Continuum electrostatics and hydration phenomena

Abstract

A formalism for a computational treatment of the polarization of a solvent and polar solutes immersed in it is presented. The solvent is modeled as a continuum dielectric. Polarization effects are represented by a polarization charge density at the dielectric boundaries and by induced dipoles at the polarizable atoms. Applications of this formalism with nonpolarizable atoms have led to excellent agreement between the calculated and experimental hydration enthalpies of a variety of polar molecules. A problem of the choice of the charge distribution of the solute is addressed in calculations of the solution dipole moment and hydration enthalpy of polarizable molecule of water in solution. Experimental values of these properties were well reproduced in calculations starting with point charges fitted to the vacuum dipole moment of the water molecule. Tests calculations for spherical models and for a 13-residue peptide show good convergence of the computational method. It is shown in calculations on simplified models that a change in the exposure of a charged side chain can lead to large changes in the potential inside protein measured at a fixed distance from the charge and at the same depth from the protein surface. Calculations performed for the C-peptide of the ribonuclease suggest that the differential screening of partial charges can reverse the sign of the vacuum potential of the helix dipole.