The dependence of hydrophobic interactions on the solute size

TL;DR

This study investigates how hydrophobic interactions depend on solute size, identifying a critical radius that distinguishes different solvation behaviors and elucidating the driving forces behind solute association in water.

Contribution

It introduces a novel analysis of hydrophobic effects based on solute size and molecular dynamics simulations, highlighting the role of hydrogen bonding in solute association.

Findings

Critical radius for solvation is 3.2 Å.

Hydrophobic interactions can be categorized into two processes.

Maximizing hydrogen bonding drives hydrophobic association.

Abstract

Based on our recent study on physical origin of hydrophobic effects, this is applied to investigate the dependence of hydrophobic interactions on the solute size. As two same hydrophobic solutes are dissolved into water, the hydration free energy is determined, and the critical radius (Rc) is calculated to be 3.2 Angstrom. With reference to the Rc, the dissolved behaviors can be divided into initial and hydrophobic solvation processes. These can be demonstrated by the molecular dynamics simulations on C60-C60 fullerenes in water, and CH4-CH4 molecules in water. In the association of C60 fullerenes in water, with decreasing the separation between C60 fullerenes, hydrophobic interactions can be divided into H1w and H2s hydrophobic processes, respectively. In addition, it can be derived that maximizing hydrogen bonding provides the driving force in the association of hydrophobic solutes in water.