Molecular dynamics studies of the properties of water around simple organic solutes

Molecular dynamics simulations of aqueous methane, ethane, methanol, benzene, acetate ion, and methylammonium ion have been performed with two different water models. The SPC/E model is a pairwise-additive potential, while the related POL3 model includes nonadditivity in the form of atomic polarizabilities. Structural and energetic quantities were collected over 90-ps simulations and compared between models and among solutes; the proximity criterion was used to divide the water into mutually exclusive sets for analysis. Overall, the agreement with previous studies and between the SPC/E and POL3 models is substantial. Results suggest that the structure of water is preserved, rather than enhanced, around hydrophobic groups and that waters hydrogen-bonding to polar solute groups sacrifice solvent-solvent interactions to some degree. Solute methyl groups are not uniformly hydrophobic; as expected, their polarity and the surrounding solvent structure depend on the neighboring functional groups.