Thermodynamics and mechanism of hydrophobic interaction (original) (raw)
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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.
Effect of Hydrophobic Interaction on Structure, Dynamics and Reactivity of Water
2013
The effect of hydrophobic interaction on water is still controversial, and requires more detailed experimental and theoretical investigation. The interaction between organic-water molecular complexes might be indicative of the perturbation of hydrogen-bond network in the tetrahedral structure of bulk waters, due to hydrophobic effect.
Molecular Theory and the Effects of Solute Attractive Forces on Hydrophobic Interactions
The Journal of Physical Chemistry B, 2016
The role of solute attractive forces on hydrophobic interactions is studied by coordinated development of theory and simulation results for Ar atoms in water. We present a concise derivation of the local molecular field (LMF) theory for the effects of solute attractive forces on hydrophobic interactions, a derivation that clarifies the close relation of LMF theory to the EXP approximation applied to this problem long ago. The simulation results show that change from purely repulsive atomic solute interactions to include realistic attractive interactions diminishes the strength of hydrophobic bonds. For the Ar-Ar rdfs considered pointwise, the numerical results for the effects of solute attractive forces on hydrophobic interactions are of opposite sign and larger in magnitude than predicted by LMF theory. That comparison is discussed from the point of view of quasi-chemical theory, and it is suggested that the first reason for this difference is the incomplete evaluation within LMF theory of the hydration energy of the Ar pair. With a recent suggestion for the system-size extrapolation of the required correlation function integrals, the Ar-Ar rdfs permit evaluation of osmotic second virial coefficients B2. Those B2 also show that incorporation of attractive interactions leads to more positive (repulsive) values. With attractive interactions in play, B2 can change from positive to negative values with increasing temperatures. This is consistent with the historical work of Watanabe, et al., that B2 ≈ 0 for intermediate cases. In all cases here, B2 becomes more attractive with increasing temperature.
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.
Statistical Analyses of Hydrophobic Interactions: A Mini-Review
The Journal of Physical Chemistry B, 2016
This review focuses on the striking recent progress in solving for hydrophobic interactions between small inert molecules. We discuss several new understandings. Firstly, the inverse temperature phenomenology of hydrophobic interactions, i.e., strengthening of hydrophobic bonds with increasing temperature, is decisively exhibited by hydrophobic interactions between atomic-scale hard sphere solutes in water. Secondly, inclusion of attractive interactions associated with atomic-size hydrophobic reference cases leads to substantial, non-trivial corrections to reference results for purely repulsive solutes. Hydrophobic bonds are weakened by adding solute dispersion forces to treatment of reference cases. The classic statistical mechanical theory for those corrections is not accurate in this application, but molecular quasi-chemical theory shows promise. Finally, because of the masking roles of excluded volume and attractive interactions, comparisons that do not discriminate the different possibilities face an interpretive danger.
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.
Hydrophobic Effects on a Molecular Scale
The Journal of Physical Chemistry B, 1998
A theoretical approach is developed to quantify hydrophobic hydration and interactions on a molecular scale, with the goal of insight into the molecular origins of hydrophobic effects. The model is based on the fundamental relation between the probability for cavity formation in bulk water resulting from molecular-scale density fluctuations, and the hydration free energy of the simplest hydrophobic solutes, hard particles. This probability is estimated using an information theory (IT) approach, incorporating experimentally available properties of bulk water -the density and radial distribution function. The IT approach reproduces the simplest hydrophobic effects: hydration of spherical nonpolar solutes, the potential of mean force (PMF) between methane molecules, and solvent contributions to the torsional equilibrium of butane. Applications of this approach to study temperature and pressure effects provide new insights into the thermodynamics and kinetics of protein folding. The IT model relates the hydrophobic-entropy convergence observed in protein unfolding experiments to the macroscopic isothermal compressibility of water. A novel explanation for pressure denaturation of proteins follows from an analysis of the pressure stability of hydrophobic aggregates, suggesting that water penetrates the hydrophobic core of proteins at high pressures. This resolves a long-standing puzzle, whether pressure denaturation contradicts the hydrophobic-core model of protein stability. Finally, issues of "dewetting" of molecularly large nonpolar solutes are discussed in the context of a recently developed perturbation theory approach.
Journal of Medicinal Chemistry, 2014
The thermodynamic consequences of systematic modifications in a ligand side chain that binds in a shallow hydrophobic pocket, in the presence and absence of a neighboring ligand carboxylate group, were evaluated using isothermal titration calorimetry (ITC). Data revealed that the carboxylate significantly changes the relative thermodynamic signatures of these modifications, likely via altering the Hbonding/organization status of the hydration waters both in the unbound and the bound states. This carboxylate group was found to be proenthalpic, antientropic in some cases, and antienthalpic, proentropic in others. A remarkable enthalpy− entropy compensation relationship was also observed, reflecting the fact that the hydrophobic effect is governed by the thermodynamic status of the associated aqueous environment. This study could improve our understanding of the hydrophobic effect and may enhance our ability to design potent ligands that are capable of modulating biological processes.