Abstract
Biodegradation tests with bacteria from activated sludge revealed the probable persistence of cyano-based ionic liquid anions when these leave waste water treatment plants. A possible biological treatment using bacteria capable of biodegrading similar compounds, namely cyanide and cyano-complexes, was therefore examined. With these bacteria from the genera Cupriavidus, the ionic liquid anions B(CN)4 −, C(CN)3 −, N(CN)2 − combined with alkaline cations were tested in different growth media using ion chromatography for the examination of their primary biodegradability. However, no enhanced biodegradability of the tested cyano-based ionic liquids was observed. Therefore, an in vitro enzymatic hydrolysis test was additionally run showing that all tested ionic liquid (IL) anions can be hydrolysed to their corresponding amides by nitrile hydratase, but not by nitrilase under the experimental conditions. The biological stability of the cyano-based anions is an advantage in technological application, but the occurrence of enzymes that are able to hydrolyse the parent compound gives a new perspective on future cyano-based IL anion treatment.
Highlights
Ionic liquids (ILs) have become an innovative substance group for industry and research purposes
Since we know from abiotic hydrolysis studies on the cyano-based IL anions that at least N(CN)2− and C(CN)3− were hydrolytically instable under harsh pH conditions, we investigated whether the nitrile hydrolysing enzymes and commercially available nitrilase and nitrile hydratase may catalyse the hydrolysis as it has been shown several times for nitrile-containing chemicals (Martínková and Kren 2010; O’Reilly and Turner 2003) and could be a hint for future bacteria selection for the biodegradation of cyano-based anions
Since the Prussian blue (PB) was agglutinating in the liquid medium, forming blue particles, whereas in agar it remained diluted
Summary
Ionic liquids (ILs) have become an innovative substance group for industry and research purposes. The generic property of being ionic and liquid below a temperature of 100 °C stems mainly from the combination of asymmetric organic cations and anions The combinability of their different components has led to a vast number of chemicals with different physico-chemical properties. Low vapour pressure and nonflammability are additional common key properties that make for improved operational safety in comparison to conventional solvents This combination of IL properties has advantages in the fields of chemical synthesis and catalysis (OlivierBourbigou et al 2010; Sheldon 2005), liquid–liquid extraction and enzyme stabilisation (Dreyer and Kragl 2008), and electrochemical (Liu and Pan 2011) and analytical applications (Berthod et al 2008) in that the relevant processes are more effective and safer (Kokorin 2011). Looking at the main source for ILs into the environment, it is probable that ILs enter the environment via waste water treatment plants when physico-chemical properties and applications of ILs are taken into account (Siedlecka et al 2010)
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