Natural bioactive compounds present in marine organisms can exert antimicrobial functions.Hence,the development of marine organism-derived antimicrobials has become a novel area of interest among marine biology industries and holds innovative potential for new antimicrobial development.Chitosan is the deacetylated product of chitin,a renewable resource in the ocean.Chitooligosaccharide is the degraded product of chitosan with better water solubility and biological activity,displaying broader application prospects in the food and biomedicine fields.To enhance the antimicrobial activity of chitooligosaccharide,a chitooligosaccharide-niacin acid derivative was synthesized using N,N'-carbonyldiimidazole as a catalyst,and its cationic derivatives were obtained through a fur-ther nucleophilic reaction between the chitooligosaccharide-niacin acid derivative and bromoalkanes.The structure of chitooligosaccharide and its derivatives was analyzed using Fourier-transform infrared spectroscopy and nuclear magnetic resonance,and its antimicrobial efficacy against two harmful bacteria was assessed using broth dilution methods and three plant-threatening fungi by hyphal measurement.The results indicated that the end products had enhanced antimicrobial activity compared with chitooligosaccharide.In particular,the chitooligosaccharide deriva-tive containing n-hexane displayed great antimicrobial effects against marine pathogens(MIC=0.125 mg/mL;MBC=0.25 mg/mL)and plant-threatening fungi(65.7%against Botrytis cinerea and 51.5%against Glomerella cingulate at 1.0 mg/mL).These results indicated that the preparation of niacinate chitooligosaccharide quaternary ammonium salt by introducing linear alkyls into chitooligosaccharides can significantly enhance antimicrobial ac-tivity.Such chitooligosaccharides will possess great application potential in food,biomedicine,and other industries.
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