Preparation And Antioxidant Activity Of Sulfur-containing Chitosan Derivatives

As a natural polysaccharide that is second only to cellulose in annual biosynthesis on earth,chitosan has drawn wide attention from various academic fields,because it is abundant,renewable,non-toxic,and has good biological activities such as:biocompatibility,biodegradability,bacteriostatic activity,and antioxidant activity,etc.However,the chitosan molecular chain has a rigid crystalline structure caused by the formation of intra-and/or interhydrogen bonding between the amino and hydroxyl groups,making it difficult to dissolve in water,and due to its limited biological activity,these factors make it difficult to use in some areas.In order to improve the solubility and biological activity of chitosan and realize the use of high added value of chitosan,chemical modification can be used to modify chitosan to obtain chitosan derivatives with excellent biological activity to meet the needs of different fields.However,due to a large number of amino（-NH₂）and hydroxyl（-OH）groups in chitosan,it is possible to perform chemical modification to improve its physical and chemical properties throough introduce various active group.The main chemical modifications of functionalized chitosan structures is N-substitution,O-substitution,N,O-substitution.The most widely used methods for the chemical modification of chitosan are:quaternization,acylation,esterification,schiff alkalization,alkylation,carboxymethylation and so on.Twelve kinds of sulfur-containing chitosan derivatives were prepared in this paper.First,a chitosan reaction intermediate is prepared through carboxymethylation and acylation reactions,and then a series of sulfur atom-containing compounds such as thiourea salt,sulfonium salt and other active groups are inserted into the chitosan molecule.The structure of welve kinds of sulfur-containing chitosan derivatives was identified and analyzed by means of and characterized by FTIR,NMR,and elemental analyses.In addition,the antioxidant potential of chitosan and chitosan derivatives was assessed in vitro,screened by 2,2-diphenyl-1 picrylhydrazyl（DPPH）free radical scavenging,hydroxyl radical scavenging,and superoxide radical scavenging,respectively.And Chitosan derivatives with good antioxidant activity and low cytotoxicity were screened by in vitro antioxidant activity and cytotoxicity test.In order to obtain chitosan derivatives with good water solubility and high antioxidant activity,a carboxymethyl chitosan reactant intermediate was first synthesized,and then thiourea salts（thiosemicarbazone,4-methylthiosemicarbazide,4,4-dimethyl-3-thiosemicarbazide,4-amino-3-indolyl-5-mercapto-1,2,4 triazole）inserted into the chitosan molecular chain,the carboxymethyl chitosan derivatives containing thiourea salts with different structures were obtained.Their structural characterization,anti-oxidant activity and cytotoxicity tests were performed.Results revealed that the four chitosan thiosemicarbazide salts could effectively scavenge DPPH radical within hibition rate of more than 90%at 1.6 mg/m L,higher than chitosan.After that,the same method was used to modify thioetherinto the chitosan molecular chain to obtain carboxymethyl chitosan sulfonium salt.The thioether groups（Dimethyl sulfide,Ethyl Sulfide,Propyl sulfide,Butyl sulfide）undergo alkylation reaction to obtain sulfonium salts of different chain lengths,and then combine the sulfonium salts with carboxymethyl chitosan to obtain carboxymethyl chitosan Sugar sulfonium salt,and structural characterization and identification,as well as antioxidant activity,cytotoxicity test.The results showed that the sulfonium carboxymethyl chitosan salt with good antioxidant activity was successfully synthesized.Finally,In order to insert the sulfide into the chitosan molecule,the graft copolymerization method is used.And the bromoacetyl chitosan reaction intermediate obtained by reacting chitosan with bromoacetyl chloride is subjected to alkylation reaction with the thioether.To obtain acetylated chitosan sulfonium salts with different chain lengths,and to carry out structural characterization and identification as well as antioxidant activity and cytotoxicity tests.The results show that the four acetylated chitosan sulfonium salts have good antioxidant activity.At 1.6 mg/m L,the acetylated chitosan containing butyl sulfonium salt has a capacity to scavenge superoxide anions 1.6 times that of chitosan.In this thesis,the active groups of sulfur-containing compounds were systematically introduced into the chitosan,and a series of sulfur-containing chitosan derivatives with good water solubility,excellent antioxidant activity and low cytotoxicity were synthesized.This thesis will become a basis on the high value-added development of chitosan applications,and at the same time,provides new ideas for new polymer antioxidant biological agents.