FREQUENCY-DEPENDENT H-2 NMR RELAXATION RATES OF SMALL UNILAMELLAR PHOSPHOLIPID-VESICLES

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 order-disorder transition temperature. 2H spin-lattice relaxation rates (R1)were measured at nine different magnetic field strengths, corresponding to Larmor frequencies (v0 = ω0/2Π) spanning 2.5 MHz to 61.4 MHz. Of three models considered, a model in which R1 ∝ω0-1/2 best described the 2H N.M.R. results, whereas fits to R1∝ ω0-1 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. © 1990 Taylor & Francis Ltd.