Biocatalysis in water-in-ionic liquid microemulsions: A case study with horseradish peroxidase

In this article we report the first results on the enzymatic activity of horseradish peroxidase (HRP) microencapsulated in water-in-ionic liquid (w/IL) microemulsions using pyrogallol as the substrate. Toward this goal, the system used in this study was composed of anionic surfactant AOT (sodium bis(2-ethyl-1-hexyl)sulfosuccinate)/hydrophobic IL [C₈mim][Tf ₂N] (1-octyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide)/ water/l-hexanol. In this system, the catalytic activity of HRP was measured as a function of substrate concentrations, W₀ (molar ratio of water to surfactant), pH, and 1-hexanol content. The curve of the activity-W₀ profile was found to be hyperbolic for the new microemulsion. The apparent Michaelis-Menten kinetic parameters (K_cat and K_m) were estimated and compared to those obtained from a conventional microemulsion. Apparently, it was found that HRP-catalyzed oxidation of pyrogallol by hydrogen peroxide in IL microemulsuions is much more effective than in a conventional AOT/water/isooctane microemulsion. The stability of HRP solubilized in the newly developed w/IL microemulsions was examined, and it was found that HRP retained almost 70% of its initial activity after incubation at 28 °C for 30 h.