Electric interactions at the lipid membrane surface

This work presents the results of an experimental study and of computer simulations concerning electric interactions in the surface layer of egg yolk lecithin (EYL) liposome membranes. The surface layer is formed by EYL polar heads, which possess features of electric dipoles, and positive charged polar heads belonging to admixtures of quaternary ammonium salts (AS). The results of the experimental study are in good agreement with the ones of the computer simulations. It was found that fluidity of the membranes, at a given concentration of AS, obtains the extremal (minimal) value. Similarly, the binding energy of the dipoles-positive charges system behaves like that in computer simulations. Moreover, the locations of the fluidity extremum and those of the binding energy depend on the charge of the AS polar heads as well as on the degree of electric interactions screening by the environment. At a certain optimal value of the screening coefficient, the energy of the system is the lowest (the most negative) and together with the rise in AS charge, the minimum of the energy moves towards its higher concentrations.