Molecular theory of asymmetrically charged bilayers: Preferred curvatures

We study the preferred curvature of asymmetrically charged bilayers (as in red blood cell membranes), in which the inner layer is negatively charged while the outer one is neutral. In particular, we present a molecular theory for the computation of the relaxed-area difference ΔA0 and the spontaneous curvature C0 of the bilayer. Our approach shows how packing properties of lipids and counterion (e.g., Ca2+) valence are intertwined. We find that Ca2+ has a dramatic effect on ΔA0 and C0: For wide parameter ranges, the presence of 0.1 mM of Ca2+ ensures positive ΔA0 and C0 that are nominally negative.