Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 5, 2001
Publication Date: N/A
Technical Abstract: Ionic liquids are molten organic salts at or near room temperature, which have been shown to be useful media for many reactions. With the possibility of incorporating another "green" solvent, supercritical carbon dioxide (SC-CO2), into the reaction/extraction processing scheme, further utility may be achieved. To date, there have been no reports in the literature of reactions in ionic liquids catalyzed by isolated enzymes. We have examined the transesterification reaction of N-acetyl-L-phenylalanine ethyl ester with 1-propanol catalyzed by chymotrypsin in the ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF6]). In addition, this reaction was studied with SC-CO2 included as a miscible co-solvent. Protease-catalyzed reactions proceed in aqueous-organic and nearly-anhydrous organic solvents with rates greatly dependent on solvent polarity, solvent water activity, and enzyme support properties. The activity of chymotrypsin was studied to determine whether the trends observed with this enzyme in conventional organic solvents hold for the novel environment provided by ionic liquids. The results indicate that [bmim][PF6] and [omim][PF6] provide an environment more similar to polar solvents such acetonitrile than nonpolar solvents, resulting in lower activities than that which can be achieved in very nonpolar solvents. Inclusion of supercritical carbon dioxide in the reaction medium increased enzyme activity substantially, indicating that the combined ionic liquid/SC-CO2 serves as a better medium than either fluid alone.