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Selective and green conversion of chitin to levulinic acid (LA) has been realized by the catalysis of the ionic liquid (IL) 1-methyl-3-(3-sulfopropyl)imidazolium hydrogen sulfate ([C3SO3Hmim]HSO4) up to a yield of 67.0%. The relationship between the structure of IL and the yield of LA was investigated, demonstrating that both acidity and the hydrogen bonding ability of IL dictate its catalytic activity. Furthermore, by means of NMR, IR, SEM, GPC analyses and determination of the degree of acetylation (DA), two approaches of deacetylation–depolymerization to glucosamine (GlcN) and direct depolymerization to N-acetylglucosamine (GlcNAc) were proposed as chitin hydrolysis mechanisms, which occur only at the outer surface while leaving the interior crystalline chitin intact. The N-acetyl groups in chitin construct strong intramolecular and intermolecular hydrogen bond networks that contribute to the integration of the crystalline structure and building up of barriers to shield the accessibility of glycosidic linkages with the acidic catalyst. [ABSTRACT FROM AUTHOR]

The crude chitin deacetylase (a novel bacterial CDA) with a molecular mass of approximately 31 kDa was produced by culturing the bacteria of Acinetobacter schindleri MCDA01. The produced CDA was directly applied to surface deacetylation of crab shell α-chitin. For enzyme production, a maximum total enzyme activity of 150.09 ± 1.66 U mL−1 was achieved through submerged fermentation following 72 hours of incubation. Increased enzyme activity was observed with EDTA and metal ions of Fe3+, Ba2+, Sr2+, K+, Na+ and Li+, while enzyme activity was inhibited by Co2+ or Cd2+. The degree of deacetylation (DDA) was increased from 6.46% to 30.58% when the chitin was treated by 12 000 U of CDA at 30 °C and pH 7.0 for 96 h. The high crystallinity of original chitin was maintained, with yield greater than 90% after enzymatic deacetylation, indicating that the CDA deacetylation occurred on the surface of crystalline chitin fibrils without destroying the crystal structure. The chitin nanofibers (CDA-ChNs) were obtained with widths mostly between 25 and 45 nm and lengths of more than several micrometers by sonication of the CDA-treated surface-deacetylated chitin (CDA-Ch) aqueous suspensions at pH 3–4. The application of bacterial CDA on chitin provides a new path to the biorefinery of chitin nanofibers, and the resulting CDA-ChNs might exhibit advanced performance in forming multifunctional materials because of their unique fiber size and high aspect ratio. [ABSTRACT FROM AUTHOR]

We report a simple route to produce chitin films with different crystalline structures. The use of a green deep-eutectic-solvent (DES) choline chloride : urea (CCU) or hexafluoroisopropanol (HFIP) allows fine-tuning of the crystallization process to produce films with β-dihydrated- or γ-chitin structures. With the advent of a Grazing-Incidence X-Ray Diffraction (GIXD) technique, we propose a new and fully indexed structure of γ-chitin. This new γ-structure is modeled as a super-cell, in contrast to the idea of a simple physical mixture of α and β phases. The influence of purification, dissolution or dispersion media on chitin's crystallinity was investigated by FTIR, solid-state NMR and XRD. Results presented here may trigger applications in which a well-defined crystalline structure is required. [ABSTRACT FROM AUTHOR]