Extraction of cytochrome c by a functionalized ionic liquid containing a crown ether

To verify the applicability of functionalized ionic liquids, so-called 'task-specific ionic liquids', to liquid-liquid extraction as solvents possessing extraction ability, we carried out the extraction of a protein cytochrome c (Cyt-c) with an ionic liquid with an attached crown ether moiety in the imidazolium cation. The functionalized ionic liquid, [18C6mim][PF ₆], was dissolved in two different ionic liquids as diluents, one having a hydroxyethyl group, [C₂OHmim][Tf₂N], and the other an ethyl group, [C₂mim] [Tf₂N], respectively. The transfer of Cyt-c from the aqueous phase to the ionic liquid phase took place with [18C6mim][PF₆] in the [C₂OHmim][Tf₂N] system. The functionalized ionic liquid with the crown ether attached provided the similar extraction behavior to that using dicyclohexano-18-crown-6 (DCH18C6) as the extradant. Although the extraction ability was lower than that of DCH18C6, the functionalized ionic liquid system gave a better stripping performance than the ordinary crown ether system. The extraction efficiency was not influenced by operating temperature when the concentration of [18C6mim] was high whereas it was greatly affected by temperature at low [18C6mim] concentration. The functionalized ionic liquids showed an extremely higher extraction performance compared to that of the ordinary ionic liquids, which have no coordination sites for the target molecule.