Dissecting Hydrophobic Hydration and Association

TL;DR

This paper investigates the roles of hydrogen bonding, van der Waals, and electrostatic interactions in water's hydrophobic effects, revealing how solute size influences dominant forces and association behaviors.

Contribution

It clarifies the distinct roles of various interactions in hydrophobic hydration and association using reference models, highlighting the importance of long-range forces for large solutes.

Findings

Hydrogen bonding dominates small solute hydration.

Long-range electrostatic and dispersion forces are crucial for large solutes.

Unbalanced long-range forces influence hydrophobic association.

Abstract

We use appropriately defined short ranged reference models of liquid water to clarify the different roles local hydrogen bonding, van der Waals attractions, and long ranged electrostatic interactions play in the solvation and association of apolar solutes in water. While local hydrogen bonding in- teractions dominate hydrophobic effects involving small solutes, longer ranged electrostatic and dis- persion interactions are found to be increasingly important in the description of interfacial structure around large solutes. The hydrogen bond network sets the solute length scale at which a crossover in solvation behavior between these small and large length scale regimes is observed. Unbalanced long ranged forces acting on interfacial water molecules are also important in hydrophobic association, illustrated here by analysis of the association of model methane and buckminsterfullerene solutes.