ION BINDING TO CHARGED LIPID MONOLAYERS - THE ROLE OF DOUBLE-LAYER AND ION BINDING MODELS

We present a new approach to the analysis of monolayer surface potential experiments, based on a lattice model for binding of ions to the monolayer and two models for the electrical double layer: Gouy-Chapman-Debye-Hückel (GCDH) theory and a recently developed model that takes into account the finite polarizability of solvent dipoles and finite ion sizes. We demonstrate this approach by reanalyzing two recent monolayer surface potential experiments. For highly charged monolayers (Lakhadar-Ghazal, F., Tichadou, J. L., and Tocanne, J. F., Eur. J. Biochem., 134, 531 (1985)) we find that the new double layer model yields a description of surface properties which is distinctly different from that of GCDH theory, while at low surface charge densities the two models are effectively the same. The results of S. Ohki and R. Kurland (Biochim. Biophys. Acta, 645, 170 (1981)), fall in the latter regime, so our analysis of these data serves to contrast different binding models. Our results suggest that interactions between bound ions, or between lipid molecules in different ionization states, may be important in understanding surface properties when there is a high degree of ion binding. © 1990.