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 (Glc) 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 Glc 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 Glc-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.