Jose Palomar

A quantum-chemical-based guide to analyze/quantify the cytotoxicity of ionic liquids

A COSMO-RS descriptor (Sσ-profile) has been used in quantitative structure–activity relationship studies (QSARs) based on a neural network for the prediction of the toxicological effect of ionic liquids (ILs) on a leukemia rat cell line (LogEC50 IPC-81) for a wide variety of compounds including imidazolium, pyridinium, ammonium, phosphonium, pyrrolidinium and quinolinium ILs. Sσ-profile is a two-dimensional quantum-chemical parameter capable of characterising the electronic structure and molecular size of cations and anions. By using a COSMO-RS descriptor for a training set of 105 compounds (96 ILs and 9 closely related salts) with known biological activities (experimental LogEC50 IPC-81 values), a reliable neural network was designed for the systematic analysis of the influence of structural IL elements (cation side chain, head group, anion type and the presence of functional groups) on the cytotoxicity of ∼450 IL compounds. The Quantitative Structure–Activity Map (QSAM), a new concept developed here, was proposed as a valuable tool for (i) the molecular understanding of IL toxicity, by relating Log EC50 IPC-81 parameters to the electronic structure of compounds given by quantum-chemical calculations; and (ii) the sustainable design of IL products with low toxicity, by linking the chemical structure of counterions to the predictions of IL cytotoxicity in handy contour plots. As a principal contribution, quantum-chemical-based QSAM guides allow the analysis/quantification of the non-linear mixture effects of the toxicophores constituting the IL structures. Based on these favorable results, the QSAR model was applied to estimate IL cytotoxicities in order to screen commercially available compounds with comparatively low toxicities.

Anion effects on kinetics and thermodynamics of CO2 absorption in ionic liquids

A thermogravimetric technique based on a magnetic suspension balance operating in dynamic mode was used to study the thermodynamics (in terms of solubility and Henrys law constants) and kinetics (i.e., diffusion coefficients) of CO2 in the ionic liquids [bmim][PF6], [bmim][NTf2], and [bmim][FAP] at temperatures of 298.15, 308.15, and 323.15 K and pressures up to 20 bar. The experimental technique employed was shown to be a fast, accurate, and low-solvent-consuming method to evaluate the suitability of the ionic liquids (ILs) to be used as CO2 absorbents. Thermodynamic results confirmed that the solubility of CO2 in the ILs followed the order [bmim][FAP] > [bmim][NTf2] > [bmim][PF6], increasing with decreasing temperatures and increasing pressures. Kinetic data showed that the diffusion coefficients of CO2 in the ILs followed a different order, [bmim][NTf2] > [bmim][FAP] > [bmim][PF6], increasing with increasing temperatures and pressures. These results evidenced the different influence of the IL structure and operating conditions on the solubility and absorption rate of CO2, illustrating the importance of considering both thermodynamic and kinetic aspects to select adequate ILs for CO2 absorption. On the other hand, the empirical Wilke-Chang correlation was successfully applied to estimate the diffusion coefficients of the systems, with results indicating the suitability of this approach to foresee the kinetic performance of ILs to absorb CO2. The research methodology proposed herein might be helpful in the selection of efficient absorption solvents based on ILs for postcombustion CO2 capture.

Interactions of Ionic Liquids and Acetone: Thermodynamic Properties, Quantum-Chemical Calculations, and NMR Analysis

The interactions between ionic liquids (ILs) and acetone have been studied to obtain a further understanding of the behavior of their mixtures, which generally give place to an exothermic process, mutual miscibility, and negative deviation of Raoults law. COSMO-RS was used as a suitable computational method to systematically analyze the excess enthalpy of IL-acetone systems (>300), in terms of the intermolecular interactions contributing to the mixture behavior. Spectroscopic and COSMO-RS results indicated that acetone, as a polar compound with strong hydrogen bond acceptor character, in most cases, establishes favorable hydrogen bonding with ILs. This interaction is strengthened by the presence of an acidic cation and an anion with dispersed charge and non-HB acceptor character in the IL. COSMO-RS predictions indicated that gas-liquid and vapor-liquid equilibrium data for IL-acetone systems can be finely tuned by the IL selection, that is, acting on the intermolecular interactions between the molecular and ionic species in the liquid phase. NMR measurements for IL-acetone mixtures at different concentrations were also carried out. Quantum-chemical calculations by using molecular clusters of acetone and IL species were finally performed. These results provided additional evidence of the main role played by hydrogen bonding in the behavior of systems containing ILs and HB acceptor compounds, such as acetone.

Efficient biodegradation of common ionic liquids by Sphingomonas paucimobilis bacterium

The biodegradation of ionic liquids (ILs) was evaluated by an indirect impedance technique, through which carbon dioxide production was measured during bioassay time. The biodegradation study was focused on finding a microorganism able to efficiently degrade common IL compounds. For the first time, a bacteria strain of Sphingomonas paucimobilis was employed in biodegradability tests of ILs, carried out for 37 commercial imidazolium-, pyridinium-, pyrrolidinium-, ammonium- and phosphonium-based ILs, including in the sample 12 different anions and 14 different cations. Remarkably, more than half of ILs studied (54% of the sample) exhibited a biodegradation percentage ≥60% after a 28-day incubation period with S. paucimobilis at 45 °C; therefore, they behave as easily biodegradable compounds from the indirect impedance test. In summary, current results suggested the possibility of biotreatment for the rapid and ultimate mineralisation of widely used ILs, such as BmimNTf2, BmimPF6, etc., which were noted as recalcitrant to biodegradation in previous standard tests with other microorganisms.

Selection of Ionic Liquids for Enhancing the Gas Solubility of Volatile Organic Compounds

A systematic thermodynamic analysis has been carried out for selecting cations and anions to enhance the absorption of volatile organic compounds (VOCs) at low concentration in gaseous streams by ionic liquids (ILs), using COSMO-RS methodology. The predictability of computational procedure was validated by comparing experimental and COSMO-RS calculated Henrys law constant data over a sample of 125 gaseous solute-IL systems. For more than 2400 solute-IL mixtures evaluated, including 9 solutes and 270 ILs, it was found that the lower the activity coefficient at infinite dilution (γ(∞)) of solutes in the ILs, the more the exothermic excess enthalpy (H(E)) of the equimolar IL-solute mixtures. Then, the solubility of a representative sample of VOC solutes, with very different chemical nature, was screened in a wide number of ILs using COSMO-RS methodology by means of γ(∞) and H(E) parameters, establishing criteria to select the IL structures that promote favorable solute-solvent intermolecular interactions. As a result of this analysis, an attempt of classification of VOCs respect to their potential solubility in ILs was proposed, providing insights to rationally select the cationic and anionic species for a possible development of absorption treatments of VOC pollutants based on IL systems.

Composition and structural effects on the adsorption of ionic liquids onto activated carbon

The applications and variety of ionic liquids (ILs) have increased during the last few years, and their use at a large scale will require their removal/recovery from wastewater streams. Adsorption on activated carbons (ACs) has been recently proposed for this aim and this work presents a systematic analysis of the influence of the IL chemical structures (cation side chain, head group, anion type and the presence of functional groups) on their adsorption onto commercial AC from water solution. Here, the adsorption of 21 new ILs, which include imidazolium-, pyridinium-, pyrrolidinium-, piperidinium-, phosphonium- and ammonium-based cations and different hydrophobic and hydrophilic anions, has been experimentally measured. This contribution allows an expansion of the range of IL compounds studied in previous works, and permits a better understanding of the influence of the IL structures through the adsorption on AC. In addition, the COSMO-RS method was used to analyze the measured adsorption isotherms, allowing the understanding of the role of the cationic and anionic structures in the adsorption process, in terms of the different interactions between the IL compound and AC surface/water solvent. The results of this work provide new insights for the development of adsorption as an effective operation to remove/recover ILs with very different chemical nature from water solution.

Thermodynamic Behavior of the Binaries 1-Butylpyridinium Tetrafluoroborate with Water and Alkanols: Their Interpretation Using 1H NMR Spectroscopy and Quantum-Chemistry Calculations

Here we present experimental data of different properties for a set of binary mixtures composed of water or alkanols (methanol to butanol) with an ionic liquid (IL), butylpyridinium tetrafluoroborate [bpy][BF(4)]. Solubility data (x(IL),T) are presented for each of the mixtures, including water, which is found to have a small interval of compositions in IL, x(IL), with immiscibility. In each case, the upper critical solubility temperature (UCST) is determined and a correlation was observed between the UCST and the nature of the compounds in the mixtures. Miscibility curves establish the composition and temperature intervals where thermodynamic properties of the mixtures, such as enthalpies H(m)(E) and volumes V(m)(E), can be determined. Hence, at 298.15 and 318.15 K these can only be found with the first four alkanols. All mixing properties are correlated with a suitable equation ξ (x(IL),T,Y(m)(E) = 0. An analysis on the influence of the temperature in the properties is shown, likewise a comparison between the results obtained here and those of analogous mixtures, discussing the position of the -CH(3) group in the pyridinic ring. The (1)H NMR spectra are determined to analyze the molecular interactions present, especially those due to hydrogen bonds. Additional information about the molecular interactions and their influence on the mixing properties is obtained by quantum chemistry calculations.

Ionic Liquid Mixtures—An Analysis of Their Mutual Miscibility

The use of ionic liquid mixtures (IL-IL mixtures) is being investigated for fine solvent properties tuning of the IL-based systems. The scarce available studies, however, evidence a wide variety of mixing behaviors (from almost ideal to strongly nonideal), depending on both the structure of the IL components and the property considered. In fact, the adequate selection of the cations and anions involved in IL-IL mixtures may ensure the absence or presence of two immiscible liquid phases. In this work, a systematic computational study of the mixing behavior of IL-IL systems is developed by means of COSMO-RS methodology. Liquid-liquid equilibrium (LLE) and excess enthalpy (H(E)) data of more than 200 binary IL-IL mixtures (including imidazolium-, pyridinium-, pyrrolidinium-, ammonium-, and phosphonium-based ILs) are calculated at different temperatures, comparing to literature data when available. The role of the interactions between unlike cations and anions on the mutual miscibility/immiscibility of IL-IL mixtures was analyzed. On the basis of proposed guidelines, a new class of immiscible IL-IL mixtures was reported, which only is formed by imidazolium-based compounds.

Excess enthalpy of monoethanolamine + ionic liquid mixtures: how good are COSMO-RS predictions?

Mixtures of ionic liquids (ILs) and molecular amines have been suggested for CO2 capture applications. The basic idea is to replace water, which volatilizes in the amine regeneration step and increases the parasitic energy load, with a nonvolatile ionic liquid solvent. To fully understand the thermodynamics of these systems, here experimental excess enthalpies for binary mixtures of monoethanolamine (MEA) and two ILs: 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [hmim][NTf2], and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [OHemim][NTf2], were obtained by calorimetry, using a Setaram C80 calorimeter, over the whole range of compositions at 313.15 K. Since it is the temperature derivative of the Gibbs energy, enthalpy is a sensitive measure of intermolecular interactions. MEA + [hmim][NTf2] is endothermic and MEA + [OHemim][NTf2] is exothermic. The reliability of COSMO-RS to predict the excess enthalpy of the (MEA+IL) systems was tested based on the implementation of two different molecular models to define the structure of the IL: the IL as separate cation and anion [C+A] and the IL as a bonded single specie [CA]. Quantum-chemical calculations were performed to gain additional insight into the intermolecular interactions between the components of the mixture. For MEA + [hmim][NTf2] both the [C+A] and [CA] models predict endothermic behavior, but the [CA] model is in better agreement with the experimental results. For MEA + [OHemim][NTf2] the [C+A] model provides the best match to the experimental exothermic results. However, what is really surprising is that two different conformations of the cation-anion pair with nearly identical energies in the [CA] model result in completely different (exothermic vs endothermic) predictions of the excess enthalpy. Nonetheless, the results do show that the influence of the structure of the IL on the thermodynamic behavior of the mixture (endothermic vs exothermic) can be attributed to hydrogen bonding between the cation and the MEA molecule. However, this study highlights the importance of carefully selecting the molecular model and conformation in order to obtain even qualitatively correct predictions with COSMO-RS. The fact that even very slightly different conformations of the IL can drastically change the thermodynamic estimations using COSMO-RS is of significant concern. Overall, we believe the present work provides a better understanding of the behavior of mixtures involving amines and ILs, which is an important aspect to consider when evaluating the use of such solvent mixtures in CO2 capture technologies.

Double- or single-well potential for GSIPT in 1-hydroxy-2-acetonaphthone?

Abstract Potential energy surfaces for intramolecular proton transfer of ground state (GSIPT) of 2-hydroxyacetophenone and 1-hydroxy-2-acetonaphthone have been calculated by using MP2 and B3LYP methods. The main results are as follows. (a) Intramolecular proton transfer shows an strong coupling with the distances between the oxygen atoms which support the intramolecular hydrogen-bonding. (b) The correlated GSIPT curves of both compounds have a single minimum in the ground state, corresponding to the enol form. (c) This previous coclusion does not support the assumption made by Douhal et al. on the HAN GSIPT curve is a double well potential curve.