General Semiempirical Quantum Mechanical Solvation Model for Nonpolar Solvation Free Energies. n-Hexadecane

A new solvation model has been developed that accurately predicts solvation free energies in the nonpolar solvent n-hexadecane. The model is based on AM1-CM1A and PM3-CM1P partial charges, and it is based on a single set of parameters that is applicable to both the AM1 and PM3 Hamiltonians. To take account of both short-range and long-range solvation-shell interactions, each atom has two surface tensions associated with different effective solvent radii. For hydrogen, one of these surface tensions depends on the bond orders to carbon, nitrogen, oxygen, and sulfur, although only weakly. In addition to presenting the general parameterization, the article provides an analysis of the surface tension parameterization based on data for three rare gases. The model yields an rms error of 0.41 kcal/mol over a set of 306 data points (153 molecules, two Hamiltonians) that includes alkanes, alkenes, alkynes, aromatics, alcohols, ethers, aldehydes, ketones, esters, amines, nitriles, pyridines, thiols, sulfides, fluorides, chlorides, bromides, iodides, water, and ammonia.