Rhenium(I)-based fluorescence resonance energy transfer probe for conformational changes of bovine serum albumin

Protein binding properties of fac-rhenium(I) complexes with general structure Re(CO)₃(N-N)L]PF₆, where N-N = 4,4′-dinanoyl-2,2-bipyridine and L = py-3-COOH (1a) and py-3-CONH₂ (1b) with bovine serum albumin (BSA) were investigated at physiological pH (7.4) using UV-visible absorption and fluorescence spectral study, excited state lifetime measurement and circular dichroism (CD). The results observed from fluorescence spectra reveal the energy transfer from BSA to Re(I) complex, and the distance r between donor (BSA) and acceptor (Re(I) complex) is 3.05 nm and 2.16 nm for 1a and 1b respectively according to Forster's non-radiative energy transfer theory. CD results show that the binding of Re(I) complex could induce the conformational change with the loss of α-helicity.