Ionic liquids, also called molten salts, are mixtures of cations and anions that melt below 100 o C. Typical ionic liquids are dialkylimidazolium cations with weakly coordinating anions such as (MeOSO 3 ) or (PF 6 ). Advanced ionic liquids such as choline citrate have biodegradable, less expensive, and less toxic anions and cations. Deep eutectic solvents are also included in the advanced ionic liquids. Deep eutectic solvents are mixtures of salts such as choline chloride and uncharged hydrogen bond donors such as urea, oxalic acid, or glycerol. For example, a mixture of choline chloride and urea in 1:2 molar ratio liquefies to form a deep eutectic solvent. Their properties are similar to those of ionic liquids. Water-miscible ionic liquids as cosolvents with water enhance the solubility of substrates or products. Although traditional water-miscible organic solvents also enhance solubility, they often inactivate enzymes, while ionic liquids do not. The enhanced solubility of substrates can increase the rate of reaction and often increases the regioor enantioselectivity. Ionic liquids can also be solvents for non-aqueous reactions. In these cases, they are especially suited to dissolve polar substrates. Polar organic solvent alternatives inactivate enzymes, but ionic liquids do not even when they have similar polarities. Besides their solubility properties, ionic liquids and deep eutectic solvents may be greener than organic solvents because ionic liquids are nonvolatile, and can be made from nontoxic components. This review covers selected examples of enzyme catalyzed reaction in ionic liquids that demonstrate their advantages and unique properties, and point out opportunities for new applications. Most examples involve hydrolases, but oxidoreductases and even whole cell reactions have been reported in ionic liquids. © KSBB hÉóïçêÇëW=áçåáÅ=äáèìáÇëI=ÇÉÉé=ÉìíÉÅíáÅ=ëçäîÉåíëI=ÜóÇêçä~ëÉëI=çñáÇçêÉÇìÅí~ëÉëI=éçäóãÉêáò~íáçå= = = = =
IONIC LIQUIDS AND DEEP EUTECTIC SOLVENTSIonic liquids, also called molten salts, are mixtures of cations and anions that melt below 100 o C. The low melting point stems from a mismatch in the size of the anion and cation that prevents crystallization. Changing the structures of the anions or cations can tune the polarities and other properties. Even though they are salts, their polarities are only moderate, similar to ethanol. Ionic liquids have negligible vapor pressure. Ionic liquids are viscous, typically 0.1 Pas or more, which is similar to glycerol or honey.The first ionic liquid -ethylammonium nitrate (mp 12 o C) -was reported in 1914 [1], but attracted limited use. The first generation of widely studied ionic liquids used the dialkylimmidazolium and related cations reported in 1982 [2], Fig. 1. Varying the cation structure varied the properties of the ionic liquid. The anions were chloroaluminate or other metal halide anions, which react with water and thus are not suited for biotransformations. The second generation of ionic liquids, discovered a decade later [3], replaced the water r...
