Parametrizing PCM to obtain solvation free energies from group contributions

A parametrization methodology for evaluating the solvation free energy, using the polarizable continuum model implemented in Gamess software, is presented in a formulation which makes use of a group contribution conception to construct the cavities. The systems studied include alkanes, alcohols, aldehydes and ketones embeded in a continuous medium simulating the water as the solvent. For each family, the CH2, OH, and C=O moieties of atoms are put together in single spheres forming a group. The cavities are constructed in two different ways, one for the electrostatic component and the other for nonelectrostatic contributions, i.e., the cavitation, dispersion, and repulsion components of free energy of solvation. A multivariate analysis is performed to obtain an assembly of variables, for each homologous series, able to give the results which are close to experiment. The analysis is addressed in order to (i) compare the theoretical free energy of solvation with the experimental trends of the solutes in aqueous media, when the chain is increased, (ii) compare the behavior of each component of free energy with the increasing CH2 number, (iii) investigate the influence of the oxygen atom on the components, and (iv) quantify the relative contribution of each component to the final free energy of solvation for some homologous series.