The Membrane Potentials of Periderm and Cuticular Membranes

The description of transport phenomena in biological membranes is still unclear from the viewpoint of physical chemistry. Transport phenomena in ion exchange membranes can be controlled by several factors such as ionic concentration within the membrane, fixed charge concentration, solution composition, ionic fluxes, and water content. The ionic transport as well as distinctive selectivity is provided by fixed groups in the ion exchange membrane, but that of co-ions is strongly restricted due to the Donnan effect. The fixed charge theory was first proposed by Teorell and Meyer and Sievers, who described the Donnan equilibria at the membrane-solution interfaces. Theoretical equations for the membrane potential and salt flux based on the irreversible thermodynamics in terms of the ionic mobility and effective charge density were derived by Toyoshima et al.5−7. The effective charge density in ion exchange membranes using the Teorell-Meyer-Sievers (TMS) theory was determined from membrane potential measurements. In general, periderm or cuticular membrane, which is a biological membrane, is adopted as a porous membrane model with the pore size depending mainly upon swelling in the presence of water. It was pointed out that the pores in the cuticle or periderm membranes have polar regions which are weakly polar compounds due to unesterified carboxyl and hydroxyl groups and have a net negative charge above pH ∗Corresponding author