Preparation And Biological Activity Of Amino-Chitin/Chitosan And Its Derivatives

Chitin is the second abundant natural polysaccharide on the earth after cellulose,and chitosan is the product of deacetylation of chitin.As a natural resource,chitin/chitosan is rich in sources and has unique physical/chemical properties and biological activities.However,chitin/chitosan is insoluble in water due to the high degree of polymerization,which limits its application.Accordingly,we can synthesize its derivatives through chemical modification and increase the water solubilility and biological activity while maintaining the original biodegradability and biocompatibility of chitin/chitosan.Many studies have reported that amino groups incorporated into polysaccharide could increase its biological activity.Therefore,in this study,we synthesized chitin/chitosan derivatives with one or two amino group,and the effect of amino groups on the biological activities of polysaccharide were investigated.However,the introduction of amino group reduces the water solubility of the chitin/chitosan derivatives.Hence,we introduced quaternary ammonium group to chitin/chitosan and synthesized quaternary ammonium salt derivative with better water solubility.The biological activities were investigated,and the relationship between quaternary ammonium groups and bioactivities of chitin/chitosan derivatives were also discussed in this paper.We synthesized 6-amino-6-deoxy chitosan in order to improve the biological activity of chitosan.6-amino-6-deoxy chitosan was prepared in five steps,namely the phthaloylation,bromination,azidation,reduction,and deprotection of the phthaloyl group.Then we evaluated the antioxidant ability and antifungal activity of chitosan and 6-amino-6-deoxy chitosan.Scavenging effect against DPPH-radical and hydrogen peroxide of 6-amino-6-deoxy chitosan were 98.2% and 92.4% at 1.6 mg/m L,respectively.Antifungal activity of 6-amino-6-deoxy chitosan was better than that of chitosan and its antifungal activity against five fungi(F.oxysporum f.sp.Cucumerium,F.oxysporum f.niveum,P.asparagi,G.zeae and G.cingulate)had improved by 13.0%-30.3% compare with chitosan at 0.5 mg/m L.These data demonstrated that the amino group would improve the antioxidant ability and antifungal activity of chitosan.In order to increase the biological activity of chitin,6-amino-6-deoxychitin and 3,6-diamino-3,6-dideoxychitin were successfully synthesized via sulfonylation,azide and azide reduction.The antifungal activities of them were tested.The antifungal activity of the derivatives was as follows: 3,6-diamino-3,6-dideoxychitin > 6-amino-6-deoxy-chitin > chitin.Compared to amphotericin B,6-amino-6-deoxy-chitin showed better inhibitory against three fungi(F.oxysporum f.sp.Cucumerium,C.lagenarium and F.oxysporum f.niveum)and 3,6-diamino-3,6-dideoxychitin showed better inhibitory against four fungi(F.oxysporum f.sp.Cucumerium,C.lagenarium,F.oxysporum f.niveum and G.zeae).The results above suggested that amino group is an active functional group in antifungal activity,and 6-amino-6-deoxychitin and 3,6-diamino-3,6-dideoxychitin might be a potential effective antifungal agent.We designed and synthesized single N-quaternized and double N-quaternized chitosan derivatives to improve the water solubility of chitosan.The antioxidant abilities and antifungal activities of chitosan and quaternized chitosan derivatives were tested in vitro.Double N-quaternized chitosan exhibited 100.0% scavenging activity against hydroxyl radicals at 1.6 mg/m L.Compared with chitosan with the inhibitory index 19.5%-27.2%at 0.6 mg/m L,the inhibitory indices of single N-quaternized chitosan and double N-quaternized chitosan against three fungi(F.oxysporum f.sp.Cucumerium,B.cinerea,F.oxysporum f.niveum and P.asparagi)were 61.8%-80.6% and 77.2%-90.2%,respectively.The results indicate that both antioxidant ability and antifungal activity of chitosan derivatives are concentration-dependent,which enhanced with increasing concentration.Our results suggested antioxidant abilities and antifungal properties were in order of double N-quaternized > single N-quaternized > chitosan.Quaternary ammonium groups enhance the positive charge density of chitosan derivatives,chitosan derivative with two quaternized groups owned higher positive charge density,and had high antioxidant ability.These results demonstrate that the number of quaternized groups can contribute to both the antioxidant ability and antifungal activity of chitosan derivativies.Novel chitin derivatives containing N-quaternized chitin and N-diquaternized chitin were synthesized by quaternization.The antifungal activities against three fungi(F.oxysporum f.niveum,P.asparagi and B.cinerea)were tested.Compared with chitin with the inhibitory index 12.3%-15.0%,the inhibitory indices of N-quaternized chitin and N-diquaternized chitin were 63.0%-73.4% and 74.4%-88.9% at 1.0 mg/m L,respectively.The results showed that antifungal activity of all the samples exhibit an upward trend with the increase of sample concentration.Our results suggested that antifungal properties were in order of N-diquaternized chitin > N-quaternized chitin > chitin,which were consistent with the number of quaternized groups.Based on the above results,it was reasonable to speculate that quaternized groups should be an important factor that influences antifungal activity.The more quaternary ammonium groups,the higher antifungal activity.N-quaternized chitin and N-diquaternized chitin are potentially effective antifungal agent.This study lays a theoretical foundation for further development and application of chitin resources,new pesticides,and antioxidants.