Solvation free energies of non-polar and polar solutes reproduced by a combination of extended scaled particle theory and the Poisson-Boltzmann equation

Abstract

A hybrid approach using extended scaled particle theory and the Poisson-Boltzmann (PB) equation is proposed for calculating the solvation free energy of a solute with partial charges in dilute aqueous solution. The applicability of this method is demonstrated by taking a series of the normal alcohols and normal alkanes. The solvation free energy of normal alkanes, which has been studied prevously based on a rather crude model, is recalculated using a more elaborate model. The electrostatic contribution to the free energy for the polar solute is calculated by the PB equation. In order to take into account the complicated boundary condition associated with the shape of molecular surface, the PB equation is solved numerically using a finite difference method. A superposition of hydrophobic and electrostatic contributions to the solvation free energy gives reasonable agreement with corresponding experimental data for the polar solute. The possibility of further applications of the method is discussed.