# Diversity of Potential (Bio)Technological Applications of Amino Acid-Based Ionic Liquids
## 2 Bioapplications of AA ILs: An Overview
### AA ILs as Media for Extraction
#### 2.7.2 AA ILs as Media for Extraction of Amino Acids and Proteins  
Chiral separation is not only crucial for ensuring the safety and efficacy of pharmaceutical drugs, but it also plays an important role in the sensory properties (taste, aroma, etc.) of foods and fragrances, as well as in the study and application of biologically active compounds in biotechnology, such as gaining a deeper understanding of the interaction between chiral compounds and enzymes, receptors, and other biological targets. AAILs have been shown to be highly enantioselective in the extraction of amino acids [137]. [PERSON] et al. demonstrated the use of Cu\({}^{2+}\)-modified [Bnim][L-Pro] or [Emim][L-Pro] for the chiral separation of amino acids via chiral ligand exchange. These AA ILs act as a solvent, an efficient and stable acceptor phase for amino acids, and a selector which, with the participation of Cu\({}^{2+}\), shows a distinct enantioselectivity in the separation of racemic amino acids. For liquid-liquid extraction with [Cu(L-Pro)\({}_{2}\)][Emim]\({}_{2}\), enantiomeric excess (e.e.) values were reported for four racemic amino acids in the order: Phe \(>\) Tyr \(>\) Trp \(>\) His [137]. Similarly, silica-supported [Emim][L-Pro], [Bnim][L-Pro], [Hmim][L-Pro], and [Omim][L-Pro] coordinated to Cu\({}^{2+}\) effectively separated underativized D,L-Phe, D,L-His, D,L-Trp, and D,L-Tyr by HPLC or capillary electrophoresis [138]. The enantioselectivity of these AA ILs was significantly higher than that of conventional AA ligands. Among the ILs tested, those with longer alkyl chain substituents in the cation showed superior efficacy [138]. [PERSON] et al. demonstrated that ILs based on AA cations, such as [L-Pro][CF\({}_{3}\)COO], [L-Pro][NO\({}_{3}\)], [L-Pro]\({}_{2}\)[SO\({}_{4}\)], and [L-Phe][CF\({}_{3}\)COO], coordinated with Cu\({}^{2+}\), can be effectively used in ligand-exchange chromatography for the separation of Trp enantiomers [139]. They reported a relatively good resolution (Rs) of 1.89 between the peaks of L-Trp and D-Trp. Similarly, ILs containing [Bmim], [Hmim], or [Omim] cations, amino acid anions, such as L-Leu, L-Val, or L-Lys, and inorganic salt show good potential for the aqueous biphasic extraction of L-Trp. Hydrogen bonding with AAILs is likely to play an important role in the phase distribution of the solute and the most effective IL for this system was [Omim][Lys] [140]. Generally, the ability of [Ch][AA]-ILs to form aqueous biphasic solutions follows the order: [Ch][L-Lys] \(>\) [Ch][L-Arg] \(>\) [Ch][L-Ser] \(>\) [Ch][Gly] \(>\) [Ch][L-His] \(>\) [Ch][L-Ala] \(>\) [Ch][\(\beta\)-Ala] \(>\) [Ch][L-Pro] \(>\) [Ch][L-Val] \(>\) [Ch][L-Phe] [141; 142; 143]. On the other hand, [Ch][AAs] are commonly mixed with a low-viscosity molecular solvent such as water to form hybrid solvents, which preserve the favorable properties of ILs while enhancing their physical properties. ATPEs based on ([Ch][AAs])\({}_{2}\)Cu complexes have been evaluated for the chiral resolution of D, L-Val [144]. The efficiency of chiral resolution depended on the specific ILs used and was ranked as follows: [Ch][Pro] \(>\) [Ch][Ala] \(>\) [Ch][Cys] \(>\) [Ch][Met] \(>\) [Ch][His]. Under optimal conditions, D-Val was preferentially distributed in the [Ch][AA]-rich phase, reaching an enantiomeric excess (e.e.) of approximately 55.6% [144]. Consistent with this result, [PERSON] et al. observed that among the various [Ch][AA]/K\({}_{3}\)PO\({}_{4}\) ATPE systems, the [Ch][L-Pro]-K\({}_{3}\)PO\({}_{4}\) system exhibited the highest separation factor for Phe enantiomers, resulting in a greater extraction of L-Phe into the top phase [145]. The ATPE system containing [Ch][Ala]-K\({}_{3}\)PO\({}_{4}\)-water and [Ch][Ala]-KH\({}_{2}\)PO\({}_{4}\)-water were evaluated for the partitioning of four N-(2,4-dinitrophenyl) (DNP) amino acids: DNP-L-Leu, DNP-L-Val, DNP-L-Ala, and DNP-Gly. A clear dependence on the type and concentration of the inorganic salt was observed.