The role of counterions in the interaction of bifunctional surface active compounds with model membranes

Interaction of two series of bifunctional surfactants (bromides and chlorides) with red blood cells and planar lipid membranes was studied. The aim of the work was to determine the role of counterions in the mechanism of interaction of bifunctional cationic surfactants with model membranes. In each case bromides influenced model membranes to a greater degree than the corresponding chlorides. The possible explanation of the obtained results is presented. It seems that the greater ability of bromides to destabilize model membranes in comparison with chlorides can be attributed to the greater mobility and the smaller radius of the hydrated bromide ion. This may underlie the greater ease that this anion can modify the surface potential of the lipid bilayer, thus enhancing the interaction of the cationic surfactant with such a modified bilayer.