Hydrolytic activities of artificial nanocellulose synthesized via phosphorylase-catalyzed enzymatic reactions

Nature-based nanocelluloses with the cellulose I allomorph are attractive one-dimensional nanomaterials because of their mass productivity and unique physicochemical properties. Our previous studies demonstrated that the activated ester, monophosphate and amide linkages of small organic substrates were hydrolyzed on the surface of nanocrystalline cellulose (NCC), which is a nature-based nanocellulose. However, fundamental knowledge of the hydrolytic activities of nanocelluloses is limited. In this study, artificial sheet-like nanocelluloses composed of cellulose oligomers with the cellulose II allomorph were synthesized by phosphorylase-catalyzed enzymatic reactions, and their hydrolytic activities against ester substrates were characterized. The as-prepared nanocelluloses exhibited relatively low hydrolytic activities. However, distorted and smaller nanocelluloses with larger surface areas, which were prepared by sonication-based mechanical treatment of the as-prepared nanocelluloses, exhibited significantly greater hydrolytic activities. These enzymatically synthesized artificial nanocelluloses exhibited hydrolytic activities, even though the molecular weights of the component cellulose, allomorphs, and morphologies were different from those of nature-based NCC.