Submitted to: Biotechnology and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 23, 2001
Publication Date: N/A
Interpretive Summary: The use of enzymes in solvents that do not pose an environmental or health risk may provide new, clean technologies for modifying and processing vegetable oils. We have investigated whether enzymes can be used in novel organic solvents called ionic liquids. Chymotrypsin, an enzyme that normally cleaves proteins but under special conditions can perform valuable synthetic reactions, was tested in ionic liquids and shown to be synthetically active. Furthermore, we demonstrated that a second clean solvent, supercritical carbon dioxide, can combine with ionic liquids to provide a superior processing method. These findings suggest that ionic liquids should be investigated further to determine whether enzymes that modify oils will also be active in these solvents. Other scientists may benefit from this research by testing whether enzyme reactions of interest to them perform better and more cleanly in ionic liquids.
Technical Abstract: The transesterification reaction of N-acetyl-L-phenylalanine ethyl ester with 1-propanol catalyzed by chymotrypsin was examined in the ionic liquids [bmim][PF6] and [omim][PF6] and in combination with supercritical carbon dioxide (SC-CO2). Chymotrypsin was studied to determine whether trends in solvent polarity and water activity, and enzyme support properties, observed with this enzyme in conventional organic solvents hold for the novel environment provided by ionic liquids. Chymotrypsin freeze-dried with K2HPO4, KCl, or poly(ethylene glycol) demonstrated no activity in [bmim][PF6] or [omim][PF6] at very low water concentrations, but moderate transesterification rates were observed with the ionic liquids containing 0.25 % water (v/v) and higher. However, the physical complexation of the enzyme with poly(ethylene glycol) or KCl did not substantially stimulate activity in the ionic liquids, unlike that observed in hexane or isooctane. Activities were considerably higher in [omim][PF6] than [bmim][PF6]. Added water was not necessary for chymotrypsin activity when ionic liquids were combined with SC- CO2. These results indicate that [bmim][PF6] and [omim][PF6] provide a relatively polar environment, which can be modified with nonpolar SC-CO2 to optimize enzyme activity.