Preparation Of Novel Ligands With Pyridine Moiety And Their Eu(Ⅲ) And Tb(Ⅲ) Complexes As Well As Their Interactions With BSA

The lanthanide ions possess outstanding luminescence, photoelectricity and pharmacodynamic properties. It has been brought to the attention of the researchers, and in material, fluorescent probes, biology and other fields have been widely used. Nevertheless, the lanthanide ions usually give weak luminescence due to the weak absorption coefficient and easily quenching by water, which restrict their practical application considerably. This can be overcome by the use of efficient absorbent chelating ligands, which serves as an antenna to sensitize rare earth ions. Much work has been done, but the antenna effects on the luminescence properties of rare earth complexes still need to be further studied.In this paper, based on pyridine-2,6-dicarboxylic acid, three novel ligands were designed and synthesized:2-methyl-6-(8-quinolinyl)-dicarboxylatepyridine(L1), methyl-6-(2-nap hthalen acetyl)-2-pyridinecarboxylic acid(L2),4-aminomethyldiethyl pyridine-2,6-dicarboxylate(L3). The structure of intermediates and ligands were characterized by EA, FT-IR and1H NMR. Meanwhile, four corresponding Eu(Ⅲ) and Tb(Ⅲ) complexes, Na4Eu(L1)2Cl4·3H2O, Na4Tb(L,)2Cl4·3H2O, Eu(L2)3·2H2O and Tb(L2)3·2H2O were prepared and the possible structures were deduced by EA, FT-IR and TGA. The luminescence spectra of Eu(Ⅲ) and Tb(Ⅲ) complexes in C2H5OH (c2.0×10-4mol/L) were investigated. The results shows that L1and L2are efficient sensitizers for Eu(Ⅲ) and Tb(Ⅲ) luminescence.Finally, the interactions of Na4Tb(L1)2Cl4·3H2O and Tb(L2)3·2H2O with bovine serum albumin (BSA) have been investigated through fluorescence spectroscopy and circular dichroism (CD) spectra under physiological conditions. The Stern-Volmer analysis indicates that the fluorescence quenching of BSA by Na4Tb(L)2Cl4·3H2O and Tb(L2)3·2H2O are resulted from static mechanism. The binding sites (n) approximates1.0and this means that interaction of Na4Tb(L)2Cl4·3H2O and Tb(L2)3·2H2O with BSA had single binding site. The binding constants (Ka) of two novel were more than1.0×104L·mol-1.The result show van der Waals interactions and hydrogen bonds are found to play major roles in the two binding reaction. Furthermore, both synchronous fluorescence and circular dichroism (CD) spectra indicate that the conformation of BSA is changed. 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 reference value to the design of new drugs as well.