Evaluation of Functional Group Contributions to Excess Volumetric Properties of Solvated Molecules

We develop extensions to a previous methodology for evaluating the excess compressibility of solvation. These extensions make it possible to analyze solution compressibilities in terms of the hydration shell model of solvation. The methodology is applied to three model solutes water, methane, and methanol in water. We find that the compressibility is accounted for by localized effects of the solute on the solvent. In addition, for the case of methanol, we find that the localized effects of one solute functional group are independent of the effects of the other. This creates the opportunity for estimation of group-additive contributions to the compressibility, and we illustrate a technique for the extraction of such contributions from molecular dynamics simulation data. The technique is easily generalized for examination of large solutes, including biologically important macromolecules.