A universal model for the quantum mechanical calculation of free energies of solvation in non-aqueous solvents

The SM5.4 quantum mechanical solvation model has been extended to calculate free energies of solvation in virtually any organic solvent. Electrostatics and solute-solvent polarization are included self-consistently by the generalized Born equation with class IV charges, and first-solvation-shell effects are modeled in terms of solvent-accessible surface areas that depend on solute geometries and four solvent descriptors. The inclusion of solvent properties in the first-solvation-shell term provides a model that predicts accurate solvation free energies in any solvent for which those properties are known. The model was developed using 1786 experimentally measured solvation free energies for 206 solutes in one or more of 90 solvents. Parameters have been obtained for solutes containing H, C, N, O, F, S, Cl, Br, and I, and the solutes used for parameterization span a wide range of organic functional groups. Solvents used in the parameterization contain H, C, N, O, F, P, S, Cl, Br, and I and include the most common organic solvents. Two general parameterizations are presented here, one for use with the AM1 Hamiltonian (SM5.4/AM1) and one for use with the PM3 Hamiltonian (SM5.4/PM3). In each case, one parameter is specially re-optimized for benzene and toluene to reduce systematic errors for these solvents. Chloroform is also treated with special parameters. The final mean unsigned error for both the SM5.4/AM1 and SM5.4/PM3 parameterizations is less than 0.5 kcal mol(-1) over the entire data set of 1786 free energies of solvation in 90 organic solvents.