A SEMIEMPIRICAL QUANTUM-MECHANICAL SOLVATION MODEL FOR SOLVATION FREE-ENERGIES IN ALL ALKANE SOLVENTS

Using a linear fit of the solvent-ordering part of the microscopic sur face tension to experimental macroscopic surface tensions, the General ized Born/Surface Tension solvation model presented previously for n-h exadecane (called Solvation Model 4 or SM4), is extended to include al l alkanes as solvents, including normal, branched, and cyclic alkanes. The general SM4 alkane model is applicable to any alkane solvent for which the macroscopic dielectric constant and surface tension are eith er known or estimable. It treats electrostatic effects, including pola rization of the solute by a reaction field, in terms of a continuum di electric model of the solvent, uses element-based surface tension term s to account for first-solvation-shell effects, and uses an element-in dependent surface tension to account for solvent-ordering effects that extend further into solution. The electrostatic terms are based on th e recently developed Charge Model 1 (CM1) for computing atomic partial charges, This charge model allows the development of a single set of parameters which is applicable to both the AM1 and PM3 Hamiltonians an d also to any other electronic structure method that provides reasonab ly accurate geometries and partial charges.