Study On The Syntheses And Antibacterial Activity Of Metallic Complexes Of Benzimidazole -5,6 - Dicarboxylic Acid

There is an overlapping toxicity phenomenon when benzoic acid as a food preservative.Therefore it is a dispute about the application with benzoic acid.In order to reduce the toxicity of benzoic acid and improve its antibacterial activity , scientist began to study the antibacterial activity of benzoic acid derivatives according to the relationship between structure and properties. Based on this theory, this thesis choose benzimidazole -5,6 - dicarboxylic acid from benzoic acid derivatives as ligand.Fifteen metallic complexes have been synthesized by the solution crystallization and hydrothermal method. These complexes were characterized by elemental analysis, IR, thermogravimetric analyses and single crystal X-ray diffraction. Microplate reader was used to detect the antibacterial activity of some metallic complexes against Escherichia coli, Pasteurella, S. enteritidis, and Bacillus subtilis which are common in the processing and storage of aquatic products in a sterile 96-well microtitre plate in the further study.The structual result show that benzimidazole -5,6 - dicarboxylic acid exist mainly in bidc2- in the complexes and a small part in Hbidc-,exhibiting nine different coordination modes.(1)chelated with four oxygens from two carboxylates, and di-monodentates coordination with two oxygens from two carboxylates (complex 1,2)(2) two monodentate coordination with two oxygens from two carboxylates, and monodentate coordination with one nitrogen from imidazole (complex 3)(3) monodentate coordination with one nitrogen from imidazole (complex 4, 5 ,8 , 9)(4) tri-monodentate coordination with three oxygens from two carboxylates, and monodentate coordination with one nitrogen from imidazole (complex 6 ,7)(5)di-monodentate coordination with two oxygens from one carboxylate, and monodentate coordination with one nitrogen from imidazole (complex 10)(6) chelated with two oxygens from one carboxylates, di-monodentate coordination with one oxygens from the other carboxylate and one nitrogen from imidazole (complex 11)(7) chelated with two oxygens from different carboxylates, di-monodentate coordination with one oxygens from one carboxylate and one nitrogen from imidazole (complex 12) (8) quadri-monodentate coordination with four oxygens from two carboxylates, including chelated with two oxygens from different carboxylates, and monodentate coordination with one nitrogen from imidazole(complex 13, 14)(9) di-monodentate coordination with one nitrogen from imidazole and one oxygen from carboxylate (complex 15)The antibacterial activities under different concentrations of ten metallic complexes were measured by Microplate reader.The results showed that the antibacterial activities of complexes has changed due to the coordination between ligand and metal. Complex 1 has obvious antibacterial activity against four bacterias with the MIC of 1250μg/mL as similar as ligand. But the isosturctural complex 2 has obvious antibacterial activity against four bacterias with the MIC of 1250μg/mL which weaker than ligand. Complex 3 has obvious antibacterial activity against four bacterias when with MIC 1250μg/mL as similar as ligand. Complex 4 has a significant inhibitory effect on Escherichia coli, Pasteurella, S. enteritidis when in 625μg/mL, and has an obvious antimicrobial effect on Bacillus subtilis when in 312μg/mL which both stronger than ligand.Complex 5 has obvious antibacterial activity against four bacterias when in 156μg/mL which stronger than ligand.Complex 10 has a significant inhibitory effect on Pasteurella, Escherichia coli, Bacillus subtilis when in 1250μg/mL like ligand, and has an obvious antimicrobial effect on S. enteritidis when in 625μg/mL which stronger than ligand.Complex 11 has a significant inhibitory effect on Escherichia coli when in 1250μg/mL like ligand, and has an obvious antimicrobial effect on Pasteurella,S. enteri t i dis,Bacillus subtilis when in 625μg/mL which stronger than ligand.Complex 12 has no inhibitory effect on Pasteurella, Bacillus subtilis even when in 2500μg/mL,but has obvious antimicrobial effect on Escherichia coli,S. enteritidis when in 625μg/mL which stronger than ligand.Complex 13 has obvious antibacterial activity against four bacterias when in 312μg/mL which stronger than ligand.Complex 14 has obvious antibacterial activity against four bacterias when in 1250μg/mL as similar as ligand.The comparative analysis shows the complex 5 has the highest inhibitory activity against Escherichia coli, Pasteurella, S. enteritidis, and Bacillus subtilis when in 156μg/mL. In the complex 5, the center Co(II) atom exhibits a distorted octahedral geometry involving an N atom from ligand and five water O atoms. There are five water molecules in the asymmetrical unit. Many intermolecular and intramolecular hydrogenbonding interactions are observed.