Preferential interactions of cosolvents with hydrophobic solutes

The variation in solute excess chemical potential has been determined for a range of nonpolar solutes (He, Ne, Ar, CH4) in a series of cosolvent solutions (sodium chloride, urea, guanidinium chloride, 2,2,2-trifluoroethanol) as a function of cosolvent concentration using computer simulations. The data are analyzed using a combination of Kirkwood-Buff theory and the concept of preferential interactions. The results demonstrate that one can accurately reproduce the excess chemical potential changes with a knowledge of the appropriate radial distribution functions over 2-3 solvation shells. The simulations indicate that cosolvent effects are not limited to direct binding of the cosolvent to the solute, although the total and direct binding are linearly related. In addition, it is observed that the effects of changes in water association can be neglected for cases in which the preferential interaction parameter, \ nu \ < 1.