The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Max L. Berkowitz - One of the best experts on this subject based on the ideXlab platform.
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Origin of the Hydration Force: water-mediated interaction between two hydrophilic plates.
The journal of physical chemistry. B, 2009Co-Authors: Changsun Eun, Max L. BerkowitzAbstract:We performed molecular dynamics simulations on systems containing phosphatidycholine headgroups attached to graphene plates (PC−headgroup plates) immersed in water to study the interaction between phosphatidylcholine bilayers in water. The potential of mean Force (PMF) between PC−headgroup plates shows that the interaction is repulsive. We observed three distinct regimes in the PMF depending on the interplate distances: the small distance regime, intermediate distance regime, and large distance regime. We believe that the repulsive interaction in the intermediate interplate distance regime is associated with the Hydration Force due to the removal of water molecules adjacent to the headgroups.
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Role of water in the Hydration Force acting between lipid bilayers
Langmuir, 1996Co-Authors: Lalith Perera, Ulrich Essmann, Max L. BerkowitzAbstract:To understand the nature of the Hydration Forces acting between biomembranes, we perform computer simulations on liquid crystalline dilauroylphosphatidylethanolamine (DLPE)/water and compare the results with previously reported dipalmitoylphosphatidylcholine (DPPC)/water systems. From our simulations of both systems we find that the influence of the surface on water properties is detectable only over a short range and that the membrane surfaces are rough on a molecular scale. We find that the Hydration Force is due to (a) the removal of only one or two layers of solvating water from the membrane surface and (b) steric interactions. The detailed structure of the solvating water is responsible for the difference in the Hydration Force acting between DLPE membranes compared to DPPC membranes.
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The origin of the Hydration interaction of lipid bilayers from MD simulation of dipalmitoylphosphatidylcholine membranes in gel and liquid crystalline phases
Langmuir, 1995Co-Authors: Ulrich Essmann, Lalith Perera, Max L. BerkowitzAbstract:The results of four molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC)/water systems are reported. To investigate the origin of the Hydration Force we follow the experiments performed recently by McIntosh and Simon. We study the DPPC/water system in both the gel phase and the liquid crystalline phase at two different water contents, namely at 11 and 20.5 water molecules/lipid. Long ranged Coulomb interactions are treated with the so-called particle mesh Ewald method. The polarization profile of the water is calculated. We find that the polarization decays smoothly within 6 A. The smoothly decaying polarization profile is a result of the roughness of the bilayer surface even in the gel phase. Furthermore we characterize the structure around the lipid head group and find a layer ofwater molecules with stronger hydrogen bonds. At low water contents we observe that a significant fraction of head groups of opposing bilayers is either in close contact or separated by just one or two water layers. In our interpretation, the region of water molecules with stronger hydrogen bonds keeps the opposing head group pairs separated by one or two water layers. Both situations, close contact and separation by one or two water layers, possibly give rise to the so-called Hydration Force.
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molecular dynamics simulation of a membrane water interface the ordering of water and its relation to the Hydration Force
Langmuir, 1993Co-Authors: Siewert J. Marrink, Max L. Berkowitz, Herman J. C. BerendsenAbstract:In order to obtain a better understanding of the origin of the Hydration Force, three molecular dynamic simulations of phospholipid/water multilamellar systems were performed. The simulated systems only differed in the amount of interbilayer water, ranging from the minimum to the maximum amount of swelling in the liquid-crystal phase. The analysis of orientational polarization, hydrogen bonding and diffusion rates of the water molecules between the membranes reveals a strong perturbing effect, which decays smoothly and approximately exponentially (with a decay length of about 0.25 nm) toward the middle of the water layer. The electrostatic potential profiles show that the decay of water ordering is directly correlated with the decay of the interfacial dipolar charges. Therefore, the propagation of the ordering of water molecules is not intrinsic to water but is merely determined by the local field from the interfacial charge distribution. The decay of the electrostatic potentials appears to be as a stretched exponential in all simulated systems. This type of decay can be interpreted as normal exponential but with a varying local decay length. We speculate that it is the fractal nature of the membrane surface which results in the stretched exponential behavior. The Hydration Force, resulting from the ordering of the water molecules between the membranes, will also exhibit this type of decay and is thus dependent on solvent as well as membrane structure.
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Molecular dynamics simulation of a membrane/water interface: the ordering of water and its relation to the Hydration Force
Langmuir, 1993Co-Authors: Siewert J. Marrink, Max L. Berkowitz, Herman J. C. BerendsenAbstract:In order to obtain a better understanding of the origin of the Hydration Force, three molecular dynamic simulations of phospholipid/water multilamellar systems were performed. The simulated systems only differed in the amount of interbilayer water, ranging from the minimum to the maximum amount of swelling in the liquid-crystal phase. The analysis of orientational polarization, hydrogen bonding and diffusion rates of the water molecules between the membranes reveals a strong perturbing effect, which decays smoothly and approximately exponentially (with a decay length of about 0.25 nm) toward the middle of the water layer. The electrostatic potential profiles show that the decay of water ordering is directly correlated with the decay of the interfacial dipolar charges. Therefore, the propagation of the ordering of water molecules is not intrinsic to water but is merely determined by the local field from the interfacial charge distribution. The decay of the electrostatic potentials appears to be as a stretched exponential in all simulated systems. This type of decay can be interpreted as normal exponential but with a varying local decay length. We speculate that it is the fractal nature of the membrane surface which results in the stretched exponential behavior. The Hydration Force, resulting from the ordering of the water molecules between the membranes, will also exhibit this type of decay and is thus dependent on solvent as well as membrane structure.
Pi-kuai Chang - One of the best experts on this subject based on the ideXlab platform.
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the role of Hydration Force on the stability of the suspension of saccharomyces cerevisiae application of the extended dlvo theory
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002Co-Authors: You-im Chang, Pi-kuai ChangAbstract:Abstract Including with the term of repulsive Hydration Force, the extended DLVO theory adopted in the present paper can successfully describe the stability of cell suspension, Saccharomyces cerevisiae THB001, over a wide range of pH and NaCl concentration. By using the experimental results of zeta potential and turbidity measurements, the parameter values of the Hydration energy equation are estimated. It is found that, since the turbidity of cell suspension decreases with the increase of NaCl concentration at isoelectric point, hence the Hydration energy existed between cells is repulsive and is an inherent surface property of S. cerevisiae THB001.
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The role of Hydration Force on the stability of the suspension of Saccharomyces cerevisiae–application of the extended DLVO theory
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002Co-Authors: You-im Chang, Pi-kuai ChangAbstract:Abstract Including with the term of repulsive Hydration Force, the extended DLVO theory adopted in the present paper can successfully describe the stability of cell suspension, Saccharomyces cerevisiae THB001, over a wide range of pH and NaCl concentration. By using the experimental results of zeta potential and turbidity measurements, the parameter values of the Hydration energy equation are estimated. It is found that, since the turbidity of cell suspension decreases with the increase of NaCl concentration at isoelectric point, hence the Hydration energy existed between cells is repulsive and is an inherent surface property of S. cerevisiae THB001.
Roe-hoan Yoon - One of the best experts on this subject based on the ideXlab platform.
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Effects of Short-Chain Alcohols and Pyridine on the Hydration Forces between Silica Surfaces.
Journal of colloid and interface science, 1998Co-Authors: Roe-hoan Yoon, Subramanian VivekAbstract:Forces between fully hydroxalated silica surfaces were measured using an atomic Force microscope. The measurements were conducted in Nanopure water and in solutions containing various organic solutes such as methanol, ethanol, trifluoroethanol (TFE), and pyridine. The results obtained in Nanopure water showed a strong short-range repulsive Force at distances below 15 nm. This non-DLVO Force can be fitted to a double-exponential Force law with its longer decay length (D2) of 2.4 nm. On the other hand, the Force curve obtained at 15% methanol by volume can be fitted to the DLVO theory perfectly, showing no signs of Hydration Force. These results suggest that the Hydration Force originate from the unique water structure in the vicinity of silica, which apparently is seriously disrupted in the presence of methanol. Methanol may adsorb on silica, displacing water molecules from the silanol groups and, thereby, breaking the H-bond network within the Hydration sheath around silica. The displacement of water by methanol is thermodynamically possible because the latter is more basic than the former. In 10-20% ethanol solutions, D2 decreases to 1.1-1.2 nm, indicating that ethanol also adsorbs on silica but to a lesser extent than methanol. In TFE and pyridine solutions, the Hydration Force changes little, suggesting that these solutes cannot readily displace water molecules from silanol groups. The results presented in this communication may have a bearing on the intoxication of humans by alcohols, which may be related to the deHydration of lipid membranes. Copyright 1998 Academic Press.
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On Secondary Hydration Force in Stannic Oxide Suspensions
RESOURCES PROCESSING, 1994Co-Authors: Hiroki Yotsumoto, Roe-hoan Yoon, Takahide Wakamatsu, Shinichi Ito, Hiroshi SakamotoAbstract:The aqueous suspensions of synthesized stannic oxide enhibit anomalous stability at NaCI concentrations 0.2 M and above. When NaCI concentration is more than 1 M, the suspensions do not coagulate completely even at its i.e.p., which cannot be explained by the classical DLVO theory. This is quite similar to the behavior of aqueous rutile suspensions where the anomalous stability has been attributed to secondary Hydration Force. The magnitudes of the secondary Hydration Forces have been estimated using an extended DLVO theory, in which the secondary Hydration Force is expressed as a double-exponential function. The secondary Hydration Force is larger at acidic pH and increases with increasing NaCI concentration, which has been also the case with rutile suspensions.The pH dependence of the secondary Hydration Force makes it difficult to explain its origin as simply being developed by the adsorption of hydrated cations onto oxide surfaces. It may be required to incorporate the adsorption of hydrated anions with the simple cation adsorption model.
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Effects of Alcohol and Surface Active Agent on the Stability of Aqueous Oxide Suspensions.
Shigen-to-Sozai, 1994Co-Authors: Hiroki Yotsumoto, Roe-hoan Yoon, Takahide Wakamatsu, Shinichi Ito, Hiroshi SakamotoAbstract:The effects of alcohol and surfactant on Hydration Forces with aqueous oxide suspensions were investigated. It was found that the primary Hydration Force with silica decreased with the increasing amount of ethanol in the suspension, while the secondary Hydration Force with rutile increased with the same condition. The surface deHydration of silica caused by ethanol may be reponsible for the decrase in the primary Hydration Force. For the case of rutile, the increase in the secondary Hydration Force may be attributed to the increased adsorption of hydrated Na+ as observed at oxide/water interfaces in mixed solvent systems reported elsewhereDodecylamine-hydrochloride (DAH) was added to the rutile suspension and its effect was investigated. The result suggested that there was a hydrophobic attraction, the magnitude of which was much larger than the Hydration Forces. At relatively high DAH concentration and at alkaline pH, an additional repulsion not considered in the classical DLVO theory was observed with rutile. The magnitude of the repulsion was comparable to the secondary Hydration Force observed with rutile at high NaCl concentrations.
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Application of Extended DLVO Theory: II. Stability of Silica Suspensions
Journal of Colloid and Interface Science, 1993Co-Authors: Hiroki Yotsumoto, Roe-hoan YoonAbstract:Abstract The aqueous suspensions of Wako precipitated silica exhibit anomalous stability due to Hydration Forces not considered in the classical DLVO theory. The magnitudes of the Hydration energies have been estimated using an extended DLVO theory, in which the Hydration energy is expressed as a double-exponential function. The results show that the Hydration Force decreases with increasing NaCl concentration, suggesting that it is an inherent property of silica as opposed to the "secondary" Hydration Forces observed with rutile and mica. The extended DLVO theory developed in the present work is useful for predicting the stability of silica suspensions over a wide range of pH and NaCl concentrations.
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A Study on Structural Force in Silica Suspensions.
Shigen-to-Sozai, 1993Co-Authors: Hiroki Yotsumoto, Roe-hoan Yoon, Takahide Wakamatsu, Shinichi Ito, Hiroshi SakamotoAbstract:The aqueous suspensions of precipitated silica exhibit anomalous stability due to the structural Forces not considered in the classical DLVO theory. The magnitudes of the structural energies have been estimated using an extended DLVO theory, in which the structural energy is expressed as a double-exponential function. The result shows that the structural Force decreases with increasing NaCl concentration as opposed to the structural Forces observed in rutile and mica. It is believed that an inherent water structure exists on silica surfaces and develops a steric repulsion, while the water structures on rutile and mica are gradually formed as hydrated cations adsorb onto each solid surface. In this regard, the Hydration Force observed with silica can be referred to as “primary Hydration Force”, while those observed with rutile and mica can be referred to as “secondary Hydration Force”. By incorporating the concept of cation bridging in silica coagulation, it has been shown that the opposite effect of cations on the structural Forces in silica and rutile can be explained consistently.
Herman J. C. Berendsen - One of the best experts on this subject based on the ideXlab platform.
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Membranes and water: An interesting relationship
Faraday Discussions, 1996Co-Authors: Siewert-jan Marrink, D. Peter Tieleman, Aldert R. Van Buuren, Herman J. C. BerendsenAbstract:The relationship between membranes and interfacial water is discussed. Various interfacial properties for a number of simulated membrane/water systems are compared. Although the simulated membranes consist of widely varying hydrophobic and hydrophilic components, some general properties emerge. A geometrical ordering principle is observed for all surfaces, resulting in a negative surface potential for all systems. The induced water order decays without any previously observed long-range oscillations. More specific properties relate to the dipolar charge distributions of the hydrophilic surfaces, which are akin to biomembranes. In contrast to the hydrophobic surfaces they have a broad interface with a high density. Compensation of local charge density is the main ordering principle for water in these systems. The interplay between membrane and water properties is further discussed in relation to the Hydration Force. It is concluded that the non-exponential decay of the surface molecules will lead to a more complicated decay of the Hydration Force than usually assumed, whether arising from water ordering or from surface protrusions.
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molecular dynamics simulation of a membrane water interface the ordering of water and its relation to the Hydration Force
Langmuir, 1993Co-Authors: Siewert J. Marrink, Max L. Berkowitz, Herman J. C. BerendsenAbstract:In order to obtain a better understanding of the origin of the Hydration Force, three molecular dynamic simulations of phospholipid/water multilamellar systems were performed. The simulated systems only differed in the amount of interbilayer water, ranging from the minimum to the maximum amount of swelling in the liquid-crystal phase. The analysis of orientational polarization, hydrogen bonding and diffusion rates of the water molecules between the membranes reveals a strong perturbing effect, which decays smoothly and approximately exponentially (with a decay length of about 0.25 nm) toward the middle of the water layer. The electrostatic potential profiles show that the decay of water ordering is directly correlated with the decay of the interfacial dipolar charges. Therefore, the propagation of the ordering of water molecules is not intrinsic to water but is merely determined by the local field from the interfacial charge distribution. The decay of the electrostatic potentials appears to be as a stretched exponential in all simulated systems. This type of decay can be interpreted as normal exponential but with a varying local decay length. We speculate that it is the fractal nature of the membrane surface which results in the stretched exponential behavior. The Hydration Force, resulting from the ordering of the water molecules between the membranes, will also exhibit this type of decay and is thus dependent on solvent as well as membrane structure.
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Molecular dynamics simulation of a membrane/water interface: the ordering of water and its relation to the Hydration Force
Langmuir, 1993Co-Authors: Siewert J. Marrink, Max L. Berkowitz, Herman J. C. BerendsenAbstract:In order to obtain a better understanding of the origin of the Hydration Force, three molecular dynamic simulations of phospholipid/water multilamellar systems were performed. The simulated systems only differed in the amount of interbilayer water, ranging from the minimum to the maximum amount of swelling in the liquid-crystal phase. The analysis of orientational polarization, hydrogen bonding and diffusion rates of the water molecules between the membranes reveals a strong perturbing effect, which decays smoothly and approximately exponentially (with a decay length of about 0.25 nm) toward the middle of the water layer. The electrostatic potential profiles show that the decay of water ordering is directly correlated with the decay of the interfacial dipolar charges. Therefore, the propagation of the ordering of water molecules is not intrinsic to water but is merely determined by the local field from the interfacial charge distribution. The decay of the electrostatic potentials appears to be as a stretched exponential in all simulated systems. This type of decay can be interpreted as normal exponential but with a varying local decay length. We speculate that it is the fractal nature of the membrane surface which results in the stretched exponential behavior. The Hydration Force, resulting from the ordering of the water molecules between the membranes, will also exhibit this type of decay and is thus dependent on solvent as well as membrane structure.
Gregor Cevc - One of the best experts on this subject based on the ideXlab platform.
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Hydration Force microscopy as a new option for studies of solid liquid interfaces some theoretical considerations
Journal of Electroanalytical Chemistry, 1992Co-Authors: Gregor Cevc, Alexei A. KornyshevAbstract:Abstract A rationale for in situ scanning Force microscopy based on Hydration Forces is given. Such microscopy would permit the distribution of the hydrated species along a polar surface to be probed directly with another polar surface, preferably of small dimensions. Formulae are derived for the relationship between the lateral correlation functions of hydrated surface groups and the correlated values of the surface Force measured by a specially designed and programmed “Gedanken” Hydration Force nanoscope. Some prospects and problems in the realization of this idea are discussed.
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lipid vesicles penetrate into intact skin owing to the transdermal osmotic gradients and Hydration Force
Biochimica et Biophysica Acta, 1992Co-Authors: Gregor Cevc, Gabriele BlumeAbstract:Gradients across the outer skin layers may result in fields enforcing a lipid flow into or through the intact skin surface provided that lipids are applied in the form of special vesicles. The osmotic gradient, for example, which is created by the difference in the total water concentrations between the skin surface and the skin interior, provides one possible source of such driving Force. It is sufficiently strong to push at least 0.5 mg of lipids per hour and cm2 through the skin permeability barrier in the region of stratum corneum. The lipid concentration gradient, on the contrary, does not contribute much to the lipid penetration into dermis. Occlusion, therefore, is detrimental for the vesicle penetration into intact skin.
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Hydration Force microscopy as a new option for studies of solid—liquid interfaces: Some theoretical considerations
Journal of Electroanalytical Chemistry, 1992Co-Authors: Gregor Cevc, Alexei A. KornyshevAbstract:Abstract A rationale for in situ scanning Force microscopy based on Hydration Forces is given. Such microscopy would permit the distribution of the hydrated species along a polar surface to be probed directly with another polar surface, preferably of small dimensions. Formulae are derived for the relationship between the lateral correlation functions of hydrated surface groups and the correlated values of the surface Force measured by a specially designed and programmed “Gedanken” Hydration Force nanoscope. Some prospects and problems in the realization of this idea are discussed.
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Hydration Force and the interfacial structure of the polar surface
Journal of the Chemical Society Faraday Transactions, 1991Co-Authors: Gregor CevcAbstract:Solvation, in particular the Hydration Force, for simple surfaces is believed to decay approximately exponentially on the length scale of a few tenths of a nanometre. For phospholipid membranes its range varies, however, with the surface at least as strongly as with the solvent characteristics. One possible reason for this is fine interfacial structure, most notably, the finite interfacial thickness. From a generalized non-local electrostatic model of Hydration discussed in this work, the spatial decay of the interfacial Hydration is concluded to be sensitive to the volume distribution and to the transverse fluctuations of the surface polar residues. If the effective interfacial width significantly exceeds the solvent–structure decay length, the interfacial width and the interfacial polarity distribution may ultimately become more important for the solvation range than the solvent characteristics themselves. For any relatively thick, for example biological, interface such effects are prone to dominate the Hydration Force and act as a messenger of the interfacial structure. Approaching or interacting macromolecules or membranes, consequently, can sense and pick up mutual surface patterns throughout the intermediate solvent, provided that the surface polarity profile has a ‘tail’ longer than the solvent–structure decay length. This may be one of the reasons for the biological significance of the Hydration Force. On the one hand, a rationale is thus proposed for the extraction of detailed structural information from the macroscopic Hydration-Force data. On the other hand, one possible reason is identified for the non-linear dependence of the maximal repulsion of Hydration as a function of the overall surface hydrophilicity.
