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

• Published in: Journal of Chromatography A 2013-08, Vol.1305, p.1-6
• Main Authors: Wu, Changzeng, Wang, Jianji, Li, Zhiyong, Jing, Jun, Wang, Huiyong
• Format: Article
• Language: English
• Subjects: Amino acids; Analytical, structural and metabolic biochemistry; Aqueous two-phase systems; Binary systems (materials); Biological and medical sciences; chromatography; cytochrome c; Extraction of cytochrome-c; Fundamental and applied biological sciences. Psychology; Glycine; Glycine ionic liquids; Hemoproteins; hydrophobic bonding; Hydrophobicity; Ionic liquids; Metalloproteins; partition coefficients; Partitions; Phases; Polarity; Proteins; Relative hydrophobicity
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2013.06.066

•Glycine ILs [N5555][Gly], [P4444][Gly], [N4444][Gly] and [N2222][Gly] were prepared.•Partition coefficients of DNP-amino acids and cytochrome-c were determined in glycine ILs/K2HPO4 ATPSs.•Gibbs energies of transfer of methylene between the two phases were calculated.•Hydrophobic interaction is the main driving force for the efficient partition of the protein in the IL-rich phases. In this work, glycine ionic liquids tetramethylammonium glycine ([N1111][Gly]), tetraethylammonium glycine ([N2222][Gly]), tetra-n-butylammonium glycine ([N4444][Gly]), tetra-n-butylphosphonium glycine ([P4444][Gly]) and tetra-n-pentylammonium glycine ([N5555][Gly]) were synthesized and used to prepare aqueous two-phase systems (ATPSs) in the presence of K2HPO4. Binodal curves of such ATPSs and partition coefficients of a series of dinitrophenylated (DNP) amino acids in these ATPSs were determined at 298.15K 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.