Search

This study revealed that mixed chitin esters with long fatty and bulky acyl substituents were efficiently synthesized by acylation using acyl chlorides in the presence of pyridine and N,N-dimethyl-4-aminopyridine in an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), at 100 °C for 24 h. A stearoyl group was selected as the first substituent, which was combined with different long fatty and bulky acyl groups as the second substituents. In addition to IR analysis of the products, which suggested progress of the acylation, 1H NMR measurement was allowed for structural confirmation for high degrees of substitution (DSs) of the desired derivatives in CDCl3/CF3CO2H solvents. Crystalline structures and thermal property of the products were evaluated by powder X-ray diffraction and differential scanning calorimetry measurements, respectively. All the products showed film formability by casting from solutions in chloroform or chloroform/trifluoroacetic acid solvents. The occurrence of halogen exchange between acyl chlorides and AMIMBr in the present system was speculated to produce highly reactive acyl bromides in situ, which efficiently reacted with hydroxy groups in chitin to obtain high DS products.

This study describes the Ku -band 70- and 30-W-class internally matched gallium nitride (GaN) power amplifiers (PAs) for multi-carrier satellite communications (SatComs). The GaN PAs maintain low third-order intermodulation distortion (IMD3) over a wide offset frequency range of up to 400 MHz, whereas in the Ku -band, one PA can deliver a high peak output power of approximately 70 W and the other PA, a peak output power of higher than 30 W. To realize a wide offset frequency operation, our proposed output-matching circuit includes three different types of difference-frequency short circuits, two of which are embedded into a tournament-shaped output-matching circuit inside the PA package and the rest is embedded into the drain bias feed placed outside the package. To verify the short-circuit design and its effectiveness, two different power classes (70 and 30 W), Ku -band GaN PAs, were designed and fabricated, and then, their output transfer characteristics focusing on IMD3 were measured. The measurements show that the 70-W-class GaN PA achieves a peak output power of 48.6 dBm while maintaining a linear output power of over 40 dBm and an IMD3 of less than −26 dBc over wide offset frequencies ranging from 1 to 400 MHz. The 30-W-class GaN PA maintains a linear output power of over 36.3 dBm and an IMD3 of less than −27 dBc over wide offset frequencies of up to approximately 600 MHz. To the best of the authors’ knowledge, these PAs have a record output power level over a wide frequency range of 1–400 MHz or higher under the condition of a low IMD3 of less than −25 dBc, compared to previously reported Ku -band GaN PAs used for multi-carrier SatComs.

In this study, we investigate what types of cellulosic materials are formed by soaking the cellulose/ionic liquid (1-butyl-3-methylimidazolium chloride, BMIMCl) solutions in various organic liquids. When the 5-wt% cellulose/BMIMCl solutions were soaked in organic liquids with high and moderate polarities (relative permittivities), the corresponding cellulosic solutions and gels were produced, respectively. On the other hand, soaking the cellulose/BMIMCl solutions in lower polar liquids resulted in aggregation of cellulose in the mixtures. As the gels with high boiling point media were stable, they were characterized by viscoelastic and compression measurements. Contents of organic media and BMIMCl in the gels were changed depending on the polarities, which affected the mechanical properties under compression mode. Furthermore, processes for production of the solution, gel, and aggregate were proposed.

Herein, we report the fabrication of paperlike chitin sheets (chitin paper) by the extensive entanglement of self-assembled nanochitins formed using a bottom-up approach involving stepwise regenera...

We previously reported the preparation of a self-assembled chitin nanofiber (ChNF) film via regeneration from an ion gel with an ionic liquid, 1-allyl-3-methylimidazolium bromide using methanol, followed by sonication and filtration. In this study, the resulting ChNF film was cationized by partial deacetylation and subsequent dispersion in aqueous formic acid, which was then employed as a reinforcing agent for composition with xanthan gum. Xanthan gum hydrogels, which were obtained by exchanging disperse media from xanthan gum ion gels with an ionic liquid, 1-butyl-3-methylimidazolium chloride, were soaked in the cationic ChNF aqueous formic acid dispersions with different degrees of deacetylation (DDAs) to progress composition by ion exchange, to fabricate the ChNF-reinforced xanthan gum hydrogels. The presence of ChNFs in the hydrogels was evaluated by SEM measurement of the lyophilized samples from the hydrogels. The amounts of ChNFs in the hydrogels were depending on the DDA values. The compression testing of the hydrogels indicated the reinforcing effect of ChNFs, which were probably induced by electrostatic interaction owing to anionic nature of xanthan gum.

This study investigated Pickering emulsion polymerization of styrene using self-assembled chitin nanofibers (CNFs) as stabilizers to produce CNF-based composite particles, which were further converted into hollow particles. Previously, we reported that regeneration from a chitin/1‑allyl‑3‑methylimidazolium bromide ion gel using methanol fabricated self-assembled CNFs. Prior to the emulsion polymerization, CNFs were maleylated by reaction with maleic anhydride in the presence of perchloric acid. After styrene was added to a dispersion of the produced anionic CNFs in ammonia aq., a mixture was ultorasonicated to give an emulsion, in which styrene droplets were stably surrounded by CNFs. Radical polymerization was then conducted in the presence of potassium persulfate as an initiator to produce the composite particles. Particle sizes became smaller as the amounts of CNFs increased. The hollow particles were prepared by solubilizing out the polystyrene cores with toluene.

Herein, the synthesis of 6-deoxygenated α(1γ4)-oligoglucans via thermostable αglucan phosphorylase (from Aquifex aeolicus VF5)-catalyzed enzymatic chain-elongation is reported from a maltotriose primer using a non-native substrate, 6-deoxy-α-D-glucose 1- phosphate. The enzymatic reaction of the two substrates mainly produced a tetrasaccharide with one 6-deoxy-α-D-glucose unit at the non-reducing end, together with a minor pentasaccharide with two 6-deoxy-α-D-glucose units. The enzymatic chain-elongation from the primer in the presence of 6-deoxy-α-D-glucose 1-phosphate and a native substrate, α-D-glucose 1- phosphate, afforded 6-deoxygenated α(1γ4)-oligoglucans with varying degrees of polymerization. This enzymatic chain-elongation catalyzed by thermostable α-glucan phosphorylase is an efficient method to produce non-natural oligosaccharides, that is, 6-deoxygenated α(1γ4)- oligoglucans.

In this study, we investigate the Pickering emulsion polymerization of styrene using scaled-down chitin nanofibers (SD-ChNFs) as stabilizers to produce nanochitin/polystyrene composite particles. Prior to emulsion polymerization, an SD-ChNF aqueous dispersion was prepared by disintegrating bundles of the parent ChNFs with an upper hierarchical scale in aqueous acetic acid through ultrasonication. After styrene was added to the resulting dispersions, the mixtures at the desired weight ratios (SD-ChNFs to styrene = 0.1:1–1.4:1) were ultrasonicated to produce Pickering emulsions. Radical polymerization was then conducted in the presence of potassium persulfate as an initiator in the resulting emulsions to fabricate the composite particles. The results show that their average diameters decreased to a minimum of 84 nm as the weight ratios of SD-ChNFs to styrene increased. The IR and 1H-NMR spectra of the composite particle supported the presence of both chitin and polystyrene in the material.

In this study, we attempted to prepare an amylose-oligo[(R)-3-hydroxybutyrate] (ORHB) inclusion complex using a vine-twining polymerization approach. Our previous studies indicated that glucan phosphorylase (GP)-catalyzed enzymatic polymerization in the presence of appropriate hydrophobic guest polymers produces the corresponding amylose–polymer inclusion complexes, a process named vine-twining polymerization. When vine-twining polymerization was conducted in the presence of ORHB under general enzymatic polymerization conditions (45 °C), the enzymatically produced amylose did not undergo complexation with ORHB. However, using a maltotriose primer in the same polymerization system at 70 °C for 48 h to obtain water-soluble amylose, called single amylose, followed by cooling the system over 7 h to 45 °C, successfully induced the formation of the inclusion complex. Furthermore, enzymatic polymerization initiated from a longer primer under the same conditions induced the partial formation of the inclusion complex. The structures of the different products were analyzed by X-ray diffraction, 1H-NMR, and IR measurements. The mechanism of formation of the inclusion complexes discussed in the study is proposed based on the additional experimental results.

Based on our previous work on successful gelation of poly(2-methyl-2-oxazoline)-grafted chitin nanofibers (ChNFs) with high polar media, in this study, we investigated the preparation and gelation behaviors of the ChNFs having different poly(2-alkyl-2-oxazoline) graft chains, that is, poly(2-methyl-2-oxazoline), poly(2-isopropyl-2-oxazoline), and poly(2-butyl-2-oxazoline), with various disperse media. The grafting was carried out by reactions of living propagating ends of poly(2-alkyl-2-oxazoline)s with amino groups present on the self-assembled ChNFs, which were obtained from a chitin ion gel. The products formed gels in the reaction mixtures, which could be converted into hydrogels. All the products with the three poly(2-alkyl-2-oxazoline) graft chains formed gels with high polar media. Besides, gelation of the product with poly(2-butyl-2-oxazoline) was observed by immersing it in relatively non-polar media such as benzyl alcohol, ethyl acetate, and toluene. The formation process of network structures by the grafting of poly(2-alkyl-2-oxazoline)s on ChNFs is proposed to induce gelation of the products.

Polymer nanohybrid materials that consist of poly(vinyl alcohol) (PVA) and aluminosilicate nanofiber imogolite were prepared by effective dispersion of aluminosilicate nanofiber in a polymer matrix by an in situ synthetic method. The as-synthesized imogolite–PVA hybrid was characterized by infrared spectroscopy, wide angle X-ray diffraction and atomic force microscopic observations. The imogolite–PVA hybrid film was highly transparent compared with imogolite–PVA blend film, which was prepared by a solution blend of the freeze-dried imogolite powder with PVA. In addition, compared with PVA film, the hybrid films showed an increase in the elastic modulus and heat distortion temperature. These results indicate that in situ synthesis of imogolite in PVA solution successfully formed the polymer nanohybrid with finely-dispersed nanofillers.

In this study, chitin was nanofibrillated, cationized, and then used as a reinforcing agent for xanthan gum hydrogels. Amidinated chitin nanofibers (CNFs), which were prepared by partial deacetylation of the nanofibrillated chitin and the subsequent reaction of the generated amino groups with N,N-dimethylacetamide dimethyl acetal, were converted into an amidinium chitin bicarbonate with nanofiber morphology by CO2 gas bubbling and ultrasonic treatments in water. Xanthan gum hydrogels, which were prepared by exchange of disperse media from xantham gum ion gels with 1-butyl-3-methylimidazolium chloride, were then soaked in the resulting cationic CNF aqueous dispersions with different degrees of substitution (DSs) of amidinium groups to progress composition, giving rise to the CNF-reinforced xanthan gum hydrogels. The presence of CNFs in the hydrogels was confirmed by SEM measurement of the lyophilized samples. The amounts of CNFs in the hydrogels increased with increasing the DS values. The compression testing of the hydrogels suggested the reinforcing effect of CNFs, which were induced by electrostatic interaction owing to anionic nature of xanthan gum.

Amylose is a natural polysaccharide with helical conformation, which spontaneously forms water-insoluble assemblies, such as double helixes and inclusion complexes, at ambient temperatures in aqueous media, whereas it is synthesized as a water-soluble single chain by thermostable phosphorylase-catalyzed enzymatic polymerization at elevated temperatures in aqueous buffer solvents. In this study, we investigated the enzymatic polymerization at 80 °C using a primer-grafted poly(γ-glutamic acid) (PGA) in the presence or absence of poly(l-lactic acid) (PLLA) as a guest polymer for inclusion by amylose. Consequently, the produced amylose-grafted PGAs formed microparticles by cooling the mixtures at room temperature after the enzymatic polymerization in either the presence or the absence of PLLA. The particle sizes, which were evaluated by SEM measurement, were dependent on the feed ratios of PLLA. Based on the characterization results by the powder X-ray diffraction, IR, and dynamic light scattering measurements, a mechanism for the formation of the microparticles in the present system is proposed.

Based on the fact that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), efficiently dissolved α-chitin, this study investigated the development of facile acylation reactions of α-chitin in AMIMBr media. Under optimal conditions in the presence of pyridine and N,N-dimethyl-4-aminopyridine as base and catalyst, respectively, lauroylation of α-chitin smoothly took place using lauroyl chloride in AMIMBr at 100 °C for 24 h to produce a chitin laurate with a high degree of substitution (DS). Chitin acylates having different substituents were also synthesized by acylation of α-chitin using various acyl chlorides under the same conditions. In addition to IR analysis of the products, 1H NMR measurement was allowed for structure confirmation owing to the dissolution of the high DS derivatives in CDCl3/CF3CO2H mixed solvents.

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...

Double helix formation from the non-natural anionic and cationic amylose analog polysaccharides (amylouronic acid and amylosamine, respectively) was achieved through electrostatic interactions. A water-insoluble complex was obtained by simply mixing the two polysaccharides in water. The 1H NMR analysis indicated that the formation of the complexes with an approximately equimolar unit ratio from the two polysaccharides was resulted regardless of feed ratios for mixing. The powder X-ray diffraction (XRD) measurement suggested that the helix had larger sizes both in diameter and pitch compared with well-known amylose double helix. The formation of the double helical structure was also examined by theoretical calculations. The double helix models, differing in a chain polarity and a charge state of the residues, were constructed based on the 6-fold left-handed amylose chain of the A-amylose crystal structure. Molecular dynamics calculations indicated that those with an antiparallel chain polarity retained an intertwined form. The antiparallel double helical model with the free form residues was suggested to be the most likely structure for the non-natural polysaccharides.

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.

This research paper takes into account of three mineralogically different high calcium fly ashes (HCFA) consisted of anhydrite, generated in power plants in Ulaanbaatar, Mongolia. The purpose of this research is to understand how the morphology and mineralogy of HCFA influence the fresh and hardened properties of concrete; how pre-curing condition influences the long term strength development in different seasons; and to investigate the durability of HCFA concrete in extreme outdoor exposure conditions and freezing and thawing environment. Compressive strength development of fly ash concretes up to 540 days in extremely cold weather, strength dependence on pre-curing condition, freezing and thawing durability and the influence of ash mineralogy on durability were investigated. As a part of the investigation, the concrete specimens were kept outdoor at sub-zero temperature for more than four months. This paper concludes that strength approximately equal to that of the control can be obtained at early ages by 20 wt% replacement of total cementitious content by fly ash. When a comparison is made with equal mixtures, but equal pre-curing, winter concrete can only be achieved approximately 80% strength of autumn concrete after 3 months and then no considerable improvement happens even at one year. When a comparison is made with equal mixtures, but different pre-curing, the specimens exposed to the outdoor a day after placement show a permanent strength loss of 24%, with compare to the specimens cured in water at 20 °C for 28 days before exposing to the outdoor in winter. Durability factors of all fly ash incorporated concretes determined by freezing and thawing test were in the range of 78–91 at 300 cycles, satisfying the threshold in which concrete is likely to perform well.

Amylose, a natural polysaccharides, is a well-known functional material, because it forms double helix and inclusion complex assemblies depending on whether guest compounds are present or not, owing to its left-handed helical conformation. Amylose is precisely synthesized by phosphorylase-catalyzed enzymatic polymerization. In this study, we investigated the phosphorylase-catalyzed enzymatic polymerization initiated from maltoheptalose (primer for the polymerization)-grafted poly(γ-glutamic acid) in the presence of different feed ratios of a guest polymer, poly(e-caprolactone) (PCL). In the absence of PCL or presence of less amount of PCL, the reaction mixtures totally turned into hydrogel form, predominantly composed of amylose double helixes. On the other hand, aggregates, which were largely composed of amylose inclusion complexes, were formed in the reaction mixtures in the presence of larger amount of PCL. The analytical results indicated that double helix cross-linking points participated into the formation of larger network structure, whereas smaller network structure was fabricated from inclusion complex cross-linking points. These structures on molecular level hierarchically constructed different macroscopic network sizes, leading to difference in the material forms.

This study investigated the fabrication of a nanochitin film via the aggregation of scaled-down chitin nanofibers (SD-ChNFs). A self-assembled ChNF film, which was prepared by regeneration from a chitin/ionic liquid ion gel using methanol, followed by filtration, was treated with aqueous NaOH for deacetylation and subsequently disintegrated by cationization and electrostatic repulsion in 1.0 mol/L aqueous acetic acid with ultrasonication to give a SD-ChNF dispersion. Isolation of the SD-ChNFs via filtration of the dispersion resulted in a highly flexible self-assembled ChNF film that bent and twisted easily. The film exhibited superior mechanical properties compared to the parent self-assembled ChNF film, where the flexibility was further enhanced by the compositing the SD-ChNFs with an anionic polysaccharide, namely ι-carrageenan, via multi-point ionic cross-linking. These enhanced mechanical properties and efficient compositing properties were attributed to the scaling down of the ChNFs.

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. Finally, we utilize MD trajectory analysis to show that the solubility of microcrystalline cellulose is well correlated with the number of intermolecular hydrogen bonds in cellulose crystals. The obtained results allow us to conclude that both anions and cations of high-dissolving-power ILs contribute to the stepwise breakage of hydrogen bonds between cellulose chains, whereas this breakage does not occur to a sufficient extent in poorly solubilizing ILs.

In this study, we investigated chmemoenzymatic synthesis of amylose-grafted poly(γ-glutamic acid) (PGA) as a new artificial saccharide-peptide conjugate composed of two biological macromolecules. Maltooligosaccharide as a primer of enzymatic polymerization by phosphorylase catalysis was first introduced on the PGA main chain by the condensation reaction using the condensing agent in NaOH aq. Thermostable phosphorylase-catalyzed enzymatic polymerization of α-d-glucose 1-phosphate (G-1-P) as a monomer was then performed from the primer chain ends of the product to obtain amylose-grafted PGAs, which formed hydrogels in reaction media depending on the G-1-P/primer feed ratios. The powder X-ray diffraction patterns of lyophilized samples (cryogels) from the hydrogels suggested that the amylose graft chains formed double helixes, which acted as cross-inking points for self-assembling hydrogelation. The scanning electron microscopic images of the cryogels showed regularly controlled porous morphologies. Moreover, pore sizes of the cryogels increased with increasing the G-1-P/primer feed ratios, whereas the degrees of substitution of primer on the PGA main chain did not obviously affect pore sizes.

Chitin is an abundant organic resource but shows poor solubility, leading to difficulty in utilization as materials. We have already reported that an ionic liquid (IL), 1-allyl-3-methylimidazolium bromide, dissolves chitin at concentrations up to ca. 5 wt %. However, the color of the resulting solution is blackened, mainly owing to the presence of bromide. On the other hand, some deep eutectic solvents (DESs) have been already reported to dissolve chitin. In this study, we found that DESs composed of imidazolium ILs and thiourea dissolved chitin without obvious coloring. DESs are systems formed from eutectic mixtures of hydrogen bond accepters and donors. We first prepared DESs by heating mixtures of imidazolium ILs with thiourea at 100 &deg, C for 30 min with stirring. Predetermined amounts of chitin were then added to the DESs, and for the dissolution, the mixtures were left standing at room temperature for 24 h, followed by heating at 100 &deg, C for 24 h with stirring. The dissolution processes were evaluated by CCD camera views, which revealed in most cases the dissolution of chitin at 2&ndash, 5 wt % concentrations with the present DESs.

This study investigated the preparation of chitin-based fluorescent hollow particles by Pickering emulsion polymerization of styrene using bifunctional chitin nanofibers (ChNFs) as stabilizer, giving CNF-based composite particles, followed by solubilizing out inner polystyrene. In addition to the introduction of anionic maleyl groups on ChNFs to improve dispersibility in aqueous ammonia, polymerizable methacryl groups were substituted on ChNFs as second functionalization to provide ability in copolymerization with styrene for stabilization of hollow structures. Consequently, after the formation of styrene-in-water Pickering emulsion using the bifunctional ChNFs as stabilizer, radical polymerization was conducted in the presence of potassium persulfate as an initiator to produce the composite particles. The hollow particles were then fabricated by solubilizing out inner polystyrene with toluene, which stably dispersed in water. Encapsulation of a fluorescent dye, pyrene, into the cavity of the hollow particles was achieved by hydrophobic interaction with polystyrene present on the inner walls, which could be released by treatment of the resulting fluorescent hollow particles with surfactant, oleyl alcohol, in water. The same Pickering emulsion polymerization system was also performed in the presence of a pyrene derivative having a polymerizable group to obtain fluorescent composite/hollow particles with pyrene moieties covalently bound to polystyrene.

We have previously reported that re-dispersible amidinium chitin nanofibers are obtained from an amidinated chitin by CO2 gas bubbling with ultrasonic treatment in water. On the other hand, amylose is precisely synthesized by phosphorylase-catalyzed enzymatic polymerization. In this study, grafting of amylose on the amidinium chitin nanofibers was investigated by the phosphorylase-catalyzed enzymatic polymerization to produce amylose-grafted chitin nanofiber materials. Depending on the reaction conditions, the reaction mixtures turned into hydrogels. The hydrogels were constructed via the formation of double helixes from a part of amylose graft chains closely present among the nanofibers. Microstructures, which were hierarchically constructed by lyophilization of the hydrogels, were changed from network to porous morphologies in accordance with the molecular weights of amylose graft chains. Most of the amylose graft chains with higher molecular weights, which did not participate in double helixes, formed amorphous membranes in the nanofiber networks by lyophilization, to construct porous structures.

&alpha, Glucan phosphorylase catalyzes the enzymatic polymerization of &alpha, d-glucose 1-phosphate (Glc-1-P) monomers from a maltooligosaccharide primer to produce &alpha, (1&rarr, 4)-glucan&mdash, i.e., amylose. In this study, by exploiting the weak specificity for the substrate recognition of a thermostable &alpha, glucan phosphorylase (from Aquifex aeolicus VF5), we investigated the enzymatic copolymerization of 2-deoxy-&alpha, d-glucose 1-phosphate (dGlc-1-P), which was produced in situ from d-glucal, with Glc-1-P to obtain non-natural heteropolysaccharides composed of &alpha, 4)-linked dGlc/Glc units&mdash, i.e., partially 2-deoxygenated amylose. The reactions were carried out at different monomer feed ratios using a maltotriose primer at 40 &deg, C for 24 h. The products were precipitated from the reaction medium, isolated by centrifugation, and subjected to 1H NMR spectroscopic and powder X-ray diffraction measurements to evaluate their chemical and crystalline structures, respectively. Owing to its amorphous nature, the partially 2-deoxygenated amylose with adapted unit ratios formed a film when subjected to a casting method.

In this study, we found that a new artificial crystalline structure was fabricated from an amylose analog polysaccharide without hydroxy groups at the C-2 position, i.e., 2-deoxyamylose. The polysaccharide with a well-defined structure was synthesized by facile thermostable α-glucan phosphorylase-catalyzed enzymatic polymerization. Powder X-ray diffraction (XRD) analysis of the product indicated the formation of a specific crystalline structure that was completely different from the well-known double helix of the natural polysaccharide, amylose. Molecular dynamics simulations showed that the isolated chains of 2-deoxyamylose spontaneously assembled to a novel double helix based on building blocks with controlled hydrophobicity arising from pyranose ring stacking. The simulation results corresponded with the XRD patterns.

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 &alpha, 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(&gamma, glutamic acid) (PGA), in the presence of poly(&epsilon, 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.

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.

We previously found that the methanol-treatment of a chitin ion gel with an ionic liquid, 1-allyl-3-methylimidazolium bromide, for regeneration and subsequent filtration of a resulting self-assembled chitin nanofiber (CNF) dispersion gave a CNF film. In this study, we investigated a chemoenzymatic approach including enzymatic polymerization catalyzed by phosphorylase for the preparation of amylose-grafted CNF network materials. Maltoheptaose (Glc7) as the primer for the enzymatic polymerization was immobilized on the CNF film by reductive amination with amino groups, generated by the partial deacetylation of chitin molecules. The enzymatic polymerization of α-d-glucose 1-phosphate as a monomer catalyzed by phosphorylase was then conducted from the Glc7 chain ends on the CNFs dispersed in a sodium acetate aqueous buffer. The elongated amylose graft chains spontaneously constructed double helixes for cross-linking among CNFs to produce networks, resulting in a hydrogel. A robust cryogel was obtained by lyop...

In this article, we report the synthesis of a hyperbranched supramolecular polymer composed of continuum of amylose-poly( l -lactide) (PLLA) inclusion complexes by phosphorylase-catalyzed enzymatic polymerization using a branched maltoheptaose-PLLA conjugate according vine-twining polymerization manner. The X-ray diffraction and 1H NMR measurements indicated the presence of the inclusion complex structure in the product. The GPC peak of the amylose segment, which was obtained by alkaline hydrolysis of the vine-twining polymerization product, shifted to the lower molecular weight region, compared with that of the product, supporting the structure of the supramolecular polymer. A hydrogel of the supramolecular polymer was obtained through the formation of an ion gel with an ionic liquid. Furthermore, a cryogel with porous morphology was produced by lyophilization of the hydrogel.

In this study, we investigated the fabrication of porous chitins with continuous channel substructure by regeneration from gels with CaBr2·2H2O/methanol solution. After rapidly removing methanol from the gels, the products were immersed in methanol, followed by washing out CaBr2 with water and lyophilization to obtain regenerated chitins with inter-connected continuous pore morphology. Scanning electron microscopic results supported that the materials were consisted of continuous substructures of porous channels. The materials were further characterized by SEM-EDX and XRD measurements. The mechanical property and water absorbability were also evaluated. The plausible mechanism for the formation of the inter-connected pore morphology during the regeneration procedure was discussed.

In this study, we investigated the preparation of chitin nanofiber (CNF)-reinforced cellulose films through stepwise regeneration procedures from the respective ion gels with ionic liquids. Self-assembled CNF dispersions were prepared by regeneration from the chitin ion gel with the ionic liquid, 1-allyl-3-methylimidazolium bromide, using methanol, followed by dilution with adjusted amounts of methanol. Cellulose ion gels with the ionic liquid, 1-butyl-3-methylimidazolium chloride, were then prepared, soaked in the CNF dispersions, and centrifuged to simultaneously occur regeneration of cellulose and compatibilization with the CNFs. Soxhlet extraction with methanol and subsequent drying of the resulting materials gave the CNF/cellulose composite films. The IR and SEM results of the films indicated the presence of CNFs not only on the surfaces of the films but also inside the films. Powder X-ray diffraction patterns showed the amorphous structure of the cellulose in the film. Tensile testing of the films suggested the reinforcing effect of the CNFs on the mechanical properties of the films.

In this study, we prepared mutiformable functional supramolecular gels by vine-twining polymerization using poly(γ-glutamic acid-graft-e-caprolactone) (PGA-g-PCL) as a new guest polymer, with subsequent procedures of lyophilization and exchange of dispersion media. When the phosphorylase-catalyzed enzymatic polymerization of the monomer α-D-glucose 1-phosphate from a maltoheptaose primer was carried out in the presence of PGA-g-PCL according to the vine-twining polymerization method, a supramolecular hydrogel was obtained. The resulting hydrogel, purified by soaking in water, had the self-standing properties. Macroscopic interfacial healing was achieved by the formation of inclusion complexes at the interface between two hydrogel pieces through enzymatic polymerization. Cryogels were obtained by the lyophilization of the hydrogels; XRD analysis of the cryogel indicated the presence of inclusion complexes of amylose with PCL graft chains in intermolecular (PGA-g-PCL)s, which acted as cross-linking points for hydrogelation. Porous morphologies were seen in scanning electron micrographs of the cryogels. Furthermore, ion gels were fabricated by soaking the hydrogels in the ionic liquid of 1-butyl-3-methylimidazolium chloride. The mechanical properties of the cryo- and ion gels were evaluated by compressive and tensile testing, respectively.

We previously reported the preparation of a self-assembled chitin nanofiber (CNF) film via regeneration from an ion gel with an ionic liquid, followed by sonication and filtration. Based on the finding that CNFs were redispersed in a mixture of the film with ammonia aqueous solution (aq.), in this study, CNF-natural rubber (NR) composite sheets were fabricated by mixing redispersed CNF with NR latex stabilized by ammonia, followed by drying under reduced pressure. Tensile testing of the sheets indicated the reinforcing effect of CNFs. Further, CNF-NR composite porous materials were fabricated by evaporating ammonia from the CNF-NR dispersion, followed by lyophilization. The mechanism for the formation of porous structures was evaluated.

This paper reports the preparation of chitin nanofiber-graft-poly(2-hydroxyethyl acrylate) (CNF-g-polyHEA) films by surface-initiated atom transfer radical polymerization (ATRP) of HEA monomer from a CNF macroinitiator film. First, a CNF film was prepared by regeneration from a chitin ion gel with an ionic liquid. Then, acylation of the CNF surface with α-bromoisobutyryl bromide was carried out to obtain the CNF macroinitiator film having the initiating moieties (α-bromoisobutyrate group). The surface-initiated graft polymerization of HEA from the CNF macroinitiator film by ATRP was performed to produce the CNF-g-polyHEA film. The IR, XRD, and SEM measurements of the resulting film indicated the progress of the graft polymerization of HEA on surface of CNFs. The molecular weights of the grafted polyHEAs increased with prolonged polymerization times, which affected the mechanical properties of the films under tensile mode.

In this paper, we report that nanofiber network structures were constructed from chitin derivatives by gas bubbling and ultrasonic treatments in water. When chitin was first subjected to N2 gas bubbling with ultrasonication in water, the SEM images of the product showed nanofiber network morphology. However, nanofiber network was not re-constructed by the same N2 gas bubbling and ultrasonic treatments after agglomeration. We then have paid attention to an amidine group to provide the agglomeration-nanofibrillation behavior of chitin derivatives. An amidinated chitin was synthesized by the reaction of the amino groups in a partially deacetylated chitin with N,N-dimethylacetamide dimethyl acetal, which was subjected to CO2 gas bubbling and ultrasonic treatments in water to convert into an amidinium chitin by protonation. The SEM images of the product clearly showed nanofiber network morphology. We further examined re-nanofibrillation of the agglomerated material, which was obtained by mixing the nanofibrillated amidinium chitin with water, followed by drying under reduced pressure. Consequently, the material was re-nanofibrillated by N2 gas bubbling with ultrasonication in water owing to electrostatic repulsion between the amidinium groups. Furthermore, deprotonation of the amidinium chitin and re-protonation of the resulting amidinated chitin were conducted by alkaline treatment and CO2 gas bubbling-ultrasonic treatments, respectively. The material showed the agglomeration-nanofibrillation behavior during the processes.

In this paper, we report acetylation of xanthan gum using acetic anhydride in an ionic liquid solvent, 1-butyl-3-methylimidazolium chloride (BMIMCl). Xanthan gum was dissolved with BMIMCl [2 % (w/w)] and the reaction was carried out in the presence of acetic anhydride (five equiv. for hydroxy groups in a repeating unit) with stirring the solution at elevated temperatures. The structures of xanthan gum acetates were confirmed by the 1H NMR and IR spectra. The degree of acetylation (DA) values determined by the 1H NMR analysis increased with the higher reaction temperatures. The thermal gravimetric analysis (TGA) indicated the enhancement of thermal stability by acetylation. Furthermore, the TGA as well as differential scanning calorimetric (DSC) analysis of the products suggested the presence of the highly and less acetylated segments in a xanthan gum chain. The DSC profile of the product with the high DA value also exhibited a small endothermic peak, which might potentially be ascribed to the melting temperature.

This article reports the enzymatic synthesis of dendritic amphoteric α-glucans having both glucuronic acid and glucosamine residues at the non-reducing ends by thermostable phosphorylase-catalyzed successive glucuronylation and glucosaminylation of a glucan dendrimer having α-(1 → 4)-glucan non-reducing ends using α-D-glucuronic acid 1-phosphate and α-D-glucosamine 1-phosphate as glycosyl donors, respectively. The structure of the products is confirmed by the (1)H NMR analysis. The products exhibit inherent isoelectric points (pIs) determined by the ζ-potential measurement. These materials self-assemble in water at pH = pI to form large aggregates, but disassemble at pH shifted from pI.

In this study, we have performed the preparation of reswellable amorphous porous celluloses through regeneration from hydrogels. The cellulose hydrogels were first prepared from solutions with an ionic liquid, 1-butyl-3-methylimidazolium chloride (BMIMCl), in different concentrations. Lyophilization of the hydrogels efficiently produced the regenerated celluloses. The powder X-ray diffraction and scanning electron microscopic measurements of the products suggest an amorphous structure and porous morphology, respectively. Furthermore, the pore sizes of the regenerated celluloses, or in turn, the network sizes of cellulose chains in the hydrogels, were dependent on the concentrations of the initially prepared solutions with BMIMCl, which also affected the tensile mechanical properties. It was suggested that the dissolution states of the cellulose chains in the solutions were different, in accordance with the concentrations, which representatively dominated the pore and network sizes of the above materials. When the porous celluloses were immersed in water, reswelling was observed to regenerate the hydrogels.