Mathematical analysis of membrane potentials for polypeptide membranes

Abstract

The membrane potentials of polypeptide membranes containing weak acid or weak acid and base groups have been obtained with a numerical integration procedure of the Nernst–Planck equation and Donnan equilibrium. The flux of the salt cations, salt anions, and protons, depending on the pH of the salt solution in the bulk phases, has been calculated iteratively by assuming a zero current flow across the membrane. Since the fixed charges of the polypeptide membrane were weak acid and/or base groups, the dissociation equilibrium of the groups has been taken into account. This procedure permitted the construction of the concentration profiles of the three mobile ions and the fixed ions in the membrane. The model has been compared with experimental data by a fitting procedure so that the values of the concentration and the equilibrium constant of the weak acid or weak acid and base groups as well as the diffusion coefficients have been obtained.