On the Mechanism of Hydrophobic Association of Nanoscopic Solutes

TLDR

The study investigates the underlying mechanism behind conflicting experimental and computational observations of water near hydrophobic solutes. Hydration of two planar nanoscopic hydrophobic solutes in water at ambient conditions is examined by computing the potential of mean force as a function of solute–solvent interaction strength. Weak solute–solvent attractions markedly affect hydration, with the crossover distance from solvent‑separated to contact pair states depending on solute size and interaction details, and the mechanism of attractive mean forces differing with interaction nature, thereby influencing the hydrophobic effect in biomolecules.

Abstract

The hydration behavior of two planar nanoscopic hydrophobic solutes in liquid water at normal temperature and pressure is investigated by calculating the potential of mean force between them at constant pressure as a function of the solute−solvent interaction potential. The importance of the effect of weak attractive interactions between the solute atoms and the solvent on the hydration behavior is clearly demonstrated. We focus on the underlying mechanism behind the contrasting results obtained in various recent experimental and computational studies on water near hydrophobic solutes. The length scale where crossover from a solvent separated state to the contact pair state occurs is shown to depend on the solute sizes as well as on details of the solute−solvent interaction. We find the mechanism for attractive mean forces between the plates is very different depending on the nature of the solute−solvent interaction which has implications for the mechanism of the hydrophobic effect for biomolecules.