Imidazolium-based ionic liquids are important solvents for the processing of natural cellulose. Little is known about their use in synthesizing cellulose via bottom-up polymerization of β-1,4-d-glucosyl chains in solution. Here, we analyzed cellodextrin phosphorylase-catalyzed synthesis of cello-oligosaccharides, and the subsequent spontaneous self-assembly of the chains, in the presence of cellulose-dissolving ionic liquid, 1,3-dimethylimidazolium dimethyl phosphate ([Dmim]DMP) or 1-ethyl-3-methylimidazolium acetate ([Emim]OAc). The average chain length dropped from ~7.4 in buffer to ~6.4 in ionic liquid (30 vol%). The synthetic cellulose exhibited allomorph II crystal structure and showed nanosheet morphology of 4-5 nm thickness and several μm length. Its suspensions were hydrogels with viscoelastic properties dependent on solvent conditions used. Reactions in 10 vol% [Dmim]DMP or [Emim]OAc gave a hydrogel with elastic modulus of ~13 kPa and loss factor of ~0.18. Collectively, interactions of the ionic liquid with enzyme and cello-oligosaccharides delimit the polymerization and tune the assembly into cellulose networks.
Keywords: Chain self-assembly; Hydrogel; Ionic liquid; Phosphorylase bio-catalysis; Synthetic cellulose.
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