Synthesis And Synergistic Effect Research Of Three Agricultural Agents Grafted Chitosan Derivatives

In the process of modern agricultural, agricultural agents including pesticides and fungicides are used in amount for a long period. The food security problem caused by agricultural agents residual become more and more serious. The research and development of novel agricultural agents with non-toxic, high efficiency and low residue properties is a global issue nowadays. Chitosan is a kind of bio-degradable and bio-compatible marine polysaccharide produced from shells of crabs and shrimps. Due to its antifungal and growth induction properties, it’s widely applied in agriculture. Novel agricultural agents with synergistic effect can be achieved by modification based on the structure of chitosan. This is a special strategy to develop new agricultural agents. Under the guidance of the idea introduced above, avermectin, hymexazol and pyrimethanil were grafted onto the chitosan structure by chemical reactions. In this way, we achieved a serious of novel agricultural agents grafted chitosan derivatives. The structures of the derivatives were confirmed by infrared spectrum, nuclear magnetic hydrogen spectrum(NMR), elemental analysis, X-ray diffraction(XRD) and high performance liquid chromatography(HPLC). The synergism of chitosan and these agricultural agents was investigated by our research. The main results were as the followings: 1. Avermectin grafted chitosan derivatives were prepared in the DCC/DMAP reacting system. The derivatives showed enhanced insecticidal activity against armyworm, carmine spider mites, black bean aphids and brown plant hoppers. The photostability was greatly improved as well. The results showed that there existed synergism by grafting avermectin with chitosan. Double-sited carboxymethylation and higher molecular weight could enhance the synergism. The synergistic effect of succinylation is more obvious than maleylation. 2. Hymexazol grafted chitosan derivatives were synthesized by using chloroacetyl chloride, chloropropionyl chloride and 4-(chloromethyl) benzoyl chloride as linkers. The obtained derivatives showed great antifungal activity against Rhizoctonia solani, Gibberella zeae, Glomerella cingulate, and Thanatephorus cucumeris. Chitosan and hymexazol showed good synergistic effect with each other. The synergistic effect increased with higher grafting ratios and less steric hindrance. 3. Pyrimethanil was grafted onto chitosan structure. The pyrimethanil grafted chitosan derivatives performed enhanced antifungal activity against Rhizoctonia solani, Gibberella zeae, and Glomerella cingulate. The pyrimethanil grafted chitosan derivatives also showed synergistic effect. The results indicated that the main influencing factors of synergism were grafting ratios and steric hindrance.In this study, three kinds of chitosan conjugates with avermectin, hymexazol and pyrimethanil were sythesised for the first time. It was found that chitosan showed synergistic effect with avermectin, hymexazol and pyrimethanil. With the synergism, the dosages of these agricultural agents could be greatly decreased by improving their efficiency and other physicochemical properties. In this way, we could possibly solve the environmental and food security problems introduced by agricultural agents. This synergistic agricultural agents grafted chitosan derivatives showed a totally different way to develop novel agricultural agents with non-toxic, high efficiency and low residue properties. This kind of agricultural agents showed great potential in application in the future.