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Thursday 19 December 2013

Degradation of nitrile-containing ionic liquids but how?


It is well known that soil bacteria and fungi bioremediate nitrile containing compounds to get at their nitrogen, and that nitrilase/nitrile hydratase pathway enzymes in a range of bacteria/fungi are amenable to such a transformation. A colleague of mine, Steve Cummings, reviewed this area a few years back in a paper entitled "The current and future applications of microorganisms in the bioremediation of cyanide contamination". One possible source of environmental cyanide contamination that Steve didn’t foresee was that from ionic liquids. These have been the subject of a lot of enthusiasm in green chemistry circles as they offer immensely useful solvation properties with no appreciable vapour pressure. Their use on anything other than a laboratory bench scale has met some resistance because of concerns about their environmental toxity. A recent paper entitled “Biodegradation potential of cyano-based ionic liquid anions in a culture of Cupriavidus spp. and their in vitro enzymatic hydrolysisby nitrile hydratase” by Stefan Stolte and co-workers in Environmental Science and Pollution Research has looked at biological hydration/hydrolysis of ionic liquids containing cyano groups.


After trying an organism, they have used a couple of Sigma enzymes to see if these will process their choice of ILs. They discover that the Sigma nitrilase isn’t interested but the Sigma NHase is quite happy to turnover. But I do wish that this information went further. Sigma does not tell you what the source organism(s) for their Nase and NHase enzymes is/are, merely that they are recombinant from E. coli. There is so much variation in substrate selectivity for both classes (for instance, glance at the slice of Steve’s Table 1 below) that getting a positive or a negative hit from a single example of unknown origin tells you not much at all in general.

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