Abstract
Considerable attention has been directed to enzymatic processes in supercritical fluids (SCFs) for theoretical and industrial applications. SCFs have unique physicochemical properties that are readily altered through changes in pressure and temperature, especially in the near-critical region and such changes may lead to different reactivities in enzymatic processes. SCFs as reaction media may result in better mass-transfer properties compared to liquids. Increased flow rate was found to promote reaction speed and water-content, choice of cosolvent and SCFs were found to have strong effect on enzymatic reaction rates with consequent effect on solvation state of substrate, product or even enzyme. In the near-critical region not only reaction rate, but stereoisomerism were noted to be improved. In the near-critical region, local density and composition of solution underwent considerable change, and occasionally solute-solvent clustering was found to affect reactivity. The effects of this formation on reactions were thus examined at the molecular level and those of the conformation of active enzymes on reactivity were elucidated. SCFs in the near-critical region may be considered to activate the enzymes by altering their characteristic structures and, thus a stereoselective mechanism would appear operative.
