The study of inhibitory effects and mechanism of carboxylate chitooligomer on melanin, prepared by laccase/TEMPO system

Preparation, antioxidant and tyrosinase inhibitory activities of chitosan oligosaccharide-hydroxypyridinone conjugates

Two novel chitosan oligosaccharide (COS)-hydroxypyridone (HPO) conjugates were prepared by reacting chitosan oligosaccharide with 2-chloromethyl-5-hydroxypyridone (HPO), which was synthesized by a series of reactions starting from kojic acid. The degree of substitution of COS-HPO2 reached 1.2, with a yield of 74.9%. The structure of the two conjugates (COS-HPO1 and COS-HPO2) was identified by NMR and FT-IR analysis. The two conjugates showed significantly higher free radical (DPPH•, ABTS^+• and •OH) scavenging activity and reducing power than those of COS and HPO (p < 0.05). Both COS-HPO1 and COS-HPO2 possessed significantly stronger tyrosinase inhibitory activity than those of COS, with IC₅₀ values of 0.67 and 0.28 mg/mL for monophenolase, 0.73 and 0.30 mg/mL for diphenolase, respectively. In addition, the conjugates were found to be non-toxic to RAW264.7 macrophages and MRC-5 human lung cells. This work proposes a facile method to enhance the oxidative and tyrosinase inhibitory properties of COS.

A complex of oxidised chitosan and silver ions grafted to cotton fibres with bacteriostatic properties

The laccase/TEMPO system was employed to oxidise the C6 primary hydroxyl group on the chitosan (CS) to form a carboxyl group to obtain oxidised chitosan (C-COS). The silver-oxidised chitosan complex(C-COS-Ag) was prepared by reacting C-COS with silver nitrate, then C-COS-Ag and cotton fibres were subjected to a reaction to prepare bacteriostatic fibres. FT-IR and XPS analysis showed that: Ag⁺ and C-COS were combined in these forms: Ag, [Ag(NH₃)₂] OH, -COOAg, and Ag₂O. C-COS-Ag was combined with cotton fibres by way of ester bonds. The inhibition zone of bacteriostatic fibres was all greater than 11 mm. After 50 washing tests, the bacteriostatic effect of bacteriostatic fibres remained at above 99 %. The amount of silver ions that had migrated from the bacteriostatic fibre was 3.336 mg/kg.

Chemoenzymatic Production and Engineering of Chitooligosaccharides and N-acetyl Glucosamine for Refining Biological Activities

Chitooligosaccharides (COS) and N-acetyl glucosamine (GlcNAc) are currently of enormous relevance to pharmaceutical, nutraceutical, cosmetics, food, and agriculture industries due to their wide range of biological activities, which include antimicrobial, antitumor, antioxidant, anticoagulant, wound healing, immunoregulatory, and hypocholesterolemic effects. A range of methods have been developed for the synthesis of COS with a specific degree of polymerization along with high production titres. In this respect, chemical, enzymatic, and microbial means, along with modern genetic manipulation techniques, have been extensively explored; however no method has been able to competently produce defined COS and GlcNAc in a mono-system approach. Henceforth, the chitin research has turned toward increased exploration of chemoenzymatic processes for COS and GlcNAc generation. Recent developments in the area of green chemicals, mainly ionic liquids, proved vital for the specified COS and GlcNAc synthesis with better yield and purity. Moreover, engineering of COS and GlcNAc to generate novel derivatives viz. carboxylated, sulfated, phenolic acid conjugated, amino derived COS, etc., further improved their biological activities. Consequently, chemoenzymatic synthesis and engineering of COS and GlcNAc emerged as a useful approach to lead the biologically-active compound-based biomedical research to an advanced prospect in the forthcoming era.