Long-term preservation of α-amylase activity in highly concentrated aqueous solutions of imidazolium ionic liquid

Abstract

The activity of the α-amylase enzyme incubated in aqueous solutions with a high concentration (80.2% w/v) of imidazolium ionic liquid, [C4C1im]Br, has been studied. Contrary to the complete deactivation hitherto reported in the literature, a way is found to preserve the enzyme, by adding the appropriate salt, so that the activity is saved for a long grace period. Different salts are studied and the concentration is optimized in view of the enzyme hydration. Due to the limited amount of free water available to the enzyme at higher salt concentrations, the activity decreases. The best results are obtained by adding potassium acetate, 0.200 mol dm-3. Some 90% of the activity is saved in a 2-week incubation, and a half activity remains in a month. Precipitates are observed in the samples of the solution without salt. No precipitation is noticed when acetate is present. Regardless of the fluorescence quenching, the activity is saved. The effect of the acetate on the α-amylase preservation is probably related to the ability of the acetate anion to interact with the imidazolium cation thus shielding the enzyme from being salted out and precipitated. Compared with potassium bromide, which does not interact with [C4C1im]Br, precipitation and fast inactivation are observed.