Selective 31P{ 1H} nuclear overhauser effect study on the polar headgroup conformation of phospholipids in micelles in organic solvents

Abstract

The polar headgroup structure of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) in inverted micelles in chloroform or benzene was investigated by the selective 31P{ 1H} nuclear Overhauser effect (NOE). In the frequency dependence of the 31P{ 1H} NOE, PC micelles in CDCl 3 showed two maxima. The larger maximum was located at the resonance of the glycerol-CH 2OP protons and the smaller at the resonance of the N-methyl protons. In PC/PE mixed micelles in C 6D 6, both PC and PE showed three maxima which were located at the resonance of the CH 2OP protons, the N-methyl protons and the amino protons in the frequency dependence of the 31P-NOE. The N-methyl protons of PC and the amino protons of PE were closely spaced to the phosphate groups of neighboring lipid molecules. The polar headgroups of PC and PE in the mixed micelles were concluded to lie in the plane perpendicular to the molecular axes. The frequency dependence of the 31P{ 1H} NOE for PS micelles in C 6D 6 showed the maxima at the resonances of the amino protons and the CH 2OP protons. The polar headgroups of PS molecules were not extended parallel to the molecular axes in the inverted micelles.