Preparation Of New Kinds Of Chitosan Heterocyclic Derivatives,Evaluation Of Their Antibacterial And Antioxidant Activity In Vitro

Traditional chemical pesticides not only weaken the disease resistance of plants, but also lead to pesticide residues and do harm to people’s health and damage the ecological balance.With the progress of the society and the improvement of human civilization, the harmonious development of man and nature become more and more important, so people put forward higher requirements for pesticide. Under the new circumstances, to develop a non-toxic harmless biological pesticide is imminent.Chitosan is a kind of natural macromolecular polysaccharide, which has the unique physical and chemical properties, such as non-toxic, non-pollution, biodegradable. Chitosan applies to agriculture will not produce any side effects. In general, chitosan is insoluble in water or most organic solvents, which limited the application of chitosan in many fields. This article studied the degradation and chemical modification of chitosan.This article studies the ultrasonic-hydrogen peroxide oxidation degradation of chitosan, and combining lyophilization method to remove moisture, got chitosan oligosaccharides. Also studies chitosan and chitosan oligosaccharide derivate.The structure of the derivatives were characterization by FT-IR analysis,1HNMR analysis, XRD analysis, and by element analysis, thermogravimetric analysis method analyzed the substitution degree and thermal stability of products. The antioxidant ability of samples was evaluated by measuring the scavenging effects on hydroxyl radical and DPPH free radical, and their reducing power. The antibacterial ability of samples was evaluated by measuring the inhibitory rate of Monilinia fructicola and Botrytis cinerea mycelial growth.1Preparation and characterization of oligosaccharides chitosanChitosan was degradation by ultrasonic-hydrogen peroxide oxidation degradation of chitosan, and combining lyophilization method to remove moisture. Get the optimum treatment condition by using the orthogonal experimental design, the reaction temperature is70℃, the reaction time is1h, nchitosan:nhydrogen peroxide is1:1.5. Under this degradation condition, the experiment preparation the viscosity-average molecular weight of chitosan oligosaccharides was4118Da. Through characterization, it is found that the structure of chitosan has not changed, but the thermal stability of oligosaccharides chitosan was reduced.2Synthesis and characteristics of N-acyl chitosan and chitosan oligosaccharide, and evaluation of their antioxidant and antibacterial activityN-furoyl chitosan and N-furoyl chitosan oligosaccharide were prepared by acylation of chitosan and chitosan oligosaccharide, there chemical structures and physical properties were characterized by FT-IR,1H NMR, XRD, elemental analysis and thermogravimetric(TG) techniques. The degrees of substitution (DS) for the derivatives were0.68and0.72respectively.Get the optimum treatment condition by using the orthogonal experimental design, for N-furoyl chitosan the reaction temperature is50℃, the reaction time is4h, nchitosan:nfuroic acid is1:4, for N-furoyl chitosan oligosaccharide the reaction temperature is50℃, the reaction time is2h, nchitosan:nfuroic acid is1:2.In general, the antimicrobial activity increased as the concentration of the samples increased. Molecular weight is an important factor of antimicrobial activity, low molecular weight samples have higher antimicrobial activity, so the antimicrobial activity of chitosan oligosaccharide was higher than chitosan, the antimicrobial activity of N-furoyl chitosan oligosaccharide was higher than N-furoyl chitosan. The active substituents are beneficial to improve the effect of antimicrobial activity, therefore the antimicrobial activity of N-furoyl chitosan oligosaccharide was higher than chitosan oligosaccharide, the antimicrobial activity of N-furoyl chitosan was higher than chitosan.The antioxidant activity of samples increased as the concentration of the samples increased. Molecular weight is an important factor of antioxidant activity, low molecular weight samples have higher antioxidant activity, so the antioxidant activity of chitosan oligosaccharide was higher than chitosan, the antioxidant activity of N-furoyl chitosan oligosaccharide was higher than N-furoyl chitosan.The amount and the activity of hydroxyl and amino groups were the important factors associated with the antioxidant activity of chitosan derivatives. Chitosan oligosaccharide had the best scavenging effect in this test system, which should mainly be owed to the fact that no active groups had been substituted.3Synthsis, characterization and antibacterial activity of2-pyrazole acylation Oligo-chitosan2-pyrazole acylation Oligo-chitosan was synthesized by the materials of Oligo-chitosan and pyrazole. The structure and the performance of the product was characterized by FT-IR,1H-NMR, Thermogravimetric Analysis (TG), solubility analysis and antibacterial activity analysis. The results showed that the prouct was2-pyrazole acylation Oligo-chitosan and the thermal stability of the product was superior to Oligo-chitosan and the solubility was0.003g/mL in the water. The antibacterial activity of2-pyrazole acylation Oligo-chitosan was stronger than that of Oligo-chitosan.