Frequency dependent2H N.M.R. relaxation rates of small unilamellar phospholipid vesicles

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Abstract
Deuterium (2H) N.M.R. spectroscopy has been used to investigate experimentally the molecular dynamics of phospholipid vesicles. 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) was deuterated specifically in both acyl chains, and aqueous suspensions of vesicles were studied above the main orderdisorder transition temperature. 2H spin-lattice relaxation rates (R 1) were measured at nine different magnetic field strengths, corresponding to Larmor frequencies (v o = ωo/2π) spanning 2·5 MHz to 61·4 MHz. Of three models considered, a model in which R 1 ∝ ω-1/2 0 best described the 2H N.M.R. results, whereas fits to R 1 ∝ ω-1 0 or to a lorentzian plus a constant dispersion were less satisfactory. Thus a broad distribution of motions exists, which must be explained by any model for the N.M.R. relaxation of liquid-crystalline phospholipids.

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