Karis A. Zecchi, Lars
D. Mosgaard and Thomas Heimburg
Niels Bohr Institute,
University of Copenhagen.
Title: Spontaneous Polarization in Lipid Membranes.
Abstract: Lipid membranes behave like capacitors whose dimensions
can change as a response to an applied voltage. This phenomenon, called
electrostriction, is more pronounced when the membrane is softer (e.g.
close to the melting transition) and it results in the membrane
capacitance being a quadratic function of the voltage. This means that a
symmetric membrane cannot distinguish between positive and negative
voltages. However, this does not hold true for asymmetric membranes, which
can display a net electric polarization in the absence of an applied
field. This spontaneous polarization can be caused by anything that breaks
the symmetry of the bilayer, Êlike a different composition of the two
membrane leaflets, or curvature (flexoelectricity) and is responsible for
interesting electromechanical properties. For instance, it gives rise to
voltage offsets that can explain inward or outward rectification of the
membrane permeability in both lipid and biological membranes. Here we discuss
spontaneous polarization in the context of lipid bilayers.