic tumor microenvironment, a pH in the range of 6.5-7.0. Poly(l-glutamic acid) (E n ), poly(l-lysine) (K n ), and a copolymer composed of histidine-glutamic acid repeats ((HE) n ) were studied for their ability to form PECs, which were analyzed for size, polydispersity, and pH sensitivity. PECs showed concentration dependent size variation at residue lengths of E 51 /K 55 and E 135 /K 127 , however, no complexes were observed when E 22 or K 21 were used, even in combination with the longer chains. (HE) 20 /K 55 PECs could encapsulate daunomycin, were stable from pH 7.4-6.5, and dissociated completely between pH 6.5-6.0. Conversely, the E 51-dauno /K 55 PEC dissociated between pH 4.0 and 3.0. These values for pH-dependent particle dissociation are consistent with the p K a 's of the ionizable groups in each formulation and indicate that the specific pH-sensitivity of (HE) 20-dauno /K 55 PECs is mediated by incorporation of histidine. This response within a pH range that is physiologically relevant to the acidic tumors suggests a potential application of these PECs in pH-dependent drug delivery.

Electron transfer of quinone self-assembled monolayers on a gold electrode.

PubMed

Nagata, Morio; Kondo, Masaharu; Suemori, Yoshiharu; Ochiai, Tsuyoshi; Dewa, Takehisa; Ohtsuka, Toshiaki; Nango, Mamoru

2008-06-15

Dialkyl disulfide-linked naphthoquinone, (NQ-Cn-S)2, and anthraquinone, (AQ-Cn-S)2, derivatives with different spacer alkyl chains (Cn: n=2, 6, 12) were synthesized and these quinone derivatives were self-assembled on a gold electrode. The formation of self-assembled monolayers (SAMs) of these derivatives on a gold electrode was confirmed by infrared reflection-absorption spectroscopy (IR-RAS). Electron transfer between the derivatives and the gold electrode was studied by cyclic voltammetry. On the cyclic voltammogram a reversible redox reaction between quinone (Q) and hydroquinone (QH2) was clearly observed under an aqueous condition. The formal potentials for NQ and AQ derivatives were -0.48 and -0.58 V, respectively, that did not depend on the spacer length. The oxidation and reduction peak currents were strongly dependent on the spacer alkyl chain length. The redox behavior of quinone derivatives depended on the pH condition of the buffer solution. The pH dependence was in agreement with a theoretical value of E 1/2 (mV)=E'-59pH for 2H+/2e(-) process in the pH range 3-11. In the range higher than pH 11, the value was estimated with E 1/2 (mV)=E'-30pH , which may correspond to H+/2e(-) process. The tunneling barrier coefficients (beta) for NQ and AQ SAMs were determined to be 0.12 and 0.73 per methylene group (CH2), respectively. Comparison of the structures and the alkyl chain length of quinones derivatives on these electron transfers on the electrode is made.

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.

Dependence of transformation product formation on pH during photolytic and photocatalytic degradation of ciprofloxacin.

PubMed

Salma, Alaa; Thoröe-Boveleth, Sven; Schmidt, Torsten C; Tuerk, Jochen

2016-08-05

Ciprofloxacin (CIP) is a broad-spectrum antibiotic with five pH dependent species in aqueous medium, which makes its degradation behavior difficult to predict. For the identification of transformation products and prediction of degradation mechanisms, a new experimental concept making use of isotopically labeled compounds together with high resolution mass spectrometry was successfully established. The utilization of deuterated ciprofloxacin (CIP-d8) facilitated the prediction of three different degradation pathways and the corresponding degradation products, four of which were identified for the first time. Moreover, two molecular structures of previously reported transformation products were revised according to the mass spectra and product ion spectra of the deuterated transformation products. Altogether, 18 transformation products have been identified during the photolytic and photocatalytic reactions at different pH values (3, 5, 7 and 9). In this work the influence of pH on both reaction kinetics and degradation mechanism was investigated for direct ultraviolet photolysis (UV-C irradiation) and photocatalysis (TiO2/UV-C). It could be shown that the removal rates strongly depended on pH with highest removal rates at pH 9. A comparison with those at pH 3 clearly indicated that under acidic conditions ciprofloxacin cannot be easily excited by UV irradiation. We could confirm that the first reaction step for both oxidative treatment processes is mainly defluorination, followed by degradation at the piperazine ring of CIP. Copyright © 2016 Elsevier B.V. All rights reserved.

Influence of pH, soil humic/fulvic acid, ionic strength, foreign ions and addition sequences on adsorption of Pb(II) onto GMZ bentonite.

PubMed

Wang, Suowei; Hu, Jun; Li, Jiaxing; Dong, Yunhui

2009-08-15

This work contributed to the adsorption of Pb(II) onto GMZ bentonite in the absence and presence of soil humic acid (HA)/fulvic acid (FA) using a batch technique. The influences of pH from 2 to 12, ionic strengths from 0.004M to 0.05M NaNO(3), soil HA/FA concentrations from 1.6 mg/L to 20mg/L, foreign cations (Li+, Na+, K+), anions (Cl(-), NO(3)(-)), and addition sequences on the adsorption of Pb(II) onto GMZ bentonite were tested. The adsorption isotherms of Pb(II) were determined at pH 3.6+/-0.1 and simulated with the Langmuir, Freundlich, and D-R adsorption models, respectively. The results demonstrated that the adsorption of Pb(II) onto GMZ bentonite increased with increasing pH from 2 to 6. HA was shown to enhance Pb(II) adsorption at low pH, but to reduce Pb(II) adsorption at high pH, whereas FA was shown to decrease Pb(II) adsorption at pH from 2 to 11. The results also demonstrated that the adsorption was strongly dependent on ionic strength and slightly dependent on the concentration of HA/FA. The adsorption of Pb(II) onto GMZ bentonite was dependent on foreign ions in solution. The addition sequences of bentonite/Pb(II)/HA had no effect on the adsorption of Pb(II).

Dependence of precipitation of trace elements on pH in standard water

NASA Astrophysics Data System (ADS)

Verma, Shivcharan; Mohanty, Biraja P.; Singh, K. P.; Behera, B. R.; Kumar, Ashok

2018-04-01

The present work aimed to study the dependence of precipitation of trace elements on the pH of solution. A standard solution was prepared by using ultrapure deionized water (18.2 MΩ/cm) as the solvent and 11 water-soluble salts having different elements as solutes. Five samples of different pH values (2 acidic, 2 basic, and 1 neutral) were prepared from this standard solution. Sodium-diethyldithiocarbamate was used as the chelating agent to precipitate the metal ions present in these samples of different pH values. The targets were prepared by collecting these precipitates on mixed cellulose esters filter of 0.4 μm pore size by vacuum filtration. Elemental analysis of these targets was performed by particle-induced X-ray emission (PIXE) using 2.7 MeV protons from the single Dee variable energy cyclotron at Panjab University, Chandigarh, India. PIXE data were analyzed using GUPIXWIN software. For most of the elements, except Hg with oxidation state +2, such as Co, Ni, Zn, Ba, and Cd, a general trend of enhancement in precipitation was observed with the increase in pH. However, for other elements such as V, As, Mo, Ag, and Bi, which have oxidation state other than +2, no definite pattern was observed. Precipitation of Ba and As using this method was negligible at all five pH values. From these results, it can be concluded that the precipitation and recovery of elements depend strongly on the pH of the water sample.

Direct and indirect effects of ocean acidification and warming on a marine plant-herbivore interaction.

PubMed

Poore, Alistair G B; Graba-Landry, Alexia; Favret, Margaux; Sheppard Brennand, Hannah; Byrne, Maria; Dworjanyn, Symon A

2013-11-01

The impacts of climatic change on organisms depend on the interaction of multiple stressors and how these may affect the interactions among species. Consumer-prey relationships may be altered by changes to the abundance of either species, or by changes to the per capita interaction strength among species. To examine the effects of multiple stressors on a species interaction, we test the direct, interactive effects of ocean warming and lowered pH on an abundant marine herbivore (the amphipod Peramphithoe parmerong), and whether this herbivore is affected indirectly by these stressors altering the palatability of its algal food (Sargassum linearifolium). Both increased temperature and lowered pH independently reduced amphipod survival and growth, with the impacts of temperature outweighing those associated with reduced pH. Amphipods were further affected indirectly by changes to the palatability of their food source. The temperature and pH conditions in which algae were grown interacted to affect algal palatability, with acidified conditions only affecting feeding rates when algae were also grown at elevated temperatures. Feeding rates were largely unaffected by the conditions faced by the herbivore while feeding. These results indicate that, in addition to the direct effects on herbivore abundance, climatic stressors will affect the strength of plant-herbivore interactions by changes to the susceptibility of plant tissues to herbivory.

Modelling coupled microbial processes in the subsurface: Model development, verification, evaluation and application

NASA Astrophysics Data System (ADS)

Masum, Shakil A.; Thomas, Hywel R.

2018-06-01

To study subsurface microbial processes, a coupled model which has been developed within a Thermal-Hydraulic-Chemical-Mechanical (THCM) framework is presented. The work presented here, focuses on microbial transport, growth and decay mechanisms under the influence of multiphase flow and bio-geochemical reactions. In this paper, theoretical formulations and numerical implementations of the microbial model are presented. The model has been verified and also evaluated against relevant experimental results. Simulated results show that the microbial processes have been accurately implemented and their impacts on porous media properties can be predicted either qualitatively or quantitatively or both. The model has been applied to investigate biofilm growth in a sandstone core that is subjected to a two-phase flow and variable pH conditions. The results indicate that biofilm growth (if not limited by substrates) in a multiphase system largely depends on the hydraulic properties of the medium. When the change in porewater pH which occurred due to dissolution of carbon dioxide gas is considered, growth processes are affected. For the given parameter regime, it has been shown that the net biofilm growth is favoured by higher pH; whilst the processes are considerably retarded at lower pH values. The capabilities of the model to predict microbial respiration in a fully coupled multiphase flow condition and microbial fermentation leading to production of a gas phase are also demonstrated.

Oxygen and carbon dioxide in the marine intertidal environment: diurnal and tidal changes in rockpools.

PubMed

Truchot, J P; Duhamel-Jouve, A

1980-03-01

Water oxygen partial pressure (PO2), pH, titration alkalinity (TA), temperature and salinity were measured hourly in rockpools during emersion periods occuring at various times of the diurnal cycle. Measurements allowed calculation of oxygen concentration (CO2), CO2 partial pressure (PCO2) and concentrations of bicarbonate, carbonate and total CO2 (CCO2). During night emersion periods, water PO2 decreased to almost zero in a few hours, pH fell, TA rose and PCO2 increased up to 1-3 Torr. During day emersion periods, water PO2 rose to 400-600 Torr, pH increased to more than 10, TA decreased substantially and PCO2 fell as low as 10(-4) Torr. The direction of the observed changes depended essentially on the illumination, indicating that respiratory and photosynthetic activities were the main processes involved. The large variations of the components of the carbonate system imply considerable changes of the CO2 capacitance coefficient in water, mainly during the day-time emersion. These changes are discussed in relation to the respiratory and acid-base physiology of the animals living in these biotopes.

How Helicobacter pylori urease may affect external pH and influence growth and motility in the mucus environment: evidence from in-vitro studies.

PubMed

Sidebotham, Ramon L; Worku, Mulugeta L; Karim, Q Najma; Dhir, Nirmal K; Baron, J Hugh

2003-04-01

Survival of Helicobacter pylori is dependent upon urease in the cytoplasm and at the bacterial surface. We have sought to clarify how alkaline ammonium salts, released from urea by this enzyme, might alter mucus pH and so affect growth and motility of the bacterium in the gastric mucus environment. Experiments were conducted in vitro to determine how the growth and motility of H. pylori are affected by changes in external pH, and how the bacterium, by hydrolysing urea, alters the pH of the bicarbonate buffer that occurs at the gastric mucosal surface. These data were fitted into experimental models that describe how pH varies within the mucus layer in the acid-secreting stomach. H. pylori was motile between pH 5 and 8, with optimal motility at pH 5. It grew between pH 6 and 8, with optimal growth at pH 6. The bacterium had urease activity between pH 2.7 and 7.4, as evidenced by pH rises in bicarbonate-buffered solutions of urea. Changes in buffer pH were dependent upon initial pH and urea concentration, with the greatest rate of pH change occurring at pH 3. Modelling experiments utilizing these data indicated that (1) in the absence of urease, H. pylori growth and motility in the mucus layer would be restricted severely by low mucus pH in the acid-secreting stomach, and (2) urease will sometimes inhibit H. pylori growth and motility in the mucus layer by elevating the pH of the mucus environment above pH 8. Urease is essential to the growth and motility of H. pylori in the mucus layer in the acid-secreting stomach, but, paradoxically, sometimes it might suppress colonization by raising the mucus pH above 8. This latter effect may protect the bacteria from the adverse consequences of overpopulation.

Proline transport in Leishmania donovani amastigotes: dependence on pH gradients and membrane potential.

PubMed

Glaser, T A; Mukkada, A J

1992-03-01

Amastigotes of Leishmania donovani develop and multiply within the acidic phagolysosomes of mammalian macrophages. Isolated amastigotes are acidophilic; they catabolize substrates and synthesize macromolecules optimally at pH 5.5. Substrate transport in amastigotes has not been characterized. Here we show that amastigotes exhibit an uphill transport of proline (active transport) with an acid pH optimum (pH 5.5). It is dependent upon metabolic energy and is driven by proton motive force. Agents which selectively disturb the component forces of proton motive force, such as carbonyl cyanide chlorophenylhydrazone, nigericin and valinomycin, inhibit proline transport. Transport is sensitive to dicyclohexylcarbodiimide and insensitive to ouabain, demonstrating the involvement of a proton ATPase in the maintenance of proton motive force. It is suggested that the plasma membrane pH gradient probably makes the greatest contribution to proton motive force that drives substrate transport in the amastigote stage.

Tumor cell membrane-targeting pH-dependent electron donor-acceptor fluorescence systems with low background signals.

PubMed

Han, Liang; Liu, Mingming; Ye, Deyong; Zhang, Ning; Lim, Ed; Lu, Jing; Jiang, Chen

2014-03-01

Minimizing the background signal is crucial for developing tumor-imaging techniques with sufficient specificity and sensitivity. Here we use pH difference between healthy tissues and tumor and tumor targeting delivery to achieve this goal. We synthesize fluorophore-dopamine conjugate as pH-dependent electron donor-acceptor fluorescence system. Fluorophores are highly sensitive to electron-transfer processes, which can alter their optical properties. The intrinsic redox properties of dopamine are oxidation of hydroquinone to quinone at basic pH and reduction of quinone to hydroquinone at acidic pH. Quinone can accept electron then quench fluorescence. We design tumor cell membrane-targeting carrier for delivery. We demonstrate quenched fluorophore-quinone can be specially transferred to tumor extracellular environment and tumor-accumulated fluorophore can be activated by acidic pH. These tumor-targeting pH-dependent electron donor-acceptor fluorescence systems may offer new opportunity for developing tumor-imaging techniques. Copyright © 2014 Elsevier Ltd. All rights reserved.

Zinc-dependent cleavage in the catalytic core of the hammerhead ribozyme: evidence for a pH-dependent conformational change

PubMed Central

Borda, Emily J.; Markley, John C.; Sigurdsson, Snorri Th.

2003-01-01

We have characterized a novel Zn2+-catalyzed cleavage site between nucleotides C3 and U4 in the catalytic core of the hammerhead ribozyme. In contrast to previously described divalent metal-ion-dependent cleavage of RNA, U4 cleavage is only observed in the presence of Zn2+. This new cleavage site has an unusual pH dependence, in that U4 cleavage products are only observed above pH 7.9 and reach a maximum yield at about pH 8.5. These data, together with the fact that no metal ion-binding site is observed in proximity to the U4 cleavage site in either of the crystal structures, point toward a pH-dependent conformational change in the hammerhead ribozyme. We have described previously Zn2+-dependent cleavage between G8 and A9 in the hammerhead ribozyme and have discovered that U4 cleavage occurs only after A9 cleavage. To our knowledge, this is the first example of sequential cleavage events as a possible regulatory mechanism in ribozymes. PMID:12736309

Cofilin is a pH sensor for actin free barbed end formation: role of phosphoinositide binding.

PubMed

Frantz, Christian; Barreiro, Gabriela; Dominguez, Laura; Chen, Xiaoming; Eddy, Robert; Condeelis, John; Kelly, Mark J S; Jacobson, Matthew P; Barber, Diane L

2008-12-01

Newly generated actin free barbed ends at the front of motile cells provide sites for actin filament assembly driving membrane protrusion. Growth factors induce a rapid biphasic increase in actin free barbed ends, and we found both phases absent in fibroblasts lacking H(+) efflux by the Na-H exchanger NHE1. The first phase is restored by expression of mutant cofilin-H133A but not unphosphorylated cofilin-S3A. Constant pH molecular dynamics simulations and nuclear magnetic resonance (NMR) reveal pH-sensitive structural changes in the cofilin C-terminal filamentous actin binding site dependent on His133. However, cofilin-H133A retains pH-sensitive changes in NMR spectra and severing activity in vitro, which suggests that it has a more complex behavior in cells. Cofilin activity is inhibited by phosphoinositide binding, and we found that phosphoinositide binding is pH-dependent for wild-type cofilin, with decreased binding at a higher pH. In contrast, phosphoinositide binding by cofilin-H133A is attenuated and pH insensitive. These data suggest a molecular mechanism whereby cofilin acts as a pH sensor to mediate a pH-dependent actin filament dynamics.

Correlation between pH dependence of O2 evolution and sensitivity of Mn cations in the oxygen-evolving complex to exogenous reductants.

PubMed

Semin, Boris K; Davletshina, Lira N; Rubin, Andrei B

2015-08-01

Effects of pH, Ca(2+), and Cl(-) ions on the extraction of Mn cations from oxygen-evolving complex (OEC) in Ca-depleted photosystem II (PSII(-Ca)) by exogenous reductants hydroquinone (H2Q) and H2O2 were studied. Two of 4 Mn cations are released by H2Q and H2O2 at pHs 5.7, 6.5, and 7.5, and their extraction does not depend on the presence of Ca(2+) and Cl(-) ions. One of Mn cations ("resistant" Mn cation) cannot be extracted by H2Q and H2O2 at any pH. Extraction of 4th Mn ion ("flexible" Mn cation) is sensitive to pH, Ca(2+), and Cl(-). This Mn cation is released by reductants at pH 6.5 but not at pHs 5.7 and 7.5. A pH dependence curve of the oxygen-evolving activity in PSII(-Ca) membranes (in the presence of exogenous Ca(2+)) has a bell-shaped form with the maximum at pH 6.5. Thus, the increase in the resistance of flexible Mn cation in OEC to the action of reductants at acidic and alkaline pHs coincides with the decrease in oxygen evolution activity at these pHs. Exogenous Ca(2+) protects the extraction of flexible Mn cation at pH 6.5. High concentration of Cl(-) anions (100 mM) shifts the pH optimum of oxygen evolution to alkaline region (around pH 7.5), while the pH of flexible Mn extraction is also shifted to alkaline pH. This result suggests that flexible Mn cation plays a key role in the water-splitting reaction. The obtained results also demonstrate that only one Mn cation in Mn4 cluster is under strong control of calcium. The change in the flexible Mn cation resistance to exogenous reductants in the presence of Ca(2+) suggests that Ca(2+) can control the redox potential of this cation.

Geochemistry and migration of contaminants at the Weldon Spring chemical plant site, St. Charles County, Missouri, 1989-91

USGS Publications Warehouse

Schumacher, John G.

1993-01-01

The geochemistry of the shallow aquifer and geochemical controls on the migration of uranium and other constituents from raffinate pits were determined at the Weldon Spring chemical plant site. Surface-water samples from the raffinate pits con- tained large concentrations of calcium, magnesium, sodium, potassium, sulfate, nitrite, lithium, moly- bdenum, strontium, vanadium, and uranium. Analyses of interstitial-water samples from raffinate pit 3 indicated that concentrations of most constituents increased with increasing depth below the water- sediment interface. Nitrate and uranium were not chemically reduced and attenuated within the raffinate pits and can be expected to migrate into the overburden. Laboratory sorption experiments were performed to evaluate the effect of pH value on the sorption of several raffinate constituents by the overburden. No sorption of calcium, sodium, sulfate, nitrate, or lithium was observed. Sorption of molybdenum was dependent on solution pH and sorption of uranium was dependent on solution pH and carbonate concentration. The sorption of uranium and molybdenum was consistent with sorption controlled by oxyhydroxides. The quality of water collected in overburden lysimeters near raffinate pit 4 can be modeled as a mixture of water from raffinate pits 3 and 4, and an uncontaminated com- ponent in a system at equilibrium with ferrihydrite and calcite. Increased constituent concentrations in a perennial spring north of the site were the result of a subsurface connection between the spring and several losing stream segments receiving runoff from the site, in addition to seepage from the raffinate pits.

Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production.

PubMed

Reynal, Anna; Pastor, Ernest; Gross, Manuela A; Selim, Shababa; Reisner, Erwin; Durrant, James R

2015-08-01

Photocatalytic systems for the reduction of aqueous protons are strongly pH-dependent, but the origin of this dependency is still not fully understood. We have studied the effect of different degrees of acidity on the electron transfer dynamics and catalysis taking place in a homogeneous photocatalytic system composed of a phosphonated ruthenium tris(bipyridine) dye ( RuP ) and a nickel bis(diphosphine) electrocatalyst ( NiP ) in an aqueous ascorbic acid solution. Our approach is based on transient absorption spectroscopy studies of the efficiency of photo-reduction of RuP and NiP correlated with pH-dependent photocatalytic H 2 production and the degree of catalyst protonation. The influence of these factors results in an observed optimum photoactivity at pH 4.5 for the RuP - NiP system. The electron transfer from photo-reduced RuP to NiP is efficient and independent of the pH value of the medium. At pH <4.5, the efficiency of the system is limited by the yield of RuP photo-reduction by the sacrificial electron donor, ascorbic acid. At pH >4.5, the efficiency of the system is limited by the poor protonation of NiP , which inhibits its ability to reduce protons to hydrogen. We have therefore developed a rational strategy utilising transient absorption spectroscopy combined with bulk pH titration, electrocatalytic and photocatalytic experiments to disentangle the complex pH-dependent activity of the homogenous RuP - NiP photocatalytic system, which can be widely applied to other photocatalytic systems.

pH-Dependent spin state population and 19F NMR chemical shift via remote ligand protonation in an iron(ii) complex.

PubMed

Gaudette, Alexandra I; Thorarinsdottir, Agnes E; Harris, T David

2017-11-30

An Fe II complex that features a pH-dependent spin state population, by virtue of a variable ligand protonation state, is described. This behavior leads to a highly pH-dependent 19 F NMR chemical shift with a sensitivity of 13.9(5) ppm per pH unit at 37 °C, thereby demonstrating the potential utility of the complex as a 19 F chemical shift-based pH sensor.

A study of the nonlinear aerodynamics of bodies in nonplanar motion. Ph.D. Thesis - Stanford Univ., Calif.; [numerical analysis of aerodynamic force and moment systems during large amplitude, arbitrary motions

NASA Technical Reports Server (NTRS)

Schiff, L. B.

1974-01-01

Concepts from the theory of functionals are used to develop nonlinear formulations of the aerodynamic force and moment systems acting on bodies in large-amplitude, arbitrary motions. The analysis, which proceeds formally once the functional dependence of the aerodynamic reactions upon the motion variables is established, ensures the inclusion, within the resulting formulation, of pertinent aerodynamic terms that normally are excluded in the classical treatment. Applied to the large-amplitude, slowly varying, nonplanar motion of a body, the formulation suggests that the aerodynamic moment can be compounded of the moments acting on the body in four basic motions: steady angle of attack, pitch oscillations, either roll or yaw oscillations, and coning motion. Coning, where the nose of the body describes a circle around the velocity vector, characterizes the nonplanar nature of the general motion.

Computational Tools for Interpreting Ion Channel pH-Dependence.

PubMed

Sazanavets, Ivan; Warwicker, Jim

2015-01-01

Activity in many biological systems is mediated by pH, involving proton titratable groups with pKas in the relevant pH range. Experimental analysis of pH-dependence in proteins focusses on particular sidechains, often with mutagenesis of histidine, due to its pKa near to neutral pH. The key question for algorithms that predict pKas is whether they are sufficiently accurate to effectively narrow the search for molecular determinants of pH-dependence. Through analysis of inwardly rectifying potassium (Kir) channels and acid-sensing ion channels (ASICs), mutational effects on pH-dependence are probed, distinguishing between groups described as pH-coupled or pH-sensor. Whereas mutation can lead to a shift in transition pH between open and closed forms for either type of group, only for pH-sensor groups does mutation modulate the amplitude of the transition. It is shown that a hybrid Finite Difference Poisson-Boltzmann (FDPB) - Debye-Hückel continuum electrostatic model can filter mutation candidates, providing enrichment for key pH-coupled and pH-sensor residues in both ASICs and Kir channels, in comparison with application of FDPB alone.

Computational Tools for Interpreting Ion Channel pH-Dependence

PubMed Central

Sazanavets, Ivan; Warwicker, Jim

2015-01-01

Activity in many biological systems is mediated by pH, involving proton titratable groups with pKas in the relevant pH range. Experimental analysis of pH-dependence in proteins focusses on particular sidechains, often with mutagenesis of histidine, due to its pKa near to neutral pH. The key question for algorithms that predict pKas is whether they are sufficiently accurate to effectively narrow the search for molecular determinants of pH-dependence. Through analysis of inwardly rectifying potassium (Kir) channels and acid-sensing ion channels (ASICs), mutational effects on pH-dependence are probed, distinguishing between groups described as pH-coupled or pH-sensor. Whereas mutation can lead to a shift in transition pH between open and closed forms for either type of group, only for pH-sensor groups does mutation modulate the amplitude of the transition. It is shown that a hybrid Finite Difference Poisson-Boltzmann (FDPB) – Debye-Hückel continuum electrostatic model can filter mutation candidates, providing enrichment for key pH-coupled and pH-sensor residues in both ASICs and Kir channels, in comparison with application of FDPB alone. PMID:25915903

Meta-analysis of effects of gender in combination with carcass weight and breed on pork quality.

PubMed

Trefan, L; Doeschl-Wilson, A; Rooke, J A; Terlouw, C; Bünger, L

2013-03-01

Meta-analysis was performed to quantify the effects of gender in combination with carcass weight and breed on pork quality. Altogether published results from 43 references were used. The traits analyzed were pH at 45 min (pH45min) and pH at 24 h (pH24hr) postmortem, objective color attributes lightness (L*), redness (a*), and yellowness (b*; CIE color system), color and marbling scores, drip loss, intramuscular fat content (IMF), and backfat thickness (P2), as well as sensory scores of juiciness and tenderness. Data for 2 muscle types, LM and Musculus semimembranosus (SMM), were used for the analysis. Swine genders were defined as intact/entire male (EM), surgically castrated male (SM), immunocastrated male (IM), and entire female (EF). After standardization of scaled traits (color, marbling scores, juiciness, tenderness) and accounting for cold carcass weight (CW), statistical analysis was performed using mixed models where breed was included as random effect. The analysis found a general effect of gender on each trait and multiple comparisons identified significant differences among the individual genders for L* (lightness), marbling scores, IMF, P2 in LM, and pH24hr in SMM. For these traits, when genders were grouped into gender categories as "castrates" (IM, SM) and "natural genders" (EM, EF), significant differences were found among estimates related to these categories. Furthermore, significant differences were found between castrates and individual gender types, indicating that castrated animals statistically segregated regarding their pork quality and regardless of type of castration. Pork of SM/EM animals has been found to be the fattest/leanest and there is indication that IM pork has the lightest meat color. Carcass weight dependence was found to be nonlinear (quadratic) for a*, P2, and marbling scores, and linear for b* and color scores in LM and pH24hr in SMM. The analysis identified significant breed effects for all traits, with large variation in the actual magnitudes (∼10 to 100%) of breed effects among individual traits. The established CW dependencies of pork quality traits in combination with the other influencing factors investigated here provides pork producers with the opportunity to achieve desired pork quality targets for a wide range of CW (∼30 to 150 kg) under standard indoor-rearing conditions.

Intraluminal measurement of papillary duct urine pH, in vivo: a pilot study in the swine kidney.

PubMed

Handa, Rajash K; Lingeman, James E; Bledsoe, Sharon B; Evan, Andrew P; Connors, Bret A; Johnson, Cynthia D

2016-06-01

We describe the in vivo use of an optic-chemo microsensor to measure intraluminal papillary duct urine pH in a large mammal. Fiber-optic pH microsensors have a tip diameter of 140-µm that allows insertion into papillary Bellini ducts to measure tubule urine proton concentration. Anesthetized adult pigs underwent percutaneous nephrolithotomy to access the lower pole of the urinary collecting system. A flexible nephroscope was advanced towards an upper pole papilla with the fiber-optic microsensor contained within the working channel. The microsensor was then carefully inserted into Bellini ducts to measure tubule urine pH in real time. We successfully recorded tubule urine pH values in five papillary ducts from three pigs (1 farm pig and 2 metabolic syndrome Ossabaw pigs). Our results demonstrate that optical microsensor technology can be used to measure intraluminal urine pH in real time in a living large mammal. This opens the possibility for application of this optical pH sensing technology in nephrolithiasis.

Anilinomethylrhodamines: pH sensitive probes with tunable photophysical properties by substituent effect.

PubMed

Best, Quinn A; Liu, Chuangjun; van Hoveln, Paul D; McCarroll, Matthew E; Scott, Colleen N

2013-10-18

A series of pH dependent rhodamine analogues possessing an anilino-methyl moiety was developed and shown to exhibit a unique photophysical response to pH. These anilinomethylrhodamines (AnMR) maintain a colorless, nonfluorescent spirocyclic structure at high pH. The spirocyclic structures open in mildly acidic conditions and are weakly fluorescent; however, at very low pH, the fluorescence is greatly enhanced. The equilibrium constants of these processes show a linear response to substituent effects, which was demonstrated by the Hammett equation.

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.

Development of a canine model to enable the preclinical assessment of pH-dependent absorption of test compounds.

PubMed

Fancher, R Marcus; Zhang, Hongjian; Sleczka, Bogdan; Derbin, George; Rockar, Richard; Marathe, Punit

2011-07-01

A preclinical canine model capable of predicting a compound's potential for pH-dependent absorption in humans was developed. This involved the surgical insertion of a gastrostomy feeding tube into the stomach of a beagle dog. The tube was sutured in position to allow frequent withdrawal of gastric fluid for pH measurement. Therefore, it was possible to measure pH in the stomach and assess the effect of gastric pH-modifying agents on the absorption of various test compounds. Fasted gastric pH in the dog showed considerable inter- and intra-animal variability. Pretreatment of pentagastrin (6 µg/kg intramuscularly) 20 min prior to test compound administration was determined to be adequate for simulating fasting stomach pH in humans. Pretreatment with famotidine [40 mg orally] 1 h prior to test compound administration was determined to be adequate for simulating human gastric pH when acid-reducing agents are coadministered. Pentagastrin and famotidine pretreatments were used to test two discovery compounds and distinct differences in their potential for pH-dependent absorption were observed. The model described herein can be used preclinically to screen out compounds, differentiate compounds, and support the assessment of various formulation- and prodrug-based strategies to mitigate the pH effect. Copyright © 2011 Wiley-Liss, Inc. and the American Pharmacists Association

Disruption of the hydrogen bonding network determines the pH-induced non-fluorescent state of the fluorescent protein ZsYellow by protonation of Glu221.

PubMed

Bae, Ji-Eun; Kim, In Jung; Nam, Ki Hyun

2017-11-04

Many fluorescent proteins (FPs) exhibit fluorescence quenching at a low pH. This pH-induced non-fluorescent state of an FP serves as a useful indicator of the cellular pH. ZsYellow is widely used as an optical marker in molecular biology, but its pH-induced non-fluorescent state has not been characterized. Here, we report the pH-dependent spectral properties of ZsYellow, which exhibited the pH-induced non-fluorescence state at a pH below 4.0. We determined the crystal structures of ZsYellow at pH 3.5 (non-fluorescence state) and 8.0 (fluorescence state), which revealed the cis-configuration of the chromophore without pH-induced isomerization. In the non-fluorescence state, Arg95, which is involved in stabilization of the exited state of the chromophore, was found to more loosely interact with the carbonyl oxygen atom of the chromophore when compared to the interaction at pH 8.0. In the fluorescence state, Glu221, which is involved in the hydrogen bonding network around the chromophore, stably interacted with Gln42 and His202. By contrast, in the non-fluorescence state, the protonated conserved Glu221 residue exhibited a large conformational change and was separated from His202 by 5.46 Å, resulting in breakdown of the hydrogen bond network. Our results provide insight into the critical role of the conserved Glu221 residue for generating the pH-induced non-fluorescent state. Copyright © 2017 Elsevier Inc. All rights reserved.

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.

Renal responses of trout to chronic respiratory and metabolic acidoses and metabolic alkalosis.

PubMed

Wood, C M; Milligan, C L; Walsh, P J

1999-08-01

Exposure to hyperoxia (500-600 torr) or low pH (4.5) for 72 h or NaHCO(3) infusion for 48 h were used to create chronic respiratory (RA) or metabolic acidosis (MA) or metabolic alkalosis in freshwater rainbow trout. During alkalosis, urine pH increased, and [titratable acidity (TA) - HCO(-)(3)] and net H(+) excretion became negative (net base excretion) with unchanged NH(+)(4) efflux. During RA, urine pH did not change, but net H(+) excretion increased as a result of a modest rise in NH(+)(4) and substantial elevation in [TA - HCO(-)(3)] efflux accompanied by a large increase in inorganic phosphate excretion. However, during MA, urine pH fell, and net H(+) excretion was 3.3-fold greater than during RA, reflecting a similar increase in [TA - HCO(-)(3)] and a smaller elevation in phosphate but a sevenfold greater increase in NH(+)(4) efflux. In urine samples of the same pH, [TA - HCO(-)(3)] was greater during RA (reflecting phosphate secretion), and [NH(+)(4)] was greater during MA (reflecting renal ammoniagenesis). Renal activities of potential ammoniagenic enzymes (phosphate-dependent glutaminase, glutamate dehydrogenase, alpha-ketoglutarate dehydrogenase, alanine aminotransferase, phosphoenolpyruvate carboxykinase) and plasma levels of cortisol, phosphate, ammonia, and most amino acids (including glutamine and alanine) increased during MA but not during RA, when only alanine aminotransferase increased. The differential responses to RA vs. MA parallel those in mammals; in fish they may be keyed to activation of phosphate secretion by RA and cortisol mobilization by MA.

The prognostic impact of clinical and CT parameters in patients with pontine hemorrhage.

PubMed

Dziewas, Rainer; Kremer, Marion; Lüdemann, Peter; Nabavi, Darius G; Dräger, Bianca; Ringelstein, Bernd

2003-01-01

In patients with pontine hemorrhage (PH), an accurate prognostic assessment is critical for establishing a reasonable therapeutic approach. The initial clinical symptoms and computed tomography (CT) features were analyzed with multivariate regression analysis in 39 consecutive patients with PH. PHs were classified into three types: (1) large paramedian, (2) basal or basotegmental and (3) lateral tegmental, and the hematomas' diameters were measured. The patients' outcome was evaluated. Twenty-seven patients (69%) died and 12 (31%) survived for more than 1 year after PH. The symptom most predictive of death was coma on admission. The large paramedian type of PH predicted a poor prognosis, whereas the lateral tegmental type was associated with a favorable outcome. The transverse hematoma diameter was also related to outcome, with the threshold value found to be 20 mm. We conclude that PH outcome can be estimated best by combining the CT parameters 'large paramedian PH' and 'transverse diameter >/=20 mm' with the clinical variable 'coma on admission'. Survival is unlikely if all 3 features are present, whereas survival may be expected if only 1 or none of these features is found. Copyright 2003 S. Karger AG, Basel

Strategies to overcome pH-dependent solubility of weakly basic drugs by using different types of alginates.

PubMed

Gutsche, S; Krause, M; Kranz, H

2008-12-01

Weakly basic drugs demonstrate higher solubility at lower pH, thus often leading to faster drug release at lower pH. The objective of this study was to achieve pH-independent release of weakly basic drugs from extended release formulations based on the naturally occurring polymer sodium alginate. Three approaches to overcome the pH-dependent solubility of the weakly basic model drug verapamil hydrochloride were investigated. First, matrix tablets were prepared by direct compression of drug substance with different types of sodium alginate only. Second, pH-modifiers were added to the drug/alginate matrix systems. Third, press-coated tablets consisting of an inner pH-modifier tablet core and an outer drug/sodium alginate coat were prepared. pH-Independent drug release was achieved from matrix tablets consisting of selected alginates and drug substance only. Alginates are better soluble at higher pH. Therefore, they are able to compensate the poor solubility of weakly basic drugs at higher pH as the matrix of the tablets dissolves faster. This approach was successful when using alginates that demonstrated fast hydration and erosion at higher pH. The approach failed for alginates with less-pronounced erosion at higher pH. The addition of fumaric acid to drug/alginate-based matrix systems decreased the microenvironmental pH within the tablets thus increasing the solubility of the weakly basic drug at higher pH. Therefore, pH-independent drug release was achieved irrespective of the type of alginate used. Drug release from press-coated tablets did not provide any further advantages as compound release remained pH-dependent.

Mycobacterium tuberculosis acyl carrier protein synthase adopts two different pH-dependent structural conformations

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

Gokulan, Kuppan; Aggarwal, Anup; Shipman, Lance

2011-07-01

Bacterial acyl carrier protein synthase plays an essential role in the synthesis of fatty acids, nonribosomal peptides and polyketides. In Mycobacterium tuberculosis, AcpS or group I phosphopentatheine transferase exhibits two different structural conformations depending upon the pH. The crystal structures of acyl carrier protein synthase (AcpS) from Mycobacterium tuberculosis (Mtb) and Corynebacterium ammoniagenes determined at pH 5.3 and pH 6.5, respectively, are reported. Comparison of the Mtb apo-AcpS structure with the recently reported structure of the Mtb AcpS–ADP complex revealed that AcpS adopts two different conformations: the orthorhombic and trigonal space-group structures show structural differences in the α2 helix andmore » in the conformation of the α3–α4 connecting loop, which is in a closed conformation. The apo-AcpS structure shows electron density for the entire model and was obtained at lower pH values (4.4–6.0). In contrast, at a higher pH value (6.5) AcpS undergoes significant conformational changes, resulting in disordered regions that show no electron density in the AcpS model. The solved structures also reveal that C. ammoniagenes AcpS undergoes structural rearrangement in two regions, similar to the recently reported Mtb AcpS–ADP complex structure. In vitro reconstitution experiments show that AcpS has a higher post-translational modification activity between pH 4.4 and 6.0 than at pH values above 6.5, where the activity drops owing to the change in conformation. The results show that apo-AcpS and AcpS–ADP adopt different conformations depending upon the pH conditions of the crystallization solution.« less

Pathways of proton release in the bacteriorhodopsin photocycle

NASA Technical Reports Server (NTRS)

Zimanyi, L.; Varo, G.; Chang, M.; Ni, B.; Needleman, R.; Lanyi, J. K.

1992-01-01

The pH dependencies of the rate constants in the photocycles of recombinant D96N and D115N/D96N bacteriorhodopsins were determined from time-resolved difference spectra between 70 ns and 420 ms after photoexcitation. The results were consistent with the model suggested earlier for proteins containing D96N substitution: BR hv----K----L----M1----M2----BR. Only the M2----M1 back-reaction was pH-dependent: its rate increased with increasing [H+] between pH 5 and 8. We conclude from quantitative analysis of this pH dependency that its reverse, the M1----M2 reaction, is linked to the release of a proton from a group with a pKa = 5.8. This suggests a model for wild-type bacteriorhodopsin in which at pH greater than 5.8 the transported proton is released on the extracellular side from this as yet unknown group and on the 100-microseconds time scale, but at pH less than 5.8, the proton release occurs from another residue and later in the photocycle most likely directly from D85 during the O----BR reaction. We postulate, on the other hand, that proton uptake on the cytoplasmic side will be by D96 and during the N----O reaction regardless of pH. The proton kinetics as measured with indicator dyes confirmed the unique prediction of this model: at pH greater than 6, proton release preceded proton uptake, but at pH less than 6, the release was delayed until after the uptake. The results indicated further that the overall M1----M2 reaction includes a second kinetic step in addition to proton release; this is probably the earlier postulated extracellular-to-cytoplasmic reorientation switch in the proton pump.

Avian Influenza Virus Infection of Immortalized Human Respiratory Epithelial Cells Depends upon a Delicate Balance between Hemagglutinin Acid Stability and Endosomal pH.

PubMed

Daidoji, Tomo; Watanabe, Yohei; Ibrahim, Madiha S; Yasugi, Mayo; Maruyama, Hisataka; Masuda, Taisuke; Arai, Fumihito; Ohba, Tomoyuki; Honda, Ayae; Ikuta, Kazuyoshi; Nakaya, Takaaki

2015-04-24

The highly pathogenic avian influenza (AI) virus, H5N1, is a serious threat to public health worldwide. Both the currently circulating H5N1 and previously circulating AI viruses recognize avian-type receptors; however, only the H5N1 is highly infectious and virulent in humans. The mechanism(s) underlying this difference in infectivity remains unclear. The aim of this study was to clarify the mechanisms responsible for the difference in infectivity between the current and previously circulating strains. Primary human small airway epithelial cells (SAECs) were transformed with the SV40 large T-antigen to establish a series of clones (SAEC-Ts). These clones were then used to test the infectivity of AI strains. Human SAEC-Ts could be broadly categorized into two different types based on their susceptibility (high or low) to the viruses. SAEC-T clones were poorly susceptible to previously circulating AI but were completely susceptible to the currently circulating H5N1. The hemagglutinin (HA) of the current H5N1 virus showed greater membrane fusion activity at higher pH levels than that of previous AI viruses, resulting in broader cell tropism. Moreover, the endosomal pH was lower in high susceptibility SAEC-T clones than that in low susceptibility SAEC-T clones. Taken together, the results of this study suggest that the infectivity of AI viruses, including H5N1, depends upon a delicate balance between the acid sensitivity of the viral HA and the pH within the endosomes of the target cell. Thus, one of the mechanisms underlying H5N1 pathogenesis in humans relies on its ability to fuse efficiently with the endosomes in human airway epithelial cells. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides.

PubMed

Chitrakar, Ramesh; Tezuka, Satoko; Sonoda, Akinari; Sakane, Kohji; Ooi, Kenta; Hirotsu, Takahiro

2005-10-01

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 degrees C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (delta-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca(+, Cl-, and SO(2-)4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of logK(F)=1.25 and 1/n=0.65, indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO(2-)4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.

A study of pH-dependence of shrink and stretch of tetrahedral DNA nanostructures.

PubMed

Wang, Ping; Xia, Zhiwei; Yan, Juan; Liu, Xunwei; Yao, Guangbao; Pei, Hao; Zuo, Xiaolei; Sun, Gang; He, Dannong

2015-04-21

We monitored the shrink and stretch of the tetrahedral DNA nanostructure (TDN) and the i-motif connected TDN structure at pH 8.5 and pH 4.5, and we found that not only the i-motif can change its structure when the pH changes, but also the TDN and the DNA double helix change their structures when the pH changes.

pH dependent green synthesis of gold nanoparticles by completely C6-carboxylated curdlan under high temperature and various pH conditions.

PubMed

Qiu, Wen-Yi; Wang, Kai; Wang, Yao-Yao; Ding, Zhi-Chao; Wu, Li-Xia; Cai, Wu-Dan; Yan, Jing-Kun

2018-01-01

A C6-carboxylated curdlan (C6-Cc) obtained from 4-acetamido-TEMPO-mediated oxidation of curdlan was used both as a reducing and stabilizing agent for green synthesis of pH-responsive AuNPs, which was carried out by controlling the pH of the C6-Cc solution at a high temperature (100°C). C6-Cc presented a semi-flexible random coil chain in the aqueous medium at pH 5.5 and became more expanded and rigid in alkaline conditions (pH 7.1-12.0), though the primary chemical structure of C6-Cc was virtually unchanged with the pH variation. The AuNPs prepared with C6-Cc at various pHs were characterized by various instrumental measurements. The shapes and sizes of AuNPs were found to be strongly dependent on the pH of the C6-Cc solution. The C6-Cc-decorated AuNPs exhibited a more well-dispersed spherical morphology with smaller particle sizes under alkaline conditions (pH 7.1-12.0). Through this study, a facile, simple, and green method has been demonstrated for preparation of stimuli-sensitive AuNPs using biocompatible polyanionic polysaccharides. Copyright © 2017 Elsevier B.V. All rights reserved.

Investigation of the effect of cucurbit[7]uril complexation on the photophysical and acid-base properties of the antimalarial drug quinine.

PubMed

Mallick, Suman; Pal, Kaushik; Chandra, Falguni; Koner, Apurba L

2016-11-09

Host-guest complexation of mono and dicationic quinine with cucurbit[7]uril (CB7), a water-soluble macrocyclic host molecule, has been investigated. Job's plot, time-resolved anisotropy as well as concentration dependent NMR titration confirm the binding of two CB7 macrocycles with one quinine molecule. The binding affinity of dicationic quinine with CB7 is one order of magnitude higher than the binding constant of mono-cationic quinine. Such preferential binding results in one unit pK a shift in the ground-state of the quinoline ring. However, using fluorescence spectroscopy we have obtained two acid-dissociation constants, one for quinoline ring nitrogen and the other for the nitrogen of the quinuclidine moiety. In the excited state, CB7 complexation causes one unit pK a shift for the quinoline ring and 1.9 unit shift for the quinuclidine moiety. Interestingly, a large enhancement of fluorescence lifetime and anisotropy of quinine at pH 2.7 and pH 9.0 upon CB7 complexation was observed due to the restriction of conformational flexibility. Moreover, at pH 3.0, a large fluorescence enhancement of quinine due to CB7 complexation was observed and it was quite significant as compared to that of quinine in 0.1 (M) HCl without CB7. We believe that this study of quinine complexation with CB7 will reduce phototoxicity, increase bioavailability and offer an alternative standard for quantum yield measurements in an amiable condition.

Highly pH-responsive sensor based on amplified spontaneous emission coupled to colorimetry.

PubMed

Zhang, Qi; Castro Smirnov, Jose R; Xia, Ruidong; Pedrosa, Jose M; Rodriguez, Isabel; Cabanillas-Gonzalez, Juan; Huang, Wei

2017-04-07

We demonstrated a simple, directly-readable approach for high resolution pH sensing. The method was based on sharp changes in Amplified Spontaneous Emission (ASE) of a Stilbene 420 (ST) laser dye triggered by the pH-dependent absorption of Bromocresol Green (BG). The ASE threshold of BG:ST solution mixtures exhibited a strong dependence on BG absorption, which was drastically changed by the variations of the pH of BG solution. As a result, ASE on-off or off-on was observed with different pH levels achieved by ammonia doping. By changing the concentration of the BG solution and the BG:ST blend ratio, this approach allowed to detect pH changes with a sensitivity down to 0.05 in the 10-11 pH range.

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.

Influence of soil pH on the sorption of ionizable chemicals: modeling advances.

PubMed

Franco, Antonio; Fu, Wenjing; Trapp, Stefan

2009-03-01

The soil-water distribution coefficient of ionizable chemicals (K(d)) depends on the soil acidity, mainly because the pH governs speciation. Using pH-specific K(d) values normalized to organic carbon (K(OC)) from the literature, a method was developed to estimate the K(OC) of monovalent organic acids and bases. The regression considers pH-dependent speciation and species-specific partition coefficients, calculated from the dissociation constant (pK(a)) and the octanol-water partition coefficient of the neutral molecule (log P(n)). Probably because of the lower pH near the organic colloid-water interface, the optimal pH to model dissociation was lower than the bulk soil pH. The knowledge of the soil pH allows calculation of the fractions of neutral and ionic molecules in the system, thus improving the existing regression for acids. The same approach was not successful with bases, for which the impact of pH on the total sorption is contrasting. In fact, the shortcomings of the model assumptions affect the predictive power for acids and for bases differently. We evaluated accuracy and limitations of the regressions for their use in the environmental fate assessment of ionizable chemicals.

Amino Acids Inhibitory Effects and Mechanism on 2-Amino-1-Methyl-6-Phenylimidazo [4,5-b]Pyridine (PhIP) Formation in the Maillard Reaction Model Systems.

PubMed

Linghu, Ziyi; Karim, Faris; Smith, J Scott

2017-12-01

This study was to investigate the inhibitory effects of amino acids (AAs) on the formation of 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) and to evaluate the inhibition mechanism of PhIP in Maillard model systems. Different AAs were individually added into model systems heat-treated at 180 °C/1 h. The PhIP, phenylacetaldehyde (PheAce), and pyrazines derivatives were determined using HPLC and GC-MS. AAs significantly reduced (P < 0.05) PhIP levels in a dose-dependent response, ranking as: Trp = Lys > Pro > Leu > Met > Val > Ile > Thr > Phe > Asp, at the highest molar ratio. The PheAce content was gradually reduced with increasing AAs levels, suggesting that AAs may inhibit PhIP formation through scavenging the available PheAce. A correlation between PhIP inhibition and PheAce-scavenging activity of AAs was observed when PheAce and AAs were heated. The variety and quantity of pyrazines formed are highly depending on the type of AAs. © 2017 Institute of Food Technologists®.

The influence of pH on the degradation of phenol and chlorophenols by potassium ferrate.

PubMed

Graham, Nigel; Jiang, Cheng-Chun; Li, Xiang-Zhong; Jiang, Jia-Qian; Ma, Jun

2004-09-01

This paper presents information concerning the influence of solution pH on the aqueous reaction between potassium ferrate and phenol and three chlorinated phenols: 4-chlorophenol (CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP). The redox potential and aqueous stability of the ferrate ion, and the reactivity of dissociating compounds, are known to be pH dependent. Laboratory tests have been undertaken over a wide range of pH (5.8-11) and reactant concentrations (ferrate:compound molar ratios of 1:1 to 8:1). The reactivity of trichloroethylene was also investigated as a reference compound owing to its non-dissociating nature. The extent of compound degradation by ferrate was found to be highly pH dependent, and the optimal pH (maximum degradation) decreased in the order: phenol/CP, DCP, TCP; at the optimal pH the degree of degradation of these compounds was similar. The results indicate that for the group of phenol and chlorophenols studied, the presence of an increasing number of chlorine substituent atoms corresponds to an increasing reactivity of the undissociated compound, and a decreasing reactivity of the dissociated compound.

[Coenzyme-induced slow transitions of NADP-sorbitol dehydrogenase from Gluconobacter oxydans].

PubMed

Liber, E E; Dorozhko, A I; Pomortseva, N V

1978-06-01

The kinetic properties of NADP-dependent sorbitol dehydrogenase from G. oxydans cell extract were studied at pH 8.8 and 9.3 in the direction of D-sorbitol oxydation. It was shown that the shape of the kinetic curves of NADPH accumulation in time is characterised by initial burst whose magnitude depends on the concentration of the enzyme extract used. Preincubation of the enzyme with NADP or D-sorbitol eliminated the initial burst on these curves and transformed them into straight lines coming from the start of co-ordinates. The dependence of the stationary reaction rate on the enzyme extract concentration is not a linear one. The kinetic dependences of stationary rate of the reaction catalysed by the enzyme on the concentration of D-sorbitol and NADP at pH 8.8 and 9.3 were examined under all conditions studied; the shape of these kinetic curves altered to considerable extent with the alteration of the enzyme extract concentration in the reaction mixture and pH. At pH 9.3 several intermiediate plateaux were found on the curves of the D-sorbitol concentration dependent stationary rate of the reaction. The preincubation of the enzyme extract with NADP during 1.5 h removed the intermediate plateau on these curves and made them hyperbolic. Disk-electrophoresis of the enzyme extract in PAAG concentration gradient showed that at pH 8.8 the enzyme exists in one active form, while at pH 9.3 it exists in three major and three minor active forms of the enzyme differing in their molecular weights are found. It is assumed that the enzyme from G. oxydans cell extract can exist in a great number of molecular equilibrium forms, the rate of quilibrium being comparable or significantly less than that of the enzymatic reaction. NADP significantly influences on the equilibrium of the molecular forms of the enzyme.

Sulfate reduction in sulfuric material after re-flooding: Effectiveness of organic carbon addition and pH increase depends on soil properties.

PubMed

Yuan, Chaolei; Fitzpatrick, Rob; Mosley, Luke M; Marschner, Petra

2015-11-15

Sulfuric material is formed upon oxidation of sulfidic material; it is extremely acidic, and therefore, an environmental hazard. One option for increasing pH of sulfuric material may be stimulation of bacterial sulfate reduction. We investigated the effects of organic carbon addition and pH increase on sulfate reduction after re-flooding in ten sulfuric materials with four treatments: control, pH increase to 5.5 (+pH), organic carbon addition with 2% w/w finely ground wheat straw (+C), and organic carbon addition and pH increase (+C+pH). After 36 weeks, in five of the ten soils, only treatment +C+pH significantly increased the concentration of reduced inorganic sulfur (RIS) compared to the control and increased the soil pore water pH compared to treatment+pH. In four other soils, pH increase or/and organic carbon addition had no significant effect on RIS concentration compared to the control. The RIS concentration in treatment +C+pH as percentage of the control was negatively correlated with soil clay content and initial nitrate concentration. The results suggest that organic carbon addition and pH increase can stimulate sulfate reduction after re-flooding, but the effectiveness of this treatment depends on soil properties. Copyright © 2015 Elsevier B.V. All rights reserved.

The origin of facet selectivity and alignment in anatase TiO 2 nanoparticles in electrolyte solutions: implications for oriented attachment in metal oxides

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

Sushko, M. L.; Rosso, K. M.

Atomic-to-mesoscale simulations were used to reveal the origin of oriented attachment between anatase TiO2 nanoparticles in aqueous HCl solutions. Analysis of the distance and pH dependence of interparticle interactions demonstrates that ion correlation forces are responsible for facet-specific attraction and rotation into lattice co-alignment at long-range. These forces give rise to a metastable solvent separated capture minimum on the disjoining pressure-distance curve, with the barrier to attachment largely due to steric hydration forces from structured intervening solvent.

Homogeneous plate based antibody internalization assay using pH sensor fluorescent dye.

PubMed

Nath, Nidhi; Godat, Becky; Zimprich, Chad; Dwight, Stephen J; Corona, Cesear; McDougall, Mark; Urh, Marjeta

2016-04-01

Receptor-mediated antibody internalization is a key mechanism underlying several anti-cancer antibody therapeutics. Delivering highly toxic drugs to cancer cells, as in the case of antibody drug conjugates (ADCs), efficient removal of surface receptors from cancer cells and changing the pharmacokinetics profile of the antibody drugs are some of key ways that internalization impacts the therapeutic efficacy of the antibodies. Over the years, several techniques have been used to study antibody internalization including radiolabels, fluorescent microscopy, flow cytometry and cellular toxicity assays. While these methods allow analysis of internalization, they have limitations including a multistep process and limited throughput and are generally endpoint assays. Here, we present a new homogeneous method that enables time and concentration dependent measurements of antibody internalization. The method uses a new hydrophilic and bright pH sensor dye (pHAb dye), which is not fluorescent at neutral pH but becomes highly fluorescent at acidic pH. For receptor mediated antibody internalization studies, antibodies against receptors are conjugated with the pHAb dye and incubated with the cells expressing the receptors. Upon binding to the receptor, the dyes conjugated to the antibody are not fluorescent because of the neutral pH of the media, but upon internalization and trafficking into endosomal and lysosomal vesicles the pH drops and dyes become fluorescent. The enabling attributes of the pHAb dyes are the hydrophilic nature to minimize antibody aggregation and bright fluorescence at acidic pH which allows development of simple plate based assays using a fluorescent reader. Using two different therapeutic antibodies--Trastuzumab (anti-HER2) and Cetuximab (anti-EGFR)--we show labeling with pHAb dye using amine and thiol chemistries and impact of chemistry and dye to antibody ration on internalization. We finally present two new approaches using the pHAb dye, which will be beneficial for screening a large number of antibody samples during early monoclonal development phase. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Lanthanide ion (III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminophosphonate (DOTA-4AmP8−) for dual biosensing of pH with CEST (chemical exchange saturation transfer) and BIRDS (biosensor imaging of redundant deviation in shifts)

PubMed Central

Huang, Yuegao; Coman, Daniel; Ali, Meser M.; Hyder, Fahmeed

2014-01-01

Relaxivity based magnetic resonance of phosphonated ligands chelated with gadolinium (Gd3+) shows promise for pH imaging. However instead of monitoring the paramagnetic effect of lanthanide complexes on the relaxivity of water protons, biosensor (or molecular) imaging with magnetic resonance is also possible by detecting either the non-exchangeable or the exchangeable protons on the lanthanide complexes themselves. The non-exchangeable protons (e.g., –CHx, where 3≥x≥1) are detected using a three-dimensional chemical shift imaging method called Biosensor Imaging of Redundant Deviation in Shifts (BIRDS), whereas the exchangeable protons (e.g., –OH or –NHy, where 2≥y≥1) are measured with Chemical Exchange Saturation Transfer (CEST) contrast. Here we tested the feasibility of BIRDS and CEST for pH imaging of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminophosphonate (DOTA-4AmP8−) chelated with thulium (Tm3+) and ytterbium (Yb3+). BIRDS and CEST experiments show that both complexes are responsive to pH and temperature changes. Higher pH and temperature sensitivities are obtained with BIRDS for either complex when using the chemical shift difference between two proton resonances vs. using the chemical shift of a single proton resonance, thereby eliminating the need to use water resonance as reference. While CEST contrast for both agents is linearly dependent on pH within a relatively large range (i.e., 6.3-7.9), much stronger CEST contrast is obtained with YbDOTA-4AmP5− than with TmDOTA-4AmP5−. In addition, we demonstrate the prospect of using BIRDS to calibrate CEST as new platform for quantitative pH imaging. PMID:24801742

JAK2 mediates lung fibrosis, pulmonary vascular remodelling and hypertension in idiopathic pulmonary fibrosis: an experimental study.

PubMed

Milara, Javier; Ballester, Beatriz; Morell, Anselm; Ortiz, José L; Escrivá, Juan; Fernández, Estrella; Perez-Vizcaino, Francisco; Cogolludo, Angel; Pastor, Enrique; Artigues, Enrique; Morcillo, Esteban; Cortijo, Julio

2018-06-01

Pulmonary hypertension (PH) is a common disorder in patients with idiopathic pulmonary fibrosis (IPF) and portends a poor prognosis. Recent studies using vasodilators approved for PH have failed in improving IPF mainly due to ventilation ( V )/perfusion ( Q ) mismatching and oxygen desaturation. Janus kinase type 2 (JAK2) is a non-receptor tyrosine kinase activated by a broad spectrum of profibrotic and vasoactive mediators, but its role in PH associated to PH is unknown. The study of JAK2 as potential target to treat PH in IPF. JAK2 expression was increased in pulmonary arteries (PAs) from IPF (n=10; 1.93-fold; P=0.0011) and IPF+PH (n=9; 2.65-fold; P<0.0001) compared with PA from control subjects (n=10). PA remodelling was evaluated in human pulmonary artery endothelial cells (HPAECs) and human pulmonary artery smooth muscle cells (HPASMCs) from patients with IPF in vitro treated with the JAK2 inhibitor JSI-124 or siRNA-JAK2 and stimulated with transforming growth factor beta. Both JSI-124 and siRNA-JAK2 inhibited the HPAEC to mesenchymal transition and the HPASMCs to myofibroblast transition and proliferation. JAK2 inhibition induced small PA relaxation in precision-cut lung slice experiments. PA relaxation was dependent of the large conductance calcium-activated potassium channel (BK Ca ). JAK2 inhibition activated BK Ca channels and reduced intracellular Ca 2+ . JSI-124 1 mg/kg/day, reduced bleomycin-induced lung fibrosis, PA remodelling, right ventricular hypertrophy, PA hypertension and V / Q mismatching in rats. The animal studies followed the ARRIVE guidelines. JAK2 participates in PA remodelling and tension and may be an attractive target to treat IPF associated to PH. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Lanthanide ion (III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminophosphonate for dual biosensing of pH with chemical exchange saturation transfer (CEST) and biosensor imaging of redundant deviation in shifts (BIRDS).

PubMed

Huang, Yuegao; Coman, Daniel; Ali, Meser M; Hyder, Fahmeed

2015-01-01

Relaxivity-based magnetic resonance of phosphonated ligands chelated with gadolinium (Gd(3+)) shows promise for pH imaging. However instead of monitoring the paramagnetic effect of lanthanide complexes on the relaxivity of water protons, biosensor (or molecular) imaging with magnetic resonance is also possible by detecting either the nonexchangeable or the exchangeable protons on the lanthanide complexes themselves. The nonexchangeable protons (e.g. -CHx, where 3 ≥ x ≥ 1) are detected using a three-dimensional chemical shift imaging method called biosensor imaging of redundant deviation in shifts (BIRDS), whereas the exchangeable protons (e.g. -OH or -NHy , where 2 ≥ y ≥ 1) are measured with chemical exchange saturation transfer (CEST) contrast. Here we tested the feasibility of BIRDS and CEST for pH imaging of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminophosphonate (DOTA-4AmP(8-)) chelated with thulium (Tm(3+) ) and ytterbium (Yb(3+)). BIRDS and CEST experiments show that both complexes are responsive to pH and temperature changes. Higher pH and temperature sensitivities are obtained with BIRDS for either complex when using the chemical shift difference between two proton resonances vs using the chemical shift of a single proton resonance, thereby eliminating the need to use water resonance as reference. While CEST contrast for both agents is linearly dependent on pH within a relatively large range (i.e. 6.3-7.9), much stronger CEST contrast is obtained with YbDOTA-4AmP(5-) than with TmDOTA-4AmP(5-). In addition, we demonstrate the prospect of using BIRDS to calibrate CEST as new platform for quantitative pH imaging. Copyright © 2014 John Wiley & Sons, Ltd.

The Listeria monocytogenes Bile Stimulon under Acidic Conditions Is Characterized by Strain-Specific Patterns and the Upregulation of Motility, Cell Wall Modification Functions, and the PrfA Regulon

PubMed Central

Guariglia-Oropeza, Veronica; Orsi, Renato H.; Guldimann, Claudia; Wiedmann, Martin; Boor, Kathryn J.

2018-01-01

Listeria monocytogenes uses a variety of transcriptional regulation strategies to adapt to the extra-host environment, the gastrointestinal tract, and the intracellular host environment. While the alternative sigma factor SigB has been proposed to be a key transcriptional regulator that facilitates L. monocytogenes adaptation to the gastrointestinal environment, the L. monocytogenes' transcriptional response to bile exposure is not well-understood. RNA-seq characterization of the bile stimulon was performed in two L. monocytogenes strains representing lineages I and II. Exposure to bile at pH 5.5 elicited a large transcriptomic response with ~16 and 23% of genes showing differential transcription in 10403S and H7858, respectively. The bile stimulon includes genes involved in motility and cell wall modification mechanisms, as well as genes in the PrfA regulon, which likely facilitate survival during the gastrointestinal stages of infection that follow bile exposure. The fact that bile exposure induced the PrfA regulon, but did not induce further upregulation of the SigB regulon (beyond that expected by exposure to pH 5.5), suggests a model where at the earlier stages of gastrointestinal infection (e.g., acid exposure in the stomach), SigB-dependent gene expression plays an important role. Subsequent exposure to bile induces the PrfA regulon, potentially priming L. monocytogenes for subsequent intracellular infection stages. Some members of the bile stimulon showed lineage- or strain-specific distribution when 27 Listeria genomes were analyzed. Even though sigB null mutants showed increased sensitivity to bile, the SigB regulon was not found to be upregulated in response to bile beyond levels expected by exposure to pH 5.5. Comparison of wildtype and corresponding ΔsigB strains newly identified 26 SigB-dependent genes, all with upstream putative SigB-dependent promoters. PMID:29467736

Characterization of morphological response of red cells in a sucrose solution.

PubMed

Rudenko, Sergey V

2009-01-01

The dynamics of red cell shape changes following transfer into sucrose media having a low chloride content was studied. Based on a large number of measurements, six types of morphological response (MR), differing both in the degree of shape changes and the time course of the process, were identified. The most prominent type of response is a triphasic sequence of shape changes consisting of a fast transformation into a sphere (phase 1), followed by restoration of the discoid shape (phase 2) and final transformation into spherostomatocytes (phase 3), with individual parameters which could vary significantly. It was found that individual morphological response exhibited day to day variations, depending on the initial state of the red blood cells and the donor, but to a larger extent depended on the composition of the sucrose solution, such as concentration and type of buffers, the presence of EDTA, calcium, as well as very small amounts of extracellular hemoglobin. MR shows strong pH and ionic strength dependence. Low pH inhibited phase 1 and high pH changed dramatically the time course of the response. Increasing ionic strength inhibited all phases of MR, and at concentrations above 10-20 mM NaCl it was fully suppressed. Tris and phosphate were also inhibitory whereas HEPES, MOPS and Tricine were less effective. MR occurred also in hypertonic or hypotonic sucrose solutions, with exception of extreme hypotonicity due to volume restrictions. It is concluded that strong membrane depolarization per se is not a causal factor leading to MR, and its different phases could be regulated independently. For some types of morphological response the fast shape transformation from sphere to disc and back to sphere occurs within a 10 s time interval and could be accelerated several fold in the presence of a small amount of hemoglobin. It is suggested that MR represents a type of general cell reaction that occurs upon exposure to low ionic strength.

pH Dependent but not P-gp Dependent Bidirectional Transport Study of S-propranolol: The Importance of Passive Diffusion.

PubMed

Zheng, Yi; Benet, Leslie Z; Okochi, Hideaki; Chen, Xijing

2015-08-01

Recent controversial publications, citing studies purporting to show that P-gp mediates the transport of propranolol, proposed that passive biological membrane transport is negligible. Based on the BDDCS, the extensively metabolized-highly permeable-highly soluble BDDCS class 1 drug, propranolol, shows a high passive permeability at concentrations unrestricted by solubility that can overwhelm any potential transporter effects. Here we reinvestigate the effects of passive diffusion and carrier-mediated transport on S-propranolol. Bidirectional permeability and inhibition of efflux transport studies were carried out in MDCK, MDCK-MDR1 and Caco-2 cell lines at different concentrations. Transcellular permeability studies were conducted at different apical pHs in the rat jejunum Ussing chamber model and PAMPA system. S-propranolol exhibited efflux ratios lower than 1 in MDCK, MDCK-MDR1 and Caco-2 cells. No significant differences of Papp, B->A in the presence and absence of the efflux inhibitor GG918 were observed. However, an efflux ratio of 3.63 was found at apical pH 6.5 with significant decrease in Papp, A->B and increase in Papp, B->A compared to apical pH 7.4 in Caco-2 cell lines. The pH dependent permeability was confirmed in the Ussing chamber model. S-propranolol flux was unchanged during inhibition by verapamil and rifampin. Furthermore, pH dependent permeability was also observed in the PAMPA system. S-propranolol does not exhibit active transport as proposed previously. The "false" positive efflux ratio can be explained by the pH partition theory. As expected, passive diffusion, but not active transport, plays the primary role in the permeability of the BDDCS class 1 drug propranolol.

pH dependent but not P-gp dependent bidirectional transport study of S-propranolol: the importance of passive diffusion

PubMed Central

Zheng, Yi; Benet, Leslie Z.; Okochi, Hideaki; Chen, Xijing

2016-01-01

Purpose Recent controversial publications, citing studies purporting to show that P-gp mediates the transport of propranolol, proposed that passive biological membrane transport is negligible. Based on the BDDCS, the extensively metabolized-highly permeable-highly soluble BDDCS class 1 drug, propranolol, shows a high passive permeability at concentrations unrestricted by solubility that can overwhelm any potential transporter effects. Here we reinvestigate the effects of passive diffusion and carrier-mediated transport on S-propranolol. Methods Bidirectional permeability and inhibition of efflux transport studies were carried out in MDCK, MDCK-MDR1 and Caco-2 cell lines at different concentrations. Transcellular permeability studies were conducted at different apical pHs in the rat jejunum Ussing chamber model and PAMPA system. Results S-propranolol exhibited efflux ratios lower than 1 in MDCK, MDCK-MDR1 and Caco-2 cells. No significant differences of Papp, B->A in the presence and absence of the efflux inhibitor GG918 were observed. However, an efflux ratio of 3.63 was found at apical pH 6.5 with significant decrease in Papp, A->B and increase in Papp, B->A compared to apical pH 7.4 in Caco-2 cell lines. The pH dependent permeability was confirmed in the Ussing chamber model. S-propranolol flux was unchanged during inhibition by verapamil and rifampin. Furthermore, pH dependent permeability was also observed in the PAMPA system. Conclusions S-propranolol does not exhibit active transport as proposed previously. The "false" positive efflux ratio can be explained by the pH partition theory. As expected, passive diffusion, but not active transport, plays the primary role in the permeability of the BDDCS class 1 drug propranolol. PMID:25690341

A novel Na+/HCO3--codependent choline transporter in the syncytial epithelium of the cestode Hymenolepis diminuta.

PubMed

Webb, R A; Xue, L

1998-02-01

Absorption of exogenous choline by the cestode Hymenolepis diminuta was found to be both Na+- and HCO3--dependent and, at pH 6 to 7, accounted for up to 65% of the total choline uptake. Na+/HCO3- dependent choline uptake was activated at approximately 6 mM HCO3- (EC50 approximately 9 mM), and, above 100 mM Na+, the rate of uptake was directly proportional to the Na+ concentration. Atempts to uncouple Na+-dependent uptake from HCO3--dependent uptake were not successful: K+-depolarization was without effect on HCO3--dependent choline uptake, and use of valinoomycin to hyperpolarize the brush-border membrane resulted in inhibition of uptake. Na-/HCO3--dependent choline uptake was not associated with solvent drag. The Na+/HCO3--dependent choline uptake displayed a Q10 of 6.4 (27 degrees to 37 degrees) and a relatively high activation energy of 126 kJ x mol(-1). At pH 6.0 and 7.0, Na-/HCO3--dependent choline uptake rates were similar, but Na+/HCO3--dependent choline uptake was reduced at pH 5.0. The Na+/HCO3--dependent choline uptake, at pH 7.0, displayed a Kt of approximately 500 microM and a Vmax of 4.01 pmol x mg wet weight(-1) x min(-1). The Na+/HCO3--dependent choline uptake was hemicholinium-3 sensitive, but not significantly inhibited by 200 microM bumetanide, 100 microM amiloride, benzamil, or EIPA or by 1 mM 4,4'-diisothiocyano-2,2'-stilbene disulfonate (DIDS) or 4-acetamido-4'-isothiocvanostilbene-2,2'-disulfonic acid (SITS). Although it remains to be shown that HCO3- uptake is coupled directly to both choline and Na+ uptake, the data suggest that choline up take occurs via choline/Na+/HCO3--co-trans porter.

A comparative study on the effect of Curcumin and Chlorin-p6 on the transport of the LDS cation across a negatively charged POPG bilayer: Effect of pH.

PubMed

Varshney, G K; Kintali, S R; Gupta, P K; Das, K

2017-02-15

We report the use of interface selective Second Harmonic generation technique to investigate the transport of the LDS cation across POPG liposomes in the pH range of 4.0 to 8.0 in the presence and absence of two amphiphilic drugs, Curcumin and Chlorin-p 6 (Cp 6 ). Our results show that bilayer permeability of liposomes is significantly affected by the presence of the drugs and pH of the medium as evidenced by significant changes in the transport kinetics of the LDS. Studies carried out in the pH range 4.0-8.0 show that while Cp 6 significantly enhanced the transport of LDS at pH4.0, the transport of the cation was seen to increase with increasing pH, with maximum effect at pH7.4 for Curcumin. The pH dependent bilayer localization of both the drugs was investigated by conducting steady state FRET studies using DPH labeled lipids as donors. The FRET results and the relative population of the various ionic/nonionic species of the drugs at different pH suggest that distance dependent interaction between the various ionic species of the drugs and polar head groups of the lipid is responsible for the observed pH dependence enhancement of the drug induced membrane permeability. Another interesting observation was that the stability of Curcumin in presence of POPG liposomes was observed to degrade significantly near physiological pH (7.4 and 8.0). Although this degradation did not affect the liposome integrity, interestingly this was observed to enhance the transport of the LDS cation across the bilayer. That the degradation products of Curcumin are equally effective as the drug itself in enhancing the membrane permeability lends additional support to the current opinion that the bioactive degradation products of the drug may have a significant contribution to its observed pharmacological effects. Copyright © 2016 Elsevier B.V. All rights reserved.

pH dependent growth of poly( L-lysine)/poly( L-glutamic) acid multilayer films and their cell adhesion properties

NASA Astrophysics Data System (ADS)

Richert, Ludovic; Arntz, Youri; Schaaf, Pierre; Voegel, Jean-Claude; Picart, Catherine

2004-10-01

The short-term interaction of chondrosarcoma cells with (PGA/PLL) polyelectrolyte multilayers was investigated in a serum-containing medium for films built at different pHs and subsequently exposed to the culture medium. The buildup of the films and their stability was first investigated by means of optical waveguide lightmode spectroscopy, quartz crystal microbalance, streaming potential measurements and atomic force microscopy. While film growth is linear at all pHs, after a few layers have been deposited the growth is much larger for the films built at basic pH and even more pronounced for those built at acidic pH. However, these latter films remain stable in the culture medium only if they have been crosslinked prior to the ionic strength and pH jumps. The films built at acidic pH were found to swell in water by about 200% whereas those built at other pHs did not swell in a physiological buffer. For thin films (≈20 nm) built at pH = 7.4, the detachment forces were dependent on the outermost layer, the forces being significantly higher on PLL-ending films than on PGA-ending ones. In contrast, for the thick films built at pH = 4.4 and at pH = 10.4 (thickness of the order of few hundred of nanometers), the detachment forces were independent of the outermost layer of the film. The films built at pH = 10.4, which shrink in contact with salt containing solutions, were highly cell adhesive whereas those built at acidic pH were highly cell resistant. Protein adsorption and film roughness (as measured by AFM) could not explain these striking differences. The high adhesion observed on the film built at pH 10.4 may rather be related to the secondary structure of the film and to its relatively low swellability in water, whereas the cell resistance of the films built at pH 4.4 may be linked to their high swellability. Therefore, for the PGA/PLL films, the cell adhesion properties can be tuned depending on the deposition pH of the polyelectrolyte solutions. This study reveals the importance of the multilayer structure and architecture to control the detachment force of cells onto such films.

A computer program incorporating Pitzer's equations for calculation of geochemical reactions in brines

USGS Publications Warehouse

Plummer, Niel; Parkhurst, D.L.; Fleming, G.W.; Dunkle, S.A.

1988-01-01

The program named PHRQPITZ is a computer code capable of making geochemical calculations in brines and other electrolyte solutions to high concentrations using the Pitzer virial-coefficient approach for activity-coefficient corrections. Reaction-modeling capabilities include calculation of (1) aqueous speciation and mineral-saturation index, (2) mineral solubility, (3) mixing and titration of aqueous solutions, (4) irreversible reactions and mineral water mass transfer, and (5) reaction path. The computed results for each aqueous solution include the osmotic coefficient, water activity , mineral saturation indices, mean activity coefficients, total activity coefficients, and scale-dependent values of pH, individual-ion activities and individual-ion activity coeffients , and scale-dependent values of pH, individual-ion activities and individual-ion activity coefficients. A data base of Pitzer interaction parameters is provided at 25 C for the system: Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O, and extended to include largely untested literature data for Fe(II), Mn(II), Sr, Ba, Li, and Br with provision for calculations at temperatures other than 25C. An extensive literature review of published Pitzer interaction parameters for many inorganic salts is given. Also described is an interactive input code for PHRQPITZ called PITZINPT. (USGS)

A pH Switch Regulates the Inverse Relationship between Membranolytic and Chaperone-like Activities of HSP-1/2, a Major Protein of Horse Seminal Plasma.

PubMed

Kumar, C Sudheer; Swamy, Musti J

2016-07-05

HSP-1/2, a major protein of horse seminal plasma binds to choline phospholipids present on the sperm plasma membrane and perturbs its structure by intercalating into the hydrophobic core, which results in an efflux of choline phospholipids and cholesterol, an important event in sperm capacitation. HSP-1/2 also exhibits chaperone-like activity (CLA) in vitro and protects target proteins against various kinds of stress. In the present study we show that HSP-1/2 exhibits destabilizing activity toward model supported and cell membranes. The membranolytic activity of HSP-1/2 is found to be pH dependent, with lytic activity being high at mildly acidic pH (6.0-6.5) and low at mildly basic pH (8.0-8.5). Interestingly, the CLA is also found to be pH dependent, with high activity at mildly basic pH and low activity at mildly acidic pH. Taken together the present studies demonstrate that the membranolytic and chaperone-like activities of HSP-1/2 have an inverse relationship and are regulated via a pH switch, which is reversible. The higher CLA observed at mildly basic pH could be correlated to an increase in surface hydrophobicity of the protein. To the best of our knowledge, this is the first study reporting regulation of two different activities of a chaperone protein by a pH switch.

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.

Unexpected dependence on pH of NO release from Paracoccus pantotrophus cytochrome cd1.

PubMed

Sam, Katharine A; Tolland, John D; Fairhurst, Shirley A; Higham, Christopher W; Lowe, David J; Thorneley, Roger N F; Allen, James W A; Ferguson, Stuart J

2008-07-11

A previous study of nitrite reduction by Paracoccus pantotrophus cytochrome cd(1) at pH 7.0 identified early reaction intermediates. The c-heme rapidly oxidised and nitrite was reduced to NO at the d(1)-heme. A slower equilibration of electrons followed, forming a stable complex assigned as 55% cFe(III)d(1)Fe(II)-NO and 45% cFe(II)d(1)Fe(II)-NO(+). No catalytically competent NO release was observed. Here we show that at pH 6.0, a significant proportion of the enzyme undergoes turnover and releases NO. An early intermediate, which was previously overlooked, is also identified; enzyme immediately following product release is a candidate. However, even at pH 6.0 a considerable fraction of the enzyme remains bound to NO so another component is required for full product release. The kinetically stable product formed at the end of the reaction differs significantly at pH 6.0 and 7.0, as does its rate of formation; thus the reaction is critically dependent on pH.

Differences in soil micro-eukaryotic communities over soil pH gradients are strongly driven by parasites and saprotrophs.

PubMed

Dupont, A Ö C; Griffiths, R I; Bell, T; Bass, D

2016-06-01

A recent large-scale assessment of bacterial communities across a range of UK soil types showed that bacterial community structure was strongly determined by soil pH. We analysed a data set of eukaryotic 454 sequencing 18S rDNA from the surveyed samples and showed significant differences in eukaryotic assemblages according to pH class, mostly between low pH and higher pH soils. Soil eukaryote communities (per sample) differed most at the taxonomic rank approximating to order level. Taxonomies assigned with the Protist Ribosomal Reference and the Silva 119 databases were taxonomically inconsistent, mostly due to differing 18S annotations, although general structure and composition according to pH were coherent. A relatively small number of lineages, mostly putative parasitic protists and fungi, drive most differences between pH classes, with weaker contributions from bacterivores and autotrophs. Overall, soil parasites included a large diversity of alveolates, in particular apicomplexans. Phylogenetic analysis of alveolate lineages demonstrates a large diversity of unknown gregarines, novel perkinsids, coccidians, colpodellids and uncharacterized alveolates. Other novel and/or divergent lineages were revealed across the eukaryote tree of life. Our study provides an in-depth taxonomic evaluation of micro-eukaryotic diversity, and reveals novel lineages and insights into their relationships with environmental variables across soil gradients. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Characterization of pH dependent Mn(II) oxidation strategies and formation of a bixbyite-like phase by Mesorhizobium australicum T-G1

USGS Publications Warehouse

Bohu, Tsing; Santelli, Cara M; Akob, Denise M.; Neu, Thomas R; Ciobota, Valerian; Rösch, Petra; Popp, Jürgen; Nietzsche, Sándor; Küsel, Kirsten

2015-01-01

Despite the ubiquity of Mn oxides in natural environments, there are only a few observations of biological Mn(II) oxidation at pH < 6. The lack of low pH Mn-oxidizing bacteria (MOB) isolates limits our understanding of how pH influences biological Mn(II) oxidation in extreme environments. Here, we report that a novel MOB isolate, Mesorhizobium australicum strain T-G1, isolated from an acidic and metalliferous uranium mining area, can oxidize Mn(II) at both acidic and neutral pH using different enzymatic pathways. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy revealed that T-G1 initiated bixbyite-like Mn oxide formation at pH 5.5 which coincided with multi-copper oxidase expression from early exponential phase to late stationary phase. In contrast, reactive oxygen species (ROS), particularly superoxide, appeared to be more important for T-G1 mediated Mn(II) oxidation at neutral pH. ROS was produced in parallel with the occurrence of Mn(II) oxidation at pH 7.2 from early stationary phase. Solid phase Mn oxides did not precipitate, which is consistent with the presence of a high amount of H2O2 and lower activity of catalase in the liquid culture at pH 7.2. Our results show that M. australicum T-G1, an acid tolerant MOB, can initiate Mn(II) oxidation by varying its oxidation mechanisms depending on the pH and may play an important role in low pH manganese biogeochemical cycling.

SABRE hyperpolarisation of vitamin B3 as a function of pH.

PubMed

Olaru, A M; Burns, M J; Green, G G R; Duckett, S B

2017-03-01

In this work we describe how the signal enhancements obtained through the SABRE process in methanol- d 4 solution are significantly affected by pH. Nicotinic acid (vitamin B3, NA ) is used as the agent, and changing pH is shown to modify the level of polarisation transfer by over an order of magnitude, with significant improvements being seen in terms of the signal amplitude and relaxation rate at high pH values. These observations reveal that manipulating pH to improve SABRE enhancements levels may improve the potential of this method to quantify low concentrations of analytes in mixtures. 1 H NMR spectroscopy results link this change to the form of the SABRE catalyst, which changes with pH, resulting in dramatic changes in the magnitude of the ligand exchange rates. The presented data also uses the fact that the chemical shifts of the nicotinic acids NMR resonances are affected by pH to establish that hyperpolarised 1 H-based pH mapping with SABRE is possible. Moreover, the strong polarisation transfer field dependence shown in the amplitudes of the associated higher order longitudinal terms offers significant opportunities for the rapid detection of hyperpolarised NA in H 2 O itself without solvent suppression. 1 H and 13 C MRI images of hyperpolarised vitamin B3 in a series of test phantoms are presented that show pH dependent intensity and contrast. This study therefore establishes that when the pH sensitivity of NA is combined with the increase in signal gain provided for by SABRE hyperpolarisation, a versatile pH probe results.

Characterization of pH dependent Mn(II) oxidation strategies and formation of a bixbyite-like phase by Mesorhizobium australicum T-G1.

PubMed

Bohu, Tsing; Santelli, Cara M; Akob, Denise M; Neu, Thomas R; Ciobota, Valerian; Rösch, Petra; Popp, Jürgen; Nietzsche, Sándor; Küsel, Kirsten

2015-01-01

Despite the ubiquity of Mn oxides in natural environments, there are only a few observations of biological Mn(II) oxidation at pH < 6. The lack of low pH Mn-oxidizing bacteria (MOB) isolates limits our understanding of how pH influences biological Mn(II) oxidation in extreme environments. Here, we report that a novel MOB isolate, Mesorhizobium australicum strain T-G1, isolated from an acidic and metalliferous uranium mining area, can oxidize Mn(II) at both acidic and neutral pH using different enzymatic pathways. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy revealed that T-G1 initiated bixbyite-like Mn oxide formation at pH 5.5 which coincided with multi-copper oxidase expression from early exponential phase to late stationary phase. In contrast, reactive oxygen species (ROS), particularly superoxide, appeared to be more important for T-G1 mediated Mn(II) oxidation at neutral pH. ROS was produced in parallel with the occurrence of Mn(II) oxidation at pH 7.2 from early stationary phase. Solid phase Mn oxides did not precipitate, which is consistent with the presence of a high amount of H2O2 and lower activity of catalase in the liquid culture at pH 7.2. Our results show that M. australicum T-G1, an acid tolerant MOB, can initiate Mn(II) oxidation by varying its oxidation mechanisms depending on the pH and may play an important role in low pH manganese biogeochemical cycling.

Impact of capillary flow hydrodynamics on carrier-mediated transport of opioid derivatives at the blood-brain barrier, based on pH-dependent Michaelis-Menten and Crone-Renkin analyses.

PubMed

Yusof, Siti R; Abbott, N Joan; Avdeef, Alex

2017-08-30

Most studies of blood-brain barrier (BBB) permeability and transport are conducted at a single pH, but more detailed information can be revealed by using multiple pH values. A pH-dependent biophysical model was applied to the mechanistic analysis of published pH-dependent BBB luminal uptake data from three opioid derivatives in rat: pentazocine (Suzuki et al., 2002a, 2002b), naloxone (Suzuki et al., 2010a), and oxycodone (Okura et al., 2008). Two types of data were processed: in situ brain perfusion (ISBP) and brain uptake index (BUI). The published perfusion data were converted to apparent luminal permeability values, P app , and analyzed by the pCEL-X program (Yusof et al., 2014), using the pH-dependent Crone-Renkin equation (pH-CRE) to determine the impact of cerebrovascular flow on the Michaelis-Menten transport parameters (Avdeef and Sun, 2011). For oxycodone, the ISBP data had been measured at pH7.4 and 8.4. The present analysis indicates a 7-fold lower value of the cerebrovascular flow velocity, F pf , than that expected in the original study. From the pyrilamine-inhibited data, the flow-corrected passive intrinsic permeability value was determined to be P 0 =398×10 -6 cm·s -1 . The uptake data indicate that the neutral form of oxycodone is affected by a transporter at pH8.4. The extent of the cation uptake was less certain from the available data. For pentazocine, the brain uptake by the BUI method had been measured at pH5.5, 6.5, and 7.4, in a concentration range 0.1-40mM. Under similar conditions, ISBP data were also available. The pH-CRE determined values of F pf from both methods were nearly the same, and were smaller than the expected value in the original publication. The transport of the cationic pentazocine was not fully saturated at pH5.5 at 40mM. The transport of the neutral species at pH7.4 appeared to reach saturation at 40mM pentazocine concentration, but not at 12mM. In the case of naloxone, a pH-dependent Michaelis-Menten equation (pH-MME) analysis of the data indicated a smooth sigmoidal transition from a higher capacity uptake process affecting cationic naloxone (pH5.0-7.0) to a lower capacity uptake process affecting the neutral drug (pH8.0-8.5), with cross-over point near pH7.4. Evidently, measurements at multiple pH values can reveal important information about both cerebrovascular flow and BBB transport kinetics. Copyright © 2017 Elsevier B.V. All rights reserved.

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 role of electrostatics in protein-protein interactions of a monoclonal antibody.

PubMed

Roberts, D; Keeling, R; Tracka, M; van der Walle, C F; Uddin, S; Warwicker, J; Curtis, R

2014-07-07

Understanding how protein-protein interactions depend on the choice of buffer, salt, ionic strength, and pH is needed to have better control over protein solution behavior. Here, we have characterized the pH and ionic strength dependence of protein-protein interactions in terms of an interaction parameter kD obtained from dynamic light scattering and the osmotic second virial coefficient B22 measured by static light scattering. A simplified protein-protein interaction model based on a Baxter adhesive potential and an electric double layer force is used to separate out the contributions of longer-ranged electrostatic interactions from short-ranged attractive forces. The ionic strength dependence of protein-protein interactions for solutions at pH 6.5 and below can be accurately captured using a Deryaguin-Landau-Verwey-Overbeek (DLVO) potential to describe the double layer forces. In solutions at pH 9, attractive electrostatics occur over the ionic strength range of 5-275 mM. At intermediate pH values (7.25 to 8.5), there is a crossover effect characterized by a nonmonotonic ionic strength dependence of protein-protein interactions, which can be rationalized by the competing effects of long-ranged repulsive double layer forces at low ionic strength and a shorter ranged electrostatic attraction, which dominates above a critical ionic strength. The change of interactions from repulsive to attractive indicates a concomitant change in the angular dependence of protein-protein interaction from isotropic to anisotropic. In the second part of the paper, we show how the Baxter adhesive potential can be used to predict values of kD from fitting to B22 measurements, thus providing a molecular basis for the linear correlation between the two protein-protein interaction parameters.

Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc01349f Click here for additional data file.

PubMed Central

Pastor, Ernest; Gross, Manuela A.; Selim, Shababa

2015-01-01

Photocatalytic systems for the reduction of aqueous protons are strongly pH-dependent, but the origin of this dependency is still not fully understood. We have studied the effect of different degrees of acidity on the electron transfer dynamics and catalysis taking place in a homogeneous photocatalytic system composed of a phosphonated ruthenium tris(bipyridine) dye (RuP) and a nickel bis(diphosphine) electrocatalyst (NiP) in an aqueous ascorbic acid solution. Our approach is based on transient absorption spectroscopy studies of the efficiency of photo-reduction of RuP and NiP correlated with pH-dependent photocatalytic H2 production and the degree of catalyst protonation. The influence of these factors results in an observed optimum photoactivity at pH 4.5 for the RuP–NiP system. The electron transfer from photo-reduced RuP to NiP is efficient and independent of the pH value of the medium. At pH <4.5, the efficiency of the system is limited by the yield of RuP photo-reduction by the sacrificial electron donor, ascorbic acid. At pH >4.5, the efficiency of the system is limited by the poor protonation of NiP, which inhibits its ability to reduce protons to hydrogen. We have therefore developed a rational strategy utilising transient absorption spectroscopy combined with bulk pH titration, electrocatalytic and photocatalytic experiments to disentangle the complex pH-dependent activity of the homogenous RuP–NiP photocatalytic system, which can be widely applied to other photocatalytic systems. PMID:28717491

Direct comparison of two different mesalamine formulations for the maintenance of remission in patients with ulcerative colitis: a double-blind, randomized study.

PubMed

Ito, Hiroaki; Iida, Mitsuo; Matsumoto, Takayuki; Suzuki, Yasuo; Aida, Yoshiyuki; Yoshida, Toyomitsu; Takano, Yuichi; Hibi, Toshifumi

2010-09-01

Mesalamine has been used as the first-line medication for the treatment of ulcerative colitis (UC). We directly compared the efficacy and safety of two different mesalamine formulations in the maintenance of remission in patients with UC. In a multicenter, double-blind, randomized study, 131 patients with quiescent UC were assigned to two groups: 65 to receive a pH-dependent release formulation of mesalamine at 2.4 g/day (pH-2.4 g) and 66 to receive a time-dependent release formulation of mesalamine at 2.25 g/day (Time-2.25 g). Both formulations were administered three times daily for 48 weeks. The primary endpoint was the proportion of patients without bloody stools. In the full analysis set (n = 130), the proportion of patients without bloody stools was 76.9% in the pH-2.4 g and 69.2% in the Time-2.25 g, demonstrating the noninferiority of pH-2.4 g to Time-2.25 g. No statistically significant difference in time to bloody stools was found between the two formulations (P = 0.27, log-rank test), but the time to bloody stools tended to be longer in pH-2.4 g compared to Time-2.25 g, and a similar trend was observed with regard to the time to relapse. No differences were observed between the safety profiles of the two formulations. The pH- and time-dependent release of mesalamine formulations were similarly safe and effective. Interestingly, the remission phase tended to be longer in the group that received the pH-dependent formulation compared to the group that received the time-dependent formulation (UMIN Clinical Trials Registry, no. C000000289).

Benthic metabolic feedbacks to carbonate chemistry on coral reefs:implications for ocean acidification

NASA Astrophysics Data System (ADS)

Price, N.; Rohwer, F. L.; Stuart, S. A.; Andersson, A.; Smith, J.

2012-12-01

The metabolic activity of resident organisms can cause spatio-temporal variability in carbonate chemistry within the benthic boundary layer, and thus potentially buffer the global impacts of ocean acidification. But, little is known about the capacity for particular species assemblages to contribute to natural daily variability in carbonate chemistry. We encapsulated replicate areas (~3m2) of reef across six Northern Line Islands in the central Pacific for 24 hrs to quantify feedbacks to carbonate chemistry within the benthic boundary layer from community metabolism. Underneath each 'tent', we quantified relative abundance and biomass of each species of corals and algae. We coupled high temporal resolution time series data on the natural diurnal variability in pH, dissolved oxygen, salinity, and temperature (using autonomous sensors) with resident organisms' net community calcification and productivity rates (using change in total dissolved carbon and total alkalinity over time) to examine feedbacks from reef metabolism to boundary layer carbonate chemistry. These reefs experienced large ranges in pH (> 0.2 amplitude) each day, similar to the magnitude of 'acidification' expected over the next century. Daily benthic pH, pCO2, and aragonite saturation state (Ωaragonite) were contrasted with seasonal threshold values estimated from open ocean climatological data extrapolated at each island to determine relative inter-island feedbacks. Diurnal amplitude in pH, pCO2, and Ωaragonite at each island was dependent upon the resident species assemblage of the benthos and was particularly reliant upon the biomass, productivity, and calcification rate of Halimeda. Net primary productivity of fleshy algae (algal turfs and Lobophora spp.) predominated on degraded, inhabited islands where net community calcification was negligible. In contrast, the chemistry over reefs on 'pristine', uninhabited islands was driven largely by net calcification of calcareous algae and stony corals. Knowledge about species specific physiological rates and relative abundances of key taxa whose metabolism significantly alters carbonate chemistry may give insight to the ability for a reef to buffer against or exacerbate ocean acidification.

Lead forms in urban turfgrass and forest soils as related to organic matter content and pH

Treesearch

Ian D. Yesilonis; Bruce R. James; Richard V. Pouyat; Bahram Momen

2008-01-01

Soil pH may influence speciation and extractability of Pb, depending on type of vegetation in urban soil environments. We investigated the relationship between soil pH and Pb extractability at forest and turf grass sites in Baltimore, Maryland. Our two hypotheses were: (1) due to lower pH values in forest soils, more Pb will be in exchangeable forms in forested than in...

pH-Dependent stability of azithromycin in aqueous solution and structure identification of two new degradation products.

PubMed

Saita, Maria Grazia; Aleo, Danilo; Melilli, Barbara; Mangiafico, Sergio; Cro, Melina; Sanfilippo, Claudia; Patti, Angela

2018-05-28

The degradation profile of azithromycin in buffered solutions was investigated using HPLC and found to be pH dependent in the range of 6.0-7.2. Desosaminylazitromycin, derived from hydrolytic loss of cladinose of the parent molecule, was the major degradation product at pH 6.0 but its amount progressively decreased moving toward pH 7.2. Two additional unreported degradation products were also observed and their structures were fully elucidated by MS- and NMR-spectroscopy to be associated with opening of the macrocyclic lactone ring. Copyright © 2018. Published by Elsevier B.V.

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.

Role of protein concentration and protein-saliva interactions in the astringency of whey proteins at low pH.

PubMed

Kelly, M; Vardhanabhuti, B; Luck, P; Drake, M A; Osborne, J; Foegeding, E A

2010-05-01

Whey protein beverages are adjusted to pH <4.5 to enhance clarity and stability, but this pH level is also associated with increased astringency. The goal of this investigation was to determine the effects of protein concentration on astringency and interactions between whey and salivary proteins. Whey protein beverages containing 0.25 to 13% (wt/wt) beta-lactoglobulin and 0.017% (wt/wt) sucralose at pH 2.6 to 4.2 were examined using descriptive sensory analysis. Controls were similar pH phosphate buffers at phosphate concentrations equivalent to the amount of phosphoric acid required to adjust the pH of the protein solution. Changes in astringency with protein concentration depended on pH. At pH 3.5, astringency significantly increased with protein concentration from 0.25 to 4% (wt/wt) and then remained constant from 4 to 13% (wt/wt). Conversely, at pH 2.6, astringency decreased with an increase in protein concentration [0.5-10% (wt/wt)]. This suggests a complex relationship that includes pH and buffering capacity of the beverages. Furthermore, saliva flow rates increased with increasing protein concentrations, showing that the physiological conditions in the mouth change with protein concentration. Maximum turbidity of whey protein-saliva mixtures was observed between pH 4.6 and 5.2. Both sensory evaluation and in vitro study of interactions between beta-LG and saliva indicate that astringency of whey proteins is a complex process determined by the extent of aggregation occurring in the mouth, which depends on the whey protein beverage pH and buffering capacity in addition to saliva flow rate. Copyright 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Transcription of the pst Operon of Clostridium acetobutylicum Is Dependent on Phosphate Concentration and pH

PubMed Central

Fischer, Ralf-Jörg; Oehmcke, Sonja; Meyer, Uta; Mix, Maren; Schwarz, Katrin; Fiedler, Tomas; Bahl, Hubert

2006-01-01

The pst operon of Clostridium acetobutylicum ATCC 824 comprises five genes, pstS, pstC, pstA, pstB, and phoU, and shows a gene architecture identical to that of Escherichia coli. Deduced proteins are predicted to represent a high-affinity phosphate-specific ABC (ATP-binding cassette) transport system (Pst) and a protein homologous to PhoU, a negative phosphate regulon regulator. We analyzed the expression patterns of the pst operon in Pi-limited chemostat cultures during acid production at pH 5.8 or solvent production at pH 4.5 and in response to Pi pulses. Specific mRNA transcripts were found only when external Pi concentrations had dropped below 0.2 mM. Two specific transcripts were detected, a 4.7-kb polycistronic mRNA spanning the whole operon and a quantitatively dominating 1.2-kb mRNA representing the first gene, pstS. The mRNA levels clearly differed depending on the external pH. The amounts of the full-length mRNA detected were about two times higher at pH 5.8 than at pH 4.5. The level of pstS mRNA increased by a factor of at least 8 at pH 5.8 compared to pH 4.5 results. Primer extension experiments revealed only one putative transcription start point 80 nucleotides upstream of pstS. Thus, additional regulatory sites are proposed in the promoter region, integrating two different extracellular signals, namely, depletion of inorganic phosphate and the pH of the environment. After phosphate pulses were applied to a phosphate-limited chemostat we observed faster phosphate consumption at pH 5.8 than at pH 4.5, although higher optical densities were recorded at pH 4.5. PMID:16855236

Chemical modification and pH dependence of kinetic parameters to identify functional groups in a glucosyltransferase from Strep. Mutans

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

Bell, J.E.; Leone, A.; Bell, E.T.

1986-05-01

A glucosyltransferase, forming a predominantly al-6 linked glucan, was partially purified from the culture filtrate of S. mutans GS-5. The kinetic properties of the enzyme, assessed using the transfer of /sup 14/C glucose from sucrose into total glucan, were studied at pH values from pH 3.5 to 6.5. From the dependence of km on pH, a group with pKa = 5.5 must be protonated to maximize substrate binding. From plots of V/sub max/ vs pH two groups, with pKa's of 4.5 and 5.5 were indicated. The results suggest the involvement of either two carboxyl groups (one protonated, one unprotonated inmore » the native enzyme) or a carboxyl group (unprotonated) and some other protonated group such as histidine, cysteine. Chemical modification studies showed that Diethylyrocarbonate (histidine specific) had no effect on enzyme activity while modification with p-phydroxy-mercuribenzoate or iodoacetic acid (sulfhydryl reactive) and carbodimide reagents (carboxyl specific) resulted in almost complete inactivation. Activity loss was dependent upon time of incubation and reagent concentration. The disaccharide lylose, (shown to be an inhibitor of the enzyme with similar affinity to sucrose) offers no protection against modification by the sulfhydryl reactive reagents.« less

AnilinoMethylRhodamines: pH Sensitive Probes with Tunable Photophysical Properties by Substituent Effect

PubMed Central

Best, Quinn A.; Liu, Chuangjun; van Hoveln, Paul D.; McCarroll, Matthew E.

2013-01-01

A series of pH dependent rhodamine analogs possessing an anilino-methyl moiety was developed and shown to exhibit a unique photophysical response to pH. These Anilinomethylrhodamines (AnMR) maintain a colorless, non-fluorescent spiro-cyclic structure at high pH. The spiro-cyclic structures open in mildly acidic conditions and are weakly fluorescent; however at very low pH, the fluorescence is greatly enhanced. The equilibrium constants of these processes show a linear response to substituent effects, which was demonstrated by the Hammett equation. PMID:24050117

Sequence dependent N-terminal rearrangement and degradation of peptide nucleic acid (PNA) in aqueous solution

NASA Technical Reports Server (NTRS)

Eriksson, M.; Christensen, L.; Schmidt, J.; Haaima, G.; Orgel, L.; Nielsen, P. E.

1998-01-01

The stability of the PNA (peptide nucleic acid) thymine monomer inverted question markN-[2-(thymin-1-ylacetyl)]-N-(2-aminoaminoethyl)glycine inverted question mark and those of various PNA oligomers (5-8-mers) have been measured at room temperature (20 degrees C) as a function of pH. The thymine monomer undergoes N-acyl transfer rearrangement with a half-life of 34 days at pH 11 as analyzed by 1H NMR; and two reactions, the N-acyl transfer and a sequential degradation, are found by HPLC analysis to occur at measurable rates for the oligomers at pH 9 or above. Dependent on the amino-terminal sequence, half-lives of 350 h to 163 days were found at pH 9. At pH 12 the half-lives ranged from 1.5 h to 21 days. The results are discussed in terms of PNA as a gene therapeutic drug as well as a possible prebiotic genetic material.

Selective Electrocatalytic Reduction of Nitrite to Dinitrogen Based on Decoupled Proton-Electron Transfer.

PubMed

He, Daoping; Li, Yamei; Ooka, Hideshi; Go, Yoo Kyung; Jin, Fangming; Kim, Sun Hee; Nakamura, Ryuhei

2018-02-14

The development of denitrification catalysts which can reduce nitrate and nitrite to dinitrogen is critical for sustaining the nitrogen cycle. However, regulating the selectivity has proven to be a challenge, due to the difficulty of controlling complex multielectron/proton reactions. Here we report that utilizing sequential proton-electron transfer (SPET) pathways is a viable strategy to enhance the selectivity of electrochemical reactions. The selectivity of an oxo-molybdenum sulfide electrocatalyst toward nitrite reduction to dinitrogen exhibited a volcano-type pH dependence with a maximum at pH 5. The pH-dependent formation of the intermediate species (distorted Mo(V) oxo species) identified using operando electron paramagnetic resonance (EPR) and Raman spectroscopy was in accord with a mathematical prediction that the pK a of the reaction intermediates determines the pH-dependence of the SPET-derived product. By utilizing this acute pH dependence, we achieved a Faradaic efficiency of 13.5% for nitrite reduction to dinitrogen, which is the highest value reported to date under neutral conditions.

Effect of dissolved oxygen concentration (microaerobic and aerobic) on selective enrichment culture for bioaugmentation of acidic industrial wastewater.

PubMed

Quan, Ying; Han, Hui; Zheng, Shaokui

2012-09-01

The successful application of bioaugmentation is largely dependent on the selective enrichment of culture with regards to pH, temperature, salt, or specific toxic organic pollutants. In this study, we investigated the effect of dissolved oxygen (DO) concentrations (aerobic, >2 mg L(-1); microaerobic, <1 mg L(-1)) on yeast enrichment culture for bioaugmentation of acidic industrial wastewater (pH 3.9-4.7). Clone library analyses revealed that the yeast community shifted in response to different DO levels, and that Candida humilis and Candida pseudolambica were individually dominant in the aerobic and microaerobic enrichment cultures. This would significantly influence the isolation results, and further hinder bioaugmentation due to differences in DO environments during the enrichment and application periods. However, differences in the selective enrichment culture cannot be predicted based on differences in pollutant removal performance. Thus, DO concentrations (aerobic/microaerobic) should be considered a secondary selective pressure to achieve successful bioaugmentation. Copyright © 2012 Elsevier Ltd. All rights reserved.

Coral calcification in a changing World and the interactive dynamics of pH and DIC upregulation

NASA Astrophysics Data System (ADS)

McCulloch, Malcolm T.; D'Olivo, Juan Pablo; Falter, James; Holcomb, Michael; Trotter, Julie A.

2017-05-01

Coral calcification is dependent on the mutualistic partnership between endosymbiotic zooxanthellae and the coral host. Here, using newly developed geochemical proxies (δ11B and B/Ca), we show that Porites corals from natural reef environments exhibit a close (r2 ~0.9) antithetic relationship between dissolved inorganic carbon (DIC) and pH of the corals' calcifying fluid (cf). The highest DICcf (~ × 3.2 seawater) is found during summer, consistent with thermal/light enhancement of metabolically (zooxanthellae) derived carbon, while the highest pHcf (~8.5) occurs in winter during periods of low DICcf (~ × 2 seawater). These opposing changes in DICcf and pHcf are shown to maintain oversaturated but stable levels of carbonate saturation (Ωcf ~ × 5 seawater), the key parameter controlling coral calcification. These findings are in marked contrast to artificial experiments and show that pHcf upregulation occurs largely independent of changes in seawater carbonate chemistry, and hence ocean acidification, but is highly vulnerable to thermally induced stress from global warming.

Room Temperature Co-Precipitation Synthesis of Magnetite Nanoparticles in a Large pH Window with Different Bases.

PubMed

Mascolo, Maria Cristina; Pei, Yongbing; Ring, Terry A

2013-11-28

Magnetite nanoparticles (Fe₃O₄) represent the most promising materials in medical applications. To favor high-drug or enzyme loading on the nanoparticles, they are incorporated into mesoporous materials to form a hybrid support with the consequent reduction of magnetization saturation. The direct synthesis of mesoporous structures appears to be of interest. To this end, magnetite nanoparticles have been synthesized using a one pot co-precipitation reaction at room temperature in the presence of different bases, such as NaOH, KOH or (C₂H₅)₄NOH. Magnetite shows characteristics of superparamagnetism at room temperature and a saturation magnetization (Ms) value depending on both the crystal size and the degree of agglomeration of individual nanoparticles. Such agglomeration appears to be responsible for the formation of mesoporous structures, which are affected by the pH, the nature of alkali, the slow or fast addition of alkaline solution and the drying modality of synthesized powders.

Optimization of Nutrients and Culture Conditions for Alkaline Protease Production Using Two Endophytic Micrococci: Micrococcus aloeverae and Micrococcus yunnanensis.

PubMed

Prakash, Om; Nimonkar, Yogesh; Chavadar, Mahesh S; Bharti, Nidhi; Pawar, Shrikant; Sharma, Ashutosh; Shouche, Yogesh S

2017-06-01

An endophytic species of Micrococcus was isolated from Aloe vera leaf (syn. Aloe barbadensis ) and screened for protease production with five other species of Micrococcus . Data indicated that endophytic Micrococcus aloeverae AE-6 MCC 2184 T and Micrococcus yunnanensis DSM 21948 T showed efficient protease production potential and secreted active protease at high salt (10%), temperature (40 °C) and in wide range of pH 8-10. Unlike M . yunnanensis DSM 21948 T , protease production by M . aloeverae AE-6 MCC 2184 T was stringently controlled by pH. Protease induction study using different group of peptides, peptide carbohydrates and peptide macronutrient combinations showed variable response with both the organisms. Result indicated that the amount of protease was not directly related to cell biomass but it depends on nature of inducible peptides. In this study we also developed a modified agar-well assay for semi-quantitative data from large number of replicates.

Leaching behaviour of incineration bottom ash in a reuse scenario: 12years-field data vs. lab test results.

PubMed

Di Gianfilippo, Martina; Hyks, Jiri; Verginelli, Iason; Costa, Giulia; Hjelmar, Ole; Lombardi, Francesco

2018-03-01

Several types of standardized laboratory leaching tests have been developed during the past few decades to evaluate the leaching behaviour of waste materials as a function of different parameters, such as the pH of the eluate and the liquid to solid ratio. However, the link between the results of these tests and leaching data collected from the field (e.g. in disposal or reuse scenarios) is not always straightforward. In this work, we compare data obtained from an on-going large scale field trial, in which municipal solid waste incineration bottom ash is being tested as road sub-base material, with the results obtained from percolation column and pH-dependence laboratory leaching tests carried out on the bottom ash at the beginning of the test. The comparisons reported in this paper show that for soluble substances (e.g. Cl, K and SO 4 ), percolation column tests can provide a good indication of the release expected in the field with deviations usually within a factor of 3. For metals characterized by a solubility-controlled release, i.e. that depends more on eluate pH than the liquid to solid ratio applied, the results of pH-dependence tests describe more accurately the eluate concentration trends observed in the field with deviations that in most cases (around 80%) are within one order of magnitude (see e.g. Al and Cd). The differences between field and lab-scale data might be in part ascribed to the occurrence in the field of weathering reactions (e.g. carbonation) but also to microbial decomposition of organic matter that modifying leachate pH affect the solubility of several constituents (e.g. Ca, Ba and Cr). Besides, weathering reactions can result in enhanced adsorption of fulvic acids to iron/aluminum (hydr)oxides, leading to a decrease in the leaching of fulvic acids and hence of elements such as Cu, Ni and Pb that strongly depend on DOC leaching. Overall, this comparison shows that percolation column tests and pH-dependence tests can represent a reliable screening tool to derive data that could be employed in risk-based analysis or life cycle assessment (LCA) frameworks for evaluating potential environmental impacts deriving from specific disposal/reuse options for waste materials. Copyright © 2017 Elsevier Ltd. All rights reserved.

Development of gastro intestinal sustained release tablet formulation containing acryl-EZE and pH-dependent swelling HPMC K 15 M.

PubMed

Lamoudi, Lynda; Chaumeil, Jean Claude; Daoud, Kamel

2012-05-01

The aim of this study was to evaluate physical properties and release from matrix tablets containing different ratios of HPMC 15 M and Acryl-EZE. A further aim is to assess their suitability for pH dependent controlled release. Matrix tablets containing HPMC 15 M and Acryl-EZE were manufactured using a fluidized bed. The release from this matrix using Sodium Diclofenac (SD) as model drug is studied in two dissolution media (0.1 N HCl or pH = 6.8 phosphate buffer solution); the release rate, mechanism, and pH dependence were characterized by fitting four kinetic models and by using a similarity factor analysis. The obtained results revealed that the presence of Acryl-EZE in the matrix tablets is effective in protecting the dosage forms from release in acid environments such as gastric fluid. In pH = 6.8 phosphate buffer, the drug release rate and mechanism of release from all matrices is mainly controlled by HPMC 15 M. The model of Korsmeyer-Peppas was found to fit experimental dissolution results.

A Dual-Mode Large-Arrayed CMOS ISFET Sensor for Accurate and High-Throughput pH Sensing in Biomedical Diagnosis.

PubMed

Huang, Xiwei; Yu, Hao; Liu, Xu; Jiang, Yu; Yan, Mei; Wu, Dongping

2015-09-01

The existing ISFET-based DNA sequencing detects hydrogen ions released during the polymerization of DNA strands on microbeads, which are scattered into microwell array above the ISFET sensor with unknown distribution. However, false pH detection happens at empty microwells due to crosstalk from neighboring microbeads. In this paper, a dual-mode CMOS ISFET sensor is proposed to have accurate pH detection toward DNA sequencing. Dual-mode sensing, optical and chemical modes, is realized by integrating a CMOS image sensor (CIS) with ISFET pH sensor, and is fabricated in a standard 0.18-μm CIS process. With accurate determination of microbead physical locations with CIS pixel by contact imaging, the dual-mode sensor can correlate local pH for one DNA slice at one location-determined microbead, which can result in improved pH detection accuracy. Moreover, toward a high-throughput DNA sequencing, a correlated-double-sampling readout that supports large array for both modes is deployed to reduce pixel-to-pixel nonuniformity such as threshold voltage mismatch. The proposed CMOS dual-mode sensor is experimentally examined to show a well correlated pH map and optical image for microbeads with a pH sensitivity of 26.2 mV/pH, a fixed pattern noise (FPN) reduction from 4% to 0.3%, and a readout speed of 1200 frames/s. A dual-mode CMOS ISFET sensor with suppressed FPN for accurate large-arrayed pH sensing is proposed and demonstrated with state-of-the-art measured results toward accurate and high-throughput DNA sequencing. The developed dual-mode CMOS ISFET sensor has great potential for future personal genome diagnostics with high accuracy and low cost.

Towards label-free and site-specific probing of the local pH in proteins: pH-dependent deep UV Raman spectra of histidine and tyrosine

NASA Astrophysics Data System (ADS)

Bröermann, Andreas; Steinhoff, Heinz-Jürgen; Schlücker, Sebastian

2014-09-01

The site-specific pH is an experimental probe for assessing models of structural folding and function of a protein as well as protein-protein and protein-ligand interactions. It can be determined by various techniques such as NMR, FT-IR, fluorescence and EPR spectroscopy. The latter require the use of external labels, i.e., employ pH-dependent dyes and spin labels, respectively. In this contribution, we outline an approach to a label-free and site-specific method for determining the local pH using deep ultraviolet resonance Raman (UVRR) spectroscopic fingerprints of the aromatic amino acids histidine and tyrosine in combination with a robust algorithm that determines the pH value using three UVRR reference spectra and without prior knowledge of the pKa.

Effects of pH and Oxygen on Photosynthetic Reactions of Intact Chloroplasts 1

PubMed Central

Heber, Ulrich; Andrews, T. John; Boardman, N. Keith

1976-01-01

Oxygen inhibition of photosynthesis was studied with intact spinach (Spinacia oleracea L.) chloroplasts which exhibited very high rates of photosynthetic CO2 reduction and were insensitive to additions of photosynthetic intermediates when CO2 was available at saturating concentrations. Photosynthetic rates were measured polarographically as O2 evolution, and the extent of the reduction of substrate was estimated from the amount of O2 evolved. With CO2 as substrate, inhibition of photosynthesis by O2 was dependent on pH. At pH values above 8, rates of O2 evolution were strongly inhibited by O2 and only a fraction of the added bicarbonate was reduced before O2 evolution ceased. The extent of O2 evolution declined with increasing O2 concentration and decreasing initial bicarbonate concentration. At pH 7.2, the initial photosynthetic rate was inhibited about 30% at high O2 levels, but the extent of O2 evolution was unaffected and most of the added bicarbonate was reduced. Photosynthetic O2 evolution with 3-phosphoglycerate as substrate was similarly dependent on pH and O2 concentration. In contrast, there was little effect of O2 and pH on oxaloacetate-dependent oxygen evolution. Acid-base shift experiments with osmotically shocked chloroplasts showed that ATP formation was not affected by O2. The results are discussed in terms of a balance between photosynthetic O2 evolution and O2 consumption by the ribulose diphosphate oxygenase reaction. PMID:16659466

Light-dependent delta pH and membrane potential changes in halobacterial vesicles coupled to sodium transport

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

Kamo, N.; Racanelli, T.; Packer, L.

1982-01-01

Bacteriorhodopsin and Halorhodopsin present in Halobacterium halobium strains have been investigated in relation to Na/sup +//H/sup +/ exchange in isolated cell envelope vesicles. Upon illumination, these retinal proteins result in extrusion of sodium ions by either an electrogenic Na/sup +//Ha/sup +/ antiporter and/or a direct sodium pump. Since a molecular characterization of these mechanism(s) of sodium extrusion has not yet been realized, it was of interest to measure directly the light- and sodium-dependent changes in delta pH and membrane potential under nearly identical conditions in S9 and R1mR cell membrane vesicles to gain information on the relation of these retinalmore » proteins to sodium extrusion. These activities were evaluated in terms of their dependence on light intensity, and on the inhibitory effect of chemical modifiers of carboxyl groups (carbodiimides); electroneutral exchanges (monensin and triphenyltin); digitoxin and some analogues; and phloretin. Under most of the conditions and treatments employed, light- and sodium-dependent delta pH led to similar effects in both membrane vesicle types. Hence, it is concluded that the delta pH and delta psi which arise from sodium transport occur by either a single mechanism or by one which shares common features.« less

Application of core-shell-structured CdTe@SiO2 quantum dots synthesized via a facile solution method for improving latent fingerprint detection

NASA Astrophysics Data System (ADS)

Gao, Feng; Han, Jiaxing; Lv, Caifeng; Wang, Qin; Zhang, Jun; Li, Qun; Bao, Liru; Li, Xin

2012-10-01

Fingerprint detection is important in criminal investigation. This paper reports a facile powder brushing technique for improving latent fingerprint detection using core-shell-structured CdTe@SiO2 quantum dots (QDs) as fluorescent labeling marks. Core-shell-structured CdTe@SiO2 QDs are prepared via a simple solution-based approach using NH2NH2·H2O as pH adjustor and stabilizer, and their application for improving latent fingerprint detection is explored. The obtained CdTe@SiO2 QDs show spherical shapes with well-defined core-shell structures encapsulating different amounts of QDs depending on the type of the pH adjustor and stabilizer. Moreover, the fluorescence of CdTe@SiO2 QDs is largely enhanced by surface modification of the SiO2 shell. The CdTe@SiO2 QDs overcome the oxidation problem of pure CdTe QDs in air, thus affording better variability with strong adhesive ability, better resolution, and bright emission colors for practical application in latent fingerprint detection. In comparison with the conventional fluorescence powders, silver powders, and others, the effectiveness of CdTe@SiO2 QD powders for detection of latent fingerprints present on a large variety of object surfaces is greatly improved. The synthesis method for CdTe@SiO2 QDs is simple, cheap, and easy for large-scale production, and thus offers many advantages in the practical application of fingerprint detection.

A Virtual Mixture Approach to the Study of Multistate Equilibrium: Application to Constant pH Simulation in Explicit Water

PubMed Central

Wu, Xiongwu; Brooks, Bernard R.

2015-01-01

Chemical and thermodynamic equilibrium of multiple states is a fundamental phenomenon in biology systems and has been the focus of many experimental and computational studies. This work presents a simulation method to directly study the equilibrium of multiple states. This method constructs a virtual mixture of multiple states (VMMS) to sample the conformational space of all chemical states simultaneously. The VMMS system consists of multiple subsystems, one for each state. The subsystem contains a solute and a solvent environment. The solute molecules in all subsystems share the same conformation but have their own solvent environments. Transition between states is implicated by the change of their molar fractions. Simulation of a VMMS system allows efficient calculation of relative free energies of all states, which in turn determine their equilibrium molar fractions. For systems with a large number of state transition sites, an implicit site approximation is introduced to minimize the cost of simulation. A direct application of the VMMS method is for constant pH simulation to study protonation equilibrium. Applying the VMMS method to a heptapeptide of 3 ionizable residues, we calculated the pKas of those residues both with all explicit states and with implicit sites and obtained consistent results. For mouse epidermal growth factor of 9 ionizable groups, our VMMS simulations with implicit sites produced pKas of all 9 ionizable groups and the results agree qualitatively with NMR measurement. This example demonstrates the VMMS method can be applied to systems of a large number of ionizable groups and the computational cost scales linearly with the number of ionizable groups. For one of the most challenging systems in constant pH calculation, SNase Δ+PHS/V66K, our VMMS simulation shows that it is the state-dependent water penetration that causes the large deviation in lysine66’s pKa. PMID:26506245

A Virtual Mixture Approach to the Study of Multistate Equilibrium: Application to Constant pH Simulation in Explicit Water.

PubMed

Wu, Xiongwu; Brooks, Bernard R

2015-10-01

Chemical and thermodynamic equilibrium of multiple states is a fundamental phenomenon in biology systems and has been the focus of many experimental and computational studies. This work presents a simulation method to directly study the equilibrium of multiple states. This method constructs a virtual mixture of multiple states (VMMS) to sample the conformational space of all chemical states simultaneously. The VMMS system consists of multiple subsystems, one for each state. The subsystem contains a solute and a solvent environment. The solute molecules in all subsystems share the same conformation but have their own solvent environments. Transition between states is implicated by the change of their molar fractions. Simulation of a VMMS system allows efficient calculation of relative free energies of all states, which in turn determine their equilibrium molar fractions. For systems with a large number of state transition sites, an implicit site approximation is introduced to minimize the cost of simulation. A direct application of the VMMS method is for constant pH simulation to study protonation equilibrium. Applying the VMMS method to a heptapeptide of 3 ionizable residues, we calculated the pKas of those residues both with all explicit states and with implicit sites and obtained consistent results. For mouse epidermal growth factor of 9 ionizable groups, our VMMS simulations with implicit sites produced pKas of all 9 ionizable groups and the results agree qualitatively with NMR measurement. This example demonstrates the VMMS method can be applied to systems of a large number of ionizable groups and the computational cost scales linearly with the number of ionizable groups. For one of the most challenging systems in constant pH calculation, SNase Δ+PHS/V66K, our VMMS simulation shows that it is the state-dependent water penetration that causes the large deviation in lysine66's pKa.

Evolution of the chemistry of Fe bearing waters during CO2 degassing

USGS Publications Warehouse

Geroni, J.N.; Cravotta, C.A.; Sapsford, D.J.

2012-01-01

The rates of Fe(II) oxidation and precipitation from groundwater are highly pH dependent. Elevated levels of dissolved CO2 can depress pH and cause difficulty in removing dissolved Fe and associated metals during treatment of ferruginous water. This paper demonstrates interdependent changes in pH, dissolved inorganic C species, and Fe(II) oxidation rates that occur as a result of the removal (degassing) of CO2 during aeration of waters discharged from abandoned coal mines. The results of field monitoring of aeration cascades at a treatment facility as well as batchwise aeration experiments conducted using net alkaline and net acidic waters in the UK are combined with geochemical modelling to demonstrate the spatial and temporal evolution of the discharge water chemistry. The aeration cascades removed approximately 67% of the dissolved CO2 initially present but varying the design did not affect the concentration of Fe(II) leaving the treatment ponds. Continued removal of the residual CO2 by mechanical aeration increased pH by as much as 2 units and resulted in large increases in the rates of Fe(II) oxidation and precipitation. Effective exsolution of CO2 led to a reduction in the required lime dose for removal of remaining Fe(II), a very important factor with regard to increasing the sustainability of treatment practices. An important ancillary finding for passive treatment is that varying the design of the cascades had little impact on the rate of CO2 removal at the flow rates measured.

Effect of adding acid solution on setting time and compressive strength of high calcium fly ash based geopolymer

NASA Astrophysics Data System (ADS)

Antoni, Herianto, Jason Ghorman; Anastasia, Evelin; Hardjito, Djwantoro

2017-09-01

Fly ash with high calcium oxide content when used as the base material in geopolymer concrete could cause flash setting or rapid hardening. However, it might increase the compressive strength of geopolymer concrete. This rapid hardening could cause problems if the geopolymer concrete is used on a large scale casting that requires a long setting time. CaO content can be indicated by pH values of the fly ash, while higher pH is correlated with the rapid setting time of fly ash-based geopolymer. This study investigates the addition of acid solution to reduce the initial pH of the fly ash and to prolong the setting time of the mixture. The acids used in this study are hydrochloric acid (HCl), sulfuric acid (H2 SO4), nitric acid (HNO3) and acetic acid (CH3 COOH). It was found that the addition of acid solution in fly ash was able to decrease the initial pH of fly ash, however, the initial setting time of geopolymer was not reduced. It was even faster than that of the control mixture. The acid type causes various influence, depending on the fly ash properties. In addition, the use of acid solution in fly ash reduces the compressive strength of geopolymer mortar. It is concluded that the addition of acid solution cannot prolong the rapid hardening of high calcium fly ash geopolymer, and it causes adverse effect on the compressive strength.

Mussel-inspired polydopamine biopolymer decorated with magnetic nanoparticles for multiple pollutants removal.

PubMed

Zhang, Shengxiao; Zhang, Yuanyuan; Bi, Guoming; Liu, Junshen; Wang, Zhigang; Xu, Qiang; Xu, Hui; Li, Xiaoyan

2014-04-15

The polydopamine polymer decorated with magnetic nanoparticles (Fe3O4/PDA) was synthesized and applied for removal of multiple pollutants. The resulted Fe3O4/PDA was characterized with elemental analysis, thermo-gravimetric analyses, vibrating sample magnetometer, high resolution transmission electron microscope, Fourier transform infrared spectra, and X-ray photoelectron spectroscopy. The self-polymerization of dopamine could be completed within 8h, and Fe3O4 nanoparticles were embedded into PDA polymer. Superparamagnetism and large saturation magnetization facilitated collection of sorbents with a magnet. Based on the catechol and amine groups, the PDA polymer provided multiple interactions to combine with pollutants. To investigate the adsorption ability of Fe3O4/PDA, heavy metal ions and dyes were selected as target pollutants. The adsorption of pollutants was pH dependent due to the variation of surface charges at different solution pH. The removal efficiencies of cation pollutants enhanced with solution pH increasing, and that of anion pollutant was just the opposite. Under the optimal solution pH, the maximum adsorption capacity calculated from Langmuir adsorption isotherm for methylene blue, tartrazine, Cu(2+), Ag(+), and Hg(2+) were 204.1, 100.0, 112.9, 259.1, and 467.3 mg g(-1), respectively. The Fe3O4/PDA shows great potential for multiple pollutants removal, and this study is the first application of PDA polymer in environmental remediation. Copyright © 2014 Elsevier B.V. All rights reserved.

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.

A comparative review of cutaneous pH.

PubMed

Matousek, Jennifer L; Campbell, Karen L

2002-12-01

This review describes the role of pH in cutaneous structure and function. We first describe the molecules that contribute to the acidity or alkalinity of the skin. Next, differences in cutaneous pH among species, among individuals of the same species and within individuals are described. The potential functions of cutaneous pH in normal and diseased skin are analysed. For example, cutaneous pH has a role in the selection and maintenance of the normal cutaneous microbiota. In addition, cutaneous acidity may protect the skin against infection by microbes. Finally, there is evidence that a cutaneous pH gradient activates pH-dependent enzymes involved in the process of keratinization.

Ligand Accessibility and Bioactivity of a Hormone-Dendrimer Conjugate Depend on pH and pH History

PubMed Central

Kim, Sung Hoon; Madak-Erdogan, Zeynep; Bae, Sung Chul; Carlson, Kathryn E.; Mayne, Christopher G.; Granick, Steve; Katzenellenbogen, Benita S.; Katzenellenbogen, John A.

2016-01-01

Estrogen conjugates with a polyamidoamine (PAMAM) dendrimer have shown remarkably selective regulation of the non-genomic actions of estrogens in target cells. In response to pH changes, however, these estrogen-dendrimer conjugates (EDCs) display a major morphological transition that alters the accessibility of the estrogen ligands that compromises the bioactivity of the EDC. A sharp break in dynamic behavior near pH 7 occurs for three different ligands on the surface of a PAMAM-G6 dendrimer: a fluorophore (tetramethylrhodamine, TMR) and two estrogens (17α-ethynylestradiol and diphenolic acid). Collisional quenching and time-resolved fluorescence anisotropy experiments with TMR-PAMAM reveal high ligand shielding above pH 7 and low shielding below pH 7. Furthermore, when pH was cycled from 8.5 (conditions of ligand-PAMAM conjugation) to 4.5 (e.g., endosome/lysosome) and through 6.5 (e.g., hypoxic environment) back to pH 8.5, the 17α-ethynylestradiol and diphenolic acid PAMAM conjugates experience a dramatic, irreversible loss in cell stimulatory activity; dynamic NMR studies indicate that the hormonal ligands had become occluded within the more hydrophobic core of the PAMAM dendrimer. Thus, the active state of these estrogen-dendrimer conjugates appears to be metastable. This pH-dependent irreversible masking of activity is of considerable relevance to the design of drug conjugates with amine-bearing PAMAM dendrimers. PMID:26186415

Sensitive SERS-pH sensing in biological media using metal carbonyl functionalized planar substrates.

PubMed

Kong, Kien Voon; Dinish, U S; Lau, Weber Kam On; Olivo, Malini

2014-04-15

Conventional nanoparticle based Surface enhanced Raman scattering (SERS) technique for pH sensing often fails due to the aggregation of particles when detecting in acidic medium or biosamples having high ionic strength. Here, We develop SERS based pH sensing using a novel Raman reporter, arene chromium tricarbonyl linked aminothiophenol (Cr(CO)3-ATP), functionalized onto a nano-roughened planar substrates coated with gold. Unlike the SERS spectrum of the ATP molecule that dominates in the 400-1700 cm(-1) region, which is highly interfered by bio-molecules signals, metal carbonyl-ATP (Cr(CO)3)-ATP) offers the advantage of monitoring the pH dependent strong CO stretching vibrations in the mid-IR (1800-2200 cm(-1)) range. Raman signal of the CO stretching vibrations at ~1820 cm(-1) has strong dependency on the pH value of the environment, where its peak undergo noticeable shift as the pH of the medium is varied from 3.0 to 9.0. The sensor showed better sensitivity in the acidic range of the pH. We also demonstrate the pH sensing in a urine sample, which has high ionic strength and our data closely correlate to the value obtained from conventional sensor. In future, this study may lead to a sensitive chip based pH sensing platform in bio-fluids for the early diagnosis of diseases. © 2013 Published by Elsevier B.V.

Participation of intracellular and extracellular pH changes in photosynthetic response development induced by variation potential in pumpkin seedlings.

PubMed

Sherstneva, O N; Vodeneev, V A; Katicheva, L A; Surova, L M; Sukhov, V S

2015-06-01

Electrical signals presented in plants by action potential and by variation potential (VP) can induce a reversible inactivation of photosynthesis. Changes in the intracellular and extracellular pH during VP generation are a potential mechanism of photosynthetic response induction; however, this hypothesis requires additional experimental investigation. The purpose of the present work was to analyze the influence of pH changes on induction of the photosynthetic response in pumpkin. It was shown that a burning of the cotyledon induced VP propagation into true leaves of pumpkin seedlings inducing a decrease in the photosynthetic CO2 assimilation and an increase in non-photochemical quenching of fluorescence, whereas respiration was activated insignificantly. The photosynthetic response magnitude depended linearly on the VP amplitude. The intracellular and extracellular concentrations of protons were analyzed using pH-sensitive fluorescent probes, and the VP generation was shown to be accompanied by apoplast alkalization (0.4 pH unit) and cytoplasm acidification (0.3 pH unit). The influence of changes in the incubation medium pH on the non-photochemical quenching of fluorescence of isolated chloroplasts was also investigated. It was found that acidification of the medium stimulated the non-photochemical quenching, and the magnitude of this increase depended on the decrease in pH. Our results confirm the contribution of changes in intracellular and extracellular pH to induction of the photosynthetic response caused by VP. Possible mechanisms of the influence of pH changes on photosynthesis are discussed.

The chemistry, physiology and pathology of pH in cancer

PubMed Central

Swietach, Pawel; Vaughan-Jones, Richard D.; Harris, Adrian L.; Hulikova, Alzbeta

2014-01-01

Cell survival is conditional on the maintenance of a favourable acid–base balance (pH). Owing to intensive respiratory CO2 and lactic acid production, cancer cells are exposed continuously to large acid–base fluxes, which would disturb pH if uncorrected. The large cellular reservoir of H+-binding sites can buffer pH changes but, on its own, is inadequate to regulate intracellular pH. To stabilize intracellular pH at a favourable level, cells control trans-membrane traffic of H+-ions (or their chemical equivalents, e.g. ) using specialized transporter proteins sensitive to pH. In poorly perfused tumours, additional diffusion-reaction mechanisms, involving carbonic anhydrase (CA) enzymes, fine-tune control extracellular pH. The ability of H+-ions to change the ionization state of proteins underlies the exquisite pH sensitivity of cellular behaviour, including key processes in cancer formation and metastasis (proliferation, cell cycle, transformation, migration). Elevated metabolism, weakened cell-to-capillary diffusive coupling, and adaptations involving H+/H+-equivalent transporters and extracellular-facing CAs give cancer cells the means to manipulate micro-environmental acidity, a cancer hallmark. Through genetic instability, the cellular apparatus for regulating and sensing pH is able to adapt to extracellular acidity, driving disease progression. The therapeutic potential of disturbing this sequence by targeting H+/H+-equivalent transporters, buffering or CAs is being investigated, using monoclonal antibodies and small-molecule inhibitors. PMID:24493747

The chemistry, physiology and pathology of pH in cancer.

PubMed

Swietach, Pawel; Vaughan-Jones, Richard D; Harris, Adrian L; Hulikova, Alzbeta

2014-03-19

Cell survival is conditional on the maintenance of a favourable acid-base balance (pH). Owing to intensive respiratory CO2 and lactic acid production, cancer cells are exposed continuously to large acid-base fluxes, which would disturb pH if uncorrected. The large cellular reservoir of H(+)-binding sites can buffer pH changes but, on its own, is inadequate to regulate intracellular pH. To stabilize intracellular pH at a favourable level, cells control trans-membrane traffic of H(+)-ions (or their chemical equivalents, e.g. ) using specialized transporter proteins sensitive to pH. In poorly perfused tumours, additional diffusion-reaction mechanisms, involving carbonic anhydrase (CA) enzymes, fine-tune control extracellular pH. The ability of H(+)-ions to change the ionization state of proteins underlies the exquisite pH sensitivity of cellular behaviour, including key processes in cancer formation and metastasis (proliferation, cell cycle, transformation, migration). Elevated metabolism, weakened cell-to-capillary diffusive coupling, and adaptations involving H(+)/H(+)-equivalent transporters and extracellular-facing CAs give cancer cells the means to manipulate micro-environmental acidity, a cancer hallmark. Through genetic instability, the cellular apparatus for regulating and sensing pH is able to adapt to extracellular acidity, driving disease progression. The therapeutic potential of disturbing this sequence by targeting H(+)/H(+)-equivalent transporters, buffering or CAs is being investigated, using monoclonal antibodies and small-molecule inhibitors.

Noninvasive pH monitoring of platelet concentrates: a large field test.

PubMed

Gkoumassi, Effimia; Klein-Bosgoed, Christa; Dijkstra-Tiekstra, Margriet J; de Korte, Dirk; de Wildt-Eggen, Janny

2013-10-01

Developing new quality control methods for platelet concentrates (PCs) can contribute to increasing transfusion safety and efficiency. The aim of this study was to investigate in a large field test the quality of expired PCs and whether 100% noninvasive pH monitoring can be used to predict PC quality. The pH of 13,693 PCs produced for transfusion was monitored daily using Blood Storage, Inc.'s pH sterile, automated fluoroscopic evaluation technology. Upon indication of compromised quality or expiration, PCs were returned and in vitro tests were performed. A total of 998 PCs were returned, of which 962 outdated, 26 had a positive BacT/ALERT reaction, seven had aggregates, one was without swirl, one had low pH, and one had high pH. BacT/ALERT was faster in identifying bacterial contamination than pH measurements. The pH at the end of the storage period was significantly lower than at the beginning. In vitro tests indicated that while the PC quality was acceptable upon expiration, it rapidly declined after expiration. In this setting where the vast majority of PCs were of good quality and within acceptable pH limits, daily, noninvasive routine pH measurement has limited added value in identifying quality-compromised PCs. © 2013 Sanquin Research. Transfusion © 2013 American Association of Blood Banks.

Mechanistic deductions from kinetic isotope effects and pH studies of pyridoxal phosphate dependent carbon-carbon lyases: Erwinia herbicola and Citrobacter freundii tyrosine phenol-lyase

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

Kiick, D.M.; Phillips, R.S.

1988-09-20

The pH dependence of the kinetic parameters and primary deuterium isotope effects have been determined for tyrosine phenol-lyase from both Erwinia herbicola and Citrobacter freundii. The primary deuterium isotope effects indicate that proton abstraction from the 2-position of the substrate is partially rate-limiting for both enzymes. The C. freundii enzyme primary deuterium isotope effects (DV = 3.5 and D(V/Ktyr) = 2.5) are pH independent, indicating that tyrosine is not sticky (i.e., does not dissociate slower than it reacts to give products). Since Vmax for both tyrosine and the alternate substrate S-methyl-L-cysteine is also pH independent, substrate binds only to themore » correctly protonated form of the enzyme. For the E. herbicola enzyme, both Vmax and V/K for tyrosine or S-methyl-L-cysteine are pH dependent, as well as both DV and D(V/Ktyr). Thus, while both the protonated and unprotonated enzyme can bind substrate, and may be interconverted directly, only the unprotonated Michaelis complex is catalytically competent. At pH 9.5, DV = 2.5 and D(V/Ktyr) = 1.5. However, at pH 6.4 the isotope effect on both parameters is equal to 4.1. From these data, the forward commitment factor (cf = 5.2) and catalytic ratio (cvf = 1.1) for tyrosine and S-methyl-L-cysteine (cf = 2.2, cvf = 24) are calculated. Also, the Michaelis complex partition ratio (cf/cvf) for substrate and products is calculated to be 4.7 for tyrosine and 0.1 for S-methyl-L-cysteine.« less

Quantification of Kinetic Rate Law Parameters of Uranium Release from Sodium Autunite as a Function of Aqueous Bicarbonate Concentrations

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

Gudavalli, Ravi; Katsenovich, Yelena; Wellman, Dawn M.

2013-09-05

ABSTRACT: Hydrogen carbonate is one of the most significant components within the uranium geochemical cycle. In aqueous solutions, hydrogen carbonate forms strong complexes with uranium. As such, aqueous bicarbonate may significantly increase the rate of uranium release from uranium minerals. Quantifying the relationship of aqueous hydrogen carbonate solutions to the rate of uranium release during dissolution is critical to understanding the long-term fate of uranium within the environment. Single-pass flow-through (SPTF) experiments were conducted to estimate the rate of uranium release from Na meta-autunite as a function of bicarbonate solutions (0.0005-0.003 M) under the pH range of 6-11 and temperaturesmore » of 5-60oC. Consistent with the results of previous investigation, the rate of uranium release from sodium autunite exhibited minimal dependency on temperature; but were strongly dependent on pH and increasing concentrations of bicarbonate solutions. Most notably at pH 7, the rate of uranium release exhibited 370 fold increases relative to the rate of uranium release in the absence of bicarbonate. However, the effect of increasing concentrations of bicarbonate solutions on the release of uranium was significantly less under higher pH conditions. It is postulated that at high pH values, surface sites are saturated with carbonate, thus the addition of more bicarbonate would have less effect on uranium release. Results indicate the activation energies were unaffected by temperature and bicarbonate concentration variations, but were strongly dependent on pH conditions. As pH increased from 6 to 11, activation energy values were observed to decrease from 29.94 kJ mol-1 to 13.07 kJ mol-1. The calculated activation energies suggest a surface controlled dissolution mechanism.« less

Multiscale modeling of a conditionally disordered pH-sensing chaperone.

PubMed

Ahlstrom, Logan S; Law, Sean M; Dickson, Alex; Brooks, Charles L

2015-04-24

The pH-sensing chaperone HdeA promotes the survival of enteropathogenic bacteria during transit through the harshly acidic environment of the mammalian stomach. At low pH, HdeA transitions from an inactive, folded, dimer to chaperone-active, disordered, monomers to protect against the acid-induced aggregation of periplasmic proteins. Toward achieving a detailed mechanistic understanding of the pH response of HdeA, we develop a multiscale modeling approach to capture its pH-dependent thermodynamics. Our approach combines pK(a) (logarithmic acid dissociation constant) calculations from all-atom constant pH molecular dynamics simulations with coarse-grained modeling and yields new, atomic-level, insights into HdeA chaperone function that can be directly tested by experiment. "pH triggers" that significantly destabilize the dimer are each located near the N-terminus of a helix, suggesting that their neutralization at low pH destabilizes the helix macrodipole as a mechanism of monomer disordering. Moreover, we observe a non-monotonic change in the pH-dependent stability of HdeA, with maximal stability of the dimer near pH5. This affect is attributed to the protonation Glu37, which exhibits an anomalously high pK(a) value and is located within the hydrophobic dimer interface. Finally, the pH-dependent binding pathway of HdeA comprises a partially unfolded, dimeric intermediate that becomes increasingly stable relative to the native dimer at lower pH values and displays key structural features for chaperone-substrate interaction. We anticipate that the insights from our model will help inform ongoing NMR and biochemical investigations. Copyright © 2015 Elsevier Ltd. All rights reserved.

pH-Dependent Solubility and Dissolution Behavior of Carvedilol--Case Example of a Weakly Basic BCS Class II Drug.

PubMed

Hamed, Rania; Awadallah, Areeg; Sunoqrot, Suhair; Tarawneh, Ola; Nazzal, Sami; AlBaraghthi, Tamadur; Al Sayyad, Jihan; Abbas, Aiman

2016-04-01

The objective of this study was to investigate the pH-dependent solubility and dissolution of weakly basic Biopharmaceutical Classification Systems (BCS) class II drugs, characterized by low solubility and high permeability, using carvedilol, a weak base with a pK a value of 7.8, as a model drug. A series of solubility and in vitro dissolution studies was carried out using media that simulate the gastric and intestinal fluids and cover the physiological pH range of the GI from 1.2 to 7.8. The effect of ionic strength, buffer capacity, and buffer species of the dissolution media on the solubility and dissolution behavior of carvedilol was also investigated. The study revealed that carvedilol exhibited a typical weak base pH-dependent solubility profile with a high solubility at low pH (545.1-2591.4 μg/mL within the pH range 1.2-5.0) and low solubility at high pH (5.8-51.9 μg/mL within the pH range 6.5-7.8). The dissolution behavior of carvedilol was consistent with the solubility results, where carvedilol release was complete (95.8-98.2% released within 60 min) in media simulating the gastric fluid (pH 1.2-5.0) and relatively low (15.9-86.2% released within 240 min) in media simulating the intestinal fluid (pH 6.5-7.8). It was found that the buffer species of the dissolution media may influence the solubility and consequently the percentage of carvedilol released by forming carvedilol salts of varying solubilities. Carvedilol solubility and dissolution decreased with increasing ionic strength, while lowering the buffer capacity resulted in a decrease in carvedilol solubility and dissolution rate.

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.

Mechanistic characterization of the HDV genomic ribozyme: a mutant of the C41 motif provides insight into the positioning and thermodynamic linkage of metal ions and protons.

PubMed

Nakano, Shu-ichi; Bevilacqua, Philip C

2007-03-20

Binding of two Mg2+ and two H+ ions influences the self-cleavage activity of the genomic HDV ribozyme. The positioning of these four ligands and their thermodynamic linkage are not fully resolved. Protonated C41 engages in a base triple, whereas protonated C75 has been implicated as an acid-base catalyst in bond cleavage. Prior studies led to the identification of one structural inner-sphere ion and one catalytic outer-sphere ion. In the present study, the contributions of the C41 base triple to the metal ion- and pH-dependence of the reaction are examined. Experiments were conducted on a CG to UA double mutant (DM), which changes the base triple to one involving an unprotonated C41. Below pH 6, the DM has a steeper dependence on pH than the wild-type (WT), consistent with a single protonation misfolding the core; this conclusion is also supported by thermal denaturation studies. Between pH 6 and 8, the WT and DM display nearly identical catalytic metal ion and H+ binding profiles. In contrast, over the same pH range, the WT and DM have distinct structural ion binding profiles; for the WT, binding is favored at lower pH, whereas the DM shows no pH dependence. These data localize the structural ion to the vicinity of the C41 motif. An overall model is presented that accommodates binding affinity, coupling, and positioning of the two metal ions and the two protons within the ribozyme. The data suggest that a protonated base triple allows the WT ribozyme to maintain appreciable activity at acidic pH, which could play an important role in the life cycle of the virus.

Dissolution-modulating mechanism of pH modifiers in solid dispersion containing weakly acidic or basic drugs with poor water solubility.

PubMed

Tran, Phuong Ha-Lien; Tran, Thao Truong-Dinh; Lee, Kyoung-Ho; Kim, Dong-Jin; Lee, Beom-Jin

2010-05-01

Although the solid dispersion method has been known to increase the dissolution rate of poorly water-soluble drugs by dispersing them in hydrophilic carriers, one obstacle of the solid dispersion method is its limited solubilization capacity, especially for pH-dependent soluble drugs. pH-modified solid dispersion, in which pH modifiers are incorporated, may be a useful method for increasing the dissolution rate of weakly acidic or basic drugs. Sufficient research, including the most recent reports, was undertaken in this review. How could the inclusion of the pH the pH modifiers in the solid dispersion system change drug structural behaviors, molecular interactions, microenvironmental pH, and/or release rate of pH modifiers, relating with the enhanced dissolution of weakly acidic or weakly basic drugs with poor water solubility? These questions have been investigated to determine the dissolution-modulating mechanism of pH modifiers in solid dispersion containing weakly acidic or basic drugs. It is believed that step-by-step mechanistic approaches could provide the ultimate solution for solubilizing several poorly water-soluble drugs with pH-dependent solubility from a solid dispersion system, as well as provide ideas for developing future dosage systems.

Active-Site Environment of Copper-Bound Human Amylin Relevant to Type 2 Diabetes.

PubMed

Seal, Manas; Dey, Somdatta Ghosh

2018-01-02

Type 2 diabetes mellitus (T2Dm) is characterized by reduced β cell mass and amyloid deposits of human islet amyloid polypeptide (hIAPP) or amylin, a 37 amino acid containing peptide around pancreatic β cells. The interaction of copper (Cu) with amylin and its mutants has been studied in detail using absorption, circular dichroism, electron paramagnetic resonance spectroscopy, and cyclic voltammetry. Cu binds amylin in a 1:1 ratio, and the binding domain lies within the first 19 amino acid residues of the peptide. Depending on the pH of the medium, Cu-amylin shows the formation of five pH-dependent components (component IV at pH 4.0, component III at pH 5.0, component II at pH 6.0, component I at pH 8.0, and another higher pH component above pH 9.0). The terminal amine, His18, and amidates are established as key residues in the peptide that coordinate the Cu center. The physiologically relevant components I and II can generate H 2 O 2 , which can possibly account for the enhanced toxicity of amylin in the presence of Cu, causing damage of the β cells of the pancreas via oxidative stress.

Trans-generational responses to low pH depend on parental gender in a calcifying tubeworm

PubMed Central

Lane, Ackley; Campanati, Camilla; Dupont, Sam; Thiyagarajan, Vengatesen

2015-01-01

The uptake of anthropogenic CO2 emissions by oceans has started decreasing pH and carbonate ion concentrations of seawater, a process called ocean acidification (OA). Occurring over centuries and many generations, evolutionary adaptation and epigenetic transfer will change species responses to OA over time. Trans-generational responses, via genetic selection or trans-generational phenotypic plasticity, differ depending on species and exposure time as well as differences between individuals such as gender. Males and females differ in reproductive investment and egg producing females may have less energy available for OA stress responses. By crossing eggs and sperm from the calcareous tubeworm Hydroides elegans (Haswell, 1883) raised in ambient (8.1) and low (7.8) pH environments, we observed that paternal and maternal low pH experience had opposite and additive effects on offspring. For example, when compared to offspring with both parents from ambient pH, growth rates of offspring of fathers or mothers raised in low pH were higher or lower respectively, but there was no difference when both parents were from low pH. Gender differences may result in different selection pressures for each gender. This may result in overestimates of species tolerance and missed opportunities of potentially insightful comparisons between individuals of the same species. PMID:26039184

Effect of pH on skin permeation enhancement of acidic drugs by l-menthol-ethanol system.

PubMed

Katayama, K; Matsui, R; Hatanaka, T; Koizumi, T

2001-09-11

The effect of pH on the skin permeation enhancement of three acidic drugs by the l-menthol-ethanol system was investigated. The total flux of acidic drugs from the system remarkably varied over the pH range 3.0-8.0, and the permeation enhancement factor depended on the system pH and drug. A skin permeation model, which consists of two permeant (unionized and ionized) species, two system (oily and aqueous) phases, and two permeation (lipid and pore) pathways, was developed. The assumptions were made that only the unionized species can distribute to the oily phase and transport via the lipid pathway. The model explained the relationship between the concentration of drug in the aqueous phase and system pH. The skin permeability data were also described by the model and permeability coefficients corresponding to the physicochemical properties of permeant were calculated for the lipid and pore pathways. The model simulation showed that the permeation of acidic drugs occurred from the aqueous phase and the oily phase acted as a reservoir. Whether the total flux increased with increase of pH was dependent on the lipophilicity of drug. These results suggest that the pH of l-menthol-ethanol system should be given attention to elicit the maximum permeation enhancement.

Confirmation of nasogastric tube position by pH testing.

PubMed

Taylor, S J; Clemente, R

2005-10-01

In 2004, the Medicines and Healthcare products Regulatory Agency (MHRA) advised that nasogastric (NG) tube position should be confirmed using pH strips or paper. However, gastric pH is raised by the use of H2-blockers and proton-pump inhibitors (PPIs) potentially producing false negative pH tests resulting in delayed feeding. In addition, colorimetric differentiation using pH strips may be more prone to bias and inaccuracy than direct pH measurements largely used to establish the threshold. To quantify this problem a 1 day survey of all the patients requiring NG and nasointestinal (NI) feeding was undertaken, to establish the numbers of patients receiving H2-Blockers or PPIs, with or without a safe swallow and the methods currently being used to confirm tube positioning. A second observational study was performed to establish the accuracy of six pH strips available to NHS trusts against four unlabelled pH solutions. Forty-two per cent of patients receiving NG feeding were on H2-blockers or PPIs, including 13% who had a safe swallow for acidic drinks that could be subsequently aspirated to confirm position. In the second study 'testers' correctly identified pH's 3, 4, 5 and 6 with Mackery-Nagel 0-6, BDH 0-6 and 0-14 strips but overestimated pH 4 as pH 5 with Johnson 0-11 paper, underestimated pH 6 as pH 5 with Pehanon 0-12 paper and with Litmus classified pH 3-5 as acid (all), but half also classified pH 6 as acid. Theoretically 29% of NG tube positions could not be confirmed by pH testing because of the usage of PPIs or H2-blockers and lack of swallow. Some pH strips are either inaccurate or their result misinterpreted by staff. Large surveys and trials of the actual efficacy and accuracy of pH testing are required.

Physiological and biochemical role of the butanediol pathway in Aerobacter (Enterobacter) aerogenes.

PubMed Central

Johansen, L; Bryn, K; Stormer, F C

1975-01-01

Aerobacter (Enterobacter) aerogenes wild type and three mutants deficient in the formation of acetoin and 2,3-butanediol were grown in a glucose minimal medium. Culture densities, pH, and diacetyl, acetoin, and 2,3-butanediol levels were recorded. The pH in wild-type cultures dropped from 7.0 to 5.8, remained constant while acetoin and 2,3-butanediol were formed, and increased to pH 6.5 after exhaustion of the carbon source. More 2,3-butanediol than acetoin was formed initially, but after glucose exhaustion reoxidation to acetoin occurred. The three mutants differed from the wild type in yielding acid cultures (pH below 4.5). The wild type and one of the mutants were grown exponentially under aerobic and anaerobic conditions with the pH fixed at 7.0, 5.8, and 5.0, respectively. Growth rates decreased with decreasing pH values. Aerobically, this effect was weak, and the two strains were affected to the same degree. Under anaerobic conditions, the growth rates were markedly inhibited at a low pH, and the mutant was slightly more affected than the wild type. Levels of alcohol dehydrogenase were low under all conditions, indicating that the enzyme plays no role during exponential growth. The levels of diacetyl (acetoin) reductase, lactate dehydrogenase, and phosphotransacetylase were independent of the pH during aerobic growth of the two strains. Under anaerobic conditions, the formation of diacetyl (acetoin) reductase was pH dependent, with much higher levels of the enzyme at pH 5.0 than at pH 7.0. Lactate dehydrogenase and phosphotransacetylase revealed the same pattern of pH-dependent formation in the mutant, but not in the wild type. PMID:239921

Unfolding Kinetics of the Human Telomere i-Motif Under a 10 pN Force Imposed by the α-Hemolysin Nanopore Identify Transient Folded-State Lifetimes at Physiological pH.

PubMed

Ding, Yun; Fleming, Aaron M; He, Lidong; Burrows, Cynthia J

2015-07-22

Cytosine (C)-rich DNA can adopt i-motif folds under acidic conditions, with the human telomere i-motif providing a well-studied example. The dimensions of this i-motif are appropriate for capture in the nanocavity of the α-hemolysin (α-HL) protein pore under an electrophoretic force. Interrogation of the current vs time (i-t) traces when the i-motif interacts with α-HL identified characteristic signals that were pH dependent. These features were evaluated from pH 5.0 to 7.2, a region surrounding the transition pH of the i-motif (6.1). When the i-motif without polynucleotide tails was studied at pH 5.0, the folded structure entered the nanocavity of α-HL from either the top or bottom face to yield characteristic current patterns. Addition of a 5' 25-mer poly-2'-deoxyadensosine tail allowed capture of the i-motif from the unfolded terminus, and this was used to analyze the pH dependency of unfolding. At pH values below the transition point, only folded strands were observed, and when the pH was increased above the transition pH, the number of folded events decreased, while the unfolded events increased. At pH 6.8 and 7.2 4% and 2% of the strands were still folded, respectively. The lifetimes for the folded states at pH 6.8 and 7.2 were 21 and 9 ms, respectively, at 160 mV electrophoretic force. These lifetimes are sufficiently long to affect enzymes operating on DNA. Furthermore, these transient lifetimes are readily obtained using the α-HL nanopore, a feature that is not easily achievable by other methods.

Characterization of pH dependent Mn(II) oxidation strategies and formation of a bixbyite-like phase by Mesorhizobium australicum T-G1

PubMed Central

Bohu, Tsing; Santelli, Cara M.; Akob, Denise M.; Neu, Thomas R.; Ciobota, Valerian; Rösch, Petra; Popp, Jürgen; Nietzsche, Sándor; Küsel, Kirsten

2015-01-01

Despite the ubiquity of Mn oxides in natural environments, there are only a few observations of biological Mn(II) oxidation at pH < 6. The lack of low pH Mn-oxidizing bacteria (MOB) isolates limits our understanding of how pH influences biological Mn(II) oxidation in extreme environments. Here, we report that a novel MOB isolate, Mesorhizobium australicum strain T-G1, isolated from an acidic and metalliferous uranium mining area, can oxidize Mn(II) at both acidic and neutral pH using different enzymatic pathways. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy revealed that T-G1 initiated bixbyite-like Mn oxide formation at pH 5.5 which coincided with multi-copper oxidase expression from early exponential phase to late stationary phase. In contrast, reactive oxygen species (ROS), particularly superoxide, appeared to be more important for T-G1 mediated Mn(II) oxidation at neutral pH. ROS was produced in parallel with the occurrence of Mn(II) oxidation at pH 7.2 from early stationary phase. Solid phase Mn oxides did not precipitate, which is consistent with the presence of a high amount of H2O2 and lower activity of catalase in the liquid culture at pH 7.2. Our results show that M. australicum T-G1, an acid tolerant MOB, can initiate Mn(II) oxidation by varying its oxidation mechanisms depending on the pH and may play an important role in low pH manganese biogeochemical cycling. PMID:26236307

The Stability of Silver Nanoparticles in a Model of Pulmonary Surfactant

PubMed Central

Fen, Leo Bey; Chen, Shu; Kyo, Yoshihiko; Herpoldt, Karla-Luise; Terrill, Nicholas J.; Dunlop, Iain E.; McPhail, David S.; Shaffer, Milo S.; Schwander, Stephan; Gow, Andrew; Zhang, Junfeng (Jim); Chung, Kian Fan; Tetley, Teresa D.; Porter, Alexandra E.; Ryan, Mary P.

2013-01-01

The growing use of silver nanoparticles (AgNPs) in consumer products has raised concerns about their potential impact on the environment and human health. Whether AgNPs dissolve and release Ag+ ions, or coarsen to form large aggregates, is critical in determining their potential toxicity. In this work, the stability of AgNPs in dipalmitoylphosphatidylcholine (DPPC), the major component of pulmonary surfactant, was investigated as a function of pH. Spherical, citrate-capped AgNPs with average diameters of 14 ± 1.6 nm (n=200) were prepared by a chemical bath reduction. The kinetics of Ag+ ion release was strongly pH-dependent. After 14 days of incubation in sodium perchlorate (NaClO4) or perchloric acid (HClO4) solutions, the total fraction of AgNPs dissolved varied from ~10 % at pH 3, to ~2 % at pH 5, with negligible dissolution at pH 7. A decrease in pH from 7 to 3 also promoted particle aggregation and coarsening. DPPC (100 mg.L−1) delayed the release of Ag+ ions, but did not significantly alter the total amount of Ag+ released after two weeks. In addition, DPPC improved the dispersion of the AgNPs and inhibited aggregation and coarsening. TEM images revealed that the AgNPs were coated with a DPPC layer serving as a semi-permeable layer. Hence, lung lining fluid, particularly DPPC, can modify the aggregation state and kinetics of Ag+ ion release of inhaled AgNPs in the lung. These observations have important implications for predicting the potential reactivity of AgNPs in the lung and the environment. PMID:23988335

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.

PalC, One of Two Bro1 Domain Proteins in the Fungal pH Signalling Pathway, Localizes to Cortical Structures and Binds Vps32

PubMed Central

Galindo, Antonio; Hervás-Aguilar, América; Rodríguez-Galán, Olga; Vincent, Olivier; Arst, Herbert N; Tilburn, Joan; Peñalva, Miguel A

2007-01-01

PalC, distantly related to Saccharomyces cerevisiaeperipheral endosomal sorting complexes required for transport III (ESCRT-III) component Bro1p and one of six Aspergillus nidulanspH signalling proteins, contains a Bro1 domain. Green fluorescent protein (GFP)-tagged PalC is recruited to plasma membrane-associated punctate structures upon alkalinization, when pH signalling is active. PalC recruitment to these structures is dependent on the seven transmembrane domain (7-TMD) receptor and likely pH sensor PalH. PalC is a two-hybrid interactor of the ESCRT-III Vps20/Vps32 subcomplex and binds Vps32 directly. This binding is largely impaired by Pro439Phe, Arg442Ala and Arg442His substitutions in a conserved region mediating interaction of Bro1p with Vps32p, but these substitutions do not prevent cortical punctate localization, indicating Vps32 independence. In contrast, Arg442Δ impairs Vps32 binding and prevents PalC-GFP recruitment to cortical structures. pH signalling involves a plasma membrane complex including the 7-TMD receptor PalH and the arrestin-like PalF and an endosomal membrane complex involving the PalB protease, the transcription factor PacC and the Vps32 binding, Bro1-domain-containing protein PalA. PalC, which localizes to cortical structures and can additionally bind a component of ESCRT-III, has the features required to bridge these two entities. A likely S. cerevisiaeorthologue of PalC has been identified, providing the basis for a unifying hypothesis of gene regulation by ambient pH in ascomycetes. PMID:17696968

Role of Secondary Transporters and Phosphotransferase Systems in Glucose Transport by Oenococcus oeni ▿

PubMed Central

Kim, Ok Bin; Richter, Hanno; Zaunmüller, Tanja; Graf, Sabrina; Unden, Gottfried

2011-01-01

Glucose uptake by the heterofermentative lactic acid bacterium Oenococcus oeni B1 was studied at the physiological and gene expression levels. Glucose- or fructose-grown bacteria catalyzed uptake of [14C]glucose over a pH range from pH 4 to 9, with maxima at pHs 5.5 and 7. Uptake occurred in two-step kinetics in a high- and low-affinity reaction. The high-affinity uptake followed Michaelis-Menten kinetics and required energization. It accumulated the radioactivity of glucose by a factor of 55 within the bacteria. A large portion (about 80%) of the uptake of glucose was inhibited by protonophores and ionophores. Uptake of the glucose at neutral pH was not sensitive to degradation of the proton potential, Δp. Expression of the genes OEOE_0819 and OEOE_1574 (here referred to as 0819 and 1574), coding for secondary transporters, was induced by glucose as identified by quantitative real-time (RT)-PCR. The genes 1574 and 0819 were able to complement growth of a Bacillus subtilis hexose transport-deficient mutant on glucose but not on fructose. The genes 1574 and 0819 therefore encode secondary transporters for glucose, and the transports are presumably Δp dependent. O. oeni codes, in addition, for a phosphotransferase transport system (PTS) (gene OEOE_0464 [0464] for the permease) with similarity to the fructose- and mannose-specific PTS of lactic acid bacteria. Quantitative RT-PCR showed induction of the gene 0464 by glucose and by fructose. The data suggest that the PTS is responsible for Δp-independent hexose transport at neutral pH and for the residual Δp-independent transport of hexoses at acidic pH. PMID:22020640

New insights into flavivirus biology: the influence of pH over interactions between prM and E proteins

NASA Astrophysics Data System (ADS)

Oliveira, Edson R. A.; de Alencastro, Ricardo B.; Horta, Bruno A. C.

2017-11-01

Diseases caused by flaviviruses, such as dengue and zika, are globally recognized as major threats. During infection, a critical point in their replicative cycle is the maturation step, which occurs throughout the cellular exocytic pathway. This step is a pH-dependent process that involves the modification of the viral envelope by converting prM (pre-membrane) into M (membrane) proteins with the release of a "pr peptide". After this reaction, the pr peptides remain bound to the viral envelope while the virions cross the acidic trans-Golgi network, and are released only at neutral pH after secretion of the virus particles. Despite this current knowledge, the molecular basis of the flavivirus maturation step is largely unknown. Here, based on the crystal structure of the dengue pr-E complex ("pr peptide" bound to virus envelope protein) and using molecular dynamics simulations, we found that the pH shift from acidic to neutral yields considerable structural changes in the system. Dynamic cross correlation maps and root mean square deviation analyses revealed that the pr-E junction is clearly unstable under neutral pH. Secondary structure analysis also revealed that the fusion loop region, present in the E protein, is sensitive to pH and tends to unstructure at a neutral environment. Moreover, we found that five residues present in the E protein, Gly102, His244, Thr70, Thr68 and Asn67 are critical to confer stability to the pr-E complex while inside the Golgi apparatus. This work brings details about the dynamical behavior of the pr-E system, helps to better understand the flavivirus biology and may also be of use in the development of novel antiviral strategies.

Distribution of branched glycerol dialkyl glycerol tetraethers in surface soils of the Qinghai-Tibetan Plateau: implications of brGDGTs-based proxies in cold and dry regions

NASA Astrophysics Data System (ADS)

Ding, S.; Xu, Y.; Wang, Y.; He, Y.; Hou, J.; Chen, L.; He, J.-S.

2015-06-01

The methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT) based on the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGT) are useful proxies for the reconstruction of mean annual air temperature (MAT) and soil pH. Recently, a series of 6-methyl brGDGTs were identified which were previously co-eluted with 5-methyl brGDGTs. However, little is known about 6-methyl brGDGTs in the Qinghai-Tibetan Plateau (QTP), a critical region of the global climate system. Here, we analyze 30 surface soils covering a large area of the QTP, among which 6-methyl brGDGTs were the most abundant components (average 53 ± 17% of total brGDGT). The fractional abundance of 6-methyl brGDGTs showed a good correlation with soil pH, while the global MBT'5ME calibration overestimates MAT in the QTP. We therefore proposed a MBT5/6 index including both 5- and 6-methyl brGDGTs, presenting a strong correlation with MAT in QTP: MAT = -20.14 + 39.51 × MBT5/6 (n = 27, r2 = 0.82; RMSE = 1.3 °C). Another index, namely IBT (isomerization of branched tetraether), based on carbon skeleton isomerization of the 5-methyl to 6-methyl brGDGTs, is dependent on soil pH: pH = 6.77 - 1.56 × IBT (n = 27; r2 = 0.74, RMSE = 0.32). Our study suggests that changing the position of methyl group of brGDGTs may be another mechanism for some soil bacteria to adapt to the ambient pH change in addition to the well-known cyclization.

Guargum and Eudragit ® coated curcumin liquid solid tablets for colon specific drug delivery.

PubMed

S Kumar, Vrinda; Rijo, John; M, Sabitha

2018-04-15

Colorectal cancer, also known as bowel cancer, is the uncontrolled cell growth in the colon or rectum (parts of the large intestine), or in the appendix. The colon specific drug delivery would alleviate the systemic side effects and would assure the safe therapy for colonic disorders with minimum dose and duration of therapy. The liquisolid technique refers to solubilisation of drug in a non-volatile solvent combined with inclusion of appropriate carrier and coating agent required for tableting. Colon specific degradation of natural polymer, guar gum and pH dependant degradative (pH-7) property of eudragit L100 restricts the delivery of curcumin in gastric and intestinal pH. Formulated curcumin liquisolid powder was evaluated for the micrometric properties, solubility and by differential thermal analysis, X ray powder diffraction and scanning electron microscopy. Curcumin loaded liquisolid tablet showed more anticancer activity against HCT-15 compared with free curcumin. Bioavailability study of the coated and uncoated liquisolid tablets were performed using Newzealand white rabbits. The present study concludes that liquisolid technique is a promising alternative for improving oral bioavailability and dissolution rate of water insoluble drug and coating liquisolid tablet with colon sensitive polymers showed site specific release of drug in the colon. Copyright © 2018 Elsevier B.V. All rights reserved.

A review on applicability of naturally available adsorbents for the removal of hazardous dyes from aqueous waste.

PubMed

Sharma, Pankaj; Kaur, Harleen; Sharma, Monika; Sahore, Vishal

2011-12-01

The effluent water of many industries, such as textiles, leather, paper, printing, cosmetics, etc., contains large amount of hazardous dyes. There is huge number of treatment processes as well as adsorbent which are available for the processing of this effluent water-containing dye content. The applicability of naturally available low cast and eco-friendly adsorbents, for the removal of hazardous dyes from aqueous waste by adsorption treatment, has been reviewed. In this review paper, we have provided a compiled list of low-cost, easily available, safe to handle, and easy-to-dispose-off adsorbents. These adsorbents have been classified into five different categories on the basis of their state of availability: (1) waste materials from agriculture and industry, (2) fruit waste, (3) plant waste, (4) natural inorganic materials, and (5) bioadsorbents. Some of the treated adsorbents have shown good adsorption capacities for methylene blue, congo red, crystal violet, rhodamine B, basic red, etc., but this adsorption process is highly pH dependent, and the pH of the medium plays an important role in the treatment process. Thus, in this review paper, we have made some efforts to discuss the role of pH in the treatment of wastewater.

Physical heterogeneity control on effective mineral dissolution rates

NASA Astrophysics Data System (ADS)

Jung, Heewon; Navarre-Sitchler, Alexis

2018-04-01

Hydrologic heterogeneity may be an important factor contributing to the discrepancy in laboratory and field measured dissolution rates, but the governing factors influencing mineral dissolution rates among various representations of physical heterogeneity remain poorly understood. Here, we present multiple reactive transport simulations of anorthite dissolution in 2D latticed random permeability fields and link the information from local grid scale (1 cm or 4 m) dissolution rates to domain-scale (1m or 400 m) effective dissolution rates measured by the flux-weighted average of an ensemble of flow paths. We compare results of homogeneous models to heterogeneous models with different structure and layered permeability distributions within the model domain. Chemistry is simplified to a single dissolving primary mineral (anorthite) distributed homogeneously throughout the domain and a single secondary mineral (kaolinite) that is allowed to dissolve or precipitate. Results show that increasing size in correlation structure (i.e. long integral scales) and high variance in permeability distribution are two important factors inducing a reduction in effective mineral dissolution rates compared to homogeneous permeability domains. Larger correlation structures produce larger zones of low permeability where diffusion is an important transport mechanism. Due to the increased residence time under slow diffusive transport, the saturation state of a solute with respect to a reacting mineral approaches equilibrium and reduces the reaction rate. High variance in permeability distribution favorably develops large low permeability zones that intensifies the reduction in mixing and effective dissolution rate. However, the degree of reduction in effective dissolution rate observed in 1 m × 1 m domains is too small (<1% reduction from the corresponding homogeneous case) to explain several orders of magnitude reduction observed in many field studies. When multimodality in permeability distribution is approximated by high permeability variance in 400 m × 400 m domains, the reduction in effective dissolution rate increases due to the effect of long diffusion length scales through zones with very slow reaction rates. The observed scale dependence becomes complicated when pH dependent kinetics are compared to the results from pH independent rate constants. In small domains where the entire domain is reactive, faster anorthite dissolution rates and slower kaolinite precipitation rates relative to pH independent rates at far-from-equilibrium conditions reduce the effective dissolution rate by increasing the saturation state. However, in large domains where less- or non-reactive zones develop, higher kaolinite precipitation rates in less reactive zones increase the effective anorthite dissolution rates relative to the rates observed in pH independent cases.

Impact of pH on hydrogen oxidizing redox processes in aquifers due to gas intrusions

NASA Astrophysics Data System (ADS)

Metzgen, Adrian; Berta, Marton; Dethlefsen, Frank; Ebert, Markus; Dahmke, Andreas

2017-04-01

Hydrogen production from excess energy and its storage can help increasing the efficiency of solar and wind in the energy mix. Therefore, hydrogen needs large-scale intermediate storage independent of the intended later use as hydrogen gas or as reactant to produce methane in the Sabatier process. A possible storage solution is using the geological subsurface such as caverns built in salt deposits or aquifers that are not used for drinking water production. However, underground storage of hydrogen gas potentially leads to accidental gas leakages into near-surface potable aquifers triggering subsequent geochemical processes. These leakages pose potential risks that are currently not sufficiently understood. To close this gap in knowledge, a high-pressure laboratory column system was used to simulate a hydrogen gas intrusion into a shallow aquifer. Water and sediment were gained from a sandy Pleistocene aquifer near Neumünster, Germany. In the first stage of the experiment, 100% hydrogen gas was used to simulate dissolved hydrogen concentrations between 800 and 4000 µM by varying pH2 between 2 and 15 bars. pH values rose to between 7.9 and 10.4, partly due to stripping CO2 from the groundwater used during H2 gas addition. In a second stage, the pH was regulated in a range of 6.7 to 7.9 by using a gas mixture of 99% H2 and 1% CO2 at 5 bars of total gas pressure. Observed processes included hydrogen oxidation, sulfate reduction, acetogenesis, formate production, and methanogenesis, which were independent of the hydrogen concentration. Hydrogen oxidation and sulfate reduction showed zeroth order reaction rates and rate constants (106 to 412 µM/h and 12 to 33 µM/h, respectively) in the pH range between 8 and 10. At pH levels between 7 and 8, both reactions started out faster near the column's inflow but then seemed limited towards the columns outflow, suggesting the dependence of sulfate reduction on the pH-value. Acetogenesis dominated the pH range between 8 and 10 (first order rate constants between 0.029 and 0.036 1/h). Between pH 7 and 8, acetogenesis showed a linear trend (zeroth order rates between 3 and 5 µM/h) whereas formate production became the main process (zeroth order rates between 38 to 197 µM/h) together with methanogenesis as a minor process. The results indicated a strong dependency of the biogeochemical hydrogenotrophic redox reactions on the pH milieu. Thus, pH buffers such as dissolved or solid phase carbonates should be taken into account when predicting effects a hydrogen leakage may have on shallow aquifers. Additionally, parameters derived from the observed processes and their rates allow the design of a process based numerical model simulating a hydrogen intrusion into a shallow aquifer. Consequently the presented outcomes allow an exemplary quantification of the resulting geochemical effects. This study was carried out within the ANGUS+ project and was funded by the German Federal Ministry of Education and Research (BMBF) energy storage funding initiative.

Simultaneous estimation of intracellular free Mg2+ and pH by use of a new pH-dependent dissociation constant of MgATP.

PubMed

Nakayama, Shinsuke; Nomura, Hideki; Smith, Lorraine M; Clark, Joseph F

2002-06-01

In the present technical note for 31P-NMR, we used a new pH-dependent dissociation constant of MgATP, and re-estimated changes in the intracellular free Mg2+ concentration and pH from the chemical shifts of beta- and gamma-ATP during Na+-removal in smooth muscle. We confirmed the role of Na+ - Mg2+ exchange.

Intracellular pH measurements made simple by fluorescent protein probes and the phasor approach to fluorescence lifetime imaging†

PubMed Central

Digman, Michelle A.; Gratton, Enrico; Storti, Barbara; Beltram, Fabio

2013-01-01

A versatile pH-dependent fluorescent protein was applied to intracellular pH measurements by means of the phasor approach to fluorescence lifetime imaging. By this fit-less method we obtain intracellular pH maps under resting or altered physiological conditions by single-photon confocal or two-photon microscopy. PMID:22517076

Model predictions of realgar precipitation by reaction of As(III) with synthetic mackinawite under anoxic conditions

USGS Publications Warehouse

Gallegos, T.J.; Han, Y.-S.; Hayes, K.F.

2008-01-01

This study investigates the removal of As(III) from solution using mackinawite, a nanoparticulate reduced iron sulfide. Mackinawite suspensions (0.1-40 g/L) effectively lower initial concentrations of 1.3 ?? 10 -5 M As(III) from pH 5-10, with maximum removal occurring under acidic conditions. Based on Eh measurements, it was found that the redox state of the system depended on the mackinawite solids concentration and pH. Higher initial mackinawite concentrations and alkaline pH resulted in a more reducing redox condition. Given this, the pH edge data were modeled thermodynamically using pe (-log[e-]) as a fitting parameter and linear pe-pH relationships within the range of measured Eh values as a function of pH and mackinawite concentration. The model predicts removal of As(III) from solution by precipitation of realgar with the formation of secondary oxidation products, greigite or a mixed-valence iron oxide phase, depending on pH. This study demonstrates that mackinawite is an effective sequestration agent for As(III) and highlights the importance of incorporating redox into models describing the As-Fe-S-H2O system. ?? 2008 American Chemical Society.

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.

Characterization of polyphenol oxidase from the Manzanilla cultivar (Olea europaea pomiformis) and prevention of browning reactions in bruised olive fruits.

PubMed

Segovia-Bravo, Kharla A; Jarén-Galan, Manuel; García-García, Pedro; Garrido-Fernandez, Antonio

2007-08-08

The crude extract of the polyphenol oxidase (PPO) enzyme from the Manzanilla cultivar (Olea europaea pomiformis) was obtained, and its properties were characterized. The browning reaction followed a zero-order kinetic model. Its maximum activity was at pH 6.0. This activity was completely inhibited at a pH below 3.0 regardless of temperature; however, in alkaline conditions, pH inhibition depended on temperature and was observed at values above 9.0 and 11.0 at 8 and 25 degrees C, respectively. The thermodynamic parameters of substrate oxidation depended on pH within the range in which activity was observed. The reaction occurred according to an isokinetic system because pH affected the enzymatic reaction rate but not the energy required to carry out the reaction. In the alkaline pH region, browning was due to a combination of enzymatic and nonenzymatic reactions that occurred in parallel. These results correlated well with the browning behavior observed in intentionally bruised fruits at different temperatures and in different storage solutions. The use of a low temperature ( approximately 8 degrees C) was very effective for preventing browning regardless of the cover solution used.

Effect of eluent pH on the HPLC-UV analysis of hyperforin from St. John's Wort (Hypericum perforatum L.).

PubMed

Fourneron, Jean-Dominique; Naït-Si, Youssef

2006-01-01

The effect of the pH of the mobile phase in HPLC analysis of hyperforin was investigated. Working with an extract of St. John's Wort (Hypericum perforatum L.) that is rich in hyperforin, significant differences were observed in conventional chromatograms depending on whether the mobile phase was acidic or alkaline. Chromatogram changes were paralleled by changes in the UV spectrum of the hyperforin peak. The structural changes in hyperforin occur in the chromatographic column itself, as has been confirmed by UV spectroscopy performed on a sample of purified hyperforin, which showed that the UV spectrum is indeed dependent on the pH of its environment.

pH sensor based on boron nitride nanotubes.

PubMed

Huang, Q; Bando, Y; Zhao, L; Zhi, C Y; Golberg, D

2009-10-14

A submicrometer-sized pH sensor based on biotin-fluorescein-functionalized multiwalled BN nanotubes with anchored Ag nanoparticles is designed. Intrinsic pH-dependent photoluminescence and Raman signals in attached fluorescein molecules enhanced by Ag nanoparticles allow this novel nanohybrid to perform as a practical pH sensor. It is able to work in a submicrometer-sized space. For example, the sensor may determine the environmental pH of sub-units in living cells where a traditional optical fiber sensor fails because of spatial limitations.

pH sensor based on boron nitride nanotubes

NASA Astrophysics Data System (ADS)

Huang, Q.; Bando, Y.; Zhao, L.; Zhi, C. Y.; Golberg, D.

2009-10-01

A submicrometer-sized pH sensor based on biotin-fluorescein-functionalized multiwalled BN nanotubes with anchored Ag nanoparticles is designed. Intrinsic pH-dependent photoluminescence and Raman signals in attached fluorescein molecules enhanced by Ag nanoparticles allow this novel nanohybrid to perform as a practical pH sensor. It is able to work in a submicrometer-sized space. For example, the sensor may determine the environmental pH of sub-units in living cells where a traditional optical fiber sensor fails because of spatial limitations.

Equilibrium and kinetic modelling of chromium(III) sorption by animal bones.

PubMed

Chojnacka, Katarzyna

2005-04-01

The paper discusses sorption of Cr(III) ions from aqueous solutions by animal bones. Animal bones were found to be an efficient sorbent with the maximum experimentally determined sorption capacity in the range 29-194 mg g(-1) that depended on pH and temperature. The maximum experimentally determined sorption capacity was obtained at 50 degrees C, pH 5. Batch kinetics and equilibrium experiments were performed in order to investigate the influence of contact time, initial concentration of sorbate and sorbent, temperature and pH. It was found that sorption capacity increased with increase of Cr(III) concentration, temperature and initial pH of metal solution. Mathematical models describing kinetics and statics of sorption were proposed. It was found that process kinetics followed the pseudo-second-order pattern. The influence of sorbent concentration was described with Langmuir-type equation and the influence of sorbate concentration was described with empirical dependence. The models were positively verified.

Sensing pH via p-cyanophenylalanine fluorescence: Application to determine peptide pKa and membrane penetration kinetics.

PubMed

Pazos, Ileana M; Ahmed, Ismail A; Berríos, Mariana I León; Gai, Feng

2015-08-15

We expand the spectroscopic utility of a well-known infrared and fluorescence probe, p-cyanophenylalanine, by showing that it can also serve as a pH sensor. This new application is based on the notion that the fluorescence quantum yield of this unnatural amino acid, when placed at or near the N-terminal end of a polypeptide, depends on the protonation status of the N-terminal amino group of the peptide. Using this pH sensor, we are able to determine the N-terminal pKa values of nine tripeptides and also the membrane penetration kinetics of a cell-penetrating peptide. Taken together, these examples demonstrate the applicability of using this unnatural amino acid fluorophore to study pH-dependent biological processes or events that accompany a pH change. Copyright © 2015 Elsevier Inc. All rights reserved.

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.

Stability of Synthetic Cathinones in Urine.

PubMed

Glicksberg, Lindsay; Kerrigan, Sarah

2018-03-01

In this report, we evaluate the concentration, pH, temperature and analyte-dependent effects on cathinone stability in preserved human urine. A total of 22 synthetic cathinones were evaluated at 100 ng/mL and 1,000 ng/mL in pH 4 and pH 8 urine over 6 months. Specimens were stored at -20°C, 4°C, 20°C and 32°C. The stability of synthetic cathinones was highly dependent on urine pH and storage temperature. Cathinones were considerably more stable in acidic urine (pH 4) at low temperature. In alkaline urine (pH 8) at 32°C, significant losses (>20%) were observed within hours for the majority of drugs. In contrast, all drugs were stable in frozen and refrigerated urine at pH 4 for the duration of the study. These results highlight the importance of sample storage and the potential for pre-analytical changes in concentration during routine shipping and handling of specimens. Significant structural influence was also observed. Cathinones bearing a tertiary amine (pyrrolidine group) were significantly more stable than their secondary amine counterparts. The methylenedioxy group also exerted a significant stabilizing effect on both the tertiary and secondary amines. In the absence of the methylenedioxy group, no significant differences in stability were observed between the unsubstituted and ring substituted secondary amines. Half-lives at ambient temperature in pH 8 urine ranged from 9 h (3-fluoromethcathinone) to 4.3 months (methylenedioxypyrovalerone and 3,4-methylenedioxy-α-pyrrolidinobutiophenone), demonstrating the importance of analyte dependence, and the dual stabilizing effect of both the pyrollidine and methylenedioxy groups. Biological evidence may be subjected to a variety of environmental conditions prior to, and during transport to the forensic laboratory. These findings demonstrate the inherent instability of certain cathinone species in biological evidence under some conditions. Moreover, this study highlights the need for quantitative drug findings in toxicological investigations to be interpreted cautiously, and within the context of specimen storage and integrity.

Extracellular pH modulates GABAergic neurotransmission in rat hypothalamus.

PubMed

Chen, Z L; Huang, R Q

2014-06-20

Changes in extracellular pH have a modulatory effect on GABAA receptor function. It has been reported that pH sensitivity of the GABA receptor is dependent on subunit composition and GABA concentration. Most of previous investigations focused on GABA-evoked currents, which only reflect the postsynaptic receptors. The physiological relevance of pH modulation of GABAergic neurotransmission is not fully elucidated. In the present studies, we examined the influence of extracellular pH on the GABAA receptor-mediated inhibitory neurotransmission in rat hypothalamic neurons. The inhibitory postsynaptic currents (IPSCs), tonic currents, and the GABA-evoked currents were recorded with whole-cell patch techniques on the hypothalamic slices from Sprague-Dawley rats at 15-26 postnatal days. The amplitude and frequency of spontaneous GABA IPSCs were significantly increased while the external pH was changed from 7.3 to 8.4. In the acidic pH (6.4), the spontaneous GABA IPSCs were reduced in amplitude and frequency. The pH induced changes in miniature GABA IPSCs (mIPSCs) similar to that in spontaneous IPSCs. The pH effect on the postsynaptic GABA receptors was assessed with exogenously applied varying concentrations of GABA. The tonic currents and the currents evoked by sub-saturating concentration of GABA ([GABA]) (10 μM) were inhibited by acidic pH and potentiated by alkaline pH. In contrast, the currents evoked by saturating [GABA] (1mM) were not affected by pH changes. We also investigated the influence of pH buffers and buffering capacity on pH sensitivity of GABAA receptors on human recombinant α1β2γ2 GABAA receptors stably expressed in HEK 293 cells. The pH influence on GABAA receptors was similar in HEPES- and MES-buffered media, and not dependent on protonated buffers, suggesting that the observed pH effect on GABA response is a specific consequence of changes in extracellular protons. Our data suggest that the hydrogen ions suppress the GABAergic neurotransmission, which is mediated by both presynaptic and postsynaptic mechanisms. Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.

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.

Iminosugar glycosidase inhibitors: structural and thermodynamic dissection of the binding of isofagomine and 1-deoxynojirimycin to beta-glucosidases.

PubMed

Zechel, David L; Boraston, Alisdair B; Gloster, Tracey; Boraston, Catherine M; Macdonald, James M; Tilbrook, D Matthew G; Stick, Robert V; Davies, Gideon J

2003-11-26

The design and synthesis of transition-state mimics reflects the growing need both to understand enzymatic catalysis and to influence strategies for therapeutic intervention. Iminosugars are among the most potent inhibitors of glycosidases. Here, the binding of 1-deoxynojirimycin and (+)-isofagomine to the "family GH-1" beta-glucosidase of Thermotoga maritima is investigated by kinetic analysis, isothermal titration calorimetry, and X-ray crystallography. The binding of both of these iminosugar inhibitors is driven by a large and favorable enthalpy. The greater inhibitory power of isofagomine, relative to 1-deoxynojirimycin, however, resides in its significantly more favorable entropy; indeed the differing thermodynamic signatures of these inhibitors are further highlighted by the markedly different heat capacity values for binding. The pH dependence of catalysis and of inhibition suggests that the inhibitory species are protonated inhibitors bound to enzymes whose acid/base and nucleophile are ionized, while calorimetry indicates that one proton is released from the enzyme upon binding at the pH optimum of catalysis (pH 5.8). Given that these results contradict earlier proposals that the binding of racemic isofagomine to sweet almond beta-glucosidase was entropically driven (Bülow, A. et al. J. Am. Chem. Soc. 2000, 122, 8567-8568), we reinvestigated the binding of 1-deoxynojirimycin and isofagomine to the sweet almond enzyme. Calorimetry confirms that the binding of isofagomine to sweet almond beta-glucosidases is, as observed for the T. maritima enzyme, driven by a large favorable enthalpy. The crystallographic structures of the native T. maritima beta-glucosidase, and its complexes with isofagomine and 1-deoxynojirimycin, all at approximately 2.1 A resolution, reveal that additional ordering of bound solvent may present an entropic penalty to 1-deoxynojirimycin binding that does not penalize isofagomine.

Transporters involved in pH and K + homeostasis affect pollen wall formation, male fertility, and embryo development

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

Padmanaban, Senthilkumar; Czerny, Daniel D.; Levin, Kara A.

Flowering plant genomes encode multiple cation/H + exchangers (CHXs) whose functions are largely unknown. AtCHX17, AtCHX18, and AtCHX19 are membrane transporters that modulate K+ and pH homeostasis and are localized in the dynamic endomembrane system. Loss of function reduced seed set, but the particular phase(s) of reproduction affected was not determined. Pollen tube growth and ovule targeting of chx17chx18chx19 mutant pollen appeared normal, but reciprocal cross experiments indicate a largely male defect. Although triple mutant pollen tubes reach ovules of a wild-type pistil and a synergid cell degenerated, half of those ovules were unfertilized or showed fertilization of the eggmore » or central cell, but not both female gametes. Fertility could be partially compromised by impaired pollen tube and/or sperm function as CHX19 and CHX18 are expressed in the pollen tube and sperm cell, respectively. When fertilization was successful in self-pollinated mutants, early embryo formation was retarded compared with embryos from wild-type ovules receiving mutant pollen. Thus CHX17 and CHX18 proteins may promote embryo development possibly through the endosperm where these genes are expressed. The reticulate pattern of the pollen wall was disorganized in triple mutants, indicating perturbation of wall formation during male gametophyte development. Lastly, as pH and cation homeostasis mediated by AtCHX17 affect membrane trafficking and cargo delivery, these results suggest that male fertility, sperm function, and embryo development are dependent on proper cargo sorting and secretion that remodel cell walls, plasma membranes, and extracellular factors.« less

Transporters involved in pH and K + homeostasis affect pollen wall formation, male fertility, and embryo development

DOE PAGES

Padmanaban, Senthilkumar; Czerny, Daniel D.; Levin, Kara A.; ...

2017-02-23

Flowering plant genomes encode multiple cation/H + exchangers (CHXs) whose functions are largely unknown. AtCHX17, AtCHX18, and AtCHX19 are membrane transporters that modulate K+ and pH homeostasis and are localized in the dynamic endomembrane system. Loss of function reduced seed set, but the particular phase(s) of reproduction affected was not determined. Pollen tube growth and ovule targeting of chx17chx18chx19 mutant pollen appeared normal, but reciprocal cross experiments indicate a largely male defect. Although triple mutant pollen tubes reach ovules of a wild-type pistil and a synergid cell degenerated, half of those ovules were unfertilized or showed fertilization of the eggmore » or central cell, but not both female gametes. Fertility could be partially compromised by impaired pollen tube and/or sperm function as CHX19 and CHX18 are expressed in the pollen tube and sperm cell, respectively. When fertilization was successful in self-pollinated mutants, early embryo formation was retarded compared with embryos from wild-type ovules receiving mutant pollen. Thus CHX17 and CHX18 proteins may promote embryo development possibly through the endosperm where these genes are expressed. The reticulate pattern of the pollen wall was disorganized in triple mutants, indicating perturbation of wall formation during male gametophyte development. Lastly, as pH and cation homeostasis mediated by AtCHX17 affect membrane trafficking and cargo delivery, these results suggest that male fertility, sperm function, and embryo development are dependent on proper cargo sorting and secretion that remodel cell walls, plasma membranes, and extracellular factors.« less

HF in clusters of molecular hydrogen. I. Size evolution of quantum solvation by parahydrogen molecules.

PubMed

Jiang, Hao; Bacić, Zlatko

2005-06-22

We present a theoretical study of the quantum solvation of the HF molecule by a small number of parahydrogen molecules, having n = 1-13 solvent particles. The minimum-energy cluster structures determined for n = 1-12 have all of the H(2) molecules in the first solvent shell. The first solvent shell closes at n = 12 and its geometry is icosahedral, with the HF molecule at the center. The quantum-mechanical ground-state properties of the clusters are calculated exactly using the diffusion Monte Carlo method. The zero-point energy of (p-H(2))(n)HF clusters is unusually large, amounting to 86% of the potential well depth for n > 7. The radial probability distribution functions (PDFs) confirm that the first solvent shell is complete for n = 12, and that the 13th p-H(2) molecule begins to fill the second solvent shell. The p-H(2) molecules execute large-amplitude motions and are highly mobile, making the solvent cage exceptionally fluxional. The anisotropy of the solvent, very pronounced for small clusters, decreases rapidly with increasing n, so that for n approximately 8-9 the solvent environment is practically isotropic. The analysis of the pair angular PDF reveals that for a given n, the parahydrogen solvent density around the HF is modulated in a pattern which clearly reflects the lowest-energy cluster configuration. The rigidity of the solvent clusters displays an interesting size dependence, increasing from n = 6 to 9, becoming floppier for n = 10, and increasing again up to n = 12, as the solvent shell is filled. The rigidity of the solvent cage appears to reach its maximum for n = 12, the point at which the first solvent shell is closed.

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.

Effect of pH on the structure, function, and stability of human calcium/calmodulin-dependent protein kinase IV: combined spectroscopic and MD simulation studies.

PubMed

Naz, Huma; Shahbaaz, Mohd; Bisetty, Krishna; Islam, Asimul; Ahmad, Faizan; Hassan, Md Imtaiyaz

2016-06-01

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV) is a member of Ser/Thr protein kinase family. It is regulated by the calcium-calmodulin dependent signal through a secondary messenger, Ca(2+), which leads to the activation of its autoinhibited form. The over-expression and mutation in CAMKIV as well as change in Ca(2+) concentration is often associated with numerous neurodegenerative diseases and cancers. We have successfully cloned, expressed, and purified a functionally active kinase domain of human CAMKIV. To observe the effect of different pH conditions on the structural and functional properties of CAMKIV, we have used spectroscopic techniques such as circular diachroism (CD) absorbance and fluorescence. We have observed that within the pH range 5.0-11.5, CAMKIV maintained both its secondary and tertiary structures, along with its function, whereas significant aggregation was observed at acidic pH (2.0-4.5). We have also performed ATPase activity assays under different pH conditions and found a significant correlation between the structure and enzymatic activities of CAMKIV. In-silico validations were further carried out by modeling the 3-dimensional structure of CAMKIV and then subjecting it to molecular dynamics (MD) simulations to understand its conformational behavior in explicit water conditions. A strong correlation between spectroscopic observations and the output of molecular dynamics simulation was observed for CAMKIV.

The Effect of Carbonate and pH on Hydrogen Oxidation and Oxygen Reduction on Pt-Based Electrocatalysts in Alkaline Media

DOE PAGES

John, Samuel St.; Atkinson, Robert W.; Roy, Asa; ...

2016-01-11

In this paper, we investigated the performance of several carbon-supported Ru xPt y electrocatalysts for their alkaline hydrogen oxidation and oxygen reduction performance in the presence of carbonate and compared their performance with monometallic, carbon-supported Pt. Our results indicate a strong dependence of HOR upon pH for the monometallic Pt catalysts (22 mV/pH) and a weak dependence upon pH for the Ru-containing electrocatalysts (3.7, 2.5, and 4.7 mV/pH on Ru 0.2Pt 0.8, Ru 0.4Pt 0.6, and Ru 0.8Pt 0.2, respectively). These results are consistent with our previous findings that illustrate a change in rds from electron transfer (on monometallic Pt)more » to dissociative hydrogen adsorption (on Ru xPt y catalysts). Analysis of the kinetic currents to determine the rate-determining step via Tafel slope analysis provides additional data supporting this conclusion. There is no difference in the performance at comparable pH values in the presence or absence of carbonate on monometallic Pt indicating that water/hydroxide is the primary proton acceptor for alkaline HOR in 0.1 M KOH aqueous electrolyte. Finally, we observe no pH or carbonate dependence for the ORR on monometallic Pt.« less

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.

The Effect of Carbonate and pH on Hydrogen Oxidation and Oxygen Reduction on Pt-Based Electrocatalysts in Alkaline Media

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

John, Samuel St.; Atkinson, Robert W.; Roy, Asa

In this paper, we investigated the performance of several carbon-supported Ru xPt y electrocatalysts for their alkaline hydrogen oxidation and oxygen reduction performance in the presence of carbonate and compared their performance with monometallic, carbon-supported Pt. Our results indicate a strong dependence of HOR upon pH for the monometallic Pt catalysts (22 mV/pH) and a weak dependence upon pH for the Ru-containing electrocatalysts (3.7, 2.5, and 4.7 mV/pH on Ru 0.2Pt 0.8, Ru 0.4Pt 0.6, and Ru 0.8Pt 0.2, respectively). These results are consistent with our previous findings that illustrate a change in rds from electron transfer (on monometallic Pt)more » to dissociative hydrogen adsorption (on Ru xPt y catalysts). Analysis of the kinetic currents to determine the rate-determining step via Tafel slope analysis provides additional data supporting this conclusion. There is no difference in the performance at comparable pH values in the presence or absence of carbonate on monometallic Pt indicating that water/hydroxide is the primary proton acceptor for alkaline HOR in 0.1 M KOH aqueous electrolyte. Finally, we observe no pH or carbonate dependence for the ORR on monometallic Pt.« less

Geochemical modeling of reactions and partitioning of trace metals and radionuclides during titration of contaminated acidic sediments.

PubMed

Zhang, Fan; Luo, Wensui; Parker, Jack C; Spalding, Brian P; Brooks, Scott C; Watson, David B; Jardine, Philip M; Gu, Baohua

2008-11-01

Many geochemical reactions that control aqueous metal concentrations are directly affected by solution pH. However, changes in solution pH are strongly buffered by various aqueous phase and solid phase precipitation/dissolution and adsorption/desorption reactions. The ability to predict acid-base behavior of the soil-solution system is thus critical to predict metal transport under variable pH conditions. This studywas undertaken to develop a practical generic geochemical modeling approach to predict aqueous and solid phase concentrations of metals and anions during conditions of acid or base additions. The method of Spalding and Spalding was utilized to model soil buffer capacity and pH-dependent cation exchange capacity by treating aquifer solids as a polyprotic acid. To simulate the dynamic and pH-dependent anion exchange capacity, the aquifer solids were simultaneously treated as a polyprotic base controlled by mineral precipitation/ dissolution reactions. An equilibrium reaction model that describes aqueous complexation, precipitation, sorption and soil buffering with pH-dependent ion exchange was developed using HydroGeoChem v5.0 (HGC5). Comparison of model results with experimental titration data of pH, Al, Ca, Mg, Sr, Mn, Ni, Co, and SO4(2-) for contaminated sediments indicated close agreement suggesting that the model could potentially be used to predictthe acid-base behavior of the sediment-solution system under variable pH conditions.

Monitoring Intracellular pH Change with a Genetically Encoded and Ratiometric Luminescence Sensor in Yeast and Mammalian Cells.

PubMed

Zhang, Yunfei; Robertson, J Brian; Xie, Qiguang; Johnson, Carl Hirschie

2016-01-01

"pHlash" is a novel bioluminescence-based pH sensor for measuring intracellular pH, which is developed based on Bioluminescence Resonance Energy Transfer (BRET). pHlash is a fusion protein between a mutant of Renilla luciferase (RLuc) and a Venus fluorophore. The spectral emission of purified pHlash protein exhibits pH dependence in vitro. When expressed in either yeast or mammalian cells, pHlash reports basal pH and cytosolic acidification. In this chapter, we describe an in vitro characterization of pHlash, and also in vivo assays including in yeast cells and in HeLa cells using pHlash as a cytoplasmic pH indicator.

Isotope effect studies of the pyruvate-dependent histidine decarboxylase from Lactobacillus 30a

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

Abell, L.M.; O'Leary, M.H.

1988-08-09

The decarboxylation of histidine by the pyruvate-dependent histidine decarboxylase of Lactobacillus 30 a shows a carbon isotope effect k/sup 12//k/sup 13/ = 1.0334 +/- 0.0005 and a nitrogen isotope effect k/sup 14//k/sup 15/ = 0.9799 +/- 0.0006 at pH 4.8, 37/sup 0/C. The carbon isotope effect is slightly increased by deuteriation of the substrate and slightly decreased in D/sub 2/O. The observed nitrogen isotope effect indicates that the imine nitrogen in the substrate-Schiff base intermediate complex is ordinarily protonated, and the pH dependence of the carbon isotope effect indicates that both protonated and unprotonated forms of this intermediate are capablemore » of undergoing decarboxylation. As with the pyridoxal 5'-phosphate dependent enzyme, Schiff base formation and decarboxylation are jointly rate-limiting, with the intermediate histidine-pyruvate Schiff base showing a decarboxylation/Schiff base hydrolysis ratio of 0.5-1.0 at pH 4.8. The decarboxylation transition state is more reactant-like for the pyruvate-dependent enzyme than for the pyridoxal 5'-phosphate dependent enzyme. These studies find no particular energetic or catalytic advantage to the use of pyridoxal 5'-phosphate over covalently bound pyruvate in catalysis of the decarboxylation of histidine.« less

Acidified seawater impacts sea urchin larvae pH regulatory systems relevant for calcification

PubMed Central

Stumpp, Meike; Hu, Marian Y.; Melzner, Frank; Gutowska, Magdalena A.; Dorey, Narimane; Himmerkus, Nina; Holtmann, Wiebke C.; Dupont, Sam T.; Thorndyke, Michael C.; Bleich, Markus

2012-01-01

Calcifying echinoid larvae respond to changes in seawater carbonate chemistry with reduced growth and developmental delay. To date, no information exists on how ocean acidification acts on pH homeostasis in echinoderm larvae. Understanding acid–base regulatory capacities is important because intracellular formation and maintenance of the calcium carbonate skeleton is dependent on pH homeostasis. Using H+-selective microelectrodes and the pH-sensitive fluorescent dye BCECF, we conducted in vivo measurements of extracellular and intracellular pH (pHe and pHi) in echinoderm larvae. We exposed pluteus larvae to a range of seawater CO2 conditions and demonstrated that the extracellular compartment surrounding the calcifying primary mesenchyme cells (PMCs) conforms to the surrounding seawater with respect to pH during exposure to elevated seawater pCO2. Using FITC dextran conjugates, we demonstrate that sea urchin larvae have a leaky integument. PMCs and spicules are therefore directly exposed to strong changes in pHe whenever seawater pH changes. However, measurements of pHi demonstrated that PMCs are able to fully compensate an induced intracellular acidosis. This was highly dependent on Na+ and HCO3−, suggesting a bicarbonate buffer mechanism involving secondary active Na+-dependent membrane transport proteins. We suggest that, under ocean acidification, maintained pHi enables calcification to proceed despite decreased pHe. However, this probably causes enhanced costs. Increased costs for calcification or cellular homeostasis can be one of the main factors leading to modifications in energy partitioning, which then impacts growth and, ultimately, results in increased mortality of echinoid larvae during the pelagic life stage. PMID:23077257

pH-dependent kinetics of copper ions binding to amyloid-β peptide.

PubMed

Bin, Yannan; Chen, Shu; Xiang, Juan

2013-02-01

Interactions of amyloid-β peptide (Aβ) with Cu(2+) are known to be pH-dependent and believed to play a crucial role in the neurotoxicity of Alzheimer's disease (AD). Some research has revealed that injured brains with lowered pH have higher risks of developing AD. However, reported experiments were performed under neutral or mildly acidic conditions, and no reports about the affinity of Aβ-Cu(2+) below pH6.0. In this study, surface plasmon resonance (SPR) sensor with immobilized Aβ was used to investigate the formation of Aβ-Cu(2+) complexes under acidic pH conditions. Dissociation constants were calculated and shown to be pH-dependent, ranging from 3.5×10(-8)M to 8.7×10(-3)M in the pH range from 7.0 to 4.0. The physiological significance of K(d) was preliminarily investigated by monitoring the generation of OH() in aerobic solutions containing Aβ-Cu(2+) and Cu(2+). The results imply that acidic conditions could aggravate the oxidative stress in the presence of Cu(2+), and the weak affinities of Aβ-Cu(2+) under mildly acidic pH of 5.0-6.0 could further enhance the oxidative damage. However, the oxidative stress effect of Aβ is negligible due to the suppressed formation of Aβ-Cu(2+) below pH5.0. This work is useful for the in-depth understanding of the role of Aβ-Cu(2+) in AD neuropathology. Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.

Underlying thermodynamics of pH-dependent allostery.

PubMed

Di Russo, Natali V; Martí, Marcelo A; Roitberg, Adrian E

2014-11-13

Understanding the effects of coupling protein protonation and conformational states is critical to the development of drugs targeting pH sensors and to the rational engineering of pH switches. In this work, we address this issue by performing a comprehensive study of the pH-regulated switch from the closed to the open conformation in nitrophorin 4 (NP4) that determines its pH-dependent activity. Our calculations show that D30 is the only amino acid that has two significantly different pKas in the open and closed conformations, confirming its critical role in regulating pH-dependent behavior. In addition, we describe the free-energy landscape of the conformational change as a function of pH, obtaining accurate estimations of free-energy barriers and equilibrium constants using different methods. The underlying thermodynamic model of the switch workings suggests the possibility of tuning the observed pKa only through the conformational equilibria, keeping the same conformation-specific pKas, as evidenced by the proposed K125L mutant. Moreover, coupling between the protonation and conformational equilibria results in efficient regulation and pH-sensing around physiological pH values only for some combinations of protonation and conformational equilibrium constants, placing constraints on their possible values and leaving a narrow space for protein molecular evolution. The calculations and analysis presented here are of general applicability and provide a guide as to how more complex systems can be studied, offering insight into how pH-regulated allostery works of great value for designing drugs that target pH sensors and for rational engineering of pH switches beyond the common histidine trigger.

Flagellum synchronization inhibits large-scale hydrodynamic instabilities in sperm suspensions

NASA Astrophysics Data System (ADS)

Schöller, Simon F.; Keaveny, Eric E.

2016-11-01

Sperm in suspension can exhibit large-scale collective motion and form coherent structures. Our picture of such coherent motion is largely based on reduced models that treat the swimmers as self-locomoting rigid bodies that interact via steady dipolar flow fields. Swimming sperm, however, have many more degrees of freedom due to elasticity, have a more exotic shape, and generate spatially-complex, time-dependent flow fields. While these complexities are known to lead to phenomena such as flagellum synchronization and attraction, how these effects impact the overall suspension behaviour and coherent structure formation is largely unknown. Using a computational model that captures both flagellum beating and elasticity, we simulate suspensions on the order of 103 individual swimming sperm cells whose motion is coupled through the surrounding Stokesian fluid. We find that the tendency for flagella to synchronize and sperm to aggregate inhibits the emergence of the large-scale hydrodynamic instabilities often associated with active suspensions. However, when synchronization is repressed by adding noise in the flagellum actuation mechanism, the picture changes and the structures that resemble large-scale vortices appear to re-emerge. Supported by an Imperial College PhD scholarship.

Effect of pH and chloroauric acid concentration on the geometry of gold nanoparticles obtained by photochemical synthesis

NASA Astrophysics Data System (ADS)

Conde Rodríguez, G. R.; Gauthier, G. H.; Ladeira, L. O.; Sanabria Cala, J. A.; Laverde Cataño, D.

2017-12-01

Due to their excellent surface properties, gold nanoparticles have been used in a wide range of applications from optics and catalysis to biology and cancer treatment by thermal therapy. Gold nanoparticles can absorb a large amount of radiation according to their geometry, such as nanospheres and nanorods. The importance of gold nanoparticles geometry is based on the electromagnetic spectrum wavelength where exists a greater absorption of radiation, which belongs to the visible region for nanospheres and ranges between visible and near infrared regions for nanorods, conferring greater biomedical applicability to the latter. When using photochemical synthesis method, which consists of reducing gold atoms to their metallic state with UV radiation, the geometry of gold nanoparticles depends on different variables such as: 1) pH, 2) concentration of chloroauric acid, 3) the surfactant, 4) concentration of silver nitrate, 5) temperature and 6) irradiation time. Therefore, in this study the geometry of the gold nanoparticles obtained by photochemical synthesis was determined as a function of solution pH and chloroauric acid concentration, using Spectrophotometry in the Ultraviolet Visible region (UV-vis) as characterization technique. From the analysis of the UV-vis spectra, it was determined that at an acidic pH the particles have two absorption bands corresponding to nanorods geometry, while at a basic pH only nanospheres are found and at a neutral pH the lower relative intensity of the second band indicates the simultaneous existence of the two geometries. The increase in the concentration of chloroauric acid produces a decrease in the amount of synthesized nanorods, seen as a decrease of the relative intensity of the second absorption band. Therefore, obtaining gold nanoparticles with nanorods geometry favours fields such as biomedicine, because they are capable of absorbing infrared radiation and can be used as photosensitive agents in localized thermal therapy against cancer.

Molecular characterization of the group II chaperonin from the hyperthermophilic archaeum Pyrococcus horikoshii OT3.

PubMed

Okochi, Mina; Matsuzaki, Hiroki; Nomura, Tomoko; Ishii, Noriyuki; Yohda, Masafumi

2005-04-01

The group II chaperonin from the hyperthermophilic archaeum Pyrococcus horikoshii OT3 (PhCPN) and its functional cooperation with the cognate prefoldin were investigated. PhCPN existed as a homo-oligomer in a double-ring structure, which protected the citrate synthase of a porcine heart from thermal aggregation at 45 degrees C, and did the same on the isopropylmalate dehydrogenase (IPMDH) of a thermophilic bacterium, Thermus thermophilus HB8, at 90 degrees C. PhCPN also enhanced the refolding of green fluorescent protein (GFP), which had been unfolded by low pH, in an ATP-dependent manner. Unexpectedly, functional cooperation between PhCPN and Pyrococcus prefoldin (PhPFD) in the refolding of GFP was not observed. Instead, cooperation between PhCPN and PhPFD was observed in the refolding of IPMDH unfolded with guanidine hydrochloride. Although PhCPN alone was not effective in the refolding of IPMDH, the refolding efficiency was enhanced by the cooperation of PhCPN with PhPFD.

Mechanism for pH-dependent gene regulation by amino-terminus-mediated homooligomerization of Bacillus subtilis anti-trp RNA-binding attenuation protein

PubMed Central

Sachleben, Joseph R.; McElroy, Craig A.; Gollnick, Paul; Foster, Mark P.

2010-01-01

Anti-TRAP (AT) is a small zinc-binding protein that regulates tryptophan biosynthesis in Bacillus subtilis by binding to tryptophan-bound trp RNA-binding attenuation protein (TRAP), thereby preventing it from binding RNA, and allowing transcription and translation of the trpEDCFBA operon. Crystallographic and sedimentation studies have shown that AT can homooligomerize to form a dodecamer, AT12, composed of a tetramer of trimers, AT3. Structural and biochemical studies suggest that only trimeric AT is active for binding to TRAP. Our chromatographic and spectroscopic data revealed that a large fraction of recombinantly overexpressed AT retains the N-formyl group (fAT), presumably due to incomplete N-formyl-methionine processing by peptide deformylase. Hydrodynamic parameters from NMR relaxation and diffusion measurements showed that fAT is exclusively trimeric (AT3), while (deformylated) AT exhibits slow exchange between both trimeric and dodecameric forms. We examined this equilibrium using NMR spectroscopy and found that oligomerization of active AT3 to form inactive AT12 is linked to protonation of the amino terminus. Global analysis of the pH dependence of the trimer-dodecamer equilibrium revealed a near physiological pKa for the N-terminal amine of AT and yielded a pH-dependent oligomerization equilibrium constant. Estimates of excluded volume effects due to molecular crowding suggest the oligomerization equilibrium may be physiologically important. Because deprotonation favors “active” trimeric AT and protonation favors “inactive” dodecameric AT, our findings illuminate a possible mechanism for sensing and responding to changes in cellular pH. PMID:20713740

LEAD AND COPPER CONTROL WITH NON-ZINC ORTHOPHOSPHATE

EPA Science Inventory

Successful application of orthophosphate formulations not containing zinc for achieving control of copper and lead corrosion requires careful consideration of the background water chemistry, particularly pH and DIC. Inhibitor performance is extremely dependent upon dosage and pH,...

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.

Norcyanine dyes with benzo[c,d]indolium moiety: Spectral sensitivity with pH change for fluorescence pH imaging in living cells.

PubMed

Guan, Li; Liu, Qi; Zhang, Borui; Wang, Lanying

2017-01-01

Fluorescence pH imaging in living cells is a rapidly expanding research direction, however, it relies on the development of pH-sensitive fluorescent imaging agents. Here four norcyanine dyes with benzo[c,d]indolium moiety, exhibiting high spectral sensitivity with pH changes, were synthesized for fluorescence pH imaging in living cells, and characterized by 1 H NMR, 13 C NMR, IR, UV-Vis and HRMS. The investigation of their spectral properties in methanol and water showed that the absorption and emission maxima were in the region 488-618nm and 583-651nm, respectively, and four dyes exhibited high photostability. The pH spectral titrations showed that selective dye D1 had pH-dependent absorption spectral changes within the pH range of 2.4 to 9.4, and high fluorescent spectral sensitivity at pH5.0-8.0, with a pK a of 5.0. A cell association study indicated that dye D1 exhibited no or mild cytotoxicity at the application dose and duration, and could be accumulated in cells and mainly distributed in the cytoplasm, giving red fluorescence imaging. In particular, dye D1 could achieve pH-dependent fluorescence imaging in living cells with the increase of pH from 3.0 to 8.0, at excitation wavelength of 543nm and receiving wavelength of 655-755nm, which was valuable for studying the weak acidic, neutral and weak alkaline biological tissue compartments. Copyright © 2016 Elsevier B.V. All rights reserved.

Decrease of U(VI) Immobilization Capability of the Facultative Anaerobic Strain Paenibacillus sp. JG-TB8 under Anoxic Conditions Due to Strongly Reduced Phosphatase Activity

PubMed Central

Reitz, Thomas; Rossberg, Andre; Barkleit, Astrid; Selenska-Pobell, Sonja; Merroun, Mohamed L.

2014-01-01

Interactions of a facultative anaerobic bacterial isolate named Paenibacillus sp. JG-TB8 with U(VI) were studied under oxic and anoxic conditions in order to assess the influence of the oxygen-dependent cell metabolism on microbial uranium mobilization and immobilization. We demonstrated that aerobically and anaerobically grown cells of Paenibacillus sp. JG-TB8 accumulate uranium from aqueous solutions under acidic conditions (pH 2 to 6), under oxic and anoxic conditions. A combination of spectroscopic and microscopic methods revealed that the speciation of U(VI) associated with the cells of the strain depend on the pH as well as on the aeration conditions. At pH 2 and pH 3, uranium was exclusively bound by organic phosphate groups provided by cellular components, independently on the aeration conditions. At higher pH values, a part (pH 4.5) or the total amount (pH 6) of the dissolved uranium was precipitated under oxic conditions in a meta-autunite-like uranyl phosphate mineral phase without supplying an additional organic phosphate substrate. In contrast to that, under anoxic conditions no mineral formation was observed at pH 4.5 and pH 6, which was clearly assigned to decreased orthophosphate release by the cells. This in turn was caused by a suppression of the indigenous phosphatase activity of the strain. The results demonstrate that changes in the metabolism of facultative anaerobic microorganisms caused by the presence or absence of oxygen can decisively influence U(VI) biomineralization. PMID:25157416

Transient kinetic studies of pH-dependent hydrolyses by exo-type carboxypeptidase P on a 27-MHz quartz crystal microbalance.

PubMed

Furusawa, Hiroyuki; Takano, Hiroki; Okahata, Yoshio

2008-02-15

pH-Dependent kinetic parameters (k(on), k(off), and k(cat)) of protein (myoglobin) hydrolyses catalyzed by exo-enzyme (carboxypeptidase P, CPP) were obtained by using a protein-immobilized quartz crystal microbalance (QCM) in acidic aqueous solutions. The formation of the enzyme-substrate (ES) complex (k(on)), the decay of the ES complex (k(off)), and the formation of the product (k(cat)) could be analyzed by transient kinetics as mass changes on the QCM plate. The Kd (k(off)/k(on)) value was different from the Michaelis constant Km calculated from (k(off) + k(cat))/k(on) due to k(cat) > k(off). The rate-determining step was the binding step (k(on), and the catalytic rate k(cat) was faster than other k(on) and k(off) values. In the range of pH 2.5-5.0, values of k(on) gradually increased with decreasing pH showing a maximum at pH 3.7, values of k(off) were independent of pH, and k(cat) increased gradually with decreasing pH. As a result, the apparent rate constant (k(cat)/Km) showed a maximum at pH 3.7 and gradually increased with decreasing pH. The optimum pH at 3.7 of k(on) is explained by the optimum binding ability of CPP to the COOH terminus of the substrate with hydrogen bonds. The increase of k(cat) at the lower pH correlated with the decrease of alpha-helix contents of the myoglobin substrate on the QCM.

Temperature- and pH-dependent aqueous-phase kinetics of the reactions of glyoxal and methylglyoxal with atmospheric amines and ammonium sulfate

NASA Astrophysics Data System (ADS)

Sedehi, Nahzaneen; Takano, Hiromi; Blasic, Vanessa A.; Sullivan, Kristin A.; De Haan, David O.

2013-10-01

Reactions of glyoxal (Glx) and methylglyoxal (MG) with primary amines and ammonium salts may produce brown carbon and N-containing oligomers in aqueous aerosol. 1H NMR monitoring of reactant losses and product appearance in bulk aqueous reactions were used to derive rate constants and quantify competing reaction pathways as a function of pH and temperature. Glx + ammonium sulfate (AS) and amine reactions generate products containing C-N bonds, with rates depending directly on pH: rate = (70 ± 60) M-1 s-1fAld [Glx]totfAm [Am]tot, where fAld is the fraction of aldehyde with a dehydrated aldehyde functional group, and fAm is the fraction of amine or ammonia that is deprotonated at a given pH. MG + amine reactions generate mostly aldol condensation products and exhibit less pH dependence: rate = 10[(0.36 ± 0.06) × pH - (3.6 ± 0.3)] M-1 s-1fAld [MG]tot [Am]tot. Aldehyde + AS reactions are less temperature-dependent (Ea = 18 ± 8 kJ mol-1) than corresponding amine reactions (Ea = 50 ± 11 kJ mol-1). Using aerosol concentrations of [OH] = 10-12 M, [amine]tot = [AS] = 0.1 M, fGlx = 0.046 and fMG = 0.09, we estimate that OH radical reactions are normally the major aerosol-phase sink for both dicarbonyl compounds. However, reactions with AS and amines together can account for up to 12 and 45% of daytime aerosol-phase glyoxal and methylglyoxal reactivity, respectively, in marine aerosol at pH 5.5. Reactions with AS and amines become less important in acidic or non-marine aerosol, but may still be significant atmospheric sources of brown carbon, imidazoles, and nitrogen-containing oligomers.

Reduced flavin: NMR investigation of N5-H exchange mechanism, estimation of ionisation constants and assessment of properties as biological catalyst.

PubMed

Macheroux, Peter; Ghisla, Sandro; Sanner, Christoph; Rüterjans, Heinz; Müller, Franz

2005-11-25

The flavin in its FMN and FAD forms is a versatile cofactor that is involved in catalysis of most disparate types of biological reactions. These include redox reactions such as dehydrogenations, activation of dioxygen, electron transfer, bioluminescence, blue light reception, photobiochemistry (as in photolyases), redox signaling etc. Recently, hitherto unrecognized types of biological reactions have been uncovered that do not involve redox shuffles, and might involve the reduced form of the flavin as a catalyst. The present work addresses properties of reduced flavin relevant in this context. N(5)-H exchange reactions of the flavin reduced form and its pH dependence were studied using the 15N-NMR-signals of 15N-enriched, reduced flavin in the pH range from 5 to 12. The chemical shifts of the N(3) and N(5) resonances are not affected to a relevant extent in this pH range. This contrasts with the multiplicity of the N(5)-resonance, which strongly depends on pH. It is a doublet between pH 8.45 and 10.25 that coalesces into a singlet at lower and higher pH values. From the line width of the 15N(5) signal the pH-dependent rate of hydrogen exchange was deduced. The multiplicity of the 15N(5) signal and the proton exchange rates are little dependent on the buffer system used. The exchange rates allow an estimation of the pKa value of N(5)-H deprotonation in reduced flavin to be >or= 20. This value imposes specific constraints for mechanisms of flavoprotein catalysis based on this process. On the other hand the pK asymptotically equal to 4 for N(5)-H protonation (to form N(5)+-H2) would be consistent with a role of N(5)-H as a base.

Molecular Insights into the pH-Dependent Adsorption and Removal of Ionizable Antibiotic Oxytetracycline by Adsorbent Cyclodextrin Polymers

PubMed Central

Zhang, Yu; Cai, Xiyun; Xiong, Weina; Jiang, Hao; Zhao, Haitong; Yang, Xianhai; Li, Chao; Fu, Zhiqiang; Chen, Jingwen

2014-01-01

Effects of pH on adsorption and removal efficiency of ionizable organic compounds (IOCs) by environmental adsorbents are an area of debate, because of its dual mediation towards adsorbents and adsorbate. Here, we probe the pH-dependent adsorption of ionizable antibiotic oxytetracycline (comprising OTCH2 +, OTCH±, OTC−, and OTC2−) onto cyclodextrin polymers (CDPs) with the nature of molecular recognition and pH inertness. OTCH± commonly has high adsorption affinity, OTC− exhibits moderate affinity, and the other two species have negligible affinity. These species are evidenced to selectively interact with structural units (e.g., CD cavity, pore channel, and network) of the polymers and thus immobilized onto the adsorbents to different extents. The differences in adsorption affinity and mechanisms of the species account for the pH-dependent adsorption of OTC. The mathematical equations are derived from the multiple linear regression (MLR) analysis of quantitatively relating adsorption affinity of OTC at varying pH to adsorbent properties. A combination of the MLR analysis for OTC and molecular recognition of adsorption of the species illustrates the nature of the pH-dependent adsorption of OTC. Based on this finding, γ-HP-CDP is chosen to adsorb and remove OTC at pH 5.0 and 7.0, showing high removal efficiency and strong resistance to the interference of coexisting components. PMID:24465975

Water bicarbonate modulates the response of the shore crab Carcinus maenas to ocean acidification.

PubMed

Maus, Bastian; Bock, Christian; Pörtner, Hans-O

2018-05-23

Ocean acidification causes an accumulation of CO 2 in marine organisms and leads to shifts in acid-base parameters. Acid-base regulation in gill breathers involves a net increase of internal bicarbonate levels through transmembrane ion exchange with the surrounding water. Successful maintenance of body fluid pH depends on the functional capacity of ion-exchange mechanisms and associated energy budget. For a detailed understanding of the dependence of acid-base regulation on water parameters, we investigated the physiological responses of the shore crab Carcinus maenas to 4 weeks of ocean acidification [OA, P(CO 2 ) w  = 1800 µatm], at variable water bicarbonate levels, paralleled by changes in water pH. Cardiovascular performance was determined together with extra-(pH e ) and intracellular pH (pH i ), oxygen consumption, haemolymph CO 2 parameters, and ion composition. High water P(CO 2 ) caused haemolymph P(CO 2 ) to rise, but pH e and pH i remained constant due to increased haemolymph and cellular [HCO 3 - ]. This process was effective even under reduced seawater pH and bicarbonate concentrations. While extracellular cation concentrations increased throughout, anion levels remained constant or decreased. Despite similar levels of haemolymph pH and ion concentrations under OA, metabolic rates, and haemolymph flow were significantly depressed by 40 and 30%, respectively, when OA was combined with reduced seawater [HCO 3 - ] and pH. Our findings suggest an influence of water bicarbonate levels on metabolic rates as well as on correlations between blood flow and pH e . This previously unknown phenomenon should direct attention to pathways of acid-base regulation and their potential feedback on whole-animal energy demand, in relation with changing seawater carbonate parameters.

Polymeric micelle for tumor pH and folate-mediated targeting.

PubMed

Lee, Eun Seong; Na, Kun; Bae, You Han

2003-08-28

Novel pH-sensitive polymeric mixed micelles composed of poly(L-histidine) (polyHis; M(w) 5000)/PEG (M(n) 2000) and poly(L-lactic acid) (PLLA) (M(n) 3000)/PEG (M(n) 2000) block copolymers with or without folate conjugation were prepared by diafiltration. The micelles were investigated for pH-dependent drug release, folate receptor-mediated internalization and cytotoxicity using MCF-7 cells in vitro. The polyHis/PEG micelles showed accelerated adriamycin release as the pH decreased from 8.0. When the cumulative release for 24 h was plotted as a function of pH, the gradual transition in release rate appeared in a pH range from 8.0 to 6.8. In order to tailor the triggering pH of the polymeric micelles to the more acidic extracellular pH of tumors, while improving the micelle stability at pH 7.4, the PLLA/PEG block copolymer was blended with polyHis/PEG to form mixed micelles. Blending shifted the triggering pH to a lower value. Depending on the amount of PLLA/PEG, the mixed micelles were destabilized in the pH range of 7.2-6.6 (triggering pH for adriamycin release). When the mixed micelles were conjugated with folic acid, the in vitro results demonstrated that the micelles were more effective in tumor cell kill due to accelerated drug release and folate receptor-mediated tumor uptake. In addition, after internalization polyHis was found to be effective for cytosolic ADR delivery by virtue of fusogenic activity. This approach is expected to be useful for treatment of solid tumors in vivo.

Dynamic behavior of Yarrowia lipolytica in response to pH perturbations: dependence of the stress response on the culture mode.

PubMed

Timoumi, Asma; Cléret, Mégane; Bideaux, Carine; Guillouet, Stéphane E; Allouche, Yohan; Molina-Jouve, Carole; Fillaudeau, Luc; Gorret, Nathalie

2017-01-01

Yarrowia lipolytica, a non-conventional yeast with a promising biotechnological potential, is able to undergo metabolic and morphological changes in response to environmental conditions. The effect of pH perturbations of different types (pulses, Heaviside) on the dynamic behavior of Y. lipolytica W29 strain was characterized under two modes of culture: batch and continuous. In batch cultures, different pH (4.5, 5.6 (optimal condition), and 7) were investigated in order to identify the pH inducing a stress response (metabolic and/or morphologic) in Y. lipolytica. Macroscopic behavior (kinetic parameters, yields, viability) of the yeast was slightly affected by pH. However, contrary to the culture at pH 5.6, a filamentous growth was induced in batch experiments at pH 4.5 and 7. Proportions of the filamentous subpopulation reached 84 and 93 % (v/v) under acidic and neutral conditions, respectively. Given the significant impact of neutral pH on morphology, pH perturbations from 5.6 to 7 were subsequently assayed in batch and continuous bioreactors. For both process modes, the growth dynamics remained fundamentally unaltered during exposure to stress. Nevertheless, morphological behavior of the yeast was dependent on the culture mode. Specifically, in batch bioreactors where cells proliferated at their maximum growth rate, mycelia were mainly formed. Whereas, in continuous cultures at controlled growth rates (from 0.03 to 0.20 h -1 ) even closed to the maximum growth rate of the stain (0.24 h -1 ), yeast-like forms predominated. This pointed out differences in the kinetic behavior of filamentous and yeast subpopulations, cell age distribution, and pH adaptive mechanisms between both modes of culture.

SABRE hyperpolarisation of vitamin B3 as a function of pH† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc04043h Click here for additional data file.

PubMed Central

Olaru, A. M.; Burns, M. J.; Green, G. G. R.

2017-01-01

In this work we describe how the signal enhancements obtained through the SABRE process in methanol-d 4 solution are significantly affected by pH. Nicotinic acid (vitamin B3, NA) is used as the agent, and changing pH is shown to modify the level of polarisation transfer by over an order of magnitude, with significant improvements being seen in terms of the signal amplitude and relaxation rate at high pH values. These observations reveal that manipulating pH to improve SABRE enhancements levels may improve the potential of this method to quantify low concentrations of analytes in mixtures. 1H NMR spectroscopy results link this change to the form of the SABRE catalyst, which changes with pH, resulting in dramatic changes in the magnitude of the ligand exchange rates. The presented data also uses the fact that the chemical shifts of the nicotinic acids NMR resonances are affected by pH to establish that hyperpolarised 1H-based pH mapping with SABRE is possible. Moreover, the strong polarisation transfer field dependence shown in the amplitudes of the associated higher order longitudinal terms offers significant opportunities for the rapid detection of hyperpolarised NA in H2O itself without solvent suppression. 1H and 13C MRI images of hyperpolarised vitamin B3 in a series of test phantoms are presented that show pH dependent intensity and contrast. This study therefore establishes that when the pH sensitivity of NA is combined with the increase in signal gain provided for by SABRE hyperpolarisation, a versatile pH probe results. PMID:28507682

Procongopain from Trypanosoma congolense is processed at basic pH: an unusual feature among cathepsin L-like cysteine proteases.

PubMed

Serveau, Carole; Boulangé, Alain; Lecaille, Fabien; Gauthier, Francis; Authié, Edith; Lalmanach, Gilles

2003-06-01

Congopain, the major cysteine protease from Trypanosoma congolense, is synthesized as an inactive zymogen, and further converted into its active form after removal of the proregion, most probably via an autocatalytic mechanism. Processing of recombinant procongopain occurs via an apparent one-step or a multistep mechanism depending on the ionic strength. The auto-activation is pH-dependent, with an optimum at pH 4.0, and no activation observed at pH 6.0. After addition of dextran sulfate (10 microg/ml), an approx. 20-fold increase of processing (expressed as enzymatic activity) is observed. Furthermore, in the presence of dextran sulfate, procongopain can be processed at pH 8.0, an unusual feature among papain-like enzymes. Detection of procongopain and trypanosomal enzymatic activity in the plasma of T. congolense-infected cattle, together with the capacity of procongopain to be activated at weakly basic pH, suggest that procongopain may be extracellularly processed in the presence of blood vessel glycosaminoglycans, supporting the hypothesis that congopain acts as a pathogenic factor in host-parasite relationships.

pH dependence of the dissociation of multimeric hemoglobin probed by high hydrostatic pressure.

PubMed

Bispo, Jose A C; Santos, Jose L R; Landini, Gustavo F; Goncalves, Juliana M; Bonafe, Carlos F S

2007-02-01

We investigated the thermodynamic features of the classic alkaline dissociation of multimeric hemoglobin (3.1 MDa) from Glossoscolex paulistus (Annelidea) using high hydrostatic pressure. Light scattering measurements up to microscopic thermodynamic equilibrium indicated a high pH dependency of dissociation and association. Electron microscopy and gel filtration corroborated these findings. The volume change of dissociation decreased in absolute values from -48.0 mL/mol of subunit at pH 6.0 to -19.2 mL/mol at pH 9.0, suggesting a lack of protein interactions under alkaline conditions. Concomitantly, an increase in pH reduced the Gibbs free energy of dissociation from 37.7 to 27.5 kJ/mol of subunit. The stoichiometry of proton release calculated from the pressure-induced dissociation curves was +0.602 mol of H(+)/mol of subunit. These results provide a direct quantification of proton participation in stabilizing the aggregated state of the hemoglobin, and contribute to our understanding of protein-protein interactions and of the surrounding conditions that modulate the process of aggregation.

Degradation kinetics of chlorogenic acid at various pH values and effects of ascorbic acid and epigallocatechin gallate on its stability under alkaline conditions.

PubMed

Narita, Yusaku; Inouye, Kuniyo

2013-01-30

5-Caffeoylquinic acid (5-CQA) is generally referred to as chlorogenic acid and exhibits various biological activities such as antioxidant activity and porcine pancreas α-amylase inhibitory activities. 5-CQA may be useful as an antioxidant for food and to prevent diabetes and obesity. The degradation of 5-CQA and caffeic acid (CA) in an aqueous solution at 37 °C and pH 5.0-9.0 was studied. The degradation of 5-CQA and CA, demonstrating time and pH dependence (i.e., the rate constant, k, was higher at higher pH), was satisfactorily described by the Weibull equation. The stability of 5-CQA at pH 7.4 and 9.0 was improved by adding (-)-epigallocatechin gallate (EGCG) and ascorbic acid (AA). Moreover, the degradation of 5-CQA in the presence of EGCG or AA could be described by the Weibull equation. The k value in the presence of EGCG or AA was dependent on their concentration.

Sorption properties of Th(IV) on the raw diatomite--effects of contact time, pH, ionic strength and temperature.

PubMed

Sheng, Guodong; Hu, Jun; Wang, Xiangke

2008-10-01

Diatomite has a number of unique physicochemical properties and has diversified industrial uses. Natural diatomite has been tested as a potential sorbent for the removal of Th(IV) from aqueous solutions. The results indicate that sorption of Th(IV) is strongly dependent on ionic strength at pH<3, and is independent of ionic strength at pH>3. Outer-sphere complexation or ion exchange may be the main sorption mechanism of Th(IV) to diatomite at low pH values, whereas the sorption of Th(IV) at pH>3 is mainly dominated by inner-sphere complexation or precipitation. The competition for Th(IV) between aqueous or surface adsorbed anions (e.g., herein ClO(4)(-), NO(3)(-) and Cl(-)) and surface functional groups of diatomite is important for Th(IV) sorption. The thermodynamic data (DeltaH(0), DeltaS(0), DeltaG(0)) are calculated from the temperature-dependent sorption isotherms. The results suggest that sorption process of Th(IV) on diatomite is spontaneous and endothermic.

Passive asymmetric transport of hesperetin across isolated rabbit cornea.

PubMed

Srirangam, Ramesh; Majumdar, Soumyajit

2010-07-15

Hesperetin, an aglycone of the flavanone hesperidin, is a potential candidate for the treatment of diabetic retinopathy and macular edema. The purpose of this investigation was to determine solubility, stability and in vitro permeability characteristics of hesperetin across excised rabbit corneas. Aqueous and pH dependent solubility was determined using standard shake flask method. Solution stability was evaluated as a function of pH (1.2-9) and temperature (25 and 40 degrees C). Permeability of hesperetin was determined across the isolated rabbit cornea utilizing a side-bi-side diffusion apparatus, in the apical to basolateral (A-B) and basolateral to apical (B-A) directions. Hesperetin displayed asymmetrical transcorneal transport with a 2.3-fold higher apparent permeability in the B-A direction compared to the A-B direction. The transport process was observed to be pH dependent. Surprisingly, however, the involvement of efflux transporters or proton-coupled carrier-systems was not evident in this asymmetric transcorneal diffusion process. The passive and pH dependent corneal transport of hesperetin could probably be attributable to corneal ultrastructure, physicochemical characteristics of hesperetin and the role of transport buffer components. Copyright (c) 2010 Elsevier B.V. All rights reserved.

Cytotoxicity and Induction of Inflammation by Pepsin in Acid in Bronchial Epithelial Cells

PubMed Central

Bathoorn, Erik; Daly, Paul; Gaiser, Birgit; Sternad, Karl; Poland, Craig; MacNee, William; Drost, Ellen M.

2011-01-01

Introduction. Gastroesophageal reflux has been associated with chronic inflammatory diseases and may be a cause of airway remodelling. Aspiration of gastric fluids may cause damage to airway epithelial cells, not only because acidity is toxic to bronchial epithelial cells, but also since it contains digestive enzymes, such as pepsin. Aim. To study whether pepsin enhances cytotoxicity and inflammation in airway epithelial cells, and whether this is pH-dependent. Methods. Human bronchial epithelial cells were exposed to increasing pepsin concentrations in varying acidic milieus, and cell proliferation and cytokine release were assessed. Results. Cell survival was decreased by pepsin exposure depending on its concentration (F = 17.4) and pH level of the medium (F = 6.5) (both P < 0.01). Pepsin-induced interleukin-8 release was greater at lower pH (F = 5.1; P < 0.01). Interleukin-6 induction by pepsin was greater at pH 1.5 compared to pH 2.5 (mean difference 434%; P = 0.03). Conclusion. Pepsin is cytotoxic to bronchial epithelial cells and induces inflammation in addition to acid alone, dependent on the level of acidity. Future studies should assess whether chronic aspiration causes airway remodelling in chronic inflammatory lung diseases. PMID:21785693

Element mobilization from Bakken shales as a function of water chemistry.

PubMed

Wang, Lin; Burns, Scott; Giammar, Daniel E; Fortner, John D

2016-04-01

Waters that return to the surface after injection of a hydraulic fracturing fluid for gas and oil production contain elements, including regulated metals and metalloids, which are mobilized through interactions between the fracturing fluid and the shale formation. The rate and extent of mobilization depends on the geochemistry of the formation and the chemical characteristics of the fracturing fluid. In this work, laboratory scale experiments investigated the influence of water chemistry on element mobilization from core samples taken from the Bakken formation, one of the most productive shale oil plays in the US. Fluid properties were systematically varied and evaluated with regard to pH, oxidant level, solid:water ratio, temperature, and chemical additives. Element mobilization strongly depended on solution pH and redox conditions and to a lesser extent on the temperature and solid:water ratio. The presence of oxygen and addition of hydrogen peroxide or ammonium persulfate led to pyrite oxidation, resulting in elevated sulfate concentrations. Further, depending on the mineral carbonates available to buffer the system pH, pyrite oxidation could lower the system pH and enhance the mobility of several metals and metalloids. Copyright © 2016 Elsevier Ltd. All rights reserved.

Prediction of equilibrium parameters of adsorption of lead (II) ions onto diatomite

NASA Astrophysics Data System (ADS)

Salman, Taylan; Ardalı, Yüksel; Gamze Turan, N.

2013-04-01

Heavy metals from industrial wastewaters are one of the most important environmental issues to be solved today. Due to their toxicity and nonbiodegradable nature, heavy metals cause environmental and public health problems. Various techniques have been developed to remove heavy metals from aqueous solutions. These include chemical precipitation, reverse osmosis, ion Exchange and adsorption. Among them, adsorption is considered to be a particularly competitive and effective process for the removal of heavy metals from aqueous solutions. There is growing interest in using low cost, commercially available materials for the adsorption of heavy metals. Diatomite is a siliceous sedimentary rock having an amorphous form of silica (SiO2. nH2O) containing a small amount of microcrystalline material. It has unique combination of physical and chemical properties such as high porosity, high permeability, small particle size, large surface area, and low thermal conductivity. In addition, it is available in Turkey and in various locations around the world. Therefore, diatomite has been successfully used as adsorbent for the removal of heavy metals. The aim of the study is to investigate the adsorption properties of diatomite. The equilibrium adsorption data were applied to the Langmuir, Freundlich and Dubinin-Radushkevic (D-R) isotherm models. Adsorption experiments were performed under batch process, using Pb (II) initial concentration, pH of solution and contact time as variables. The results demonstrated that the adsorption of Pb (II) was strongly dependent on pH of solution. The effect of pH on adsorption of Pb(II) on diatomite was conducted by varying pH from 2 to 12 at 20 oC. In the pH range of 2.0-4.0, the adsorption percentage increases slightly as the pH increasing. At pH>4, the adsorption percentage decreases with increasing pH because hydrolysis product and the precipitation begin to play an important role in the sorption of Pb (II). At pH4, the maximum adsorption capacity of diatomite was found as 26.158 mg/g. The adsorption isotherms of Pb (II) on diatomite can be described well by the Freundlich model. The high adsorption capacity of diatomite makes it suitable low-cost material in the removal of Pb (II) from aqueous solutions.

How to avoid glucose degradation products in peritoneal dialysis fluids.

PubMed

Erixon, Martin; Wieslander, Anders; Lindén, Torbjörn; Carlsson, Ola; Forsbäck, Gunita; Svensson, Eva; Jönsson, Jan Ake; Kjellstrand, Per

2006-01-01

The formation of glucose degradation products (GDPs) during sterilization of peritoneal dialysis fluids (PDFs) is one of the most important aspects of biocompatibility of glucose-containing PDFs. Producers of PDFs are thus trying to minimize the level of GDPs in their products. 3,4-Dideoxyglucosone-3-ene (3,4-DGE) has been identified as the most bioreactive GDP in PDFs. It exists in a temperature-dependent equilibrium with a pool of 3-deoxyglucosone (3-DG) and is a precursor in the irreversible formation of 5-hydroxymethyl furaldehyde (5-HMF). The aim of the present study was to investigate how to minimize GDPs in PDFs and how different manufacturers have succeeded in doing so. Glucose solutions at different pHs and concentrations were heat sterilized and 3-DG, 3,4-DGE, 5-HMF, formaldehyde, and acetaldehyde were analyzed. Conventional as well as biocompatible fluids from different manufacturers were analyzed in parallel for GDP concentrations. The concentrations of 3-DG and 3,4-DGE produced during heat sterilization decreased when pH was reduced to about 2. Concentration of 5-HMF decreased when pH was reduced to 2.6. After further decrease to a pH of 2.0, concentration of 5-HMF increased slightly, and below a pH of 2.0 it increased considerably, together with formaldehyde; 3-DG continued to drop and 3,4-DGE remained constant. Inhibition of cell growth was paralleled by 3,4-DGE concentration at pH 2.0 - 6.0. A high glucose concentration lowered concentrations of 3,4-DGE and 3-DG at pH 5.5 and of 5-HMF at pH 1. At pH 2.2 and 3.2, glucose concentration had a minor effect on the formation of GDPs. All conventional PDFs contained high levels of 3,4-DGE and 3-DG. Concentrations were considerably lower in the biocompatible fluids. However, the concentration of 5-H M F was slightly higher in all the biocompatible fluids. The best way to avoid reactive GDPs is to have a pH between 2.0 and 2.6 during sterilization. If pHs outside this range are used, it becomes more important to have high glucose concentration during the sterilization process. There are large variations in GDPs, both within and between biocompatible and conventionally manufactured PDFs.

Rewritable and pH-Sensitive Micropatterns Based on Nanoparticle "Inks"

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

Wang, D. W.; Lagzi, Istvan; Wesson, Paul J.

2010-08-16

Rewritable micropatterns based on nanoparticle “inks” are created in gel substrates by wet stamping. The colors of the patterns depend on pH, reflect the degree of nanoparticle aggregation, and can be written using acids and erased using bases. Micropatterns imprinted with salts are “permanent” but can change color upon pH changes; these patterns act as multiple-use pH sensors.

Dose validation of PhIP hair level as a biomarker of heterocyclic aromatic amines exposure: a feeding study

PubMed Central

Le Marchand, Loïc; Yonemori, Kim; White, Kami K.; Franke, Adrian A.; Wilkens, Lynne R.; Turesky, Robert J.

2016-01-01

Hair measurement of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a promising biomarker of exposure to this carcinogen formed in cooked meats. However, the dose relationship between normal range intake and hair levels and the modulating effects of CYP1A2 metabolism and hair melanin need to be evaluated. We conducted a randomized, cross-over feeding study among 41 non-smokers using ground beef cooked to two different levels of doneness, 5 days a week for 1 month. PhIP was measured by liquid chromatography/mass spectrometry in food (mean low dose = 0.72 µg/serving; mean high dose = 2.99 µg/serving), and change in PhIP hair level was evaluated. CYP1A2 activity was assessed in urine with the caffeine challenge test and head hair melanin was estimated by UV spectrophotometry. We observed a strong dose-dependent increase in hair PhIP levels. This increase was highly correlated with dose received (ρ = 0.68, P < 0.0001). CYP1A2 activity and normalizing for hair melanin did not modify the response to the intervention. Consumption of PhIP at doses similar to those in the American diet results in a marked dose-dependent accumulation of PhIP in hair. Hair PhIP levels may be used as a biomarker of dietary exposure in studies investigating disease risk. PMID:27207666

Ligand accessibility and bioactivity of a hormone–dendrimer conjugate depend on pH and pH history

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

Kim, Sung Hoon; Madak-Erdogan, Zeynep; Bae, Sung Chul

Estrogen conjugates with a polyamidoamine (PAMAM) dendrimer have shown remarkably selective regulation of the nongenomic actions of estrogens in target cells in this paper. In response to pH changes, however, these estrogen–dendrimer conjugates (EDCs) display a major morphological transition that alters the accessibility of the estrogen ligands that compromises the bioactivity of the EDC. A sharp break in dynamic behavior near pH 7 occurs for three different ligands on the surface of a PAMAM-G6 dendrimer: a fluorophore (tetramethylrhodamine [TMR]) and two estrogens (17α-ethynylestradiol and diphenolic acid). Collisional quenching and time-resolved fluorescence anisotropy experiments with TMR–PAMAM revealed high ligand shielding abovemore » pH 7 and low shielding below pH 7. Furthermore, when the pH was cycled from 8.5 (conditions of ligand–PAMAM conjugation) to 4.5 (e.g., endosome/lysosome) and through 6.5 (e.g., hypoxic environment) back to pH 8.5, the 17α-ethynylestradiol– and diphenolic acid–PAMAM conjugates experienced a dramatic, irreversible loss in cell stimulatory activity; dynamic NMR studies indicated that the hormonal ligands had become occluded within the more hydrophobic core of the PAMAM dendrimer. Thus, the active state of these estrogen–dendrimer conjugates appears to be metastable. Finally, this pH-dependent irreversible masking of activity is of considerable relevance to the design of drug conjugates with amine-bearing PAMAM dendrimers.« less

Ligand accessibility and bioactivity of a hormone–dendrimer conjugate depend on pH and pH history

DOE PAGES

Kim, Sung Hoon; Madak-Erdogan, Zeynep; Bae, Sung Chul; ...

2015-07-17

Estrogen conjugates with a polyamidoamine (PAMAM) dendrimer have shown remarkably selective regulation of the nongenomic actions of estrogens in target cells in this paper. In response to pH changes, however, these estrogen–dendrimer conjugates (EDCs) display a major morphological transition that alters the accessibility of the estrogen ligands that compromises the bioactivity of the EDC. A sharp break in dynamic behavior near pH 7 occurs for three different ligands on the surface of a PAMAM-G6 dendrimer: a fluorophore (tetramethylrhodamine [TMR]) and two estrogens (17α-ethynylestradiol and diphenolic acid). Collisional quenching and time-resolved fluorescence anisotropy experiments with TMR–PAMAM revealed high ligand shielding abovemore » pH 7 and low shielding below pH 7. Furthermore, when the pH was cycled from 8.5 (conditions of ligand–PAMAM conjugation) to 4.5 (e.g., endosome/lysosome) and through 6.5 (e.g., hypoxic environment) back to pH 8.5, the 17α-ethynylestradiol– and diphenolic acid–PAMAM conjugates experienced a dramatic, irreversible loss in cell stimulatory activity; dynamic NMR studies indicated that the hormonal ligands had become occluded within the more hydrophobic core of the PAMAM dendrimer. Thus, the active state of these estrogen–dendrimer conjugates appears to be metastable. Finally, this pH-dependent irreversible masking of activity is of considerable relevance to the design of drug conjugates with amine-bearing PAMAM dendrimers.« less

Hepatectomy-Related Hypophosphatemia: A Novel Phosphaturic Factor in the Liver-Kidney Axis

PubMed Central

Nomura, Kengo; Miyagawa, Atsumi; Shiozaki, Yuji; Sasaki, Shohei; Kaneko, Ichiro; Ito, Mikiko; Kido, Shinsuke; Segawa, Hiroko; Sano, Mitsue; Fukuwatari, Tsutomu; Shibata, Katsumi

2014-01-01

Marked hypophosphatemia is common after major hepatic resection, but the pathophysiologic mechanism remains unknown. We used a partial hepatectomy (PH) rat model to investigate the molecular basis of hypophosphatemia. PH rats exhibited hypophosphatemia and hyperphosphaturia. In renal and intestinal brush-border membrane vesicles isolated from PH rats, Na+-dependent phosphate (Pi) uptake decreased by 50%–60%. PH rats also exhibited significantly decreased levels of renal and intestinal Na+-dependent Pi transporter proteins (NaPi-IIa [NaPi-4], NaPi-IIb, and NaPi-IIc). Parathyroid hormone was elevated at 6 hours after PH. Hyperphosphaturia persisted, however, even after thyroparathyroidectomy in PH rats. Moreover, DNA microarray data revealed elevated levels of nicotinamide phosphoribosyltransferase (Nampt) mRNA in the kidney after PH, and Nampt protein levels and total NAD concentration increased significantly in the proximal tubules. PH rats also exhibited markedly increased levels of the Nampt substrate, urinary nicotinamide (NAM), and NAM catabolites. In vitro analyses using opossum kidney cells revealed that NAM alone did not affect endogenous NaPi-4 levels. However, in cells overexpressing Nampt, the addition of NAM led to a marked decrease in cell surface expression of NaPi-4 that was blocked by treatment with FK866, a specific Nampt inhibitor. Furthermore, FK866-treated mice showed elevated renal Pi reabsorption and hypophosphaturia. These findings indicate that hepatectomy-induced hypophosphatemia is due to abnormal NAM metabolism, including Nampt activation in renal proximal tubular cells. PMID:24262791

Phloretin induces apoptosis of non-small cell lung carcinoma A549 cells via JNK1/2 and p38 MAPK pathways.

PubMed

Min, Jie; Huang, Kenan; Tang, Hua; Ding, Xinyu; Qi, Chen; Qin, Xiong; Xu, Zhifei

2015-12-01

Phloretin (Ph) existing in apples, pears and various vegetables is known to have antitumor activities in several cancer cell lines. However, little is known about its effect on human lung cancer cells. The aim of the present study was to see whether Ph could induce apoptosis of non-small cell lung cancer (NSCLC) cells, and explore the possible underlying mechanism of action. We found that Ph markedly induced cell apoptosis of NSCLC cell line A549, and inhibited the migration of A549 cells in a dose-dependent manner. The expression level of BAX, cleaved caspase-3 and -9, and degraded form of PARP was increased and Bcl-2 was decreased after Ph treatment. In addition, the phosphorylation of P38 MAPK, ERK1/2 and JNK1/2 was increased in a dose‑dependent manner in parallel with Ph treatment. Inhibition of P38 MAPK and JNK1/2 by specific inhibitors significantly abolished the Ph-induced activation of the caspase-3 and -9. In vivo tumor-suppression assay further indicated that Ph (20 mg/kg) displayed a more significant inhibitory effect on A549 xenografts in tumor growth. All these findings indicate that Ph is able to inhibit NSCLC A549 cell growth by inducing apoptosis through P38 MAPK and JNK1/2 pathways, and therefore may prove to be an adjuvant to the treatment of NSCLC.

Phloretin induces apoptosis of non-small cell lung carcinoma A549 cells via JNK1/2 and p38 MAPK pathways

PubMed Central

MIN, JIE; LI, XU; HUANG, KENAN; TANG, HUA; DING, XINYU; QI, CHEN; QIN, XIONG; XU, ZHIFEI

2015-01-01

Phloretin (Ph) existing in apples, pears and various vegetables is known to have antitumor activities in several cancer cell lines. However, little is known about its effect on human lung cancer cells. The aim of the present study was to see whether Ph could induce apoptosis of non-small cell lung cancer (NSCLC) cells, and explore the possible underlying mechanism of action. We found that Ph markedly induced cell apoptosis of NSCLC cell line A549, and inhibited the migration of A549 cells in a dose-dependent manner. The expression level of BAX, cleaved caspase-3 and -9, and degraded form of PARP was increased and Bcl-2 was decreased after Ph treatment. In addition, the phosphorylation of P38 MAPK, ERK1/2 and JNK1/2 was increased in a dose-dependent manner in parallel with Ph treatment. Inhibition of P38 MAPK and JNK1/2 by specific inhibitors significantly abolished the Ph-induced activation of the caspase-3 and -9. In vivo tumor-suppression assay further indicated that Ph (20 mg/kg) displayed a more significant inhibitory effect on A549 xenografts in tumor growth. All these findings indicate that Ph is able to inhibit NSCLC A549 cell growth by inducing apoptosis through P38 MAPK and JNK1/2 pathways, and therefore may prove to be an adjuvant to the treatment of NSCLC. PMID:26503828

Coral calcifying fluid pH is modulated by seawater carbonate chemistry not solely seawater pH.

PubMed

Comeau, S; Tambutté, E; Carpenter, R C; Edmunds, P J; Evensen, N R; Allemand, D; Ferrier-Pagès, C; Tambutté, S; Venn, A A

2017-01-25

Reef coral calcification depends on regulation of pH in the internal calcifying fluid (CF) in which the coral skeleton forms. However, little is known about calcifying fluid pH (pH CF ) regulation, despite its importance in determining the response of corals to ocean acidification. Here, we investigate pH CF in the coral Stylophora pistillata in seawater maintained at constant pH with manipulated carbonate chemistry to alter dissolved inorganic carbon (DIC) concentration, and therefore total alkalinity (A T ). We also investigate the intracellular pH of calcifying cells, photosynthesis, respiration and calcification rates under the same conditions. Our results show that despite constant pH in the surrounding seawater, pH CF is sensitive to shifts in carbonate chemistry associated with changes in [DIC] and [A T ], revealing that seawater pH is not the sole driver of pH CF Notably, when we synthesize our results with published data, we identify linear relationships of pH CF with the seawater [DIC]/[H + ] ratio, [A T ]/ [H + ] ratio and [[Formula: see text

Sulfide-dependent photosynthetic electron flow coupled to proton translocation in thylakoids of the cyanobacterium Oscillatoria limnetica.

PubMed

Shahak, Y; Arieli, B; Binder, B; Padan, E

1987-12-01

Light-induced proton translocation coupled to sulfide-dependent electron transport has been studied in isolated thylakoids of the cyanobacterium Oscillatoria limnetica. The thylakoids are obtained by osmotic shock of washed spheroplasts, prepared with glycine-betaine as the osmotic stabilizer. 13C NMR studies suggests that betaine is the major osmoregulator in O. limnetica. Thylakoid preparations obtained from both sulfide-induced anoxygenic cells and noninduced oxygenic cells are capable of proton pumping coupled to phenazinemethosulfate-mediated cyclic electron flow. However, only in the induced thylakoids can sulfide-dependent proton gradient (delta pH) formation be measured, using either NADP or methyl viologen as the terminal acceptor. Sulfide-dependent delta pH formation correlates with a high-affinity electron donation site (apparent Km 44 microM at pH 7.9). This site is not lost upon washing of the thylakoids. In addition, both sulfide-dependent electron transport and delta pH formation are sensitive to inhibitors of the cytochrome b6f complex such as 2-n-nonyl-4-hydroxyquinoline-N-oxide, 2,4-dinitrophenyl ether of 2-iodo-4-nitrothymol, or stigmatellin. Sulfide-dependent NADP photoreduction of low affinity (which does not saturate by as much as 7 mM sulfide) is detected in both induced and noninduced thylakoids, but this activity is insensitive to the inhibitors and is not coupled to proton transport. It is suggested that the adaptation of O. limnetica to anoxygenic photosynthesis involves the induction of a thylakoid factor(s) which creates a high-affinity site for sulfide, and the transfer of its electrons via the cytochrome b6f complex, coupled to proton translocation.

pH-dependent structural change of the extracellular sensor domain of the DraK histidine kinase from Streptomyces coelicolor

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

Yeo, Kwon Joo; Kim, Eun Hye; Hwang, Eunha

2013-02-15

Highlights: ► We described the biochemical and biophysical properties of the extracellular sensory domain (ESD) of DraK histidine kinase. ► The ESD of DraK showed a reversible pH-dependent conformational change in a wide pH range. ► The E83 is an important residue for the pH-dependent conformational change. -- Abstract: Recently, the DraR/DraK (Sco3063/Sco3062) two-component system (TCS) of Streptomycescoelicolor has been reported to be involved in the differential regulation of antibiotic biosynthesis. However, it has not been shown that under which conditions and how the DraR/DraK TCS is activated to initiate the signal transduction process. Therefore, to understand the sensing mechanism,more » structural study of the sensory domain of DraK is highly required. Here, we report the biochemical and biophysical properties of the extracellular sensory domain (ESD) of DraK. We observed a reversible pH-dependent conformational change of the ESD in a pH range of 2.5–10. Size-exclusion chromatography and AUC (analytical ultracentrifugation) data indicated that the ESD is predominantly monomeric in solution and exists in equilibrium between monomer and dimer states in acidic condition. Using NMR (nuclear magnetic resonance) and CD (circular dichroism) spectroscopy, our findings suggest that the structure of the ESD at low pH is more structured than that at high pH. In particular, the glutamate at position 83 is an important residue for the pH-dependent conformational change. These results suggest that this pH-dependent conformational change of ESD may be involved in signal transduction process of DraR/DraK TCS.« less

Prestroke physical activity is associated with good functional outcome and arterial recanalization after stroke due to a large vessel occlusion.

PubMed

Ricciardi, Ana Clara; López-Cancio, Elena; Pérez de la Ossa, Natalia; Sobrino, Tomás; Hernández-Pérez, María; Gomis, Meritxell; Munuera, Josep; Muñoz, Lucía; Dorado, Laura; Millán, Mónica; Dávalos, Antonio; Arenillas, Juan F

2014-01-01

Although multiple studies and meta-analyses have consistently suggested that regular physical activity (PhA) is associated with a decreased stroke risk and recurrence, there is limited data on the possible preconditioning effect of prestroke PhA on stroke severity and prognosis. We aimed to study the association of prestroke PhA with different outcome variables in patients with acute ischemic stroke due to an anterior large vessel occlusion. The Prestroke Physical Activity and Functional Recovery in Patients with Ischemic Stroke and Arterial Occlusion trial is an observational and longitudinal study that included consecutive patients with acute ischemic stroke admitted to a single tertiary stroke center. Main inclusion criteria were: anterior circulation ischemic stroke within 12 h from symptom onset; presence of a confirmed anterior large vessel occlusion, and functional independence previous to stroke. Prestroke PhA was evaluated with the International Physical Activity Questionnaire and categorized into mild, moderate and high levels by means of metabolic equivalent (MET) minutes per week thresholds. The primary outcome measure was good functional outcome at 3 months (modified Rankin scale ≤2). Secondary outcomes were severity of stroke at admission, complete early recanalization, early dramatic neurological improvement and final infarct volume. During the study period, 159 patients fulfilled the above criteria. The mean age was 68 years, 62% were men and the baseline NIHSS score was 17. Patients with high levels of prestroke PhA were younger, had more frequently distal occlusions and had lower levels of blood glucose and fibrinogen at admission. After multivariate analysis, a high level of prestroke PhA was associated with a good functional outcome at 3 months. Regarding secondary outcome variables and after adjustment for relevant factors, a high level of prestroke PhA was independently associated with milder stroke severity at admission, early dramatic improvement, early arterial recanalization after intravenous thrombolysis and lower final infarct volume. The beneficial association of prestroke PhA with stroke outcomes was already present with a cutoff point of 1,000 MET min/week, a level of PhA easily achieved by walking 1 h/day during 5 days or by doing a vigorous aerobic activity 1 h/day twice a week. Prestroke PhA is independently associated with favorable stroke outcomes after a large vessel occlusion. Future research on the underlying mechanisms is needed to understand this neuroprotective effect of PhA. © 2014 S. Karger AG, Basel.

An Eulerian model for scavenging of pollutants by raindrops

NASA Astrophysics Data System (ADS)

Kumar, Sudarshan

An Eulerian model for simulating the coupled processes of gas-phase depletion and aqueousphase accumulation of the pollutant species during a rain event has been formulated. The model is capable of taking into account any realistic vertical profile of pollutant species concentrations and time-dependent initial aqueous-phase concentrations at the cloud base. The model considers the processes of single species absorption and dissociation in the aqueous phase. The coupled partial differential equations constituting the model are discretized into a set of ordinary differential equations by using the Galerkin method with chapeau functions as the basis functions. These equations are solved to obtain the pollutant concentrations of the gas phase and raindrops as well as the pH of raindrops as a function of time and distance below cloud-base. Simulations are performed for scavenging of gaseous HNO 3, H 2O 2, SO 2, formaldehyde and NH 3. For the case of highly soluble HNO 3 and H 2O 2, raindrops are far from equilibrium with the gas phase and their capacity for absorption of these gases is undiminished even as they reach ground level. The gas-phase concentrations for these species decrease exponentially with time and the washout is determined primarily by the rain intensity and mass-transfer coefficient of the gaseous species to the raindrops. The pollutant species concentrations in raindrops are an almost linear function of the distance below the cloud base. For the simulation conditions considered in this study, the half-life periods of these gases for removal from the atmosphere range from 15 to 40 min. For SO 2 and formaldehyde, the aqueous-phase concentrations approach equilibrium as the drops fall to ground level and the gas-phase concentrations show large gradients in the vertical. Half-life periods for SO 2 range from 1.3 to 13 h depending on the initial raindrop pH and rain intensity. For formaldehyde, the half-life ranges from 19 to 63 min. Solubility of NH 3 is a strong function of the raindrop pH. As NH 3 is absorbed, the raindrop pH increases and NH 3 solubility decreases. For pre-acidified drops (pH = 4.6), ammonia solubility is very high and the drops are far from equilibrium with the gas phase throughout the falling period. The half-life for ammonia ranges from 11 min to over 3 h in our simulations.

Use of natural pH variation to increase the flocculation of the marine microalgae Nannochloropsis oculata.

PubMed

Sales, Rafael; Abreu, Paulo Cesar

2015-02-01

Microalgae is largely used in aquaculture as feed. More recently, these microorganisms have been considered as an important feedstock for biodiesel production. However, the concentration of produced biomass represents a large parcel of production costs. In this study, we have evaluated the influence of natural pH variation of culture medium, caused by photosynthetic activity, on the flocculation of the marine microalgae Nannochloropsis oculata. Experiments were conducted with the same culture with different pH values (8.5 and 9.6), obtained after exposing the cells to different light conditions. For each pH value, different treatments were composed by adding 0, 5, 10, and 30 mM of NaOH and the flocculant Flopam® (FO4800 SH) at concentrations of 0, 0.5, 1, and 5 ppm. Higher flocculation efficiencies were obtained for the culture with pH 9.6 in comparison to 8.5 for the same NaOH and Flopam concentrations. Lower concentrations of base and flocculant were needed for flocculating the culture in higher pH, representing an economy of 20 % in the costs of crop harvesting.

Extracellular acidosis and very low [Na+ ] inhibit NBCn1- and NHE1-mediated net acid extrusion from mouse vascular smooth muscle cells.

PubMed

Bonde, L; Boedtkjer, E

2017-10-01

The electroneutral Na + , HCO3- cotransporter NBCn1 and Na + /H + exchanger NHE1 regulate acid-base balance in vascular smooth muscle cells (VSMCs) and modify artery function and structure. Pathological conditions - notably ischaemia - can dramatically perturb intracellular (i) and extracellular (o) pH and [Na + ]. We examined effects of low [Na + ] o and pH o on NBCn1 and NHE1 activity in VSMCs of small arteries. We measured pH i by 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-based fluorescence microscopy of mouse mesenteric arteries and induced intracellular acidification by NH4+ prepulse technique. NBCn1 activity - defined as Na + -dependent, amiloride-insensitive net base uptake with CO 2 /HCO3- present - was inhibited equally when pH o decreased from 7.4 (22 mm HCO3-/5% CO 2 ) by metabolic (pH o 7.1/11 mm HCO3-: 22 ± 8%; pH o 6.8/5.5 mm HCO3-: 61 ± 7%) or respiratory (pH o 7.1/10% CO 2 : 35 ± 11%; pH o 6.8/20% CO 2 : 56 ± 7%) acidosis. Extracellular acidosis more prominently inhibited NHE1 activity - defined as Na + -dependent net acid extrusion without CO 2 /HCO3- present - at both pH o 7.1 (45 ± 9%) and 6.8 (85 ± 5%). Independently of pH o , lowering [Na + ] o from 140 to 70 mm reduced NBCn1 and NHE1 activity <20% whereas transport activities declined markedly (25-50%) when [Na + ] o was reduced to 35 mm. Steady-state pH i decreased more during respiratory (ΔpH i /ΔpH o  = 71 ± 4%) than metabolic (ΔpH i /ΔpH o  = 30 ± 7%) acidosis. Extracellular acidification inhibits NBCn1 and NHE1 activity in VSMCs. NBCn1 is equivalently inhibited when pCO 2 is raised or [HCO3-] o decreased. Lowering [Na + ] o inhibits NBCn1 and NHE1 markedly only below the typical physiological and pathophysiological range. We propose that inhibition of Na + -dependent net acid extrusion at low pH o protects against cellular Na + overload at the cost of intracellular acidification. © 2017 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.

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

Begg, James D.; Zavarin, Mavrik; Kersting, Annie B.

Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. In this article, we evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with K d values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in K d, indicating that true sorption equilibrium was not achieved withinmore » the first 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6 months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. In addition, a conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50–100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.« less

Desorption of plutonium from montmorillonite: An experimental and modeling study

DOE PAGES

Begg, James D.; Zavarin, Mavrik; Kersting, Annie B.

2017-01-15

Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. In this article, we evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with K d values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in K d, indicating that true sorption equilibrium was not achieved withinmore » the first 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6 months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. In addition, a conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50–100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.« less

pH-dependence of pesticide adsorption by wheat-residue-derived black carbon.

PubMed

Yang, Yaning; Chun, Yuan; Sheng, Guangyao; Huang, Minsheng

2004-08-03

The potential of black carbon as an adsorbent for pesticides in soils may be strongly influenced by the properties of the adsorbent and pesticides and by the environmental conditions. This study evaluated the effect of pH on the adsorption of diuron, bromoxynil, and ametryne by a wheat (Triticum aestivum L.) residue derived black carbon (WC) as compared to a commercial activated carbon (AC). The pH drift method indicated that WC had a point of zero charge of 4.2, much lower than that of 7.8 for AC. The density of oxygen-containing surface functional groups, measured by the Boehm titration, on WC was 5.4 times higher than that on AC, resulting in a pesticide adsorption by WC being 30-50% of that by AC, due to the blockage of WC surface by the waters associated with the functional groups. A small decrease (5.5%/unit pH) in diuron adsorption by WC with increase in pH resulted from increased deprotonation of surface functional groups at higher pH values. A much larger decrease (14-21%/unit pH) in bromoxynil adsorption by WC with increase in pH resulted from the deprotonation of both the adsorbate and surface functional groups of the adsorbent. The deprotonation reduced the adsorptive interaction between bromoxynil and the neutral carbon surface and increased the electrical repulsion between the negatively charged WC surface and bromoxynil anions. Deprotonation of ametryne with increase in pH over the low pH range increased its fraction of molecular form and thus adsorption on WC by 15%/unit pH. Further increase in pH resulted in a 20%/unit pH decrease in ametryne adsorption by WC due primarily to the development of a negative charge on the surface of WC. The pH-dependent adsorption of pesticides by black carbon may significantly influence their environmental fate in soils.

Desorption of plutonium from montmorillonite: An experimental and modeling study

NASA Astrophysics Data System (ADS)

Begg, James D.; Zavarin, Mavrik; Kersting, Annie B.

2017-01-01

Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. We evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with Kd values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in Kd, indicating that true sorption equilibrium was not achieved within the first 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6 months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. A conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50-100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.

Surface-enhanced Raman scattering (SERS) study of anthocyanidins

NASA Astrophysics Data System (ADS)

Zaffino, Chiara; Russo, Bianca; Bruni, Silvia

2015-10-01

Anthocyanins are an important class of natural compounds responsible for the red, purple and blue colors in a large number of flowers, fruits and cereal grains. They are polyhydroxy- and polymethoxy-derivatives of 2-phenylbenzopyrylium (flavylium) salts, which are present in nature as glycosylated molecules. The aim of the present study is to assess the identification of anthocyanidins, i.e. anthocyanins without the glycosidic moiety, by means of surface-enhanced Raman spectroscopy (SERS), a very chemically-specific technique which is moreover sensitive to subtle changes in molecular structures. These features can lead to elect SERS, among the spectroscopic tools currently at disposal of scientists, as a technique of choice for the identification of anthocyanidins, since: (1) anthocyanidins structurally present the same benzopyrylium moiety and differentiate only for the substitution pattern on their phenyl ring, (2) different species are present in aqueous solution depending on the pH. It will be demonstrated that, while resonance Raman spectra of anthocyanidins are very similar to one another, SER spectra show greater differences, leading to a further step in the identification of such important compounds in diluted solutions by means of vibrational spectroscopy. Moreover, the dependence on the pH of the six most common anthocyanidins, i.e. cyanidin, delphinidin, pelargonidin, peonidin, malvidin and petunidin, is studied. To the best of the authors' knowledge, a complete SERS study of such important molecules is reported in the present work for the first time.

Negative supercoiling of DNA by gyrase is inhibited in Salmonella enterica serovar Typhimurium during adaptation to acid stress.

PubMed

Colgan, Aoife M; Quinn, Heather J; Kary, Stefani C; Mitchenall, Lesley A; Maxwell, Anthony; Cameron, Andrew D S; Dorman, Charles J

2018-03-01

DNA in intracellular Salmonella enterica serovar Typhimurium relaxes during growth in the acidified (pH 4-5) macrophage vacuole and DNA relaxation correlates with the upregulation of Salmonella genes involved in adaptation to the macrophage environment. Bacterial ATP levels did not increase during adaptation to acid pH unless the bacterium was deficient in MgtC, a cytoplasmic-membrane-located inhibitor of proton-driven F 1 F 0 ATP synthase activity. Inhibiting ATP binding by DNA gyrase and topo IV with novobiocin enhanced the effect of low pH on DNA relaxation. Bacteria expressing novobiocin-resistant (Nov R ) derivatives of gyrase or topo IV also exhibited DNA relaxation at acid pH, although further relaxation with novobiocin was not seen in the strain with Nov R gyrase. Thus, inhibition of the negative supercoiling activity of gyrase was the primary cause of enhanced DNA relaxation in drug-treated bacteria. The Salmonella cytosol reaches pH 5-6 in response to an external pH of 4-5: the ATP-dependent DNA supercoiling activity of purified gyrase was progressively inhibited by lowering the pH in this range, as was the ATP-dependent DNA relaxation activity of topo IV. We propose that DNA relaxation in Salmonella within macrophage is due to acid-mediated impairment of the negative supercoiling activity of gyrase. © 2018 John Wiley & Sons Ltd.

pH triggered in vivo photothermal therapy and fluorescence nanoplatform of cancer based on responsive polymer-indocyanine green integrated reduced graphene oxide.

PubMed

Sharker, Shazid Md; Lee, Jung Eun; Kim, Sung Han; Jeong, Ji Hoon; In, Insik; Lee, Haeshin; Park, Sung Young

2015-08-01

We have synthesized a pH-dependent, NIR-sensitive, reduced graphene oxide (rGO) hybrid nano-composite via electrostatic interaction with indocyanine green (ICG) which is designed not only to destroy localized cancer cells but also be minimally invasive to surrounding normal cells. The near-infrared (NIR) irradiated hybrid nano-composites showed pH dependent photo-thermal heat generation capability from pH 5.0 to 7.4 due to the pH response relief and quenching effects of poly(2-dimethyl amino ethyl methacrylate) [poly(PDMAEMA)] with ICG on a single rGO sheet. This pH-triggered relief and quenching mechanism regulated in vitro photo-thermolysis as the pH changed from 5.0 to 7.4. The in vitro cellular uptake and confocal laser scan microscopic (CLSM) images at different pH values show promise for environment sensitive bio-imaging. The NIR-absorbing hybrid nanomaterials showed a remarkably improved in vitro cancer cell targeted photothermal destruction compared to free ICG. Upon local NIR irradiation, these hybrid nano-composites-treated tumors showed necrotic, shrunken, ablation of malignant cells and totally healed after 18 days treatment. Our finding regarding the acidic pH stimulus of cancer cellular environment has proven to be a wining platform for the fight against cancer. Copyright © 2015 Elsevier Ltd. All rights reserved.

Use of metallurgical dust for removal chromium ions from aqueous solutions

NASA Astrophysics Data System (ADS)

Pająk, Magdalena; Dzieniszewska, Agnieszka; Kyzioł-Komosińska, Joanna; Chrobok, Michał

2018-01-01

The aim of the study was to determine the potential for the application of dust from steel plant as an effective sorbent for removing Cr(III) and Cr(VI) in the form of simple and complex ions - Acid Blue 193 dye from aqueous solutions. Three isotherms models were used to interpret the experimental results namely: Langmuir, Freundlich, and Dubinin-Radushkevich. Estimated equations parameters allowed to determine the binding mechanism. Based on laboratory studies it was found that the dust was characterized by high sorption capacities for Cr ions and dye from the aqueous solution. The sorption capacity of the dust for Cr(III) and Cr(VI) ions depended on the degree of oxidation, pH of solution and kind of anion and changed in series: Cr(III)-Cl pH=5.0> Cr(III)-SO4 pH=5.0> Cr(III)-Cl pH=3.0> Cr(III)-SO4 pH=3.0> Cr(VI) pH=5.0> Cr(VI) pH=3.0. Dust was also characterized by a high maximum sorption capacity of dye at a range of 38.2 - 91.7 mg/g, depending on the dose of dust. Based on the study it was found that dust from a steel plant, containing iron oxides, can be used as low-cost and effective sorbent to remove pollutions containing chromium ions, especially from acidic wastewater.

Effect of pH value of probe molecule on the graphene oxide-based surface enhanced Raman scattering

NASA Astrophysics Data System (ADS)

Cui, Shao-li; Du, Xiao-qing; Zeng, Chao; Li, Lu; Bao, Jun

2017-06-01

The dependence of graphene oxide (GO)-based surface enhanced Raman scattering (SERS) on the pH value of probe molecule was investigated. Water-soluble copper phthalocyanine (TSCuPc) was used as probe molecule and its pH value was adjusted with HCl and NaOH solution. The Raman spectra of TSCuPc with pH equaling 3, 8, and 11 on GO base were tested, respectively. The results show that both Raman enhanced intensity and full width at half maximum (FWHM) of characteristic peaks vary with the pH value of TSCuPc. It is shown that there is no obvious spectral widening of TSCuPc characteristic peaks when TSCuPc is neutral or acidic, and the chemical enhancement intensity of neutral TSCuPc on GO is biggest. In contrast, when TSCuPc is alkaline, the characteristic Raman peaks between 1350 and 1600 cm-1 of TSCuPc on GO are much wider and the intensities of characteristic peaks decrease considerably. The reasons for the pH dependence of GO-based Raman spectra were explored by comparing the wettability of molecule droplet on GO and the absorbance of different pH-adjusted TSCuPc films. It is found that the effect of molecule's pH value on SERS can be contributed to the differences of concentration and distributions on GO surface for varied pH-treated molecule.

Supersaturation of aqueous species and hydrothermal crystal growth of ZnO

NASA Astrophysics Data System (ADS)

Gelabert, M. C.

2015-05-01

Synthesis of ZnO crystals prepared with zinc acetate or chloride, disodium dihydrogen ethylenediaminetetraacetate (EDTA), potassium hydroxide and sodium triflate at 200 °C and variable pH 8-12 is reported. Crystals were imaged and size-analyzed with optical microscopy. Using aqueous speciation modeling software, supersaturation dependence on pH was calculated for five zinc species-Zn2+, Zn(OH)+, Zn(OH)2, Zn(OH)3- and Zn(OH)42- -to investigate connections between predominate crystal habits at different pH and dominant aqueous species. For zinc acetate and chloride systems, the zinc species with highest supersaturation was Zn(OH)42- throughout the pH 8-12 range, and the second highest was Zn2+ or Zn(OH)3-, with a crossover pH of 10.2-10.4 depending on counterion. The prominence of the tetrahydroxyl zinc species in ZnO crystal growth is supported by these calculations, and total supersaturation is inversely proportional to average crystal sizes, as expected. Optical microscopy and size analysis on products revealed crystals with a needle or prismatic habit throughout the studied pH range, and the change in aspect ratio correlates with supersaturation changes for the Zn2+ in this pH range, thus suggesting that growth rates along the [001] crystallographic direction are affected by small concentration changes of this ion.

Effect of Exposed Surface Area, Volume and Environmental pH on the Calcium Ion Release of Three Commercially Available Tricalcium Silicate Based Dental Cements.

PubMed

Rajasekharan, Sivaprakash; Vercruysse, Chris; Martens, Luc; Verbeeck, Ronald

2018-01-13

Tricalcium silicate cements (TSC) are used in dental traumatology and endodontics for their bioactivity which is mostly attributed to formation of calcium hydroxide during TSC hydration and its subsequent release of calcium and hydroxide ions. The aim of this study was to determine the effect of volume (Vol), exposed surface area (ESA) and pH of surrounding medium on calcium ion release. Three commercially available hydraulic alkaline dental cements were mixed and condensed into cylindrical tubes of varying length and diameter ( n = 6/group). For the effect of ESA and Vol, tubes were immersed in 10 mL of deionized water. To analyze the effect of environmental pH, the tubes were randomly immersed in 10 mL of buffer solutions with varying pH (10.4, 7.4 or 4.4). The solutions were collected and renewed at various time intervals. pH and/or calcium ion release was measured using a pH glass electrode and atomic absorption spectrophotometer respectively. The change of pH, short-term calcium ion release and rate at which calcium ion release reaches maximum were dependent on ESA ( p < 0.05) while maximum calcium ion release was dependent on Vol of TSC ( p < 0.05). Maximum calcium ion release was significantly higher in acidic solution followed by neutral and alkaline solution ( p < 0.05).