Rhenium(I) Polypyridine Complexes as Luminescence-Based Sensors for the BSA Protein

The binding interaction of rhenium(I) complexes fac-[Re(CO)₃(NN)(py)]⁺, py = pyridine and NN = 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (ph₂phen) or 4,7-dichloro-1,10-phenanthroline (Cl₂phen), and bovine serum albumin (BSA) was investigated at physiological pH using emission intensity variation and circular dichroism (CD) spectroscopy. The photophysical investigations showed that in the presence of BSA, the metal-to-ligand-charge transfer (³MLCT) emission of the rhenium(I) complexes was quenched due to entrapment of the complex within the protein environment. Additionally, high Stern-Volmer (K_SV) and binding (K_b) constants were determined from luminescence data, revealing the occurrence of a strong interaction and/or association. The differences in K_SV values can be tentatively associated with an electron-withdrawing constant (σ) defined by Hammett equation. The CD results showed that the extent of α-helicity of the BSA decreased upon the addition of rhenium complexes, which provided further support for the interaction of rhenium(I) complexes and the protein.

Keywords:
rhenium(I) polypyridine complexes; BSA; luminescence-based sensor