Examples of Biocatalytic Reactions in Ionic Liquids

Whole Cell Systems and Enzymes Other than Upases in Ionic Liquids 

In 1984 Magnuson et al. investigated the influence of ethylammonium nitrate/ water-mixtures on enzyme activity and stability [30]. At low [H3NEt][NOj] concentrations an increased activity of alkaline phosphatase was reported. The same ionic liquid was used by Flowers and coworkers who found improved protein refolding after denaturation [31]. 

Compared to enzyme catalysis much less information on the use of ionic liquids with whole cell systems has been reported [32,33]. In most cases [BMIM][PF6] vras used in a two-phase system as substrate reservoir and/or for in situ removal of the 

Alkaline phosphatase 30 Enzyme activity and stability assayed by 30 

Pyranose oxidase Enzyme screening using MALDI-ToF 87 

Thanks to their special properties and potential advantages, ionic liquids may be interesting solvents for biocatalytic reactions to solve some of the problems discussed above. After initial trials more than 15 years ago, in which ethylammonium nitrate was used in salt/water mixtures [29], results from the use of ionic liquids as pure solvent, as co-solvent, or for biphasic systems have recently been reported. The reaction systems are summarized in Tables 8.3-1 and 8.3-2, below. Table 8.3-1 compiles all biocatalytic systems except lipases, which are shown separately in 8.3-2. Some of the entries are discussed in more detail below. 

---

Examples of Biocatalytic Reactions in Ionic Liquids 645 Table 8-2 Enzymes other than lipases in ionic liquids... 

In this report, the nse of ionic Uquids/supercritical carbon dioxide in biocatalytic reactions has been extensively reviewed. Properties of supercritical carbon dioxide, ionic liquids and ionic liqnids/supercritical carbon dioxide biphasic systems have been analysed. Representative examples of the enzyme catalytic reactions in IL/ scCOj biphasic systems have been included. Finally, the effect of the biphasic systems on activity, selectivity and stability of enzymes has been carefully analysed. 

Despite many efforts the use of classical organic solvents for biocatalytic transformations using whole cells remains limited. Water as a natural reaction medium limits the number of applications, since only a small number of substrates are sufficiently water soluble. As an alternative the use of an ionic liquid may be considered. A very early example for such a reaction has been reported by Cull in 2000 [360]. 

---