Lipase-Catalyzed Hydrolysis of -Phenylethyl Esters in a Hydrophobic Ionic Liquid-Based Bicontinuous Microemulsion Stabilized by Zwitterionic Surfactant

In the present work, the biocompatible sulfobetaine-type zwitterionic surfactant (SB-n) was selected to construct hydrophobic ionic liquid (HIL)-based bicontinuous microemulsion (BME). It is shown that the [C(8)mim][PF6] (1-octyl-3-methylimidazolium hexafluorophosphate)-based BME stabilized by mixed SB-8/SB-16 is more suitable for the expression of lipase activity than that stabilized by a single SB-12. It is also demonstrated that the lipase activity in the present BME is higher than in the corresponding droplet-type microemulsion. The lipase-catalyzed hydrolysis of racemic alpha-phenylethyl esters was used as a model reaction. It is found that the yield and the enantiomeric excess (ee) value of the product alpha-phenylethanol depend on the lipase sources. In the SB-8/SB-16-stabilized BME, Candida antarctica lipase (B) has the best hydrolysis activity and stereoselectivity toward alpha-phenylethyl esters. It is also found that the surfactant content, buffer pH and substrate chain length affect the yield and the ee value of the product. Under optimized conditions, a yield of 41 % and an ee value of similar to 100 % were obtained. The present study is helpful for the development of an effective and environmentally benign medium for lipase-based conversions.