Evaluation of functional group contributions to excess volumetric properties of solvated molecules

We develop extensions to a previous methodology for evaluating the excess c ompressibility of solvation. These extensions make it possible to analyze s olution compressibilities in terms of the hydration shell model of solvatio n. The methodology is applied to three model solutes-water, methane, and me thanol-in water. We find that the compressibility is accounted for by local ized effects of the solute on the solvent. In addition, for the case of met hanol, we find that the localized effects of one solute functional group ar e 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 fi om molec ular dynamics simulation data. The technique is easily generalized for exam ination of large solutes, including biologically important macromolecules.