Simulation studies of the hydration entropy of simple, hydrophobic solutes

The contribution of solute-water correlations to the entropy of solution of monatomic, hydrophobic solutes in water is calculated by Monte Carlo simulations using an expansion in terms of multiparticle correlation functions. The solute-water orientational correlations are found to decay linearly with intermolecular distance and virtually vanish in the second hydration shell. The results for the hydration entropies of inert gases, compared to experimental values, appear to be reasonable. The dependence of the entropy on the solute size and the solute-solvent pair interaction energy is examined by simulations of model Lennard-Jones particles in water. The primary factor determining the solute-water entropy is found to be solute size, with the pair interaction energy playing a secondary, but significant, role. The dependence of the orientational entropy on the curvature of the solute surface is discussed in connection with enthalpy-entropy compensation phenomena.