Amino Acids Ionic Liquids
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Amino Acids Ionic Liquids Meng Ye and Yanlong Gu Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Material Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, People’s Republic of China
Introduction Amino acids have attracted considerable attention because of their remarkable properties, including wide sources, low cost, and high suitability for modifications. There are more than 20 kinds of natural amino acids (such as glycine, alanine, methionine, glutamic acid, etc.), which contain natural chiral sources and are ideal precursors for the preparation of chiral compounds. Amino acid contains both amino and carboxylic acid residues in a single molecule, forming strong hydrogen bonding ability. Amino acid ionic liquids with specific functions can be designed and synthesized by modifying or changing the substituent groups of amino acid side chains with a simple method. Amino acids can be used as cations or anions to provide stable chiral centers, which is one of the few chiral ionic liquids provided by anions. In addition, compared with conventional ionic liquids, AAILs are more environmentally © Springer Nature Singapore Pte Ltd. 2021 S. Zhang (ed.), Encyclopedia of Ionic Liquids, https://doi.org/10.1007/978-981-10-6739-6_127-1
friendly with strong biocompatibility.
biodegradability
and
Types of AAILs Ohno et al. [1] first synthesized amino acid ionic liquids with 1-ethyl-3-methylimidazolium cation ([emim]) as cation and 20 kinds of natural amino acids as anion in 2004. The synthesized AAILs are liquid at room temperature, almost colorless and transparent (Fig. 1). In Fig. 1, upper row (left to right) were: [emim][Leu] (R ¼ CH2CH(CH3)2, R was the side chain amino acid), [emim][Lys] (R ¼ (CH2)4NH2), [emim][Met] (R ¼ (CH2)2SCH3), [emim][Phe] (R ¼ CH2C6H5), [emim][Pro] ((2-pyrrolidine)COO), [emim] [Ser] (R ¼ CH2OH), [emim][Thr] (R ¼ CH(OH) CH3), [emim][Trp] (R ¼ CH2(3-indolyl)), [emim] [Tyr] (R ¼ CH2C6H4OH), and [emim][Val] (R ¼ CH(CH3)2); and lower row (left to right) were: [emim][Ala] (R ¼ CH3), [emim][Arg] (R ¼ (CH2)3NHC(¼NH)NH2), [emim][Asn] (R ¼ CH2CONH2), [emim][Asp] (R ¼ CH2COOH), [emim][Cys] (R ¼ CH2SH), [emim][Gln] (R ¼ (CH2)2CONH2), [emim][Glu] (R ¼ (CH2)2COOH), [emim][Gly] (R ¼ H), [emim][His] (R ¼ CH2(4-imidazolyl)), and [emim][Ile] (R ¼ CH(CH3)CH2CH3). They can be miscible with a variety of organic solvents (such as methanol, propiononitrile, and chloroform).
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Amino Acids Ionic Liquids
Amino Acids Ionic Liquids, Fig. 1 Amino acid ionic liquids prepared by coupling [emim] with AAs [1]. (Reproduced with permission from Ref. [1]. Copyright 2005, American Chemical Society)
Amino Acids Ionic Liquids, Fig. 2 Structural formula of different cations
The thermal stability of these [emim][AA]s was less satisfactory. They began to decompose at approximately 200 °C. So scientists worked with the phosphonium cation and also the ammonium, pyrrolidinium, and pyridin
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