Showing papers in "Journal of Solution Chemistry in 2015"

Interaction of an Amphiphilic Drug and Sodium Bis(2-ethylhexyl)sulfosuccinate at Low Concentrations in the Absence and Presence of Sodium Chloride

Abstract: In the present study mixed micelles of the amphiphilic phenothiazine drug promazine hydrochloride (PMZ) and the anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) have been studied using conductometry at different compositions and temperatures in aqueous as well as aqueous electrolyte (25 mmol·kg−1 NaCl) solutions to determine various physicochemical properties of the solutions. The experimental and ideal critical micelle concentration (CMC and CMC id) values suggest attractive interactions in PMZ–AOT mixed systems. The negative values of interaction parameter (β) obtained from regular solution theory indicate synergistic interactions; the negative values of β decrease further with the addition of salt. From the CMC values obtained as a function of temperature, various other thermodynamic properties have been evaluated.

Density and viscosity of ionic liquid binary mixtures of 1-n-butyl-3-methylimidazolium tetrafluoroborate with acetonitrile, N,N-dimethylacetamide, methanol, and N-methyl-2-pyrrolidone

Abstract: In this study, thermodynamic properties of the binary mixtures of ionic liquid with an organic compound, as potential solvent systems in pharmaceutical industry applications, are studied. The densities and viscosities of the binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) with acetonitrile, N,N-dimethylacetamide, methanol, and N-methyl-2-pyrrolidone were measured at atmospheric pressure over the [C4mim][BF4] mole fraction range from 0.1 to 0.9 and at temperatures from 303.15 to 333.15 K at intervals of 10 K. The densities were measured using a vibrating-tube digital density meter and the viscosities were measured using a capillary viscometer. The excess molar volumes (V E) and viscosity deviations (Δη) were calculated from densities and viscosities of mixture, respectively, and fitted to the Redlich–Kister polynomial. The optimally fitted parameters are also determined and the correlation results are in satisfactory agreement with the experimental data. In addition, the excess molar volumes of binary mixtures of ionic liquid with different organic compounds are compared and discussed using the Hansen solubility parameter.

Solution Thermodynamics and Preferential Solvation of Sulfamerazine in Methanol + Water Mixtures

Abstract: The solubility of sulfamerazine (SMR) in methanol + water co-solvent mixtures was measured at five temperatures from 293.15 to 313.15 K. The mole fraction solubility of this sulfonamide was maximal in pure methanol (δ 1 = 29.6 MPa1/2) and minimal in water (δ 2 = 47.8 MPa1/2) at all the temperatures studied. The apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Apparent thermodynamic quantities of mixing were also calculated by using the ideal solubilities reported in the literature. A non-linear enthalpy–entropy relationship was observed for SMR in the plot of enthalpy versus Gibbs energy of mixing. This plot shows two different trends according to the slopes obtained when the mixture’s composition changes. Accordingly, the driving mechanism for the SMR solution process in water-rich mixtures is the entropy whereas it is the enthalpy in mixtures with mass fractions of methanol greater than 0.20. Additionally, the preferential solvation of this drug by the solvents was analyzed by means of the inverse Kirkwood–Buff integrals, which indicate that it is preferentially solvated by water in water-rich mixtures but preferentially solvated by methanol in methanol-rich mixtures.

CO2 Capture in Wet and Dry Superbase Ionic Liquids

Abstract: The solubility of carbon dioxide in five tetraalkylphosphonium superbase ionic liquids, namely the trihexyltetradecylphoshonium phenoxide, trihexyltetradecylphoshonium benzotriazolide, trihexyltetradecylphoshonium benzimidazolide, trihexyltetradecylphoshonium 1,2,3-triazolide, and trihexyltetradecylphoshonium 1,2,4-triazolide was studied experimentally under dry and wet conditions at 22 °C and at atmospheric pressure, using a gravimetric saturation technique. The effects of anion structure and of the presence or absence of water in the solution on the carbon dioxide solubility were then deduced from the data. 1H and 13C-NMR spectroscopy and ab initio calculations were also conducted to probe the interactions in these solutions, as carbon dioxide and water can compete in the ionic liquid structure during the absorption process. Additionally, the viscosity of selected superbase ionic liquids was measured under dry and wet conditions, in the presence or absence of CO2, to evaluate their practical application in carbon dioxide capture processes. Finally, the recyclability of the trihexyltetradecylphoshonium 1,2,4-triazolide under dry and wet conditions was determined to probe the ability of selected solvents to solubilize chemically a high concentration of carbon dioxide and then release it in a low energy demand process.

Transport and Thermodynamic Properties of Ethylammonium Nitrate–Water Binary Mixtures: Effect of Temperature and Composition

Abstract: Physical properties such as densities, ρ, viscosities, η, and conductivities, κ, have been measured for the binary mixtures of the ionic liquid ethylammonium nitrate, EtNH3NO3, with water over the entire molar fraction range at various temperatures ranging from 293.15 to 318.15 K and under ambient pressure. Strong effects of the composition and temperature on these properties have been observed. Experimental densities and viscosities were used to calculate the corresponding excess properties. The variations of excess molar volume and excess Gibbs energy against the ionic liquid fraction show complementary extrema (minima and maxima with opposite signs). The excess molar volumes and excess viscosity deviations are well fitted using the Redlich–Kister polynomial. Moreover, the viscosity was found to be temperature dependent and followed the Arrhenius law. Variations of the activation energies for viscous flow versus the ionic liquid content revealed a modification in the medium’s structure. The conductivity–temperature relationship was found to be better represented by the Vogel–Tammann–Fulcher model than with the Arrhenius equation. In addition, variations of the conductivity with composition are well described by the Casteel–Amis equation. The impact of addition of the ionic liquid to water on the viscosity and the conductivity have been also examined using Walden’s rule, which shows that viscosity is highly correlated to conductivity for ionic liquid molar fractions higher than ca. 0.2. Activation thermodynamic parameters for viscous flow, calculated from the viscosity data, reveal that changes in the medium structure occur at ca. 0.2 and 0.8 molar fractions of ionic liquid.

Activity Coefficients at Infinite Dilution and Physicochemical Properties for Organic Solutes and Water in the Ionic Liquid 1-Ethyl-3-methylimidazolium trifluorotris(perfluoroethyl)phosphate.

Abstract: New data of activity coefficients at infinite dilution, γ13∞, for 65 different solutes including alkanes, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, ethers, ketones, aldehydes, esters and water in the ionic liquid 1-ethyl-3-methylimidazolium trifluorotris(perfluoroethyl)phosphate, were determined using inverse gas chromatography within the temperature range from 318.15 to 368.15 K. This is a continuation of our study of ionic liquids based on this anion. The results are compared with the other trifluorotris(perfluoroethyl)phosphate ionic liquids. The γ13∞ values were used to calculate thermodynamic functions such as partial molar excess Gibbs energies ΔG1E,∞, enthalpies ΔH1E,∞ and entropies ΔS1E,∞ as well as gas–liquid partition coefficients of the solutes, KL. These values were used to determine the linear free energy relationship (LFER) system constants as a function of temperature. The selectivities at infinite dilution needed for some extraction problems were calculated and compared with literature data of ionic liquids based on the trifluorotris(perfluoroethyl)phosphate anion and the 1-ethyl-3-methylimidazolium cation. Additionally, the density and viscosity of the investigated ionic liquid at temperatures from 298.15 to 348.15 K were measured. Electronic supplementary material The online version of this article (doi:10.1007/s10953-014-0274-0) contains supplementary material, which is available to authorized users.

Synthesis and Thermophysical Properties of Hydrogensulfate Based Acidic Ionic Liquids

Abstract: Three ionic liquids (ILs): 1-butyl-3-methyl-imidazolium hydrogensulfate [C4C1Im][HSO4], 1-butyl-imidazolium hydrogensulfate [C4C0Im][HSO4], and 1-methyl-imidazolium hydrogensulfate [C1C0Im][HSO4], were synthesized and characterized. The effect of alky group incorporation into the imidazolium cation was evaluated in terms of changes in density, surface tension, viscosity, and thermal degradation of the ILs. The viscosity and density were measured within the temperature range of 293.15–373.15 K, and experimental values of density were used to calculate molar volume, standard molar entropy, lattice energy, and thermal expansion coefficients. Glasser’s approach was used to calculate the lattice energies of the ILs. Surface tensions in the temperature range of 293.15–353.15 K were also measured and surface tension values were used to estimate the surface entropy and enthalpy of the ILs. Refractive indices were measured with an ATAGO refractometer (RX-5000α) within the temperature range of 293.15–323.15 K. Thermal gravimetric analysis was performed in the temperature range of 323.15–773.15 K.

Application of Phosphonium Ionic Liquids as Ion Carriers in Polymer Inclusion Membranes (PIMs) for Separation of Cadmium(II) and Copper(II) from Aqueous Solutions.

Abstract: Facilitated transport through polymer inclusion membranes (PIMs) is a promising method for simultaneous separation and removal of valuable and toxic metal ions from aqueous solutions. Recently, ionic liquids (ILs) have been used as extracting agents for metal ions due to their unique physicochemical properties. This paper presents research on the facilitated transport of cadmium(II) and copper(II) ions from aqueous chloride solutions through PIMs with phosphonium ILs as new selective ion carriers. Cellulose triacetate membranes containing o-nitrophenyl octyl ether (ONPOE) as a plasticizer and Cyphos IL 101 [trihexyl(tetradecyl)phosphonium chloride] or Cyphos IL 104 [trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate] as the ion carriers have been prepared and applied for investigations. Cd(II) ions were transported preferably from hydrochloric acid solutions containing Cu(II) ions through the PIMs. Higher selectivity coefficient of Cd(II) over Cu(II) (SCd/Cu) from 0.1 mol·dm−3 hydrochloric acid was obtained for PIM with Cyphos IL 104 as the ion carrier. The influence of HCl and NaCl concentrations in the source phase on metal ion transport across PIM doped with Cyphos 104 was studied. It was found that the initial fluxes of Cd(II) and Cu(II) increase with increasing chloride ions concentration in the source phase. The selectivity coefficient for Cd(II) over Cu(II) decreases with increasing HCl concentration in the source phase. The results suggest that the separation system presented in this paper can be useful for the removal of Cd(II) from acidic chloride solutions in the presence of Cu(II).

The Solvation of Anions in Propylene Carbonate

Abstract: The solubilities of some univalent potassium salts (KF, KCl, KBr, KI, KClO4, KSCN, and KCNO) in propylene carbonate (PC) were determined at different temperatures from (25.0 to 45.0) °C through flame emission spectroscopy. From the solubility measurements, the thermodynamic parameters ∆G 0, ∆H 0 and ∆S 0 of solution were calculated. Measurements were carried out via electrical conductimetry and FTIR to investigate the formation of ion pairs and the ion–solvent interactions. This study was motivated by the open question of whether specific ion (Hofmeister) effects are related to the structure of the solvent (i.e., hydrogen bonding). As for water, these effects are due to solute-induced solvent structure changes not accounted for by electrostatic forces.

SO2 Solvation in the 1-Ethyl-3-Methylimidazolium Thiocyanate Ionic Liquid by Incorporation into the Extended Cation–Anion Network

Abstract: We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO2) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO2. Whereas, the anions tend to form a thiocyanate- and much less often an isothiocyanate-SO2 adduct, the cations create a “cage” around SO2 with those groups of atoms that donate weak interactions like the alkyl hydrogen atoms as well as the heavy atoms of the π-system. Despite these similarities between the solvation of SO2 and CO2 in ionic liquids, an essential difference was observed with respect to the acidic protons. Whereas CO2 avoids accepting hydrogen bonds form the acidic hydrogen atoms of the cations, SO2 can from O(SO2)–H(cation) hydrogen bonds and thus together with the strong anion-adduct it actively integrates in the hydrogen bond network of this particular ionic liquid. The fact that SO2 acts in this way was termed a linker effect by us, because the SO2 can be situated between cation and anion operating as a linker between them. The particular contacts are the H(cation) ⋯ O(SO2) hydrogen bond and a S(anion)–S(SO2) sulfur bridge. Clearly, this observation provides a possible explanation for the question of why the SO2 solubility in these ionic liquids is so high. Electronic supplementary material The online version of this article (doi:10.1007/s10953-015-0321-5) contains supplementary material, which is available to authorized users.

Thermodynamic Insights in the Separation of Cellulose/Hemicellulose Components from Lignocellulosic Biomass Using Ionic Liquids

Abstract: This work reports on the ionic liquid (IL) based separation of cellulose/hemicellulose from lignocellulosic biomass, by means of macroscale predictions using the COnductor like Screening MOdel for Real Solvents (COSMO-RS) model that is based on a statistical mechanical framework. For the benchmarking studies the experimental infinite dilution activity coefficient values for 13 components were predicted in 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulphonyl}imide with an average absolute deviation (%AAD) of 15 %. Further, the solid–liquid equilibria of glucose, fructose, galactose, and xylose in [EMIM][EtSO4] and Aliquat®336 were predicted successfully with 15 % root-mean-square deviation. Afterwards, the selectivities were predicted at infinite dilution for cellulose/hemicellulose in 1,156 ILs with a combination of 34 cations and 34 anions. Based on these values, the ammonium-based ILs 1-methyl-4-aminotriazolium hexafluorophosphate [14MATAZ][PF6] and 4-aminotriazolium bis(oxalato(2)borate) [4ATAZ][BOB] were found to be good candidates for cellulose and hemicellulose extraction, respectively. The ILs selected using the COSMO-RS methodology were then studied qualitatively in terms of interaction energies and HOMO–LUMO energy gap. The binding energy for [1-methyl-4-aminotriazolium][PF6] + cellulose and [4-aminotriazolium][BOB] + cellulose systems are higher as compared with IL + cellulose + hemicellulose, indicating greater stability.

Thermal Properties of Alkyl-triethylammonium bis{(trifluoromethyl)sulfonyl}imide Ionic Liquids

Abstract: In this work, we address the thermal properties of selected members of a homologous series of alkyltriethylammonium bisf(trifluoromethyl)sulfonylgimide ionic liquids. Their phase and glass transition behavior, as well as their standard isobaric heat capacities at 298.15 K, were studied using differential scanning calorimetry (DSC), whereas their decomposition temperature was determined by thermal gravimetry analysis. DSC was further used to measure standard molar heat capacities of the studied ionic liquids and standard molar heat capacity as a function of temperature for hexyltriethylammonium, octyltriethylammonium, and dodecyltriethylammonium bisf(trifluoromethyl)sulfonylg- imide ionic liquids. Based on the data obtained, we discuss the influence of the alkyl chain length of the cation on the studied ionic liquids on the measured properties. Using viscosity data obtained in a previous work, the liquid fragility of the ionic liquids is then discussed. Viscosity data were correlated by the VTF equation using a robust regression along a gnostic influence function. In this way, more reliable VTF model parameters were obtained

Structure of a Binary Mixture of Ethylammonium Nitrate and Methanol

Abstract: We report a joint experimental (X-ray and neutron diffraction) and computational study on a binary mixture of ethylammonium nitrate (EAN), a protic ionic liquid, and methanol, the shortest alcohol. These two amphiphilic compounds are also characterized by the existence of an extended hydrogen bonding network in their neat states. We explore how these similar compounds structurally organize at the micro- and mesoscopic levels when mixed in a homogeneous state. The study demonstrates that the mixture is organized similarly to neat EAN, where the polar versus apolar dualism of the ionic liquid determines the segregation of alkyl tails into domains embedded into the ionic, percolating matrix. Methanol, due to the strong hydrogen bond with the nitrate anion, tends to intrude into this polar network, merging at EAN’s polar–apolar interface. Further studies are proposed to rationalize the emerging mesoscopic density fluctuations that develop when approaching methanol-rich conditions.

Solubilities, Fugacities and All That in Solution Chemistry

Abstract: Solution chemistry is at the heart of many research areas in the pure and applied sciences. In fact, for more than a century, experimental as well as theoretical work on solution properties and phase equilibria involving liquid/fluid solutions in general, and aqueous liquid/fluid solutions in particular, have held prominent positions in (bio-)physical chemistry. The scientific insights gained thereby are invaluable and have not only contributed decisively to the creation of the formal structure of chemical thermodynamics but have also paved the way for the development of practically useful molecular-based models describing real solution behavior. In the first part of this review, I shall present a concise overview of the thermodynamic formalism relevant in solubility studies on liquid/fluid nonelectrolyte systems. In the second part, selected aspects of solubility data reduction and data correlation will be touched upon, including a critical evaluation of some popular approximations and a survey of current estimation technique for indispensable auxiliary quantities, such as virial coefficients and partial molar volumes at infinite dilution. One of the goals will be to clarify issues frequently overlooked and to dispel misconceptions encountered in the literature. Pride of place will be given to the Henry fugacity (also known as Henry’s law constant), which is one of the most misunderstood thermodynamic quantities, and to various caloric quantities derived via van’t Hoff analysis of high-precision solubility data.

Enthalpies of Solution and Enthalpies of Solvation in Water: The Anion Effect in Ionic Liquids with Common 1-Ethyl-3-methyl-imidazolium Cation

Abstract: Thermochemical studies of ionic liquids (ILs) in aqueous solution were carried out using solution calorimetry. Heat effects of dissolution in water at 298.15 K and molar limiting enthalpies of solution were measured for ILs having a common cation, 1-ethyl-3-methyl-imidazolium, connected with different anions: diethylphosphate, ethylsulfate, tetracyanoborate, thiocyanate, and trifluoroacetate. Molar enthalpies of solvation of ILs in water were derived from experimental data for solution and vaporization enthalpies. Enthalpic data were correlated with ionic liquid specific parameters and descriptors. The best correlation was observed with hydrogen-bonding interaction energies. This result confirmed that hydrogen bonding is one of the main types of intermolecular interactions inherent for ILs in aqueous solutions.

Density, Refractive Index, Speed of Sound and Computational Studies of Intermolecular Interactions in Binary Mixtures of 2-Chloroaniline with Butanols (1-Butanol, 2-Butanol) at T = (303.15–318.15) K

Abstract: Densities (ρ), refractive indices (n D) and speeds of sound (u) were measured for the binary mixtures of 2-chloroaniline with butanols (1-butanol, 2-butanol) over the entire range of mole fraction at 303.15, 308.15, 313.15 and 318.15 K under atmospheric pressure. From the experimental data, the values of molar volume (V m), isentropic compressibility (k S ), intermolecular free length (L f), specific acoustic impedance (Z), molar refraction (R m), atomic polarization (P a), polarizability (α), deviation in molar volume (ΔV m), deviation in isentropic compressibility (Δk s ), deviation in intermolecular free length (ΔL f) and deviation in refractive index (Δn D) have been calculated and fitted with Redlich–Kister type polynomial equations by the method of least-squares. The experimental reduced Redlich–Kister deviation properties were also determined, and the results reveal formation of hydrogen bonds between 2-chloroaniline and the butanol mixtures. The formation of hydrogen bonds in the binary mixture systems was further confirmed by FT-IR spectra. The optimized geometry, harmonic vibrational wave numbers and bond characteristics, of pure and equimolar hydrogen bonded complexes, have been calculated theoretically from the ab-intio Hartree–Fock (HF) and density functional theory (DFT-B3LYP) methods with 6-31 + G and 6-311 + G basis sets using Gaussian 09 software.

Studies of the Micellization of Cationic–Anionic Surfactant Systems in Water and Methanol–Water Mixed Solvents

Abstract: Measurements of the conductance of binary mixtures of cetyltrimethylammonium bromide and sodium dodecylsulfate in pure water and in methanol–water mixed solvent media containing 0.10, 0.20, and 0.30 volume fractions of methanol at 308.15, 318.15, and 323.15 K are reported. The concentration of sodium dodecylsulfate varied from 0.001 to 0.04 mol·L−1 in the presence of ~5.0 × 10−4 mol·L−1 cetyltrimethylammonium bromide. The results showed a sharp increase in the conductance with increasing concentrations of the surfactant mixture. The conductance is found to increase with increasing temperature over the entire concentration range in pure water and in a given mixed solvent medium but is found to decrease with increasing methanol content in the solvent. Estimation of the pre-cmc (S 1) and post-cmc (S 2) slopes for the CTAB–SDS system, to calculate the critical micelle concentration, provides important insight regarding the solution behavior of the mixed surfactants. The critical micelle concentration (cmc) and degree of micellar dissociation (α) of sodium dodecylsulfate in the presence of cetyltrimethylammonium bromide increase in the methanol–water mixed solvent medium. Additionally, the values of cmc and α increase with increasing temperature. The thermodynamic functions for the micellization were calculated at various conditions.

Ternary Liquid–Liquid Equilibria for Mixtures of {Ionic Liquid + Thiophene or Benzothiophene + Heptane} at T = 308.15 K

Abstract: In this work, the desulfurization ability of alkyl-piperidinium-based and phosphonium-based ionic liquids (ILs) for (thiophene or benzothiophene + heptane) mixtures are studied. With this aim, ternary liquid-liquid phase equilibrium data (LLE) have been obtained for mixtures of {IL (1) + thiophene, or benzothiophene (2) + heptane (3)} at T = 308.15 K and p = 101.33 kPa. For this study 1-pentyl-1-methylpiperidinium bis{(trifluoromethyl)sulfonyl}imide, [C1C5PIP][NTf2], and tributylethylphosphonium diethylphosphate, [P2,4,4,4][DEP], were used. The suitability of these ILs as solvents for extractive desulfurization has been evaluated in terms of the solute distribution ratio and selectivity. Immiscibility was observed in the binary liquid systems of (thiophene, or benzothiophene + heptane) with both ILs. One of the studied ILs, [C1C5PIP][NTf2], shows high distribution ratios and high selectivities for extraction of sulfur compounds. The data obtained have been correlated with the non-random two liquid NRTL model. The experimental tie-lines and the phase compositions in mole fractions in the ternary systems were calculated with an average root mean square deviation of 0.0052.

Interesting Viscosity Changes in the Aqueous Urea–Ionic Liquid System: Effect of Alkyl Chain Length Attached to the Cationic Ring of an Ionic Liquid

Abstract: In the present article, we demonstrate the effect of urea on the structure of the ionic liquids in their aqueous solutions through viscometric methods. We unravel the structure altering effect of urea in its aqueous solutions of ionic liquids possessing higher alkyl chains. The finding is an attempt to discern the anomalous behavior of urea as shown in the past with the help of many techniques. Interestingly, in the aqueous solutions of the imidazolium based ionic liquids having substitution of –C4H9 and –C6H13 groups on the imidazolium ring, urea exhibits kosmotropic behavior. Further increase in the substituted alkyl group such as –C8H17 alters the urea behavior to be chaotropic.

Determination of pKaIL Values of Three Chelating Extractants in ILs: Consequences for the Extraction of 4f Elements

Abstract: Aqueous–ionic liquid biphasic systems have been examined in terms of water and acid solubilities in the IL-rich phase at ambient temperature. The biphasic mixtures were comprised of acids of various concentrations (H+; Cl−, H+; \( {\text{NO}}_{3}^{ - } \), H+; \( {\text{ClO}}_{4}^{ - } \), mainly from 1 × 10−2 to 1 × 10−4 mol·dm−3) and four ionic liquids of the imidazolium family [C1Cnim][Tf2N] (n = 4, 6, 8 and 10). The effects of ionic medium (μ = 0.1 mol·dm−3, by use of Na+; Cl−, Na+; \( {\text{NO}}_{3}^{ - } \) or Na+; \( {\text{ClO}}_{4}^{ - } \), according to the acid investigated), the nature of the IL cation as well as the nature of the acid on the mutual solubilities of (H2O, H+, [C1Cnim]+ and [Tf2N]−) entities were determined. Then, three chelating compounds (HL), which belong to the β-diketone family (thenoyltrifluoroacetone (HTTA), 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP) and 4-benzoyl-3-phenyl-5-isoxazolone (HPBI)), were added to [C1C4im][Tf2N] and subsequent determination of the H+ distribution between the two phases allowed the determination of their dissociation constants (pKaIL) in the water-saturated ionic liquid phase. A very strong effect of the IL cation on the HTTA pKaIL value was observed from n = 4 to n = 10. The influence of this phenomenon on the lanthanide extraction process is discussed.

How Can a Free Amino Acid Stabilize a Protein? Insights from Molecular Dynamics Simulation

Abstract: Amino acids such as proline are known as natural osmolytes that can stabilize proteins. But, there is no distinct mechanism at the molecular levels that can explain the stabilization effects of such osmolytes. In this paper, for the first time, the molecular level mechanism of protein stabilization by amino acid proline was studied using molecular dynamics simulation, which led to the following interesting points. Simulations were performed at room and high temperatures using lysozyme as a protein model. Although lysozyme was partially unfolded in the aqueous solution at high temperatures, the structure remained relatively native in the presence of 3 mol·L−1 proline. Protein residues showed slower dynamics in aqueous proline solution than that in water. These results are in agreement with experimental observations that show enhanced protein thermal stability in the presence of proline. It was also found that proline molecules are excluded from the protein surface and water molecules in the hydration shell around the protein increase, thus inducing thermodynamic stabilization of the protein. Moreover, it was shown that proline molecules form molecular aggregates in the solution, in agreement with previous experimental observations. We found that these aggregates can increase the order of water molecules and also the water–water hydrogen bond strength. This also leads to higher thermal stability of the protein in such solutions. The results of this paper shed some light on the molecular mechanism of protein stabilization by natural amino acids.

Liquid Electrolytes Based on Ionic Liquids for Lithium-Ion Batteries

Abstract: Low-melting temperature ionic liquids (ILs), based on aliphatic quaternary ammonium N1xxx and 1-ethyl-3-methylimidazolium cations with the imide anion, were prepared and characterized. The physicochemical and electrochemical properties of these ILs, including melting point, degradation temperature, viscosity, density, ionic conductivity and electrochemical stability, were determined. The fluorinated imidazolium cation was also studied because of its better electrochemical stability compared to the non-fluorinated form. Due to the high viscosity of aliphatic ammonium based ILs, addition of an organic solvent to the ionic liquid was investigated and found to be without detriment to the interesting properties of ILs (i.e., nonvolatility, non-flammability, high thermal stability, electrochemical stability). The cycling performance of the mixtures IL–ethylene carbonate was characterized using LiMn2O4 based electrode materials in the voltage range of 3.5–4.3 V.

Thermophysical Properties of Two Ammonium-Based Protic Ionic Liquids

Abstract: Experimental data for density, viscosity, refractive index and surface tension are reported, for the first time, in the temperature range between 288.15 K and 353.15 K and at atmospheric pressure for two protic ionic liquids, namely 2-(dimethylamino)-N,N-dimethylethan-1-ammonium acetate, [N11{2(N11)}H][CH3CO2], and N-ethyl-N,N-dimethylammonium phenylacetate, [N112H][C7H7CO2]. The effect of the anion aromaticity and the cation's aliphatic tails on the studied properties is discussed. From the measured properties temperature dependency the derived properties, such as the isobaric thermal expansion coefficient, the surface entropy and enthalpy, and the critical temperature, were estimated.

Conductometric Studies on Micellization of Cationic Surfactants in the Presence of Glycine

Abstract: Values of the critical micelle concentration (cmc) and degree of counterion dissociation (α) of four cationic surfactants: cetyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC) and benzyldimethylhexadecylammonium chloride (BDHAC) in aqueous–glycine medium (concentration of glycine (Gly) varied from 0 to 0.20 mol·dm−3) were determined through conductometric measurements at 303 K. The effect of temperature on the micellization in the presence of 0.10 mol·dm−3 Gly were studied for the surfactants CTAB, CPC and BDHAC. With respect to the concentration of Gly, a decrease in the cmc was observed for CTAB, CPC and CPB whereas an increase was observed for BDHAC. A regular increase in α was obtained for CPB, CPC and BDHAC with respect to the concentration of Gly whereas values were roughly constant in the case of CTAB. Thermodynamic parameters were computed from the temperature dependence of the cmc values and it was found that the micellization process is exothermic. Compensation of enthalpy and entropy was observed for the micellization of CTAB, CPC and BDHAC in the presence of 0.10 mol·dm−3 Gly.

Volumetric and Acoustic Properties of a DBU (1,8-Diazobicyclo[5.4.0]undec-7-ene) Based Protic Ionic Liquid in Water at T = (293.15 to 328.15) K

Abstract: The protic ionic liquid, 1,8-diazabicyclo[5.4.0]undec-7-en-8-ium trifluroacetate [DBUTFA], has been synthesized and densities of and speeds of sound in (DBUTFA + water) binary mixtures were measured simultaneously using a vibrating-tube digital density and speed of sound analyzer (Anton Paar, DSA 5000 M) at T = (293.15 to 328.15) K, with 5 K interval, and at atmospheric pressure. From the experimental density and speed of sound data, apparent molar volumes, \( V_{\phi } \), and apparent molar isentropic compressibilities, \( K_{S,\phi } \), were determined and further analyzed using Redlich–Mayer type equations to evaluate the corresponding infinite dilution apparent molar volumes, \( V_{2}^{\infty } \), infinite dilution apparent molar isentropic compressibilities, \( K_{S,2}^{\infty } \), and empirical parameters (SV, BV, Sk and Bk). The positive magnitude of the limiting volumetric slopes, SV versus m1/2 for this protic ionic liquid (PIL) in aqueous solutions, suggests that PIL–water interactions are weak.

Phase Equilibria in the Aqueous Ternary System (LiBO 2 + CaB 2 O 4 + H 2 O) at 288.15 and 298.15 K

Abstract: The solubilities and physicochemical properties, including density and pH, in the ternary system (LiBO2 + CaB2O4 + H2O) at (288.15 and 298.15) K were investigated using the isothermal dissolution equilibrium method. According to the experimental results of the ternary system at (288.15 and 298.15) K, the stable phase diagrams and the diagrams of physicochemical properties were plotted versus composition. In the phase diagrams of the ternary system at (288.15 and 298.15) K, there is one invariant point (LiBO2·8H2O + CaB2O4·6H2O), two univariant isotherm dissolution curves, and two crystallization regions corresponding to lithium metaborate octahydrate (LiBO2·8H2O) and calcium metaborate hexahydrate (CaB2O4·6H2O), respectively. This system at both temperatures belongs to hydrate type I classification and neither double salt nor solid solution were found. A comparison of the phase diagrams for the ternary system at (288.15 and 298.15) K shows that the numbers of solid phase and the minerals present are the same; the crystallized area of CaB2O4·6H2O increased at the higher temperature, while that of LiBO2·8H2O decreased. The physicochemical properties (density and pH values) of the ternary system at the two temperatures change regularly with increasing lithium metaborate concentration. The calculated values of density using empirical equations of the ternary system are in good agreement with the experimental values.

A New Pitzer Parameterization for the Binary NaOH–H 2 O and Ternary NaOH–NaCl–H 2 O and NaOH–LiOH–H 2 O Systems up to NaOH Solid Salt Saturation, from 273.15 to 523.15 K and at Saturated Vapor Pressure

Abstract: This paper presents a new set of Pitzer ion interaction model parameters for the binary NaOH–H2O system for concentrations up to over 30 mol·kg−1 and temperatures ranging from 273.15 to 523.15 K. Assuming that the electrolyte is only partially dissociated, the model requires the adjustment of (i) the three classical binary interaction parameters β (0), β (1) and C ϕ , (ii) the equilibrium constant of formation of the aqueous complex NaOH0(aq), and iii) one binary (λ NaOH/NaOH) and one ternary (\( \zeta_{{{\text{NaOH}}/{\text{Na}}^{ + } /{\text{OH}}^{-} }} \)) interaction parameter. This approach, which provides much better results than the approach of treating NaOH as a fully dissociated electrolyte, was chosen to extend the description of the system to high temperatures and high concentrations. The temperature functions of the solubility products of anhydrous NaOH(cr) and five hydrated salts, NaOH·nH2O(cr) (where n = 1, 2, 3.11, 3.5, 4α), were determined. In order to evaluate the quality of the new set of parameters, several tests were run on various properties using various literature data. These include the boiling point elevation in the NaOH–H2O system and the phase diagrams of the two ternary systems NaOH–NaCl–H2O and NaOH–LiOH–H2O. Interaction parameters for the two related binary systems NaCl–H2O and LiOH–H2O were taken from previous studies. To ensure consistency, four new mixing parameters were revised (\( \zeta_{{{\text{Na}}^{ + } /{\text{Cl}}^{-} /{\text{NaOH}}}} \) and \( \varPsi_{{{\text{Cl}}^{-} /{\text{OH}}^{-} /{\text{Na}}^{ + } }} \) for the ternary system NaOH–NaCl–H2O and \( \lambda_{{{\text{Li}}^{ + } /{\text{NaOH}}}} \) and \( \varPsi_{{{\text{OH}}^{ - } /{\text{Na}}^{ + } /{\text{Li}}^{ + } }} \) for the ternary system NaOH–LiOH–H2O). Consistent with Pitzer’s equations, our new set of parameters can be used to satisfactorily describe the quaternary Na+–Li+–Cl−–OH−–H2O system to very high concentrations and temperatures.

Effect of [C n mim][Br] Based Ionic Liquids on the Aggregation Behavior of Tetradecyltrimethylammonium Bromide in Aqueous Medium

Abstract: In order to gain insight into the role of environmentally benign imidazolium based ionic liquids (ILs) to alter the physicochemical properties of single chain cationic surfactants, we have investigated the effect of 1-hexyl-3-methylimidazolium bromide ([C6mim][Br]) and 1-octyl-3-methylimidazolium bromide ([C8mim][Br]) on the aggregation behavior of aqueous tetradecyltrimethylammonium bromide (TTAB). The critical micelle concentration (CMC) of TTAB at different concentrations of ILs was determined through conductance, surface tension, spectral change of a dye by UV–Vis measurement, and the pyrene fluorescence probe measurement techniques at 298.15 K. Decreasing of the CMC of aqueous TTAB with increasing ILs concentration proves the micellization is favorable. The effect of ILs on the properties of TTAB was verified by using NaBr. Surface tension measurements complimented by dynamic light scattering (DLS) data revealed the packing density of TTAB aggregates at different concentrations of ILs. The effective area of TTAB molecules at the air/water interface was calculated by the Gibbs adsorption isotherm and found to decrease up to 0.6 wt% of ILs followed by an increase at higher concentration. DLS data revealed an increase in micellar size of TTAB at higher concentration of IL with decrease in the aggregation number (N agg), determined by the fluorescence quenching method.

Precise Method for Determining the Enthalpy of Vaporization of Concentrated Salt Solutions Using a Bubble Column Evaporator

Abstract: An improved bubble column evaporator (BCE) system was used to determine accurate and precise enthalpy of vaporization (ΔH vap) values for concentrated salt solutions. The method is based on the steady state volumetric energy balance developed in a BCE. The BCE system offers a novel and simple approach for ΔH vap measurements because it only requires measurement of the hydrostatic differential pressure across the column and the temperatures of the steady state column and the inlet gas. In this work an automatic acquisition system was developed in order to study the frequency distribution of ΔH vap values. It was established that vacuum insulation of the bubble column and a data acquisition system enhanced both the accuracy and precision of ΔH vap measurements. In addition, a hygrometer was used to measure vapor pressures of concentrated Li2SO4 and ZnSO4 solutions to determine new ΔH vap values. The results obtained are in better agreement with expected values and indicate the conditions required to enhance evaporative cooling systems and improve thermal desalination. An analysis was also carried out on the effect of salt concentration on ΔH vap and on calculated values of the partial molar enthalpy of dilution (ΔH dil).

Combined Raman Scattering and X-ray Diffraction Study of Phase Transition of the Ionic Liquid [BMIM][TFSI] Under High Pressure

Abstract: In situ solidification of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]) from melt has been investigated by using a diamond anvil cell under pressures up to about 6.0 GPa at room temperature. The results indicate that non-monotonic pressure induced Raman shifts and variation of the full width at half-maximum are suggestive of a phase transition at about 1.8 GPa upon compression, which was further confirmed to be a phase transition from liquid to a superpressurized glass by line broadening measurements of the sharp R (1) ruby fluorescence line and synchrotron X-ray diffraction measurements. The conformational changes of C (1) and C (2) conformers of the [TFSI] anion under high pressure are discussed; the C (2) conformers are predominant under high pressures. In addition, the Raman spectra of [BMIM][TFSI] under different conditions are compared in detail. The results show that the structure of the glassy state at low temperature is different from that of the high pressure state, while the glassy state is mainly composed of C (2) anion conformers, which is similar to the high pressure state.