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The phase behavior of the pseudo ternary system 1-tetradecyl-3-methylimidazolium bromide ([C14mim]Br)/Triton X-100/H2O/1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6) has been studied at 35°C. With the increase in the mole fraction of Triton X-100 in the mixed surfactants, the water solubilization capacity increases and the monophasic area enlarges. The H2O-in-[Bmim]PF6 (W/IL) microemulsion was identified via electrical conductivity measurement. The existence of bulk water in the W/IL microemulsion was demonstrated based on the change of the O-D vibration frequency with content of D2O added and confirmed using UV-vis technique with CoCl2 as probe. Laccase can be solubilized in the W/IL microemulsion and exhibits a catalytic activity. The interface of the W/IL microemulsion has an inhibitory effect on the expression of the laccase activity, and the inhibitory effect is varied with the molar ratio of the mixed surfactants., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Abstract: Choline acetate is an ionic liquid composed of a kosmotropic anion and a chaotropic cation. According to Hofmeister series, a kosmotropic anion and/or a chaotropic cation could stabilize an enzyme, thereby facilitating the retention of the catalytic activity of the enzyme. In this work, we first report the influence of choline acetate on the activity and stability of lipase in AOT/water/isooctane reverse micelles. The indicator reaction is the lipase-catalyzed hydrolysis of 4-nitrophenyl butyrate. The results show that a low level of choline acetate does not affect the microstructure of the AOT reverse micelles, but the ionic liquid can improve the catalytic efficiency of lipase. Fluorescence spectra show that a high level of choline acetate has an impact on the conformation of lipase, so the activation is mainly due to the influence of choline acetate on the nucleophilicity of water. Infrared spectra demonstrate that choline acetate can form stronger hydrogen bonds with water surrounding lipase, and therefore enhance the nucleophilicity of the water, which makes it easier to attack the acyl enzyme intermediate, thereby increasing the activity of the lipase-catalyzed hydrolysis of the ester. A study on the stability of lipase in AOT reverse micelles indicates that the ionic liquid is able to maintain the activity of lipase to a certain extent. The effect of choline acetate is consistent with that predicted based on Hofmeister series. [Copyright &y& Elsevier]