Solubility of seven amino acids in two acetate ionic liquids from 298.15 K to 328.15 K

The number of studies on the solubilities of amino acids in pure ionic liquids is currently very scarce. Focusing on fundamental studies for the recovery of added-value compounds from fisheries and aquaculture discards, in this work the solubility of several amino acids in acetate ionic liquids and their mixtures with water were determined at temperatures ranging from 298.15 K to 328.15 K and atmospheric pressure. Sharing the acetate anion, solubilities were higher in the ionic liquid with 1-ethyl-3-methylimidazolium than with 1-hexyl-3-methylimidazolium cation. Increasing temperatures resulted in enhanced solubilisation. Solubilities in the ionic liquids ranked thus: Pro > OH-Pro > Lys·HCl > Ala > Gly > Cys, with an intermediate position of Arg (the amino acid most influenced by the hydrophobic environment and temperature). In the case of the mixtures with water, the ranking was Pro > Lys·HCl > Ala > Arg > OH-Pro > Gly > Cys. The van't Hoff equation adequately correlated experimental solubilities in the range of temperatures studied, and the process of dissolution was found endothermic and entropy-driven in all the cases. The ionic liquid 1-ethyl-3-methylimidazolium should be considered for the target application and the water content a design variable to analyse.