Syntheses of phosphatidylcholines, sphingomyelins and cholesterol substituted with azido fatty acids. Photocrosslinking with nearest neighbouring lipids in liposomes chemical and mass spectroscopic proof.

The chemical synthesis of azido-substituted saturated, monoenoic and dienoic fatty acids of high specific tritium radioactivity, together with improved methods for their introduction into phosphatidylcholine, sphingomyelin and cholesteryl ester molecules are outlined. Phospholipid vesicles with these photosensitive probes were irradiated and the main crosslinking products isolated and characterized by high resolution mass spectroscopy.