Characterization of the Interaction between Cationic Thulium (III)– Porphyrin Complex with Bovine Serum Albumin

Abstract

The interaction of cationic Thulium (III)-porphyrin complex (Tm-Porp) with Bovine Serum Albumin (BSA) has been investigated by fluorescence quenching spectra. The quenching mechanism of fluorescence was suggested as a static quenching with a high-affinity according to the Stern-Volmer equation. The no. of binding sites and the apparent binding const. Ka of the Tm-Porp on BSA were explained by a modified Scatchard equation and the site probe competition. The corresponding thermodn. parameters ΔH0, ΔG0 and ΔS0 at different temps. are discussed. The results indicated that the electrostatic and hydrophobic interactions are the predominant intermol. forces in stabilizing complex. Binding distance between the donor and acceptor was obtained in terms of Forester's non-radiative energy transfer theory. Furthermore, the effects of the Tm-Porp on the BSA configuration were elucidated by CD (CD) spectra method along with UV-Vis absorption and Synchronous Fluorescence Spectroscopy (SFS). The results indicated that the secondary structures of BSA have been perturbed in the presence of drug. Finally, we showed that the cationic Tm-Porp can preferentially bind at the site-I and site-II of BSA with equal occupancy. [on SciFinder(R)]