Insights into the effect of imidazolium-based ionic liquids on chemical structure and hydrolytic activity of...

This work studied the effect of the cation alkyl chain length of 1-alkyl-n-methylimidazolium chloride ([C_nmim]Cl)-based ILs on the activity of Aspergillus niger lipase. First, the lipase activity in the presence of different ILs concentration over time was determined. ILs with shorter cation alkyl side chain length, namely [C₄mim]Cl and [C₆mim]Cl, promoted an increase of lipase activity; while, [C₈mim]Cl, depending on its concentration, maintained or decreased the enzyme activity. In the presence of ILs with longer cation alkyl chain length, i.e., [C₁₀mim]Cl and [C₁₂mim]Cl, the lipase relative activity was reduced with 0.1 (%v/v) and until suppressed ([C₁₂mim]Cl at 0.3 (%v/v)) as a result of irreversible changes in its secondary structure. Fluorescence and circular dichroism spectroscopy analysis confirmed the results achieved. These findings show that [C_nmim]Cl-based ILs can exert different behavior on the lipase' activity (enhance, maintain or even inhibit) and structural conformation, depending on the cation alkyl chain length and their relative concentration.