Head-Group Conformation in Phospholipids: A Phosphorus-31 Nuclear Magnetic Resonance Study of Oriented Monodomain Dipalmitoylphosphatidylcholine Bilayers

Abstract

Angular-dependent (^{31}P) NMR spectra of oriented biaxial monodomain DPPG (H_20) multilayers are employed to study head-group conformation in this phospholipid. The results indicate that the 0-P-0 plane of the phosphate, where the 0’s are the nonesterified oxygens of the phosphodiester, is tilted at (47 \pm 5^{\circ}) with respect to the bilayer normal. This (PO_4) orientation could result in the choline moiety being extended parallel to the bilayer plane, and it will explain the breadth of the axially symmetric (^{31}P) powder spectrum observed for DPPC in excess water. This work is the first direct observation of this conformation for lecithins and it illustrates the utility of high-resolution solid-state NMR in structural studies of disordered systems.