ESR STUDY OF THE LIPOSOME MEMBRANE PHYSICAL PARAMETERS IN THE HEATING-COOLING CYCLES

Changes of dynamic and structural parameters of egg yolk lecithin (EYL ) liposome membranes in the heating-cooling cycles have been studied u sing the ESR The investigations were conducted in the range of tempera tures from -18 degrees C to +60 degrees C. It has been found that in t he range of temperatures -15 degrees C to +45 degrees C in both the he ating and the cooling run the spectroscopic parameters changed practic ally along the same curve (reversible changes). However, after exceedi ng this range of temperatures one of the parameters (partition coeffic ient of the spin probe 2,2,6,6-tetramethylpiperidine -1-oxyl; TEMPO) c hanged along a closed curve, showing the phenomenon of thermal hystere sis. In the heating process the TEMPO content in liposome membranes wa s smaller than this in the cooling process. We assume that during the heating, the lipid molecules of the enter liposome layers dissolve in the aqueous medium. In the cooling process they can aggregate and form new liposomes, what in turn increases the surface of liposome membran es, accessible for the TEMPO probe (active surface).