# Diversity of Potential (Bio)Technological Applications of Amino Acid-Based Ionic Liquids
## 2 Bioapplications of AA ILs: An Overview
### Other Applications  
#### 2.10.1 Utilization and Capture of Toxic Gases  
The main strategies for eliminating CO\({}_{2}\) SO\({}_{2}\), NO\({}_{2}\), and other toxic gases using ILs include physical absorption and chemically reactive absorption [226; 227]. In the latter, the IL interacts with CO\({}_{2}\) to form reversible compounds such as carbamates or bicarbonate. Additionally, ILs can act as catalysts to incorporate CO\({}_{2}\) into valuable compounds via carboxylation and cycloaddition reactions, as demonstrated in the examples mentioned above. ILs can also be used as electrolytes in the electrochemical reduction of CO\({}_{2}\) to produce fuels such as methane, ethylene, or alcohols. Some examples from the literature are given below. Pure AA ILs based on tetraalkylphosphonium cations and AA ILs, such as [P\({}_{1111}\)][Gly], [P\({}_{4444}\)][Gly], [P\({}_{4442}\)]\({}_{2}\)[Ser], [P\({}_{4444}\)][Ala], [P\({}_{4444}\)][Met], [P\({}_{4444}\)][Ile], [P\({}_{66614}\)][Gly], [P\({}_{66614}\)][Met], and [P\({}_{66614}\)][Pro], exhibit excellent CO\({}_{2}\) absorption capacity [228; 229; 230]. Cations with longer alkyl chain substituents exhibit an 11% increase in absorption capacity. Interestingly, [P\({}_{66614}\)][Met] and [P\({}_{66614}\)][Pro] absorb CO\({}_{2}\) in an almost 1:1 stoichiometry [231]. However, due to the very high viscosity of these AA ILs, SO\({}_{2}\) absorption is hindered, resulting in some selectivity for CO\({}_{2}\) over SO\({}_{2}\)[227]. Among the series of pure [Ch][AAs], glycinate appears to be the most effective sorbent for CO\({}_{2}\)[232]. High CO\({}_{2}\) absorption capacity and stable regeneration are achieved with aqueous biphasic systems containing AA ILs based on tetraalkylammonium and 1,3-disubstituted imidazolium cations, such as Emim, 1-propyl-3-methylimidazolium, and 1-vinyl-3-methylimidazolium [233; 234; 235; 236; 237; 238; 239; 240; 241; 242; 243]. Numerous studies have demonstrated enhanced absorption capacity and over 90% regeneration efficiency for [N\({}_{1111}\)][Gly] and [Bmim][Lys] when blended with aqueous solutions of amines or amino alcohols, including N-methyldiethanolamine and 2-amino-2-methyl-1-propanol [244; 245; 246; 247]. Furthermore, mixed solutions of monoethanolamine (MEA) with [C\({}_{2-\text{OH}}\)mim][Gly] or [MEA]Gly, as well as more complex systems such as diethylenediamine-serine ionic liquid/polyethylene glycol dimethyl ether/water, also exhibit high CO\({}_{2}\) absorption capacity [248; 249; 250]. Good cyclic adsorption-desorption performance has been reported for various [Emim][AAs], [P\({}_{4444}\)][AA], [Bmim][Gly], and [N\({}_{2222}\)][Gly], supported on meso-, micro-, and nanoporous silica materials such as SBA-15, MCM-41, MCM-48, KIT-6, and zeolites, including silica particles grafted with polymethylmethacrylate, polydivinylbenzene, and other materials [251; 252; 253; 254; 255; 256; 257; 258; 259]. It is noteworthy that [P\({}_{4444}\)][AAs] and [Ch][AAs], when grafted onto thin film composites or membranes based on cellulose acetate, organometallic frameworks, Teflon, polyacrylamide, poly(ethylene oxide), and other materials, exhibit high permeability and exceptional selectivity for CO\({}_{2}\) over N\({}_{2}\)[260; 261; 262; 263; 264; 265; 266]. On the other hand, a system containing low-molecular-weight (200-400 Da) polyethylene glycol and [P\({}_{4444}\)][Ala] [P\({}_{4444}\)][Gly] or [P\({}_{4444}\)][Pro] is highly selective for CO\({}_{2}\) over H\({}_{2}\)[267]. AA ILs, which operate via a chemically reactive adsorption mechanism, have shown intriguing potential for CO\({}_{2}\) utilization. Ultrathin metal-porphyrin metal-organic framework nanosheets, functionalized with [Bmim][Glu] or [Bmim][His], have been shown to facilitate substrate-specific cycloaddition of CO\({}_{2}\), yielding cyclic carbonates in 84-99% under mild conditions (solvent-free, 80 \({}^{\circ}\)C, 1 atm CO\({}_{2}\)) [268].