Physical origin underlying the entropy loss upon hydrophobic hydration

TL;DR

This paper challenges the traditional entropic explanation of the hydrophobic effect, proposing a new view based on many-body correlations and electrostatic field fluctuations revealed through computer simulations.

Contribution

It introduces a novel perspective on hydrophobic hydration, emphasizing many-body correlations and electrostatic effects over local configurational entropy reduction.

Findings

Hydrophobic hydration involves many-body correlations affecting hydrogen bond switching.

Electrostatic field fluctuations are non-local and compensate for reduced local fluctuations.

The traditional entropy-based picture of hydrophobic effect is not supported by simulation results.

Abstract

The hydrophobic effect (HE) is commonly associated with the demixing of oil and water at ambient conditions and plays the leading role in determining the structure and stability of biomolecular assembly in aqueous solutions. On the molecular scale HE has an entropic origin. It is believed that hydrophobic particles induce order in the surrounding water by reducing the volume of con- figuration space available for hydrogen bonding. Here we show with computer simulation results that this traditional picture is not correct. Analyzing collective fluctuations in water clusters we are able to provide a fundamentally new picture of HE based on pronounced many-body correlations affecting the switching of hydrogen bonds between molecules. These correlations emerge as a non-local compensation of reduced fluctuations of local electrostatic fields in the presence of an apolar solute.