Hydrophobic hydration: Heat capacity of solvation from computer simulations and from an information theory approximation

Hydrophobic hydration is studied with an information theory approximation, using the first two moments of the number of solvent centers in a cavity in liquid water, calculated from the density and the pair correlation functio n. The excess chemical potential, entropy, and heat capacity of solvation a re determined for three cases: the two-dimensional MB model of water, in bo th the (i) NPT and (ii) NVT ensembles, and (iii) the central force CF1 mode l of water in the NPT ensemble. The results are compared with Monte Carlo s imulations and experimental measurements from the literature. The informati on theory approximation, using only the first two moments, accurately deter mines the excess chemical potential and entropy of solvation but is unable to predict the excess heat capacity of solvation. Little difference is foun d between the results obtained using the uniform prior and the ideal gas pr ior. Molecular dynamics simulations are performed to calculate the excess c hemical potential of solvation of soft-spheres as a function of solute size . These results are compared with the solvation of a hard sphere using the information theory approximation and previous molecular dynamics simulation s of Lennard-Jones spheres in water. The information theory approximation i s found to predict the free energy of solvation as a function of size accur ately up to a cavity diameter of approximately 3.5 Angstrom. (C) 1999 Ameri can Institute of Physics. [S0021-9606(99)50212-2].