Electrostatics of a DNA-like polyelectrolyte: Effects of solvent dielectric saturation and polarization of ion hydration shells

The modified Poisson-Boltzmann (MPB) equations together with the Booth's th eory of water dielectric saturation and an experimental dependence of water dielectric constant on ionic concentrations have been numerically solved t o calculate the mean electrostatic potential and ionic distributions around a DNA-like highly charged cylindrical polyion. The model is explored for d iluted mono- and multivalent electrolyte solutions. As follows from compari sons with the MPB and Poisson-Boltzmann (PB) calculations for the uniform p ermittivity solvent model, the solvent dielectric saturation and ion hydrat ion shell polarization can be a significant contributor in the mean electro static potential and free energy of a highly charged macromolecule. Such ef fects may not be neglected in the case of a multivalent electrolyte. In con trast, the influence of solvent dielectric saturation and ionic polarizatio n is negligible for a moderately charged spherical macroion, which confirms the success of numerous PB applications to calculations of pK values of pr otein charged groups.