Relative hydrophobicity between the phases and partition of cytochrome-c in glycine ionic liquids aqueous two-phase systems

In this work, glycine ionic liquids tetramethylammonium glycine ([N 1111 ][Gly]), tetraethylammonium glycine ([N 2222 ][Gly]), tetra-n-butylammonium glycine ([N 4444 ][Gly]), tetra-n-butylphosphonium glycine ([P 4444 ][Gly]) and tetra-n-pentylammonium glycine ([N 5555 ][Gly]) were synthesized and used to prepare aqueous two-phase systems (ATPSs) in the presence of K 2 HPO 4 . Binodal curves of such ATPSs and partition coefficients of a series of dinitrophenylated (DNP) amino acids in these ATPSs were determined at 298.15   K to understand the effect of cationic structure of the ionic liquids on the phase-forming ability of glycine ionic liquids, relative hydrophobicity between the phases in the ionic liquids ATPSs, and polarity of the ionic liquids-rich phases. With the attempt to correlate the relative hydrophobicity of the phases in the ATPSs with their extraction capability for proteins, partition coefficients of cytochrome-c in the ATPSs were also determined. It was shown that partition coefficients of cytochrome-c were in the range from 2.83 to 20.7 under the studied pH conditions. Then, hydrophobic interactions between cytochrome-c and the ionic liquid are suggested to be the main driving force for the preferential partition of cytochrome-c in the glycine ionic liquid-rich phases of the ATPSs. Result derived from polarity of the ionic liquids-rich phases supports this mechanism.