Anion effects on the cytotoxicity of ionic liquids

Most recent investigations concerning the toxicological and ecotoxicological risk potentials of ionic liquids are predominantly focusing on the cation moieties. In this study we elucidate, whether the anion species commonly used in ionic liquids are exhibiting intrinsic cytotoxic effects and if these effects can be rationalised by thinking in terms of structure-activity relationships (T-SAR). As test system to measure the cell viability as toxicologically relevant endpoint the IPC-81 rat leukemia cell line and the WST-1 assay were employed. Our results show an anion effect in ionic liquids on cytotoxicity for 10 of 27 tested anions. For the remaining 17 anions from our test kit no significant effect was found. With respect to structure-activity relationships, lipophilicity and/or vulnerability to hydrolytic cleavage seem to be the key structural features leading to the observed anion cytotoxicity. We also conclude that the model of concentration addition may be useful to estimate the EC50 values of ionic liquids that have not been tested or even synthesised yet. This can help to design not only task specific but also inherently safer ionic liquids.