Preparation Of Chitooligosaccharide Derivatives Bearing Pyridinium And Assessment Of Their Antimicrobial Activities

Chitooligosaccharide,as a natural cationic oligosaccharide,possesses excellent water solubility,high biocompatibility,and easy bioavailability.It exhibits various biological activities,including antioxidant,anti-inflammatory,and antimicrobial properties,which have attracted widespread attention from academic communities.However,its antimicrobial activity is extremely weak and cannot meet the requirements for efficient development.Introducing active functional groups into chitooligosaccharide through chemical modification is an effective way to enhance antimicrobial activity and thus improve its application value.In this study,a total of 15 chitooligosaccharide pyridinium were synthesized,which included derivatives containing linear alkyl,trialkyl ammonium and halogenated benzene.The structures of the derivatives were confirmed by Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance.The antibacterial activities of chitooligosaccharide derivatives against harmful bacteria were evaluated in vitro using broth dilution method,Kirby-Bauer method,and disk diffusion method.And the antifungal activities common plant pathogenic fungi were assessed using the mycelium growth rate method and disk diffusion method.We screened chitooligosaccharide derivatives with excellent activity and studied the activity patterns of target compounds with different structures in the same series.In this work,in order to prepare chitooligosaccharide derivatives with enhanced antimicrobial activity,chitooligosaccharide-niacin acid conjugate was designed and synthesized through the reaction of chitooligosaccharide and nicotinic acid with the aid of N,N′-carbonyldiimidazole.And its cationic derivatives were prepared by the further nucleophilic substitution reaction between chitooligosaccharide-niacin acid conjugate and bromoalkanes with different lengths based on previous research.The structures of the derivatives were characterized,and antimicrobial activities were evaluated.The results showed that introducing pyridinium cations to increase the positive charge density and introducing linear alkyl groups to enhance hydrophobicity and lipophilicity significantly improved the antimicrobial activities of chitooligosaccharide.One effective approach to enhancing the antimicrobial activity of chitooligosaccharide derivatives is increasing their positive charge density.In this paper,increasing the positive charge density was taken as the basic point.Different chain lengths of bromopropyl trialkyl ammonium bromide were synthesized,followed by reacting with chitooligosaccharide-niacin acid conjugate.One interesting finding was that the pyridinium salt not only acted as the active group to enhance the antimicrobial activity directly but also acted as a bridge to connect the quaternary ammonium salt bearing trialkyl.The positive charge density in the chitooligosaccharide derivative was further increased,which enhanced its antimicrobial activity.Although the antimicrobial activities of chitooligosaccharide containing linear alkyl,trialkyl ammonium were enhanced,there is still room for improvement.Aromatic compounds containing halogens usually exhibit good biological activity and have a wide range of applications.In this study,benzyl bromides containing different types of halogens and different numbers of fluorine atoms were introduced into chitooligosaccharide-niacin acid conjugate.The end compounds were structurally characterized and evaluated for their antimicrobial activity.The results showed that all chitooligosaccharide containing halogenated benzene exhibited significantly enhanced antimicrobial activity.In particular,of all chitooligosaccharide derivatives,chitooligosaccharide derivative containing2,3,4-trifluorobenzene possessed remarkable antimicrobial activity,the MIC against Vibrio harveyi was 0.03125 mg/m L,and the MBC was 0.0625 mg/m L,then the inhibition index against Botryis cinerea was 84.35 % at 1.0 mg/m L.The combination of pyridinium cation with strong antimicrobial activity and fluorine with the most robust electron-withdrawing capacity extended the methodology to acquire chitooligosaccharide derivatives with distinguished antimicrobial capabilities.This research systematically synthesized a series of chitooligosaccharide derivatives containing linear alkyl,trialkyl ammonium and halogenated benzene,providing a solid theoretical basis for the development of high value-added applications of chitooligosaccharide and providing new ideas for novel polymeric antimicrobial biopreparations.