Chronoamperometry Insight into the pH Effect on the Electrical Properties of Bilayer Lipid Membrane Formed from Phosphatidylcholine

This paper discusses the effect of adsorption of hydrogen and hydroxide ions which are present in the solution upon electrical capacitance and electrical resistance of the bilayer membrane formed by phosphatidylcholine. Both electrical parameters of the membrane were determined as a function of pH from chronoamperometric measurements. Two models were tested to explain the phenomena occurring on the membrane surface. The models display changes in the capacitance and the resistance values, particularly in the ranges distant from the isoelectric point. In Model I, the surface is continuous with uniformly distributed functional groups constituting the centers of the hydrogen and hydroxide ions adsorption. In Model II, the surface is built of lipid molecules, free or with adsorbed H+ and/or OH-. In both models, the contributions of the individual lipid molecule forms to the electrical parameters of the membrane were assumed to be additive. Theoretical equations were derived to describe the electrical parameters as a function of pH for proposed models.