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The specific conductance (κ) of copper sulfate in binary mixtures (methanol–water) with the alcohol mass fractions of 0%, 20% and 40% at different temperatures of (298.15, 303.15, 308.15 and 313.15) K was measured experimentally. The conductivity data have been analyzed using the Fuoss–Shedlovsky conductivity equation. The molar conductance (Λ M ), the limiting molar conductance (Λ 0 ), the association constants (K A ), the Walden product (Λ 0 η 0 ), and the standard thermodynamic parameters of association (ΔG° A , ΔH° A and ΔS° A ) were calculated and discussed. The results show that, the molar conductance and the limiting molar conductance values were decreased as the relative permittivity of the solvent decreased while, the association constant increased. Also the results show that the values of the molar conductance, the limiting molar conductance and the association constant were increased as the temperature increased indicating that the association process is an endothermic one.

© 2015 Elsevier B.V. The properties of aqueous ionic solutions are determined by strong electrostatic interactions, which are influenced by polarizability and charge transfer interactions. Potential models which include polarizability and charge transfer have been developed for water and single ion properties. Here, the ion-ion interactions are optimized so that the osmotic pressure as a function of concentration is reproduced. Using the optimized potentials, the amount of ion pairing and larger cluster formation is calculated. For NaCl, NaI, and KCl, there is a small amount of pairing, with larger clusters present as well. For KI, there is much more pairing and much larger clusters are observed. The amount of pairing is consistent with the law of matching affinities, with the pairs that show the least pairing also being the most mis-matched in terms of size or solvation free energy. The charge transfered from the anions to water is more than from is transferred from the water to cations, so the water molecules acquire a negative charge, which increases with ion concentration.

A micro-volume spectrofluorimetric coupled ultrasound-assisted ion association dispersive liquid–liquid microextraction (USA-IA-DLLME) procedure for the total determination and speciation of chromium(III & VI) species has been established. This demonstration was based upon the formation of a complex ion associate between halochromate (CrO3Cl−) and rhodamine 6G hydrochloride dye (RG+). At optimal conditions, the method exhibited a three order of magnitude wide linear concentration range (1.0–1000 μg L−1), with detection and quantification limits of 0.57 μg L−1 and 1.9 μg L−1, respectively. Competent cations, anions and oxoanions did not interfere with the chromium(VI) determination. Chromium(III) was also evaluated after its conversion to chromate with H2O2 in alkaline media. The nature of the extractant and the disperser, their volumes and the extraction time were optimized. The fluorescence quenching mechanism of the complex ion associate was discussed. The method was validated by the determination of chromium(VI) in real water (sea and tap water) samples. The results were also compared successfully with those from inductively coupled plasma-optical emission spectrometry (ICP-OES) in terms of the student’s t- and F test data at 95% confidence.

Cleaner and lower-cost recovery and separation of samarium(III) and cobalt(II) from waste SmCo magnets can effectively alleviate supply risks of the strategic metals. Based on this goal, a family of renewable, low-cost, biocompatible, non-toxic fatty acid-based ionic liquids (FAILs), including [N1888][DA], [N1888][LA] and [N1888][PA] were synthesized and developed for the separation of Sm(III)/Co(II) from samarium-cobalt simulated solution. The effect factors, i.e. equilibrium time, FAIL molar concentration, salting-out agent concentration and initial pH of aqueous solution were investigated. The extraction mechanism was proposed to be ion association by slope analysis and FT-IR. Under the optimized extraction conditions, a higher purity CoCl2 (99.5%) product was obtained by a simple extraction-stripping-washing process with the consumption of Na2C2O4 and NH3·H2O. The produced salty wastewater with lower concentration from the process could be recycled. Sm2O3 with a purity of 99% were obtained by roasting the Sm2(C2O4)3 at 800 °C for two hours. The whole process was simple and sustainable, illustrating its potential for industrial applications.

Ionic liquid (IL) based on tetraheptylammonium cooking oil (TC) was used for the first time to recovery rare earth elements (REEs) from leaching liquor of ion-adsorbed-type rare earths ores. Firstly, extraction performances of tetraheptylammonium oleate (TO) and tetraheptylammonium linoleate (TL) type ILs were investigated. It was shown that these ILs had good extraction performances, such as short equilibrium time less than 1 min, good extraction capacity of 0.225 mol/L and high stripping efficiency of 99%. Additionally, REEs extraction occurred in the solutions with high acidity (pH = 0.24) because the cation (C7H15)4N+ of TO and TL could form a strong amine salt with hydrogen ion to decrease acidity of the feed solution. Also, an ion association mechanism of REEs extraction was proposed by FT-IR spectra, 1H NMR investigation and slope analysis method. Secondly, TC was synthesized in water bath by mixing tetraheptylammonium bromide with saponified peanut oil. Then, comparative study of commercial extractants showed that TC had the highest REEs recovery yield of 100% from the leaching liquor. The sustainability, biocompatibility and non-toxicity, as well as simple synthesis route and well extraction performances make these cooking oil based ILs promising for REEs recovery from the leaching liquor.

In the present work it was shown that low lattice energy ammonium salts are not favorable for polymer electrolyte preparation for electrochemical device applications. Polymer blend electrolytes based on chitosan:poly(ethylene oxide) (CS:PEO) incorporated with various amounts of low lattice energy NH4BF4ammonium salt have been prepared using the solution cast technique. Both structural and morphological studies were carried out to understand the phenomenon of ion association. Sharp peaks appeared in X-ray diffraction (XRD) spectra of the samples with high salt concentration. The degree of crystallinity increased from 8.52 to 65.84 as the salt concentration increased up to 40 wt.%. These are correlated to the leakage of the associated anions and cations of the salt to the surface of the polymer. The structural behaviors were further confirmed by morphological study. The morphological results revealed the large-sized protruded salts at high salt concentration. Based on lattice energy of salts, the phenomena of salt leakage were interpreted. Ammonium salts with lattice energy lower than 600 kJ/mol are not preferred for polymer electrolyte preparation due to the significant tendency of ion association among cations and anions. Electrical impedance spectroscopy was used to estimate the conductivity of the samples. It was found that the bulk resistance increased from 1.1 &times, 104 ohm to 0.7 &times, 105 ohm when the salt concentration raised from 20 wt.% to 40 wt.%, respectively, due to the association of cations and anions. The low value of direct current (DC) conductivity (7.93 &times, 10&minus, 7 S/cm) addressed the non-suitability of the electrolytes for electrochemical device applications. The calculated values of the capacitance over the interfaces of electrodes-electrolytes (C2) were found to drop from 1.32 &times, 6 F to 3.13 &times, 7 F with increasing salt concentration. The large values of dielectric constant at low frequencies are correlated to the electrode polarization phenomena while their decrements with rising frequency are attributed to the lag of ion polarization in respect of the fast orientation of the applied alternating current (AC) field. The imaginary part of the electric modulus shows obvious peaks known as conduction relaxation peaks.

Herein, we propose an evanescent-wave fiber optic sensing technique for the anionic dye uranine based on ion association extraction. The sensor was prepared by removing a section of the cladding from a multimode fiber and hydrophobization of the exposed core surface. Uranine was extracted in association along with hexadecyltrimethylammonium (CTA) ion onto the fiber surface and detected via absorption of the evanescent wave generated on the surface of the exposed fiber core. The effect of CTA+ concentration added for ion association was investigated, revealing that the absorbance of uranine increased with increasing CTA+ concentration. A change in the sensor response as a function of the added uranine concentration was clearly observed. The extraction data were analyzed using a distribution equilibrium model and a Freundlich isotherm. The uranine concentration in the evanescent field of the fiber optic was up to 54 times higher than that in the bulk solution, and the limit of detection (3&sigma, ) for uranine was found to be 1.3 nM.

It is urgently needed to develop highly efficient and selective adsorbents for enrichment and separation of Re(VII) from Mo(VI) to obtain metallic rhenium. By tuning cross-link of chitosan, ionic gel capsules (CSN) were prepared, which had a core-shell structure and wrapped N263 (methyl trioctyl ammonium chloride) as an extractant. After being characterized, the CSN capsules were used as a green adsorbent for separation of ReO4− from MoO42−. It was found that the gel yielded good adsorption capacities for Re(VII) in a wide pH range from pH 2 to 12. The adsorption of Re(VII) on the gel followed the Langmuir model, exhibiting a maximum adsorption capacity of 222 mg g−1 for Re. The adsorbent showed good adsorption capacities for Mo(VI) at pH 3.5. Therefore, the enrichment and separation of Re(VII) from Mo(VI) could be easily achieved by using the gel adsorbent in a wide pH range from 4 to 12, showing a separation factor βRe/Mo with values of 103–5 × 104. A mechanism was proposed for the selective adsorption of Re(VII). The extractant N263 wrapped in the capsule core provides excellent extractive adsorption ability for Re(VII) through ion association extraction, generating ion association complex R4N+∙ReO4− in the adsorbent. The gel shell was composed of cross-linked chitosan induced by sodium tripolyphosphate, and functioned as a blocking layer for the adsorption of Mo(VI), being possibly related to a special interaction between Mo and P as observed in the formation of phosphorus molybdenum heteropolyacid and/or the crosslinking with Mo and chitosan. The CSN gel was successfully applied to separate ReO4− from a practical alkaline solution.

In this work, viscosities (η), conductivities (Ʌ) and refractive index (nD) for the ternary systems of 1-octyl-3-methylimidazolium bromide [OMIm]Br ionic liquid in the Ethanol/1-propanol+water mixtures were measured in different mass fractions of alcohol in water (w/w% = wAlcohol/wmixture = 0, 10, 20 and 30%) at T = (298.2, 308.2 and 318.2) K. The viscosity data was analyzed using jones-dole equation to derive the viscosity B-coefficient which indicates the solute-solvent interactions. The temperature dependence of the viscosity was described by fluidity equation. Ion association constants (Ka) and limiting molar conductivities (Ʌ0) of [OMIm]Br were obtained by using Fuoss–Onsager equation based on conductivity measurements. In addition, refractive index (nD) of [OMIm]Br were measured for the binary and ternary water+[OMIm]Br + Ethanol/1-propanol mixtures. The obtained results were compared to the predicted values using the Heller equation. Excess refractive index (nDE) for binary and ternary mixtures and regression parameters of the Redlich–Kister and Cibulka equation were obtained at different temperatures.

The predictive electrolyte model COSMO-RS-ES is refined to improve the description of systems at 25{\deg}C in which strong ion pairing is expected due to a low static permittivity of the liquid phase. Furthermore, the short-range ion energy interaction equations have been modified to better describe the misfit and energy interaction terms between ions and solvent molecules. In addition, the salt solubility database is extended with additional non-aqueous systems containing solvents that have a low (\epsilon_s

Author(s): Crothers, AR; Darling, RM; Kusoglu, A; Radke, CJ; Weber, AZ | Abstract: We present and validate a mathematical model for multicomponent thermodynamic activity in phase-separated cation-exchange membranes (e.g., perfluorinated sulfonic-acid ionomers). The model consists of an expression for the free energy of the membrane and of the surrounding electrolyte solution. A modified Stokes-Robinson ionic solvation framework treats the solution-like non-idealities resulting from hydration, electrostatics, ion association, and physical interactions in bulk solution and in ionomer hydrophilic domains. Inside the membrane, a mechanics-based composite approach accounts for the swelling of the hydrophobic matrix. Treating the membrane microstructure as a disordered system of domains calculates steric exclusion of ions. Electroneutrality guarantees that the charge of mobile ions in the membrane is equal to the charge on polymer groups. Osmotic coefficients for electrolytes from literature parameterize solution-like interactions while mechanical and X-ray scattering characterization gives most membrane-specific parameters. Model predictions compare favorably to measured membrane thermodynamics (i.e., water and ion uptake) in dilute and concentrated binary and ternary salt electrolytes and in water vapor. Interactions between ions in the membrane are similar to those present in bulk electrolytes. Our results reveal that water and ion uptake is dictated by a balance between solution-like energetics and membrane swelling.

Quantifying ion association and collective dynamical processes in organic electrolytes is essential for fundamental property interpretation and optimization for electrochemical applications. The extent of ion correlation depends on both the ion concentration and dielectric strength of the solvent; ions may be largely uncorrelated in sufficiently high-dielectric solvents at low concentration, but properties of concentrated electrolytes are dictated by correlated and collective ion processes. In this work, we utilize molecular dynamics simulations to characterize ion association and collective ion dynamics in organic electrolytes composed of binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM^+][BF^4–] and 1,2-dichloroethane, acetone, acetonitrile, and water solvents. We illustrate different physical regimes of characteristically distinct ion correlations for the systematic range of electrolyte concentrations and solvent dielectric strengths. Dilute electrolytes composed of low-dielectric solvents exhibit significant counterion correlation in the form of ion pairing and clustering driven by both weak screening and relatively low solvation energies. This regime is characterized by enhanced ion coordination numbers and near equality of cation and anion diffusion coefficients, despite the significantly different ion sizes. In contrast, ion correlation in highly concentrated electrolytes is dominated by the anti-correlated motion of both like-charge and opposite-charge ions, approaching neat ionic liquid behavior. We show that the cross-over of these correlation regimes is clearly illuminated by quantifying the fractional self and distinct contributions to the net ionic conductivity. For organic electrolytes composed of low-dielectric solvents, we conclude that significant ion correlation exists at all concentrations but the nature of the correlation changes markedly from the dilute electrolyte to the pure ionic liquid limit.

Background: The application of an ion selective technique for the determination of analyte concentrations is considered one of the most economical techniques for quality control purposes. Objective: To elaborate and investigate the construction and general performance characteristics of potentiometric PVC membrane sensors for venlafaxine cation (Ven+). Method: The sensors are based on the use of the ion association complexes of the venlafaxine cation with phosphotungstate (PT) and silicotungstate (ST) counter anions as ion exchange sites in the plasticized PVC matrix. They are characterized by potentiometric and conductimetric measurements, performed under various conditions. Results: The electrodes showed a fast (response time around 15 s), stable (life span 45 days) and linear (r2 0.995) response for venlafaxine over the concentration range of 5x10-5 - 1x10-2 M venlafaxine hydrochloride. The solubility product of the ion pair and the formation of the precipitation reaction leading to the ion pair, were determined conductimetrically. The electrodes were found to be very selective, precise (RSD < 1%) and applicable to the potentiometric determination of venlafaxine hydrochloride in pure solutions or in pharmaceutical preparation and in biological fluid (serum), without any interference. Validation of the method shows the suitability of the proposed electrodes for use in the quality assessment of venlafaxine hydrochloride. Conclusion: Using only a pH meter in combination with the selective electrodes, drug substance or drug product could be determined accurately in a few seconds. In addition, the in-house made electrodes were tested to monitor venlafaxine in serum. Acceptable results were achieved using the standard addition technique.

The equilibria of the chelate formation and ion-association in the liquid-liquid extraction system Mo(VI)‒3,5-DNC‒INT‒H 2 O‒CHCl 3 were studied by spectrophotometry. The optimum conditions for the chelate formation and extraction of the ion-associated complex formed between the anionic chelate of Mo(VI)‒3,5-dinitrocatechol (3,5-DNC) and the cation of 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2 H -tetrazolium chloride (INT) were established. The validity of Beer’s law was checked and some analytical characteristics were calculated. The effect of various co-existing ions and reagents on the process of complex formation was investigated. The molar ratio of the components in the ternary ion-associated complex Mo(VI)–3,5-DNC–INT was determined by independent methods. The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized. The following key constants of the processes were calculated: association constant, distribution constant, extraction constant and recovery factor. Based on this, a reaction scheme, a general formula and a structure of the complex were suggested.

Since dyes are available in huge quantities and have the well-established chemistry involved in their synthesis, their use in chemosensing could be continued. In the current study, a new and reversible colorimetric and fluorometric chemosensor based on available triaryl methane dye (brilliant green (BG)) - phosphotungstic acid (PTA) complex has been designed for determination of ascorbate (AscH-1) ion in water/DMSO (90:10v/v, 1.0mmolL-1 HEPES, pH7.0). The "ON-OFF" fluorescence and colorimetric responses of this ion association complex to AscH-1 were based on a displacement mechanism. For the detection of AscH-1, the linear ranges achieved for UV-Vis absorbance and fluorescence experiments were 3.9-62.6μmolL-1 and 1.9-85.4μmolL-1, respectively. The limits of detection for both of them were also calculated to be 0.4 and 0.2μmolL-1. The proposed method was also successfully utilized for rapid recognition of ascorbate in juice samples, human serum, and the formulation of supplement products. Moreover, the proposed chemosensor capability of functioning as INHIBITION-type sensor with PTA and AscH-1 as chemical inputs was indicated by the investigation of the molecular logic behavior of this chemosensor. Eventually, a sequential memory unit displaying "Write-Read-Erase-Read" function could be integrated based on the reversible and reproducible system.

Ion association and dissociation influences the transport properties in polymer electrolytes. The interaction between PMMA/ENR 50 blend and NH4SCN salt was investigated using Fourier Transform Infrared Spectroscopy (FTIR) and also to determine the effect of ion dissociation and association. Deconvolution of spectra band in the SCN− mode of NH4SCN has been carried out to estimate the spectroscopically free form of SCN−. The variation in the number of available free mobile ions has influenced the variation of dielectric constant of polymer electrolyte blends.

When room-temperature ionic liquids (IL) are used as an electrolyte, their transport behaviors are still under heavy debate due to their complicated ion-associations. In this article, we conducted molecular dynamics simulations to study the molecular scale ion associations from the very dilute 1-butyl-3-methylimidazolium iodide/water solution to the pure IL. It revealed that ions are localized in a multicoordinated ion cage structure with nanoseconds in concentrated IL solutions. Dynamics analyses indicate that the transport of this solution can be depicted by the Debye-Hückel model only in dilute IL/water electrolyte. The velocity and rotational correlation functions showed that the lifetime of translational and rotational motions are at the level of picoseconds and nanoseconds, respectively, because of the ion cage effect. The lifetime of ion association demonstrated that the recombination of association ions was prevalent in IL solutions. It means that the dipolar or stable contact ion-pairs model may not be suitable for depicting the IL transport.

In this study, a series of new ionic liquids (ILs) with tropine as cationic nucleus and hexafluorophosphate as anion were synthesized. As two types of functional groups, aliphatic chains and benzyl with different substituents have been linked on the tropine nucleus in order to modulate the physicochemical properties of the ILs. The whole family of ILs was comprehensively identified by FT-IR, NMR and MS. Furthermore, the thermal properties of these ILs were evaluated by different scanning calorimetry (DSC) together with their melting points and enthalpy of fusion. Then the polarities of these tropine-type ILs were investigated and discussed. Resultantly, it was proved that their polarity was comparable with that of short-chain alcohols. Moreover, the Hammett function values of these involved ILs were determined to describe their Bronsted acidities. Finally, molar conductivities ( Λ ) of the tropine-type ILs in dilute solutions at 298.15 K were determined. The data were correlated with the Arrhenius–Ostwald model to obtain limiting molar conductivities ( Λ ∞ ) and association constants ( K A ). The influences of the branch chain of ILs on the ion transfer and association were also discussed. It was found that the size of cation was the main factor influencing the ion transfer. And the weak ion association of tropine-type ILs in water was proved by K A , which was less than 7 L·mol − 1 .

Liquid–liquid phase separation was observed in aqueous MgSO4 solutions with excess H2SO4 at elevated temperatures; the aqueous MgSO4/H2SO4 solutions separated into MgSO4-rich droplets (fluid F1) and a MgSO4-poor phase (fluid F2) during heating. The phase separation temperature increases with SO4(2–)/Mg2+ ratio at a constant MgSO4 concentration. At a MgSO4/H2SO4 ratio of 5, the liquid–liquid phase separation temperature decreases with an increase in MgSO4 concentration up to ∼1.0 mol/kg and then increases at higher concentrations, showing a typical macroscale property of polymer solutions with a lower critical solution temperature (LCST) of ∼271.4 °C. In situ Raman spectroscopic analyses show that the MgSO4 concentration in fluid F1 increases with an increase in temperature, whereas that in fluid F2 decreases with an increase in temperature. In addition, HSO4(–), which does not readily form complexes with Mg(2+), tends to accumulate in fluid F2. Analyses of the v1(SO4(2–)) bands confirmed the presence of four-sulfate species of unassociated SO4(2–) (∼980 cm(–1)), contact ion pairs (CIPs; ∼995 cm(–1)), and triple ion pairs (TIPs; ∼1005 cm(–1)) in aqueous solution, and more complex ion pair chain structure (∼1020 cm(–1)) in fluid F1. Comparison of the sulfate species in fluids F1 and F2 at 280 °C suggests that SO4(2–) in fluid F2 is less associated with Mg(2+). On the basis of in situ visual and Raman spectroscopic observations, we suggest that the formation of the complex Mg(2+)–SO4(2–) ion association might be responsible for the liquid–liquid phase separation. In addition, Raman spectroscopic analyses of the OH stretching bands indicate that the hydrogen bonding in fluid F1 is stronger than that in fluid F2, which might be ascribed to the increasing probability of collision of H2O with Mg(2+) and SO4(2–) in fluid F1.

We extend the SAFT-VR+DE equation of state to describe 19 aqueous electrolyte solutions with both a fully dissociated and a partially dissociated model. The approach is found to predict thermodynamic properties such as the osmotic coefficient, water activity coefficient, and solution density, across different salt concentrations at room temperature and pressure in good agreement with experiment using only one or two fitted parameters. At higher temperatures and pressures, without any additional fitting, the theory is found to be in qualitative agreement with experimental mean ionic activities and osmotic coefficients. The behavior of the dielectric constant as a function of salt concentration is also reported for the first time using a statistical associating fluid theory (SAFT)-based equation of state. At high salt concentrations, the stronger electrostatic interactions between the ionic species due to the dielectric decrement, is captured through the inclusion of ion association. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3053–3072, 2015

The binary and ternary aqueous solutions of sodium phosphate or/and sulfate were studied using the hygrometric method from dilution to saturation in the temperature range from (298.15 to 353.15) K. The hygrometric measurements of the binary systems were combined with reference pure water, Na3PO4(s), and Na2SO4(s) solubility data to construct a chemical model that calculates solute and solvent activities from dilute to saturated solution concentration (for (Na3PO4(s)) up to mmax = 9.00 mol·kg–1 at 353.15 K; and up to mmax(Na2SO4(s)) = 3.40 mol·kg–1at 313.15 K). The constructed model was also used to calculate thermodynamic solubility product (K°sp) of Na3PO4(s) and Na2SO4(s) in the temperature range (298.15 to 353.15) K. The excess Gibbs energies of Na3PO4(aq) and Na2SO4(aq) were evaluated at various temperatures. The results for these aqueous solutions were influenced by the effect of hydration shell, with ion association or formation ion pairing. The anion solute PO4 or SO4 influences the hydration in an...

A selective separation and recycling system for metal ions was developed by homogeneous liquid-liquid extraction (HoLLE) using a fluorosurfactant. Sixty-two different elemental ions (e.g., Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, In, Ir, La, Lu, Mg, Mn, Mo, Nb, Nd, Ni, Os, P, Pb, Pd, Pr, Pt, Re, Rh, Ru, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Te, Ti, Tl, Tm, V, W, Y, Yb, Zn, and Zr) were examined. By changing pH from a neutral or alkaline solution (pH ≥ 6.5) to that of an acidic solution (pH &lt, 4.0), gallium, zirconium, palladium, silver, platinum, and rare earth elements were extracted at &gt, 90% efficiency into a sedimented Zonyl FSA® (CF3(CF2)n(CH2)2S(CH2)2COOH, n = 6–8) liquid phase. Moreover, all rare earth elements were obtained with superior extraction and stripping percentages. In the recycling of rare earth elements, the sedimented phase was maintained using a filter along with a mixed solution of THF and 1 M sodium hydroxide aqueous solution. The Zonyl FSA® was filtrated and the rare earth elements were recovered on the filter as a hydroxide. Furthermore, the filtrated Zonyl FSA was reusable by conditioning the subject pH.

The complex formation and solvent extraction were studied in a system containing iron(II), 4- nitrocatechol (4NC), 2,3,5-triphenyl-2H-tetrazolium chloride (TTC), water, and chloroform. Under the optimum conditions, the extracted complex has a composition of 1 : 1 : 2 (Fe-4NC-TTC) and could be represented with the formula (TT+)2[FeII(4NC2–)(OH)2]. Theoretical calculations were performed at the HF/3- 21G* level in order to elucidate the geometric structure of the complex and electron distribution according to the crystal field theory. The results showed that the most stable configuration is tetrahedral low-spin structure. Some equilibrium constants (association, distribution, and extraction) and characteristics (absorption maximum, molar absorption coefficient, recovery factor, Beer’s law limits, etc.) concerning the application potential of the studied extraction-chromogenic system were determined.

Saline aqueous solutions at elevated pressures and temperatures play an important role in processes such as supercritical water oxidation (SCWO) and supercritical water gasification (SCWG), as well as in natural geochemical processes in Earth and planetary interiors. Some solutions exhibit a negative temperature coefficient of solubility at high temperatures, thereby leading to salt precipitation with increasing temperature. Using modulated FT-IR Raman spectroscopy and classical molecular dynamics simulations (MD), we studied the solute speciation in solutions of 10 wt % Na2SO4, at conditions close to the saturation limit. Our experiments reveal that ion pairing and cluster formation are favored as solid saturation is approached, and ionic clusters form prior to the precipitation of solid sulfate. The proportion of such clusters increases as the phase boundary is approached either by decreasing pressure or by increasing temperature in the vicinity of the three-phase (vapor-liquid-solid) curve.

A potentiometric carbon paste sensor was fabricated for determination of clarithromycin based on incorporation of the ion association complex of the clarithromycin-phosphotungstate. The proposed sensor exhibited a Nernstian slope of 59.2±0.3 mV per decade for clarithromycin over a wide concentration range of 7.4×10−7 to 1.5×10−3 M, with a low detection limit of 5.0×10−7 M. The proposed sensor manifested advantages of very fast response, long life time and, most importantly, excellent selectivity for clarithromycin relative to a wide variety of common foreign inorganic cation, and also biological species. The sensor was successfully applied to determine clarithromycin in clarithromycin tablet, blood serum and urine samples. The inclusion complex formation between β-cyclodextrin and clarithromycin was studied by the proposed sensor. The influence of the temperature on the response of the sensor was investigated and the temperature coefficient of the sensor was calculated.

The enthalpies of dissolution of [C4mim]OTf, [C4mim]NTf2, and [C4mpy]NTf2 ionic liquids in isopropanol and isopropanol-water mixtures of three compositions are measured with an isothermal calorimeter at 298.15 K. The enthalpies of dilution of [C4mim]OTf solutions in an isopropanol-water mixture containing 50.0 mol % of alcohol are also determined. Enthalpies and constants of ion association are estimated and the standard enthalpies of dissolution are found for [C4mim]OTf, [C4mim]NTf2, and [C4mpy]NTf2 in isopropanol and its mixtures with water.

In this work, ion association characteristics in MgCl2 and CaCl2 aqueous solutions have been investigated using density functional theory (DFT) and molecular dynamics (MD) simulation at various temperatures and pressures. Results all indicate that the ion association is more obvious in MgCl2 solution than in CaCl2 solution, due to the hydration characteristics of Mg2+ and Ca2+. Although ion association can occur in concentrated MgCl2 solution, contact ion pair (CIP) structures and solvent-shared ion pair (SSIP) with single Cl− dissociated (SSIP/s) ([MgCl(H2O)6Cl]0) are quite unstable. CIP and SSIP/s conformers are almost iso-energetic even in CaCl2 solution, and the lifetime of CIP conformer is much longer than that of SSIP/s conformer in concentrated CaCl2 solution. However, the possibility of CIP conformer found in concentrated CaCl2 solution is obviously lower than its SSIP/s isomers. MD simulations exhibit that ion association characteristics do not change as pressure ranges from 0.5 to 20.0 bar in Mg...

A novel, sensitive, and rapid UV spectrophotometric and colorimetric method was developed for estimation of etizolam (ETZ) in bulk and tablet. The UV spectrophotometric method (method I) is based on quantitative estimation of ETZ using 0.1N NaOH as the solvent which exhibits maximal absorption at 378 nm. Colorimetric methods (method II and III) were based on the formation of color complex in association with ions between basic nitrogen of the drug with methyl orange (MO) and bromocresol green (BCG) in acidic medium. The formed color complexes were quantitatively extracted with chloroform and measured at 509 nm for Drug–MO complex and at 442 nm for Drug–BCG complex, respectively. Beer's law was obeyed over the linear ranges 2–16 µg/ml (method I), 5–45 µg/ml (method II), and 2–20 µg/ml (method III). The correlation coefficient (r2) for ETZ was 0.999, 0.997, and 0.998 for method I, II, and III, respectively. All methods were successfully applied for the assay of the drug in tablet. The % purity was found to ...

Ionic equilibria in the LiBF4-dimethyl sulfoxide (DMSO) system were studied by Raman spectroscopy at 50°C at salt concentrations of 0.05–0.25 mole fractions. The spectral signals of hydrogen bonds between the DMSO molecules and the fluoroborate ions were found. The concentrations of the monomer and dimer DMSO molecules and DMSO molecules in the solvation sphere of the lithium cation; free solvent molecules and those in the solvation sphere of the fluoroborate ion; free anions, ion pairs separated by the solvent, and contact ion pairs were determined.

A detailed investigation of the dilute solutions of several imidazolium-based ([BMIM][Br], [EMIM][BF 4 ], [BMIM][BF 4 ], [HexMIM][BF 4 ], [BMIM][Tf]) and pyridinium-based ([BMP][BF 4 ]) ionic liquids, and two tetraalkylammonium salts (Bu 4 NBr and Bu 4 NBPh 4 ) in methanol was carried out between 278.15 and 328.15 K. The limiting molar and ionic association constants were derived using the Lee–Wheaton equation. The limiting molar conductivity for room-temperature ionic liquids with common anion ([BF 4 ] − ) is found to obey the Stokes' law: Λ 0 increases as the cation size decreases. Ionic association in all studied systems does not show definite correlation with cation structure, while it strongly depends on anion size and structure. Ion association constants are discussed and the role of non-Coulombic forces is demonstrated with the help of short-range square-mound potential. Performed data analysis indicates the formation of contact ion pair of similar structure in studied solutions of ionic liquids, with anion coordinated by imidazole or pyridine ring. The formation of H-bonding between bromide-anion and hydroxy-group of methanol was observed.

Densities, speeds of sound and molar conductivities of acetaminophen in 0.1, 0.2, 0.3 and 0.4 mol.kg − 1 aqueous solution of ionic liquid, 1-hexyl-3-methylimidazolium bromide ([HMIm]Br), against the molality of acetaminophen have been measured at T = (293.15 to 308.15) K. Using the density and speed of sound data, standard partial molar volume ( V ϕ 0 ) and partial molar isentropic compressibility ( K φ , s 0 ) have been calculated. These parameters have been used to calculation transfer volume and transfer compressibility for acetaminophen from water to aqueous ionic liquid solution. The transfer quantities are positive and increase with increasing molality of the ionic liquid and decrease with temperature which indicate the dominance of ion or hydrophilic–hydrophilic interactions between [HMIm]Br and acetaminophen and dehydration effect of ionic liquid on the acetaminophen solutions. To confirm the above results, the limiting molar conductivities ( Λ 0 ) and ion association constants ( K a ), for [HMIm]Br in aqueous acetaminophen solutions have been estimated. The association constants were also used to obtain the thermodynamic functions of ion association process of the ionic liquid.

Variable temperature ionic conductivity, viscosity and 1H NMR spin-lattice relaxation times, linewidths and chemical shifts measurements were determined for various concentrations of aqueous ammonium metavanadate (NH4VO3) and vanadyl sulfate (VOSO4) over the temperature range of 20–100 °C. Concentration ranges of 0.05–2 M and 0.05–0.2 M were investigated for VOSO4 and NH4VO3 respectively in 2 M H2SO4. Results show ion and proton transport processes that are mediated strongly by increasing solution viscosity, especially in the case of VOSO4. Activation energies calculated from ionic conductivity and solution viscosity show greater energy being needed for translational ion dynamics with increasing concentration for both solutions. Additionally, data suggest that with greater metal ion concentration ion association is more prevalent for the vanadyl ion. The differences between the transport capabilities of the two solution are discussed in terms of the 1H NMR, ionic conductivity and viscosity data.

By means of Raman spectroscopy coupled with density functional theory (DFT) calculations and perturbation correlation moving window two-dimensional correlation spectroscopy intermolecular interactions were assessed in mixtures of ionic liquid (IL) 1-n-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) with polar aprotic solvent γ-butyrolactone (γ-BL) over the entire range of compositions. The symmetrical P―F stretching vibration of the IL anion was found to be insensitive to the changes in mixture concentration in contrast to the CO stretching vibration of the γ-BL and the imidazolium ring C―H stretching vibrations of the IL cation. Each of these vibrational profiles was decomposed in various spectral contributions, and their number was rationalized by the results of quantum-chemical calculations and/or previous controversial published data. Progressive redshift of the ring C―H stretching wavenumbers was referred to pronounced solvation of the cation at the imidazolium ring site accompanied with H-bond formation. This was especially pronounced at IL mole fraction less than 0.18. Complicated variations in the intensities of the individual contributions of the CO profile were treated as a manifestation of the changing with concentration pattern of the intermolecular interactions. The self-association of γ-BL molecules and distinct cation solvation as dominant intermolecular interactions at low IL content are replaced with weaker cation solvation and ion association at high concentrations of IL. Possible representative molecular structures were proposed on the basis of DFT calculations. Copyright © 2015 John Wiley & Sons, Ltd.

A group of new asymmetric branched alkyl sulfoxides was synthesized and applied in palladium(II) extraction for the first time. According to the experimental data, the concentration of hydrochloric acid in aqueous phase greatly influenced Pd(II) extraction, which could be interpreted by different mechanisms (ligand substitution mechanism at low acidity and ion association mechanism at high acidity). In regard to structure effect, the steric hindrance of branched alkyl showed remarkable influence on the extraction performance of sulfoxides. On the basis of thermodynamic analysis, it was demonstrated that higher temperature exerted positive influence on the Pd(II) extraction reaction. As for the separation of Pd(II) and Pt(IV), low concentration of hydrochloric acid was considered to be appropriate for highly effective separation. Furthermore, ammonia solution was proven to be an efficient stripping agent for palladium recovery from organic phase.

Royal Society of Chemistry, A new micellar-mediated, cloud-point extraction (CPE) method has been developed for the quantification of trace levels of fluoride by means of spectrophotometry. The method is based on the selective ion association of stable anionic complexes, Sn(OH)F2- or Sn(OH)F32- of fluoride with Sn(ii) in presence of cationic dye (Nile blue A) at pH 5.0, and its extraction to the micellar-rich phase of nonionic surfactant polyoxyethylene (7.5) nonylphenyl ether (PONPE 7.5) as the extracting agent. Afterwards, the ternary complex formed was spectrophotometrically detected at 638 nm after preconcentration with CPE. Under optimized conditions, the calibration curves were rectilinear in the ranges of 5-25 and 25-360 ?g L-1 in the linear region with changing sensitivity. The limits of detection and quantification (LOD and LOQ) (3?blank/m and 10?blank/m) was 1.45 and 4.83 ?g L-1, respectively, and the precision (as RSD) for determination of 15, 75, and 150 ?g L-1 of fluoride was in the range of 2.35-4.65%. The validity of the method was checked through recovery experiments, independent analysis by potentiometry and analysis of the standard reference material SRM 2695. The developed method was successfully applied to the accurate, sensitive and reliable quantification of total acid hydrolyzed fluoride present in selected beverage and food samples. © 2015 The Royal Society of Chemistry., Altunay, N.; University of Cumhuriyet, Faculty of Sciences, Department of ChemistryTurkey

The formation and liquid-liquid extraction of ion-association complexes between Co(II)-4-(2-Pyridylazo)resorcinol (PAR) anionic chelates and cations of three ditetrazolium chlorides were studied: Blue Tetrazolium chloride (BTC), Neotetrazolium chloride (NTC) and Nitro Blue Tetrazolium chloride (NBT). The optimum conditions for the formation and solvent extraction of the ion-association comlpex chelates were determined. It has been found that in the systems of Co(II)-PAR-DTS, the reactants are reacted in molar ratios 1:2:1 and the general formula of complexes was suggested. The extraction equilibria were investigated and quantitatively characterized by the equilibrium constants and the recovery factors. The analytical characteristics of the complexes were calculated.

Solid-state polymer electrolytes, as an alternative to traditional liquid electrolytes, have been intensively investigated for energy conversion and storage devices. The transport rate of single ions is the key to their high performance. For application in emerging sodium batteries, we have developed three dual-cation polymeric ionomers, which contain bulky tetraalkylammonium ions in addition to the sodium ion. The sizes and relative contents of the ammonium ions vary relative to the sodium ion contents. Comparative studies of ion dynamics, thermal properties, phase behaviours and ionic conductivities were carried out, taking advantage of various spectroscopic and thermal chemistry methods. The ion conductivities of the ionomers are greatly enhanced by the introduction of bulky counterions, as a result of the additional free volume and decreased sodium ion association. Raman spectroscopy and thermal analysis as well as the solid-state nuclear magnetic resonance studies are used to probe the conductivity behaviour.

Newly recorded Raman spectra of aqueous sulfuric acid provide scattering shifts of very high sensitivity hence signal-to-noise ratios, at a broad concentration range, up to 17 M. I interpret the spectra as (a) providing no evidence for incomplete H2SO4 ionization at low concentration, (b) reflecting only one dissociation event below ∼5 M, (c) indicating a gradual ion association at ∼5–12.5 M, and (d) exhibiting further structural changes of the sulfate above 12.5 M. The analysis of the Raman shifts supports the postulated presence in solution of the para-bisulfate anion HSO53− as a sole sulfate ion up to ∼5 M, as concluded before (D. Fraenkel, J. Phys. Chem. B, 2012, 116, 11662; D. Fraenkel, J. Phys. Chem. B, 2012, 116, 11678; D. Fraenkel, J. Chem. Thermodyn., 2014, 78, 215), an ion association producing para-sulfuric acid, H4SO5 between 5 and 12.5 M, and a dehydration of H4SO5 to H2SO4 above 12.5 M. These conclusions are rationalized and corroborated by (1) a correlation of the Raman spectra with well-known physicochemical properties of aqueous sulfuric acid, and (2) structural analogies between the proposed para-sulfates and related compounds and anions.

Fabrication of the PVC membrane sensor incorporating clopidogrel-tetraido mercurate as an electro active material for the determination of clopidogrel bisulphate is demonstrated. Sensor matrix having a composition of PVC 32%, ion association 2.5% and Di-n-butyl phthalate 56.5 % showed best nernstian behavior in the concentration range 1×10−2 −1×10−7 M with a lower detection limit of 2.9 × 10−8 M. Working pH range and response time was found to be 1.8–4.0 and 5s respectively. The sensor was fruitfully utilized for the quantification of clopidogrel from Clopilet tablets. Comparative studies on the various parameters that depend on the performance characteristics of the present sensor with that of the literature reports were also included.

International audience; We performed molecular dynamics simulations of carboxylate/methylated ammonium ion pairs solvated in bulk water and of carboxylate/methylated ammonium salt solutions at ambient conditions using an ab initio-based polarizable force field whose parameters are assigned to reproduce only high end quantum computations, at the Møller-Plesset second-order perturbation theory/complete basis set limit level, regarding single ions and ion pairs as isolated and micro-hydrated in gas phase. Our results agree with the available experimental results regarding carboxylate/ammonium salt solutions. For instance, our force field approach predicts the percentage of acetate associated with ammonium ions in CH3COO−/CH3NH3+ solutions at the 0.2–0.8M concentration scale to range from 14% to 35%, in line with the estimates computed from the experimental ion association constant in liquid water. Moreover our simulations predict the number of water molecules released from the ion first hydration shell to the bulk upon ion association to be about 2.0 ± 0.6 molecules for acetate/protonated amine ion pairs, 3.1 ± 1.5 molecules for the HCOO−/NH4+ pair and 3.3 ± 1.2 molecules for the CH3COO−/(CH3)4N+ pair. For protonated amine-based ion pairs, these values are in line with experiment for alkali/halide pairs solvated in bulk water. All these results demonstrate the promising feature of ab initio-based force fields, i.e., their capacity in accurately modeling chemical systems that cannot be readily investigated using available experimental techniques.

Giant charge reversal has been identified for the first time by Monte Carlo simulation for a discretely charged surface in contact with a trivalent electrolyte solution. It takes place regardless of the surface charge density under study and the monovalent salt. In stark contrast to earlier predictions based on the 2-dimensional Wigner crystal model to describe strong correlation of counterions at the macroion surface, we find that giant charge reversal reflects an intricate interplay of ionic volume effects, electrostatic correlations, surface charge heterogeneity, and the dielectric response of the confined fluids. While the novel phenomenon is yet to be confirmed with experiment, the simulation results appear in excellent agreement with a wide range of existing observations in the subregime of charge inversion. Our findings may have far-reaching implications to understanding complex electrochemical phenomena entailing ionic fluids under dielectric confinements.

Chitosan (CS) films doped with sodium triflate (NaTf) were prepared by the solution cast technique. The structural and morphological behaviors of the samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD patterns were deconvoluted to estimate the degree of crystallinity of the samples. The SEM micrograph showed the crystalline structure of the sample contained 50 wt % of NaTf salt. The disappearance of broad peaks of chitosan at 2θ ≈ 21° and 2θ ≈ 32° confirmed the occurrence of ion association at 50 wt % of NaTf salt. In impedance plots, a low frequency spike region and a high frequency semicircle, were distinguishable for low salt concentrations. The highest ambient temperature direct current (DC) electrical conductivity obtained for CS:NaTf was found to be 2.41 × 10−4 S/cm for the sample containing 40 wt % of NaTf salt. The role of lattice energy of salts on DC ionic conductivity was also discussed. The temperature dependence of DC conductivity was found to follow the well-known Arrhenius relationship. From the alternating current (AC) conductivity spectra, three distinct regions were recognized for the samples with NaTf salt concentration ranging from 10 wt % to 30 wt %. The plateau region of AC spectra was used to estimate the DC conductivity.