(174a) Aqueous Partial Molar Volumes from Simulation and Individual Group Contributions

Partial molar volumes for a range of organic solutes in aqueous solution are evaluated from molecular simulations using Kirkwood-Buff theory. Long-range oscillatory variations in the Kirkwood-Buff integrals are suppressed using the techniques of Lockwood, Rossky, and Levy, enhancing convergence of the calculated partial molar volumes to within the first hydration shell (Daren M. Lockwood and Peter J. Rossky, J. Phys. Chem. B 1999, 103, 1982-1990). Contributions from individual constituent groups, such as methylene carbons and alcohol oxygens, are evaluated using proximal correlation functions extended here to heterogeneous molecular species. We find the simulation partial molar volumes are systematically greater than experiment, with the difference between simulation and experiment increasing with solute size. These differences are attributed to possible deficiencies in the volumetric properties of the interaction potentials employed. Nevertheless, we find that the structure of water near identical groups on different solutes is effectively indistinguishable, as quantified by proximal correlation functions. As a result, we propose a new group contribution correlation for the partial molar volume rooted in Kirkwood-Buff theory and the proximity approximation.