Alpha-chymotrypsin catalysis in imidazolium-based ionic liquids

Area of Science:

• Biocatalysis
• Enzyme Engineering
• Green Chemistry

Background:

• Ionic liquids (ILs) offer unique solvent properties for enzymatic reactions.
• Understanding enzyme behavior in ILs is crucial for developing novel biocatalytic processes.
• Supercritical carbon dioxide (SC-CO2) is a tunable, environmentally friendly co-solvent.

Purpose of the Study:

• To examine the transesterification activity of alpha-chymotrypsin in ILs ([bmim][PF(6)] and [omim][PF(6)]) and with SC-CO2.
• To determine if established trends in enzyme activity (solvent polarity, water, support) apply to IL environments.
• To evaluate the impact of IL structure and water content on enzyme performance.

Main Methods:

• Investigated alpha-chymotrypsin-catalyzed transesterification of N-acetyl-L-phenylalanine ethyl ester with 1-propanol.
• Utilized ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF(6)]).
• Combined ILs with supercritical carbon dioxide (SC-CO2) and varied water concentrations.

Main Results:

• Enzyme showed no activity at very low water concentrations in ILs.
• Moderate transesterification rates were achieved with >=0.25% water (v/v) in ILs.
• Enzyme activity was significantly higher in [omim][PF(6)] compared to [bmim][PF(6)].
• No added water was required for activity when ILs were combined with SC-CO2.
• Enzyme support complexation (PEG, KCl) did not enhance activity in ILs as it did in organic solvents.

Conclusions:

• Ionic liquids ([bmim][PF(6)], [omim][PF(6)]) create a polar environment affecting enzyme activity.
• Water content is critical for alpha-chymotrypsin activity in these ILs.
• [omim][PF(6)] is a more favorable medium than [bmim][PF(6)] for this enzymatic reaction.
• Combining ILs with SC-CO2 optimizes enzyme activity by modifying the polar environment without needing added water.