Anisotropic and restricted molecular motion in lecithin bilayers

Abstract

A treatment has been developed which accounts for the prominent features of the PMR spectra and proton relaxation data of unsonicated lecithin bilayers. The spin-lattice relaxation time T 1 and the spin-spin relaxation time T 2 of the protons of a methyl top undergoing anisotropic and restricted reorientation have been calculated employing the theory of Woessner, but modified to include the effects of orientational anisotropies on long time scales. Analysis of the nmr data in terms of this theory permitted determination of the mobility of the lecithin hydrocarbon chains in the bilayer phase. These results indicate that the hydrophobic core of an unsonicated bilayer is more appropriately described as a soft solid rather than as a highly mobile fluid, contrary to the suggestions of recent esr spin label studies.