| Chitosan,a polysaccharide polymer from deacetylation of chitin,is the second abundant resources only to cellulose existing in the natural.Due to its close molecular structure leads to a poor water solubility,which limits its application and development in many fields.In order to improve the application value of such high value-added marine biological resources,chitosan can be degraded by bio-enzymatic methods to obtain a chitooligosaccharide fine product.It has good biocompatibility,biodegradability,moisture absorption-retention and water solubility,and has a wide application prospect in the cosmetics field.In this dissertation,the functional chitooligosaccharide derivative was prepared based on the molecular modification of chitooligosaccharide,and as far as possible to investigate its high moisture absorption-retention mechanism and explore its application feasibility in the cosmetic market.In this study,carboxyl-chitooligosaccharide(C-COS)biofunctional material was prepared by catalytic oxidation of chitooligosaccharide(COS)using the laccase/TEMPO system,and converting the C6 hydroxyl group of the glucosamine unit into carboxyl group.The molecular structure changes of C-COS were characterized by FTIR,13C NMR,conductivity titration,TGA and SEM,and moisture absorption and moisture retention activities also were detection.The results showed that laccase/TEMPO could selectively oxidize C6-OH of COS to form C600H.Under the conditions of 400 ?L laccase and TEMPO with 2%mass fraction,the carboxyl group content of C-COS was 2.28%and its surface exhibited a dense spherical structure.The moisture absorption-retention property was significantly enhanced and higher than that of commercial Oligo-HA.In addition,it had a better thermal stability,therefore,it can be considered as an excellent moisture absorption moisturizer to replace Oligo-HA.Secondly,the hydrogen bonding effect in C-COS molecules was investigated by using FTIR,DSC and NMR and speculate its moisture-absorption and moisture-retention mechanism.The results showed that there was an intermolecular hydrogen bonding force between polymer molecules and water in the process of moisture absorption of C-COS.The more polar carboxyl groups on the C-COS molecules generated a new hydrogen bonding effect,combined with a decrease in the intensity of the absorption peaks at 3363 and 1643 cm-1 by the temperature-increased infrared and a blue shift of the absorption peak frequency at the same wave number.The increase in the intensity of the absorption peak at 1643 cm-1 by swelling infrared confirmed the formation of hydrated hydrogen bond(H-O-H…O-C=O)between the carboxyl groups in the C-COS molecule and water.In addition,13C NMR analysis combined with different solvents,we found that when the solvent system from DMSO to D2O,the chemical shift value of the carboxylate was shifted from 169.68 to 174.62,which was caused by changes in intermolecular hydrogen bonds.Therefore,the moisturizing mechanism of C-COS was that the polymer dissolved in the water system can form a huge polymer-water network structure,which promoted that the water molecules are firmly locked in this network structure in the form of hydrogen bonds.So it had a higher moisture-retention effect.Finally,the aqueous products of COS,C-COS and Oligo-HA were tested for moisture retention,anti-oxidant performance and skin moisture content,and the feasibility of their application was analyzed.The results showed that C-COS had a good water solubility and the aqueous solution exhibited weakly alkaline(pH=7.5-8.0).The moisture retention ability,skin water content and anti-oxidant capacity of C-COS were significantly higher than that of COS and far stronger than that of Oligo-HA.These make it potentially useful in cosmetics,medicine and other fields. |
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