Molecular Assembly-Assisted Biocatalytic Reactions in Ionic Liquids
Room temperature ionic liquids (RTILs), having no measurable vapor pressure, represent an interesting class of tunable designer solvents. Due to their many unique properties, ILs have been used as attractive alternatives to environmentally harmful ordinary organic solvents in a wide range of applications including enzymatic biotransformation. Compared to conventional organic solvents, ILs offer many advantages for biocatalysis such as enhanced conversion rates, high enantioselectivity, better enzyme stability, and improved catalyst recoverability and recyclability. However, biocatalysis in ILs has not yet fully achieved its potential because many biocatalysts are insoluble in most ILs. This limitation could be overcome by the formation of nano/micrometer-sized aqueous microemulsion droplets in an IL continuous phase (referred to as water-in-IL microemulsions) stabilized by a layer of surfactants. Enzymes can be dissolved in such water droplets and protected from the unfavorable effect of ILs by the surfactant layer. In this chapter, a simple and effective method for the development of aqueous microemulsion droplets in a hydrophobic IL comprising an anionic surfactant sodium bis(2-ethyl-1-hexyl) sulfosuccinate (AOT) is presented. For this approach, we have synthesized a hydrophobic IL [C8mim][Tf2N] (1-octyl-3-methyl imidazolium bis(trifluoromethyl sulfonyl) amide) containing a long pendant hydrocarbon chain to facilitate the dissolution of AOT molecules. A detailed description of the procedure for the potential use of this newly developed water-in-IL reverse microemulsion for biocatalysis is also included.
Key wordsIonic liquids enzymatic biocatalysis lipase horseradish peroxidase AOT biotransformation microemulsions water droplets 1-hexanol green chemistry
We gratefully acknowledge the JSPS (Japan Society for the Promotion of Science) for a JSPS Postdoctoral Fellowship (M. Moniruzzaman) and the necessary funding for this work. The authors would like to thank Prof. N. Kamiya for very helpful discussions.
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