Order and Dynamics in Lipid Bilayers from 1,2-Dipalmitoyl-sn-glycero-phospho-diglycerol as Studied by NMR Spectroscopy

Abstract

The conformational and dynamic behavior of a new model membrane1,2-dipalmitoyl-sn-glycero-phospho-diglycerol (DPPG2)is studied for the first time by 2H and 31P NMR spectroscopy. The investigations are focused on the evaluation of the molecular properties of the lipid molecules as a function of temperature and sample composition. 2H NMR studies are performed on water dispersions with lipids bearing either selectively deuterated (at position C-6 of both aliphatic chains) or perdeuterated acyl chains. The present studies demonstrate that the introduction of the hydrophilic diglycerol headgroup is accompanied by a reduction of the orientational and conformational order of the acyl chains. The combined analysis of the 2H NMR line shape and FT IR dataobtained from experiments on DPPG2 samples with both perdeuterated and selectively deuterated acyl chainsprovides the conformational properties of the methylene positions along the fatty acid chains. 2H NMR line shapes and spin−spin and spin−lattice relaxation data are further analyzed and provide insight into the dynamic features of these model membranes. By means of computer simulations, different motional modes can be distinguished, comprising (overall) anisotropic rotational diffusion, chain isomerization, and lateral diffusion. It is found that the bulky diglycerol headgroup has a significant effect on the molecular mobility of the lipid molecules, as shown by comparison with other lipid systems, such as DMPC and DPPC.