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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.

Herein, we report that chitin hexanoate-graft-poly(ε-caprolactone) (ChHex-g-PCL) is thermoplastic, as confirmed by the formation of a melt-pressed film. Chitin hexanoates with degrees of substitution (DSs) of 1.4-1.8 and bearing free hydroxy groups were first prepared by the hexanoylation of chitin using adjusted feed equivalents of hexanoyl chloride in the presence of pyridine and N,N-dimethyl-4-aminopyridine in 1-allyl-3-methylimidazolium bromide, an ionic liquid. Surface-initiated ring-opening graft polymerization of ε-caprolactone from the hydroxy groups of the chitin hexanoates was conducted in the presence of tin(II) 2-ethylhexanoate as the catalyst at 100 °C to produce (ChHex-g-PCL)s. The feed equivalent of the catalyst, reaction time, and DS value were found to affect the molar substitution and degree of polymerization of the PCL graft chains. Longer PCL graft chains formed their crystalline structures and the (ChHex-g-PCL)s largely contained uncrystallized chitin chains. Accordingly, these (ChHex-g-PCL)s exhibited melting points associated with the PCL graft chains, leading to thermoplasticity.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

The self-assembling properties of the 6-O- and 6′-O-alkylsucrose mixtures with different chain lengths including octyl, decyl, dodecyl, and tetradecyl under aqueous conditions were studied and compared with those of the 6-O- and 6′-O-hexadecylsucrose mixture previously reported. The title compounds were synthesized from sucrose in five steps. The results of scanning and transmission electron microscopes, powder X-ray diffraction, and dynamic light scattering measurements indicated that the self-assembling properties of octyl, decyl, and dodecyl derivatives were completely different from those of the 6-O- and 6′-O-hexadecylsucrose mixture. The three derivatives reported here primarily formed lamellar planes, which further induced the formation of vesicle-type particles under aqueous conditions, whereas the previous derivatives primarily formed spherical micelles in water, which further assembled according to face-centered cubic organization by a drying process from the aqueous dispersion. It was also found that the 6-O- and 6′-O-tetradecylsucrose mixture showed concentration-induced micelle-lamellar transition behavior in an aqueous dispersion. Furthermore, the mixing of a regioisomer, 6′-O-hexadecylsucrose, with 6-O-hexadecylsucrose induced different self-assembling properties from that of 6-O-hexadecylsucrose alone, but this effect did not appear in the self-assembling of the 6-O- and 6′-O-octylsucrose mixture.

In this paper, we report atom transfer radical polymerization of N -isopropylacrylamide (NIPAAm) by an enzyme mimetic catalyst, that is, hematin of a ferriprotoporphyrin complex. The hematin-catalyzed polymerization of NIPAAm was carried out in the presence of an alkyl halide as an initiator and a reducing agent in DMF/H 2 O solvent. The reaction proceeded at room temperature and the M n s increased with increasing monomer conversions. The M n values were relatively close to the theoretical ones. The reaction did not take place in the absence of any one of the initiator, catalyst, and reducing agent. The 1 H NMR spectrum of the low molecular weight polyNIPAAm indicated the presence of the moieties from the initiator at the polymer ends. These results suggested that the reaction was initiated from radical species, which were produced by bromide abstraction from the initiator by the reduced catalyst.

The detailed action mechanism of dextrin dextranase (EC 2.4.1.2, DDase) from Acetobacter capsulatus ATCC 11894 was investigated. DDase catalyzed the transglucosylation action of the non-reducing terminal glucosyl residue of a donor substrate, and three transglucosylation modes were recognized; (1) transfer of an α-1,4 linked glucosyl residue forming an α-1,6 linkage, (2) transfer of an α-1,4 linked glucosyl residue forming an α-1,4 linkage, (3) transfer of an α-1,6 linked glucosyl residue forming an α-1,6 linkage. From these results, the action of DDase was considered to transfer α-1,4 or α-1,6 linked glucosyl residues at non-reducing termini of oligosaccharides to glucose molecules or glucosyl residues at non-reducing termini of other oligosaccharides forming α-1,4 or α-1,6 linkages. As the α-1,6 linked terminal glucosyl residues were less reactive than α-1,4linked terminal glucosyl residues, DDase accumulated the α-1,6linked glucosyl residues, which is dextran.

α-Glucan phosphorylase catalyzes enzymatic polymerization of α- d -glucose 1-phosphate (Glc-1-P) as a monomer from a maltooligosaccharide primer to produce α(1→4)-glucan, i.e., amylose, with liberating inorganic phosphate (Pi). Because of quite weak specificity for the recognition of substrates by thermostable α-glucan phosphorylase (from Aquifex aeolicus VF5), in this study, we investigated the enzymatic copolymerization of Glc-1-P with its analogue monomer, α- d -mannose 1-phosphate (Man-1-P) under the conditions for removal of Pi as the precipitate with ammonium and magnesium in ammonia buffer containing Mg2+ ion to produce α(1→4)-linked non-natural mannoglucans composed of Glc/Man units. The reaction was conducted in different feed ratios using the maltotriose primer at 40 °C for 7 days. The MALDI-TOF mass and 1H NMR spectra of the products fully supported the mannoglucan structures.

This paper reports the synthesis and self-assembling properties of 6-O-hexadecyl- and 6-O-octylsucroses. Mono-etherification of 2,3,4,1′,3′,4′-hexa-O-benzylsucrose with the corresponding alkyl bromides predominantly took place at the glucose 6-position and the products were isolated by silica gel column chromatography. Benzyl groups in the isolated products were cleaved to yield the target derivatives. The SEM, TEM, XRD, and DLS results indicated that 6-O-alkylsucroses formed vesicle-type particles via formation of lamellar-like planes under aqueous conditions, which were further merged by fusion of the planes to construct larger aggregates. The self-assembling properties of the materials were different from those of the previously reported 6-O- and 6’-O-hexadecylsucroses mixture.

This paper reports the preparation of chitin nanofiber-graft-poly( l -lactide-co-e-caprolactone) films by surface-initiated ring-opening graft copolymerization of l -lactide (LA)/e-caprolactone (CL) monomers from chitin nanofiber films. First, the chitin nanofiber film was prepared according to our previous method. Then, the film was immersed in water and lyophilized for pre-treatment. The non-treated or pre-treated film was immersed in a solution of LA/CL in toluene for 12 h. After tin(II)-2-ethylhexanoate as a polymerization catalyst was added to the mixture, which was heated at 80 °C for 48 h for the progress of copolymerization, the resulting film was washed and further subjected to Soxhlet extraction with chloroform. The IR spectrum of the obtained film exhibited carbonyl absorption at 1739 cm−1 due to the ester linkage of poly(LA-co-CL), suggesting the presence of poly(LA-co-CL). The powder X-ray diffraction and SEM measurements of the obtained film indicated that the graft copolymerization of LA/CL was initiated from hydroxy groups on surface of the chitin nanofibers. The mechanical properties of the films, which were evaluated by tensile testing, were affected by the amounts and the LA/CL composition ratios of the grafted polyesters.

In this study, we report the self-assembling properties of 6-O-alkyltrehaloses with different chain lengths, that is, octyl, decyl, dodecyl, tetradecyl, and hexadecyl, under aqueous conditions. The materials were synthesized from trehalose via five reaction steps. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and dynamic light scattering (DLS) measurements indicated that the self-assembling property of 6-O-dodecyltrehalose was completely different from that of the other derivatives. The former primarily formed spherical micelles in water, which further assembled into face-centered cubic-based aggregates when dried. The latter derivatives, on the other hand, formed vesicle-type particles via the formation of lamellar-like planes, which further merged with each other, most likely by the fusion of the planes, to construct larger aggregates.

Poly(spiropyran)s were synthesized by polycondensation of a bis(indoline) monomer with bis( o -positioned formyl and hydroxy)-substituted aromatic monomers in alcoholic solvents. The structures of the products and their molecular weights were determined by the 1 H NMR and GPC measurements, respectively. Furthermore, photoisomerization behaviors of the poly(spiropyran)s were analyzed by the UV–Vis and 1 H NMR measurements of their solutions in dichloromethane upon the UV and visible light irradiations.

This paper reports the chemoenzymatic synthesis of an amylose-grafted xanthan gum. An amine-functionalized maltooligosaccharide was chemically introduced to xanthan gum by condensation with its carboxylates using a condensing agent to produce a maltooligosaccharide-grafted xanthan gum. Then, a phosphorylase-catalyzed enzymatic polymerization of glucose 1-phosphate from the graft chain ends on the xanthan gum derivative was performed, giving an amylose-grafted xanthan gum. Furthermore, the product formed a gel with an ionic liquid, which was converted into a hydrogel with high water content by replacement of the ionic liquid with water. The ionically cross-linked hydrogel was also provided by soaking the primary formed hydrogel in FeCl 3 aqueous solution. The mechanical properties of the resulting hydrogels were evaluated by compressive testing.

We report here a reversible self-assembly formation system using block copolymers with thermo-tunable properties. A series of double-responsive block copolymers, poly(N-isopropylacrylamide (NIPAAm))-block-poly(NIPAAm-co-N-(isobutoxymethyl)acrylamide (BMAAm)) with two lower critical solution temperatures were synthesized by one-pot atom transfer radical polymerization via sequential monomer addition. When dissolved in aqueous solution at room temperature, the block copolymers remained unimeric. Upon heating above room temperature, the block copolymers self-assembled into micellar structures. The micelle formation temperature and the resulting diameter were controlled by varying the BMAAm content. 1H Nuclear Magnetic Resonance, dynamic light scattering, field-emission scanning electron microscopy, and fluorescence spectra revealed the presence of a monodisperse nanoassembly, and demonstrated the assembly formation/inversion process was fully reversible. Moreover, a model hydrophobic molecule, pyrene, was successfully loaded into the micelle core by including pyrene in the original polymer solution. Further heating resulted in mesoscopic micelle aggregation and precipitation. This dual micelle and aggregation system will find utility in drug delivery applications as a thermal trigger permits both aqueous loading of hydrophobic drugs and their subsequent release. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

In this thesis, we studied the convenient synthesis and characterizations of thermo-responsive materials with double response. To achieve these, AB-type diblock copolymers comprising of poly(N-isopropylacrylamide) (NIPAAm) segment and poly(NIPAAm-co-(N-(hydroxymethyl)acrylamide) (HMAAm)) one were designed. That was synthesized in one-pot using an atom transfer radical polymerization (ATRP) technique. Poly(NIPAAm-co-HMAAm)s synthesized separately showed sensitive thermo-response and the cloud point was completely tunable by the composition of HMAAm. As expected, the block copolymers exhibited double thermo-responsive profiles in aqueous solution. The responsive behavior was discussed by precise trace by 1H NMR and turbidity measurements. From these results, we could confirm almost independent dehydration of each segment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6142–6150, 2008

This paper reports an investigation of enzymatic phosphorolysis of α(1→4)- linked oligo-d-glucosaminide substrates by thermo stable α-glucan phosphorylase (from Aquifex aeolicus VF5) catalysis. α-Glucan phosphorylase catalyzes both phosphorolysis and glucosylation/polymerization at the nonreducing end of α(1→4)-linked glucose substrates depending on conditions. The authors also found that α(1→4)-linked d-glucosaminide polymer (chitosan stereoisomer) was obtained by the thermostable α-glucan phosphorylase-catalyzed enzymatic polymerization of α-d-glucosamine 1-phosphate from a maltooligosaccharide primer. In the present study, we intend to reveal whether the enzyme catalyzes phosphorolysis of substrates containing such d-glucosaminide chains. The α(1→4)-linked oligo-d-glucosaminide substrates elongated from maltotriose were first prepared by the thermostable α-glucan phosphorylase-catalyzed enzymatic polymerization of α-d-glucosamine 1-phosphate from the maltotriose primer and subsequent purification by preparative HPLC. The phosphorolysis of the resulting substrates are conducted in the presence of thermostable α-glucan phosphorylase in phosphate buffer. The analytical results of the products fully supported the occurrence of phosphorolysis at the nonreducing end of both the chains of d-glucosamine-α(1→4)-d-glucosamine and d-glucosamine-α(1→4)-d-glucose sequences.

The effects of the aspect ratio of multi-walled carbon nanotubes (MWNTs) on the rheology and flammability of polystyrene/MWNT nanocomposites are studied using two MWNTs having average aspect ratios (length to outer diameter) of 49 and 150. Dynamic rheological experiments show that the particles with the larger aspect ratio impart much higher storage moduli and complex viscosities to the nanocomposites compared to equivalent mass loadings of particles with the smaller aspect ratio. Additionally, in flammability experiments, the larger aspect ratio particles lead to a greater reduction in mass loss rate, i.e., they are more effective at reducing flammability. These results demonstrate that the aspect ratio of MWNTs is a key parameter in controlling the rheology and flammability of polymer nanocomposites.

Particle spatial dispersion is a crucial characteristic of polymer composite materials and this property is recognized as especially important in nanocomposite materials due to the general tendency of nanoparticles to aggregate under processing conditions. We introduce dispersion metrics along with a specified dispersion scale over which material homogeneity is measured and consider how the dispersion metrics correlate quantitatively with the variation of basic nanocomposite properties. We then address the general problem of quantifying nanoparticle spatial dispersion in model nanocomposites of single-walled carbon nanotubes (SWNTs) dispersed in poly(methyl methacrylate) (PMMA) at a fixed SWNT concentration of 0.5% using a ‘coagulation’ fabrication method. Two methods are utilized to measure dispersion, UV–vis spectroscopy and optical confocal microscopy. Quantitative spatial dispersion levels were obtained through image analysis to obtain a ‘relative dispersion index’ (RDI) representing the uniformity of the dispersion of SWNTs in the samples and through absorbance. We find that the storage modulus, electrical conductivity, and flammability property of the nanocomposites correlate well with the RDI. For the nanocomposites containing the same amount of SWNTs, the relationships between the quantified dispersion levels and physical properties show about four orders of magnitude variation in storage modulus, almost eight orders of magnitude variation in electric conductivity, and about 70% reduction in peak mass loss rate at the highest dispersion level used in this study. The observation of such a profound effect of SWNT dispersion indicates the need for objective dispersion metrics for correlating and understanding how the properties of nanocomposites are determined by the concentration, shape and size of the nanotubes.

The adsorption of proteins on poly(2-hydroxyethyl methacrylate) (PHEMA) brushes was systematically studied by quartz crystal microbalance (QCM) and fluorescence microscopy as a function of graft density and protein size. The graft density σ (chains/nm2) ranged from 0.007 (dilute or semidilute brush regime) to 0.7 (concentrated brush regime), and the protein size ranged from 2 to 13 nm in an effective diameter. The lowest-density brush (σ = 0.007) adsorbed all the tested four proteins, while the highest-density brush (σ = 0.7) adsorbed none of them. The middle-density brush (σ = 0.06) showed an intermediate behavior, adsorbing the smallest two proteins but effectively repelling the largest two. PHEMA cast films adsorbed a probe protein with the adsorbed amount increasing approximately proportionally to the film thickness, indicating that the adsorption mainly occurred in the bulk of the film. The noted results for the brushes support the idea of size-exclusion effect, an effect characteristic of concentrat...

Novel photo-cross-linkable polymers were synthesized for the preparation of the hydrogels with both pH- and temperature-responsive properties. Photo-reactive 4-aminobenzophenone (BP) was introduced into the side groups of poly(N-isopropyl-acrylamide-co-2-carboxyisopropylacrylamide). This starting copolymer was designed for the highly random sequences of comonomers. The introduction degree of BP was controlled by changing the ratio between the BP and the carboxyl groups. The cylinder-shaped hydrogel was easily prepared by UV irradiation for a few minutes. The photo-cross-linked hydrogels exhibited clear volume phase transitions in response to both pH and temperature changes and expected to be used for drug delivery systems.

Novel polymer nanohybrid was prepared by free radical polymerization of methyl methacrylate in the presence of inorganic nanofiber ‘imogolite’ as reinforcing nanofiller. Imogolite is a hydrous aluminosilicate with a unique nanofiber structure. The surface of imogolite was modified with 2-acidphosphoxyethyl methacrylate, which has a polymerizable methacrylate group and a phosphoric acid moiety, before preparation of polymer hybrid. The polymer nanohybrid was prepared by free radical polymerization in the presence of surface modified imogolite. The mechanical properties of (PMMA/modified imogolite) hybrid with the modified imogolite were improved in comparison with those of PMMA and (PMMA/unmodified imogolite) blend. Furthermore, the hybrid film prepared from the surface modified imogolite kept the transparency similar to PMMA film. These results indicate the usefulness of the surface modification method with phosphoric acid groups and imogolite nanofibers as a reinforcing material.

A well-defined, high-density poly(2-hydroxyethyl methacrylate) (PHEMA) brush was fabricated on the surface of a poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film by surface-initiated living radical polymerization (LRP). First, a sufficient amount of peroxides as initiating moieties were successfully introduced on the film surface without causing etching by the O2-plasma treatment. Subsequently, the polymerization mediated by reversible addition−fragmentation chain transfer (RAFT) was carried out at a mild temperature in a nonsolvent for FEP to minimize the swelling of the FEP film surface and avoid the growth of chains from deep inside of the film. The contact angle and ESCA measurements indicated that the boundary intermixing layer between FEP and PHEMA layers was reasonably thin (≤10 nm), meaning that the PHEMA brush was grown nearly regioselectively from the surface of the FEP film. The graft density was estimated to be about 0.3 chains/nm2, which is almost the same as the one achievable by t...

Polymer-grafted magnetite (Fe3O4) nanoparticles (diameter about 10 nm) were prepared through a direct polymer grafting reaction from their surfaces. The chemisorbed initiator (TEMPO-based alkoxyamine) for nitroxide-mediated radical polymerization with a phosphoric acid group gave controlled polystyrene (PS) and poly(3-vinylpyridine) (P3VP) graft layers on the surface. The graft densities of polymers on the surfaces of magnetite particles were estimated at 0.12−0.20 chains/nm2 by thermogravimetric analysis (TGA). The improvement in the dispersibility of PS-modified magnetite in good solvents was verified by ultraviolet−visible (UV−vis) absorption spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). In the case of P3VP-modified magnetite, the particles were stably dispersed in good solvents, by protonation, in acid solution, and by quarternization with iodomethane, in neutral aqueous solution. The magnetic response of the polymer-grafted magnetite against an external mag...

Free radical copolymerization of water-soluble N-vinylamides such as N-vinylacetamide (NVA) and N-vinylformamide (NVF) with hydrophobic vinyl acetate (VAc) gave amphiphilic copolymers. The monomer reactivity ratios were determined as r 1 = 5.8 and r 2 = 0.68 (M 1 = NVA, M 2 = VAc) and r 1 = 6.2 and r 2 = 0.37 (M 1 = NVF, M 2 = VAc), respectively. The growing radical of the terminals of N-vinylamides propagates more favorably for N-vinylamide monomers than for VAc monomer, resulting in the possible formation of blocky copolymers. It is found that aqueous solutions of these amphiphilic copymers exhibited a lower critical solution temperature (LCST), depending on their chemical composition, followed by coacervate formation above the LCST. Furthermore, thermosensitive hydrogels could be prepared by the free radical copolymerization of N-vinylamide and VAc in the presence of the crosslinker butylenebis(N-vinylacetamide) (Bis-NVA). The swelling ratios of these hydrogels decreased with an immediate increase in temperature from 20 to 80°C, and then reversibly increased with decreasing temperature. These hydrogels showed the same thermosensitive properties as linear copolymers of NVF and VAc.

The relationship between two aminopolysaccharide stereoisomers, namely α-(1→4)- and β-(1→4)-linked (N-acetyl)-D-glucosamine polymers, is of significant interest within the field of polysaccharide science, as they correspond to amino analogs of the representative abundant natural polysaccharides, viz. amylose and cellulose. While the latter glucosamine polymer is the basis of well-known natural polysaccharides, chitin and chitosan (linear polysaccharides composed of β-(1→4)-linked N-acetyl-D-glucosamine and D-glucosamine), to the best of our knowledge, the former (α-(1→4)-linked) has not been observed in nature. For the purpose of these studies, the synthesis of such non-natural aminopolysaccharides was performed by the thermostable α-glucan phosphorylase (from Aquifex aeolicus VF5)-catalyzed enzymatic polymerization of α-D-glucosamine 1-phosphate (GlcN-1-P), via successive α-glucosaminylations, in ammonia buffer containing Mg(2+) ions, resulting in the production of the α-(1→4)-linked D-glucosamine polymers, corresponding to the structure of the chitosan stereoisomer. Subsequent N-acetylation of the products gave the aminopolysaccharides, corresponding to the chitin stereoisomer.

Thermoresponsive ultrathin hydrogels were prepared by the sequential chemical reaction of poly(vinylamine-co-N-vinylisobutyramide) [poly(VAm-co-NVIBA)] and poly(acrylic acid) (polyAAc) on a gold surface. The carboxyl group of polyAAc was activated by 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC) for the reaction with the amino group of poly(VAm-co-NVIBA) to yield the amide linkage. This stepwise assembly was analyzed quantitatively by a quartz crystal microbalance (QCM), which revealed that the 39 mol % VAm content of poly(VAm-co-NVIBA) was suitable for the preparation of ultrathin hydrogels. A detailed analysis was performed by the assembly of poly(VAm-co-NVIBA), with a 39 mol % VAm content and polyAAc. The reflection−absorption spectra (RAS) showed the presence of both polymers in the assembly. Atomic force microscopic (AFM) observations confirmed the hydrogel structure of the assembly; the thickness of the hydrogel in an aqueous medium (around 320 nm) was 2 times greater than that...

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

The thermoresponsive and pH-responsive intelligent copolymers of N-vinylformamide (NVF) and N-vinylisobutyramide (NVIBA), and their derivatives with primary amino groups, were synthesized. Hydrolys...

In this study, we synthesized an amphiphilic polyhedral oligomeric silsesquioxane (POSS) having controlled numbers of hydrophilic and fluorescent hydrophobic groups (seven and one, respectively) by...

Colloidal platinum nanoparticles in the size range of 5–35 A have been successfully prepared in water at room temperature by NaBH4 reduction of ionic platinum in the presence of poly[(vinylamine)-co-(N-vinylisobutyramide)] (PVAm-co-PNVIBA). To our knowledge, the temperature- and pH-responsive copolymer was used for the first time as the stabilizer of colloidal metal particles. Three PVAm-co-PNVIBA copolymers with PVAm contents of 4.1, 8.3, and 19.8 mol-% were examined. The particle size and morphology of the platinum colloids varied with the copolymer composition, as confirmed by TEM measurements. The polymer-stabilized Pt nanoparticles precipitated on heating above their critical flocculation temperatures (CFTs), which were strongly dependent on the solution pH and the copolymer composition. The CFTs were 0.2–1.6°C lower than the lower critical solution temperatures (LCSTs) of the copolymers free in water and the differences increased with increasing PVAm content. The catalytic activity of the Pt nanoparticles was investigated in the aqueous hydrogenation of allyl alcohol. It was found that the activity was regulated through temperature- and pH-induced phase separation. The PVAm content also strongly effected the catalytic activity and the morphology of phase separated catalysts. With a PVAm content of 4.1 mol-%, the colloidal platinum sol reversibly changed its catalytic activity with changes in temperature.