Biocatalytic Reactions in Ionic Liquids

In this chapter, we try to summarize the work so far reported in this field. We first give a short introduction into the different forms of biocatalytic reactions, highlighting some special properties of biocatalysts. 

Sandra Klembt, Susanne Dreyer, Marrit Eckstein, and Udo KragI 

Biotechnological processes can be divided into fermentation processes and biotransformations. In a fermentation process products are formed as primary or secondary metabolites by microorganisms or higher cells from components in the fermentation broth. Product examples are amino acids, vitamins or antibiotics such as penicillin or cephalosporine. In these cases co-solvents are sometimes used for m situ product extraction. The term biotransformation or biocatalysis is used for processes where a starting material (precursor) is converted into the desired product 

Ionic Liquids in Synthesis, Second Edition. P. Wasserscheid and T. Welton (Eds.) Copyright 2008 WILEY-VCH Verlags GmbH Co. KGaA, Weinheim ISBN 978-3-527-31239-9 

Nature has optimized its biocatalysts to perform best in an aqueous environment, at neutral pH, temperatures below 40 °C and at low osmotic pressure. Sometimes, these conditions are contrary to the requirements of the chemist or process engineer to optimize a reaction with respect to space-time yield or high product concentration in order to facilitate downstream processing. Furthermore, enzymes and whole cells are often inhibited by products or substrates. This might be overcome by using continuously operated stirred tank reactors, fed-batch reactors or reactors with in situ product removal [14,15]. To increase the solubility of substrates and/or products the addition of organic solvents is a common practice [16]. 

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Here, we will review the various issues related to biocatalytic reactions in ionic liquids. Biocatalyst tested in ionic liquids will be discussed firstly, and then the effect of ionic liquids on the activity, selectivity as well as on the stability of biocatalyst in ionic liquids will be surveyed. Finally, various applications of ionic liquids as reaction medium for biocatalytic transformations will be reviewed. 

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

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