Toxicity of various anions associated with methoxyethyl methyl imidazolium-based ionic liquids on Clostridium sp.

We investigated the effects on the growth of the anaerobic bacterium, Clostridium sp., of the ionic liquid, 1-methoxyethyl-3-methyl imidazolium [MOEMIM](+), derived from imidazolium cation and paired with one of a variety of counter-ions, viz., tetrafluoroborate [BF₄]⁻, hexafluorophosphate [PF₆]⁻(,) trifluoroacetate [CF₃COO]⁻, bis(trifluoromethane)sulfonamide [Tf₂N]⁻, methane sulfonate [OMS], and 1-butyl-3-methyl imidazolium tetrafluoroborate [BMIM][BF₄]. These anions, in association with [MOEMIM](+) lowered the growth rate of the bacterium, showing the following trend: [Tf₂N]⁻ ≧ [PF₆]⁻ > [BF₄]⁻ > [CF₃COO]⁻ > [OMS]⁻. Anions incorporating fluorine were more toxic than those without it, and their toxicity rose with an increase in the number of fluorine atoms. Also, [MOEMIM](+)[BF₄]⁻ was less toxic than [BMIM](+)[BF₄]⁻, probably due to the presence of a methoxyethyl functional group integrated in the cation side chain.