General Parameterized SCF Model for Free Energies of Solvation in Aqueous Solution

We present a new general parameterization for aqueous solvation free energies of molecules and ions in aqueous solution. It is obtained by extending a semianalytic treatment of solvation recently proposed for use with molecular mechanics and liquid simulations by Still et al. As extended here, the solvation terms are included in a Fock operator. The model incorporates reaction field polarization effects through the generalized Born functional with charges obtained by AM1 molecular orbital calculations, and it includes cavitation, dispersion, and hydrophobic effects through an empirical function of solvent-accessible surface area. A general parameter set, including parameters for H, C, N, O, F, S, Cl, Br, and I, has been obtained by considering a data set consisting of 141 neutral molecules, 10 cations, and 17 anions. The neutral molecules include alkanes, cycloalkanes, alkenes, arenes, alkynes, ethers, heterocycles, carboxylic acids, esters, nitriles, aldehydes, ketones, alcohols, amines, nitro compounds, sulfides, thiols, halides, and polyfunctional compounds. The general parameterization is called Solvation Model 1, and it is particularly well suited for chemical reaction dynamics and reaction intermediates. We also discuss how the model may be refined for solvation free energies for stable neutral molecules.