Direct Numerical Test of the Statistical Mechanical Theory of Hydrophobic Interactions

TL;DR

This paper empirically tests the statistical mechanical theory of hydrophobic interactions using cavity methods, revealing that contact interactions are more attractive than predicted and providing new insights into temperature dependence of the second virial coefficient.

Contribution

It develops cavity methods to test the Pratt-Chandler theory and provides new quantitative data on hydrophobic interactions between atomic-sized spheres in water.

Findings

Contact hydrophobic interactions are more attractive than predicted by PC theory.

The osmotic second virial coefficient is attractive and becomes more so with increasing temperature.

Provides new data essential for refining molecular-scale theories of hydrophobic interactions.

Abstract

This work tests the statistical mechanical theory of hydrophobic interactions, isolates consequences of excluded volume interactions, and obtains B2 for those purposes. Cavity methods that are particularly appropriate for study of hydrophobic interactions between atomic-size hard spheres in liquid water are developed and applied to test aspects of the Pratt-Chandler (PC) theory that have not been tested. Contact hydrophobic interactions between Ar-size hard-spheres in water are significantly more attractive than predicted by the PC theory. The corresponding results for the osmotic second virial coefficient are attractive (B2 <0), and more attractive with increasing temperature (Delta B2/Delta T < 0) in the temperature range 300K < T < 360K. This information has not been available previously, but is essential for development of the molecular-scale statistical mechanical theory of hydrophobic interactions, particularly for better definition of the role of attractive intermolecular interactions associated with the solutes.