The Preparation And Performance Analysis Of Quaternary Ammonium/Zwitterionic Chitosan

Chitosan(CS)has been widely applied in biomedical,food,cosmetics,and bioengineering field due to its abundance,antimicrobial activity,biocompatibility and biodegradability.However,CS is insoluble in neutral,alkaline aqueous solution and most organic solvents,limiting its application.In addition,most antibacterial agents exist high toxicity,so synthetize new chitosan derivatives with good solubility,antibacterical activity and low toxicity is still a significant challenge.In this thesis,terminal isocyanate sulfobetaine(NCO-Betaine)and long chain quaternary ammonium salt containing isocyanate(NCO-QAS)were designed and synthesized as two novel antibacterial modifiers that could be chemically bonded to to CS via chemical reaction between NCO and OH or NH2 groups.And then selectively N-substituted zwitterionic chitosan(N-Ba CSb),O-substituted zwitterionic chitosan(O-Ba CSb),N-substituted quaternary ammonium chitosan(N-Qa CSb)and quaternary ammonium/ zwitterionic chitosan(QBa CSb)derivatives were obtained.The relationship between structure and antibacterial activity was systematically investigated in detail.The results showed that the solubility,antibacterial activity and biocompatibility of chitosan were improved to some extent after modification.Compared with chitosan,N-Ba CSb?O-Ba CSb and QBa CSb can be dissolved in distilled water with various solubility values.And the water solubility increased with the degree of substitution.Chitosan derivatives were cultured together with E.coli and S.aureus for 24 h to evaluated their antibacterial activities.The results showed that the antibacterial activities of chitosan derivatives were greater than that of CS,and the MIC of O-Ba CSb was 500~1000 ?g/m L.In addition,the antibacterial activity of QBa CSb was best among the chitosan derivatives,and the MIC of QBCS was 500 ?g/m L.In order to explore the cytoxicity of chitosan derivatives on mouse embryonic fibroblasts,the Cell viability was evaluated by cell counting kit-8(CCK-8)and Live/Dead assay.The results showed that N-Qa CSb had high cytoxicity due to the presence of quaternary ammonium group,and the cytoxicity of QBa CSb was lower that that of N-QCS.The introduction of zwitterionic and quaternary ammonium salts can destroy the intramolecular and intermolecular hydrogen bonds of chitosan,resulting in improving the water solubility,antibacterial activity and biocompatibility.QBa CSb has great potential as new chitosan derivatives with good solubility,antibacterical activity and low toxicity,although there are some deficiencies in quaternary ammonium/ zwitterionic chitosan.