Analytical Calculation of Diffusion Coefficient Drop at the Liquid-Gel Phase Transition in Lipid Membrane

Abstract

Diffusion coefficient drop by an order of magnitude at the liquid-gel phase transition in the lipid membranes so far was missing theoretical description. Subdiffusion regime, which takes place on 1ps-10ns timescale, is captured by our microscopic model and shows a jump of the self-diffusion coefficient. We developed the analytical theory of the first order liquid-gel phase transition of a lipid bilayer using the microscopic model of semi-flexible strings. We have shown that the van der Waals attraction between the lipids tails is the essential component of the free energy. In the framework of the free volume theory, we calculated a diffusion coefficient in the subdiffusive regime drop by an order of magnitude at the main phase transition. We found that the main contribution to the diffusion drop is due to compression factor as opposed to activation-like factor. The calculated temperature dependencies of the major thermodynamic characteristics of the lipid membranes including diffusion coefficient, membrane thickness, area and volume per lipid molecule are in a good quantitative agreement with experimental data. The work was supported by the Russian Science Foundation (project #17-79-20440).