Solution Polarizability Dependence of Lipid Bilayer Interactions

Neutral lipid bilayers attract each other due to van der Waals (vdW) forces. These forces depend on the electrical polarizability of the aqueous medium in which lipid bilayers are formed. Because attractive vdW forces are balanced by repulsive forces, lipid bilayers form multilamellar vesicles. The equilibrium repeat spacing of multilamellar lipid bilayers is therefore a sensitive and accurate indicator of the force balance between membranes. We present a series of small angle x-ray scattering measurements in which vdW forces are controlled by the nature and electrical polarizabilities of aqueous solutes. We then discuss the interplay of vdW and electrostatic interactions inherent in these systems and heighlight their relevance to biological membranes.