EVALUATION OF ION-BINDING OF ZWITTERIONIC MEMBRANES BASED ON EXTENDEDGOUY-CHAPMAN-STERN THEORY

The Gouy-Chapman-Stern theory is extended, and analytic expressions ar e obtained for the ion binding constant (K) and the density of binding sites (N). Parameters of ion binding to dimyristoylphosphatidylcholin e (DMPC) and dipalmitoylphosphatidylcholine (DPPC) membranes are deter mined simultaneously from the extrema of the vesicle zeta (or surface) potential vs ion concentration curves without arbitrary suppositions concerning the ion-to-lipid binding ratio, using the values of the thi ckness of the shearing layer delta = 0 and 0.2 nm.