Communication: On the locality of Hydrogen bond networks at hydrophobic interfaces (original) (raw)
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The Journal of Chemical Physics, 1999
Assessing the thermodynamic signatures of hydrophobic hydration for several common water models Heat capacity effects associated with the hydrophobic hydration and interaction of simple solutes: A detailed structural and energetical analysis based on molecular dynamics simulations Hydrophobic hydration: Heat capacity of solvation from computer simulations and from an information theory approximation
Microscopic probing of the size dependence in hydrophobic solvation
The Journal of Chemical Physics, 2012
We report small angle x-ray scattering data demonstrating the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in hydrophobic solvation. By increasing the side chain length of amphiphilic tetraalkyl-ammonium (C n H 2n+1 ) 4 N + (R 4 N + ) cations in aqueous solution we observe diffraction peaks indicating association between cations at a solute size between 4.4 and 5 Å, which show temperature dependence dominated by hydrophobic attraction. Using O K-edge x-ray absorption we show that small solutes affect hydrogen bonding in water similar to a temperature decrease, while large solutes affect water similar to a temperature increase. Molecular dynamics simulations support, and provide further insight into, the origin of the experimental observations.
Water's Hydrogen Bonds in the Hydrophobic Effect: A Simple Model
The Journal of Physical Chemistry B, 2005
We propose a simple analytical model to account for water's hydrogen bonds in the hydrophobic effect. It is based on computing a mean-field partition function for a water molecule in the first solvation shell around a solute molecule. The model treats the orientational restrictions from hydrogen bonding, and utilizes quantities that can be obtained from bulk water simulations. We illustrate the principles in a 2-dimensional Mercedes-Benz-like model. Our model gives good predictions for the heat capacity of hydrophobic solvation, reproduces the solvation energies and entropies at different temperatures with only one fitting parameter, and accounts for the solute size dependence of the hydrophobic effect. Our model supports the view that water's hydrogen bonding propensity determines the temperature dependence of the hydrophobic effect. It explains the puzzling experimental observation that dissolving a nonpolar solute in hot water has positive entropy.
Molecular dynamics computer simulations of solvation in hydrogen bonded systems
Pure and Applied Chemistry, 2000
This review first discusses briefly some of he various models used in large scale computer simulations of water and aqueous systems. The radial pair distribution functions describing the structures of the hydration shells of divalent ions, as determined from MD simulations of 1.lm solutions of the chloride salts, are then presented. The ion-water potentials for these studies were determined by quantum mechanical ab initio calculations. Then a few typical structural results for non-isotropic systems, such as an aqueous solution near a metal surface or a solvated ion inside a transmembrane channel, are presented. The final sections focus on dynamical results . After a few remarks about cori'elation functions, the influence of solvated ions on the translational, rotational and vibrational motions of the water molecules are studied. Finally the 0-H vibrations in liquid methanol are discussed.
On independence of the solvation of interaction sites of a water molecule
The Journal of Chemical Physics, 2003
To support simplifying assumptions used in analytic theories of aqueous systems, we have used computer simulations to examine correlations in the bonding of the individual sites of a water molecule using two qualitatively different extended primitive models, EPM4 and EPM5. We have studied these correlations not only for the fully interacting water molecule ͑considered as a solute͒ but also for a series of other solutes made from the water molecule by turning off some of its interaction sites. We have found that for the EPM5 solvent the local density of water molecules bound to a specific site is independent of the state of the other sites being turned on or off; for the EPM4 solvent such an independence does not hold exactly, but the correlations have been found to be very small. These facts fully justify previously used speculative approximations for the calculation of the solvation Helmholtz free energy of a water molecule, and also lend support to the first-order thermodynamic perturbation theory of Wertheim.
Current Opinion in Colloid & Interface Science, 2011
A water molecule in the vicinity of a hydrophobic surface forms fewer and energetically altered hydrogen bonds compared to a bulk molecule because the hydrophobic surface restricts the space available for other water molecules necessary for its hydrogen bonding. In this vicinity, the number of hydrogen bonds per water molecule depends on its distance to the surface and its orientation. We review recent advances in analytic models of water hydrogen bonding and of its role in hydrophobic hydration and hydrophobic interactions with the emphasis on the models providing the number of hydrogen bonds per liquid water molecule as a function of its distance to a hydrophobic surface. The first such model [Luzar A, Svetina S, Zeks B. J Chem Phys. 1985;82:5146-54] was based on two reference quantities: energy of a hydrogen bond and ratio of number of broken and formed bonds, both in the vicinity of the surface. In the recent, probabilistic hydrogen bond model [Djikaev YS, Ruckenstein E. J Chem Phys. 2010; 133: doi:10.1063/1.3499318.] the number of hydrogen bonds per bulk water molecule serves as a single reference to obtain an analytic expression for this dependence (the number of hydrogen bonds per water molecule vs its distance to a hydrophobic surface). This function can be used to develop analytic models for the role of hydrogen bonding in the hydration of hydrophobic particles and their solvent-mediated interaction and to examine the temperature effects on these phenomena.
Collective properties of hydration: long range and specificity of hydrophobic interactions
Biophysical Journal, 1997
We report results of molecular dynamics (MD) simulations of composite model solutes in explicit molecular water solvent, eliciting novel aspects of the recently demonstrated, strong many-body character of hydration. Our solutes consist of identical apolar (hydrophobic) elements in fixed configurations. Results show that the many-body character of PMF is sufficiently strong to cause 1) a remarkable extension of the range of hydrophobic interactions between pairs of solute elements, up to distances large enough to rule out pairwise interactions of any type, and 2) a SIF that drives one of the hydrophobic solute elements toward the solvent rather than away from it. These findings complement recent data concerning SIFs on a protein at single-residue resolution and on model systems. They illustrate new important consequences of the collective character of hydration and of PMF and reveal new aspects of hydrophobic interactions and, in general, of SIFs. Their relevance to protein recognition, conformation, function, and folding and to the observed slight yet significant nonadditivity of functional effects of distant point mutations in proteins is discussed. These results point out the functional role of the configurational and dynamical states (and related statistical weights) corresponding to the complex configurational energy landscape of the two interacting systems: biomolecule + water.
The Journal of Chemical Physics, 2010
A water molecule in the vicinity of a hydrophobic surface forms fewer hydrogen bonds than a bulk molecule because the surface restricts the space available for other water molecules necessary for its hydrogen-bonding. In this vicinity, the number of hydrogen bonds per water molecule depends on its distance to the surface. Considering the number of hydrogen bonds per bulk water molecule ͑available experimentally͒ as the only reference quantity, we propose an improved probabilistic approach to water hydrogen-bonding that allows one to obtain an analytic expression for this dependence. ͑The original version of this approach ͓Y. S. Djikaev and E. Ruckenstein, J. Chem. Phys. 130, 124713 ͑2009͔͒ provides the number of hydrogen bonds per water molecule in the vicinity of a hydrophobic surface as an average over all possible locations and orientations of the molecule.͒ This function ͑the number of hydrogen bonds per water molecule versus its distance to a hydrophobic surface͒ can be used to develop analytic models for the effect of hydrogen-bonding on the hydration of hydrophobic particles and their solvent-mediated interaction. Presenting a model for the latter, we also examine the temperature effect on the solvent-mediated interaction of two parallel hydrophobic plates.