Study On Preperation, Antifungal And Antioxidant Activities Of Novel Quaternary Chitosan Derivatives

Environmental and human health questions were threatened by leftover of chemical agricultural bactericide. The preparation of the biologic agricultural bactericide has been stared us in the face. Chitosan is a kind of natural polysaccharide, which is reproducible and it has non-toxicity, good biocompatibility and biodegradability, their researches have received considerable interests. However, the most concentration was put on the molecular weight and degree of deacetylation of chitosan on its antibacterial activity. Little work has been reported on the antibacterial activity of chitosan derivatives and much less work has been reported on the inhibitory activity of chitosan derivatives against plant fungus. Reactive oxygen species have extensive pathological effects and can cause many diseases. The role of the synthetic antioxidants has received increased attention during the past decade. However, the use of such antioxidants has potential health hazards. Therefore, interests have been developed for searching effective natural antioxidants. Chitosan, as a natural renewable resource, it has non-toxicity, good biocompatibility, as well as antioxidant activity properties. Therefore, it's significative to search more effective chitosan derivatives as antioxidants. In this paper, more than 10 kinds of novel derivatives of chitosan which contained halo-salicylaldehyde Schiff base substituent chloracetyl chitosan, halo-benzaldehyde Schiff base substituent chloracetyl chitosan, acyl-N-trimethyl chitosan chloride, 2-pyridine-acetyle-N-trimethyl chitosan chloride were prepared. Based on the results of the antifungal activity of the above mentioned chitosan derivatives, we found that all of the derivatives had better antifungal activity than their material chitosan against 7 kinds of fungi (Cladosporium cucumerinum, Monilinia fructicola, Colletotrichum lagenarium, Fusarium oxysporium, gloeosporium theae-sinensis, Phomopsis asparagi, Cladosporium car pophilum Thum). Four of the derivatives (CHPACS, BHPACS, DCBPACS and CATMCS) showed potent antifungal activity against some kinds of fungi with the inhibitory index 100 % at 500μg/mL.The rule and influence reason of antifungal activity of the deffrent groups grafted onto the chitosan was studied, and the mechanism of their antifungal activity was further discussed in this paper. The results suggested that the Schiff base groups by condensing halo-salicylaldehyde or 2,4-dichlorobenzaldehyde with 4-amino-pyridine grafted onto chloracetyl chitosan can improve the antifungal activity. For the two novel chitosan derivatives—CHPACS and BHPACS, the antifungal activity against Cladosporium cucumerinum and Monilinia fructicola was especially potent. At 500μg/mL, the inhibitory indices were 100 %. DCBPACS exhibited better extensive antifungal activity against six fungi. The inhibitory indices were more than 85 % at 1000μg/mL. For N-trimethyl chitosan chloride, the graft of the groups of acyl with halogen or aromatic nucleus can improve the antifungal activity. When comparing the antifungal activity and the physical and chemical characters of these novel chitosan derivatives in this paper, the results indicated that DCBPACS, BTMCS and CATMCS exhibited better antifungal activity than others. And BTMCS and CATMCS (inhibitory indices were more than 80 % at 1000μg/mL) was slightly less than DCBPACS (inhibitory indices were more than 85 % at 1000μg/mL), but the water solubility of BTMCS and CATMCS were better than DCBPACS which can enlarge the scope of the application of them. So the acyl-N-trimethyl chitosan chloride derivative deserves further investigation.The novel chitosan derivative with double quaternary ammonium salt—2-pyridine-acetyl-N-trimethyl chitosan chloride had good ?OH scavenging ability which has relationship with its high density of positive charge in the molecule. The above results are theoretically fundamental for further develop and make use of chitosan resources to prepare new agricultural bactericide and antioxidant.