Physical studies of phospholipids VIII. Nuclear magnetic resonance studies of diacyl-l-phosphatidylcholines (lecithins)

Nuclear Magnetic Relaxation and the Biological Membrane

“…The sharp reduction in second moment at -ISO°C could be due to onset of motion of the -NMe 3 + group; this would be consistent with the absence of a similar reduction of second moment in phosphatidyl ethanolamines (Chapman and Salsbury, 1966). At higher temperatures, line sharpening is attributed to oscillation of the -CH2-groups in the fatty acid chains (Salsbury and Chapman, 1968) as postulated to occur in a number of soap phases (Grant and Dunell, 1960;Barr and Dunell, 1964;van Putte, 1970).…”

“…Since this is not the case for the lipids, estimates have to be made on the basis of data for long-chain paraffins. Salsbury and Chapman (1968) estimate a rigid lattice second moment for distearoyl lecithin of 31 gauss 2 • As with a number of paraffins (Odajima et al, 1962), the measured second moment at -196°C is less than the calculated rigid-lattice value, indicating some methyl group rotation at this temperature. The sharp reduction in second moment at -ISO°C could be due to onset of motion of the -NMe 3 + group; this would be consistent with the absence of a similar reduction of second moment in phosphatidyl ethanolamines (Chapman and Salsbury, 1966).…”

“…3 gauss (Salsbury and Chapman, 1968). Narrowing of the broad line will then be observed if motion occurs at a rate greater than ca.…”

“…The linewidth and second moment are, however, still very much greater than expected for an isotropic liquid, so that the rapid molecular motions must still be anisotropic. Chapman and Salsbury (Chapman and Salsbury, 1966;Salsbury and Chapman, 1968) consider the motions to be oscillatory wagging and flexing motions of the chains and unlikely to be due to translational diffusion. It should be noted that Woodward (1972) has suggested that the second moments reported by Chapman and coworkers might be distorted by saturation effects.…”

Dynamics of lipids in membranes: Heterogeneity and the role of cholesterol

“…Proton Wide-Line and Pulsed NMR Early wide-line studies indicated that NMR was a promising technique with which to study molecular mobility in membrane systems [ 14]. Anhydrous lecithins at liquid nitrogen temperatures were shown to have chain proton linewidths of ~ 1.6 mT* and this was gradually reduced on heating to 0.8 mT (distearoyl lecithin), [15] or in the presence of water, 0.4 mT [16], in the a-crystalline gel phase. It was apparent, however, that the headgroups had considerable mobility, especially near the thermal phase transition [16].…”