A local fingerprint for hydrophobicity and hydrophilicity: from methane to peptides

TL;DR

This paper introduces a local fingerprint based on water-solute radial distribution functions to quantify hydrophobicity and hydrophilicity, applicable to molecules from methane to peptides, and demonstrates its usefulness in simulations.

Contribution

The authors develop a novel, computationally inexpensive local fingerprint for hydrophobicity and hydrophilicity that reflects environmental effects and can be used as a collective variable in enhanced sampling.

Findings

The fingerprint aligns with chemical intuition for amino acids and other molecules.

It reveals how local environment alters hydrophilicity/hydrophobicity.

It effectively facilitates transitions in host-guest simulations.

Abstract

An important characteristic that determines the behavior of a solute in water is whether it is hydrophobic or hydrophilic. The traditional classification is based on chemical experience and heuristics. However, this does not reveal how the local environment modulates this important property. We present a local fingerprint for hydrophobicity and hydrophilicity inspired by the two body contribution to the entropy. This fingerprint is an inexpensive, quantitative and physically meaningful way of studying hydrophilicity and hydrophobicity that only requires as input the water-solute radial distribution functions. We apply our fingerprint to octanol, benzene and the 20 proteinogenic amino acids. Our measure of hydrophilicity is coherent with chemical experience and, moreover, it also shows how the character of an atom can change as its environment is changed. Lastly, we use the fingerprint as collective variable in a funnel metadynamics simulation of a host-guest system. The fingerprint serves as a desolvation collective variable that enhances transitions between the bound and unbound states.