Microscopic description of thermodynamics of Lipid Membrane at Liquid-Gel Phase Transition
B. Kheyfets+, T. Galimzyanov+*, S. Mukhin+
+National University of Science and Technology "MISIS", 119049 Moscow, Russia
*A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 119071 Moscow, Russia
Abstract
A microscopic model of the lipid membrane is constructed that
provides analytically tractable description of the physical mechanism of the
first order liquid-gel phase transition. We demonstrate that liquid-gel phase
transition is cooperative effect of the three major interactions: inter-lipid
van der Waals attraction, steric repulsion and hydrophobic tension. The model
explicitly shows that temperature-dependent inter-lipid steric repulsion
switches the system from liquid to gel phase when the temperature decreases.
The switching manifests itself in the increase of lateral compressibility of
the lipids as the temperature decreases, making phase with smaller area more
preferable below the transition temperature. The model gives qualitatively
correct picture of abrupt change at transition temperature of the area per
lipid, membrane thickness and volume per hydrocarbon group in the lipid
chains. The calculated dependence of phase transition temperature on lipid
chain length is in quantitative agreement with experimental data. Steric
repulsion between the lipid molecules is shown to be the only driver of the
phase transition, as van der Waals attraction and hydrophobic tension are
weakly temperature dependent.