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    • Plant pathogenic fungi have caused a

    2024-03-29

    Plant pathogenic fungi have caused a lot of economic losses to agricultural production worldwide every year. It is necessary to develop an bio-sourced antifungal agent for agricultural use. Many researches have shown that the antifungal activity of quaternized chitosan derivatives is mainly affected by the positive charge [9]. In that case, the density of positive charge could influence the efficiency of antifungal activities. Therefore, we designed and synthesized two kinds of chitosan derivatives with triple quaternary ammonium groups using 3-aminopyridine and 3-amino-4-methylpyridine. The theoretical structures were analyzed by density functional theory (DFT). We optimized the lowest PYR-41 form of the molecules, calculated the reaction energy barrier and constructed a theoretical model by Gaussian 09 and verified the structure by other analytical methods. In addition, the antifungal properties of TQCSPX against crop-threatening pathogenic fungi (P. capsici, R. solani, F. oxysporum and F. solani) were evaluated. By using the theoretical model, the transition states of the grafted groups were also studied. This type of chitosan derivative may serve as a new leading structure for the further design of antifungal agent.
    Materials and methods
    Results and discussion
    Conclusions In this study, two kinds of chitosan derivatives with triple quaternary ammonium groups were synthesized. FTIR, 1H NMR, 13C NMR, and elemental analysis confirmed that aminopyridine groups had been successfully introduced to the chitosan backbone. Antifungal activity against P. capsici, R. solani, F. oxysporum and F. solani were also evaluated. In general, the results of the fungal growth inhibition tests indicate differences in the sensitivity of the four fungi against the sample tested, with P. capsici and R. solani being the most inhibited. Moreover, the prepared chitosan derivatives showed better activities than the positive control Oligosaccharins against R. solani. The findings described here suggested that aminopyridine groups should be excellent antifungal function groups. In addition, the reaction transition state was precisely analyzed, the route of reaction and the structure of intermediates were discussed. This type of chitosan derivatives may serve as a new leading structure for the further design of antifungal agents.
    Acknowledgements The study was supported by the National Natural Science Foundation of China (No. 41306071), the Scientific and Technological Innovation Project Financially Supported by Qingdao National Laboratory for Marine Science and Technology (No. 2015ASKJ02) and the Science and Technology Program Supported by Qingdao (No. 17-3-3-60-nsh).
    Introduction In the last few decades, a number of natural polysaccharides have been developed as biomaterials to meet an urgent need of sustainable development on account of their renewable and biodegradable properties [[1], [2], [3]]. Polysaccharides such as chitosan and starch are natural, nontoxic, cheap, quite abundant, and economically important biomaterials. They are amenable to be modified on purpose which makes them especially attractive biomaterials to produce value-added materials in such fields as drug delivery, tissue engineering scaffolds, biomedical devices, and waste water treatment [[4], [5], [6], [7], [8], [9], [10], [11]]. Like these polysaccharides, inulin, being a kind of carbohydrate storage reserve for plants, is widely distributed in >36,000 plant species. Commercially it is extracted primarily from chicory, dahlia, and Jerusalem artichoke [12]. It is a type of fructose polymer linked by β (2→1) linkages of d-fructosyl fructose and commonly terminated by a glucose residue [13]. This fantastic structure can prevent inulin from being digested like a typical carbohydrate in the upper gastrointestinal tract [14]. Therefore, inulin generates low caloric value and is generally used as a fat or sugar replacer in food industry [15,16]. Furthermore, inulin shows a prebiotic effect as it stimulates the proliferation of bifidobacterium in the colon [[17], [18], [19]]. Inulin also exerts favorable properties in decreasing the risk of many diseases of the intestinal tract, particularly irritable bowel diseases (IBD) and colon cancer [19]. Based on these properties, inulin is widely utilized as an additive in many products such as functional foods, health care products, and some natural medicine [[20], [21], [22], [23]]. However, its weak antimicrobial activity limits its further utilization. Because biological activities of polysaccharides are related with their molecular structure, we may improve inulin antimicrobial activity by chemical modification, which can introduce wide range of functional groups to its framework.