Chemoenzymatic Preparation of Amylose-Grafted Chitin Nanofiber Network Materials

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 lyophilization of the hydrogel by the reaction at 80 °C, while the same procedure from the hydrogel produced by the reaction at 45 °C gave a flimsy cryogel. The scanning electron microscopic images of the former and latter samples observed uniform and nonuniform network morphologies, respectively. We revealed that dispersion behaviors of the Glc₇-grafted CNFs in a sodium acetate aqueous buffer were different depending on temperatures, which affected the morphologies of the resulting networks formed in the enzymatic polymerization.