A H-2-NMR COMPARATIVE-STUDY OF O-GLYCOSYL DIGLYCERIDE AND S-GLYCOSYLDIGLYCERIDE MEMBRANES

Physical properties of synthetic glyceroglycolipids possessing saturat ed hydrocarbon chains, 1,2-di-[2-H-2(2)](-)palmitoyl-3-O-(beta w-D-gal actopyranosyl) rac-glycerol and its S-glycoside analog were investigat ed by H-2-NMR spectroscopy. It was shown that fully hydrated membranes either annealed by long-term storage at -5 degrees C or not annealed, which were formed of the investigated O- and S-glyceroglycolipids, di splay in the 30-95 degrees C temperature range transitions of the type s gel/liquid crystal and bilayer/nonbilayer structures. Different type s of membranes exhibited different bilayer/nonbilayer structure transi tions. S-glycerogiycolipid membranes show the bilayer/inverted hexagon al phase transition, while O-glyceroglycolipid ones - the bilayer/isot ropic phase and isotropic phase/inverted hexagonal phase transitions. The H-2-NMR spectra for both types of membranes existing in the liquid crystalline bilayer phase are characterized by a superposition of 3 s ignales, whose intensities arranged in the Increasing order of quadrop olar splitting magnitudes form a ratio of 1:1:2. The assignment of the se signals to the acyl chains based on the T-1-relaxation measurements , led us to the conclusion that the acyl chains of both O- and S-galac tosyldiglycerides are conformationally inequivalent. The interdependen ce of the conformational differences observed in the orientations of t he 1st and 2nd acyl chains of O- and S-galactosyldiglycerides relative to the bilayer director axis and the differences in the bilayer/nonbi layer structure transitions exhibited by both types of the membranes i nvestigated is discussed.