Process intensification of whole-cell biocatalysis with ionic liquids

The unique properties of room temperature ionic liquids such as non-volatility, nonflammability, and, in many cases, high thermal and chemical stability have made them an environmentally attractive alternative to organic solvents. Biphasic biocatalytic processes with nonmiscible liquid phases are usually applied with whole-cell biocatalysts to overcome low water solubility of substrates or products, inhibitory effects of the reactants on the biocatalyst, or low stability of substrates or products in the aqueous phase. The surprising noninvasive effects on cellular membranes of hydrophobic ionic liquids especially of those with hexafluorophosphate and bis(trifluoromethylsulfonyl) imide anions in biphasic ionic liquid/water systems make them superior to many organic solvents so far applied in whole-cell biotransformations. Impressive process intensification in simple biphasic batch processes was recently demonstrated on the examples of asymmetric synthesis with whole-cell biocatalysts, if the distribution coefficients of inhibitory substrates and products between ionic liquids and aqueous phase exceed a log D of about 2 (e.g., ketones and β-ketoesters with lipophilic side chains and their corresponding chiral alcohols).