ELECTRICAL POTENTIAL DISTRIBUTION OVER THE BILAYER LIPID-MEMBRANE DUE TO AMPHIPHILIC ION ADSORPTION

Potential drops at the boundary of the bilayer lipid membrane (BLM) due to amphiphilic anion (dodecylsulfate) adsorption have been investigated. The magnitude of these drops was determined by different experimental methods: inner field compensation (IFC), electrophoretic mobility and current relaxation (tetraphenylboron and dipicrylamine were taken as probe anions). The boundary potential (BP) drops (IFC method) do not depend on the electrolyte concentration for neutral membranes. The ζ-potential values in the same conditions are considerably smaller than the BP drops measured by the IFC method. The potential drops, determined with the help of the initial BLM conductivity changes (current relaxation method) coincide with the BP drops (IFC method). The adsorption of amphiphilic ions leads to a decrease in the rate constant of the movement of hydrophobic ions through the BLM (current relaxation method). To explain the results obtained, it is suggested that a potential drop due to amphiphilic ion adsorption is located not only in the diffuse double layer, but also in a layer inside the membrane. The latter is not screened by electrolyte solution ions and could not be registered by the electrophoretic method. © 1990.