Spin-lattice relaxation and lineshape parameters in nuclear magnetic resonance of lamellar lipid systems: Fluctuation spectroscopy of disordering mechanisms

Abstract

Selected nuclear magnetic resonance (NMR) applications to lamellar lipid systems are reviewed with special emphasis on methods sensitive to fluctuation properties. The time scales of these techniques range from 10 -10s to 10 0s. We shall consider the effect of rotametric isomerism on the orientational disorder of lipid hydrocarbon segments and relate this to the thermodynamic state. New proton spin-lattice relaxation dispersion results for dipalmitoylphosphatidylcholine (DPPC) multilamellar liposomes are represented for the frequency range 10 4-10 8 Hz. In addition lineshape parameters have been investigated and correlated with the spin-lattice relaxation data. Several fluctuation processes both in the gel and in the liquid crystalline state can be distinguished. We interpret these as being due to the one-dimensional diffusion of orientation-conserving defects, the fluctuation of headgroup domains around the bilayer normal, and the two-dimensional self-diffusion in the curved bilayer plane. Futhermore we suggest that fluctuations of the polar head groups are correlated with those of the alkyl chains. The natures of the phase transitions, including the so-called subtransition, are discussed on the basis of these results.