Montserrat Domínguez-Pérez

On the Interactions between Amino Acids and Ionic Liquids in Aqueous Media

The understanding of the molecular-level interactions between biomolecules and ionic liquids (ILs) in aqueous media is crucial for the optimization of a number of relevant biotechnological processes. In this work, the influence of a series of amino acids on the liquid-liquid equilibria between 1-butyl-3-methylimidazolium tricyanomethane and water was studied to evaluate the preferential interactions between these three compounds. The solubility effects observed are dependent on the polarity, size, and charge distribution of the amino acid side chains and are explained in terms of a refined version of the model proposed earlier (Freire et al. J. Phys. Chem. B 2009, 113, 202; Tome et al. J. Phys. Chem. B 2009, 113, 2815) for ion specific effects on aqueous solutions of imidazolium-based ILs. Although acting through different mechanisms, salting-in and salting-out phenomena possess a common basis which is the competition between water-amino acid side chain, IL-amino acid side chain, and water-IL interactions. The delicate balance between these interactions is dependent on the relative affinities of the biomolecules to water molecules or to IL cation and anion and determines the trend and magnitude of the solubility effect observed.

Surface Tension of Binary Mixtures of 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids: Experimental Measurements and Soft-SAFT Modeling

Ionic liquids have attracted a large amount of interest in the past few years. One approach to better understand their peculiar nature and characteristics is through the analysis of their surface properties. Some research has provided novel information on the organization of pure ionic liquids at the vapor-liquid interface; yet, a systematic study on the surface properties of mixtures of ionic liquids and their organization at the surface has not previously been carried out in the literature. This work reports, for the first time, a comprehensive analysis of the surface organization of mixtures of ionic liquids constituted by 1-alkyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, [C(n)mim][NTf(2)]. The surface tension of mixtures composed of [C(4)mim][NTf(2)] + [C(n)mim][NTf(2)] (n = 1, 2, 5, 6, 8, and 10) was experimentally determined, at 298.2 K and atmospheric pressure, in the whole composition range. From the experimental data, the surface tension deviations and the relative Gibbs adsorption isotherms were estimated showing how the surface composition of an ionic liquid mixture differs from that of the liquid bulk and that the surface is enriched by the ionic liquid with the longest alkyl chain length. Finally, the soft-SAFT equation of state coupled with the density gradient theory (DGT) was used, for the first time, to successfully reproduce the surface tension experimental data of binary mixtures of ionic liquids using a molecular-based approach. In addition, the DGT was used to compute the density profiles of the two components across the interface, confirming the experimental results for the components distribution at the bulk and at the vapor-liquid interface.

Densities, surface tensions, and refractive indexes of propyl propanoate + hexane + m-xylene at 298.15 K

This paper reports experimental densities, surface tensions, and refractive indexes of the ternary system (propyl propanoate + hexane + m-xylene) at the temperature 298.15 K and atmospheric pressure over the whole composition range. Also, the corresponding binary mixtures not published before are presented. The excess molar volumes, surface tension deviations, and changes in the refractive index on mixing have been calculated. Finally, we will compare the experimental data of surface tension and refractive index with different theoretical and empirical approximations.

Mesostructure and physical properties of aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl sulfate doped with divalent sulfate salts in the liquid and the mesomorphic states

This paper extends the study of the induced temperature change in the mesostructure and in the physical properties occurring in aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl-sulfate [EMIm][OSO4]. For some compositions, these mixtures undergo a phase transition between the liquid (isotropic in the mesoscale) and the mesomorphic state (lyotropic liquid crystalline) at about room temperature. The behavior of mixtures doped with a divalent metal sulfate was investigated in order to observe their applicability as electrolytes. Calcium sulfate salt is almost insoluble even in the 20 wt% water mixture. The magnesium salt, in contrast, can be dissolved up to concentrations of 730 ppm in the same mixture and it has a profound impact on its properties. Six aqueous mixtures (with water content from 10 wt% to 33 wt%) of [EMIm][OSO4] were saturated with magnesium sulfate salt, producing the ternary mixture [EMIm][OSO4] + H2O + MgSO4. Viscosity, density and ionic conductivity for these samples were measured from 10 °C to 90 °C. In addition, SAXS, FTIR, diffussion NMR and Raman spectroscopy of the most interesting samples have been performed, and structural data indicate a transition between a hexagonal lyotropic liquid crystalline phase below and an isotropic solution phase above room temperature. The octyl sulfate anions of the cylindrical micelles in the hexagonal phase are coordinated with water molecules through H-bonds (about four per sulfate anion), while the [EMIm] cations seem to be poorly coordinated and so free to move. Inorganic salt addition reinforces that network, increasing the phase transition temperature.

Physical Properties of Binary Mixtures of ILs with Water and Ethanol. A Review.

The interest on ionic liquids (ILs) began in the present century, because these compounds have many physico-chemical interesting properties to be one of the most promising new materials family for the development of the novel Green Chemical industry, where generated pollution would be negligible (Rogers & Seddon, 2002; Rogers et al., 2002). To develop the novel green processes in the chemical industry using ILs it is necessary to know and to understand the physical properties of the fluids to be used, both pure ILs as mixed with other solvents (Rogers & Seddon, 2005; Danek, 2006). This last is particularly important to develop one of the most promising uses of the ILs, as electrolytes for lithium batteries, dye-sensitized solar cells (DSSC) and electrochemical processes (as deposition or metal recovery) (Ohno, 2005; Brennecke et al., 2007). Electrolytes are materials with free ions, which can move transporting electrical charge. They can be solid, liquid or even gaseous, but the most interesting for the chemical industries are liquid or gel. The use of a pure liquid as electrolyte is not very common, because the optimum efficiency in the charge transport process is given by a mixture of different substances, as it is well known for molten salt electrolytes (Danek, 2006). Furthermor, pure ILs have the problem of being very viscous at room temperature, and hence its electrical conductivity is relatively low. If we heat the IL those problems are minimized, because viscosity reduces and electrical conductivity increases, both exponentially. Usually pure ILs have a boiling temperature high enough to allow warming, although decomposition temperature is usually much lower (not higher than 400 K) (Rogers & Seddon, 2002). A much cheaper alternative to decrease viscosity and to increase electrical conductivity of the ionic liquid is to make a solution using a solvent. Thus, while viscosity decreases exponentially with the solvent molar fraction, electrical conductivity increases more than 10 times for a given IL + solvent concentration (Seddon et al., 2000). This last behaviour have been observed in aqueous solutions of metal salts, as aluminium halogen ones (Vila et al., 2005) and indicates that the increase of mobility of the IL ions is higher than the decrease of ion concentration when solvent is added, up to an optimum content. In spite of its interest, the measurement of the physical properties of IL mixtures begins in the present decade, and before 2005 the amount of papers published about it was scarce (Marsh et al., 2004). From that year the publication rhythm increased a lot, as can be

Imidazolium decyl sulfate: a very promising selfmade ionic hydrogel

In this paper, we show, for the first time, the synthesis, structural characterization, phase diagram and physical properties of the ionic liquid, 1-ethyl-3-methyl imidazolium decyl sulfate [EMIm][DSO4]. At 25 °C it is either a crystalline solid or a liquid depending on the thermal history as its melting point is about 33 °C and its point of solidification is about 22 °C. The interest of this new IL lies in its ability to become a rigid hydrogel when mixed with water. As observed in many ILs, the as-prepared IL is hygroscopic and it adsorbs about 14 wt% of water at usual laboratory conditions and up to 27 wt% in a 100% saturated atmosphere. Due to the H-bonds between water and the amphiphilic [DSO4] anions, a lyotropic HI liquid crystalline phase is formed in the hydrated state, which can be observed in micrographs recorded using white polarized light. The moisture adsorption is a completely reversible process; thus, the rigid-gel sample loses all adsorbed water when it is left in a dry atmosphere for a few hours, transitioning to the liquid state. Phase diagrams of the temperature-water concentration is presented and compared with that of the parent compound [EMIm] octyl sulfate, [OSO4]. X-ray diffraction revels that below 15 °C the hydrated compound crystallizes into a P2/m monoclinic structure. The structure of the new compound was confirmed by NMR, FTIR and mass spectroscopy (MS). In addition, the temperature behavior of ionic conductivity was experimentally measured and analyzed for the pure compound and for two samples hydrated with 10 wt% and 39 wt% of water. Viscosity and density were also measured vs. temperature for the pure sample. The as-prepared IL shows great potential for numerous practical applications.