Photolabeling of human serum albumin by 4-azido-2-([14C]-methylamino) trifluorobenzonitrile. A high-efficiency, long wavelength photolabel

N-alkyl derivatives of perfluoroarylazides are excellent candidates for photolabeling of proteins since they have absorption spectra in the 340–350 nm range permitting photolabel absorption without direct protein photolysis. The [14C]-N-methylamino derivative of 4-azido-tetrafluorobenzonitrile has been used to demonstrate that 80% of the photo-induced nitrene transient becomes covalently attached to HSA during photolysis. Multiwavelength detection of the photoprobe-protein separation by size exclusion chromatography is shown to be an effective tool for assessing the conjugation of the photoprobe to the protein.