Study On Design, Synthesis And Antifungal Activity Of Chitosan Based Organometallic Complexes

Plant diseases cause considerable losses to crop yields every year.Plant pathogenic fungi are one of the main causes of plant diseases.Chemical pesticides have been used to control plant diseases for a long time.Among them,metal pesticides are widely used because of their advantages such as low cost,broad antimicrobial spectrum and strong sterilization effect.However,the use of metal fungicides will also cause problems such as phytotoxicity and heavy metal contamination.Therefore,the design and synthesis of natural organic metal pesticides based on traditional chemical metal pesticides is the main direction of research and development of metal pesticides.Chitosan is a natural macromolecule compound.It is innoxious and harmless and is rich in resources.Chitosan has antifungal effects,but its application is limited because of its poor effect and poor water solubility.Hence,we expect that grafting Schiff base and metal ions onto chitosan may result in the development of a new metal complex with a novel character and enhanced antifungal activity,so as to solve the problems of traditional metal fungicides.In this paper,the chitosan obtained from marine organisms was chemically modified by Schiff base and metal complexation respectively.Fourteen kinds of chitosan Schiff bases and twenty-four kinds of chitosan Schiff base complexes were synthesized.The physical and chemical properties of the derivatives were comprehensively analyzed by infrared spectroscopy(FTIR),nuclear magnetic resonance spectroscopy(NMR),elemental analysis,differential scanning calorimetry(DSC)and X-ray diffraction(XRD).At the same time,the new density functional theory(DFT)was used,and the molecular conformations of chitosan derivatives were calculated with the combination of computational chemistry.The bactericidal spectrum of chitosan derivatives was investigated through the antifungal activity experiments in vitro.Four kinds of derivatives were screened out for pot experiments,18 derivatives were tested for phytotoxicity and cytotoxicity.The main results were as the followings:1.Six kinds of chitosan aminobenzoic acid Schiff base and six kinds of chitosan aminobenzoic acid Schiff base copper complexes were prepared.The unit structure and configuration of chitosan copper complex were analyzed by density functional theory(DFT)for the first time.The antifungal results showed that the antifungal activity of twelve kinds of chitosan derivatives are better than that of chitosan and thiediazole copper.The inhibition of chitosan copper complex against Phytophthora capsici has a positive correlation with the dihedral angle between the phenyl and carbon-nitrogen p-? conjugate groups in chitosan copper complex.2.Two kinds of chitosan nicotinamide Schiff base and six kinds of chitosan nicotinamide Schiff base metal complexes were prepared.Fungistatic experiments showed that the antifungal effects of the six chitosan metal complexes were better than that of chitosan,and the antifungal effect of nicotinamide modified metal complexes was better than that of metal complexes modified with isonicotinamide.The complex of different metal ions also showed different fungistasis to different pathogenic fungi.The inhibitory effect of copper complex against Phytophthora capsici was the best,and the nickel complex had the best inhibition effect against Botrytis cinerea.The phytotoxicity assay showed that the toxicity of six kinds of metal complexes on wheat leaves was less than that of free metal ions and had no significant effect on plant growth.Moreover,the content of chlorophyll in wheat leaves could be improved by the zinc complexes.3.Four kinds of chitosan aminopyridine Schiff base and twelve kinds of chitosan aminopyridine Schiff base metal complexes were prepared.The results of fungistasis in vitro showed that the twelve kinds of metal complexes had good fungistasis effect and broad-spectrum fungicidal effect.The inhibition effect of copper complexes on Phytophthora capsici and Verticillium alboatrum was better,and the inhibitory effect of nickel complex on the Botrytis cinerea was better.Pot experiments showed that the antifungal activity of the complexes was related to the kinds of substituents on aminopyridine.Methyl group was the best.In this paper,six kinds of chitosan derivatives with novel structure and good antifungal activity were prepared and screened,and their phytotoxicity and other characteristics were studied.The derivatives basically retain the advantages of chitosan,such as low toxicity and good biocompatibility.Moreover,the antifungal activity of the derivatives is better than that of thiediazole copper and oligosaccharides.The experimental results may provide a novel direction for the development of metal fungicides,and the characterization of new derivatives provides a novel research idea in structural analysis.