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Water-in-Ionic Liquid Microemulsion Formation in Solvent Mixture of Aprotic and Protic Imidazolium-Based Ionic Liquids
Abstract
We report that water-in-ionic liquid microemulsions (MEs) are stably formed in an organic solvent-free system, i.e., a mixture of aprotic (aIL) and protic (pIL) imidazolium-based ionic liquids (ILs) containing anionic surfactant, dioctyl sulfosuccinate sodium salt (AOT). Structural investigations using dynamic light, small-angle X-ray, and small-angle neutron scatterings were performed for MEs formed in mixtures of aprotic 1-octyl-3-methylimidazolium ([C8mIm+]) and protic 1-alkylimidazolium ([CnImH+], n = 4 or 8) IL with a common anion, bis(trifluoromethanesulfonyl)amide ([TFSA-]). It was found that the ME structure strongly depends on the mixing composition of the aIL/pIL in the medium. The ME size appreciably increases with increasing pIL content in both [C8mIm+][TFSA-]/[C8ImH+][TFSA-] and [C8mIm+][TFSA-]/[C4ImH+][TFSA-] mixtures. The size is larger for the n = 8 system than that for the n = 4 system. These results indicate that the shell part of MEs is composed of both AOT and pIL cation and the ME size can be tuned by pIL content in the aIL/pIL mixtures.
... A mixture of 1-octylimidazolium-based aprotic and protic ILs with Na[AOT] was used to successfully control the size of RMs as a function of protic IL content. 35 However, the solubility of AOT and water with the ILs was limited in this system. ...
... 47,48 Thus, the R g values for each f w can be obtained from the slope of the Guinier plots in the Guinier region (q o 1/R g ). The R g increased linearly with increasing f w as shown in Fig. 3b; this behavior was similar to that in our previous work with water-in-IL MEs in an aprotic/protic IL mixture system 35 Fig. 4 shows the SAXS profiles across the f w range of 0.1 to 0.99. The SAXS profiles at f w = 0.1 and 0.11 exhibited intense scattering in the low-q region (q o 10 À2 Å À1 ), suggesting the existence of significantly larger MEs than that at the lower f w described above. ...
We report the water-in-ionic-liquid microemulsions (ME) formed in a binary water/ionic liquid system, without organic solvents, using a surfactant ionic liquid (SAIL) based on 1-butyl-3-methylimidazolium (C4mIm+) as the cation and dioctyl sulfosuccinate (AOT−) as the anion. Small-angle X-ray scattering (SAXS) revealed that MEs were stably formed in the binary water/SAIL solutions in the low water content region (water volume fraction, ɸw < 0.12), and the ME size systematically increased with increasing ɸw. We further investigated the nanostructures of the high ɸw region using a combination of SAXS and rheological measurements and found that the MEs changed to a stacked lamellar structure comprising SAIL bilayers and water phases at ɸw > 0.12. At the largest water content, ɸw = 0.99, vesicle structures were obtained.
... In view of the volatility of conventional organic solvents (oils), hydrophobic ionic liquids (ILs) with low vapor pressure have been tried in recent years to replace the oils and formulate IL based microemulsion [14][15][16][17][18][19][20][21][22][23][24][25]. 1-Butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF 6 ) and 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Omim]Tf 2 N) are typical ILs used for the purpose. ...
... To circumvent this problem, some additives are added. With the aid of 1-hexanol [16] or the protic ionic liquid 1-octylimidazolium bis(trifluoromethanesulfonyl)imide ([OmiH]Tf 2 N) [24], a water-in-[Omim]Tf 2 N microemulsion stabilized by sodium bis(2-ethyl-1-hexyl)sulfosuccinate (NaAOT) has been prepared. In the presence of the nonionic surfactant polyoxyethylene (10) octylphenyl ether (Triton X-100), a water-in-[Bmim]PF 6 microemulsion stabilized by NaAOT has also been formulated [18]. ...
A new strategy is proposed here to formulate a bis(2-ethyl-1-hexyl)sulfosuccinate (AOT⁻) stabilized water-in-ionic liquid microemulsion without any additives. Replacing the inorganic counter ion Na⁺ by the organic 1-butyl-3-methylimidazolium ([Bmim]⁺) ion greatly improves the solubility of AOT⁻ in hydrophobic 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim]Tf2N) (IL) and favors the formation of water-in-IL (W/IL) microdroplets. The existence of the W/IL microdroplets has been confirmed by dynamic light scattering, Fourier transform infrared absorption spectroscopy and ultraviolet–visible absorption spectroscopy. Also, presented for the first time are the effects of salts and alcohols on the microstructure and water solubilization capacity of the ternary H2O/[Bmim]AOT/[Bmim]Tf2N system. For inorganic salts, larger concentrations of the salt and higher charge density of the cation result in smaller microdroplet size and weak water solubilization capacity. For 1-hexanol, a high concentration of this alcohol results in small microdroplet size but high water solubilization capacity. Analyses indicate that the salts compress the electric double layers of W/IL microemulsions, decrease the size of the microdroplets and consequently reduce the water solubilization capacity; the alcohol, however, facilitates the aggregation of AOT⁻, increases the number of W/IL microdroplets, and therefore improves the water solubilization capacity of the system.
... However, with time, aqueous IL-MEs are drawing more and more attention, as theyin terms of green chemistry principlesconstitute a more promising alternative. [29][30][31][32][33][34][35][36][37][38] In contrast to conventional MEs, IL-ME systems may contain highly conductive polar, nonpolar or both phases that undergo a variety of specic interactions, and hence constitute new, interesting media. In addition, the role of the ILs in ME formation may be extended to that of surfactants stabilizing two immiscible liquids. ...
... 41 Therefore, in this work we concentrate on the dependence of the transport properties of IL-based systems upon IL content, focusing especially on IL-rich systemssolutions or water-in-IL (W/IL) MEs. To date, multitechnique evidence of W/IL-ME formation has been provided only for water/AOT/(1-octyl-3-methylimidazolium-and 1-alkylimidazolium bis(triuoromethanesulfonyl)imide) 36 and water/Brij-35/ 1-butyl-3-methylimidazolium hexauorophosphate MEs. 33 Moreover, although W/IL systems have been presented in the literature as media for enzymatic reactions 42 or nanoparticle synthesis, 43 these studies have been concentrated on specic composition in the given ternary (or pseudo-ternary) system and have not delivered explanations for the denite qualitative or quantitative choice of components. ...
The specific conductivity, dynamic viscosity and apparent diffusion coefficient of each of four aqueous ionic liquid microemulsions (IL-MEs) were measured as a function of ionic liquid (IL) content. The investigated systems were composed of water, hydrophobic ILs (1-butyl-3-methylimidazolium hexafluorophosphate or bis(trifluoromethanesulphonyl)imide) and the nonionic surfactant Triton X-100 or its mixture with cosurfactant (butanol). Measurements were conducted across the whole IL content range, and results are discussed in terms of the anion type and the influence of cosurfactant. The comparative approach revealed that IL-MEs exhibit higher conductivity than pure ILs, that addition of cosurfactant further increases the conductivity of the system, and that the increase depends on the anion structure. Furthermore, addition of cosurfactant causes a serious decrease in viscosity which is beneficial since high viscosity is one of the factors limiting the broader use of ILs. The apparent diffusion coefficients, measured with cyclic voltammetry, exhibited good consistency with values obtained by other techniques and allowed closer insight into the properties and structures of the studied systems. The conclusions were supported by UV-Vis as well as FTIR spectrophotometric measurements. The pronounced facilitation of transport properties is favorable to many applications such as synthesis or separation processes. This is the first work regarding the dependence of IL-based ME properties on IL content.
... Ionic liquids (ILs) are environmentally friendly green solvents due to its unique physical and chemical properties such as the low saturated vapor pressure, the wide liquid temperature range, and the functional design ability [1][2][3]. ILs have been widely used in the fields of chemical or biochemical catalysis [4,5], extraction [6], electrochemistry [7][8][9], inorganic material synthesis [10,11], colloid, and interface chemistry [12,13]. ...
Series of hydrophobic hexafluoroantimonate [Cneim][SbF6] (n = 4, 5, 6) were synthesized and characterized by 1H NMR and ESI-MS. It is obvious that the reactive hydrogen is replaced with ethyl group on N-3 position of imidazole cation, and it could have an effect on the corresponding physicochemical properties. The density, surface tension, refractive index, and conductivity of the hydrophobic ILs [Cneim][SbF6] (n = 4, 5, 6) were measured in the temperature range of (293.15 to 343.15) ± 0.05 K with an interval of 5 K. The volume properties and surface properties were calculated. According to Kabo’s method, the vaporization enthalpy was also calculated, and the polarities were predicted. The applications of the mole surface Gibbs free energy were investigated. In addition, the relationship between the conductivity and temperature was also explored, and the molar conductivity and diffusion coefficient for ILs were obtained.
... Different microstructures ranging from droplets of oil dispersed in a continuous water phase (O/W) over a bicontinuous phase, to water droplets dispersed in a continuous oil phase (W/O), can be formed in microemulsion mixtures. Recently, ionic liquids (IL) have been used in mixtures of microemulsions [8][9][10][11]. The microemulsion systems have some utility in drug delivery such as controlling drug release, increasing drugs solubility and bioavailability and reducing variability in patients. The ILs are organic salts with melting points under 100 °C and most of them are liquid at room temperature. ...
Active pharmaceutical ingredients with poor solubility in water and some organic solvents are a challenge in the pharmaceutical industry. To overcome this limitation, microemulsion systems are a choice to increase the solubility of a sparingly soluble active ingredient. The purpose of this study is to introduce and compare two types of oil-in-water (O/W) and ionic liquid-in-water (IL/W) microemulsions, which were formulated to increase the solubility of celecoxib as an active pharmaceutical ingredient. The proposed formulations are composed of the same nonionic surfactant/co-surfactant of Tween-80/transcutol®P, and different oil phases of isopropyl myristate, [BMIM][PF6] and [OMIM][PF6]. The pseudo-ternary phase diagrams for the microemulsion systems have been determined at a surfactant-to-co-surfactant mass ratio of 3:1 and 298.15 K. From the microemulsion region of the phase diagrams, four formulations was selected and their physico-chemical properties as density, viscosity, refractive index, electrical conductivity and surface tension were measured at 298.15 K. The solubilities of celecoxib in all selected formulations were also determined and compared. The results show considerable increases in solubility of the celecoxib in the ionic liquid-based microemulsion systems.
... The mixture of the protic and aprotic polar solvents strongly attracts to industrial application as co-solvents in ionic liquids, dissolution, polymerisation medium, etc., because of its unmatchable benefits [19][20][21][22][23][24]. Particularly, dimethyl sulfoxide (DMSO) and N,Ndimethyl formamide (DMF) are aprotic polar solvents where it as many industrial and research application. ...
We report herein the thermophysical properties of pure protic and aprotic polar solvents (water, dimethyl sulfoxide and N,N-dimethyl formamide) and their mixed (binary and ternary) systems. The experimental density (ρ) and viscosity (η) were determined for these systems by varying temperature range from 293.15 K to 343.15 K. The excess properties (viz., excess molar volumes (V E ), excess thermal expansion coefficient (α E ), viscosity deviation (Δη) and excess Gibb's free energy (ΔG E ) for viscous flow) were computed for mixed systems from experimental values. The excess properties of the mixed systems show clearly a non-ideal behaviour. Especially, a mixture of water with aprotic polar component show better thermophysical properties than pure systems. The pure (DMF) system shows increasing dynamic viscosity values at higher temperature region. Both the binary as well as ternary mixed systems show maximum activation energy (E a ) in the presence of water depicts their thermal stability of the mixed systems. The thermal expansion coefficient (α) also revealed increase in the thermal behaviour for the protic-aprotic systems. In addition to that, thermodynamic parameters are also evaluated for better understanding of thermal stability.
... They are being increasingly studied as environmentally benign media or catalysts for chemical reactions and new style functional materials with promising applications in many fields, due to their unique and attractive physicochemical properties, including zero volatility, nonflammability, high chemical/thermal stability, and low toxicity [39][40][41]. Furthermore, in recent years, great attention has been paid to IL microemulsions due to their special physical and chemical properties [42][43][44]. Therefore, an IL microemulsion is a potential abrasive-free jet fluid for KDP polishing. ...
Traditional potassium dihydrogen phosphate (KDP) polishing methods, such as magnetorheological finishing (MRF), ion-beam figuring (IBF), and chemical mechanical polishing (CMP), are limited by either hard-to-remove residual particles, unavoidable heating effects, or an applicability restricted to large-sized KDP. In this paper, we present a novel abrasive-free jet polishing (AFJP) mechanism that can be implemented for abrasive-free and no-residue polishing on KDP surfaces. KDP AFJP makes use of a thermodynamically and kinetically stable ionic liquid (IL) microemulsion that contains nanometer range water droplets evenly dispersed in the non-aqueous carrier liquid. The sprayed out nanoscale water droplets can remove material through dissolution. The feasibility of this approach has first been analyzed through several experiments, namely compatibility tests and assessments of removal controllability and uniformity of the IL microemulsion. The material removal mechanisms in contact removal and slipping removal were then studied. KDP AFJP experiments were then conducted to validate the polishing performance. The experimental results show that an IL microemulsion as an abrasive-free jet can indeed improve the quality of a KDP surface, leaving no residue.
... 20 Later, our group elucidated the mechanism of formation of these microemulsions and predicted greater stability of protic TMG based microemulsions compared to aprotic imidazolium based systems. 21 Very recently, Kusano et al. 22 formulated and characterized waterin-IL microemulsions in mixtures of aprotic and protic imidazolium-based ILs. Apart from these studies, reports on the formulation and characterization of pIL based microemulsions or the effects of pILs on W/O microemulsions are very limited. ...
In an attempt to increase the stability and water uptake capacity of water-in-oil (W/O) microemulsions, here we study the physicochemical behavior of a series of protic ionic liquid based water/oil microemulsions, wherein solute amount of biocompatible tetramethylguanidinium cation-based ionic liquids (ILs) are added to the aqueous phase of water-in-oil (W/O) microemulsions. FTIR, time-resolved fluorescence measurements showed an increased water uptake in these reverse micellar droplets, compared to the conventional W/O microemulsions of similar compositions. Dynamic light scattering and differential scanning calorimetric measurements suggested greater thermal stability of the droplets in presence of the ILs. NMR, FTIR measurements, and ab initio calculations explained these findings by showing extended hydrogen bonding network between interfacial water and protic IL ions and strong electrostatic association between the surfactant headgroups and IL anions. Our results pave way for potential applications of protic ionic liquids in emulsion and microemulsion science and technology.
... 5 Different concepts can be, and have been, realized in this regard, including mostly nonaqueous microemulsions, where water is replaced with room-temperature ionic liquids, for example in the well-studied system {1-butyl-3-methylimidazolium tetrafluoroborate, [C 4 mim][BF 4 ]/toluene/Triton X-100}. 6 Other examples include water−ionic liquid microemulsions, e.g., {H 2 O/1-butyl-3-methylimidazolium hexafluorophosphate, [C 4 mim][PF 6 ]/Triton X-100}, 7−9 or even a microemulsion of two intrinsically immiscible ionic liquids, e.g., 1-octylimidazolium aprotic and protic ionic liquids with the anionic surfactant, 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxobutane-2-sulfonate (commonly known as docusate or [AOT] − ) 10 all of them stabilized by the addition of one or more conventional surfactants. Less attention has been focused on the use of ionic liquids as amphiphiles themselves, and only a few examples exist where surface-active ionic liquids are used to reduce the interfacial tension of two immiscible solvents to form stable microemulsions. ...
The design and properties of surface-active ionic liquids that are able to form stable microemulsions with heptane and water are presented, and their promise as reaction media for thermomorphic palladium-catalyzed cross-coupling reactions is demonstrated.
... In contrast to emulsions, microemulsions form upon only mixing of components-with no additional mechanical forces being implemented on. [1][2][3][4][5] In a microemlusion, two liquid components, a polar and a non-polar, are separated by surfactant and/or co-surfactant molecules. The surfactant and/or co-surfactant molecules constitute monolayers at the interface of the polar and non-polar components. ...
Microemulsions comprising an ionic liquid (IL)- 1-ethyl-3-methylimmidazolium
trifluoromethane sulphonate ([emim][OTf]) - as the polar component, Triton X-100 as a
surfactant and cyclohexane as the non-polar medium were prepared and characterized.
Conductivity and dynamic viscosity data were critically analyzed to confirm dynamic
percolation among the droplets that are in continuous motion, aggregation and fission. The
transition from oil-continuous phase to bi-continuous phase was observed at the conductance and
viscosity percolation thresholds and sharp changes in the values of conductivity and dynamic
viscosity could be identified. Dynamic light scattering measurements revealed swelling of the
droplets, which varied within the hydrodynamic diameter range of 10-100 nm. Diffusivity of the
droplets suggested less Brownian movement with increased amount of the IL. Moreover,
changes in the droplet sizes and diffusivity- with increase in IL content- supported dynamic
percolation within the systems.
... Recently, the protic ILs (PILs) have been the principal focus of several studies (Chen et al., 2014;Huang et al., 2014;Kusano et al., 2014;Peric et al., 2014;Santos et al., 2014). They are synthesized by proton transfer from a Brønsted acid to a Brønsted base (Anouti et al., 2008;Mirjafari et al., 2013). ...
Ionic liquids (ILs) are often claimed to be “environmentally friendly” compounds however, the knowledge of their potential toxicity towards different organisms and trophic levels is still limited, in particular when protic ionic liquids (PILs) are addressed. This study aims to evaluate the toxicity against various microorganisms and the biodegradability of four PILs namely, N-methyl-2-hydroxyethylammonium acetate, m-2-HEAA; N-methyl-2-hydroxyethylammonium propionate, m-2-HEAPr; N-methyl-2-hydroxyethylammonium butyrate, m-2-HEAB; and N-methyl-2-hydroxyethylammonium pentanoate, m-2-HEAP. The antimicrobial activity was determined against the two bacteria, Sthaplylococcus aureus ATCC-6533 and Escherichia coli CCT-0355; the yeast Candida albicans ATCC-76645; and the fungi Fusarium sp. LM03. The toxicity of all PILs was tested against the aquatic luminescent marine bacterium Vibrio fischeri using the Microtox® test. The impact of the PILs was also studied regarding their effect on lettuce seeds (Lactuta sativa). The biodegradability of these PILs was evaluated using the ratio between the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD). The results show that, in general, the elongation of the alkyl chain tends to increase the negative impact of the PILs towards the organisms and biological systems under study. According to these results, m-2-HEAA and m-2-HEAP are the less and most toxic PILs studied in this work, respectively. Additionally, all the PILs have demonstrated low biodegradability.
Ionic Liquids: Eco-friendly Substitutes for Surface and Interface Applications explores the growing interest in utilizing ionic liquids as sustainable alternatives for various industrial and biological applications. With their unique properties and environmentally friendly nature, ionic liquids have emerged as promising substitutes for toxic and volatile solvents, offering significant advantages in surface and interface chemistry.
This book is divided into two parts: Part 1 covers the basics of ionic liquids, their surface/interface properties, and interactions with metallic surfaces. Part 2 focuses on the wide range of surface and interface applications of ionic liquids, including wastewater treatment, corrosion protection, catalysis, separation processes, medical devices, and sensing applications.
Key Features:
A complete book fully dedicated to the surface and interface chemistry of ionic liquids with seventeen chapters Covers fundamentals, recent progress, and applications in surface/interface chemistry Presents up-to-date research and interdisciplinary insights Includes relevant references and resources for further exploration
This is a valuable reference for scientists and engineers who want to learn about ionic liquids' chemistry and applications
The aim of this study was to introduce new ionic liquid (IL)-based microemulsions and microemulgels as topical delivery systems for celecoxib. Ex-vivo diffusion of celecoxib loaded in IL-based microemulsions and microemulgels through the rat skin by using Franz diffusion cell was investigated and compared with traditional microemulsions. The investigated systems composed of the same nonionic surfactant/co-surfactant of tween-80/transcutol®P, and different oil phases of [BMIM][PF6], [OMIM][PF6] and isopropyl myristate, for construction of ILs/W and O/W microemulsions. The particle size of the ILs/W and O/W microemulsion systems was determined by DLS method. The ex-vivo release results of ILs/W and O/W formulations, at similar conditions, showed that the celecoxib permeability of the ILs/W formulations is more than that of the O/W formulation, either as microemulsion or as microemulgel. As an interesting result, the celecoxib release percent and release rate from the ILs/W systems was more and faster than the O/W system. The kinetic mechanism for ILs/W systems had followed from first-order model and for O/W systems followed Higuchi zero-order model.
Discrete water domains in hydrophobic environment find relevance in aerosols, oil refinery, the human body, etc. The interfacial microstructure plays a crucial role in the stability of such water domains. Over the decades, the amphiphile-induced electrostatic interaction is considered to be the major stabilizing factor operating at these interfaces. Here we take the representative water/AOT/oil microemulsion to show that creating a strong H-bonding network through suitable additive, such as protic ionic liquid (IL) at the interface, helps both the growth and stability of water domains in the hydrophobic phase. On the other hand, common electrolytes and aprotic ILs fail to replicate such behavior as seen by Raman, Fourier transform infrared spectroscopy, dynamic light scattering (DLS), and electron microscopy measurements. Experimental results are further supported by the all-atomic molecular dynamics (MD) simulations that showed extended H-bonding mediated by the protic IL cations that were localized at the interface. High temperature DLS and rheology studies have shown greater thermal stability and mechanical strengths of our biocompatible microemulsions, which have potential to become suitable templates for in situ synthesis of nanoparticle and various organic compounds.
In the present work, the sulfobetaine-type zwitterionic surfactant (SB-n) was tried for the first time to construct hydrophobic ionic liquid (HIL)-based bicontinuous microemulsions. The composition-dependent phase behavior of the HIL/water (buffer)/SB-n ternary microemulsion system was determined by the method of T-γ fishlike phase diagram. It is found that the phase inversion temperature increases markedly with the increase of the alkyl chain length (n) of SB-n, but the surfactant efficiency changes little. The HIL greatly affects the phase behavior, depending on the ion structure. It is found that the SB-12 stabilized [C8mim][PF6]-based microemulsion system has moderate phase inversion temperature, and moreover, its surfactant efficiency is the highest among the reported HIL-based bicontinuous microemulsions stabilized by conventional surfactants. The composition-dependent microstructure of the SB-12-stabilized [C8mim][PF6]-based bicontinuous microemulsion was characterized by SAXS technique, and its influence on the catalytic performance of solubilized lipase was also explored. With the increase of the mass ratio of the HIL to water (α), the correlation length (ξ) changes slightly, but the microdomain size (d) decreases steadily. Unlike α, with the increase of the surfactant concentration (γ), the d changes little, but the ξ increases markedly. This abnormal change of ξ with γ should be ascribed to the interface rigidity of the microemulsion. The catalytic efficiency of lipase depends on the rigidity of the interface and its interfacial area. The above original studies not only enrich HIL-based microemulsion systems, but also provide scientific support for lipase-based green synthesis and transformation.
Over the past few years an increasing number of studies dealt with microemulsions, in which either the aqueous phase, the oil phase, the surfactant or even two of these components constitute of an ionic liquid. Many examples demonstrated that water and oil are not necessarily the required polar and non-polar components that contribute to the formation of microemulsions but can be replaced by targeted ionic liquids. Moreover, in many cases ionic liquids are used as amphiphiles that assist in the formation of microemulsions in aqueous or non-aqueous media due to their unique surface activity.
In the present review, we highlight the properties of three types of ionic liquid based microemulsions, namely non-aqueous ionic liquid microemulsions, aqueous ionic liquid microemulsions and ionic liquid/oil/water microemulsions. Various characterization techniques applied for the confirmation of their formation and the detailed elucidation of their properties are discussed herein. Additionally, we present a comprehensive summary of the recent applications of ionic liquid based microemulsions in different fields, such as synthesis, (bio-)catalysis, polymerization, (nano-)material preparation, drug delivery and separations.
The composition-dependent phase behavior of the [Cmmim][PF6]/buffer/[Cnmim][AOT]/n-butanol pseudoternary microemulsion system was investigated by the method of T-γ fishlike phase diagram. It is found that the phase inversion temperature and the surfactant efficiency decrease with the increase of the alkyl chain length (n) of the surfactant counterion and that (m) of the cation of the hydrophobic ionic liquid (HIL). The [C2mim][AOT]-stabilized [Omim][PF6]-based pseudoternary microemulsion system was found to have high surfactant efficiency and moderate phase inversion temperature. The microstructure of bicontinuous microemulsion formed in the pseudoternary system was characterized by SAXS technique, and the influence of microstructure on the catalytic performance of solubilized laccase was also explored. As the mass ratio of HIL to water increases, the microdomain size of the system decreases, and the catalytic efficiency (kcat/Km) of laccase also decreases. When the surfactant content gradually increases, the microdomain size of the system changes little, but its interfacial rigidity increases, and also the interaction between the interface and the solubilized enzyme increases accordingly, resulting in a decrease in the kcat/Km of the solubilized laccase. The variation of temperature over 35 °C–55 °C has little effect on the microdomain size of the system, but it has marked effect on the kcat/Km of the solubilized laccase. The optimal catalytic efficiency of laccase in the present microemulsion is estimated to be ca. 50 °C, which is significantly higher than that (40 °C) in the aqueous medium system, indicating that the bicontinuous microstructure in the system is helpful to improve the thermal stability of laccase. The present study is helpful for the rational formulation of laccase-compatible anionic surfactant-stabilized hydrophobic ionic liquid-based bicontinuous microemulsions, which is suitable for template-assisted biosynthesis of conducting polymers.
In this work, the fishlike phase diagram of the H2O/[Bmim][AOT]/[Bmim][PF6]/n-alcohol as a function of temperature (T) and the mass fraction of [Bmim][AOT] (with or without n-alcohol) in the total mixture (γ) has been observed for the first time at several mass ratios of [Bmim][PF6] to H2O (α) and with different n-alcohols. The larger area of the three-phase region occurs at α ≤ 0.500, and the resulting fish-shapes are similar to each other. For a given α, a temperature scan (from lower to higher) at several γ values reveals that the present system forms an upper phase microemulsion first and then a lower phase microemulsion. The formation of hydrophobic ionic liquid-in-water (HIL/W) microemulsion at low temperature and water-in-hydrophobic ionic liquid (W/HIL) microemulsion at high temperature was confirmed by DLS and SAXS techniques. Here, the phase sequence occurred during the temperature scan is opposite to that of a classic H2O/NaAOT/Oil system. At the lower temperature, the H-bonding interaction is considered to be the main driving force for the aggregation; at the higher temperature, however, the main driving force may be the hydrophobic interaction. n-Alcohols with medium/long alkyl chain have a great influence on the fish-tail coordinates of the present systems. Compared with the ternary system without alcohol, the addition of n-alcohols (C4 ~ C8) decreases the phase inversion temperature (T ̃) and the surfactant efficiency. With the increase of the alkyl chain length of n-alcohols, however, the decrement in T ̃ become smaller due to the increase of the interfacial rigidity. A comparison of these results with those obtained for the H2O/NaAOT/Oil system indicates that there are some similarities and also some differences, depending on the relative density, polarity or hydrophobicity among the HIL, oil and n-alcohols. The above insight into the phase behavior of the present HIL-based system helps to formulate biocompatible HIL-based AOT-stabilized microemulsions which are important templates for the biosynthesis of conducting polymers.
Bio- and aqueous applications of ionic liquids (IL) such as catalysis in micelles formed in aqueous IL solutions, or extraction of chemicals from biologic materials rely on surface-active and self-assembly properties of ILs. Here, we discuss qualitative relations of the interfacial and bulk structuring of a water-soluble surface-active IL ([C8MIm][Cl]) on chemically controlled surfaces over a wide-range of water concentrations using both force probe and X-ray scattering experiments. Our data indicates that IL structuring evolves from surfactant-like surface adsorption at low IL concentrations, to micellar bulk structure adsorption above the critical micelle concentration, to planar bilayer formation in ILs with <1 w.t.% of water and at high charging of the surface. Interfacial structuring is controlled by mesoscopic bulk structuring at high water concentrations. Surface chemistry and surface charges decisively steer interfacial ordering of ions if the water concentration is low and/or the surface charge is high. We also demonstrate that controlling interfacial forces by using self-assembled monolayer chemistry allows tuning of interfacial structures. Both the ratio of the head group size to the hydrophobic tail volume as well as the surface charging trigger the bulk structure and offer a tool for predicting interfacial structures. Based on the applied techniques and analyses a qualitative prediction of molecular layering of ILs in aqueous systems is possible.
Considering the contemporary interests of water-free reverse micelles (RMs) in the field of organic reaction medium and potential drug delivery carrier, we synthesized two different classes of ionic liquids (ILs), protic N-methyl-2-pyrrolidonium hexanoate, [NMP][Hex] and aprotic choline hexanoate, [Chl][Hex] and subsequently incorporated in mixture of polyoxyethylene(20)sorbitan monooleate (Tween-80) and cyclohexane. In order to understand the differential nature of inter-interionic interaction of two ILs, we performed DFT calculations on pure ILs to correlate with experimental results. The formation of IL-in-oil RMs was confirmed from phase behaviour and DLS studies. Interestingly, [NMP][Hex]-based systems showed larger monophasic region and droplet size along with higher shear viscosity compared to [Chl][Hex]-based systems. Stronger interaction between [NMP]+ and Tween-80 due to their protic nature might be the driving force for such observations which supported from the resonance stabilisation energy [E(2)] and charge population analysis by NBO calculation. Smaller E(2) values along with lesser NBO charges on atoms involved in H-bonding in pure [NMP][Hex] than [Chl][Hex] corroborated with the experimental observations. This primary hypothesis was further confirmed from FTIR and time-resolved fluorescence studies. These systems showed efficient thermal stability. Taken together the results, we anticipate that these RMs could use as efficient delivery systems and nanomaterial synthesis.
Liping Liu is currently working at Shanxi Normal University. Her research interests are ordered aggregates and nanoscience.
Abstract
In this study, ionic liquid (IL), specifically ethylammonium nitrate (EAN), was used instead of water to form nonaqueous microemulsions with cyclohexane and the nonionic surfactant Triton X-100 (TX-100). The phase behavior of the ternary system was investigated, and the microemulsions of ionic liquid-in-oil (IL/O) and oil-in-ionic liquid (O/IL) and the bicontinuous microregion were identified through traditional electrical conductivity measurement. The micropolarities of the IL/O microemulsions were determined via UV–Vis spectroscopy with methyl orange as an absorption probe. Results indicated that the polarity of the reverse micelles remained constant but that of the IL/O microemulsions increased when IL pools were formed. Fourier transform infrared spectroscopy was used to study the interaction mechanism between TX-100 and EAN molecules in IL/O microemulsions. We demonstrated that IL/O microemulsions may be promising for application due to the unique features of ILs and microemulsions.
In the last two decades, while searching for interesting applications of ionic liquids as potent solvents, their solvation properties and their general impact on biomolecules, and in particular on proteins, gained interest. It turned out that ionic liquids are excellent solvents for protein refolding and crystallization. Biomolecules showed increased solubilities and stabilities, both operational and thermal, in ionic liquids, which also seem to prevent self-aggregation during solubilization. Biomolecules can be immobilized, e.g. in highly viscous ionic liquids, for particular biochemical processes and can be designed to some extent by the proper choice of the ionic liquid cations and anions, which can be characterized by the Hofmeister series.
The ε-β fishlike phase diagram of the system [C16mim]Br/[Omim]Tf2N/water was constructed in the presence of different additives (alcohol and inorganic salt). From the diagram some additive-dependent characteristic physicochemical parameters were obtained. Results show that with the increase of the alkyl chain length of alcohols, the solubility of the alcohol in [Omim]Tf2N, and the optimum solubilization parameter (SP∗) decrease, while the maximum alcohol width (Δε) for the phase inversion and the mass fraction of the alcohol in the balanced interfacial film (Aⁱⁿ) increase. For inorganic salts, an increase in [NaCl], or an increase of the radius of halides (X⁻) at constant [NaX], or the substitution of the divalent anion SO42- by the same molar concentration of monovalent anion Cl⁻ makes both SP∗ and Δε increase, but Aⁱⁿ decrease. Overall, the alcohol effect on the phase behavior of the microemulsion is greater than the salt effect, and the composition effect of an inorganic salt is greater than the concentration effect. These effects could be rationalized based on their influence on the dissolution and aggregation behavior of the surfactant [C16mim]Br in the system.
Ionic liquids (ILs) have received increased attention from both academic and industrial research communities all over the world due to their unusual properties and immense application potential in various fields of science and technology. During the past decade, ionic-liquid-based systems have become the subject of considerable interest as a promising media for extraction and purification of several macro-/biomolecules. ILs are attractive designer solvents with tunable physicochemical properties. Using IL-based systems as alternative solvents for forming surfactant self-assemblies has several advantages. For example, the properties of surfactant self-assemblies in these media can be easily modulated by tuning the structure of ILs; ILs can dissolve a large variety of organic and inorganic substances and their properties are designable to satisfy the requirements of various applications. This may enhance the application potential of both ILs and surfactants in many important fields. Consequently, the study on surfactant self-assemblies within IL-based aqueous systems has attracted considerable attention in recent years. This chapter overviews the investigation carried out on the formation of surfactant self-assemblies within IL-based aqueous systems and their applications in various fields.
Microemulsions (MEs) comprising of 2-hydroxyethylammonium formate, (HO-EAF), isooctane and dioctylsulfosuccinate proliniumisopropylester ([ProC3]AOT) have been constructed and used to prepare and stabilize CdS Quantum Dots (QDs) at room temperature. Such hybrid materials exhibited tunable light emission wherein the photoluminescence chromaticity could be precisely adjusted to pure white with a quantum efficiency (QE) of ∼43%, by adjusting the droplet size of MEs.
Research into the properties and applications of ionic liquids (ILs) has accelerated over the last few decades, driven principally by the advanced reaction kinetics and specificity they offered for synthesis and catalysis. ILs display many highly desirable properties, including high electrical and thermal conductivities and wide electrochemical windows, all of which can be tuned by altering the nature of their constituent ions. The discovery that ILs mediate surfactant self-assembly increased interest further. X-ray and neutron scattering are powerful tools for elucidating structure in both simple and complex, mesostructured liquids that were soon applied to IL-based systems. Early work revealed that many IL solvents are themselves nanostructured, and comprise distinct polar and apolar domains produced by the solvophobic segregation of alkyl moieties. Over the last decade scattering techniques have been used to characterise the nanostructure of a diverse range of ILs. Recently, nanostructure changes in ILs produced by the dissolution of salts, polymers, small molecules and amphiphiles have begun to be elucidated. X-ray and neutron scattering have, and will continue to, play a fundamental role in understanding structure-property relationships in IL-based systems.
A silver-catalyzed highly efficient and regioselective synthesis of ketones from a wide range of alkynes is described. The reaction is dramatically accelerated by its performance in aqueous emulsion, which is self-assembled by the addition of silver perfluorooctanesulfonate (1) and perfluorooctanesulfonic acid (PFOS) to water. The reaction is conducted under convenient conditions with broad substrate scope, including a variety of aromatic and aliphatic terminal alkynes and internal alkynes. Furthermore, the air- and light-stable silver catalytic microemulsion can be reused for 4 times with minimal change in catalytic efficiency.
This review is devoted to the problem of aggregation in solutions of ionic liquids (ILs) and the results of relevant studies published in recent years. To a great extent, this problem remains urgent, because the ability to self-organization extends the possibilities of the practical application of ILs. The fields of IL application in which their amphiphilicity is of importance in connection with widening the spectrum of objects under investigation are discussed. The results of studying the aggregation behavior of different systems are briefly considered, including IL solutions in water, water-organic, and organic solvents; aqueous solutions of IL-classical surfactant mixtures; and solutions in which one IL plays the role of a solvent, while another IL or a classical surfactant serves as an amphiphilic solute. Some experimental results are analyzed, and thermodynamic aspects of micellization and problems of molecular-thermodynamic simulation are discussed.
A tungsten-containing task-specific ionic liquid (IL) [(C6H13)3PC14H29]2W6O19 was synthesized and applied in the desulfurization process of a dibenzothiophene-containing model oil with aqueous hydrogen peroxide. In the desulfurization process, a novel aqueous hydrogen peroxide-in-IL emulsion catalytic system was found. The task-specific IL not only acted as extraction media for the organo-sulfur compounds and served as a catalyst for the hydrogen peroxide but also provided an oxidation micro-environment for the conversion from sulfur compounds to sulfones by forming IL emulsions. The self-emulsifiable IL played two roles in the emulsification process: the surfactant and the dispersion medium.
The H atom has a large incoherent scattering cross section and is a major source of incoherent scattering intensity, (dΣ/dΩ)inc, in small-angle neutron scattering. By taking account of multiple scattering from H atoms, a useful method (the transmission method or T method) is proposed for the estimation of (dΣ/dΩ)inc for various types of hydrogen-containing systems. The incoherent scattering intensity is calculated simply from the transmission, T, and the thickness of the sample, t, i.e. (dΣ/dΩ)inc≅ [exp(Σtott) − 1]/(4πt) = (1 −T)/(4πtT), where Σtot≡−(lnT)/t is the macroscopic total cross section per unit volume. This method provides a reasonably accurate value of incoherent scattering intensity for various systems. The validity and the extent of applicability of the T method are examined for several samples, including light/heavy water mixtures, polymer gels and surfactant aqueous dispersions.
The insolubility of enzymes in most ionic liquids has been overcome by the formation of aqueous microemulsion droplets in a hydrophobic ionic liquid stabilized by a layer of anionic surfactantsodium bis(2-ethyl-1-hexyl) sulfosuccinate (AOT) in the presence of 1-hexanol as a cosurfactant and the catalytic activity of one of the enzymes studied (lipase PS) became higher than in microemulsions of AOT in isooctane.
A series of hydrophilic and hydrophobic 1-alkyl-3-methylimidazolium room temperature ionic liquids (RTILs) have been prepared and characterized to determine how water content, density, viscosity, surface tension, melting point, and thermal stability are affected by changes in alkyl chain length and anion. In the series of RTILs studied here, the choice of anion determines water miscibility and has the most dramatic effect on the properties. Hydrophilic anions (e.g., chloride and iodide) produce ionic liquids that are miscible in any proportion with water but, upon the removal of some water from the solution, illustrate how sensitive the physical properties are to a change in water content. In comparison, for ionic liquids containing more hydrophobic anions (e.g., PF6− and N(SO2CF3)2−), the removal of water has a smaller affect on the resulting properties. For a series of 1-alkyl-3-methylimidazolium
cations, increasing the alkyl chain length from butyl to hexyl to octyl increases the hydrophobicity and the viscosities of the ionic liquids increase, whereas densities and surface tension values decrease. Thermal analyses indicate high temperatures are attainable prior to decomposition and DSC studies reveal a glass transition for several samples. ILs incorporating PF6− have been used in liquid/liquid partitioning of organic molecules from water and the results for two of these are also discussed here. On a cautionary note, the chemistry of the individual cations and anions of the ILs should not be overlooked as, in the case of certain conditions for PF6− ILs, contact with an aqueous phase may result in slow hydrolysis of the PF6− with the concomitant release of HF and other species.
Liquid structures of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [BDMI+][TFSA(-)] and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)amide [BDMI+][TFSA(-)] were studied by large-angle X-ray scattering (LAXS) experiments to elucidate methyl substitution effect at the C2 position of imidazolium cation on the long-range ordering of the ionic liquids. Radial distribution functions for both ionic liquids showed that the intermolecular correlations of ca. 5.5 and 10 angstrom a e significantly different from each other, unlike that of ca. 15 angstrom. MD simulations were also performed. It turns out that the methyl substitution at the C2 position of imidazolium causes variation of the orientation of the nearest neighboring ion-ion interactions without significant changes in the long-range ordering, probably longer than 15 angstrom, of the ionic liquids.
Problems of self-assembling in systems containing ionic liquids (ILs) are discussed. Main attention is paid to micellization
in aqueous solutions of dialkylimidazolium ILs and their mixtures with classical surfactants. Literature data are reviewed,
the results obtained by the authors and co-workers are presented. Thermodynamic aspects of the studies and problems of molecular-thermodynamic
modeling receive special emphasis. It is shown that the aggregation behavior of dialkylimidazolium ILs is close to that of
alkyltrimethylammonium salts (cationic surfactants) though ILs have a higher ability to self-organize, especially as it concerns
long-range ordering. Some aspects of ILs applications are outlined where their common features with classical surfactants
and definite specificity are of value.
Short- and long-range liquid structures of [C(n)mIm(+)][TFSA(-)] with n = 2, 4, 6, 8, 10, and 12 have been studied by high-energy x-ray diffraction (HEXRD) and small-angle neutron scattering (SANS) experiments with the aid of MD simulations. Observed x-ray structure factor, S(Q), for the ionic liquids with the alkyl-chain length n > 6 exhibited a characteristic peak in the low-Q range of 0.2-0.4 Å(-1), indicating the heterogeneity of their ionic liquids. SANS profiles I(H)(Q) and I(D)(Q) for the normal and the alkyl group deuterated ionic liquids, respectively, showed significant peaks for n = 10 and 12 without no form factor component for large spherical or spheroidal aggregates like micelles in solution. The peaks for n = 10 and 12 evidently disappeared in the difference SANS profiles ΔI(Q) [=I(D)(Q) - I(H)(Q)], although that for n = 12 slightly remained. This suggests that the long-range correlations originated from the alkyl groups hardly contribute to the low-Q peak intensity in SANS. To reveal molecular origin of the low-Q peak, we introduce here a new function; x-ray structure factor intensity at a given Q as a function of r, S(Q) (peak)(r). The S(Q) (peak)(r) function suggests that the observed low-Q peak intensity depending on n is originated from liquid structures at two r-region of 5-8 and 8-15 Å for all ionic liquids examined except for n = 12. Atomistic MD simulations are consistent with the HEXRD and SANS experiments, and then we discussed the relationship between both variations of low-Q peak and real-space structure with lengthening the alkyl group of the C(n)mIm.
The major achievements from the field of materials synthesis with the reverse micelles to view typical problems dominating the field were discussed. Reverse micellar synthesis of materials belongs to the class of wet materials synthesis procedures that exhibits all the advantages that accompany other wet approaches. Improved control of the particle sizes, shapes, uniformity and dispersity are general advantages of reversal micellar synthesis compared to other bulk wet approaches. It was found that the formation of nanoparticles with high specific surface area can enable calcination temperature to be set lower compared to traditional solid-state approaches.
Magnetic nanoparticles have been attracting much interest as a labeling material in the fields of advanced biological and medical applications such as drug delivery, magnetic resonance imaging, and array-based assaying. In this review, synthesis of iron oxide magnetic nanoparticles via a reverse micelle system and modification of their surface by an organosilane agent are discussed. Furthermore, as a practical biological assay system, the magnetic detection of biomolecular interactions is demonstrated by using the combination of a patterned substrate modified with a self-assembled monolayer and the magnetic nanoparticles.
The structure of bis(trifluoromethanesulfonyl) imide (TFSI-) in the liquid state has been studied by means of Raman spectroscopy and DFT calculations. Raman spectra of 1-ethyl-3-methylimidazolium (EMI+) TFSI- show relatively strong bands arising from TFSI- at about 398 and 407 cm(-1). Interestingly, the 407 cm(-1) band, relative to the 398 cm(-1) one, is appreciably intensified with raising temperature, suggesting that an equilibrium is established between TFSI- conformers in the liquid state. According to DFT calculations followed by normal frequency analyses, two conformers of C2 and C1 symmetry, respectively, constitute global and local minima, with an energy difference 2.2-3.3 kJ mol(-1). The wagging omega-SO2 vibration appears at 396 and 430 cm(-1) for the C1 conformer and at 387 and 402 cm(-1) for the C2 one. Observed Raman spectra over the range 380-440 cm(-1) were deconvoluted to extract intrinsic bands of TFSI- conformers, and the enthalpy of conformational change from C2 to C1 was evaluated. The enthalpy value is in good agreement with that obtained by theoretical calculations. We thus conclude that a conformational equilibrium is established between the C1 and C2 conformers of TFSI- in the liquid EMI+TFSI-, and the C2 conformer is more favorable than the C1 one.
In contrast to a recently expressed, and widely cited, view that "Ionic liquids are starting to leave academic labs and find their way into a wide variety of industrial applications", we demonstrate in this critical review that there have been parallel and collaborative exchanges between academic research and industrial developments since the materials were first reported in 1914 (148 references).
Liquid-liquid extraction technology has been successfully used in the separation of compounds in chemical, petrochemical, or hydrometallurgical industries for many years. It is only recently, however, that liquid-liquid extraction technology has been recognized as potentially useful in biotechnology, namely in the purification procedure of biomolecules, such as proteins (Kadam, 1986; Abbott and Hatton, 1988). Two classes of two-phase extraction system are suitable for protein recovery: (a) biphasic aqueous polymer systems, and (b) systems in which an organic, reverse micellar solution is in equilibrium with a conjugated aqueous phase. Both systems are based on the differential partitioning of protein(s) between the immiscible feed and solvent phase to effect the extraction of the desired protein from the complex production mixture. However, the principles of solubilization greatly differ. In the following we will describe the micellar extraction system in more detail and show its usefulness in the selective extraction of proteins from crude mixtures.
Reverse micelles (or w/o microemulsions) have found wide applications in enzymology, protein chemistry and other areas assisting in a variety of biotransformations. Being considered as an individual ‘nanobioreactors’ these systems allow one to reveal or to add new properties to biocatalysts.
Aggregation structures of 1-alkyl-3-methylimidazolium based ionic liquids (ILs) in aqueous solution were investigated by small-angle neutron scattering (SANS) from the viewpoint of alkyl chain length, n, and anions (Cl−, Br− and trifluoromethanesulfonate, \( {\text{CF}}_{3} {\text{SO}}_{3}^{ - } \)). In [C4mIm+]-based IL systems, no noticeable SANS intensity was observed for all of the systems examined here, although aqueous [C4mIm+][\( {\text{BF}}_{4}^{ - } \)] solutions show a significant SANS profile originating from concentration fluctuations in the solution (Almasy et al. J Phys Chem B 112:2382–2387, 2008). This suggests that [C4mIm+][Cl−], [C4mIm+][Br−] and [C4mIm+][\( {\text{CF}}_{3} {\text{SO}}_{3}^{ - } \)] homogeneously mix with water, unlike the [C4mIm+][\( {\text{BF}}_{4}^{ - } \)] system, due to preferential hydration of the ions. In the case of the Cn
mIm cations with longer alkyl chain lengths (n = 8 and 12), SANS profiles were clearly observed in the aqueous solutions at IL concentrations of C
IL > 230 and 20.0 mmol·dm−3, respectively. For aqueous [C8mIm+][Br−] solutions, the asymptotic behavior of the scattering function varied largely from I(q) ~ q
−2 to ~q
−4 with increasing C
IL, indicating that the solution changes from an inhomogeneous mixing state to a nano-scale micelle state. Aqueous [C12mIm+][Br−] solutions show a typical SANS profile for micelle formation in solution. It was found from a model-fitting analysis that the structure of the [C12mIm+][Br−] micelle is ellipsoidal, not spherical, in solutions over the C
IL range examined here.
The phase behaviour of different ternary mixtures containing water, a hydrophobic ionic liquid (IL) and Triton X-100 have been examined as a function of surfactant concentration and temperature, maintaining equal volumes of water and IL. In all previously published studies on water–IL microemulsions the hydrophobic IL contained hexafluorophosphate (PF6−) as anion. As this anion is not stable towards hydrolysis, our aim was to replace it by the hydrolysis-stable anion bis-triflimide (NTf2−). The challenge was to find a suitable cation, which, in combination with the chosen anion, forms microemulsions with an efficiency equal or greater than reported values. The cation leading to the most efficient microemulsion was [ali336]+, which is based on the phase transfer catalyst aliquat 336. Thus the IL [ali336]NTf2 turned out to be a suitable choice for a hydrophobic room temperature IL which forms microemulsions of efficiencies comparable to those of water–[bmim]PF6 systems, whilst being stable towards hydrolysis.
The tremendous potential of room temperature ionic liquids as an alternative to environmentally harmful ordinary organic solvents is well recognized. Ionic liquids, having no measurable vapor pressure, are an interesting class of tunable and designer solvents, and they have been used extensively in a wide range of applications including enzymatic biotransformation. In fact, ionic liquids can be designed with different cation and anion combinations, which allow the possibility of tailoring reaction solvents with specific desired properties, and these unconventional solvent properties of ionic liquids provide the opportunity to carry out many important biocatalytic reactions that are impossible in traditional solvents. As compared to those observed in conventional organic solvents, the use of enzymes in ionic liquids has presented many advantages such as high conversion rates, high enantioselectivity, better enzyme stability, as well as better recoverability and recyclability. To date, a wide range of pronounced approaches have been taken to further improve the performance of enzymes in ionic liquids. This review presents the recent technological developments in which the advantages of ionic liquids as a medium for enzymes have been gradually realized.
As green solvents, ionic liquids (ILs) can be substitutes for traditional organic solvents, and form useful microemulsions with water. Microemulsions consisting of the IL, 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), the non-ionic surfactant Tween 20 and water were formed at 30.0 °C, and the phase behavior of the ternary system was investigated. Three regions of the microemulsions: water-in-bmimPF6 (W/IL), bicontinuous, and bmimPF6-in-water (IL/W) were identified by cyclic voltammetry using potassium ferrocyanide K4Fe(CN)6 as an electroactive probe. The polarity of the microemulsion environment was investigated by UV-Visible spectroscopy using methyl orange as a probe. Use of the ionic compound K3Fe(CN)6 in UV-Visible measurements revealed that the bmimPF6/Tween 20/H2O microemulsions could solubilize salt species into the microemulsion droplets. Moreover, the solubilization of riboflavin in the microemulsions was also shown by UV-Visible spectra. These results show that these IL-based microemulsions have potential in the production of metal nanomaterials, in biological extractions or as solvents for enzymatic reactions.
Micellar and microemulsion phases can be used to synthesize and disperse nanometre-sized colloids. The self-organization of the parent surfactant phases can control the final size and, in some cases, shape of the particles. Metallic, semiconductor, superconductor and magnetic particles can be made as well as polymeric materials.
Metal particles of silver (Ag) have been synthesized by the photoreduction of silver nitrate (AgNO3) in water-in-ionic liquid (IL) microemulsions consisting of nonionic surfactant Tween 20 or Triton X-100, water and ionic liquid, 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIm][PF6]). The formation of microemulsions as well as Ag particles produced by the photoreduction has been investigated by UV-vis, cryo-TEM, small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) measurements. At the early stage of Ag particle formation under ambient pressure, the size of Ag particles in water/[OMIm][PF6]/TX-100 microemulsions was slightly larger than that in water/[OMIm][PF6]/Tween20 microemulsions. With an increase in photoirradiation time beyond 30min, precipitation of larger Ag aggregates occurred. In contrast to the preparation under ambient pressure, the growth of Ag particles and aggregates was suppressed in preparing under high pressure (25MPa) of CO2, leading to no precipitation of Ag aggregates. The average diameters of the finally-obtained metallic Ag particles prepared under high pressure of CO2 in water/[OMIm][PF6]/Tween20 and water/[OMIm][PF6]/TX-100 microemulsions were estimated from cryo-TEM to be 3.7nm and 2.8nm, respectively. By using Guinier plots at q (<0.16nm(-1)), it was demonstrated that the diameter of the water droplets during Ag particle formation under high pressure of CO2 remained unchanged in the range of 33-37nm due to their higher stability compared to water droplets, whereas under ambient pressure the diameter drastically increases from 28nm to 40nm during the first 60min of photoirradiation, resulting in the precipitation of larger Ag aggregates, especially in the case of water/[OMIm][PF6]/Tween20 microemulsions.
Inverse micelles play an important role in the stability of high internal phase water in oil (W/O) emulsions.
The influence of both solvent and temperature has been investigated on the structure of inverse
micelles prepared from the polyisobutylene-based surfactant, PIBSA, using small-angle neutron scattering
(SANS). By collecting data over an extended range of scattering vector (Q), combined with the
use of solvent deuteration, SANS has highlighted an additional contribution to the anticipated micellar
scattering, namely a signal characteristic of rod-like scattering that is consistent with single dissolved
molecules of the PIBSA surfactant and its primarily hydrogenated (mainly alkane oil) solvent (both MW
ca. 1000 Da). The solvency effect of three different solvents (hexadecane, cyclohexane and toluene) on
micellar–monomer (rod) equilibrium has also been evaluated. The volume fractions of rods and micelles
in solution are found to agree with the sample compositions, as does the intensity of the observed incoherent
background. This consistency across fit parameters not only highlights the sensitivity of the model
but also the value of extended Q range, enhanced signal-to-noise studies in such soft matter systems. The
data show the extent to which quantitative measurements can be carried at the molecular level using
small angle scattering.
Water-in-oil microemulsions have been used for the synthesis of a variety of nanoparticles since the technique was introduced in 1982. In this paper we have reviewed the synthesis of nanoparticles in microemulsions and described in some detail our research efforts in the past decade in the synthesis of nanoparticles of silver halides, superconductors and magnetic materials using W/O microemulsions as nano-reactors.
The first example of a water-in-ionic liquid (w/IL) microemulsion generated using a zwitterionic surfactant was presented. Studying the surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate in two different exemplary water-immiscible ILs systems, it was found that the addition of a critical amount of ethanol as co-polar phase is required for reverse micelle swelling to occur upon the introduction of water. The results show that when ethanol is present within the system, significant amounts of water are soluble, which initiates the formation of w/IL microemulsions. The presence of water renders the color of Co pink and this color evolution to pink indicates the presence of bulk water as would be the case if w/IL microemulsions were formed. The population of ethanol aids the formation of reverse micelle-type aggregates of SB-12 within the system as revealed by the DLS and Co absorbance data.
BACKGROUND: [bmim][PF 6 ] is a hydrophobic ionic liquid which could be considered as an environmentally friendly solvent for biocatalysis. In pure [bmim][PF 6 ], however, alcohol dehydrogenase from yeast (YADH) has no catalytic activity. The aim of the present work was (1) to quantitatively study the negative effect of [bmim][PF 6 ] on the catalytic activity of YADH and the related mechanism and (2) to made an attempt to lessen the negative effect of [bmim][PF 6 ] on YADH by microemulsifying [bmim][PF 6 ].
RESULTS: The activity of YADH in the homogeneous solution formed by H 2 O, CH 3 CH 2 OH and [bmim][PF 6 ] decreased rapidly with the increase of the molar fraction of [bmim][PF 6 ]. The inhibitory effect of [bmim][PF 6 ] on YADH was probably caused by the competition of the imidazole group of [bmim][PF 6 ] with the coenzyme NAD ⁺ for the binding sites on YADH. In a water‐in‐[bmim][PF 6 ] microemulsion, YADH was catalytically active due to the formation of the interfacial membrane of the nonionic surfactant TritonX‐100, which separated YADH from [bmim][PF 6 ] and avoided the direct inactivation of [bmim][PF 6 ] on YADH. Under optimal conditions, the activity of YADH was as high as 51 µmol L ⁻¹ min ⁻¹ .
CONCLUSION: [bmim][PF 6 ] was an inhibitor of YADH and its negative effect on YADH could be lessened by its microemulsification. Copyright © 2008 Society of Chemical Industry
Water-in-ionic liquid (w/IL) microemulsions formulated with non-ionic surfactants, (Tween 20 or Triton X-100) in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6), were used as media for lipase-catalyzed esterification reactions. The catalytic behavior and stability of lipases from Candida rugosa, Chromobacterium viscosum and Thermomyces lanuginosa in these novel microemulsions were investigated and compared to other microheterogeneous media used so far for enzyme-catalyzed reactions. The catalytic behavior of the enzymes depends strongly on the surfactant concentration and the water content. The dependence of the esterification activity of lipases on molar ratio of water to surfactant (wo) follows a bell-shaped profile, presenting a maximum at wo≈5. The operational stability of lipases in w/IL microemulsions, especially at high incubation temperature (50 °C), was significantly increased compared to that observed in other microheterogeneous media. The highest half-life times (>100 h) were obtained in w/IL microemulsions with low water content. Conformational studies via Fourier transform-infrared (FT-IR) and circular dichroism (CD) spectroscopy indicated that lipases entrapped in w/IL microemulsions in most cases retain their native structure or adapt a more rigid structure compared to other microheterogeneous media, which correlated well with the stability results. A simple procedure suitable for ester separation and enzyme reuse was developed. T. lanuginosa lipase retained 90% of activity after ten reaction cycles in w/IL microemulsions formulated with Tween 20.
Reverse micelles create unique environment in organic media. They are capable of solubilizing hydrophilic biomolecules (e.g., proteins, peptides, amino acids, and DNAs) in their aqueous interior. This feature brings about the practical use of biomaterials in organic media because reverse micelles solubilize them with the intrinsic activity. In this paper, we focus on recent two topics concerning protein extraction and chiral separation of biomolecules using liquid membranes. In the first topic, we present recent attempts to extract proteins from an aqueous solution into isooctane using reverse micelles, and some important operational parameters to achieve an efficient protein transfer are discussed. Furthermore, novel function of reverse micelles as a protein activation medium is introduced. In the reverse micellar phase, denatured proteins were completely reactivated in the reverse micellar solution. The reverse micellar technique is found to be a useful tool not only for protein separation but also for protein refolding. Furthermore, we found that a cyclic ligand carixarene has an extraction ability to set up optimum conditions for protein transfer. In the second topic, we have found that a supported liquid membrane (SLM) encapsulating enzymes shows high enantioselectivity (enantioselective excess value is over 96%) in the transport of racemic pharmaceutical compound ibuprofen. A different experiment also suggests that the α-chymotrypsin-catalyzed reactions droved the enantioselective transport of L-phenylalanine based on the enantioselectivity of the enzyme. The SLM encapsulating the surfactant-enzyme complex enabled the highly enantioselective separation of racemic mixtures. It can be envisioned that arrangement of appropriate enzymes in the SLM system will allow enantioselective separation of various useful organic compounds.
CONTIN is a portable Fortran IV package for inverting noisy linear operator equations. These problems occur in the analysis of data from a wide variety experiments. They are generally ill-posed problems, which means that errors in an unregularized inversion are unbounded. Instead, CONTIN seeks the optimal solution by incorporating parsimony and any statistical prior knowledge into the regularizor and absolute prior knowledge into equallity and inequality constraints. This can be greatly increase the resolution and accuracyh of the solution. CONTIN is very flexible, consisting of a core of about 50 subprograms plus 13 small “USER” subprograms, which the user can easily modify to specify special-purpose constraints, regularizors, operator equations, simulations, statistical weighting, etc. Specjial collections of USER subprograms are available for photon correlation spectroscopy, multicomponent spectra, and Fourier-Bessel, Fourier and Laplace transforms. Numerically stable algorithms are used throughout CONTIN. A fairly precise definition of information content in terms of degrees of freedom is given. The regularization parameter can be automatically chosen on the basis of an F-test and confidence region. The interpretation of the latter and of error estimates based on the covariance matrix of the constrained regularized solution are discussed. The strategies, methods and options in CONTIN are outlined. The program itself is described in the following paper.
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In the water-in-[Bmim][PF(6)] microemulsion stabilized by both AOT and Triton X-100, the lipase-catalyzed hydrolysis of 4-nitrophenyl butyrate (p-NPB) was investigated to evaluate the catalytic efficiency of lipase in this novel microemulsion. The structural parameters of the microemulsion and the conditions of the enzymatic reaction affect the catalytic activity of lipase, especially the concentration of Tris-HCl buffer. Under optimum conditions, the catalytic activity of lipase in the present microemulsion is much higher than that in H(2)O saturated [Bmim][PF(6)]. When the partitioning of the substrate in the microemulsion is taken into account, the catalytic efficiency of lipase in this novel microemulsion is 14.3 times that in H(2)O saturated [Bmim][PF(6)] due to the significant decrease of the Michaelis constant in the microemulsion. Due to the large interface, high water activity, and probably the activating effect of the imidazolium cation in the water pool, the present microemulsion is demonstrated to be a promising medium for the lipase-catalyzed hydrolytic reaction. To demonstrate an important biocatalytic application in the IL-based microemulsion, the lipase-catalyzed synthesis of the flavoring agent benzyl acetate via transesterification of vinyl acetate with benzyl alcohol was also studied in the medium. Due to the high dispersion of lipase, large interface and removal of the byproduct, a maximum yield of 94% was obtained, indicating that the novel microemulsion is really important and useful.
A scientific review focuses on the use of room-temperature ionic liquids (IL) as solvents in synthesis and catalysis. The review concentrates on those studies that have sought to understand how ionic liquids can affect the reactivity of solute materials. A number of such room-temperature ionic liquids have bee prepared over a period of time to be used as solvents in synthesis and catalysis. The vast majority of these ionic liquid cations are based upon alkylated amines, with a smaller number of phosphonium and sulfonium salts used. It has also been demonstrated that the IL can be prepared by metathesis of the halide salt with a metal or ammonium salt or the conjugate acid of the required anion. This can be done in aqueous solution for hydrophobic ionic liquids with the product separating during the reaction. The aqueous solution can be washed with CH2Cl2 and the ionic liquid isolated from the CH 2Cl2 solution to increase the overall yield.
It is of great significance to develop an appropriate water-in-ionic liquid (W/IL) microemulsion suitable for the expression of the catalytic activity of a given enzyme. In this paper, the phase diagram of a new AOT/Triton X-100/H(2)O/[Bmim][PF(6)] pseudo ternary system is presented. With the aid of nonionic surfactant Triton X-100, AOT could be dissolved in hydrophobic ionic liquid [Bmim][PF(6)], forming a large single phase microemulsion region. The water-in-[Bmim][PF(6)] (W/IL) microemulsion domain was identified electrochemically by using K(3)Fe(CN)(6) as a probe. The existence of W/IL microemulsions was demonstrated spectrophotometrically by using CoCl(2) as a probe. New evidences from the FTIR spectroscopic study, which was first introduced to the W/IL microemulsion by substituting D(2)O for H(2)O to eliminate the spectral interference, demonstrated that there existed bulk water at larger ω(0) values (ω(0) was defined as the molar ratio of water to the total surfactant) in the W/IL microemulsion, which had remained unclear before. In addition to the inorganic salts, biomacromolecule laccase could be solubilized in the W/IL microemulsion. The laccase hosted in the microemulsion exhibited a catalytic activity and the activity could be regulated by the composition of the interfacial membrane.
Molecular dynamics (MD) simulations were conducted for systems in vacuo consisting of n AOT(-) anions (bis(2-ethylhexyl)sulfosuccinate ions) and n+/- 1 or n Na(+) ions up to n = 20. For n = 15, positively charged systems with Li(+), K(+), and Cs(+) cations were also considered. All systems were observed to form reverse micelle-like aggregates whose centre is occupied by cations and polar heads in a very compact solid-like way, while globally the aggregate has the form of an elongated and rather flat ellipsoid. Various types of statistical analyses were carried out on the systems to enlighten structural and dynamical properties including gyration radius, atomic pair correlation functions, atomic B-factor and moment of inertia tensor. For completeness and comparison the stability of reverse micelle is tested in the case of neutral n = 20 system in CCl(4) solution.
Formation of water-in-ionic liquid [bmim][PF 6] microemulsions by the nonionic surfactant triton X-100 can be observed from the color change of Co II within the solution (see picture).
Experimental data on micellization in aqueous solutions of 1-alkyl-3-methylimidazolium salts [C(n)mim]X and their mixtures with sodium dodecyl sulfate (NaDS) are reviewed. New results (the critical micelle concentration and enthalpy of micellization) are presented for mixtures of [C(4)mim]PF(6), [C(6)mim]BF(4), [C(6)mim]Br and [C(10)mim]Br with NaDS. Our data cover a wide range (from 0 to 0.9) of solvent-free based mole fractions of ionic liquid (IL). Even very small addition of ILs substantially decreases the cmc of NaDS due to the combined effect of electrostatic and hydrophobic interactions, and formation of mixed micelles. It is shown that the quasichemical aggregation model by Nagarajan and Ruckenstein may be successfully applied to aqueous solutions of long-chain ILs and their mixtures with NaDS. The local structure of micelles is obtained from all-atom MD simulations for [C(n)mim]Br and [C(n)mim]X+NaDS in aqueous medium.
In this article we report the first results on the enzymatic activity of horseradish peroxidase (HRP) microencapsulated in water-in-ionic liquid (w/IL) microemulsions using pyrogallol as the substrate. Toward this goal, the system used in this study was composed of anionic surfactant AOT (sodium bis(2-ethyl-1-hexyl)sulfosuccinate)/hydrophobic IL [C(8)mim][Tf(2)N] (1-octyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide)/water/1-hexanol. In this system, the catalytic activity of HRP was measured as a function of substrate concentrations, W(0) (molar ratio of water to surfactant), pH, and 1-hexanol content. The curve of the activity-W(0) profile was found to be hyperbolic for the new microemulsion. The apparent Michaelis-Menten kinetic parameters (k(cat) and K(m)) were estimated and compared to those obtained from a conventional microemulsion. Apparently, it was found that HRP-catalyzed oxidation of pyrogallol by hydrogen peroxide in IL microemulsuions is much more effective than in a conventional AOT/water/isooctane microemulsion. The stability of HRP solubilized in the newly developed w/IL microemulsions was examined, and it was found that HRP retained almost 70% of its initial activity after incubation at 28 degrees C for 30 h.
The phase behavior and microstructure of the ternary system water/1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6))/Triton X-100 was studied as a function of temperature and ionic liquid (IL) mass fraction alpha. In the present study, a hydrophobic IL instead of commonly used organic solvents such as n-alkanes is used. The fish-shaped region is distorted at low and high values of alpha, whereas it is symmetric at intermediate alpha. With increasing alpha, the extension of the three-phase region decreases regarding the surfactant concentration range, whereas it increases regarding the temperature range. For comparison the phase behavior of two ternary water/bmimPF(6)/alkyl oligoethyleneoxide (C(i)E(j)) systems has been investigated. Our results are compared with those obtained for water/n-alkane/C(i)E(j) and IL/n-alkane/C(i)E(j) systems, respectively.
Reverse micelles are nanometer-sized (1-10 nm) water droplets dispersed in organic media obtained by the action of surfactants. Surfactant molecules organize with the polar part to the inner side able to solubilize water and the apolar part in contact with the organic solvent. Proteins can be solubilized in the water pool of reverse micelles. Studies on the structure-function relationships of proteins in reverse micelles are very important since the microenvironment in which the protein is solubilized has physico-chemical properties distinct from a bulk aqueous solution. Some of the unique characteristics of reverse micelles make them very useful for biotechnological applications. Charge and hydrophilic/hydrophobic characteristics of the protein and the selection of surfactant can be used to achieve selective solubilization of proteins. This has been used to extend the classical liquid-liquid extraction with solvents to protein bioseparation. For biocatalysis the presence of a bulk organic solvent allow synthetic reactions to be performed via the control of water content and the solubilization of hydrophobic substrates. This is accomplished with a higher interfacial area (about 100 m2/mL) than the conventional biphasic systems, minimizing mass transfer problems.
Ionic liquids are composed entirely of ions. Because of the wide range of possible binary and ternary ionic liquids, they offer a potentially wide range of solvent properties. In their Perspective, [Rogers and Seddon][1] review recent progress on developing new ionic liquid solvents for use in chemical synthesis, catalysis, fuel cells, and other applications. Ionic liquids are considered advantageous not only because of their versatility but also for their "green" credentials, although it is important to remember that not all ionic liquids are environmentally benign. One industrial process has been reported, and others may not be far behind. The authors conclude that in the next decade, ionic liquids are likely to replace conventional solvents in many applications.
[1]: http://www.sciencemag.org/cgi/content/full/302/5646/792
Both ionic liquids and water are typical green solvents. In this work, the phase behavior of the ternary system consisting of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), TX-100, and water was determined at 25.0 degrees C. The water-in-bmimPF6, bicontinuous, and bmimPF6-in-water microregions of the microemulsions were identified by cyclic voltammetry method using potassium ferrocyanide K4Fe(CN)6 as the electroactive probe. Dynamic light scattering (DLS) and the UV-vis method were used to characterize the microemulsions. It was demonstrated that the hydrodynamic diameter (Dh) of the bmimPF6-in-water microemulsions is nearly independent of the water content but increases with increasing bmimPF6 content due to the swelling of the micelles by the ionic liquid. The UV-vis further confirmed the existence of water domains in the water-in-bmimPF6 microemulsions, and the salt potassium ferricyanide K3Fe(CN)6 could be dissolved in the water domains.
Several types of imidazolium salt ionic liquids were prepared derived from poly(oxyethylene)alkyl sulfate and used as an additive or coating material for lipase-catalyzed transesterification in an organic solvent. A remarkably increased enantioselectivity was obtained when the salt was added at 3-10 mol % versus substrate in the Burkholderia cepacia lipase (lipase PS-C)-catalyzed transesterification of 1-phenylethanol by using vinyl acetate in diisopropyl ether or a hexane solvent system. In particular, a remarkable acceleration was accomplished by the ionic liquid coating with lipase PS in an iPr(2)O solvent system while maintaining excellent enantioselectivity; it reached approximately 500- to 1000-fold acceleration for some substrates with excellent enantioselectivity. A similar acceleration was also observed for IL 1-coated Candida rugosa lipase. MALDI-TOF mass spectrometry experiments of the ionic-liquid-coated lipase PS suggest that ionic liquid binds with lipase protein.
The surface, phase and aggregation behaviour of mixtures of 1-alkyl-3-methylimidazolium halide, [C(n)mim]X, where n is the alkyl chain length, with water has been explored using a variety of methods. Critical micelle concentrations (cmc) and micelle structures have been determined for aqueous [C(n)mim]Br solutions for n=2, 4, 6, 8, and 10. Small-angle neutron scattering (SANS) measurements reveal that for the n=8 and 10 systems, at concentrations just above the cmc, small near-spherical aggregates exist, which, after initial growth, possess core radii (aggregation numbers) at intermediate concentrations of 10.5+/-0.5 Angstrom (22+/-2) and 13.2+/-0.5 Angstrom (40+/-3), respectively, for n=8 and n=10. Towards higher concentrations, the aggregates appear to grow, with the aggregates in the [C(10)mim]Br system becoming increasingly elongated (prolate) with increasing concentration. No evident aggregates are formed in the systems with n=2 and 4. In the n=6 system, it appears that oblate aggregates with radius approximately 9 Angstrom form at the cmc and that the radius increases with increasing concentration. For longer alkyl chain lengths, at high concentrations lyotropic mesophases form in some systems. The mesophase region for the [C(8)mim]Cl system has been explored across the composition range using X-ray diffraction and (2)H NMR spectroscopy. Both techniques suggest that a major hexagonal phase with lattice parameter of 29.5+/-0.5 Angstrom coexists with a minor lamellar phase (23.5+/-0.3 Angstrom) or possibly a second hexagonal phase (27.1+/-0.4 Angstrom). The area per adsorbed molecule at the surface of [C(8)mim]Br solutions has been measured as a function of concentration using neutron reflectometry. A minimum in the area per molecule behaviour is coincident with a minimum identified in the surface tension isotherm occurring close to the cmc. The data suggest depletion of [C(8)mim]Br from the surface region occurs at concentrations immediately above the cmc.
Various issues that surround biocatalysis in ionic liquids are reviewed and presented in details. The effects of ionic liquids (ILs) on the structure and activity of enzymes as well as their thermal and operational stability is surveyed. Included also in the review is the effects of ILs on the (enantio)selectivity of biocatalytic transformations in comparison with conventional reaction media and the design of efficient reaction procedures based on its unconventional solvent characteristics. The study showed that there is hardly an IL that is not tolerated by any enzyme, and the impression is generally tolerated to higher concentrations than water-miscible molecular solvents. Ionic liquids have potential as reaction media for biotransformation of highly polar substrates, such as polysaccharides, which cannot be performed in water, owing to equilibrium limitations. It is expected that green and biocompatible ionic liquids will become available to contribute to a greener chemical industry.
Generally, ionic liquids (ILs) are defined as those fused salts with a melting point less than 100°C with salts that has higher melting points referred to as molten salts. However, a view to include all protic ILs (PILs) and protic molten salts with melting point up to 200°C has been initialized. The inclusion of fused salts with higher melting points was to allow structure and property correlations to be made across a wider range of complexes. PILs with stoichiometric ratios of Brøonsted acid to base have also been covered. The ionicity, physicochemical and thermal properties of the PILs including thermal phase behavior, glass transition, melting point, thermal stability, density and molar volume, refractive index and molar refractivity, surface tension, viscosity, ionic conductivity and polarity are covered followed by description of application where they have been used including organic synthesis, chromatography, biological applications, fuel cells, explosives, and recently, industrial lubricants.
(Graph Presented) Nanopools of water in ionic liquids: The surfactant AOT forms reverse micelles with water domains in a hydrophobic ionic liquid in the presence of 1-hexanol (see optically transparent sample B, in figure). These nanopools increase in size with increasing water content.
The liquid structure of 1-ethyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imide (EMI(+)TFSI(-)) has been studied by means of large-angle X-ray scattering (LAXS), (1)H, (13)C, and (19)F NMR, and molecular dynamics (MD) simulations. LAXS measurements show that the ionic liquid is highly structured with intermolecular interactions at around 6, 9, and 15 A. The intermolecular interactions at around 6, 9, and 15 A are ascribed, on the basis of the MD simulation, to the nearest neighbor EMI(+)...TFSI(-) interaction, the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions, and the second neighbor EMI+...TFSI(-) interaction, respectively. The ionic liquid involves two conformers, C(1) (cis) and C(2) (trans), for TFSI(-), and two conformers, planar cis and nonplanar staggered, for EMI(+), and thus the system involves four types of the EMI(+)...TFSI(-) interactions in the liquid state by taking into account the conformers. However, the EMI(+)...TFSI(-) interaction is not largely different for all combinations of the conformers. The same applies alsoto the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions. It is suggested from the 13C NMR that the imidazolium C(2) proton of EMI(+) strongly interacts with the O atom of the -SO(2)(CF(3)) group of TFSI(-). The interaction is not ascribed to hydrogen-bonding, according to the MD simulation. It is shown that the liquid structure is significantly different from the layered crystal structure that involves only the nonplanar staggered EMI(+) and C(1) TFSI(-) conformers.
For hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]), an H(2)O-in-[BMIM][PF(6)] microemulsion could be formed in the presence of nonionic surfactant Triton X-100 (TX-100). In such a medium, both lignin peroxidase (LiP) and laccase could express their catalytic activity with the optimum molar ratio of H(2)O to TX-100 at 8.0 for LiP and >20 for laccase, and the optimum pH values at 3.2 for LiP and 4.2 for laccase, respectively. As compared with pure or water saturated [BMIM][PF(6)], in which the two oxidases had negligible catalytic activity due to the strong inactivating effect of [BMIM][PF(6)] on both enzymes, the use of the [BMIM][PF(6)]-based microemulsion had some advantages. Not only the catalytic activities of both fungal oxidases greatly enhanced, but also the apparent viscosity of the medium decreased.
Angle Neutron Scattering Study on Aggregation of 1-Alkyl-3-methylimida-zolium-Based Ionic Liquids in Aqueous Solution (39) Pavlidis, I.; Gournis, D.; Papadopoulos, G.; Stamatics, H. Lipases in Water-in-Ionic Liquid Microemulsions: Structural and Activity Studies
- M Tabata
- M Shibayama
- Small
Tabata, M.; Shibayama, M. Small-Angle Neutron Scattering Study on Aggregation of 1-Alkyl-3-methylimida-zolium-Based Ionic Liquids in Aqueous Solution. J. Solution Chem. 2013, 42, 1888. (39) Pavlidis, I.; Gournis, D.; Papadopoulos, G.; Stamatics, H. Lipases in Water-in-Ionic Liquid Microemulsions: Structural and Activity Studies. J. Mol. Catal. B: Enzym. 2009, 60, 50−56. Langmuir (40) Xue, L.; Li, Y.; Zou, F.; Lu, L.; Zhao, Y.; Huang, X.; Qu, Y. The Catalytic Efficiency of Lipase in a Novel Water-in-[Bmim][PF 6 ] Microemulsion Stabilized by Both AOT and Triton X-100. Colloids Surf., B 2012, 92, 360−366.
Catalyzed Transesterification by Using an Imidazolium PEG-Alkyl Sulfate Ionic Liquid Protic Ionic Liquids: Properties and Applications Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2
- M Morimoto
- T L Greaves
- C J Drummond
- J P Hallett
- T Welton
- E A Safonova
- I B Pukinsky
Morimoto, M.; Hirose, Y. Increased Enantioselectivity and Remarkable Acceleration of Lipase-Catalyzed Transesterification by Using an Imidazolium PEG-Alkyl Sulfate Ionic Liquid. Chem.Eur. J. 2006, 12, 9228−9237. (31) Greaves, T. L.; Drummond, C. J. Protic Ionic Liquids: Properties and Applications. Chem. Rev. 2008, 108, 206−237. (32) Hallett, J. P.; Welton, T. Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2. Chem. Rev. 2011, 111, 3508− 3576. (33) Plechkova, N. V.; Seddon, K. R. Applications of Ionic Liquids in the Chemical Industry. Chem. Soc. Rev. 2008, 37, 123−150. (34) Smirnova, N. A.; Vanin, A. A.; Safonova, E. A.; Pukinsky, I. B.;