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Chitin nanocrystals prepared by oxidation of α-chitin using the O2/laccase/TEMPO system

Jiang, Jie, Ye, Wenbo, Yu, Juan, Fan, Yimin, Ono, Yuko, Saito, Tsuguyuki, Isogai, Akira
Carbohydrate polymers 2018 v.189 pp. 178-183
Fourier transform infrared spectroscopy, X-ray diffraction, adsorption, buffers, chitin, crystal structure, electrostatic interactions, laccase, nanocrystals, oxidation, pH, sonication
Laccase mediator oxidation was applied to chitin at pH 6.8 and 30 °C to prepare chitin nanocrystals with a catalytic amount of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO). When 40 mM TEMPO and a total of 500 U laccase were added to 1 g chitin, the yield of water-insoluble oxidized chitin was more than 95%, and the carboxylate content was 0.43 mmol/g. Adsorption of laccase molecules on chitin particles occurred in a buffer at pH 6.8, which may have been caused by electrostatic interactions between positively charged C2-ammonium groups of chitin and anionically charged groups of laccase. Rod-like chitin nanocrystals (ChNCs) were obtained with average lengths and widths of 480 ± 200 nm and 24 ± 17 nm, respectively, by sonication of the oxidized chitin/water suspensions. The O2/laccase/TEMPO oxidation caused no decrease in the degree of N-acetylation or the crystallinity of the original chitin based on FTIR and X-ray diffraction data.