Ionic salt permeabilities and membrane potentials of glutamic acid-methyl-L-glutamate copolymer membranes

The ionic salt permeabilities and membrane potentials of charged polypeptide membranes of glutamic acid-methyl-L-glutamate co-polymers were studied as a function of glutamic acid content of the membranes. The basic membrane properties of the copolymer, such as fixed-charge concentration and water-containing capacity, could be controlled by adjusting the glutamic acid content of the membranes. The observed concentration dependences of ionic permeability and membrane potential in the external concentration range from 10−4 mol/liter to 10−1 mol/liters were interpreted on the basis of the Nernst-Planck flux equation and the Donnan distribution. In this interpretation, to obtain a satisfactory agreement between experimental results and theoretical predictions, it was necessary to introduce the standard chemical potential difference of the ion between the membrane and external solution phase, and the concentration dependence of the effective charge density of the membrane. Applying the free-volume theory to the temperature dependence of ionic permeability, it was confirmed that the magnitude of ionic permeability depends quantitatively on the membrane parameters, such as the free volume of the system, the degree of hydration of the membrane, the effective charge density of the membrane, the equilibrium partition coefficient, and the critical diffusant ion size.