Chemoinformatic Approaches To Predict the Viscosities of Ionic Liquids and Ionic Liquid-Containing Systems.

Modelling, predicting, and understanding the factors influencing the viscosities of ionic liquids and related mixtures are sequentially checked in this work. The molecular maps of atom-level properties (MOLMAP codification system) is adapted for a straightforward inclusion of ionic liquids and mixtures containing ionic liquids. Random Forest models have been tested in this context and an optimal model was selected. The interpretability of the selected Random Forest model is highlighted with selected structural features that might contribute to identify low viscosities. The constructed model is able to recognize the influence of different structural variables, temperature, and pressure for a correct classification of the different systems. The codification and interpretation systems are highlighted in this work.

Solid-liquid equilibria of binary mixtures of fluorinated ionic liquids.

Within ionic liquids, fluorinated ionic liquids (FILs) present unique physico-chemical properties and potential applications in several fields. However, the melting point of these neoteric compounds is usually higher due to the presence of fluorine atoms. This drawback may be resolved by, for instance, mixing different FILs to create eutectic mixtures. In this work, binary mixtures of fluoro-containing and fluorinated ionic liquids were considered with the aim of decreasing their melting temperatures as well as understanding and characterizing these mixtures and their phase transitions. Five FILs were selected, allowing the investigation of four binary mixtures, each of them with a common ion. Their solid-liquid and solid-solid equilibria were studied by differential scanning calorimetry and the non-ideality of the mixtures was investigated. Overall, a variety of solid-liquid equilibria with systems exhibiting eutectic behavior, polymorphs with solid-solid phase transitions, and the formation of intermediate compounds and solid solutions were surprisingly found. In addition to these intriguing behaviours, novel FILs with lower melting temperatures were obtained by the formation of binary systems, thus enlarging the application range of FILs at lower temperatures.

Mixtures of the 1-ethyl-3-methylimidazolium acetate ionic liquid with different inorganic salts: insights into their interactions.

In this work, we explore the interactions between the ionic liquid 1-ethyl-3-methylimidazolim acetate and different inorganic salts belonging to two different cation families, those based on ammonium and others based on sodium. NMR and Raman spectroscopy are used to screen for changes in the molecular environment of the ions in the ionic liquid + inorganic salt mixtures as compared to pure ionic liquid. The ion self-diffusion coefficients are determined from NMR data, allowing the discussion of the ionicity values of the ionic liquid + inorganic salt mixtures calculated using different methods. Our data reveal that preferential interactions are established between the ionic liquid and ammonium-based salts, as opposed to sodium-based salts. Computational calculations show the formation of aggregates between the ionic liquid and the inorganic salt, which is consistent with the spectroscopic data, and indicate that the acetate anion of the ionic liquid establishes preferential interactions with the ammonium cation of the inorganic salts, leaving the imidazolium cation less engaged in the media.

Viscosity mixing rules for binary systems containing one ionic liquid.

In this work the applicability of four of the most commonly used viscosity mixing rules to [ionic liquid (IL)+molecular solvent (MS)] systems is assessed. More than one hundred (IL+MS) binary mixtures were selected from the literature to test the viscosity mixing rules proposed by 1) Hind (Hi), 2) Grunberg and Nissan (G-N), 3) Herric (He) and 4) Katti and Chaudhri (K-C). The analyses were performed by estimating the average (absolute or relative) deviations, AADs and ARDs, between the available experimental data and the predicted ideal mixture viscosity values obtained by means of each rule. The interaction terms corresponding to the adjustable parameters inherent to each rule were also calculated and their trends discussed.

High ionicity ionic liquids (HIILs): comparing the effect of ethylsulfonate and ethylsulfate anions.

The subject of ionicity has been extensively discussed in the last decade, due to the importance of understanding the thermodynamic and thermophysical behaviour of ionic liquids. In our previous work, we established that ionic liquids' ionicity could be improved by the dissolution of simple inorganic salts in their milieu. In this work, a comparison between the thermophysical properties of two binary systems of ionic liquid + inorganic salt is presented. The effect of the ammonium thiocyanate salt on the ionicity of two similar ionic liquids, 1-ethyl-3-methylimidazolium ethylsulfonate and ethylsulfate, is investigated in terms of the related thermophysical properties, such as density, viscosity and ionic conductivity in the temperature range 298.15-323.15 K. In addition, spectroscopic (NMR and Raman) and molecular dynamic studies were conducted in order to better understand the interactions that occur at a molecular level. The obtained results reveal that although the two anions of the ionic liquid exhibit similar chemical structures, the presence of one additional oxygen in the ethylsulfate anion has a major impact on the thermophysical properties of the studied systems.

Probing ionic liquid aqueous solutions using temperature of maximum density isotope effects.

This work is a new development of an extensive research program that is investigating for the first time shifts in the temperature of maximum density (TMD) of aqueous solutions caused by ionic liquid solutes. In the present case we have compared the shifts caused by three ionic liquid solutes with a common cation-1-ethyl-3-methylimidazolium coupled with acetate, ethylsulfate and tetracyanoborate anions-in normal and deuterated water solutions. The observed differences are discussed in terms of the nature of the corresponding anion-water interactions.

The distillation and volatility of ionic liquids.

It is widely believed that a defining characteristic of ionic liquids (or low-temperature molten salts) is that they exert no measurable vapour pressure, and hence cannot be distilled. Here we demonstrate that this is unfounded, and that many ionic liquids can be distilled at low pressure without decomposition. Ionic liquids represent matter solely composed of ions, and so are perceived as non-volatile substances. During the last decade, interest in the field of ionic liquids has burgeoned, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes, fuel cells and batteries, and new composite materials. Much of this potential is underpinned by their presumed involatility. This characteristic, however, can severely restrict the attainability of high purity levels for ionic liquids (when they contain poorly volatile components) in recycling schemes, as well as excluding their use in gas-phase processes. We anticipate that our demonstration that some selected families of commonly used aprotic ionic liquids can be distilled at 200-300 degrees C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized.

Vaporisation of a dicationic ionic liquid revisited.

The vaporization of a dicationic ionic liquid at moderate temperatures and under reduced pressures--recently studied by line-of-sight mass spectrometry--was further analyzed using an ion-cyclotron resonance mass spectroscopy technique that allows the monitoring of the different species present in the gas phase through the implementation of controlled ion-molecule reactions. The results support the view that the vapour phase of an aprotic dicationic ionic liquid is composed of neutral ion triplets (one dication attached to two anions). Molecular dynamics simulations were also performed in order to explain the magnitude of the vaporization enthalpies of dicationic ionic liquids vis-à-vis their monocationic counterparts.

Ion specific effects on the mutual solubilities of water and hydrophobic ionic liquids.

Ion specific effects on the mutual solubilities between hydrophobic ionic liquids (ILs) and water are complex and not fully understood. The aim of this work is to obtain further evidence about the molecular mechanism behind this phenomenon by evaluating the effect of a large series of inorganic and organic salts on the mutual solubilities of water and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(4)mim][Tf(2)N]. The magnitudes of the salting-in and salting-out effects were assessed by changing either the cation or the anion, in a series of salts, as well as the salt concentration. It was observed that the influence of the ions on the solubility followed the Hofmeister series. Both salting-in and salting-out effects were observed and they showed to be dependent on both the nature of the salt and its concentration, while the pH had only a marginal effect on the studied solubilities. On the basis of the solubility changes of the ionic liquid in water in the presence of salts and on NMR spectroscopic data, it will be shown that salting-out inducing ions (high charge density) and salting-in inducing ions (low charge density) act through different mechanisms. While the former act mainly through an entropic effect resulting from the formation of water-ion hydration complexes which cause the dehydration of the solute and the increase of the surface tension of the cavity, the salting-in results from a direct ion binding of the low charge density ions to the hydrophobic moieties of the solute.

Human cytotoxicity and octanol/water partition coefficients of fluorinated ionic liquids.

The use of fluorinated ionic liquids (FILs) as novel materials in biological and pharmaceutical applications is an emerging research field. The knowledge of their cytotoxicity and that of 1-octanol/water partition coefficients are essential to assess their environmental risks, to estimate their toxicity and activity, or the hydrophilic/lipophilic balance, as well as to explore their properties as solvents in extraction processes or for successful drug design. The study of the cytotoxicity in four different human cell lines and the experimental measurement of the partition coefficient between 1-octanol and water (Po/w), using the slow-stirring method, were carried out for several FILs. In both studies, the effect of the cation ([C2C1Im]+, [C2C1py]+, [C4C1pyr]+, [N1112(OH)]+, or [N4444]+), the cationic alkyl side-chain length ([CnC1Im]+, with n = 2, 6, 8 or 12), and the anionic fluorinated chain length/anionic fluorinated domain size ([C4F9SO3]¯, [C8F17SO3]¯, or [N(C4F9SO3)2]¯) were analysed. The results reveal that both toxicity and partition properties are mainly influenced by the size of the cationic hydrogenated alkyl side-chain and that of the anionic fluorinated domain. The intrinsic tuneability of the FILs allows for their selection according to the lipophilic or hydrophilic character of the target biological system under consideration. The toxicity studies corroborate the biocompatible nature of some FILs tested in this work. Along, for all the FILs under study Po/w < 1.00. Accordingly, a decadic logarithm of the bioconcentration factor in fish of 0.5 would be estimated, which is below the regulatory endpoint used by regulatory agencies.

Salting-out effects in aqueous ionic liquid solutions: cloud-point temperature shifts.

The effects of the addition of three inorganic salts, namely, NaCl, Na(2)SO(4), and Na(3)PO(4), on the liquid-liquid (L-L) phase diagram of aqueous solutions containing the model ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF(4)], were investigated. All three inorganic salts trigger salting-out effects, leading to significant upward shifts of the L-L demixing temperatures of the systems. The magnitude of the shifts depends on both the water-structuring nature of the salt and its concentration; that is, the effects are correlated with the ionic strength of the solution and the Gibbs free energy of hydration of the inorganic salt. The pH effect and the occurrence of salt precipitation in concentrated solutions are also discussed.

A simple quantum statistical thermodynamics interpretation of an impressive phase diagram pressure shift upon (H/D) isotopic substitution in water + 3-methylpyridine.

In a previous work (J. Phys. Chem. B 2003, 107, 9837), we reported liquid-liquid-phase splitting at negative pressures in mixtures of H2O + D2O + 3-methylpyridine (3-MP) at the limit of pure H2O as the solvent, thus extending for the first time the L-L phase diagrams to this metastable region. We showed that there is an intimate relation between pressure and solvent deuterium content. Isotopic substitution (H/D) in water provokes subtle entropic effects that, in turn, trigger a significant pressure shift, opening a pressure-wide miscibility window of as much as 1600 bar. Isotope effects are quantum in origin. Therefore, a model that is both pressure-dependent and considers quantization constitutes a necessary tool if one wishes to fully describe the p, T, x critical demixing in these systems. In the current work, the statistical-mechanical theory of isotope effects is combined with a compressible pressure-dependent model. This combination enabled us to predict successfully the overall L-L phase diagram via differences in the vibrational mode frequencies of water on its transfer from the pure state to that of dilution in 3-MP: each of the three librational modes undergo a calculated red-shift of -(250 +/- 30) cm(-1), while the overall internal frequencies contribution is estimated as a total +(400 +/- 25) cm(-1) blue-shift.

Condensed phase behaviour of ionic liquid-benzene mixtures: congruent melting of a [emim][NTf2].C6H6 inclusion crystal.

The solid-liquid phase diagram of the (1-ethyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl} amide + benzene) system was determined and allowed us to identify and characterize an equimolar inclusion compound, [emim][NTf2].C6H6, with a congruent melting temperature: this type of behaviour, reported here for the first time, together with the X-ray structure of the inclusion compound lays emphasis upon the interactions that are responsible for the existence of liquid clathrates at higher benzene concentrations.

Protonic Ammonium Nitrate Ionic Liquids and Their Mixtures: Insights into Their Thermophysical Behavior.

This study is centered on the thermophysical characterization of different families of alkylammonium nitrate ionic liquids and their binary mixtures, namely the determination at atmospheric pressure of densities, electric conductivities and viscosities in the 288.15 < T/K < 353.15 range. First, measurements focusing on ethylammonium, propylammonium and butylammonium nitrate systems, and their binary mixtures, were determined. These were followed by studies involving binary mixtures composed of ethylammonium nitrate (with three hydrogen bond donor groups) and different homologous ionic liquids with differing numbers of hydrogen bond donor groups: diethylammonium nitrate (two hydrogen bond donors), triethylammonium nitrate (one hydrogen bond donor) and tetraethylammonium nitrate (no hydrogen bond donors). Finally, the behavior of mixtures with different numbers of equivalent carbon atoms in the alkylammonium cations was analyzed. The results show a quasi-ideal behavior for all monoalkylammonium nitrate mixtures. In contrast, the other mixtures show deviations from ideality, namely when the difference in the number of carbon atoms present in the cations increases or the number of hydrogen bond donors present in the cation decreases. Overall, the results clearly show that, besides the length and distribution of alkyl chains present in a cation such as alkylammonium, there are other structural and interaction parameters that influence the thermophysical properties of both pure compounds and their mixtures.

On the critical temperature, normal boiling point, and vapor pressure of ionic liquids.

One-stage, reduced-pressure distillations at moderate temperature of 1-decyl- and 1-dodecyl-3-methylimidazolium bistriflilamide ([Ntf(2)](-)) ionic liquids (ILs) have been performed. These liquid-vapor equilibria can be understood in light of predictions for normal boiling points of ILs. The predictions are based on experimental surface tension and density data, which are used to estimate the critical points of several ILs and their corresponding normal boiling temperatures. In contrast to the situation found for relatively unstable ILs at high-temperature such as those containing [BF(4)](-) or [PF(6)](-) anions, [Ntf(2)](-)-based ILs constitute a promising class in which reliable, accurate vapor pressure measurements can in principle be performed. This property is paramount for assisting in the development and testing of accurate molecular models.

Deviations from ideality in mixtures of two ionic liquids containing a common ion.

Excess molar volumes of six binary mixtures composed of two ionic liquids of the 1-methyl-3-alkyl-imidazolium bis(trifluoromethylsulfonyl)amide family -- ([C(m)()mim] + [C(n)()mim])[NTf(2)] with n and m ranging from 2 to 10 -- were measured for several compositions at 298 and 333 K. Similarly, three other binary systems containing [C(4)mim](+) (1-methyl-3-butylimidazolium) as a common cation have been studied: [C(4)mim]([NTf(2)] + [PF(6)]), [C(4)mim]([NTf(2)] + [BF(4)]) and [C(4)mim]([BF(4)] + [PF(6)]). Thus, the mixing process of two distinct ions of equal sign embedded in a constant field network of a given counterion was analyzed. All systems exhibit small, positive V(E) values of the order of a few tenths of cm(3) mol(-1), which are essentially temperature and pressure independent. The results show additive trends, for instance, the V(E) values become larger as the difference between the alkyl chain lengths of the two cations increases. The Flory theory of mixtures provides a useful, semiquantitative correlation between the excess volumes and excess enthalpies in these systems, allowing for comparison with analogous results obtained within the linear primary alcohols.

Organocatalyzed One-Step Synthesis of Functionalized N-Alkyl-Pyridinium Salts from Biomass Derived 5-Hydroxymethylfurfural.

An efficient and scalable method has been developed for the synthesis of N-alkylpyridinium salts from biomass derived 5-hydroxymethylfurfural and alkyl amines using a catalytic amount of formic acid. This protocol is also extended to various diamines providing the exclusive formation of mono-N-alkylpyridinium salts. In addition, the mechanism for the formation of pyridinium salts was studied by DFT and using H2(18)O isotope labeled experiments showing no incorporation of (18)O in the product.

Investigating Aspergillus nidulans secretome during colonisation of cork cell walls.

Cork, the outer bark of Quercus suber, shows a unique compositional structure, a set of remarkable properties, including high recalcitrance. Cork colonisation by Ascomycota remains largely overlooked. Herein, Aspergillus nidulans secretome on cork was analysed (2DE). Proteomic data were further complemented by microscopic (SEM) and spectroscopic (ATR-FTIR) evaluation of the colonised substrate and by targeted analysis of lignin degradation compounds (UPLC-HRMS). Data showed that the fungus formed an intricate network of hyphae around the cork cell walls, which enabled polysaccharides and lignin superficial degradation, but probably not of suberin. The degradation of polysaccharides was suggested by the identification of few polysaccharide degrading enzymes (ß-glucosidases and endo-1,5-α-l-arabinosidase). Lignin degradation, which likely evolved throughout a Fenton-like mechanism relying on the activity of alcohol oxidases, was supported by the identification of small aromatic compounds (e.g. cinnamic acid and veratrylaldehyde) and of several putative high molecular weight lignin degradation products. In addition, cork recalcitrance was corroborated by the identification of several protein species which are associated with autolysis. Finally, stringent comparative proteomics revealed that A. nidulans colonisation of cork and wood share a common set of enzymatic mechanisms. However the higher polysaccharide accessibility in cork might explain the increase of ß-glucosidase in cork secretome. BIOLOGICAL SIGNIFICANCE: Cork degradation by fungi remains largely overlook. Herein we aimed at understanding how A. nidulans colonise cork cell walls and how this relates to wood colonisation. To address this, the protein species consistently present in the secretome were analysed, as well as major alterations occurring in the substrate, including lignin degradation compounds being released. The obtained data demonstrate that this fungus has superficially attacked the cork cell walls apparently by using both enzymatic and Fenton-like reactions. Only a few polysaccharide degrading enzymes could be detected in the secretome which was dominated by protein species associated with autolysis. Lignin degradation was corroborated by the identification of some degradation products, but the suberin barrier in the cell wall remained virtually intact. Comparative proteomics revealed that cork and wood colonisation share a common set of enzymatic mechanisms.

Proteomic alterations induced by ionic liquids in Aspergillus nidulans and Neurospora crassa.

This study constitutes the first attempt to understand at the proteomic level the fungal response to ionic liquid stress. Ascomycota are able to grow in media supplemented with high concentrations of an ionic liquid, which, in turn, lead to major alterations in the fungal metabolic footprint. Herein, we analysed the differential accumulation of mycelial proteins in Aspergillus nidulans and Neurospora crassa after their exposure to two of the most commonly used ionic liquids: 1-ethyl-3-methylimidazolium chloride or cholinium chloride. Data obtained showed that numerous stress-responsive proteins (e.g. anti-ROS defence proteins) as well as several critical biological processes and/or pathways were affected by either ionic liquid. Amongst other changes, these compounds altered developmental programmes in both fungi (e.g. promoting the development of Hülle cells or conidiation) and led to accumulation of osmolytes, some of which may play an important role in multiple stress responses. In particular, in N. crassa, both ionic liquids increased the levels of proteins which are likely involved in the biosynthesis of unusual metabolites. These data potentially open new perspectives on ionic liquid research, furthering their conscious design and their use to trigger production of targeted metabolites. BIOLOGICAL SIGNIFICANCE: The present study emphasises the importance of understanding ionic liquid's stress responses, crucial to further their safe large-scale usage. Knowledge of the alterations prompted at a cellular and biochemical level gives also fresh perspectives on how to employ these "novel" compounds to manipulate proteins or pathways of biotechnological value. The results presented here provide meaningful insights into the understanding of fungi stress and adaptation responses to anthropogenic chemicals used in industry.

Hydrogen-bonding and the dissolution mechanism of uracil in an acetate ionic liquid: new insights from NMR spectroscopy and quantum chemical calculations.

The dissolution of uracil-a pyrimidine nucleic acid base-in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][CH3COO]) has been investigated by methods of (1)H and (13)C NMR spectroscopy, (1)H-(1)H NOESY NMR spectroscopy, and quantum chemical calculations. The uracil-[C2mim][CH3COO] interactions that define the dissolution mechanism comprise the hydrogen bonds between the oxygen atoms of the acetate anion and the hydrogen atoms of the N1-H and N3-H groups of uracil and also the hydrogen bonds between the most acidic aromatic hydrogen atom (H2) of the imidazolium cation and the oxygen atoms of the carbonyl groups of uracil. The bifunctional solvation nature of the ionic liquid can be inferred from the presence of interactions between both ions of the ionic liquid and the uracil molecule. The location of such interaction sites was revealed using NMR data ((1)H and (13)C chemical shifts both in the IL and in the uracil molecule), complemented by DFT calculations. NOESY experiments provided additional evidence concerning the cation-uracil interactions.