Nanoscale organization of ionic liquids and their interaction with peptides probed by C NMR spectroscopy

An NMR study of 10 l-alanine- and l-valine-containing peptides was carried out in the native C₂MIM]Cl], C₄MIM]Cl], C₆MIM]Cl], C₄MIM]BF₄], C₄MIM]PF₆], and C₄Py]BF₄] ionic liquid media. A unique high sensitivity of the ionic liquid system to the nature of peptide and ability to tune solvent–solute interactions were observed in contrast to regular organic solvents. The l-valine peptides can be selectively dissolved in C₄MIM]Cl] and C₆MIM]Cl], whereas their solubility in C₂MIM]Cl] and other ionic liquids was dramatically lower. In spite of structural similarity between the amino acids, a distinct behavior was observed for the l-alanine peptides. Solvent–solute interactions with an ionic liquid impose significant changes, and NMR spectroscopy is a useful probe for the molecular-level and nanoscale organization of the studied systems. An even/odd effect of the number of amino acids in the peptide on molecular interactions in ionic liquids was observed. Enhancement of chemical properties of peptides in ionic liquids and application of ionic liquids in the separation of peptides are the areas of practical interest in the studied systems.