Free radical label: new approach to the study of super-slow molecular dynamics of lipid systems

A new method of EPR-spectroscopy, the recombination of free radicals appearing as a result of indirect radiolysis of biological molecules after a low temperature irradiation, was applied to the study of molecular dynamics of dimyristoyl phosphatidylcholine in mass and in the structure of liposomes above and below the transition temperature. It was shown that the mobility of lipid molecules in crystalline liposomes was lower than in the structure of liquid-crystalline liposomes. The addition of cholesterol in liposome membranes decreased the lateral molecular motion of lipids in crystalline and liquid-crystalline states; in the latter case, the effect of cholesterol addition was more pronounced. The activation energy for the displacement of the fragments of lipid molecules and the lipid molecule as a whole was estimated, and it was shown that the lipid matrix possesses a high degree of heterogeneity. The solubility of oxygen in the lipid bilayer and the mechanism of lipid diffusion are discussed.