Dependence of Hydration Free Energy on Solute Size

Abstract

The dielectrically consistent reference interaction site model theory (DRISM) was used to calculate excess chemical potentials of solvation for the immersion of a nonpolar solute molecule (Lennard-Jones sphere) in a molecular model of water in a wide variety of state conditions. The chemical potential was found to be predominantly entropic. In all cases the chemical potential was found to consist almost entirely of a solute surface area and a solute volume term. Both these terms were significant over a range of solute sizes and pressure/temperature states. It was concluded that the volume-dependent term must include contributions in addition to that from the system pressure. An exactly solvable lattice model of solvation was also investigated, and the model conditions for which the chemical potential becomes predominantly entropic were determined. One situation was shown where a volume-dependent entropic term in the chemical potential, other than pressure, arises.