IL Solutions Research Articles

High Ionic Liquid Concentration-Induced Structural Change of Protein in Aqueous Solution: A Case Study of Lysozyme

The structural change of chicken egg white lysozyme in aqueous 1-butyl-3-methylimidazolium nitrate ([bmim][NO(3)]) solutions (0-24 M) has been investigated by optical spectroscopy and small-angle X-ray scattering (SAXS) methods. Fourier-transform infrared (FTIR) and circular dichroism (CD) spectra and SAXS profiles indicated that the addition of up to 6 M of [bmim][NO(3)] induces unfolding of lysozyme resulting from disruption of the α-helix by the NO(3)(-) ion. On the other hand, even with the addition of more than 10 M of [bmim][NO(3)], lysozyme aggregation is inhibited and the protein adopts a partially globular state (the secondary structure is partially refolded while the tertiary structure is disrupted). Observation of the structural features of the aqueous [bmim][NO(3)] solution by Raman OD stretching spectra indicated that bulk-like water still remains at concentrations above 10 M and form an "aggregated water" (water pool) in the nanoheterogeneous structure consisting of a polar domain (the high charge-density region) and nonpolar areas (the alkyl-chain region) in the IL. At these concentrations (above 10 M), lysozyme is not sufficiently hydrated because of the reduced number of water molecules. Consequently lysozyme above 10 M assumes the partially globular state. We propose that the changes of the unique IL solution structure (nanoheterogeneous) between the lower and higher [bmim][NO(3)] concentrations strongly correlated to the differences in the protein stability of the present results.

Universal Charge Quenching and Stability of Proteins in 1-Methyl-3-alkyl (Hexyl/Octyl) Imidazolium Chloride Ionic Liquid Solutions

This study reports pH dependent stability of protein dispersions of five common proteins, bovine serum albumin (BSA), human serum albumin (HSA), immunoglobulin (IgG), β-lactoglobulin (β-Lg), and gelatin-B (Gel-B), all having isoelectric pH, pI ≈ 5, in room temperature ionic liquid solutions of 1-methyl-3-alkyl (hexyl/octyl) imidazolium chloride (concentration 0-0.2% w/v). Molecular hydrophobicity index, (H-index = hydrophobicity/hydrophilicity) of these molecules spanned the range 0.43-0.87. Electrophoretic characteristics, surface tension data and hydrodynamic size information revealed that IL solutions provide dispersion stability owing to specific protein-IL binding which did not alter their pI values though their surface charge was considerably screened. Change in maximum (ζ(max)) and minimum (ζ(min)) zeta potential values observed at pH ~3 (maximum protonated state) and pH ~8 (maximum deprotonated state) could be described universally as function of IL concentration, c as Δζ(x) = [1 - exp(-ac)] where Δζ(x) is either |(ζ(max) - ζ(w))|/ζ(w) or |(ζ(min) - ζ(w))|/ζ(w), and ζ(w) is the corresponding value in water. Tensiometry data showed two major stages of protein-IL interactions: (i) for c < cmc of IL, the IL molecules selectively bind with imidazolium cation through electrostatic forces forming protein-IL (complex) and (ii) for c> cmc free IL-aggregates begin to form. Similarly, we can define Δγ(x) as either |(γ(max) - γ(w))|/γ(w) at pH 3 or |(γ(min) - γ(w))|/γ(w) at pH 8. Both Δζ(x) and Δγ(x) showed linear dependence with c, Δγ(min, max) (or Δζ(min, max)) = (1 - K(γ) (or K(ζ)) H-index), where the slopes K(ζ) and K(γ) defined intermolecular interactions. Hydrodynamic radii data revealed protein stabilization, circular dichroism spectra implied retention of secondary structures, and Raman spectra confirmed a marginal increase in water structure. Results concluded that selective binding of IL molecules to protein surface in the form of bilayer screen protein surface charge, thereby, contributing to its dispersion stability.

Solvent Effect on the Enthalpy of Solution and Partial Molar Volume of the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate

Enthalpies of solution and partial molar volumes of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate were determined in 15 solvents of different polarity. Very large differences of the enthalpies of solution (ΔΔsolHIL=38.9 kJ⋅mol−1) and partial molar volumes (ΔVIL=43 cm3⋅mol−1) are nearly the same as observed for lithium perchlorate solutions. These results clearly indicate that the low values of the macroscopic polarity parameters of [bmim]BF4 do not correspond with the large differences of the intermolecular interactions in IL solutions. The values of the partial molar volume of the cation, \(V_{[\mathrm{bmim}]^{+}}\), were estimated for the first time. The changes of the partial molar volumes, VIL, reflect mainly the changes of anion volume, \(V_{\mathrm{BF}_{4}^{-}}\). The rate of the Diels–Alder reaction of 9,10-dimethylanthracene with maleic anhydride in the [bmim]BF4 medium was nearly the same as in common molecular solvents.

An in-situ extraction–preconcentration method using ionic liquid-based surfactants for the determination of organic contaminants contained in marine sediments

The determination of a group of organic contaminants from marine sediments samples including three polycyclic aromatic hydrocarbons, five alkylphenols (i.e., bisphenol-A or nonylphenol) and one paraben has been carried out using an extraction/preconcentration strategy with ionic liquid-based surfactants and high-performance liquid chromatography (HPLC) with diode array detection (DAD). Sediments are first extracted using two IL-based surfactants, specifically 1-hexadecyl-3-methyl imidazolium bromide (C16MIm–Br) and 1-hexadecyl-3-butyl imidazolium bromide (C16C4Im–Br), as the extraction media in a microwave-assisted extraction (MAE) procedure, followed by a novel in situ preconcentration method. The optimized MAE method requires 0.1g of sediment and 5mL of 40mM C16MIm–Br IL solution. The extracts are then centrifuged and filtered. The subsequent preconcentration in situ approach consists of the insolubilization of an IL-based surfactant formed by a metathesis reaction using the anion-exchange reagent lithium bis[(trifluoromethane)sulfonyl]imide (LiNTf2), which produces an analyte enriched IL microdroplet. The optimized in situ approach utilizes 4mL of the filtered extract, which are mixed with acetonitrile and 92μL of LiNTf2 solution (0.5gmL−1), heated, vortexed and centrifuged. The formed IL microdroplet is then simply diluted with acetonitrile (∼100μL) and injected in the chromatograph without any further clean-up steps. The overall extraction/preconcentration method requires approximately 25min in spite of dealing with complex solid samples, is nearly free of organic solvent (requires ∼900μL of acetonitrile per sample), and produces high preconcentration factors and quantification limits down to 0.04mgkg−1 using HPLC–DAD.

Ionic liquid-supported solid–liquid extraction of bioactive alkaloids. I. New HPLC method for quantitative determination of glaucine in Glaucium flavum Cr. (Papaveraceae)

A series of hydrophilic 1-alkyl-3-methylimidazolium-based ionic liquids were used as extractants for the effective extraction of S-(+)-glaucine from plant material of Glaucium flavum Crantz (Papaveraceae). The extractions were carried out both under ultrasonic and conventional heating conditions and the extraction efficiency was monitored by HPLC. The influence of the anion (chloride, bromide, acesulfamate and saccharinate), alkyl chain length in the imidazolium ion, concentration, extraction time, and plant material/extractant ratio was investigated. A comparative study between conventional Soxhlet extraction with methanol as a solvent (total extraction) and water solutions of ILs shows the same extraction ability of ILs, but with significantly reduced extraction time. Moreover, the extraction efficiency was shown to be strongly anion dependent. The results obtained provide a fast and safe method for determination of glaucine in G. flavum Cr.

The role of long-range interactions in the phase behavior of ionic liquids

The COSMO-type liquid activity coefficient models are among the most successful methods for the prediction of the phase behaviours of fluids containing ionic liquids. However, these models consider only interactions between species that are in close contact; in other words, the long-range Coulomb interactions, which are known to be important for systems containing charged species, are completely ignored. Here we show that the inclusion of long-range terms (with, e.g., the Pitzer-Debye-Hückel model) is indeed critical to obtain the correct osmotic coefficients and the asymptotic behaviours in the infinite dilution of IL solutions. However, the direct combination of PDH and COSMO-type models does not produce accurate activity coefficient over the whole concentration range because both models contain short range interactions. We show that a recent revision of the COSMO-SAC model, which includes the PDH contributions and a specific treatment of solvent-ion and ion-ion interactions, is capable of providing an accurate description of the properties (phase behaviour, osmotic coefficients) of aqueous IL solutions over the whole concentration range.

Agarose processing in protic and mixed protic–aprotic ionic liquids: dissolution, regeneration and high conductivity, high strength ionogels

We have shown that low viscosity alkyl or hydroxyalkyl ammonium formate (ILs) can dissolve agarose, and higher dissolution can be achieved in the mixed, alkyl or hydroxyalkyl ammonium + imidazolium or pyridinium ILs. The polarity parameters α, β, π*, ET(30) and ETN of these IL systems were measured to explain their dissolution ability for agarose. Dissolved agarose was either regenerated using methanol as a precipitating solvent or ionogels were formed by cooling the agarose–IL solutions to ambient temperature. Exceptionally high strength ionogels were obtained from the agarose solutions in N-(2-hydroxyethyl)ammonium formate or its mixture with 1-butyl-3-methylimidazolium chloride. Regenerated material and ionogels are characterized for their possible degradation/conformational changes and gel properties (thermal hysteresis, strength, viscoelasticity and conductivity) respectively. A high strength, high conducting ionogel was demonstrated to be able to build an electrochromic window. Such ionogels can also be utilized for other soft matter electronic devices and biomedical applications.

Hydrolysis study of fluoroorganic and cyano-based ionic liquid anions – consequences for operational safety and environmental stability

The hydrolytic stability of ionic liquid anions is a key property with regard to their technical applicability and environmental stability. From a technical point of view hydrolytic processes may lead to reduced durability, diminished technical performance and reduced operational safety in that corrosive and/or toxic hydrolysis products are formed. On the other hand, susceptibility to hydrolytic processes is advantageous where environmental stability and persistency are concerned, since hydrolysis is the most important abiotic degradation pathway in the environment. We investigated the hydrolytic stability of the most common ionic liquid anions, dicyanimide [N(CN)2]−, tricyanmethanide [C(CN)3]−, tetracyanidoboranate [B(CN)4]−, bis(trifluoromethylsulphonyl)imide [(CF3SO2)2N]−, trifluorotris(pentafluoroethyl)phosphate [(C2F5)3PF3]− and 1,1,2,2-tetrafluoroethanesulphonic acid [H(C2F4)SO3]−, as a function of pH (1, 7, 9 and 13) and temperature. The results show that there was no difference in hydrolytic stability as recorded for 1-ethyl-3-methylimidazolium (IM12) or for the alkali cations. All the anions were stable under neutral and slightly basic conditions (half-lives at 25 °C ⇒1 year). In strongly acidic and basic solutions, however, B(CN)4−, (CF3SO2)2N−, (C2F5)3PF3− and H(C2F4)SO3− were hydrolytically stable, whereas N(CN)2− and C(CN)3− were not. The kinetics of hydrolysis were recorded and Arrhenius plots were generated for the latter two anions. In addition, their hydrolysis pathways and the resulting products were identified via mass spectrometry. The cytotoxicity of hydrolysed IL solutions towards the mammalian cell line IPC-81 and the identified hydrolysis products (pure compounds) was investigated for a first estimate of their toxicological properties.

Viscosity and Density Measurements for Six Binary Mixtures of Water (Methanol or Ethanol) with an Ionic Liquid ([BMIM][DMP] or [EMIM][DMP]) at Atmospheric Pressure in the Temperature Range of (293.15 to 333.15) K

The experimental data of viscosity and density for six binary mixtures of water (methanol or ethanol) with an ionic liquid, 1-butyl-3-methylimidazolium dimethylphosphate ([BMIM][DMP]) or 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]), were measured in the temperature range of (293.15 to 333.15) K at atmospheric pressure using a viscometer and densimeter. The solution behavior of the mixtures is discussed in terms of the variation of the excess viscosity and excess volume with temperatures and compositions. It is found that both excess volume and viscosity of the mixtures studied show a negative deviation from the ideal solution behavior, and the viscosity of the mixtures decreases drastically with the increase of temperatures and mole fractions of solvents. The excess volume of the binary mixtures is quite low, in the range of (1.0 to 1.9) cm3·mol–1; moreover, it shows a monotonic decrease with increasing temperature for the aqueous solution of ILs and a reverse trend for the IL solutions of ...

Synthesis and usage of common and functionalized ionic liquids for biogas upgrading

Halide imidazolium-based ionic liquids 1-butyl-3-methylimidazolium bromide [bmim][Br] and 1-propylamine-3-methylimidazolium bromide [pamim][Br] were synthesised and tested experimentally as absorbents for biogas upgrading . The former solvent is a conventional off-the-shelf room temperature ionic liquid (RTIL), which is soluble in water and expected to have a high CO 2 solubility. The second solvent is a new type of task-specific ionic liquid (TSIL) and has a straight amine-alkyl substitute incorporated to enhance CO 2 solubility. Experimental evidence suggests that the majority of known imidazolium-based ionic liquids are good CO 2 absorbents; adding these to a designed solvent that combines a long amino-alkyl lineal group is expected to improve the performance of CO 2 absorption over other alternatives under discussion. CO 2 absorption experiments were conducted in an absorbing column packed with randomly placed Raschig rings. A biogas model consisting of CO 2 (43% v/v) diluted in N 2 was used to test CO 2 uptake with aqueous solutions of the above-mentioned ILs at 5%, 10% and 15% (w/w) concentrations. The gaseous and liquid streams were operated under concurrent flow with a gas–liquid volumetric ratio of 1:2. Additionally, absorption tests were conducted with aqueous solutions of monoethanolamine (MEA) mixed with the ILs under investigation to elucidate potential activations of these amino solutions. In this experiment, the ILs used for biogas upgrading do not present a higher absorption than amino solutions, and there were no significant synergy results from mixing them with MEA, which could have enhanced the CO 2 uptake.

Surfactant Self-Assembly Nanostructures in Protic Ionic Liquids

The existence and properties of mesoscopic self-assembly structures formed by surfactants in protic ionic liquid solutions are reported. Micellar aggregates of n-alkyltrimethylammonium (n = 10, 12, 14, 16) chlorides and bromides and of n-alkylpyridinium (n = 12, 16) chlorides in ethylammonium nitrate and propylammonium nitrate were observed by means of several experimental techniques, including surface tension, transmission electron micrography, dynamic light scattering, and potentiometry using surfactant-selective electrodes. The effect of the alkyl chain length of both solute and solvent molecules on the critical micelle concentration is discussed, and a Stauff-Klevens law is seen to apply to surfactant solutions in both protic ionic liquids. The counterion role is also a matter of study in the case of alkyltrimethylammonium-based surfactants, and the presently reported evidence suggests that the place of the surfactant counterion in the Hoffmeister's series could determine its effect on micellization in IL solution. The size distribution of the aggregates is also analyzed together with the Gibbs free energies of micellization and the minimum surface area per monomer in all of the studied cases. All of the hereby reported evidence suggests that the negative entropic contribution arising from the release of the solvent layer upon micellization is also the driving force of conventional surfactant self-association in protic ionic liquids.

Plasma Electrochemistry in 1‐Butyl‐3‐methylimidazolium dicyanamide: Copper Nanoparticles from CuCl and CuCl2

AbstractWe report on the reaction of CuCl and CuCl2, each dissolved in 1‐butyl‐3‐methylimidazolium dicyanamide ([BMIm]dca), with a glow discharge argon plasma. The interaction of the plasma with the solutions exhibits a strong reaction with gas evolution and the growth of copper nanoparticles. The particle size was determined with transmission electron microscopy (from the particle/ionic liquid, IL solution). The chemical composition was investigated by ex situ X‐ray photoelectron spectroscopy (XPS). We found that the mean diameter of the copper particles produced in CuCl/[BMIm]dca and CuCl2/[BMIm]dca was in the same order of magnitude (between 2 and 10 nm). Despite the strong reaction we found no hints for IL degradation products in the liquids with infrared spectroscopy. XPS showed that ex situ treatment of the particles leads to the formation of CuO. magnified image

Effect of simple electrolytes on the thermodynamic properties of room temperature ionic liquids in aqueous solutions

Density, sound velocity and conductivity measurements are carried out on 1-heptyl-3-methylimidazolium bromide ([C 7mim][Br]) in pure water and in aqueous solutions of sodium di-hydrogen citrate, di-sodium hydrogen citrate and tri-sodium citrate over a range of temperatures at atmospheric pressure. The experimental density and sound velocity data are used to calculate the apparent molar volume and isentropic compressibility as a function of temperature and concentration. The effects of temperature and charge on the anion of sodium citrate salts on the apparent molar volume and isentropic compressibility of [C 7mim][Br] are studied. It was found that both of the apparent molar volume and isentropic compressibility of [C 7mim][Br] in aqueous sodium citrate solutions are larger than those in pure water and increase by increasing temperature. The effects of temperature and charge on the anion of sodium citrate salts on the conductivity behavior of the investigated IL solutions are also studied.

Methods for stabilizing and activating enzymes in ionic liquids—a review

AbstractIonic liquids (ILs) have evolved as a new type of non‐aqueous solvents for biocatalysis, mainly due to their unique and tunable physical properties. A number of recent review papers have described a variety of enzymatic reactions conducted in IL solutions; on the other hand, it is important to systematically analyze methods that have been developed for stabilizing and activating enzymes in ILs. This review discusses the biocatalysis in ILs from two unique aspects (1) factors that impact the enzyme's activity and stability, (2) methods that have been adopted or developed to activate and/or stabilize enzymes in ionic media. Factors that may influence the catalytic performance of enzymes include IL polarity, hydrogen‐bond basicity/anion nucleophilicity, IL network, ion kosmotropicity, viscosity, hydrophobicity, the enzyme dissolution, and surfactant effect. To improve the enzyme's activity and stability in ILs, major methods being explored include the enzyme immobilization (on solid support, sol–gel, or CLEA), physical or covalent attachment to PEG, rinsing withn‐propanol methods (PREP and EPRP), water‐in‐IL microemulsions, IL coating, and the design of enzyme‐compatible ionic solvents. It is exciting to notice that new ILs are being synthesized to be more compatible with enzymes. To utilize the full potential of ILs, it is necessary to further improve these methods for better enzyme compatibility. This is what has been accomplished in the field of biocatalysis in conventional organic solvents. Copyright © 2010 Society of Chemical Industry

High pressure solubility data of carbon dioxide in (tri- iso-butyl(methyl)phosphonium tosylate + water) systems

Ionic liquids are attracting great attention nowadays due to their interesting properties which make them useful in a broad range of applications including reaction media or separation/capture of environmentally hazardous gases such as carbon dioxide. In many cases, for practical and/or economical reasons, the use of aqueous solutions of ILs would be preferable to their use as pure compounds. In this work, high pressure equilibrium data for the {carbon dioxide (CO 2) + tri- iso-butyl(methyl)phosphonium tosylate [ iBu 3MeP][TOS] + water system were measured at temperatures ranging from (276 to 370) K and pressures up to 100 MPa. Measurements were performed using a high-pressure cell with a sapphire window that allows direct observation of the liquid–vapour transition. Mixtures with different IL concentrations were studied in order to check the influence of the amount of IL on the solubility of CO 2 in the aqueous mixture. The results show that the presence of IL enhances the solubility of CO 2 in the (IL + water) system revealing a salting-in effect of the IL on the solubility of CO 2. The appearance of a three phase region was observed for IL concentrations higher than 4 mol% of IL in water when working at pressures between 4 and 8 MPa and temperatures between (280 and 305) K. In this range, the upper limit of the VLE region observed is shown to increase with the temperature being almost independent of the IL initial concentration in the mixture.