The switching of a Rhenium(i) complex from turn-off to turn-on sensor system through protein binding

Abstract

New luminescent Re(I)-polypyridine complexes (1a and 1b) containing an amide–pyridine pendant carrying the N–H group have been synthesized, characterized and used as an anion sensor by utilizing UV-visible and luminescence titration methods. Both the complexes exhibit luminescence quenching upon addition of anions and the binding constants are in the range of 10³–10⁵ M⁻¹. Thus these probes act as a turn off sensor for anions in acetonitrile and show a color change from colorless to yellow on the addition of the fluoride ion. This turn-off sensor becomes a turn-on sensor for F⁻ in the presence of bovine serum albumin (BSA) which serves as a platform for the sensor design. The study of the interaction between Re(I) complexes (1a and 1b) and BSA in buffer (pH = 7.4) shows that 1a and 1b bind BSA strongly with a binding constant of 10⁴ M⁻¹.