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Theory of cold denaturation of proteins  [PDF]
Arieh Ben-Naim
Advances in Biological Chemistry (ABC) , 2013, DOI: 10.4236/abc.2013.31005
Abstract:

A new approach to the problem of cold denaturation is presented. It is based on solvent-induced effects operating on hydrophilic groups along the protein. These effects are stronger than the corresponding hydrophobic effects, and they operate on the hydrophilic groups which are plentiful than hydrophobic groups. It is shown that both heat and cold denaturation can be explained by these hydrophilic effects.

Cold and Warm Denaturation of Hydrophobic Polymers  [PDF]
Paolo De Los Rios,Guido Caldarelli
Physics , 1999,
Abstract: We introduce a polymer model where the transition from swollen to compact configurations is due to interactions between the monomers and the solvent. These interactions are the origin of the effective attractive interactions between hydrophobic amminoacids in proteins. We find that in the low and high temperature phases polymers are swollen, and there is an intermediate phase where the most favorable configurations are compact. We argue that such a model captures in a single framework both the cold and the warm denaturation experimentally detected for proteins. Some consequences for protein folding are discussed.
Hydrophobic Interactions and Dewetting between Plates with Hydrophobic and Hydrophilic Domains  [PDF]
Lan Hua,Ronen Zangi,B. J. Berne
Physics , 2008,
Abstract: We study by molecular dynamics simulations the wetting/dewetting transition and the dependence of the free energy on distance between plates that contain both hydrophobic and hydrophilic particles. We show that dewetting and strength of hydrophobic interaction is very sensitive to the distribution of hydrophobic and hydrophilic domains. In particular, we find that plates characterized by a large domain of hydrophobic sites induce a dewetting transition and an attractive solvent-induced interaction. On the other hand, a homogeneous distribution of the hydrophobic and hydrophilic particles on the plates prevents the dewetting transition and produces a repulsive solvent-induced interaction. We also present results for a kind of Janus interface in which one plate consists of hydrophobic particles and the other of hydrophilic particles showing that the inter-plate gap remains wet until steric constraints at small separations eject the water molecules. Our results indicate that the Cassie equation, for the contact angle of a heterogeneous plate, can not be used to predict the critical distance of dewetting. These results indicate that hydrophobic interactions between nanoscale surfaces with strong large length-scale hydrophobicity can be highly cooperative and thus they argue against additivity of the hydrophobic interactions between different surface domains in these cases. These findings are pertinent to certain protein-protein interactions where additivity is commonly assumed.
Random Hydrophilic-Hydrophobic Copolymers  [PDF]
T. Garel,L. Leibler,H. Orland
Physics , 1994, DOI: 10.1051/jp2:1994252
Abstract: We study a single statistical amphiphilic copolymer chain AB in a selective solvent (e.g.water). Two situations are considered. In the annealed case, hydrophilic (A) and hydrophobic (B) monomers are at local chemical equilibrium and both the fraction of A monomers and their location along the chain can vary, whereas in the quenched case (which is relevant to proteins), the chemical sequence along the chain is fixed by synthesis. In both cases, the physical behaviour depends on the average hydrophobicity of the polymer chain. For a strongly hydrophobic chain (large fraction of B), we find an ordinary continuous $\theta$ collapse, with a large conformational entropy in the collapsed phase. For a weakly hydrophobic, or a hydrophilic chain, there is an unusual first-order collapse transition. In particular, for the case of Gaussian disorder, this discontinuous transition is driven by a change of sign of the third virial coefficient. The entropy of this collapsed phase is strongly reduced with respect to the $\theta$ collapsed phase. Email contact: orland@amoco.saclay.cea.fr
Nanoparticle Formulation for Hydrophilic & Hydrophobic Drugs
Vivek Kumar Gupta, Alok Gupta,P.K.Karar,S.Ramesh,S.P.Misra
International Journal of Research in Pharmaceutical Sciences , 2010,
Abstract: Nanoparticle formulations have many advantages over traditional dosage forms, such as enhanced dissolution properties and the potential for intracellular drug delivery. Specifically, pure drug nanoparticles, polymeric nanoparticles and polyelectrolyte complexes offer some encouraging results for delivering drugs to various organs and through various routes. Traditional techniques such as spray drying and grinding, and more recent advances in supercritical fluid extraction, precipitation, and double solvent evaporation have been employed to produce nanoparticle formulations for delivery of hydrophilic & hydrophobic drugs here, the benefits of nanoparticle formulations and current progress are compared in light of the practical encumbrances of producing formulations, and possible toxicological effects of these materials.
Experiments and Considerations through the Phase Diagram in Open Tubular Capillary Chromatography Based on Tube Radial Distribution of Ternary Mixed Solvents Using a Fused-Silica Capillary Tube  [PDF]
Yusuke Tanigawa, Naoya Jinno, Masahiko Hashimoto, Kazuhiko Tsukagoshi
American Journal of Analytical Chemistry (AJAC) , 2012, DOI: 10.4236/ajac.2012.34041
Abstract: Capillary chromatography using an untreated open tubular capillary tube and a ternary solvent mixture consisting of water-hydrophilic/hydrophobic organic solvent as a carrier solution has been developed. The system is called tube radical distribution chromatography (TRDC). Separation performance of the TRDC system using a fused-silica capillary tube was examined through the phase diagram for the ternary water-acetonitrile-ethyl acetate solvent mixture. The TRDC system required homogeneous carrier solutions with solvent component ratios around the boundary curve between homogeneous and heterogeneous solution in the phase diagram. The data obtained using the fused-silica capillary tube were compared with those obtained using a polytetrafluoroethylene capillary tube in our previous study.
Fluctuations of water near extended hydrophobic and hydrophilic surfaces  [PDF]
Amish J. Patel,David Chandler
Physics , 2009, DOI: 10.1021/jp909048f
Abstract: We use molecular dynamics simulations of the SPC-E model of liquid water to derive probability distributions for water density fluctuations in probe volumes of different shapes and sizes, both in the bulk as well as near hydrophobic and hydrophilic surfaces. To obtain our results, we introduce a biased sampling of coarse-grained densities, which in turn biases the actual solvent density. The technique is easily combined with molecular dynamics integration algorithms. Our principal result is that the probability for density fluctuations of water near a hydrophobic surface, with or without surface-water attractions, is akin to density fluctuations at the water-vapor interface. Specifically, the probability of density depletion near the surface is significantly larger than that in bulk. In contrast, we find that the statistics of water density fluctuations near a model hydrophilic surface are similar to that in the bulk.
Surface tension of electrolytes: Hydrophilic and hydrophobic ions near an interface  [PDF]
Akira Onuki
Physics , 2008, DOI: 10.1063/1.2936992
Abstract: We calculate the ion distributions around an interface in fluid mixtures of highly polar and less polar fluids (water and oil) for two and three ion species. We take into account the solvation and image interactions between ions and solvent. We show that hydrophilic and hydrophobic ions tend to undergo a microphase separation at an interface, giving rise to an enlarged electric double layer. We also derive a general expression for the surface tension of electrolyte systems, which contains a negative electrostatic contribution proportional to the square root of the bulk salt density. The amplitude of this square-root term is small for hydrophilic ion pairs, but is much increased for hydrophilic and hydrophobic ion pairs. For three ion species including hydrophilic and hydrophobic ions, we calculate the ion distributions to explain those obtained by x-ray reflectivity measurements.
Microscopic mechanism for cold denaturation  [PDF]
Cristiano L. Dias,Tapio Ala-Nissila,Mikko Karttunen,Ilpo Vattulainen,Martin Grant
Physics , 2007, DOI: 10.1103/PhysRevLett.100.118101
Abstract: We elucidate the mechanism of cold denaturation through constant-pressure simulations for a model of hydrophobic molecules in an explicit solvent. We find that the temperature dependence of the hydrophobic effect is the driving force/induces/facilitates cold denaturation. The physical mechanism underlying this phenomenon is identified as the destabilization of hydrophobic contact in favor of solvent separated configurations, the same mechanism seen in pressure induced denaturation. A phenomenological explanation proposed for the mechanism is suggested as being responsible for cold denaturation in real proteins.
Crossovers in supercooled solvation water: Effects of hydrophilic & hydrophobic interactions  [PDF]
John T. Titantah,Mikko Karttunen
Physics , 2014,
Abstract: We use systematic 8 ns ab initio molecular dynamics (AIMD) to study the structure and dynamics of water in bulk, and close to both hydrophobic and hydrophilic (carbonyl) groups of tetramethylurea (TMU). We observe crossovers in the dynamical behavior around the hydrophobic group at $T_X = 256 \pm 4$K and another one at $265 \pm 5$K related to the relative strength of water-water and water-carbonyl hydrogen bonds (HBs). For bulk water, the temperature of the apparent divergence in relaxation times is located at $T_c = 210 \pm 10$K. To better identify the effects arising from the hydrophilic carbonyl group, systems of water with a methane molecule were used as references. These findings are related to the structural and thermodynamic transitions reported for proteins in solution and may also play a role in the mechanism of cold denaturation of proteins.
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