QUANTUM-CHEMICAL CALCULATIONS OF THE HYDRATION ENERGIES OF ORGANIC CATIONS AND ANIONS IN THE FRAMEWORK OF A CONTINUUM SOLVENT APPROXIMATION

We investigate the method of calculation of solvation energies using the continuum solvent model and the semiempirical NDDO quantum-chemical background. The electrostatic part of the calculation is based on the Miertus-Scrocco-Tomasi procedure treating the solvent as a dielectric continuum with a cavity and numerically solving the integral equation for the charge distribution on the cavity surface. Its efficiency was significantly increased by accelerating the convergence of the surface integration procedure and modifying the iterative scheme. The calculated solvation free energies of numerous organic ions agree with the experimental estimates within 2-3 kcal/mol. The specific solute-solvent interactions are shown to be important in several cases and a consistent procedure of calculating their contribution to the solvation energy is elaborated.