Anisotropic deuterium NMR spin-lattice relaxation in L.alpha.-phase cerebroside bilayers

Abstract

A series of 2H NMR inversion recovery experiments in the L alpha phase of the cerebroside N-palmitoylgalactosylsphingosine (NPGS) have been performed. In these liquid crystalline lipid bilayers we have observed substantial anisotropy in the spin-lattice relaxation of the CD2 groups in the acyl chains. The form and magnitude of the anisotropy varies with position in the chain, being positive in the upper region, decreasing to zero at the 4-position, and reversing sign at the lower chain positions. It is also shown that addition of cholesterol to the bilayer results in profound changes in the anisotropy. These observations are accounted for by a simple motional model of discrete hops among nine sites, which result from the coupling of two modes of motion--long-axis rotational diffusion and gauche-trans isomerization. This model is employed in quantitative simulations of the spectral line shapes and permits determination of site populations and motional rates. These results, plus preliminary results in sphingomyelin and lecithin bilayers, illustrate the utility of T1 anisotropy measurements as a probe of dynamics in L alpha-phase bilayers.

Order parameters based on 13C1H, 13C1H2 and 13C1H3 heteronuclear dipolar powder patterns: a comparison of MAS‐based solid‐state NMR sequences

“…The measured dipolar coupling constant is scaled in both experiments by a constant that depends on the experimentally calibrated RF fields. The experimental scaling constant is inherently included in the simulations by using the experimental RF fields in Eqn (11).…”

Dynamics of lipid bilayers from comparative analysis of H2 and C13 nuclear magnetic resonance relaxation data as a function of frequency and temperature

“…24,28,41 Consideration of collective mechanisms of relaxation has also been regarded as unnecessary for computer simulations of lipid membranes. 30 In other work, 16,24,25,[42][43][44] the approach has been to fit separately the angular-and frequency-dependent relaxation data for individual segment positions of the lipid acyl chains, which has led in some cases to a large discrepancy of the fitting parameters for the same model. Moreover, the analysis of the dependence of the relaxation on bilayer orientation 25,44 in fluid lipid membranes has not shown a dramatic change of the relaxation times with the angle between the bilayer normal and the magnetic field, 25,[42][43][44] making it difficult to fit the data uniquely.…”

“…30 In other work, 16,24,25,[42][43][44] the approach has been to fit separately the angular-and frequency-dependent relaxation data for individual segment positions of the lipid acyl chains, which has led in some cases to a large discrepancy of the fitting parameters for the same model. Moreover, the analysis of the dependence of the relaxation on bilayer orientation 25,44 in fluid lipid membranes has not shown a dramatic change of the relaxation times with the angle between the bilayer normal and the magnetic field, 25,[42][43][44] making it difficult to fit the data uniquely. Proton ( 1 H) field-cycling NMR techniques 41 have enabled studies over a very broad frequency range, but have not made it possible to investigate the dynamics of individual segments; instead, the relaxation arising from the cumulative effect of all the protons has been observed.…”

Model for the structure of the lipid bilayer.

“…Unfortunately, many significant lipid motions are slow relative to the molecular dynamics subnanosecond time scale. The trans-gauche isomerization rate of the chain dihedrals is between 109 and 1010 s-1 (18), the rotational diffusion constants of the lipids are on the order of 108-101o s-1 (3,7,8,19), translational diffusion constants are =10-8 cm2/s (4), and collective motions are in the regimes of 103-1 s-' (7).…”

“…At higher temperature, the bilayer enters the partially ordered liquid crystal (L,,) phase observed for biologically active membranes (1, 2). On going from Lp3 to La, the volume and fluidity of the bilayer increase, the thickness decreases, and the individual lipid undergoes a wide range of motions including: gauche-trans isomerizations, axial rotation, collective and noncollective tilting, out-of-plane deformations, and lateral diffusion (3)(4)(5)(6)(7)(8). The precise time scales, amplitudes, and degree of coupling of these motions remain uncertain both experimentally and theoretically.…”