Kinetics of gas-phase hydrolysis of ethyl acetate catalyzed by immobilized lipase

Reactions catalyzed by supported enzymes present important advantages when compared with those in aqueous media or organic solvents: separation of enzymes from substrate is easily accomplished, enzyme stability may be improved, and control of the reaction products is more accurate. We present the experimental results of the kinetic study of ethyl acetate hydrolysis in gaseous phase catalyzed by a commercial immobilized lipase (Lipozyme IM; Novo Nordisk). The hydrolysis reaction was studied as a function of ethyl ester and water partial pressure at a constant temperature of 318 K. The amount of biocatalyst used was varied between 100 and 300 mg, and the reaction was studied in a flow-through glass microreactor. Under the conditions used, water was an important parameter in the gas-phase reaction. Activation energy was 24.8 kJ/mol and the overall order of reaction was one. Finally, a Bi-Bi reaction mechanism is proposed.

Stabilization and activation of alpha-chymotrypsin in water-organic solvent systems by complex formation with oligoamines

Formation of enzyme-oligoamine complexes was suggested as an approach to obtain biocatalysts with enhanced resistance towards inactivation in water-organic media. Complex formation results in broadening (by 20-40% v/v ethanol) of the range of cosolvent concentrations where the enzyme retains its catalytic activity (stabilization effect). At moderate cosolvent concentrations (20-40% v/v) complex formation activates the enzyme (by 3-6 times). The magnitude of activation and stabilization effects increases with the number of possible electrostatic contacts between the protein surface and the molecules of oligoamines (OA). Circular dichroism spectra in the far-UV region show that complex formation stabilizes protein conformation and prevents aggregation in water-organic solvent mixtures. Two populations of the complexes with different thermodynamic stabilities were found in alpha-chymotrypsin (CT)-OA systems depending on the CT/OA ratio. The average dissociation constants and stoichiometries of both low- and high-affinity populations of the complexes were estimated. It appears that it is the low-affinity sites on the CT surface that are responsible for the activation effect.

Biocatalysis in nonaqueous media. Patents and literature

Biocatalysis in nonaqueous media is being used in increasing regularity both in academic and industrial research. A variety of biocatalysts have been used in organic media including enzymes, multi-enzyme systems, and whole cells. In addition, the nonaqueous media has encompassed both monophasic and biphasic solvent systems, enzymes and whole cells in reversed micelles, enzymes and cells in nearly anhydrous (no added water) solvents, and enzymes catalytically active in supercritical fluids and the gas phase. Recent US and overseas patents and scientific literature on biocatalysis in nonaqueous media are surveyed. Patent abstracts are summarized individually, and literature references are divided into major subheadings.