화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.107, No.36, 9918-9928, 2003
Chain order in lipid bilayers: FTIR and solid state NMR studies on bilayer membranes from 1,2-dimyristoyl-sn-glycero-3-phosphoglucose
Multilamellar dispersions from a new synthetic phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphoglucose (DMPGE), bearing a glucose ring in the polar headgroup, are studied by means of FTIR, H-2, and P-31 NMR spectroscopy. The investigations are focused on the evaluation of the molecular ordering of the lipid molecules as a function of temperature and cholesterol content. Information about the conformational order of the acyl chains is obtained from variable temperature FTIR investigations. Analysis of the CH2 stretching and wagging modes of nondeuterated compounds provides the relative changes in conformational order in the vicinity of the main transition and integral values of distinct gauche conformers over the whole acyl chains, respectively. Likewise, CD2 rocking bands are used to derive the amount of gauche conformers at a specific chain segment in samples containing selectively deuterated acyl chains. The present work represents the first report where the orientational order parameter simultaneously is obtained via two independent procedures. The first method is based on the combination of the CD2 rocking band data with those from complementary H-2 NMR studies. The second procedure refers to a line shape analysis of variable temperature P-31 NMR spectra. A comparison of the available data for the present lipids with those from related systems, such as 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), reveals a minor influence of the glucose headgroup on the (overall) orientational order while some effect is registered for the conformational order of the lipid molecules. In summary, the present work demonstrates the future potential of such combined FTIR and solid-state NMR studies in order to get detailed information of the lipid ordering in phospholipid bilayers. As shown here, such techniques are of general help in order to separate orientational and segmental (conformational) order in disordered alkyl chains, as there is no restriction to lipid systems as examined in the present work.