Preparation,Characterization And Antifungal Properties Of Sulfonated And Oxidized Chitosan With Different Molecular Weights

Chitosan is obtained by removing acetyl groups from chitin and can be extracted from food processing waste such as shrimp and crab shells.It is the only natural alkaline polysaccharide in nature.Chitosan has a variety of biological activities,but its solubility is poor,which greatly limits the application of chitosan.To improve the solubility of chitosan,chitosan herein chemically modified to enhance the solubility of chitosan derivatives.Taking wheat head blight（Fusarium graminearum）as the research object,we studied the bactericidal activity of the chitosan and its derivatives and its effect on the germination of wheat seeds which can provide technical support for the application of chitosan in the agricultural field.The specific research contents are as follows:7 kinds of chitosan with different molecular weights were oxidized by NO₂,and6-carboxylchitosan with different molecular weights were obtained by oxidizing the alcohol hydroxyl group at the C6 position of chitosan to carboxyl group.The degree of oxidation was determined,and the 6-carboxylchitosan was sulfonated and modified to prepare 7 kinds of sulfonated 6-carboxylchitosan.The samples were characterized and analyzed by X-ray diffractometer（XRD）,field emission scanning electron microscope（FESEM）,fourier transform infrared spectroscopy（FTIR）,thermogravimetry,and ¹H NMR.The results showed that the degree of oxidation of6-carboxychitosan increased with the increase of the molecular weight of chitosan,and the degree of oxidation was 18.28%,24.26%,32.85%,35.24%,39.94%,47.65%,53.59%,respectively.The thermal stability of 6-carboxyl chitosan is worse than that of chitosan,but the amorphous structure of chitosan crystal is not changed by the oxidation of alcohol hydroxyl group to carboxyl group,and the crystallinity is worse after the sulfonation modification.The solubility of 6-carboxy chitosan and sulfonated 6-carboxy chitosan in different solvents was studied.The results show that 6-carboxy chitosan is slightly soluble in DMSO,benzene,pyridine and sodium hydroxide solution,and soluble in water and dilute acetic acid,the larger the molecular weight,the better the solubility.Sulfonated 6-carboxy chitosan is slightly soluble in DMSO,DMF,benzene and pyridine,and soluble in water,sodium hydroxide and dilute acetic acid solution.The solubility of sulfonated 6-carboxy chitosan is better than that of 6-carboxy chitosan.The antifungal activity of modified chitosan and its derivatives and the effect on the germination activity of wheat seeds were studied.The results show that,compared with the control,6-carboxychitosan has better antifungal activity.The greater the concentration,the higher the antifungal rate.Among them,the 40 k Da molecular weight 6-carboxychitosan has the best antifungal activity,with an EC50 of 581.68.μg/mL.The inhibitory effect of sulfonated 6-carboxy chitosan on Gibberella triticina has a non-linear relationship with the concentration,and all the measured concentrations have a certain antifungal activity.Chitosan has the best antifungal activity when the concentration was 100μg/mL at acidic p H.In addition,the various concentrations of chitosan and 6-carboxylchitosan can increase the germination potential and germination rate of wheat seeds.