Thermal stability and activity regain of horseradish peroxidase in aqueous mixtures of imidazolium-based ionic liquids

Thermal deactivation kinetics of horseradish peroxidase (HRP) were studied from 45 to 90 degrees C in phosphate buffer and 5-25% (v,w/v) 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] and 1-butyl-3-methylimidazolium chloride [BMIM][Cl]. HRP activity at 25 degrees C was not affected by the presence of ionic liquids up to 20% (v,w/v). Increasing the ionic liquids concentration up to 25% (v,w/v) changed the biphasic character of deactivation kinetics to an apparent single first-order step. The presence of 5-10% (v/v) [BMIM][BF4] significantly improved HRP thermal stability with lower activation energies for the deactivation second phase (83-87 kJ mol(-1)). After deactivation, enhanced activity regain of the enzyme, up to 70-80% of the initial activity, was found in 25% (v/v) [BMIM][BF4] and 10% (w/v) [BMIM][Cl] and correlated to prevalence of the deactivation first phase.