Accumulation of ionic liquids in Escherichia coli cells

Abstract

Ionic liquids accumulate within Escherichia colicells and can be detected by Fourier transform infrared (FT-IR) spectroscopy. Harvested cells were incubated with the biocompatible, water-immiscible ionic liquids, trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P6,6,6,14][NTf2]) and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([N1,8,8,8][NTf2]), and with the toxic chlorides, [P6,6,6,14][Cl] and [N1,8,8,8][Cl]. The cells were harvested, washed and dried, and their FT-IR spectra were recorded. The ionic liquid spectra could be detected against the background spectra of the cells, demonstrating that they were accumulating within the cells. The toxic ionic liquids accumulated more rapidly than the biocompatible ionic liquids. Principal components analysis followed by discriminant function analysis showed that, compared to control cells, the toxic ionic liquids produced much bigger changes in the FT-IR fingerprint of the cellular chemicals than the biocompatible ionic liquids. Subcellular fractionation, followed by FT-IR analysis, demonstrated that [P6,6,6,14][NTf2] accumulated specifically in the membrane fraction of the cells and not the cytoplasm.