Dependencies of liquid-gel phase transition temperature and area per lipid on lipid type: Analytic theory

Available experimental data for a single component lipid bilayer reveal opposite dependencies on the lipid structure of two important parameters: mean area per lipid and main phase transition temperature. The mean area per lipid increases with lipid head size or tails unsaturation, and decreases with the number of hydrocarbon groups per tail. The main phase transition temperature changes reversely: it decreases with lipid head size, or tails unsaturation, and increases with the number of hydrocarbon groups per tail. In this paper we derive these effects theoretically from the flexible strings model of lipid bilayer previously introduced by the authors. The model describes a single component lipid bilayer by considering a single lipid in an entropic repulsive mean field created by its neighbors. Dipalmitoylphosphatidylcholine (DPPC) is used as a reference lipid: particular changes are computed by considering deviations of parameters from their DPPC values.