Amino acid ionic liquids

Waseda University, Edo, Tōkyō, Japan
Accounts of Chemical Research (Impact Factor: 24.35). 12/2007; 40(11):1122-9. DOI: 10.1021/ar700053z
Source: PubMed

ABSTRACT The preparation of ionic liquids derived from amino acids, and their properties, are outlined. Since amino acids have both a carboxylic acid residue and an amino group in a single molecule, they can be used as either anions or cations. These groups are also useful in their ability to introduce functional group(s). Twenty different natural amino acids were used as anions, to couple with the 1-ethyl-3-methylimidazolium cation. The salts obtained were all liquid at room temperature. The properties of the resulting ionic liquids (AAILs) depend on the side groups of the amino acids involved. These AAILs, composed of an amino acid with some functional groups such as a hydrogen bonding group, a charged group, or an aromatic ring, had an increased glass transition (or melting) temperature and/or higher viscosity as a result of additional interactions among the ions. Viscosity is reduced and the decomposition temperature of imidazolium-type salts is improved by using the tetrabutylphosphonium cation. The chirality of AAILs was maintained even upon heating to 150 degrees C after acetylation of the free amino group. The amino group was also modified to introduce a strong acid group so as to form hydrophobic and chiral ionic liquids. Unique phase behavior of the resulting hydrophobic ionic liquids and water mixture is found; the mixture is clearly phase separated at room temperature, but the solubility of water in this IL increases upon cooling, to give a homogeneous solution. This phase change is reversible, and separation occurs again by raising the temperature a few degrees. It is extraordinary for an IL/water mixture to display such behavior with a lower critical solution temperature. Some likely applications are proposed for these amino acid derived ionic liquids.

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    ABSTRACT: Four N-functionalized imidazole derivatives with α-ami-no acid residues were prepared and subsequently used for the construction of ten new optically pure imidazolium ionic liquids. The prepared imidazolium salts comprise three derivatives bearing one α-amino acid residue, five derivatives with two residues, and two derivatives possessing two bridged imidazolium ions. The molecular structure of one N-substituted imidazole was also confirmed by X-ray crystal structure analysis. Iodide and (di)bromide ions in five representative imidazolium salts were replaced with tetrafluorobo-rate ion in an attempt to lower the melting temperatures of these salts. In general, the properties of all target imidazolium ionic liquids could easily be tuned by N1/N3-substitution and the counterion used.
    Synthesis 05/2014; 2(4202). DOI:10.1055/s-0034-1378347 · 2.44 Impact Factor
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    ABSTRACT: An extended electronegativity equalization method/molecular mechanics (EEM/MM) model for ionic liquids is used to investigate the structures and properties of 1-alkyl-3-methylimidazolium glycine ionic liquids [Cnmim][Gly] (n = 1-4) with alkyl substituents of different lengths. The EEM/MM model describes the electrostatic interactions of atoms and their changes in different ambient environments. This property is the most outstanding characteristic of the model. EEM parameters (i.e., valence electronegativities and valence hardness parameters) are calibrated using linear regression and least-squares methods, which can accurately predict the gas-phase properties of [Cnmim](+), [Gly](-), and [Cnmim][Gly] ion pairs. We utilize the EEM/MM force field to systematically investigate the effects of polarizability on the accuracy of [Cnmim][Gly] properties predicted through the molecular dynamic simulations. EEM/MM explicitly describes the atom-based polarizability of [Cnmim][Gly]; thus, the densities, enthalpies of vaporization, self-diffusion coefficients, and conductivities of the [Cnmim][Gly] are consistent with the experimental values. The calculated radial distribution functions provide a mechanistic understanding of the effects of polarizability on ionic aggregations in amino acid ionic liquids. The effects of alkyl chain length on the diffusion coefficient and conductivity are also discussed.
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