Synthesis, Luminescence Properties Of Pyridine-2,6-dicarboxylic Acid （H₂DPC） Ligands And Rare Earth Complexes As Well As Their Interactions With Bovine Serum Albumin

Rare earth ions are widely applied in the fields of material, probe, biology, time-resolved immunoassay (TR-FIA), etc., due to their well-defined luminescence properties such as strong luminescence intensity, optically pure colors, long radiative lifetime and strong affinity with biological molecules. Nevertheless, the rare-earth ions complexes usually give weak luminescence due to the weak absorption coefficient which limits their practical application considerably. This can be overcome by the use of efficient absorbent chelating ligands, which served as an antenna to sensitize rare earth ions. Much work has been done, but the effects on the luminescence properties of rare earth complexes still need to be further studied.In this paper, six novel ligands were designed and synthesized:6-[N,N-bis(ethyloic)carbamoyl]pyridine-2-carboxylic acid (L1),2,6-bis(1-phenyl-5-pyrazolone-3-yl)pyridine(L2), Methyl6-(3-methyl-1-phenyl-5-pyrazolone-4-carbonyl)pyridine-2-carboxylic acid(L3),2,6-Bis (3-methyl-l-phenyl-5-pyrazolone-4-yl)pyridinedione(L4),1-(4-methoxylphenyl)-3-(pyrazole-1,5-diphenyl-1H-3-yl)-1,3-propanedione(L5),2,6-Bis (3-methyl-1-phenyl-5-pyrazolone-4-yl) pyridine(L6). The structure of intermediates and ligands were characterized by EA, FT-IR and1H-NMR. Meanwhile, four corresponding Eu(Ⅲ) and Tb(Ⅲ) complexes, Na3Eu (L1)Cl·3H2O Na3Tb (L1) C13·3H2O, Eu(L3)3·2H2O and Tb(L3)3·2H2O, were prepared successfully and the possible structures were deduced by EA, FT-IR and TGA. The luminescence spectra of Eu(Ⅲ) and Tb(Ⅲ) complexes were investigated and the results showed that L1and L3were efficient sensitizers for Eu(Ⅲ) and Tb(Ⅲ) luminescence.The study of the interactions between the rare earth complexes and serum albumins is important for the exploration of their biological effects. The interactions of L1, Na3Eu(L1)Cl3·2H2O, Na3Tb(L1)Cl3·3H2O and Tb(L3)3·2H2O 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 them were resulted from static mechanism. The binding site numbers (n) were all equal to1.0and the binding constants (Ka) were2.20×104L·mml-1,1.33×105L·mo;-1,427×105L·mol-1and1.54×104L·mol-1at300K, respectively. The corresponding thermodynamic parameters△H,△S, and△G 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. In addition, owing to the binding affinity of L1, Na3Eu(L1)Cl3·2H2O, Na3Tb(L1)Cl3·3H2O with BSA, indicating that the addition of the rare earth ions is helpful to the binding of L1with BSA. Moreover, the investigation of the interaction mechanism between rare earth complexes and BSA is of great importance to understand the general rules of their interactions and shows great reference value to the design of new drugs as well.