Study On Synthesis, Characterization And Application Of Amino-acid Schiff Base Europium Complexes

Rare earth chelates are widely used as fluorescence probe in Time-resolved Fluorescence Immunoassay. As significant biological ligands, Schiff bases derived from amino acid have a few atoms such as nitrogen and oxygen for coordination. These Schiff bases coordinated with metal ion have activity in many fields, such as catalytic transamination and racemization, fluorescence, bacteriostasis, antitumor, inhibiting superoxide free radical, etc. Study on their structure and physicochemical property is helpful to disclosure structural characteristic of vitamin B6 enzyme, explore mechanics of catalytic racemization, select ideal reagent for fluorescence assay, screen highly active and harmfulless drug for bacteriostasis or antitumor, etc.Seven Schiff base ligands derived from ortho-aminobenzoic acid, valine, phenylalanine, leucine, isoleucine, α-alanine, β-alanine , salicylaldehyde and its derivatives have been synthesized in this article. At the same time, eleven complexes are synthesized by these ligands coordinated with Europium ion. These ligands and complexes have been characterized by elemental analysis, infrared spectrum analysis, ultraviolet spectrum analysis, molar conductance analysis and thermal-gravity analysis.The synthesis condition for the complexes is strict. Reaction temperature is controlled at 55℃ or so. Complexes derived from ortho-aminobenzoic acid may be synthesized in ethanol where pH is adjusted by triethylamine at 5.5 or so. When enough potassium hydrate is added, Complexes derived from amino acid may be synthesized at certain molar ratio in ethanol aqueous solution.In complexes' internal layer, C=N bond's nitrogen atom coordinates with europium ion. Carboxy coordinates with Europium ion at single-point. Nitrate radical coordinates with europium ion at double-point. Whether or not free nitrate ion exists in complexes' external layer may be judged by molar conductance analysis. Whether or not crystal water and coordinated water exist may be judged by conductance analysis. The ligands and complexes are tested by Fluorescence spectrum. The result indicates that Europium ion's fluorescence isn't sensitized by these Schiff base ligands, which is because the lowest triplet energy level of the ligands doesn't match the excited state energy level of Europium ion. Fluorescence intensity by the ligands and complexes derived from ortho-aminobenzoic acid is greater than from amino acid, which is because the former has greater conjugate system and plane rigidity than the latter. Fluorescence spectrum shape and Fluorescence intensity are greatly affected by pH, which is because the complexes have acidic or alkalinous base so that they are sensitive to solution's pH and hydrogen bond capability. The ligands and complexes are tested by bacteriostasic activity. The result indicates that all compounds have bacteriostasis. The bacteriostasic activity to Candida albicans and Escherichia coli is more intensive than to other bacteria. When the ligands are coordinated with Europium ion and the second ligand ortho-phenanthroline is Coordinated, the bacteriostasis gets more intensive. The variation of bacteriostasic activity isn't the same as the variable tendency of compounds' concentration, but there is an optimum concentration at a given range.