Direct spectroscopic observation of inner and outer hydrocarbon chains of lipid bilayer vesicles.

Abstract
Distearoylphosphatidylcholines labeled with gem-difluoro groups at selected positions of the fatty acid chains were prepared. These lipids were incorporated into sonicated vesicles and were examined by F NMR spectroscopy. All spectra are characterized by 2 well-separated F resonances. Paramagnetic ions added to the exterior solution of vesicles of fluorinated lipid broaden the upfield resonances, ions trapped in the vesicle interior broaden the downfield resonances. The F chemical shift of these compounds is sensitive to differences between the inner and outer monolayers of sonicated vesicles.