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Nuclear magnetic resonance line-shape analysis of fluorine-19-labeled phospholipids.

The application of a fluorine-19 probe to the problem of motions present in the hydrophobic region of phospholipid dispersions and biological membranes has been extended to the study of phospholipids labeled with fluorine-19 in the 8 position and with deuterium in the 2, 7, and 9 positions of the 2-acyl chain. 1-Myristoyl-2-(8,8-difluoro[2,2,7,7,9,9-2H6]myristoyl)-sn-glycero-3- phosphocholine and its nondeuterated analogue have been investigated by 19F nuclear magnetic resonance at 282.4 MHz. Spectra obtained from macroscopically oriented bilayers exhibit Pake doublets from which order parameters can be obtained. The spectra obtained from nonoriented liposomes of the phospholipids can be explained in a satisfactory manner as a random superposition of doublets broadened by heteronuclear magnetic dipole-dipole interactions. From an analysis of the data, several conclusions about the motional state of the hydrocarbon chains in the liquid-crystalline phase can be drawn. The present results show that appropriate fluorine-19 probes in the acyl chains of phospholipids can be used to investigate the structure and dynamics of model and biological membranes.