Synthesis, luminescence properties of Eu(III) and Tb(III) complexes with a novel aromatic carboxylic acid and their interactions with bovine serum albumin

Abstract

A novel aromatic carboxylic acid ligand (L) was synthesized and its corresponding Eu(III) and Tb(III) complexes, Na3EuLCl3·2H2O (EuL) and Na3TbLCl3·3H2O (TbL), were successfully prepared. L and its corresponding complexes were characterized by means of MS, elemental analysis, IR, 1H NMR and TG. The luminescence spectra of Eu(III) and Tb(III) complexes were investigated and the results showed that L was an efficient sensitizer for Eu(III) and Tb(III) luminescence. The interactions of L, EuL and TbL with bovine serum albumin (BSA) have been investigated through fluorescence spectroscopy under physiological conditions. The Stern–Volmer analysis indicated that the fluorescence quenching of BSA by L, EuL and TbL was resulted from static mechanism, and the binding constants (Ka) were 2.22×104, 1.33×105 and 4.27×105 at 300K, respectively. The binding sites (n) and the corresponding thermodynamic parameters ΔH, ΔS, and ΔG were calculated at different temperatures. According to the theoretical and experimental results, van der Waals interactions and hydrogen bonds were found to play major roles in the binding reaction. Furthermore, UV–Vis absorption spectroscopy and synchronous fluorescence spectra indicated that the conformation of BSA was changed. The results obtained in the work can help understand the action mode between L and its corresponding Eu(III) and Tb(III) complexes with BSA, and they are also expected to provide important information of designs of new inspired drugs based on Eu and Tb.