# Diversity of Potential (Bio)Technological Applications of Amino Acid-Based Ionic Liquids
## 2 Bioapplications of AA ILs: An Overview
### AA ILs as Catalysts  
AA ILs have remarkable catalytic properties. The amino group (-NH\({}_{2}\)) or the carboxylate group (-COO-) in these ILs can act as Lewis bases because the carboxylate anion is electron-rich and can coordinate with metal ions or other electron-deficient species. This property allows AA ILs to coordinate with metal catalysts in catalytic cycles and to activate substrates such as CO\({}_{2}\), where the lone pairs on nitrogen or oxygen facilitate such interactions. The carboxylate group (-COO-) in the anion of these ILs is also a strong Bronsted base capable of deprotonating acidic substrates. Zwitterionic forms of amino acids, when paired with suitable cations, retain basic properties and act as proton acceptors. Such ILs are effective catalysts for reactions requiring proton abstraction, such as aldol condensations and Knoevenagel reactions. In addition, they can neutralize acidic by-products in organic synthesis. AA ILs containing a protonated amine group (-NH\({}_{3}\)+) in the amino acid-derived cation can function as Bronsted acids. Functionalized ILs with acidic groups, such as sulfonic acid (-SO\({}_{3}\)H), exhibit enhanced Bronsted acidity. These ILs are particularly useful for acid-catalyzed reactions, including esterification, hydrolysis, and cyclization. They also provide acidic media suitable for biocatalysis and polymerization reactions. Numerous studies have demonstrated the excellent catalytic activities of AA ILs in a wide range of reactions, including esterification, hydrolysis, carbon-carbon bond formation, cyclization, oxidation, asymmetric synthesis, the cycloaddition of CO\({}_{2}\), and reduction (see Table 3). These ILs are environmentally benign compared to conventional catalysts, with many showing good stability and activity over several consecutive catalytic cycles. \begin{table}
\begin{tabular}{c c c c} \hline
**AA IL Catalyst** & **Reaction/Mechanism** & **Advantages of the AA IL Catalyst** & **References** \\ \hline \multirow{4}{*}{[pyridine-N-sulfonyl glycine][Cl]} & Biginelli reaction; & \multicolumn{2}{c}{_Target product(s):_} & \\  & Knoevenagel condensation; & dihydropyrimidines; & \\  & media: water, at reflux & remarkable catalytic activity, water as & \\  & temperature & a solvent, high yields, short & \\  & reaction time & & \\ \hline \multirow{4}{*}{AA IL solvent} & intermolecular & \multicolumn{2}{c}{_Target product(s):_} & \\  & Knoevenagel reaction; & caulerpin (61 \% yield) & \\  & media: toluene, reflux & 50\% higher yield than that obtained & \\  & & with conventional catalysts & \\ \hline \multirow{4}{*}{[Pro][H\({}_{2}\)PO4]} & Biginelli reaction & \multicolumn{2}{c}{_Target product(s):_} & \\  & (aminoalkylation) & aminoalkyl naphthols & \\  & & the yield of the derivatives is within & \\  & & the range of 84–97\% & \\ \hline \multirow{4}{*}{[ValOLauryl]\({}_{2}\)[CuCl\({}_{4}\)]} & cross-dehydrogenase & \multicolumn{2}{c}{_Target product(s):_} & \\  & coupling reaction & \multicolumn{2}{c}{properly amines} & \\  & (C-C bond formation); & (up to 94 \% yield) & \\ \cline{1-1}  & media: water & & \\ \hline \multirow{4}{*}{[L-Pro][NO\({}_{3}\)]} & \multirow{4}{*}{cyclocondenzation reaction} & \multicolumn{2}{c}{_Target product(s):_} & \\  & & 5-aryl-1,2,4-thiazol-3-thiones & \\ \cline{1-1}  & & the yield of the derivatives is within & \\ \cline{1-1}  & & the range of 80–95\%; & \\ \cline{1-1}  & & 5 cycles of catalyst reuse without & \\ \cline{1-1}  & & significant loss of activity & \\ \hline \end{tabular}
\end{table} 
Table 3: Catalytic application of AA ILs.