Keto-dextran with high density of carbonyl groups was synthesized by the reactions of three enzymes (pyranose 2-oxidase, catalase, and dextransucrase). To evaluate the structure and interaction of keto-dextran with carbonyl groups in water, the viscosity of keto-dextran was compared with that of dextran. At a dilute concentration, the viscosity of keto-dextran is lower than that of dextran, because keto-dextran contracted due to intra-molecular interactions via hydrogen bonding with the carbonyl groups. Dynamic light scattering results showed that the hydrodynamic radii of dextran and keto-dextran were 24.1 and 16.7 nm, respectively. To evaluate only the inter-molecular interactions of the carbonyl groups, viscosities of glucose and keto-glucose were determined. The difference in the viscosity between keto-glucose and glucose was apparent within the concentrated region due to the inter-molecular interactions of the carbonyl groups in keto-glucose. The coefficients estimated by the extended Jones-Dole equation confirmed that keto-sugars have stronger hydration and association characteristics.
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