Oxidation Of Chitosan By Laccase-TEMPO System To Product Hyaluronic Substitutes

Study on the preparation of hyaluronic acid substitute by using green chemical system modified chitosan.The aim of this study was to investigate the oxidation of chitooligomer by a laccase-TEMPO system which had not previously been examined,and then to optimize the experiment.Chitooligomer was treated with laccase and TEMPO in order to evaluate the potential of a laccase-TEMPO system to improve the moisture absorption,moisture retention,and antioxidant abilities of chitooligomer.On the basis of environmental protection to produce inexpensive hyaluronic acid substitute and chitosan fine substitute broaden the market of chitosan refined products.To begin with,Oligochitosan was obtained by the degrading process of hydrogen peroxide under neutral conditions,then it was oxidated with laccase-TEMPO system in a homogeneous system.And through the comparative experiments to explore the reaction mechanism of laccase-TEMPO system oxidation chitosan on C6 hydroxyl.13C NMR,carboxylate ion content detection and FTIR results indicated that the laccase-TEMPO system could selectively oxidise the C6 hydroxyl group of the chitooligomer into carboxyl group.Molecular weight distribution changes suggest that the structure of the oxidised product had changed and the molecular size and molecular weight decreased with the molecules in aqueous solution having a compact structure.As the Na+in the samples was from the carboxylate ions-carrying Na+ and the residues of the purification process,High-performance ion chromatography(HPIC)was utilized to detect the Na+ content and characterize the carboxylate ions content.By testing the hygroscopic and moisture resistance,oxidation resistance and thermal stability of samples to characterization the improvement degree of the performance of physical-chemical levels of the oxidised product of chitooligomer.The results indicated that oxidation of chitooligomer by a laccase-TEMPO system resulted in a significant improvement in the moisture absorption,moisture retention,thermal stability and antioxidant abilities.And moisture absorption and antioxidant properties superior to commercial HA-oligo sodium,moisture retention similar to commercial HA-oligo sodium.The oxidation products with the best performance were obtained by the optimization experiment(Hydrogen peroxide degradation of 6 h,TEMPO adding amount was 4%).Moisture absorption of the oxidation products with the best performance is three times as many commercial HA-oligo sodium,its moisture retention is superior to the commercial HA-oligo sodium,and its ABTS ·+?radical scavenging ability was 92.67%,which have strong antioxidant properties,while commercial HA-oligo sodium is only 9.7%.The oxidised product has potential application values in the pharmaceutical and cosmetics industries.