Synthesis and luminescent properties of Tb(III) complex with a novel pyrazolone ligand and its interaction with bovine serum albumin

A novel aromatic pyrazolone ligand, methyl 6-(3-methyl-1-phenyl-5-pyrazolone-4-carbonyl) pyridine-2-carboxylic acid (L), and its corresponding Tb(III) complexes, Tb(L)3·2H2O, was successfully prepared. L and its complex were characterized by means of mass spectrum (MS), elemental analysis, infrared spectroscopy (IR), 1HNMR and thermogravimetric analysis (TGA). The luminescence spectra showed that L was an efficient sensitizer for Tb(III) luminescence. The interaction of Tb(L)3·2H2O with bovine serum albumin (BSA) has been investigated through fluorescence spectroscopy under physiological conditions. The Stern–Volmer analysis indicated that the fluorescence quenching of BSA by Tb(L)3·2H2O was resulted from static mechanism, and the binding constants (Ka) were 2.36 × 104, 1.54 × 104 and 1.12 × 104 at 288 K, 298 K and 310 K, 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, synchronous fluorescence spectra and circular dichroism (CD) spectra indicated that the conformation of BSA was changed. The results obtained in the work can help understand the action mode between rare earth complexes with BSA, and they are also expected to provide important information of designs of new inspired drugs based on rare earth compounds.