Assessing toxicity and biodegradation of novel, environmentally benign ionic liquids (1-alkoxymethyl-3-hydroxypyridinium chloride, saccharinate and acesulfamates) on cellular and molecular level

Ionic liquids are widely studied as alternative solvents in organic synthesis and catalysis, in electrochemistry and the separation sciences; with their many applications they will soon be produced on an industrial scale. Available toxicological data of ionic liquids have already suggested initial guidelines for the conscious design of safer chemicals. In this study a new group of such redesigned ionic liquids—1-alkoxymethyl-3-hydroxypyridinium cations+acesulphamate, saccharinate and chloride anions—was assayed with respect to their inhibitory activity towards acetylcholinesterase and their cellular toxicity towards the IPC-81 rat promyelocytic leukaemia cell line: the acute biological activity of these compounds is very low. Effective concentrations lie in the millimole range, which is well above possible intracellular concentrations. Only the compounds with the longest alkoxymethyl chain inhibit the enzyme at effective concentrations that are one order of magnitude smaller. No significant differences are observed when the anion compartment in the enzymatic assay is varied. However, the cytotoxicity data show EC50 for acesulphamates and saccharinates to be higher than the values for the chloride analogues. Also, a slight alkoxymethyl chain length effect on the overall cytotoxicity is discernible. The biodegradability of the 1-alkoxymethyl-3-hydroxypyridinium salts varies from 21% to 72% and depends on the type of anion the cation is linked with. It improves with lengthening alkyl chain, but only in the range from 4 to 11 carbon atoms.