Bilayers of phosphatidyldiacylglycerol and phosphatidylcholesterol give 31P-NMR spectra characteristic for hexagonal and isotropic phases

Abstract

Aqueous dispersions of phosphatidyldiacylglycerol and phosphatidylcholesterol are shown to form bilayers by differential scanning calorimetry, diphenylhexatriene fluorescence polarization, and electron microscopy; however, 31P-nuclear magnetic resonance spectra of these dispersions are characteristic of the ‘hexagonal’ and ‘isotropic’ phases, respectively. The theoretical relationship between the conformation of phospholipid molecules in bilayers and the shape of the 31P-NMR line is examined. It is shown that differences in the various characteristic spectral line shapes can result from differences in the phospholipid headgroup conformation without significant changes in the organization of the acyl chains in the bilayer phase.