Fatty acyl chain order in lecithin model membranes determined from proton magnetic resonance

Abstract

H NMR was used to compare the local orientational order of acyl chains in phospholipid bilayers of multilamellar and small sonicated vesicular membranes of dipalmitoyllecithin (DPL) at 50.degree. C and egg yolk lecithin (EYL) at 31.degree. C. The orientational order of the multilamellar systems was characterized using deuterium magnetic resonance order parameters and H NMR second moments. H NMR line shapes in the vesicle samples were calculated using vesicle size distributions, determined directly using EM, and a theory of motional narrowing, which takes into account the symmetry properties of the bilayer systems. The predicted non-Lorentzian line shapes and widths were in good agreement with experimental results, indicating that the local orientational order (called packing by many workers) in the bilayers of small vesicles and in multilamellar membranes is substantially the same. This result was true not only for the largest H NMR line associated with the nonterminal methylene protons but also for the resolved 1H NMR lines due to the .alpha.-CH2 and the terminal CH3 positions on the acyl chain. Analysis of the vesicle H NMR spectra of EYL taken with different medium viscosities yielded a value of approximately 4 .times. 10-8 cm2 s-1 for the lateral diffusion constant of the phospholipid molecules at 31.degree. C.