For example, certain types of membrane proteins allow cells to identify and interact with
each other. Other types of membrane proteins regulate the transport of ions and other
molecules across the membrane. Membrane functionality is mediated by a complex array
of interactions including mechanical, hydrophobic and electrostatic. In this thesis we will
focus on the electrostatic aspects of these membranes.
1.3 Membrane electrostatics
Many different types of lipid species found in biological membranes carry net charges at
physiological pH values. These charged lipids result in the presence of various surface
potentials that are different from the potential of the bulk electrolyte. Thus, the
concentration profiles of ions close to the lipid surface is a lot more complicated than that
of the bulk [2]. These charged lipids are instrumental in electrostatic membrane
interactions. The electrostatic interactions near and around the membrane are
characterized by three potentials, illustrated in Figure 1.4. The transmembrane potential
(ψtr), drives ion transport through channels in cell membranes, a basic step in many
biological processes [3]. The surface potential (ψs) regulates the interaction of cytosolic
and environmental factors with cell membranes [4]. These two potentials are well studied
and have clearly demonstrable effects on membrane function. The third membrane
potential, known as the dipole potential (<∕∕√) however yet to be conclusively
characterized, this is a relatively large potential barrier (~ 100’s of mV across a 5 nm
spacing) at the membrane midplane created by inward-pointing molecular dipoles at the
interfacial planes [5].