Characterization of pH Dependent-Charged Structures of Valine and Aspartic Acid Through Their Partitioning into Imidazolium-Based Ionic Liquids

Imidazolium-based ionic liquids 1-hexyl-3-methylimidazolium hexaflorophosphate, and 1-hexyl-3-methylimidazolium tetrafloroborate were used to determine pH dependent-ionic forms of Valine and Aspartic acid in aqueous solutions. For this purpose, the partitioning behaviors of both compounds between the aqueous phase with different pH values and ionic liquid phase were investigated. The results revealed that due to having different pH-dependent ionic forms, each compound showed different partitioning behavior. Partitioning behaviors of Valine and Aspartic acid depend strongly to aqueous solution acidity and chemical structures of ionic liquids. Water content of ionic liquid phase and charge density of anionic and cationic constituents of ionic liquids are effective parameters for extraction of studied amino acids into ionic liquid phase. This study was considered as a basis for introducing a green technique to realize the real ionic species of different amphoteric compounds such as amino acids in the aqueous solutions.