Design and synthesis of new fluorescent photoaffinity labels to study membrane structure

Abstract

Photoaffinity labelling has been used as a technique to study membrane structure. This technique necessitates design and synthesis of suitable carbene and nitrene precursors referred to as photoaffinity (PA) labels. The PA labels should preferably be hydrophobic in nature, photolyse with light of wavelength greater than 300 nm to give reactive intermediates i.e., caroenes which should undergo intermolecular insertion exclusively. The latter reaction, on incorporation of the PA labels in membranes, gives rise to crosslinked products, the analyses of which give useful information on the nature of bio-molecular interaction in membranes. We have prepared diazofluorene and quantitatively studied the products formed on photolysis in polar and nonpolar organic solvents. Products from both singlet and triplet carbenes were observed. Various other analogues like iodo, carboxy and alkyl substituted diazofluorenes have been prepared to get greater extinction coefficients and absorptions above 300 nm. These extrinsic PA probes have been incorporated in artificial membranes and photolysed. The covalently-linked fluorescent products so formed have been analysed. Fatty acids containing the diazofluorene unit have also been synthesized and linked to phospholipids. Studies with these intrinsic photolabelled phospholipids as well as erythrocytes are in progress.