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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.

In recent years, Schiff bases and their metal complexes in the presence of ionic liquids (ILs) have been used in synthesis of various chemical compounds. To better understanding of ionic liquid influence on these processes, it is required to obtain information about the ion association behavior of the ionic liquids. Therefore, in this work, the molar conductivities of the ILs [RMIm]X (R= propyl, pentyl, and hexyl; X= Br − and Cl − ) in different concentrations of N,N′- bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base + acetonitrile solutions were determined at 298.15 K. The obtained conductivity data were analyzed by low concentration Chemical Model (lcCM) conductivity equation to calculate the limiting molar conductivities (Λ 0 ) and ion association constants ( K A ). The results show that BPIE, alkyl chain length of cation, and anion type have effect on the ionic association process of the ILs. The Λ 0 and K A values decrease as the Schiff base concentration, alkyl chain length of cation, and anion size increase in the solution. The association constants were also used to calculate the standard Gibbs energy (Δ G 0 A ) of ion-pairing association. The resulted Δ G 0 A values are negative and become more negative as the alkyl chain length of the cation and the size of anion increase. The large negative values of the standard Gibbs energy obtained for [HMIm]Br indicates the more spontaneity and the more feasibility of the association process for this ionic liquid.

Elution and solvation processes in liquid chromatography may be controlled by temperature changes. In the case of solvent adsorption, the temperature influences the amount of adsorbed solvent as well as the enthalpy and entropy of the solvation process. In this work, the thermodynamic parameters of organic solvents used as organic modifiers in the reversed-phase high-performance liquid chromatography elution process were determined. The changes of enthalpy and entropy in a series of chemically bonded stationary phases were measured to determine the effects of the temperature and surface coverage density of octadecyl ligands on the thermodynamic parameters of the solvation. For both the enthalpy and entropy a parabolic trend was observed with the minimum for medium surface coverage. The correlation of solvent adsorption values with the enthalpy of solvation was also investigated. The highest influence of the temperature on solvation process was observed for stationary phases with high surface coverage.

Surface active agents (SAA) with negative charge of polar group are named as anionic compounds. They are the main constituent of most products containing synthetic surfactants. Anionic surfactants after use are passed into sewage-treatment plants, where they are partially degraded and adsorbed to sewage sludge. Therefore, it is important to investigate the environmental fate of those classes of compounds in more details. A sensitive, selective and inexpensive method for the determination of anionic surfactants in waste water of sewage has been developed. This research involves determination the concentration of anionic surfactants sodium dodecyl sulphate (SDS) with use appropriated analytical techniques in environmental samples. The official methodology for determination of anionic surfactant (AS) in liquid samples is based on the ion-pair reaction of these analysts’ compounds with crystal violet (CV) and an extraction with organic solvent benzene. In an organic solvent benzene anionic surfactant SDS and a cationic dye CV forms an ion association complex. This ion associate exhibits an absorption maximum wave length (λ max) at 560 nm. The method proposed has been found much easier, accurate and rapid, and there is no use of any toxic chemicals.

The ion-association equilibrium of the dipicrylaminate ion (DPA(-)) was investigated in an aqueous solution with alkali metal ions and with its 18-crown-6 ether complexes as pairing cations by capillary zone electrophoresis (CZE). Although DPA(-) is precipitable with the pairing cations of K(+) and Cs(+) in a homogenous aqueous solution, a low concentration of DPA(-) below its solubility suppressed the formation of the precipitates, and DPA(-) was detected as a usual CZE signal. Changes in the electrophoretic mobility of DPA(-) was analyzed for its ion-association equilibrium. The ion association constants determined were almost comparable among alkali metal ions, while the ion association constants were meaningfully large with a hydrophobic 18-crown-6 ether complex of K(+). The CZE separation was also proved to be useful for the equilibrium analysis under precipitating conditions. It was suggested that the precipitable property of DPA(-) with K(+) and Cs(+) could not be attributed to the ion-association process in an aqueous solution, but to the condensation process concerning the intermolecular CH···O bond in the precipitate crystals, as reported.

The equilibrium constants of formation of inner- and outer-sphere cation-anion complexes (ion pairs) in aqueous solutions of different metal acetates in a wide temperature range have been calculated by integrating the density function of distribution of ligands around the cation. The standard Gibbs energies, enthalpies, and entropies of formation of 1: 1 complexes have been calculated. It has been shown that, in all solutions under consideration, contact and solvent-separated ion pairs coexist. A conclusion has been drawn that the temperature dependence of ion association constants is mainly determined by the temperature dependence of the water dielectric constant.

This work develops an empirical model to evaluate the dielectric constant of single or multi-solvents containing multiple ions, using only one adjustable parameter per ion. Correlations are performed for 35 salts in water, 9 in methanol, and 3 in ethanol. The dielectric constant of 9 two-solvent solutions (containing water, methanol, ethanol, 1-propanol, 2-propanol, or acetone) is predicted. In addition, predictions of the dielectric constant of a mixture containing water, methanol, and NaCl are presented. Besides the specific parameter for each ion, a general parameter for cations and another for anions, specific to the each solvent, are obtained. They are recommended for calculating the dielectric constant in solutions whose experimental data are unavailable in the literature.

A simple and highly sensitive method developed for preconcentration and spectrophotometric determination of ultra trace amounts of azide ion (N3−) in water and biological samples using dispersive liquid-liquid microextraction (DLLME) technique. The method is based on ion association formation of azide ion with malachite green and extraction of the ion pairing product using DLLME technique. Some important parameters, such as reaction conditions and the kind and volume of extraction solvent and disperser solvent were studied and optimized. The calibration curve was linear in the range of 0.5–50 μg/L of azide ion. Also, the enrichment factor and extraction recovery obtained were 24.7 and 98.7%, respectively. The method was applied to the determination of azide ion in water and biological samples.

Data on water activity in solutions of a series of 3 : 1 and 1 : 3 electrolytes [AlCl3, Al(NO3)3, LaCl3, La(NO3)3, H3PO4, NaH2PO4] have been generalized in the frame of solvation excesses concept. Solvation excess reflects the distribution of the selected structural elements (ions or solvent particles) in the solution. The computed values have demonstrated the opposite contributions of ion association and hydration of ions and ion associates. Solvation excess concept allows determination of water molecules fraction constituting the excess at ions and their associates. The comparison of results obtained with different choice of model structural units has shown the electrolyte concentration ranges of validity of the respective models.

There is overwhelming evidence that ions are present near the vapor-liquid interface of aqueous salt solutions. Charged groups can also be driven to interfaces by attaching them to hydrophobic moieties. Despite their importance in many self-assembly phenomena, how ion-ion interactions are affected by interfaces is not understood. We use molecular simulations to show that the effective forces between small ions change character dramatically near the water vapor-liquid interface. Specifically, the water-mediated attraction between oppositely charged ions is enhanced relative to that in bulk water. Further, the repulsion between like-charged ions is weaker than that expected from a continuum dielectric description and can even become attractive as the ions are drawn to the vapor side. We show that thermodynamics of ion association are governed by a delicate balance of ion hydration, interfacial tension, and restriction of capillary fluctuations at the interface, leading to nonintuitive phenomena, such as water-mediated like charge attraction. "Sticky" electrostatic interactions may have important consequences on biomolecular structure, assembly, and aggregation at soft liquid interfaces. We demonstrate this by studying an interfacially active model peptide that changes its structure from α-helical to a hairpin-turn-like one in response to charging of its ends.

The electrical conductances of the solutions of ammonium thiocyanate (NH4SCN), and potassium thiocyanate (KSCN) in 2-methoxyethanol + water mixed solvent media containing 0.25, 0.48, and 0.72 mole fractions of 2-methoxyethanol (x1) have been reported at (298.15, 308.15, 313.15, 318.15, and 323.15) K. Analyses of the conductance data have been made on the basis of the 1978 Fuoss conductance-concentration equation yielding the limiting molar conductance (Λ0), the association constant (KA) and the distance of closest approach of ions (R). These two electrolytes are found to be very weakly associated in the 2-methoxyethanol + water mixed solvent medium containing 0.25 mole fraction of 2-methoxyethanol, whereas these are found be moderately associated in the media containing 0.48, and 0.72 mole fractions of 2-methoxyethanol within the temperature range (298.15 to 323.15) K. The limiting molar conductances and the association constants of these electrolytes are found to increase with temperature. The results indicate a changing solvodynamic size of the constituting ions with the composition of the media. The solvation of ions is weakened as soon as the ion-pair is formed due to the release of solvent molecules from the ionic solvation sheaths. Noncoulombic interactions are found to play an important role in the ion-association processes for the present system.

The ozone in an air sample was trapped by H3BO3-LK solution to produce iodine (I2) that interacted with excess I– to form I3–. In pH 4.0 acetate buffer solutions, the I3– reacted with acridine red to form acridine red–I3 ion association particles that resulted in the fluorescence peak decreased at 553 nm. The decreased value ΔF553 nm is linear to the O3 concentration in the range 0.08–53.3 × 10–6 mol/L, with a detection limit of 4 × 10–8 mol/L. This fluorescence method was used to determine ozone in air samples, and the results were in agreement with that of indigo carmine spectrophotometry. Copyright © 2014 John Wiley & Sons, Ltd.

The effects of alkalis on the dechlorination of chlorinated organic substances were systematically studied with molecular dynamics (MD) simulation and experiment method. The association interaction of alkali appears in the SCW solution, which affects the dechlorination reaction performance. The ion association interactions of sodium hydroxide and potassium hydroxide in the supercritical water (SCW) were investigated by analyzing Radical Distribution Function in a temperature range of 623.15–823.15 K and density range of 0.1–0.4 g/cm3. The simulation results indicated that Na+, K+ and OH− associated directly, which is bad for the dechlorination of o-chlorophenol. Meanwhile, the ion association interaction decreased with density, but increased with temperature. The effects of sodium hydroxide and potassium hydroxide on the dechlorination of o-chlorophenol were compared. The results showed that the addition of alkalis accelerated the dechlorination of o-chlorophenol, and the effect of potassium hydroxide was better than that of sodium hydroxide. The simulation results were proved by experiment.

Low-density supercritical fluids are suspected of being able to transport metals, but it is unclear what the speciation/complexation would be in such conditions. In this work, we used ab initio molecular dynamics simulations to investigate the complexation, ion association and hydration of Cu + and Au + in NaCl brines as a function of solution density, from ambient to supercritical conditions (to 1000 C, 5000 bar). Cu(I) and Au(I) form distorted linear complexes with two chloride ligands (i.e., CuCl2 � and AuCl2 � ) in subcritical chloride brines. We have discovered that these charged complexes remain in high density supercritical fluids even at high temperature; however, with decreasing density, these complexes become progressively neutralized by ion association with Na + to form low-charge (NanCuCl2) n� 1 and (NanAuCl2) n� 1 complexes. In these species, the Na + ion is very weakly bonded in the outer coordination sphere, resulting in highly disordered structures and fast (few picoseconds) exchange among coordinated and solvent Na + ions. Thermodynamic models to predict the solubility of metals in low-density magmatic or metamorphic fluids must account for these species. In addition, we found that the number of water

The equivalent conductivities of anhydrous ferric chloride (FeCl3) and anhydrous chromic chloride (CrCl3) were measured in nonaqueous aprotic solvents such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) at temperatures between 278.15 and 318.15 K. In both DMF and DMSO, conductivity values for FeCl3 were found to be higher than those for CrCl3. In addition, the conductivity values for both FeCl3 and CrCl3 in DMF were higher than those in DMSO at all temperatures. The conductivity data were analyzed by the Robinson–Stokes equations. The limiting equivalent ionic conductivities for ferric ion (Fe3+) and chromic ion (Cr3+) and the ion association constants (K A ) for FeCl3 and CrCl3 were determined in DMF and DMSO. The K A values calculated for both FeCl3 and CrCl3 in DMF were higher than those in DMSO. This can be ascribed to an increase of the ion association constants with a decrease of the relative permittivity of solvents used in this study. The K A values increased with the increase in temperature in the studied solvents. Thermodynamic functions (Gibbs’ free energy, entropy, and enthalpy of ion association) were estimated from the temperature dependence of the ion association constant. The positive values of entropy and enthalpy found for FeCl3 and CrCl3 at all temperatures indicate that the association process in DMF and DMSO is endothermic.

The chemical equilibrium in the soil solution determines the dynamics of its material composition, migration and accumulation of salts. In the soil solution are formed electrically neutral ion pairs ÐiаÐiО3°; CaSO4°, MgCO3°, MgSO4°, charged ion pairs CaHCO3+, MgHCO3+, NaCO3-, NaSO4-, CaOH+, MgOH+. The calculation method proposed for quantitative assessment of real ion forms in the soil solution of solonetz taking into account the ions association. Determination of real condition of the main ions in soil solution is based on ion association and its influence on physical and chemical properties of solution. Were calculated the free and associated ion form concentration according to analytical ion concentration. Were used an iteration to solve the equations of ion material balance, a linear interpolation of equilibrium constants, a Method of Ionic Pairs including a law of initial concentration preservation, a law of the operating masses of equilibrium system, the concentration constants of ion pair dissociation following the law of operating masses. Upon completion of iterative procedure, was determined the quantity of ion free form and a coefficient of ion association I³e as the ratio of ions free form to its analytical content I³e = Cass/Can. For calculation procedure were used the own software products. The association of ions varies in individual soils and soil layers, Nˆncreasing the soil solution salinity amplifies the ions association. Depending on concentration and composition of soil solution the ionic pairs are: 15-45% Ca2+; 16-49% Mg2+; 0,6-8,4% Na+; 2,2-17,6% HCO3-, 16-51% SO42-, up to 88% CO32-. The proposed thermodynamic calculation method for quantitative assessment of real ion forms in the soil solution helps to explain the evolution of salted soils, maintain the soil, improve plant nutrition and irrigation.

Complex formation and liquid-liquid extraction (LLE) were studied in systems containing vanadi-um(V), 5-methyl-4-(2-thiazolylazo)resorcinol (TAO), tetrazolium salt (TZS), water and chloroform. The following three TZSs were used: 3-(4,5-dimethyl-2-thiazol)-2,5-diphenyl-2H-tetrazolium bromide (MTT), 3-(2-naphtyl)-2,5-diphenyl-2H-tetrazolium chloride (Tetrazolium violet, TV), and 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT). Concentration of the reagents (TAO and TZS), pH of the aqueous medium, and shaking time were subjects of optimization experi-ments. Formation of ternary complexes with a composition of 2:2:2 was demonstrated by a set of dif-ferent methods. Some key characteristics concerning the analytical application of the studied LLE-chromogenic systems were established as well.

Small-angle X-ray scattering (SAXS) studies of aqueous [Ta6O19](8-) compared to prior studies of aqueous [Nb6O19](8-) reveals key differences in behaviour, which is likely at the root of the difficultly in developing polyoxotantalate chemistry. Specifically, where contact ion-pairing dominates between [Nb6O19](8-) and its counterions, solvent-separated ion-pairing between [Ta6O19](8-) and its counterions has been unveiled in the current study.

A new method for the determination of Gemifloxacin (GMFX) by using Resonance Rayleigh scattering was put forward. In HAc-NaAc buffer solution of pH 5 - 6, terbium (III) and antibiotics GMFX could form cationic complexes, which coulf further form 1 :2 : 1 (Tb3+ : GMFX :AR) ternary ion association complexes by the reaction with Alizarin Red (AR) anion through electrostatic and hydrophobic interaction. The new Resonance Rayleigh scattering (RRS) spectra would appear, and the two scattering peaks were located at 370nm and 590 nm. At 370 nm, the scattering enhancement (ΔI) was proportional to GMFX of certain concentration and its linear range and detection limit (3σ) were 0.005 ~ 4.00 μg.mL-1and 14.5 ng.mL-1. This method is simple, fast, with good selectivity and reproducibility, and it can be used for determination of GMFX drug in various body fluids.

For the three molecular ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-butyl-3-methylimidazolium tetrafluoroborate, dielectric spectra were calculated from molecular dynamics simulations based on polarizable force fields. Using the reaction field continuum model the dielectric spectra were converted to the solvation dynamics of coumarin 153. It is shown in detail that the inclusion of the static conductivity in this model is essential. When simplifying the dielectric spectrum to the static conductivity hyperbola, the solvation response function becomes mono-exponential. Taking into account the frequency dependence of the conductivity, the typical two time-regimes of the solvation response function in ionic liquids are already obtained. However, the mean relaxation time remains the same. When converting the complete dielectric spectrum, i.e. also including frequency-dependent dielectric permittivity, quantitative changes are observed, but the qualitative shape is conserved. In accordance with previous experimental studies, solvation dynamics in ionic liquids predicted by the reaction field continuum model is too fast for longer times. This correlates with the suppression of the fine structure of the dielectric spectrum at low frequencies by the static conductivity hyperbola. By scaling down the static conductivity this effect can be partially amended. In addition to the impact of the solvent dielectric spectrum on solvation dynamics, solute-specific effects, i.e. anisotropy in shape and charge distribution as well as polarizability, were also studied.

Earlier measurements of the self-diffusion coefficients of 1-alkyl-3-methylimidazolium (or [RMIM], R = alkyl) tetrafluoroborates and hexafluorophosphates have been revised and extended to 90 °C. The main changes are to DS+ and DS– for [HMIM][PF6] ([C6C1Im][PF6]) and DS– for [OMIM][BF4] ([C8C1Im][BF4]). New atmospheric pressure self-diffusion, density, and conductivity data are provided for [HMIM][BF4] ([C6C1Im][BF4]). Velocity cross-correlation, distinct diffusion, and Laity resistance coefficients have been calculated. There is no evidence for ion association. A new relation between the Nernst–Einstein deviation parameter (Δ) and resistance coefficients (rij) is derived; Δ tends toward 0.5 when the like-ion rii are much smaller than the unlike-ion rij, i.e., when the counterion interactions dominate. [OMIM]+ ion salts approach this limit. Stokes–Einstein–Sutherland and Walden plots overlap almost quantitatively for [BF4]−, [PF6]−, and Cl– salts with a common [RMIM]+ cation. That is, in thermodynamic stat...

Phase separation solvents for CO2 absorption constructed with amine/ether/water have been designed which transform into two liquid phases after CO2 absorption. We also found that phase separation solvent can reduce the temperature difference between absorber and desorber that can reduce the required energy for CO2 capture. In this study, we develop a model for the CO2 solubility of phase-separation type CO2 absorbent which is necessary for process simulation. Ion species in the liquid phase was estimated by 13C NMR, and the ion association form was inferred from the Walden plot based on conductivity and viscosity. The CO2 solubility model expressed the vapour-liquid equilibrium as the Henry's law constant, the liquid-liquid equilibrium as the non-random two-liquid activity coefficient model, and the liquid phase CO2 chemical absorption as the equilibrium constant. The model can predict CO2 solubility at temperature range (313–363 K) and CO2 partial pressure range (1–100 kPa) and compositions of CO2-lean and CO2-rich phases can be calculated when phase separation occurs.

The influence of two innovative ionic liquids consisting ibuprofenate anion as active pharmaceutical ingredient ionic liquids (API-ILs) on the volumetric, ultrasonic, viscometric, conductometric and refractometric properties of aqueous solutions of glycine has been surveyed. To reach this purpose, the densities, sounds velocity, viscosities, electrical conductivities and refractive indices of ternary solutions of (glycine + API-ILs, 1-methyl-3-hexylimidazolium ibuprofenate [C6mim][Ibu] or 1-methyl-3-octylimidazolium ibuprofenate, [C8mim][Ibu] + water) have been determined at different concentrations of API-ILs and T = 298.2 K. The experimental data have been employed to calculate the properties such as partial apparent molar volume Vϕ0, partial molar volume of transfer ΔtrVϕ0, partial molar isentropic compression κφ0, ion association constant KA, molar refraction RD, viscosity B-coefficients, and hydration number nH. All of these properties were discussed in the terms of the competitive interactions existing between glycine-[C6mim][Ibu] or [C8mim][Ibu] in aqueous media and the hydration properties of glycine.

Ulipristal acetate is used to treat uterine fibroids and for emergency birth control. The present study is a first report on development of a visible spectrophotometric method for determination of Ulipristal acetate present in bulk and tablet formulation. The method involves the sequential addition of HCl (0.1 N) and Napthol Blue Black solution to Ulipristal acetate. Cation formed on tertiary amine group of Ulipristal acetate attracts anion of naphthol blue black (an acid dye) to develop a coloured ion-association complex. From the aqueous phase, the chromophore is extractable into chloroform, which exhibits λmax at 640 nm. As per the existing guidelines of ICH, various parameters of the method were tested for validation. Regression analysis (r > 0.999) shows that the plotted calibration curve exhibits good linearity in the studied range of concentration (2.50 – 15.00 μg mL-1). The % recovery values falls in 99.80 – 100.72 range. %RSD results of both precision studies were observed in the range 0.007 – 0.560, indicating the satisfactory precision of the method. Low values of R.S.D. (< 1 %) were observed indicating that the proposed method is reproducible, accurate and precise. The proposed method can be used in quality control laboratories for routine analysis of Ulipristal acetate (bulk drug and pharmaceutical dosage forms) without requirement of expensive instruments.

Gouverneur et al. have recently reported "effective transport numbers" for mixtures of lithium and 1-ethyl-3-methylimidazolium salts with common (fluorinated) anions using 7Li, 1H and 19F and electrophoretic NMR to determine the electrophoretic mobilities of all three ionic species. The "effective transport number" for lithium is small, but negative. From this they deduce that the Li+ ions are each associated with two or more anions to form negatively charged complexes. However this interpretation may be incorrect: only a single independent transport number can be measured in such a system as the three ion fluxes are not independent. One ion flow must define the reference frame and then the transport numbers for the other two ions must sum to unity. Electrophoretic NMR appears to produce what are called "external" ion mobilities and transport numbers in the notation used by Klemm and Haase for molten salts. These are defined in the laboratory frame of reference and can depend on the boundary conditions of the experiment. Simple relations exist for their conversion to "internal" transport numbers where ion mobilities for two ions are given relative to that of the third, analogous to the more familiar Hittorf transport numbers of ions in electrolyte solutions which are given in the "solvent-fixed" frame of reference, i.e. relative to the flow of solvent. It is not unusual for a cation external transport number to be negative in molten salt mixtures, e.g. (LiNO3 + AgNO3) in a Hittorf experiment employing nitrate electrodes whereas true ion association would produce negative internal transport numbers. In the examples studied by Gouverneur et al. the cation internal transport numbers are both positive. Those for Li+ are also very small, and close to zero within experimental error. This may simply reflect that the mixtures employed are dilute in lithium ions.

The heterogeneous equilibrium of the solubility of calcium hydroxide in water is used to predict both its solubility product from solubility and solubility values from solubility product when inert salts, in any concentration, are present. Accepting the necessity of including activity coefficients to treat the saturated solution of calcium hydroxide (and by extension, all electrolyte solutions) and the inadequacy of any general or nonspecific equation (such as the Debye–Huckel limiting law or Davies equations) to calculate activity coefficients of 1:2 electrolytes, our results uncover (i) how the inclusion of ion pairs in the last mentioned equations makes them adequate for low ionic strength solutions and (ii) the need of sophisticated models, such as the ion-interaction Pitzer equations, for calculating the activity coefficients when ionic strength is high. In addition, we have developed a set of MATLAB scripts and propose the use of the free code PHREEQC version 3 to perform all the calculations descri...

Continuum solvent model is the common used strategy for computing the solvation free energy. However, the dielectric polarization from Gauss's law differs from that obtained from molecular dynamics simulations. To mimic the dielectric polarization surrounding a solute in molecular dynamics simulations, the first-shell water molecule was modeled using a charge distribution of TIP4P molecule in a hard sphere. The dielectric polarization of the first-shell water was modeled as a pair of surface charge layers with a fixed distance between them, but with variable, equal, and opposite charge magnitudes that respond to the electric field on the first-shell water. The water outside the first shell water is treated as a bulk solvent, and the electric effect of the bulk solvent can be modeled as a surface charge. Based on this strategy, the analytical solution describing the solvation free energy of ions was derived, and the values of computed solvation free energy were compared to the values of experiments.

The heat capacity and density of the ternary solutions of NaI–KI–N-methylpyrrolidone (MP), NaI–RbI–MP, KI–RbI–MP, and KI–BaI2–MP at 298.15 K were studied by calorimetry and densimetry. The changes in the heat capacity and volume during the formation of the ternary systems from binary solutions were calculated and discussed. Ion association was found to dominate during the mixing of electrolyte solutions of this type in MP, with ion resolvation occasionally producing a significant effect on ion association.

We report a combined experimental and theoretical study on the swelling behavior of polyelectrolyte gels with various types of counterions. Experimental research was focused on poly(methacrylic acid) and poly(acrylic acid) gels in methanol neutralized with different bases providing sodium, cesium, tetramethyl-, tetraethyl- or tetrabutylammonium counterions. The novelty of the theoretical treatment is that the counterion size is explicitly taken into account as well as the dependence of the ion association constant on the volume fraction of polymer within the gel. We demonstrate that, depending on the counterion size, three different regimes of the gel behavior are realized. In case of bulky tetrabutylammonium counterions the gel swells upon ionization. For small counterions (Na+, Cs+) the gel swelling at low ionization degrees is succeeded by its collapse. New type of behavior was observed and theoretically described for the gels with counterions of intermediate sizes (tetramethyl- and tetraethylammonium)...

Molar conductivities of dilute solutions for the complexes: Co(II)(alanine + valine), Ni(II)(valine + serine), Ca(II)(alanine + serine), Mg(II)(valine + serine) in water were measured in the temperature range from (293.16–313.16K). The ionic molar conductivity (Λ), the association constant (KA), distance parameter (R), and (σΛ) at best fit values were determined by treating experimental data with Lee-Wheaton conductivity equation. Thermodynamic quantities for the ion association reaction were derived from the temperature dependence of KA. The obtained results provide information on ion – ion and ion-solvent interactions.

The equivalent conductivities of tris-(ethylenediamine)cobalt(III) complexes, [Co(en) 3 ]X 3 (X = Cl − , Br − , I − ; en = ethylenediamine) were measured as functions of temperature (288.15–328.15 T /K) and concentration (1.958 × 10 − 4 –10.260 × 10 − 4 c/mol·dm − 3 ) in dimethyl sulfoxide (DMSO). Equivalent conductivity values for [Co(en) 3 ]X 3 in DMSO were varied in the order Cl − > Br − > I − . The conductivity data were analyzed by using Robinson–Stokes equations. For [Co(en) 3 ]X 3 , the limiting equivalent ionic conductivities of [Co(en) 3 ] 3 + and the ion association constants ( K A ) of the ion pair formed between [Co(en) 3 ] 3 + with monovalent halide anions were determined in DMSO. K A values for three complex salts in DMSO were decreased in the order Cl − > Br − > I − . While K A values for [Co(en) 3 ]Cl 3 apparently increased with increase in temperature, those of [Co(en) 3 ]Br 3 and [Co(en) 3 ]I 3 slightly increased with temperature. The temperature variations of the association constants for [Co(en) 3 ]X 3 in DMSO have also been studied to get the thermodynamic functions (standard Gibbs energy, enthalpy and entropy changes).

Considering that cationic polymethine cyanine dyes such as 3,3′-diethylthiadicarbocyanine (DTDC) are used for near-IR (NIR) probes of biological tissues such as mitochondria, we synthesize DTDC organic nanoparticles based on ion association between the dye cation and hydrophobic tetrakis(4-fluorophenyl)borate (TFPB) anion in the presence of neutral stabilizing polymer. Size tuning of the dye nanoparticles is successful by varying the molar ratio of the loaded anion to the dye cation. Binding of DTDC with TFPB results in the prominent appearance of a broad electronic absorption band at 580–590 nm, which we assign to an H-aggregate of DTDC chromophore. The dye nanoparticles show an interesting size-dependent spectroscopic property; linewidth narrowing of H-bands. Spectral deconvolution analysis in terms of a linear combination of Gaussian bands reveals the existence of three types of H-aggregates possessing different transition energies, and the linewidth narrowing of all H-bands is detected as a function of particle size. Meanwhile, monomer bandwidths are almost unchanged. The results suggest that H-aggregates of DTDC dye are readily subject to inhomogeneous broadening that is associated with size-dependent stochastic fluctuations or conformational heterogeneity in the nanoparticles.

Atomistic and first-principles molecular dynamics simulations are employed to investigate the structure formation in a hydrated Nafion membrane and the solvation and transport of protons in the water channel of the membrane. For the water/Nafion systems containing more than 4 million atoms, it is found that the observed microphase-segregated morphology can be classified as bicontinuous: both majority (hydrophobic) and minority (hydrophilic) subphases are 3D continuous and organized in an irregular ordered pattern, which is largely similar to that known for a bicontinuous double-diamond structure. The characteristic size of the connected hydrophilic channels is about 25–50 Å, depending on the water content. A thermodynamic decomposition of the potential of mean force and the calculated spectral densities of the hindered translational motions of cations reveal that ion association observed with decreasing temperature is largely an entropic effect related to the loss of low-frequency modes. Based on the results from the atomistic simulation of the morphology of Nafion, we developed a realistic model of ion-conducting hydrophilic channel within the Nafion membrane and studied it with quantum molecular dynamics. The extensive 120 ps-long density functional theory (DFT)-based simulations of charge migration in the 1200-atom model of the nanochannel consisting of Nafion chains and water molecules allowed us to observe the bimodality of the van Hove autocorrelation function, which provides the direct evidence of the Grotthuss bond-exchange (hopping) mechanism as a significant contributor to the proton conductivity.

The method of continuous variation, in conjunction with UV–visible, Raman and infrared spectroscopy, has been applied to the structural characterization of complexes resulting from tributyl phosphate (TBP), Li+ and FeCl3 in an organic extraction solvent. Data derived from various spectroscopic analyses confirmed the presence of FeCl4− in the solvent, and also demonstrated that the combination of Li+ and FeCl3 produces LiFeCl4. From the method of continuous variation, it was determined that more than one complex results during the extraction of Li+ from aqueous solution, and that these complexes have the general structural formula LiFeCl4·nTBP, where n is greater than or equal to 1. The coordination mode of the complex was investigated by applying a curve-fitting algorithm to the IR spectra of the organic solvent following the extraction of various cations. The results showed that high molecular weight organic cations are produced by the coordination of the TBP extractant and the cation, and that the selective recovery of Li+ occurs via an ion association reaction involving the organic cation and the FeCl4− anion. Finally, the structural formulae of the complexes formed during the extraction were confirmed to be [Li(TBP)(H2O)3]+·FeCl4– and [Li(TBP)2(H2O)2]+·FeCl4–, and the planar and stereo structures of both are given.

Literature data and own experimental results on structural characteristics of the halide ions nearest surrounding in the aqueous electrolyte solutions under standard conditions has been summarized. Structural parameters like coordination number, interparticle distance, and ion association type have been discussed. It has been shown that in the halide ions series, from fluoride to iodide, the coordination number gradually increases from 6 to 8. In the same row, the coordination sphere stability decreases, this is reflected in more asymmetrical arrangement of water molecules of the nearest surrounding.

The electrical conductances of tris-(ethylenediamine)chromium chloride, ([Cr(en)3]Cl3; en = ethylenediamine) were measured as functions of temperature and concentration in 20–80 wt% dimethyl sulfoxide (DMSO)–water mixtures. Conductance data were analyzed by the Kraus–Bray and Shedlovsky models. Also, density and viscosity values for 20–80 wt% DMSO–water mixtures have been determined experimentally at temperatures varying from (288.15 to 318.15) K. The limiting molar conductance, Λ 0, and the association constant, K A, for ([Cr(en)3]Cl3 were computed by using Shedlovsky’s equation. The Λ 0 values decrease with increase in the percentage of DMSO in the mixed solvent. The K A values increase with increasing temperature and increasing percentage of DMSO in the mixed solvent at all temperatures. This may be attributed to the increase in association constant with the decrease in the relative permittivity of the mixed solvent. Thermodynamic parameters (Gibbs energy, enthalpy and entropy changes) were determined from the temperature dependence of K A for ([Cr(en)3]Cl3. The results of the study have been interpreted in terms of ion–solvent interactions and solvent properties.

Although a few groups have recently published transport properties for extensive sets of imidazolium- and pyridinium-based room-temperature ionic liquids (RTILs) and their solutions, there are still no prediction techniques for the conductivity maximum in these systems. We contribute to the discussion by reporting own conductometric data and establishing implicit empirical correlations between ionic structure, concentration and temperature. Our analysis is based on binary systems containing ionic (RTIL) and molecular (acetonitrile) co-solvent. The molar fraction of RTIL in each system ranges from 0 to 50% whereas temperature ranges from 278.15 to 328.15 K. Imidazolium-based RTILs are sampled by 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium and 1-hexyl-3-methylimidazolium tetrafluoroborates, 1-n-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium bromide. 1-butyl-4-methylpyridinium tetrafluoroborate is employed to distinguish a role of aromatic ring. Ionic association in all RTIL–AN systems poorly correlates with the cation structure, although strongly depends on the anion size and structure. Cation and anion of RTILs form the ‘contact ion pairs’ (CIPs) where anion is coordinated by imidazole and pyridine rings. Notably, all binary systems exhibit conductivity maximum between χ (RTIL) = 10 and 20%. This maximum slightly shifts towards smaller χ (RTIL), as counterion gets larger. Smaller cations and anions lead to substantial conductivity growth. Conductivity maximum can be boosted and observed at larger χ (RTIL) even at insignificant temperature increase. Our observations provide novel insights into a complicated functional dependence of ionic conductivity versus ionic concentration and temperature. The results may be of extensive practical application, particularly for construction of high-performance electrolyte systems.

In this work, a new type of sorbent (low density polyhydroxy polyurethane Foam, LPPF) was synthesis by using water hydrolysis of polyurethanediazonium chloride salt. LPPF was characterized using different tools e.g. elemental analysis, UV-vis and IR spectra, TGA, SEM, density and pHZPC. It was tested for separation, preconcentration and determination of gold in environmental samples using batch and dynamic techniques. The sorption experimental data was fitted by the pseudo-first kinetic mathematical equation (R(2)=0.991). The sorption rate of the Au (III) ions is very fast, the half-life (t1/2)≈34 s. The equilibrium process is well described by the Freundlich isotherm model, the R(2) value is 0.967, which attributed to the heterogeneous surface structure of the LPPF. The breakthrough capacity of LPPF and the recovery of gold ions were 0.36 mmol g(-1) (70.5 mg g(-1)) and 99-100%, respectively. The lower detection limit of gold by using spectrophotometric method is 3.3 ng L(-1) with preconcentration factors≈450 (RSD∼1.66%, n=4). The values of ΔG and ΔH for the sorption of gold onto LPPF were -12.5 and -103.5 kJ mol(-1), respectively, which indicate that the sorption of Au (III) onto LPPF is spontaneous and exothermic reaction. The obtained results indicate that the ion chelation and ion association might be the most probable mechanism of gold sorption onto LPPF. The study shows LPPF has the potential of application as an efficient sorbent for the extraction and determination of gold in water, gold alloys pharmaceutical and granite samples.

The authors report experimental investigation on a solid polymer electrolyte PEO + NH4PF6. The solid thin films of different compositions of PEO + NH4PF6 complex were synthesized using solution cast technique and characterized. Complexation between polymer and the salt has been established using X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, and thermogravimetric analysis. Ion transport in the polymer material has been studied by electrical conductivity measurements with composition, temperature, and humidity; by total ionic transference number measurement; and by dielectric measurements. The maximum room temperature (∼29°C) conductivity of the material has been found to be 1.04 × 10−6 S cm−1 for at RH = 60%. The conductivity shows strong humidity dependence. The temperature dependence of the conductivity shows the Arrhenius behavior. The total ionic transference number of the electrolyte material has been found to be between 0.94 and 0.97.

The ion association constants in nonaqueous solutions of singly and doubly charged metal perchlorates in organic solvents in a wide range of temperatures have been calculated by integrating the ligand distribution density function. The standard Gibbs energies, entropies, and enthalpies of formation of ion pairs have been calculated. Comparison with experimental data have shown that diluted solutions of doubly charged metal perchlorates are dominated by solvent-separated ion pairs, whereas such pairs coexist with contact ion pairs in solutions of alkali metal perchlorates. It has been demonstrated that the dielectric continuum approximation satisfactorily predicts the temperature dependence of ion association constants.

The concentration dependence of molar conductance for 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium hexafluorophosphate in binary mixtures of acetonitrile + methanol was investigated to explore the ion association behavior of imidazolium based ionic liquids. The limiting molar conductance \((\Uplambda_{m}^{0})\), association constants (Ka0) and the maximal distance between the oppositely charged ions in ion pairs (Rij) in the mixed solvent mixtures were evaluated following the framework of Barthel’s low-concentration chemical model. The investigated ILs display opposing trends in ion association behavior with change in solvent composition of acetonitrile + methanol binary mixtures. The results are discussed in light of ionic liquid and solvent specific ion−solvent and ion−ion interactions in the mixed solvent systems.

The existence of conductivity maxima in pure molten salt was interpreted by Grantham and Yosim to be due to ion association at low densities. Tödheide used a chloride-transfer shifting-equilibrium hypothesis to explain ion association in the case of bismuth trichloride. We have performed density-functional-theory based molecular dynamics simulations of the molten chlorides of Bi(III), Sn(II), and Hg(II), and Tödheide's hypothesis is not supported. Instead, the simulations imply a hopping barrier for ions between counterions, and we develop this concept into a density-dependent Arrhenius equation to explain the conductivity maxima.

This is the first time a microscopic theory-based bottom-up approach has been implemented to derive an analytical expression for the solvation energy for a finite (N) system, including the bulk. This bottom-up approach provides the information on solvation energies of anionic solutes in finite-size clusters, including the bulk (N = ∞), from the knowledge of the detachment energies for the system containing a few numbers of solvent molecules. However, in the case of dielectric constant, a microscopic theory-based top-down approach has been prescribed to derive an analytical expression for the static dielectric constant for the finite system. In this approach, the knowledge of the dielectric constant for the bulk provides a scheme to obtain the same quantity for a wide numbers of solvent molecules. As an illustrative example, the hydrated doubly charged anions, SO−2 4.NH2O and C2O−2 4.NH2O, have been considered, and the calculated bulk solvation energy for the SO−2 4.NH2O system is found to be in very good ...

The construction and general performance of four novel potentiometric membrane sensors for the determination of fluoxetine have been described. The sensors are based on the formation of the ion association complex of fluoxetine with sodium tetraphenylborate and phosphotungstic acid as electroactive materialles, dispersed in a PVC matrix with dibuthyl sebacate (or diethyl sebacate) as a plasticizer. These sensors exhibit fast, stable and near-Nernstian response for the monocharged fluoxetine cation over wide concentration range from 3.0 × 10−6 to 1.2 × 10−2 M and pH 4.0–7.5. No interferences are caused by many inorganic and organic species. Direct potentiometric determinations of 5–100 μg/mL of fluoxetine in drug and urine samples show good recovery of fluoxetine. The developed membrane electrodes have been used as an end point indicator electrode; the potentiometric titration of fluoxetine with sodium tetraphenylborate as a titrant has been monitored.

Published data obtained by various research methods and our own experimental results on the structural characteristics of the nearest environment of aluminum, gallium, indium, thallium, as well as scandium, yttrium and lanthanum ions in aqueous solutions of their salts under ambient conditions are summarized. The structural parameters, like coordination number, interparticle distance, parameters of the second coordination sphere and the types of ion association are discussed. The hydrate complexes of the ions of aluminum and gallium subgroups are compared.