Characterization of the interaction between cationic Erbium (III)–porphyrin complex with bovine serum albumin

The interaction of cationic Erbium (III)–porphyrin complex (Er–Porp) with bovine serum albumin (BSA) has been investigated by fluorescence quenching spectra, UV–vis absorbance, circular dichroism (CD) and three-dimensional (3D) fluorescence spectra. It is proved that the fluorescence quenching of BSA by Er–Porp was mainly for the formation of Er–Porp–BSA complex. The Stern–Volmer quenching constants KSV and corresponding thermodynamic parameters ΔH,ΔG and ΔSΔS were estimated by fluorescence quenching method. The results indicated that the electrostatic and hydrophobic interactions were the predominant intermolecular forces in stabilizing the complex. The binding distance was obtained according to Förster’s non-radiative energy transfer theory. Displacement experiment and the number of binding sites calculation show that the cationic Er–Porp ring can inset in site-I (in subdomain IIA) of BSA. The effect of Er–Porp on the conformation of BSA was observed using CD, UV and 3D fluorescence spectra methods. The results show that the conformation of BSA was changed dramatically in the presence of Er–Porp by binding to the Trp residues of BSA. The interaction between BSA and Er–Porp can be used as a model for drug design and pharmaceutical research.