Molecular Extraction of Peptides in Ionic Liquid Systems

The extraction of peptides was studied in a two-phase ionic liquid (IL)/organic solvent system, which displayed outstanding chain length sensitivity (dipeptide vs tripeptide) and separation ability, even for structurally similar peptides (divaline vs dialanine). The extraction process could be performed under substoichiometric conditions; an IL-to-peptide ratio as low as 3:1 led to a high extraction selectivity of divaline/dialanine = 6. For practical applications, two systems were developed for the extraction of peptides from ILs under heterogeneous and homogeneous conditions, with selectivities of 6 and 3.5, respectively. The developed system has shown excellent recycling properties and was reused several times without any visible changes in the selectivity and extraction efficiency. A nuclear magnetic resonance (NMR) experiment with molecular-level spatial resolution was successfully performed to study the mechanism of the extraction process and to visualize the two-phase system.