Characterisation and selection of room temperature ionic liquids as co- solvents for redox biocatalysis

The use of biocatalysis to create chiral centres for chemical pharmaceuticals is rapidly becoming a standard industrial technology. Often, the compounds of interest are poorly soluble in aqueous solvents leading to the use of organic co­ solvents to deliver substrate into the environment of the biocatalyst. Unfortunately these co-solvents can impact negatively on the stability of the biocatalyst. Recently, room temperature ionic liquids have been attracting interest as potential replacements for organic solvents in such reactions as they offer lower toxicity and an increased rate of reaction. This thesis describes an original experimental study into the use of ionic liquids with biocatalytic redox reactions. Initially, the stereospecific reduction of 6-Br-p-tetralone to its corresponding alcohol (S)-6-Br-P-tetralol was carried out by the yeast Trichosporon capitatum MY 1890 and by the bacterium Rhodococcus erythropolis MA7213 using a range of ionic liquids chosen on the diversity of their composition. The decrease in cell viability of both types of whole cell biocatalyst upon exposure to ionic liquids was found to be intermediate to that determined for cells residing purely in fermentation media and cells residing in a two-phase mixture of media and organic solvent (toluene). For T. capitatum MY 1890 bioconversions, the ionic liquid [Emim][TOS] gave a reaction profile comparable to that observed in the previously studied water-ethanol system, in terms of overall rate of reaction (0.2g(prod)L'1hr'1) and conversion (100% w/w). For bioconversions carried out with R. erythropolis MA7213, through use of 20% v/v [Emim][TOS] as a co­ solvent the conversion yield doubled and a four-fold increase in initial rate was found compared to the standard ethanol co-solvent. Subsequent flow cytometric analysis of the R. erythropolis MA7213 in these ionic liquids showed that the stability of the biocatalyst was increased in ionic liquids, such as [Emim][TOS] and [Oc3 MeN][BTA] accounting for the increased rates of reaction and overall conversion observed. The potential for multi parameter flow cytometry to be used as a tool for identifying biocompatible ionic