SLOW MOTIONS IN LIPID BILAYERS - DIRECT DETECTION BY 2-DIMENSIONAL SOLID-STATE DEUTERIUM NUCLEAR-MAGNETIC-RESONANCE

Two-dimensional solid-state H-2 NMR spectroscopy of specifically deuteriated lipids is used to detect and to characterize the rate and mode of slow motions in two lipid bilayer systems. Lateral diffusion of lipid molecules over the curved surface of dipalmitoylphosphatidylcholine liposomes can be detected by two-dimensional exchange H-2 NMR and it is shown that molecular orientation exchange is complete on the timescale of 100 ms. In contrast, it is shown that for the glycolipid 1,2-di-O-tetradecyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol (beta-DTGL), there is no evidence of a corresponding orientational exchange in the liquid-crystalline phase suggesting that this lipid forms relatively flat bilayers. In the gel phase of hydrated multibilayers of beta-DTGL, a slow (10-3 S-1) whole molecule axial motion is demonstrated at 10-degrees-C. Comparison of the experimental and simulated 2D-NMR ridge patterns suggests that large angle jumps about the long molecular axis, rather than small step Brownian diffusion, can best account for the 2D-exchange spectra of beta-DTGL in the gel phase. The significance of this technique for the study of dynamics in other biological systems is discussed.