Surface Tensions of Ionic Liquids: Non-Regular Trend Along the Number of Cyano Groups.

Ionic liquids (ILs) with cyano-functionalized anions are a set of fluids that are still poorly characterized despite their remarkably low viscosities and potential applications. Aiming at providing a comprehensive study on the influence of the number of -CN groups through the surface tension and surface organization of ILs, the surface tensions of imidazolium-based ILs with cyano-functionalized anions were determined at atmospheric pressure and in the (298.15 to 343.15) K temperature range. The ILs investigated are based on 1-alkyl-3-methylimidazolium cations (alkyl = ethyl, butyl and hexyl) combined with the [SCN]-, [N(CN)2]-, [C(CN)3]- and [B(CN)4]-anions. Although the well-known trend regarding the surface tension decrease with the increase of the size of the aliphatic moiety at the cation was observed, the order obtained for the anions is more intricate. For a common cation and at a given temperature, the surface tension decreases according to: [N(CN)2]- > [SCN]- > [C(CN)3]- > [B(CN)4]-. Therefore, the surface tension of this homologous series does not decrease with the increase of the number of -CN groups at the anion as has been previously shown by studies performed with a more limited matrix of ILs. A maximum in the surface tension and critical temperature was observed for [N(CN)2]-based ILs. Furthermore, a minimum in the surface entropy, indicative of a highly structured surface, was found for the same class of ILs. All these evidences seem to be a result of stronger hydrogen-bonding interactions occurring in [N(CN)2]-based ILs, when compared with the remaining CN-based counterparts, and as sustained by cation-anion interaction energies derived from the Conductor Like Screening Model for Real Solvents (COSMO-RS).

Densities, Viscosities and Derived Thermophysical Properties of Water-Saturated Imidazolium-Based Ionic Liquids.

In order to evaluate the impact of the alkyl side chain length and symmetry of the cation on the thermophysical properties of water-saturated ionic liquids (ILs), densities and viscosities as a function of temperature were measured at atmospheric pressure and in the (298.15 to 363.15) K temperature range, for systems containing two series of bis(trifluoromethylsulfonyl)imide-based compounds: the symmetric [C n C n im][NTf2] (with n = 1-8 and 10) and asymmetric [C n C1im][NTf2] (with n = 2-5, 7, 9 and 11) ILs. For water-saturated ILs, the density decreases with the increase of the alkyl side chain length while the viscosity increases with the size of the aliphatic tails. The saturation water solubility in each IL was further estimated with a reasonable agreement based on the densities of water-saturated ILs, further confirming that for the ILs investigated the volumetric mixing properties of ILs and water follow a near ideal behaviour. The water-saturated symmetric ILs generally present lower densities and viscosities than their asymmetric counterparts. From the experimental data, the isobaric thermal expansion coefficient and energy barrier were also estimated. A close correlation between the difference in the energy barrier values between the water-saturated and pure ILs and the water content in each IL was found, supporting that the decrease in the viscosity of ILs in presence of water is directly related with the decrease of the energy barrier.

Controlling the Formation of Ionic-Liquid-based Aqueous Biphasic Systems by Changing the Hydrogen-Bonding Ability of Polyethylene Glycol End Groups.

The formation of aqueous biphasic systems (ABS) when mixing aqueous solutions of polyethylene glycol (PEG) and an ionic liquid (IL) can be controlled by modifying the hydrogen-bond-donating/-accepting ability of the polymer end groups. It is shown that the miscibility/immiscibility in these systems stems from both the solvation of the ether groups in the oxygen chain and the ability of the PEG terminal groups to preferably hydrogen bond with water or the anion of the salt. The removal of even one hydrogen bond in PEG can noticeably affect the phase behavior, especially in the region of the phase diagram in which all the ethylene oxide (EO) units of the polymeric chain are completely solvated. In this region, removing or weakening the hydrogen-bond-donating ability of PEG results in greater immiscibility, and thus, in a higher ability to form ABS, as a result of the much weaker interactions between the IL anion and the PEG end groups.

Hydrogen-bond acidity of ionic liquids: an extended scale.

One of the main drawbacks comprising an appropriate selection of ionic liquids (ILs) for a target application is related to the lack of an extended and well-established polarity scale for these neoteric fluids. Albeit considerable progress has been made on identifying chemical structures and factors that influence the polarity of ILs, there still exists a high inconsistency in the experimental values reported by different authors. Furthermore, due to the extremely large number of possible ILs that can be synthesized, the experimental characterization of their polarity is a major limitation when envisaging the choice of an IL with a desired polarity. Therefore, it is of crucial relevance to develop correlation schemes and a priori predictive methods able to forecast the polarity of new (or not yet synthesized) fluids. In this context, and aiming at broadening the experimental polarity scale available for ILs, the solvatochromic Kamlet-Taft parameters of a broad range of bis(trifluoromethylsulfonyl)imide-([NTf2](-))-based fluids were determined. The impact of the IL cation structure on the hydrogen-bond donating ability of the fluid was comprehensively addressed. Based on the large amount of novel experimental values obtained, we then evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond acidity of ILs. A three-parameter model based on the cation-anion interaction energies was found to adequately describe the experimental hydrogen-bond acidity or hydrogen-bond donating ability of ILs. The proposed three-parameter model is also shown to present a predictive capacity and to provide novel molecular-level insights into the chemical structure characteristics that influence the acidity of a given IL. It is shown that although the equimolar cation-anion hydrogen-bonding energies (EHB) play the major role, the electrostatic-misfit interactions (EMF) and van der Waals forces (EvdW) also contribute, admittedly in a lower extent, towards the hydrogen-bond acidity of ILs. The new extended scale provided for the hydrogen-bond acidity of ILs is of high value for the design of new ILs for task-specific applications.

Contact angles and wettability of ionic liquids on polar and non-polar surfaces.

Many applications involving ionic liquids (ILs) require the knowledge of their interfacial behaviour, such as wettability and adhesion. In this context, herein, two approaches were combined aiming at understanding the impact of the IL chemical structures on their wettability on both polar and non-polar surfaces, namely: (i) the experimental determination of the contact angles of a broad range of ILs (covering a wide number of anions of variable polarity, cations, and cation alkyl side chain lengths) on polar and non-polar solid substrates (glass, Al-plate, and poly-(tetrafluoroethylene) (PTFE)); and (ii) the correlation of the experimental contact angles with the cation-anion pair interaction energies generated by the Conductor-like Screening Model for Real Solvents (COSMO-RS). The combined results reveal that the hydrogen-bond basicity of ILs, and thus the IL anion, plays a major role through their wettability on both polar and non-polar surfaces. The increase of the IL hydrogen-bond accepting ability leads to an improved wettability of more polar surfaces (lower contact angles) while the opposite trend is observed on non-polar surfaces. The cation nature and alkyl side chain lengths have however a smaller impact on the wetting ability of ILs. Linear correlations were found between the experimental contact angles and the cation-anion hydrogen-bonding and cation ring energies, estimated using COSMO-RS, suggesting that these features primarily control the wetting ability of ILs. Furthermore, two-descriptor correlations are proposed here to predict the contact angles of a wide variety of ILs on glass, Al-plate, and PTFE surfaces. A new extended list is provided for the contact angles of ILs on three surfaces, which can be used as a priori information to choose appropriate ILs before a given application.

Mutual solubilities between water and non-aromatic sulfonium-, ammonium- and phosphonium-hydrophobic ionic liquids.

Although previous studies attempted to characterize the liquid-liquid phase behaviour between water and ionic liquids (ILs), the impact of non-cyclic cations on the solubilities is poorly studied and yet to be understood. In this work, the mutual solubilities between water and ILs containing the anion bis(trifluoromethylsulfonyl)imide, [NTf2](-), combined with the cations diethylmethylsulfonium, [S221][NTf2], triethylsulfonium, [S222][NTf2], butyltrimethylammonium, [N4111][NTf2], tributylmethylammonium, [N4441][NTf2], methyltrioctylammonium, [N1888][NTf2], and methyltrioctylphosphonium, [P1888][NTf2], from (288.15 to 318.15) K and at 0.1 MPa, were experimentally measured and further compared with predictions from the COnductor-like Screening MOdel for Real Solvents (COSMO-RS). All the studied phase diagrams display an upper critical solution temperature (UCST). The binary system composed of [P1888][NTf2] exhibits the widest immiscibility gap, followed by [N18888][NTf2], [N4441][NTf2], [S222][NTf2], [N4111][NTf2], and [S221][NTf2]. The COSMO-RS is able to correctly predict the experimental UCST behaviour and the cation impact on the immiscibility regimes observed. Natural Population Analysis (NPA) calculations were additionally performed for the isolated cations in the gas phase indicating that the differences in the water-IL mutual miscibilities might not result only from the hydrophobicity of the cation (derived from the increase of the alkyl chains length) but also from the charge distribution of the central atom and attached methylene groups. This fact explains the enhanced solubility of ammonium-based ILs in water here identified.

Aqueous biphasic systems composed of ionic liquids and acetate-based salts: phase diagrams, densities and viscosities.

Ionic-liquid-based aqueous biphasic systems (IL-based ABS) have been largely investigated as promising extraction and purification routes. In this context, the determination of their phase diagrams and the physical properties of the coexisting phases are of high relevance when envisaging their large-scale applications. Low viscosities improve the mass transfer and reduce energy consumptions, while the knowledge on their densities is important for the equipment design. In this work, novel phase diagrams for aqueous solutions of imidazolium-based ILs combined with acetate-based salts, namely KCH3CO2 or NaCH3CO2, are reported and discussed. The ability of the acetate-based salts to induce the phase separation not only depends on the ions hydration energy, but also on the concentration of "free" ions in solution. The tie-lines, tie-line lengths and critical points are also addressed. Experimental measurements of density and viscosity of the coexisting phases, for the different systems and at several compositions and temperatures, are additionally presented. The Othmer-Tobias and Bancroft equations are also applied to ascertain on the tie-lines coherence. It is here shown that low-viscous IL-based ABS, with a high difference in the densities of the coexisting phases, can be formed with organic and biodegradable salts thus offering enhanced features over conventional polymer-based systems.

Comprehensive Study on the Impact of the Cation Alkyl Side Chain Length on the Solubility of Water in Ionic Liquids.

A comprehensive study on the phase behaviour of two sets of ionic liquids (ILs) and their interactions with water is here presented through combining experimental and theoretical approaches. The impact of the alkyl side chain length and the cation symmetry on the water solubility in the asymmetric [C N-1C1im][NTf2] and symmetric [C N-1C N-1im][NTf2] series of ILs (N up to 22), from 288.15 K to 318.15 K and at atmospheric pressure, was studied. The experimental data reveal that the solubility of water in ILs with an asymmetric cation is higher than in those with the symmetric isomer. Several trend shifts on the water solubility as a function of the alkyl side chain length were identified, namely at [C6C1im][NTf2] for asymmetric ILs and at [C4C4im][NTf2] and [C7C7im][NTf2] for the symmetric ILs. To complement the experimental data and to further investigate the molecular-level mechanisms behind the dissolution process, Density Functional Theory calculations, using the Conductor-like Screening Model for Real Solvents (COSMO-RS) and the Electrostatic potential-derived CHelpG, were performed. The COSMO-RS model is able to qualitatively predict water solubility as function of temperature and alkyl chain lengths of both symmetric and asymmetric cations. Furthermore, the model is also capable to predict the somewhat higher water solubility in the asymmetric cation, as well as the trend shift as function of alkyl chain lengths experimentally observed. Both COSMO-RS and the electrostatic potential-derived CHelpG show that the interactions of water and the IL cation take place on the IL polar region, namely on the aromatic head and adjacent methylene groups what explains the differences in water solubility observed for cations with different chain lengths. Furthermore, the CHelpG calculations for the isolated cations in the gas phase indicates that the trend shift of water solubility as function of alkyl chain lengths and the difference of water solubility in symmetric may also result from the partial positive charge distribution/contribution of the cation.

The impact of ionic liquid fluorinated moieties on their thermophysical properties and aqueous phase behaviour.

In this work, we demonstrate that the presence of fluorinated alkyl chains in Ionic Liquids (ILs) is highly relevant in terms of their thermophysical properties and aqueous phase behaviour. We have measured and compared the density and viscosity of pure 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, [C2C1im][FAP], with that of pure 1-ethyl-3-methylimidazolium hexafluorophosphate, [C2C1im][PF6], at atmospheric pressure and in the (288.15 to 363.15) K temperature range. The results show that the density of [C2C1im][PF6] is lower than that of [C2C1im][FAP], while the viscosity data reveal the opposite trend. The fluid phase behaviour of aqueous solutions of the two ILs was also evaluated under the same conditions and it was found that the mutual solubilities of [C2C1im][FAP] and water are substantially lower than those verified with [C2C1im][PF6]. The experimental data were lastly interpreted at a molecular level using Molecular Dynamics (MD) simulation results revealing that the interactions between the IL ions and the water molecules are mainly achieved via the six fluorine atoms of [PF6](-) and the three analogues in [FAP](-). The loss of three interaction centres when replacing [PF6](-) by [FAP](-), coupled with the bulkiness and relative inertness of the three perfluoroethyl groups, reduces its mutual solubility with water and also contributes to a lower viscosity displayed by the pure [FAP]-based IL as compared to that of the [PF6]-based compound.

Molecular interactions in aqueous biphasic systems composed of polyethylene glycol and crystalline vs. liquid cholinium-based salts.

The relative ability of cholinium-([Ch](+))-based salts, including ionic liquids (ILs), to form biocompatible aqueous biphasic systems (ABS) with polyethylene glycols (PEGs) was deeply scrutinized in this work. Aqueous solutions of low molecular weight PEG polymers (400, 600, and 1000 g mol(-1)) and [Ch](+) salts of chloride, acetate, bicarbonate, glycolate, lactate, dihydrogenphosphate, dihydrogencitrate, and bitartrate can undergo liquid-liquid demixing at certain concentrations of the phase-forming components and at several temperatures. Cholinium butanoate and propanoate were also studied; however, these long alkyl side chain ILs are not able to promote an immiscibility region with PEG aqueous solutions. The ternary liquid-liquid phase diagrams, binary water activities, PEG-salt and salt-H2O solubility data, and binary and ternary excess enthalpies estimated by COSMO-RS (COnductor-like Screening MOdel for Realistic Solvation) were used to obtain new insights into the molecular-level mechanisms responsible for phase separation. Instead of the expected and commonly reported salting-out phenomenon induced by the [Ch](+) salts over the polymer, the formation of PEG-[Ch](+) salt ABS was revealed to be an end result of a more intricate molecular scenario. The multifaceted approach employed here reveals that the ability to promote an ABS is quite different for the higher melting salts vs. the lower melting or liquid ILs. In the latter systems, the ABS formation seems to be controlled by the interplay of the relative strengths of the ion-ion, ion-water, ion-PEG, and water-PEG interactions, with a significant contribution from specific hydrogen-bonding between the IL anion and the PEG hydroxyl groups.

The effect of the cation alkyl chain branching on mutual solubilities with water and toxicities.

The design of ionic liquids has been focused on the cation-anion combinations but other more subtle approaches can be used. In this work the effect of the branching of the cation alkyl chain on the design of ionic liquids (ILs) is evaluated. The mutual solubilities with water and toxicities of a series of bis(trifluoromethylsulfonyl)-based ILs, combined with imidazolium, pyridinium, pyrrolidinium, and piperidinium cations with linear or branched alkyl chains, are reported. The mutual solubility measurements were carried out in the temperature range from (288.15 to 323.15) K. From the obtained experimental data, the thermodynamic properties of the solution (in the water-rich phase) were determined and discussed. The COnductor like Screening MOdel for Real Solvents (COSMO-RS) was used to predict the liquid-liquid equilibrium. Furthermore, molecular dynamic simulations were also carried out aiming to get a deeper understanding of these fluids at the molecular level. The results show that the increase in the number of atoms at the cation ring (from five to six) leads to a decrease in the mutual solubilities with water while increasing their toxicity, and as expected from the well-established relationship between toxicities and hydrophobicities of ILs. The branching of the alkyl chain was observed to decrease the water solubility in ILs, while increasing the ILs solubility in water. The inability of COSMO-RS to correctly predict the effect of branching alkyl chains toward water solubility on them was confirmed using molecular dynamic simulations to be due to the formation of nano-segregated structures of the ILs that are not taken into account by the COSMO-RS model. In addition, the impact of branched alkyl chains on the toxicity is shown to be not trivial and to depend on the aromatic nature of the ILs.

An eco-friendly approach for the recovery of astaxanthin and ß-carotene from Phaffia rhodozyma biomass using bio-based solvents.

There is a growing demand in the development of environmentally friendly technologies, based on the use of more biocompatible solvents for the recovery of natural bioactive compounds. In this work, the red yeast Phaffia rhodozyma biomass was used as a source of carotenoids to develop an integrative and efficient platform that promotes the recovery of astaxanthin and ß-carotene using bio-based solvents (BioSs). The extraction aptitude of pure BioSs was evaluated and compared with the conventional organic method. At this point, the influence of the BioSs molecular structures involved in the extraction procedures were also investigated. Overall, envisaging the industrial application of the process, an integrative platform was proposed for the recovery of astaxanthin/ß-carotene from P. rhodozyma biomass and the recycle of the BioSs. The life cycle assessment of the proposed technology using EtOH was evaluated, validating the sustainability of BioSs in the process with environmental impact reduction of 3-12%.

Photophysical properties of ammonium, pyrrolidinium, piperidinium, imidazolium, and pyridinium as a guide to prepare ionic-organic hybrid materials.

Ionic liquid cations (ILCs) have been utilized in hybrid organic-inorganic perovskites (HOIPs) to enhance their photoluminescence performance. However, the high number of possible cations and anions needed to form ILCs makes the experimental measurement time and cost consuming. Computational methods that could assist the selection of ILCs for this task-specific application are highly desirable. Therefore, in this work, the photophysical properties of various ILCs, including linear aliphatic, five-membered, and six-membered cyclic aliphatic, and aromatic ILCs, were investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Fluorescence and phosphorescence were analyzed using excited state dynamics (ESD) modules on ORCA at the B3LYP/def2TZVP level theory. All the investigated cations show fluorescence spectra either the UV or visible range. The cations with long-chain branches show fluorescence spectra in the visible range. Five membered rings show the phosphorescence spectra in the visible range, while the six-membered rings show the phosphorescence spectra in the near-infrared range.

Comparison of two computational methods for solvent screening in countercurrent and centrifugal partition chromatography.

Countercurrent and centrifugal partition chromatography are techniques applied in the separation and isolation of compounds from natural extracts. One of the key design parameters of these processes is the selection of the biphasic solvent system that provides for the adequate partitioning of the solutes. To address this challenging task, the fully predictive Conductor-like Screening Model for Real Solvents (COSMO-RS) and the semi-predictive Non-Random Two-Liquid Segment Activity Coefficient (NRTL-SAC) model were applied to estimate the partition coefficients (K) of four model phenolic compounds (vanillin, ferulic acid, (S)-hesperetin and quercetin) in different solvent systems. Complementing the experimental data collected in the literature, partition coefficients of each solute in binary, or quaternary, solvent systems were measured at 298.2 K. Higher deviations from the experimental data were obtained using the predictive COSMO-RS model, with an average RMSD (root-mean-square deviation) in log(K) of 1.17 of all four solutes (61 data points), providing a satisfactory quantitative description only for the systems containing vanillin (RSMD = 0.57). For the NRTL-SAC model, the molecular parameters of the solutes were initially calculated by correlating a set of K and solubility (x, in mole fraction) data (16 partition coefficients and 44 solubility data points), for which average RMSD values of 0.07 and 0.41 were obtained in log(K) and log(x), respectively. The predictions of the remaining log(K) data (45 partition coefficients) resulted in an average RMSD of 0.43, suggesting that the NRTL-SAC model was a more reliable quantitative solvent screening tool. Depending on the amount of available solubility and partition data, both models can be valuable alternatives in the preliminary stages of solvent screening destined to select the optimal mobile and stationary phases for a given separation.

Temperature dependency of aqueous biphasic systems: an alternative approach for exploring the differences between Coulombic-dominated salts and ionic liquids.

Herein we propose an alternative way to distinguish ionic liquids from Coulombic-dominated salts, based not on their upper limit melting temperature (100 °C), but on the trend of their phase-forming abilities to create aqueous biphasic systems as a function of temperature, in which a wider plethora of interactions can be appraised.

Phase Behavior and Physical Properties of New Biobased Ionic Liquid Crystals.

Protic ionic liquids (PILs) have emerged as promising compounds and attracted the interest of the industry and the academy community, due to their easy preparation and unique properties. In the context of green chemistry, the use of biocompounds, such as fatty acids, for their synthesis could disclose a possible alternative way to produce ILs with a low or nontoxic effect and, consequently, expanding their applicability in biobased processes or in the development of bioproducts. This work addressed efforts to a better comprehension of the complex solid-[liquid crystal]-liquid thermodynamic equilibrium of 20 new PILs synthesized by using fatty acids commonly found in vegetable oils, as well as their rheological profile and self-assembling ability. The work revealed that their phase equilibrium and physical properties are significantly impacted by the structure of the ions used for their synthesis. The use of unsaturated fatty acids and bis(2-hydroxyethyl)ammonium for the synthesis of these biobased ILs led to a drastic decreasing of their melting temperatures. Also, the longest alkyl chain fatty acids promoted higher self-assembling and more stable mesophases. Besides their sustainable appeal, the marked high viscosity, non-Newtonian profile, and very low critical micellar concentration values of the PIL crystals here disclosed make them interesting renewable compounds with potential applications as emulsifiers, stabilizers, thickeners, or biolubricants.

Computational and experimental study of the behavior of cyano-based ionic liquids in aqueous solution.

The solvation of cyano- (CN-) based ionic liquids (ILs) and their capacity to establish hydrogen bonds (H-bonds) with water was studied by means of experimental and computational approaches. Experimentally, water activity data were measured for aqueous solutions of ILs based on 1-butyl-3-methylimidazolium ([BMIM](+)) cation combined with one of the following anions: thiocyanate ([SCN](-)), dicyanamide ([DCA](-)), or tricyanomethanide ([TCM](-)), and of 1-ethyl-3-methylimidazolium tetracyanoborate ([EMIM][TCB]). From the latter data, water activity coefficients were estimated showing that [BMIM][SCN] and [BMIM][DCA], unlike [BMIM][TCM] and [EMIM][TCB], are able to establish favorable interactions with water. Computationally, the conductor like screening model for real solvents (COSMO-RS) was used to estimate the water activity coefficients which compare well with the experimental ones. From the COSMO-RS results, it is suggested that the polarity of each ion composing the ILs has a strong effect on the solvation phenomena. Furthermore, classical molecular dynamics (MD) simulations were performed for obtaining an atomic level picture of the local molecular neighborhood of the different species. From the experimental and computational data it is showed that increasing the number of CN groups in the ILs' anions does not enhance their ability to establish H-bonds with water but decreases their polarities, being [BMIM][DCA] and [BMIM][SCN] the ones presenting higher propensity to interact.

Effect of polyvalent ions in the formation of ionic-liquid-based aqueous biphasic systems.

Two main approaches were combined aiming at evaluating the impact of polyvalent salt cations on the formation of ionic-liquid-based aqueous biphasic systems (ABS): (i) experimental determination of a large array of ternary phase diagrams composed of sodium-, magnesium-, and aluminum-based salts with 1-butyl-3-methylimidazolium-based ionic liquids and (ii) determination of the ions speciation in each of these systems. The results here reported show, for the first time, that the phase behavior of ionic-liquid-based aqueous biphasic systems is not only dominated by the ability of the strong and "free" salting-out ions to interact with water creating thus hydration complexes but also a result of the interactions occurring between the different ions and, particularly, on their speciation in aqueous solutions. The gathered data indicate that the higher the salt ion valence, the more complex is its speciation with a number of different species in aqueous media present. Further results based on NMR spectroscopy and a proper analysis of the pH influence clearly demonstrated the impact of ion speciation through the phase separation and ABS formation.

Probing the interactions between ionic liquids and water: experimental and quantum chemical approach.

For an adequate choice or design of ionic liquids, the knowledge of their interaction with other solutes and solvents is an essential feature for predicting the reactivity and selectivity of systems involving these compounds. In this work, the activity coefficient of water in several imidazolium-based ionic liquids with the common cation 1-butyl-3-methylimidazolium was measured at 298.2 K. To contribute to a deeper insight into the interaction between ionic liquids and water, COSMO-RS was used to predict the activity coefficient of water in the studied ionic liquids along with the excess enthalpies. The results showed good agreement between experimental and predicted activity coefficient of water in ionic liquids and that the interaction of water and ionic liquids was strongly influenced by the hydrogen bonding of the anion with water. Accordingly, the intensity of interaction of the anions with water can be ranked as the following: [CF3SO3](-) < [SCN](-) < [TFA](-) < Br(-) < [TOS](-) < Cl(-) < [CH3SO3](-) [DMP](-) < [Ac](-). In addition, fluorination and aromatization of anions are shown to reduce their interaction with water. The effect of temperature on the activity coefficient of water at infinite dilution was measured by inverse gas chromatography and predicted by COSMO-RS. Further analysis based on COSMO-RS provided information on the nature of hydrogen bonding between water and anion as well as the possibility of anion-water complex formation.