Science.gov

Sample records for hydrophobic iminoxyl radicals

  1. Iminoxyl radical-promoted dichotomous cyclizations: efficient oxyoximation and aminooximation of alkenes.

    PubMed

    Peng, Xie-Xue; Deng, Yun-Jing; Yang, Xiu-Long; Zhang, Lin; Yu, Wei; Han, Bing

    2014-09-05

    A novel iminoxyl radical-involved metal-free approach to vicinal oxyoximation and aminooximation of unactivated alkenes is developed. This method utilizes the dichotomous reactivity of the iminoxyl radical to furnish a general difunctionalization on alkenes using simple tert-butyl nitrite (TBN) as the iminoxyl radical initiator as well the carbon radical trap. By using this protocol, oxime featured 4,5-dihydroisoxazoles and cyclic nitrones were facilely prepared from β,γ- and γ,δ-unsaturated ketoximes, respectively.

  2. Method of making a membrane having hydrophilic and hydrophobic surfaces for adhering cells or antibodies by using atomic oxygen or hydroxyl radicals

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L. (Inventor); Spaulding, Glenn F. (Inventor)

    1994-01-01

    A portion of an organic polymer article such as a membrane is made hydrophilic by exposing a hydrophobic surface of the article to a depth of about 50 to about 5000 angstroms to atomic oxygen or hydroxyl radicals at a temperature below 100C., preferably below 40 C, to form a hydrophilic uniform surface layer of hydrophilic hydroxyl groups. The atomic oxygen and hydroxyl radicals are generated by a flowing afterglow microwave discharge, and the surface is outside of a plasma produced by the discharge. A membrane having both hydrophilic and hydrophobic surfaces can be used in an immunoassay by adhering antibodies to the hydrophobic surface. In another embodiment, the membrane is used in cell culturing where cells adhere to the hydrophilic surface. Prior to adhering cells, the hydrophilic surface may be grafted with a compatibilizing compound. A plurality of hydrophilic regions bounded by adjacent hydrophobic regions can be produced such that a maximum of one cell per each hydrophilic region adheres.

  3. The Hydrophobic Effect.

    ERIC Educational Resources Information Center

    Huque, Entazul M.

    1989-01-01

    Discusses the physical basis and current understanding of hydrophobic effects. The thermodynamic background of the effects, hydrophobic hydration, and hydrophobic interactions are described. Four existing controversies are outlined. (YP)

  4. Preparation of hydrophobic coatings

    DOEpatents

    Branson, Eric D.; Shah, Pratik B.; Singh, Seema; Brinker, C. Jeffrey

    2009-02-03

    A method for preparing a hydrophobic coating by preparing a precursor sol comprising a metal alkoxide, a solvent, a basic catalyst, a fluoroalkyl compound and water, depositing the precursor sol as a film onto a surface, such as a substrate or a pipe, heating, the film and exposing the film to a hydrophobic silane compound to form a hydrophobic coating with a contact angle greater than approximately 150.degree.. The contact angle of the film can be controlled by exposure to ultraviolet radiation to reduce the contact angle and subsequent exposure to a hydrophobic silane compound to increase the contact angle.

  5. The synthesis and rheological characterization of a hydrophobically-modified acrylamide/acrylamide copolymer

    SciTech Connect

    Brady, T.A.; Davis, R.M.; Peiffer, D.G.

    1993-12-31

    The synthesis of a anionic, hydrophobically-modified acrylonitrile derivative is described, as the aqueous free-radical copolymerization of this monomer with acrylamide. The hydrophobic monomer contains a long-chain alkyl group and the pendant chain is terminated by a sulfonate group. Past rheological characterization has yielded viscosity profiles atypical for a conventional polyelectrolyte. Preliminary rheological data suggest that the copolymer in aqueous solution exhibits the polyelectrolyte effect, as well as interchain hydrophobic association.

  6. Hydrophobic, Porous Battery Boxes

    NASA Technical Reports Server (NTRS)

    Bragg, Bobby J.; Casey, John E., Jr.

    1995-01-01

    Boxes made of porous, hydrophobic polymers developed to contain aqueous potassium hydroxide electrolyte solutions of zinc/air batteries while allowing air to diffuse in as needed for operation. Used on other types of batteries for in-cabin use in which electrolytes aqueous and from which gases generated during operation must be vented without allowing electrolytes to leak out.

  7. Osteoclast radicals.

    PubMed

    Silverton, S

    1994-11-01

    In biological research, new ideas arise and quickly spread to encompass the entire field. Thus, the evolution of molecular biology has significantly changed our methods of approaching our research. A similar far-reaching finding has been the advent of radical reactions into biology. Although radical chemistry has been utilized for many technological advances that affect our daily lives, the appreciation of this same process within our cells has opened an unexplored arena for research enquiry. As cellular messengers, radical molecules seem whimsically designed: they are evanescent, rapidly and apparently indiscriminately reactive, and barely detectable by most biological methods. Yet, our initial probing of these reactive agents in cells and organisms has led us to postulate a virtually undescribed system of communication within and among cells which may have significant effects in multiple organs. In bone, radical reactants have been attributed with an important role in the control of bone resorption.

  8. Hydrophobic sugar holograms

    NASA Astrophysics Data System (ADS)

    Mejias-Brizuela, N. Y.; Olivares-Pérez, A.; Páez-Trujillo, G.; Hernández-Garay, M. P.; Fontanilla-Urdaneta, R.; Fuentes-Tapia, I.

    2008-02-01

    The sugar matrix is used to record of phase holograms; it was modified with the purpose of obtaining a hydrophobic material to improve the stability of the registered image and to stimulate the photosensitivity of the sugar. The new material is formed by a sugar, pectin and vanillin dissolution. The diffraction efficiency parameter increases in comparison with only the sugar matrix, obtaining already of 10%.

  9. Microstructure of Hydrophobically Modified Alkyl Acrylamide Polymers

    NASA Astrophysics Data System (ADS)

    Tian, Jun; Seery, T. A. P.; Weiss, R. A.

    2002-03-01

    Hydrophobically modified water soluble polymers of poly(N,N-dimethylacrylamide-co-2-(N-ethylfluorooctanesulfonamido)ethyl acrylate) (polyDMA/FOSA) with different compositions were prepared by solution free radical polymerization. The molecular weights ranged from Mw/Mn=53000/23000 to 95000/40000. The intrinsic viscosity decreased with the increasing FOSA content. The glass transition temperature of the copolymer decreased with FOSA content, and exhibited positive deviation from that predicted by the Fox equation. Small angle X-ray scattering (SAXS) curves exhibited a peak that indicated the copolymer had a microphase separated structure, presumably due to hydrophobic association of FOSA groups. The SAXS peak position shifted to higher q value with the increasing FOSA content in the dry polymers, while for the water swollen gel, it shifted to lower q value with the increasing water uptake in the gels. These results suggested that the origin of the peak was related to the spacing between hydrophobic microdomains. The failure of time-temperature superposition of the dynamic shear moduli supported the conclusion of a microphase separated structure in the copolymer.

  10. Hydrophobic ionic liquids

    SciTech Connect

    Koch, V.R.; Nanjundiah, C.; Carlin, R.T.

    1998-10-27

    Ionic liquids having improved properties for application in non-aqueous batteries, electrochemical capacitors, electroplating, catalysis and chemical separations are disclosed. Exemplary compounds have one of the following formulas shown in a diagram wherein R{sub 1}, R{sub 2}, R{sub 3}, R{sub 4}, R{sub 5}, and R{sub 6} are either H; F; separate alkyl groups of from 1 to 4 carbon atoms, respectively, or joined together to constitute a unitary alkylene radical of from 2 to 4 carbon atoms forming a ring structure converging on N; or separate phenyl groups; and wherein the alkyl groups, alkylene radicals or phenyl groups may be substituted with electron withdrawing groups, preferably F-, Cl-, CF{sub 3}-, SF{sub 5}-, CF{sub 3}S-, (CF{sub 3}){sub 2}CHS- or (CF{sub 3}){sub 3}CS-; and X{sup {minus}} is a non-Lewis acid-containing polyatomic anion having a van der Waals volume exceeding 100 {angstrom}{sup 3}. 4 figs.

  11. Hydrophobic ionic liquids

    DOEpatents

    Koch, Victor R.; Nanjundiah, Chenniah; Carlin, Richard T.

    1998-01-01

    Ionic liquids having improved properties for application in non-aqueous batteries, electrochemical capacitors, electroplating, catalysis and chemical separations are disclosed. Exemplary compounds have one of the following formulas: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are either H; F; separate alkyl groups of from 1 to 4 carbon atoms, respectively, or joined together to constitute a unitary alkylene radical of from 2 to 4 carbon atoms forming a ring structure converging on N; or separate phenyl groups; and wherein the alkyl groups, alkylene radicals or phenyl groups may be substituted with electron withdrawing groups, preferably F--, Cl--, CF.sub.3 --, SF.sub.5 --, CF.sub.3 S--, (CF.sub.3).sub.2 CHS-- or (CF.sub.3).sub.3 CS--; and X.sup.- is a non-Lewis acid-containing polyatomic anion having a van der Waals volume exceeding 100 .ANG..sup.3.

  12. Hydrophobic encapsulation of hydrocarbon gases.

    PubMed

    Leontiev, Alexander V; Saleh, Anas W; Rudkevich, Dmitry M

    2007-04-26

    [reaction: see text] Encapsulation data for hydrophobic hydrocarbon gases within a water-soluble hemicarcerand in aqueous solution are reported. It is concluded that hydrophobic interactions serve as the primary driving force for the encapsulation, which can be used for the design of gas-separating polymers with intrinsic inner cavities.

  13. Voltage-Gated Hydrophobic Nanopores

    SciTech Connect

    Lavrik, Nickolay V

    2011-01-01

    Hydrophobicity is a fundamental property that is responsible for numerous physical and biophysical aspects of molecular interactions in water. Peculiar behavior is expected for water in the vicinity of hydrophobic structures, such as nanopores. Indeed, hydrophobic nanopores can be found in two distinct states, dry and wet, even though the latter is thermodynamically unstable. Transitions between these two states are kinetically hindered in long pores but can be much faster in shorter pores. As it is demonstrated for the first time in this paper, these transitions can be induced by applying a voltage across a membrane with a single hydrophobic nanopore. Such voltage-induced gating in single nanopores can be realized in a reversible manner through electrowetting of inner walls of the nanopores. The resulting I-V curves of such artificial hydrophobic nanopores mimic biological voltage-gated channels.

  14. Changing water affinity from hydrophobic to hydrophilic in hydrophobic channels.

    PubMed

    Ohba, Tomonori; Yamamoto, Shotaro; Kodaira, Tetsuya; Hata, Kenji

    2015-01-27

    The behavior of water at hydrophobic interfaces can play a significant role in determining chemical reaction outcomes and physical properties. Carbon nanotubes and aluminophosphate materials have one-dimensional hydrophobic channels, which are entirely surrounded by hydrophobic interfaces. Unique water behavior was observed in such hydrophobic channels. In this article, changes in the water affinity in one-dimensional hydrophobic channels were assessed using water vapor adsorption isotherms at 303 K and grand canonical Monte Carlo simulations. Hydrophobic behavior of water adsorbed in channels wider than 3 nm was observed for both adsorption and desorption processes, owing to the hydrophobic environment. However, water showed hydrophilic properties in both adsorption and desorption processes in channels narrower than 1 nm. In intermediate-sized channels, the hydrophobic properties of water during the adsorption process were seen to transition to hydrophilic behavior during the desorption process. Hydrophilic properties in the narrow channels for both adsorption and desorption processes are a result of the relatively strong water-channel interactions (10-15 kJ mol(-1)). In the 2-3 nm channels, the water-channel interaction energy of 4-5 kJ mol(-1) was comparable to the thermal translational energy. The cohesive water interaction was approximately 35 kJ mol(-1), which was larger than the others. Thus, the water affinity change in the 2-3 nm channels for the adsorption and desorption processes was attributed to weak water-channel interactions and strong cohesive interactions. These results are inherently important to control the properties of water in hydrophobic environments.

  15. Method for producing hydrophobic aerogels

    DOEpatents

    Hrubesh, Lawrence W.; Poco, John F.; Coronado, Paul R.

    1999-01-01

    A method for treating a dried monolithic aerogel containing non-dispersed particles, with an organometallic surface modifying agent to produce hydrophobic aerogels. The dried, porous hydrophobic aerogels contain a protective layer of alkyl groups, such as methyl groups, on the modified surfaces of the pores of the aerogel. The alkyl groups at the aerogel surface typically contain at least one carbon-metal bond per group.

  16. Hydrophobic gating in ion channels.

    PubMed

    Aryal, Prafulla; Sansom, Mark S P; Tucker, Stephen J

    2015-01-16

    Biological ion channels are nanoscale transmembrane pores. When water and ions are enclosed within the narrow confines of a sub-nanometer hydrophobic pore, they exhibit behavior not evident from macroscopic descriptions. At this nanoscopic level, the unfavorable interaction between the lining of a hydrophobic pore and water may lead to stochastic liquid-vapor transitions. These transient vapor states are "dewetted", i.e. effectively devoid of water molecules within all or part of the pore, thus leading to an energetic barrier to ion conduction. This process, termed "hydrophobic gating", was first observed in molecular dynamics simulations of model nanopores, where the principles underlying hydrophobic gating (i.e., changes in diameter, polarity, or transmembrane voltage) have now been extensively validated. Computational, structural, and functional studies now indicate that biological ion channels may also exploit hydrophobic gating to regulate ion flow within their pores. Here we review the evidence for this process and propose that this unusual behavior of water represents an increasingly important element in understanding the relationship between ion channel structure and function.

  17. Modulation of graft architectures for enhancing hydrophobic interaction of biomolecules with thermoresponsive polymer-grafted surfaces.

    PubMed

    Idota, Naokazu; Kikuchi, Akihiko; Kobayashi, Jun; Sakai, Kiyotaka; Okano, Teruo

    2012-11-01

    This paper describes the effects of graft architecture of poly(N-isopropylacrylamide) (PIPAAm) brush surfaces on thermoresponsive aqueous wettability changes and the temperature-dependent hydrophobic interaction of steroids in silica capillaries (I.D.: 50 μm). PIPAAm brushes were grafted onto glass substrates by surface-initiated atom transfer radical polymerization (ATRP) that is one of the living radical polymerization techniques. Increases in the graft density and chain length of PIPAAm brushes increased the hydration of polymer brushes, resulting in the increased hydrophilic properties of the surface below the transition temperature of PIPAAm at 32 °C. More hydrophobic surface properties were also observed on surfaces modified with the block copolymers of IPAAm and n-butyl methacrylate (BMA) than that with IPAAm homopolymer-grafted surfaces over the transition temperature. Using PBMA-b-PIPAAm-grafted silica capillaries, the baseline separation of steroids was successfully achieved by only changing temperature. The incorporation of hydrophobic PBMA chains in grafted PIPAAm enhanced the hydrophobic interaction with testosterone above the transition temperature. The surface modification of hydrophobicity-enhanced thermoresponsive polymers is a promising method for the preparation of thermoresponsive biointerfaces that can effectively modulated their biomolecule and cell adsorption with the wide dynamic range of hydrophilic/hydrophobic property change across the transition temperature.

  18. Molecular origins of fluorocarbon hydrophobicity

    PubMed Central

    Dalvi, Vishwanath H.; Rossky, Peter J.

    2010-01-01

    We have undertaken atomistic molecular simulations to systematically determine the structural contributions to the hydrophobicity of fluorinated solutes and surfaces compared to the corresponding hydrocarbon, yielding a unified explanation for these phenomena. We have transformed a short chain alkane, n-octane, to n-perfluorooctane in stages. The free-energy changes and the entropic components calculated for each transformation stage yield considerable insight into the relevant physics. To evaluate the effect of a surface, we have also conducted contact-angle simulations of water on self-assembled monolayers of hydrocarbon and fluorocarbon thiols. Our results, which are consistent with experimental observations, indicate that the hydrophobicity of the fluorocarbon, whether the interaction with water is as solute or as surface, is due to its “fatness.” In solution, the extra work of cavity formation to accommodate a fluorocarbon, compared to a hydrocarbon, is not offset by enhanced energetic interactions with water. The enhanced hydrophobicity of fluorinated surfaces arises because fluorocarbons pack less densely on surfaces leading to poorer van der Waals interactions with water. We find that interaction of water with a hydrophobic solute/surface is primarily a function of van der Waals interactions and is substantially independent of electrostatic interactions. This independence is primarily due to the strong tendency of water at room temperature to maintain its hydrogen bonding network structure at an interface lacking hydrophilic sites. PMID:20643968

  19. Hydrophobic Solvation: Aqueous Methane Solutions

    ERIC Educational Resources Information Center

    Konrod, Oliver; Lankau, Timm

    2007-01-01

    A basic introduction to concept of a solvation shell around an apolar solute as well as its detection is presented. The hydrophobic solvation of toluene is found to be a good teaching example which connects macroscopic, phenomenological thermodynamic results with an atomistic point of view.

  20. ATOM TRANSFER RADICAL POLYMERIZATION OF N-BUTYL METHACRYLATE IN AQUEOUS DISPERSED SYSTEMS: A MINIEMULSION APPROACH. (R826735)

    EPA Science Inventory

    Ultrasonication was applied in combination with a hydrophobe for the copper-mediated atom transfer radical polymerization of n-butyl methacrylate in an aqueous dispersed system. A controlled polymerization was successfully achieved, as demonstrated by a linear correlation between...

  1. Contemporary Radical Economics.

    ERIC Educational Resources Information Center

    Sherman, Howard J.

    1984-01-01

    The origins of contemporary radical economics are examined. Applications of radical economics to price and value theory, labor segmentation theory, business cycles, industrial organization, government and business, imperialism and development, and comparative systems are reviewed. (Author/RM)

  2. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...: (i) Amorphous fumed hydrophobic silica: Not less than 99.0 percent silicon dioxide after ignition... dichlorodimethylsilane. (ii) Precipated hydrophobic silica: Not less than 94.0 percent silicon dioxide after...

  3. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...: (i) Amorphous fumed hydrophobic silica: Not less than 99.0 percent silicon dioxide after ignition... dichlorodimethylsilane. (ii) Precipated hydrophobic silica: Not less than 94.0 percent silicon dioxide after...

  4. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...: (i) Amorphous fumed hydrophobic silica: Not less than 99.0 percent silicon dioxide after ignition... dichlorodimethylsilane. (ii) Precipated hydrophobic silica: Not less than 94.0 percent silicon dioxide after...

  5. The radical amplifier

    NASA Technical Reports Server (NTRS)

    Hastie, D. R.

    1994-01-01

    The radical amplifier as a method for measuring radical concentrations in the atmosphere has received renewed attention lately. In principle, it can measure the total concentration of HO(x) and RO(x) radicals by reacting ambient air with high concentrations of CO (3-10 percent) and NO (2-6 ppmv), and measuring the NO2 produced.

  6. Hydrophobic effect at aqueous interfaces

    NASA Technical Reports Server (NTRS)

    Pohorille, Andrew

    2005-01-01

    Conceptual basis for hydrophobic effects in bulk water and at aqueous interfaces have similar conceptual basis but often manifests itself differently. Using a wide range of computer simulations as the basis, I will review different forms of hydrophobic effects at a variety of interfaces starting from simple liquid-vapor and water-oil interfaces and progressing to water-membrane interfaces. I will start with discussing how water is organized at different interfaces, stressing both similarities and differences. The main thread is that, as in the bulk liquid, hydrophobic effects have profound influence on conformational equilibria and organization of both small molecules and macromolecules, but the result of this influence is quite different. Specifically, it will be shown that many small, but not necessarily amphiphilic molecules tend to accumulate at the interface and, and this tendency will be explained. Furthermore, I will show that many short peptides that are disordered in water spontaneously fold into well-defined structures in the interfacial environment. Biological implications of this self-organizing effect will be discussed.

  7. [Lavoisier and radicals].

    PubMed

    Lafont, Olivier

    2007-01-01

    Lavoisier and his co-workers (Guyton de Morveau, Bertholet, Fourcroy) considered that acids were constituted of oxygen and of something else that they called radicals. These radicals were known in some cases, i.e. nitrogen for nitrous acid, carbon for carbonic acid, phosphorus for phosphoric acid. In the case of sulfur, the sulfuric radical could be associated with different quantities of oxigen leading to sulfuric or sulfurous acids. In other cases radicals remained unknown at the time i.e. muriatic radical for muriatic acid, or benzoyl radical for benzoic acid. It is interesting to notice that Lavoisier evoked the case of compound radicals constituted of different substances such as carbon and hydrogen.

  8. Hydrophobic-Core Microcapsules and Their Formation

    NASA Technical Reports Server (NTRS)

    Calle, Luz M. (Inventor); Li, Wenyan (Inventor); Buhrow, Jerry W. (Inventor); Jolley, Scott T. (Inventor)

    2016-01-01

    Hydrophobic-core microcapsules and methods of their formation are provided. A hydrophobic-core microcapsule may include a shell that encapsulates a hydrophobic substance with a core substance, such as dye, corrosion indicator, corrosion inhibitor, and/or healing agent, dissolved or dispersed therein. The hydrophobic-core microcapsules may be formed from an emulsion having hydrophobic-phase droplets, e.g., containing the core substance and shell-forming compound, dispersed in a hydrophilic phase. The shells of the microcapsules may be capable of being broken down in response to being contacted by an alkali, e.g., produced during corrosion, contacting the shell.

  9. Polymeric photoresist nanoparticles: light-induced degradation of hydrophobic polymers in aqueous dispersion.

    PubMed

    Klinger, Daniel; Landfester, Katharina

    2011-12-15

    Nanoparticles consisting of a photoreactive polymer able to radically switch its hydrophobicity are successfully prepared by miniemulsion polymerization. Irradiation with UV light causes degradation of the particles where at complete dissolution is achieved by changing the initial hydrophobic photoresist polymer into hydrophilic poly(methacrylic acid). Incorporation of the fluorescence-sensitive Nile red serves as a solvatochromic probe to study the particle degradation. Diffusion of either Nile red out from or water into the former hard spherical nanoparticles is studied and not only renders the described material an ideal system for applications, where in situ dissolution of nanoparticles may be needed, but also bears the additional advantage of performing controlled burst release.

  10. Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation

    PubMed Central

    Xu, Zhemi; Ao, Zhimin; Chu, Dewei; Younis, Adnan; Li, Chang Ming; Li, Sean

    2014-01-01

    Although the reversible wettability transition between hydrophobic and hydrophilic graphene under ultraviolet (UV) irradiation has been observed, the mechanism for this phenomenon remains unclear. In this work, experimental and theoretical investigations demonstrate that the H2O molecules are split into hydrogen and hydroxyl radicals, which are then captured by the graphene surface through chemical binding in an ambient environment under UV irradiation. The dissociative adsorption of H2O molecules induces the wettability transition in graphene from hydrophobic to hydrophilic. Our discovery may hold promise for the potential application of graphene in water splitting. PMID:25245110

  11. Hydrophobic Compounds Reshape Membrane Domains

    PubMed Central

    Barnoud, Jonathan; Rossi, Giulia; Marrink, Siewert J.; Monticelli, Luca

    2014-01-01

    Cell membranes have a complex lateral organization featuring domains with distinct composition, also known as rafts, which play an essential role in cellular processes such as signal transduction and protein trafficking. In vivo, perturbations of membrane domains (e.g., by drugs or lipophilic compounds) have major effects on the activity of raft-associated proteins and on signaling pathways, but they are difficult to characterize because of the small size of the domains, typically below optical resolution. Model membranes, instead, can show macroscopic phase separation between liquid-ordered and liquid-disordered domains, and they are often used to investigate the driving forces of membrane lateral organization. Studies in model membranes have shown that some lipophilic compounds perturb membrane domains, but it is not clear which chemical and physical properties determine domain perturbation. The mechanisms of domain stabilization and destabilization are also unknown. Here we describe the effect of six simple hydrophobic compounds on the lateral organization of phase-separated model membranes consisting of saturated and unsaturated phospholipids and cholesterol. Using molecular simulations, we identify two groups of molecules with distinct behavior: aliphatic compounds promote lipid mixing by distributing at the interface between liquid-ordered and liquid-disordered domains; aromatic compounds, instead, stabilize phase separation by partitioning into liquid-disordered domains and excluding cholesterol from the disordered domains. We predict that relatively small concentrations of hydrophobic species can have a broad impact on domain stability in model systems, which suggests possible mechanisms of action for hydrophobic compounds in vivo. PMID:25299598

  12. Designed metalloprotein stabilizes a semiquinone radical

    NASA Astrophysics Data System (ADS)

    Ulas, Gözde; Lemmin, Thomas; Wu, Yibing; Gassner, George T.; Degrado, William F.

    2016-04-01

    Enzymes use binding energy to stabilize their substrates in high-energy states that are otherwise inaccessible at ambient temperature. Here we show that a de novo designed Zn(II) metalloprotein stabilizes a chemically reactive organic radical that is otherwise unstable in aqueous media. The protein binds tightly to and stabilizes the radical semiquinone form of 3,5-di-tert-butylcatechol. Solution NMR spectroscopy in conjunction with molecular dynamics simulations show that the substrate binds in the active site pocket where it is stabilized by metal-ligand interactions as well as by burial of its hydrophobic groups. Spectrochemical redox titrations show that the protein stabilized the semiquinone by reducing the electrochemical midpoint potential for its formation via the one-electron oxidation of the catechol by approximately 400 mV (9 kcal mol-1). Therefore, the inherent chemical properties of the radical were changed drastically by harnessing its binding energy to the metalloprotein. This model sets the basis for designed enzymes with radical cofactors to tackle challenging chemistry.

  13. Is Br2 hydration hydrophobic?

    NASA Astrophysics Data System (ADS)

    Alcaraz-Torres, A.; Gamboa-Suárez, A.; Bernal-Uruchurtu, M. I.

    2017-02-01

    The spectroscopic properties of bromine in aqueous systems suggest it can behave as either hydrophilic or hydrophobic solute. In small water clusters, the halogen bond and the hydrogen-halogen interaction are responsible for its specific way of binding. In water hydrates, it is efficiently hosted by two different cages forming the crystal structure and it has been frequently assumed that there is little or no interaction between the guest and the host. Bromine in liquid solution poses a challenging question due to its non-negligible solubility and the large blue shift measured in its absorption spectra. Using a refined semi-empirical force field, PM3-PIF, we performed a Born-Oppenheimer molecular dynamics study of bromine in liquid water. Here we present a detailed study in which we retrieved the most representative hydration structures in terms of the most frequent positions around bromine and the most common water orientations. Albeit being an approximate description of the total hydration phenomenon, it captures the contribution of the leading molecular interactions in form of the recurrent structures. Our findings confirm that the spectroscopic signature is mainly caused by the closest neighbors. The dynamics of the whole first hydration shell strongly suggests that the external molecules in that structure effectively isolate the bulk from the presence of bromine. The solvation structure fluctuates from a hydrophilic to a hydrophobic-like environment along the studied trajectory.

  14. Preparation of hydrophobic organic aeorgels

    DOEpatents

    Baumann, Theodore F.; Satcher, Jr., Joe H.; Gash, Alexander E.

    2007-11-06

    Synthetic methods for the preparation of hydrophobic organics aerogels. One method involves the sol-gel polymerization of 1,3-dimethoxybenzene or 1,3,5-trimethoxybenzene with formaldehyde in non-aqueous solvents. Using a procedure analogous to the preparation of resorcinol-formaldehyde (RF) aerogels, this approach generates wet gels that can be dried using either supercritical solvent extraction to generate the new organic aerogels or air dried to produce an xerogel. Other methods involve the sol-gel polymerization of 1,3,5 trihydroxy benzene (phloroglucinol) or 1,3 dihydroxy benzene (resorcinol) and various aldehydes in non-aqueous solvents. These methods use a procedure analogous to the one-step base and two-step base/acid catalyzed polycondensation of phloroglucinol and formaldehyde, but the base catalyst used is triethylamine. These methods can be applied to a variety of other sol-gel precursors and solvent systems. These hydrophobic organics aerogels have numerous application potentials in the field of material absorbers and water-proof insulation.

  15. Preparation of hydrophobic organic aeorgels

    DOEpatents

    Baumann, Theodore F.; Satcher, Jr., Joe H.; Gash, Alexander E.

    2004-10-19

    Synthetic methods for the preparation of hydrophobic organics aerogels. One method involves the sol-gel polymerization of 1,3-dimethoxybenzene or 1,3,5-trimethoxybenzene with formaldehyde in non-aqueous solvents. Using a procedure analogous to the preparation of resorcinol-formaldehyde (RF) aerogels, this approach generates wet gels that can be dried using either supercritical solvent extraction to generate the new organic aerogels or air dried to produce an xerogel. Other methods involve the sol-gel polymerization of 1,3,5 trihydroxy benzene (phloroglucinol) or 1,3 dihydroxy benzene (resorcinol) and various aldehydes in non-aqueous solvents. These methods use a procedure analogous to the one-step base and two-step base/acid catalyzed polycondensation of phloroglucinol and formaldehyde, but the base catalyst used is triethylamine. These methods can be applied to a variety of other sol-gel precursors and solvent systems. These hydrophobic organics aerogels have numerous application potentials in the field of material absorbers and water-proof insulation.

  16. Forgotten Radicals in Biology

    PubMed Central

    Luc, Rochette; Vergely, Catherine

    2008-01-01

    Redox reactions play key roles in intra- and inter-cellular signaling, and in adaptative processes of tissues towards stress. Among the major free radicals with essential functions in cells are reactive oxygen species (ROS) including superoxide anion (O2•-), hydroxyl radical (•OH) and reactive nitrogen species (RNS) such as nitric oxide (•NO). In this article, we review the forgotten and new radicals with potential relevance to cardiovascular pathophysiology. Approximately 0.3% of O2•- present in cytosol exists in its protonated form: hydroperoxyl radical (HO2•). Water (H2O) can be split into two free radicals: •OH and hydrogen radical (H•). Several free radicals, including thiyl radicals (RS•) and nitrogen dioxide (NO2•) are known to isomerize double bonds. In the omega-6 series of poly-unsaturated fatty acids (PUFAs), cis-trans isomerization of γ-linolenate and arachidonate catalyzed by RS• has been investigated. Evidence is emerging that hydrogen disulphide (H2S) is a signaling molecule in vivo which can be a source of free radicals. The Cu-Zn superoxide dismutase (SOD) enzyme can oxidize the ionized form of H2S to hydro-sulphide radical: HS•. Recent studies suggest that H2S plays an important function in cardiovascular functions. Carbonate radical, which can be formed when •OH reacts with carbonate or bicarbonate ions, is also involved in the activity of Cu-Zn-SOD. Recently, it has been reported that carbonate anion were potentially relevant oxidants of nucleic acids in physiological environments. In conclusion, there is solid evidence supporting the formation of many free radicals by cells leading which may play an important role in their homeostasis. PMID:23675099

  17. Radical prostatectomy - discharge

    MedlinePlus

    ... prostatectomy - discharge; Laparoscopic radical prostatectomy - discharge; LRP - discharge; Robotic-assisted laparoscopic prostatectomy - discharge ; RALP - discharge; Pelvic lymphadenectomy - discharge; Prostate cancer - prostatectomy

  18. Expulsion of ions from hydrophobic hydration shells.

    PubMed

    Rankin, Blake M; Ben-Amotz, Dor

    2013-06-19

    Raman spectroscopy is combined with multivariate curve resolution to quantify interactions between ions and molecular hydrophobic groups in water. The molecular solutes in this study all have similar structures, with a trimethyl hydrophobic domain and a polar or charged headgroup. Our results imply that aqueous sodium and fluoride ions are strongly expelled from the first hydration shells of the hydrophobic (methyl) groups, while iodide ions are found to enter the hydrophobic hydration shell, to an extent that depends on the methyl group partial charge. However, our quantitative estimates of the corresponding ion binding equilibrium constants indicate that the iodide concentration in the first hydrophobic hydration shell is generally lower than that in the surrounding bulk water, and so an iodide ion cannot be viewed as having a true affinity for the molecular hydrophobic interface, but rather is less strongly expelled from such an interface than fluoride.

  19. Characterisation of nanomaterial hydrophobicity using engineered surfaces

    NASA Astrophysics Data System (ADS)

    Desmet, Cloé; Valsesia, Andrea; Oddo, Arianna; Ceccone, Giacomo; Spampinato, Valentina; Rossi, François; Colpo, Pascal

    2017-03-01

    Characterisation of engineered nanomaterials (NMs) is of outmost importance for the assessment of the potential risks arising from their extensive use. NMs display indeed a large variety of physico-chemical properties that drastically affect their interaction with biological systems. Among them, hydrophobicity is an important property that is nevertheless only slightly covered by the current physico-chemical characterisation techniques. In this work, we developed a method for the direct characterisation of NM hydrophobicity. The determination of the nanomaterial hydrophobic character is carried out by the direct measurement of the affinity of the NMs for different collectors. Each collector is an engineered surface designed in order to present specific surface charge and hydrophobicity degrees. Being thus characterised by a combination of surface energy components, the collectors enable the NM immobilisation with surface coverage in relation to their hydrophobicity. The experimental results are explained by using the extended DLVO theory, which takes into account the hydrophobic forces acting between NMs and collectors.

  20. Stability of proteins inside a hydrophobic cavity

    NASA Astrophysics Data System (ADS)

    Radhakrishna, Mithun; Sharma, Sumit; Kumar, Sanat K.

    2011-03-01

    Previous studies have shown that enclosing a protein in an athermal cavity stabilizes the protein against reversible unfolding by virtue of eliminating many open chain conformations. Examples of such confined spaces include pores in chromatographic columns, Anfinsen's cage in Chaperonins, interiors of Ribosomes or regions of steric occlusion inside cells. However, the situation is more complex inside a hydrophobic cavity. The protein has a tendency to adsorb on the surface of the hydrophobic cavity, but at the same time it loses conformational entropy because of confinement. We study this system using a simple Hydrophobic Polar (HP) lattice protein model. Canonical Monte Carlo (MC) simulations at different temperatures and surface hydrophobicity show that proteins are stabilized at low and moderate hydrophobicity upon adsorption. The range of surface hydrophobicity over which a protein is stable increases with a decrease in radius of the cavity.

  1. How specific halide adsorption varies hydrophobic interactions.

    PubMed

    Stock, Philipp; Müller, Melanie; Utzig, Thomas; Valtiner, Markus

    2016-03-11

    Hydrophobic interactions (HI) are driven by the water structure around hydrophobes in aqueous electrolytes. How water structures at hydrophobic interfaces and how this influences the HI was subject to numerous studies. However, the effect of specific ion adsorption on HI and hydrophobic interfaces remains largely unexplored or controversial. Here, the authors utilized atomic force microscopy force spectroscopy at well-defined nanoscopic hydrophobic interfaces to experimentally address how specific ion adsorption of halide ions as well as NH4 (+), Cs(+), and Na(+) cations alters interaction forces across hydrophobic interfaces. Our data demonstrate that iodide adsorption at hydrophobic interfaces profoundly varies the hydrophobic interaction potential. A long-range and strong hydration repulsion at distances D > 3 nm, is followed by an instability which could be explained by a subsequent rapid ejection of adsorbed iodides from approaching hydrophobic interfaces. In addition, the authors find only a weakly pronounced influence of bromide, and as expected no influence of chloride. Also, all tested cations do not have any significant influence on HI. Complementary, x-ray photoelectron spectroscopy and quartz-crystal-microbalance with dissipation monitoring showed a clear adsorption of large halide ions (Br(-)/I(-)) onto hydrophobic self-assembled monolayers (SAMs). Interestingly, iodide can even lead to a full disintegration of SAMs due to specific and strong interactions of iodide with gold. Our data suggest that hydrophobic surfaces are not intrinsically charged negatively by hydroxide adsorption, as it was generally believed. Hydrophobic surfaces rather interact strongly with negatively charged large halide ions, leading to a surface charging and significant variation of interaction forces.

  2. Method for making nanoporous hydrophobic coatings

    DOEpatents

    Fan, Hongyou; Sun, Zaicheng

    2013-04-23

    A simple coating method is used to form nanoporous hydrophobic films that can be used as optical coatings. The method uses evaporation-induced self-assembly of materials. The coating method starts with a homogeneous solution comprising a hydrophobic polymer and a surfactant polymer in a selective solvent. The solution is coated onto a substrate. The surfactant polymer forms micelles with the hydrophobic polymer residing in the particle core when the coating is dried. The surfactant polymer can be dissolved and selectively removed from the separated phases by washing with a polar solvent to form the nanoporous hydrophobic film.

  3. The physical origin of hydrophobic effects

    NASA Astrophysics Data System (ADS)

    Sun, Qiang

    2017-03-01

    From the structural studies on water and air/water interface, hydration free energy is derived, and used to investigate the origin of hydrophobic effects. As a solute is dissolved into water, hydration free energy increases, and is divided into initial and hydrophobic solvation processes. In the initial process, hydration free energy is dominated by hydrogen bonding in interfacial water (topmost water layer at solute/water interface). For hydrophobic process, hydration free energy is related to the hydrogen bonding in bulk and interfacial water. Therefore, hydrophobic effects originate from the structural competition between hydrogen bonding in bulk water and that in interfacial water.

  4. Hydrophobic coatings for MEMS applications

    NASA Astrophysics Data System (ADS)

    Doms, M.; Feindt, H.; Kuipers, W. J.; Shewtanasoontorn, D.; Matar, A. S.; Brinkhues, S.; Welton, R. H.; Mueller, J.

    2008-05-01

    Different kinds of thin-film coatings were investigated with regard to their applicability as hydrophobic coatings for MEMS. The films were deposited onto silicon and borosilicate glass substrates by spincoating of Dyneon™ PTFE and PFA, plasmapolymerization of HMDS-N and C4F8 as well as liquid-phase and vapor-phase coating of SAMs from DDMS, FDTS, FOTS and Geleste Aquaphobe™ CM. The layer properties were analyzed using profilometry, FTIR, SEM and contact angle measurements. Furthermore, the adhesion of the layers to the substrates was determined in an acetone ultrasonic bath. The influence of various deposition process parameters on the properties of the films was investigated. As these layers can be used in microfluidic systems, as water-repellent layers and as anti-stiction coatings, they are suited for versatile fields of application.

  5. The effect of micellization on the EPR spectra and reactivity of 2,2,4,4-tetramethylpiperidinoxyl (TEMPO) radicals.

    PubMed

    Aliaga, Carolina; Rezende, Marcos Caroli; Mena, Geraldine

    2016-11-01

    A series of 4-alkanoyloxy-2,2,6,6-tetramethylpiperidinoxyl radicals was prepared, and their reactivity in water vis-à-vis antioxidant Trolox was compared. Spectral (electron paramagnetic resonance) and dynamic-light-scattering measurements suggested the formation of micelles for the more hydrophobic members of the series. The observed increase in reactivity for the micelle-forming radicals reflected the increased local concentration of the radical fragment on the micellar interface. Copyright © 2016 John Wiley & Sons, Ltd.

  6. An Information Theory of Hydrophobic Effects

    NASA Astrophysics Data System (ADS)

    Pratt, Lawrence R.

    1998-03-01

    The hydrophobic effect is a central concept in rationalizing the structure and stability of proteins in solution. However, a consensus has not been achieved on a molecular scale physical theory explaining the broad array of hydrophobic effects. Here we present an information theory designed to achieve consensus by identifying and limiting the physical information and assumptions sufficient to predict hydrophobic effects. The information theory is based upon the study of the probabilities of occupancy by water molecule centers of molecular scale volumes observed in neat liquid water. Predictions for hydrophobic effects can be extracted from this probability distribution. Simulation results show that this probability distribution is accurately predicted by a maximum entropy model using the two moments that are obtained from the experimental liquid density and the experimental radial distribution of oxygen atoms. We show the role of solvent molecule correlation functions of higher order than pairs. We show that this two moment model predicts known atomic scale hydrophobic effects: hydrophobic solubilities, potentials of mean force, and hydrophobic effects on conformational equilibria. We comment on the kinship between the two moment maximum entropy model and the earlier Pratt-Chandler theory of hydrophobic effects. We show that the model predicts the entropy convergence emphasized by high sensitivity calorimetry on the thermal denaturation of globular proteins and explains why this entropy convergence is insensitive to solute molecular details within the broad category of hydrophobic solutes. Finally, we consider the pressure denaturation of globular proteins and discuss the perspective that emerges from the information theory treatment: increasing pressure squeezes water molecules into the protein globule eventually separating hydrophobic components analogously to the separation of hydrophobic solutes in formation of clathrate hydrates.

  7. Exploring Hydrophobic Binding Surfaces Using Comfa and Flexible Hydrophobic Ligands

    NASA Astrophysics Data System (ADS)

    Thakkar, Shraddha; Sanchez, Rosa. I.; Bhuveneswaran, Chidambaram; Compadre, Cesar M.

    2011-06-01

    Cysteine proteinases are a very important group of enzymes involved in a variety of physiological and pathological processes including cancer metastasis and rheumatoid arthritis. In this investigation we used 3D-Quantitative Structure Activity Relationships (3D-QSAR) techniques to model the binding of a variety of substrates to two cysteine proteinases, papain, and cathepsin B. The analysis was performed using Comparative Molecular Field Analysis (CoMFA). The molecules were constructed using standard bond angles and lengths, minimized and aligned. Charges were calculated using the PM3 method in MOPAC. The CoMFA models derived for the binding of the studied substrates to the two proteinases were compared with the expected results from the experimental X-ray crystal structures of the same proteinases. The results showed the value of CoMFA modeling of flexible hydrophobic ligands to analyze ligand binding to protein receptors, and could also serve as the basis to design specific inhibitors of cysteine proteinases with potential therapeutic value.

  8. Composite, nanostructured, super-hydrophobic material

    DOEpatents

    D'Urso, Brian R.; Simpson, John T.

    2007-08-21

    A hydrophobic disordered composite material having a protrusive surface feature includes a recessive phase and a protrusive phase, the recessive phase having a higher susceptibility to a preselected etchant than the protrusive phase, the composite material having an etched surface wherein the protrusive phase protrudes from the surface to form a protrusive surface feature, the protrusive feature being hydrophobic.

  9. Hydrophobic Silsesquioxane Nanoparticles and Nanocomposite Surfaces (POSTPRINT)

    DTIC Science & Technology

    2006-05-04

    Fluorinated Polyhedral Oligomeric Silsesquioxanes are hydrophobic nanoparticles. One compound, FD8T8, is ultrahydrophobic, possessing a water contact ... angle of 154 deg. This is believed to be the most hydrophobic and lowest surface tension crystalline substance known. Analysis of the x-ray crystal

  10. Why are water-hydrophobic interfaces charged?

    PubMed

    Kudin, Konstantin N; Car, Roberto

    2008-03-26

    We report ab initio molecular dynamics simulations of hydroxide and hydronium ions near a hydrophobic interface, indicating that both ions behave like amphiphilic surfactants that stick to a hydrophobic hydrocarbon surface with their hydrophobic side. We show that this behavior originates from the asymmetry of the molecular charge distribution which makes one end of the ions strongly hydrophobic while the other end is even more hydrophilic than the regular water (H2O) molecules. The effect is more pronounced for the hydroxide than for the hydronium. Our results are consistent with several experimental observations and explain why hydrophobic surfaces in contact with water acquire a net negative charge, a phenomenon that has important implications for biology and polymer science.

  11. Enthalpic and Entropic Contributions to Hydrophobicity

    PubMed Central

    2016-01-01

    Hydrophobic hydration plays a key role in a vast variety of biological processes, ranging from the formation of cells to protein folding and ligand binding. Hydrophobicity scales simplify the complex process of hydration by assigning a value describing the averaged hydrophobic character to each amino acid. Previously published scales were not able to calculate the enthalpic and entropic contributions to the hydrophobicity directly. We present a new method, based on Molecular Dynamics simulations and Grid Inhomogeneous Solvation Theory, that calculates hydrophobicity from enthalpic and entropic contributions. Instead of deriving these quantities from the temperature dependence of the free energy of hydration or as residual of the free energy and the enthalpy, we directly obtain these values from the phase space occupied by water molecules. Additionally, our method is able to identify regions with specific enthalpic and entropic properties, allowing to identify so-called “unhappy water” molecules, which are characterized by weak enthalpic interactions and unfavorable entropic constraints. PMID:27442443

  12. Radical chemistry of artemisinin

    NASA Astrophysics Data System (ADS)

    Denisov, Evgenii T.; Solodova, S. L.; Denisova, Taisa G.

    2010-12-01

    The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

  13. Radical aminomethylation of imines.

    PubMed

    Fujii, Shintaro; Konishi, Takehito; Matsumoto, Yusuke; Yamaoka, Yousuke; Takasu, Kiyosei; Yamada, Ken-Ichi

    2014-09-05

    Taking advantage of the high level of performance of N-alkoxycarbonyl-imines, we achieved the first example of addition of the aminomethyl radical to imine. The reaction efficiency depended on the structure of the radical precursor, whether it is an iodide or a xanthate, and an electron-withdrawing group on the nitrogen atom of the radical. This reaction allows direct introduction of an N-substituted aminomethyl group onto imine to provide 1,2-diamine as well as the short-step synthesis of ICI-199,441.

  14. Quantification of hydrophobic interaction affinity of colloids

    NASA Astrophysics Data System (ADS)

    Saini, G.; Nasholm, N.; Wood, B. D.

    2009-12-01

    Colloids play an important role in a wide variety of disciplines, including water and wastewater treatment, subsurface transport of metals and organic contaminants, migration of fines in oil reservoirs, biocolloid (virus and bacteria) transport in subsurface, and are integral to laboratory transport studies. Although the role of hydrophobicity in adhesion and transport of colloids, particularly bacteria, is well known; there is scarcity of literature regarding hydrophobicity measurement of non-bacterial colloids and other micron-sized particles. Here we detail an experimental approach based on differential partitioning of colloids between two liquid phases (hydrocarbon and buffer) as a measure of the hydrophobic interaction affinity of colloids. This assay, known as Microbial adhesion to hydrocarbons or MATH, is frequently used in microbiology and bacteriology for quantifying the hydrophobicity of microbes. Monodispersed colloids and particles, with sizes ranging from 1 micron to 33 micron, were used for the experiments. A range of hydrophobicity values were observed for different particles. The hydrophobicity results are also verified against water contact angle measurements of these particles. This liquid-liquid partitioning assay is quick, easy-to-perform and requires minimal instrumentation. Estimation of the hydrophobic interaction affinity of colloids would lead to a better understanding of their adhesion to different surfaces and subsequent transport in porous media.

  15. Ice adhesion on super-hydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Kulinich, S. A.; Farzaneh, M.

    2009-06-01

    In this study, ice adhesion strength on flat hydrophobic and rough super-hydrophobic coatings with similar surface chemistry (based on same fluoropolymer) is compared. Glaze ice, similar to naturally accreted, was prepared on the surfaces by spraying super-cooled water microdroplets at subzero temperature. Ice adhesion was evaluated by spinning the samples at constantly increasing speed until ice delamination occurred. Super-hydrophobic surfaces with different contact angle hysteresis were tested, clearly showing that the latter, along with the contact angle, also influences the ice-solid adhesion strength.

  16. Super-hydrophobic fluorine containing aerogels

    DOEpatents

    Coronado, Paul R.; Poco, John F.; Hrubesh, Lawrence W.

    2007-05-01

    An aerogel material with surfaces containing fluorine atoms which exhibits exceptional hydrophobicity, or the ability to repel liquid water. Hydrophobic aerogels are efficient absorbers of solvents from water. Solvents miscible with water are separated from it because the solvents are more volatile than water and they enter the porous aerogel as a vapor across the liquid water/solid interface. Solvents that are immisicble with water are separated from it by selectively wetting the aerogel. The hydrophobic property is achieved by formulating the aerogel using fluorine containing molecules either directly by addition in the sol-gel process, or by treating a standard dried aerogel using the vapor of fluorine containing molecules.

  17. Hydrophobic interactions increase attachment of gum Arabic- and PVP-coated Ag nanoparticles to hydrophobic surfaces.

    PubMed

    Song, Jee Eun; Phenrat, Tanapon; Marinakos, Stella; Xiao, Yao; Liu, Jie; Wiesner, Mark R; Tilton, Robert D; Lowry, Gregory V

    2011-07-15

    A fundamental understanding of attachment of surface-coated nanoparticles (NPs) is essential to predict the distribution and potential risks of NPs in the environment. Column deposition studies were used to examine the effect of surface-coating hydrophobicity on NP attachment to collector surfaces in mixtures with varying ratios of octadecylichlorosilane (OTS)-coated (hydrophobic) glass beads and clean silica (hydrophilic) glass beads. Silver nanoparticles (AgNPs) coated with organic coatings of varying hydrophobicity, including citrate, polyvinylpyrrolidone (PVP), and gum arabic (GA), were used. The attachment efficiencies of GA and PVP AgNPs increased by 2- and 4-fold, respectively, for OTS-coated glass beads compared to clean glass beads. Citrate AgNPs showed no substantial change in attachment efficiency for hydrophobic compared to hydrophilic surfaces. The attachment efficiency of PVP-, GA-, and citrate-coated AgNPs to hydrophobic collector surfaces correlated with the relative hydrophobicity of the coatings. The differences in the observed attachment efficiencies among AgNPs could not be explained by classical DLVO, suggesting that hydrophobic interactions between AgNPs and OTS-coated glass beads were responsible for the increase in attachment of surface-coated AgNPs with greater hydrophobicity. This study indicates that the overall attachment efficiency of AgNPs will be influenced by the hydrophobicity of the NP coating and the fraction of hydrophobic surfaces in the environment.

  18. Free Radical Reactions in Food.

    ERIC Educational Resources Information Center

    Taub, Irwin A.

    1984-01-01

    Discusses reactions of free radicals that determine the chemistry of many fresh, processed, and stored foods. Focuses on reactions involving ascorbic acid, myoglobin, and palmitate radicals as representative radicals derived from a vitamin, metallo-protein, and saturated lipid. Basic concepts related to free radical structure, formation, and…

  19. Erosion and flow of hydrophobic granular materials

    NASA Astrophysics Data System (ADS)

    Utter, Brian; Benns, Thomas; Foltz, Benjamin; Mahler, Joseph

    2015-03-01

    We experimentally investigate submerged granular flows of hydrophobic and hydrophilic grains both in a rotating drum geometry and under erosion by a surface water flow. While slurry and suspension flows are common in nature and industry, effects of surface chemistry on flow behavior have received relatively little attention. In the rotating drum, we use varying concentrations of hydrophobic and hydrophilic grains of sand submerged in water rotated at a constant angular velocity. Sequential images of the resulting avalanches are taken and analyzed. High concentrations of hydrophobic grains result in an effectively cohesive interaction between the grains forming aggregates, with aggregate size and repose angle increasing with hydrophobic concentration. However, the formation and nature of the aggregates depends significantly on the presence of air in the system. We present results from a related experiment on erosion by a surface water flow designed to characterize the effects of heterogeneous granular surfaces on channelization and erosion.

  20. Erosion and flow of hydrophobic granular materials

    NASA Astrophysics Data System (ADS)

    Utter, Brian; Benns, Thomas; Mahler, Joseph

    2013-11-01

    We experimentally investigate submerged granular flows of hydrophobic and hydrophilic grains both in a rotating drum geometry and under erosion by a surface water flow. While slurry and suspension flows are common in nature and industry, effects of surface chemistry on flow behavior have received relatively little attention. In the rotating drum , we use varying concentrations of hydrophobic and hydrophilic grains of sand submerged in water rotated at a constant angular velocity. Sequential images of the resulting avalanches are taken and analyzed. High concentrations of hydrophobic grains result in an effectively cohesive interaction between the grains forming aggregates, with aggregate size and repose angle increasing with hydrophobic concentration. However, the formation and nature of the aggregates depends significantly on the presence of air in the system. We present results from a related experiment on erosion by a surface water flow designed to characterize the effects of heterogeneous granular surfaces on channelization and erosion. Supported by NSF CBET Award 1067598.

  1. Hydrophobic hydrophilic phenomena in biochemical processes.

    PubMed

    Ben-Naim, Arieh

    2003-09-01

    The evolution of concepts developed in the study of the hydrophobic affect is surveyed, within the more general context of solvent-induced effects. A systematic analysis of the solvent-induced contribution to the driving force for the process of protein folding has led to two important modifications in our understanding of these effects. First, the conventional concepts of hydrophobic solvation and hydrophobic interactions had to be replaced by their respective conditional effects. Second, each of the hydrophobic effects has also a corresponding hydrophilic counterpart. Some of the latter effects could contribute significantly to the total driving force for the process of protein folding, and perhaps even dominate the driving force for biochemical processes.

  2. Preparation and characterization of hydrophobic superparamagnetic gel.

    SciTech Connect

    Liu, X.; Kaminski, M. D.; Guan, Y.; Chen, H.; Liu, H.; Rosengart, A. J.; Chemical Engineering; Univ. of Chicago; Pritzker School of Medicine; Chinese Academy of Sciences

    2006-01-01

    The present study describes the preparation and analysis of a highly concentrated hydrophobic oleic acid-coated magnetite gel. By contrast to conventional techniques to prepare magnetic fluids, herein the oleic acid was introduced as a reactant during the initial crystallization phase of magnetite that was obtained by the co-precipitation of Fe(II) and Fe(III) salts by addition of ammonium hydroxide. The resulting gelatinous hydrophobic magnetite was characterized in terms of morphology, particle size, magnetic properties, crystal structure, and hydrophobicity/hydrophilicity. This magnetic gel exhibited superparamagnetism with a saturation magnetization of 46.0 emu/g at room temperature and could be well dispersed both in polar and nonpolar carrier liquids. This protocol produced highly concentrated hydrophobic magnetic gel for biopolymer encapsulations.

  3. Chemistry of ascorbic acid radicals

    SciTech Connect

    Bielski, B.H.J.

    1982-01-01

    The chemistry of ascorbic acid free radicals is reviewed. Particular emphasis is placed on identification and characterization of ascorbate radicals by spectrophotometric and electron paramagnetic resonance techniques, the kinetics of formation and disappearance of ascorbate free radicals in enzymatic and nonenzymatic reactions, the effect of pH upon the spectral and kinetic properties of ascorbate anion radical, and chemical reactivity of ascorbate free radicals.

  4. Surface analysis of selected hydrophobic materials

    NASA Astrophysics Data System (ADS)

    Wisniewska, Sylwia Katarzyna

    This dissertation contains a series of studies on hydrophobic surfaces by various surface sensitive techniques such as contact angle measurements, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Hydrophobic surfaces have been classified as mineral surfaces, organic synthetic surfaces, or natural biological surfaces. As a model hydrophobic mineral surface, elemental sulfur has been selected. The sulfur surface has been characterized for selected allotropic forms of sulfur such as rhombic, monoclinic, plastic, and cyclohexasulfur. Additionally, dextrin adsorption at the sulfur surface was measured. The structure of a dextrin molecule showing hydrophobic sites has been presented to support the proposed hydrophobic bonding nature of dextrin adsorption at the sulfur surface. As a model organic hydrophobic surface, primary fatty amines such as dodecylamine, hexadecylamine, and octadecylamine were chosen. An increase of hydrophobicity, significant changes of infrared bands, and surface topographical changes with time were observed for each amine. Based on the results it was concluded that hydrocarbon chain rearrangement associated with recrystallization took place at the surface during contact with air. A barley straw surface was selected as a model of biological hydrophobic surfaces. The differences in the contact angles for various straw surfaces were explained by the presence of a wax layer. SEM images confirmed the heterogeneity and complexity of the wax crystal structure. AFM measurements provided additional structural details including a measure of surface roughness. Additionally, straw degradation as a result of conditioning in an aqueous environment was studied. Significant contact angle changes were observed as soon as one day after conditioning. FTIR studies showed a gradual wax layer removal due to straw surface decomposition. SEM and AFM images revealed topographical changes and biological

  5. Radicals in ionic liquids.

    PubMed

    Strehmel, Veronika

    2012-05-14

    Stable radicals and recombination of photogenerated lophyl radicals are investigated in ionic liquids. The 2,2,6,6-tetramethylpiperidine-1-yloxyl derivatives contain various substituents at the 4-position to the nitroxyl group, including hydrogen-bond-forming or ionic substituents that undergo additional interactions with the individual ions of the ionic liquids. Some of these spin probes contain similar ions to ionic liquids to avoid counter-ion exchange with the ionic liquid. Depending on the ionic liquid anion, the Stokes-Einstein theory or the Spernol-Gierer-Wirtz theory can be applied to describe the temperature dependence of the average rotational correlation time of the spin probe in the ionic liquids. Furthermore, the spin probes give information about the micropolarity of the ionic liquids. In this context the substituent at the 4-position to the nitroxyl group plays a significant role. Covalent bonding of a spin probe to the imidazolium ion results in bulky spin probes that are strongly immobilized in the ionic liquid. Furthermore, lophyl radical recombination in the dark, which is chosen to understand the dynamics of bimolecular reactions in ionic liquids, shows a slow process at longer timescale and a rise time at a shorter timescale. Although various reactions may contribute to the slower process during lophyl radical recombination, it follows a second-order kinetics that does not clearly show solvent viscosity dependence. However, the rise time, which may be attributed to radical pair formation, increases with increasing solvent viscosity.

  6. Hydrophobicity of silver surfaces with microparticle geometry

    NASA Astrophysics Data System (ADS)

    Macko, Ján; Oriňaková, Renáta; Oriňak, Andrej; Kovaľ, Karol; Kupková, Miriam; Erdélyi, Branislav; Kostecká, Zuzana; Smith, Roger M.

    2016-11-01

    The effect of the duration of the current deposition cycle and the number of current pulses on the geometry of silver microstructured surfaces and on the free surface energy, polarizability, hydrophobicity and thus adhesion force of the silver surfaces has been investigated. The changes in surface hydrophobicity were entirely dependent on the size and density of the microparticles on the surface. The results showed that formation of the silver microparticles was related to number of current pulses, while the duration of one current pulse played only a minor effect on the final surface microparticle geometry and thus on the surface tension and hydrophobicity. The conventional geometry of the silver particles has been transformed to the fractal dimension D. The surface hydrophobicity depended predominantly on the length of the dendrites not on their width. The highest silver surface hydrophobicity was observed on a surface prepared by 30 current pulses with a pulse duration of 1 s, the lowest one when deposition was performed by 10 current pulses with a duration of 0.1 s. The partial surface tension coefficients γDS and polarizability kS of the silver surfaces were calculated. Both parameters can be applied in future applications in living cells adhesion prediction and spectral method selection. Silver films with microparticle geometry showed a lower variability in final surface hydrophobicity when compared to nanostructured surfaces. The comparisons could be used to modify surfaces and to modulate human cells and bacterial adhesion on body implants, surgery instruments and clean surfaces.

  7. Characterization of surface hydrophobicity of engineered nanoparticles.

    PubMed

    Xiao, Yao; Wiesner, Mark R

    2012-05-15

    The surface chemistry of nanoparticles, including their hydrophobicity, is a key determinant of their fate, transport and toxicity. Engineered NPs often have surface coatings that control the surface chemistry of NPs and may dominate the effects of the nanoparticle core. Suitable characterization methods for surface hydrophobicity at the nano-scale are needed. Three types of methods, surface adsorption, affinity coefficient and contact angle, were investigated in this study with seven carbon and metal based NPs with and without coatings. The adsorption of hydrophobic molecules, Rose Bengal dye and naphthalene, on NPs was used as one measure of hydrophobicity and was compared with the relative affinity of NPs for octanol or water phases, analogous to the determination of octanol-water partition coefficients for organic molecules. The sessile drop method was adapted for measuring contact angle of a thin film of NPs. Results for these three methods were qualitatively in agreement. Aqueous-nC(60) and tetrahydrofuran-nC(60) were observed to be more hydrophobic than nano-Ag coated with polyvinylpyrrolidone or gum arabic, followed by nano-Ag or nano-Au with citrate-functionalized surfaces. Fullerol was shown to be the least hydrophobic of seven NPs tested. The advantages and limitations of each method were also discussed.

  8. Evaporation-induced failure of hydrophobicity

    NASA Astrophysics Data System (ADS)

    Luo, H.; Liu, T.; Ma, J.; Wang, P.; Wang, Y.; Leprince-Wang, Y.; Jing, G.

    2016-09-01

    Hydrophobic coatings have tremendous applications in many fields of industries, and their robustness is an important subject of investigation. Here we experimentally demonstrate the detachment of hydrophobic coating and the formation of the residual deposit resulting from an evaporating drop of water. A hydrophobic octadecanethiol (ODT) coating is employed to enhance the hydrophobicity of ZnO nanowire arrays (advancing and receding contact angle of 165° and 128°, respectively). Being a model system of the unique bonding interaction between ODT and ZnO, water drop drying on the structure of ODT/ZnO is examined. Our experimental results showed the significant depression and even failure of the hydrophobicity on this composite surface resulting from collecting the deposits of ODT molecules during the drop drying. By analyzing energy criterion and force balance, surface tension at the moving contact line is identified as a dominating destructive force to unstick the coating molecules. Interestingly, a normal rinsing stream does not damage this coating to alter its hydrophobicity, but rather is overshadowed by the evaporation of the tinny water drop. The drops of rain or condensed water outdoor may thus play the same role to damage the functional coatings after their evaporation. Our findings indicate that more delicate designs are needed to prevent the destructive effects of drop evaporation on superhydrophobic surfaces.

  9. Designing a hydrophobic barrier within biomimetic nanopores.

    PubMed

    Trick, Jemma L; Wallace, E Jayne; Bayley, Hagan; Sansom, Mark S P

    2014-11-25

    Nanopores in membranes have a range of potential applications. Biomimetic design of nanopores aims to mimic key functions of biological pores within a stable template structure. Molecular dynamics simulations have been used to test whether a simple β-barrel protein nanopore can be modified to incorporate a hydrophobic barrier to permeation. Simulations have been used to evaluate functional properties of such nanopores, using water flux as a proxy for ionic conductance. The behavior of these model pores has been characterized as a function of pore size and of the hydrophobicity of the amino acid side chains lining the narrow central constriction of the pore. Potential of mean force calculations have been used to calculate free energy landscapes for water and for ion permeation in selected models. These studies demonstrate that a hydrophobic barrier can indeed be designed into a β-barrel protein nanopore, and that the height of the barrier can be adjusted by modifying the number of consecutive rings of hydrophobic side chains. A hydrophobic barrier prevents both water and ion permeation even though the pore is sterically unoccluded. These results both provide insights into the nature of hydrophobic gating in biological pores and channels, and furthermore demonstrate that simple design features may be computationally transplanted into β-barrel membrane proteins to generate functionally complex nanopores.

  10. RF plasma based selective modification of hydrophilic regions on super hydrophobic surface

    NASA Astrophysics Data System (ADS)

    Lee, Jaehyun; Hwang, Sangyeon; Cho, Dae-Hyun; Hong, Jungwoo; Shin, Jennifer H.; Byun, Doyoung

    2017-02-01

    Selective modification and regional alterations of the surface property have gained a great deal of attention to many engineers. In this paper, we present a simple, a cost-effective, and amendable reforming method for disparate patterns of hydrophilic regions on super-hydrophobic surfaces. Uniform super-hydrophobic layer (Contact angle; CA > 150°, root mean square (RMS) roughness ∼0.28 nm) can be formed using the atmospheric radio frequency (RF) plasma on top of the selective hydrophilic (CA ∼ 70°, RMS roughness ∼0.34 nm) patterns imprinted by electrohydrodynamic (EHD) jet printing technology with polar alcohols (butyl carbitol or ethanol). The wettability of the modified surface was investigated qualitatively utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM), and wavelength scanning interferometer (WSI). Secondary ion mass spectroscopy (SIMS) analysis showed that the alcohol addiction reaction changed the types of radicals on the super-hydrophobic surface. The wettability was found to depend sensitively on chemical radicals on the surface, not on surface morphology (particle size and surface roughness). Furthermore, three different kinds of representative hydrophilic samples (polystyrene nano-particle aqueous solution, Salmonella bacteria medium, and poly(3,4-ethylenediocythiophene) ink) were tested for uniform deposition onto the desired hydrophilic regions. This simple strategy would have broad applications in various research fields that require selective deposition of target materials.

  11. Contribution of Hydrophobic Interactions to Protein Stability

    PubMed Central

    Pace, C. Nick; Fu, Hailong; Fryar, Katrina Lee; Landua, John; Trevino, Saul R.; Shirley, Bret A.; Hendricks, Marsha McNutt; Iimura, Satoshi; Gajiwala, Ketan; Scholtz, J. Martin; Grimsley, Gerald R.

    2011-01-01

    Our goal was to gain a better understanding of the contribution of hydrophobic interactions to protein stability. We measured the change in conformational stability, Δ(ΔG), for hydrophobic mutants of four proteins: villin head piece subdomain (VHP) with 36 residues, a surface protein from Borrelia burgdorferi (VlsE) with 341 residues, and two proteins previously studied in our laboratory, ribonucleases Sa and T1. We compare our results with previous studies and reach the following conclusions. 1. Hydrophobic interactions contribute less to the stability of a small protein, VHP (0.6 ± 0.3 kcal/mole per –CH2– group), than to the stability of a large protein, VlsE (1.6 ± 0.3 kcal/mol per –CH2– group). 2. Hydrophobic interactions make the major contribution to the stability of VHP (40 kcal/mol) and the major contributors are (in kcal/mol): Phe 18 (3.9), Met 13 (3.1), Phe 7 (2.9), Phe 11 (2.7), and Leu 21 (2.7). 3. Based on Δ(ΔG) values for 148 hydrophobic mutants in 13 proteins, burying a –CH2– group on folding contributes, on average, 1.1 ± 0.5 kcal/mol to protein stability. 4. The experimental Δ(ΔG) values for aliphatic side chains (Ala, Val, Ile, and Leu) are in good agreement with their ΔGtr values from water to cyclohexane. 5. For 22 proteins with 36 to 534 residues, hydrophobic interactions contribute 60 ± 4% and hydrogen bonds 40 ± 4% to protein stability. 6. Conformational entropy contributes about 2.4 kcal/mol per residue to protein instability. The globular conformation of proteins is stabilized predominately by hydrophobic interactions. PMID:21377472

  12. Radical Socioeducational Analysis.

    ERIC Educational Resources Information Center

    Sigmon, Scott B.

    This book describes an interactive-interdisciplinary way of looking at the social conditions which impinge upon schooling, and which impact upon the social facts of life. It examines current schooling problems from the perspective of radical social democratic thought. The book is organized into four major sections. Part 1 provides an overview and…

  13. Against Radical Multiculturalism.

    ERIC Educational Resources Information Center

    Zorn, Jeff

    This essay presents two strands of arguments against radical or critical emancipatory multiculturalism. In strand 1, "'Culture' is...whatever..." the looseness of the core concept of "culture," which can refer to anything at all concerning a social group that itself may exist only theoretically, is shown. In strand 2, "From ideology to leveling,…

  14. Beyond Radical Educational Cynicism.

    ERIC Educational Resources Information Center

    Wood, George H.

    1982-01-01

    An alternative is presented to counter current radical arguments that the schools cannot bring about social change because they are instruments of capitalism. The works of Samuel Bowles, Herbert Gintis, and Louis Althusser are discussed. Henry Giroux's "Ideology, Culture and the Process of Schooling" provides an alternative to cynicism.…

  15. Radically enhanced molecular recognition

    NASA Astrophysics Data System (ADS)

    Trabolsi, Ali; Khashab, Niveen; Fahrenbach, Albert C.; Friedman, Douglas C.; Colvin, Michael T.; Cotí, Karla K.; Benítez, Diego; Tkatchouk, Ekaterina; Olsen, John-Carl; Belowich, Matthew E.; Carmielli, Raanan; Khatib, Hussam A.; Goddard, William A.; Wasielewski, Michael R.; Stoddart, J. Fraser

    2010-01-01

    The tendency for viologen radical cations to dimerize has been harnessed to establish a recognition motif based on their ability to form extremely strong inclusion complexes with cyclobis(paraquat-p-phenylene) in its diradical dicationic redox state. This previously unreported complex involving three bipyridinium cation radicals increases the versatility of host-guest chemistry, extending its practice beyond the traditional reliance on neutral and charged guests and hosts. In particular, transporting the concept of radical dimerization into the field of mechanically interlocked molecules introduces a higher level of control within molecular switches and machines. Herein, we report that bistable and tristable [2]rotaxanes can be switched by altering electrochemical potentials. In a tristable [2]rotaxane composed of a cyclobis(paraquat-p-phenylene) ring and a dumbbell with tetrathiafulvalene, dioxynaphthalene and bipyridinium recognition sites, the position of the ring can be switched. On oxidation, it moves from the tetrathiafulvalene to the dioxynaphthalene, and on reduction, to the bipyridinium radical cation, provided the ring is also reduced simultaneously to the diradical dication.

  16. Radical School Reform.

    ERIC Educational Resources Information Center

    Gross, Beatrice, Ed.; Gross, Ronald, Ed.

    This book provides a comprehensive examination of the nature of the school crisis and the ways in which radical thinkers and educators are dealing with it. Excerpts from the writings of Jonathan Kozol, John Holt, Kenneth Clark, and others are concerned with the realities of education in ghettos and suburbs. Paul Goodman, Marshall McLuhan, Sylvia…

  17. Origin of hydrophobicity and enhanced water hydrogen bond strength near purely hydrophobic solutes

    PubMed Central

    Grdadolnik, Joze; Merzel, Franci; Avbelj, Franc

    2017-01-01

    Hydrophobicity plays an important role in numerous physicochemical processes from the process of dissolution in water to protein folding, but its origin at the fundamental level is still unclear. The classical view of hydrophobic hydration is that, in the presence of a hydrophobic solute, water forms transient microscopic “icebergs” arising from strengthened water hydrogen bonding, but there is no experimental evidence for enhanced hydrogen bonding and/or icebergs in such solutions. Here, we have used the redshifts and line shapes of the isotopically decoupled IR oxygen–deuterium (O-D) stretching mode of HDO water near small purely hydrophobic solutes (methane, ethane, krypton, and xenon) to study hydrophobicity at the most fundamental level. We present unequivocal and model-free experimental proof for the presence of strengthened water hydrogen bonds near four hydrophobic solutes, matching those in ice and clathrates. The water molecules involved in the enhanced hydrogen bonds display extensive structural ordering resembling that in clathrates. The number of ice-like hydrogen bonds is 10–15 per methane molecule. Ab initio molecular dynamics simulations have confirmed that water molecules in the vicinity of methane form stronger, more numerous, and more tetrahedrally oriented hydrogen bonds than those in bulk water and that their mobility is restricted. We show the absence of intercalating water molecules that cause the electrostatic screening (shielding) of hydrogen bonds in bulk water as the critical element for the enhanced hydrogen bonding around a hydrophobic solute. Our results confirm the classical view of hydrophobic hydration. PMID:28028244

  18. Evaporation rate of water in hydrophobic confinement.

    PubMed

    Sharma, Sumit; Debenedetti, Pablo G

    2012-03-20

    The drying of hydrophobic cavities is believed to play an important role in biophysical phenomena such as the folding of globular proteins, the opening and closing of ligand-gated ion channels, and ligand binding to hydrophobic pockets. We use forward flux sampling, a molecular simulation technique, to compute the rate of capillary evaporation of water confined between two hydrophobic surfaces separated by nanoscopic gaps, as a function of gap, surface size, and temperature. Over the range of conditions investigated (gaps between 9 and 14 Å and surface areas between 1 and 9 nm(2)), the free energy barrier to evaporation scales linearly with the gap between hydrophobic surfaces, suggesting that line tension makes the predominant contribution to the free energy barrier. The exponential dependence of the evaporation rate on the gap between confining surfaces causes a 10 order-of-magnitude decrease in the rate when the gap increases from 9 to 14 Å. The computed free energy barriers are of the order of 50 kT and are predominantly enthalpic. Evaporation rates per unit area are found to be two orders of magnitude faster in confinement by the larger (9 nm(2)) than by the smaller (1 nm(2)) surfaces considered here, at otherwise identical conditions. We show that this rate enhancement is a consequence of the dependence of hydrophobic hydration on the size of solvated objects. For sufficiently large surfaces, the critical nucleus for the evaporation process is a gap-spanning vapor tube.

  19. Enzymatic Hydrophobic Modification of Jute Fibers via Grafting to Reinforce Composites.

    PubMed

    Liu, Ruirui; Dong, Aixue; Fan, Xuerong; Yu, Yuanyuan; Yuan, Jiugang; Wang, Ping; Wang, Qiang; Cavaco-Paulo, Artur

    2016-04-01

    Horseradish peroxidase (HRP)/H2O2 system catalyzes the free-radical polymerization of aromatic compounds such as lignins and gallate esters. In this work, dodecyl gallate (DG) was grafted onto the surfaces of lignin-rich jute fabrics by HRP-mediated oxidative polymerization with an aim to enhance the hydrophobicity of the fibers. The DG-grafted jute fibers and reaction products of their model compounds were characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results clearly indicated the grafting of DG to the jute fiber by HRP. Furthermore, the hydrophobicity of jute fabrics was determined by measuring the wetting time and static contact angle. Compared to the control sample, the wetting time and static contact angle of the grated fabrics changed from ~1 s to 1 h and from ~0° to 123.68°, respectively. This clearly proved that the hydrophobicity of jute fabrics improved considerably. Conditions of the HRP-catalyzed DG-grafting reactions were optimized in terms of the DG content of modified jute fabrics. Moreover, the results of breaking strength and elongation of DG-grafted jute/polypropylene (PP) composites demonstrated improved reinforcement of the composite due to enzymatic hydrophobic modification of jute fibers.

  20. Hydrophobicity in Lennard-Jones solutions.

    PubMed

    Ishizaki, Mario; Tanaka, Hideki; Koga, Kenichiro

    2011-02-14

    The analogue of the hydrophobic hydration is explored for Lennard-Jones solutions. The free energy of solvation and its temperature derivatives, both in the constant-pressure process and in the constant-volume process, are obtained numerically for a variety of the size and energy parameters for the solute-solvent Lennard-Jones potential. We identify in the parameter space a region in which the solvation is of hydrophobic character, with an understanding that hydrophobicity is characterized by both the solvation free energy being positive and the solvation process being exothermic. Such a region is found in each case of the isobaric and isochoric conditions and the region is seen to be much wider in the isochoric process than in the isobaric one. Its origin and implication are discussed.

  1. The search for the hydrophobic force law

    PubMed Central

    Hammer, Malte U.; Anderson, Travers H.; Chaimovich, Aviel; Scott Shell, M.

    2010-01-01

    After nearly 30 years of research on the hydrophobic interaction, the search for the hydrophobic force law is still continuing. Indeed, there are more questions than answers, and the experimental data are often quite different for nominally similar conditions, as well as, apparently, for nano-, micro-, and macroscopic surfaces. This has led to the conclusion that the experimentally observed force–distance relationships are either a combination of different ‘fundamental’ interactions, or that the hydrophobic force-law, if there is one, is complex – depending on numerous parameters. The only unexpectedly strong attractive force measured in all experiments so far has a range of D ≈ 100–200 Å, increasing roughly exponentially down to ~ 10–20 Å and then more steeply down to adhesive contact at D = 0 or, for power-law potentials, effectively at D ≈ 2 Å. The measured forces in this regime (100–200 Å) and especially the adhesive forces are much stronger, and have a different distance-dependence from the continuum VDW force (Lifshitz theory) for non-conducting dielectric media. We suggest a three-regime force-law for the forces observed between hydrophobic surfaces: In the first, from 100–200 Å to thousands of ångstroms, the dominating force is created by complementary electrostatic domains or patches on the apposing surfaces and/or bridging vapour cavities; a ‘pure’ but still not well-understood ‘long-range hydrophobic force’ dominates the second regime from ~ 150 to ~ 15 Å, possibly due to an enhanced Hamaker constant associated with the ‘proton-hopping’ polarizability of water; while below ~ 10–15 Å to contact there is another ‘pure short-range hydrophobic force’ related to water structuring effects associated with surface-induced changes in the orientation and/or density of water molecules and H-bonds at the water–hydrophobic interface. We present recent SFA and other experimental results, as well as a simplified model for

  2. Fluid infiltration pressure for hydrophobic nanochannels

    NASA Astrophysics Data System (ADS)

    Mo, Jingwen; Li, Long; Zhou, Jianfeng; Xu, Dongyan; Huang, Baoling; Li, Zhigang

    2015-03-01

    We investigate water infiltration pressure for hydrophobic nanochannels through molecular dynamics simulations. It is found that the entrance energy barrier significantly raises the infiltration pressure, which makes the classic Young-Laplace equation invalid for nanochannels. As the channel surface is tuned from superhydrophobic to hydrophobic, the infiltration pressure is greatly reduced mainly due to the decrease of the capillary pressure (Young-Laplace equation) caused by the contact angle change, while the contribution of the entrance energy barrier to the infiltration pressure, which is termed entrance barrier pressure, increases from 25% to 60%.

  3. Toward Radicalizing Community Service Learning

    ERIC Educational Resources Information Center

    Sheffield, Eric C.

    2015-01-01

    This article advocates a radicalized theoretical construction of community service learning. To accomplish this radicalization, I initially take up a discussion of traditional understandings of CSL rooted in pragmatic/progressive thought. I then suggest that this traditional structural foundation can be radicalized by incorporating Deborah…

  4. Radicals in melanin biochemistry.

    PubMed

    Riley, P A

    1988-01-01

    Melanins are light-absorbant polymeric pigments found widely dispersed in nature. They possess many interesting physicochemical properties. One of these is the expression in the polymer of stable free radicals which appear to have a protective action in cells, probably by acting as a sink for diffusible free-radical species. Polymer formation is thought to occur by a free-radical process in which semiquinones are added to the chain. Semiquinones are formed by redox equilibration interactions between metabolic intermediates formed during the tyrosinase-catalyzed oxidation process. In the continued presence of substrate, steady-state concentrations of reactive species are predicted in the reaction system, and the melanogenic pathway may be considered as potentially hazardous for pigment-generating cells. This feature has been exploited by the use of analogue substrates to generate cytotoxic species as a possible rational approach to the treatment of malignant melanoma. One such substance is 4-hydroxyanisole, the oxidation of which gives rise to semiquinone radical species. The possibility that the anisyl semiquinone initiates a mechanism leading to cell damage has not been excluded. However, the current view is that the major cytotoxicity due to the oxidation products of this compound is the result of the action of the corresponding orthoquinone. A number of mechanisms exist for detoxifying quinones if they reach the cytosol such as O-methylation and the formation of thiol adducts with cysteine or glutathione, and these can be used as markers of melanogenesis. In general, however, only small amounts of reactive intermediates of melanogenesis escape from the confines of the melanosome, probably because of their limited lipid solubility. The selective toxic action of anisyl quinone in the treatment of melanoma may, in part, be due to membrane defects in the melanosomes of malignant melanocytes.

  5. Free radical explosive composition

    DOEpatents

    Walker, Franklin E.; Wasley, Richard J.

    1979-01-01

    An improved explosive composition is disclosed and comprises a major portion of an explosive having a detonation velocity between about 1500 and 10,000 meters per second and a minor amount of a getter additive comprising a compound or mixture of compounds capable of capturing or deactivating free radicals or ions under mechanical or electrical shock conditions and which is not an explosive. Exemplary getter additives are isocyanates, olefins and iodine.

  6. Probability and radical behaviorism

    PubMed Central

    Espinosa, James M.

    1992-01-01

    The concept of probability appears to be very important in the radical behaviorism of Skinner. Yet, it seems that this probability has not been accurately defined and is still ambiguous. I give a strict, relative frequency interpretation of probability and its applicability to the data from the science of behavior as supplied by cumulative records. Two examples of stochastic processes are given that may model the data from cumulative records that result under conditions of continuous reinforcement and extinction, respectively. PMID:22478114

  7. Free radical propulsion concept

    NASA Technical Reports Server (NTRS)

    Hawkins, C. E.; Nakanishi, S.

    1981-01-01

    The concept of a free radical propulsion system, utilizing the recombination energy of dissociated low molecular weight gases to produce thrust, is analyzed. The system, operating at a theoretical impulse with hydrogen, as high as 2200 seconds at high thrust to power ratio, is hypothesized to bridge the gap between chemical and electrostatic propulsion capabilities. A comparative methodology is outlined by which characteristics of chemical and electric propulsion for orbit raising mission can be investigated. It is noted that free radicals proposed in rockets previously met with difficulty and complexity in terms of storage requirements; the present study proposes to eliminate the storage requirements by using electric energy to achieve a continuous-flow product of free radicals which are recombined to produce a high velocity propellant. Microwave energy used to dissociate a continuously flowing gas is transferred to the propellant via three-body-recombination for conversion to propellant kinetic energy. Microwave plasma discharge was found in excess of 90 percent over a broad range of pressure in preliminary experiments, and microwave heating compared to electrothermal heating showed much higher temperatures in gasdynamic equations.

  8. THERMOCHEMISTRY OF HYDROCARBON RADICALS

    SciTech Connect

    Kent M. Ervin, Principal Investigator

    2004-08-17

    Gas phase negative ion chemistry methods are employed to determine enthalpies of formation of hydrocarbon radicals that are important in combustion processes and to investigate the dynamics of ion-molecule reactions. Using guided ion beam tandem mass spectrometry, we measure collisional threshold energies of endoergic proton transfer and hydrogen atom transfer reactions of hydrocarbon molecules with negative reagent ions. The measured reaction threshold energies for proton transfer yield the relative gas phase acidities. In an alternative methodology, competitive collision-induced dissociation of proton-bound ion-molecule complexes provides accurate gas phase acidities relative to a reference acid. Combined with the electron affinity of the R {center_dot} radical, the gas phase acidity yields the RH bond dissociation energy of the corresponding neutral molecule, or equivalently the enthalpy of formation of the R{center_dot} organic radical, using equation: D(R-H) = {Delta}{sub acid}H(RH) + EA(R) - IE(H). The threshold energy for hydrogen abstraction from a hydrocarbon molecule yields its hydrogen atom affinity relative to the reagent anion, providing the RH bond dissociation energy directly. Electronic structure calculations are used to evaluate the possibility of potential energy barriers or dynamical constrictions along the reaction path, and as input for RRKM and phase space theory calculations. In newer experiments, we have measured the product velocity distributions to obtain additional information on the energetics and dynamics of the reactions.

  9. Types of radical hysterectomies

    PubMed Central

    Marin, F; Plesca, M; Bordea, CI; Moga, MA; Blidaru, A

    2014-01-01

    Abstract The treatment for cervical cancer is a complex, multidisciplinary issue, which applies according to the stage of the disease. The surgical elective treatment of cervical cancer is represented by the radical abdominal hysterectomy. In time, many surgeons perfected this surgical technique; the ones who stood up for this idea were Thoma Ionescu and Ernst Wertheim. There are many varieties of radical hysterectomies performed by using the abdominal method and some of them through vaginal and mixed way. Each method employed has advantages and disadvantages. At present, there are three classifications of radical hysterectomies which are used for the simplification of the surgical protocols: Piver-Rutledge-Smith classification which is the oldest, GCG-EORTC classification and Querlow and Morrow classification. The last is the most evolved and recent classification; its techniques can be adapted for conservative operations and for different types of surgical approaches: abdominal, vaginal, laparoscopic or robotic. Abbreviations: GCG-EORTC = Gynecologic Cancer Group of the European Organization of Research and Treatment of Cancer; LEEP = loop electrosurgical excision procedure; I.O.B. = Institute of Oncology Bucharest; PRS = Piver-Rutledge-Smith PMID:25408722

  10. [Radical prostatectomy - pro robotic].

    PubMed

    Gillitzer, R

    2012-05-01

    Anatomical radical prostatectomy was introduced in the early 1980s by Walsh and Donker. Elucidation of key anatomical structures led to a significant reduction in the morbidity of this procedure. The strive to achieve similar oncological and functional results to this gold standard open procedure but with further reduction of morbidity through a minimally invasive access led to the establishment of laparoscopic prostatectomy. However, this procedure is complex and difficult and is associated with a long learning curve. The technical advantages of robotically assisted surgery coupled with the intuitive handling of the device led to increased precision and shortening of the learning curve. These main advantages, together with a massive internet presence and aggressive marketing, have resulted in a rapid dissemination of robotic radical prostatectomy and an increasing patient demand. However, superiority of robotic radical prostatectomy in comparison to the other surgical therapeutic options has not yet been proven on a scientific basis. Currently robotic-assisted surgery is an established technique and future technical improvements will certainly further define its role in urological surgery. In the end this technical innovation will have to be balanced against the very high purchase and running costs, which remain the main limitation of this technology.

  11. Distance-dependent hydrophobic-hydrophobic contacts in protein folding simulations.

    PubMed

    Onofrio, Angelo; Parisi, Giovanni; Punzi, Giuseppe; Todisco, Simona; Di Noia, Maria Antonietta; Bossis, Fabrizio; Turi, Antonio; De Grassi, Anna; Pierri, Ciro Leonardo

    2014-09-21

    Successful prediction of protein folding from an amino acid sequence is a challenge in computational biology. In order to reveal the geometric constraints that drive protein folding, highlight those constraints kept or missed by distinct lattices and for establishing which class of intra- and inter-secondary structure element interactions is the most relevant for the correct folding of proteins, we have calculated inter-alpha carbon distances in a set of 42 crystal structures consisting of mainly helix, sheet or mixed conformations. The inter-alpha carbon distances were also calculated in several lattice "hydrophobic-polar" models built from the same protein set. We found that helix structures are more prone to form "hydrophobic-hydrophobic" contacts than beta-sheet structures. At a distance lower than or equal to 3.8 Å (very short-range interactions), "hydrophobic-hydrophobic" contacts are almost absent in the native structures, while they are frequent in all the analyzed lattice models. At distances in-between 3.8 and 9.5 Å (short-/medium-range interactions), the best performing lattice for reproducing mainly helix structures is the body-centered-cubic lattice. If protein structures contain sheet portions, lattice performances get worse, with few exceptions observed for double-tetrahedral and body-centered-cubic lattices. Finally, we can observe that ab initio protein folding algorithms, i.e. those based on the employment of lattices and Monte Carlo simulated annealings, can be improved simply and effectively by preventing the generation of "hydrophobic-hydrophobic" contacts shorter than 3.8 Å, by monitoring the "hydrophobic-hydrophobic/polar-polar" contact ratio in short-/medium distance ranges and by using preferentially a body-centered-cubic lattice.

  12. Anionic surfactant with hydrophobic and hydrophilic chains for nanoparticle dispersion and shape memory polymer nanocomposites.

    PubMed

    Iijima, Motoyuki; Kobayakawa, Murino; Yamazaki, Miwa; Ohta, Yasuhiro; Kamiya, Hidehiro

    2009-11-18

    An anionic surfactant comprising a hydrophilic poly(ethylene glycol) (PEG) chain, hydrophobic alkyl chain, and polymerizable vinyl group was synthesized as a capping agent of nanoparticles. TiO(2) nanoparticles modified by this surfactant were completely dispersible in various organic solvents with a wide range of polarities, such as nitriles, alcohols, ketones, and acetates. Furthermore, these particles were found to be dispersible in various polymers with different properties, such as thermosetting epoxy resins and radical polymerized poly(methylmethacrylate) (PMMA). A polymer composite of surface-modified TiO(2) nanoparticles in epoxy resins prepared by using the developed surfactant also possessed temperature-induced shape memory properties.

  13. Fluoroalkyl and alkyl chains have similar hydrophobicities in binding to the "hydrophobic wall" of carbonic anhydrase.

    PubMed

    Mecinović, Jasmin; Snyder, Phillip W; Mirica, Katherine A; Bai, Serena; Mack, Eric T; Kwant, Richard L; Moustakas, Demetri T; Héroux, Annie; Whitesides, George M

    2011-09-07

    The hydrophobic effect, the free-energetically favorable association of nonpolar solutes in water, makes a dominant contribution to binding of many systems of ligands and proteins. The objective of this study was to examine the hydrophobic effect in biomolecular recognition using two chemically different but structurally similar hydrophobic groups, aliphatic hydrocarbons and aliphatic fluorocarbons, and to determine whether the hydrophobicity of the two groups could be distinguished by thermodynamic and biostructural analysis. This paper uses isothermal titration calorimetry (ITC) to examine the thermodynamics of binding of benzenesulfonamides substituted in the para position with alkyl and fluoroalkyl chains (H(2)NSO(2)C(6)H(4)-CONHCH(2)(CX(2))(n)CX(3), n = 0-4, X = H, F) to human carbonic anhydrase II (HCA II). Both alkyl and fluoroalkyl substituents contribute favorably to the enthalpy and the entropy of binding; these contributions increase as the length of chain of the hydrophobic substituent increases. Crystallography of the protein-ligand complexes indicates that the benzenesulfonamide groups of all ligands examined bind with similar geometry, that the tail groups associate with the hydrophobic wall of HCA II (which is made up of the side chains of residues Phe131, Val135, Pro202, and Leu204), and that the structure of the protein is indistinguishable for all but one of the complexes (the longest member of the fluoroalkyl series). Analysis of the thermodynamics of binding as a function of structure is compatible with the hypothesis that hydrophobic binding of both alkyl and fluoroalkyl chains to hydrophobic surface of carbonic anhydrase is due primarily to the release of nonoptimally hydrogen-bonded water molecules that hydrate the binding cavity (including the hydrophobic wall) of HCA II and to the release of water molecules that surround the hydrophobic chain of the ligands. This study defines the balance of enthalpic and entropic contributions to the

  14. Binding Hydrated Anions with Hydrophobic Pockets.

    PubMed

    Sokkalingam, Punidha; Shraberg, Joshua; Rick, Steven W; Gibb, Bruce C

    2016-01-13

    Using a combination of isothermal titration calorimetry and quantum and molecular dynamics calculations, we demonstrate that relatively soft anions have an affinity for hydrophobic concavity. The results are consistent with the anions remaining partially hydrated upon binding, and suggest a novel strategy for anion recognition.

  15. COSOLVENCY AND SOPRTION OF HYDROPHOBIC ORGANIC CHEMICALS

    EPA Science Inventory

    Sorption of hydrophobic organic chemicals (HOCs) by two soils was measured from mixed solvents containing water plus completely miscible organic solvents (CMOSs) and partially miscible organic solvents (PMOSs). The utility of the log-linear cosolvency model for predicting HOC sor...

  16. Hydrophobic and hydrophilic control in polyphosphazene materials

    NASA Astrophysics Data System (ADS)

    Steely, Lee Brent

    This thesis is the culmination of several recent studies focused on the surface characterization of polyphosphazenes specifically the properties of water repellency or hydrophobicity. Chapter 1 is a background account of polyphosphazene chemistry and the hydrophobicity of polyphosphazenes. Chapter 2 provides an examination of the role of surface morphology on hydrophobicity. This study deals in depth with the electrospinning of poly[bis(2,2,2-trifluoroethoxy)phosphazene] in tetrahydrofuran. This process yields fiber mats or bead and fiber mats which exhibit roughness in continuous contact with the water droplet (fiber mats) or discontinuous contact (bead and fiber mats). These surface roughness types are compared to spun cast films using water contact angles to measure the air-water-polymer interface. The influence of aromatic moieties and fluorine content on the air-water-polymer interface is examined in Chapter 3. This study examines the influence of fluorine content and aryloxy groups on the hydrophobicity of a polyphosphazene surface via static water contact angle measurements on a goniometer. Polymer surfaces of spun cast and electrospun mats were probed with advancing, receeding, and static water contact angle and dip coated slides of the same materials were also examined with a Langmuir-Blogett trough. Chapter 4 is a description of the environmental plasma surface treatments of polyphosphazenes as a method of functionalizing solid polymer surfaces. The treatment procedure of functionalizing spun cast and electrospun poly[bis(2,2,2-trifluoroethoxy)phosphazene] surfaces with plasma gases of oxygen, nitrogen, methane, and tetrafluoromethane is detailed. The resulting functionalization of the surface is examined with XPS and water contact angle data. In Chapter 5 fluoroalkoxy polyphosphazenes were processed with liquid carbon dioxide into foams. The foams were then tested for flame retardance and hydrophobicity. Appendixes A-C contain studies on moisture

  17. Site reactivity in the free radicals induced damage to leucine residues: a theoretical study.

    PubMed

    Medina, M E; Galano, A; Alvarez-Idaboy, J R

    2015-02-21

    Several recent computational studies have tried to explain the observed selectivity in radical damage to proteins. In this work we use Density Functional Theory and Transition State Theory including tunnelling corrections, reaction path degeneracy, the effect of diffusion, and the role of free radicals to get further insights into this important topic. The reaction between a leucine derivative and free radicals of biological significance, in aqueous and lipid media, has been investigated. Both thermochemical and kinetic analyses, in both hydrophilic and hydrophobic environments, have been carried out. DPPH, ˙OOH, ˙OOCH3, ˙OOCH2Cl, ˙OOCHCl2 and ˙OOCHCH2 radicals do not react with the target molecule. The reactions are proposed to be kinetically controlled. The leucine gamma site was the most reactive for the reactions with ˙N3, ˙OOCCl3, ˙OCH3, ˙OCH2Cl, and ˙OCHCl2 radicals, with rate constants equal to 1.97 × 10(5), 3.24 × 10(4), 6.68 × 10(5), 5.98 × 10(6) and 8.87 × 10(8) M(-1) s(-1), respectively, in aqueous solution. The ˙Cl, ˙OH and ˙OCCl3 radicals react with leucine at the beta, gamma, and delta positions at rates close to the diffusion limit with the alpha position which is the slowest path and the most thermodynamically favored. The presented results confirm that the Bell-Evans-Polanyi principle does not apply for the reactions between amino acid residues and free radicals. Regarding the influence of the environment on the reactivity of the studied series of free radicals towards leucine residues, it is concluded that hydrophilic media slightly lower the reactivity of the studied radicals, compared to hydrophobic ones, albeit the trends in reactivity are very similar.

  18. Competition of electrostatic and hydrophobic interactions between small hydrophobes and model enclosures

    PubMed Central

    Wang, Lingle; Friesner, Richard A.; Berne, B.J.

    2010-01-01

    The binding affinity between a probe hydrophobic particle and model hydrophobic plates with different charge (or dipole) densities in water was investigated through molecular dynamics simulations free-energy perturbation calculations. We observed a reduced binding affinity when the plates are charged, in agreement with previous findings. With increased charge density, the plates can change from “hydrophobic like” (pulling the particle into the interplate region) to “hydrophilic like” (ejecting the particle out of the interplate region), demonstrating the competition between hydrophobic and electrostatic interactions. The reduction of the binding affinity is quadratically dependent on the magnitude of the charge for symmetric systems, but linear and cubic terms also make a contribution for asymmetric systems. Statistical perturbation theory explains these results and shows when and why implicit solvent models fail. PMID:20443643

  19. Catalysis of Radical Reactions: A Radical Chemistry Perspective.

    PubMed

    Studer, Armido; Curran, Dennis P

    2016-01-04

    The area of catalysis of radical reactions has recently flourished. Various reaction conditions have been discovered and explained in terms of catalytic cycles. These cycles rarely stand alone as unique paths from substrates to products. Instead, most radical reactions have innate chains which form products without any catalyst. How do we know if a species added in "catalytic amounts" is a catalyst, an initiator, or something else? Herein we critically address both catalyst-free and catalytic radical reactions through the lens of radical chemistry. Basic principles of kinetics and thermodynamics are used to address problems of initiation, propagation, and inhibition of radical chains. The catalysis of radical reactions differs from other areas of catalysis. Whereas efficient innate chain reactions are difficult to catalyze because individual steps are fast, both inefficient chain processes and non-chain processes afford diverse opportunities for catalysis, as illustrated with selected examples.

  20. Oligorotaxane Radicals under Orders.

    PubMed

    Wang, Yuping; Frasconi, Marco; Liu, Wei-Guang; Sun, Junling; Wu, Yilei; Nassar, Majed S; Botros, Youssry Y; Goddard, William A; Wasielewski, Michael R; Stoddart, J Fraser

    2016-02-24

    A strategy for creating foldameric oligorotaxanes composed of only positively charged components is reported. Threadlike components-namely oligoviologens-in which different numbers of 4,4'-bipyridinium (BIPY(2+)) subunits are linked by p-xylylene bridges, are shown to be capable of being threaded by cyclobis(paraquat-p-phenylene) (CBPQT(4+)) rings following the introduction of radical-pairing interactions under reducing conditions. UV/vis/NIR spectroscopic and electrochemical investigations suggest that the reduced oligopseudorotaxanes fold into highly ordered secondary structures as a result of the formation of BIPY(•+) radical cation pairs. Furthermore, by installing bulky stoppers at each end of the oligopseudorotaxanes by means of Cu-free alkyne-azide cycloadditions, their analogous oligorotaxanes, which retain the same stoichiometries as their progenitors, can be prepared. Solution-state studies of the oligorotaxanes indicate that their mechanically interlocked structures lead to the enforced interactions between the dumbbell and ring components, allowing them to fold (contract) in their reduced states and unfold (expand) in their fully oxidized states as a result of Coulombic repulsions. This electrochemically controlled reversible folding and unfolding process, during which the oligorotaxanes experience length contractions and expansions, is reminiscent of the mechanisms of actuation associated with muscle fibers.

  1. Oligorotaxane Radicals under Orders

    PubMed Central

    2016-01-01

    A strategy for creating foldameric oligorotaxanes composed of only positively charged components is reported. Threadlike components—namely oligoviologens—in which different numbers of 4,4′-bipyridinium (BIPY2+) subunits are linked by p-xylylene bridges, are shown to be capable of being threaded by cyclobis(paraquat-p-phenylene) (CBPQT4+) rings following the introduction of radical-pairing interactions under reducing conditions. UV/vis/NIR spectroscopic and electrochemical investigations suggest that the reduced oligopseudorotaxanes fold into highly ordered secondary structures as a result of the formation of BIPY•+ radical cation pairs. Furthermore, by installing bulky stoppers at each end of the oligopseudorotaxanes by means of Cu-free alkyne–azide cycloadditions, their analogous oligorotaxanes, which retain the same stoichiometries as their progenitors, can be prepared. Solution-state studies of the oligorotaxanes indicate that their mechanically interlocked structures lead to the enforced interactions between the dumbbell and ring components, allowing them to fold (contract) in their reduced states and unfold (expand) in their fully oxidized states as a result of Coulombic repulsions. This electrochemically controlled reversible folding and unfolding process, during which the oligorotaxanes experience length contractions and expansions, is reminiscent of the mechanisms of actuation associated with muscle fibers. PMID:27163033

  2. Radically innovative steelmaking technologies

    NASA Astrophysics Data System (ADS)

    Szekely, Julian

    1980-09-01

    The steel industry is faced with serious problems caused by the increasing cost of energy, labor and capital and by tough overseas competition, employing new highly efficient process plants. The very high cost of capital and of capital equipment renders the construction of new green field site plants, exemplifying the best available technology economically unattractive. For this reason, over the long term the development radically innovative steelmaking technologies appears to be the only satisfactory resolution of this dilemma. The purpose of this article is to present a critical review of some of the radically innovative steelmaking technologies that have been proposed during the past few years and to develop the argument that these indeed do deserve serious consideration at the present time. It should be stressed, however, that these innovative technologies can be implemented only as part of a carefully conceived long range plan, which contains as a subset short term solutions, such as trigger prices improved investment credits, and so forth and intermediate term solutions, such as more extensive use of continuous casting, external desulfurization and selective modernization in general.

  3. Poly(N-isopropylacrylamide) (PNIPAM) is never hydrophobic.

    PubMed

    Pelton, Robert

    2010-08-15

    PNIPAM chains have hydrophobic and hydrophilic domains below and above the LCST. Temperature dependent interactions between PNIPAM and solutes arise because of changes in the local environment around the hydrophobic isopropyl domains. Below the LCST the isopropyl groups are surrounded by water, whereas above the LCST the hydrophobic groups are in contact with both water and polymer segments. Contrary to numerous claims in the literature, PNIPAM is not a hydrophobic material at temperatures above the LCST.

  4. Biodegradable, hydrophobic coatings based on crosslinked polycaprolactone

    SciTech Connect

    Koenig, M.F.

    1993-12-31

    Crosslinked poly(caprolactone) (PCL) has been explored as a hydrophobic and biodegradable coating for hydrophilic substrates. Crosslinking of PCL is known to retard its degradation rate, but does not affect its biodegradability. The cross-linking efficiencies of several organic peroxides have been determined for PCL. This has been accomplished by calculating the crosslink density (M{sub c} from dynamic mechanical data) for a given molar concentration of organic peroxide. Various thicknesses of crosslinked PCL have been coated on several different hydrophilic substrates, including paper, MaterBi (regsign), and PCL/starch composites. The hydrophobicity of the coating has been measured by following the weight gain of the coated samples upon exposure to water and a high relative humidity for various lengths of time. Results show that a coating as thin as 10 {mu}m reduces water absorption of paper by a factor of five, and thicker coatings (0.25 mm) by more than two orders of magnitude.

  5. Hydrophobic sponge structure-based triboelectric nanogenerator.

    PubMed

    Lee, Keun Young; Chun, Jinsung; Lee, Ju-Hyuck; Kim, Kyeong Nam; Kang, Na-Ri; Kim, Ju-Young; Kim, Myung Hwa; Shin, Kyung-Sik; Gupta, Manoj Kumar; Baik, Jeong Min; Kim, Sang-Woo

    2014-08-06

    Hydrophobic sponge structure-based triboelectric nanogenerators using an inverse opal structured film for sustainable energy harvesting over a wide range of humid atmosphere have been successfully demonstrated. The output voltage and current density reach a record value of 130 V and 0.10 mA cm(-2) , respectively, giving over 10-fold power enhancement, compared with the flat film-based triboelectric nanogenerator.

  6. Hydrophobic metallic nanorods with Teflon nanopatches.

    PubMed

    Khudhayer, Wisam J; Sharma, Rajesh; Karabacak, Tansel

    2009-07-08

    Introducing a hydrophobic property to vertically aligned hydrophilic metallic nanorods was investigated experimentally and theoretically. The platinum nanorod arrays were deposited on flat silicon substrates using a sputter glancing angle deposition technique (GLAD). Then a thin layer of Teflon (nanopatch) was partially deposited on the tips of platinum nanorods at a glancing angle of theta(dep) = 85 degrees for different deposition times. Teflon deposition on Pt nanorods at normal incidence (theta(dep) = 0 degrees) was also performed for comparison. Morphology and elemental analysis of Pt/Teflon nanocomposite structures were carried out using scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDAX), respectively. It was found that the GLAD technique is capable of depositing ultrathin isolated Teflon nanostructures on selective regions of nanorod arrays due to the shadowing effect during obliquely incident deposition. Contact angle measurements on nanocomposite Pt nanorods with Teflon nanopatches exhibited contact angle values as high as 138 degrees, indicating a significant increase in the hydrophobicity of originally hydrophilic Pt nanostructures that had an angle of about 52 degrees. The enhanced hydrophobicity of the Pt nanorod/Teflon nanopatch composite is attributed to the presence of nanostructured Teflon coating, which imparted a low surface energy. Surface energy calculations were performed on Pt nanorods, Teflon thin film, and Pt/Teflon composite using the two-liquid method to confirm the contact angle measurements. Furthermore, a new contact angle model utilizing Cassie and Baxter theory for heterogeneous surfaces was developed in order to explain the enhanced hydrophobicity of Pt/Teflon nanorods. According to our model, it is predicted that the solid-liquid interface is mainly at the Teflon tips when the composite nanorods are in contact with water.

  7. Hydrophobic metallic nanorods with Teflon nanopatches

    NASA Astrophysics Data System (ADS)

    Khudhayer, Wisam J.; Sharma, Rajesh; Karabacak, Tansel

    2009-07-01

    Introducing a hydrophobic property to vertically aligned hydrophilic metallic nanorods was investigated experimentally and theoretically. The platinum nanorod arrays were deposited on flat silicon substrates using a sputter glancing angle deposition technique (GLAD). Then a thin layer of Teflon (nanopatch) was partially deposited on the tips of platinum nanorods at a glancing angle of θdep = 85° for different deposition times. Teflon deposition on Pt nanorods at normal incidence (θdep = 0°) was also performed for comparison. Morphology and elemental analysis of Pt/Teflon nanocomposite structures were carried out using scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDAX), respectively. It was found that the GLAD technique is capable of depositing ultrathin isolated Teflon nanostructures on selective regions of nanorod arrays due to the shadowing effect during obliquely incident deposition. Contact angle measurements on nanocomposite Pt nanorods with Teflon nanopatches exhibited contact angle values as high as 138°, indicating a significant increase in the hydrophobicity of originally hydrophilic Pt nanostructures that had an angle of about 52°. The enhanced hydrophobicity of the Pt nanorod/Teflon nanopatch composite is attributed to the presence of nanostructured Teflon coating, which imparted a low surface energy. Surface energy calculations were performed on Pt nanorods, Teflon thin film, and Pt/Teflon composite using the two-liquid method to confirm the contact angle measurements. Furthermore, a new contact angle model utilizing Cassie and Baxter theory for heterogeneous surfaces was developed in order to explain the enhanced hydrophobicity of Pt/Teflon nanorods. According to our model, it is predicted that the solid-liquid interface is mainly at the Teflon tips when the composite nanorods are in contact with water.

  8. Interaction between silica and hydrophobic cations.

    PubMed Central

    Depasse, J

    1978-01-01

    The interactions between silica and some molecules which have a high affinity for its surface have been studied. The hydrophobic properties and the positive charge of these molecules are likely to be responsible for their strong adsorption on to silica. These observations should be useful in research into new inhibitors of the effects of silica. One of the cations tested, chloroquine, has been shown to be an effective inhibitor of the haemolytic activity of quartz. PMID:204326

  9. Diameter-dependent hydrophobicity in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kyakuno, Haruka; Fukasawa, Mamoru; Ichimura, Ryota; Matsuda, Kazuyuki; Nakai, Yusuke; Miyata, Yasumitsu; Saito, Takeshi; Maniwa, Yutaka

    2016-08-01

    Single-wall carbon nanotubes (SWCNTs) are a good model system that provides atomically smooth nanocavities. It has been reported that water-SWCNTs exhibit hydrophobicity depending on the temperature T and the SWCNT diameter D. SWCNTs adsorb water molecules spontaneously in their cylindrical pores around room temperature, whereas they exhibit a hydrophilic-hydrophobic transition or wet-dry transition (WDT) at a critical temperature Twd ≈ 220-230 K and above a critical diameter Dc ≈ 1.4-1.6 nm. However, details of the WDT phenomenon and its mechanism remain unknown. Here, we report a systematic experimental study involving X-ray diffraction, optical microscopy, and differential scanning calorimetry. It is found that water molecules inside thick SWCNTs (D > Dc) evaporate and condense into ice Ih outside the SWCNTs at Twd upon cooling, and the ice Ih evaporates and condenses inside the SWCNTs upon heating. On the other hand, residual water trapped inside the SWCNTs below Twd freezes. Molecular dynamics simulations indicate that upon lowering T, the hydrophobicity of thick SWCNTs increases without any structural transition, while the water inside thin SWCNTs (D < Dc) exhibits a structural transition, forming an ordered ice. This ice has a well-developed hydrogen bonding network adapting to the cylindrical pores of the SWCNTs. Thus, the unusual diameter dependence of the WDT is attributed to the adaptability of the structure of water to the pore dimension and shape.

  10. Hydrophobic meshes for oil spill recovery devices.

    PubMed

    Deng, Da; Prendergast, Daniel P; MacFarlane, John; Bagatin, Roberto; Stellacci, Francesco; Gschwend, Philip M

    2013-02-01

    Widespread use of petrochemicals often leads to accidental releases in aquatic environments, occasionally with disastrous results. We have developed a hydrophobic and oleophilic mesh that separates oil from water continuously in situ via capillary action, providing a means of recovering spilt oil from surface waters. Steel mesh is dip-coated in a xylene solution of low-density polyethylene, creating a hydrophobic surface with tunable roughness and opening size. The hydrophobic mesh allows oil to pass through the openings while preventing the concomitant passage of water. A bench-top prototype demonstrated the efficacy of such an oil recovery device and allowed us to quantify the factors governing the ability of the mesh to separate oil and water. Preliminary data analysis suggested that the oleophilic openings behave somewhat like capillary tubes: the oil flux is inversely proportional to oil viscosity, and directly proportional to the size of the mesh openings. An unpinned meniscus model was found to predict the water intrusion pressure successfully, which increased as the opening size decreased. The trade-off between water intrusion and oil flow rate suggests an optimal pore size for given oil properties and sea conditions.

  11. Cationic Hydrophobic Peptides with Antimicrobial Activity

    PubMed Central

    Stark, Margareta; Liu, Li-Ping; Deber, Charles M.

    2002-01-01

    The MICs of cationic, hydrophobic peptides of the prototypic sequence KKAAAXAAAAAXAAWAAXAAAKKKK-amide (where X is one of the 20 commonly occurring amino acids) are in a low micromolar range for a panel of gram-negative and gram-positive bacteria, with no or low hemolytic activity against human and rabbit erythrocytes. The peptides are active only when the average segmental hydrophobicity of the 19-residue core is above an experimentally determined threshold value (where X is Phe, Trp, Leu, Ile, Met, Val, Cys, or Ala). Antimicrobial activity could be increased by using peptides that were truncated from the prototype length to 11 core residues, with X being Phe and with 6 Lys residues grouped at the N terminus. We propose a mechanism for the interaction between these peptides and bacterial membranes similar to the “carpet model,” wherein the Lys residues interact with the anionic phospholipid head groups in the bacterial membrane surface and the hydrophobic core portion of the peptide is then able to interact with the lipid bilayer, causing disruption of the bacterial membrane. PMID:12384369

  12. Nonflammable, Hydrophobic Aerogel Composites for Insulation

    NASA Technical Reports Server (NTRS)

    Redouane, Begag

    2005-01-01

    Aerogel composites that are both nonflammable and hydrophobic have been developed for use as lightweight thermal- insulation materials for cryogenic systems. Aerogels are well known in the industry for their effectiveness as thermal insulators under cryogenic conditions, but the treatments used heretofore to render them hydrophobic also make them flammable. Nonflammability would make it safer to use aerogel insulation, especially in oxygen-rich environments and on cryogenic systems that contain liquid oxygen. A composite of this type is a silica aerogel reinforced with fibers. In comparison with unreinforced aerogels, the aerogel composite is about ten times as stiff and strong, better able to withstand handling, and more amenable to machining to required shapes. The composite can be made hydrophobic and nonflammable by appropriate design of a sol-gel process used to synthesize the aerogel component. In addition to very low thermal conductivity needed for insulation, aerogel composites of this type have been found to exhibit high resistance to moisture and nonflammability in oxygen-rich atmospheres: Samples floating on water for months gained no weight and showed no signs of deterioration. Samples were found to be nonflammable, even in pure oxygen at atmospheric pressure [14.7 psia (0.10 MPa)

  13. Phenylalanine containing hydrophobic nanospheres for antibody purification.

    PubMed

    Türkmen, Deniz; Denizli, Adil; Oztürk, Nevra; Akgöl, Sinan; Elkak, Assem

    2008-01-01

    In this study, novel hydrophobic nanospheres with an average size of 158 nm utilizing N-methacryloyl-(L)-phenylalanine methyl ester (MAPA) as a hydrophobic monomer were produced by surfactant free emulsion polymerization of 2-hydroxyethyl methacrylate (HEMA) and MAPA conducted in an aqueous dispersion medium. MAPA was synthesized using methacryloyl chloride and L-phenylalanine methyl ester. Specific surface area of the nonporous nanospheres was found to be 1874 m2/g. Poly(HEMA-MAPA) nanospheres were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Average particle size, size distribution, and surface charge measurements were also performed. Elemental analysis of MAPA for nitrogen was estimated as 0.42 mmol/g polymer. Then, poly(HEMA-MAPA) nanospheres were used in the adsorption of immunoglobulin G (IgG) in batch system. Higher adsorption values (780 mg/g) were obtained when the poly (HEMA-MAPA) nanospheres were used from both aqueous solutions and human plasma. The adsorption phenomena appeared to follow a typical Langmuir isotherm. It was observed that IgG could be repeatedly adsorbed and desorbed without significant loss in adsorption amount. These findings show considerable promise for this material as a hydrophobic support in industrial processes.

  14. Radicals in Berkeley?

    PubMed Central

    Linn, Stuart

    2015-01-01

    In a previous autobiographical sketch for DNA Repair (Linn, S. (2012) Life in the serendipitous lane: excitement and gratification in studying DNA repair. DNA Repair 11, 595–605), I wrote about my involvement in research on mechanisms of DNA repair. In this Reflections, I look back at how I became interested in free radical chemistry and biology and outline some of our bizarre (at the time) observations. Of course, these studies could never have succeeded without the exceptional aid of my mentors: my teachers; the undergraduate and graduate students, postdoctoral fellows, and senior lab visitors in my laboratory; and my faculty and staff colleagues here at Berkeley. I am so indebted to each and every one of these individuals for their efforts to overcome my ignorance and set me on the straight and narrow path to success in research. I regret that I cannot mention and thank each of these mentors individually. PMID:25713083

  15. Radicals in Berkeley?

    PubMed

    Linn, Stuart

    2015-04-03

    In a previous autobiographical sketch for DNA Repair (Linn, S. (2012) Life in the serendipitous lane: excitement and gratification in studying DNA repair. DNA Repair 11, 595-605), I wrote about my involvement in research on mechanisms of DNA repair. In this Reflections, I look back at how I became interested in free radical chemistry and biology and outline some of our bizarre (at the time) observations. Of course, these studies could never have succeeded without the exceptional aid of my mentors: my teachers; the undergraduate and graduate students, postdoctoral fellows, and senior lab visitors in my laboratory; and my faculty and staff colleagues here at Berkeley. I am so indebted to each and every one of these individuals for their efforts to overcome my ignorance and set me on the straight and narrow path to success in research. I regret that I cannot mention and thank each of these mentors individually.

  16. Free radical propulsion concept

    NASA Technical Reports Server (NTRS)

    Hawkins, C. E.; Nakanishi, S.

    1981-01-01

    A free radical propulsion concept utilizing the recombination energy of dissociated low molecular weight gases to produce thrust was examined. The concept offered promise of a propulsion system operating at a theoretical impulse, with hydrogen, as high as 2200 seconds at high thrust to power ratio, thus filling the gas existing between chemical and electrostatic propulsion capabilities. Microwave energy used to dissociate a continuously flowing gas was transferred to the propellant via three body recombination for conversion to propellant kinetic energy. Power absorption by the microwave plasma discharge was in excess of 90 percent over a broad range of pressures. Gas temperatures inferred from gas dynamic equations showed much higher temperatures from microwave heating than from electrothermal heating. Spectroscopic analysis appeared to corroborate the inferred temperatures of one of the gases tested.

  17. Radical Change by Entrepreneurial Design

    DTIC Science & Technology

    1998-01-01

    This article offers a conceptual framework to understand radical change. It opens with a typology that defines change in terms of its pace and scope...known entrepreneurs who have been successful in molding and shaping the radical change process. The implications of this conceptual framework to

  18. A new procedure for the hydrophobization of cellulose fibre using laccase and a hydrophobic phenolic compound.

    PubMed

    Garcia-Ubasart, Jordi; Colom, Josep F; Vila, Carlos; Gómez Hernández, Nuria; Blanca Roncero, M; Vidal, Teresa

    2012-05-01

    A new biotechnological procedure using laccase in combination with a hydrophobic phenolic compound (lauryl gallate) for the hydrophobization of cellulose fibres and internal sizing of paper was developed. Cellulose fibres from hardwood kraft pulp were incubated with laccase (Lac), in combination with lauryl gallate (LG). The Lac-LG treatment resulted in the internal sizing of paper, and also in significantly reduced water penetration in the handsheets and wettability of the paper surface. Paper was found not to be effectively rendered hydrophobic by LG alone. SEM images of the fibre network revealed the presence of the sizing agent: a product of the reaction between laccase and lauryl gallate. Binding of lauryl gallate to cellulose fibres was suggested by the increase in kappa number of the pulp and further confirmed by IR spectroscopy.

  19. Studies of radiation-produced radicals and radical ions

    SciTech Connect

    Williams, T.F.

    1991-01-01

    The radiolytic oxidation of anti-5-methylbicyclo(2.1.0)pentane gives the 1-methylcyclopentene radical cation as the sole rearrangement product H migration whereas oxidation of its syn isomer results in the highly selective formation of the 3-methylcyclopentene radical cation by methyl group migration. Since exactly the same stereoselectivity of olefin formation was observed in corresponding PET (photosensitized electron transfer) studies in the liquid phase, it is concluded that the rearrangement in this case also occurs through the intermediacy of radical cations. Clearly, the radical cation rearrangement must occur very rapidly (10{sup {minus}8}--10{sup {minus}9}s) under liquid-phase conditions at room temperature to compete with back electron transfer, and therefore the hydrogen (or methyl) migration is a fast process under these conditions. An intramolecular cycloaddition reaction was demonstrated in the radical cation rearrangement of 4-vinylcyclohexene to bicyclo(3.2.1)oct-2-ene. ESR studies show that the radiolytic oxidation of quadricyclane in Freon matrices under conditions of high substrate dilution leads to the bicyclo(3.2.0)hepta-2,6-diene radical cation as well as the previously reported norbornadiene radical cation, the former species predominating at sufficiently low concentrations.

  20. Hydrophobic pocket targeting probes for enteroviruses

    NASA Astrophysics Data System (ADS)

    Martikainen, Mari; Salorinne, Kirsi; Lahtinen, Tanja; Malola, Sami; Permi, Perttu; Häkkinen, Hannu; Marjomäki, Varpu

    2015-10-01

    Visualization and tracking of viruses without compromising their functionality is crucial in order to understand virus targeting to cells and tissues, and to understand the subsequent subcellular steps leading to virus uncoating and replication. Enteroviruses are important human pathogens causing a vast number of acute infections, and are also suggested to contribute to the development of chronic diseases like type I diabetes. Here, we demonstrate a novel method to target site-specifically the hydrophobic pocket of enteroviruses. A probe, a derivative of Pleconaril, was developed and conjugated to various labels that enabled the visualization of enteroviruses under light and electron microscopes. The probe mildly stabilized the virus particle by increasing the melting temperature by 1-3 degrees, and caused a delay in the uncoating of the virus in the cellular endosomes, but could not however inhibit the receptor binding, cellular entry or infectivity of the virus. The hydrophobic pocket binding moiety of the probe was shown to bind to echovirus 1 particle by STD and tr-NOESY NMR methods. Furthermore, binding to echovirus 1 and Coxsackievirus A9, and to a lesser extent to Coxsackie virus B3 was verified by using a gold nanocluster labeled probe by TEM analysis. Molecular modelling suggested that the probe fits the hydrophobic pockets of EV1 and CVA9, but not of CVB3 as expected, correlating well with the variations in the infectivity and stability of the virus particles. EV1 conjugated to the fluorescent dye labeled probe was efficiently internalized into the cells. The virus-fluorescent probe conjugate accumulated in the cytoplasmic endosomes and caused infection starting from 6 hours onwards. Remarkably, before and during the time of replication, the fluorescent probe was seen to leak from the virus-positive endosomes and thus separate from the capsid proteins that were left in the endosomes. These results suggest that, like the physiological hydrophobic content

  1. Thermoresponsive hyaluronic acid nanogels as hydrophobic drug carrier to macrophages.

    PubMed

    Fernandes Stefanello, Talitha; Szarpak-Jankowska, Anna; Appaix, Florence; Louage, Benoit; Hamard, Lauriane; De Geest, Bruno G; van der Sanden, Boudewijn; Nakamura, Celso Vataru; Auzély-Velty, Rachel

    2014-11-01

    Delivery systems for macrophages are particularly attractive since these phagocytic cells play a important role in immunological and inflammatory responses, also acting as host cells for microorganisms that are involved in deadly infectious diseases, such as leishmaniasis. Hyaluronic acid (HA) is specifically recognized by macrophages that are known to express HA receptors. Therefore, in this study, we focused on HA-based nanogels as drug carriers for these cells. The drug delivery was validated in an in vivo study on mice using intravital two-photon laser scanning microscopy. HA derivatives were modified with a biocompatible oligo(ethylene glycol)-based thermoresponsive polymer to form nanogels. These HA conjugates were readily prepared by varying the molar mass of initial HA and the degree of substitution via radical-mediated thiol-ene chemistry in aqueous solution. The derivatives were shown to self-assemble into spherical gel particles with diameters ranging from 150 to 214 nm above 37 °C. A poorly water-soluble two-photon dye was successfully loaded into the nanogels during this self-assembly process. In vitro cellular uptake tests using a RAW 264.7 murine macrophage cell line showed successful intracellular delivery of the hydrophobic dye. After intravenous injection in mice, the nanogels circulated freely in the blood but were rapidly phagocytized within 13 min by circulating macrophages and stored in the liver and spleen, as observed by two-photon microscopy. Benefit can be thus expected in using such a delivery system for the liver and spleen macrophage-associated diseases.

  2. Free radicals and male reproduction.

    PubMed

    Agarwal, Ashok; Allamaneni, Shyam S R

    2011-03-01

    Male factor accounts for almost 50% cases of infertility. The exact mechanism of sperm dysfunction is not known in many cases. Extensive research in the last decade has led to the identification of free radicals (reactive oxygen species) as mediators of sperm dysfunction in both specific diagnoses and idiopathic cases of male infertility. Elevated levels of reactive oxygen species are seen in up to 30-80% of men with male infertility. The role of free radicals has been studied extensively in the process of human reproduction. We know now that a certain level of free radicals is necessary for normal sperm function, whereas an excessive level of free radicals can cause detrimental effect on sperm function and subsequent fertilisation and offspring health. Oxidative stress develops when there is an imbalance between generation of free radicals and scavenging capacity of anti-oxidants in reproductive tract. Oxidative stress has been shown to affect both standard semen parameters and fertilising capacity. In addition, high levels of free radicals have been associated with lack of or poor fertility outcome after natural conception or assisted reproduction. Diagnostic techniques to quantify free radicals in infertile patients can assist physicians treating patients with infertility to plan for proper treatment strategies. In vivo anti-oxidants can be used against oxidative stress in male reproductive tract. Supplementation of in vitro anti-oxidants can help prevent the oxidative stress during sperm preparation techniques in assisted reproduction.

  3. Potential for plastics to transport hydrophobic contaminants.

    PubMed

    Teuten, Emma L; Rowland, Steven J; Galloway, Tamara S; Thompson, Richard C

    2007-11-15

    Plastic debris litters marine and terrestrial habitats worldwide. It is ingested by numerous species of animals, causing deleterious physical effects. High concentrations of hydrophobic organic contaminants have also been measured on plastic debris collected from the environment, but the fate of these contaminants is poorly understood. Here, we examine the uptake and subsequent release of phenanthrene by three plastics. Equilibrium distribution coefficients for sorption of phenanthrene from seawater onto the plastics varied by more than an order of magnitude (polyethylene > polypropylene > polyvinyl chloride (PVC)). In all cases, sorption to plastics greatly exceeded sorption to two natural sediments. Desorption rates of phenanthrene from the plastics or sediments back into solution spanned several orders of magnitude. As expected, desorption occurred more rapidly from the sediments than from the plastics. Using the equilibrium partitioning method, the effects of adding very small quantities of plastic with sorbed phenanthrene to sediment inhabited by the lugworm (Arenicola marina) were evaluated. We estimate that the addition of as little as 1 microg of contaminated polyethylene to a gram of sediment would give a significant increase in phenanthrene accumulation by A. marina. Thus, plastics may be important agents in the transport of hydrophobic contaminants to sediment-dwelling organisms.

  4. The Dewetting Transition and The Hydrophobic Effect.

    SciTech Connect

    Choudhury, Niharendu; Pettitt, Bernard M.

    2007-03-27

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. A molecular-level description of the behavior of water in hydrophobic spaces is presented in terms of the coupled effects of solute size and atomic solute-solvent interactions. For model solutes with surface areas near those of protein contacts, we identify three different regions of solute-water interaction to be associated with three distinctly different structural characteristics of water in the intersolute region: dry, oscillating, and wet. A first orderlike phase transition is confirmed from the wet to dry state bridged by a narrow region with liquid-vapor oscillations in the intersolute region as the strength of the solute-water attractive dispersion interaction decreases. We demonstrate that the recent idea that cavitation in the intersolute region of nanoscopic solutes is preceded by the formation of a vapor layer around an individual solute is not the general case. The appearance of density waves pulled up around and outside of a nanoscopic plate occurs at lower interaction strengths than are required to obtain a wet state between such plates. We further show that chemically reasonable estimates of the interaction strength lead to a microscopically wet state and a hydrophobic interaction characterized by traps and barriers to association and not by vacuum induced collapse.

  5. The effect of lithium ions on the hydrophobic effect: does lithium affect hydrophobicity differently than other ions?

    PubMed

    Beauchamp, David L; Khajehpour, Mazdak

    2012-04-01

    Ionic species have been shown to significantly perturb the interactions between non-polar solutes in aqueous solution. These perturbations are often analyzed in terms of the interactions existing between hydrophobic surfaces and ions. It has been known for some time, that ions with a high charge density are repelled from hydrophobic surfaces while ions with a low charge density tend to stick to these surfaces. Therefore, from a continuum model standpoint, small monovalent ions promote hydrophobicity by minimizing the exposed hydrophobic surface area, while "sticky" large monovalent ions interact with the hydrophobic surfaces and discourage aggregation. However, the charge-dense lithium ion often exhibits anomalous behaviour different from these predicted trends: instead of enhancing, the addition of lithium ions often seems to weaken the hydrophobic effect and on the contrary help dissolve hydrophobic molecules. This weakening of apparent hydrophobicity is considered to be one of the reasons for the protein denaturing properties of lithium salts. Recent theoretical and experimental results however have shown that lithium cations can interact with a variety of molecular functional groups. This suggests that this apparent lithium-induced lowering of hydrophobicity, that is often reported in the literature may be a result of specific interactions between these molecular functional groups and lithium, rather than weakening the interaction between hydrophobic surfaces. This work examines these possibilities by studying the effect of various cations on the simple hydrophobic interaction existing between methyl and phenyl contact-pairs and demonstrates that the effect of lithium cations on the hydrophobic effect follows the trend predicted by continuum models. In other words, the influence of an ion on the hydrophobic interaction between two non-polar surfaces is a function of the interaction of that ion and each non-polar surface.

  6. Redox Properties of Free Radicals.

    ERIC Educational Resources Information Center

    Neta, P.

    1981-01-01

    Describes pulse radiolysis as a useful means in studing one-electron redox potentials. This method allows the production of radicals and the determination of their concentration and rates of reaction. (CS)

  7. [Simultaneous radical retropubic prostatectomy, diverticulectomy].

    PubMed

    Loran, O B; Sokolov, A E; Guspanov, R I; Polegen'kiĭ, V V

    2014-01-01

    Presented clinical case demonstrates a combination of rare congenital abnormality - giant true diverticula of the bladder - and high-risk prostate cancer, as well as a successful result of simultaneous operation - a radical prostatectomy with diverticulectomy.

  8. Free radical inactivation of pepsin

    NASA Astrophysics Data System (ADS)

    Josimović, Lj; Ruvarac, I.; Janković, I.; Jovanović, S. V.

    1994-06-01

    Alkylperoxy radicals containing one, two or three chlorine atoms, CO -2, O 2 - were reacted with pepsin in aqueous solutions. It was found that only Cl 3COO and CO -2 inactive pepsin, attacking preferentially the disulfide bridge. Transient spectra obtained upon completion of the Cl 3COO + pepsin reaction at pH 5 indicate that 20% of initially produced Cl 3COO radicals oxidizes tryptophan residues, and 40% disulfide bridges. The inactivation induced by the Cl 3COO radical increases at lower pH, and the maximal inactivation, Gin = 5.8, was observed at pH 1.5. The inactivation of pepsin by CO -2 radicals depends on the absorbed dose. The maximal inactivation, Gin = 4.5, was determined in the dose range from 38 to 53 Gy.

  9. On the thermodynamics and kinetics of hydrophobic interactions at interfaces.

    PubMed

    Vembanur, Srivathsan; Patel, Amish J; Sarupria, Sapna; Garde, Shekhar

    2013-09-05

    We have studied how primitive hydrophobic interactions between two or more small nonpolar solutes are affected by the presence of surfaces. We show that the desolvation barriers present in the potential of mean force between the solutes in bulk water are significantly reduced near an extended hydrophobic surface. Correspondingly, the kinetics of hydrophobic contact formation and breakage are faster near a hydrophobic surface than near a hydrophilic surface or in the bulk. We propose that the reduction in the desolvation barrier is a consequence of the fact that water near extended hydrophobic surfaces is akin to that at a liquid-vapor interface and is easily displaced. We support this proposal with three independent observations. First, when small hydrophobic solutes are brought near a hydrophobic surface, they induce local dewetting, thereby facilitating the reduction of desolvation barriers. Second, our results and those of Patel et al. (Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 17678-17683) show that, whereas the association of small solutes in bulk water is driven by entropy, that near hydrophobic surfaces is driven by enthalpy, suggesting that the physics of interface deformation is important. Third, moving water away from its vapor-liquid coexistence, by applying hydrostatic pressure, leads to recovery of bulklike signatures (e.g., the presence of a desolvation barrier and an entropic driving force) in the association of solutes. These observations for simple solutes also translate to end-to-end contact formation in a model peptide with hydrophobic end groups, for which lowering of the desolvation barrier and acceleration of contact formation are observed near a hydrophobic surface. Our results suggest that extended hydrophobic surfaces, such as air-water or hydrocarbon-water surfaces, could serve as excellent platforms for catalyzing hydrophobically driven assembly.

  10. New Hydrophobic IOL Materials and Understanding the Science of Glistenings.

    PubMed

    Tetz, Manfred; Jorgensen, Matthew R

    2015-01-01

    An introduction to the history of intraocular lenses (IOLs) is given, leading up to modern hydrophobic examples. The roles of hydrophobicity, hygroscopy, materials chemistry, and edge design are discussed in the context of IOLs. The four major types of IOL materials are compared in terms of their chemistry and biocompatibility. An example of a modern "hydrophobic" acrylic polymer with higher water content is discussed in detail.

  11. Conductive hydrophobic hybrid textiles modified with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kowalczyk, D.; Brzeziński, S.; Makowski, T.; Fortuniak, W.

    2015-12-01

    The paper presents the results of modifying and testing modern hybrid polyester-cotton woven fabrics with deposited multi-wall carbon nanotubes and imparted hydrophobicity. The effect of the carbon nanotubes deposited on these fabrics on their conductive properties and hydrophobicity has been assessed. The electro-conductive and hydrophobic composite fabrics obtained in this way, being light, elastic and resistant to mechanical effects, make it possible to be widely used in various industrial fields.

  12. Self Assembled, Ultra-Hydrophobic Micro/Nano-Textured Surfaces

    DTIC Science & Technology

    2007-04-01

    Self Assembled, Ultra-Hydrophobic Micro / Nano -Textured Surfaces by Adam M. Rawlett, Joshua A. Orlicki, Nicole Zander, Afia Karikari, and...5069 ARL-TN-275 April 2007 Self Assembled, Ultra-Hydrophobic Micro / Nano -Textured Surfaces Adam M. Rawlett, Joshua A. Orlicki, and...NUMBER 5b. GRANT NUMBER 4. TITL Self A bled, Ultra-Hydrophobic Micro / Nano -Textured Surfaces 5c. PROGRAM ELEMENT NUMBER E ssem AND SUBTITLE 5d

  13. Combined Hydrophobicity and Mechanical Durability through Surface Nanoengineering

    PubMed Central

    Elliott, Paul R.; Stagon, Stephen P.; Huang, Hanchen; Furrer, David U.; Burlatsky, Sergei F.; Filburn, Thomas P.

    2015-01-01

    This paper reports combined hydrophobicity and mechanical durability through the nanoscale engineering of surfaces in the form of nanorod-polymer composites. Specifically, the hydrophobicity derives from nanoscale features of mechanically hard ZnO nanorods and the mechanical durability derives from the composite structure of a hard ZnO nanorod core and soft polymer shell. Experimental characterization correlates the morphology of the nanoengineered surfaces with the combined hydrophobicity and mechanical durability, and reveals the responsible mechanisms. Such surfaces may find use in applications, such as boat hulls, that benefit from hydrophobicity and require mechanical durability. PMID:25851026

  14. Modulation of hydrophobic interactions by proximally immobilized ions.

    PubMed

    Ma, C Derek; Wang, Chenxuan; Acevedo-Vélez, Claribel; Gellman, Samuel H; Abbott, Nicholas L

    2015-01-15

    The structure of water near non-polar molecular fragments or surfaces mediates the hydrophobic interactions that underlie a broad range of interfacial, colloidal and biophysical phenomena. Substantial progress over the past decade has improved our understanding of hydrophobic interactions in simple model systems, but most biologically and technologically relevant structures contain non-polar domains in close proximity to polar and charged functional groups. Theories and simulations exploring such nanometre-scale chemical heterogeneity find it can have an important effect, but the influence of this heterogeneity on hydrophobic interactions has not been tested experimentally. Here we report chemical force microscopy measurements on alkyl-functionalized surfaces that reveal a dramatic change in the surfaces' hydrophobic interaction strengths on co-immobilization of amine or guanidine groups. Protonation of amine groups doubles the strength of hydrophobic interactions, and guanidinium groups eliminate measurable hydrophobic interactions in all pH ranges investigated. We see these divergent effects of proximally immobilized cations also in single-molecule measurements on conformationally stable β-peptides with non-polar subunits located one nanometre from either amine- or guanidine-bearing subunits. Our results demonstrate the importance of nanometre-scale chemical heterogeneity, with hydrophobicity not an intrinsic property of any given non-polar domain but strongly modulated by functional groups located as far away as one nanometre. The judicious placing of charged groups near hydrophobic domains thus provides a strategy for tuning hydrophobic driving forces to optimize molecular recognition or self-assembly processes.

  15. Thermally stable hydrophobicity in electrospun silica/polydimethylsiloxane hybrid fibers

    NASA Astrophysics Data System (ADS)

    Wei, Zhonglin; Li, Jianjun; Wang, Chao; Cao, Jungang; Yao, Yongtao; Lu, Haibao; Li, Yibin; He, Xiaodong

    2017-01-01

    In order to improve practical performances of silica-based inorganic/organic hybrid fibers, silica/polydimethylsiloxane hydrophobic fibers were successfully prepared by electrospinning. Silica sol and polydimethylsiloxane can be mixed homogeneously and become stable precursor solution in dichloromethane, which allows the transformation of silica/polydimethylsiloxane precursor solution into ultrafine fibers. Flame can ignite organic groups in polydimethylsiloxane directly and destroy the hydrophobicity of hybrid fibers, but hydrophobic feature may survive if electrospun hybrid membrane is combined with thin stainless-steel-304 gauze of 150 meshes due to its thermally stable hydrophobicity (>600 °C).

  16. Combined hydrophobicity and mechanical durability through surface nanoengineering

    DOE PAGES

    Elliott, Paul R.; Stagon, Stephen P.; Huang, Hanchen; ...

    2015-04-08

    This paper reports combined hydrophobicity and mechanical durability through the nanoscale engineering of surfaces in the form of nanorod-polymer composites. Specifically, the hydrophobicity derives from nanoscale features of mechanically hard ZnO nanorods and the mechanical durability derives from the composite structure of a hard ZnO nanorod core and soft polymer shell. Experimental characterization correlates the morphology of the nanoengineered surfaces with the combined hydrophobicity and mechanical durability, and reveals the responsible mechanisms. Such surfaces may find use in applications, such as boat hulls, that benefit from hydrophobicity and require mechanical durability.

  17. Modulation of hydrophobic interactions by proximally immobilized ions

    NASA Astrophysics Data System (ADS)

    Ma, C. Derek; Wang, Chenxuan; Acevedo-Vélez, Claribel; Gellman, Samuel H.; Abbott, Nicholas L.

    2015-01-01

    The structure of water near non-polar molecular fragments or surfaces mediates the hydrophobic interactions that underlie a broad range of interfacial, colloidal and biophysical phenomena. Substantial progress over the past decade has improved our understanding of hydrophobic interactions in simple model systems, but most biologically and technologically relevant structures contain non-polar domains in close proximity to polar and charged functional groups. Theories and simulations exploring such nanometre-scale chemical heterogeneity find it can have an important effect, but the influence of this heterogeneity on hydrophobic interactions has not been tested experimentally. Here we report chemical force microscopy measurements on alkyl-functionalized surfaces that reveal a dramatic change in the surfaces' hydrophobic interaction strengths on co-immobilization of amine or guanidine groups. Protonation of amine groups doubles the strength of hydrophobic interactions, and guanidinium groups eliminate measurable hydrophobic interactions in all pH ranges investigated. We see these divergent effects of proximally immobilized cations also in single-molecule measurements on conformationally stable β-peptides with non-polar subunits located one nanometre from either amine- or guanidine-bearing subunits. Our results demonstrate the importance of nanometre-scale chemical heterogeneity, with hydrophobicity not an intrinsic property of any given non-polar domain but strongly modulated by functional groups located as far away as one nanometre. The judicious placing of charged groups near hydrophobic domains thus provides a strategy for tuning hydrophobic driving forces to optimize molecular recognition or self-assembly processes.

  18. Characterization and comparison of hydrophobic neutral and hydrophobic acid dissolved organic carbon isolated from three municipal landfill leachates

    USGS Publications Warehouse

    Nanny, Mark A.; Ratasuk, Nopawan

    2002-01-01

    The acid-precipitated (AP) and acid-soluble (AS) fractions of the combined hydrophobic neutral and hydrophobic acid dissolved organic carbon (DOC) were isolated from leachate collected from three municipal landfills of different age and redox conditions. The AP and the AS combined hydrophobic neutral and hydrophobic acid DOC comprised 6–15% and 51–66%, respectively, of the leachate nonpurgable organic carbon. Elemental analysis, infra-red spectroscopy, 13C CP-MAS nuclear magnetic resonance spectroscopy and dipolar dephasing experiments, and thermochemolysis gas chromatography/mass spectrometry results showed that the AP and AS fractions of hydrophobic neutral and hydrophobic acid DOC are highly aliphatic, with linear and branching moieties, and less oxidized than most terrestrial and aquatic humic substances. Very little, if any, polysaccharide or cellulose, lignin, or cutin components comprise these fractions. It is hypothesized that a majority of the organic carbon in these fractions originates highly branched, cyclic aliphatic organic compounds.

  19. Floating behavior of hydrophobic glass spheres.

    PubMed

    Liu, Xinjie; Wang, Xiaolong; Liang, Yongmin; Zhou, Feng

    2009-08-15

    When a hydrophobic solid sphere is floating on water or salt solutions with different concentrations, it is at equilibrium under the impact of gravity, buoyancy force, and curvature force, the component of surface tension in the vertical direction. We have changed the diameters of the spheres and the concentrations of the two selected salts, NaCl and NaNO(3), to study the floating behaviors of these spheres and the contributions of surface tension and buoyancy force to their floatation. Generally speaking, the surface tension plays a more important role than the buoyancy force when the gravity is small, but the buoyancy force plays an identical or a more important role when the spheres are big enough. The wettability of the spheres significantly influences the height below the contact perimeter especially in salt solutions. The theoretical calculation meniscus slope angles at the sphere three-phase contact line are in agreement with experimental results.

  20. Penetration of surfactant solutions into hydrophobic capillaries.

    PubMed

    Bain, Colin D

    2005-08-21

    The initial rise velocity of surfactant solutions in hydrophobic capillaries is independent of time (F. Tiberg, B. Zhmud, K. Hallstensson and M. von Bahr, Phys. Chem. Chem. Phys., 2000, 2, 5189). By analogy with the hydrodynamics of an overflowing cylinder, we present a steady-state solution for capillary penetration in which the velocity is determined by the adsorption kinetics at the air-water interface. Good agreement between the model predictions and experimental data of Tiberg and coworkers is obtained for the non-ionic surfactant C10E6 under the assumption of diffusion-controlled adsorption. The longer chain homologue, C14E6, shows evidence of kinetic barriers to adsorption.

  1. Hydrophobicity and Charge Shape Cellular Metabolite Concentrations

    PubMed Central

    Bar-Even, Arren; Noor, Elad; Flamholz, Avi; Buescher, Joerg M.; Milo, Ron

    2011-01-01

    What governs the concentrations of metabolites within living cells? Beyond specific metabolic and enzymatic considerations, are there global trends that affect their values? We hypothesize that the physico-chemical properties of metabolites considerably affect their in-vivo concentrations. The recently achieved experimental capability to measure the concentrations of many metabolites simultaneously has made the testing of this hypothesis possible. Here, we analyze such recently available data sets of metabolite concentrations within E. coli, S. cerevisiae, B. subtilis and human. Overall, these data sets encompass more than twenty conditions, each containing dozens (28-108) of simultaneously measured metabolites. We test for correlations with various physico-chemical properties and find that the number of charged atoms, non-polar surface area, lipophilicity and solubility consistently correlate with concentration. In most data sets, a change in one of these properties elicits a ∼100 fold increase in metabolite concentrations. We find that the non-polar surface area and number of charged atoms account for almost half of the variation in concentrations in the most reliable and comprehensive data set. Analyzing specific groups of metabolites, such as amino-acids or phosphorylated nucleotides, reveals even a higher dependence of concentration on hydrophobicity. We suggest that these findings can be explained by evolutionary constraints imposed on metabolite concentrations and discuss possible selective pressures that can account for them. These include the reduction of solute leakage through the lipid membrane, avoidance of deleterious aggregates and reduction of non-specific hydrophobic binding. By highlighting the global constraints imposed on metabolic pathways, future research could shed light onto aspects of biochemical evolution and the chemical constraints that bound metabolic engineering efforts. PMID:21998563

  2. How the hydrophobic factor drives protein folding.

    PubMed

    Baldwin, Robert L; Rose, George D

    2016-11-01

    How hydrophobicity (HY) drives protein folding is studied. The 1971 Nozaki-Tanford method of measuring HY is modified to use gases as solutes, not crystals, and this makes the method easy to use. Alkanes are found to be much more hydrophobic than rare gases, and the two different kinds of HY are termed intrinsic (rare gases) and extrinsic (alkanes). The HY values of rare gases are proportional to solvent-accessible surface area (ASA), whereas the HY values of alkanes depend on special hydration shells. Earlier work showed that hydration shells produce the hydration energetics of alkanes. Evidence is given here that the transfer energetics of alkanes to cyclohexane [Wolfenden R, Lewis CA, Jr, Yuan Y, Carter CW, Jr (2015) Proc Natl Acad Sci USA 112(24):7484-7488] measure the release of these shells. Alkane shells are stabilized importantly by van der Waals interactions between alkane carbon and water oxygen atoms. Thus, rare gases cannot form this type of shell. The very short (approximately picoseconds) lifetime of the van der Waals interaction probably explains why NMR efforts to detect alkane hydration shells have failed. The close similarity between the sizes of the opposing energetics for forming or releasing alkane shells confirms the presence of these shells on alkanes and supports Kauzmann's 1959 mechanism of protein folding. A space-filling model is given for the hydration shells on linear alkanes. The model reproduces the n values of Jorgensen et al. [Jorgensen WL, Gao J, Ravimohan C (1985) J Phys Chem 89:3470-3473] for the number of waters in alkane hydration shells.

  3. How the hydrophobic factor drives protein folding

    PubMed Central

    Baldwin, Robert L.; Rose, George D.

    2016-01-01

    How hydrophobicity (HY) drives protein folding is studied. The 1971 Nozaki–Tanford method of measuring HY is modified to use gases as solutes, not crystals, and this makes the method easy to use. Alkanes are found to be much more hydrophobic than rare gases, and the two different kinds of HY are termed intrinsic (rare gases) and extrinsic (alkanes). The HY values of rare gases are proportional to solvent-accessible surface area (ASA), whereas the HY values of alkanes depend on special hydration shells. Earlier work showed that hydration shells produce the hydration energetics of alkanes. Evidence is given here that the transfer energetics of alkanes to cyclohexane [Wolfenden R, Lewis CA, Jr, Yuan Y, Carter CW, Jr (2015) Proc Natl Acad Sci USA 112(24):7484–7488] measure the release of these shells. Alkane shells are stabilized importantly by van der Waals interactions between alkane carbon and water oxygen atoms. Thus, rare gases cannot form this type of shell. The very short (approximately picoseconds) lifetime of the van der Waals interaction probably explains why NMR efforts to detect alkane hydration shells have failed. The close similarity between the sizes of the opposing energetics for forming or releasing alkane shells confirms the presence of these shells on alkanes and supports Kauzmann's 1959 mechanism of protein folding. A space-filling model is given for the hydration shells on linear alkanes. The model reproduces the n values of Jorgensen et al. [Jorgensen WL, Gao J, Ravimohan C (1985) J Phys Chem 89:3470–3473] for the number of waters in alkane hydration shells. PMID:27791131

  4. How hydrophobic buckminsterfullerene affects surrounding water structure.

    PubMed

    Weiss, Dahlia R; Raschke, Tanya M; Levitt, Michael

    2008-03-13

    The hydrophobic hydration of fullerenes in water is of significant interest as the most common Buckminsterfullerene (C60) is a mesoscale sphere; C60 also has potential in pharmaceutical and nanomaterial applications. We use an all-atom molecular dynamics simulation lasting hundreds of nanoseconds to determine the behavior of a single molecule of C60 in a periodic box of water, and compare this to methane. A C60 molecule does not induce drying at the surface; however, unlike a hard sphere methane, a hard sphere C60 solute does. This is due to a larger number of attractive Lennard-Jones interactions between the carbon atom centers in C60 and the surrounding waters. In these simulations, water is not uniformly arranged but rather adopts a range of orientations in the first hydration shell despite the spherical symmetry of both solutes. There is a clear effect of solute size on the orientation of the first hydration shell waters. There is a large increase in hydrogen-bonding contacts between waters in the C60 first hydration shell. There is also a disruption of hydrogen bonds between waters in the first and second hydration shells. Water molecules in the first hydration shell preferentially create triangular structures that minimize the net water dipole near the surface near both the methane and C60 surface, reducing the total energy of the system. Additionally, in the first and second hydration shells, the water dipoles are ordered to a distance of 8 A from the solute surface. We conclude that, with a diameter of approximately 1 nm, C60 behaves as a large hydrophobic solute.

  5. Crystalline bipyridinium radical complexes and uses thereof

    DOEpatents

    Fahrenbach, Albert C.; Barnes, Jonathan C.; Li, Hao; Stoddart, J. Fraser; Basuray, Ashish Neil; Sampath, Srinivasan

    2015-09-01

    Described herein are methods of generating 4,4'-bipyridinium radical cations (BIPY.sup..cndot.+), and methods for utilizing the radical-radical interactions between two or more BIPY.sup..cndot.+ radical cations that ensue for the creation of novel materials for applications in nanotechnology. Synthetic methodologies, crystallographic engineering techniques, methods of physical characterization, and end uses are described.

  6. Structures of benzylsuccinate synthase elucidate roles of accessory subunits in glycyl radical enzyme activation and activity

    PubMed Central

    Funk, Michael A.; Judd, Evan T.; Marsh, E. Neil G.; Elliott, Sean J.; Drennan, Catherine L.

    2014-01-01

    Anaerobic degradation of the environmental pollutant toluene is initiated by the glycyl radical enzyme benzylsuccinate synthase (BSS), which catalyzes the radical addition of toluene to fumarate, forming benzylsuccinate. We have determined crystal structures of the catalytic α-subunit of BSS with its accessory subunits β and γ, which both bind a [4Fe-4S] cluster and are essential for BSS activity in vivo. We find that BSSα has the common glycyl radical enzyme fold, a 10-stranded β/α-barrel that surrounds the glycyl radical cofactor and active site. Both accessory subunits β and γ display folds related to high potential iron–sulfur proteins but differ substantially from each other in how they interact with the α-subunit. BSSγ binds distally to the active site, burying a hydrophobic region of BSSα, whereas BSSβ binds to a hydrophilic surface of BSSα that is proximal to the active site. To further investigate the function of BSSβ, we determined the structure of a BSSαγ complex. Remarkably, we find that the barrel partially opens, allowing the C-terminal region of BSSα that houses the glycyl radical to shift within the barrel toward an exit pathway. The structural changes that we observe in the BSSαγ complex center around the crucial glycyl radical domain, thus suggesting a role for BSSβ in modulating the conformational dynamics required for enzyme activity. Accompanying proteolysis experiments support these structural observations. PMID:24982148

  7. EPR studies on a stable sulfinyl radical observed in the iron-oxygen-reconstituted Y177F/I263C protein R2 double mutant of ribonucleotide reductase from mouse.

    PubMed

    Adrait, Annie; Ohrström, Maria; Barra, Anne-Laure; Thelander, Lars; Gräslund, Astrid

    2002-05-21

    Ribonucleotide reductase (RNR) catalyzes the biosynthesis of deoxyribonucleotides. The active enzyme contains a diiron center and a tyrosyl free radical required for enzyme activity. The radical is located at Y177 in the R2 protein of mouse RNR. The radical is formed concomitantly with the mu-oxo-bridged diferric center in a reconstitution reaction between ferrous iron and molecular oxygen in the protein. EPR at 9.6 and 285 GHz was used to investigate the reconstitution reaction in the double-mutant Y177F/I263C of mouse protein R2. The aim was to produce a protein-linked radical derived from the Cys residue in the mutant protein to investigate its formation and characteristics. The mutation Y177F hinders normal radical formation at Y177, and the I263C mutation places a Cys residue at the same distance from the iron center as Y177 in the native protein. In the reconstitution reaction, we observed small amounts of a transient radical with a probable assignment to a peroxy radical, followed by a stable sulfinyl radical, most likely located on C263. The unusual radical stability may be explained by the hydrophobic surroundings of C263, which resemble the hydrophobic pocket surrounding Y177 in native protein R2. The observation of a sulfinyl radical in RNR strengthens the relationship between RNR and another free radical enzyme, pyruvate formate-lyase, where a similar relatively stable sulfinyl radical has been observed in a mutant. Sulfinyl radicals may possibly be considered as stabilized forms of very short-lived thiyl radicals, proposed to be important intermediates in the radical chemistry of RNR.

  8. Standard Electrode Potentials Involving Radicals in Aqueous Solution: Inorganic Radicals

    SciTech Connect

    Armstrong, David A.; Huie, Robert E.; Koppenol, Willem H.; Lymar, Sergei V.; Merenyi, Gabor; Neta, Pedatsur; Ruscic, Branko; Stanbury, David M.; Steenken, Steen; Wardman, Peter

    2015-12-01

    Recommendations are made for standard potentials involving select inorganic radicals in aqueous solution at 25 °C. These recommendations are based on a critical and thorough literature review and also by performing derivations from various literature reports. The recommended data are summarized in tables of standard potentials, Gibbs energies of formation, radical pKa’s, and hemicolligation equilibrium constants. In all cases, current best estimates of the uncertainties are provided. An extensive set of Data Sheets is appended that provide original literature references, summarize the experimental results, and describe the decisions and procedures leading to each of the recommendations

  9. Developing a general interaction potential for hydrophobic and hydrophilic interactions.

    PubMed

    Donaldson, Stephen H; Røyne, Anja; Kristiansen, Kai; Rapp, Michael V; Das, Saurabh; Gebbie, Matthew A; Lee, Dong Woog; Stock, Philipp; Valtiner, Markus; Israelachvili, Jacob

    2015-02-24

    We review direct force measurements on a broad class of hydrophobic and hydrophilic surfaces. These measurements have enabled the development of a general interaction potential per unit area, W(D) = -2γ(i)Hy exp(-D/D(H)) in terms of a nondimensional Hydra parameter, Hy, that applies to both hydrophobic and hydrophilic interactions between extended surfaces. This potential allows one to quantitatively account for additional attractions and repulsions not included in the well-known combination of electrostatic double layer and van der Waals theories, the so-called Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The interaction energy is exponentially decaying with decay length D(H) ≈ 0.3-2 nm for both hydrophobic and hydrophilic interactions, with the exact value of D(H) depending on the precise system and conditions. The pre-exponential factor depends on the interfacial tension, γ(i), of the interacting surfaces and Hy. For Hy > 0, the interaction potential describes interactions between partially hydrophobic surfaces, with the maximum hydrophobic interaction (i.e., two fully hydrophobic surfaces) corresponding to Hy = 1. Hydrophobic interactions between hydrophobic monolayer surfaces measured with the surface forces apparatus (SFA) are shown to be well described by the proposed interaction potential. The potential becomes repulsive for Hy < 0, corresponding to partially hydrophilic (hydrated) interfaces. Hydrated surfaces such as mica, silica, and lipid bilayers are discussed and reviewed in the context of the values of Hy appropriate for each system.

  10. Evidence for hydrophobic catalysis of DNA strand exchange.

    PubMed

    Feng, B; Westerlund, F; Nordén, B

    2015-04-30

    The catalytic role of hydrophobic co-solutes in DNA strand exchange is demonstrated by FRET kinetics. Two mechanisms that contribute to this are base stacking destabilisation and nucleation-promoted DNA strand invasion. We propose that hydrophobic catalysis is involved in the strand-exchange activity of recombination enzymes.

  11. Hydroglyphics: Demonstration of Selective Wetting on Hydrophilic and Hydrophobic Surfaces

    ERIC Educational Resources Information Center

    Kim, Philseok; Alvarenga, Jack; Aizenberg, Joanna; Sleeper, Raymond S.

    2013-01-01

    A visual demonstration of the difference between hydrophilic and hydrophobic surfaces has been developed. It involves placing a shadow mask on an optically clear hydrophobic plastic dish, corona treating the surface with a modified Tesla coil, removing the shadow mask, and visualizing the otherwise invisible message or pattern by applying water,…

  12. Electronic properties and free radical production by nitrofuran compounds.

    PubMed

    Paulino-Blumenfeld, M; Hansz, M; Hikichi, N; Stoppani, A O

    1992-01-01

    Substitution of nifurtimox tetrahydrothiazine moiety by triazol-4-yl, benzimidazol-l-yl, pyrazol-l-yl or related aromatic nitrogen heterocycles determines changes in the quantum chemistry descriptors of the molecule, namely, (a) greater negative LUMO energy; (b) lesser electron density on specific atoms, especially on the nitro group atoms, and (c) modification of individual net atomic charges at relevant atoms. These variations correlate with the greater capability of nifurtimox analogues for redox-cycling and oxygen radical production, after one-electron reduction by ascorbate or reduced flavoenzymes. Variation of the nitrofurans electronic structure can also explain the greater activity of nifurtimox analogues as inhibitors of glutathione reductase and Trypanosoma cruzi growth, although other factors, such as molecular hydrophobicity and connectivity may contribute to the latter inhibition.

  13. Plasma-induced polymerization for enhancing paper hydrophobicity.

    PubMed

    Song, Zhaoping; Tang, Jiebin; Li, Junrong; Xiao, Huining

    2013-01-30

    Hydrophobic modification of cellulose fibers was conducted via plasma-induced polymerization in an attempt to graft the hydrophobic polymer chains on paper surface, this increasing the hydrophobicity of paper. Two hydrophobic monomers, butyl acrylate (BA) and 2-ethylhexyl acrylate (2-EHA), were grafted on cellulose fibers, induced by atmospheric cold plasma. Various influencing factors associated with the plasma-induced grafting were investigated. Contact-angle measurement, Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) were used to ascertain the occurrence of the grafting and characterized the changes of the cellulose fiber after modification. The results showed that the hydrophobicity of the modified paper sheet was improved significantly after the plasma-induced grafting. The water contact angle on the paper surface reached up to 130°. The morphological differences between modified and unmodified samples were also revealed by SEM observation. The resulting paper is promising as a green-based packaging material.

  14. Adsorption of crude oil on anhydrous and hydrophobized vermiculite.

    PubMed

    da Silva, Umberto G; de F Melo, Marcus A; da Silva, Adaílton F; de Farias, Robson F

    2003-04-15

    This publication reports the adsorption of crude oil on vermiculite samples, expanded and hydrophobized with carnauba (Copernícia Cerífera) wax. The adsorption studies were performed by using columns filled with the vermiculite matrices and by dispersion of the vermiculite samples in an oil-water (50 ppm of oil) emulsion. The hydrate vermiculite exhibits a very low adsorption capacity against crude oil. On the other hand, anhydrous (expanded) and hydrophobized matrices show a high adsorption capacity. The 10% hydrophobized matrix show a 50% increased adsorption capacity, in comparison with the expanded one. For adsorption performed in the water-oil emulsion, saturation of the solid hydrophobized matrix is achieved after 60 min. The hydrophobized samples exhibit adsorption factors in the 0.7-1.0 range.

  15. Radical-Mediated Enzymatic Polymerizations

    PubMed Central

    Zavada, Scott R.; Battsengel, Tsatsral; Scott, Timothy F.

    2016-01-01

    Polymerization reactions are commonly effected by exposing monomer formulations to some initiation stimulus such as elevated temperature, light, or a chemical reactant. Increasingly, these polymerization reactions are mediated by enzymes―catalytic proteins―owing to their reaction efficiency under mild conditions as well as their environmental friendliness. The utilization of enzymes, particularly oxidases and peroxidases, for generating radicals via reduction-oxidation mechanisms is especially common for initiating radical-mediated polymerization reactions, including vinyl chain-growth polymerization, atom transfer radical polymerization, thiol–ene step-growth polymerization, and polymerization via oxidative coupling. While enzyme-mediated polymerization is useful for the production of materials intended for subsequent use, it is especially well-suited for in situ polymerizations, where the polymer is formed in the place where it will be utilized. Such polymerizations are especially useful for biomedical adhesives and for sensing applications. PMID:26848652

  16. Epistemological barriers to radical behaviorism.

    PubMed

    O'Donohue, W T; Callaghan, G M; Ruckstuhl, L E

    1998-01-01

    The historian and philosopher of science Gaston Bachelard proposed the concept of epistemological barriers to describe the intellectual challenges encountered by scientists in their work. In order to embrace novel ways of approaching a problem in science, scientists must overcome barriers or obstacles posed by their prior views. For example, Einsteinian physics presents scientists with claims that space is curved and that time and space are on the same continuum. We utilize Bachelard's concept of epistemological barriers to describe the differences between the intellectual journeys students pursuing advanced studies face when attempting to accept cognitive psychology or radical behaviorism. We contend that the folk psychological beliefs that students typically hold when entering these studies pose less challenge to cognitive psychology than to radical behaviorism. We also suggest that these barriers may also partly be involved in the problematic exegesis that has plagued radical behaviorism. In close, we offer some suggestions for dealing with these epistemological barriers.

  17. Epistemological barriers to radical behaviorism

    PubMed Central

    O'Donohue, William T.; Callaghan, Glenn M.; Ruckstuhl, L. E.

    1998-01-01

    The historian and philosopher of science Gaston Bachelard proposed the concept of epistemological barriers to describe the intellectual challenges encountered by scientists in their work. In order to embrace novel ways of approaching a problem in science, scientists must overcome barriers or obstacles posed by their prior views. For example, Einsteinian physics presents scientists with claims that space is curved and that time and space are on the same continuum. We utilize Bachelard's concept of epistemological barriers to describe the differences between the intellectual journeys students pursuing advanced studies face when attempting to accept cognitive psychology or radical behaviorism. We contend that the folk psychological beliefs that students typically hold when entering these studies pose less challenge to cognitive psychology than to radical behaviorism. We also suggest that these barriers may also partly be involved in the problematic exegesis that has plagued radical behaviorism. In close, we offer some suggestions for dealing with these epistemological barriers. PMID:22478314

  18. Hydrophobic polymers modification of mesoporous silica with large pore size for drug release

    NASA Astrophysics Data System (ADS)

    Zhu, Shenmin; Zhang, Di; Yang, Na

    2009-04-01

    Mesostructure cellular foam (MCF) materials were modified with hydrophobic polyisoprene (PI) through free radical polymerization in the pores network, and the resulting materials (MCF-PI) were investigated as matrices for drug storage. The successful synthesis of PI inside MCF was characterized by Fourier transform infrared (FT-IR), hydrogen nuclear magnetic resonance (1H NMR), X-ray diffraction patterns (XRD) and nitrogen adsorption/desorption measurements. It was interesting to find the resultant system held a relatively large pore size (19.5 nm) and pore volume (1.02 cm3 g-1), which would benefit for drug storage. Ibuprofen (IBU) and vancomycin were selected as model drugs and loaded onto unmodified MCF and modified MCF (MCF-PI). The adsorption capacities of these model drugs on MCF-PI were observed increase as compared to that of on pure MCF, due to the trap effects induced by polyisoprene chains inside the pores. The delivery system of MCF-PI was found to be more favorable for the adsorption of IBU (31 wt%, IBU/silica), possibly attributing to the hydrophobic interaction between IBU and PI formed on the internal surface of MCF matrix. The release of drug through the porous network was investigated by measuring uptake and release of IBU.

  19. Side Chain Hydrophobicity Modulates Therapeutic Activity and Membrane Selectivity of Antimicrobial Peptide Mastoparan-X

    PubMed Central

    Gjetting, Torben; Andresen, Thomas L.

    2014-01-01

    The discovery of new anti-infective compounds is stagnating and multi-resistant bacteria continue to emerge, threatening to end the “antibiotic era”. Antimicrobial peptides (AMPs) and lipo-peptides such as daptomycin offer themselves as a new potential class of antibiotics; however, further optimization is needed if AMPs are to find broad use as antibiotics. In the present work, eight analogues of mastoparan-X (MPX) were investigated, having side chain modifications in position 1, 8 and 14 to modulate peptide hydrophobicity. The self-association properties of the peptides were characterized, and the peptide-membrane interactions in model membranes were compared with the bactericidal and haemolytic properties. Alanine substitution at position 1 and 14 resulted in higher target selectivity (red blood cells versus bacteria), but also decreased bactericidal potency. For these analogues, the gain in target selectivity correlated to biophysical parameters showing an increased effective charge and reduction in the partitioning coefficient for membrane insertion. Introduction of an unnatural amino acid, with an octyl side chain by amino acid substitution, at positions 1, 8 and 14 resulted in increased bactericidal potency at the expense of radically reduced membrane target selectivity. Overall, optimized membrane selectivity or bactericidal potency was achieved by changes in side chain hydrophobicity of MPX. However, enhanced potency was achieved at the expense of selectivity and vice versa in all cases. PMID:24621994

  20. PEGMA/MMA copolymer graftings: generation, protein resistance, and a hydrophobic domain.

    PubMed

    Stadler, Volker; Kirmse, Robert; Beyer, Mario; Breitling, Frank; Ludwig, Thomas; Bischoff, F Ralf

    2008-08-05

    We synthesized various graft copolymer films of poly(ethylene glycol) methacrylate (PEGMA) and methyl methacrylate (MMA) on silicon to examine the dependency of protein-surface interactions on grafting composition. We optimized atom transfer radical polymerizations to achieve film thicknesses from 25 to 100 nm depending on the monomer mole fractions, and analyzed the resulting surfaces by X-ray photoelectron spectroscopy (XPS), ellipsometry, contact angle measurements, and atomic force microscopy (AFM). As determined by XPS, the stoichiometric ratios of copolymer graftings correlated with the concentrations of provided monomer solutions. However, we found an unexpected and pronounced hydrophobic domain on copolymer films with a molar amount of 10-40% PEGMA, as indicated by advancing contact angles of up to 90 degrees . Nevertheless, a breakdown of the protein-repelling character was only observed for a fraction of 15% PEGMA and lower, far in the hydrophobic domain. Investigation of the structural basis of this exceptional wettability by high-resolution AFM demonstrated the independence of this property from morphological features.

  1. β-Cyclodextrin polymer brushes decorated magnetic colloidal nanocrystal clusters for the release of hydrophobic drugs

    NASA Astrophysics Data System (ADS)

    Lv, Shaonan; Zhao, Meiqin; Cheng, Changjing; Zhao, Zhigang

    2014-05-01

    β-Cyclodextrin (β-CD) polymer brushes decorated magnetic Fe3O4 colloidal nanocrystal clusters (Fe3O4@PG-CD) were fabricated by a combination of surface-initiated atom transfer radical polymerization on the surface of Br-anchored Fe3O4 colloidal nanocrystal clusters (Fe3O4-Br) and ring-opening reaction of epoxy groups. The resulted Fe3O4@PG-CD hybrid nanoparticles were characterized by several methods including Fourier transform infrared, transmission electron microscope, dynamic light scattering instrument, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer. Moreover, the potential of as-synthesized Fe3O4@PG-CD as a carrier of hydrophobic anticancer drug 5-fluorouracil (5-FU) was also investigated. The results showed that the prepared Fe3O4@PG-CD have core/shell structure and high saturated magnetism. 5-FU could be loaded into the Fe3O4@PG-CD via the formation of β-CD/5-FU inclusion complex. Furthermore, the Fe3O4@PG-CD displayed a high loading capacity and pH-dependent release behavior for 5-FU. The release behavior demonstrated a simple Fickian diffusion in the acidic environment (pH 2.0 and 4.0) but neither non-Fickian nor anomalous when neutral. The results reveal that this nanosystem seems to be a very promising vehicle for the hydrophobic drugs for pH-dependent controlled release.

  2. Poly(N-vinylpyrrolidone)-block-poly(vinyl acetate) as a drug delivery vehicle for hydrophobic drugs.

    PubMed

    Bailly, Nathalie; Thomas, Mark; Klumperman, Bert

    2012-12-10

    Poly((N-vinylpyrrolidone)-block-poly(vinyl acetate)) (PVP-b-PVAc) block copolymers of varying molecular weight and hydrophobic block lengths were synthesized via controlled radical polymerization and investigated as carriers for the solubilization of highly hydrophobic riminophenazine compounds. These compounds have recently been shown to exhibit a strong activity against a variety of cancer types. PVP-b-PVAc self-assembles into polymer vesicles in aqueous media, and the dialysis method was used to load the water-insoluble drug (clofazimine) into these polymer vesicles. The polymer vesicles were characterized by 1H NMR spectroscopy to confirm vesicle formation and the incorporation of the anticancer drugs into the polymer vesicles. Dynamic light scattering was used to determine the particle size and particle size distribution of the drug-loaded vesicles as well as the stability of the vesicles under physiological conditions. The size of the polymer vesicles did not increase upon loading with clofazimine, and the particle size of 180-200 nm and the narrow particle size distribution were maintained. The morphology of the vesicles was examined by transmission electron microscopy. The polymer vesicles had a relatively high drug loading capacity of 20 wt %. In vitro cytotoxicity studies of PVP-b-PVAc and drug-loaded PVP-b-PVAc were performed against MDA-MB-231 multidrug-resistant breast epithelial cancer cells and MCF12A nontumorigenic breast epithelial cells. In vitro experiments demonstrated that the PVP-b-PVAc drug carrier showed no cytotoxicity, which confirms the biocompatibility of the PVP-b-PVAc drug carrier. The results indicate that the present PVP-b-PVAc block copolymer could be a potential candidate as a drug carrier for hydrophobic drugs.

  3. VUV Photoionisation of hydrocarbon radicals

    NASA Astrophysics Data System (ADS)

    Alcaraz, C.; Noller, Bastian; Hemberger, Patrick; Fischer, Ingo; Gans, Bérenger; Boyé-Peronne, Séverine; Douin, Stéphane; Gauyacq, Dolorès; Soldi-Lose, Héloïse; Garcia, Gustavo

    2008-09-01

    Hydrocarbon radicals CxHy are constituents of various planetary atmospheres, in particular Titan, as a result of the methane photochemistry induced by the solar radiation. They contribute to the neutral chemistry, but are also important for the ionosphere through their photoionisation leading to their cations CxHy +. These cations are also produced by ion-molecule reactions starting from the reaction of the primary ions CH4 + and CH3 + which are created in the non-dissociative and dissociative photoionisation of CH4. This work aims at caracterizing the VUV photoionisation of small hydrocarbon radicals as a function of photon energy. The objective is to provide laboratory data for modelers on the spectroscopy, the thermochemistry, and the reactivity of the radicals and their cations. The hydrocarbon radicals are much less caracterized than stable molecules since they have to be produced in situ in the laboratory experiment. We have adapted at Orsay [1-3] a pyrolysis source (Figure 1) well suited to produce cold beams of hydrocarbon radicals to our experimental setups. Available now at Orsay, we have two new sources of VUV radiation, complementary in terms of tunability and resolution, that can be used for these studies. The first one is the DESIRS beamline [4] at the new french synchrotron, SOLEIL. The second one is the VUV laser developped at the Centre Laser de l'Université Paris-Sud (CLUPS) [5]. At SOLEIL, a photoelectron-photoion coincidence spectrometer is used to monitor the photoionisation on a large photon energy range. At the CLUPS, a pulsedfield ionisation (PFI-ZEKE) spectrometer allows studies at higher resolution on selected photon energies. The first results obtained with these new setups will be presented. References [1] Fischer, I., Schussler, T., Deyerl, H.J., Elhanine, M. & Alcaraz, C., Photoionization and dissociative photoionization of the allyl radical, C3H5. Int. J. Mass Spectrom., 261 (2-3), 227-233 (2007) [2] Schüßler, T., Roth, W., Gerber

  4. Donor free radical explosive composition

    DOEpatents

    Walker, Franklin E. [15 Way Points Rd., Danville, CA 94526; Wasley, Richard J. [4290 Colgate Way, Livermore, CA 94550

    1980-04-01

    An improved explosive composition is disclosed and comprises a major portion of an explosive having a detonation velocity between about 1500 and 10,000 meters per second and a minor amount of a donor additive comprising an organic compound or mixture of organic compounds capable of releasing low molecular weight free radicals or ions under mechanical or electrical shock conditions and which is not an explosive, or an inorganic compound or mixture of inorganic compounds capable of releasing low molecular weight free radicals or ions under mechanical or electrical shock conditions and selected from ammonium or alkali metal persulfates.

  5. Laparoscopic radical and partial cystectomy

    PubMed Central

    Challacombe, Ben J.; Rose, Kristen; Dasgupta, Prokar

    2005-01-01

    Radical cystectomy remains the standard treatment for muscle invasive organ confined bladder carcinoma. Laparoscopic radical cystoprostatectomy (LRC) is an advanced laparoscopic procedure that places significant demands on the patient and the surgeon alike. It is a prolonged procedure which includes several technical steps and requires highly developed laparoscopic skills including intra-corporeal suturing. Here we review the development of the technique, the indications, complications and outcomes. We also examine the potential benefits of robotic-assisted LRC and explore the indications and technique of laparoscopic partial cystectomy. PMID:21206662

  6. Microstructure of Hydrophobically Modified Alkyl Acrylamide Hydrogels

    NASA Astrophysics Data System (ADS)

    Tian, Jun; Seery, Thomas A. P.; Ho, Derek L.; Weiss, R. A.

    2004-03-01

    Hydrophobically modified water-soluble acrylamide polymers have a variety of applications, including viscosity thickeners, microencapsulation, biosensors and controlled drug delivery systems. The microstructure of copolymer hydrogels of N,N-dimethylacrylamide (DMA) or N-isopropylacrylamide(NIPA) modified with 2-(N-ethylfluorooctanesulfonamido)ethyl acrylate, FOSA, was studied by small angle x-ray (SAXS) and neutron scattering (SANS). Swelling and DSC measurements showed that FOSA/NIPA gels exhibited a volume phase transition (VPT), but that FOSA/DMA gels did not. A modified interacting core-shell model was used to explain the SAXS and SANS data for both gels. The crosslink junctions of the gel consisted of nanophase-separated FOSA domains as the core surrounded by a water-poor layer of the alkyl acrylamide. These nanodomains were dispersed in a matrix of water-swollen alkyl acrylamide that had large scale heterogeneities. The average spherical core radius ranged from 1 to 3 nm and the average shell thickness ranged from 1 to 1.5 nm; the aggregation number ranged from 10 to 200.

  7. Size selective hydrophobic adsorbent for organic molecules

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K. (Inventor); Hickey, Gregory S. (Inventor)

    1997-01-01

    The present invention relates to an adsorbent formed by the pyrolysis of a hydrophobic silica with a pore size greater than 5 .ANG., such as SILICALITE.TM., with a molecular sieving polymer precursor such as polyfurfuryl alcohol, polyacrylonitrile, polyvinylidene chloride, phenol-formaldehyde resin, polyvinylidene difluoride and mixtures thereof. Polyfurfuryl alcohol is the most preferred. The adsorbent produced by the pyrolysis has a silicon to carbon mole ratio of between about 10:1 and 1:3, and preferably about 2:1 to 1:2, most preferably 1:1. The pyrolysis is performed as a ramped temperature program between about 100.degree. and 800.degree. C., and preferably between about 100.degree. and 600.degree. C. The present invention also relates to a method for selectively adsorbing organic molecules having a molecular size (mean molecular diameter) of between about 3 and 6 .ANG. comprising contacting a vapor containing the small organic molecules to be adsorbed with the adsorbent composition of the present invention.

  8. Hydrophobic peptide auxotrophy in Salmonella typhimurium.

    PubMed Central

    Brãnes, L V; Somers, J M; Kay, W W

    1981-01-01

    The growth of a pleiotropic membrane mutant of Salmonella typhimurium with modified lipopolysaccharide composition was found to be strictly dependent on the peptone component of complex media. Nutritional Shiftdown into minimal media allowed growth for three to four generations. Of 20 commercial peptones, only enzymatic digests supported growth to varying degrees. Neither trace cations, amino acids, vitamins, carbohydrates, lipids, glutathione, polyamines, carbodimides, nor synthetic peptides stimulated growth; however, cells still metabolized carbohydrates, and amino acid transport systems were shown to be functional. A tryptic digest of casein was fractionated into four electrophoretically different peptide fractions of 1,000 to 1,200 molecular weight which supported growth to varying degrees. The best of these was further fractionated to two highly hydrophopic peptides. N-terminal modifications eliminated biological activity. Fluorescein-conjugated goat antibody to rabbit immunoglobulin G was used as a probe to detect antipeptide antibody-peptide complexes on membrane preparations. Cells grown on peptone distributed the peptide into both inner and outer membranes. The peptide could be removed with chaotropic agents, and cells had to be pregrown in peptone-containing media to bind the hydrophobic peptide. The gene (hyp) responsible for peptide auxotrophy was mapped at 44 to 45 units by conjugation. Images PMID:7024254

  9. Intermolecular Vibrations of Hydrophobic Amino Acids

    NASA Astrophysics Data System (ADS)

    Williams, Michael Roy Casselman

    Hydrophobic amino acids interact with their chemical environment through a combination of electrostatic, hydrogen bonding, dipole, induced dipole, and dispersion forces. These interactions all have their own characteristic energy scale and distance dependence. The low-frequency (0.1-5 THz, 5-150 cm-1) vibrational modes of amino acids in the solid state are a direct indicator of the interactions between the molecules, which include interactions between an amino acid functional group and its surroundings. This information is central to understanding the dynamics and morphology of proteins. The alpha-carbon is a chiral center for all of the hydrophobic amino acids, meaning that they exist in two forms, traditionally referred to as L- and D-enantiomers. This nomenclature indicates which direction the molecule rotates plane-polarized visible light (levorotory and dextrorotory). Chiral a-amino acids in proteins are exclusively the L-variety In the solid state, the crystal lattice of the pure L-enantiomer is the mirror image of the D-enantiomer crystal lattice. These solids are energetically identical. Enantiomers also have identical spectroscopic properties except when the measurement is polarization sensitive. A mixture of equal amounts D- and L-amino acid enantiomers can crystallize into a racemic (DL-) structure that is different from that of the pure enantiomers. Whether a solution of both enantiomers will crystallize into a racemic form or spontaneously resolve into a mixture of separate D- and L-crystals largely depends on the interactions between molecules available in the various possible configurations. This is an active area of research. Low-frequency vibrations with intermolecular character are very sensitive to changes in lattice geometry, and consequently the vibrational spectra of racemic crystals are usually quite distinct from the spectra of the crystals of the corresponding pure enantiomers in the far-infrared (far-IR). THz time-domain spectroscopy (THz

  10. Sequestration of hydrophobic organic contaminants by geosorbents

    USGS Publications Warehouse

    Luthy, Richard G.; Aiken, George R.; Brusseau, Mark L.; Cunningham, Scott D.; Gschwend, Philip M.; Pignatello, Joseph J.; Reinhard, Martin; Traina, Samuel J.; Weber, Walter J.; Westall, John C.

    1997-01-01

    The chemical interactions of hydrophobic organic contaminants (HOCs) with soils and sediments (geosorbents) may result in strong binding and slow subsequent release rates that significantly affect remediation rates and endpoints. The underlying physical and chemical phenomena potentially responsible for this apparent sequestration of HOCs by geosorbents are not well understood. This challenges our concepts for assessing exposure and toxicity and for setting environmental quality criteria. Currently there are no direct observational data revealing the molecular-scale locations in which nonpolar organic compounds accumulate when associated with natural soils or sediments. Hence macroscopic observations are used to make inferences about sorption mechanisms and the chemical factors affecting the sequestration of HOCs by geosorbents. Recent observations suggest that HOC interactions with geosorbents comprise different inorganic and organic surfaces and matrices, and distinctions may be drawn along these lines, particularly with regard to the roles of inorganic micropores, natural sorbent organic matter components, combustion residue particulate carbon, and spilled organic liquids. Certain manipulations of sorbates or sorbent media may help reveal sorption mechanisms, but mixed sorption phenomena complicate the interpretation of macroscopic data regarding diffusion of HOCs into and out of different matrices and the hysteretic sorption and aging effects commonly observed for geosorbents. Analytical characterizations at the microscale, and mechanistic models derived therefrom, are needed to advance scientific knowledge of HOC sequestration, release, and environmental risk.

  11. Role of surfactant derived intermediates in the efficacy and mechanism for radiation chemical degradation of a hydrophobic azo dye, 1-phenylazo-2-naphthol.

    PubMed

    Das, Laboni; Chatterjee, Suchandra; Naik, Devidas B; Adhikari, Soumyakanti

    2015-11-15

    A combined methodology involving gamma and pulse radiolysis, product analysis and toxicity studies has been adopted to comprehend the degradation process of a model hydrophobic azo dye, 1-phenylazo-2-naphthol, emphasizing the role of the surfactant, which is an integral part of textile waste. Two new and important findings are underlined in this article. The first is the direct attestation of the hydrazyl radical-parent adduct, formed in the reaction of the dye with e(-)aq followed by protonation and subsequent addition to the unreacted dye molecule. This has been confirmed from concentration dependent studies. Secondly, we have clearly shown that in the reaction of hydroxyl radical with the dye in Triton X-100 media, the initially produced TX radicals cause reductive degradation of the dye. Identification and detailed analysis of HPLC and GCMS data reveals that similar products are formed in both the reactions of e(-)aq and OH radicals. Moreover, the cytotoxicity of 10(-4)moldm(-3) dye was found to be reduced significantly after irradiation. Thus, the present study not only depicts new pathways for the degradation of hydrophobic azo dye, but also demonstrates the role of a surfactant in the entire process.

  12. Thermodynamics of hydrophobic interaction between silica surfaces coated with octadecyltrichlorosilane.

    PubMed

    Li, Zuoli; Yoon, Roe-Hoan

    2013-02-15

    Surface force measurements conducted with thiolated gold surfaces showed previously that hydrophobic interaction entails a decrease in excess film entropy, suggesting that hydrophobic force originates from changes in the structure of the medium (water) confined between hydrophobic surfaces. As a follow-up work, surface force measurements have been conducted in the present work using an atomic force microscope (AFM) with silica surfaces coated with octadecyltrichlorosilane (OTS) at temperatures in the range of 10-40°C. A thermodynamic analysis of the results show that both the excess film entropy (ΔS(f)) and excess film enthalpy (ΔH(f)) decrease with decreasing thickness of the water films between the hydrophobic surfaces. It has been found also that |ΔH(f)|>|TΔS(f)|, which represents a necessary condition for the excess free energy change (ΔG(f)) to be negative and hence the hydrophobic interaction be attractive. Thus, the results obtained with both the thiolated and silylated surfaces show that hydrophobic forces originate from the structural changes in the medium. It is believed that the water molecules in the thin liquid films (TLFs) of water form clusters as a means to reduce the free energy when they cannot form H-bonds to neighboring hydrophobic surfaces.

  13. Students' Ideas and Radical Constructivism

    ERIC Educational Resources Information Center

    Sánchez Gómez, Pedro J.

    2016-01-01

    In this article, I study, from the point of view of the analytic philosophy of mind, the compatibility of students' ideas studies (SIS) with radical constructivism (RC). I demonstrate that RC is based on a psychology of "narrow mental states"; that is, the idea that the mental content of an individual can be fully characterised without…

  14. The Other Women: Radicalizing Feminism.

    ERIC Educational Resources Information Center

    Puigvert, Lidia; Darder, Antonia; Merrill, Barbara; de los Reyes, Eileen; Stromquist, Nelly

    A recent international symposium on radicalizing feminism explored ways of developing a dialogic feminism that emphasizes working in different settings under the common goal of including women who have been invisible in the dominant feminist literature by furthering theories and practices based on the principles of dialogic feminism. The seminar…

  15. Mitigating Radicalism in Northern Nigeria

    DTIC Science & Technology

    2013-08-01

    radicalization in northern Nigeria. u Active engagement of youth and communities in peacebuilding programs that facilitate interactions among individuals...leaders, sustained development investments in marginalized communities , promotion of values of inclusivity to mitigate the spread of extremist ideology...claiming to have repelled Boko Haram, the militants return, regroup, and seek revenge. As a result, social and economic activities in the northern

  16. Spatially selective modification of PLLA surface: From hydrophobic to hydrophilic or to repellent

    NASA Astrophysics Data System (ADS)

    Bastekova, Kristina; Guselnikova, Olga; Postnikov, Pavel; Elashnikov, Roman; Kunes, Martin; Kolska, Zdenka; Švorčík, Vaclav; Lyutakov, Oleksiy

    2017-03-01

    A universal approach to controlled surface modification of polylactic acid (PLLA) films using diazonium chemistry was proposed. The multistep procedure includes surface activation of PLLA by argon plasma treatment and chemical activation of arenediazonium tosylates by NaBH4. The surface of PLLA film was grafted with different functional organic groups (OFGs), changing the PLLA surface properties (wettability, morphology, zeta potential, chemical composition, and mechanical response). Three approaches of OFG grafting were examined: (i) plasma treatment following by PLLA immersion into diazonium salt aqueous solution; (ii) grafting of PLLA surface through the reaction with chemically created aryl radicals; (iii) mutual combination of both methods The best results were achieved in the last case, where the previous plasma treatment was combined with further reaction of PLLA surface with generated aryl radicals. Using this method PLLA surface was successfully grafted with amino, carboxyl, aliphatic and fluorinated OFGs. Further investigation of surface properties from potential biological and medical points of view was performed using zeta potential, biodegradation and biofouling tests. It was shown that proposed technique allows preparation of biorepellent or bioabsorptive surfaces, tuning of PLLA biodegradation rate and nanomechanical properties, as well as the introduction of inverse properties (such as hydrophilic and hydrophobic) on both sides of PLLA films.

  17. Solubility Enhanced Oxidation of Hydrophobic Organic Contaminants

    NASA Astrophysics Data System (ADS)

    Boving, T. B.; Eberle, D. E.; Ball, R.

    2012-12-01

    In-situ chemical oxidation (ISCO) is a remediation technique considered to be effective at overcoming some of the limitations of conventional subsurface treatment processes for volatile and semi-volatile organic contaminants (VOC, SVOC). ISCO reactions occur predominately in the aqueous phase and as a result, contaminant availability is a major limiting factor, i.e. contaminants with higher aqueous solubility's are typically more accessible for oxidation than more hydrophobic, sorbed compounds. The purpose of this study was to determine the feasibility of a new integrated desorption-oxidation process for the remediation of contaminated waters and sediments. Specifically, this study examined the potential of using hydroxypropyl-β-cyclodextrin (HPCD), a modified cyclic sugar, and a blend of oxidants commercially known as OxyZone® (U.S. patent No. 7,667,087) for the remediation of polycyclic aromatic hydrocarbons (PAH). Laboratory scale batch experiments confirmed prior studies that HPCD increases the aqueous concentration of these contaminants, making a greater mass of contaminant available for subsequent oxidation. When exposed to the same amount of oxidant, the mass of PAH destroyed increased linearly with increasing HPCD concentration. Relative to PAH saturated solutions without HPCD, 11 times more PAH mass was destroyed when a PAH saturated 15 g/L HPCD solution was treated with the same mass of oxidant. Destruction of the aqueous phase contaminants followed first order exponential decay kinetics in both deionized water and HPCD solutions. However, the destruction of complexed PAH was slower than for uncomplexed PAH. The cause of this is likely due to the preferential destruction of the HPCD molecule by the oxidant, followed by the subsequent oxidation of the PAH. The destruction of the cyclodextrin was minimized by modifying the oxidant formulation. Overall, these findings establish the potential of utilizing HPCD and OxyZone® as an integrated desorption

  18. Electrokinetic instability near charge-selective hydrophobic surfaces.

    PubMed

    Shelistov, V S; Demekhin, E A; Ganchenko, G S

    2014-07-01

    The influence of the texture of a hydrophobic surface on the electro-osmotic slip of the second kind and the electrokinetic instability near charge selective surfaces (permselective membranes, electrodes, or systems of microchannels and nanochannels) is investigated theoretically using a simple model based on the Rubinstein-Zaltzman approach. A simple formula is derived to evaluate the decrease in the instability threshold due to hydrophobicity. The study is complemented by numerical investigations both of linear and nonlinear instabilities near a hydrophobic membrane surface. Theory predicts a significant enhancement of the ion flux to the surface and shows a good qualitative agreement with the available experimental data.

  19. Electrokinetic instability near charge-selective hydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Shelistov, V. S.; Demekhin, E. A.; Ganchenko, G. S.

    2014-07-01

    The influence of the texture of a hydrophobic surface on the electro-osmotic slip of the second kind and the electrokinetic instability near charge selective surfaces (permselective membranes, electrodes, or systems of microchannels and nanochannels) is investigated theoretically using a simple model based on the Rubinstein-Zaltzman approach. A simple formula is derived to evaluate the decrease in the instability threshold due to hydrophobicity. The study is complemented by numerical investigations both of linear and nonlinear instabilities near a hydrophobic membrane surface. Theory predicts a significant enhancement of the ion flux to the surface and shows a good qualitative agreement with the available experimental data.

  20. Strong hydrophobizer: laterally chemisorbed low-molecular-weight polydimethylsiloxane.

    PubMed

    Chae, Soo Sang; Oh, Jin Young; Park, Jee Ho; Choi, Won Jin; Han, Jeong Hwan; Lee, Jeong-O; Baik, Hong Koo; Lee, Tae Il

    2015-04-07

    We introduce a siloxane chain-based hydrophobizer that exhibits superior thermal and chemical stability compared to the conventional hydrophobizing silane agent under conditions of over 300 °C and pH 2-13. To demonstrate the capability of the siloxane chain-based hydrophobizer to serve as a highly robust chemical surface modifier, we present two applications: the formation of fine metal nanoparticles with a narrow size distribution by thermal aggregation of a metal thin film and the selective deposition of a ruthenium thin film by atomic layer deposition.

  1. Inhibition of hydroxyl radical reaction with aromatics by dissolved natural organic matter

    SciTech Connect

    Lindsey, M.E.; Tarr, M.A.

    2000-02-01

    Remediation of hydrophobic pollutants is complicated by sorption of these compounds to hydrophobic sites of dissolved natural organic matter (NOM), suspended particulates, soil, and sediment. This sorption causes the pollutants to be less easily degraded by remediation techniques. Reaction of aromatic compounds with hydroxyl radical is inhibited by dissolved natural organic matter (NOM). The degree of inhibition is significantly greater than that expected based on a simple model in which aromatic compound molecules bound to NOM are considered to be unreactive. In this study, hydroxyl radical was produced at steady-state concentrations using Fenton chemistry (H{sub 2}O{sub 2} + Fe{sup 2+} {yields} Fe{sup 3+} + HO{sup {minus}} + HO{sm_bullet}). Suwannee River fulvic acid and humic acid were used as NOM. The most likely mechanism for the observed inhibition is that hydroxyl radical formation occurs in microenvironmental sites remote from the aromatic compounds. In addition to changes in kinetics, pyrene hydroxyl radical reaction also exhibited a mechanistic change in the presence of fulvic acid. The mechanism changed from a reaction that was apparently first-order in pyrene to one that was apparently second-order in pyrene, indicating that pyrene self-reaction may have become the dominant mechanism in the presence of fulvic acid. Dissolved NOM causes significant changes in the rate and mechanism of hydroxyl radical degradation of aromatic compounds. Consequently, literature rate constants measured in pure water will not be useful for predicting the degradation of pollutants in environmental systems. The kinetic and mechanistic information in this study will be useful for developing improved degradation methods involving Fenton chemistry.

  2. Oxidation of ultrafast radical clock substrate probes by the soluble methane monooxygenase from Methylococcus capsulatus (Bath).

    PubMed

    Valentine, A M; LeTadic-Biadatti, M H; Toy, P H; Newcomb, M; Lippard, S J

    1999-04-16

    Radical clock substrate probes were used to assess the viability of a discrete substrate radical species in the mechanism of hydrocarbon oxidation by the soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath). New substituted cyclopropane probes were used with very fast ring-opening rate constants and other desirable attributes, such as the ability to discriminate between radical and cationic intermediates. Oxidation of these substrates by a reconstituted sMMO system resulted in no rearranged products, allowing an upper limit of 150 fs to be placed on the lifetime of a putative radical species. This limit strongly suggests that there is no such substrate radical intermediate. The two enantiomers of trans-1-methyl-2-phenyl-cyclopropane were prepared, and the regioselectivity of their oxidation to the corresponding cyclopropylmethanol and cyclopropylphenol products was determined. The results are consistent with selective orientation of the two enantiomeric substrates in the hydrophobic cavity at the active site of sMMO, specific models for which were examined by molecular modeling.

  3. Hydrophobic and hydrophilic interactions in aqueous mixtures of alcohols at a hydrophobic surface.

    PubMed

    Ballal, Deepti; Chapman, Walter G

    2013-09-21

    Aqueous solutions of alcohols are interesting because of their anomalous behavior that is believed to be due to the molecular structuring of water and alcohol around each other in solution. The interfacial structuring and properties are significant for application in alcohol purification processes and biomolecular structure. Here we study aqueous mixtures of short alcohols (methanol, ethanol, 1-propanol, and 2-propanol) at a hydrophobic surface using interfacial statistical associating fluid theory which is a perturbation density functional theory. The addition of a small amount of alcohol decreases the interfacial tension of water drastically. This trend in interfacial tension can be explained by the structure of water and alcohol next to the surface. The hydrophobic group of an added alcohol preferentially goes to the surface preserving the structure of water in the bulk. For a given bulk alcohol concentration, water mixed with the different alcohols has different interfacial tensions with propanol having a lower interfacial tension than methanol and ethanol. 2-propanol is not as effective in decreasing the interfacial tension as 1-propanol because it partitions poorly to the surface due to its larger excluded volume. But for a given surface alcohol mole fraction, all the alcohol mixtures give similar values for interfacial tension. For separation of alcohol from water, methods that take advantage of the high surface mole fraction of alcohol have advantages compared to separation using the vapor in equilibrium with a water-alcohol liquid.

  4. Surface hydrophobization by electrostatic deposition of hydrophobically modified poly(acrylates) and their complexes with surfactants

    NASA Astrophysics Data System (ADS)

    Gîfu, Ioana Cătălina; Maxim, Monica Elisabeta; Iovescu, Alina; Simion, Elena Livia; Aricov, Ludmila; Anastasescu, Mihai; Munteanu, Cornel; Anghel, Dan-Florin

    2016-05-01

    The present study demonstrates the hydrophobic effect of poly(electrolyte) multilayer films when they are alkyl-grafted and complexed or not with surfactants. For this purpose, sodium hydrophobically modified poly(acrylates) (PACnNa, n = 10, 18) or their anionic complexes with alkyltrimethylammonium bromides (CxTAB, x = 10, 12, 14, 18), and the cationic poly(diallyldimethyldiammonium chloride) (PDDAMAC) are assembled by layer-by-layer deposition on a glass substrate. Contact angle (CA) measurements reveal that films constructed with PACnNa-CxTAB/PDADMAC are superior water repellants than those of PACnNa/PDADMAC. For example, the highest CA is obtained for the PAC18Na-C18TAB/PDADMAC. Moreover, it has been observed that the CA increases with the alkyl chain length of PACnNa and of surfactant. The film roughness and thickness have the same trend as wettability. Thinner and less coarse films are obtained by NaCl addition, as witnessed by SEM and AFM.

  5. Fluoroalkyl and Alkyl Chains Have Similar Hydrophobicities in Binding to the “Hydrophobic Wall” of Carbonic Anhydrase

    PubMed Central

    Mecinović, Jasmin; Snyder, Phillip W.; Mirica, Katherine A.; Bai, Serena; Mack, Eric T.; Kwant, Richard L.; Moustakas, Demetri T.; Heroux, Annie; Whitesides, George M.

    2011-01-01

    The hydrophobic effect—the free-energetically favorable association of non-polar solutes in water—makes a dominant contribution to binding of many systems of ligands and proteins. The objective of this study was to examine the hydrophobic effect in biomolecular recognition using two chemically different, but structurally similar hydrophobic groups—aliphatic hydrocarbons and aliphatic fluorocarbons—and to determine whether the hydrophobicity of the two groups could be distinguished by thermodynamic and biostructural analysis. This paper uses isothermal titration calorimetry (ITC) to examine the thermodynamics of binding of benzenesulfonamides substituted in the para position with alkyl and fluoroalkyl chains (H2NSO2C6H4-CONHCH2(CX2)nCX3, n = 0–4, X = H, F) to human carbonic anhydrase II (HCA II). Both alkyl and fluoroalkyl substituents contribute favorably to the enthalpy and the entropy of binding; these contributions increase as the length of chain of the hydrophobic substituent increases. Crystallography of the protein-ligand complexes indicates that the benzenesulfonamide groups of all ligands examined bind with similar geometry, that the tail groups associate with the hydrophobic wall of HCA II (which is made up of the side chains of residues Phe131, Val135, Pro202, and Leu204), and that the structure of the protein is indistinguishable for all but one of the complexes (the longest member of the fluoroalkyl series). Analysis of the thermodynamics of binding as a function of structure is compatible with the hypothesis that hydrophobic binding of both alkyl and fluoroalkyl chains to hydrophobic surface of carbonic anhydrase is due primarily to the release of non-optimally hydrogen-bonded water molecules that hydrate the binding cavity (including the hydrophobic wall) of HCA II and to the release of water molecules that surround the hydrophobic chain of the ligands. This study defines the balance of enthalpic and entropic contributions to the hydrophobic

  6. Fluoroalkyl and Alkyl Chains Have Similar Hydrophobicities in Binding to the “Hydrophobic Wall” of Carbonic Anhydrase

    SciTech Connect

    J Mecinovic; P Snyder; K Mirica; S Bai; E Mack; R Kwant; D Moustakas; A Heroux; G Whitesides

    2011-12-31

    The hydrophobic effect, the free-energetically favorable association of nonpolar solutes in water, makes a dominant contribution to binding of many systems of ligands and proteins. The objective of this study was to examine the hydrophobic effect in biomolecular recognition using two chemically different but structurally similar hydrophobic groups, aliphatic hydrocarbons and aliphatic fluorocarbons, and to determine whether the hydrophobicity of the two groups could be distinguished by thermodynamic and biostructural analysis. This paper uses isothermal titration calorimetry (ITC) to examine the thermodynamics of binding of benzenesulfonamides substituted in the para position with alkyl and fluoroalkyl chains (H{sub 2}NSO{sub 2}C{sub 6}H{sub 4}-CONHCH{sub 2}(CX{sub 2}){sub n}CX{sub 3}, n = 0-4, X = H, F) to human carbonic anhydrase II (HCA II). Both alkyl and fluoroalkyl substituents contribute favorably to the enthalpy and the entropy of binding; these contributions increase as the length of chain of the hydrophobic substituent increases. Crystallography of the protein-ligand complexes indicates that the benzenesulfonamide groups of all ligands examined bind with similar geometry, that the tail groups associate with the hydrophobic wall of HCA II (which is made up of the side chains of residues Phe131, Val135, Pro202, and Leu204), and that the structure of the protein is indistinguishable for all but one of the complexes (the longest member of the fluoroalkyl series). Analysis of the thermodynamics of binding as a function of structure is compatible with the hypothesis that hydrophobic binding of both alkyl and fluoroalkyl chains to hydrophobic surface of carbonic anhydrase is due primarily to the release of nonoptimally hydrogen-bonded water molecules that hydrate the binding cavity (including the hydrophobic wall) of HCA II and to the release of water molecules that surround the hydrophobic chain of the ligands. This study defines the balance of enthalpic and

  7. Rapid magnetic catch-and-release purification by hydrophobic interactions.

    PubMed

    Iijima, Motoyuki; Mikami, Yuzuru; Yoshioka, Tomohiko; Kim, Shokaku; Kamiya, Hidehiro; Chiba, Kazuhiro

    2009-09-15

    A reversible, conventional, and rapid purification method of hydrophobically tagged products using hydrophobic magnetic nanoparticles was developed. The reversible purification system entails simply controlling the polarity of solvents. First, for the catching procedure, poor solvents were added into a well-dispersed system of magnetic nanoparticles and tagged products. Once the poor solvents were added to the system, the products were recrystallized among the nanoparticles and the aggregation of magnetic nanoparticles occurred due to hydrophobic interactions. These aggregates with the products contained within them were able to be collected rapidly by magnets. Then, the releasing procedure can be easily performed by redispersing the collected aggregates into good solvents. The availability of this purification protocol was confirmed by using a hydrophobically tagged fluorescent model product. Furthermore, this rapid purification method was successfully applied to a peptide elongation reaction system which enabled the synthesis of peptides such as Leu-Enkephalin in high purity, in high yield, and in a short time.

  8. Hydrophobic composition based on mixed-molecular weight polyethylene

    NASA Astrophysics Data System (ADS)

    Gorlenko, Nikolay; Debelova, Natalya; Sarkisov, Yuriy; Volokitin, Gennadiy; Zavyalova, Elena; Lapova, Tatyana

    2016-01-01

    The paper presents investigations of compositions based on low and high molecular weight polyethylene so as to synthesize a hydrophobic composition for moisture protection of timber. X-ray phase analysis and measurements of the tear-off force of hydrophobic coating needed to apply to the timber surface and the limiting wetting angle are carried out to detect the hydrophobic, adhesive, electrophysical, and physicochemical properties of compositions. Kinetic dependencies are given for moisture absorption of timber specimens. It is shown that the preliminary formation of the texture by the surface patterning or its treatment with low-temperature plasma with the following protective coating results in the improvement of hydrophobic properties of the suggested compositions. These compositions can be used in the capacity of water repellents to protect building materials from moisture including restoration works.

  9. Hydrophobicity – Shake Flasks, Protein Folding and Drug Discovery

    PubMed Central

    Sarkar, Aurijit; Kellogg, Glen E.

    2009-01-01

    Hydrophobic interactions are some of the most important interactions in nature. They are the primary driving force in a number of phenomena. This is mostly an entropic effect and can account for a number of biophysical events such as protein-protein or protein-ligand binding that are of immense importance in drug design. The earliest studies on this phenomenon can be dated back to the end of the 19th century when Meyer and Overton independently correlated the hydrophobic nature of gases to their anesthetic potency. Since then, significant progress has been made in this realm of science. This review briefly traces the history of hydrophobicity research along with the theoretical estimation of partition coefficients. Finally, the application of hydrophobicity estimation methods in the field of drug design and protein folding is discussed. PMID:19929828

  10. CHEMICAL DYNAMICS OF HYDROPHOBIC ORGANIC CONTAMINANTS DURING RESUSPENSION

    EPA Science Inventory

    Laboratory experiments were designed to study the chemical-particle dynamics of toxic hydrophobic organics during resuspension episodes using a particle entrainment simulator (PES). The purpose was to obtain insight into chemical transport mechanisms during resuspension. Informat...

  11. Inverse colloidal crystal membranes for hydrophobic interaction membrane chromatography.

    PubMed

    Vu, Anh T; Wang, Xinying; Wickramasinghe, S Ranil; Yu, Bing; Yuan, Hua; Cong, Hailin; Luo, Yongli; Tang, Jianguo

    2015-08-01

    Hydrophobic interaction membrane chromatography has gained interest due to its excellent performance in the purification of humanized monoclonal antibodies. The membrane material used in hydrophobic interaction membrane chromatography has typically been commercially available polyvinylidene fluoride. In this contribution, newly developed inverse colloidal crystal membranes that have uniform pores, high porosity and, therefore, high surface area for protein binding are used as hydrophobic interaction membrane chromatography membranes for humanized monoclonal antibody immunoglobulin G purification. The capacity of the inverse colloidal crystal membranes developed here is up to ten times greater than commercially available polyvinylidene fluoride membranes with a similar pore size. This work highlights the importance of developing uniform pore size high porosity membranes in order to maximize the capacity of hydrophobic interaction membrane chromatography.

  12. Differentiation of hydrophobic from hydrophilic submicrometer aerosol particles

    SciTech Connect

    Juozaitis, A.; Ulevicius, V.; Girgzdys, A. ); Willeke, K. )

    1993-02-01

    A method has been developed that differentiates hydrophobic from hydrophilic submicrometer aerosol particles in air environments containing polydisperse aerosols composed of different chemical species. First, a narrow particle size range is extracted from the polydisperse aerosol by an electrostatic aerosol classifier. Then the monodisperse aerosols of different origins are exposed to preselected supersaturation levels and are size-classified again by a second electrostatic classifier. Hydrophobic aerosol particles pass through the second classifier when its size window matches that of the first classifier. Hydrophilic aerosol particles grow to a larger size and are removed by the second classifier. The method has been applied in the field by measuring the fraction of hydrophobic atmospheric particles in a suburb of Vilnius, Lithuania, during a period of high emission of hydrophobic soot particles from residential coal and industrial oil burning in winter. 33 refs., 4 figs.

  13. SEQUESTRATION OF HYDROPHOBIC ORGANIC CONTAMINANTS BY GEOSORBENTS. (R822626)

    EPA Science Inventory

    The chemical interactions of hydrophobic organic contaminants (HOCs) with soils and sediments (geosorbents) may result in strong binding and slow subsequent release rates that significantly affect remediation rates and endpoints. The underlying physical and chemical phenomena ...

  14. Hydrophobic kenaf nanocrystalline cellulose for the binding of curcumin.

    PubMed

    Zainuddin, Norhidayu; Ahmad, Ishak; Kargarzadeh, Hanieh; Ramli, Suria

    2017-05-01

    Nanocrystalline cellulose (NCC) extracted from lignocellulosic materials has been actively investigated as a drug delivery excipients due to its large surface area, high aspect ratio, and biodegradability. In this study, the hydrophobically modified NCC was used as a drug delivery excipient of hydrophobic drug curcumin. The modification of NCC with a cationic surfactant, cetyl trimethylammonium bromide (CTAB) was used to modulate the loading of hydrophobic drugs that would not normally bind to NCC. The FTIR, Elemental analysis, XRD, TGA, and TEM were used to confirm the modification of NCC with CTAB. The effect of concentration of CTAB on the binding efficiency of hydrophobic drug curcumin was investigated. The amounts of curcumin bound onto the CTAB-NCC nanoparticles were analyzed by UV-vis Spectrophotometric. The result showed that the modified CTAB-NCC bound a significant amount of curcumin, in a range from 80% to 96% curcumin added. Nevertheless, at higher concentration of CTAB resulted in lower binding efficiency.

  15. Sorption of heavy metals onto hydrophobic parts of aquatic plants

    SciTech Connect

    Smith, R.W.; Robichaud, K.; Misra, M.

    1995-12-31

    The ability of the roots of Eichhornia crassipes (water hyacinth), Tripha latifolia (common cattail) and Sparganium minimum (burr reed) to accumulate lead and mercury ions from aqueous solution was investigated. The relative abilities of the hydrophilic and hydrophobic portions of the root material to accumulate these ions was studied and it was found that the hydrophilic portion accumulates substantially more of the heavy metal ions than the hydrophobic portion. An attempt is made to explain this better sorption ability.

  16. Prediction of transmembrane helices from hydrophobic characteristics of proteins.

    PubMed

    Ponnuswamy, P K; Gromiha, M M

    1993-10-01

    Membrane proteins, requiring to be embedded into the lipid bilayers, have evolved to have amino acid sequences that will fold with a hydrophobic surface in contact with the alkane chains of the lipids and polar surface in contact with the aqueous phases on both sides of the membrane and the polar head groups of the lipids. It is generally assumed that the characteristics of the aqueous parts of the membrane proteins are similar to those of normal globular proteins, and the embedded parts are highly hydrophobic. In our earlier works, we introduced the concept of 'surrounding hydrophobicity' and developed a hydrophobicity scale for the 20 amino acid residues, and applied it successfully to the study of the family of globular proteins. In this work we use the concept of surrounding hydrophobicity to indicate quantitatively how the aqueous parts of membrane proteins compare with the normal globular proteins, and how rich the embedded parts are in their hydrophobic activity. We then develop a surrounding hydrophobicity scale applicable to membrane proteins, by mixing judicially the surrounding hydrophobicities observed in the crystals of the membrane protein, photosynthetic reaction center from the bacterium Rhodopseudomonas viridis, porin from Rhodobacter capsulatus and a set of 64 globular proteins. A predictive scheme based on this scale predicts from amino acid sequence, transmembrane segments in PRC and randomly selected 26 membrane proteins to 80% level of accuracy. This is a much higher predictive power when compared to the existing popular methods. A new procedure to measure the amphipathicity of sequence segments is proposed, and it is used to characterize the transmembrane parts of the sample membrane proteins.

  17. Hydrogen evolution on hydrophobic aligned carbon nanotube arrays.

    PubMed

    Misra, Abha; Giri, Jyotsnendu; Daraio, Chiara

    2009-12-22

    We investigate for the first time hydrophobic carbon nanotube-based electrochemical cells as an alternative solution to hydrogen sorting. We show that the electrically conducting surface of the nanotube arrays can be used as a cathode for hydrogen generation and absorption by electrolyzing water. We support our findings with Raman and gas chromatography measurements. These results suggest that carbon nanotube forests, presenting a unique combination of hydrophobicity and conductivity, are suitable for application in fuel cells and microelectromechanical devices.

  18. The Radical Axis: A Motion Study

    ERIC Educational Resources Information Center

    McGivney, Ray; McKim, Jim

    2006-01-01

    Interesting problems sometimes have surprising sources. In this paper we take an innocent looking problem from a calculus book and rediscover the radical axis of classical geometry. For intersecting circles the radical axis is the line through the two points of intersection. For nonintersecting, nonconcentric circles, the radical axis still…

  19. Free-radical chemistry of sulfite.

    PubMed Central

    Neta, P; Huie, R E

    1985-01-01

    The free-radical chemistry of sulfite oxidation is reviewed. Chemical transformations of organic and biological molecules induced by sulfite oxidation are summarized. The kinetics of the free-radical oxidations of sulfite are discussed, as are the kinetics of the reactions of the sulfite-derived radicals SO3 and the peroxy derivative SO5 with organic compounds. PMID:3830699

  20. REACTIONS OF FREE RADICALS CONTAINING NITROGEN.

    DTIC Science & Technology

    deduced. The reactions of methyl and ethyl radicals with a variety of amino compounds were studied. The reactions of difluoroamino radicals in the...Hydrazines, Anilines and Cyanides were pyrolysed and the heats of formation of the resultant radicals and the strengths of the bonds formed by them

  1. Condensation Dynamics on Mimicked Metal Matrix Hydrophobic Nanoparticle-Composites

    NASA Astrophysics Data System (ADS)

    Damle, Viraj; Sun, Xiaoda; Rykaczewski, Konrad

    2014-11-01

    Use of hydrophobic surfaces promotes condensation in the dropwise mode, which is significantly more efficient than the common filmwise mode. However, limited longevity of hydrophobic surface modifiers has prevented their wide spread use in industry. Recently, metal matrix composites (MMCs) having microscale hydrophobic heterogeneities dispersed in hydrophilic metal matrix have been proposed as durable and self-healing alternative to hydrophobic surface coatings interacting with deposited water droplets. While dispersion of hydrophobic microparticles in MMC is likely to lead to surface flooding during condensation, the effect of dispersion of hydrophobic nanoparticles (HNPs) with size comparable to water nuclei critical radii and spacing is not obvious. To this end, we fabricated highly ordered arrays of Teflon nanospheres on silicon substrates that mimic the top surface of the MMCs with dispersed HNPs. We used light and electron microscopy to observe breath figures resulting from condensation on these surfaces at varied degrees of subcooling. Here, we discuss the relation between the droplet size distribution, Teflon nanosphere diameter and spacing, and condensation mode. KR acknowledges startup funding from ASU.

  2. Mechanisms for Enhanced Hydrophobicity by Atomic-Scale Roughness

    PubMed Central

    Katasho, Yumi; Liang, Yunfeng; Murata, Sumihiko; Fukunaka, Yasuhiro; Matsuoka, Toshifumi; Takahashi, Satoru

    2015-01-01

    It is well known that the close-packed CF3-terminated solid surface is among the most hydrophobic surfaces in nature. Molecular dynamic simulations show that this hydrophobicity can be further enhanced by the atomic-scale roughness. Consequently, the hydrophobic gap width is enlarged to about 0.6 nm for roughened CF3-terminated solid surfaces. In contrast, the hydrophobic gap width does not increase too much for a rough CH3-terminated solid surface. We show that the CF3-terminated surface exists in a microscopic Cassie–Baxter state, whereas the CH3-terminated surface exists as a microscopic Wenzel state. This finding elucidates the underlying mechanism for the different widths of the observed hydrophobic gap. The cage structure of the water molecules (with integrated hydrogen bonds) around CH3 terminal assemblies on the solid surface provides an explanation for the mechanism by which the CH3-terminated surface is less hydrophobic than the CF3-terminated surface. PMID:26337567

  3. Vector description of electric and hydrophobic interactions in protein homodimers.

    PubMed

    Mozo-Villarías, Angel; Cedano, Juan; Querol, Enrique

    2016-05-01

    This article describes the formation of homodimers from their constituting monomers, based on the rules set by a simple model of electric and hydrophobic interactions. These interactions are described in terms of the electric dipole moment (D) and hydrophobic moment vectors (H) of proteins. The distribution of angles formed by the two dipole moments of monomers constituting dimers were analysed, as well as the distribution of angles formed by the two hydrophobic moments. When these distributions were fitted to Gaussian curves, it was found that for biological dimers, the D vectors tend mostly to adopt a perpendicular arrangement with respect to each other, in which the constituting dipoles have the least interaction. A minor population tends towards an antiparallel arrangement implying maximum electric attraction. Also in biological dimers, the H vectors of most monomers tend to interact in such a way that the total hydrophobic moment of the dimer increases with respect to those of the monomers. This shows that hydrophobic moments have a tendency to align. In dimers originating in the crystallisation process, the distribution of angles formed by both hydrophobic and electric dipole moments appeared rather featureless, probably because of unspecific interactions in the crystallisation processes. The model does not describe direct interactions between H and D vectors although the distribution of angles formed by both vectors in dimers was analysed. It was found that in most cases these angles tended to be either small (both moments aligned parallel to each other) or large (antiparallel disposition).

  4. Spontaneous formation of hydrophobic domains in isolated peptides.

    PubMed

    Gloaguen, Eric; Loquais, Yohan; Thomas, Jessica A; Pratt, David W; Mons, Michel

    2013-05-02

    Aromatic amino acids are known for their hydrophobicity and the active role they play in protein folding. Here, we investigate the intrinsic propensity of small peptides to form hydrophobic domains in the absence of solvent water molecules. The structures of three aromatic-rich isolated peptides, Ac-Phe-Phe-NH2 (FF), Ac-Trp-Tyr-NH2 (WY), and Ac-Phe-Phe-Phe-NH2 (FFF), all in the gas phase, have been studied by infrared-ultraviolet (IR/UV) double resonance laser spectroscopy, aided by dispersion-corrected density functional theory (DFT-D) calculations. Spontaneous formation of hydrophobic domains is systematically observed, whatever the secondary structure adopted by the backbone. Various types of aromatic-aromatic arrangements have been identified and associated to specific secondary structures, illustrating the interplay between the hydrophobic clusters and the backbone. Backbone NH amide groups surrounded by aromatic rings have also been evidenced and are found to contribute significantly to the stabilization of aromatic pairs. These results suggest that the formation of aromatic clusters involving contiguous residues might be a very efficient process leading to the formation of hydrophobic domains in the early stages of protein folding, well before a hydrophobic collapse into the tertiary structure.

  5. Hydrophobicity of protein surfaces: Separating geometry from chemistry.

    PubMed

    Giovambattista, Nicolas; Lopez, Carlos F; Rossky, Peter J; Debenedetti, Pablo G

    2008-02-19

    To better understand the role of surface chemical heterogeneity in natural nanoscale hydration, we study via molecular dynamics simulation the structure and thermodynamics of water confined between two protein-like surfaces. Each surface is constructed to have interactions with water corresponding to those of the putative hydrophobic surface of a melittin dimer, but is flattened rather than having its native "cupped" configuration. Furthermore, peripheral charged groups are removed. Thus, the role of a rough surface topography is removed, and results can be productively compared with those previously observed for idealized, atomically smooth hydrophilic and hydrophobic flat surfaces. The results indicate that the protein surface is less hydrophobic than the idealized counterpart. The density and compressibility of water adjacent to a melittin dimer is intermediate between that observed adjacent to idealized hydrophobic or hydrophilic surfaces. We find that solvent evacuation of the hydrophobic gap (cavitation) between dimers is observed when the gap has closed to sterically permit a single water layer. This cavitation occurs at smaller pressures and separations than in the case of idealized hydrophobic flat surfaces. The vapor phase between the melittin dimers occupies a much smaller lateral region than in the case of the idealized surfaces; cavitation is localized in a narrow central region between the dimers, where an apolar amino acid is located. When that amino acid is replaced by a polar residue, cavitation is no longer observed.

  6. Ions and hydrogen bonding in a hydrophobic environment: CCl(4).

    PubMed

    Bisson, Patrick; Xiao, Han; Kuo, Margaret; Kamelamela, Noe; Shultz, Mary Jane

    2010-04-01

    It is generally expected that ions in an aqueous ionic solution in contact with a hydrophobic phase enter the hydrophobic phase accompanied by a hydration shell. This expectation suggests that the ion mole fraction in the hydrophobic phase is less than, or at most, equal to that of water. Both gravimetric and spectroscopic evidence shows that for a model hydrophobic phase, carbon tetrachloride, this is not the case: In contact with a 1 M simple salt solution (sodium or potassium halide), the salt concentration in carbon tetrachloride ranges from 1.4 to nearly 3 times that of water. Infrared spectra of the OH stretch region support a model in which water associates with the cation, primarily as water monomers. Salts containing larger, more polarizable anions can form outer-sphere ion pairs that support water dimers, giving rise to a spectral signature at 3440 cm(-1). In CCl(4), the infrared spectral signature of the normally strongly ionized acid HCl clearly shows the presence of molecular HCl. Additionally, the presence of a Q branch for HCl indicates restricted rotational motion. The spectral and gravimetric data provide compelling evidence for ion clusters in the hydrophobic phase, which is a result that may have implications for hydrophobic matter in both biological and environmental systems.

  7. Hydrophobic substances induce water stress in microbial cells

    PubMed Central

    Bhaganna, Prashanth; Volkers, Rita J. M.; Bell, Andrew N. W.; Kluge, Kathrin; Timson, David J.; McGrath, John W.; Ruijssenaars, Harald J.; Hallsworth, John E.

    2010-01-01

    Summary Ubiquitous noxious hydrophobic substances, such as hydrocarbons, pesticides and diverse industrial chemicals, stress biological systems and thereby affect their ability to mediate biosphere functions like element and energy cycling vital to biosphere health. Such chemically diverse compounds may have distinct toxic activities for cellular systems; they may also share a common mechanism of stress induction mediated by their hydrophobicity. We hypothesized that the stressful effects of, and cellular adaptations to, hydrophobic stressors operate at the level of water : macromolecule interactions. Here, we present evidence that: (i) hydrocarbons reduce structural interactions within and between cellular macromolecules, (ii) organic compatible solutes – metabolites that protect against osmotic and chaotrope‐induced stresses – ameliorate this effect, (iii) toxic hydrophobic substances induce a potent form of water stress in macromolecular and cellular systems, and (iv) the stress mechanism of, and cellular responses to, hydrophobic substances are remarkably similar to those associated with chaotrope‐induced water stress. These findings suggest that it may be possible to devise new interventions for microbial processes in both natural environments and industrial reactors to expand microbial tolerance of hydrophobic substances, and hence the biotic windows for such processes. PMID:21255365

  8. Transmembrane passage of hydrophobic compounds through a protein channel wall.

    PubMed

    Hearn, Elizabeth M; Patel, Dimki R; Lepore, Bryan W; Indic, Mridhu; van den Berg, Bert

    2009-03-19

    Membrane proteins that transport hydrophobic compounds have important roles in multi-drug resistance and can cause a number of diseases, underscoring the importance of protein-mediated transport of hydrophobic compounds. Hydrophobic compounds readily partition into regular membrane lipid bilayers, and their transport through an aqueous protein channel is energetically unfavourable. Alternative transport models involving acquisition from the lipid bilayer by lateral diffusion have been proposed for hydrophobic substrates. So far, all transport proteins for which a lateral diffusion mechanism has been proposed function as efflux pumps. Here we present the first example of a lateral diffusion mechanism for the uptake of hydrophobic substrates by the Escherichia coli outer membrane long-chain fatty acid transporter FadL. A FadL mutant in which a lateral opening in the barrel wall is constricted, but which is otherwise structurally identical to wild-type FadL, does not transport substrates. A crystal structure of FadL from Pseudomonas aeruginosa shows that the opening in the wall of the beta-barrel is conserved and delineates a long, hydrophobic tunnel that could mediate substrate passage from the extracellular environment, through the polar lipopolysaccharide layer and, by means of the lateral opening in the barrel wall, into the lipid bilayer from where the substrate can diffuse into the periplasm. Because FadL homologues are found in pathogenic and biodegrading bacteria, our results have implications for combating bacterial infections and bioremediating xenobiotics in the environment.

  9. Mutagenicity of Oxygen Free Radicals

    NASA Astrophysics Data System (ADS)

    Moody, Carmella S.; Hassan, Hosni M.

    1982-05-01

    Paraquat 1,1'-dimethyl-4,4'-bipyridinium dichloride) was used as an intracellular generator of oxygen free radicals and was found to be highly mutagenic for Salmonella typhimurium. It caused both base-pair substitution and frameshift mutations. Paraquat was much more toxic and mutagenic in a simple nutritionally restricted medium than in a rich complex medium. The mutagenicity of paraquat was dependent upon the presence of a supply of both electrons and oxygen. Cells containing high levels of superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1) were more resistant to the toxicity and the mutagenicity of paraquat than were cells containing normal levels of this enzyme. The mutagenicity of paraquat thus appears to be due to its ability to exacerbate the intracellular production of superoxide radicals.

  10. Highly durable photochromic radical complexes having no steric protections of radicals.

    PubMed

    Kobayashi, Yoichi; Mishima, Yasuhiro; Mutoh, Katsuya; Abe, Jiro

    2017-04-21

    Steric protection groups are usually necessary for stable radicals. However, here, we developed novel photochromic radical complexes which generate sterically unprotected imidazolyl and phenoxyl radicals upon UV light irradiation based on the phenoxyl-imidazolyl radical complex (PIC) framework. These photochromic compounds show excellent durability against repeated irradiation of intense nanosecond laser pulses even in polar protic solvents, such as ethanol.

  11. Geoscientists and the Radical Middle

    NASA Astrophysics Data System (ADS)

    Tinker, S. W.

    2015-12-01

    Addressing the great challenges facing society requires industry, government, and academia to work together. I call this overlap space, where compromises are made and real solutions determined, the Radical Middle. Radical because it can appear at times as if the loudest and most publicly influential voices lie outside of the actual solution space, content to provoke but not problem-solve. One key area where geoscientists can play a lead role in the Radical Middle is in the overlap between energy, the environment, and the economy. Globally, fossil fuels still represent 85% of the aggregate energy mix. As existing conventional oil and natural-gas reservoir production continues to slowly decline, unconventional reservoirs, led today by shale and other more expensive resources, will represent a growing part of the oil and gas production mix. Many of these unconventional reservoirs require hydraulic fracturing. The positive economic impact of hydraulic fracturing and associated natural gas and oil production on the United States economy is well documented and undeniable. Yet there are environmental concerns about fracking, and some states and nations have imposed moratoria. This energy-environment-economy space is ideal for leadership from the geosciences. Another such overlap space is the potential for geoscience leadership in relations with China, whose economy and global presence continue to expand. Although China is building major hydropower and natural-gas power plants, as well as nuclear reactors, coal is still king—with the associated environmental impacts. Carbon sequestration—onshore in brine and to enhance oil recovery, as well as offshore—could prove viable. It is vital that educated and objective geoscientists from industry, government, and academia leave their corners and work together in the Radical Middle to educate the public and develop and deliver balanced, economically sensible energy and environmental strategies.

  12. Radical Islam in East Africa

    DTIC Science & Technology

    2009-01-01

    track may not be feasible because of lack of political will on either side, but an effort should be made to detach the moderate (or less radical...Director, Sub-Saharan African Orientation Course, U.S. Air Force Special Operations School, February 15, 2008. 12 Among those arrested were the party’s...Sudan is the Tijaniyya Niassiyya, which has grown rapidly since 1950.7 The Sudanese Niassiyya is a millennial movement that preaches the imminence

  13. Radical scavengers from heavy hydrocarbons

    SciTech Connect

    Kubo, Junichi

    1996-10-01

    The hydrogen-donating properties of some hydrocarbons form the basis for processes such as coal liquefaction and heavy oil upgrading. However, these hydrocarbons have seldom been used for other purposes, because their potential applications have not been well recognized. Research has indicated that these hydrogen-donating hydrocarbons can be used in important reactions as radical scavengers and have properties particular to those of pure hydrocarbons without functional groups containing heteroatoms. Over years of study researchers have found that pure hydrocarbons with radical-scavenging effects nearly as high as those in conventional hindered phenolic antioxidants can be produced from petroleum, and these hydrogen-donating hydrocarbons exhibit such effects even in oxidative atmospheres (i.e., they function as antioxidants). He has also shown that these mixtures have some properties particular to pure hydrocarbons without functional groups containing heteroatoms, and they`ve seen that a mechanism based on the steric effects appears when these hydrocarbons are used in heavy oil hydroprocessing. Hydrogen-donating hydrocarbons should be a viable resource in many applications. In this article, he presents radical-scavenging abilities, characteristics as pure hydrocarbons, and applications on the basis of the studies.

  14. Free-radical-mediated DNA binding.

    PubMed Central

    O'Brien, P J

    1985-01-01

    Free-radical metabolites can be generated metabolically by a one-electron reductase-catalyzed reaction or a "peroxidase" catalyzed oxidation or by photoactivation of a wide variety of aromatic xenobiotics. Radicals may also be generated during lipid peroxidation. Some radicals can react with DNA or bind covalently or noncovalently as a dismutation product or as a dimer, trimer or polymeric product. Modification to the DNA can result in single-strand breaks, loss of template activity, and crosslinking. The binding can prevent enzymic digestion. In some cases, the radicals react with oxygen, resulting before conversion to DNA reactive oxygen species. Most radicals probably do not interact with DNA. PMID:3007090

  15. Oxidative stress, free radicals and protein peroxides.

    PubMed

    Gebicki, Janusz M

    2016-04-01

    Primary free radicals generated under oxidative stress in cells and tissues produce a cascade of reactive secondary radicals, which attack biomolecules with efficiency determined by the reaction rate constants and target concentration. Proteins are prominent targets because they constitute the bulk of the organic content of cells and tissues and react readily with many of the secondary radicals. The reactions commonly lead to the formation of carbon-centered radicals, which generally convert in vivo to peroxyl radicals and finally to semistable hydroperoxides. All of these intermediates can initiate biological damage. This article outlines the advantages of the application of ionizing radiations to studies of radicals, with particular reference to the generation of desired radicals, studies of the kinetics of their reactions and correlating the results with events in biological systems. In one such application, formation of protein hydroperoxides in irradiated cells was inhibited by the intracellular ascorbate and glutathione.

  16. Surfactant Facilitated Spreading of Aqueous Drops on Hydrophobic Surfaces

    NASA Technical Reports Server (NTRS)

    Kumar, Nitin; Couzis, Alex; Maldarelli, Charles; Singh, Bhim S. (Technical Monitor)

    2000-01-01

    Microgravity technologies often require aqueous phases to spread over nonwetting hydrophobic solid/surfaces. At a hydrophobic surface, the air/hydrophobic solid tension is low, and the solid/aqueous tension is high. A large contact angle forms as the aqueous/air tension acts together with the solid/air tension to balance the large solid/aqueous tension. The aqueous phase, instead of spreading, is held in a meniscus by the large angle. Surfactants facilitate the wetting of water on hydrophobic surfaces by adsorbing on the water/air and hydrophobic solid/water interfaces and lowering the surface tensions of these interfaces. The tension reductions decrease the contact angle, which increases the equilibrium wetted area. Hydrocarbon surfactants (i.e. amphiphiles with a hydrophobic chain of methylene groups attached to a large polar group to give aqueous solubility) do not reduce significantly the contact angles of the very hydrophobic surfaces such as parafilm or polyethylene. Trisiloxane surfactants (amphiphiles with a hydrophobe consisting of methyl groups linked to a trisiloxane backbone in the form of a disk ((CH3)3-Si-O-Si-O-Si(CH3)3)) and an extended ethoxylate (-(OCH2CH2)n-) polar group in the form of a chain with seven or eight units) can significantly reduce the contact angle of water on a very hydrophobic surface and cause rapid and complete (or nearly complete) spreading (lermed superspreading). The overall goal of the research described in this proposal is to establish and verify a theory for how trisiloxanes cause superspreading, and then use this knowledge as a guide to developing more general hydrocarbon based surfactant systems which superspread and can be used in microgravity. We propose that the trisiloxane surfactants superspread when the siloxane adsorbs, the hydrophobic disk parts of the molecule adsorb onto the surface removing the surface water. Since the cross sectional area of the disk is larger than that of the extended ethoxylate chain, the

  17. Single water entropy: hydrophobic crossover and application to drug binding.

    PubMed

    Sasikala, Wilbee D; Mukherjee, Arnab

    2014-09-11

    Entropy of water plays an important role in both chemical and biological processes e.g. hydrophobic effect, molecular recognition etc. Here we use a new approach to calculate translational and rotational entropy of the individual water molecules around different hydrophobic and charged solutes. We show that for small hydrophobic solutes, the translational and rotational entropies of each water molecule increase as a function of its distance from the solute reaching finally to a constant bulk value. As the size of the solute increases (0.746 nm), the behavior of the translational entropy is opposite; water molecules closest to the solute have higher entropy that reduces with distance from the solute. This indicates that there is a crossover in translational entropy of water molecules around hydrophobic solutes from negative to positive values as the size of the solute is increased. Rotational entropy of water molecules around hydrophobic solutes for all sizes increases with distance from the solute, indicating the absence of crossover in rotational entropy. This makes the crossover in total entropy (translation + rotation) of water molecule happen at much larger size (>1.5 nm) for hydrophobic solutes. Translational entropy of single water molecule scales logarithmically (Str(QH) = C + kB ln V), with the volume V obtained from the ellipsoid of inertia. We further discuss the origin of higher entropy of water around water and show the possibility of recovering the entropy loss of some hypothetical solutes. The results obtained are helpful to understand water entropy behavior around various hydrophobic and charged environments within biomolecules. Finally, we show how our approach can be used to calculate the entropy of the individual water molecules in a protein cavity that may be replaced during ligand binding.

  18. Compatibility assessment of methods used for soil hydrophobicity determination

    NASA Astrophysics Data System (ADS)

    Papierowska, Ewa; Szatyłowicz, Jan; Kalisz, Barbara; Łachacz, Andrzej; Matysiak, Wojciech; Debaene, Guillaume

    2016-04-01

    Soil hydrophobicity is a global problem. Effect of hydrophobicity on the soil environment is very important, because it can cause irreversible changes in ecosystems, leading to their complete degradation. The choice of method used to determine soil hydrophobicity is not simple because there is no obvious criteria for their selection. The results obtained by various methods may not be coherent and may indicate different degrees of hydrophobicity within the same soil sample. The objective of the study was to assess the compatibility between methods used to determine the hydrophobicity of selected organic and mineral-organic soils. Two groups of soil materials were examined: hydrogenic (87 soil samples) and autogenic soils (19 soil samples) collected from 41 soil profiles located in north-eastern Poland. Air-dry soil samples were used. Hydrophobicity was determined using two different methods i.e. on the basis of wetting contact angle measurements between water and solid phase of soils and with water drop penetration time tests. The value of the wetting contact angle was measured using the sessile drop method with optical goniometer CAM 100 (KSV Instruments). The wetting contact angles were determined at room temperature (20° C) within 10 min after sample preparation using standard procedure. In addition, water drop penetration time was measured. In order to compare the methods used for the assessment of soil hydrophobicity, the agreement between observers model was applied. In this model five categories of soil hydrophobicity were proposed according to the class used in the soil hydrofobicity classification based on water drop penetration time test. Based on this classification the values of the weighted kappa coefficients were calculated using SAS 9.4 (SAS Institute, 2013, Cary NC) for evaluating relationships between between the different investigated methods. The results of agreement were presented in forms of agreement charts. Research results indicated good

  19. Autoactivation of blood factor XII at hydrophilic and hydrophobic surfaces.

    PubMed

    Zhuo, Rui; Siedlecki, Christopher A; Vogler, Erwin A

    2006-08-01

    Contact activation of blood factor XII (FXII, Hageman factor) in neat-buffer solution is shown not to be specific for anionic hydrophilic procoagulants as proposed by the accepted biochemistry of surface activation. Rather, FXII activation in the presence of plasma proteins leads to an apparent specificity for hydrophilic surfaces that is actually due to a relative diminution of the FXII-->FXIIa reaction at hydrophobic surfaces. FXII activation in neat-buffer solution was effectively instantaneous upon contact with either hydrophilic (fully water-wettable clean glass) or hydrophobic (poorly water-wettable silanized glass) procoagulant particles, with greater FXIIa yield obtained by activation with hydrophobic procoagulants. In sharp contrast, both activation rate and yield was found to be significantly attenuated at hydrophobic surfaces in the presence of plasma proteins. Putative FXIIa produced by surface activation with both hydrophilic and hydrophobic procoagulants was shown to hydrolyze blood factor XI (FXI) to the activated form FXIa (FXIFXIIa-->FXIa) that causes FXI-deficient plasma to rapidly coagulate.

  20. Titration of hydrophobic polyelectrolytes using Monte Carlo simulations.

    PubMed

    Ulrich, Serge; Laguecir, Abohachem; Stoll, Serge

    2005-03-01

    The conformation and titration curves of weak (or annealed) hydrophobic polyelectrolytes have been examined using Monte Carlo simulations with screened Coulomb potentials in the grand canonical ensemble. The influence of the ionic concentration pH and presence of hydrophobic interactions has been systematically investigated. A large number of conformations such as extended, pearl-necklace, cigar-shape, and collapsed structures resulting from the subtle balance of short-range hydrophobic attractive interactions and long-range electrostatic repulsive interactions between the monomers have been observed. Titration curves were calculated by adjusting the pH-pK(0) values (pK(0) represents the intrinsic dissociation constant of an isolated monomer) and then calculating the ionization degree alpha of the polyelectrolyte. Important transitions related to cascades of conformational changes were observed in the titration curves, mainly at low ionic concentration and with the presence of strong hydrophobic interactions. We demonstrated that the presence of hydrophobic interactions plays an important role in the acid-base properties of a polyelectrolyte in promoting the formation of compact conformations and hence decreasing the polyelectrolyte degree of ionization for a given pH-pK(0) value.

  1. Characterization method of hydrophobic anti-icing coatings

    NASA Astrophysics Data System (ADS)

    Morita, Katsuaki; Sakaue, Hirotaka

    2015-11-01

    For anti-icing, supercooled water should be removed before frozen onto the contact surface. We use a hydrophobic coating for anti-icing and introduce the static- and dynamic-evaluation methods. The methods describe the contact surface between the hydrophobic surface and a supercooled-water droplet. The former is based on the contact angle, and the latter is based on the sliding angle. The temperature factor is included in these models to evaluate the hydrophobic coating under the supercooled conditions. Four hydrophobic coatings are experimentally evaluated based on the static- and dynamic evaluation methods: C1-C3 (commercial fluorocarbon coatings), and Jaxa coating (original fluorocarbon coating). These are evaluated under the supercooled conditions of -10 to 0 °C. The static-evaluation shows variations in the temperature. However, change in the contact angle by the temperature is relatively small compared to that of the sliding angle for the dynamic evaluation. Only C3 and Jaxa coatings are tolerant to the sliding angle under the supercooled conditions tested. The dynamic evaluation shows that even if the coating is hydrophobic, the dynamic evaluation should be included to understand the characteristic of removal for a supercooled-water droplet.

  2. How protein chemists learned about the hydrophobic factor.

    PubMed Central

    Tanford, C.

    1997-01-01

    It is generally accepted today that the hydrophobic force is the dominant energetic factor that leads to the folding of polypeptide chains into compact globular entities. This principle was first explicitly introduced to protein chemists in 1938 by Irving Langmuir, past master in the application of hydrophobicity to other problems, and was enthusiastically endorsed by J.D. Bernal. But both proposal and endorsement came in the course of a debate about a quite different structural principle, the so-called "cyclol hypothesis" proposed by D. Wrinch, which soon proved to be theoretically and experimentally unsupportable. Being a more tangible idea, directly expressed in structural terms, the cyclol hypothesis received more attention than the hydrophobic principle and the latter never actually entered the mainstream of protein science until 1959, when it was thrust into the limelight in a lucid review by W. Kauzmann. A theoretical paper by H.S. Frank and M. Evans, not itself related to protein folding, probably played a major role in the acceptance of the hydrophobicity concept by protein chemists because it provided a crude but tangible picture of the origin of hydrophobicity per se in terms of water structure. PMID:9194199

  3. Predicting the bioconcentration factor of highly hydrophobic organic chemicals.

    PubMed

    Garg, Rajni; Smith, Carr J

    2014-07-01

    Bioconcentration refers to the process of uptake and buildup of chemicals in living organisms. Experimental measurement of bioconcentration factor (BCF) is time-consuming and expensive, and is not feasible for a large number of chemicals of regulatory concern. Quantitative structure-activity relationship (QSAR) models are used for estimating BCF values to help in risk assessment of a chemical. This paper presents the results of a QSAR study conducted to address an important problem encountered in the prediction of the BCF of highly hydrophobic chemicals. A new QSAR model is derived using a dataset of diverse organic chemicals previously tested in a United States Environmental Protection Agency laboratory. It is noted that the linear relationship between the BCF and hydrophobic parameter, i.e., calculated octanol-water partition coefficient (ClogP), breaks down for highly hydrophobic chemicals. The parabolic QSAR equation, log BCF=3.036 ClogP-0.197 ClogP(2)-0.808 MgVol (n=28, r(2)=0.817, q(2)=0.761, s=0.558) (experimental log BCF range=0.44-5.29, ClogP range=3.16-11.27), suggests that a non-linear relationship between BCF and the hydrophobic parameter, along with inclusion of additional molecular size, weight and/or volume parameters, should be considered while developing a QSAR model for more reliable prediction of the BCF of highly hydrophobic chemicals.

  4. Biofilm, adherence, and hydrophobicity as virulence factors in Malassezia furfur.

    PubMed

    Angiolella, Letizia; Leone, Claudia; Rojas, Florencia; Mussin, Javier; de Los Angeles Sosa, María; Giusiano, Gustavo

    2017-03-09

    Malassezia species are natural inhabitants of the healthy skin. However, under certain conditions, they may cause or exacerbate several skin diseases. The ability of this fungus to colonize or infect is determined by complex interactions between the fungal cell and its virulence factors. This study aims to evaluate "in vitro" the hydrophobicity levels, the adherence on a plastic surface and the biofilm formation of 16 clinical isolates of Malassezia furfur. Cellular surface hydrophobicity (CSH) levels were determined by two-phase system. The biofilm formation was determined by tetrazolium salt (XTT) reduction assay and by Scanning Electron Microscopy (SEM). Results showed many isolates were hydrophobic, adherent, and producers of biofilm on abiotic surfaces with different capacity. SEM observations confirmed an abundant extracellular matrix after 48 h of biofilm formation. About 63% of strains with high production of biofilm showed medium to high percentage of hydrophobicity and/or adherence. In addition, it has been demonstrated a correlation between hydrophobicity, adherence, and biofilm formation in about 60% of strains examined. These important virulence factors could be responsible of this yeast changing from a commensal to a pathogenic status.

  5. Interplay Between Hydrophobic Effect and Dipole Interactions in Peptide Aggregation

    NASA Astrophysics Data System (ADS)

    Ganesan, Sai; Matysiak, Silvina

    In the past decade, the development of various coarse-grained models for proteins have provided key insights into the driving forces in folding and aggregation.We recently developed a low resolution Water Explicit Polarizable PROtein coarse-grained Model by adding oppositely charged dummy particles inside protein backbone beads.With this model,we were able to achieve significant α/ β secondary structure content,without any added bias.We now extend the model to study peptide aggregation at hydrophobic-hydrophilic interface using elastin-like octapeptides (GV)4 as a model system.A condensation-ordering mechanism of aggregation is observed in water.Our results suggest that backbone interpeptide dipolar interactions,not hydrophobicity,plays a more significant role in fibril-like peptide aggregation.We observe a cooperative effect in hydrogen bonding or dipolar interactions, with increase in aggregate size in water and interface.Based on this cooperative effect, we provide a potential explanation for the observed nucleus size in peptide aggregation pathways.Without dipolar particles,peptide aggregation is not observed at the hydrophilic-hydrophobic interface.Thus,the presence of dipoles,not hydrophobicity plays a key role in aggregation observed at hydrophobic interfaces.

  6. Characterization method of hydrophobic anti-icing coatings.

    PubMed

    Morita, Katsuaki; Sakaue, Hirotaka

    2015-11-01

    For anti-icing, supercooled water should be removed before frozen onto the contact surface. We use a hydrophobic coating for anti-icing and introduce the static- and dynamic-evaluation methods. The methods describe the contact surface between the hydrophobic surface and a supercooled-water droplet. The former is based on the contact angle, and the latter is based on the sliding angle. The temperature factor is included in these models to evaluate the hydrophobic coating under the supercooled conditions. Four hydrophobic coatings are experimentally evaluated based on the static- and dynamic evaluation methods: C1-C3 (commercial fluorocarbon coatings), and Jaxa coating (original fluorocarbon coating). These are evaluated under the supercooled conditions of -10 to 0 °C. The static-evaluation shows variations in the temperature. However, change in the contact angle by the temperature is relatively small compared to that of the sliding angle for the dynamic evaluation. Only C3 and Jaxa coatings are tolerant to the sliding angle under the supercooled conditions tested. The dynamic evaluation shows that even if the coating is hydrophobic, the dynamic evaluation should be included to understand the characteristic of removal for a supercooled-water droplet.

  7. Hydrophobic and electrostatic cell surface properties of Cryptosporidium parvum.

    PubMed

    Drozd, C; Schwartzbrod, J

    1996-04-01

    Microbial adhesion to hydrocarbons and microelectrophoresis were investigated in order to characterize the surface properties of Cryptosporidium parvum. Oocysts exhibited low removal rates by octane (only 20% on average), suggesting that the Cryptosporidium sp. does not demonstrate marked hydrophobic properties. A zeta potential close to -25 mV at pH 6 to 6.5 in deionized water was observed for the parasite. Measurements of hydrophobicity and zeta potential were performed as a function of pH and ionic strength or conductivity. Hydrophobicity maxima were observed at extreme pH values, with 40% of adhesion of oocysts to octane. It also appeared that ionic strength (estimated by conductivity) could influence the hydrophobic properties of oocysts. Cryptosporidium oocysts showed a pH-dependent surface charge, with zeta potentials becoming less negative as pH was reduced, starting at -35 mV for alkaline pH and reaching 0 at isoelectric points for pH 2.5. On the other hand, variation of surface charge with respect to conductivity of the suspension tested in this work was quite small. The knowledge of hydrophobic properties and surface charge of the parasite provides information useful in, for example, the choice of various flocculation treatments, membrane filters, and cleaning agents in connection with oocyst recovery.

  8. Kinase regulation by hydrophobic spine assembly in cancer.

    PubMed

    Hu, Jiancheng; Ahuja, Lalima G; Meharena, Hiruy S; Kannan, Natarajan; Kornev, Alexandr P; Taylor, Susan S; Shaw, Andrey S

    2015-01-01

    A new model of kinase regulation based on the assembly of hydrophobic spines has been proposed. Changes in their positions can explain the mechanism of kinase activation. Here, we examined mutations in human cancer for clues about the regulation of the hydrophobic spines by focusing initially on mutations to Phe. We identified a selected number of Phe mutations in a small group of kinases that included BRAF, ABL1, and the epidermal growth factor receptor. Testing some of these mutations in BRAF, we found that one of the mutations impaired ATP binding and catalytic activity but promoted noncatalytic allosteric functions. Other Phe mutations functioned to promote constitutive catalytic activity. One of these mutations revealed a previously underappreciated hydrophobic surface that functions to position the dynamic regulatory αC-helix. This supports the key role of the C-helix as a signal integration motif for coordinating multiple elements of the kinase to create an active conformation. The importance of the hydrophobic space around the αC-helix was further tested by studying a V600F mutant, which was constitutively active in the absence of the negative charge that is associated with the common V600E mutation. Many hydrophobic mutations strategically localized along the C-helix can thus drive kinase activation.

  9. Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states

    NASA Astrophysics Data System (ADS)

    Wåhlander, Martin; Nilsson, Fritjof; Carlmark, Anna; Gedde, Ulf W.; Edmondson, Steve; Malmström, Eva

    2016-08-01

    We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been immobilised on anionic GO and subsequently grafted with hydrophobic polymer grafts. Dense grafts of PBA, PBMA and PMMA with a wide range of average graft lengths (MW: 1-440 kDa) were polymerised by surface-initiated controlled radical precipitation polymerisation from the statistical MI. The surface modification is designed similarly to bimodal graft systems, where the cationic MI generates nanoparticle repulsion, similar to dense short grafts, while the long grafts offer miscibility in non-polar environments and cohesion. The state-of-the-art dispersions of grafted GO were in the isotropic state. Transparent and translucent matrix-free GO-composites could be melt-processed directly using only grafted GO. After processing, birefringence due to nematic alignment of grafted GO was observed as a single giant Maltese cross, 3.4 cm across. Permeability models for composites containing aligned 2D-fillers were developed, which were compared with the experimental oxygen permeability data and found to be consistent with isotropic or nematic states. The storage modulus of the matrix-free GO-composites increased with GO content (50% increase at 0.67 wt%), while the significant increases in the thermal stability (up to 130 °C) and the glass transition temperature (up to 17 °C) were dependent on graft length. The tuneable matrix-free GO-composites with rapid thermo-responsive shape-memory effects are promising candidates for a vast range of applications, especially selective membranes and sensors.We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been

  10. Laser spectroscopy of hydrocarbon radicals

    SciTech Connect

    Chen, P.

    1993-12-01

    The author reports the application of supersonic jet flash pyrolysis to the specific preparation of a range of organic radicals, biradicals, and carbenes in a skimmed molecular beam. Each species was produced cleanly and specifically, with little or no secondary reactions by the thermal dissociation of appropriately designed and synthesized organic precursors. Photoelectron spectra of the three isomeric C{sub 3}H{sub 2} carbenes, ortho-benzyne, and the {alpha},3-dehydrotoluene biradical, were used to establish adiabatic ionization potentials for use in thermochemical determinations.

  11. Aromatic-radical oxidation chemistry

    SciTech Connect

    Glassman, I.; Brezinsky, K.

    1993-12-01

    The research effort has focussed on discovering an explanation for the anomalously high CO{sub 2} concentrations observed early in the reaction sequence of the oxidation of cyclopentadiene. To explain this observation, a number of plausible mechanisms have been developed which now await experimental verification. One experimental technique for verifying mechanisms is to probe the reacting system by perturbing the radical concentrations. Two forms of chemical perturbation of the oxidation of cyclopentadiene were begun during this past year--the addition of NO{sub 2} and CO to the reacting mixture.

  12. Neuroprotective strategies in radical prostatectomy.

    PubMed

    Schiff, Jonathan D; Mulhall, John P

    2005-01-01

    In this section, authors from New York give their views on the various neuroprotective strategies for patients having a radical prostatectomy, such as the use of nerve grafts and other approaches. A joint study from Korea, the USA, Canada and the UK is presented in a paper on the importance of patient perception in the clinical assessment and management of BPH. There is also a review of robotic urological surgery. Finally, authors from New York give a review on the life of Isaac Newton. This is a new historical review in the journal, but one that will be of general interest.

  13. Iron and iron derived radicals

    SciTech Connect

    Borg, D.C.; Schaich, K.M.

    1987-04-01

    We have discussed some reactions of iron and iron-derived oxygen radicals that may be important in the production or treatment of tissue injury. Our conclusions challenge, to some extent, the usual lines of thought in this field of research. Insofar as they are born out by subsequent developments, the lessons they teach are two: Think fastexclamation Think smallexclamation In other words, think of the many fast reactions that can rapidly alter the production and fate of highly reactive intermediates, and when considering the impact of competitive reactions on such species, think how they affect the microenvironment (on the molecular scale) ''seen'' by each reactive molecule. 21 refs., 3 figs., 1 tab.

  14. Preservation of York Minster historic limestone by hydrophobic surface coatings

    PubMed Central

    Walker, Rachel A.; Wilson, Karen; Lee, Adam F.; Woodford, Julia; Grassian, Vicki H.; Baltrusaitis, Jonas; Rubasinghege, Gayan; Cibin, Giannantonio; Dent, Andrew

    2012-01-01

    Magnesian limestone is a key construction component of many historic buildings that is under constant attack from environmental pollutants notably by oxides of sulfur via acid rain, particulate matter sulfate and gaseous SO2 emissions. Hydrophobic surface coatings offer a potential route to protect existing stonework in cultural heritage sites, however, many available coatings act by blocking the stone microstructure, preventing it from ‘breathing' and promoting mould growth and salt efflorescence. Here we report on a conformal surface modification method using self-assembled monolayers of naturally sourced free fatty acids combined with sub-monolayer fluorinated alkyl silanes to generate hydrophobic (HP) and super hydrophobic (SHP) coatings on calcite. We demonstrate the efficacy of these HP and SHP surface coatings for increasing limestone resistance to sulfation, and thus retarding gypsum formation under SO2/H2O and model acid rain environments. SHP treatment of 19th century stone from York Minster suppresses sulfuric acid permeation. PMID:23198088

  15. Fractionation and recovery of whey proteins by hydrophobic interaction chromatography.

    PubMed

    Santos, Maria João; Teixeira, José A; Rodrigues, Lígia R

    2011-03-01

    A method for the recovery and fractionation of whey proteins from a whey protein concentrate (80%, w/w) by hydrophobic interaction chromatography is proposed. Standard proteins and WPC 80 dissolved in phosphate buffer with ammonium sulfate 1 M were loaded in a HiPrep Octyl Sepharose FF column coupled to a fast protein liquid chromatography (FPLC) system and eluted by decreasing the ionic strength of the buffer using a salt gradient. The results showed that the most hydrophobic protein from whey is α-lactalbumin and the less hydrophobic is lactoferrin. It was possible to recover 45.2% of β-lactoglobulin using the HiPrep Octyl Sepharose FF column from the whey protein concentrate mixture with 99.6% purity on total protein basis.

  16. Recyclable hydrophilic-hydrophobic micropatterns on glass for microarray applications.

    PubMed

    Zhang, Hua; Lee, Yong Yeow; Leck, Kwong Joo; Kim, Namyong Y; Ying, Jackie Y

    2007-04-24

    A novel method for fabricating recyclable hydrophilic-hydrophobic micropatterns on glass chips is presented. TiOx patterns (100-2000 microm) were sputtered on glass chips via a through-hole mask. The patterned chips were then vapor-coated with fluoroalkylsilane, for example, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FTES) to form a hydrophobic coating layer. The fluoroalkyl chain of FTES film on TiOx patterns was photocleaved under UV irradiation, exposing the fresh hydrophilic TiOx patterns. The resulting chip could be used multiple times by repeating the coating and photocleaving processes with negligible deterioration of the hydrophobic FTES film coated on glass. If desired, bare glass patterns could also be generated by removing the TiOx patterns with KOH. The patterned glass chips have been successfully used for microarray fabrication.

  17. Forces between hydrophobic solids in concentrated aqueous salt solution.

    PubMed

    Mastropietro, Dean J; Ducker, William A

    2012-03-09

    Much research has focused on the discovery and description of long-ranged forces between hydrophobic solids immersed in water. Here we show that the force between high contact-angle solids in concentrated salt solution (1 M KCl) agrees very well with van der Waals forces calculated from Lifshitz theory for separations greater than 5 nm. The hydrophobic solids are octadecyltrichlorosilane-coated glass, with an advancing contact angle of 108°. Thus, in 1 M salt solution, it is unnecessary to invoke the presence of a hydrophobic force at separations greater than 5 nm. Through measurement in salt solution, we avoid the necessity of accounting for large electrostatic forces that frequently occur in pure water and may obscure resolution of other forces.

  18. A script to highlight hydrophobicity and charge on protein surfaces

    PubMed Central

    Hagemans, Dominique; van Belzen, Ianthe A. E. M.; Morán Luengo, Tania; Rüdiger, Stefan G. D.

    2015-01-01

    The composition of protein surfaces determines both affinity and specificity of protein-protein interactions. Matching of hydrophobic contacts and charged groups on both sites of the interface are crucial to ensure specificity. Here, we propose a highlighting scheme, YRB, which highlights both hydrophobicity and charge in protein structures. YRB highlighting visualizes hydrophobicity by highlighting all carbon atoms that are not bound to nitrogen and oxygen atoms. The charged oxygens of glutamate and aspartate are highlighted red and the charged nitrogens of arginine and lysine are highlighted blue. For a set of representative examples, we demonstrate that YRB highlighting intuitively visualizes segments on protein surfaces that contribute to specificity in protein-protein interfaces, including Hsp90/co-chaperone complexes, the SNARE complex and a transmembrane domain. We provide YRB highlighting in form of a script that runs using the software PyMOL. PMID:26528483

  19. Preservation of York Minster historic limestone by hydrophobic surface coatings

    NASA Astrophysics Data System (ADS)

    Walker, Rachel A.; Wilson, Karen; Lee, Adam F.; Woodford, Julia; Grassian, Vicki H.; Baltrusaitis, Jonas; Rubasinghege, Gayan; Cibin, Giannantonio; Dent, Andrew

    2012-11-01

    Magnesian limestone is a key construction component of many historic buildings that is under constant attack from environmental pollutants notably by oxides of sulfur via acid rain, particulate matter sulfate and gaseous SO2 emissions. Hydrophobic surface coatings offer a potential route to protect existing stonework in cultural heritage sites, however, many available coatings act by blocking the stone microstructure, preventing it from `breathing' and promoting mould growth and salt efflorescence. Here we report on a conformal surface modification method using self-assembled monolayers of naturally sourced free fatty acids combined with sub-monolayer fluorinated alkyl silanes to generate hydrophobic (HP) and super hydrophobic (SHP) coatings on calcite. We demonstrate the efficacy of these HP and SHP surface coatings for increasing limestone resistance to sulfation, and thus retarding gypsum formation under SO2/H2O and model acid rain environments. SHP treatment of 19th century stone from York Minster suppresses sulfuric acid permeation.

  20. Hierarchical silicon etched structures for controlled hydrophobicity/superhydrophobicity.

    PubMed

    Xiu, Yonghao; Zhu, Lingbo; Hess, Dennis W; Wong, C P

    2007-11-01

    Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surfaces generated by KOH anisotropic etching. Results demonstrated that by altering the surface hydrophobicity, the apparent contact angle changed in accord with the Wenzel equation for surface structures with inclined side walls. Hierarchical structures were also constructed from Si pyramids where nanostructures were added by Au-assisted electroless HF/H2O2 etching. Surface hydrophobicity and superhydrophobicity were achieved by surface modification with a variety of silanes. Stability of the Cassie state of superhydrophobicity is described with respect to the Laplace pressure as indicated by the water droplet meniscus in contact with the hierarchical structures. The contact angle hysteresis observed is also discussed with respect to water/substrate adhesion.

  1. Compositional fingerprint of soy sauces via hydrophobic surface interaction.

    PubMed

    Jakobi, Victoria; Salmen, Paul; Paulus, Michael; Tolan, Metin; Rosenhahn, Axel

    2017-03-01

    In this work, the interaction of soy sauces with hydrophobic surfaces has been analyzed. Hydrophobic self-assembled monolayers on gold or silicon dioxide were used to harvest conditioning layers from soy sauce products with varying amounts of additives. The data was compared to adsorption of soy protein and glutamic acid as common ingredients. Spectral ellipsometry revealed that all tested sauces led to the formation of thin overlayers on hydrophobic surfaces. Products with less additives yielded adlayers in the same thickness range as pure soy protein. In contrast, sauces with more ingredients create distinctly thicker films. Using water contact angle goniometry, it is shown that all adlayers render the substrate more hydrophilic. Infrared spectroscopy provided a deeper insight into the adlayer chemistry and revealed that the adlayer composition is dominated by protein rich components. X-ray reflectivity on selected films provided further insight into the density profiles within the adlayers on the molecular scale.

  2. Protein folding, stability, and solvation structure in osmolyte solutions hydrophobicity

    NASA Astrophysics Data System (ADS)

    Montgomery Pettitt, B.

    2008-03-01

    The hydrophobic effect between solutes in aqueous solutions plays a central role in our understanding of recognition and folding of proteins and self assembly of lipids. Hydrophobicity induces nonideal solution behavior which plays a role in many aspects of biophysics. Work on the use of small biochemical compounds to crowd protein solutions indicates that a quantitative description of their non-ideal behavior is possible and straightforward. Here, we will show what the structural origin of this non-ideal solution behavior is from expression derived from a semi grand ensemble approach. We discuss the consequences of these findings regarding protein folding stability and solvation in crowded solutions through a structural analysis of the m-value or the change in free energy difference of a macromolecule in solution with respect to the concentration of a third component. This effect has recently been restudied and new mechanisms proposed for its origins in terms of transfer free energies and hydrophobicity.

  3. Surface geometry based hydrophobicity of the PDMS for microfluidic devices

    NASA Astrophysics Data System (ADS)

    Pelayo, J. C.; Badiola, R. A.; Castañares, J.; Pili, U.; Violanda, R.; Bacabac, R.

    2015-06-01

    In this report, the surface hydrophobicity of PDMS was investigated using two methods of preparations. The first method was performed by changing the surface roughness through the use of different molds. The second method was performed by varying the reconstitution ratio (volume of elastomer base to volume of elastomer curing) of the PDMS. Variation in the hydrophobicity of the PDMS was characterized by measuring the contact angle of a liquid droplet against the surface of the PDMS. The results showed that both the surface roughness and the reconstitution ratio of the PDMS positively correlated with the contact angle measured regardless of the liquid used. The maximum and minimum contact angle obtained were θr = (138 ± 3)° and θr = (99 ± 3)°, respectively. The results demonstrate a straightforward way of fabricating microfluidic devices using PDMS with controlled hydrophobicity.

  4. A biologically inspired hydrophobic membrane for application in pervaporation.

    PubMed

    Jullok, Nora; Martínez, Rodrigo; Wouters, Christine; Luis, Patricia; Sanz, María Teresa; Van der Bruggen, Bart

    2013-02-05

    An artificial polydimethylsiloxane/polyphenylsulfone (PDMS/PPSU) membrane, which emulates the hydrophobic behavior of natural membranes, was synthesized. Hydrophobicity was achieved by coating the membrane surface sublayer using conventional silicon material, which imitates the character of epicuticular wax (EW) of Prunus laurocerasus L. leaves. It was then applied as a separation medium in pervaporation (PV) of diluted mixtures of ethyl acetate and aroma compounds. The membrane's biomimetic characteristics were evaluated using surface morphology analyses, that is, Fourier transform infrared (FTIR), water contact angle measurements, and SEM imaging. A comparison of properties of the membranes synthesized in this work against selected hydrophobic plant leaves indicated a good agreement. PV using these biologically inspired artificial membranes demonstrated preference for the permeation of ethyl acetate. Besides intrinsic characteristics, it was also observed that the chemical potential is highly influential in activating sorption, diffusion, and desorption of a specific compound.

  5. Strong, reversible underwater adhesion via gecko-inspired hydrophobic fibers.

    PubMed

    Soltannia, Babak; Sameoto, Dan

    2014-12-24

    Strong, reversible underwater adhesion using gecko-inspired surfaces is achievable through the use of a hydrophobic structural material and does not require surface modification or suction cup effects for this adhesion to be effective. Increased surface energy can aid in dry adhesion in an air environment but strongly degrades wet adhesion via reduction of interfacial energy underwater. A direct comparison of structurally identical but chemically different mushroom shaped fibers shows that strong, reversible adhesion, even in a fully wetted, stable state, is feasible underwater if the structural material of the fibers is hydrophobic and the mating surface is not strongly hydrophilic. The exact adhesion strength will be a function of the underwater interfacial energy between surfaces and the specific failure modes of individual fibers. This underwater adhesion has been calculated to be potentially greater than the dry adhesion for specific combinations of hydrophobic surfaces.

  6. Ice friction: The effects of surface roughness, structure, and hydrophobicity

    SciTech Connect

    Kietzig, Anne-Marie; Hatzikiriakos, Savvas G.; Englezos, Peter

    2009-07-15

    The effect of surface roughness, structure, and hydrophobicity on ice friction is studied systematically over a wide range of temperature and sliding speeds using several metallic interfaces. Hydrophobicity in combination with controlled roughness at the nanoscale is achieved by femtosecond laser irradiation to mimic the lotus effect on the slider's surface. The controlled roughness significantly increases the coefficient of friction at low sliding speeds and temperatures well below the ice melting point. However, at temperatures close to the melting point and relatively higher speeds, roughness and hydrophobicity significantly decrease ice friction. This decrease in friction is mainly due to the suppression of capillary bridges in spite of the presence of surface asperities that facilitate their formation. Finally, grooves oriented in the sliding direction also significantly decrease friction in the low velocity range compared to scratches and grooves randomly distributed over a surface.

  7. Determining protein similarity by comparing hydrophobic core structure.

    PubMed

    Gadzała, M; Kalinowska, B; Banach, M; Konieczny, L; Roterman, I

    2017-02-01

    Formal assessment of structural similarity is - next to protein structure prediction - arguably the most important unsolved problem in proteomics. In this paper we propose a similarity criterion based on commonalities between the proteins' hydrophobic cores. The hydrophobic core emerges as a result of conformational changes through which each residue reaches its intended position in the protein body. A quantitative criterion based on this phenomenon has been proposed in the framework of the CASP challenge. The structure of the hydrophobic core - including the placement and scope of any deviations from the idealized model - may indirectly point to areas of importance from the point of view of the protein's biological function. Our analysis focuses on an arbitrarily selected target from the CASP11 challenge. The proposed measure, while compliant with CASP criteria (70-80% correlation), involves certain adjustments which acknowledge the presence of factors other than simple spatial arrangement of solids.

  8. Activity of catalytic silver nanoparticles modulated by capping agent hydrophobicity.

    PubMed

    Janani, Seralathan; Stevenson, Priscilla; Veerappan, Anbazhagan

    2014-05-01

    In this paper, a facile in situ method is reported for the preparation of catalytic silver nanoparticles (AgNPs) using N-acyl tyramine (NATA) with variable hydrophobic acyl length. Scanning electron microscopic analysis shows that NATA exists initially as larger aggregates in alkaline aqueous solution. The addition of AgNO3 dissociates these larger aggregate and subsequently promotes the formation of self-assembled NATA and AgNPs. Characterization of AgNPs using UV-vis spectroscopy, scanning electron microscope and transmission electron microscope revealed that the hydrophobic acyl chain length of NATA does not influence the particle size, shape and morphology. All NATA-AgNPs yielded relatively identical values in full width at half-maximum (FWHM) analysis, indicating that the AgNPs prepared with NATA are relatively polydispersed at all tested acyl chain lengths. These nanoparticles are able to efficiently catalyze the reduction of 4-nitro phenol to 4-amino phenol, 2-nitro aniline to 1,2-diamino benzene, 2,4,6-trinitro phenol to 2,4,6-triamino phenol by NaBH4 in an aqueous environment. The reduction reaction rate is determined to be pseudo-first order and the apparent rate constant is linearly dependent on the hydrophobic acyl chain length of the NATA. All reaction kinetics presented an induction period, which is dependent on the N-acyl chain length, indicating that the hydrophobic effects play a critical role in bringing the substrate to the metal nanoparticle surface to induce the catalytic reaction. In this study, however, the five catalytic systems have similar size and polydispersity, differing only in terms of capping agent hydrophobicity, and shows different catalytic activity with respect to the alkyl chain length of the capping agent. As discussed, the ability to modulate the metal nanoparticles catalytic property, by modifying the capping agent hydrophobicity represents a promising future for developing an efficient nanocatalyst without altering the size

  9. Thermodynamics of solvophobic interaction between hydrophobic surfaces in ethanol.

    PubMed

    Li, Zuoli; Yoon, Roe-Hoan

    2014-11-11

    AFM surface force measurements were conducted in pure ethanol using gold surfaces hydrophobized with alkanethiols (CnSH) with n = 2-16. The forces measured at 5-35 °C were net attractive and became stronger with decreasing temperature and with increasing surface hydrophobicity. Thermodynamic analysis of the experimental data showed that the macroscopic solvophobic interactions were enthalpic but exhibited significant enthalpy-entropy compensations. The enthalpy decreases may represent the energy gained in forming H-bonded structures of ethanol, while the entropy decreases represent the thermodynamic costs for building structures. These results are consistent with those obtained previously in pure water.

  10. Intercalation of small hydrophobic molecules in lipid bilayers containing cholesterol

    SciTech Connect

    Worcester, D.L.; Hamacher, K.; Kaiser, H.; Kulasekere, R.; Torbet, J.

    1994-12-31

    Partitioning of small hydrophobic molecules into lipid bilayers containing cholesterol has been studied using the 2XC diffractometer at the University of Missouri Research Reactor. Locations of the compounds were determined by Fourier difference methods with data from both deuterated and undeuterated compounds introduced into the bilayers from the vapor phase. Data fitting procedures were developed for determining how well the compounds were localized. The compounds were found to be localized in a narrow region at the center of the hydrophobic layer, between the two halves of the bilayer. The structures are therefore intercalated structures with the long axis of the molecules in the plane of the bilayer.

  11. Sticking polydisperse hydrophobic magnetite nanoparticles to lipid membranes.

    PubMed

    Paulus, Michael; Degen, Patrick; Brenner, Thorsten; Tiemeyer, Sebastian; Struth, Bernd; Tolan, Metin; Rehage, Heinz

    2010-10-19

    The formation of a layer of hydrophobic magnetite (Fe(3)O(4)) nanoparticles stabilized by lauric acid is analyzed by in situ X-ray reflectivity measurements. The data analysis shows that the nanoparticles partially disperse their hydrophobic coating. Consequently, a Langmuir layer was formed by lauric acid molecules that can be compressed into an untilted condensed phase. A majority of the nanoparticles are attached to the Langmuir film integrating lauric acid residue on their surface into the Langmuir film. Hence, the particles at the liquid-gas interface can be identified as so-called Janus beads, which are amphiphilic solids having two sides with different functionality.

  12. Wetting in hydrophobic nanochannels: a challenge of classical capillarity.

    PubMed

    Helmy, Roy; Kazakevich, Yuri; Ni, Chaoying; Fadeev, Alexander Y

    2005-09-14

    We report an investigation of the water-hydrophobic interface in well-defined nanochannels (R approximately 2-4 nm). Wetting in these systems cannot be described by classical (macroscopic) capillary theory: (1) water occupies only a fraction ( approximately 60%) of the pore volume, and (2) the capillary pressures are approximately 60-90% greater than predicted by the Laplace equation. The results suggest the presence of approximately 0.6 nm layer of low-density fluid (vapor) separating water from the hydrophobic solid.

  13. Global thermodynamics of hydrophobic cavitation, dewetting, and hydration

    NASA Astrophysics Data System (ADS)

    Ben-Amotz, Dor

    2005-11-01

    Pure water experimental and simulation results are combined to predict the thermodynamics of cavity formation, spanning atomic to macroscopic length scales, over the entire ambient liquid temperature range. The resulting cavity equation of state is used to quantify dewetting excess contributions to cavity formation thermodynamics and construct a thermodynamic perturbation theory of hydrophobic hydration. Predictions are compared with large cavity simulations and experimental rare-gas hydration thermodynamics data (for He, Ne, Ar, Kr, Xe, and Rn). Key findings include the strong temperature dependence of the critical length scale for hydrophobic dewetting and the evaluation of fundamental solute-solvent interaction contributions to rare-gas hydration chemical potentials.

  14. Hydrophobically modified nanoparticle suspensions to enhance water evaporation rate

    NASA Astrophysics Data System (ADS)

    Huang, Zhi; Li, Xiaoying; Yuan, Hao; Feng, Yanhui; Zhang, Xinxin

    2016-10-01

    The evaporation rates of water can be enhanced by adding the hydrophobically modified nanoparticles as a suspension. The magnitudes of enhancement are related to the diameter and mass concentration of nanoparticles. In particular, a 15% enhancement was achieved after adding the modified Al2O3 nanoparticle with a diameter of 13 nm and mass percentage of 0.02%. A theoretical model was established in order to estimate the evaporation rates of hydrophobic particle-based nanofluids. The obtained results indicate that the enhanced evaporation rates are attributed to the elevated saturated vapor pressures of the nanofluids. These results may have important applications for energy-efficient enhancement of water evaporation rates.

  15. The tyrosyl free radical in ribonucleotide reductase.

    PubMed Central

    Gräslund, A; Sahlin, M; Sjöberg, B M

    1985-01-01

    The enzyme, ribonucleotide reductase, catalyses the formation of deoxyribonucleotides from ribonucleotides, a reaction essential for DNA synthesis in all living cells. The Escherichia coli ribonucleotide reductase, which is the prototype of all known eukaryotic and virus-coded enzymes, consists of two nonidentical subunits, proteins B1 and B2. The B2 subunit contains an antiferromagnetically coupled pair of ferric ions and a stable tyrosyl free radical. EPR studies show that the tyrosyl radical, formed by loss of ferric ions and a stable tyrosyl free radical. EPR studies show that the tyrosyl radical, formed by loss of an electron, has its unpaired spin density delocalized in the aromatic ring of tyrosine. Effects of iron-radical interaction indicate a relatively close proximity between the iron center and the radical. The EPR signal of the radical can be studied directly in frozen packed cells of E. coli or mammalian origin, if the cells are made to overproduce ribonucleotide reductase. The hypothetic role of the tyrosyl free radical in the enzymatic reaction is not yet elucidated, except in the reaction with the inhibiting substrate analogue 2'-azido-CDP. In this case, the normal tyrosyl radical is destroyed with concomitant appearance of a 2'-azido-CDP-localized radical intermediate. Attempts at spin trapping of radical reaction intermediates have turned out negative. In E. coli the activity of ribonucleotide reductase may be regulated by enzymatic activities that interconvert a nonradical containing form and the fully active protein B2. In synchronized mammalian cells, however, the cell cycle variation of ribonucleotide reductase, studied by EPR, was shown to be due to de novo protein synthesis. Inhibitors of ribonucleotide reductase are of medical interest because of their ability to control DNA synthesis. One example is hydroxyurea, used in cancer therapy, which selectively destroys the tyrosyl free radical. PMID:3007085

  16. Quantitative determination of atmospheric hydroperoxyl radical

    DOEpatents

    Springston, Stephen R.; Lloyd, Judith; Zheng, Jun

    2007-10-23

    A method for the quantitative determination of atmospheric hydroperoxyl radical comprising: (a) contacting a liquid phase atmospheric sample with a chemiluminescent compound which luminesces on contact with hydroperoxyl radical; (b) determining luminescence intensity from the liquid phase atmospheric sample; and (c) comparing said luminescence intensity from the liquid phase atmospheric sample to a standard luminescence intensity for hydroperoxyl radical. An apparatus for automating the method is also included.

  17. Bioinspired terpene synthesis: a radical approach.

    PubMed

    Justicia, José; Álvarez de Cienfuegos, Luis; Campaña, Araceli G; Miguel, Delia; Jakoby, Verena; Gansäuer, Andreas; Cuerva, Juan M

    2011-07-01

    This tutorial review highlights the development of radical-based bioinspired synthesis of terpenes from the initial proposal to the development of modern catalytic methods for performing such processes. The power of the radical approach is demonstrated by the straightforward syntheses of many natural products from readily available starting materials. The efficiency of these processes nicely complements the described cationic polyolefin cyclisations and even suggests that modern radical methods provide means to improve upon nature's synthetic pathways.

  18. Formation of free radicals during phacoemulsification.

    PubMed

    Holst, A; Rolfsen, W; Svensson, B; Ollinger, K; Lundgren, B

    1993-04-01

    During phacoemulsification cavitation bubbles are formed. These bubbles are believed to be one source of damage to corneal endothelium seen after phacoemulsification. Free radicals are induced whenever cavitation bubbles implode. The aim of this study was to confirm the initiation of free radicals by phacoemulsification and to correlate the power of ultrasound in the phacoemulsification process to the amount of free radicals formed, using both in vitro and in vivo techniques. The formation of free radicals was determined by adding luminol to a buffer and measuring the chemoluminescence in vitro and in rabbit eyes (Lumacounter 2080 or a single-photon-counting apparatus) during phacoemulsification. The data obtained show that free radicals are formed during phacoemulsification and that the amount of free radicals correlates with the power of ultrasound. Furthermore, the radical formation could be inhibited by the radical scavengers SOD, Healon and Healon GV. These results were achieved both in vitro in the test tube and in vivo in rabbit eyes. By showing that the addition of SOD to the irrigation buffer during phacoemulsification decreases the corneal endothelial cell damage, we show that free radicals could have a role in postoperative complications seen clinically.

  19. Dynamics of Radical-Mediated Enzyme Catalyses

    NASA Astrophysics Data System (ADS)

    Warncke, Kurt

    1997-11-01

    An emergent class of enzymes harnesses the extreme reactivity of electron-deficient free radical species to perform some of the most difficult reactions in biology. The regio- and stereo-selectivity achieved by these enzymes defies long-held ideas that radical reactions are non-specific. The common primary step in these catalyses is metal- or metallocenter-assisted generation of an electron-deficient organic "initiator radical". The initiator radical abstracts a hydrogen atom from the substrate, opening a new reaction channel for rearrangement to the product. Our aim is to elucidate the detailed molecular mechanisms of the radical pair separation and radical rearrangement steps. Radical pair separation and substrate radical rearrangement are tracked by using time-resolved (10-7 to 10-3 s) techniques of pulsed-electron paramagnetic resonance spectroscopy (FT-EPR, ESEEM). Synchronous time-evolution of the reactions is attained by triggering with a visible laser pulse. Transient non-Boltzmann population of the states of the spin-coupled systems, and resultant electron spin polarization, facilitates study at or near room temperature under conditions where the enzymes are operative. The systems examined include ethanolamine deaminase, a vitamin B12 coenzyme-dependent enzyme, ribonucleotide reductase and photosynthetic reaction centers. The electronic and nuclear structural and kinetic information obtained from the pulsed-EPR studies is used to address how the initiator radicals are stabilized against deleterious recombination with the metal, and to distinguish the participation of concerted versus sequential rearrangement pathways.

  20. Surfactant Facilitated Spreading of Aqueous Drops on Hydrophobic Surfaces

    NASA Technical Reports Server (NTRS)

    Kumar, Nitin; Couzis, Alex; Maldareili, Charles; Singh, Bhim (Technical Monitor)

    2001-01-01

    Microgravity technologies often require aqueous phases to spread over nonwetting hydrophobic solid surfaces. Surfactants facilitate the wetting of water on hydrophobic surfaces by adsorbing on the water/air and hydrophobic solid/water interfaces and lowering the surface tensions of these interfaces. The tension reductions decrease the contact angle, which increases the equilibrium wetted area. Hydrocarbon surfactants; (i.e., amphiphiles with a hydrophobic moiety consisting of an extended chain of (aliphatic) methylene -CH2- groups attached to a large polar group to give aqueous solubility) are capable of reducing the contact angles on surfaces which are not very hydrophobic, but do not reduce significantly the contact angles of the very hydrophobic surfaces such as parafilm, polyethylene or self assembled monolayers. Trisiloxane surfactants (amphiphiles with a hydrophobe consisting of methyl groups linked to a trisiloxane backbone in the form of a disk ((CH3)3-Si-O-Si-O-Si(CH3)3) and an extended ethoxylate (-(OCH2CH2)a-) polar group in the form of a chain with four or eight units) can significantly reduce the contact angle of water on a very hydrophobic surface and cause rapid and complete (or nearly complete) spreading (termed superspreading). The overall goal of the research described in this proposal is to establish and verify a theory for how trisiloxanes cause superspreading, and then use this knowledge as a guide to developing more general hydrocarbon based surfactant systems which superspread. We propose that the trisiloxane surfactants superspread because their structure allows them to strongly lower the high hydrophobic solid/aqueous tension when they adsorb to the solid surface. When the siloxane adsorbs, the hydrophobic disk parts of the molecule adsorb onto the surface removing the surface water. Since the cross-sectional area of the disk is larger than that of the extended ethoxylate chain, the disks can form a space-filling mat on the surface which

  1. Kinetics Studies of Radical-Radical Reactions: The NO2 + N2H3 System

    DTIC Science & Technology

    2013-10-01

    investigating the kinetics of this elementary reaction . 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES...Viewgraph 3. DATES COVERED (From - To) September 2013- October 2013 4. TITLE AND SUBTITLE Kinetics Studies of Radical-Radical Reactions (I): The NO2...characteristics in relevant operating environments. Here we report theoretical results obtained on the prototypical radical- radical reaction : NO2 + N2H3

  2. Students' Ideas and Radical Constructivism

    NASA Astrophysics Data System (ADS)

    Sánchez Gómez, Pedro J.

    2016-08-01

    In this article, I study, from the point of view of the analytic philosophy of mind, the compatibility of students' ideas studies (SIS) with radical constructivism (RC). I demonstrate that RC is based on a psychology of narrow mental states; that is, the idea that the mental content of an individual can be fully characterised without any reference external to her or him. I show that this fact imposes some severe restrictions to SIS to be incorporated into RC. In particular, I argue that only qualitative studies can comply with the requirement of narrowness. Nevertheless, I propose that quantitative works can be employed as sources of types in order to study token actual students. I use this type-token dichotomy to put forward an outline of a theory of the relation between school contents and mental contents. In this view, token mental contents regarding a given topic can be defined, and probed, only by resorting to typical school contents.

  3. Peroxy radical measurements with NCAR's chemical amplifier

    NASA Technical Reports Server (NTRS)

    Cantrell, Christopher; Shetter, Richard; Calvert, Jack G.

    1994-01-01

    The present NCAR instrument for HO2/RO2 measurements has been described previously. It is based on the reactions involving HO2, RO2, and HO radicals with CO and NO. Since (HO2) + (RO2) + (HO) is much greater than (HO) for most atmospheres, it is useful as a peroxy radical detector. Operation of the instrument depends on the creation of a chemical chain reaction which is initiated as HO2 and RO2 radicals in ambient air encounter added NO gas; this forms an NO2 molecule and an HO or RO radical: HO2(RO2) + NO yields HO(RO) + NO2. RO radicals react relatively efficiently with O2 to form an HO2 radical, and subsequently an HO-radical, by reaction with NO. CO gas added to the reaction chamber during part of the operating cycle, recycles the HO to HO2; HO + CO (+O2) yields HO2 + CO2. The reaction sequence may form several hundred NO2 molecules per HO2 (RO2) originally present, before chain termination occurs. The added CO is replaced by N2 addition periodically so that the chain reaction is suppressed, and a 'blank' signal resulting from NO2, O3 and possibly other NO2-forming species (non-chain processes) in ambient air is recorded. The difference between the signal with and without CO is proportional to the peroxy radical concentration. The NO2 produced is monitored using a sensitive luminol chemiluminescence detector system. In the NCAR instrument the length of the amplification chain is determined using a stable source of HO2 radicals (H2O2 thermal decomposition); the ratio of the signal seen with CO present to that with N2 present gives the sensitivity of the instrument to HO2 (molecules of NO2 formed/peroxy radical). The instrument is automated to carry out in hourly repeated cycles: (1) chain length determination; (2) NO2 calibration; and (3) linearity check on the response of signals. One minute averages of signals are normally recorded. The sensitivity of the instrument to detect peroxy radicals is in the pptv range. The present instrument has operated

  4. Fourier Transform Infrared Spectroscopy of Radicals

    NASA Astrophysics Data System (ADS)

    Rohrs, Henry William

    Radicals occur in many areas of chemistry as they are intermediates in reactions. They arise in combustion processes and several atmospheric phenomena and they have been located in interstellar space. In order to elucidate these areas of chemistry it is important to understand radicals. This is no easy task as these species are short -lived. This work focuses on determining the structure and bonding of these species using experimental measurements. Since it is specifically aimed at gas phase radicals, spectroscopy is the tool of choice for probing the radicals. This work developed a general technique for taking the rotation-vibration spectra of jet-cooled radicals. The work was based in the infrared since the desired structural information can be obtained in this region of the spectrum. The jet-cooling simplifies the enormous task of spectral assignment. A BOMEM FTIR was optically coupled to a supersonic expansion of radicals streaming from a homemade silicon carbide pyrolysis nozzle. This nozzle was heated to wall temperatures of 1500 K. A suitable organic precursor was entrained in an inert carrier gas, usually helium. Conditions were adjusted such that this precursor was nearly completely decomposed to produce high number densities of the radical of choice. The gas flows were adjusted such that the time for recombination and other radical destroying reactions were minimized. The first radical species observed was nitric oxide, NO, made from the pyrolysis of alkyl nitrites. Spectra with rotational temperatures from 20 K to 80 K were observed. This proved the viability of the method. It also demonstrated that fluid dynamics modeling and a separate photoionization mass spectrometry experiment would be invaluable aids in maximizing radical concentrations since the best chance of recording the spectra is when the most radicals are present.

  5. Case study of hydrogen bonding in a hydrophobic cavity.

    PubMed

    Chen, Yi-Chen; Cheng, Chao-Sheng; Tjong, Siu-Cin; Yin, Hsien-Sheng; Sue, Shih-Che

    2014-12-18

    Protein internal hydrogen bonds and hydrophobicity determine protein folding and structure stabilization, and the introduction of a hydrogen bond has been believed to represent a better interaction for consolidating protein structure. We observed an alternative example for chicken IL-1β. The native IL-1β contains a hydrogen bond between the Y157 side-chain OηH and I133 backbone CO, whereby the substitution from Tyr to Phe abolishes the connection and the mutant without the hydrogen bond is more stable. An attempt to explain the energetic view of the presence of the hydrogen bond fails when only considering the nearly identical X-ray structures. Here, we resolve the mechanism by monitoring the protein backbone dynamics and interior hydrogen bond network. IL-1β contains a hydrophobic cavity in the protein interior, and Y157 is one of the surrounding residues. The Y157 OηH group introduces an unfavorable energy in the hydrophobic cavity, therefore sequestering itself by forming a hydrogen bond with the proximate residue I133. The hydrogen bonding confines Y157 orientation but exerts a force to disrupt the hydrogen bond network surrounding the cavity. The effect propagates over the entire protein and reduces the stability, as reflected in the protein backbone dynamics observed by an NMR hydrogen-deuterium (H/D) exchange experiment. We describe the particular case in which a hydrogen bond does not necessarily confer enhanced protein stability while the disruption of hydrophobicity must be integrally considered.

  6. Controlled effect of ultrasonic cavitation on hydrophobic/hydrophilic surfaces.

    PubMed

    Belova, Valentina; Gorin, Dmitry A; Shchukin, Dmitry G; Möhwald, Helmuth

    2011-02-01

    Controlling cavitation at the solid surface is of increasing interest, as it plays a major role in many physical and chemical processes related to the modification of solid surfaces and formation of multicomponent nanoparticles. Here, we show a selective control of ultrasonic cavitation on metal surfaces with different hydrophobicity. By applying a microcontact printing technique we successfully formed hydrophobic/hydrophilic alternating well-defined microstructures on aluminium surfaces. Fabrication of patterned surfaces provides the unique opportunity to verify a model of heterogeneous nucleation of cavitation bubbles near the solid/water interface by varying the wettability of the surface, temperature and ultrasonic power. At the initial stage of sonication (up to 30 min), microjets and shock waves resulting from the collapsing bubbles preferably impact the hydrophobic surface, whereas the hydrophilic areas of the patterned Al remain unchanged. Longer sonication periods affect both surfaces. These findings confirm the expectation that higher contact angle causes a lower energy barrier, thus cavitation dominates at the hydrophobic surfaces. Experimental results are in good agreement with expectations from nucleation theory. This paper illustrates a new approach to ultrasound induced modification of solid surfaces resulting in the formation of foam-structured metal surfaces.

  7. Hydrophobic and Oleophobic Fluoroalkyl Functionalized Silsesquioxane Nanostructures (Preprint)

    DTIC Science & Technology

    2007-01-25

    framework have received much interest as robust nanoscale building blocks for the development of high performance materials . Notable applications...oxygen core framework have received much interest as robust nanoscale building blocks for the development of high performance materials . Notable...From - To) 25-01-2007 Journal Article 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Hydrophobic and Oleophobic Fluoroalkyl Functionalized

  8. Biochemical characterization of the small hydrophobic protein of avian metapneumovirus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Avian metapneumovirus (aMPV) is a paramyxovirus that has three membrane-associate proteins: glycoprotein (G), fusion (F), and small hydrophobic (SH) proteins. Among them, the SH protein is a small type II integral membrane protein that is incorporated into virions and is only present in certain para...

  9. Anionic and cationic Hofmeister effects on hydrophobic and hydrophilic surfaces.

    PubMed

    Schwierz, Nadine; Horinek, Dominik; Netz, Roland R

    2013-02-26

    Using a two-step modeling approach, we address the full spectrum of direct, reversed, and altered ionic sequences as the charge of the ion, the charge of the surface, and the surface polarity are varied. From solvent-explicit molecular dynamics simulations, we extract single-ion surface interaction potentials for halide and alkali ions at hydrophilic and hydrophobic surfaces. These are used within Poisson-Boltzmann theory to calculate ion density and electrostatic potential distributions at mixed polar/unpolar surfaces for varying surface charge. The resulting interfacial tension increments agree quantitatively with experimental data and capture the Hofmeister series, especially the anomaly of lithium, which is difficult to obtain using continuum theory. Phase diagrams that feature different Hofmeister series as a function of surface charge, salt concentration, and surface polarity are constructed from the long-range force between two surfaces interacting across electrolyte solutions. Large anions such as iodide have a high hydrophobic surface affinity and increase the effective charge magnitude on negatively charged unpolar surfaces. Large cations such as cesium also have a large hydrophobic surface affinity and thereby compensate an external negative charge surface charge most efficiently, which explains the well-known asymmetry between cations and anions. On the hydrophilic surface, the size-dependence of the ion surface affinity is reversed, explaining the Hofmeister series reversal when comparing hydrophobic with hydrophilic surfaces.

  10. Flexible starch-polyurethane films: Physiochemical characteristics and hydrophobicity.

    PubMed

    Tai, N L; Adhikari, Raju; Shanks, Robert; Adhikari, Benu

    2017-05-01

    Starch-polyurethane (PU) composite films with improved mechanical and hydrophobic properties were developed in this work. A simple and effective microwave-aided starch gelatinisation instrument was used to prepare glycerol plasticized high amylose starch (HAGS) material. Polyethylene glycol-isocyanate (PEG-iso) linker was prepared by reacting PEG 1000 with hexamethylene diisocyanate (HMDI). PEG-iso linker was then grafted into HAGS forming three dimensional urethane networks (PEG-PU). HAGS-PEG-PU composite blends were prepared and dried at ambient temperature to obtain HAGS-PEG-PU films. The mechanical properties and hydrophobicity (as contact angle, CA) of the HAGS-PEG-PU films were measured and analysed. Fourier transform infrared spectroscopy showed good grafting of PEG-iso into starch structure. Increase of PEG-iso concentration up to 20% (w/w) improved the molecular mixing and interpenetration between the starch and PEG-PU. The HAGS-PEG-PU films had improved hydrophobicity as indicated by CA values ranging from 51 to 110°and very high flexibility as evidenced from elongation at break (εB) values from 17 to 1000%. The HAGS-PEG-PU film formulation containing 20% (w/w) PEG-iso provided the best flexibility (εB>1000%) and hydrophobicity (CA>110°).

  11. The Hydrophobic Effect in Solute Partitioning and Interfacial Tension

    NASA Astrophysics Data System (ADS)

    Jackson, Meyer B.

    2016-01-01

    Studies of the partitioning of hydrophobic solutes between water and nonpolar solvents provide estimates for the energy cost of creating hydrophobic-water contacts. This energy is a factor of three lower than the work of adhesion derived from interfacial tension measurements. This discrepancy noted by Tanford in 1979 is widely viewed as a serious challenge to our understanding of hydrophobic interactions. However, the interfacial energy of a water-alkane interface depends on chain length. A simple analysis of published data shows that the loss of rotational freedom of an alkane chain at an interface accounts quantitatively for the length-dependent contribution to interfacial tension, leaving a length-independent contribution very close to the free energy of transfer per unit of solvent accessible surface area. This analysis thus clarifies the discrepancy between the thermodynamic and interfacial tension measurements of hydrophobic interaction energy. Alkanes do not loose rotational freedom when transferred between two different liquid phases but they do at an interface. This reconciles the difference between microscopic and macroscopic measurements. Like the partitioning free energy, the work of adhesion also has a large entropy and small enthalpy at 20 oC.

  12. Nanocarriers from GRAS Zein Proteins to Encapsulate Hydrophobic Actives.

    PubMed

    Weissmueller, Nikolas T; Lu, Hoang D; Hurley, Amanda; Prud'homme, Robert K

    2016-11-14

    One factor limiting the expansion of nanomedicines has been the high cost of the materials and processes required for their production. We present a continuous, scalable, low cost nanoencapsulation process, Flash Nanoprecipitation (FNP) that enables the production of nanocarriers (NCs) with a narrow size distribution using zein corn proteins. Zein is a low cost, GRAS protein (having the FDA status of "Generally Regarded as Safe") currently used in food applications, which acts as an effective encapsulant for hydrophobic compounds using FNP. The four-stream FNP configuration allows the encapsulation of very hydrophobic compounds in a way that is not possible with previous precipitation processes. We present the encapsulation of several model active compounds with as high as 45 wt % drug loading with respect to zein concentration into ∼100 nm nanocarriers. Three examples are presented: (1) the pro-drug antioxidant, vitamin E-acetate, (2) an anticholera quorum-sensing modulator CAI-1 ((S)-3-hydroxytridecan-4-one; CAI-1 that reduces Vibrio cholerae virulence by modulating cellular communication), and (3) hydrophobic fluorescent dyes with a range of hydrophobicities. The specific interaction between zein and the milk protein, sodium caseinate, provides stabilization of the NCs in PBS, LB medium, and in pH 2 solutions. The stability and size changes in the three media provide information on the mechanism of assembly of the zein/active/casein NC.

  13. Nanoparticle flotation collectors II: the role of nanoparticle hydrophobicity.

    PubMed

    Yang, Songtao; Pelton, Robert

    2011-09-20

    The ability of polystyrene nanoparticles to facilitate the froth flotation of glass beads was correlated to the hydrophobicity of the nanoparticles. Contact angle measurements were used to probe the hydrophobicity of hydrophilic glass surfaces decorated with hydrophobic nanoparticles. Both sessile water drop advancing angles, θ(a), and attached air bubble receding angle measurements, θ(r), were performed. For glass surfaces saturated with adsorbed nanoparticles, flotation recovery, a measure of flotation efficiency, increased with increasing values of each type of contact angle. As expected, the advancing water contact angle on nanoparticle-decorated, dry glass surfaces increased with surface coverage, the area fraction of glass covered with nanoparticles. However, the nanoparticles were far more effective at raising the contact angle than the Cassie-Baxter prediction, suggesting that with higher nanoparticle coverages the water did not completely wet the glass surfaces between the nanoparticles. A series of polystyrene nanoparticles was prepared to cover a range of surface energies. Water contact angle measurements, θ(np), on smooth polymer films formed from organic solutions of dissolved nanoparticles were used to rank the nanoparticles in terms of hydrophobicity. Glass spheres were saturated with adsorbed nanoparticles and were isolated by flotation. The minimum nanoparticle water contact angle to give high flotation recovery was in the range of 51° < θ(np(min)) ≤ 85°.

  14. Water uptake in biochars: The roles of porosity and hydrophobicity

    EPA Science Inventory

    We assessed the effects of porosity and hydrophobicity on water uptake by biochars. Biochars were produced from two feedstocks (hazelnut shells and Douglas fir chips) at three production temperatures (370 °C, 500 °C, and 620 °C). To distinguish the effects of porosity from the ...

  15. Role of the lid hydrophobicity pattern in pancreatic lipase activity.

    PubMed

    Thomas, Annick; Allouche, Maya; Basyn, Frédéric; Brasseur, Robert; Kerfelec, Brigitte

    2005-12-02

    Pancreatic lipase is a soluble globular protein that must undergo structural modifications before it can hydrolyze oil droplets coated with bile salts. The binding of colipase and movement of the lipase lid open access to the active site. Mechanisms triggering lid mobility are unclear. The *KNILSQIVDIDGI* fragment of the lid of the human pancreatic lipase is predicted by molecular modeling to be a tilted peptide. Tilted peptides are hydrophobicity motifs involved in membrane fusion and more globally in perturbations of hydrophobic/hydrophilic interfaces. Analysis of this lid fragment predicts no clear consensus of secondary structure that suggests that its structure is not strongly sequence determined and could vary with environment. Point mutations were designed to modify the hydrophobicity profile of the [240-252] fragment and their consequences on the lipase-mediated catalysis were tested. Two mutants, in which the tilted peptide motif was lost, also have poor activity on bile salt-coated oil droplets and cannot be reactivated by colipase. Conversely, one mutant in which a different tilted peptide is created retains colipase dependence. These results suggest that the tilted hydrophobicity pattern of the [240-252] fragment is neither important for colipase binding to lipase, nor for interfacial binding but is important to trigger the maximal catalytic efficiency of lipase in the presence of bile salt.

  16. Hydrophobic Flocculation of Galena Fines in Aqueous Suspensions.

    PubMed

    Song; Lopez-Valdivieso; Reyes-Bahena; Bermejo-Perez; Trass

    2000-07-15

    The hydrophobic flocculation of galena fines induced by potassium amyl xanthate (PAX) in aqueous suspensions has been studied using laser diffraction, electrophoretic light scattering, contact angle, and microflotation measurements. The measurements were performed on <2 µm, 2-5 µm, 5-10 µm, and <30 µm size galena by varying several parameters, including PAX concentration, pH, original particle size, kerosene concentration, and suspension stirring. The experimental results have demonstrated that the hydrophobic flocculation was closely correlated with the particle hydrophobicity, but was not lowered upon increasing the particle surface charges due to PAX adsorption, which is contrary to the DLVO theory. This flocculation has been observed to increase with a reduction of the original particle size and an increase in kerosene concentration, and to require sufficient stirring strength and magnitudes of kinetic energy input to achieve the maximum aggregation degree. From the microflotation results, it has been found that the flotation response of galena fines is markedly improved due to the formation of hydrophobic flocs, suggesting that floc flotation is a promising means to recover galena in the fine size range. Copyright 2000 Academic Press.

  17. Use and application of hydrophobic interaction chromatography for protein purification.

    PubMed

    McCue, Justin T

    2014-01-01

    The objective of this section is to provide the reader with guidelines and background on the use and experimental application of Hydrophobic Interaction chromatography (HIC) for the purification of proteins. The section will give step by step instructions on how to use HIC in the laboratory to purify proteins. General guidelines and relevant background information is also provided.

  18. A comprehensive study to protein retention in hydrophobic interaction chromatography.

    PubMed

    Baca, Martyna; De Vos, Jelle; Bruylants, Gilles; Bartik, Kristin; Liu, Xiaodong; Cook, Ken; Eeltink, Sebastiaan

    2016-10-01

    The effect of different kosmotropic/chaotropic salt systems on retention characteristics of intact proteins has been examined in hydrophobic interaction chromatography (HIC). The performance was assessed using different column chemistries, i.e., polyalkylamide, alkylamine incorporating hydrophobic moieties, and a butyl chemistry. Selectivity in HIC is mainly governed by the salt concentration and by the molal surface tension increment of the salt. Typically, a linear relationship between the natural logarithm of the retention factor and the salt concentration is obtained. Using a 250mm long column packed with 5μm polyalkylamide functionalized silica particles and applying a 30min linear salt gradient, a peak capacity of 78 was achieved, allowing the baseline separation of seven intact proteins. The hydrophobicity index appeared to be a good indicator to predict the elution order of intact proteins in HIC mode. Furthermore, the effect of adding additives in the mobile phase, such as calcium chloride (stabilizing the 3D conformation of α-lactalbumin) and isopropanol, on retention properties has been assessed. Results indicate that HIC retention is also governed by conformational in the proteins which affect the number of accessible hydrophobic moieties.

  19. Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP).

    PubMed

    Lu, Chunliang; Urban, Marek W

    2016-04-13

    Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (>10(6) g/mol) molecular weight pDMAEMA-b-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli.

  20. Hydroxyl radical reaction with trans-resveratrol: initial carbon radical adduct formation followed by rearrangement to phenoxyl radical.

    PubMed

    Li, Dan-Dan; Han, Rui-Min; Liang, Ran; Chen, Chang-Hui; Lai, Wenzhen; Zhang, Jian-Ping; Skibsted, Leif H

    2012-06-21

    In the reaction between trans-resveratrol (resveratrol) and the hydroxyl radical, kinetic product control leads to a short-lived hydroxyl radical adduct with an absorption maximum at 420 nm and a lifetime of 0.21 ± 0.01 μs (anaerobic acetonitrile at 25 °C) as shown by laser flash photolysis using N-hydroxypyridine-2(1H)-thione (N-HPT) as a "photo-Fenton" reagent. The transient spectra of the radical adduct are in agreement with density functional theory (DFT) calculations showing an absorption maximum at 442 or 422 nm for C2 and C6 hydroxyl adducts, respectively, and showing the lowest energy for the transition state leading to the C2 adduct compared to other radical products. From this initial product, the relative long-lived 4'-phenoxyl radical of resveratrol (τ = 9.9 ± 0.9 μs) with an absorption maximum at 390 nm is formed in a process with a time constant (τ = 0.21 ± 0.01 μs) similar to the decay constant for the C2 hydroxyl adduct (or a C2/C6 hydroxyl adduct mixture) and in agreement with thermodynamics identifying this product as the most stable resveratrol radical. The hydroxyl radical adduct to phenoxyl radical conversion with concomitant water dissociation has a rate constant of 5 × 10(6) s(-1) and may occur by intramolecular hydrogen atom transfer or by stepwise proton-assisted electron transfer. Photolysis of N-HPT also leads to a thiyl radical which adds to resveratrol in a parallel reaction forming a sulfur radical adduct with a lifetime of 0.28 ± 0.04 μs and an absorption maximum at 483 nm.

  1. How water meets a hydrophobic surface: Reluctantly and with flucuations

    NASA Astrophysics Data System (ADS)

    Poynor Torigoe, Adele Nichole

    By definition hydrophobic substances hate water. Water placed on a hydrophobic surface will form a drop in order to minimize its contact area. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low density region forms near the surface. This depleted region would have implications in such diverse areas as colloidal self-assembly, and the boundary conditions of fluid flow. However, the literature still remains divided as to whether or not such a depleted region exists. To investigate the existence of this layer, we have employed three surface-sensitive techniques, time-resolved phase-modulated ellipsometry, surface plasmon resonance, and X-ray reflectivity. Both ellipsometry and X-ray reflectivity provide strong evidence for the low-density layer and illuminate unexpected temporal behavior. Using all three techniques, we found surprising fluctuations at the interface with a non-Gaussian distribution and a single characteristic time on the order of tenths of seconds. This information supports the idea that the boundary fluctuates with something akin to capillary waves. We have also investigated the dependence of the static and dynamic properties of the hydrophobic/water interface on variables such as temperature, contact angle, pH, dissolved gasses, and sample quality, among others, in a hope to discover the root of the controversy in the literature. We found that the depletion layer is highly dependent on temperature, contact angle and sample quality. This dependence might explain some of the discrepancies in the literature as different groups often use hydrophobic surfaces with different properties.

  2. Hydrophobic Agglomeration of Mineral Fines in Aqueous Suspensions and its Application in Flotation: a Review

    NASA Astrophysics Data System (ADS)

    Yang, Bingqiao; Song, Shaoxian

    2014-05-01

    Hydrophobic agglomeration is originated from the hydrophobic attraction between particles, which is essentially different from electrolyte coagulation and polymer flocculation. It is applied to mineral processing in floc-flotation process to improve the recovery of mineral fines. In this paper, the applications of this phenomenon in mineral fines were summarized, including the origin of hydrophobic agglomeration, the main factors affect hydrophobic agglomeration (particle hydrophobicity, shear rate and duration, nonpolar oil and tank geometry), as well as hydrophobic agglomeration based separation processes (carrier flotation and floc-flotation).

  3. Magnitude and spatial orientation of the hydrophobic moments of multi-domain proteins.

    PubMed

    Zhou, Ruhong; Royyuru, Ajay; Athma, Prasanna; Suits, Frank

    2006-01-01

    The distributions of residue hydrophobicity for individual domains as well as for the aggregates of domains on a single chain have been found to exhibit well-defined second-order hydrophobic moment profiles. This indicates that most of the domains do fold into a stable entity with a core composed predominantly of hydrophobic residues as well as a prevalence of hydrophobic residues at the interface between domains. A simple scoring function based upon the relative hydrophobic moment dipole orientations shows that 80% of the dipoles of adjacent domains point to each other, highlighting hydrophobic residue prevalence at the domain interfaces.

  4. Alex Bloom, Pioneer of Radical State Education

    ERIC Educational Resources Information Center

    Fielding, Michael

    2005-01-01

    Alex Bloom is one of the greatest figures of radical state education in England. His approach to "personalised learning" and the development of a negotiated curriculum was immeasurably more profound and more inspiring than anything to emerge thus far from the current DfES. His approach to student voice was much more radical than anything…

  5. Ideals Adrift: An Educational Approach to Radicalization

    ERIC Educational Resources Information Center

    van San, Marion; Sieckelinck, Stijn; de Winter, Micha

    2013-01-01

    These days, the radicalization of young people is above all viewed as a security risk. Almost all research into this phenomenon has been carried out from a legal, criminological or socio-psychological perspective with a focus on detecting and containing the risks posed by radicalization. In the light of the political developments since September…

  6. THE RADICAL OF A JORDAN ALGEBRA

    PubMed Central

    McCrimmon, Kevin

    1969-01-01

    In this paper we define a Jacobson radical for Jordan algebras analogous to that for associative algebras and show that it enjoys many of the properties of the associative radical. We then relate the corresponding notion of “semisimplicity” to the previously defined notion of “nondegeneracy” (Jacobson, N., these Proceedings, 55, 243-251 (1966)). PMID:16591736

  7. Modified Pfannenstiel approach for radical retropubic prostatectomy.

    PubMed

    Manoharan, M; Gomez, Pablo; Sved, Paul; Soloway, Mark S

    2004-08-01

    Radical retropubic prostatectomy is traditionally performed using a vertical midline incision and occasionally using a transverse Pfannenstiel incision. We describe a technique for performing radical retropubic prostatectomy using a modified Pfannenstiel approach. This involves a Y incision of the rectus sheath, instead of a pure transverse incision, and provides both excellent exposure and better cosmetic results.

  8. Victimology: A Consideration of the Radical Critique.

    ERIC Educational Resources Information Center

    Friedrichs, David O.

    1983-01-01

    Discusses the emergence of a new radical model in criminology and a new subdisciplinary area of concern, victimology, with roots in Marx and Engels' original formulations. Argues that the radical understanding of victimization provides an important corrective to mainstream approaches and broadens the focus of the concept of victimization. (JAC)

  9. Free Radical Mechanisms in Autoxidation Processes.

    ERIC Educational Resources Information Center

    Simic, Michael G.

    1981-01-01

    Discusses the use of steady-state radiation chemistry and pulse radiolysis for the generation of initial free radicals and formation of peroxy radicals in the autoxidation process. Provides information regarding the autoxidation process. Defines autoxidation reactions and antioxidant action. (CS)

  10. Organic chemistry: A radical step forward

    NASA Astrophysics Data System (ADS)

    Zhang, Wenhao; Li, Ang

    2017-02-01

    Free radicals are notorious for unselective coupling reactions; however, the coupling of free radicals generated from acyl tellurides has now been shown to form C-C bonds with remarkable fidelity, which enables easy one-step assembly of densely oxygenated natural product motifs.

  11. Radical Behaviorism and Buddhism: Complementarities and Conflicts

    ERIC Educational Resources Information Center

    Diller, James W.; Lattal, Kennon A.

    2008-01-01

    Comparisons have been made between Buddhism and the philosophy of science in general, but there have been only a few attempts to draw comparisons directly with the philosophy of radical behaviorism. The present review therefore considers heretofore unconsidered points of comparison between Buddhism and radical behaviorism in terms of their…

  12. Measurement of atmospheric radicals by chemical amplification

    NASA Astrophysics Data System (ADS)

    Arias, Maria Corina

    1998-11-01

    In this work, atmospheric radicals were measured using the chemical amplification technique. To calibrate the chemical amplifier, an UV water photolysis radical source was built and tested. This source proved to be reliable and portable, and capable of delivering radical concentrations within the range of values found in the troposphere. We tested the performance of our instrument at the Peroxy Radical InterComparison Exercise II (PRICE II). In this intercomparison seven chemical amplifiers participated measuring several HO2 and CH3O2 concentrations. Results from this campaign indicate that all of the chemical amplifiers are equally capable of measuring HO2 and CH3O2 radicals from two different radical sources (ICG-HO2 source and UEA- CH3O2 source). The average response towards the ICG and UEA sources were 70% and 45%, respectively. Losses in the delivery system are thought to be responsible for these low responses. Radical measurements were taken at 4 contrasting sites: Atlantic '96 (clean continental), SONTOS '92 and '93 (rural), Calabozo '93 (tropical clean continental), and Pacific '93 (predominantly urban), where maximum ROx concentrations ranged from 17 to 52 pptv. These values are consistent with those found in the literature for similar regions. The measured radical concentrations reflect the interaction between the main production and loss processes at the different sites, as for example ozone photolysis and HNO3 formation. At Calabozo, the combination of moderate O3, low NOx and small Zenith angles resulted in the highest ROx measured. At the Pacific '93 site, O3 is higher, but NOx concentrations are also very high, enhancing the radical loss processes, and explaining the moderate radical concentrations observed. At Atlantic '96 the very low NOx concentration might account for the radical concentrations observed, even in the presence of low O3 concentrations. At SONTOS, the highest ozone concentrations were observed, so we would expect the radical

  13. Partitioning MOF-5 into Confined and Hydrophobic Compartments for Carbon Capture under Humid Conditions.

    PubMed

    Ding, Nan; Li, Haiwei; Feng, Xiao; Wang, Qianyou; Wang, Shan; Ma, Li; Zhou, Junwen; Wang, Bo

    2016-08-17

    Metal-organic frameworks (MOFs), by virtue of their remarkable uptake capability, selectivity, and ease of regeneration, hold great promise for carbon capture from fossil fuel combustion. However, their stability toward moisture together with the competitive adsorption of water against CO2 drastically dampens their capacity and selectivity under real humid flue gas conditions. In this work, an effective strategy was developed to tackle the above obstacles by partitioning the channels of MOFs into confined, hydrophobic compartments by in situ polymerization of aromatic acetylenes. Specifically, polynaphthylene was formed via a radical reaction inside the channels of MOF-5 and served as partitions without altering the underlying structure of the framework. Compared with pristine MOF-5, the resultant material (PN@MOF-5) exhibits a doubled CO2 capacity (78 vs 38 cm(3)/g at 273 K and 1 bar), 23 times higher CO2/N2 selectivity (212 vs 9), and significantly improved moisture stability. The dynamic CO2 adsorption capacity can be largely maintained (>90%) under humid conditions during cycles. This strategy can be applied to other MOF materials and may shed light on the design of new MOF-polymer materials with tunable pore sizes and environments to promote their practical applications.

  14. Hydrophobic modification of polymethyl methacrylate as intraocular lenses material to improve the cytocompatibility.

    PubMed

    Wang, Bailiang; Lin, Quankui; Shen, Chenghui; Tang, Junmei; Han, Yuemei; Chen, Hao

    2014-10-01

    The development of posterior capsule opacification (PCO) after intraocular lenses (IOL) implantation for dealing with cataract is mainly due to the severe loss of the human lens epithelial cells (HLECs) during surgery contact. A novel poly (hedral oligomeric silsesquioxane-co-methyl methacrylate) copolymer (allyl POSS-PMMA) was synthesized by free radical polymerization method to promote the adhesion of HLECs. FT-IR and (1)H NMR measurements indicated the existence of POSS cage in the product, which demonstrated the successful synthesis of allyl POSS-PMMA copolymer. Effect of allyl POSS in the hybrids on crystal structure, surface wettability and morphology, optical transmission, thermodynamic properties and cytocompatibility was investigated in detail. X-ray diffraction peaks at 2θ∼11° and 12° indicated that POSS molecules had aggregated and crystallized. Thermogravimetric analysis-differential scanning calorimeter and optical transmission measurements confirmed that the allyl POSS-PMMA copolymer had high glass transition temperatures (more than 100°C) and good transparency. The hydrophilicity and morphology of PMMA and copolymers surfaces were characterized by static water contact angle and atomic force microscopy. The results revealed that the surface of the allyl POSS-PMMA copolymer displayed higher hydrophobicity and higher roughness than that of pure PMMA. The surface biocompatibility was evaluated by morphology and activity measurement with HLECs in vitro. The results verified that the surface of allyl POSS-PMMA copolymer films had more HLECs adhesion and better spreading morphology than that of PMMA film.

  15. Synchrotron threshold photoelectron photoion coincidence spectroscopy of radicals produced in a pyrolysis source: The methyl radical

    NASA Astrophysics Data System (ADS)

    Zhu, Yupeng; Wu, Xiangkun; Tang, Xiaofeng; Wen, Zuoying; Liu, Fuyi; Zhou, Xiaoguo; Zhang, Weijun

    2016-11-01

    We present here a flash pyrolysis source coupled with a threshold photoelectron photoion coincidence (TPEPICO) spectrometer and vacuum ultraviolet synchrotron radiation to investigate the spectroscopy and photochemistry of free radicals. The radicals are produced from pyrolysis in a heated silicon carbide tube, and the TPEPICO scheme provides a strategy to obtain pure spectra of the radicals without contamination from other byproducts. As a representative example, the methyl radical was studied, and its threshold photoelectron spectrum shows a series of umbrella vibrational transitions. The adiabatic ionization energy of the methyl radical was determined to be 9.84 ± 0.01 eV.

  16. Polymers based on stable phenoxyl radicals for the use in organic radical batteries.

    PubMed

    Jähnert, Thomas; Häupler, Bernhard; Janoschka, Tobias; Hager, Martin D; Schubert, Ulrich S

    2014-05-01

    Polymers with pendant phenoxyl radicals are synthesized and the electrochemical properties are investigated in detail. The monomers are polymerized using ring-opening metathesis polymerization (ROMP) or free-radical polymerization methods. The monomers and polymers, respectively, are oxidized to the radical either before or after the polymerization. These phenoxyl radicals containing polymers reveal a reversible redox behavior at a potential of -0.6 V (vs Ag/AgCl). Such materials can be used as anode-active material in organic radical batteries (ORBs).

  17. Flocculation, hydrophobic agglomeration and filtration of ultrafine coal

    NASA Astrophysics Data System (ADS)

    Yu, Zhimin

    In coal preparation plant circuits, fine coal particles are aggregated either by oil agglomeration or by flocculation. In a new hydrophobic agglomeration process, recently developed hydrophobic latices are utilized. While the selectivity of such aggregation processes determines the beneficiation results, the degree of aggregation has a strong effect on fine coal filtration. The aim of this research was to study the fundamentals and analyze the common grounds for these processes, including the potential effect of the coal surface properties. The selective flocculation tests, in which three types of coal, which differed widely in surface wettability, and three additives (hydrophobic latices, a semi-hydrophobic flocculant and a typical hydrophilic polyelectrolyte) were utilized, showed that coal wettability plays a very important role in selective flocculation. The abstraction of a hydrophobic latex on coal and silica revealed that the latex had a much higher affinity towards hydrophobic coal than to hydrophilic mineral matter. As a result, the UBC-1 hydrophobic latex flocculated only hydrophobic coal particles while the polyelectrolyte (PAM) flocculated all the tested coal samples and minerals, showing no selectivity in the fine coal beneficiation. The oil agglomeration was tested using kerosene emulsified with various surfactants (e.g. cationic, anionic and non-ionic). Surfactants enhance not only oil emulsification, hence reducing oil consumption (down to 0.25--0.5%), but also entirely change the electrokinetic properties of the droplets and affect the interaction energy between oil droplets and coal particles. Consequently, the results found in the course of the experimental work strongly indicate that even oxidized coals can be agglomerated if cationic surfactants are used to emulsify the oil. Oil agglomeration of the Ford-4 ultrafine coal showed that even at extremely low oil consumption (0.25 to 0.5%), a clean coal product with an ash content around 5% at over

  18. Purification and in vitro antioxidative effects of giant squid muscle peptides on free radical-mediated oxidative systems.

    PubMed

    Rajapakse, Niranjan; Mendis, Eresha; Byun, Hee-Guk; Kim, Se-Kwon

    2005-09-01

    Low molecular weight peptides obtained from ultrafiltration (UF) of giant squid (Dosidicus gigas) muscle protein were studied for their antioxidative effects in different in vitro oxidative systems. The most potent two peptides, Asn-Ala-Asp-Phe-Gly-Leu-Asn-Gly-Leu-Glu-Gly-Leu-Ala (1307 Da) and Asn-Gly-Leu-Glu-Gly-Leu-Lys (747 Da), exhibited their antioxidant potential to act as chain-breaking antioxidants by inhibiting radical-mediated peroxidation of linoleic acid, and their activities were closer to highly active synthetic antioxidant, butylated hydroxytoluene. Addition of these peptides could enhance the viability of cytotoxic embryonic lung fibroblasts significantly (P<.05) at a low concentration of 50 microg/ml, and it was presumed due to the suppression of radical-induced oxidation of membrane lipids. Electron spin trapping studies revealed that the peptides were potent scavengers of free radicals in the order of carbon-centered (IC(50) 396.04 and 304.67 microM), hydroxyl (IC(50) 497.32 and 428.54 microM) and superoxide radicals (IC(50) 669.34 and 573.83 microM). Even though the exact molecular mechanism for scavenging of free radicals was unclear, unusually high hydrophobic amino acid composition (more than 75%) of giant squid muscle peptides was presumed to be involved in the observed activities.

  19. Characteristics of Radical Reactions, Spin Rules, and a Suggestion for the Consistent Use of a Dot on Radical Species

    ERIC Educational Resources Information Center

    Wojnarovits, Laszlo

    2011-01-01

    In many chemical reactions, reactive radicals have been shown to be transient intermediates. The free radical character of a chemical species is often, but not always, indicated by adding a superscript dot to the chemical formula. A consistent use of this radical symbol on all species that have radical character is suggested. Free radicals have a…

  20. Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate

    SciTech Connect

    Guo, Q.X.; Qin, X.Z.; Wang, J.T.; Williams, F.

    1988-03-16

    The classical example of a neutral carbon-centered radical cyclization reaction is the regioselective 1,5-ring closure (exocyclization) of the 5-hexenyl radical to the cyclopentylcarbinyl radical. Here the authors report the title reaction, a comparable addition process whereby an ..cap alpha.., omega-diene radical cation reacts by endocyclization and hydrogen shift(s) to produce a cycloolefin radical cation.

  1. Halogenated silanes, radicals, and cations

    NASA Astrophysics Data System (ADS)

    Wang, Liming; He, Yi-Liang

    2008-09-01

    Quantum chemistry study has been carried out on the structure and energetics of halogenated silanes, radicals, and cations (SiHxXy0,+1, X = F, Cl, Br; x + y = 1-4). The geometries are optimized at B3LYP/6-31+G(2df,p) level. The adiabatic ionization energiess (IEas), relative energetics of cations, proton affinities (PAs) of silanes, and the enthalpies of formation are predicted using G3(CC) model chemistry. Non-classical ion complex structures are found for hydrogenated cations and transition states connecting classical and non-classical structures are also located. The most stable cations for silylene and silyl radicals have their classical divalent and trivalent structures, and those for silanes have non-classical structures except for SiH3Br+ and SiH2Br2+. The non-classical structures for halosilane cations imply difficulty in experimentally measurement of the adiabatic ionization energies using photoionization or photoelectron studies. For SiH3X, SiH2X2, and SiHX3, the G3(CC) adiabatic IEas to classical ionic structures closest to their neutrals agree better with the photoelectron spectroscopic measurements. The transition states between classical and non-classical structures also hamper the photoionization determination of the appearance energies for silylene cations from silanes. The G3(CC) results for SiHx0,+1 agree excellently with the photoionization mass spectrometric study, and the results for fluorinated and chlorinated species also agree with the previous theoretical predictions at correlation levels from BAC-MP4 to CCSD(T)/CBS. The predicted enthalpy differences between SiH2Cl+, SiHCl2+, and SiCl3+ are also in accordance with previous kinetics study. The G3(CC) results show large discrepancies to the collision-induced charge transfer and/or dissociation reactions involving SiFx+ and SiClx+ ions, for which the G3(CC) enthalpies of formation are also significantly differed from the previous theoretical predictions, especially on SiFx+ (x = 2-4). The G3

  2. Order and correlation contributions to the entropy of hydrophobic solvation

    NASA Astrophysics Data System (ADS)

    Liu, Maoyuan; Besford, Quinn Alexander; Mulvaney, Thomas; Gray-Weale, Angus

    2015-03-01

    The entropy of hydrophobic solvation has been explained as the result of ordered solvation structures, of hydrogen bonds, of the small size of the water molecule, of dispersion forces, and of solvent density fluctuations. We report a new approach to the calculation of the entropy of hydrophobic solvation, along with tests of and comparisons to several other methods. The methods are assessed in the light of the available thermodynamic and spectroscopic information on the effects of temperature on hydrophobic solvation. Five model hydrophobes in SPC/E water give benchmark solvation entropies via Widom's test-particle insertion method, and other methods and models are tested against these particle-insertion results. Entropies associated with distributions of tetrahedral order, of electric field, and of solvent dipole orientations are examined. We find these contributions are small compared to the benchmark particle-insertion entropy. Competitive with or better than other theories in accuracy, but with no free parameters, is the new estimate of the entropy contributed by correlations between dipole moments. Dipole correlations account for most of the hydrophobic solvation entropy for all models studied and capture the distinctive temperature dependence seen in thermodynamic and spectroscopic experiments. Entropies based on pair and many-body correlations in number density approach the correct magnitudes but fail to describe temperature and size dependences, respectively. Hydrogen-bond definitions and free energies that best reproduce entropies from simulations are reported, but it is difficult to choose one hydrogen bond model that fits a variety of experiments. The use of information theory, scaled-particle theory, and related methods is discussed briefly. Our results provide a test of the Frank-Evans hypothesis that the negative solvation entropy is due to structured water near the solute, complement the spectroscopic detection of that solvation structure by

  3. Order and correlation contributions to the entropy of hydrophobic solvation

    SciTech Connect

    Liu, Maoyuan; Besford, Quinn Alexander; Mulvaney, Thomas; Gray-Weale, Angus

    2015-03-21

    The entropy of hydrophobic solvation has been explained as the result of ordered solvation structures, of hydrogen bonds, of the small size of the water molecule, of dispersion forces, and of solvent density fluctuations. We report a new approach to the calculation of the entropy of hydrophobic solvation, along with tests of and comparisons to several other methods. The methods are assessed in the light of the available thermodynamic and spectroscopic information on the effects of temperature on hydrophobic solvation. Five model hydrophobes in SPC/E water give benchmark solvation entropies via Widom’s test-particle insertion method, and other methods and models are tested against these particle-insertion results. Entropies associated with distributions of tetrahedral order, of electric field, and of solvent dipole orientations are examined. We find these contributions are small compared to the benchmark particle-insertion entropy. Competitive with or better than other theories in accuracy, but with no free parameters, is the new estimate of the entropy contributed by correlations between dipole moments. Dipole correlations account for most of the hydrophobic solvation entropy for all models studied and capture the distinctive temperature dependence seen in thermodynamic and spectroscopic experiments. Entropies based on pair and many-body correlations in number density approach the correct magnitudes but fail to describe temperature and size dependences, respectively. Hydrogen-bond definitions and free energies that best reproduce entropies from simulations are reported, but it is difficult to choose one hydrogen bond model that fits a variety of experiments. The use of information theory, scaled-particle theory, and related methods is discussed briefly. Our results provide a test of the Frank-Evans hypothesis that the negative solvation entropy is due to structured water near the solute, complement the spectroscopic detection of that solvation structure by

  4. Erectile preservation following radical prostatectomy

    PubMed Central

    Segal, Robert; Burnett, Arthur L.

    2011-01-01

    Prostate cancer is the most common cancer among men, representing approximately 25% of all new cancer diagnoses in the USA. For clinically localized prostate cancer, the gold standard for therapy remains radical prostatectomy. One of the main adverse effects of this procedure is erectile dysfunction, which can have a significant impact on the patient’s quality of life. There are several mechanisms of erectile dysfunction postprostatectomy, including arteriogenic, venogenic and neurogenic types, as well as the potentially heightened risk of postprostatectomy patients to develop Peyronie’s disease. The purpose of this review is to explain the various treatment options available, including phosphodiesterase type 5 inhibitors, intracavernosal injections, intraurethral alprostadil suppositories, vacuum erection devices, and penile prostheses. The role of these therapies in an erectile-dysfunction-treatment function, as well as in penile rehabilitation, will be discussed. Finally, a review of research on novel therapies will also be presented. A comprehensive literature review was performed using the PubMed database. Articles were chosen based on topical relevance and assessed for methodology and major findings. There are data to support the use of each of the therapeutic options in both treatment and rehabilitative roles. More study is needed, however, specifically in regard to penile rehabilitation, to confirm its benefits, as well as to determine optimal rehabilitation protocols. PMID:21789097

  5. Erectile preservation following radical prostatectomy.

    PubMed

    Segal, Robert; Burnett, Arthur L

    2011-02-01

    Prostate cancer is the most common cancer among men, representing approximately 25% of all new cancer diagnoses in the USA. For clinically localized prostate cancer, the gold standard for therapy remains radical prostatectomy. One of the main adverse effects of this procedure is erectile dysfunction, which can have a significant impact on the patient's quality of life. There are several mechanisms of erectile dysfunction postprostatectomy, including arteriogenic, venogenic and neurogenic types, as well as the potentially heightened risk of postprostatectomy patients to develop Peyronie's disease. The purpose of this review is to explain the various treatment options available, including phosphodiesterase type 5 inhibitors, intracavernosal injections, intraurethral alprostadil suppositories, vacuum erection devices, and penile prostheses. The role of these therapies in an erectile-dysfunction-treatment function, as well as in penile rehabilitation, will be discussed. Finally, a review of research on novel therapies will also be presented. A comprehensive literature review was performed using the PubMed database. Articles were chosen based on topical relevance and assessed for methodology and major findings. There are data to support the use of each of the therapeutic options in both treatment and rehabilitative roles. More study is needed, however, specifically in regard to penile rehabilitation, to confirm its benefits, as well as to determine optimal rehabilitation protocols.

  6. Kinetics of Propargyl Radical Dissociation.

    PubMed

    Klippenstein, Stephen J; Miller, James A; Jasper, Ahren W

    2015-07-16

    Due to the prominent role of the propargyl radical for hydrocarbon growth within combustion environments, it is important to understand the kinetics of its formation and loss. The ab initio transition state theory-based master equation method is used to obtain theoretical kinetic predictions for the temperature and pressure dependence of the thermal decomposition of propargyl, which may be its primary loss channel under some conditions. The potential energy surface for the decomposition of propargyl is first mapped at a high level of theory with a combination of coupled cluster and multireference perturbation calculations. Variational transition state theory is then used to predict the microcanonical rate coefficients, which are subsequently implemented within the multiple-well multiple-channel master equation. A variety of energy transfer parameters are considered, and the sensitivity of the thermal rate predictions to these parameters is explored. The predictions for the thermal decomposition rate coefficient are found to be in good agreement with the limited experimental data. Modified Arrhenius representations of the rate constants are reported for utility in combustion modeling.

  7. Consciousness: the radical plasticity thesis.

    PubMed

    Cleeremans, Axel

    2008-01-01

    In this chapter, I sketch a conceptual framework which takes it as a starting point that conscious and unconscious cognition are rooted in the same set of interacting learning mechanisms and representational systems. On this view, the extent to which a representation is conscious depends in a graded manner on properties such as its stability in time or its strength. Crucially, these properties are accrued as a result of learning, which is in turn viewed as a mandatory process that always accompanies information processing. From this perspective, consciousness is best characterized as involving (1) a graded continuum defined over "quality of representation", such that availability to consciousness and to cognitive control correlates with quality, and (2) the implication of systems of metarepresentations. A first implication of these ideas is that the main function of consciousness is to make flexible, adaptive control over behavior possible. A second, much more speculative implication, is that we learn to be conscious. This I call the "radical plasticity thesis"--the hypothesis that consciousness emerges in systems capable not only of learning about their environment, but also about their own internal representations of it.

  8. Involvement of free radicals in breast cancer.

    PubMed

    Ríos-Arrabal, Sandra; Artacho-Cordón, Francisco; León, Josefa; Román-Marinetto, Elisa; Del Mar Salinas-Asensio, María; Calvente, Irene; Núñez, Maria Isabel

    2013-08-27

    Researchers have recently shown an increased interest in free radicals and their role in the tumor microenvironment. Free radicals are molecules with high instability and reactivity due to the presence of an odd number of electrons in the outermost orbit of their atoms. Free radicals include reactive oxygen and nitrogen species, which are key players in the initiation and progression of tumor cells and enhance their metastatic potential. In fact, they are now considered a hallmark of cancer. However, both reactive species may contribute to improve the outcomes of radiotherapy in cancer patients. Besides, high levels of reactive oxygen species may be indicators of genotoxic damage in non-irradiated normal tissues. The purpose of this article is to review recent research on free radicals and carcinogenesis in order to understand the pathways that contribute to tumor malignancy. This review outlines the involvement of free radicals in relevant cellular events, including their effects on genetic instability through (growth factors and tumor suppressor genes, their enhancement of mitogenic signals, and their participation in cell remodeling, proliferation, senescence, apoptosis, and autophagy processes; the possible relationship between free radicals and inflammation is also explored. This knowledge is crucial for evaluating the relevance of free radicals as therapeutic targets in cancer.

  9. Magnetic fields, radicals and cellular activity.

    PubMed

    Montoya, Ryan D

    2017-01-01

    Some effects of low-intensity magnetic fields on the concentration of radicals and their influence on cellular functions are reviewed. These fields have been implicated as a potential modulator of radical recombination rates. Experimental evidence has revealed a tight coupling between cellular function and radical pair chemistry from signaling pathways to damaging oxidative processes. The effects of externally applied magnetic fields on biological systems have been extensively studied, and the observed effects lack sufficient mechanistic understanding. Radical pair chemistry offers a reasonable explanation for some of the molecular effects of low-intensity magnetic fields, and changes in radical concentrations have been observed to modulate specific cellular functions. Applied external magnetic fields have been shown to induce observable cellular changes such as both inhibiting and accelerating cell growth. These and other mechanisms, such as cell membrane potential modulation, are of great interest in cancer research due to the variations between healthy and deleterious cells. Radical concentrations demonstrate similar variations and are indicative of a possible causal relationship. Radicals, therefore, present a possible mechanism for the modulation of cellular functions such as growth or regression by means of applied external magnetic fields.

  10. Chromatographic hydrophobicity index: pH profile for polyprotic compounds.

    PubMed

    Fuguet, Elisabet; Ràfols, Clara; Bosch, Elisabeth; Rosés, Martí

    2009-11-06

    The Chromatographic Hydrophobicity Index (CHI) has been measured for several diprotic compounds. In order to model the variation of CHI with pH, a general equation for polyprotic compounds which allows the calculation of CHI for each one of the species has been proposed. Different types of diprotic solutes have been selected: neutral acids, neutral bases, and amphiprotic compounds (non-zwitterionic and zwitterionic). The applicability of the model to these complex polyprotic compounds, its advantages and limitations, as well as the information provided by the fits is discussed. In general, the model fits the experimental behaviour of all kind of solutes very well, obtaining the higher hydrophobicity values for the neutral form of the compounds, except for the zwitterionic phenylalanine. The equation and parameters obtained allow an easy calculation of CHI of the compound at any pH value.

  11. Repulsive effects of hydrophobic diamond thin films on biomolecule detection

    NASA Astrophysics Data System (ADS)

    Ruslinda, A. Rahim; Ishiyama, Y.; Penmatsa, V.; Ibori, S.; Kawarada, H.

    2015-02-01

    The repulsive effect of hydrophobic diamond thin film on biomolecule detection, such as single-nucleotide polymorphisms and human immunodeficiency virus type 1 trans-activator of transcription peptide protein detection, was investigated using a mixture of a fluorine-, amine-, and hydrogen-terminated diamond surfaces. These chemical modifications lead to the formation of a surface that effectively resists the nonspecific adsorption of proteins and other biomolecules. The effect of fluorine plasma treatment on elemental composition was also investigated via X-ray photoelectron spectroscopy (XPS). XPS results revealed a fluorocarbon layer on the diamond thin films. The contact angle measurement results indicated that the fluorine-treated diamond thin films were highly hydrophobic with a surface energy value of ∼25 mN/m.

  12. How does a hydrocarbon staple affect peptide hydrophobicity?

    PubMed

    Sim, Adelene Y L; Verma, Chandra

    2015-04-15

    Water is essential for the proper folding of proteins and the assembly of protein-protein/ligand complexes. How water regulates complex formation depends on the chemical and topological details of the interface. The dynamics of water in the interdomain region between an E3 ubiquitin ligase (MDM2) and three different peptides derived from the tumor suppressor protein p53 are studied using molecular dynamics. The peptides show bimodal distributions of interdomain water densities across a range of distances. The addition of a hydrocarbon chain to rigidify the peptides (in a process known as stapling) results in an increase in average hydrophobicity of the peptide-protein interface. Additionally, the hydrophobic staple shields a network of water molecules, kinetically stabilizing a water chain hydrogen-bonded between the peptide and MDM2. These properties could result in a decrease in the energy barrier associated with dehydrating the peptide-protein interface, thereby regulating the kinetics of peptide binding.

  13. Fabrication of Hydrophobic Nanostructured Surfaces for Microfluidic Control.

    PubMed

    Morikawa, Kyojiro; Tsukahara, Takehiko

    2016-01-01

    In the field of micro- and nanofluidics, various kinds of novel devices have been developed. For such devices, not only fluidic control but also surface control of micro/nano channels is essential. Recently, fluidic control by hydrophobic nanostructured surfaces have attracted much attention. However, conventional fabrication methods of nanostructures require complicated steps, and integration of the nanostructures into micro/nano channels makes fabrication procedures even more difficult and complicated. In the present study, a simple and easy fabrication method of nanostructures integrated into microchannels was developed. Various sizes of nanostructures were successfully fabricated by changing the plasma etching time and etching with a basic solution. Furthermore, it proved possible to construct highly hydrophobic nanostructured surfaces that could effectively control the fluid in microchannels at designed pressures. We believe that the fabrication method developed here and the results obtained are valuable contributions towards further applications in the field of micro- and nanofluidics.

  14. Direct Biofluid Analysis Using Hydrophobic Paper Spray Mass Spectrometry.

    PubMed

    Damon, Deidre E; Davis, Kathryn M; Moreira, Camila R; Capone, Patricia; Cruttenden, Riley; Badu-Tawiah, Abraham K

    2016-02-02

    Ambient electrostatic paper spray ionization from a hydrophobic paper occurs when a DC potential is applied to the dry paper triangle. Online liquid/liquid extraction of small organic compounds from a drop of biological fluid present on the dry hydrophobic paper is achieved with an organic spray solvent in under 1 min and utilizes in situ electrostatic-spray ionization for more efficient detection of extracted molecules. Direct analysis of small volumes of biofluids with no sample pretreatment is possible, which is applicable in point-of-care analyses. High sensitivity and quantitative accuracy was achieved for the direct analysis of illicit drugs in 4 μL of raw blood, serum, and whole urine. The study was extended to monitor the activity of alanine transaminase enzyme, a key biomarker for the detection of liver injury in patients (with HIV and tuberculosis) who typically take several medications at once.

  15. Development of hydrophobicity of mica surfaces by ion beam sputtering

    NASA Astrophysics Data System (ADS)

    Metya, Amaresh; Ghose, Debabrata; Ray, Nihar Ranjan

    2014-02-01

    The hydrophilic mica surface can be made hydrophobic by low energy Ar+ ion sputtering. The ion sputtering leads to both topographical and physicochemical changes of the surface which are thought to be responsible for the water repelling behavior. The sessile drop method is used to evaluate the wetting properties of the sputtered mica surfaces. It has been shown that the sputter-pattern at the nano-length scale has little influence on the development of hydrophobicity. On the other hand, the wettability appears to be strongly connected with the chemistry of the bombarded surface. We have also studied the temporal evolution of contact angle as the water evaporates due to difference in vapor pressures between the droplet surface and the surroundings. The analysis offers a simple method to estimate the diffusion coefficient of water vapor.

  16. Morphology of Air Nanobubbles Trapped atHydrophobic Nanopatterned Surfaces

    SciTech Connect

    Checco, A.; Hofmann, T.; DiMasi, E.; Black, C.T.; Ocko, B.M.

    2010-04-01

    The details of air nanobubble trapping at the interface between water and a nanostructured hydrophobic silicon surface are investigated using X-ray scattering and contact angle measurements. Large-area silicon surfaces containing hexagonally packed, 20 nm wide hydrophobic cavities provide ideal model surfaces for studying the morphology of air nanobubbles trapped inside cavities and its dependence on the cavity depth. Transmission small-angle X-ray scattering measurements show stable trapping of air inside the cavities with a partial water penetration of 5-10 nm into the pores, independent of their large depth variation. This behavior is explained by consideration of capillary effects and the cavity geometry. For parabolic cavities, the liquid can reach a thermodynamically stable configuration - a nearly planar nanobubble meniscus - by partially penetrating into the pores. This microscopic information correlates very well with the macroscopic surface wetting behavior.

  17. Interfacial entropy of water on rigid hydrophobic surfaces.

    PubMed

    Taherian, Fereshte; Leroy, Frédéric; van der Vegt, Nico F A

    2013-08-06

    A simple theoretical model is proposed for computing the interfacial entropy of water at rigid hydrophobic surfaces. The interfacial entropy, which is not considered in mean field models of static wettability, is evaluated from the fluctuations of the water-surface dispersion energy at the single particle level and represents the configurational bias imposed on the fluid molecules by the attractive external potential of a solid wall. A comparison with results obtained from molecular dynamics simulations shows that the model quantitatively describes the entropy loss of water when a water-vapor interface turns to water in contact with hydrophobic surfaces such as graphene, graphite, and diamond, while it overestimates this quantity on hydrophilic surfaces.

  18. Phase behavior of a lattice hydrophobic oligomer in explicit water.

    PubMed

    Romero-Vargas Castrillón, Santiago; Matysiak, Silvina; Stillinger, Frank H; Rossky, Peter J; Debenedetti, Pablo G

    2012-08-09

    We investigate the thermodynamics of hydrophobic oligomer collapse using a water-explicit, three-dimensional lattice model. The model captures several aspects of protein thermodynamics, including the emergence of cold- and thermal-unfolding, as well as unfolding at high solvent density (a phenomenon akin to pressure-induced denaturation). We show that over a range of conditions spanning a ≈14% increase in solvent density, the oligomer transforms into a compact, strongly water-penetrated conformation at low temperature. This contrasts with thermal unfolding at high temperature, where the system "denatures" into an extended random coil conformation. We report a phase diagram for hydrophobic collapse that correctly captures qualitative aspects of cold and thermal unfolding at low to intermediate solvent densities.

  19. Structural and Spectroscopic Properties of Water Around Small Hydrophobic Solutes

    PubMed Central

    Montagna, Maria; Sterpone, Fabio; Guidoni, Leonardo

    2013-01-01

    We investigated the structural, dynamical and spectroscopic properties of water molecules around a solvated methane by means of Car-Parrinello molecular dynamics simulations. Despite their mobility, in the first-shell water molecules are dynamically displaced in a clathrate-like cage around the hydrophobic solute. No significant differences in water geometrical parameters, in molecular dipole moments or in hydrogen bonding properties are observed between in-shell and out-shell molecules, indicating that liquid water can accommodate a small hydrophobic solute without altering its structural properties. The calculated contribution of the first shell water molecules to the infrared spectra does not show significant differences with respect the bulk signal once the effects of the missing polarization of second-shell molecules has been taken into account. Small fingerprints of the clathrate-like structure appear in the vibrational density of states in the libration and OH stretching regions. PMID:22946539

  20. Studies on synthesis esterified zirconium glyphosates and their hydrophobic properties

    NASA Astrophysics Data System (ADS)

    Zhang, Yaqing; Li, Minglei; Ji, Xuemei; Xu, Qinghong

    2010-03-01

    A series of new organic-modified zirconium glyphosate compounds were synthesized based on the reactions between esterified glyphosates and ZrOCl 2. FT-IR spectra, solid-state 31P MAS NMR and elementary analysis proved the formation of these new compounds. Powder X-ray diffraction (PXRD) patterns and transmission electron microscope (TEM) images proved these compounds had lamellar structures. Scanning electronic microscope (SEM) images showed that solvents used in synthesis had great influence on the morphologies of products. Water contact angle measurements showed that the hydrophobic property of the products was a function of the number of carbon in esterified glyphosates, increased from 0° of zirconium glyphosate to 133° of dodecyl zirconium glyphosate. The present study offered a new route to synthesize organic-modified α-Zr(HPO 4) 2·H 2O (α-ZrP) materials with various morphology and controllable hydrophobic property.

  1. Pathways of arachidonic acid peroxyl radical reactions and product formation with guanine radicals.

    PubMed

    Crean, Conor; Geacintov, Nicholas E; Shafirovich, Vladimir

    2008-02-01

    Peroxyl radicals were derived from the one-electron oxidation of polyunsaturated fatty acids by sulfate radicals that were generated by the photodissociation of peroxodisulfate anions in air-equilibrated aqueous solutions. Reactions of these peroxyl and neutral guanine radicals, also generated by oxidation with sulfate radicals, were investigated by laser kinetic spectroscopy, and the guanine oxidation products were identified by HPLC and mass spectrometry methods. Sulfate radicals rapidly oxidize arachidonic (ArAc), linoleic (LnAc), and palmitoleic (PmAc) acids with similar rate constants, (2-4) x 10 (9) M (-1) s (-1). The C-centered radicals derived from the oxidation of ArAc and LnAc include nonconjugated Rn(.) ( approximately 80%) and conjugated bis-allylic Rba(.) ( approximately 20%) radicals. The latter were detectable in the absence of oxygen by their prominent, narrow absorption band at 280 nm. The Rn(.) radicals of ArAc (containing three bis-allylic sites) transform to the Rba(.) radicals via an intramolecular H-atom abstraction [rate constant (7.5 +/- 0.7) x 10 (4) s (-1)]. In contrast, the Rn(.) radicals of LnAc that contain only one bis-allylic site do not transform intramolecularly to the Rba(.) radicals. In the case of PmAc, which contains only one double bond, the Rba(.) radicals are not observed. The Rn(.) radicals of PmAc rapidly combine with oxygen with a rate constant of (3.8 +/- 0.4) x 10(9) M(-1) s(-1). The Rba(.) radicals of ArAc are less reactive and react with oxygen with a rate constant of (2.2 +/- 0.2) x 10 (8) M (-1) s (-1). The ArAc peroxyl radicals formed spontaneously eliminate superoxide radical anions [rate constant = (3.4 +/- 0.3) x 10 (4) M (-1) s (-1)]. The stable oxidative lesions derived from the 2',3',5'-tri- O-acetylguanosine or 2',3',5'-tri- O-acetyl-8-oxo-7,8-dihydroguanosine radicals and their subsequent reactions with ArAc peroxyl radicals were also investigated. The major products found were the 2,5-diamino-4 H

  2. Hydrophobic properties of a fluoropolymer film covering gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Safonov, A. I.; Starinskii, S. V.; Sulyaeva, V. S.; Timoshenko, N. I.; Gatapova, E. Ya.

    2017-02-01

    Thin fluoropolymer films were deposited on gold nanoparticles with different diameters by the hot-wire chemical-vapor-deposition method. The contact angles of wetting of samples with water and CH2I2 were determined using a DSA-100 KRUSS device, and the free surface energy of the coated surface was also determined. The influence of encapsulated gold particles on the hydrophobic properties of the obtained coatings was determined.

  3. From hydrophobic to superhydrophobic and superhydrophilic siloxanes by thermal treatment.

    PubMed

    Karapanagiotis, Ioannis; Manoudis, Panagiotis N; Zurba, Andreea; Lampakis, Dimitrios

    2014-11-11

    The cross-influence effects of treatment temperature and time on the wettability of a siloxane elastomer is investigated in detail, through static and tilt contact angle measurements. The material is heated at 400, 500, 600, 650, 700, and 800 °C for various periods, ranging from 1 to 300 s. The siloxane surface is subjected to multiple wettability transitions with treatment time: from intrinsic hydrophobicity to superhydrophobicity (and water repellency) and then through intermediate stages (hydrophobicity and hydrophilicity) to superhydrophilicity. For the time scale used herein (1-300 s), this scenario is recorded for treatment at 650, 700, and 800 °C. For treatment at lower temperatures (400, 500, and 600 °C) only the first transition, from intrinsic hydrophobicity to superhydrophobicity, is recorded. Scanning electron microscopy, micro-Fourier transform infrared (micro-FTIR), and micro-Raman spectroscopies are employed to correlate the aforementioned wettability transitions with structural and chemical changes of the siloxane surface, developed during thermal treatment. It is shown that the first transition from intrinsic hydrophobicity to superhydrophobicity is accompanied by a severe surface-structure evolution that increases surface roughness. Once superhydrophobicity is achieved, the surface structure reaches a saturation point and it is not subjected to any other change with further thermal treatment. FTIR spectroscopy shows that the intensity of the O-H/C-H peaks increases/decreases with treatment time, and Raman measurements show that the C-Si-C vibrations gradually disappear with treatment time. The evaporation of a droplet resting on a superhydrophobic, water-repellent siloxane surface, which was produced after appropriate thermal treatment, is monitored. It is shown that droplet evaporation initially follows the constant contact area mode. At later evaporation stages, a transition to the constant contact angle mode is recorded. Finally, it is

  4. Hydrophobically Modified Chitosan Gauze for Control of Massive Hemorrhage

    DTIC Science & Technology

    2016-01-01

    NUMBER 6. AUTHOR(S) Mayur Narayan, MD, MBA 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S...PERFORMING ORGANIZATION REPORT NUMBER AFRL-SA-WP-SR-2016-0002 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING...thereby utilizing blood cells as crosslinks in the formation of a polymer matrix. In addition, hydrophobic modification of both chitosan and

  5. A computational solution to analyze hydrophobic characteristics in protein chains

    NASA Astrophysics Data System (ADS)

    Soares, Marilia Amável Gomes; Azevedo, Alexandre; Missailidis, Sotiris; Silva, Dilson

    2016-12-01

    This paper presents a program developed to facilitate calculations of the total or partial hidrophobicity value of polypeptides and proteins chains. It was built using the Fortran 77 language and performs additional functions, determining the total free energy and the electromotive force of an amino acid in a protein. These values were then used to estimate the average hydrophobicity of the protein or fragment sequence.

  6. Colony counting on hydrophobic grid-membrane filters.

    PubMed

    Sharpe, A N; Diotte, M P; Dudas, I; Malcolm, S; Peterkin, P I

    1983-07-01

    A device to facilitate manual scoring of hydrophobic grid-membrane filters (HGMF) is described. Variations in scores were generally less than 2.5% between 41 analysts from six laboratories, who, using the apparatus, scored a set of five specimen HGMF in different ways, and there was good agreement between scores from positive and negative grid-cell counts by each analyst. A scoring procedure for use in routine microbiological analysis, suitable for HGMF at various degrees of saturation, is recommended.

  7. Fabrication of super-hydrophobic duo-structures

    NASA Astrophysics Data System (ADS)

    Zhang, X. Y.; Zhang, F.; Jiang, Y. J.; Wang, Y. Y.; Shi, Z. W.; Peng, C. S.

    2015-04-01

    Recently, super-hydrophobicity has attracted increasing attention due to its huge potential in the practical applications. In this paper, we have presented a duo-structure of the combination of micro-dot-matrix and nano-candle-soot. Polydimethylsiloxane (PDMS) was used as a combination layer between the dot-matrix and the soot particles. Firstly, a period of 9-μm dot-matrix was easily fabricated on the K9 glass using the most simple and mature photolithography process. Secondly, the dot-matrix surface was coated by a thin film of PDMS (elastomer: hardener=10:1) which was diluted by methylbenzene at the volume ratio of 1:8. Thirdly, we held the PDMS modified surface over a candle flame to deposit a soot layer and followed by a gentle water-risen to remove the non-adhered particles. At last, the samples were baked at 85°C for 2 hours and then the duo-structure surface with both micro-size dot-matrix and nano-size soot particles was obtained. The SEM indicated this novel surface morphology was quite like a lotus leaf of the well-know micro-nano-binary structures. As a result, the contact angle meter demonstrated such surface exhibited a perfect super-hydrophobicity with water contact angle of 153° and sliding angle of 3°. Besides, just listed as above, the fabrication process for our structure was quite more easy, smart and low-cost compared with the other production technique for super-hydrophobic surfaces such as the phase separation method, electrochemical deposition and chemical vapor deposition etc. Hence, this super-hydrophobic duo-structure reported in this letter was a great promising candidate for a wide and rapid commercialization in the future.

  8. Effect of surfactants on wetting of super-hydrophobic surfaces.

    PubMed

    Mohammadi, R; Wassink, J; Amirfazli, A

    2004-10-26

    The effect of surfactants on wetting behavior of super-hydrophobic surfaces was investigated. Super-hydrophobic surfaces were prepared of alkylketene dimer (AKD) by casting the AKD melt in a specially designed mold. Time-dependent studies were carried out, using the axisymmetric drop shape analysis method for contact angle measurement of pure water on AKD surfaces. The results show that both advancing and receding contact angles of water on the AKD surfaces increase over time ( approximately 3 days) and reach the values of about 164 and 147 degrees , respectively. The increase of contact angles is due to the development of a prickly structure on the surface (verified by scanning electron microscopy), which is responsible for its super-hydrophobicity. Aqueous solutions of sodium acetate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and n-decanoyl-n-methylglucamine were used to investigate the wetting of AKD surfaces. Advancing and receding contact angles for various concentrations of different surfactant solutions were measured. The contact angle results were compared to those of a number of pure liquids with surface tensions similar to those of surfactant solutions. It was found that although the surface tensions of pure liquids and surfactant solutions at high concentrations are similar, the contact angles are very different. Furthermore, the usual behavior of super-hydrophobic surfaces that turn super-hydrophilic when the intrinsic contact angle of liquid on a smooth surface (of identical material) is below 90 degrees was not observed in the presence of surfactants. The difference in the results for pure liquids and surfactant solutions is explained using an adsorption hypothesis.

  9. Expanding Radical SAM Chemistry by Using Radical Addition Reactions and SAM Analogues.

    PubMed

    Ji, Xinjian; Li, Yongzhen; Xie, Liqi; Lu, Haojie; Ding, Wei; Zhang, Qi

    2016-09-19

    Radical S-adenosyl-l-methionine (SAM) enzymes utilize a [4Fe-4S] cluster to bind SAM and reductively cleave its carbon-sulfur bond to produce a highly reactive 5'-deoxyadenosyl (dAdo) radical. In almost all cases, the dAdo radical abstracts a hydrogen atom from the substrates or from enzymes, thereby initiating a highly diverse array of reactions. Herein, we report a change of the dAdo radical-based chemistry from hydrogen abstraction to radical addition in the reaction of the radical SAM enzyme NosL. This change was achieved by using a substrate analogue containing an olefin moiety. We also showed that two SAM analogues containing different nucleoside functionalities initiate the radical-based reactions with high efficiencies. The radical adduct with the olefin produced in the reaction was found to undergo two divergent reactions, and the mechanistic insights into this process were investigated in detail. Our study demonstrates a promising strategy in expanding radical SAM chemistry, providing an effective way to access nucleoside-containing compounds by using radical SAM-dependent reactions.

  10. Competition of charge- versus radical-directed fragmentation of gas-phase protonated cysteine sulfinyl radicals.

    PubMed

    Love, Chasity B; Tan, Lei; Francisco, Joseph S; Xia, Yu

    2013-04-24

    The fragmentation behavior of various cysteine sulfinyl ions (intact, N-acetylated, and O-methylated), new members of the gas-phase amino acid radical ion family, was investigated by low-energy collision-induced dissociation (CID). The dominant fragmentation channel for the protonated cysteine sulfinyl radicals ((SO•)Cys) was the radical-directed Cα-Cβ homolytic cleavage, resulting in the formation of glycyl radical ions and loss of CH2SO. This channel, however, was not observed for protonated N-acetylated cysteine sulfinyl radicals (Ac-(SO•)Cys); instead, charge-directed H2O loss followed immediately by SH loss prevailed. Counterintuitively, the H2O loss did not derive from the carboxyl group but involved the sulfinyl oxygen, a proton, and a Cβ hydrogen atom. Theoretical calculations suggested that N-acetylation significantly increases the barrier (~14 kcal mol(-1)) for the radical-directed fragmentation channel because of its reduced capability to stabilize the thus-formed glycyl radical ions via the captodative effect. N-Acetylation also assists in moving the proton to the sulfinyl site, which reduces the barrier for H2O loss. Our studies demonstrate that for cysteine sulfinyl radical ions, the stability of the product ions (glycyl radical ions) and the location of the charge (proton) can significantly modulate the competition between radical- and charge-directed fragmentation.

  11. Water transport through functionalized nanotubes with tunable hydrophobicity

    SciTech Connect

    Moskowitz, Ian; Snyder, Mark A.; Mittal, Jeetain

    2014-11-14

    Molecular dynamics simulations are used to study the occupancy and flow of water through nanotubes comprised of hydrophobic and hydrophilic atoms, which are arranged on a honeycomb lattice to mimic functionalized carbon nanotubes (CNTs). We consider single-file motion of TIP3P water through narrow channels of (6,6) CNTs with varying fractions (f) of hydrophilic atoms. Various arrangements of hydrophilic atoms are used to create heterogeneous nanotubes with separate hydrophobic/hydrophilic domains along the tube as well as random mixtures of the two types of atoms. The water occupancy inside the nanotube channel is found to vary nonlinearly as a function of f, and a small fraction of hydrophilic atoms (f ≈ 0.4) are sufficient to induce spontaneous and continuous filling of the nanotube. Interestingly, the average number of water molecules inside the channel and water flux through the nanotube are less sensitive to the specific arrangement of hydrophilic atoms than to the fraction, f. Two different regimes are observed for the water flux dependence on f – an approximately linear increase in flux as a function of f for f < 0.4, and almost no change in flux for higher f values, similar to the change in water occupancy. We are able to define an effective interaction strength between nanotube atoms and water's oxygen, based on a linear combination of interaction strengths between hydrophobic and hydrophilic nanotube atoms and water, that can quantitatively capture the observed behavior.

  12. Contact-angle hysteresis on super-hydrophobic surfaces.

    PubMed

    McHale, G; Shirtcliffe, N J; Newton, M I

    2004-11-09

    The relationship between perturbations to contact angles on a rough or textured surface and the super-hydrophobic enhancement of the equilibrium contact angle is discussed theoretically. Two models are considered. In the first (Wenzel) case, the super-hydrophobic surface has a very high contact angle and the droplet completely contacts the surface upon which it rests. In the second (Cassie-Baxter) case, the super-hydrophobic surface has a very high contact angle, but the droplet bridges across surface protrusions. The theoretical treatment emphasizes the concept of contact-angle amplification or attenuation and distinguishes between the increases in contact angles due to roughening or texturing surfaces and perturbations to the resulting contact angles. The theory is applied to predicting contact-angle hysteresis on rough surfaces from the hysteresis observable on smooth surfaces and is therefore relevant to predicting roll-off angles for droplets on tilted surfaces. The theory quantitatively predicts a "sticky" surface for Wenzel-type surfaces and a "slippy" surface for Cassie-Baxter-type surfaces.

  13. Marginally hydrophobic transmembrane α-helices shaping membrane protein folding

    PubMed Central

    De Marothy, Minttu T; Elofsson, Arne

    2015-01-01

    Cells have developed an incredible machinery to facilitate the insertion of membrane proteins into the membrane. While we have a fairly good understanding of the mechanism and determinants of membrane integration, more data is needed to understand the insertion of membrane proteins with more complex insertion and folding pathways. This review will focus on marginally hydrophobic transmembrane helices and their influence on membrane protein folding. These weakly hydrophobic transmembrane segments are by themselves not recognized by the translocon and therefore rely on local sequence context for membrane integration. How can such segments reside within the membrane? We will discuss this in the light of features found in the protein itself as well as the environment it resides in. Several characteristics in proteins have been described to influence the insertion of marginally hydrophobic helices. Additionally, the influence of biological membranes is significant. To begin with, the actual cost for having polar groups within the membrane may not be as high as expected; the presence of proteins in the membrane as well as characteristics of some amino acids may enable a transmembrane helix to harbor a charged residue. The lipid environment has also been shown to directly influence the topology as well as membrane boundaries of transmembrane helices—implying a dynamic relationship between membrane proteins and their environment. PMID:25970811

  14. Hydrophobically derivatized hyperbranched polyglycerol as a human serum albumin substitute.

    PubMed

    Kainthan, Rajesh K; Janzen, Johan; Kizhakkedathu, Jayachandran N; Devine, Dana V; Brooks, Donald E

    2008-04-01

    There is a huge clinical demand for Human Serum Albumin (HSA), with a world market of approximately $1.5B/year. Concern over prion and viral transmission in the blood supply has led to a need for safer substitutes and offers the opportunity for development of materials with enhanced properties over the presently available plasma expanders. We report here the synthesis and testing of a new synthetic plasma expander that can replace not only the osmotic and volume expansion properties of HSA but, uniquely, its binding and transport properties. We have synthesized several hyperbranched polyglycerols derivatized with hydrophobic groups and short poly(ethylene glycol) (PEG) chains. The hydrophobic groups provide regions for binding fatty acids and other hydrophobic materials while PEG imparts the necessary protection from host defense systems and enhances circulation longevity. These polymers, being hyperbranched, have only a small effect on plasma viscosity. We have shown in vitro that our materials bind 2-3 moles palmitic acid per mole, do not activate the platelet, coagulation or complement systems and do not cause red cell aggregation. In mice these materials are non-toxic with circulation half-lives as high as 34h, controllable by manipulating the molecular weight and the degree of PEG derivatization.

  15. Hydrophobic Core Flexibility Modulates Enzyme Activity in HIV-1 Protease

    SciTech Connect

    Mittal, Seema; Cai, Yufeng; Nalam, Madhavi N.L.; Bolon, Daniel N.A.; Schiffer, Celia A.

    2012-09-11

    Human immunodeficiency virus Type-1 (HIV-1) protease is crucial for viral maturation and infectivity. Studies of protease dynamics suggest that the rearrangement of the hydrophobic core is essential for enzyme activity. Many mutations in the hydrophobic core are also associated with drug resistance and may modulate the core flexibility. To test the role of flexibility in protease activity, pairs of cysteines were introduced at the interfaces of flexible regions remote from the active site. Disulfide bond formation was confirmed by crystal structures and by alkylation of free cysteines and mass spectrometry. Oxidized and reduced crystal structures of these variants show the overall structure of the protease is retained. However, cross-linking the cysteines led to drastic loss in enzyme activity, which was regained upon reducing the disulfide cross-links. Molecular dynamics simulations showed that altered dynamics propagated throughout the enzyme from the engineered disulfide. Thus, altered flexibility within the hydrophobic core can modulate HIV-1 protease activity, supporting the hypothesis that drug resistant mutations distal from the active site can alter the balance between substrate turnover and inhibitor binding by modulating enzyme activity.

  16. Droplet evaporation on heated hydrophobic and superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Dash, Susmita; Garimella, Suresh V.

    2014-04-01

    The evaporation characteristics of sessile water droplets on smooth hydrophobic and structured superhydrophobic heated surfaces are experimentally investigated. Droplets placed on the hierarchical superhydrophobic surface subtend a very high contact angle (˜160°) and demonstrate low roll-off angle (˜1°), while the hydrophobic substrate supports corresponding values of 120° and ˜10°. The substrates are heated to different constant temperatures in the range of 40-60 °C, which causes the droplet to evaporate much faster than in the case of natural evaporation without heating. The geometric parameters of the droplet, such as contact angle, contact radius, and volume evolution over time, are experimentally tracked. The droplets are observed to evaporate primarily in a constant-contact-angle mode where the contact line slides along the surface. The measurements are compared with predictions from a model based on diffusion of vapor into the ambient that assumes isothermal conditions. This vapor-diffusion-only model captures the qualitative evaporation characteristics on both test substrates, but reasonable quantitative agreement is achieved only for the hydrophobic surface. The superhydrophobic surface demonstrates significant deviation between the measured evaporation rate and that obtained using the vapor-diffusion-only model, with the difference being amplified as the substrate temperature is increased. A simple model considering thermal diffusion through the droplet is used to highlight the important role of evaporative cooling at the droplet interface in determining the droplet evaporation characteristics on superhydrophobic surfaces.

  17. Phenylalanine functionalized zwitterionic monolith for hydrophobic interaction electrochromatography.

    PubMed

    Wang, Jiabin; Jia, Wenchao; Lin, Xucong; Wu, Xiaoping; Xie, Zenghong

    2013-12-01

    A novel phenylalanine (Phe) functionalized zwitterionic monolith for hydrophobic electrochromatography was prepared by a two-step procedure involving the synthesis of glycidyl methacrylate based polymer monolith and subsequent on-column chemical modification with Phe via ring-opening reaction of epoxides. Benefitting from the hydrophobicity of both methacrylate-based matrix and aromatic group of Phe, this monolith could exhibit good hydrophobic interaction for the separation. Typical RP chromatographic behavior was observed toward various solutes. The well-controlled cathodic or anodic EOF of the prepared column could be facilely switched by altering the pH values of running buffers. The separation mechanism of this Phe functionalized zwitterionic monolith is discussed in detail. Two mixed-mode mechanisms of RP/cation exchange and RP/anion exchange could be further realized on the same monolith in different pH condition of the mobile phase. Versatile separation capabilities of neutral, basic, and acidic analytes have been successfully achieved in this zwitterionic monolith by CEC method.

  18. Surprising high hydrophobicity of polymer networks from hydrophilic components.

    PubMed

    Attanasio, Agnese; Bayer, Ilker S; Ruffilli, Roberta; Ayadi, Farouk; Athanassiou, Athanassia

    2013-06-26

    We report a simple and inexpensive method of fabricating highly hydrophobic novel materials based on interpenetrating networks of polyamide and poly(ethyl cyanoacrylate) hydrophilic components. The process is a single-step solution casting from a common solvent, formic acid, of polyamide and ethyl cyanoacrylate monomers. After casting and subsequent solvent evaporation, the in situ polymerization of ethyl cyanoacrylate monomer forms polyamide-poly(ethyl cyanoacrylate) interpenetrating network films. The interpenetrating networks demonstrate remarkable waterproof properties allowing wettability control by modulating the concentration of the components. In contrast, pure polyamide and poly(ethyl cyanoacrylate) films obtained from formic acid solutions are highly hygroscopic and hydrophilic, respectively. The polymerization of ethyl cyanoacrylate in the presence of polyamide promotes molecular interactions between the components, which reduce the available hydrophilic moieties and render the final material hydrophobic. The wettability, morphology, and thermo-physical properties of the polymeric coatings were characterized. The materials developed in this work take advantage of the properties of both polymers in a single blend and above all, due to their hydrophobic nature and minimal water uptake, can extend the application range of the individual polymers where water repellency is required.

  19. Functional bacterial amyloid increases Pseudomonas biofilm hydrophobicity and stiffness

    PubMed Central

    Zeng, Guanghong; Vad, Brian S.; Dueholm, Morten S.; Christiansen, Gunna; Nilsson, Martin; Tolker-Nielsen, Tim; Nielsen, Per H.; Meyer, Rikke L.; Otzen, Daniel E.

    2015-01-01

    The success of Pseudomonas species as opportunistic pathogens derives in great part from their ability to form stable biofilms that offer protection against chemical and mechanical attack. The extracellular matrix of biofilms contains numerous biomolecules, and it has recently been discovered that in Pseudomonas one of the components includes β-sheet rich amyloid fibrils (functional amyloid) produced by the fap operon. However, the role of the functional amyloid within the biofilm has not yet been investigated in detail. Here we investigate how the fap-based amyloid produced by Pseudomonas affects biofilm hydrophobicity and mechanical properties. Using atomic force microscopy imaging and force spectroscopy, we show that the amyloid renders individual cells more resistant to drying and alters their interactions with hydrophobic probes. Importantly, amyloid makes Pseudomonas more hydrophobic and increases biofilm stiffness 20-fold. Deletion of any one of the individual members of in the fap operon (except the putative chaperone FapA) abolishes this ability to increase biofilm stiffness and correlates with the loss of amyloid. We conclude that amyloid makes major contributions to biofilm mechanical robustness. PMID:26500638

  20. Dynamics of Defrosting on Hydrophobic and Superhydrophobic Surfaces

    NASA Astrophysics Data System (ADS)

    Murphy, Kevin; McClintic, William; Lester, Kevin; Collier, Patrick; Boreyko, Jonathan

    2016-11-01

    It has recently been demonstrated that frost can grow in a suspended Cassie state on nanostructured superhydrophobic surfaces, which has implications for enhanced defrosting rates. However, to date there have been no direct comparisons of the defrosting kinetics of Cassie frost versus frost on conventional surfaces. Here, we fabricate a hybrid aluminum plate where half of the top face exhibits a superhydrophobic nanostructure while the other half is smooth and hydrophobic. By growing frost to varying thicknesses and melting at several tilt angles, we reveal the advantages and disadvantages of each surface with regards to the extent and speed of the shedding of melt water. For sufficiently thick frost layers, the Cassie state of frost on the superhydrophobic surface uniquely enabled the rapid and effective shedding of melt water even at low tilt angles. On the other hand, the hydrophobic surface was more effective at removing very thin frost sheets, as the reduced contact angle of water on the surface facilitated the coalescence of droplets to grow the melt water beyond the capillary length for gravitational removal. Therefore, the utilization of superhydrophobic versus hydrophobic surfaces for defrosting applications depends upon the context of the system conditions.

  1. Granulation of increasingly hydrophobic formulations using a twin screw granulator.

    PubMed

    Yu, Shen; Reynolds, Gavin K; Huang, Zhenyu; de Matas, Marcel; Salman, Agba D

    2014-11-20

    The application of twin screw granulation in the pharmaceutical industry has generated increasing interest due to its suitability for continuous processing. However, an understanding of the impact of formulation properties such as hydrophobicity on intermediate and finished product quality has not yet been established. Hence, the current work investigated the granulation behaviour of three formulations containing increasing amounts of hydrophobic components using a Consigma™-1 twin screw granulator. Process conditions including powder feed rate, liquid to solid ratio, granulation liquid composition and screw configuration were also evaluated. The size of the wet granules was measured in order to enable exploration of granulation behaviour in isolation without confounding effects from downstream processes such as drying. The experimental observations indicated that the granulation process was not sensitive to the powder feed rate. The hydrophobicity led to heterogeneous liquid distribution and hence a relatively large proportion of un-wetted particles. Increasing numbers of kneading elements led to high shear and prolonged residence time, which acted to enhance the distribution of liquid and feeding materials. The bimodal size distributions considered to be characteristic of twin screw granulation were primarily ascribed to the breakage of relatively large granules by the kneading elements.

  2. Protein interactions in hydrophobic charge induction chromatography (HCIC).

    PubMed

    Ghose, Sanchayita; Hubbard, Brian; Cramer, Steven M

    2005-01-01

    A quantitative understanding of how proteins interact with hydrophobic charge induction chromatographic resins is provided. Selectivity on this mode of chromatography for monoclonal antibodies as compared to other model proteins is probed by means of a linear retention vs pH plot. The pH-dependent adsorption behavior on this mode of chromatography for a hydrophobic, charged solute is described by taking into account the equilibrium between a hydrophobic, charged solute and an ionizable, heterocyclic ligand. By analogy, an equation that is seen to adequately describe macromolecular retention under linear conditions over a range of pH is developed. A preparative, nonlinear isotherm that can capture both pH and salt concentration dependency for proteins is proposed by using an exponentially modified Langmuir isotherm model. This model is seen to successfully simulate adsorption isotherms for a variety of proteins over a range of pHs and mobile phase salt concentrations. Finally, the widely differing retention characteristics of two monoclonal antibodies are used to derive two different strategies for improving separations on this mode of chromatography. A better understanding of protein binding to this class of resins is seen as an important step to future exploitation of this mode of chromatography for industrial scale purification of proteins.

  3. Structures of multidomain proteins adsorbed on hydrophobic interaction chromatography surfaces.

    PubMed

    Gospodarek, Adrian M; Sun, Weitong; O'Connell, John P; Fernandez, Erik J

    2014-12-05

    In hydrophobic interaction chromatography (HIC), interactions between buried hydrophobic residues and HIC surfaces can cause conformational changes that interfere with separations and cause yield losses. This paper extends our previous investigations of protein unfolding in HIC chromatography by identifying protein structures on HIC surfaces under denaturing conditions and relating them to solution behavior. The thermal unfolding of three model multidomain proteins on three HIC surfaces of differing hydrophobicities was investigated with hydrogen exchange mass spectrometry (HXMS). The data were analyzed to obtain unfolding rates and Gibbs free energies for unfolding of adsorbed proteins. The melting temperatures of the proteins were lowered, but by different amounts, on the different surfaces. In addition, the structures of the proteins on the chromatographic surfaces were similar to the partially unfolded structures produced in the absence of a surface by temperature as well as by chemical denaturants. Finally, it was found that patterns of residue exposure to solvent on different surfaces at different temperatures can be largely superimposed. These findings suggest that protein unfolding on various HIC surfaces might be quantitatively related to protein unfolding in solution and that details of surface unfolding behavior might be generalized.

  4. Surface modification of electrospun fibres for biomedical applications: A focus on radical polymerization methods.

    PubMed

    Duque Sánchez, Lina; Brack, Narelle; Postma, Almar; Pigram, Paul J; Meagher, Laurence

    2016-11-01

    The development of electrospun ultrafine fibres from biodegradable and biocompatible polymers has created exciting opportunities for biomedical applications. Fibre meshes with high surface area, suitable porosity and stiffness have been produced. Despite desirable structural and topographical properties, for most synthetic and some naturally occurring materials, the nature of the fibre surface chemistry has inhibited development. Hydrophobicity, undesirable non-specific protein adsorption and bacterial attachment and growth, coupled with a lack of surface functionality in many cases and an incomplete understanding of the myriad of interactions between cells and extracellular matrix (ECM) proteins have impeded the application of these systems. Chemical and physical treatments have been applied in order to modify or control the surface properties of electrospun fibres, with some success. Chemical modification using controlled radical polymerization, referred to here as reversible-deactivation radical polymerization (RDRP), has successfully introduced advanced surface functionality in some fibre systems. Atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) are the most widely investigated techniques. This review analyses the practical applications of electrospinning for the fabrication of high quality ultrafine fibres and evaluates the techniques available for the surface modification of electrospun ultrafine fibres and includes a detailed focus on RDRP approaches.

  5. 13C Nuclear Magnetic Resonance and Electron Paramagnetic Spectroscopic Comparison of Hydrophobic Acid, Transphilic Acid, and Reverse Osmosis May 2012 Isolates of Organic Matter from the Suwannee River

    PubMed Central

    Nwosu, Ugwumsinachi G.; Cook, Robert L.

    2015-01-01

    Abstract Dissolved organic matter (DOM) is found in most natural waters at concentrations low enough to make DOM isolation methodologies critical to full analytical characterization and preservation. During the last few decades, two major protocols have been developed for the extraction of DOM isolates from natural waters. These methods utilize XAD resins and reverse osmosis (RO). In this work, the hydrophobic acid (May 2012 HPOA) and transphilic acid (May 2012 TPIA) isolates from XAD-8 and XAD-4 resins, respectively, were compared with the RO (May 2012 RO) natural organic matter isolate of the Suwannee River water using 13C nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies. 13C NMR analysis showed that the May 2012 RO isolate could be viewed as a hybrid of the more hydrophobic May 2012 HPOA isolate and more hydrophilic May 2012 TPIA isolate. The May 2012 HPOA isolate is shown to be higher in alkyl and aromatic moieties, while the May 2012 TPIA isolate is higher in O-alkyl moieties. EPR analysis revealed that the May 2012 TPIA and, in particular, May 2012 HPOA isolates had higher radical concentrations than the May 2012 RO isolate. It is postulated that some of the radical concentrations came from the use of base during the isolation procedures, especially in the XAD method. PMID:25565761

  6. Water interaction with hydrophobic and hydrophilic soot particles.

    PubMed

    Popovicheva, Olga; Persiantseva, Natalia M; Shonija, Natalia K; DeMott, Paul; Koehler, Kirsten; Petters, Markus; Kreidenweis, Sonia; Tishkova, Victoria; Demirdjian, Benjamin; Suzanne, Jean

    2008-05-07

    The interaction of water with laboratory soots possessing a range of properties relevant for atmospheric studies is examined by two complementary methods: gravimetrical measurement of water uptake coupled with chemical composition and porosity analysis and HTDMA (humidified tandem differential mobility analyzer) inference of water uptake accompanied by separate TEM (transmission electron microscopy) analysis of single particles. The first method clarifies the mechanism of water uptake for bulk soot and allows the classification of soot with respect to its hygroscopicity. The second method highlights the dependence of the soot aerosol growth factor on relative humidity (RH) for quasi-monodisperse particles. Hydrophobic and hydrophilic soot are qualitatively defined by their water uptake and surface polarity: laboratory soot particles are thus classified from very hydrophobic to very hydrophilic. Thermal soot particles produced from natural gas combustion are classified as hydrophobic with a surface of low polarity since water is found to cover only half of the surface. Graphitized thermal soot particles are proposed for comparison as extremely hydrophobic and of very low surface polarity. Soot particles produced from laboratory flame of TC1 aviation kerosene are less hydrophobic, with their entire surface being available for statistical monolayer water coverage at RH approximately 10%. Porosity measurements suggest that, initially, much of this surface water resides within micropores. Consequently, the growth factor increase of these particles to 1.07 at RH > 80% is attributed to irreversible swelling that accompanies water uptake. Hysteresis of adsorption/desorption cycles strongly supports this conclusion. In contrast, aircraft engine soot, produced from burning TC1 kerosene in a gas turbine engine combustor, has an extremely hydrophilic surface of high polarity. Due to the presence of water soluble organic and inorganic material it can be covered by many water

  7. Tunable Surface Hydrophobicity and Fluid Transport through Nanoporous Membranes

    NASA Astrophysics Data System (ADS)

    Ostrowski, Joseph H. J.

    There are more than three billion people across the globe that struggle to obtain clean drinkable water. One of the most promising avenues for generating potable water is through reverse osmosis and nanofiltration. Both solutions require a semipermeable membrane that prohibits passage of unwanted solute particles but allows passage of the solvent. Atomically thin two-dimensional membranes based on porous graphene show great promise as semipermeable materials, but modeling fluid flow on length scales between the microscopic (nanometer and smaller) and macroscopic (micron and larger) regimes presents formidable challenges. This thesis explores both equilibrium and nonequilibrium aspects of this problem and develops new methodology for simulating systems away from thermal equilibrium. First, we hypothesize that there is a wetting penalty for water as it tries to breach a sheet of graphene that should be naturally hydrophobic. By using equilibrium molecular dynamics simulations, we show that the hydrophobicity depends sensitively on the degree of electrical doping, offering an opportunity to tune the hydrophobic effect of graphene using small amounts of doping. The wetting contact angle, a measure of hydrophobicity, changes dramatically with the voltage applied to single layer graphene. We find that the sensitivity of the hydrophobic effect to voltage depends not on hydrogen bonding motifs at the interface between graphene and water, but instead on a phenomenon known as electrowetting. The theory of electrowetting predicts that the difference in surface tensions that defines the contact angle is quartic in the voltage, rather than quadratic, as it would be in bilayer graphene or in a two-dimensional metal. To explore the nonequilibrium aspects of fluid passage through atomically thin membranes, we developed a molecular dynamics methodology for simulating fluid flow at constant flux based on Gauss's principle of least constraint. This method develops microscopic

  8. Fast beam studies of free radical photodissociation

    SciTech Connect

    Neumark, D.M.

    1993-12-01

    The authors have developed a novel technique for studying the photodissociation spectroscopy and dynamics of free radicals. In these experiments, radicals are generated by laser photodetachment of a fast (6-8 keV) mass-selected negative ion beam. The resulting radicals are photodissociated with a second laser, and the photofragments are collected and detected with high efficiency using a microchannel plate detector. The overall process is: ABC{sup -} {yields} ABC + e{sup -} {yields} A + BC, AB + C. Two types of fragment detection schemes are used. To map out the photodissociation cross-section of the radical, the photodissociation laser is scanned and the total photofragment yield is measured as a function of wavelength. In other experiments, the photodissociation frequency is fixed and the photofragment masses, kinetic energy release, and scattering angle is determined for each photodissociation event.

  9. RADICALLY CONTESTED ASSERTIONS IN ECOSYSTEM MANAGEMENT

    EPA Science Inventory

    Ecosystem management is a magnet for controversy, in part because some of its formulations rest on questionable assertions that are radically contested. These assertions are important to understanding much of the conflict surrounding ecosystem management and, therrefore, deserve...

  10. Magnetic Trapping of Cold Methyl Radicals

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Vashishta, Manish; Djuricanin, Pavle; Zhou, Sida; Zhong, Wei; Mittertreiner, Tony; Carty, David; Momose, Takamasa

    2017-03-01

    We have demonstrated that a supersonic beam of methyl radicals (CH3 ) in the ground rotational state of both para and ortho species has been slowed down to standstill with a magnetic molecular decelerator, and successfully captured spatially in an anti-Helmholtz magnetic trap for >1 s . The trapped CH3 radicals have a mean translational temperature of about 200 mK with an estimated density of >5.0 ×1 07 cm-3 . The methyl radical is an ideal system for the study of cold molecules not only because of its high reactivities at low temperatures, but also because further cooling below 1 mK is plausible via sympathetic cooling with ultracold atoms. The demonstrated trapping capability of methyl radicals opens up various possibilities for realizing ultracold ensembles of molecules towards Bose-Einstein condensation of polyatomic molecules and investigations of reactions governed by quantum statistics.

  11. Psychopathology according to behaviorism: a radical restatement.

    PubMed

    Pérez-Alvarez, Marino

    2004-11-01

    This article is a radical restatement of the predominant psychopathology, which is characterized by nosological systems and by its approach towards a neurobiological conception of the so-called mental disorders. The "radical" sense of this restatement is that of radical behaviorism itself. As readers will recall, "radical" applied to behaviorism means total (not ignoring anything that interests psychology), pragmatic (referring to the practical sense of knowledge), and it also derives from the Latin word for "root" (and thus implies change beginning at a system's roots or getting to the root of things, in this case, of psychological disorders). Based on this, I introduce the Aristotelian distinction of material and form, which, besides being behaviorist avant la lettre, is used here as a critical instrument to unmask the hoax of psychopathology as it is presented. The implications of this restatement are discussed, some of them already prepared for clinical practice.

  12. Surfactant Facilitated Spreading of Aqueous Drops on Hydrophobic Surfaces

    NASA Technical Reports Server (NTRS)

    Kumar, Nitin; Couzis, Alex; Maldareili, Charles; Singh, Bhim (Technical Monitor)

    2001-01-01

    Microgravity technologies often require aqueous phases to spread over nonwetting hydrophobic solid surfaces. Surfactants facilitate the wetting of water on hydrophobic surfaces by adsorbing on the water/air and hydrophobic solid/water interfaces and lowering the surface tensions of these interfaces. The tension reductions decrease the contact angle, which increases the equilibrium wetted area. Hydrocarbon surfactants; (i.e., amphiphiles with a hydrophobic moiety consisting of an extended chain of (aliphatic) methylene -CH2- groups attached to a large polar group to give aqueous solubility) are capable of reducing the contact angles on surfaces which are not very hydrophobic, but do not reduce significantly the contact angles of the very hydrophobic surfaces such as parafilm, polyethylene or self assembled monolayers. Trisiloxane surfactants (amphiphiles with a hydrophobe consisting of methyl groups linked to a trisiloxane backbone in the form of a disk ((CH3)3-Si-O-Si-O-Si(CH3)3) and an extended ethoxylate (-(OCH2CH2)a-) polar group in the form of a chain with four or eight units) can significantly reduce the contact angle of water on a very hydrophobic surface and cause rapid and complete (or nearly complete) spreading (termed superspreading). The overall goal of the research described in this proposal is to establish and verify a theory for how trisiloxanes cause superspreading, and then use this knowledge as a guide to developing more general hydrocarbon based surfactant systems which superspread. We propose that the trisiloxane surfactants superspread because their structure allows them to strongly lower the high hydrophobic solid/aqueous tension when they adsorb to the solid surface. When the siloxane adsorbs, the hydrophobic disk parts of the molecule adsorb onto the surface removing the surface water. Since the cross-sectional area of the disk is larger than that of the extended ethoxylate chain, the disks can form a space-filling mat on the surface which

  13. Mechanism of disproportionation of ascorbate radicals

    SciTech Connect

    Bielski, B.H.J.; Allen, A.O.; Schwarz, H.A.

    1981-06-17

    Existing data on the kinetics of ascorbate radical decay, together with some new data on the effects of temperature, ionic strength, and presence of phosphate buffers, suggest a mechanism in which the ascorbate radical ion is in equilibrium with a dimer. This dimer reacts with hydrogen ion, or with other proton donors present including water and buffers (at rates depending upon their acid strengths), to form the disproportionation products ascorbate ion and dehydroascorbate acid.

  14. The stabilization energies of polyenyl radicals

    NASA Astrophysics Data System (ADS)

    Luo, Yu-Ran; Holmes, John L.

    1994-10-01

    The resonance stabilization energies, Es, of polyenyl radicals can be estimated by the equation Es( N)=-13.2+[3.95-15.8(2) -2/ n] kcal mol -1, where N is the number of C, C-π bonds in the polyenyl radicals. This correlation has been extended for predicting the weakest HC, CC and COH bond dissociation energies in vitamin A and similar compounds.

  15. Hydroxyl radical generation by red tide algae.

    PubMed

    Oda, T; Akaike, T; Sato, K; Ishimatsu, A; Takeshita, S; Muramatsu, T; Maeda, H

    1992-04-01

    The unicellular marine phytoplankton Chattonella marina is known to have toxic effects against various living marine organisms, especially fishes. However, details of the mechanism of the toxicity of this plankton remain obscure. Here we demonstrate the generation of superoxide and hydroxyl radicals from a red tide unicellular organism, C. marina, by using ESR spectroscopy with the spin traps 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and N-t-butyl-alpha-phenylnitrone (PBN), and by using the luminol-enhanced chemiluminescence response. The spin-trapping assay revealed productions of spin adduct of superoxide anion (O2-) (DMPO-OOH) and that of hydroxyl radical (.OH) (DMPO-OH) in the algal suspension, which was not observed in the ultrasonic-ruptured suspension. The addition of superoxide dismutase (500 U/ml) almost completely inhibited the formation of both DMPO-OOH and DMPO-OH, and carbon-centered radicals were generated with the disappearance of DMPO-OH after addition of 5% dimethyl sulfoxide (Me2SO) and 5% ethanol. Furthermore, the generation of methyl and methoxyl radicals, which are thought to be produced by the reaction of hydroxyl radical and Me2SO under aerobic condition, was identified using spin trapping with a combination of PBN and Me2SO. Luminol-enhanced chemiluminescence assay also supported the above observations. These results clearly indicate that C. marina generates and releases the superoxide radical followed by the production of hydroxyl radical to the surrounding environment. The velocity of superoxide generation by C. marina was about 100 times faster than that by mammalian phagocytes per cell basis. The generation of oxygen radical is suggested to be a pathogenic principle in the toxication of red tide to susceptible aquaculture fishes and may be directly correlated with the coastal pollution by red tide.

  16. Radicals: Reactive Intermediates with Translational Potential

    PubMed Central

    2016-01-01

    This Perspective illustrates the defining characteristics of free radical chemistry, beginning with its rich and storied history. Studies from our laboratory are discussed along with recent developments emanating from others in this burgeoning area. The practicality and chemoselectivity of radical reactions enable rapid access to molecules of relevance to drug discovery, agrochemistry, material science, and other disciplines. Thus, these reactive intermediates possess inherent translational potential, as they can be widely used to expedite scientific endeavors for the betterment of humankind. PMID:27631602

  17. Laser Studies of Gas Phase Radical Reactions.

    DTIC Science & Technology

    1989-01-01

    Acremonium chrysogenum , was prepared according to the published procedure [6]. This fungal enzyme had a specific activity of 0.023 IUmg1, and was estimated to...Dist-lbitionj Avdielbiity Codes jAvail atidjor Dist 6a A-I . p -1- Laser Studies of Gas Phase Radical Reactions G. Hancock Physical Chemistry...some additional experiments concerning the formation of carbene radicals in liquid phase enzyme cleavage studies are described. Keywords Laser

  18. Radical behaviorism and buddhism: complementarities and conflicts.

    PubMed

    Diller, James W; Lattal, Kennon A

    2008-01-01

    Comparisons have been made between Buddhism and the philosophy of science in general, but there have been only a few attempts to draw comparisons directly with the philosophy of radical behaviorism. The present review therefore considers heretofore unconsidered points of comparison between Buddhism and radical behaviorism in terms of their respective goals, conceptualization of human beings, and the outcomes of following either philosophy. From these comparisons it is concluded that the commonalities discerned between these two philosophies may enhance both philosophical systems.

  19. Spontaneous association of hydrophobized dextran and poly-beta-cyclodextrin into nanoassemblies. Formation and interaction with a hydrophobic drug.

    PubMed

    Daoud-Mahammed, S; Ringard-Lefebvre, C; Razzouq, N; Rosilio, V; Gillet, B; Couvreur, P; Amiel, C; Gref, R

    2007-03-01

    New nanoassemblies were instantaneously prepared by mixing two aqueous solutions, one containing a beta-cyclodextrin polymer (pbetaCD), and the other a hydrophobically modified by alkyl chains dextran (MD). The formation mechanism and the inner structure of these nanoassemblies were analysed using surface tension measurements and (1)H NMR spectroscopy. The effect of a hydrophobic guest molecule, such as benzophenone (BZ), on the formation and stability of the nanoassemblies was also evaluated. MD exhibited the typical behaviour of a soluble amphiphilic molecule and adsorbed at the air/water interface. Whereas the injection of native beta-CDs in the solution beneath the adsorbed MD monolayer did not produce any change in the surface tension, that of the pbetaCD resulted in an increase in the surface tension, indicating the desorption of the polymer from the interface. This result accounts for a cooperative effect of beta-CDs linked together in the pbetaCD polymer on dextran desorption. The presence of benzophenone in the system hindered the sequestration of dextran alkyl moieties by beta-CD in the polymer without impeding the formation of associative nanoassemblies of 100-200 nm. (1)H NMR investigations demonstrated that, in the BZ-loaded nanoassemblies, the hydrophobic molecule was mainly located into the cyclodextrin cavities.

  20. Inactivation of Bacillus atrophaeus by OH radicals

    NASA Astrophysics Data System (ADS)

    Ono, Ryo; Yonetamari, Kenta; Tokumitsu, Yusuke; Yonemori, Seiya; Yasuda, Hachiro; Mizuno, Akira

    2016-08-01

    The inactivation of Bacillus atrophaeus by OH radicals is measured. This study aims to evaluate the bactericidal effects of OH radicals produced by atmospheric-pressure nonthermal plasma widely used for plasma medicine; however, in this study, OH radicals are produced by vacuum ultraviolet (VUV) photolysis of water vapor instead of plasma to allow the production of OH radicals with almost no other reactive species. A 172 nm VUV light from a Xe2 excimer lamp irradiates a He-H2O mixture flowing in a quartz tube to photodissociate H2O to produce OH, H, O, HO2, H2O2, and O3. The produced reactive oxygen species (ROS) flow out of the quartz tube nozzle to the bacteria on an agar plate and cause inactivation. The inactivation by OH radicals among the six ROS is observed by properly setting the experimental conditions with the help of simulations calculating the ROS densities. A 30 s treatment with approximately 0.1 ppm OH radicals causes visible inactivation.

  1. Hydroxyl radical oxidation of feruloylated arabinoxylan.

    PubMed

    Bagdi, Attila; Tömösközi, Sándor; Nyström, Laura

    2016-11-05

    Feruloylated arabinoxylan (AX) has a unique capacity to form covalent gels in the presence of certain oxidizing agents. The present study demonstrates that hydroxyl radical oxidation does not provoke ferulic acid dimerization and thus oxidative gelation. We studied the hydroxyl radical mediated oxidation of an alkali-extracted AX preparation (purity: 92g/100g dry matter) that showed gel-forming capability upon peroxidase/hydrogen peroxide treatment. Hydroxyl radicals were produced with ascorbate-driven Fenton reaction and the radical formation was monitored with electron paramagnetic resonance, using a POBN/EtOH spin trapping system. Oxidation was carried out at different catalytic concentrations of iron (50 and 100μM) and at different temperatures (20°C, 50°C, and 80°C). It was demonstrated that hydroxyl radical oxidation does not provoke gel formation, but viscosity decrease in AX solution, which suggests polymer degradation. Furthermore, it was demonstrated that hydroxyl radical formation in AX solution can be initiated merely by increasing temperature.

  2. Hydroxyl radical scavengers inhibit lymphocyte mitogenesis.

    PubMed Central

    Novogrodsky, A; Ravid, A; Rubin, A L; Stenzel, K H

    1982-01-01

    Agents that are known to be scavengers of hydroxyl radicals inhibit lymphocyte mitogenesis induced by phorbol myristate acetate (PMA) to a greater extent than they inhibit mitogenesis induced by concanavalin A or phytohemagglutinin. These agents include dimethyl sulfoxide, benzoate, thiourea, dimethylurea, tetramethylurea, L-tryptophan, mannitol, and several other alcohols. Their inhibitory effect is not associated with cytotoxicity. The hydroxyl radical scavengers do not inhibit PMA-dependent amino acid transport in T cells or PMA-induced superoxide production by monocytes. Thus, they do not inhibit the primary interaction of PMA with responding cells. Treatment of peripheral blood mononuclear cells with PMA increased cellular guanylate cyclase in most experiments, and dimethyl sulfoxide tended to inhibit this increase. In addition to inhibition of PMA-induced mitogenesis, hydroxyl radical scavengers markedly inhibited the activity of lymphocyte activating factor (interleukin 1). The differential inhibition of lymphocyte mitogenesis induced by different mitogens appears to be related to the differential macrophage requirements of the mitogens. The data suggest that hydroxyl radicals may be involved in mediating the triggering signal for lymphocyte activation. Some of the hydroxyl radical scavengers are inducers of cellular differentiation,. nd it is possible that their differentiating activity is related to their ability to scavenge free radicals. PMID:6122209

  3. Radicalization and Radical Catalysis of Biomass Sugars: Insights from First-principles Studies

    PubMed Central

    Yang, Gang; Zhu, Chang; Zou, Xianli; Zhou, Lijun

    2016-01-01

    Ab initio and density functional calculations are conducted to investigate the radicalization processes and radical catalysis of biomass sugars. Structural alterations due to radicalization generally focus on the radicalized sites, and radicalization affects H-bonds in D-fructofuranose more than in D-glucopyranose, potentially with outcome of new H-bonds. Performances of different functionals and basis sets are evaluated for all radicalization processes, and enthalpy changes and Gibbs free energies for these processes are presented with high accuracy, which can be referenced for subsequent experimental and theoretical studies. It shows that radicalization can be utilized for direct transformation of biomass sugars, and for each sugar, C rather than O sites are always preferred for radicalization, thus suggesting the possibility to activate C-H bonds of biomass sugars. Radical catalysis is further combined with Brønsted acids, and it clearly states that functionalization fundamentally regulates the catalytic effects of biomass sugars. In presence of explicit water molecules, functionalization significantly affects the activation barriers and reaction energies of protonation rather than dehydration steps. Tertiary butyl and phenyl groups with large steric hindrances or hydroxyl and amino groups resulting in high stabilities for protonation products drive the protonation steps to occur facilely at ambient conditions. PMID:27405843

  4. Radicalization and Radical Catalysis of Biomass Sugars: Insights from First-principles Studies

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Zhu, Chang; Zou, Xianli; Zhou, Lijun

    2016-07-01

    Ab initio and density functional calculations are conducted to investigate the radicalization processes and radical catalysis of biomass sugars. Structural alterations due to radicalization generally focus on the radicalized sites, and radicalization affects H-bonds in D-fructofuranose more than in D-glucopyranose, potentially with outcome of new H-bonds. Performances of different functionals and basis sets are evaluated for all radicalization processes, and enthalpy changes and Gibbs free energies for these processes are presented with high accuracy, which can be referenced for subsequent experimental and theoretical studies. It shows that radicalization can be utilized for direct transformation of biomass sugars, and for each sugar, C rather than O sites are always preferred for radicalization, thus suggesting the possibility to activate C-H bonds of biomass sugars. Radical catalysis is further combined with Brønsted acids, and it clearly states that functionalization fundamentally regulates the catalytic effects of biomass sugars. In presence of explicit water molecules, functionalization significantly affects the activation barriers and reaction energies of protonation rather than dehydration steps. Tertiary butyl and phenyl groups with large steric hindrances or hydroxyl and amino groups resulting in high stabilities for protonation products drive the protonation steps to occur facilely at ambient conditions.

  5. LapF and Its Regulation by Fis Affect the Cell Surface Hydrophobicity of Pseudomonas putida

    PubMed Central

    Lahesaare, Andrio; Ainelo, Hanna; Teppo, Annika; Kivisaar, Maia; Heipieper, Hermann J.; Teras, Riho

    2016-01-01

    The ability of bacteria to regulate cell surface hydrophobicity is important for the adaptation to different environmental conditions. The hydrophobicity of cell surface can be determined by several factors, including outer membrane and surface proteins. In this study, we report that an adhesin LapF influences cell surface hydrophobicity of Pseudomonas putida. Cells lacking LapF are less hydrophobic than wild-type cells in stationary growth phase. Moreover, the overexpression of the global regulator Fis decreases surface hydrophobicity by repressing the expression of lapF. Flow cytometry analysis revealed that bacteria producing LapF are more viable when confronted with methanol (a hydrophilic compound) but are more susceptible to 1-octanol (a hydrophobic compound). Thus, these results revealed that LapF is the hydrophobicity factor for the cell surface of P. putida. PMID:27812186

  6. Practicing Radical Pedagogy: Balancing Ideals with Institutional Constraints.

    ERIC Educational Resources Information Center

    Sweet, Stephen

    1998-01-01

    Describes radical pedagogy and observes that an overview of "Teaching Sociology" suggests that few teachers fully practice it. Argues that while professors are free to teach radical theory, radical pedagogy is hindered by institutional constraints. Concludes that radical teachers may benefit from remaining more within the confines imposed by their…

  7. Studies on polyurethane adhesives and surface modification of hydrophobic substrates

    NASA Astrophysics Data System (ADS)

    Krishnamoorthy, Jayaraman

    studies involved making functionalized, thickness-controlled, wettability-controlled multilayers on hydrophobic substrates and the adsorption of carboxylic acid-terminated poly(styrene-b-isoprene) on alumina/silica substrates. Poly(vinyl alcohol) has been shown to adsorb onto hydrophobic surfaces irreversibly due to hydrophobic interactions. This thin semicrystalline coating is chemically modified using acid chlorides, butyl isocyanate and butanal to form thicker and hydrophobic coatings. The products of the modification reactions allow adsorption of a subsequent layer of poly(vinyl alcohol) that could subsequently be hydrophobized. This 2-step (adsorption/chemical modification) allows layer-by-layer deposition to prepare coatings with thickness, chemical structure and wettability control on any hydrophobic surface. Research on adsorption characteristics of carboxylic acid-terminated poly(styrene-b-isoprene) involved syntheses of block copolymers with the functional group present at specific ends. Comparative adsorption studies for carboxylic acid-terminated and hydrogen-terminated block copolymers was carried out on alumina and silica substrates.

  8. Iterative Assembly of Helical Proteins by Optimal Hydrophobic Packing

    PubMed Central

    Wu, G. Albert; Coutsias, Evangelos A.; Dill, Ken A.

    2008-01-01

    SUMMARY We present a method for the computer-based iterative assembly of native-like tertiary structures of helical proteins from alpha-helical fragments. For any pair of helices, our method, called MATCHSTIX, first generates an ensemble of possible relative orientations of the helices with various ways to form hydrophobic contacts between them. Those conformations having steric clashes, or a large radius of gyration of hydrophobic residues, or with helices too far separated to be connected by the intervening linking region, are discarded. Then, we attempt to connect the two helical fragments by using a robotics-based loop-closure algorithm. When loop closure is feasible, the algorithm generates an ensemble of viable interconnecting loops. After energy minimization and clustering, we use a representative set of conformations for further assembly with the remaining helices, adding one helix at a time. To efficiently sample the conformational space, the order of assembly generally proceeds from the pair of helices connected by the shortest loop, followed by joining one of its adjacent helices, always proceeding with the shorter connecting loop. We tested MATCHSTIX on 28 helical proteins each containing up to 5 helices and found it to heavily sample native-like conformations. The average RMSD of the best conformations for the 17 helix-bundle proteins that have 2 or 3 helices is less than 2 Å; errors increase somewhat for proteins containing more helices. Native-like states are even more densely sampled when disulfide bonds are known and imposed as restraints. We conclude that, at least for helical proteins, if the secondary structures are known, this rapid rigid-body maximization of hydrophobic interactions can lead to small ensembles of highly native-like structures. It may be useful for protein structure prediction. PMID:18682227

  9. Staphylococcus epidermidis adhesion on hydrophobic and hydrophilic textured biomaterial surfaces.

    PubMed

    Xu, Li-Chong; Siedlecki, Christopher A

    2014-06-01

    It is of great interest to use nano- or micro-structured surfaces to inhibit microbial adhesion and biofilm formation and thereby to prevent biomaterial-associated infection, without modification of the surface chemistry or bulk properties of the materials and without use of the drugs. Our previous study showed that a submicron textured polyurethane surface can inhibit staphylococcal bacterial adhesion and biofilm formation. To further understand the effect of the geometry of textures on bacterial adhesion as well as the underlying mechanism, in this study, submicron and micron textured polyurethane surfaces featuring ordered arrays of pillars were fabricated and modified to have different wettabilities. All the textured surfaces were originally hydrophobic and showed significant reductions in Staphylococcus epidermidis RP62A adhesion in phosphate buffered saline or 25% platelet poor plasma solutions under shear, as compared to smooth surfaces. After being subjected to an air glow discharge plasma treatment, all polyurethane surfaces were modified to hydrophilic, and reductions in bacterial adhesion on surfaces were subsequently found to be dependent on the size of the patterns. The submicron patterned surfaces reduced bacterial adhesion, while the micron patterned surfaces led to increased bacterial adhesion. The extracellular polymeric substances (EPS) from the S. epidermidis cell surfaces were extracted and purified, and were coated on a glass colloidal surface so that the adhesion force and separation energy in interactions of the EPS and the surface could be measured by colloidal probe atomic force microscopy. These results were consistent with the bacterial adhesion observations. Overall, the data suggest that the increased surface hydrophobicity and the decreased availability of the contact area contributes to a reduction in bacterial adhesion to the hydrophobic textured surfaces, while the availability of the contact area is the primary determinant factor

  10. Identification of hydrophobic proteins as biomarker candidates for colorectal cancer.

    PubMed

    Alvarez-Chaver, Paula; Rodríguez-Piñeiro, Ana M; Rodríguez-Berrocal, Francisco J; Martínez-Zorzano, Vicenta S; Páez de la Cadena, María

    2007-01-01

    Nowadays, colorectal cancer is one of the major causes of cancer death in Western countries. Due to the lack of biomarkers with clinical utility for this pathology, and considering that membrane and hydrophobic proteins have not been studied in depth, we performed a prefractionation of colorectal tissues prior to two-dimensional gel electrophoresis in order to identify hydrophobic proteins differentially expressed in colorectal cancer patients. Fractions enriched in hydrophobic proteins were obtained from healthy mucosa and tumor tissue by a specific extraction method based on temperature-dependent phase partitioning with Triton X-114. Proteins were separated by two-dimensional gel electrophoresis and gels were silver-stained, scanned and compared using the PDQuest software. Those spots presenting significantly different abundance were submitted to mass spectrometry for protein identification. Alterations in the expression of cytoskeletal proteins, including a decrease of vimentin and the absence of desmin, were found. We also detected alterations in antioxidant and transport proteins, chaperones, and in two isoforms of the calcium-binding protein S100A6. On the other hand, vimentin was chosen to corroborate the electrophoretic results by specific immunodetection. Most of the altered proteins have been related to cellular membranes, many of them to lipid rafts microdomains in the plasma membrane, and they have also been implicated in the control of cell proliferation, apoptosis, or metastasis. In conclusion, all the proteins found altered in colorectal tumor samples could be considered as candidates for future studies focused on their utility as markers for colorectal diagnosis and prognosis, or as targets for colorectal cancer therapy.

  11. Impact of particle nanotopology on water transport through hydrophobic soils.

    PubMed

    Truong, Vi Khanh; Owuor, Elizabeth A; Murugaraj, Pandiyan; Crawford, Russell J; Mainwaring, David E

    2015-12-15

    The impact of non- and poorly wetting soils has become increasingly important, due to its direct influence on the water-limited potential yield of rain-fed grain crops at a time of enhanced global competition for fresh water. This study investigates the physical and compositional mechanisms underlying the influence of soil organic matter (SOM) on the wetting processes of model systems. These model systems are directly related to two sandy wheat-producing soils that have contrasting hydrophobicities. Atomic force microscopy (AFM), contact angle and Raman micro-spectroscopy measurements on model planar and particulate SOM-containing surfaces demonstrated the role of the hierarchical surface structure on the wetting dynamics of packed particulate beds. It was found that a nanoscale surface topology is superimposed over the microscale roughness of the packed particles, and this controls the extent of water ingress into particulate packed beds of these particles. Using two of the dominant component organic species found in the SOM of the two soils used in this study, it was found that the specific interactions taking place between the SOM components, rather than their absolute quantities, dictated the formation of highly hydrophobic surface nanotopologies. This hydrophobicity was demonstrated, using micro-Raman imaging, to arise from the surface being in a composite Cassie-Baxter wetting state. Raman imaging demonstrated that the particle surface nanotopography influenced the degree of air entrapment in the interstices within the particle bed. The influence of a conventional surfactant on the wetting kinetics of both the model planar surfaces and packed particulate beds was quantified in terms of their respective advancing contact angles and the capillary wetting force vector. The information obtained for all of the planar and particulate surfaces, together with that obtained for the two soils, allowed linear relationships to be obtained in plots of the contact angle

  12. Modelling Soil Water Characteristic Curves for the Investigation of Hydrophobicity

    NASA Astrophysics Data System (ADS)

    Hallin, Ingrid; Matthews, Peter; Laudone, Maurizio; Van Keulen, Geertje; Doerr, Stefan; Francis, Lewis; Dudley, Ed; Gazze, Andrea; Quinn, Gerry; Whalley, Richard; Ashton, Rhys

    2016-04-01

    Soil hydrophobicity presents a major challenge for the future, as it reduces both plant-available water and irrigation efficiency, and can increase flooding hazards and erosion. A collaborative research project has been set up in the UK to study hydrophobicity over a wide range of length scales. At core scale, we are investigating the wetting behaviour of water repellent soils in order to model percolation through hydrophobic pore spaces. To that end, water retention measurements were carried out on both wettable and forcibly-wetted water-repellent soils collected from three locations in England and Wales. The data were then fitted with both the commonly used Van Genuchten model and an alternative model from PoreXpert, a software program that analyses and models porous materials. The Van Genuchten model fits a curve to the data using parameters related to air entry suction, irreducible water content and pore size distribution. By contrast, PoreXpert uses a Boltzmann-annealed simplex to find a best-fit curve based on parameters directly related to the void structure of the soil: the size of the voids, the shape of the void size distribution, and how the voids are connected to each other. Both Van Genuchten and PoreXpert fit the experimental data well, but where Van Genuchten forces an S-shaped curve that can mask small variations, PoreXpert gives a closer fit of no pre-defined shape that captures subtle differences between data points. This allows us to calculate differences in the effective pore and throat size distributions, and provides a mechanistic framework from which to model additional hydrologic behaviour in water repellent soil. Simulations of capillary induced wetting based on these mechanistic postulates are then compared to wicking experiments at the core scale, which can then be upscaled and applied to other soils.

  13. Hydrophobic and moisture-stable metal–organic frameworks

    SciTech Connect

    Fernandez, Carlos A.; Nune, Satish K.; Annapureddy, Harsha V.; Dang, Liem X.; McGrail, B. Peter; Zheng, Feng; Polikarpov, Evgueni; King, David L.; Freeman, Charles J.; Brooks, Kriston P.

    2015-08-15

    Metal-organic frameworks (MOFs) have proved to be very attractive for applications including gas storage, separation, sensing and catalysis. In particular, CO2 separation from flue gas in post-combustion processes is one of the main focuses of research among the scientific community. One of the major issues that are preventing the successful commercialization of these novel materials (e.g., MgDOBDC and NiDOBDC) is their high affinity towards water that not only compromises gas sorption capacity but also the chemical stability. In this paper, we demonstrate a novel post-synthesis modification approach to modify MOFs towards increasing hydrophobic behavior and chemical stability against moisture without compromising CO2 sorption capacity. Our approach consists of incorporating hydrophobic moieties on the external surface of the MOFs via physical adsorption. The rationale behind this concept is to increase the surface hydrophobicity in the porous materials without the need of introducing bulky functionalities inside the pore which compromises the sorption capacity toward other gases. This allows MOF interaction/sorption of CO2 molecules comparable to unmodified MOFs. We herein report preliminary results on three routinely studied MOF materials [MIL-101(Cr), MgDOBDC and NiDOBDC] demonstrating that the polymer-modified MOFs retain CO2 sorption capacity while reducing the water adsorption up to three times, respect to the un-modified materials, via an equilibrium effect. Furthermore, the water stability of the polymer-functionalized MOFs is significantly higher than the water stability of the bare material. Molecular dynamic simulations demonstrated that this equilibrium effect implies a fundamental and permanent change in the water sorption capacity of MOFs. This approach can also be employed to render moisture stability and selectivity to MOFs that find applications in gas separations, catalysis and sensing where water plays a critical role in compromising MOF

  14. How hydrophobically modified chitosans are stabilized by biocompatible lipid aggregates.

    PubMed

    Ruocco, Nino; Frielinghaus, Heide; Vitiello, Giuseppe; D'Errico, Gerardino; Leal, Leslie G; Richter, Dieter; Ortona, Ornella; Paduano, Luigi

    2015-08-15

    Nanostructured hydrogels composed by biocompatible molecules are formulated and characterized. They are based on a polymer network formed by hydrophobically modified chitosans (HMCHIT or CnCHIT) in which vesicles of monoolein (MO) and oleic acid or sodium oleate (NaO), depending on pH, are embedded. The best conditions for gel formation, in terms of pH, length of the hydrophobic moieties of chitosan, and weight proportion among the three components were estimated by visual inspection of a large number of samples. Among all possible combinations, the system C12CHIT-MO-NaO in the weight proportion (1:1:1) is optimal for the formation of a well-structured gel-like system, which is also confirmed by rheological experiments. Electron paramagnetic resonance (EPR) measurements unambiguously show the presence of lipid bilayers in this mixture, indicating that MO-NaO vesicles are stabilized by C12CHIT even at acid pH. A wide small angle neutron scattering investigation performed on several ternary systems of general formula CnCHIT-MO-NaO shows that the length of the hydrophobic tail Cn is a crucial parameter in stabilizing the polymer network in which lipid vesicles are embedded. Structural parameters for the vesicles are determined by using a multilamellar model that admits the possibility of displacement of the center of each shell. The number of shells tends to be reduced by increasing the polymer content. The thickness and the distance between consecutive lamellae are not influenced by either the polymer or MO-NaO concentration. The hydrogel presented in this work, being fully biocompatible and nanostructured, is well-suited for possible application in drug delivery.

  15. Antioxidant Activity of Caffeic Acid against Iron-Induced Free Radical Generation—A Chemical Approach

    PubMed Central

    Genaro-Mattos, Thiago C.; Maurício, Ângelo Q.; Rettori, Daniel; Alonso, Antonio; Hermes-Lima, Marcelo

    2015-01-01

    Caffeic acid (CA) is a phenolic compound widely found in coffee beans with known beneficial effects in vivo. Many studies showed that CA has anti-inflammatory, anti-mutagenic, antibacterial and anti-carcinogenic properties, which could be linked to its antioxidant activity. Taking in consideration the reported in vitro antioxidant mechanism of other polyphenols, our working hypothesis was that the CA antioxidant activity could be related to its metal-chelating property. With that in mind, we sought to investigate the chemical antioxidant mechanism of CA against in vitro iron-induced oxidative damage under different assay conditions. CA was able to prevent hydroxyl radical formation promoted by the classical Fenton reaction, as determined by 2-deoxyribose (2-DR) oxidative degradation and DMPO hydroxylation. In addition to its ability to prevent hydroxyl radical formation, CA had a great inhibition of membrane lipid peroxidation. In the lipid peroxidation assays CA acted as both metal-chelator and as hydrogen donor, preventing the deleterious action promoted by lipid-derived peroxyl and alkoxyl radicals. Our results indicate that the observed antioxidant effects were mostly due to the formation of iron-CA complexes, which are able to prevent 2-DR oxidation and DMPO hydroxylation. Noteworthy, the formation of iron-CA complexes and prevention of oxidative damage was directly related to the pH of the medium, showing better antioxidant activity at higher pH values. Moreover, in the presence of lipid membranes the antioxidant potency of CA was much higher, indicating its enhanced effectiveness in a hydrophobic environment. Overall, our results show that CA acts as an antioxidant through an iron chelating mechanism, preventing the formation of free hydroxyl radicals and, therefore, inhibiting Fenton-induced oxidative damage. The chemical properties of CA described here—in association with its reported signaling effects—could be an explanation to its beneficial effects

  16. Durable hydrophobic sol-gel finishing for textiles

    NASA Astrophysics Data System (ADS)

    Vihodceva, S.; Kukle, S.; Bitenieks, J.

    2015-03-01

    The surface of cotton textile was modified to create a water-repellent finishing by depositing a modifying coatings using the sol-gel technique. Treated textiles evaluated using scanning electron microscopy, X-Ray powder diffraction (XRD). The wettability of treated fabrics was characterized by water contact angle and drop test. The results showed that the cotton textile treated with 7.5 wt.% zinc acetate dihydrate sol showed excellent hydrophobic properties, water contact angle could reach 145°C without decreasing after 50 hydrothermal treatment cycles.

  17. Stable highly hydrophobic and oleophilic meshes for oil water separation

    NASA Astrophysics Data System (ADS)

    Wang, Qingjun; Cui, Zhe; Xiao, Yi; Chen, Qingmin

    2007-09-01

    This paper describes a simple method for fabricating both highly hydrophobic and oleophilic meshes by coating thin fluoro-containing films. The static contact angle of such meshes is greater than 150° for water, and close to 0° for kerosene, xylene and toluene. These meshes can separate water from oil effectively without resorting to any extra power or chemical agent. Moreover, they exhibited stable water resisting, anti-chemical erosion and anti-hot aging properties. It promises as a candidate for the separation of oil and water.

  18. High contact angle hysteresis of superhydrophobic surfaces: Hydrophobic defects

    NASA Astrophysics Data System (ADS)

    Chang, Feng-Ming; Hong, Siang-Jie; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2009-08-01

    A typical superhydrophobic surface is essentially nonadhesive and exhibits very low water contact angle (CA) hysteresis, so-called Lotus effect. However, leaves of some plants such as scallion and garlic with an advancing angle exceeding 150° show very serious CA hysteresis. Although surface roughness and epicuticular wax can explain the very high advancing CA, our analysis indicates that the unusual hydrophobic defect, diallyl disulfide, is the key element responsible for contact line pinning on allium leaves. After smearing diallyl disulfide on an extended polytetrafluoroethylene (PTFE) film, which is originally absent of CA hysteresis, the surface remains superhydrophobic but becomes highly adhesive.

  19. Does the rhizosphere hydrophobicity limit root water uptake?

    NASA Astrophysics Data System (ADS)

    Zare, Mohsen; Ahmed, Mutez; Kroener, Eva; Carminati, Andrea

    2015-04-01

    The ability of plants to extract water from the soil is influenced by the hydraulic conductivity of roots and their rhizosphere. Recent experiments showed that the rhizosphere turned hydrophobic after drying and it remained dry after rewetting [1]. Our objective was to investigate whether rhizosphere hydrophobicity is a limit to root water uptake after drying. To quantify the effect of rhizosphere hydrophobicity on root water uptake, we used neutron radiography to trace the transport of deuterated water (D2O) in the roots of lupines experiencing a severe, local soil drying. The plants were grown in aluminum containers (30×30×1 cm) filled with sandy soil. The soil was partitioned into nine compartments using three horizontal and three vertical layers of coarse sand (thickness of 1cm) as capillary barrier. When the plants were 28 days old, we let one of the upper lateral compartments dry to a water content of 2-4%, while keeping the other compartments to a water content of 20%. Then we injected 10 ml of D2O in the dry compartment and 10 ml in the symmetric location. The radiographs showed that root water uptake in the soil region that was let dry and then irrigated was 4-8 times smaller than in the wet soil region[2]. In a parallel experiment, we used neutron radiography to monitor the rehydration of lupine roots that were irrigated after a severe drying experiment. Based on root swelling and additional data on the xylem pressure, we calculated the hydraulic conductivity of the root-rhizosphere continuum. We found that the hydraulic conductivity of the root-rhizosphere continuum was initially 5.75×10-14 m s-1and it increased to 4.26×10-12 m s-1after four hours. Both experiments show that rhizosphere hydrophobicity after drying is associated with a reduction in root water uptake and a big decrease in hydraulic conductivity of the soil-root system. [1] Carminati et al (2010) Plant and Soil. Vol. 332: 163-176. [2] Zarebanadkouki and Carmianti (2013) Journal of Plant

  20. Big Hydrophobic Capillary Fluidics; Basically Water Ping Pong in Space

    NASA Astrophysics Data System (ADS)

    Weislogel, Mark; Attari, Babak; Wollman, Andrew; Cardin, Karl; Geile, John; Lindner, Thomas

    2016-11-01

    Capillary surfaces can be enormous in environments where the effects of gravity are small. In this presentation we review a number of interesting examples from demonstrative experiments performed in drop towers and aboard the International Space Station. The topic then focuses on large length scale hydrophobic phenomena including puddle jumping, spontaneous particle ejections, and large drop rebounds akin to water ping pong in space. Unseen footage of NASA Astronaut Scott Kelly playing water ping pong in space will be shown. Quantitative and qualitative results are offered to assist in the design of experiments for ongoing research. NASA NNX12A047A.

  1. Dewetting-Controlled Binding of Ligands to Hydrophobic Pockets

    PubMed Central

    Setny, P.; Wang, Z.; Cheng, L.-T.; Li, B.; McCammon, J. A.; Dzubiella, J.

    2010-01-01

    We report on a combined atomistic molecular dynamics simulation and implicit solvent analysis of a generic hydrophobic pocket-ligand (host-guest) system. The approaching ligand induces complex wetting-dewetting transitions in the weakly solvated pocket. The transitions lead to bimodal solvent fluctuations which govern magnitude and range of the pocket-ligand attraction. A recently developed implicit water model, based on the minimization of a geometric functional, captures the sensitive aqueous interface response to the concave-convex pocket-ligand configuration semiquantitatively. PMID:19905832

  2. Fluorescence characterization of the hydrophobic pocket of cyclophilin B.

    PubMed

    Albani, J R; Carpentier, M; Lansiaux, C

    2008-01-01

    Human cyclophilin B is a monomeric protein that contains two tryptophan residues, Trp104 and 128. Trp128-residue belongs to the binding site of cyclosporin A and is the homologous of Trp 121 in CyPA, while Trp104 residue belongs to the hydrophobic pocket. In the present work, we studied the dynamics of Trp residue(s) of cyclophilin B and of the CyPB(w128A) mutant and of TNS-mutant complex. Our results showed that Trp-104 and TNS show restricted motions within their environments and that energy transfer between the two fluorophores is occurring.

  3. Polymer hydrophilicity and hydrophobicity induced by femtosecond laser direct irradiation

    NASA Astrophysics Data System (ADS)

    Wang, Z. K.; Zheng, H. Y.; Lim, C. P.; Lam, Y. C.

    2009-09-01

    Controlled modification of surface wettability of polymethyl methacrylate (PMMA) was achieved by irradiation of PMMA surface with femtosecond laser pulses at various laser fluences and focus distances. Fluences from 0.40 to 2.1 J/cm2 produced a hydrophobic surface and 2.1 to 52.7 J/cm2 (maximum investigated) produced a hydrophilic surface. Fluences less than 0.31 J/cm2 had no effect on the wettability of the raw PMMA. This change in wettability was caused dominantly by laser induced chemical structure modification and not by a change in surface roughness.

  4. Environmentally persistent free radicals (EPFRs)-2. Are free hydroxyl radicals generated in aqueous solutions?

    PubMed

    Khachatryan, Lavrent; Dellinger, Barry

    2011-11-01

    A chemical spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed to measure the production of hydroxyl radical (·OH) in aqueous suspensions of 5% Cu(II)O/silica (3.9% Cu) particles containing environmentally persistent free radicals (EPFRs) of 2-monochlorophenol (2-MCP). The results indicate: (1) a significant differences in accumulated DMPO-OH adducts between EPFR containing particles and non-EPFR control samples, (2) a strong correlation between the concentration of DMPO-OH adducts and EPFRs per gram of particles, and (3) a slow, constant growth of DMPO-OH concentration over a period of days in solution containing 50 μg/mL EPFRs particles + DMPO (150 mM) + reagent balanced by 200 μL phosphate buffered (pH = 7.4) saline. However, failure to form secondary radicals using standard scavengers, such as ethanol, dimethylsulfoxide, sodium formate, and sodium azide, suggests free hydroxyl radicals may not have been generated in solution. This suggests surface-bound, rather than free, hydroxyl radicals were generated by a surface catalyzed-redox cycle involving both the EPFRs and Cu(II)O. Toxicological studies clearly indicate these bound free radicals promote various types of cardiovascular and pulmonary disease normally attributed to unbound free radicals; however, the exact chemical mechanism deserves further study in light of the implication of formation of bound, rather than free, hydroxyl radicals.

  5. Tuning the Reactivity of Radical through a Triplet Diradical Cu(II) Intermediate in Radical Oxidative Cross-Coupling

    PubMed Central

    Zhou, Liangliang; Yi, Hong; Zhu, Lei; Qi, Xiaotian; Jiang, Hanpeng; Liu, Chao; Feng, Yuqi; Lan, Yu; Lei, Aiwen

    2015-01-01

    Highly selective radical/radical cross-coupling is paid more attention in bond formations. However, due to their intrinsic active properties, radical species are apt to achieve homo-coupling instead of cross-coupling, which makes the selective cross-coupling as a great challenge and almost untouched. Herein a notable strategy to accomplish direct radical/radical oxidative cross-coupling has been demonstrated, that is metal tuning a transient radical to a persistent radical intermediate followed by coupling with another transient radical. Here, a transient nitrogen-centered radical is tuned to a persistent radical complex by copper catalyst, followed by coupling with a transient allylic carbon-centered radical. Firstly, nitrogen-centered radical generated from N-methoxybenzamide stabilized by copper catalyst was successfully observed by EPR. Then DFT calculations revealed that a triplet diradical Cu(II) complex formed from the chelation N-methoxybenzamide nitrogen-centered radical to Cu(II) is a persistent radical species. Moreover, conceivable nitrogen-centered radical Cu(II) complex was observed by high-resolution electrospray ionization mass spectrometry (ESI-MS). Ultimately, various allylic amides derivatives were obtained in good yields by adopting this strategy, which might inspire a novel and promising landscape in radical chemistry. PMID:26525888

  6. Evidence for hydroxyl radical generation during lipid (linoleate) peroxidation.

    PubMed

    Frenette, Mathieu; Scaiano, Juan C

    2008-07-30

    The autoxidation of methyl linoleate in benzene at 37 degrees C by peroxyl radicals was found to generate hydroxyl radicals (.OH) from a secondary oxidation mechanism. The yield of hydroxyl radicals (approximately 2%) was determined by trapping these reactive radicals with benzene to give phenol. We propose that alphaC-H hydrogen abstraction from lipid hydroperoxides, the main autoxidation products, is the source of hydroxyl radicals.

  7. Formation and reactivity of phenylperoxyl radicals in aqueous solutions

    SciTech Connect

    Alfassi, Z.B.; Marguet, S.; Neta, P. )

    1994-08-18

    The reaction of phenyl radicals with oxygen, to produce phenylperoxyl radicals, and the reactions of several phenylperoxyl radicals with a number of organic compounds in aqueous solutions have been studied by pulse radiolysis. Phenyl radicals were produced by reduction of aryl halides with hydrated electrons. The rate constant for the reaction of 4-carboxyphenyl with O[sub 2] was determined from the rate of buildup of the peroxyl radical absorption at 520 nm as a function of [O[sub 2

  8. Substrate radical intermediates in soluble methane monooxygenase.

    PubMed

    Liu, Aimin; Jin, Yi; Zhang, Jingyan; Brazeau, Brian J; Lipscomb, John D

    2005-12-09

    EPR spin-trapping experiments were carried out using the three-component soluble methane monooxygenase (MMO). Spin-traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), alpha-4-pyridyl-1-oxide N-tert-butylnitrone (POBN), and nitrosobenzene (NOB) were used to investigate the possible formation of substrate radical intermediates during catalysis. In contrast to a previous report, the NADH-coupled oxidations of various substrates did not produce any trapped radical species when DMPO or POBN was present. However, radicals were detected by these traps when only the MMO reductase component and NADH were present. DMPO and POBN were found to be weak inhibitors of the MMO reaction. In contrast, NOB is a strong inhibitor for the MMO-catalyzed nitrobenzene oxidation reaction. When NOB was used as a spin-trap in the complete MMO system with or without substrate, EPR signals from an NOB radical were detected. We propose that a molecule of NOB acts simultaneously as a substrate and a spin-trap for MMO, yielding the long-lived radical and supporting a stepwise mechanism for MMO.

  9. Modeling Radicalization Phenomena in Heterogeneous Populations

    PubMed Central

    2016-01-01

    The phenomenon of radicalization is investigated within a mixed population composed of core and sensitive subpopulations. The latest includes first to third generation immigrants. Respective ways of life may be partially incompatible. In case of a conflict core agents behave as inflexible about the issue. In contrast, sensitive agents can decide either to live peacefully adjusting their way of life to the core one, or to oppose it with eventually joining violent activities. The interplay dynamics between peaceful and opponent sensitive agents is driven by pairwise interactions. These interactions occur both within the sensitive population and by mixing with core agents. The update process is monitored using a Lotka-Volterra-like Ordinary Differential Equation. Given an initial tiny minority of opponents that coexist with both inflexible and peaceful agents, we investigate implications on the emergence of radicalization. Opponents try to turn peaceful agents to opponents driving radicalization. However, inflexible core agents may step in to bring back opponents to a peaceful choice thus weakening the phenomenon. The required minimum individual core involvement to actually curb radicalization is calculated. It is found to be a function of both the majority or minority status of the sensitive subpopulation with respect to the core subpopulation and the degree of activeness of opponents. The results highlight the instrumental role core agents can have to hinder radicalization within the sensitive subpopulation. Some hints are outlined to favor novel public policies towards social integration. PMID:27166677

  10. Vibronic Spectroscopy of the Phenylcyanomethyl Radical

    NASA Astrophysics Data System (ADS)

    Mehta, Deepali N.; Kidwell, Nathanael M.; Zwier, Timothy S.

    2011-06-01

    Resonance stabilized radicals (RSRs) are thought to be key intermediates in the formation of larger molecules in planetary atmospheres. Given the nitrogen-rich atmosphere of Titan, and the prevalence of nitriles there, it is likely that nitrile and isonitrile RSRs could be especially important in pathways leading to the formation of more complex nitrogen-containing compounds and the aerosols ("tholins") that are ultimately produced. In this talk, the results of a gas phase, jet-cooled vibronic spectroscopy study of the phenylcyanomethyl radical (C_6H_5.{C}HCN), the nitrogen-containing analog of the 1-phenylpropargyl radical, will be presented. A resonant two color photon ionization spectrum over the range 21,350-22,200 Cm-1 (450.0-468.0 nm) has been recorded, and the D_0-D_1 origin band has been tentatively identified at 21,400 Cm-1. Studies identifying the ionization threshold, and characterizing the vibronic structure will also be presented. An analogous study of the phenylisocyanomethyl radical, C_6H_5.{C}HNC, is currently being pursued for comparison with that of phenylcyanomethyl radical.

  11. Electrochemistry and spectroelectrochemistry of nitroxyl free radicals

    SciTech Connect

    Fish, J.R.; Swarts, S.G.; Sevilla, M.D.; Malinski, T.

    1988-06-30

    This work reports electrochemical and spectroelectrochemical studies of the two nitroxyl radicals 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (3-carbamoyl-PROXYL). Oxidation and reduction reactions have been observed in aqueous media over the pH range 2-12 in the potential range -0.8 to +0.8 V by differential pulse voltammetry, cyclic voltammetry, and thin-layer UV-visible spectroelectrochemistry, and the reaction products have been characterized by IR, NMR, and ESR spectrometry. At pH values less than 10, characteristic electrochemical behavior is observed to be analogous for both radicals, and the products from electron transfer compare quite favorably with those found by pulse radiolysis of aqueous solutions of nitroxyl radicals. At pH 2-9, a stable cation from a reversible oxidation and hydroxylamine following an irreversible reduction, as well as hydroxylated cation at pH higher than 9, are the same as those obtained in pulse radiolysis experiments. Spectroscopic evidence indicates that behavior following reduction at high pH differs for the two radicals. At pH 12, reduced TEMPO may undergo structural changes leading to the formation of a new radical consisting of a seven-membered ring.

  12. Hydrophobic drying and hysteresis at different length scales by molecular dynamics simulations.

    PubMed

    Lei, Yajie; Leng, Yongsheng

    2012-02-14

    We performed molecular dynamics simulations to investigate hydrophobic interactions between two parallel hydrophobic plates immersed in water. The two plates are separated by a distance D ranging from contact to a few nanometers. To mimic the attractive hydrophobic force measurement in a surface force experiment, a driving spring is used to measure the hydrophobic force between two hydrophobic plates. The force-distance curves, in particular the force variations from spontaneous drying to hydrophobic collapse are obtained. These details are usually not accessible in the surface force measurement due to the unstable jump into contact. The length-scale effect on the hydrophobic drying during normal approach and the hydrophobic hysteresis during retraction has been studied. We find that the critical distance at which a spontaneous drying occurs is determined by the shorter characteristic dimension of the plate, whereas the hydrophobic hysteresis is determined by the longer characteristic dimension of the plate. The variations of the potential of mean force versus separation during approach and retraction are also calculated. The results show that water confined between two parallel hydrophobic plates is in a thermodynamic metastable state. This comparably high energy state leads to the spontaneous drying at some critical distance.

  13. Recent experimental advances on hydrophobic interactions at solid/water and fluid/water interfaces.

    PubMed

    Zeng, Hongbo; Shi, Chen; Huang, Jun; Li, Lin; Liu, Guangyi; Zhong, Hong

    2015-03-15

    Hydrophobic effects play important roles in a wide range of natural phenomena and engineering processes such as coalescence of oil droplets in water, air flotation of mineral particles, and folding and assembly of proteins and biomembranes. In this work, the authors highlight recent experimental attempts to reveal the physical origin of hydrophobic effects by directly quantifying the hydrophobic interaction on both solid/water and fluid/water interfaces using state-of-art nanomechanical techniques such as surface forces apparatus and atomic force microscopy (AFM). For solid hydrophobic surfaces of different hydrophobicity, the range of hydrophobic interaction was reported to vary from ∼10 to >100 nm. With various characterization techniques, the very long-ranged attraction (>100 nm) has been demonstrated to be mainly attributed to nonhydrophobic interaction mechanisms such as pre-existing nanobubbles and molecular rearrangement. By ruling out these factors, intrinsic hydrophobic interaction was measured to follow an exponential law with decay length of 1-2 nm with effective range less than 20 nm. On the other hand, hydrophobic interaction measured at fluid interfaces using AFM droplet/bubble probe technique was found to decay with a much shorter length of ∼0.3 nm. This discrepancy of measured decay lengths is proposed to be attributed to inherent physical distinction between solid and fluid interfaces, which impacts the structure of interface-adjacent water molecules. Direct measurement of hydrophobic interaction on a broader range of interfaces and characterization of interfacial water molecular structure using spectroscopic techniques are anticipated to help unravel the origin of this rigidity-related mismatch of hydrophobic interaction and hold promise to uncover the physical nature of hydrophobic effects. With improved understanding of hydrophobic interaction, intrinsic interaction mechanisms of many biological and chemical pathways can be better

  14. Tuning hydrophobicity and water adhesion by electrospinning and silanization.

    PubMed

    Pisuchpen, Thanarath; Chaim-ngoen, Navarun; Intasanta, Narupol; Supaphol, Pitt; Hoven, Voravee P

    2011-04-05

    Electrospinning and silanization were synergistically employed to fabricate poly(vinyl alcohol) (PVA) and PVA/silica mixtures into flexible and chemically modifiable nanostructured surfaces with varying degrees of hydrophobicity and water adhesion. Surfaces possessing the greatest advancing water contact angle yet exhibiting a high level of water adhesion (θ(A)/θ(R) ≈ 168°/0°) were achieved by the reaction of PVA fiber mats with multiple cycles of SiCl(4)/H(2)O treatment, followed by silanization with (1H,1H,2H,2H-perfluorooctyl)trichlorosilane. It is postulated that the strong pinning effect and hence the water adhesion originated from the collapse of the underlying fibrous structures and the removal of air pockets. The addition of silica to the PVA matrix improved the rigidity and thus prevented the fibers from collapsing, allowing air to remain trapped within the fibrous structure and giving the surface greater water repellency. Throughout the investigation, the three wetting models--Wenzel's, Cassie-Baxter's, and the Cassie-impregnating--were regularly referred to as a conceptual framework. The hydrophobic surface that exhibited strong water adhesion, or the so-called "Petal effect", was elucidated in correlation with the fibrous structure of the film, as reviewed by microscopic analysis. In summary, electrospinning as a facile and cost-effective method provides promising opportunities for investigating the mechanistic character of nanowetting, nanoprinting, and nanocoating where the precise control of the dynamical three-phase contact line is of paramount importance.

  15. Controlled self-assembly of hydrophobic quantum dots through silanization.

    PubMed

    Yang, Ping; Ando, Masanori; Murase, Norio

    2011-09-01

    We demonstrate the formation of one-, two-, and three-dimensional nanocomposites through the self-assembly of silanized CdSe/ZnS quantum dots (QDs) by using a controlled sol-gel process. The self-assembly behavior of the QDs was created when partially hydrolyzed silicon alkoxide monomers replaced hydrophobic ligands on the QDs. We examined systematically self-assembly conditions such as solvent components and QD sizes in order to elucidate the formation mechanism of various QD nanocomposites. The QD nanocomposites were assembled in water phase or on the interface of water and oil phase in emulsions. The partially hydrolyzed silicon alkoxides act as intermolecules to assemble the QDs. The QD nanocomposites with well-defined solid or hollow spherical, fiber-like, sheet-like, and pearl-like morphologies were prepared by adjusting the experimental conditions. The high photoluminescence efficiency of the prepared QD nanocomposites suggests partially hydrolyzed silicon alkoxides reduced the surface deterioration of QDs during self-assembly. These techniques are applicable to other hydrophobic QDs for fabricating complex QD nanocomposites.

  16. Hydrophobic Moiety of Cationic Lipids Strongly Modulates Their Transfection Activity

    SciTech Connect

    Koynova, Rumiana; Tenchov, Boris; Wang, Li; MacDonald, Robert C.

    2010-01-18

    Synthetic cationic lipids are widely used components of nonviral gene carriers, and the factors regulating their transfection efficiency are the subject of considerable interest. In view of the important role that electrostatic interactions with the polyanionic nucleic acids play in formation of lipoplexes, a common empirical approach to improving transfection has been the synthesis and testing of amphiphiles with new versions of positively charged polar groups, while much less attention has been given to the role of the hydrophobic lipid moieties. On the basis of data for {approx}20 cationic phosphatidylcholine (PC) derivatives, here we demonstrate that hydrocarbon chain variations of these lipids modulate by over 2 orders of magnitude their transfection efficiency. The observed molecular structure-activity relationship manifests in well-expressed dependences of activity on two important molecular characteristics, chain unsaturation and total number of carbon atoms in the lipid chains, which is representative of the lipid hydrophobic volume and hydrophilic-lipophilic ratio. Transfection increases with decrease of chain length and increase of chain unsaturation. Maximum transfection was found for cationic PCs with monounsaturated 14:1 chains. It is of particular importance that the high-transfection lipids strongly promote cubic phase formation in zwitterionic membrane phosphatidylethanolamine (PE). These remarkable correlations point to an alternative, chain-dependent process in transfection, not related to the electrostatic cationic-anionic lipid interactions.

  17. Biofilm retention on surfaces with variable roughness and hydrophobicity.

    PubMed

    Tang, Lone; Pillai, Saju; Revsbech, Niels Peter; Schramm, Andreas; Bischoff, Claus; Meyer, Rikke Louise

    2011-01-01

    Biofilms on food processing equipment cause food spoilage and pose a hazard to consumers. The bacterial community on steel surfaces in a butcher's shop was characterized, and bacteria representative of this community enriched from minced pork were used to study biofilm retention. Stainless steel (SS) was compared to two novel nanostructured sol-gel coatings with differing hydrophobicity. Surfaces were characterized with respect to roughness, hydrophobicity, protein adsorption, biofilm retention, and community composition of the retained bacteria. Fewer bacteria were retained on the sol-gel coated surfaces compared to the rougher SS. However, the two sol-gel coatings did not differ in either protein adsorption, biofilm retention, or microbial community composition. When polished to a roughness similar to sol-gel, the SS was colonized by the same amount of bacteria as the sol-gel, but the bacterial community contained fewer Pseudomonas cells. In conclusion, biofilm retention was affected more by surface roughness than chemical composition under the condition described in this study.

  18. Extending the Hydrophobic Mismatch Concept to Amphiphilic Membranolytic Peptides.

    PubMed

    Grau-Campistany, Ariadna; Strandberg, Erik; Wadhwani, Parvesh; Rabanal, Francesc; Ulrich, Anne S

    2016-04-07

    A series of nine amphiphilic, pore-forming α-helical KIA peptides (KIAGKIA repeats) with lengths between 14 and 28 residues were studied by solid-state (15)N NMR to determine their alignment in oriented lipid bilayers. In a 2:1 mixture of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) with its corresponding 1-myristoyl-2-hydroxy-sn-glycero-3-phosphocholine (lyso-MPC), which has a highly positive spontaneous curvature, the helix tilt angle was found to vary steadily with peptide length. The shortest peptide was aligned transmembrane and upright, while the longer ones successively became tilted away from the membrane normal. This behavior is in agreement with the hydrophobic matching concept, conceived so far only for hydrophobic helices. In 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine, with a negative spontaneous curvature, all KIA peptides remained flat on the bilayer surface, while the cylindrical DMPC lipids permitted a slight tilt. Peptide insertion thus depends critically on the intrinsic lipid curvature, and helix orientation is then fine-tuned by membrane thickness. A refined toroidal pore model is proposed.

  19. Differences in hydration structure near hydrophobic and hydrophilic amino acids.

    PubMed Central

    Head-Gordon, T; Sorenson, J M; Pertsemlidis, A; Glaeser, R M

    1997-01-01

    We use molecular dynamics to simulate recent neutron scattering experiments on aqueous solutions of N-acetyl-leucine-amide and N-acetyl-glutamine-amide, and break down the total scattering function into contributions from solute-solute, solute-water, water-water, and intramolecular correlations. We show that the shift of the main diffraction peak to smaller angle that is observed for leucine, but not for glutamine, is attributable primarily to alterations in water-water correlations relative to bulk. The perturbation of the water hydrogen-bonded network extends roughly two solvation layers from the hydrophobic side chain surface, and is characterized by a distribution of hydrogen bonded ring sizes that are more planar and are dominated by pentagons in particular than those near the hydrophilic side chain. The different structural organization of water near the hydrophobic solute that gives rise to the inward shift in the main neutron diffraction peak under ambient conditions may also provide insight into the same directional shift for pure liquid water as it is cooled and supercooled. Images FIGURE 4 FIGURE 5 FIGURE 6 PMID:9336206

  20. Solvent and temperature effects on crambin, a hydrophobic protein

    SciTech Connect

    Llinas, M.; Lecomte, J.T.J.; De Marco, A.

    1980-10-01

    Crambin, a 5000-mol. wt. water-insoluble protein found in crambe abyssinica seeds is presently being studied by x-ray diffraction to 0.9 A resolution and /sup 1/H-nuclear magnetic resonance (NMR) spectroscopy. Preliminary /sup 1/H-NMR data at 250 and 600 MHz have suggested that this hydrophobic protein retains a similar globular conformation in both glacial acetic acid (AA), a Bronsted acid, and dimethylformamide (DMF), a Lewis base. These observations suggest that the globular conformation observed in these organic solvents is most likely the native structure present in the crystalline state. As suggested by the high intrinsic resolution of the crystallographic x-ray diffraction pattern, and demonstrated by the NMR data, crambin is a very rigid protein. Work is in progress to assign the /sup 1/H-resonances and to correlate H and /sup 13/C NMR dynamic data with the crystallographic model. It is hoped that unravelling conformational features of this hydrophobic protein will provide clues to help us understand other membrane-bound functional proteins.

  1. Stability of triglyceride liquid films on hydrophilic and hydrophobic glasses.

    PubMed

    Vazquez, Rosa; Nogueira, Rui; Orfão, Marta; Mata, José Luís; Saramago, Benilde

    2006-07-01

    Wetting and dewetting of solid surfaces by oily fluids were investigated in terms of the stability of the liquid film formed between an air bubble and the solid surface. With the objective of understanding how molecules with low polarity but relatively complex molecular structure behave at the solid/liquid interface, three liquid triglycerides with different chain length and saturation were chosen, namely, tributyrin, tricaprylin, and triolein. Tributyrin and tricaprylin exist in milkfat while triolein is present in vegetable oils. The stability of the liquid films may be inferred from the shape of the disjoining pressure isotherms, which represent the dependence of the disjoining pressure on the film thickness. Disjoining pressure isotherms for films of the three triglycerides on hydrophilic and hydrophobic glasses were obtained using a recently developed apparatus, based on the interferometric technique. The experimental curves are compared with the theoretical predictions of London-Hamaker. The deviations between theory and experiment are interpreted in terms of a structural component of the disjoining pressure. All triglycerides form metastable films on both hydrophilic and hydrophobic glasses which means that for disjoining pressures higher than a critical value, pi(c), a wetting transition occurs and the film ruptures. The mechanisms for film rupture are discussed and a correlation between film stability and the apolar (Lifshitz-van der Waals) and the polar components of the spreading coefficient is proposed.

  2. Dynamic exposure of organisms and passive samplers to hydrophobic chemicals.

    PubMed

    Bayen, Stéphane; Ter Laak, Thomas L; Buffle, Jacques; Hermens, Joop L M

    2009-04-01

    An insight into the dynamic aspects of the accumulation process is essential for understanding bioaccumulation as well as effect studies of hydrophobic organic chemicals. This review presents an overview of kinetic studies with organisms (fish, bivalve, crustacean, insect, worm, algae, and protozoan) as well as passive samplers (solid and liquid phase microextraction, semipermeable membrane device, polymer sheet, solid-phase extraction, Chemcatcher, etc.) for the uptake of neutral nonpolar chemicals from the aqueous phase. Information about uptake rates, elimination rates, and 95% equilibration times was collected and analyzed with diffusion based models. The present literature review suggests that the surface to volume ratio appears to be a critical parameter for the uptake rate of the more hydrophobic chemicals both for samplers and organisms. In addition, as a very first approximation, the combination of the first-order kinetic model with the assumption that diffusion through the aqueous boundary layers is rate limiting, gives a reasonable description of the experimental kinetic data. In this way, the presented model might be used to estimate uptake and elimination rate constants of chemicals by organisms or passive samplers.

  3. Hydrophobic trichome layers and epicuticular wax powders in Bromeliaceae.

    PubMed

    Pierce, S; Maxwell, K; Griffiths, H; Winter, K

    2001-08-01

    The distinctive foliar trichome of Bromeliaceae has promoted the evolution of an epiphytic habit in certain taxa by allowing the shoot to assume a significant role in the uptake of water and mineral nutrients. Despite the profound ecophysiological and taxonomic importance of this epidermal structure, the functions of nonabsorbent trichomes in remaining Bromeliaceae are not fully understood. The hypothesis that light reflection from these trichome layers provides photoprotection was not supported by spectroradiometry and fluorimetry in the present study; the mean reflectance of visible light from trichome layers did not exceed 6.4% on the adaxial surfaces of species representing a range of ecophysiological types nor was significant photoprotection provided by their presence. Several reports suggesting water repellency in some terrestrial Bromeliaceae were investigated. Scanning electron microscopy (SEM) and a new technique-fluorographic dimensional imaging (FDI)-were used to assess the interaction between aqueous droplets and the leaf surfaces of 86 species from 25 genera. In the majority of cases a dense layer of overlapping, stellate or peltate trichomes held water off the leaf epidermis proper. In the case of hydrophobic tank-forming tillandsioideae, a powdery epicuticular wax layer provided water repellency. The irregular architecture of these indumenta resulted in relatively little contact with water droplets. Most mesic terrestrial Pitcairnioideae examined either possessed glabrous leaf blades or hydrophobic layers of confluent trichomes on the abaxial surface. Thus, the present study indicates that an important ancestral function of the foliar trichome in Bromeliaceae was water repellency. The ecophysiological consequences of hydrophobia are discussed.

  4. Stable ferrofluids of magnetite nanoparticles in hydrophobic ionic liquids.

    PubMed

    Mestrom, Luuk; Lenders, Jos J M; de Groot, Rick; Hooghoudt, Tonnis; Sommerdijk, Nico A J M; Artigas, Marcel Vilaplana

    2015-07-17

    Ferrofluids (FFs) of metal oxide nanoparticles in ionic liquids (ILs) are a potentially useful class of magnetic materials for many applications because of their properties related to temperature/pressure stability, hydrophobicity, viscosity and recyclability. In this work, the screening of several designer surfactants for their stabilizing capabilities has resulted in the synthesis of stable FFs of superparamagnetic 7 ± 2 nm magnetite (Fe3O4) nanoparticles in the hydrophobic IL 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(R)MIM][NTf2]). The designed and synthesized 1-butyl-3-(10-carboxydecyl)-1H-imidazol-3-ium bromide (ILC10-COOH) surfactant that combines the same imidazole moiety as the IL with a long alkyl chain ensured compatibility with the IL and increased the steric repulsion between the magnetite nanoparticles sufficiently such that stable dispersions of up to 50 wt% magnetite were obtained according to stability tests in the presence of a magnetic field (0.5-1 Tesla). Cryo-transmission electron microscopy (cryo-TEM) of the IL-based FFs allowed direct visualization of the surfactant-stabilized nanoparticles in the ILs and the native, hardly aggregated state of their dispersion.

  5. Bioaccumulation of hydrophobic chemicals in an agricultural food chain

    SciTech Connect

    McLachlan, M.S.

    1995-12-31

    The concentrations of PCDD/Fs, PCBs and hexachlorobenzene were measured in an air-plant/soil-cow-human food chain in southern Germany. The data were interpreted using the fugacity modeling concept. The fugacities in air, soil and plants were found to be similar for many of the compounds, suggesting near equilibrium partitioning, while the fugacities increased somewhat from feed to cows` milk, indicating that moderate biomagnification takes place in the cow. However, a decrease in fugacity of several orders of magnitude from air to plants to cows` milk was observed for more involatile, hydrophobic compounds. This phenomenon, termed biodilution, could be attributed to two processes. Firstly, the air/plant partitioning of involatile compounds does not approach equilibrium due to the kinetically limiting air side resistance. Secondly, very hydrophobic compounds are more poorly absorbed in the digestive tract of the cow. Metabolism in cows also resulted in biodilution of certain congeners. The fugacities in human milk were 20 to 50 times higher than in cows` milk, indicating strong biomagnification.

  6. Viscous boundary lubrication of hydrophobic surfaces by mucin.

    PubMed

    Yakubov, Gleb E; McColl, James; Bongaerts, Jeroen H H; Ramsden, Jeremy J

    2009-02-17

    The lubricating behavior of the weakly charged short-side-chain glycoprotein mucin "Orthana" (Mw=0.55 MDa) has been investigated between hydrophobic and hydrophilic PDMS substrates using soft-contact tribometry. It was found that mucin facilitates lubrication between hydrophobic PDMS surfaces, leading to a 10-fold reduction in boundary friction coefficient for rough surfaces. The presence of mucin also results in a shift of the mixed lubrication regime to lower entrainment speeds. The observed boundary lubrication behavior of mucin was found to depend on the bulk concentration, and we linked this to the structure and dynamics of the adsorbed mucin films, which are assessed using optical waveguide light spectroscopy. We observe a composite structure of the adsorbed mucin layer, with its internal structure governed by entanglement. The film thickness of this adsorbed layer increases with concentration, while the boundary friction coefficient for rough surfaces was found to be inversely proportional to the thickness of the adsorbed film. This link between lubrication and structure of the film is consistent with a viscous boundary lubrication mechanism, i.e., a thicker adsorbed film, at a given sliding speed, results in a lower local shear rate and, hence, in a lower local shear stress. The estimated local viscosities of the adsorbed layer, derived from the friction measurements and the polymer layer density, are in agreement with each other.

  7. Quantitative structure-hydrophobicity relationships of molecular fragments and beyond.

    PubMed

    Zou, Jian-Wei; Huang, Meilan; Huang, Jian-Xiang; Hu, Gui-Xiang; Jiang, Yong-Jun

    2016-03-01

    Quantitative structure-property relationship (QSPR) models were firstly established for the hydrophobic substituent constant (πX) using the theoretical descriptors derived solely from electrostatic potentials (EPSs) at the substituent atoms. The descriptors introduced are found to be related to hydrogen-bond basicity, hydrogen-bond acidity, cavity, or dipolarity/polarizability terms in linear solvation energy relationship, which endows the models good interpretability. The predictive capabilities of the models constructed were also verified by rigorous Monte Carlo cross-validation. Then, eight groups of meta- or para-disubstituted benzenes and one group of substituted pyridines were investigated. QSPR models for individual systems were achieved with the ESP-derived descriptors. Additionally, two QSPR models were also established for Rekker's fragment constants (foct), which is a secondary-treatment quantity and reflects average contribution of the fragment to logP. It has been demonstrated that the descriptors derived from ESPs at the fragments, can be well used to quantitatively express the relationship between fragment structures and their hydrophobic properties, regardless of the attached parent structure or the valence state. Finally, the relations of Hammett σ constant and ESP quantities were explored. It implies that σ and π, which are essential in classic QSAR and represent different type of contributions to biological activities, are also complementary in interaction site.

  8. Stable ferrofluids of magnetite nanoparticles in hydrophobic ionic liquids

    NASA Astrophysics Data System (ADS)

    Mestrom, Luuk; Lenders, Jos J. M.; de Groot, Rick; Hooghoudt, Tonnis; Sommerdijk, Nico A. J. M.; Vilaplana Artigas, Marcel

    2015-07-01

    Ferrofluids (FFs) of metal oxide nanoparticles in ionic liquids (ILs) are a potentially useful class of magnetic materials for many applications because of their properties related to temperature/pressure stability, hydrophobicity, viscosity and recyclability. In this work, the screening of several designer surfactants for their stabilizing capabilities has resulted in the synthesis of stable FFs of superparamagnetic 7 ± 2 nm magnetite (Fe3O4) nanoparticles in the hydrophobic IL 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CRMIM][NTf2]). The designed and synthesized 1-butyl-3-(10-carboxydecyl)-1H-imidazol-3-ium bromide (ILC10-COOH) surfactant that combines the same imidazole moiety as the IL with a long alkyl chain ensured compatibility with the IL and increased the steric repulsion between the magnetite nanoparticles sufficiently such that stable dispersions of up to 50 wt% magnetite were obtained according to stability tests in the presence of a magnetic field (0.5-1 Tesla). Cryo-transmission electron microscopy (cryo-TEM) of the IL-based FFs allowed direct visualization of the surfactant-stabilized nanoparticles in the ILs and the native, hardly aggregated state of their dispersion.

  9. Hydrophobicity and thermodynamic response for aqueous solutions of amphiphiles

    NASA Astrophysics Data System (ADS)

    Zemánková, Katerina; Troncoso, Jacobo; Cerdeiriña, Claudio A.; Romaní, Luis; Anisimov, Mikhail A.

    2016-06-01

    The anomalous behavior of aqueous solutions of amphiphiles in the water-rich region is analyzed via a phenomenological approach that utilizes the isobaric heat capacity Cp as an experimental probe. We report extensive data for solutions of 14 amphiphiles as a function of temperature at atmospheric pressure. Beyond that, Cp data but also isobaric thermal expansivities and isothermal compressibilities for three solutions of tert-butanol as a function of both temperature and pressure are presented. Results rule out the possibility that the observed phenomenology is associated with the anomalous thermodynamics of pure water. Indeed, our Cp data, quantitatively consistent with recent spectroscopic analyses, suggest that water-mediated interactions between the nonpolar parts of amphiphiles are at the origin of anomalies, with the effects of such "hydrophobic aggregation" being observed at mole fractions as small as 0.01. Physicochemical details like the size, the electronic charge distribution and the geometry of amphiphile molecules as well as third-order derivatives of the Gibbs energy and the associated Koga lines support the above claims while they further contribute to characterizing the role of hydrophobicity in these phenomena. Progress with a view to gain a deeper, more concrete understanding remains.

  10. Effect of morphology of hydrophobic surfaces on cavitation kinetics

    SciTech Connect

    LUZAR,ALENKA; LEUNG,KEVIN

    2000-04-24

    Cavitation has been suggested to be a possible source of long range interactions between mesoscopic hydrophobic surfaces. While evaporation is predicted by thermodynamics, little is known about its kinetics. Glauber dynamics Monte Carlo simulations of a lattice gas close to liquid-gas coexistence and confined between partially drying surfaces are used to model the effect of water confinement on the dynamics of surface-induced phase transition. Specifically, they examine how kinetics of induced evaporation change as the texture of hydrophobic surfaces is varied. Evaporation rates are considerably slowed with relatively small amount of hydrophilic coverage. However, the distribution of hydrophilic patches is found to be crucial, with the homogeneous one being much more effective in slowing the formation of vapor tubes which triggers the evaporation process. They estimate the free energy barrier of vapor tube formation via transition state theory, using a constrained forward-backward umbrella sampling technique applied to the metastable, confined liquid. Furthermore, to relate simulation rates to experimental ones, they perform simulations using the mass-conserving Kawasaki algorithm. They predict evaporation time scales that range from hundreds of picoseconds in the case of mesoscopic surfaces {approximately} 10{sup 4} nm{sup 2} to tens of nanoseconds for smaller surfaces {approximately} 40 nm{sup 2}, when the two surfaces are {approximately} 10 solvent layers apart. The present study demonstrates that cavitation is kinetically viable in real systems and should be considered in studies of processes at confined geometry.

  11. Urea impedes the hydrophobic collapse of partially unfolded proteins.

    PubMed

    Stumpe, Martin C; Grubmüller, Helmut

    2009-05-06

    Proteins are denatured in aqueous urea solution. The nature of the molecular driving forces has received substantial attention in the past, whereas the question how urea acts at different phases of unfolding is not yet well understood at the atomic level. In particular, it is unclear whether urea actively attacks folded proteins or instead stabilizes unfolded conformations. Here we investigated the effect of urea at different phases of unfolding by molecular dynamics simulations, and the behavior of partially unfolded states in both aqueous urea solution and in pure water was compared. Whereas the partially unfolded protein in water exhibited hydrophobic collapses as primary refolding events, it remained stable or even underwent further unfolding steps in aqueous urea solution. Further, initial unfolding steps of the folded protein were found not to be triggered by urea, but instead, stabilized. The underlying mechanism of this stabilization is a favorable interaction of urea with transiently exposed, less-polar residues and the protein backbone, thereby impeding back-reactions. Taken together, these results suggest that, quite generally, urea-induced protein unfolding proceeds primarily not by active attack. Rather, thermal fluctuations toward the unfolded state are stabilized and the hydrophobic collapse of partially unfolded proteins toward the native state is impeded. As a result, the equilibrium is shifted toward the unfolded state.

  12. Injectable micellar supramolecular hydrogel for delivery of hydrophobic anticancer drugs.

    PubMed

    Fu, CuiXiang; Lin, XiaoXiao; Wang, Jun; Zheng, XiaoQun; Li, XingYi; Lin, ZhengFeng; Lin, GuangYong

    2016-04-01

    In this paper, an injectable micellar supramolecular hydrogel composed of α-cyclodextrin (α-CD) and monomethoxy poly(ethylene glycol)-b-poly(ε-caplactone) (MPEG5000-PCL5000) micelles was developed by a simple method for hydrophobic anticancer drug delivery. By mixing α-CD aqueous solution and MPEG5000-PCL5000 micelles, an injectable micellar supramolecular hydrogel could be formed under mild condition due to the inclusion complexation between α-CD and MPEG segment of MPEG5000-PCL5000 micelles. The resultant supramolecular hydrogel was thereafter characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The effect of α-CD amount on the gelation time, mechanical strength and thixotropic property was studied by a rheometer. Payload of hydrophobic paclitaxel (PTX) to supramolecular hydrogel was achieved by encapsulation of PTX into MPEG5000-PCL5000 micelles prior mixing with α-CD aqueous solution. In vitro release study showed that the release behavior of PTX from hydrogel could be modulated by change the α-CD amount in hydrogel. Furthermore, such supramolecular hydrogel could enhance the biological activity of encapsulated PTX compared to free PTX, as indicated by in vitro cytotoxicity assay. All these results indicated that the developed micellar supramolecular hydrogel might be a promising injectable drug delivery system for anticancer therapy.

  13. MWNT-hybrided supramolecular hydrogel for hydrophobic camptothecin delivery.

    PubMed

    Mu, Shansong; Liang, Yuanyuan; Chen, Shuaijun; Zhang, Liming; Liu, Tao

    2015-05-01

    To encapsulate the hydrophobic camptothecin (CPT) into hydrogel matrix with a high loading amount, a supramolecular hydrogel hybrided with multi-walled carbon nanotubes (MWNTs) was developed by the host-guest interactions and used for loading and delivering CPT. Firstly, carboxylated MWNTs were modified by polyethylene glycol monomethyl ether (MPEG), which resulted in the water-dispersed MPEG-MWNTs. Then α-cyclodextrin (α-CD) was mixed with MPEG-MWNTs and the hybrid supramolecular hydrogel was fabricated by the inclusion interactions between α-CD and MPEG. The used MPEG not only dispersed MWNTs in aqueous solution, but also functioned as hydrogel matrix by interacting with α-CD. The gelation time for the sol-gel transition and rheological properties of the resultant hydrogels were studied. Due to the excellent application of MWNTs in drug delivery, hydrophobic CPT could be loaded into the hydrogel matrix by a higher amount compared with micelles. By in vitro release and cell viability tests, it was found that the encapsulated CPT could exhibit a controlled and sustained release behavior as well as sustained antitumor efficacy.

  14. Hydrophobic flocculation flotation for beneficiating fine coal and minerals

    SciTech Connect

    Song, S.; Valdivieso, A.L.

    1998-06-01

    It is shown that hydrophobic flocculation flotation (HFF) is an effective process to treat finely ground ores and slimes so as to concentrate coal and mineral values at a fine size range. The process is based on first dispersing the fine particles suspension, followed by flocculation of fine mineral values or coal in the form of hydrophobic surfaces either induced by specifically adsorbed surfactants or from nature at the conditioning of the slurry with the shear field of sufficient magnitude. The flocculation is intensified by the addition of a small amount of nonpolar oil. finely ground coals, ilmenite slimes, and gold finely disseminated in a slag have been treated by this process. Results are presented indicating that cleaned coal with low ash and sulfur remaining and high Btu recovery can be obtained, and the refractory ores of ilmenite slimes and fine gold-bearing slag can be reasonably concentrated, leading to better beneficiation results than other separation techniques. In addition, the main operating parameters affecting the HFF process are discussed.

  15. Kinetically forbidden transformations of water molecular assemblies in hydrophobic micropores.

    PubMed

    Ohba, Tomonori; Kaneko, Katsumi

    2011-06-21

    Water adsorption hysteresis is one of the most important phenomena observed during the interaction of water with hydrophobic surfaces. Adsorption hysteresis in micropores has strong relevance to the structure of adsorbed water. We used three typical models (cluster, monolayer, and uniform distribution structure models) to determine the structure of the water molecules adsorbed in hydrophobic slit-shaped carbon micropores. In each model, stabilization energy profiles were calculated for various fractional fillings by using the interaction potential theory. Simultaneously, molecular dynamics (MD) simulations of water adsorbed in the micropore of 1.1 nm pore width, which shows significant adsorption hysteresis, were performed to determine the kinetics of the observed structural transformations. The transformations between monolayer and cluster were slow, that is, kinetically forbidden at the fractional filling of 0.2 and 0.6, whereas the cluster-uniform distribution structure and uniform distribution structure-monolayer transformations were kinetically allowed. The kinetically forbidden transformation resulted in the occurrence of metastable structure of adsorbed water and was responsible for the observed adsorption hysteresis.

  16. Temperature dependence of hydrophobic hydration dynamics: from retardation to acceleration.

    PubMed

    Duboué-Dijon, Elise; Fogarty, Aoife C; Laage, Damien

    2014-02-13

    The perturbation induced by a hydrophobic solute on water dynamics is essential in many biochemical processes, but its mechanism and magnitude are still debated. A stringent test of the different proposed pictures is provided by recent NMR measurements by Qvist and Halle (J. Am. Chem. Soc. 2008, 130, 10345-10353) which showed that, unexpectedly, the perturbation changes in a non-monotonic fashion when the solution is cooled below room temperature. Here we perform and analyze molecular dynamics simulations of a small paradigm amphiphilic solute, trimethylamine N-oxide (TMAO), in dilute aqueous solutions over the 218-350 K temperature range. We first show that our simulations properly reproduce the non-monotonic temperature dependence. We then develop a model which combines our previously suggested entropic excluded-volume effect with a perturbation factor arising from the difference between local structural fluctuations in the shell and the bulk. Our model provides a detailed molecular understanding of the hydrophobic perturbation over the full temperature range investigated. It shows that the excluded-volume factor brings a dominant temperature-independent contribution to the perturbation at all temperatures, and provides a very good approximation at room temperature. The non-monotonic temperature dependence of the perturbation is shown to arise from the structural factor and mostly from relative shifts between the shell and bulk distributions of local structures, whose amplitude remains very small compared to the widths of those distributions.

  17. Potential for Modulation of the Hydrophobic Effect Inside Chaperonins

    PubMed Central

    England, Jeremy L.; Pande, Vijay S.

    2008-01-01

    Despite the spontaneity of some in vitro protein-folding reactions, native folding in vivo often requires the participation of barrel-shaped multimeric complexes known as chaperonins. Although it has long been known that chaperonin substrates fold upon sequestration inside the chaperonin barrel, the precise mechanism by which confinement within this space facilitates folding remains unknown. We examine the possibility that the chaperonin mediates a favorable reorganization of the solvent for the folding reaction. We discuss the effect of electrostatic charge on solvent-mediated hydrophobic forces in an aqueous environment. Based on these physical arguments, we construct a simple, phenomenological theory for the thermodynamics of density and hydrogen-bond order fluctuations in liquid water. Within the framework of this model, we investigate the effect of confinement inside a chaperonin-like cavity on the configurational free energy of water by calculating solvent free energies for cavities corresponding to the different conformational states in the ATP-driven catalytic cycle of the prokaryotic chaperonin GroEL. Our findings suggest that one function of chaperonins may involve trapping unfolded proteins and subsequently exposing them to a microenvironment in which the hydrophobic effect, a crucial thermodynamic driving force for folding, is enhanced. PMID:18599630

  18. Dynamics of hydrophobic organic contaminants in the Baltic proper pelagial

    SciTech Connect

    Axelman, J.; Broman, D.; Naef, C.; Pettersen, H.

    1995-12-31

    Hydrophobic organic contaminants occur in different forms in natural water. Apart from being truly dissolved in water they partition into dissolved organic carbon (DOC) and particles of different sizes including pelagic bacteria, phytoplankton and zooplankton. The distribution between the different forms is dependent on carbon turnover rates in and transport between the different compartments and on the physical and chemical properties of the compound in focus. The water phase, the DOC-phase and two particle size fractions, 0.2--2pm and 2--20 pm representing the base of the pelagic food web, were analyzed for their content of PCBs and PAHs during summer and winter conditions in the open sea in the Baltic proper. New methods for separating truly dissolved from DOC-bound compounds have been developed using a high capacity perfusion adsorbent and large scale gas sparging. The small particle size fraction was sampled using high volume tangential flow filtration. The possibility to separate between these four different compartments has given a more detailed picture of the short term dynamics of hydrophobic organic compounds in the important base of the pelagial food web.

  19. Hydrophobicity of 43 potting media: Its implications for raising seedlings in revegetation programs

    NASA Astrophysics Data System (ADS)

    Gautam, Resham; Ashwath, Nanjappa

    2012-04-01

    SummaryThe practice of using nursery-raised seedlings is becoming popular in revegetation programs, as this will allow rapid establishment of plants. However, this practice often results in low survival of seedlings in the field, especially in the tropics under rain fed conditions. Part of this can be attributed to hydrophobicity of the media being used in raising the seedlings. Hydrophobicity is the property of potting media which make the media not able to readily absorb water from the surrounding soil once the media dry out. Thus, 41 commercially available potting media and media components and two soil samples (Control) were assessed for hydrophobicity at different moisture levels via Water Droplet Penetration Test (WDPT). At the driest state (oven dried samples), the tested media were classified into five hydrophobicity classes, viz., extremely hydrophobic (WDP time >3600 s, 28% of the tested media), severely hydrophobic (WDP time 600-3600 s, 35%), strongly hydrophobic (WDP time 60-600 s, 21%), slightly hydrophobic (WDP time 5-60 s, 12%) and non-hydrophobic (WDP time <5 s, 5%). The test showed that hydrophobicity decreased with an increase in moisture content of the media. For example, when samples were oven dried, 63% of the media were found severely to extremely hydrophobic whereas only 14% of the media remained in these categories when moisture content increased to 15%. Significant (P < 0.05) negative correlation was observed between hydrophobicity and pH (R2 = 0.92), and hydrophobicity and water holding capacity (P < 0.05) of the media (R2 = 0.89). However, no significant correlation was observed between hydrophobicity to electrical conductivity of the media (R2 = 0.03). The media wettability (ratio of hydrophilic and hydrophobic functional group of organic matter) as determined by FTIR spectroscopy was significantly (P < 0.001) higher in non-hydrophobic media than in hydrophobic media. Most Probable Number (MPN) adapted from a "Sheen Screen" method

  20. Mechanically controlled radical polymerization initiated by ultrasound

    NASA Astrophysics Data System (ADS)

    Mohapatra, Hemakesh; Kleiman, Maya; Esser-Kahn, Aaron Palmer

    2016-10-01

    In polymer chemistry, mechanical energy degrades polymeric chains. In contrast, in nature, mechanical energy is often used to create new polymers. This mechanically stimulated growth is a key component of the robustness of biological materials. A synthetic system in which mechanical force initiates polymerization will provide similar robustness in polymeric materials. Here we show a polymerization of acrylate monomers initiated and controlled by mechanical energy provided by ultrasonic agitation. The activator for an atom-transfer radical polymerization is generated using piezochemical reduction of a Cu(II) precursor complex, which thus converts a mechanical activation of piezoelectric particles to the synthesis of a new material. This polymerization reaction has some characteristics of controlled radical polymerization, such as narrow molecular-weight distribution and linear dependence of the polymeric chain length on the time of mechanical activation. This new method of controlled radical polymerization complements the existing methods to synthesize commercially useful well-defined polymers.

  1. Free radicals, antioxidant defense systems, and schizophrenia.

    PubMed

    Wu, Jing Qin; Kosten, Thomas R; Zhang, Xiang Yang

    2013-10-01

    The etiopathogenic mechanisms of schizophrenia are to date unknown, although several hypotheses have been suggested. Accumulating evidence suggests that excessive free radical production or oxidative stress may be involved in the pathophysiology of schizophrenia as evidenced by increased production of reactive oxygen or decreased antioxidant protection in schizophrenic patients. This review aims to summarize the basic molecular mechanisms of free radical metabolism, the impaired antioxidant defense system and membrane pathology in schizophrenia, their interrelationships with the characteristic clinical symptoms and the implications for antipsychotic treatments. In schizophrenia, there is accumulating evidence of altered antioxidant enzyme activities and increased levels of lipid peroxidation, as well as altered levels of plasma antioxidants. Moreover, free radical-mediated abnormalities may contribute to specific aspects of schizophrenic symptomatology and complications of its treatment with antipsychotic drugs, as well as the development of tardive dyskinesia (TD). Finally, the potential therapeutic strategies implicated by the accumulating data on oxidative stress mechanisms for the treatment of schizophrenia are discussed.

  2. High-Power-Density Organic Radical Batteries.

    PubMed

    Friebe, Christian; Schubert, Ulrich S

    2017-02-01

    Batteries that are based on organic radical compounds possess superior charging times and discharging power capability in comparison to established electrochemical energy-storage technologies. They do not rely on metals and, hence, feature a favorable environmental impact. They furthermore offer the possibility of roll-to-roll processing through the use of different printing techniques, which enables the cost-efficient fabrication of mechanically flexible devices. In this review, organic radical batteries are presented with the focus on the hitherto developed materials and the key properties thereof, e.g., voltage, capacity, and cycle life. Furthermore, basic information, such as significant characteristics, housing approaches, and applied additives, are presented and discussed in the context of organic radical batteries.

  3. Resveratrol products resulting by free radical attack

    NASA Astrophysics Data System (ADS)

    Bader, Yvonne; Quint, R. M.; Getoff, Nikola

    2008-06-01

    Trans-resveratrol ( trans-3,4',5-trihydroxystilbene; RES), which is contained in red wine and many plants, is one of the most relevant and extensively investigated stilbenes with a broad spectrum of biological activities. Among other duties, RES has been reported to have anti-carcinogenetic activities, which could be attributed to its antioxidant properties. The degradation of RES was studied under various conditions. The products (aldehydes, carboxylic acids, etc.) generated from RES by the attack of free radicals were registered as a function of the radical concentration (absorbed radiation dose). Based on the obtained data it appears that the OH radicals are initiating the rather complicated process, which involves of the numerous consecutive reactions. A possible starting reaction mechanism is presented.

  4. Antioxidant and radical scavenging properties of curcumin.

    PubMed

    Ak, Tuba; Gülçin, Ilhami

    2008-07-10

    Curcumin (diferuoyl methane) is a phenolic compound and a major component of Curcuma longa L. In the present paper, we determined the antioxidant activity of curcumin by employing various in vitro antioxidant assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH*) scavenging, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, N,N-dimethyl-p-phenylenediamine dihydrochloride (DMPD) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination by the Fe(3+)-Fe(2+) transformation method, superoxide anion radical scavenging by the riboflavin/methionine/illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe(2+)) chelating activities. Curcumin inhibited 97.3% lipid peroxidation of linoleic acid emulsion at 15 microg/mL concentration (20 mM). On the other hand, butylated hydroxyanisole (BHA, 123 mM), butylated hydroxytoluene (BHT, 102 mM), alpha-tocopherol (51 mM) and trolox (90 mM) as standard antioxidants indicated inhibition of 95.4, 99.7, 84.6 and 95.6% on peroxidation of linoleic acid emulsion at 45 microg/mL concentration, respectively. In addition, curcumin had an effective DPPH* scavenging, ABTS*(+) scavenging, DMPD*(+) scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, ferric ions (Fe(3+)) reducing power and ferrous ions (Fe(2+)) chelating activities. Also, BHA, BHT, alpha-tocopherol and trolox, were used as the reference antioxidant and radical scavenger compounds. According to the present study, curcumin can be used in the pharmacological and food industry because of these properties.

  5. Resonance ionization detection of combustion radicals

    SciTech Connect

    Cool, T.A.

    1993-12-01

    Fundamental research on the combustion of halogenated organic compounds with emphasis on reaction pathways leading to the formation of chlorinated aromatic compounds and the development of continuous emission monitoring methods will assist in DOE efforts in the management and disposal of hazardous chemical wastes. Selective laser ionization techniques are used in this laboratory for the measurement of concentration profiles of radical intermediates in the combustion of chlorinated hydrocarbon flames. A new ultrasensitive detection technique, made possible with the advent of tunable VUV laser sources, enables the selective near-threshold photoionization of all radical intermediates in premixed hydrocarbon and chlorinated hydrocarbon flames.

  6. Evolution of radical mastectomy for breast cancer

    PubMed Central

    Plesca, M; Bordea, C; El Houcheimi, B; Ichim, E; Blidaru, A

    2016-01-01

    Surgical treatment of breast cancer has been marked by a constant evolution since the Halsted radical mastectomy described in the late 19th century has become the current standard Madden radical mastectomy, a breast surgery that involves the ablation of tissue with the axillary lymphatic preserving both pectoral muscles. The purpose of this paper was to present the stages that have marked the evolution of this intervention and to provide an overview of the way breast cancer has been understood and treated in the last century. PMID:27453752

  7. Radical Behaviorism and Buddhism: Complementarities and Conflicts

    PubMed Central

    Diller, James W; Lattal, Kennon A

    2008-01-01

    Comparisons have been made between Buddhism and the philosophy of science in general, but there have been only a few attempts to draw comparisons directly with the philosophy of radical behaviorism. The present review therefore considers heretofore unconsidered points of comparison between Buddhism and radical behaviorism in terms of their respective goals, conceptualization of human beings, and the outcomes of following either philosophy. From these comparisons it is concluded that the commonalities discerned between these two philosophies may enhance both philosophical systems. PMID:22478509

  8. Effects of the protein denaturant guanidinium chloride on aqueous hydrophobic contact-pair interactions.

    PubMed

    Macdonald, Ryan D; Khajehpour, Mazdak

    2015-01-01

    Guanidinium chloride (GdmCl) is one of the most common protein denaturants. Although GdmCl is well known in the field of protein folding, the mechanism by which it denatures proteins is not well understood. In fact, there are few studies looking at its effects on hydrophobic interactions. In this work the effect of GdmCl on hydrophobic interactions has been studied by observing how the denaturant influences model systems of phenyl and alkyl hydrophobic contact pairs. Contact pair formation is monitored through the use of fluorescence spectroscopy, i.e., measuring the intrinsic phenol fluorescence being quenched by carboxylate ions. Hydrophobic interactions are isolated from other interactions through a previously developed methodology. The results show that GdmCl does not significantly affect hydrophobic interactions between small moieties such as methyl groups and phenol; while on the other hand, the interaction of larger hydrophobes such as hexyl and heptyl groups with phenol is significantly destabilized.

  9. Residence time dependent desorption of Staphylococcus epidermidis from hydrophobic and hydrophilic substrata.

    PubMed

    Boks, Niels P; Kaper, Hans J; Norde, Willem; Busscher, Henk J; van der Mei, Henny C

    2008-12-01

    Adhesion and desorption are simultaneous events during bacterial adhesion to surfaces, although desorption is far less studied than adhesion. Here, desorption of Staphylococcus epidermidis from substratum surfaces is demonstrated to be residence time dependent. Initial desorption rate coefficients were similar for hydrophilic and hydrophobic dimethyldichlorosilane (DDS)-coated glass, likely because initial desorption is controlled by attractive Lifshitz-Van der Waals interactions, which are comparable on both substratum surfaces. However, significantly slower decay times of the desorption rate coefficients are found for hydrophilic glass than for hydrophobic DDS-coated glass. This difference is suggested to be due to the acid-base interactions between staphylococci and these surfaces, which are repulsive on hydrophilic glass and attractive on hydrophobic DDS-coated glass. Final desorption rate coefficients are higher on hydrophilic glass than on hydrophobic DDS-coated glass, due to the so called hydrophobic effect, facilitating a closer contact on hydrophobic DDS-coated glass.

  10. Effect of hydrophobicity of core on the anticancer efficiency of micelles as drug delivery carriers.

    PubMed

    Sun, Chun-Yang; Ma, Yin-Chu; Cao, Zi-Yang; Li, Dong-Dong; Fan, Feng; Wang, Jun-Xia; Tao, Wei; Yang, Xian-Zhu

    2014-12-24

    Recently, micelles, which are self-assembled by amphiphilic copolymers, have attracted tremendous attention as promising drug delivery systems for cancer treatment. Thus, the hydrophobic core of the micelles, which could efficiently encapsulate small molecular drug, will play a significant role for the anticancer efficiency. Unfortunately, the effect of hydrophobicity of micellar core on its anticancer efficiency was rarely reported. Herein, the amphiphilic diblock polymers of poly(ethylene glycol) and polyphosphoester with different side groups (butyl, hexyl, octyl) were synthesized to tune the hydrophobicity of the micellar core. We found that the in vitro cytotoxicity of the DOX-loaded micelles decreased with the increasing hydrophobicity of micellar core due to the drug release rate. However, following systemic delivery, the DOX-loaded micelles with the most hydrophobic core exhibited the most significant inhibition of tumor growth in a MDA-MB-231 tumor model, indicating the importance of hydrophobicity of core on the antitumor efficacy of drug delivery systems.

  11. Elementary radical formation and conversion processes in. gamma. -irradiated polyvinylchloride

    SciTech Connect

    Torikai, A.; Adachi, T.; Fueki, K.

    1981-11-01

    Elementary processes of ..gamma..-irradiated polyvinylchloride (PVC) have been investigated by both electron spin resonance (ESR) and optical absorption measurements. On irradiating PVC film with ..gamma.. rays at -196/sup 0/C, alkyl-type radicals are produced. When the PVC film is warmed to room temperature, the radicals convert to polyenyl type. ..gamma.. irradiation of PVC film containing biphenyl (Ph/sub 2/) or pyrene (Py) at -196/sup 0/C yields the corresponding radical cation. The relative ESR peak heights of the radicals decrease and the G values for the formation of cation radicals increase with increasing additive concentrations. These facts indicate that energy is transferred from the precursor of the radicals to the additive. In the case of PVC film containing Py, the Py cation radical decreases the cyclohexadienyl-type radical from Py is produced by thermal annealing. A possible mechanism for radical formation and conversion is proposed.

  12. Peroxy Radical Chemistry and Partitioning under a Ponderosa Pine Canopy

    NASA Astrophysics Data System (ADS)

    Wolfe, G. M.; Cantrell, C. A.; Mauldin, L.; Kim, S.; Henry, S. B.; Boyle, E. S.; Karl, T.; Harley, P. C.; Turnipseed, A.; Zheng, W.; Flocke, F. M.; Apel, E. C.; Hornbrook, R. S.; Hall, S. R.; Ullmann, K.; Guenther, A. B.; DiGangi, J. P.; Kaser, L.; Schnitzhofer, R.; Hansel, A.; Graus, M.; Nakashima, Y.; Kajii, Y. J.; Keutsch, F. N.

    2012-12-01

    As the first intermediates in the OH-initiated oxidation of hydrocarbons, peroxy radicals are central to the photochemistry of the lower atmosphere. Peroxy radical abundance and partitioning controls relative rates of radical propagation and termination in low-NOx regimes, and the coupled cycling of these molecules lies at the heart of recently-highlighted deficiencies in traditional chemical mechanisms. Using observations of hydroperoxy (HO2) and total peroxy (HO2 + RO2) radicals acquired during the summer 2010 BEACHON-ROCs campaign, we explore the processes affecting radical-mediated chemistry within a rural Ponderosa pine forest in central Colorado. Steady-state and fully-coupled 0-D modeling studies are used to provide complementary perspectives on our understanding of the radical budget in this environment. Analysis will focus on the nature and impact of unidentified radical sources and sinks and on how the composition of the peroxy radical pool modulates radical regeneration.

  13. Design and fabrication of highly hydrophobic Mn nano-sculptured thin films and evaluation of surface properties on hydrophobicity

    NASA Astrophysics Data System (ADS)

    Hosseini, Somaye; Savaloni, Hadi; Gholipour-Shahraki, Mehran

    2017-03-01

    The wettability of solid surfaces is important from the aspects of both science and technology. The Mn nano-sculptured thin films were designed and fabricated by oblique angle deposition of Mn on glass substrates at room temperature. The obtained structure was characterized by field emission scanning electron microscopy and atomic force microscopy. The wettability of thin films samples was investigated by water contact angle (WCA). The 4-pointed helical star-shaped structure exhibits hydrophobicity with static WCAs of more than 133° for a 10-mg distilled water droplet. This sample also shows the rose petal effect with the additional property of high adhesion. The Mn nano-sculptured thin films also act as a sticky surface which is confirmed by hysteresis of the contact angle obtained from advancing and receding contact angles measurements. Physicochemical property of liquid phase could effectively change the contact angle, and polar solvents in contact with hydrophobic solid surfaces do not necessarily show high contact angle value.

  14. Glutathione--hydroxyl radical interaction: a theoretical study on radical recognition process.

    PubMed

    Fiser, Béla; Jójárt, Balázs; Csizmadia, Imre G; Viskolcz, Béla

    2013-01-01

    Non-reactive, comparative (2 × 1.2 μs) molecular dynamics simulations were carried out to characterize the interactions between glutathione (GSH, host molecule) and hydroxyl radical (OH(•), guest molecule). From this analysis, two distinct steps were identified in the recognition process of hydroxyl radical by glutathione: catching and steering, based on the interactions between the host-guest molecules. Over 78% of all interactions are related to the catching mechanism via complex formation between anionic carboxyl groups and the OH radical, hence both terminal residues of GSH serve as recognition sites. The glycine residue has an additional role in the recognition of OH radical, namely the steering. The flexibility of the Gly residue enables the formation of further interactions of other parts of glutathione (e.g. thiol, α- and β-carbons) with the lone electron pair of the hydroxyl radical. Moreover, quantum chemical calculations were carried out on selected GSH/OH(•) complexes and on appropriate GSH conformers to describe the energy profile of the recognition process. The relative enthalpy and the free energy changes of the radical recognition of the strongest complexes varied from -42.4 to -27.8 kJ/mol and from -21.3 to 9.8 kJ/mol, respectively. These complexes, containing two or more intermolecular interactions, would be the starting configurations for the hydrogen atom migration to quench the hydroxyl radical via different reaction channels.

  15. Direct assembly of multiply oxygenated carbon chains by decarbonylative radical-radical coupling reactions

    NASA Astrophysics Data System (ADS)

    Masuda, Kengo; Nagatomo, Masanori; Inoue, Masayuki

    2016-10-01

    Pentoses and hexoses contain more than three oxygen-bearing stereocentres and are ideal starting materials for the synthesis of multiply oxygenated natural products such as sagittamide D, maitotoxin and hikizimycin. Here we demonstrate new radical-radical homocoupling reactions of sugar derivatives with minimal perturbation of their chiral centres. The radical exchange procedure using Et3B/O2 converted sugar-derived α-alkoxyacyl tellurides into α-alkoxy radicals via decarbonylation and rapidly dimerized the monomeric radicals. The robustness of this process was demonstrated by a single-step preparation of 12 stereochemically diverse dimers with 6-10 secondary hydroxy groups, including the C5-C10 stereohexad of sagittamide D and the enantiomer of the C51-C60 stereodecad of maitotoxin. Furthermore, the optimally convergent radical-radical cross-coupling reaction achieved a one-step assembly of the protected C1-C11 oxygenated carbon chain of the anthelmintic hikizimycin. These exceptionally efficient homo- and heterocoupling methods together provide a powerful strategy for the expedited total synthesis of contiguously hydroxylated natural products.

  16. Glutathione – Hydroxyl Radical Interaction: A Theoretical Study on Radical Recognition Process

    PubMed Central

    Fiser, Béla; Jójárt, Balázs; Csizmadia, Imre G.; Viskolcz, Béla

    2013-01-01

    Non-reactive, comparative (2×1.2 μs) molecular dynamics simulations were carried out to characterize the interactions between glutathione (GSH, host molecule) and hydroxyl radical (OH•, guest molecule). From this analysis, two distinct steps were identified in the recognition process of hydroxyl radical by glutathione: catching and steering, based on the interactions between the host-guest molecules. Over 78% of all interactions are related to the catching mechanism via complex formation between anionic carboxyl groups and the OH radical, hence both terminal residues of GSH serve as recognition sites. The glycine residue has an additional role in the recognition of OH radical, namely the steering. The flexibility of the Gly residue enables the formation of further interactions of other parts of glutathione (e.g. thiol, α- and β-carbons) with the lone electron pair of the hydroxyl radical. Moreover, quantum chemical calculations were carried out on selected GSH/OH• complexes and on appropriate GSH conformers to describe the energy profile of the recognition process. The relative enthalpy and the free energy changes of the radical recognition of the strongest complexes varied from −42.4 to −27.8 kJ/mol and from −21.3 to 9.8 kJ/mol, respectively. These complexes, containing two or more intermolecular interactions, would be the starting configurations for the hydrogen atom migration to quench the hydroxyl radical via different reaction channels. PMID:24040010

  17. Inhibitory effect of super-hydrophobicity on silver release and antibacterial properties of super-hydrophobic Ag/TiO2 nanotubes.

    PubMed

    Zhang, Licheng; Zhang, Lihai; Yang, Yun; Zhang, Wei; Lv, Houchen; Yang, Fei; Lin, Changjian; Tang, Peifu

    2016-07-01

    The antibacterial properties of super-hydrophobic silver (Ag) on implant surface have not yet to be fully illuminated. In our study, we investigate the protective effects of super-hydrophobic coating of silver/titanium dioxide (Ag/TiO2 ) nanotubes against bacterial pathogens, as well as its pattern of Ag release. Ag/TiO2 nanotubes are prepared by a combination of electrochemical anodization and pulse electrodeposition. The super-hydrophobic coating is prepared by modifying the surface of Ag/TiO2 nanotubes with 1H, 1H, 2H, 2H-perfluorooctyl-triethoxysilane (PTES). Surface features and Ag release are examined by SEM, X-ray photoelectron spectroscopy, contact-angle measurement, and inductively coupled plasma-mass spectrometry (ICP-MS). The antibacterial activity of super-hydrophobic coating Ag/TiO2 nanotubes is investigated both in vitro and in vivo. Consequently, the super-hydrophobic coating on Ag/TiO2 nanotubes shows a regularly arranged structure; and nano-Ag particles (10-30 nm) are evenly distributed on the surface or inside the nanotubes. The contact angles of water on the super-hydrophobic coating Ag/TiO2 nanotubes are all above 150°. In addition, the super-hydrophobic character displays a certain conserved effect that contributes to the sustained release of Ag. The super-hydrophobic Ag/TiO2 nanotubes are also effective in inhibiting bacterial adhesion, killing the adhering bacteria and preventing postoperative infection in rabbits. Therefore, it is expected that the super-hydrophobic Ag/TiO2 nanotubes which can contain the release of Ag, leading to stable release, may show a consistent surface antibacterial capability. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1004-1012, 2016.

  18. Self-Assembled, Ultra-Hydrophobic Micro/Nano-Textured Surfaces

    DTIC Science & Technology

    2006-11-01

    SELF ASSEMBLED, ULTRA-HYDROPHOBIC MICRO / NANO -TEXTURED SURFACES Adam M. Rawlett,* Joshua A. Orlicki, Nicole Zander U.S. Army Research...These micro / nano -textured surfaces have enhanced the hydrophobicity of the textured polymer when measured by contact angle. This method of pro...REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE Self Assembled, Ultra-Hydrophobic Micro / Nano -Textured Surfaces 5a. CONTRACT NUMBER 5b

  19. Self-Assembled, Ultra-Hydrophobic Micro/Nano-Textured Surfaces

    DTIC Science & Technology

    2005-08-01

    Self-Assembled, Ultra-Hydrophobic Micro / Nano -Textured Surfaces by Adam M. Rawlett, Joshua A. Orlicki, Afia Karikari, and Tim Long ARL-TR...3547 August 2005 Self-Assembled, Ultra-Hydrophobic Micro / Nano -Textured Surfaces Adam M. Rawlett and Joshua A. Orlicki, Weapons and...AND SUBTITLE Self-Assembled, Ultra-Hydrophobic Micro / Nano -Textured Surfaces 5c. PROGRAM ELEMENT NUMBER 5d. PROJECT NUMBER AH84 5e. TASK NUMBER

  20. Preparation of Highly Hydrophobic and Oleophobic Textile Surfaces Using Microwave-Promoted Silane Coupling (Postprint)

    DTIC Science & Technology

    2010-12-01

    AFRL-RX-TY-TP-2011-0109 PREPARATION OF HIGHLY HYDROPHOBIC AND OLEOPHOBIC TEXTILE SURFACES USING MICROWAVE-PROMOTED SILANE COUPLING POSTPRINT...Include area code) 31-DEC-2010 Journal Article POSTPRINT 02-JAN-2009 to 31-DEC-2010 Preparation of Highly Hydrophobic and Oleophobic Textile Surfaces...DOI 10.1007/ s10853-010-5100-5 Preparation of highly hydrophobic and oleophobic textile surfaces using microwave-promoted silane coupling 1 23 Your

  1. Investigating How Contact Angle Effects the Interaction between Water and a Hydrophobic Surface

    NASA Astrophysics Data System (ADS)

    Poynor, Adele; Neidig, Caitlyn

    2012-02-01

    By definition hydrophobic substances hate water. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low-density region forms near the surface. Contact angle is a measure of how hydrophobic a surface is. We have employed an automated home-built Surface Plasmon Resonance (SPR) apparatus to investigate the effect of varying the contact angle on the depletion layer

  2. Titania-lanthanum phosphate photoactive and hydrophobic new generation catalyst

    SciTech Connect

    Jyothi, Chembolli K.; Jaimy, Kanakkanmavudi B.; Ghosh, Swapankumar; Sankar, Sasidharan; Smitha, V.S.; Warrier, K.G.K.

    2011-07-15

    Titania-lanthanum phosphate nanocomposites with multifunctional properties have been synthesized by aqueous sol-gel method. The precursor sols with varying TiO{sub 2}:LaPO{sub 4} ratios were applied as thin coating on glass substrates in order to be transparent, hydrophobic, photocatalytically active coatings. The phase compositions of the composite powders were identified by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The anatase phase of TiO{sub 2} in TiO{sub 2}-LaPO{sub 4} composite precursors was found to be stable even on annealing at 800 deg. C. The glass substrates, coated with TL1 (TiO{sub 2}-LaPO{sub 4} composition with 1 mol% LaPO{sub 4}) and TL50 (composite precursor containing TiO{sub 2} and LaPO{sub 4} with molar ratio 1:1) sols and annealed at 400 deg. C, produced contact angles of 74 deg. and 92 deg., respectively, though it is only 62 deg. for pure TiO{sub 2} coating. The glass substrates, coated with TL50 sol, produced surfaces with relatively high roughness and uneven morphology. The TL1 material, annealed at 800 deg. C, has shown the highest UV photoactivity with an apparent rate constant, k{sub app}=24x10{sup -3} min{sup -1}, which is over five times higher than that observed with standard Hombikat UV 100 (k{sub app}=4x10{sup -3} min{sup -1}). The photoactivity combined with a moderate contact angle (85.3 deg.) shows that this material has a promise as an efficient self-cleaning precursor. - Graphical abstract: Multifunctional TiO{sub 2}-LaPO{sub 4} composite stabilizes anatase phase with enhanced photocatalytic activity, and moderately higher hydrophobicity is a promising material for self-cleaning application. Highlights: > Titania-lanthanum phosphate nanocomposites were synthesized by aqueous sol-gel method. > Transparent, hydrophobic, photoactive coatings were developed on glass substrates. > The glass substrates, coated with TL1 annealed at 400 deg. C, produced a contact angle of 74 deg

  3. Sweeping Gas Membrane Desalination Using Commercial Hydrophobic Hollow Fiber Membranes

    SciTech Connect

    EVANS, LINDSEY; MILLER, JAMES E.

    2002-01-01

    Water shortages affect 88 developing countries that are home to half of the world's population. In these places, 80-90% of all diseases and 30% of all deaths result from poor water quality. Furthermore, over the next 25 years, the number of people affected by severe water shortages is expected to increase fourfold. Low cost methods of purifying freshwater, and desalting seawater are required to contend with this destabilizing trend. Membrane distillation (MD) is an emerging technology for separations that are traditionally accomplished via conventional distillation or reverse osmosis. As applied to desalination, MD involves the transport of water vapor from a saline solution through the pores of a hydrophobic membrane. In sweeping gas MD, a flowing gas stream is used to flush the water vapor from the permeate side of the membrane, thereby maintaining the vapor pressure gradient necessary for mass transfer. Since liquid does not penetrate the hydrophobic membrane, dissolved ions are completely rejected by the membrane. MD has a number of potential advantages over conventional desalination including low temperature and pressure operation, reduced membrane strength requirements, compact size, and 100% rejection of non-volatiles. The present work evaluated the suitability of commercially available technology for sweeping gas membrane desalination. Evaluations were conducted with Celgard Liqui-Cel{reg_sign} Extra-Flow 2.5X8 membrane contactors with X-30 and X-40 hydrophobic hollow fiber membranes. Our results show that sweeping gas membrane desalination systems are capable of producing low total dissolved solids (TDS) water, typically 10 ppm or less, from seawater, using low grade heat. However, there are several barriers that currently prevent sweeping gas MD from being a viable desalination technology. The primary problem is that large air flows are required to achieve significant water yields, and the costs associated with transporting this air are prohibitive. To

  4. Tropospheric aqueous-phase free-radical chemistry: radical sources, spectra, reaction kinetics and prediction tools.

    PubMed

    Herrmann, Hartmut; Hoffmann, Dirk; Schaefer, Thomas; Bräuer, Peter; Tilgner, Andreas

    2010-12-17

    The most important radicals which need to be considered for the description of chemical conversion processes in tropospheric aqueous systems are the hydroxyl radical (OH), the nitrate radical (NO(3)) and sulphur-containing radicals such as the sulphate radical (SO(4)(-)). For each of the three radicals their generation and their properties are discussed first in the corresponding sections. The main focus herein is to summarize newly published aqueous-phase kinetic data on OH, NO(3) and SO(4)(-) radical reactions relevant for the description of multiphase tropospheric chemistry. The data compilation builds up on earlier datasets published in the literature. Since the last review in 2003 (H. Herrmann, Chem. Rev. 2003, 103, 4691-4716) more than hundred new rate constants are available from literature. In case of larger discrepancies between novel and already published rate constants the available kinetic data for these reactions are discussed and recommendations are provided when possible. As many OH kinetic data are obtained by means of the thiocyanate (SCN(-)) system in competition kinetic measurements of OH radical reactions this system is reviewed in a subchapter of this review. Available rate constants for the reaction sequence following the reaction of OH+SCN(-) are summarized. Newly published data since 2003 have been considered and averaged rate constants are calculated. Applying competition kinetics measurements usually the formation of the radical anion (SCN)(2)(-) is monitored directly by absorption measurements. Within this subchapter available absorption spectra of the (SCN)(2)(-) radical anion from the last five decades are presented. Based on these spectra an averaged (SCN)(2)(-) spectrum was calculated. In the last years different estimation methods for aqueous phase kinetic data of radical reactions have been developed and published. Such methods are often essential to estimate kinetic data which are not accessible from the literature. Approaches for

  5. COST Action CM1201 "Biomimetic Radical Chemistry": free radical chemistry successfully meets many disciplines.

    PubMed

    Ferreri, Carla; Golding, Bernard T; Jahn, Ullrich; Ravanat, Jean-Luc

    2016-11-01

    The COST Action CM1201 "Biomimetic Radical Chemistry" has been active since December 2012 for 4 years, developing research topics organized into four working groups: WG1 - Radical Enzymes, WG2 - Models of DNA damage and consequences, WG3 - Membrane stress, signalling and defenses, and WG4 - Bio-inspired synthetic strategies. International collaborations have been established among the participating 80 research groups with brilliant interdisciplinary achievements. Free radical research with a biomimetic approach has been realized in the COST Action and are summarized in this overview by the four WG leaders.

  6. Model of waterlike fluid under confinement for hydrophobic and hydrophilic particle-plate interaction potentials.

    PubMed

    Krott, Leandro B; Barbosa, Marcia C

    2014-01-01

    Molecular dynamic simulations were employed to study a waterlike model confined between hydrophobic and hydrophilic plates. The phase behavior of this system is obtained for different distances between the plates and particle-plate potentials. For both hydrophobic and hydrophilic walls, there are the formation of layers. Crystallization occurs at lower temperature at the contact layer than at the middle layer. In addition, the melting temperature decreases as the plates become more hydrophobic. Similarly, the temperatures of maximum density and extremum diffusivity decrease with hydrophobicity.

  7. Hydrophobic Molecular Similarity from MST Fractional Contributions to the Octanol/water Partition Coefficient

    NASA Astrophysics Data System (ADS)

    Muñoz-Muriedas, Jordi; Perspicace, Samantha; Bech, Nuria; Guccione, Salvatore; Orozco, Modesto; Luque, F. Javier

    2005-06-01

    The use of a recently proposed hydrophobic similarity index for the alignment of molecules and the prediction of their differences in biological activity is described. The hydrophobic similarity index exploits atomic contributions to the octanol/water transfer free energy, which are evaluated by means of the fractional partitioning scheme developed within the framework of the Miertus-Scrocco-Tomasi continuum model. Those contributions are used to define global and local measures of hydrophobic similarity. The suitability of this computational strategy is examined for two series of compounds (ACAT inhibitors and 5-HT3 receptor agonists), which are aligned to maximize the global hydrophobic similarity using a Monte Carlo-simulated protocol. Indeed, the concept of local hydrophobic similarity is used to explore structure-activity relationships in a series of COX-2 inhibitors. Inspection of the 3D distribution of hydrophobic/hydrophilic contributions in the aligned molecules is valuable to identify regions of very similar hydrophobicity, which can define pharmacophoric recognition patterns. Moreover, low similar regions permit to identify structural elements that modulate the differences in activity between molecules. Finally, the quantitative relationships found between the pharmacological activity and the hydrophobic similarity index points out that not only the global hydrophobicity, but its 3D distribution, is important to gain insight into the activity of molecules.

  8. Synthesis of biocompatible hydrophobic silica-gelatin nano-hybrid by sol-gel process.

    PubMed

    Smitha, S; Shajesh, P; Mukundan, P; Nair, T D R; Warrier, K G K

    2007-03-15

    Silica-biopolymer hybrid has been synthesised using colloidal silica as the precursor for silica and gelatin as the biopolymer counterpart. The surface modification of the hybrid material has been done with methyltrimethoxysilane leading to the formation of biocompatible hydrophobic silica-gelatin hybrid. Here we are reporting hydrophobic silica-gelatin hybrid and coating precursor for the first time. The hybrid gel has been evaluated for chemical modification, thermal degradation, hydrophobicity, particle size, transparency under the UV-visible region and morphology. FTIR spectroscopy has been used to verify the presence of CH(3) groups which introduce hydrophobicity to the SiO2-MTMS-gelatin hybrids. The hydrophobic property has also been tailored by varying the concentration of methyltrimethoxysilane. Contact angle by Wilhelmy plate method of transparent hydrophobic silica-gelatin coatings has been found to be as high as approximately 95 degrees . Oxidation of the organic group which induces the hydrophobic character occurs at 530 degrees C which indicates that the surface hydrophobicity is retained up to that temperature. Optical transmittance of SiO2-MTMS-gelatin hybrid coatings on glass substrates has been found to be close to 100% which will enable the hybrid for possible optical applications and also for preparation of transparent biocompatible hydrophobic coatings on biological substrates such as leather.

  9. On-demand microfluidic droplet manipulation using hydrophobic ferrofluid as a continuous-phase.

    PubMed

    Zhang, Kai; Liang, Qionglin; Ai, Xiaoni; Hu, Ping; Wang, Yiming; Luo, Guoan

    2011-04-07

    Multiple essential microdroplet operation units, including splitting, dispensing, oil-phase exchange, trapping, release and demulsification, were successfully implemented by combining hydrophobic ferrofluid with microfluidic chips.

  10. Bioconcentration kinetics of hydrophobic chemicals in different densities of Chlorella pyrenoidosa

    SciTech Connect

    Sijm, D.T.H.M.; Broersen, K.W.; Roode, D.F. de; Mayer, P.

    1998-09-01

    Algal density-dependent bioconcentration factors and rate constants were determined for a series of hydrophobic compounds in Chlorella pyrenoidosa. The apparent uptake rate constants of the hydrophobic compounds in algae varied between 200 and 710,000 L/kg/d, slightly increased with hydrophobicity within an experiment, were relatively constant for each algal density, and fitted fairly within existing allometric relationships. The bioavailability of the hydrophobic test compounds was significantly reduced by sorption by algal exudates. The sorption coefficients of the hydrophobic compounds to the algal exudates were between 80 and 1,200 L/kg, and were for most algal densities in the same order of magnitude as the apparent bioconcentration factors to the algae, that is, between 80 and 60,200 L/kg. In typical field situations, however, no significant reduction in bioavailability due to exudates is expected. The apparent elimination rate constants of the hydrophobic compounds were high and fairly constant for each algal density and varied between 2 and 190/d. Because the apparent elimination rate constants were higher than the growth rate constant, and were independent of hydrophobicity, the authors speculated that other factors dominate excretion, such as exudate excretion-enhanced elimination. Bioconcentration factors increased less than proportional with hydrophobicity, i.e., the octanol-water partition coefficient [K{sub ow}]. The role of algal composition in bioconcentration is evaluated. Bioconcentrations (kinetics) of hydrophobic compounds that are determined at high algal densities should be applied with caution to field situations.

  11. Characterizing hydrophobicity of interfaces by using cavity formation, solute binding, and water correlations

    PubMed Central

    Godawat, Rahul; Jamadagni, Sumanth N.; Garde, Shekhar

    2009-01-01

    Hydrophobicity is often characterized macroscopically by the droplet contact angle. Molecular signatures of hydrophobicity have, however, remained elusive. Successful theories predict a drying transition leading to a vapor-like region near large hard-sphere solutes and interfaces. Adding attractions wets the interface with local density increasing with attractions. Here we present extensive molecular simulation studies of hydration of realistic surfaces with a wide range of chemistries from hydrophobic (−CF3, −CH3) to hydrophilic (−OH, −CONH2). We show that the water density near weakly attractive hydrophobic surfaces (e.g., −CF3) can be bulk-like or larger, and provides a poor quantification of surface hydrophobicity. In contrast, the probability of cavity formation or the free energy of binding of hydrophobic solutes to interfaces correlates quantitatively with the macroscopic wetting properties and serves as an excellent signature of hydrophobicity. Specifically, the probability of cavity formation is enhanced in the vicinity of hydrophobic surfaces, and water–water correlations correspondingly display characteristics similar to those near a vapor–liquid interface. Hydrophilic surfaces suppress cavity formation and reduce the water–water correlation length. Our results suggest a potentially robust approach for characterizing hydrophobicity of more complex and heterogeneous surfaces of proteins and biomolecules, and other nanoscopic objects. PMID:19706896

  12. Understanding political radicalization: The two-pyramids model.

    PubMed

    McCauley, Clark; Moskalenko, Sophia

    2017-04-01

    This article reviews some of the milestones of thinking about political radicalization, as scholars and security officials struggled after 9/11 to discern the precursors of terrorist violence. Recent criticism of the concept of radicalization has been recognized, leading to a 2-pyramids model that responds to the criticism by separating radicalization of opinion from radicalization of action. Security and research implications of the 2-pyramids model are briefly described, ending with a call for more attention to emotional experience in understanding both radicalization of opinion and radicalization of action. (PsycINFO Database Record

  13. Free radicals in adolescent varicocele testis.

    PubMed

    Romeo, Carmelo; Santoro, Giuseppe

    2014-01-01

    We examine the relationship between the structure and function of the testis and the oxidative and nitrosative stress, determined by an excessive production of free radicals and/or decreased availability of antioxidant defenses, which occur in the testis of adolescents affected by varicocele. Moreover, the effects of surgical treatment on oxidative stress were provided. We conducted a PubMed and Medline search between 1980 and 2014 using "adolescent," "varicocele," "free radicals," "oxidative and nitrosative stress," "testis," and "seminiferous tubules" as keywords. Cross-references were checked in each of the studies, and relevant articles were retrieved. We conclude that increased concentration of free radicals, generated by conditions of hypoxia, hyperthermia, and hormonal dysfunction observed in adolescent affected by varicocele, can harm germ cells directly or indirectly by influencing nonspermatogenic cells and basal lamina. With regard to few available data in current literature, further clinical trials on the pre- and postoperative ROS and RNS levels together with morphological studies of the cellular component of the testis are fundamental for complete comprehension of the role played by free radicals in the pathogenesis of adolescent varicocele and could justify its pharmacological treatment with antioxidants.

  14. Radical Change: Digital Age Literature and Learning.

    ERIC Educational Resources Information Center

    Dresang, Eliza T.; McClelland, Kathryn

    1999-01-01

    Describes the concept of radical change, a theoretical construct that identifies and explains books with characteristics reflecting the types of interactivity, connectivity, and access that permeate the emerging digital society. Highlights innovative ways that authors, illustrators, and designers incorporate these features into books for…

  15. Globins Scavenge Sulfur Trioxide Anion Radical*

    PubMed Central

    Gardner, Paul R.; Gardner, Daniel P.; Gardner, Alexander P.

    2015-01-01

    Ferrous myoglobin was oxidized by sulfur trioxide anion radical (STAR) during the free radical chain oxidation of sulfite. Oxidation was inhibited by the STAR scavenger GSH and by the heme ligand CO. Bimolecular rate constants for the reaction of STAR with several ferrous globins and biomolecules were determined by kinetic competition. Reaction rate constants for myoglobin, hemoglobin, neuroglobin, and flavohemoglobin are large at 38, 120, 2,600, and ≥ 7,500 × 106 m−1 s−1, respectively, and correlate with redox potentials. Measured rate constants for O2, GSH, ascorbate, and NAD(P)H are also large at ∼100, 10, 130, and 30 × 106 m−1 s−1, respectively, but nevertheless allow for favorable competition by globins and a capacity for STAR scavenging in vivo. Saccharomyces cerevisiae lacking sulfite oxidase and deleted of flavohemoglobin showed an O2-dependent growth impairment with nonfermentable substrates that was exacerbated by sulfide, a precursor to mitochondrial sulfite formation. Higher O2 exposures inactivated the superoxide-sensitive mitochondrial aconitase in cells, and hypoxia elicited both aconitase and NADP+-isocitrate dehydrogenase activity losses. Roles for STAR-derived peroxysulfate radical, superoxide radical, and sulfo-NAD(P) in the mechanism of STAR toxicity and flavohemoglobin protection in yeast are suggested. PMID:26381408

  16. Globins Scavenge Sulfur Trioxide Anion Radical.

    PubMed

    Gardner, Paul R; Gardner, Daniel P; Gardner, Alexander P

    2015-11-06

    Ferrous myoglobin was oxidized by sulfur trioxide anion radical (STAR) during the free radical chain oxidation of sulfite. Oxidation was inhibited by the STAR scavenger GSH and by the heme ligand CO. Bimolecular rate constants for the reaction of STAR with several ferrous globins and biomolecules were determined by kinetic competition. Reaction rate constants for myoglobin, hemoglobin, neuroglobin, and flavohemoglobin are large at 38, 120, 2,600, and ≥ 7,500 × 10(6) m(-1) s(-1), respectively, and correlate with redox potentials. Measured rate constants for O2, GSH, ascorbate, and NAD(P)H are also large at ∼100, 10, 130, and 30 × 10(6) m(-1) s(-1), respectively, but nevertheless allow for favorable competition by globins and a capacity for STAR scavenging in vivo. Saccharomyces cerevisiae lacking sulfite oxidase and deleted of flavohemoglobin showed an O2-dependent growth impairment with nonfermentable substrates that was exacerbated by sulfide, a precursor to mitochondrial sulfite formation. Higher O2 exposures inactivated the superoxide-sensitive mitochondrial aconitase in cells, and hypoxia elicited both aconitase and NADP(+)-isocitrate dehydrogenase activity losses. Roles for STAR-derived peroxysulfate radical, superoxide radical, and sulfo-NAD(P) in the mechanism of STAR toxicity and flavohemoglobin protection in yeast are suggested.

  17. Free Radicals in Adolescent Varicocele Testis

    PubMed Central

    Romeo, Carmelo; Santoro, Giuseppe

    2014-01-01

    We examine the relationship between the structure and function of the testis and the oxidative and nitrosative stress, determined by an excessive production of free radicals and/or decreased availability of antioxidant defenses, which occur in the testis of adolescents affected by varicocele. Moreover, the effects of surgical treatment on oxidative stress were provided. We conducted a PubMed and Medline search between 1980 and 2014 using “adolescent,” “varicocele,” “free radicals,” “oxidative and nitrosative stress,” “testis,” and “seminiferous tubules” as keywords. Cross-references were checked in each of the studies, and relevant articles were retrieved. We conclude that increased concentration of free radicals, generated by conditions of hypoxia, hyperthermia, and hormonal dysfunction observed in adolescent affected by varicocele, can harm germ cells directly or indirectly by influencing nonspermatogenic cells and basal lamina. With regard to few available data in current literature, further clinical trials on the pre- and postoperative ROS and RNS levels together with morphological studies of the cellular component of the testis are fundamental for complete comprehension of the role played by free radicals in the pathogenesis of adolescent varicocele and could justify its pharmacological treatment with antioxidants. PMID:25580183

  18. Albert Einstein: Radical Pacifist and Democrat

    NASA Astrophysics Data System (ADS)

    Jayaraman, T.

    We draw attention here to the radical political grounding of Einstein's pacifism. We also drescribe some less commonly known aspects of his commitment to civil liberties, particularly in the context of the anti-l hysteria and anti-racism current in the United States of the late 1940s and 1950s. We also examine briefly his views on socialism.

  19. Radical Constructivism, and the Sin of Relativism

    ERIC Educational Resources Information Center

    Quale, Andreas

    2007-01-01

    The epistemology of "relativism" that is featured by the theory of radical constructivism is addressed. In particular, I examine several objections, all based on this epistemic position of relativism, that are often raised by critics of the theory: the charge of "reality denial" (which, it is often claimed, must lead ultimately to the…

  20. DNP with Trityl Radicals in Deuterated Polyethylene

    NASA Astrophysics Data System (ADS)

    Wang, Li; Meyer, W.; Berlin, A.; Herick, J.; Hess, C.; Reicherz, G.

    2016-02-01

    Chemically doping with trityl radicals was performed in fully deuterated polyethylene. The behavior of paramagnetic centers has been investigated by ESR X-band spectrometer. The highest deuteron polarization was 8% at 2.5 T and 1 K with a spin concentration of 3 × 1019 spins/g.

  1. Radical Negativity: Music Education for Social Justice

    ERIC Educational Resources Information Center

    McLaren, Peter

    2011-01-01

    According to Hedges (2010), the real enemies of the liberal class are radical thinkers such as Noam Chomsky and Ralph Nader, iconoclastic intellectuals who possess the moral autonomy to defy the power elite. While this author agrees with Hedges, he would take this argument even further. In this article, the author argues that the real enemy of…

  2. Praxis: Implication for "Really" Radical Education.

    ERIC Educational Resources Information Center

    Allman, Paula; Wallis, John

    1990-01-01

    Explicates the concept of praxis in Marx's dialectical analysis of capitalism and relates it to radical education: issues of access to educational opportunities, the challenge to the status quo through curriculum change, the role of the intellectual, and the relationship between knowledge and action. (SK)

  3. Free Radical Mechanisms of Xenobiotic Mammalian Cytotoxicities

    DTIC Science & Technology

    1991-06-30

    isolated in Peganum harmala , and related alkaloids are widely distributed in medicinal plants. Harmala alkaloids have been used in hallucinogenic...University 3800, Reservoir Road, N.W. Washington D.C. 20007. Short title : Anti-oxidative Actions of Harmala Alkaloids Keywords : free radicals, lipid...peroxidation, harmane, harmine, harmalol, harmine, tryptamine, 5-hydroxytryptamine, ’ 5- methoxytryptamine, 5-hydroxytryptophan, harmala alkaloids

  4. Hydroxyl Radical Dosimetry for High Flux Hydroxyl Radical Protein Footprinting Applications Using a Simple Optical Detection Method.

    PubMed

    Xie, Boer; Sharp, Joshua S

    2015-11-03

    Hydroxyl radical protein footprinting (HRPF) by fast photochemical oxidation of proteins (FPOP) is a powerful benchtop tool used to probe protein structure, interactions, and conformational changes in solution. However, the reproducibility of all HRPF techniques is limited by the ability to deliver a defined concentration of hydroxyl radicals to the protein. This ability is impacted by both the amount of radical generated and the presence of radical scavengers in solution. In order to compare HRPF data from sample to sample, a hydroxyl radical dosimeter is needed that can measure the effective concentration of radical that is delivered to the protein, after accounting for both differences in hydroxyl radical generation and nonanalyte radical consumption. Here, we test three radical dosimeters (Alexa Fluor 488, terepthalic acid, and adenine) for their ability to quantitatively measure the effective radical dose under the high radical concentration conditions of FPOP. Adenine has a quantitative relationship between UV spectrophotometric response, effective hydroxyl radical dose delivered, and peptide and protein oxidation levels over the range of radical concentrations typically encountered in FPOP. The simplicity of an adenine-based dosimeter allows for convenient and flexible incorporation into FPOP applications, and the ability to accurately measure the delivered radical dose will enable reproducible and reliable FPOP across a variety of platforms and applications.

  5. Neutron structure of the hydrophobic plant protein crambin

    SciTech Connect

    Teeter, M.M.; Kossiakoff, A.A.

    1982-01-01

    Crystals of the small hydrophobic protein crambin have been shown to diffract to a resolution of at least 0.88 A. This means that crambin presents a rare opportunity to study a protein structure at virtually atomic resolution. The high resolution of the diffraction pattern coupled with the assets of neutron diffraction present the distinct possibility that crambin's analysis may surpass that of any other protein system in degree and accuracy of detail. The neutron crambin structure is currently being refined at 1.50 A (44.9% of the data to 1.2 A has also been included). It is expected that a nominal resolution of 1.0 A can be achieved. 15 references, 6 figures, 2 tables.

  6. Super-hydrophobic bandages and method of making the same

    DOEpatents

    Simpson, John T [Clinton, TN; D'Urso, Brian R [Pittsburgh, PA

    2012-06-05

    A bandage that includes a material, which can be breathable, having a first surface, and a plurality of superhydrophobic particles attached to the first surface. The plurality of superhydrophobic particles ranging in size from about 100 nanometers to about 10 micrometers. The superhydrophobic particles including a protrusive material defining a plurality of nanopores and a plurality of spaced apart nanostructures that define an external boundary of the hydrophobic particles. The nanopores providing a flow through porosity. The first surface can be rendered superhydrophobic by the attached superhydrophobic particles. The material can have a second surface opposite the first surface that is hydrophilic. The superhydrophobic particles can be adhered to the first surface by a binder. Also included is a method of making the bandages described herein.

  7. Intramolecular hydrophobic interactions are critical mediators of STAT5 dimerization.

    PubMed

    Fahrenkamp, Dirk; Li, Jinyu; Ernst, Sabrina; Schmitz-Van de Leur, Hildegard; Chatain, Nicolas; Küster, Andrea; Koschmieder, Steffen; Lüscher, Bernhard; Rossetti, Giulia; Müller-Newen, Gerhard

    2016-10-18

    STAT5 is an essential transcription factor in hematopoiesis, which is activated through tyrosine phosphorylation in response to cytokine stimulation. Constitutive activation of STAT5 is a hallmark of myeloid and lymphoblastic leukemia. Using homology modeling and molecular dynamics simulations, a model of the STAT5 phosphotyrosine-SH2 domain interface was generated providing first structural information on the activated STAT5 dimer including a sequence, for which no structural information is available for any of the STAT proteins. We identified a novel intramolecular interaction mediated through F706, adjacent to the phosphotyrosine motif, and a unique hydrophobic interface on the surface of the SH2 domain. Analysis of corresponding STAT5 mutants revealed that this interaction is dispensable for Epo receptor-mediated phosphorylation of STAT5 but essential for dimer formation and subsequent nuclear accumulation. Moreover, the herein presented model clarifies molecular mechanisms of recently discovered leukemic STAT5 mutants and will help to guide future drug development.

  8. Laboratory analyses of two explanted hydrophobic acrylic intraocular lenses.

    PubMed

    Dai, Yunhai; Huang, Yusen; Liu, Ting; Xie, Lixin

    2014-06-01

    Two three-piece hydrophobic acrylic intraocular lenses (IOLs) were explanted from two patients at 7 and 9 years, respectively, after implantation, because of poor fundus visualisation and/or a clinically significant decrease in visual acuity related to their opacified IOLs. In addition to light microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy, confocal laser scanning microscopy was used for the first time to observe the explanted IOLs. The clinical aspect seemed to correspond to the phenomenon of surface light scattering, while laboratory analyses showed dense glistenings in the central layer of the IOL optic, which had no change next to the surface. Further studies on these phenomena are needed.

  9. Giant Osmotic Pressure in the Forced Wetting of Hydrophobic Nanopores.

    PubMed

    Michelin-Jamois, Millan; Picard, Cyril; Vigier, Gérard; Charlaix, Elisabeth

    2015-07-17

    The forced intrusion of water in hydrophobic nanoporous pulverulent material is of interest for quick storage of energy. With nanometric pores the energy storage capacity is controlled by interfacial phenomena. With subnanometric pores, we demonstrate that a breakdown occurs with the emergence of molecular exclusion as a leading contribution. This bulk exclusion effect leads to an osmotic contribution to the pressure that can reach levels never previously sustained. We illustrate, on various electrolytes and different microporous materials, that a simple osmotic pressure law accounts quantitatively for the enhancement of the intrusion and extrusion pressures governing the forced wetting and spontaneous drying of the nanopores. Using electrolyte solutions, energy storage and power capacities can be widely enhanced.

  10. Determination on Monod kinetic coefficients for volatile hydrophobic organic compounds

    SciTech Connect

    Guha, S.; Jaffe, P.R.

    1996-06-20

    A new procedure is presented to determine Monod kinetic coefficients and the microbial yield coefficient for volatile hydrophobic compounds such as phenanthrene. Batch experiments were conducted with a mixed culture capable of degrading phenanthrene. The phenanthrene disappearance and carbon dioxide production were monitored with time. A maximum likelihood estimator was formulated to fit the set of equations that describe the system to the measured data. The model takes into account a number of processes such as partition onto the apparatus, volatilization, and partition onto the biomass. The parameters required to describe these processes were obtained by independent experiments. The yield coefficient could be determined within a small range. However, the specific growth rate and the half-saturation constant were found to vary widely, with pairs of them describing the system adequately. It was shown that partition and volatilization processes can significantly affect the determination of the yield and Monod kinetic coefficients and need to be taken into account.

  11. Modification of Deeply Buried Hydrophobic Interfaces by Ionic Surfactants

    SciTech Connect

    Ocko, B.M.; Tamam, L.; Pontoni, D.; Sapir, Z.; Yefet, S.; Sloutskin, E.; Reichert, H.; Deutsch, M.

    2011-04-05

    Hydrophobicity, the spontaneous segregation of oil and water, can be modified by surfactants. The way this modification occurs is studied at the oil-water interface for a range of alkanes and two ionic surfactants. A liquid interfacial monolayer, consisting of a mixture of alkane molecules and surfactant tails, is found. Upon cooling, it freezes at T{sub s}, well above the alkane's bulk freezing temperature, T{sub b}. The monolayer's phase diagram, derived by surface tensiometry, is accounted for by a mixtures-based theory. The monolayer's structure is measured by high-energy X-ray reflectivity above and below T{sub s}. A solid-solid transition in the frozen monolayer, occurring approximately 3 C below T{sub s}, is discovered and tentatively suggested to be a rotator-to-crystal transition.

  12. Modification of Deeply Buried Hydrophobic Interfaces by Ionic Surfactants

    SciTech Connect

    L Tamam; D Pontoni Z Sapir; S Yefet; S Sloutskin; B Ocko; H Reichert; M Deutsch

    2011-12-31

    Hydrophobicity, the spontaneous segregation of oil and water, can be modified by surfactants. The way this modification occurs is studied at the oil-water interface for a range of alkanes and two ionic surfactants. A liquid interfacial monolayer, consisting of a mixture of alkane molecules and surfactant tails, is found. Upon cooling, it freezes at T{sub s}, well above the alkane's bulk freezing temperature, T{sub b}. The monolayer's phase diagram, derived by surface tensiometry, is accounted for by a mixtures-based theory. The monolayer's structure is measured by high-energy X-ray reflectivity above and below T{sub s}. A solid-solid transition in the frozen monolayer, occurring approximately 3 C below T{sub s}, is discovered and tentatively suggested to be a rotator-to-crystal transition.

  13. Harvesting electrostatic energy using super-hydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Pociecha, Dominik; Zylka, Pawel

    2016-11-01

    Almost all environments are now being extensively populated by miniaturized, nano-powered electronic sensor devices communicated together through wireless sensor networks building Internet of Things (IoT). Various energy harvesting techniques are being more and more frequently proposed for battery-less powering of such remote, unattended, implantable or wearable sensors or other low-power electronic gadgets. Energy harvesting relays on extracting energy from the ambient sources readily accessible at the sensor location and converting it into electrical power. The paper exploits possibility of generating electric energy safely accessible for nano-power electronics using tribo-electric and electrostatic induction phenomena displayed at super-hydrophobic surfaces impinged by water droplets. Mechanism of such interaction is discussed and illustrated by experimental results.

  14. Intramolecular hydrophobic interactions are critical mediators of STAT5 dimerization

    NASA Astrophysics Data System (ADS)

    Fahrenkamp, Dirk; Li, Jinyu; Ernst, Sabrina; Schmitz-van de Leur, Hildegard; Chatain, Nicolas; Küster, Andrea; Koschmieder, Steffen; Lüscher, Bernhard; Rossetti, Giulia; Müller-Newen, Gerhard

    2016-10-01

    STAT5 is an essential transcription factor in hematopoiesis, which is activated through tyrosine phosphorylation in response to cytokine stimulation. Constitutive activation of STAT5 is a hallmark of myeloid and lymphoblastic leukemia. Using homology modeling and molecular dynamics simulations, a model of the STAT5 phosphotyrosine-SH2 domain interface was generated providing first structural information on the activated STAT5 dimer including a sequence, for which no structural information is available for any of the STAT proteins. We identified a novel intramolecular interaction mediated through F706, adjacent to the phosphotyrosine motif, and a unique hydrophobic interface on the surface of the SH2 domain. Analysis of corresponding STAT5 mutants revealed that this interaction is dispensable for Epo receptor-mediated phosphorylation of STAT5 but essential for dimer formation and subsequent nuclear accumulation. Moreover, the herein presented model clarifies molecular mechanisms of recently discovered leukemic STAT5 mutants and will help to guide future drug development.

  15. Influence of the surface hydrophobicity on fluorescence correlation spectroscopy measurements

    NASA Astrophysics Data System (ADS)

    Boutin, Céline; Jaffiol, Rodolphe; Plain, Jérome; Royer, Pascal

    2007-02-01

    Fluorescence correlation spectroscopy (FCS) is a powerful experimental technique used to analyze the diffusion at the single molecule level in solution. FCS is based on the temporal autocorrelation of fluorescent signal generated by dye molecules diffusing through a small confocal volume. These measurements are mostly carried out in a chambered coverglass, close to the glass substrate. In this report, we discuss how the chemical nature of the glass-water interface may interact with the free diffusion of molecules. Our results reveal a strong influence, up to a few μm from the interface, of the surface hydrophobicity degree. This influence is assessed through the relative weight of the two dimension diffusion process observed at the vicinity of the surface.

  16. Hydrophobic starch nanocrystals preparations through crosslinking modification using citric acid.

    PubMed

    Zhou, Jiang; Tong, Jin; Su, Xingguang; Ren, Lili

    2016-10-01

    Biodegradable starch nanocrystals prepared by an acid treatment process were modified through crosslinking modification using citric acid as reactant by a dry reaction method. The occurrence of crosslinking modification was evaluated by Fourier transform infrared spectroscopy and swelling degree. X-ray diffraction, wettability tests and contact angle measurements were used to characterize the modified starch nanocrystals. It was found that the crosslinked starch nanocrystals displayed a higher affinity for low polar solvents such as dichloromethane. The surface of starch nanocrystals became more roughness after crosslinking modification with citric acid and the size decreased as revealed by scanning electron microscopy and dynamic light scattering results. XRD analysis showed that the crystalline structure of starch nanocrystals was basically not changed after the crosslinking modification with shorter heating time. The resulting hydrophobic starch nanocrystals are versatile precursors to the development of nanocomposites.

  17. Asymmetry of Drop Impacts on Patterned Hydrophobic Microstructures

    NASA Astrophysics Data System (ADS)

    Willmott, Geoff; Robson, Simon; Broom, Matheu

    2016-11-01

    When a water drop falls on to a flat solid surface, asymmetries in the geometry of the spreading drop can be specifically determined by patterned surface microstructures. For hydrophobic (or superhydrophobic) micropillar arrays, the most important asymmetric mechanisms appear to be the surface energy of contact lines, and pathways for gas escaping from penetrated microstructure. In this presentation, static wetting and drop impact experiments will be discussed in relation to drop asymmetries. In addition to micropillar arrays, natural superhydrophobic surfaces (leaves) have been studied, and may suggest possibilities for controlling drop impacts in applications. Some of the clearest large scale drop asymmetries on leaves, which are similar to those associated with low drop impact contact times on synthetic surfaces, appear to be caused by features which generate high contact angle hysteresis, and are therefore indicative of poor superhydrophocity.

  18. Hydrophobic conjugated microporous polymers for sorption of human serum albumin

    NASA Astrophysics Data System (ADS)

    Zheng, Chunli; Du, Miaomiao; Feng, Shanshan; Sun, Hanxue; Li, An; He, Chi; Zhang, TianCheng; Wang, Qiaorui; Wei, Wei

    2016-02-01

    This paper investigated the sorption of human serum albumin (HSA) from water by three kinds of conjugated microporous polymers (CMPs) with surface hydrophobicity and intrinsic porosity. It was found that the three CMPs captured HSA with fast sorption kinetics and good working capacity. Equilibrium was obtained at 80 min for all the tests, and the maximum sorption quantity (qm) ranged from 0.07 to 0.14 mg/mg. With the increase in the particle external surface area of the CMPs, a greater extent of HSA sorption was achieved. Moreover, promoting the dispersion of CMPs in HSA aqueous solution was also beneficial to the extraction. Attenuated Total Reflection Fourier Transform Infrared spectroscopy verified the interactions between the CMPs and the Nsbnd H, Cdbnd O, and Csbnd N groups of HSA. This paper might provide fundamental guidance for the practical application of CMPs to proteins separation and recovery.

  19. Intramolecular hydrophobic interactions are critical mediators of STAT5 dimerization

    PubMed Central

    Fahrenkamp, Dirk; Li, Jinyu; Ernst, Sabrina; Schmitz-Van de Leur, Hildegard; Chatain, Nicolas; Küster, Andrea; Koschmieder, Steffen; Lüscher, Bernhard; Rossetti, Giulia; Müller-Newen, Gerhard

    2016-01-01

    STAT5 is an essential transcription factor in hematopoiesis, which is activated through tyrosine phosphorylation in response to cytokine stimulation. Constitutive activation of STAT5 is a hallmark of myeloid and lymphoblastic leukemia. Using homology modeling and molecular dynamics simulations, a model of the STAT5 phosphotyrosine-SH2 domain interface was generated providing first structural information on the activated STAT5 dimer including a sequence, for which no structural information is available for any of the STAT proteins. We identified a novel intramolecular interaction mediated through F706, adjacent to the phosphotyrosine motif, and a unique hydrophobic interface on the surface of the SH2 domain. Analysis of corresponding STAT5 mutants revealed that this interaction is dispensable for Epo receptor-mediated phosphorylation of STAT5 but essential for dimer formation and subsequent nuclear accumulation. Moreover, the herein presented model clarifies molecular mechanisms of recently discovered leukemic STAT5 mutants and will help to guide future drug development. PMID:27752093

  20. Energetics of Intermolecular Hydrogen Bonds in a Hydrophobic Protein Cavity

    NASA Astrophysics Data System (ADS)

    Liu, Lan; Baergen, Alyson; Michelsen, Klaus; Kitova, Elena N.; Schnier, Paul D.; Klassen, John S.

    2014-05-01

    This work explores the energetics of intermolecular H-bonds inside a hydrophobic protein cavity. Kinetic measurements were performed on the gaseous deprotonated ions (at the -7 charge state) of complexes of bovine β-lactoglobulin (Lg) and three monohydroxylated analogs of palmitic acid (PA): 3-hydroxypalmitic acid (3-OHPA), 7-hydroxypalmitic acid (7-OHPA), and 16-hydroxypalmitic acid (16-OHPA). From the increase in the activation energy for the dissociation of the (Lg + X-OHPA)7- ions, compared with that of the (Lg + PA)7- ion, it is concluded that the -OH groups of the X-OHPA ligands participate in strong (5 - 11 kcal mol-1) intermolecular H-bonds in the hydrophobic cavity of Lg. The results of molecular dynamics (MD) simulations suggest that the -OH groups of 3-OHPA and 16-OHPA act as H-bond donors and interact with backbone carbonyl oxygens, whereas the -OH group of 7-OHPA acts as both H-bond donor and acceptor with nearby side chains. The capacity for intermolecular H-bonds within the Lg cavity, as suggested by the gas-phase measurements, does not necessarily lead to enhanced binding in aqueous solution. The association constant (Ka) measured for 7-OHPA [(2.3 ± 0.2) × 105 M-1] is similar to the value for the PA [(3.8 ± 0.1) × 105 M-1]; Ka for 3-OHPA [(1.1 ± 0.3) × 106 M-1] is approximately three-times larger, whereas Ka for 16-OHPA [(2.3 ± 0.2) × 104 M-1] is an order of magnitude smaller. Taken together, the results of this study suggest that the energetic penalty to desolvating the ligand -OH groups, which is necessary for complex formation, is similar in magnitude to the energetic contribution of the intermolecular H-bonds.

  1. Thiolated graphene oxide as promising mucoadhesive carrier for hydrophobic drugs.

    PubMed

    Pereira de Sousa, Irene; Buttenhauser, Katrin; Suchaoin, Wongsakorn; Partenhauser, Alexandra; Perrone, Mara; Matuszczak, Barbara; Bernkop-Schnürch, Andreas

    2016-07-25

    The aim of this study was to improve the mucoadhesive properties of graphene by conjugating thiol ligands, in order to formulate an oral delivery system for hydrophobic drugs showing long mucus residence time. Graphene oxide was obtained by oxidation of graphite and then was thiolated following two synthetic paths. On the one hand, the hydroxyl groups were conjugated with thiourea passing through the formation of a brominated intermediate. On the other hand, the carboxylic acid groups were conjugated with cysteamine via carbodiimide chemistry. The mucoadhesive properties of thiolated graphene were evaluated by rheological measurements and by residence time assay. Then, valsartan was loaded on thiolated graphene and the release profile was evaluated in simulated intestinal fluid. Following both synthetic paths it was possible to obtain thiolated graphene bearing 215-302μmol SH/g product. Both products induced after 1h incubation an increase of mucus viscosity of about 22-33-fold compared to unmodified graphite. The residence time assay confirmed that 60% of thiolated graphene could be retained on intestinal mucosa after 4h incubation, whereas just 20% of unmodified graphite could be retained. Valsartan could be loaded with a drug loading of about 31±0.3% and a sustained release profile was observed for both formulations. According to the presented data, the thiolation of graphene could improve its mucoadhesive properties. Therefore, thiolated graphene represents a promising platform for oral delivery of hydrophobic drugs, possessing a long residence time on intestinal mucosa which allows the release of the loaded drug close to the adsorptive epithelium.

  2. Effects of geometry and chemistry on hydrophobic solvation.

    PubMed

    Harris, Robert C; Pettitt, B Montgomery

    2014-10-14

    Inserting an uncharged van der Waals (vdw) cavity into water disrupts the distribution of water and creates attractive dispersion interactions between the solvent and solute. This free-energy change is the hydrophobic solvation energy (ΔG(vdw)). Frequently, it is assumed to be linear in the solvent-accessible surface area, with a positive surface tension (γ) that is independent of the properties of the molecule. However, we found that γ for a set of alkanes differed from that for four configurations of decaalanine, and γ = -5 was negative for the decaalanines. These findings conflict with the notion that ΔG(vdw) favors smaller A. We broke ΔG(vdw) into the free energy required to exclude water from the vdw cavity (ΔG(rep)) and the free energy of forming the attractive interactions between the solute and solvent (ΔG(att)) and found that γ < 0 for the decaalanines because -γ(att) > γ(rep) and γ(att) < 0. Additionally, γ(att) and γ(rep) for the alkanes differed from those for the decaalanines, implying that none of ΔG(att), ΔG(rep), and ΔG(vdw) can be computed with a constant surface tension. We also showed that ΔG(att) could not be computed from either the initial or final water distributions, implying that this quantity is more difficult to compute than is sometimes assumed. Finally, we showed that each atom's contribution to γ(rep) depended on multibody interactions with its surrounding atoms, implying that these contributions are not additive. These findings call into question some hydrophobic models.

  3. Understanding the drop impact on moving hydrophilic and hydrophobic surfaces.

    PubMed

    Almohammadi, H; Amirfazli, A

    2017-03-08

    In this paper, a systematic study was performed to understand the drop impact on hydrophilic and hydrophobic surfaces that were moving in the horizontal direction. Drops (D0 = 2.5 mm) of liquids with three different viscosities were used. Wide ranges of drop normal velocity (0.5 to 3.4 m s(-1)) and surface velocity (0 to 17 m s(-1)) were studied. High speed imaging from the top and side was used to capture the impact phenomena. It was found that drop impact behavior on a moving surface significantly differs from that on a stationary surface at both the lamella extension stage (i.e. t ≤ tmax) and the retraction stage (t > tmax). Starting with the lamella extension stage, it was observed that the drop spreads asymmetrically over a moving surface. It was also found that the splashing behavior of the drop upon impact on a moving surface, unlike the understanding in the literature, is azimuthally different along the lamella contact line. In the case of the drop spreading over a moving surface, the surface movement stretches the expanded lamella in the direction of the surface motion. For hydrophilic surfaces, the stretched lamella pins to the surface and moves with the surface velocity; however, for hydrophobic surfaces, the lamella recoils during such stretching. A new model was developed to determine the splashing threshold of the drop impact on a moving surface. The model is capable of describing the azimuthally different behavior of the splashing which is a function of normal capillary and Weber numbers, surface velocity, and surface wettability. It was also found that the increase of the viscosity decreases the splashing threshold. Finally, comprehensive regime maps of the drop impact outcome on a moving surface were provided for both t ≤ tmax and t > tmax stages.

  4. Interaction of engineered nanomaterials with hydrophobic organic pollutants

    NASA Astrophysics Data System (ADS)

    Sahle-Demessie, E.; Han, Changseok; Zhao, Amy; Hahn, Bill; Grecsek, Heidi

    2016-07-01

    As nanomaterials become an increasing part of everyday consumer products, it is imperative to monitor their potential release during production, use and disposal, and to assess their impact on the health of humans and the ecosystem. This necessitates research to better understand how the properties of engineered nanomaterials (ENMs) lead to their accumulation and redistribution in the environment, and to assess whether they could become novel pollutants or if they can affect the mobility and bioavailability of other toxins. This study focuses on understanding the influence of nanostructured-TiO2 and the interaction of multi-walled carbon nanotubes with organic pollutants in water. We studied the adsorption and water phase dispersion of model pollutants with relatively small water solubility (i.e., two- and three-ring polyaromatic hydrocarbons and insecticides) with respect to ENMs. The sorption of pollutants was measured based on water phase analysis, and by separating suspended particles from the water phase and analyzing dried samples using integrated thermal-chromatographic-mass spectroscopic (TGA/GC/MS) techniques. Solid phase analysis using a combination of TGA/GC/MS is a novel technique that can provide real-time quantitative analysis and which helps to understand the interaction of hydrophobic organic pollutants and ENMs. The adsorption of these contaminants to nanomaterials increased the concentration of the contaminants in the aqueous phase as compared to the ‘real’ partitioning due to the octanol-water partitioning. The study showed that ENMs can significantly influence the adsorption and dispersion of hydrophobic/low water soluble contaminants. The type of ENM, the exposure to light, and the water pH have a significant influence on the partitioning of pollutants.

  5. TRANSITION METAL CATALYSIS IN CONTROLLED RADICAL POLYMERIZATION: ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    EPA Science Inventory

    Novel and diversified macromolecular structures, which include polymers with designed topologies (top), compostions (middle), and functionalities (bottom), can be prepared by atom transfer radical polymerization processes. These polymers can be synthesized from a large variety of...

  6. Understanding the microsolvation of radicals: Infrared spectroscopy of benzyl radical water clusters

    NASA Astrophysics Data System (ADS)

    Leicht, Daniel; Kaufmann, Matin; Schwan, Raffael; Schäfer, Jan; Schwaab, Gerhard; Havenith, Martina

    2016-11-01

    The IR spectrum of benzyl radical:water clusters was recorded. Benzyl radicals were produced by vacuum flash pyrolysis and trapped in superfluid helium nanodroplets. The infrared spectrum of benzyl radical water aggregates in the range 2585-2820 cm-1 was recorded by subsequent addition of deuterated water. A total of seven peaks are observed at 2766, 2750, 2656, 2638, 2633, 2598, and 2593 cm-1. Based on pressure dependent measurements and comparison to accompanying ab initio calculations, five of these bands are assigned to distinct O-D stretch vibrations of benzyl:water clusters with one and two water molecules. In line with previous experiments on benzene:water clusters, we observe the formation of a water dimer-like motif that is attached to one face of the benzyl radical.

  7. Pressure effects on the radical-radical recombination reaction of photochromic bridged imidazole dimers.

    PubMed

    Mutoh, Katsuya; Abe, Jiro

    2014-09-07

    The bridged imidazole dimers are some of the attractive fast photochromic compounds which have potential applications to the ophthalmic lenses, real-time hologram and molecular machines. The strategy for expanding their photochromic properties such as the colour variation and tuning the decolouration rates has been vigorously investigated, but the insight into the structural changes along the photochromic reactions has not been demonstrated in detail. Here, we demonstrated the pressure dependence of the radical-radical recombination reaction of the bridged imidazole dimers. The radical-radical interaction can be controlled by applying high pressure. Our results give fundamental information about the molecular dynamics of the bridged imidazole dimers, leading to the development of new functional photochromic machines and pressure-sensitive photochromic materials.

  8. Radical scavenging activity of antioxidants evaluated by means of electrogenerated HO radical.

    PubMed

    Oliveira, Raquel; Geraldo, Dulce; Bento, Fátima

    2014-11-01

    A method is proposed and tested concerning the characterization of antioxidants by means of their reaction with electrogenerated HO radicals in galvanostatic assays with simultaneous O2 evolution, using a Pt anode fairly oxidized. The consumption of a set of species with antioxidant activity, ascorbic acid (AA), caffeic acid (CA), gallic acid (GA) and trolox (T), is described by a first order kinetics. The rate of the processes is limited by the kinetics of reaction with HO radicals and by the kinetics of charge transfer. Information regarding the scavenger activity of antioxidants is obtained by the relative value of the rate constant of the reaction between antioxidants and HO radicals, k(AO,HO)/k(O2). The number of HO radicals scavenged per molecule of antioxidant is also estimated and ranged from 260 (ascorbic acid) to 500 (gallic acid). The method is applied successfully in the characterization of the scavenger activity of ascorbic acid in a green-tea based beverage.

  9. Monolignol radical-radical coupling networks in western red cedar and Arabidopsis and their evolutionary implications

    NASA Technical Reports Server (NTRS)

    Kim, Myoung K.; Jeon, Jae-Heung; Davin, Laurence B.; Lewis, Norman G.

    2002-01-01

    The discovery of a nine-member multigene dirigent family involved in control of monolignol radical-radical coupling in the ancient gymnosperm, western red cedar, suggested that a complex multidimensional network had evolved to regulate such processes in vascular plants. Accordingly, in this study, the corresponding promoter regions for each dirigent multigene member were obtained by genome-walking, with Arabidopsis being subsequently transformed to express each promoter fused to the beta-glucuronidase (GUS) reporter gene. It was found that each component gene of the proposed network is apparently differentially expressed in individual tissues, organs and cells at all stages of plant growth and development. The data so obtained thus further support the hypothesis that a sophisticated monolignol radical-radical coupling network exists in plants which has been highly conserved throughout vascular plant evolution.

  10. Carbon radicals. Direct observation and kinetics of a hydroperoxyalkyl radical (QOOH).

    PubMed

    Savee, John D; Papajak, Ewa; Rotavera, Brandon; Huang, Haifeng; Eskola, Arkke J; Welz, Oliver; Sheps, Leonid; Taatjes, Craig A; Zádor, Judit; Osborn, David L

    2015-02-06

    Oxidation of organic compounds in combustion and in Earth's troposphere is mediated by reactive species formed by the addition of molecular oxygen (O2) to organic radicals. Among the most crucial and elusive of these intermediates are hydroperoxyalkyl radicals, often denoted "QOOH." These species and their reactions with O2 are responsible for the radical chain branching that sustains autoignition and are implicated in tropospheric autoxidation that can form low-volatility, highly oxygenated organic aerosol precursors. We report direct observation and kinetics measurements of a QOOH intermediate in the oxidation of 1,3-cycloheptadiene, a molecule that offers insight into both resonance-stabilized and nonstabilized radical intermediates. The results establish that resonance stabilization dramatically changes QOOH reactivity and, hence, that oxidation of unsaturated organics can produce exceptionally long-lived QOOH intermediates.

  11. Oxidative modification of citrate synthase by peroxyl radicals and protection with novel antioxidants.

    PubMed

    Chepelev, Nikolai L; Bennitz, Joshua D; Wright, James S; Smith, Jeffrey C; Willmore, William G

    2009-12-01

    In mammals, aging is linked to a decline in the activity of citrate synthase (CS; E.C. 2.3.3.1), the first enzyme of the citric acid cycle. We used 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), a water-soluble generator of peroxyl and alkoxyl radicals, to investigate the susceptibility of CS to oxidative damage. Treatment of isolated mitochondria with AAPH for 8-24 h led to CS inactivation; however, the activity of aconitase, a mitochondrial enzyme routinely used as an oxidative stress marker, was unaffected. In addition to enzyme inactivation, AAPH treatment of purified CS resulted in dityrosine formation, increased protein surface hydrophobicity, and loss of tryptophan fluorescence. Propyl gallate, 1,8-naphthalenediol, 2,3-naphthalenediol, ascorbic acid, glutathione, and oxaloacetate protected CS from AAPH-mediated inactivation, with IC(50) values of 9, 14, 34, 37, 150, and 160 muM, respectively. Surprisingly, the antioxidant epigallocatechin gallate offered no protection against AAPH, but instead caused CS inactivation. Our results suggest that the current practice of using the enzymatic activity of CS as an index of mitochondrial abundance and the use of aconitase activity as an oxidative stress marker may be inappropriate, especially in oxidative stress-related studies, during which alkyl peroxyl and alkoxyl radicals can be generated.

  12. Spectroscopic Identification of New Benzyl-Type Radicals in Corona Excitation: CHLORO-α-METHYLBENZYL Radicals

    NASA Astrophysics Data System (ADS)

    Yoon, Young Wook; Lee, Seung Woon; Lee, Sang Kuk; Lee, Gi Woo

    2010-06-01

    Using a pinhole-type glass nozzle coupled with corona excited supersonic expansion (CESE), precursors o- and p-chloro-ethylbenzenes seeded in a large amount of inert carrier gas helium were corona discharged to produce jet-cooled benzyl-type radicals. The vibronic emission spectra were recorded with a long path monochromator to observe vibronic bands of benzyl-type radicals in the visible region. The analysis of the spectra shows the evidence of the o- and p-chlorobenzyl radicals as typical products in corona excitation as well as the o- and p-chloro-α-methylbenzyl radicals as unexpected species. After subtracting the bands belonging to chlorobenzyl radicals, we could construct the vibronic emission spectra of the o- and p-chloro-α-methylbenzyl radical in the D_1 → D_0 electronic transition at the gas phase. By comparing with those of ab initio calculation and of the known vibrational mode frequencies with similar structures, we could obtain the electronic transition and assign the vibrational modes to the bands observed. H. G. Ahn, G. W. Lee, and S. K. Lee J. Phys. Chem. A, 112 (51), 13427 (2008).

  13. Nature of the lowest excited states of neutral polyenyl radicals and polyene radical cations

    NASA Astrophysics Data System (ADS)

    Starcke, Jan Hendrik; Wormit, Michael; Dreuw, Andreas

    2009-10-01

    Due to the close relation of the polyenyl radicals C2n+1H2n+3• and polyene radical cations C2nH2n+2•+ to the neutral linear polyenes, one may suspect their excited states to possess substantial double excitation character, similar to the famous S1 state of neutral polyenes and thus to be equally problematic for simple excited state theories. Using the recently developed unrestricted algebraic-diagrammatic construction scheme of second order perturbation theory and the equation-of-motion coupled-cluster method, the vertical excitation energies, their corresponding oscillator strengths, and the nature of the wave functions of the lowest excited electronic states of the radicals are calculated and analyzed in detail. For the polyenyl radicals two one-photon allowed states are found as D1 and D4 states, with two symmetry-forbidden D2 and D3 states in between, while in the polyene radical cations D1 and D2 are allowed and D3 is forbidden. The order of the states is conserved with increasing chain length. It is found that all low-lying excited states exhibit a significant but similar amount of doubly excited configuration in their wave functions of 15%-20%. Using extrapolation, predictions for the excitation energies of the five lowest excited states of the polyene radical cations are made for longer chain lengths.

  14. Pyrimidine nucleobase radical reactivity in DNA and RNA

    NASA Astrophysics Data System (ADS)

    Greenberg, Marc M.

    2016-11-01

    Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

  15. Free radical metabolism of ethanol by deermouse microsomes

    SciTech Connect

    Knecht, K.T.; Thurman, R.G.; Mason, R.P. NIEHS, Research Triangle Park, NC )

    1991-03-15

    One-electron oxidation of ethanol to the {alpha}-hydroxyethyl radical by rat liver microsomes was previously found to be cytochrome P-450-dependent in the presence of Desferal. With deermouse microsomes, the formation of {alpha}-hydroxyethyl radical from ethanol was demonstrated with the electron paramagnetic resonance (EPR) technique of spin trapping. Free radical formation was enhanced by pretreatment of the animals with ethanol. Boiling of the microsomes, omission of NADPH, or addition of superoxide dismutase abolished free radical formation, but addition of catalase or azide had no affect. Free radicals from the hydroxyl radical scavenger formate were detected when ethanol in the incubation medium was replaced by formate. When equal concentrations of ethanol and formate were added to microsomes, the intensity of each radical adduct signal was decreased by half. Thus, it is concluded that free radical formation in deermouse microsomes is mediated by a P-450-derived, superoxide-dependent oxidizing species.

  16. Some Pluses and Minuses of Radical Constructivism in Mathematics Education.

    ERIC Educational Resources Information Center

    Ellerton, Nerida; Clements, M. A.

    1992-01-01

    Reviews the radical constructivism movement in mathematics education. Benefits identified include learner ownership of mathematical learning; importance of social interaction; and identification of principles for improving mathematics teaching and learning. Weaknesses identified include overzealousness of some radical constructivists; downplaying…

  17. Top-down mass spectrometry of hybrid materials with hydrophobic peptide and hydrophilic or hydrophobic polymer blocks.

    PubMed

    Alalwiat, Ahlam; Grieshaber, Sarah E; Paik, Bradford A; Kiick, Kristi L; Jia, Xinqiao; Wesdemiotis, Chrys

    2015-11-21

    A multidimensional mass spectrometry (MS) methodology is introduced for the molecular level characterization of polymer-peptide (or polymer-protein) copolymers that cannot be crystallized or chromatographically purified. It encompasses electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) coupled with mass analysis, tandem mass spectrometry (MS(2)) and gas-phase separation by ion mobility mass spectrometry (IM-MS). The entire analysis is performed in the mass spectrometer ("top-down" approach) within milliseconds and with high sensitivity, as demonstrated for hybrid materials composed of hydrophobic poly(tert-butyl acrylate) (PtBA) or hydrophilic poly(acrylic acid) (PAA) blocks tethered to the hydrophobic decapeptide VPGVGVPGVG (VG2) via triazole linkages. The composition of the major products can be rapidly surveyed by MALDI-MS and MS(2). For a more comprehensive characterization, the ESI-IM-MS (and MS(2)) combination is more suitable, as it separates the hybrid materials based on their unique charges and shapes from unconjugated polymer and partially hydrolyzed products. Such separation is essential for reducing spectral congestion, deconvoluting overlapping compositions and enabling straightforward structural assignments, both for the hybrid copolymers as well as the polymer and peptide reactants. The IM dimension also permits the measurement of collision cross-sections (CCSs), which reveal molecular architecture. The MS and MS(2) spectra of the mobility separated ions conclusively showed that [PtBA-VG2]m and [PAA-VG2]m chains with the expected compositions and sequences were formed. Single and double copolymer blocks (m = 1-2) could be detected. Further, the CCSs of the hybrids, which were prepared via azide/alkyne cycloadditions, confirmed the formation of macrocyclic structures. The top-down methodology described would be particularly useful for the detection and identification of peptide/protein-polymer conjugates which are

  18. Reference interaction site model with hydrophobicity induced density inhomogeneity: An analytical theory to compute solvation properties of large hydrophobic solutes in the mixture of polyatomic solvent molecules

    SciTech Connect

    Cao, Siqin; Sheong, Fu Kit; Huang, Xuhui

    2015-08-07

    Reference interaction site model (RISM) has recently become a popular approach in the study of thermodynamical and structural properties of the solvent around macromolecules. On the other hand, it was widely suggested that there exists water density depletion around large hydrophobic solutes (>1 nm), and this may pose a great challenge to the RISM theory. In this paper, we develop a new analytical theory, the Reference Interaction Site Model with Hydrophobicity induced density Inhomogeneity (RISM-HI), to compute solvent radial distribution function (RDF) around large hydrophobic solute in water as well as its mixture with other polyatomic organic solvents. To achieve this, we have explicitly considered the density inhomogeneity at the solute-solvent interface using the framework of the Yvon-Born-Green hierarchy, and the RISM theory is used to obtain the solute-solvent pair correlation. In order to efficiently solve the relevant equations while maintaining reasonable accuracy, we have also developed a new closure called the D2 closure. With this new theory, the solvent RDFs around a large hydrophobic particle in water and different water-acetonitrile mixtures could be computed, which agree well with the results of the molecular dynamics simulations. Furthermore, we show that our RISM-HI theory can also efficiently compute the solvation free energy of solute with a wide range of hydrophobicity in various water-acetonitrile solvent mixtures with a reasonable accuracy. We anticipate that our theory could be widely applied to compute the thermodynamic and structural properties for the solvation of hydrophobic solute.

  19. Reference interaction site model with hydrophobicity induced density inhomogeneity: An analytical theory to compute solvation properties of large hydrophobic solutes in the mixture of polyatomic solvent molecules.

    PubMed

    Cao, Siqin; Sheong, Fu Kit; Huang, Xuhui

    2015-08-07

    Reference interaction site model (RISM) has recently become a popular approach in the study of thermodynamical and structural properties of the solvent around macromolecules. On the other hand, it was widely suggested that there exists water density depletion around large hydrophobic solutes (>1 nm), and this may pose a great challenge to the RISM theory. In this paper, we develop a new analytical theory, the Reference Interaction Site Model with Hydrophobicity induced density Inhomogeneity (RISM-HI), to compute solvent radial distribution function (RDF) around large hydrophobic solute in water as well as its mixture with other polyatomic organic solvents. To achieve this, we have explicitly considered the density inhomogeneity at the solute-solvent interface using the framework of the Yvon-Born-Green hierarchy, and the RISM theory is used to obtain the solute-solvent pair correlation. In order to efficiently solve the relevant equations while maintaining reasonable accuracy, we have also developed a new closure called the D2 closure. With this new theory, the solvent RDFs around a large hydrophobic particle in water and different water-acetonitrile mixtures could be computed, which agree well with the results of the molecular dynamics simulations. Furthermore, we show that our RISM-HI theory can also efficiently compute the solvation free energy of solute with a wide range of hydrophobicity in various water-acetonitrile solvent mixtures with a reasonable accuracy. We anticipate that our theory could be widely applied to compute the thermodynamic and structural properties for the solvation of hydrophobic solute.

  20. Predicting the behaviour of proteins in hydrophobic interaction chromatography. 1: Using the hydrophobic imbalance (HI) to describe their surface amino acid distribution.

    PubMed

    Salgado, J Cristian; Rapaport, Ivan; Asenjo, Juan A

    2006-02-24

    This paper focuses on the prediction of the dimensionless retention time of proteins (DRT) in hydrophobic interaction chromatography (HIC) by means of mathematical models based on characteristics of the surface hydrophobicity distribution. We introduce a new parameter, called hydrophobic imbalance (HI), obtained from the three-dimensional structure of proteins. This parameter quantifies the displacement of the superficial geometric centre of the protein when the effect of the hydrophobicity of each amino acid is considered. This parameter is simpler and less expensive than those reported previously. We use HI as a way to incorporate information about the surface hydrophobicity distribution in order to improve the prediction of DRT. We tested the performance of our DRT predictive models in a set of 15 proteins. This set includes four proteins whose DRTs are known as very difficult to predict. By means of the variable HI, it was possible to improve the predictive characteristics obtained by models based on the average surface hydrophobicity (ASH) by 9.1%. Also, we studied linear multivariable models based on characteristics determined from the HI. By using this multivariable model, a correlation coefficient of 0.899 was obtained. With this model, we managed to improve the predictive characteristics shown by previous models based on ASH by 31.8%.