Angular anisotropy of 2H NMR spectral densities in phospholipid bilayers containing cholesterol

Abstract

Spin—lattice ( R 1Z) and quadrupolar order ( R 1Q) relaxation rates were measured for bilayers of macroscopically oriented 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC- d 54) containing cholesterol (1:1 molar ratio), using inversion recovery and broadband Jeener—Broekaert pulse sequences, respectively. Anisotropic deuterium ( 2H) NMR spin relaxation data were obtained for the first time along the entire flexible acyl chains of the phospholipid molecules in the liquid-crystalline state. Individual spectral densities J 1(ω 0) and J 2(2ω 0) were calculated from these relaxation rates, and a strong dependence on the angle θ between the macroscopic bilayer normal and the static magnetic field was observed. The spectral densities exhibited opposite angular anisotropies, which were explained in terms of a simple rotational diffusion model for the molecular dynamics of membrane lipid constituents.