A 31P- and 2H-NMR study on lecithins in liquid crystalline polyoxyethylene detergents

Phosphatidylcholines were incorporated into hexagonal liquid crystalline mixtures of the non-ionic detergents Triton X-100 and octaethyleneglycoldodecylether with D2O. It is shown by nuclear magnetic resonance (NMR) that the phospholipids adopt the hexagonal liquid crystalline structure of the detergent host lattice. The anisotropic motion of the phospholipid headgroups seems to be unaffected, whereas the acyl chains are disordered. Increasing phospholipid concentration leads to separation of a lamellar phase. The lamellar structure is also preferred at elevated temperatures. Phosphatidylcholines with saturated acyl chains undergo a transition from the hexagonal liquid crystalline to an ordered lamellar state. The shape of the 31P-NMR signals suggests that pure gel phase phospholipid separates out. The headgroup region of this gel phase phospholipid becomes immobilized after a few weeks of storage below the transition temperature as judged from 31P-NMR. At the same time 2H-NMR exhibits a new signal from D2O undergoing slow isotropic motion. This behavior bears resemblance to the formation of a coagel in fatty acid-water systems.