Microscopic Description of Thermodynamics of Lipid Membrane at Liquid-Gel Phase Transition

TL;DR

This paper presents a microscopic model explaining the liquid-gel phase transition in lipid membranes as a cooperative effect driven mainly by temperature-dependent steric repulsion, aligning well with experimental observations.

Contribution

The model provides an analytically tractable description of the lipid membrane phase transition emphasizing steric repulsion as the primary driver, with quantitative agreement to experimental data.

Findings

Steric repulsion causes the phase transition.

Transition temperature depends on lipid chain length.

Model matches experimental data on membrane properties.

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.