Architecture of amylose supramolecules in form of inclusion complexes by phosphorylase-catalyzed enzymatic polymerization

Fabrication of Nanostructured Supramolecules through Helical Inclusion of Amylose toward Hydrophobic Polyester Guests, Biomimetically through Vine-Twining Polymerization Process

This review article presents the biomimetic helical inclusion of amylose toward hydrophobic polyesters as guests through a vine-twining polymerization process, which has been performed in the glucan phosphorylase (GP)-catalyzed enzymatic polymerization field to fabricate supramolecules and other nanostructured materials. Amylose, which is a representative abundant glucose polymer (polysaccharide) with left-handed helical conformation, is well known to include a number of hydrophobic guest molecules with suitable geometry and size in its cavity to construct helical inclusion complexes. Pure amylose is prepared through enzymatic polymerization of α-d-glucose 1-phosphate as a monomer using a maltooligosaccharide as a primer, catalyzed by GP. It is reported that the elongated amylosic chain at the nonreducing end in enzymatic polymerization twines around guest polymers with suitable structures and moderate hydrophobicity, which is dispersed in aqueous polymerization media, to form amylosic nanostructured inclusion complexes. As the image of this system is similar to how vines of a plant grow around a support rod, this polymerization has been named 'vine-twining polymerization'. In particular, the helical inclusion behavior of the enzymatically produced amylose toward hydrophobic polyesters depending on their structures, e.g., chain lengths and substituents, has been systematically investigated in the vine-twining polymerization field. Furthermore, amylosic supramolecular network materials, such as hydrogels, are fabricated through vine-twining polymerization by using copolymers, where hydrophobic polyester guests or maltooligosaccharide primers are covalently modified on hydrophilic main-chain polymers. The vine-twining polymerization using such copolymers in the appropriate systems induces the formation of amylosic nanostructured inclusion complexes among them, which act as cross-linking points, giving rise to supramolecular networks at the nanoscale. The resulting materials form supramolecular hydrogels, films, and microparticles.

Short-chain glucan self-assembly for green synthesis of functional biomaterials: Mechanism, synthesis, and microstructural control

Short-chain glucan (SCG) is a linear homopolymer containing 10 to 50 glucose units linked with α(1,4) glycosidic bonds. With its abundant, low-cost, nontoxic, biodegradable/biocompatible nature, self-assembled SCG particles (SSC) have emerged as functional biomaterials, which have recently attracted tremendous attentions in various fields. SCG self-assembly occurs through the spontaneous association of molecules under equilibrium conditions into stable and structurally well-defined nanoscale or micrometer-scale aggregates, which is governed by various intermolecular non-covalent interactions, including hydrogen-bonding, electrostatic, hydrophobic, and van der Waals. With precise and effective control of the self-assembly process of SSC, its structural modulation and function integration can be expected. Thus, we convinced that SCG self-assembly could provide an effective means of developing starch-based functional biomaterials with beneficial health properties and wide application in food industries. In this review, we provide an overview of recent advances in the green approach for the self-assembly of SSC, as well as the influence of thermodynamic and kinetic factors on its morphology and physicochemical properties. We highlight recent contributions to developing strategies for the construction of SSC with increasing complexity and functionality that are suitable for a variety of food applications. Finally, we briefly outline our perspectives and discuss the challenges in the field.

Vine-Twining Inclusion Behavior of Amylose towards Hydrophobic Polyester, Poly(β-propiolactone), in Glucan Phosphorylase-Catalyzed Enzymatic Polymerization

This study investigates inclusion behavior of amylose towards, poly(β-propiolactone) (PPL), that is a hydrophobic polyester, via the vine-twining process in glucan phosphorylase (GP, isolated from thermophilic bacteria, Aquifex aeolicus VF5)-catalyzed enzymatic polymerization. As a result of poor dispersibility of PPL in sodium acetate buffer, the enzymatically produced amylose by GP catalysis incompletely included PPL in the buffer media under the general vine-twining polymerization conditions. Alternatively, we employed an ethyl acetate-sodium acetate buffer emulsion system with dispersing PPL as the media for vine-twining polymerization. Accordingly, the GP (from thermophilic bacteria)-catalyzed enzymatic polymerization of an α-d-glucose 1-phosphate monomer from a maltoheptaose primer was performed at 50 °C for 48 h in the prepared emulsion to efficiently form the inclusion complex. The powder X-ray diffraction profile of the precipitated product suggested that the amylose-PPL inclusion complex was mostly produced in the above system. The ¹H NMR spectrum of the product also supported the inclusion complex structure, where a calculation based on an integrated ratio of signals indicated an almost perfect inclusion of PPL in the amylosic cavity. The prevention of crystallization of PPL in the product was suggested by IR analysis, because it was surrounded by the amylosic chains due to the inclusion complex structure.

Preparation of Amylose-Oligo[(R)-3-hydroxybutyrate] Inclusion Complex by Vine-Twining Polymerization

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.

Migration of surrogate contaminants from paperboard to foods: Effect of food and surrogate properties

The current research describes an alternative test method to evaluate the impact of food properties and compound characteristics on migration from paperboard to food. Tightly sealed bottles containing paperboard spiked with surrogate components as a donor, together with modified polyphenylene oxide (MPPO or Tenax®) or one of the nine considered foods as a receptor, were stored at 22°C. Instead of analysing the receptor, migration from donor to receptor was followed up by evaluating the recovery of surrogates from the donor over time, thus avoiding challenges in the analysis of the foods as such. Free fat content affected the migration more than the specific surface area of the food, reaching a plateau at fat contents >8.1%. The highest migration was observed to fatty foods such as biscuits (8% to 25% fat) and chocolate (40% fat). Intermediate migration occurred to starchy and particulate foods such as egg-based wheat pasta (2.6% fat), wheat flour (1% fat) and rice flour (0.5% fat). Low migration occurred in the case of paperboard in contact with wheat pasta (0.4% fat). Native starch was found to be more sensitive to migration than gelatinised starch. Volatility was identified as the most important characteristic of the migrating compounds. MPPO was considered as a suitable surrogate for dry foods as it did not underestimate migration in any case. However, for low-fat foods such as wheat pasta, clear overestimations could occur, but only for volatile surrogates with vapour pressure over 1.45 mTorr.

Formation of microparticles from amylose-grafted poly(γ-glutamic acid) networks obtained by thermostable phosphorylase-catalyzed enzymatic polymerization

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.

Formation of Supramolecular Soft Materials from Amylosic Inclusion Complexes with Designed Guest Polymers Obtained by Vine-Twining Polymerization

Amylose forms supramolecular inclusion complexes with polymeric guests in the phosphorylase-catalyzed enzymatic polymerization field, so-called "vine-twining polymerization". However, such inclusion complexes have not exhibited specific properties and processability as functional supramolecular materials. In this study, we found that amylosic inclusion complexes, which were obtained by vine-twining polymerization using a designed guest polymer, that is, an amphiphilic triblock copolymer poly(2-methyl-2-oxazoline-block-tetrahydrofuran-block-2-methyl-2-oxazoline), exhibited gel and film formation properties. The characterization results of the products suggested that enzymatically elongated amylose chains complexed with the polytetrahydrofuran block in the triblock copolymer. Accordingly, the outer poly(2-methyl-2-oxazoline) blocks constructed hydrophilic spaces among the inclusion complex segments. Furthermore, the presence of such outer blocks affected the lower regularity of crystalline alignment among the inclusion complex segments in the products. Such higher-order structures probably induced the formation of supramolecular soft materials, such as gels and films.

Preparation of Amylose-Carboxymethyl Cellulose Conjugated Supramolecular Networks by Phosphorylase-Catalyzed Enzymatic Polymerization

Enzymatic polymerization has been noted as a powerful method to precisely synthesize polymers with complicated structures, such as polysaccharides, which are not commonly prepared by conventional polymerization. Phosphorylase is one of the enzymes which have been used to practically synthesize well-defined polysaccharides. The phosphorylase-catalyzed enzymatic polymerization is conducted using α-d-glucose 1-phosphate as a monomer, and maltooligosaccharide as a primer, respectively, to obtain amylose. Amylose is known to form supramolecules owing to its helical conformation, that is, inclusion complex and double helix, in which the formation is depended on whether a guest molecule is present or not. In this paper, we would like to report the preparation of amylose-carboxymethyl cellulose (CMC) conjugated supramolecular networks, by the phosphorylase-catalyzed enzymatic polymerization, using maltoheptaose primer-grafted CMC. When the enzymatic polymerization was carried out using the graft copolymer, either in the presence or in the absence of a guest polymer poly (ε-caprolactone) (PCL), the enzymatically elongated amylose chains from the primers on the CMC main-chain formed double helixes or inclusion complexes, depending on the amounts of PCL, which acted as cross-linking points for the construction of network structures. Accordingly, the reaction mixtures totally turned into hydrogels, regardless of the structures of supramolecular cross-linking points.

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

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(ε-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.

Preparation and Material Application of Amylose-Polymer Inclusion Complexes by Enzymatic Polymerization Approach

This review presents our researches on the preparation and material application of inclusion complexes that comprises an amylose host and polymeric guests through phosphorylase-catalyzed enzymatic polymerization. Amylose is a well-known polysaccharide and forms inclusion complexes with various hydrophobic small molecules. Pure amylose is produced by enzymatic polymerization by using α-d-glucose 1-phosphate as a monomer and maltooligosaccharide as a primer catalyzed by phosphorylase. We determined that a propagating chain of amylose during enzymatic polymerization wraps around hydrophobic polymers present in the reaction system to form inclusion complexes. We termed this polymerization “vine-twining polymerization” because it is similar to the way vines of a plant grow around a rod. Hierarchical structured amylosic materials, such as hydrogels and films, were fabricated by inclusion complexation through vine-twining polymerization by using copolymers covalently grafted with hydrophobic guest polymers. The enzymatically produced amyloses induced complexation with the guest polymers in the intermolecular graft copolymers, which acted as cross-linking points to form supramolecular hydrogels. By including a film-formable main-chain in the graft copolymer, a supramolecular film was obtained through hydrogelation. Supramolecular polymeric materials were successfully fabricated through vine-twining polymerization by using primer-guest conjugates. The products of vine-twining polymerization form polymeric continuums of inclusion complexes, where the enzymatically produced amylose chains elongate from the conjugates included in the guest segments of the other conjugates.

Evaluation of Stability of Amylose Inclusion Complexes Depending on Guest Polymers and Their Application to Supramolecular Polymeric Materials

This paper describes the evaluation of the stability of amylose-polymer inclusion complexes under solution state in dimethyl sulfoxide (DMSO) depending on guest polymers. The three complexes were prepared by the vine-twining polymerization method using polytetrahydrofuran (PTHF), poly(ε-caprolactone) (PCL), and poly(l-lactide) (PLLA) as guest polymers. The stability investigation was conducted at desired temperatures (25, 30, 40, 60 °C) in DMSO solutions of the complexes. Consequently, the amylose-PTHF inclusion complex was dissociated at 25 °C, while the other complexes were stable under the same conditions. When the temperatures were elevated, the amylose-PCL and amylose-PLLA complexes were dissociated at 40 and 60 °C, respectively. We also found that amylose inclusion supramolecular polymers which were prepared by the vine-twining polymerization using primer-guest conjugates formed films by the acetylation of amylose segments. The film from acetylated amylose-PLLA supramolecular polymer had higher storage modulus than that from acetylated amylose-PTHF supramolecular polymer, as a function of temperature.

Amylose engineering: phosphorylase-catalyzed polymerization of functional saccharide primers for glycobiomaterials

Interest in amylose and its hybrids has grown over many decades, and a great deal of work has been devoted to developing methods for designing functional amylose hybrids. In this context, phosphorylase-catalyzed polymerization shows considerable promise as a tool for preparing diverse amylose hybrids. Recently, advances have been made in the chemoenzymatic synthesis and characterization of amylose-block-polymers, amylose-graft-polymers, amylose-modified surfaces, hetero-oligosaccharides, and cellodextrin hybrids. Many of these saccharides provide clear opportunities for advances in biomaterials because of their biocompatibility and biodegradability. Important developments in bioapplications of amylose hybrids have also been made, and such newly developed amylose hybrids will help promote the development of new generations of glyco materials. WIREs Nanomed Nanobiotechnol 2017, 9:e1423. doi: 10.1002/wnan.1423 For further resources related to this article, please visit the WIREs website.

Precision Synthesis of Functional Polysaccharide Materials by Phosphorylase-Catalyzed Enzymatic Reactions

In this review article, the precise synthesis of functional polysaccharide materials using phosphorylase-catalyzed enzymatic reactions is presented. This particular enzymatic approach has been identified as a powerful tool in preparing well-defined polysaccharide materials. Phosphorylase is an enzyme that has been employed in the synthesis of pure amylose with a precisely controlled structure. Similarly, using a phosphorylase-catalyzed enzymatic polymerization, the chemoenzymatic synthesis of amylose-grafted heteropolysaccharides containing different main-chain polysaccharide structures (e.g., chitin/chitosan, cellulose, alginate, xanthan gum, and carboxymethyl cellulose) was achieved. Amylose-based block, star, and branched polymeric materials have also been prepared using this enzymatic polymerization. Since phosphorylase shows a loose specificity for the recognition of substrates, different sugar residues have been introduced to the non-reducing ends of maltooligosaccharides by phosphorylase-catalyzed glycosylations using analog substrates such as α-d-glucuronic acid and α-d-glucosamine 1-phosphates. By means of such reactions, an amphoteric glycogen and its corresponding hydrogel were successfully prepared. Thermostable phosphorylase was able to tolerate a greater variance in the substrate structures with respect to recognition than potato phosphorylase, and as a result, the enzymatic polymerization of α-d-glucosamine 1-phosphate to produce a chitosan stereoisomer was carried out using this enzyme catalyst, which was then subsequently converted to the chitin stereoisomer by N-acetylation. Amylose supramolecular inclusion complexes with polymeric guests were obtained when the phosphorylase-catalyzed enzymatic polymerization was conducted in the presence of the guest polymers. Since the structure of this polymeric system is similar to the way that a plant vine twines around a rod, this polymerization system has been named "vine-twining polymerization". Through this approach, amylose supramolecular network materials were fabricated using designed graft copolymers. Furthermore, supramolecular inclusion polymers were formed by vine-twining polymerization using primer⁻guest conjugates.

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysaccharides and functionalized polyesters. The enzymatic polymerizations allowed the first in vitro synthesis of natural polysaccharides having complicated structures like cellulose, amylose, xylan, chitin, hyaluronan, and chondroitin. These polymerizations are "green" with several respects; nontoxicity of enzyme, high catalyst efficiency, selective reactions under mild conditions using green solvents and renewable starting materials, and producing minimal byproducts. Thus, the enzymatic polymerization is desirable for the environment and contributes to "green polymer chemistry" for maintaining sustainable society.

Photocrosslinkable polysaccharide hydrogel composites based on dextran or pullulan–amylose blends with cytokines for a human co-culture model of human osteoblasts and endothelial cells

Polysaccharide hyrogel composites demonstrate fundamental potential as biomaterials for bone regeneration in vitro.

Preparation of multiformable supramolecular gels through helical complexation by amylose in vine-twining polymerization

Supramolecular hydrogels with macroscopic interfacial healing behavior were obtained through helical complexation by amylose in vine-twining polymerization using poly(γ-glutamic acid-graft-ε-caprolactone), which were further converted into cryo- and ion gels.