Presence Of Imidazolium-based Ionic Liquids Research Articles

Thermodynamics and structure of model bio-membrane of liver lipids in presence of imidazolium-based ionic liquids

Ionic liquids (ILs) are the attractions of researchers today due to their vast area of potential applications. For biomedical uses, it becomes essential to understand their interactions with cellular membrane. Here, the membrane is mimicked with lipid bilayer and monolayer composed of liver lipids extract. Three archetypal imidazolium based ILs, 1-decyl-3-methylimidazolium tetrafluoroborate ([DMIM][BF4] or [C10MIM][BF4]), 1-octyl-3-methylimidazolium tetrafluoroborate, ([OMIM][BF4] or [C8MIM][BF4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4] or [C2MIM][BF4]) having different alkyl chain lengths are used in the present study. The isothermal titration calorimetry (ITC) measurements showed that [DMIM][BF4] interacts strongest with the liver lipid membrane compared to other two ILs which have relatively shorter alkyl chain length. The low values of stoichiometry ratio of ILs indicates that ILs penetrate within the core of the lipid bilayer. The interaction of ILs with the liver lipid membrane is found to be mainly driven by entropy which could be due to the change in the structure of the lipid membrane at local or global scales. Dynamic light scattering (DLS) measurements indicate that there are no changes in the size of vesicles due to addition of [DMIM][BF4] indicating stability of the vesicles. On the other hand, x-ray reflectivity (XRR) measurements showed a concentration dependent change in the monolayer structure. At low concentration of the IL, the monolayer thickness decreases, exhibiting an increase in the electron density of the layer. However, at higher concentrations, the monolayer thickness increases proving a concentration dependent effects of the IL on the arrangement of the molecules.

Physicochemical studies on the micellization of anionic surfactants in the presence of long alkyl chain ionic liquid

The physicochemical properties on micellization of anionic surfactant, sodium dodecyl sulphate (SDS) and lithium dodecyl sulphate (LDS) in the presence of imidazolium-based ionic liquid 1-decyl-3-methylimidazolium tetrafluoroborate [Dmim][BF4] have been studied using surface tension and conductivity techniques. The interfacial and thermodynamic parameters have also been determined. FTIR has studied the aggregation behavior while aggregation number and Stern-Volmer constant is determined by fluorescence measurement. The current results indicate that the addition of [Dmim][BF4] to the anionic surfactant leads to a dramatic decrease in the CMC. The interaction of human serum albumin with micellar solution of SDS and LDS have been examined.

Effect of immidazolium-based green solvents on the moisture absorption and thickness swelling behavior of wood flour/polyethylene composites

The water transport kinetics and moisture-induced thickness swelling behavior of wood-plastic composites (WPCs) in the presence of two imidazolium-based ionic liquids (ILs) were studied. The wood flour chemically treated with ILs were compounded through melt mixing of high-density polyethylene and coupling agent, and finally, the test specimens were produced by compression molding. Hygroscopic rates of the composites were evaluated by immersing them in the water at room temperature and monitoring moisture sorption and thickness changes for several weeks. Besides, the water diffusion coefficients and swelling rate parameters were measured for all composites. It was found that the water absorption and thickness swelling of the WPC specimens reduced as a result of ILs treatment. The SEM analysis revealed that the presence of ILs can improve the quality of adhesion between the polymer matrix and the cellulosic materials, to decrease the gaps in the interfacial region and block the hydrophilic groups. Studying the water sorption process in the specimens showed that the process follows kinetics and mechanisms described by Fick’s law. The highest water diffusion coefficients and swelling rate parameters were found in composites with untreated wood.

Role of ionic liquids in the efficient transfer of lithium by Cyanex 923 in solvent extraction system

AbstractThe solvent extraction of Li+ by Cyanex 923 was investigated upon the addition of different imidazolium‐based ionic liquids (ILs). The results showed 1‐hydroxylethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([HOEmim][NTf2]) can improve the extraction of Li+ most effectively. The fundamental mechanism is that [HOEmim][NTf2] can remarkably enhance the coordination ability of Cyanex 923 to Li+ to form more stable and hydrophobic ion‐pair species [Li(Cyanex 923)n][NTf2] (nmax = 3) resulting from the electrostatic interaction and typical hydrogen bonding of IL, and thus facilitating the transfer of Li+ into organic phase. This work has revealed the transfer mechanism of Li+ in a solvent extraction system comprising of IL and neural ligand. The knowledge of the coordination environment of Li+ in the presence of IL also gives us a new insight into the separation of 6Li/7Li. The disadvantage of this process is the loss of IL. However, this study provides guidance for the design of better IL‐based systems for the separation of metal ions.

Insights into the Composition and Function of a Bismuth-Based Catalyst for Reduction of CO2 to CO

The electrochemical conversion of CO2 to CO is a process important for generation of carbon-based fuels using energy produced from intermittent, renewable energy sources. Electrodeposited thin films of bismuth-based materials are promising platforms for this transformation when used for CO2 electrolysis in the presence of imidazolium-based ionic liquids including [BMIM]OTf and [EMIM]OTF. In this study, the composition and function of a bismuth-based carbon monoxide evolving catalyst (Bi-CMEC) has been probed. In particular, the composition of both the electrodeposited bismuth material and the catholyte has been scrutinized in an effort to understand the factors that drive efficient catalyst operation. A combination of XPS depth profiling, XANES, and EXAFS experiments were employed to identify the bulk composition of the bismuth catalyst, which is shown to be composed of both metallic and oxidized phases. The identity of the catholyte solvent has been shown to influence the nature and efficacy of CO2 reduc...

NaCl enhances Escherichia coli growth and isoprenol production in the presence of imidazolium-based ionic liquids

Certain ionic liquids (ILs) can be used to pretreat biomass to improve enzymatic hydrolysis of polysaccharides; however, residual ILs may inhibit biofuel production. In this study, the impact of NaCl on cell growth and isoprenol production of E. coli in the presence of ILs was studied. The final biomass of E. coli MG1655 and DH1 were in the presence of 50 mM 1-butyl-3-methylimidazolium chloride ([C4C1Im]Cl) and 50 mM 1-butyl-3-methylimidazolium acetate ([C4C1Im][OAc]) when 200 mM NaCl was added. Isoprenol production by E. coli DH1's was also increased in the presence of imidazolium-based ionic liquids when the culture emedia were amended with 200 mM NaCl. However, isoprenol production by E. coli MG1655's isoprenol production was decreased or less affected in the presence of ILs.

Efficient Approach for the Tritylation of Alcohols Using Recyclable Lewis Acid-Based Ionic Liquid (EMIM·AlCl4).

A new efficient approach has been reported for the tritylation of primary alcohols over secondary alcohols using triphenyl methyl alcohol and 4-monomethoxyl trityl alcohols in the presence of imidazolium-based ionic liquid 1-ethyl-3-methylimidazolium tetrachloroaluminate as catalyst. At room temperature, 5 mol % of catalyst in dichloromethane and acetonitrile solvent has been shown to be excellent for the tritylation of benzyl alcohol and various other alcohols The method was compatible with Fmoc/acetyl protecting group of amino and tert-butyldiphenylsilyl ether protecting group of alcohol. Moreover, the catalyst was reused for three to four catalytic cycles with little loss of catalytic activity. Excellent yields, reusability, chemoselectivity, and easy workup are advantages of this protocol.

Thermodynamic modeling of methane hydrate formation in the presence of imidazolium-based ionic liquids using two-step hydrate formation theory and CPA EoS

In this study, thermodynamic modeling is performed to predict the P-T equilibrium conditions of methane gas hydrate formation in presence of ionic liquids. The imidazolium-based ionic liquids including [EMIM][HSO4], [EMIM][EtSO4], [BMIM][BF4], [OH-EMIM][BF4], [BMIM][Cl] and [BMIM][Br] are modeled through two-step hydrate formation theory of Chen and Guo coupled with CPA EoS for calculating the fugacities of species in liquid and gas phase. The CPA pure component parameters for ionic liquids and also the majority of binary interaction parameters are adjusted using the liquid density and binary VLE data, respectively. The thermodynamic modeling is carried out in the presence of 0.1 weight fractions of all the studied imidazolium based ionic liquids. Moreover, the effect of three various concentrations of [BMIM][BF4] on the P-T equilibrium diagram of methane hydrate are predicted at 0.1, 0.15 and 0.20 weight fractions of this ionic liquid. The results indicate that the CPA EoS can satisfactorily model the phase behavior of aqueous solutions of imidazolium based ionic liquids considering 2B scheme for the association term. In addition, the results indicate good predictions of the proposed model for methane hydrate equilibrium conditions in the presence of imidazolium-based studied ionic liquids including concentration changes such that the absolute average deviations of methane hydrate formation pressures is obtained below 4.2%.

How Does a Smart Polymer Respond to Imidazolium-Based Ionic Liquids?

In this research article, we have explored the changes in the lower critical solution temperature (LCST) of the poly(N-vinylcaprolactam) (PVCL) in the presence of imidazolium-based ionic liquids (ILs) with fixed cation 1-butyl-3-methylimidazolium cation [Bmim+], and commonly used anions such as SCN–, I–, Br–, Cl–, CH3COO–, and HSO4–. The series of anions also reflect the Hofmeister series of ILs. The results reveal that the LCST of the PVCL increases with increasing IL concentration. Interestingly, the results are the reverse of the PNIPAM with the same ILs where the LCST of PNIPAM decreases linearly with increase in the IL concentration following the Hofmeister series. Herein, we observed that the increase in the LCST of PVCL follows the order of ILs as, HSO4– < CH3COO– < Cl– < Br– < I– < SCN–. This is the reverse order for Hofmeister series anions effect on the polymer. Furthermore, the different kind of interactions occur between ILs and PVCL observed using UV-absorbance, fluorescence, and FTIR spectro...

Experimental and DFT studies of 1-methylimidazolium trinitrophenoxide as modifier for corrosion inhibition of SDS for mild steel in hydrochloric acid

PurposeThe purpose of this paper is to investigate the surface properties, particle sizes and corrosion inhibition performance of sodium dodecyl sulfate (SDS) in the presence of imidazolium-based ionic liquid as an additive. Up to now, different properties of alone surfactants and ionic liquids have been studied. However, few studies have been devoted to mixed ionic liquid and surfactant. The significance and novelty of this research is the investigation of 1-methylimidazolium trinitrophenoxide ([MIm][TNP]) as ionic liquid effects on SDS corrosion behavior.Design/methodology/approachThe inhibition effect of [MIm][TNP], SDS and their mixtures on mild steel surface in 2 M hydrochloric acid (HCl) solution was examined by electrochemical impedance spectroscopy, potentiodynamic polarization (PDP), scanning electron microscopy (SEM), atomic force microscopy and quantum chemical calculations as well as dynamic light scattering (DLS) and surface tension measurements to discuss surface properties of studied solutions.FindingsBased on the results, ionic liquid/SDS mixtures significantly indicated better inhibition properties than pure surfactant solution. PDP curves indicated that the studied compounds act as mixed-type of inhibitors. The critical micelle concentration, surface properties and particle sizes were investigated from the surface tension measurements and DLS results.Originality/valueAdsorption of the inhibitors on the steel surface obeyed the Villamil adsorption model. SEM was used for surface analysis and verified the inhibition efficiency of mixed IL/SDS system. Quantum chemical calculations were performed using density functional theory, and a good relationship between experimental and theoretical data has been obtained.

Assessing the efficiency of imidazolium-based ionic liquids on the phase behavior of a synthetic biomedical thermoresponsive polymer

HypothesisTemperature-responsive polymers (TRPs) with a phase transition temperature close to human physiological body temperature have attracted much attention in biomedical and pharmaceutical fields. Addition of small amount of cosolvent to TRPs is expected to influence the molecular interactions, thereby affecting the phase transition temperature of TRPs. Hence, it is possible to tune the phase behavior of TRPs and also drive transitions in TRPs by variation of chemical structure of cosolvent. ExperimentsTo elucidate the conformational changes of the phase transition of TRP aqueous solution in ionic liquids (ILs), poly(N-vinylcaprolactam) (PVCL), a well known TRP was synthesized by solution polymerization. The lower critical solution temperature (LCST) behavior of polymer aqueous solution, with the addition of imidazolium-based ILs possessing same Cl− anion and a set of cations [Cnmim]+ such as 1-ethyl-3-methylimidazolium ([Emim]+), 1-butyl-3-methylimidazolium ([Bmim]+), 1-hexyl-3-methylimidazolium ([Hmim]+), 1-decyl-3-methylimidazolium ([Dmim]+), 1-allyl-3-methylimidazolium ([Amim]+) and 1-benzyl-3-methylimidazolium ([Bzmim]+), was monitored by using various sophisticated experimental techniques. FindingsThe modulations on the LCST of PVCL aqueous solutions follow the order of [Emim][Cl]<[Amim][Cl]<[Bmim][Cl]<[Hmim][Cl]<[Bzmim][Cl]<[Dmim][Cl]. This order shows that the LCST value increase with increasing the alkyl chain length of cation from [Emim]+ to [Dmim]+ of IL. To the best of our knowledge, this is the first report on comprehensive unequivocal evidence of the phase transition behavior of PVCL in presence of imidazolium-based ILs.

Microwave-assisted degradation of guaifenesin (GGE) to produce novel compounds in the presence of imidazolium-based ionic liquids

Thermal stabilities and degradation behaviors of guaifenesin (guaiacol glycerol ether = GGE) were studied by means of the differential scanning calorimetry and thermogravimetric (TG/DTG, in nitrogen atmosphere) analyses. To investigate the microwave-assisted pathways of guaiacol production from lignin, guaiacol glycerol ether (GGE) as a nonphenolic lignin model compound was exposed to microwave irradiation in the presence of three 1-butyl-3-methylimidazolium-based ionic liquids ([BMIm]-based ILs). GGE was subjected to microwave irradiation of 300 W in a batch reactor at a temperature of 200 °C, residence times of 5 min and air atmosphere. Based on the distribution of GGE conversion products identified by gas chromatography/mass spectrometry, the most degradation pathways of GGE were discussed. The highest yields of 2-methoxyphenol (guaiacol), 1-(2-methoxy-phenoxy)-propan-2-one, and 2-hydroxymethyl-1,4-benzodioxan were obtained using [BMIm][HSO4]. [BMIm][HSO4] was recovered and reused for three times without any loss of catalytic activity. It was found that it is possible to increase the yield of guaiacol from GGE by controlling of the different parameters such as temperature, molar ratio of water to GGE, acidity and anion effect of [BMIm]-based IL, amount of [BMIm]-based IL, microwave power and irradiation time.

Spectroscopic insight into the interaction of bovine serum albumin with imidazolium-based ionic liquids in aqueous solution.

The study of protein-ionic liquid interactions is very important because of the widespread use of ionic liquids as protein stabilizer in the recent years. In this work, the interaction of bovine serum albumin (BSA) with different imidazolium-based ionic liquids (ILs) such as [1-ethyl-3-methyl-imidazolium ethyl sulfate (EmimESO4 ), 1-ethyl-3-methyl-imidazolium chloride (EmimCl) and 1-butyl-3-methyl-imidazolium chloride (BmimCl)] has been investigated using different spectroscopic techniques. The intrinsic fluorescence of BSA is quenched by ILs by the dynamic mechanism. The thermodynamic analysis demonstrates that very weak interactions exist between BSA and ILs. 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence and lifetime measurements reveal the formation of the compact structure of BSA in IL medium. The conformational changes of BSA were monitored by CD analysis. Temperature-dependent ultraviolet (UV) measurements were done to study the thermal stability of BSA. The thermal stability of BSA in the presence of ILs follows the trend EmimESO4 >EmimCl > BmimCl and in the presence of more hydrophobic IL, destabilization increases rapidly as a function of concentration.

Effect of 1-ethyl-3-methylimidazolium bromide on interfacial and aggregation behavior of mixed cationic and anionic surfactants

Aggregation behavior and interaction of sodium dodecyl sulfate (SDS), tetradecyl trimethyl ammonium bromide (TTAB) and their mixtures with an excess of anionic surfactant in the presence of imidazolium-based ionic liquid, 1-ethyl-3-methylimidazolium bromide (EMIm Br) were investigated using surface tension, electrical conductivity, dynamic light scattering (DLS), transmission electron microscopy (TEM) and cyclic voltammetry measurements. Different physicochemical properties such as critical micelle concentration (CMC), degree of counterion dissociation (αdiss), interfacial properties, the standard Gibbs energy of adsorption and the size of aggregates were determined. The effects of ionic liquid (IL) as additive on the interactions between the surfactants; TTAB, SDS and their mixtures were analyzed on the basis of regular solution theory, both for mixed monolayers at the air/liquid interface (βδ) and for mixed micelles (βM). Interaction parameter values suggested that the formation of aggregates is due to the synergistic interactions in the case of SDS/TTAB systems and becomes more affected by adding IL. It was shown that an excess of cationic surfactant and IL resulted in an increase in the nano-aggregate sizes. The synergism observed for three component systems (surfactant–water–IL) revealed the effect of attractive electrostatic interaction, formation of a three-dimensional hydrogen bond network and hydrophobic forces on mixed micelle formation.

Thermal and conformational stability of insulin in the presence of imidazolium-based ionic liquids

Stabilization of the monomeric form of insulin (In) under condition of low pH has been a recent challenge. This research aims to reveal the effect of a series of 1-butyl-3-methylimidazolium-based ionic liquids (ILs) on the stability of In dissolved in highly acidic solution (pH 2.0). Differential scanning calorimetry was applied to assess the thermal stability of In in the presence of these ILs. In addition, we monitored the IL-induced changes in the In secondary structure using Fourier transformed infrared spectroscopy. The peak of In thermal denaturation was shifted to higher temperatures in the presence of the tested acetate, trifluoroacetate and dicyanamide salts. At the same time, chloride and thiocyanate ILs had no effect on the thermal stability of the insulin, while the tricyanomethanide salt slightly destabilized the protein. The change in the In conformation affected not only the position but also the sharpness and the shape of the transition peak. As a whole, those ILs which were able to preserve or enhance helical structure of In produced stabilizing effect and those which stimulated the formation of unordered and random-coiled structures deteriorated its thermal stability. No aggregation of In in the presence of the imidazolium-based ILs was observed under the tested acidic media.

Experimental investigation on the dissociation conditions of methane hydrate in the presence of imidazolium-based ionic liquids

In this work, the performance of nine ionic liquids (ILs) as thermodynamic hydrate inhibitors is investigated. The dissociation temperature is determined for methane gas hydrates using a high pressure micro deferential scanning calorimeter between (3.6 and 11.2)MPa. All the aqueous IL solutions are studied at a mass fraction of 0.10. The performance of the two best ILs is further investigated at various concentrations. Electrical conductivity and pH of these aqueous IL solutions (0.10 mass fraction) are also measured. The enthalpy of gas hydrate dissociation is calculated by the Clausius–Clapeyron equation. It is found that the ILs shift the methane hydrate (liquid+vapour) equilibrium curve (HLVE) to lower temperature and higher pressure. Our results indicate 1-(2-hydroxyethyl) 3-methylimidazolium chloride is the best among the ILs studied as a thermodynamic hydrate inhibitor. A statistical analysis reveals there is a moderate correlation between electrical conductivity and the efficiency of the IL as a gas hydrate inhibitor. The average enthalpies of methane hydrate dissociation in the presence of these ILs are found to be in the range of (57.0 to 59.1)kJ⋅mol−1. There is no significant difference between the dissociation enthalpy of methane hydrate either in the presence or in absence of ILs.

The stability of insulin in the presence of short alkyl chain imidazolium-based ionic liquids

Fibril or aggregation formation in insulin (In) has been a subject of severe biomedical and biotechnological complications. The search for a novel solvent/co-solvent that can provide long term stabilization for In monomeric form has not been completed yet. In this quest, for the first time we have successfully explored the stability of the monomeric form of In in the presence of ammonium-based ionic liquids (ILs) [A. Kumar and P. Venkatesu, RSC Adv., 2013, 3, 362–367]. Further, in continuation, in this study, we have established the stability of In in the presence of imidazolium-based ILs with different anions. These anions represent the Hofmeister series of anions of ILs. In this regard, we have carried out UV-vis, fluorescence, circular dichroism spectral analysis and dynamic light scattering (DLS) measurements of In in various concentrations of these ILs. Our experimental findings reveal that Br− and Cl− ILs stabilized the native state while the rest of the ILs with anions such as SCN−, HSO4−, CH3COO− and I− were denaturants for the In. Further, the results show that IL–In interactions are difficult to classify on the basis of the Hofmeister series, as bromide containing ILs show more stabilizing properties on the In structure. The disulfide bonds were almost intact in the presence of Br− IL as compared to Cl− and the rest of the Hofmeister anions. On the other hand, a strongly hydrated kosmotropic anion like HSO4− interacts with the structure of In, leading it towards complete denaturation of the In structure. Additionally, all ILs failed to protect the native state of In with increasing temperature.

Imidazolium-Based Ionic Liquids as Modulators of Physicochemical Properties and Nanostructures of CTAB in Aqueous Solution: The Effect of Alkyl Chain Length, Hydrogen Bonding Capacity, and Anion Type

The aggregation behavior of the cationic surfactant, cetyl trimethylammonium bromide (CTAB), in aqueous solution of various imidazolium-based ionic liquids (ILs) was investigated using tensiometry, conductometry, transmission electron microscopy (TEM), and cyclic voltammetry (CV) methods. The data obtained from tensiometry and conductometry measurments were used to specify the critical micelle concentrations (CMCs) and other physicochemical parameters. The CMC of the surfactant was found to significantly decrease in the presence of ILs. The surface activity parameters of CTAB were observed to be a function of structural properties of ILs. Furthermore, intermicellar interaction parameter (kd) was measured using cyclic voltametry. The intermicellar interaction parameter was also found to decrease slightly with addition of IL. However, in the presence of HMImBr or HMImCl, the intermicellar interaction parameter is not changed significantly, as a result of phase transition from spherical to cylindrical micell...

Kinetic Modeling of Methane Hydrate Formation in the Presence of Low‐Dosage Water‐Soluble Ionic Liquids

AbstractThe kinetic and thermodynamic effects of three typical low‐dosage imidazolium‐based ionic liquids (ILs) on methane hydrate formation and dissociation were investigated, considering the anion nature and subcooling and/or overpressure driving forces. Isochoric hydrate formation and dissociation data were obtained by the modified slow step‐heating method. ILs proved to have a dual effect on both formation and dissociation of methane hydrate including thermodynamic and kinetic inhibition. Kinetic modeling of methane hydrate inhibition by low‐dosage ILs was performed. Kinetic analysis showed that IL inhibitors mainly cause a delay in the nucleation or hydrate growth step. The related inhibition mechanism was resolved regarding the ionic nature and electrostatic interactions of ILs with water molecules. Two binomial exponential kinetic relations were derived and used for simple methane hydrate formation in the presence of ILs as kinetic hydrate inhibitors. The proposed relations can serve for a quick estimation of the nature, extent, strength, and effectiveness of ILs on various gas hydrates.

Ionic Liquid Assisted Dispersion of Reduced Graphene Oxide in Epoxy Composites with Improved Mechanical Properties

Graphene nanosheets were prepared by chemical reduction of the exfoliated graphite oxide using sodium borohydride (NaBH4). The graphene/epoxy composites were separately fabricated in the absence or presence of imidazolium-based ionic liquids, and their dynamic thermomechanical and tensile properties were studied. TEM examinations show that graphene sheets are well dispersed in the epoxy resin and have strong interface adhesion with the matrix due to the π-π and/or cation-π interactions between graphene and imidazolium ions. The composite fabricated by assistance of ionic liquids shows larger increases in Youngs modulus, tensile strength, storage modulus and glass transition temperature compared to the composite without using ionic liquids. This work provides a method for the fabrication of multifunctional graphene-based polymer composites.