Water-miscible Ionic Liquids Research Articles

Toward an Understanding of the Salting-Out Effects in Aqueous Ionic Liquid Solutions: Vapor−Liquid Equilibria, Liquid−Liquid Equilibria, Volumetric, Compressibility, and Conductivity Behavior

The action of particular electrolytes in altering the solution properties of ionic liquids is well documented, although the origin of this effect is not clearly defined. In order to clarify this point, the aim of this work is to obtain further evidence about the salting-out effect produced by the addition of different salts to aqueous solutions of water miscible ionic liquids by evaluating the effect of a large series of salts on the vapor-liquid equilibria, liquid-liquid phase diagram, volumetric, compressibility, and conductometric properties of ionic liquids 1-alkyl-3-methylimidazolium halide ([C(n)mim][X]). In the first part of this work, the experimental measurements of water activity at 298.15 and 308.15 K for aqueous binary and ternary solutions containing 1-alkyl-3-methylimidazolium bromide ([Rmim][Br], R = butyl (C(4)), heptyl (C(7)), and octyl (C(8))), sodium dihydrogen citrate (NaH(2)Cit), disodium hydrogen citrate (Na(2)HCit), and trisodium citrate (Na(3)Cit) are taken using both vapor pressure osmometry (VPO) and improved isopiestic methods. The effect of temperature, charge on the anion of sodium citrate salts, and alkyl chain length of ionic liquids on the vapor-liquid equilibria properties of the investigated systems are studied. The constant water activity lines of all the ternary systems show large negative deviation from the linear isopiestic relation (Zdanovskii-Stokes-Robinson rule) derived using the semi-ideal hydration model, and the vapor pressure depression for a ternary solution is much larger than the sum of those for the corresponding binary solutions with the same molality of the ternary solution. The results have been interpreted in terms of the solute-water and solute-solute interactions. In the second part of this work, the effects of the addition of (NH(4))(3)Cit, K(3)Cit, Na(3)Cit, (NH(4))(2)HPO(4), and (NH(4))(3)PO(4) on the liquid-liquid phase diagram, apparent molar volume, isentropic compressibility, and conductivity of aqueous solutions containing the model ionic liquid 1-butyl-3-methylimidazolium iodide, [C(4)mim][I], are investigated at different temperatures. It was found that there is a relation between the relative concentration of various salts to form two-phase systems with [C(4)mim][I] and apparent molar volume or isentropic compressibility of transfer of [C(4)mim][I] from water to aqueous solutions of the investigated salts.

Ionic liquid facilitates biocatalytic conversion of hardly water soluble ketones

Ionic liquids represent a promising alternative to conventional cosolvents as biocompatible solubilisers for biocatalysis. This was shown using water miscible ionic liquids to facilitate the stereoselective reduction of hardly water soluble, aliphatic ketones catalysed by the alcohol dehydrogenase from Lactobacillus brevis. Ten ionic liquids were screened for activity and solubility. Improved storage stabilities besides improved enzyme activities, as well as reduced substrate surplus and product inhibitions were found, while applying the most promising AMMOENG™ 101 in more detailed investigations. Batch reactions with cofactor regeneration via a glucose dehydrogenase showed increased reaction rates; thus underlining the positive influence of AMMOENG™ 101. For (R)-3-octanol, (R)-2-nonanol, (R)-2-decanol, and (R)-2-octanol space time yields between 250 and 350 mmol L−1 d−1 were achieved.

Effect of ionic liquids on the structure, stability and activity of two related α-amylases

Ionic liquids are recognized as green solvents for carbohydrates dissolution. However, only a limited number of studies have been carried out to investigate their effect on carbohydrate hydrolyzing enzymes. We have investigated the influence of two water miscible ionic liquids on the activity, stability and structure of two related α-amylases from Bacillus amyloliquefaciens and Bacillus lichiniformis. Upon changes in ionic liquids concentrations, both enzymes activity and stability were reduced. Associated thermodynamic and conformational changes were observed using differential scanning calorimetry and fluorescence techniques. Thermal denaturation was accompanied by aggregation in both aqueous buffer and [BMIm][Cl] but [HMIm][Cl] significantly suppressed aggregation.

Characterization of the Influence of the Ionic Liquid 1-Butyl-3-methylimidazolium Chloride on the Structure and Thermal Stability of Green Fluorescent Protein

Ionic liquids (ILs) are finding a vast array of applications as novel solvents for a wide variety of processes that include enzymatic chemistry, particularly as more biocompatible ILs are designed and discovered. While it is assumed that a native or near-native structure is required for enzymatic activity, there is some evidence that ILs alter protein structure and oligomerization states in a manner than can negatively impact function. The IL 1-butyl-3-methylimidazolium chloride, [bmim]Cl, is a well-studied, water-miscible member of the popular 1-alkyl-3-methylimidazolium IL family. To improve our understanding of the impact of water-miscible ILs on proteins, we have characterized the structure and oligomerization state of green fluorescent protein (GFP) in aqueous solutions containing 25 and 50 vol % [bmim]Cl using a combination of optical spectroscopy and small-angle neutron scattering (SANS). Measurements were also performed as a function of temperature to provide insight into the effect of the IL on the thermal stability of GFP. While GFP exists as a dimer in water, the presence of 25 vol % [bmim]Cl causes GFP to transition to a monomeric state. The SANS data indicate that GFP is a great deal less compact in 50 vol % [bmim]Cl than in neat water, indicative of unfolding from the native structure. The oligomerization state of the protein in IL-containing aqueous solution changes from a dimer to a monomer in response to the IL, but does not change as a function of temperature in the IL-containing solution. The SANS and spectroscopic results also demonstrate that the addition of [bmim]Cl to the solution decreases the thermal stability of GFP, allowing the protein to unfold at lower temperatures than in aqueous solution.

In Situ Solvent Formation Microextraction in the Presence of Ionic Liquid for Preconcentration and Speciation of Arsenic in Saline Samples and Total Arsenic in Biological Samples by Electrothermal Atomic Absorption Spectrometry

In this modality, the extraction phase is formed in situ while simultaneously extracting analytes. First, a water-miscible ionic liquid (IL) ([Hmim][BF(4)]), capable of complete dissolving in the aqueous solution, was added to the sample. Then, an ion-exchange reagent (NaPF(6)) was added to obtain the hydrophobic IL ([Hmim][PF(6)]) that acted as the analyte extractant to form the cloudy homogeneous solution for the preconcentration and speciation of trace amounts of As (III) and As (V) with electrothermal atomic absorption spectrometry (ETAAS) detection. In situ solvent formation microextraction is a simple and rapid method for extraction and preconcentration of metal ions from sample solutions containing high concentration of salt. Some effective factors that influence the microextraction efficiency were investigated and optimized. Under the optimum experimental conditions, the limit of detection (3 σ) and the enrichment factor were 6 ng L(-1) and 198, respectively. The obtained relative standard deviation was 4.78%. The proposed method was successfully applied for the determination of As (III) and As (V) in water samples, food salts, and total As in biological samples.

Salting-Out Effect, Preferential Exclusion, and Phase Separation in Aqueous Solutions of Chaotropic Water-Miscible Ionic Liquids and Kosmotropic Salts: Effects of Temperature, Anions, and Cations

The phase diagrams and the liquid−liquid equilibrium (LLE) data of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) + tripotassium citrate and 1-butyl-3-methylimidazolium bromide ([C4mim]Br) + trisodium citrate aqueous two-phase systems (ATPS’s) were determined experimentally at T = (278.15, 298.15, and 318.15) K. The Merchuk equation with three dependent-temperature adjustable parameters was used for reproducing the binodal curves. In the studied systems, the salting-out effect caused by the addition of the inorganic salts to the aqueous solutions of the water-miscible ionic liquids (ILs) was investigated. The effects were analyzed using the corresponding composition phase diagrams. The effect of temperature on the phase-forming ability in the investigated systems was also evaluated based on a salting-out coefficient obtained from fitting the tie-line data to a Setschenow-type equation. The values of the salting-out coefficients may reflect the extent of the preferential hydration of the IL. Furthermore,...

Toward advanced ionic liquids. Polar, enzyme-friendly solvents for biocatalysis.

Ionic liquids, also called molten salts, are mixtures of cations and anions that melt below 100 °C. Typical ionic liquids are dialkylimidazolium cations with weakly coordinating anions such as [MeOSO3] or [PF6]. 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 liquifies 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 regio- or 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 non-volatile and can be made from non-toxic components. This review covers selected examples of enzyme catalyzed reaction 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.

Effect of π–π stacking of water miscible ionic liquid template with different cation chain length and content on morphology of mesoporous TiO 2 prepared via sol–gel method and the applications

In this study, the imidazolium π–π stacking of two water miscible imidazolium ionic liquids (ILs) in the TiO 2 matrix formed during the sol–gel polymerization was studied by FT-IR, XRD, TEM and BET measurements. It was found that the mesoporous morphology, including surface area, average pore size and wormhole-like structure, and thermal stability of the as-prepared TiO 2 particle were varied with the imidazolium chain length and content of the IL used due to different extent of imidazolium π–π stacking. Besides, the wormhole-like mesoporous anatase TiO 2 particles with high surface area exhibited higher photodegradation efficiencies of methylene blue (MB) under 1 h UV irradiation, while those with large pore size used for the electrode materials showed higher efficiency in dye-sensitized solar cells.

Improvement of shear stress tolerance of enzymes in the existence of water-miscible ionic liquids

Improvement of shear stress tolerance of enzymes in the existence of water-miscible ionic liquids

Ionic Liquids as Performance Additives for Electroenzymatic Syntheses

Electroenzymatic syntheses combine oxidoreductase-catalysed reactions with electrochemical reactant supply. The use of ionic liquids as performance additives can contribute to overcoming existing limitations of these syntheses. Here, we report on the influence of different water-miscible ionic liquids on critical parameters such as conductivity, biocatalyst activity and stability or substrate solubility for three typical electroenzymatic syntheses. In these investigations promising ionic liquids were identified and have been used as additives for batch electrolyses on preparative scale for the three electroenzymatic systems. It was possible to improve the space-time-yield for the electrochemical regeneration of NADPH by a factor of three. For an amino acid oxidase catalysed resolution of a methionine racemate with ferrocene-mediated electrochemical regeneration of the enzyme-bound cofactor FAD a 50% increase in space time yield and 140% increase in catalyst utilisation (TTN) were achieved. Furthermore, for the chloroperoxidase-catalysed synthesis of (R)-phenylmethylsulfoxide with electrochemical generation of the required cosubstrate H2O2 the space time yield and the catalyst utilisation were improved by a factor of up to 4.2 depending on the ionic liquids used.

A facile approach to construction of a stable water-miscible ionic liquid/electrolyte interface with interactions between imidazolium moiety and carbon nanotubes

A stable water-miscible ionic imidazolium-based ionic liquid/electrolyte interface is constructed in aqueous media based on the interaction between the imidazolium moiety in ionic liquids (ILs) and single-walled carbon nanotubes (SWNTs). 1- n-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF 4]) is used as one kind of typical water-miscible ILs for this study. The nanocomposite of IL and SWNTs is prepared by dispensing SWNTs into IL and the as-prepared nanocomposite is confined onto glassy carbon (GC) electrodes to construct the IL/electrolyte interface. X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy and cyclic voltammetry (CV) results demonstrate that the imidazolium moiety in ILs could interact with SWNTs to form a stable nanocomposite possibly through π-cation or other kinds of interactions between both components. CV results with Fe ( CN ) 6 4 - / 3 - redox probe suggest the electrochemical interfacial is relatively stable in the aqueous media with a fast electron transfer property. This study may be useful both for the fundamental electrochemical studies and for the practical applications associated with the water-miscible imidazolium-based ILs.

Effects of water-miscible ionic liquids on cell growth and nitro reduction using Clostridium sporogenes

Water miscible ionic liquids had various effects on the physiology of Clostridium sporogenes when tested as additives in culture media or reaction media for reduction of nitrobenzene. 2-Hydroxy ethyl trimethyl-ammonium dimethyl phosphate ([EtOHNMe3][Me2PO4]) and N,N-dimethylethanolammonium acetate (DMEAA) increased the growth rate of C. sporogenes by as much as 28%, suggesting that they were either metabolised or increased the availability of nutrients. By contrast, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMim][BF4]) and AMMOENG™ 100 inhibited growth. Although 1-ethyl-3-methyl imidazolium ethylsulfate ([EMim][EtSO4]; 2% w/v) inhibited growth by 58%, it was sufficiently non-toxic to allow efficient reduction of nitrobenzene using harvested cells, providing aniline yields up to 79%. The high product yield with reactions in [EMim][EtSO4] represented a significant improvement over conventional solvents, since the yield was only 8% in aqueous ethanol (4% v/v) and 45% in a biphasic heptane/aqueous system (phase ratio 0.33). The ionic liquid appeared to suppress unproductive substrate consumption by an unknown mechanism

Effects of Structural Difference of Ionic Liquids on the Catalysis of Horseradish Peroxidase

The dependence of the catalytic properties of horseradish peroxidase on the structural changes of ionic liquids was investigated with two water-miscible ionic liquids, N-butyl-3- methypyridinium tetrafluoroborate ([BMPy][BF4]) and 1-butyl- 3-methylimidazolium methylsulfate ([BMIM][MeSO4]), each of which shares an anion (BF4 -) or a cation (BMIM+) with 1-butyl- 3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), respectively. The oxidation of guaiacol (2-methoxyphenol) with H2O2 was used as a model reaction. In order to minimize the effect of solution viscosity on the kinetic constants of the enzymatic catalysis, the enzymatic reactions for the kinetic study were performed in water-ionic liquid mixtures containing 25% (v/v) ionic liquid at maximum. Similarly to the previously reported results for [BMIM][BF4], as the concentration of [BMPy][BF4] increased, the Km value increased with a decrease in the kcat value: the Km value increased markedly from 2.8 mM in 100% water to 12.6 mM in 25% (v/v) ionic liquid, indicating that ionic liquid significantly weakens the binding affinity of guaiacol to the enzyme. On the contrary, [BMIM][MeSO4] decreased the Km value to 1.4 mM in 25% (v/v) ionic liquid. [BMIM][MeSO4] also decreased kcat more than 3- folds [from 13.8 s-1 in 100% water to 4.1 s-1 in 25% (v/v) ionic liquid]. These results indicate that the ionic liquids interact with the enzyme at the molecular level as well as at a macroscopic thermodynamic scale. Specifically, the anionic component of the ionic liquids influenced the catalysis of horseradish peroxidase in different ways.

A high throughput screen to test the biocompatibility of water-miscible ionic liquids

Download options Please wait... Additions and corrections Addition HTM (3K) Article information DOI https://doi.org/10.1039/B815951C Article type Paper Submitted 12 Sep 2008 Accepted 12 Dec 2008 First published 23 Jan 2009 Download Citation Green Chem., 2009,11, 402-408 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions A high throughput screen to test the biocompatibility of water-miscible ionic liquids M. Rebros, H.Q. N. Gunaratne, J. Ferguson, K. R. Seddon and G. Stephens, Green Chem., 2009, 11, 402 DOI: 10.1039/B815951C To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Martin Rebros H.Q. Nimal Gunaratne Jamie Ferguson Kenneth R. Seddon Gillian Stephens

Small-angle neutron scattering studies of model protein denaturation in aqueous solutions of the ionic liquid 1-butyl-3-methylimidazolium chloride

Abstract As we advance our understanding, ionic liquids (ILs) are finding ever broader scope within the chemical sciences including, most recently, pharmaceutical, enzymatic, and bioanalytical applications. With examples of enzymatic activity reported in both neat ILs and in IL/water mixtures, enzymes are frequently assumed to adopt a quasi-native conformation, even if little work has been carried out to date toward characterizing the conformation, dynamics, active-site perturbation, cooperativity of unfolding transitions, free energy of stabilization, or aggregation/oligomerization state of enzymes in the presence of an IL solvent component. In this study, human serum albumin and equine heart cytochrome c were characterized in aqueous solutions of the fully water-miscible IL 1-butyl-3-methylimidazolium chloride, [bmim]Cl, by small-angle neutron and X-ray scattering. At [bmim]Cl concentrations up to 25 vol.%, these two proteins were found to largely retain their higher-order structures whereas both proteins become highly denatured at the highest IL concentration studied here (i.e., 50 vol.% [bmim]Cl). The response of these proteins to [bmim]Cl is analogous to their behavior in the widely studied denaturants guanidine hydrochloride and urea which similarly lead to random coil conformations at excessive molar concentrations. Interestingly, human serum albumin dimerizes in response to [bmim]Cl, whereas cytochrome c remains predominantly in monomeric form. These results have important implications for enzymatic studies in aqueous IL media, as they suggest a facile pathway through which biocatalytic activity can be altered in these nascent and potentially green electrolyte systems.

Heat Capacities and Excess Enthalpies of 1-Ethyl-3-methylimidazolium-Based Ionic Liquids and Water

Heat capacities and excess enthalpies were determined for three different binary water + ionic liquid systems, from (283.15 to 348.15) K, and covering the entire composition range. Specifically, the three completely water-miscible ionic liquids used were 1-ethyl-3-methylimidazolium ethylsulfate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium trifluoroacetate. The influence of temperature and composition was assessed, and suitable equations were used to correlate the experimental data. In addition, it was found that 1-ethyl-3-methylimidazolium ethylsulfate decomposes in the presence of water to form 1-ethyl-3-methylimidazolium hydrogen sulfate and ethanol under ambient conditions.

Dye Redissolution after Precipitation with a Water-miscible Ionic Liquid

Abstract Redissolution of five popular cationic dyes with a water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate after their near quantitative precipitation from aqueous solutions is observed. The behavior of the ionic liquid is similar to that of a salt at lower concentrations, while it acts like a cosolvent at higher concentrations.

Iodination of Organic Compounds with Elemental Iodine in the Presence of Hydrogen Peroxide in Ionic Liquid Media

Iodo-transformations using the reagent system I2/H2O2 were studied in the water miscible ionic liquid (IL) 1-butyl-3-methyl imidazolium tetrafluoroborate (bmimBF4) and in water immiscible IL, 1-butyl-3-methyl imidazolium hexafluorophosphate (bmimPF6). Two different forms of H2O2 as mediators of iodination were investigated, namely 30% aq. H2O2 and urea-H2O2 (UHP) in solid form. The role of the oxidant during the course of a reaction could be distinguished based on the amount of reagent required for the most efficient transformation. Two types of iodo-functionalizations through an electrophilic process were observed depending on the structure of the substrates. Whereas ring iodination took place in the case of dimethoxy- and trimethoxy-benzenes, with arylalkyl ketones the alkyl group α to the carbonyl was regioselectively iodinated. The results were further evaluated in comparison with iodination using the reagent system I2/H2O2 in water as medium, and under solvent-free reaction conditions, in terms of efficiency, selectivity, mechanism, and the ‘green’ aspects. The reusability/recycling of water immiscible bmimPF6 was investigated for 1,3,5-trimethoxy benzene (1b), which required a 1/0.5/0.6 molar ratio of substrat/I2/oxidant, and for 1,2,3-trimethoxy benzene (1f), which required a 1/1/1 ratio for complete iodine introduction. In addition, the efficiency of iodination was tested by varying the substrates, and employing the recycled hydrophobic IL bmimPF6.

Strong substrate-stabilizing effect of a water-miscible ionic liquid [BMIM][BF4] in the catalysis of horseradish peroxidase

The effects of a water-miscible ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]), on both thermodynamics and kinetic mechanism of the horseradish peroxidase (HRP)-catalyzed oxidation of guaiacol (2-methoxyphenol) by H(2)O(2) were investigated. The ionic liquid stabilized the ground state of guaiacol by causing an 8-fold increase of K(m) from 3 to 23 mM upon the addition of 25% (v/v) [BMIM][BF(4)]. In addition, the effect of [BMIM][BF(4)] in decreasing the k(cat) value of HRP catalysis was described by a non-competitive inhibition mechanism. The value of the inhibition constant of [BMIM][BF(4)] was 2.9 M indicating that the ionic liquid plays the role of a weak non-competitive inhibitor for HRP catalysis.

Asymmetric biocatalytic reduction of ketones using hydroxy-functionalised water-miscible ionic liquids as solvents

Bi- and monophasic ionic liquid (IL)/buffer systems were successfully employed for the biocatalytic reduction of ketones catalysed by the alcohol dehydrogenase ADH-‘A’ from Rhodococcus ruber via hydrogen transfer. Two different catalyst preparations were employed, namely recombinant ADH-‘A’ ‘immobilised’ in Escherichia coli and partially purified ADH-‘A’. For biphasic systems conversions were acceptable until 20% v v −1 of IL. In contrast, hydroxy-functionalised ‘Tris-like’-ILs were successfully employed in monophasic systems up to 90% v v −1 IL. The use of these solvents allowed highly stereoselective enzymatic carbonyl reductions at substrate concentrations from 1.2 to 1.5 M.