Enzymatic transformations in supersaturated substrate solutions: I. A general study with glycosidases

The results of an initial study of enzymatic catalysis in metastable supersaturated solutions of carbohydrates are presented. It has been shown that such solutions, formed in the presence of small amounts of water and alcohol as plasticizers, are sufficiently stable under ambient conditions to enable enzymatic transformations of substrates. A partial phase diagram for a system consisting of glucose, water, and (poly)ethylene glycol was constructed to identify the regions which are most suitable for biotransformations. It was confirmed that the glass transition in this system occurred below the reaction temperature at any given composition of the constituent components. Several glycosidases were found to be catalytically active in this medium and the activity of beta-glucosidase from almond was determined at several compositions of the reaction mixture and related to the corresponding regions of the phase diagram. The synthetic utility of the system was illustrated by glucosylation of several alpha,omega-alkyldiols, short-chain polyethylene glycols, and hydroxyalkyl and glyceryl monoacrylates.