X-ray studies of the density depletion at hydrophobic water-solid interfaces (original) (raw)
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Langmuir, 1999
Theoretical interpretations of the, as yet, poorly understood long-range hydrophobic attraction are briefly reviewed. We report long-range hydrophobic attractive forces between silica surfaces made hydrophobic by adsorption of the cationic surfactants cetyltrimethylammonium bromide and cetylpyridinium chloride onto silica surfaces. The effects of dissolved gas, surface approach velocity, and neutron irradiation on the measured interaction have been studied in order to investigate possible non-electrostatic mechanisms for the long-range hydrophobic attraction. At large separations the presence of dissolved gas, neutron irradiation, and reduced approach velocities are, in each case, found to result in a stronger attraction between the hydrophobic surfaces. These results are consistent with mechanisms related to the metastability of the thin aqueous film separating the approaching hydrophobic surfaces.
A View of the Hydrophobic Effect
Oil and water do not mix. The disaffinity of oil for water, with its unusual temperature dependence, is called the hydrophobic effect. It is important to understand the factors underlying the hydrophobic effect because they appear to play key roles in membrane and micelle formation, protein folding, ligand-protein and proteinprotein binding, chromatographic retention, possibly nucleic acid interactions, and the partitioning of drugs, metabolites, and toxins throughout the environment and living systems. Here, we survey experimental and theoretical studies of nonpolar solute partitioning into water. We note that the hydrophobic effect is not just due to "water ordering" and not merely due to small size effects of water. The properties vary substantially with temperature and solute shape. Also, we discuss the limitations of using oil/water partitioning as the basis for some thermodynamic models in chemistry and biology.
Shedding light on the hydrophobicity puzzle
Pure and Applied Chemistry, 2016
A general theory of hydrophobic hydration and pairwise hydrophobic interaction has been developed in the last years. The main ingredient is the recognition that: (a) cavity creation (necessary to insert a solute molecule into water) causes a solvent-excluded volume effect that leads to a loss in the translational entropy of water molecules; (b) the merging of two cavities (necessary to form the contact minimum configuration of two nonpolar molecules) causes a decrease in the solvent-excluded volume effect and so an increase in the translational entropy of water molecules. The performance of the theoretical approach is tested by reproducing both the hydration thermodynamics of xenon and the thermodynamics associated with the formation of the contact minimum configuration of two xenon atoms, over a large temperature range.
Towards a microscopic theory of hydrophobic solutions
Journal of the Chemical Society, Faraday Transactions 2, 1978
The distinguishing features of water and apolar solute molecular potentials responsible for the behaviour of hydrophobic solutions are inferred from a consideration of the thermodynamic properties of bulk water. These molecular properties are built into exactly soluble models in one dimension, and their necessity underlined by a comparison of models which give normal and hydrophobic solution thermodynamics. The form of solute-solvent and solute-solute molecular distribution functions is explored, and used to infer the nature of solute induced structure and the solventmediated hydrophobic interaction between apolar molecules in water.
Hydrophobicity-Its Origin and an Important Example
Studying the formation of a cavity in molecular water and the associated change in free energy can deliver useful information for the analysis of hydrophobic phenomena. We focus on the entropy of this process and describe a straightforward way to quantify its partial contribution. Free energy calculations are carried out considering perturbations that introduce spherical particles of a certain size. The outlined activity describes a case that can only be explored by scientific high performance computing.
ChemInform Abstract: A View of the Hydrophobic Effect
ChemInform, 2002
Oil and water do not mix. The disaffinity of oil for water, with its unusual temperature dependence, is called the hydrophobic effect. It is important to understand the factors underlying the hydrophobic effect because they appear to play key roles in membrane and micelle formation, protein folding, ligand-protein and proteinprotein binding, chromatographic retention, possibly nucleic acid interactions, and the partitioning of drugs, metabolites, and toxins throughout the environment and living systems. Here, we survey experimental and theoretical studies of nonpolar solute partitioning into water. We note that the hydrophobic effect is not just due to "water ordering" and not merely due to small size effects of water. The properties vary substantially with temperature and solute shape. Also, we discuss the limitations of using oil/water partitioning as the basis for some thermodynamic models in chemistry and biology. . Methane-methane potential of mean force. Idealized potential of mean force between two methanes as a function of distance in angstroms. Left: methanes (in black) at contact, middle: at the barrier distance (which has an unfavorable free energy), and right: in a solventseparated configuration.
Structure and Depletion at Fluorocarbon and Hydrocarbon/Water Liquid/Liquid Interfaces
Physical Review Letters, 2008
The results of x-ray reflectivity studies of two oil/water (liquid/liquid) interfaces are inconsistent with recent predictions of the presence of a vapor-like depletion region at hydrophobic/aqueous interfaces. One of the oils, perfluorohexane, is a fluorocarbon whose super-hydrophobic interface with water provides a stringent test for the presence of a depletion layer. The other oil, heptane, is a hydrocarbon and, therefore, is more relevant to the study of biomolecular hydrophobicity. These results are consistent with the sub-angstrom proximity of water to soft hydrophobic materials. PACS Numbers: 82.70.Uv, 68.05.-n, 61.05.cm Kaoru et al., "Structure and Depletion…" 2
New perspectives on hydrophobic effects
Chemical Physics, 2000
Recent breakthroughs in the theory of hydrophobic eects permit new analyses of several characteristics of hydrophobic hydration and interaction. Heat capacities of non-polar solvation, and their temperature dependences, are analyzed within an information theory approach, using experimental information available from bulk liquid water. Non-polar solvation in aqueous electrolytes is studied by computer simulations, and interpreted within the information theory. We also study the preferential solvation of small non-polar molecules in heavy water (D 2 O) relative to light water (H 2 O) and ®nd that this revealing dierence can be explained by the higher compressibility of D 2 O. We develop a quasi-chemical description of hydrophobic hydration that incorporates the hydration structure and permits quantummechanical treatment of the solute. Finally, these new results are discussed in the context of hydrophobic eects in protein stability and folding, and of mesoscopic hydrophobic eects such as dewetting.