Transient cavities and the excess chemical potentials of hard-spheroid solutes in dipolar hard sphere solvents

TL;DR

This study uses Monte Carlo simulations to analyze transient cavities and solvation of hard-spheroid solutes in dipolar hard sphere solvents, revealing how solute shape and temperature influence chemical potential and solubility.

Contribution

It provides new insights into the relationship between solute shape, solvent properties, and solvation thermodynamics, supported by a scaled-particle theory that matches simulation results.

Findings

Spherical solutes have the lowest excess chemical potential.

Prolate solutes are more soluble than oblate ones of the same volume.

Excess chemical potential increases with temperature.

Abstract

Monte Carlo computer simulations are used to study transient cavities and the solvation of hard-spheroid solutes in dipolar hard sphere solvents. The probability distribution of spheroidal cavities in the solvent is shown to be well described by a Gaussian function, and the variations of fit parameters with cavity elongation and solvent properties are analyzed. The excess chemical potentials of hard-spheroid solutes with aspect ratios $x$ in the range $1/5 \leq x \leq 5$, and with volumes between one and twenty times that of a solvent molecule, are presented. It is shown that for a given molecular volume and solvent dipole moment (or temperature) a spherical solute has the lowest excess chemical potential and hence the highest solubility, while a prolate solute with aspect ratio $x$ should be more soluble than an oblate solute with aspect ratio $1/x$. For a given solute molecule, the excess chemical potential increases with increasing temperature; this same trend is observed in the case of hydrophobic solvation. To help interpret the simulation results, comparison is made with a scaled-particle theory that requires prior knowledge of a solute-solvent interfacial tension and the pure-solvent equation of state, which parameters are obtained from simulation results for spherical solutes. The theory shows excellent agreement with simulation results over the whole range of solute elongations considered.