Hydration of an apolar solute in a two-dimensional waterlike lattice fluid

TL;DR

This study extends a 2D lattice water model to include apolar solutes, revealing hydrophobic hydration signatures such as positive transfer free energy and temperature-dependent enthalpy and entropy.

Contribution

It introduces a novel extension of a waterlike lattice model to simulate hydrophobic solutes and analyzes their thermodynamic behavior.

Findings

Apolar molecules exhibit hydrophobic hydration signatures.

Transfer free energy is large and positive.

Transfer entropy is negative at low temperatures.

Abstract

In a previous work, we investigated a two-dimensional lattice-fluid model, displaying some waterlike thermodynamic anomalies. The model, defined on a triangular lattice, is now extended to aqueous solutions with apolar species. Water molecules are of the "Mercedes Benz" type, i.e., they possess a D3 (equilateral triangle) symmetry, with three equivalent bonding arms. Bond formation depends both on orientation and local density. The insertion of inert molecules displays typical signatures of hydrophobic hydration: large positive transfer free energy, large negative transfer entropy (at low temperature), strong temperature dependence of the transfer enthalpy and entropy, i.e., large (positive) transfer heat capacity. Model properties are derived by a generalized first order approximation on a triangle cluster.