Is the ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate [emim][MeSO3] capable of rigidly binding water?

Do Electrostatics Control the Diffusive Dynamics of Solitary Water? NMR and MD Studies of Water Translation and Rotation in Dipolar and Ionic Solvents

NMR-based measurements of the diffusion coefficients and rotation times of solitary water and benzene at 300 K are reported in a diverse collection of 13 conventional organic solvents and 10 imidazolium ionic liquids. Proton chemical shifts of water are found to be correlated to water OH-stretching frequencies, confirming the importance of electrostatic interactions in these shifts. However, the influence of magnetic interactions in aromatic solvents renders chemical shifts a less reliable indicator of electrostatics. Diffusion coefficients (DB) and rotational correlation times (τB) of benzene in the solvents examined are accurately described as functions of viscosity (η) by DB ∝ η-0.81 and τB ∝ η0.64. Literature values of DB and τB in alkane and normal alcohols, which were not included among the solvents studied here, are systematically faster than predicted by these correlations, indicating that factors beyond solvent viscosity play a role in determining the friction on benzene. In contrast to benzene, water diffusion and rotation are poorly described in terms of viscosity alone, even in the dipolar and ionic solvents measured here. The present data and the substantial literature data already available on dilute water diffusion show a systematic dependence of DW on solvent polarity among isoviscous solvents. The aspect of solvent polarity most relevant to water dynamics is the ability of a solvent to accept hydrogen bonds from water, as conveniently quantified by the frequency of water's OH stretching band, ΔνOH. The friction on translation, ζtr = kBT/DW, and rotation, ζrot = kBTτW, are both well correlated by functions of the form ζ(η, ΔνOH) = a1ηa2 exp (a3ΔνOH), where the ai are adjustable parameters. Molecular dynamics simulations reveal a strong coupling between electrostatic and nonelectrostatic water-solvent interactions, which makes it impossible to dissect the friction on water into additive dielectric and hydrodynamic components. Simulations also provide a tentative explanation for the unusual form of the correlating function ζ(η, ΔνOH), at least in the case of ζrot.

Experimentally measured methane hydrate phase equilibria and ionic liquids inhibition performance in Qatar's seawater

Qatar has the third-largest natural gas reserves in the world and is the second largest Liquefied natural gas (LNG) exporter in the world. These reserves are mainly located in its offshore North Field where the gas is extracted, transported to the onshore units, and is converted to LNG for international export. The formation of natural gas hydrates in the offshore subsea lines can cause unwanted blockages and hinder the smooth supply of gas supply from offshore to onshore units. In the present work, the formation and dissociation of methane gas hydrates have been studied in the ultra pure water system (UPW), artificial seawater (ASW), and Qatar seawater (QSW) at different conditions (4-10 MPa) using standard rocking cell rig. The naturally occurring seawater was collected from Ras Laffan seacoast located in Doha, Qatar. The seawater sample was examined for elemental analysis (SO₄, Cl, Na, Ca, Mg, K, and Fe) using inductively coupled plasma atomic emission spectroscopy (ICP-AES) technique and its other properties like density, electrical conductivity, and pH were also measured. The experimental results show that the CH₄ pure water HLVE curve is suppressed by about 3 K in Qatar seawater and 2 K in artificial seawater. The hydrate inhibition strength of the Ionic liquids (ILs) salts 3-Ethyl-1-methyl-1H-imidazol-3-ium methane-sulfonate [C₇H₁₄N₂O₃S] and 3-Ethyl-1-methyl-1H-imidazol-3-ium dicyanoazanide [C₈H₁₁N₅] was evaluated in both the ultra pure water and Qatar seawater systems. Their performance was compared with methanol and other ILs salts reported in the literature. The selected ILs exhibited poor hydrate inhibition effect in the ultra pure water systems, but they show a noticeable thermodynamic and kinetic hydrate inhibition effect in the Qatar seawater system. The computational 3D molecular models of ILs and methanol were generated to cognize the plausible hydrate inhibition mechanism in the presence of these inhibitors.

Equilibrium Thermodynamic Properties of Aqueous Solutions of Ionic Liquid 1-Ethyl-3-Methylimidazolium Methanesulfonate [EMIM][MeSO3]

The ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MeSO₃]) has been considered as a promising alternative desiccant to triethylene glycol and lithium bromide commonly used in the industry. In this paper, the water activity coefficient of this binary system was measured from 303 K to 363 K with water concentration from 18% to 92%. The interaction energies between the ionic liquid molecules ([Formula: see text]) and between the ionic liquid and water molecules ([Formula: see text]) for the [EMIM][MeSO₃]/water binary system were determined from the water activity coefficient data using the Non-Random Two-Liquid (NRTL) model. The magnitude of the interaction energy between the [EMIM][MeSO₃] and water molecules ([Formula: see text]) was found to be in the range of 45~49 kJ/mol, which was about 20% larger than that between the water molecules ([Formula: see text]) in the [EMIM][MeSO₃]/water system. The large ([Formula: see text]) can explain many observed macroscopic thermodynamic properties such as strong hygroscopicity in the ionic liquid [EMIM][MeSO₃]. These interaction energies were used to determine the heat of desorption of the [EMIM][MeSO₃]/water system, and the obtained heat of desorption was in good agreement with that calculated from the conventional Clausius-Clapeyron Equation.

Liquid crystalline microspheres of azobenzene amphiphiles formed by thermally induced pH changes in binary water-hydrolytic ionic liquid media

Anionic azobenzene-containing bilayered membranes dispersed in binary water-ionic liquid (IL) media undergo proton-responsive transformation into liquid crystalline microspheres (LCMs). This transformation was induced by protons released by the heat-induced hydrolysis of tetrafluoroborate ions in the ILs. This work demonstrates the first beneficial use of hydrolysis-susceptible ILs in chemistry.

Effect of molecular solvents of varying polarity on the self-assembly of 1-n-dodecyl-3-methylimidazolium octylsulfate ionic liquid

Large-scale molecular dynamics simulations consisting of more than 88,000–106,000 atoms for approximately 250 ns (including equilibration and production) were conducted to assess the effect of polar, nonpolar and amphiphilic molecular solvents on the nanoscale structuring of 1-[Formula: see text]-dodecyl-3-methylimidazolium [C[Formula: see text]mim] octylsulfate [C8SO4] ionic liquid (IL). Water [H2O], [Formula: see text]-octane [C8H[Formula: see text]] and 1-octanol [C8H[Formula: see text]OH] are employed as examples of polar, nonpolar, and amphiphilic molecules, respectively. The results indicate that each of these molecular solvents modify the nanosegregation behavior of the ionic liquid in a unique way. Water induces a high order of structuring of the ionic liquid as indicated by extremely high nematic order parameter for the system. In addition, the morphology of the neat ionic liquid is transformed from layer-like to that of bilayer-like in which the polar and nonpolar domains alternate. The presence of water also causes the stretching of the nonpolar domain, thus, increasing its size. At the concentration examined in this work, [Formula: see text]-octane is found to be only partially miscible with the ionic liquid. The polar network is maintained; however, the continuous cationic nonpolar domain is split into multiple domains. [Formula: see text]-octane is accommodated in the ionic liquid nonpolar domain. Similarly, the amphiphilicity of 1-octanol leads to an increase in the number of cationic as well as anionic domains. The overall nonpolar domain length, however, remains nearly identical to that found for the pure ionic liquid. Additional characterization of structural features of the three systems is discussed in terms of one-dimensional number densities, nematic order parameters for the overall systems and their components and structure factors.

Effect of water on the transport properties of protic and aprotic imidazolium ionic liquids - an analysis of self-diffusivity, conductivity, and proton exchange mechanism

In this paper we report on the transport properties of protic and aprotic ionic liquids of the imidazolium cation (C2C1Im(+) or C2HIm(+)) and the TFSI(-) or TfO(-) anion as a function of added water. We observe that the self-diffusion coefficient of the ionic species increases upon addition of water, and that the cation diffuses faster than the anion in the entire water concentration range investigated. We also observe that the overall increase of anionic and cationic diffusion coefficients is significant for C2HImTfO while it is rather weak for C2C1ImTFSI, the former being more hydrophilic. Moreover, the difference between cationic and anionic self-diffusivity specifically depends on the structure of the ionic liquid's ions. The degree of ion-ion association has been investigated by comparing the molar conductivity obtained by impedance measurements with the molar conductivity calculated from NMR data using the Nernst-Einstein equation. Our data indicate that the ions are partly dissociated (Λimp/ΛNMR in the range 0.45-0.75) but also that the degree of association decreases in the order C2HImTfO > C2HImTFSI ≈ C2C1ImTfO > C2C1ImTFSI. From these results, it seems that water finds different sites of interaction in the protic and aprotic ionic liquids, with a strong preference for hydrogen bonding to the -NH group (when available) and a stronger affinity to the TfO anion as compared to the TFSI. For the protic ionic liquids, the analysis of (1)H NMR chemical shifts (upon addition of H2O and D2O, respectively) indicates a water-cation interaction of hydrogen bonding nature. In addition, we could probe proton exchange between the -NH group and deuterated water for the protic cation, which occurs at a significantly faster rate if associated with the TfO anion as compared to the TFSI.

Molecular level interactions in binary mixtures of 1-ethyl 3-methylimidazolium tetrafluoroborate and water

NIR spectroscopic analysis and DLS measurements were carried out to study hydrogen bonding and aggregation in ionic liquid–water binary mixtures.

Probing structural patterns of ion association and solvation in mixtures of imidazolium ionic liquids with acetonitrile by means of relative1H and13C NMR chemical shifts

Competition between ion solvation and association in mixtures of imidazolium ionic liquids and molecular solvents can be systematically addressed by the analysis of relative chemical shift variation with mixture composition.

Physicochemical properties of novel cholinium ionic liquids for the recovery of silver from nitrate media

Linear and ramified cholinium based ionic liquids have been synthesized and their physicochemical properties have been investigated by ¹H NMR, ¹³C NMR, ATR-FTIR and ESI-MS as well as their extraction properties towards Ag(i), Cu(ii) and Fe(iii).

Self-assembly of azobenzene bilayer membranes in binary ionic liquid-water nanostructured media

Anionic azobenzene-containing amphiphile 1 (sodium 4-[4-(N-methyl-N-dodecylamino)phenylazo]benzenesulfonate) forms ordered bilayer membranes in binary ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, [C2mim][C2OSO3])-water mixtures. The binary [C2mim][C2OSO3]-water mixture is macroscopically homogeneous at any mixing ratio; however, it possesses fluctuating nanodomains of [C2mim][C2OSO3] molecules as observed by dynamic light scattering (DLS). These nanodomains show reversible heat-induced mixing behavior with water. Although the amphiphile 1 is substantially insoluble in pure water, it is dispersible in the [C2mim][C2OSO3]-water mixtures. The concentration of [C2mim][C2OSO3] and temperature exert significant influences on the self-assembling characteristics of 1 in the binary media, as shown by DLS, transmission electron microscopy (TEM), UV-vis spectroscopy, and zeta-potential measurements. Bilayer membranes with rod- or dotlike nanostructures were formed at a lower content of [C2mim][C2OSO3] (2-30 v/v %), in which azobenzene chromophores adopt parallel molecular orientation regardless of temperature. In contrast, when the content of [C2mim][C2OSO3] is increased above 60 v/v %, azobenzene bilayers showed thermally reversible gel-to-liquid crystalline phase transition. The self-assembly of azobenzene amphiphiles is tunable depending on the volume fraction of [C2mim][C2OSO3] and temperature, which are associated with the solvation by nanoclusters in the binary [C2mim][C2OSO3]-water media. These observations clearly indicate that mixtures of water-soluble ionic liquids and water provide unique and valiant environments for ordered molecular self-assembly.

State of hydrophobic and hydrophilic ionic liquids in aqueous solutions: are the ions fully dissociated?

Molecular dynamics simulations were performed for aqueous solutions of five ionic liquids (ILs): 1-ethyl-3-methylimidazolium ([C2mim]) bis(trifluoromethanesulfonyl) imide ([NTf2]), 1-n-butyl-3-methylimidazolium ([C4mim]) [NTf2], 1-n-hexyl-3-methylimidazolium ([C6mim]) [NTf2], [C2mim] ethylsulfate ([C2H5SO4]), and [C2mim] chloride (Cl) to determine whether the ions of these ILs are associated at relatively high dilutions and whether the association is governed by hydrophobicity/hydrophilicity of the ILs. The adaptive biasing force technique was applied to calculate the potential of mean force (PMF) for each IL ion pair. For all of the ILs, the PMF is characterized by two distinct contact minima in which the ions have different relative conformations. The hydrophobic ILs bearing the anion [NTf2](-) exist predominantly in the associative state; the strength of the association of these ILs increases with increase in the alkyl chain length. The most hydrophilic IL [C2mim] Cl was determined to be almost fully dissociated at the concentration examined in the study. [C2mim] [C2H5SO4] showed hydration behavior that was intermediate between that exhibited by the ILs in which the anion is substituted with either Cl(-) or [NTf2](-) paired with [C2mim](+). Association constants for these ILs were also computed. Radial distribution functions calculated by constraining the ions at the contact minima showed that hydration of the anion plays the dominant role in determining the microscopic behavior of these ILs in aqueous solutions.