Toxicity of Ionic Liquids: Eco(cyto)activity as Complicated, but Unavoidable Parameter for Task-Specific Optimization

Rapid progress in the field of ionic liquids in recent decades led to the development of many outstanding energy‐conversion processes, catalytic systems, synthetic procedures, and important practical applications. Task‐specific optimization emerged as a sharpening stone for the fine‐tuning of structure of ionic liquids, which resulted in unprecedented efficiency at the molecular level. Ionic‐liquid systems showed promising opportunities in the development of green and sustainable technologies; however, the chemical nature of ionic liquids is not intrinsically green. Many ionic liquids were found to be toxic or even highly toxic towards cells and living organisms. In this Review, we show that biological activity and cytotoxicity of ionic liquids dramatically depend on the nature of a biological system. An ionic liquid may be not toxic for particular cells or organisms, but may demonstrate high toxicity towards another target present in the environment. Thus, a careful selection of biological activity data is a must for the correct assessment of chemical technologies involving ionic liquids. In addition to the direct biological activity (immediate response), several indirect effects and aftereffects are of primary importance. The following principal factors were revealed to modulate toxicity of ionic liquids: i) length of an alkyl chain in the cation; ii) degree of functionalization in the side chain of the cation; iii) anion nature; iv) cation nature; and v) mutual influence of anion and cation. Eco to be or not to be: Principal factors modulating the biological activity of ionic liquids (ILs) and dependence of bioactivity on the nature of a biological system are summarized. Green and sustainable technologies based on ILs should include bioactivity data as the necessary task‐specific optimization parameters. Not only the direct immediate response of biological systems to ILs, but also several indirect effects and aftereffects of ILs on these systems are of primary importance.