Chemoenzyamtic synthesis and self-assembling gelation behavior of amylose-grafted poly(γ-glutamic acid)

Amino acid derived biopolymers: Recent advances and biomedical applications

Over the past few years, amino acids (AA) have emerged as promising biomaterials for the synthesis of functional polymers. Owing to the diversity of functional groups in amino acids, various polymerization methods may be used to make a wide range of well-defined functional amino-acid/peptide-based optically active polymers with varying polymer lengths, compositions, and designs. When incorporated with chirality and self-assembly, they offer a wide range of applications and are particularly appealing in the field of drug delivery, tissue engineering, and biosensing. There are several classes of these polymers that include polyamides (PA), polyesters (PE), poly(ester-amide)s (PEA)s, polyurethanes (PU)s, poly(depsipeptide)s (PDP)s, etc. They offer the ability to control functionality, conjugation, crosslinking, stimuli responsiveness, and tuneable mechanical/thermal properties. In this review, we present the recent advancements in the synthesis strategies for obtaining these amino acid-derived bio-macromolecules, their self-assembly properties, and the wealth of prevalent applications.

Evaluation of artificial crystalline structure from amylose analog polysaccharide without hydroxy groups at C-2 position

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.

Enzymatic synthesis of functional amylosic materials and amylose analog polysaccharides

Because polysaccharides have very complicated chemical structures constructed by a great diversity of monosaccharide residues and glycosidic linkages, enzymatic approaches have been identified as powerful tools to precisely synthesize polysaccharides as the reactions progress in highly controlled regio- and stereoarrangements. α-Glucan phosphorylase (GP) is one of the enzymes that have acted as catalysts for the practical production of well-defined polysaccharides. GP can catalyze enzymatic polymerization of α-d-glucose 1-phosphate (Glc-1-P) as a monomer from a maltooligosaccharide primer to produce a pure amylose with well-defined structure via the formation of α(1→4)-glycosidic linkages. Here, the author presents methods which achieve the enzymatic synthesis of functional amylosic materials and amylose analog polysaccharides by GP-catalyzed enzymatic polymerization approaches. As the polymerization progresses at the non-reducing end of the primer, it can be conducted using polymeric primers that are modified at the reducing end and covalently attached on suitable polymeric chains. By using such polymeric primers, various amylose-grafted functional materials can be enzymatically synthesized. For example, the detailed protocol for the synthesis of amylose-grafted poly(γ-glutamic acid) is described. GP shows loose specificity for the recognition of substrates, which allows to recognize some monosaccharide 1-phosphates as analog substrates of Glc-1-P. Representatively, the experimental procedure of the GP-catalyzed enzymatic polymerization of α-d-glucosamine 1-phosphate as the analog substrate is presented to synthesize an α(1→4)-linked glucosamine polymer, that is called amylosamine. By means of a similar approach catalyzed by GP, several amylose analog polysaccharides have been obtained.

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.

Synthesis and function of amphiphilic glucan dendrimers as nanocarriers for protein delivery

We report the combined enzymatic synthesis of five glucan dendrimers with control of molecular weight and particle size. Amphiphilic properties were introduced through dodecyl group substitution. A Tokyo-green fluorescence assay showed that amphiphilic glucan dendrimers were able to successfully deliver active β-galactosidase to cells.

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.

Enzymatic preparation of functional polysaccharide hydrogels by phosphorylase catalysis

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