Antimicrobial effects of short chained imidazolium-based ionic liquids—Influence of anion chaotropicity

• Toxicological profile of ILs towards Listeria monocytogenes and Escherichia coli.
• Influences of different anions with similar cation cores were tested.
• Two distinct toxicological effects were identified: “side chain effect” and “hofmeister effect”.
• Hofmeister effects of the anion are able to modulate the side chain effect of the cation.

Ionic liquids (ILs), a new solvent class composed solely of ions, have already found their way into numerous chemical and biochemical applications. Due to their unique properties and wide application range, research utilizing this new technology for biotechnological applications is steadily increasing. However, progress is hampered by lack of toxicological data, especially concerning IL anions and their general underlying toxicity mechanisms. The present study investigated for the first time the influence of the chaotropicity of the anion for nine imidazole based ILs on their antimicrobial behavior. The results indicate that for ILs with small cations ([Cnmim]+ with n=2 and 4), the chaotropicity of the anion is a major factor regarding antimicrobial behavior, while for [C6mim]+ based ILs a surfactant-like behavior was identified that explains their high toxicity. It could also be shown that with increasing anion chaotropicity the surfactant-like behavior of the cation is strengthened. Identification of chaotropicity as an underlying mode of antimicrobial action of ILs presents a new point of adjustment for future design with regard to their toxicological behavior.