Peptides in aqueous protic ionic liquid solutions: Apparent and transfer volumes at 298.15 K and at 0.1 MPa

Abstract

The densities of glycine based peptides namely glycyl-glycine (digly), glycine-ւ-valine (gly-val), glycyl-ւ-leucine (gly-leu) and glycyl-glycyl-glycine (triglycine/trigly) in aqueous solutions containing ~0.20 mol·kg−1 of triethylammonium acetate [TEAA], triethylammonium glycolate [TEAG], triethylammonium pyruvate [TEAPy] and triethylammonium propionate [TEAP] protic ionic liquids (PILs) are reported at 298.15 K and at atmospheric pressure. Experimental density data obtained for these systems were used to estimate apparent molar volume (ϕV), the limiting apparent molar volume (ϕV0), partial molar volume of solute (V¯2) and partial molar volume of mixed solvent (PILs + water) (V¯1). The change in limiting apparent molar volume due to transfer (ΔtrϕV0) of peptides from water to aqueous ionic liquid solutions were also estimated. The outcomes obtained from all these thermodynamic parameters were discussed in terms of ion–peptide interactions, ion–ion interactions, hydrophobic solvation, peptide group contributions to limiting volumes, etc.