Influence Of Grafted Groups And Amino Cation On The Antifungal Activity Of Water-soluble Chitosan Derivatives

Chitosan is a natural cationic aminopolysaccharide copolymer of glucosamine and N-acetylglucosamine. It can be easily obtained from the natural resource, such as crustacean animals, fungi and insects. And it has a number of unique properties such as biocompatibility, biodegradability, and non-toxicity, which have attracted much attention in the field of biotechnology, pharmaceutics, cosmetics, textiles, agriculture, etc.With the development of study on the science of chitosan and chitosan derivatives, the antifungal activity of chitosan has received considerable interests. But, the most concentration was put on the molecular weight and degree of deacetylation of chitosan, which affect the antifungal activity, little work has been reported on the antifungal activity of chitosan derivatives. In this paper, Schiff bases of carboxymethyl chitosan (CMCTS), N-substituted CMCTS, urea-substituted CMCTS, quaternized chitosan and quaternized CMCTS were synthesized, and their antifungal activity was assessed.Antifungal activity of Schiff bases of CMCTS against Valsa mali (V. mali), Alternaria solani (A. solani) and Fusarium oxysporium f. sp. Vasinfectum (F. oxysporium f. sp. Vasinfectum) was assessed according to earlier method in vitro. The results indicated that 2-(2-hydroxyl-5-nitrobenzaldimino)-CMCTS and 2-(2-hydroxyl-5-chlorobenzaldimino)-CMCTS had better antifungal activity than chitosan, CMCTS, and 2-(2-hydroxybenzaldimino)-CMCTS. And the reason is the groups of 2-hydroxyl-5-nitrobenzaldimino and 2-hydroxyl-5-chlorobenzaldimino grafted to chitosan; N-substituted CMCTS derivatives had less antifungal activity against Alternaria Solani and Physalospora piricola Nose than chitosan and CMCTS; urea-substituted CMCTS derivatives had better antifungal activity against Alternaria Solani and Physalospora piricola Nose than CMCTS. Antifungal activity of quaternized chitosan against Botrytis cinerea Pers. (B. cinerea pers.) and Colletotrichum lagenarium (Pass) Ell.et halst (C. lagenarium (Pass) Ell.et halst) was assessed. The result indicated that quaternized chitosan had better antifungal activity than chitosan. Because the target site of the cation of chitosan is the negatively charged cell surface membrane, strong cation of quaternized chitosan can increase the antifungal activity. And so, the activity was increased when electronegative groups were grafted for the same reason. High molecular weight chitosan has better antifungal activity than low molecular weight chitosan because of the big volume.In order to prove the conclusion above-mentioned, quaternized CMCTS were synthesized and their antifungal activity against B. cinerea pers. and C. lagenarium (Pass) Ell.et halst was assessed. Quaternized CMCTS have better antifungal activity than CMCTS, and part of the quaternized CMCTS derivatives have better antifungal activity than chitosan. At the concentration of 500μg/mL, N-(2-hydroxy-5-nitrylbenzal)-N, N-dimethyl CMCTS and N-(2-hydroxy-5-chlorobenzal)-N, N- dimethyl CMCTS can inhibit the growth of Physalospora piricola Nose completely. The effect of the cation of chitosan and quaternized chitosan (or CMCTS) is proved again.