Evaluating the transfer free energies of amino acids from water to ammonium-based ionic liquids at 298.15Â K

The interactions between ionic liquids (ILs) and amino acids (AAs) can easily be quantified using the apparent transfer free energy (∆G′tr) values that can be used to interpret the stability of the proteins in the same solvent medium. In this study, ∆G′tr values of AAs such as phenylalanine (Phe), histidine (His), threonine (Thr), glutamine (Gln) and serine (Ser) from the water to ILs have been obtained from the solubility measurements, as a function of IL concentration at 298.15 K under atmospheric pressure. The investigated ILs contain diethylammonium acetate (DEAA), diethylammonium hydrogen sulfate (DEAS), triethylammonium acetate (TEAA), triethylammonium hydrogen sulfate (TEAS), triethylammonium dihydrogen phosphate (TEAP), and trimethylammonium acetate (TMAA). The results reveal that the IL effect was specific and independent for each AA in the aqueous medium. Apparently, we observed a positive as well as negative ∆G′tr values for Phe, His, Glu, Thr, and Ser AAs in the ammonium-based ILs.