Synthesis and fluorescence properties of Tb(III) complex with a novel aromatic carboxylic acid (L) as well as spectroscopic studies on the interaction between Tb(III) complex and bovine serum albumin

A novel aromatic polycarboxylic acid ligand, 2,6-bis(3,5-dicarboxypyrazol-1-ylmethyl) pyridine (L) was designed and synthesized. Its corresponding Tb(III) complex [TbL(H2O)4]Cl·H2O was successfully prepared. The ligand L and the complex [TbL(H2O)4]Cl·H2O were characterized by elemental analysis, IR, 1HNMR, EI–MS and TG–DSC. The investigation of fluorescence property of the complex showed that the Tb(III) ion could be sensitized efficiently by the ligand. In order to explore the potential biologically active value of [TbL(H2O)4]Cl·H2O, the interaction of [TbL(H2O)4]Cl·H2O with bovine serum albumin (BSA) has been investigated by fluorescence quenching spectra, UV–vis absorbance and synchronous fluorescence spectra. The fluorescence quenching mechanism of BSA by [TbL(H2O)4]Cl·H2O was analyzed. The binding site number n and binding constant Ka were calculated according to the double logarithm regression equation. The thermodynamic parameters showed the van der Waals and hydrogen bond interactions were the predominant intermolecular forces in the interaction of [TbL(H2O)4]Cl·H2O with BSA. Furthermore, the effect of [TbL(H2O)4]Cl·H2O on the conformation of BSA was analyzed according to synchronous fluorescence.