Molecular Biomarkers & Diagnosis

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

Abstract

Xi-Liang Lu, Huai-Cheng Yang, Hui Wu and An-Xin Hou

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 highaffinity according to the Stern–Volmer equation. The number of binding sites and the apparent binding constant a K of the Tm–Porp on BSA were explained by a modified Scatchard equation and the site probe competition. The corresponding thermodynamic parameters ΔH0 ,ΔG0 and ΔS0 at different temperatures are discussed. The results indicated that the electrostatic and hydrophobic interactions are the predominant intermolecular 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 Circular Dichroism (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.