AN ADSORPTION-ISOTHERM FOR THE INTERACTION OF MEMBRANE-PERMEABLE HYDROPHOBIC IONS WITH LIPID VESICLES

An adsorption isotherm is presented which describes the association of membrane-permeable hydrophobic ions with lipid vesicles. The theory is based upon the Langmuir adsorption isotherm, but it has been significantly extended to take into account diffusion of ions across the membrane and dissociation into the intravesicular space as well as electrical effects due to the build up of boundary potentials within the membrane. The boundary potentials are calculated according to the three-capacitor model of the lipid membrane. In contrast to the Gouy-Chapman theory, which is only applicable when the charged group is located directly at the membrane-solution interface, the theory presented here allows the charge to be located at any position within the membrane.