Showing papers by "Jun-ichi Kadokawa published in 2022"

Application of ionic liquids for the functional materialization of chitin

Abstract: Ionic liquids (ILs) have been shown to efficiently dissolve substrates with poor solubility. In particular, they act as powerful solvents for structural polysaccharides, which are difficult to dissolve using conventional...

Hydrogelation from Scaled-Down Chitin Nanofibers by Reductive Amination of Monosaccharide Residues

Abstract: Polysaccharides are widely distributed in nature and are regarded as structural materials and reservoirs of water and energy [1]. Among the natural polysaccharides, chitin, comprising main chains of β(1 →4)-linked N -acetyl-D-glucosamine (GlcNAc) residues, is an important biomass resource because it is one of the most abundant polysaccharides present in nature, mainly prevalent in the exoskeletons of crustaceans [2‒4]. However, chitin remains largely underutilized because of its poor solubility and processability, owing to its intractable bulk structure composed of numerous intraand inter-molecular hydrogen bonds. The fabrication of nanoscale polymeric assemblies (e.g., nanofibers and nanowhiskers) is a useful method for the functionalization of chitin [5‒7] because of the remarkable properties of bio-based nanomaterials, such as low weight, high tensile strength, and biocompatibility [8‒14]. Efficient procedures for the preparation of chitin nanofibers (ChNFs) and nanowhiskers have been developed using a top-down approach that breaks down the starting bulk materials from native chitin sources [5, 6, 15‒18]. Based on another approach‒the bottom-up technique‒we previously developed a facile method to fabricate ChNFs with a width of approximately 20‒60 nm and length of several hundred nanometers. Selfassembling regeneration at the nanoscale from an ion gel of a chitin/ionic liquid, namely, 1-allyl-3methylimidazolium bromide (AMIMBr), was achieved using methanol [19, 20]. This was based on our previous findings that AMIMBr efficiently dissolves and swells chitin [21]. Isolation of the resulting ChNFs from the methanol dispersion via filtration produced a ChNF film possessing a heavily entangled nanofiber morphology. Furthermore, the self-assembled ChNFs had a bundle-like structure consisting of an assembly of thinner fibrils [22]. The treatment of the ChNF film with an aqueous NaOH induced the partial generation of amino groups on the chitin chains (i.e., partially deacetylated chitin nanofibers (PDA-ChNFs)). This led to the successful disentanglement of the bundles by cationization and electrostatic repulsion in 1.0 mol/L aqueous acetic acid with ultrasonication, yielding 【Transaction】

Fabrication of Chitosan-Based Network Polysaccharide Nanogels

Abstract: In this study, we developed a method to fabricate chitosan-based network polysaccharides via the condensation between amino groups in water-soluble chitosan (WSCS) and a carboxylate-terminated maltooligosaccharide crosslinker. We previously reported on the fabrication of network-polysaccharide-based macroscopic hydrogels via the chemical crosslinking of water-soluble chitin (WSCh) with the crosslinker. Because the molecular weight of the WSCS was much smaller than that of the WSCh, in the present investigation, the chemical crosslinking of the WSCS with the crosslinker was observed at the nanoscale upon the condensation between amino and carboxylate groups in the presence of a condensing agent, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, and N-hydroxysuccinimide, affording nano-sized chitosan-based network polysaccharides. The occurrence of the crosslinking via the formation of amido linkages was supported by the IR analysis and 1H NMR measurements after the dissolution via acid hydrolysis in DCl/D2O. The products formed nanogels, whose sizes depended on the amino/carboxylate feed ratio. The nanoscale morphology and size of the products were evaluated via scanning electron microscopy, dynamic light scattering analyses, and transition electron microscopy. In the present study, we successfully developed the method to fabricate nanogel materials based on network polysaccharide structures, which can practically be applied as new polysaccharide-based 3D bionanomaterials.

Preparation of Nanochitin Films with Oligochitin Graft Chains

Abstract: Even nowadays, chitin is mostly unutilized as a biomass resource, although it is abundantly present in nature. To develop an efficient method to use chitin as the component in new functional bio-based materials, in this study, we investigated the preparation of a flexible nanochitin (chitin nanofiber, ChNF) film with oligochitin dihexanoate graft chains. The parent ChNF film was prepared by regeneration of a chitin ion gel with an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), using methanol and subsequent filtration. However, the obtained film showed a quite brittle nature, probably because of the high crystallinity of the chitin chains. To reduce the crystallinity, oligochitin dihexanoate, which was provided by partial depolymerization of the parent chitin dihexanoate under acidic conditions, was modified on the partially deacetylated ChNF film by reductive amination. The introduction of the oligochitin dihexanoate graft chains was supported by 1H NMR and IR measurements. The powder X-ray diffraction (XRD) profile of a film, which was obtained from an aqueous acetic acid suspension of the grafted product, indicated a reduction in chitin crystallinity, which contributes to the disappearance of nanofiber morphology and enhancement of flexibility. The removal of hexanoyl groups from the film was performed by treatment with aqueous NaOH. The IR and XRD measurements of the obtained film suggested the compete dehexanoylation and the reformation of the chitin crystalline structure, respectively. This study provides a method to fabricate new bio-based graft and soft materials entirely comprising chitin moieties.