We first succeeded in synthesizing ionic liquids from 20 natural amino acids. Amino acid ionic liquids dissolved native amino acids, despite water-free conditions. Furthermore, these ionic liquids are soluble in various organic solvents, such as chloroform. Effects of acidity, hydrogen bonding ability, and steric factors on the properties of these ionic liquids were analyzed as the function of side groups.

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.

No abstract

Tetraalkylphosphonium-based amino-acid ionic liquids show lower viscosities and higher decomposition temperatures (>300 degrees C) than previously reported ammonium-based amino-acid ionic liquids.

Hydrophobic ionic liquids composed of tetrabutylphosphonium cation and chiral anions derived from amino acids modified with trifluoromethane sulfonyl groups have been synthesized using a simple method.

No abstract

2006 Ionic liquids V 2000Effect of Tetrabutylphosphonium Cation on the Physico-Chemical Properties of Amino Acid Ionic Liquids. -Tetraalkylphosphonium-based amino acid ionic liquids show lower viscosities and higher decomposition temperatures than the previously reported ammonium-based amino acid ionic liquids. -(KAGIMOTO, J.; FUKUMOTO, K.; OHNO*, H.; Chem. Commun. (Cambridge) 2006, 21, 2254-2256; Dep. Biotech., Tokyo Univ. Agric. Technol., Koganei, Tokyo 184, Japan; Eng.) -M. Paetzel 37-190

No abstract