Showing papers by "Jun-ichi Kadokawa published in 2018"

Cellulose Crystal Dissolution in Imidazolium-Based Ionic Liquids: A Theoretical Study.

Abstract: The highly crystalline nature of cellulose results in poor processability and solubility, necessitating the search for solvents that can efficiently dissolve this material. Thus, ionic liquids (ILs) have recently been shown to be well suited for this purpose, although the corresponding dissolution mechanism has not been studied in detail. Herein, we adopt a molecular dynamics (MD) approach to study the dissolution of model cellulose crystal structures in imidazolium-based ILs and gain deep mechanistic insights, demonstrating that dissolution involves IL penetration-induced cleavage of hydrogen bonds between cellulose molecular chains. Moreover, we reveal that in ILs with high cellulose dissolving power (powerful solvents, such as 1-allyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium chloride), the above molecular chains are peeled from the crystal phase and subsequently dispersed in the solvent, whereas no significant structural changes are observed in poor-dissolving-power solvents. Finall...

Understanding dissolution process of chitin crystal in ionic liquids: theoretical study.

Abstract: Chitin is a promising biomass resource and has high potential for industrial applications owing to its huge annual production in nature. However, it exhibits poor processability and solubility due to its very stable and crystalline character. Recently, ionic liquids (ILs) have attracted attention as solvents for structural polysaccharides – for example, 1-allyl-3-methylimidazolium bromide (AMIMBr) has been found to dissolve chitin. As few ILs are known to dissolve chitin, little research has been conducted on the dissolution mechanism involved. In this study, we have adopted a molecular dynamics (MD) approach to study the dissolution of chitin crystals in imidazolium-based ILs. The MD simulation in AMIMBr has demonstrated that the dissolution process involved peeling of chitin chains from the crystal surface, with Br− cleaving the chitin hydrogen bonds, and AMIM+ preventing a return to the crystalline phase after the peeling. By contrast, in imidazolium acetates, which has also been reported to dissolve chitin, although the molecular chains are peeled off, the peeled chains occasionally return to the crystalline phase. Furthermore, the MD trajectory analysis has revealed that the solubility of chitin is well correlated with the number of intermolecular hydrogen bonds by acetamido groups in the chitin crystal. It has been experimentally proven that mixing a small amount of 2-bromoethyl acetate, as a bromide generator, with 1-allyl-3-methylimidazolium chloride can enhance chitin solubility, which supports the dissolution mechanism indicated by the above theoretical results.

Enzymatic preparation of functional polysaccharide hydrogels by phosphorylase catalysis

Abstract: Abstract This article reviews enzymatic preparation of functional polysaccharide hydrogels by means of phosphorylase-catalyzed enzymatic polymerization. A first topic of this review deals with the synthesis of amylose-grafted polymeric materials and their formation of hydrogels, composed of abundant natural polymeric main-chains, such as chitosan, cellulose, xantham gum, carboxymethyl cellulose, and poly(γ-glutamic acid). Such synthesis was achieved by combining the phosphorylase-catalyzed enzymatic polymerization forming amylose with the appropriate chemical reaction (chemoenzymatic method). An amylose-grafted chitin nanofiber hyrogel was also prepared by the chemoenzymatic approach. As a second topic, the preparation of glycogen hydrogels by the phosphorylase-catalyzed enzymatic reactions was described. When the phosphorylase-catalyzed enzymatic polymerization from glycogen as a polymeric primer was carried out, followed by standing the reaction mixture at room temperature, a hydrogel was obtained. pH-Responsive amphoteric glycogen hydrogels were also fabricated by means of the successive phosphorylase-catalyzed enzymatic reactions.

α-Glucan Phosphorylase-Catalyzed Enzymatic Reactions Using Analog Substrates to Synthesize Non-Natural Oligo- and Polysaccharides

Abstract: As natural oligo- and polysaccharides are important biomass resources and exhibit vital biological functions, non-natural oligo- and polysaccharides with a well-defined structure can be expected to act as new functional materials with specific natures and properties. α-Glucan phosphorylase (GP) is one of the enzymes that have been used as catalysts for practical synthesis of oligo- and polysaccharides. By means of weak specificity for the recognition of substrates by GP, non-natural oligo- and polysaccharides has precisely been synthesized. GP-catalyzed enzymatic glycosylations using several analog substrates as glycosyl donors have been carried out to produce oligosaccharides having different monosaccharide residues at the non-reducing end. Glycogen, a highly branched natural polysaccharide, has been used as the polymeric glycosyl acceptor and primer for the GP-catalyzed glycosylation and polymerization to obtain glycogen-based non-natural polysaccharide materials. Under the conditions of removal of inorganic phosphate, thermostable GP-catalyzed enzymatic polymerization of analog monomers occurred to give amylose analog polysaccharides.

Preparation of Cationic/Anionic Chitin Nanofiber Composite Materials

Abstract: In this study, we investigated the preparation of cationic/anionic chitin nanofiber (CNF) composite materials by electrostatic interaction. An aqueous dispersion of amidinium CNF was prepared by a top-down approach, and a maleylated CNF film was obtained by a bottom-up approach from a chitin ion gel in an ionic liquid with subsequent maleylation on the CNFs. The resulting film was dispersed in ammonia (aq), which was then mixed with the aqueous cationic CNF dispersion to give the composite film. The composition of the two CNFs was evaluated by scanning electron microscopy and X-ray diffraction measurements. Tensile testing results indicated that the mechanical properties of the composites were enhanced with increasing degrees of substitution of the cationic and anionic groups on CNFs, and also when the molar ratio of these groups approached 1:1. The dissociation of the two kinds of CNFs by alkaline treatment of the composite film was achieved, suggesting the presence of an electrostatic interaction among the interactions between them.

Gel Formation from Self-assembled Chitin Nanofiber Film by Grafting of Poly(2-methyl-2-oxazoline)

Abstract: In this study, the grafting of poly(2-methyl-2-oxazoline) onto a self-assembled chitin-nanofiber film was investigated by reacting its living propagating ends with amino groups generated on the fil...

Difference in Macroscopic Morphologies of Amylosic Supramolecular Networks Depending on Guest Polymers in Vine-Twining Polymerization.

Abstract: Amylose, a natural polysaccharide, acts as a host molecule to form supramolecular inclusion complexes in its enzymatically formation process, that is, phosphorylase-catalyzed enzymatic polymerization using the α-d-glucose 1-phosphate monomer and the maltooligosaccharide primer, in the presence of appropriate guest polymers (vine-twining polymerization). Furthermore, in the vine-twining polymerization using maltooligosaccharide primer-grafted polymers, such as maltoheptaose (G7)-grafted poly(γ-glutamic acid) (PGA), in the presence of poly(e-caprolactone) (PCL), the enzymatically elongated amylose graft chains have formed inclusion complexes with PCL among the PGA main-chains to construct supramolecular networks. Either hydrogelation or aggregation as a macroscopic morphology from the products was observed in accordance with PCL/primer feed ratios. In this study, we evaluated macroscopic morphologies from such amylosic supramolecular networks with different guest polymers in the vine-twining polymerization using G7-grafted PGA in the presence of polytetrahydrofuran (PTHF), PCL, and poly(l-lactide) (PLLA). Consequently, we found that the reaction mixture using PTHF totally turned into a hydrogel form, whereas the products using PCL and PLLA were aggregated in the reaction mixtures. The produced networks were characterized by powder X-ray diffraction and scanning electron microscopic measurements. The difference in the macroscopic morphologies was reasonably explained by stabilities of the complexes depending on the guest polymers.

Hierarchically controlled assemblies from amylose analog aminopolysaccharides by reductive amination: From nano- to macrostructures

Abstract: In this study, we found that hierarchically controlled assemblies from amylose analog aminopolysaccharides occurred by reductive amination to obtain nanoparticles, microaggregates, and macrohydrogels depending on reaction conditions. The polysaccharide substrate composed of α(1→4)-linked glucosamine residues was synthesized by thermostable phosphorylase (from Aquifex aeolicus VF5)–catalyzed enzymatic polymerization of α-d-glucosamine 1-phosphate according to the reaction manner reported in our previous study. The reductive amination of the produced polysaccharide was carried out in the presence of NaBH3CN as reductant in 0.1 mol/L acetic acid aq. at 60 °C for 1 h. When lower feed ratios of reductant to the reducing end of the substrate were employed for the reaction, nanoparticles were obtained. With increasing feed ratios of reductant, more α(1→4)-GlcNn molecules assembled to further form water-insoluble microaggregates and macrohydrogels. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45890

Gel Formation by Non-covalent Cross-Linking from Amylose Through Enzymatic Polymerization

Abstract: Polymer gels are constructed by polymeric network structures with cross-linking points, which stably include a large amount of dispersion media, leading to functional soft materials. The specific formation of cross-linking points contributes to exhibiting unique properties of the resulting gels. In this chapter, we focus on the gel formation through non-covalent cross-linking from amylose, a natural polysaccharide. Amylose has a helical conformation, which is able to form two types of complexes, that is, double helix by two amylose chains and inclusion complex with other molecules having suitable structures and sizes. Because a well-defined amylose can be synthesized by enzymatic polymerization by phosphorylase catalysis, the studies on the dynamic gel formation through non-covalent, double helical, and inclusion complexing, cross-linking from amylose has been achieved by means of the enzymatic polymerization field. The resulting gels showed unique properties and functions.