Extraction of Cytochrome C by Ionic Liquid 1-Butyl-3-trimethylsilylimidazolium Hexafluorophosphate

A novel method was developed for the extraction of cytochrome c (Cyt-c) from aqueous solution into ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate (BtmsimPF6). At pH 1, an extraction efficiency of ca. 85% was achieved by extracting 3 ml of Cyt-c aqueous solution (5 ng μl−1) with 400 μl of BtmsimPF6 for 30 min. The extraction mechanisms were investigated by UV-Vis and Circular Dichroism (CD) spectra. It was demonstrated that conformation change of Cyt-c was encountered in an acidic medium (pH < 5.0) accompanied by the unfolding of peptide chain and the exposure of hydrophobic groups of heme, which results in the dissolution of Cyt-c in ionic liquid BtmsimPF6. Meanwhile, a cleavage of the sixth coordination bond of the iron atom occurred at pH 1.0 by releasing the Met-80 ligand and giving rise to a vacant coordination position. Thus, the covalent coordination between the cationic Btmsim+ of ionic liquid and the iron atom of heme group facilitates the transfer of Cyt-c into ionic liquid BtmsimPF6.