The Effect of pH on the Electrical Capacitance of Phosphatidylcholine–Phosphatidylserine System in Bilayer Lipid Membrane

Abstract This paper reports measurements on the pH dependence of the electrical capacitance of lipid mem-branes formed by 1:1 phosphatidylcholine-phosphati-dylserine mixtures. A theoretical model was developed to describe this dependence, in which the contributions of functional groups (as the active centers of adsorption of the hydrogen and hydroxide ions) to the overall membrane capacitance were assumed to be additive. The proposed model was verified experimentally using electrochemical impedance spectroscopy. The theoretical predictions agreed with the experimental results over the measured pH range. A minimum corresponding to the isoelectric point appeared in both the theoretical equation and the experi-mental data