Physical studies of phospholipids. Part 5.—Proton magnetic resonance studies of molecular motion in some 2,3-diacyl-DL-phosphatidylethanolamines

Abstract

Proton magnetic resonance spectra of anhydrous polycrystalline 2,3-dimyristoyl- and 2-oleoyl-3-stearoyl-DL-phosphatidylethanolamine have been obtained at temperatures between –196 and 160°C. The line widths and second moments decrease gradually with increasing temperature up to a transition point which is different for the two phospholipids and at which abrupt reductions occur. The variation of line width and second moment up to the transition temperature is analyzed in terms of rotatory and oscillatory reorientations of the hydrocarbon chains. A crystalline-crystalline phase transition is observed below the first transition temperature. At the first transition temperature, a crystalline mesomorphic transition takes place and, at higher temperatures, a mesomorphic-mesomorphic transition occurs. Considerable molecular motion of the hydrocarbon chains is occurring in the mesomorphic phases. The n.m.r. spectra of other anhydrous phosphatidyl-ethanolamines of different chain lengths and degrees of unsaturation, as well as a phospholipid extract from brain, have been obtained at 23°C.