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Excess thermodynamic properties of a wide variety of aqueous electrolyte solutions at elevated temperatures have been determined with the ORNL high-temperature isopiestic facility. This unique experimental apparatus provides very precise results over the useful temperature range of 110 to 250 C. The isopiestic method is a comparative technique which, in the present case, uses the Pitzer-Peiper-Busey formulation for NaCl(aq) as the reference electrolyte. At elevated temperatures the ion-interaction model of Pitzer continues to be the most useful description of the experimental results. The authors experimental program has included the alkali metal chlorides, sulfates, hydroxides, bromides, and bisulfates, the alkaline earth metal chlorides, and several specific compounds of scientific and practical interest. Numerous common-ion mixed electrolyte solutions have also been investigated in this program. In general, the activity coefficients of all the studied electrolytes decrease with increasing temperature. However, prominent differences between members of the same family remain, particularly when considered as the excess Gibbs free energy. The tendency for ion association increases with increasing temperature and becomes a factor at the higher temperatures. Trends and specific effects are illustrated with examples taken from the database generated in their high-temperature thermodynamic program.

Amelioration and remediation technology was developed for phosphogypsum utilization in Haplic Chernozem of South-European facies (Rostov Region). The technology comprises phosphogypsum dispersed application into the soil layer of 20–45 cm during intra-soil milling. In the model experiment, the phosphogypsum doses 0 (control), 10, 20, and 40 t ha−1 were studied. The Cd thermodynamic forms in soil solution were calculated via the developed mathematical chemical-thermodynamic model and program ION–3. The form of ion in soil solution (or water extract) was considered accounting the calcium-carbonate equilibrium (CCE) and association of ion pairs CaCO30; CaSO40, MgCO30, MgSO40, CaHCO3+, MgHCO3+, NaCO3−, NaSO4−, CaOH+, MgOH+. For calculation of the equilibrium of microelements concentration in soil solution ion including heavy metals (HMs), the coefficient of microelement association kas was proposed. According to calculations, Cd2+ ion in soil solution was mostly bounded to associates CdOH+, partly to associates CdCO30 and CdHCO3+. The calculated kas of Cd was 1.24 units in the control option of experiment and decreased to 0.95 units at phosphogypsum dose 40 t ha−1. The ratio of “active [Cd2+] to total Cd” reduced from 33.5% in control option to 28.0% in the option of phosphogypsum dose 40 t ha−1. The biogeochemical barrier for penetration of HMs from soil to plant roots was high after application of phosphogypsum. According to calculation by ION–3, the standard soil environmental limitations overestimate the toxicity of Cd in soil solution. New decision for intra-soil milling and simultaneous application of phosphogypsum was developed to provide the environmentally safe waste recycling.

Activity coefficients in aqueous solutions of alkali metal nitrates at 298 K have been calculated by the generalized Debye–Huckel theory using experimental values of the static dielectric constant of solutions. It has been shown that calculation without optimization of model parameters in a number of systems reproduces the dependence of activity coefficients on cation radius and the levelling of potassium, rubidium, and cesium cations influence on activity coefficients in the presence of nitrate ions. The effect of hydration and ion association on the thermodynamic properties in the series of studied systems has been considered.

Functionalized ionic liquids (FILs) as extractants were employed for the separation of tungsten and molybdenum from a sulfate solution for the first time. The effects of initial pH, extractant concentration, metal concentrations in the feed were comprehensively investigated. The results showed that tricaprylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate ([A336][Cyanex272]) could selectively extract W over Mo at an initial pH value of 5.5; the best separation factor βW/Mo of 25.61 was obtained for a solution with low metal concentrations (WO3: 2.49 g/L, Mo: 1.04 g/L). The [A336][Cyanex272] system performed effectively for solutions of different W/Mo molar ratios and different metal ion concentrations in the feed. The chemical reaction between [A336][Cyanex272] and W followed the ion association mechanism, which was further proved by the Fourier-transform infrared (FTIR) spectra of loaded [A336][Cyanex272] and the free extractant. The stripping experiments indicated that 95.48% W and 100.00% Mo were stripped using a 0.20 mol/L sodium hydroxide solution. Finally, the selective extractions of W and Mo from two synthetic solutions of different high metal concentrations were obtained; the separation factor βW/Mo reached 23.24 and 17.59 for the first and second solutions, respectively. The results suggest the feasibility of [A336][Cyanex272] as an extractant for the separation of tungsten and molybdenum.

Ion specific effects are ubiquitous in solutions and govern a large number of colloidal phenomena. To date, a substantial and sustained effort has been directed at understanding the underlying molecular interactions. As a new approach, we address this issue by sensitive 1H NMR methods that measure the electrophoretic mobility and the self-diffusion coefficient of poly(N-isopropylacrylamide) (PNIPAM) chains in bulk aqueous solution in the presence of salts with the anion component varied from kosmotropes to chaotropes along the Hofmeister series. The accuracy of the applied electrophoretic NMR experiments is exceptionally high, on the order of 10–10 m2/(V s), corresponding to roughly 10–4 elementary charges per monomer effectively associated with the neutral polymer. We find that chaotropic anions associate to PNIPAM with an apparent Langmuir-type saturation behavior. The polymer chains remain extended upon ion association, and momentum transfer from anion to polymer is only partial which indicates weak attractive short-range forces between anion and polymer and, thereby and in contrast to some other ion–polymer systems, the lack of well-defined binding sites. QC 20210607

During lithium-ion battery charging and discharging, carbonate electrolytes degrade from redox side reactions to produce electrode surface films. The composition of these films depends on the compo...

A study is performed of the electrical conductivity of a number of ionic liquids based on 1-alkyl-3-methylimidazolium quaternary salts with inorganic anions in acetonitrile. The Lee–Wheaton approach is used to calculate the ion association constants Ka, limiting molar electrical conductivity (λ0), and the Gibbs energy of association (ΔG) in solutions. It is shown that the nature and size of the anion has a decisive influence on the association of the studied ionic liquids. It is found that the limiting molar electrical conductivity of bromides is lower than that of hexafluorophosphates and tetrafluoroborates.

Sodium citrate (Na3Cit) has a crucial role in many biological and industrial processes. Yet, quantitative information on its hydration and the ion association between Na+ and Cit3– ions in a broad ...

The review generalizes and analyzes published data on different methods of studying structural characteristics of the solvation environment of alkali metal ions (except for Li+) in various electron-donor oxygen-containing solvents. Coordination numbers of alkali metal ions, interspecies distances, and types of ion association are discussed. The solvation structures of alkali metal cations in water and some nonaqueous systems are compared. The number of solvent molecules and the distance between the cation and oxygen atom of solvent molecule in the first coordination sphere are independent of physicochemical properties of the solvent.

The activity coefficients in aqueous solutions of lithium and sodium sulfates at 298 K were calculated by the generalized Debye–Huckel theory using the experimental values of the static permittivity of the solutions. The effect of the hydration and ion association on the dielectric and thermodynamic properties of the electrolyte solutions was considered.

Tritopic ion‐pair receptors can bind bivalent salts in solution; yet, these salts have a tendency to form ion‐pairs even in the absence of receptors. The extent to which such receptors can enhance ion pairing has however remained elusive. Here, we study ion pairing of M2+ (Ba2+, Sr2+) and X− (I−, ClO4 −) in acetonitrile with and without a dichlorooxacalix[2]arene[2]triazine‐related receptor containing a pentaethylene‐glycol moiety. We find marked ion association already in receptor‐free solutions. When present, most of the MX+ ion‐pairs are bound to the receptor and the overall degree of ion association is enhanced due to coordinative, hydrogen‐bonding, and anion‐π interactions. The receptor shows higher selectivity for iodides but also stabilizes perchlorates, despite the latter are often considered as weakly coordinating anions. Our results show that ion‐pair binding is strongly correlated to ion pairing in these solutions, thereby highlighting the importance of taking ion association in organic solvents into account., Pairing in the spotlight: Sr2+ and Ba2+ salts form ion pairs with iodide and perchlorate anions in acetonitrile. Adding a dichlorooxacalix[2]arene[2]triazine‐related ion‐pair receptor stabilizes these ion pairs and enhances the overall degree of ion pairing, as evidenced from their contribution to the dielectric loss spectra.

The correlations present in the ionic liquids (ILs) are essential to interpret the ion association and dynamics processes. The correlated and uncorrelated ionic conductivities reported from two different types of experiments were calculated employing molecular dynamics methods by exercising appropriate care to obtain the diffusive regions. The ionic conductivity is found to be correlated with lifetimes of the ion-pair and ion-cage formation. In this study, the structure and dynamic properties of five cyclic ammonium-based ILs were investigated by comparing the experimental results with the calculated transport properties: (1) 1-allyl-1-methylpyrrolidinium, (2) 1-propyl-1-methylpyrrolidinum, (3) 1-methyl-1-allylpiperidinium, (4) 4-allyl-4-methylmorpholin-4-ium, and (5) 4-allyl-4-ethylmorpholin-4-ium with bis(trifluoromethanesulfonyl)imide anion as the common anion. We observed the linear relationship between the inverse of ion-pair lifetimes and ionic conductivities. The diffusion coefficients obtained from velocity autocorrelation functions follow a trend similar to that of the experiment as compared to mean square displacements (MSDs). The ionic conductivities from correlated MSD and current autocorrelation functions are compared to the ionic conductivities from the conductometer experiment. The time correlation functions of the ion-pair and ion-cage dynamics were calculated. The correlation functions were used to obtain the lifetimes. Pyrrolidinium-based ILs show lower lifetimes than other ILs, which correlates with the conductivity. Morpholinium-based ILs show higher interaction between ions than other ILs. This result supports the slower dynamics present in morpholinium-based ILs than in other ILs. In this work, our objective is to give atomic insight into the dynamics of IL, which could not be extracted from the experiment, and relate microscopic properties with macroscopic properties.

A simple, sensitive and selective spectrofluorometric method has been developed for the determination of enoxaparin sodium in bulk and dosage forms (injection). The method was based on the quantitative quenching effect of enoxaparin on the native fluorescence of acriflavine due to the formation of nonfluorescent supramolecular ion issociation complex between the studied drug and acriflavine dye in aqueous solution. The decrease of acriflavine fluorescence was observed at 506 nm after excitation at 402 nm. The relationship between quenching fluorescence intensity and concentration of enoxaparin sodium was linear in the range 0.05-20 µg/ml and with correlation coefficient 0.9990 and with LOD and LOQ 0.011 and 0.035 µg/ml respectively. The average recovery was 100.51% and RSD is less than 3.23%. The stoichiometry of enoxaparin to acriflavine was calculated a 1:4. The method was applied successfully to the determination of enoxaparin form injection samples and the results were in a good agreement with certified value and standard addition procedure.

A simple and efficient cloud point spectrophotometric method has been used for the determination of salbutamol sulphate and methyldopa both in pure and pharmaceutical preparations. The procedure was based on the ion association formation with eosin Y. The extraction of ion association, drown to Triton X-114 micelles, was measured spectrophotometrically. The phase separation was studied and optimized. Beer's law was rectilinear over the concentration ranges of 0.1-20 and 0.3-10 µg/mL with molar absorptivity 4x104 and 5.7x104 L.mol-1 cm-1 and average recovery 98.21% and 101.27% for the above drugs, respectively. The method was applied successfully for the determination of salbutamol sulphate and methyldopa in pharmaceuticals.

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

Electrolyte additives play an important role in suppressing lithium dendrites through tailoring the composition/property of the SEI, however lacking of additives can achieve high performances both in ether and carbonate electrolytes hinders further enhancement of the high voltage lithium-metal batteries. Here, lithium perchlorate (LiClO4) has been presented as an excellent additive to meet the above requirements. An optimized chemical composition of SEI can be achieved through the formation of ionic association. Our results indicate that the LiClO4 behaves like a catalyst, which promotes LiTFSI to form a better SEI to inhibit further reaction. Superior coulombic efficiencies and cycling performances were obtained both in ether and carbonate electrolytes. This study paves a new pathway for designing bi-soluble additives for safe lithium metal batteries.

This work presents a successfulness of the methodology of solution cast technique for fabrication of polymer blend electrolytes based on chitosan (CS): potato starch (PS) doped with various amounts of ammonium tetrafluoroborate (NH4BF4). In this work we demonstrated that association of ions is the main drawback for the NH4BF4 salt. Low DC conductivity of the films displays the non availability of the present system for applications. To look at the electrical properties, structural, and morphological properties, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and Field emission scanning electron microscopy (FESEM), respectively were used. From the EIS measurement the highest conductivity of the system was found to be 3.07 × 10−8 S/cm which is too low for device applications including batteries and supercapacitors. The increase of bulk resistance is an indication for the recombination of cation and anion of the salt at high concentration. Sharp peaks were observed in the XRD spectra at high salt concentration. The morphological outcomes display protruded salts with large size at high salt concentration. The large value of dielectric constant at low frequency region is associated to electrode polarization (EP) while their decline with increasing frequency is ascribed to the lag of polarization of ion with respect to the quick orientation of dipole species because of the applied AC field. The M″ peak asymmetry displays the distribution of relaxation time.

The NaCl–H2O binary is a first approximation to fluids in the deep crust and upper mantle. Such fluids are fundamental to understanding geophysical properties, metal transport, and ore genesis within the Earth. Consequently, recent experimental studies have sought to determine the equation of state of the NaCl–H2O binary as a function of composition. However, experimental characterization is not straightforward at extreme conditions and there is so far little understanding of the molecular nature of associated fluids. Variations in the structure of water, ion solvation, and ion association affect properties such as ionic strength and electrical conductivity. These properties in turn influence geophysical signatures and metal solubilities at high pressure and temperature (P,T). We performed a series of NPT ab initio molecular dynamics simulations as a function of pressure (0.5–4.5 GPa), temperature (20–800 °C), and composition (1–14 m NaCl) to develop a molecular-level understanding of high P,T NaCl brines. Comparison of simulation results with experimental and theoretical densities provides a foundation for testing current levels of theory. The simulations have allowed us to determine the nature of ion solvation, ion association, and the effect of solutes on the solvent at high P,T. The PBE functional used here is known to over-structure water and overestimate the density of aqueous fluids at ambient conditions. This is due to an inadequate treatment of hydrogen bonding and dispersion. However, we find excellent agreement between theory and experimental densities at elevated P,T. Accordingly, we have extrapolated the existing equation of state to regions that have not been measured experimentally. From the O–O pair distribution functions, we interpret the improved agreement as resulting from the breakdown of hydrogen bonding at high P,T. At ambient conditions, the presence of Na and Cl has a strong effect on the structure of water. However, at high P,T, even 14 m NaCl has no effect on water structure. Nevertheless, Na and Cl are highly associated. We propose that NaCl brines at high P,T are best described as hydrous melts rather than as aqueous electrolytes.

Solid polymer electrolytes are key components in many electrochemical devices. For an in-depth study of the basic parameters of such electrolytes, we developed a previously proposed method in order to determine the charge carrier density (n), mobility (μ), and diffusion coefficient (D) of ionic conductors using electrochemical impedance analysis. This reinforced method was tested with a composite solid electrolyte based on polyethylene oxide, ethylene carbonate, LiCF3SO3, and alumina filler by analyzing DC conductivity, frequency dependence of AC conductivity, and the complex dielectric function. The results show a clear picture of the temperature dependence of the parameters n, μ, and D; for example, at 20 °C, more than 15% of the total number of ions available in the electrolyte are mobile, and this value decreases with increasing temperature, most probably due to increased ion association in agreement with measurements using other techniques. The increase in ionic conductivity with increasing temperature is thus due to an increased mobility of the ionic species.

Calorimeter with an isothermal shell was used at a temperature of 298.15 K to measure the following parameters: enthalpy of NiSO4(k) dissolution in water followed by generation of two molar concentration solutions; enthalpy of four NiSO4 aqueous solutions dilution having various molar concentrations followed by generation of solutions with approximately the same concentration values. Based on the data obtained, enthalpy and ion association constant in the NiSO4 aqueous solution, as well as standard enthalpy of the aqueous solution formation, were determined for the indicated compound. The latter value made it possible to establish a more accurate value of standard enthalpy in the Ni2+ cation formation in an aqueous solution, which turned out to be equal to --52.3 ± 0.5 kJ/mol.

The use of dielectric relaxation spectroscopy (DRS) for studying electrolyte solutions is reviewed, focussing on the authors’ investigations over the last three decades. It is shown that this often-overlooked technique provides powerful insights into the nature of ion-ion and ion-solvent interactions. DRS is revealed to be particularly useful for detection of weak ion association and, due to its unique ability to detect solvent-separated species, the quantitation of ion pairing. It is demonstrated that DRS correctly determines chemical speciation for ion-paired systems where major spectroscopic techniques (NMR, Raman, UV-vis) fail. DRS also provides important insights into ion solvation. In aqueous solutions, it has been used to build up a coherent set of ‘effective’ hydration numbers for ions based on the dynamics of proximate water molecules, and has a unique ability to detect ‘slow’ water resulting from hydrophilic and hydrophobic hydration of solutes. DRS has been especially useful for characterising the behaviour of ionic liquids (ILs), e.g. showing they possess rather low dielectric constants and, surprisingly, contain no significant concentrations of ion pairs. Neat ILs and their mixtures with molecular solvents are shown by ultra-broadband DRS to exhibit extremely complicated behaviour especially at frequencies in the THz region.

ChemPhysChem 10, (2021). doi:10.1002/cphc.202100602, Published by Wiley-VCH Verl., Weinheim

Superconcentrated electrolytes, being highly thermodynamically nonideal, provide a stringent proving ground for continuum transport theories. Herein, we test an ostensibly complete model of LiPF6 in ethyl-methyl carbonate (EMC) based on the Onsager-Stefan-Maxwell theory from irreversible thermodynamics. We perform synchronous magnetic resonance imaging (MRI) and chronopotentiometry to examine how superconcentrated LiPF6:EMC responds to galvanostatic polarization and open-circuit relaxation. We simulate this experiment using an independently parametrized model with six composition-dependent electrolyte properties, quantified up to saturation. Spectroscopy reveals increasing ion association and solvent coordination with salt concentration. The potentiometric MRI data agree closely with the predicted ion distributions and overpotentials, providing a completely independent validation of the theory. Superconcentrated electrolytes exhibit strong cation-anion interactions and extreme solute-volume effects that mimic elevated lithium transference. Our simulations allow surface overpotentials to be extracted from cell-voltage data to track lithium interfaces. Potentiometric MRI is a powerful tool to illuminate electrolytic transport phenomena.

Ionic liquid (IL) materials are promising electrolytes with striking physicochemical properties for energy and environmental applications. Heterogeneous structures and transport quantities of monomeric and polymeric ILs are intrinsically intercorrelated and span multiple spatiotemporal scales, which is more feasible for coarse-grained (CG) simulations than atomistic modelling. Herein we constructed a novel CG model for ethyl-imidazolium tetrafluoroborate ILs with varied cation alkyl chains ranging from C2 to C20, and the interaction parameters were validated against representative static and dynamic properties that were obtained from atomistic reference simulations and experimental characterizations at relevant thermodynamic states. This CG model was extended to study thermotropic phase behaviors of monomeric ILs and to explore ion association structures and ion transport quantities in polymeric ILs with different architectures. A systematic analysis of structural and dynamical quantities identifies an evolution of liquid morphology from homogeneous to nanosegregated structures and then a smectic mesomorphism via a gradual lengthening of cation alkyl chains, and thereafter a distinct structural transition characterized by a monotonic decrease in orientational and translational order parameters in a sequential heating cascade. Backbone and pendant polymeric ILs exhibit evident anion association structures with cation monomers and polymer chains, and striking intra- and interchain coordinations between cation monomers owing to an intrinsic polymer architecture effect. Such a peculiar ion pairing association leads to a progressive increase in anion intrachain hopping probabilities, and a concomitant decrease in anion interchain hopping events with a gradual lengthening of polymeric ILs. The anion diffusivities in polymeric ILs are intrinsically correlated with ion pairing association lifetimes and ion structural relaxation times via a universal power law correlation D ∼ τ−1, irrespective of polymer architectures.

Conductivity plays vital role in drug diffusion. Thermodynamic parameters affected by substituents of drug. Thermodynamic parameters of 1, 3, 5 –triazinothiocarbamide (1a) have been investigated by using conductometrically carried out at different molar concentrations. This work highlights investigation of G, K and µ values. The thermodynamic parameters viz. ΔH, ΔS and ∆G for ion pair formation determine from the value of ion association constant. This technique is suitable and accurate to study of pharmokinetics and pharmodynamics parameters.

Liquid-liquid extraction-chromogenic systems for vanadium(V) based on xylometazoline hydrochloride (XMZ) and azo derivatives of resorcinol (ADRs) were studied. The following ADRs were used: 4-(2-thiazolylazo)resorcinol (TAR), 5-methyl-4-(2-thiazolylazo)resorcinol (MTAR), and 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR). Concentration of the reagents, pH of the aqueous medium and shaking time were subjects of optimization experiments. The chloroform-extracted ternary complexes were of composition 1:1:1. The molar absorptivity coefficients ( e l ), absorption maxima ( l ), constants of extraction (Log K ), and fractions extracted ( E %) were found to be e 553 = 2.50 ´ 10 4 dm 3 mol –1 cm –1 , Log K = 3.5, and E = 96% (ADR = TAR); e 550 = 1.88 ´ 10 4 dm 3 mol –1 cm –1 , Log K = 3.4, and E = 98% (ADR = MTAR); and e 554 = 2.62 ´ 10 4 dm 3 mol –1 cm –1 , Log K = 5.0, and E = 99.5% (ADR = HTAR). The Sandell’s sensitivities and Beer’s law limits were determined as well.

We report amplified near-IR (NIR) fluorescence in organic rhodamine dye nanoparticles, which can be synthesized on the basis of ion association between rhodamine-800 (Rho-800) cation and tetrakis(4...

The complex formation and the ion-association of the ion-pair formed between the anionic chelate of molybdenum(VI)‒3,5-dinitrocatechol (3,5-DNC) with the cation of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) in the liquid–liquid extraction system Mo(VI)‒3,5-DNC‒MTT‒H2O‒CHCl3 was studied by spectrophotometry. The optimum conditions for the chelate formation and extraction of the ion-associated complex Mo(VI)‒3,5-DNC‒MTT were established. The molar ratio of the components in the ion-associated complex Mo(VI)–3,5-DNC–MTT 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 structural formula of the complex were suggested.

Complex crystallization pathways are common in protein crystallization, tetrahedrally coordinated systems, and biomineralization, where single or multiple precursors temporarily appear before the formation of the crystal. The emergence of precursors is often explained by a unique property of the system, such as short-range attraction, directional bonding, or ion association. But, structural characteristics of the prenucleation phases found in multistep crystallization remain unclear, and models are needed for testing and expanding the understanding of fluid-to-solid ordering pathways. Here, we report 3 instances of 2-step crystallization of hard-particle fluids. Crystallization in these systems proceeds via a high-density precursor fluid phase with prenucleation motifs in the form of clusters, fibers and layers, and networks, respectively. The density and diffusivity change across the fluid-fluid phase transition increases with motif dimension. We observe crystal nucleation to be catalyzed by the interface between the 2 fluid phases. The crystals that form are complex, including, notably, a crystal with 432 particles in the cubic unit cell. Our results establish the existence of complex crystallization pathways in entropic systems and reveal prenucleation motifs of various dimensions.

Background: The thermophysical properties of 1-octyl-3-methylimidazolium salicylate as an active pharmaceutical ingredient based on ionic liquid have been investigated in the presence of aqueous solutions of glycine. Therefore, the scope of this article was to determine these properties by measuring the densities, speeds of sound, viscosities, electrical conductances and refractive indices for ternary (glycine + 1-octyl-3-methylimidazolium salicylate + water) soloutions at T = 298.15 K. Methods: A commercial density and speed of sound measurement apparatus was used to measure the density and speed of sound data. Viscosities, electrical conductivities and refractive indices of the studied solutions were measured using digital viscometer, conductivity meter and refractometer, respectively. Results: Variety of properties such as partial molar volume of transfer ∆traV0ϕ, partial molar isentropic compressibility of transfer ∆traK0ϕ, viscosity B-coefficients of transfer ∆traB, ion association constants (KA) and molar refraction RD were determined to investigate the solute-solute and solute-solvent interactions in these systems. Conclusion: The positive values of transfer properties including partial molar volume of transfer (∆traV0ϕ), partial molar isentropic compressibility of transfer (∆traK0ϕ), and viscosity B-coefficients of transfer (∆traB) indicated that in these systems, the ion-polar and polar-polar interactions are dominant. The calculated hydration number showed that dehydration of glycine occurs in presence of this ionic liquid.

We have developed a novel one-step method for photoreduction synthesis of morphology-controlled Ag nanoparticles (AgNPs) under the irradiation of narrow band blue light emitting diodes. The results showed that AgNPs with different morphologies can be prepared by controlling the irradiation time. More importantly, a new spectrophotometry based on the silver phenanthroline-eosin ion association system was established to detect the concentration of Ag+. In the presence of polyvinyl alcohol, Ag+ can combine with 2,4,5-7-tetrabromofluorescein disodium salt and 1,10-phenanthroline monohydrate forming red ternary complex in ammonium acetate buffer (pH 7.0). The new method was applied to determine the concentration of Ag+ during the formation of AgNPs. According to the changes of Ag+ concentration and morphologies, a potential mechanism for the structural transition of AgNPs was given.

Electrical conductances of solutions of tetraphenylphosphonium chloride, sodium tetraphenylborate, and sodium chloride in polyethylene glycol (PEG) + water mixed solvent systems having 0.200, 0.400, and 0.600 mass fractions of PEG are reported at 298.15 K. In this study three different average molar masses of PEG, e.g., 300 (designated as PEG 300), 400 (designated as PEG 400), and 600 (designated as PEG 600) g·mol−1 were employed. The conductance data have been analyzed using the 1978 Fuoss conductance–concentration equation in terms of the limiting molar conductance, the association constant and the association diameter of the electrolytes. The ionic contributions to the limiting molar conductances have been estimated using tetraphenylphosphonium tetraphenylborate as the “reference electrolyte”, considering the similarity of the sizes and chemical characters of the tetraphenylphosphonium and tetraphenylborate ions possessing a quasi-spherical surface of the phenyl rings. Analyses of the results provided important information as to the ion-association and solvation behavior of the electrolytes/ions investigated in PEG + water mixed solvent media.

Glyme solvents are a promising avenue of research in novel electrolytes, due to their thermal and chemical stability, large electrochemical window, and tunable properties. This work investigates the transport properties of LiPF6 and NaPF6 salts in Monoglyme (G1), Diglyme (G2), and Tetraglyme (G4). Self-Diffusion coefficients, and degrees of ion association were found through spectroscopic techniques. Raman and Fourier-Transform Infrared (FTIR) spectroscopy exhibited an absorbance peak at 740 cm−1, corresponding to the a1g mode; known to signify the presence of solvent-separated and contact ion pairs. The increased intensity of this peak for G1 compared to G4 suggests that the electrolyte exhibits stronger association with decreasing solvent size. Nuclear Magnetic Resonance Diffusometry measurements yield self-diffusion coefficients for 7Li, 23Na, and 19F across all samples to be on the order of 10−9 m2s−1 in G1, to 10−11 m2s−1 in G4. Comparison of conductivities calculated from the measured diffusivities and the Nernst-Einstein equation with conductivity measurements deduced from Electrochemical Impedance Spectroscopy (EIS) determined the ion association degree; the electrolytes were shown to exhibit stronger ion pairing with increased temperature which is attributed to a decrease in the dielectric constant of the solvents with increasing temperature. Additionally, the ion association was shown to decrease with increasing solvent molecular size, consistent with FTIR findings.

A better understanding of the solution chemistry of the lanthanide (Ln) salts in water would have wide ranging implications in materials processing, waste management, element tracing, medicine and many more fields. This is particularly true for minerals processing, given governmental concerns about lanthanide security of supply and the drive to identify environmentally sustainable processing routes. Despite much effort, even in simple systems, the mechanisms and thermodynamics of LnIII association with small anions remain unclear. In the present study, molecular dynamics (MD), using a newly developed force field, provide new insights into LnCl3(aq) solutions. The force field accurately reproduces the structure and dynamics of Nd3+, Gd3+ and Er3+ in water when compared to calculations using density functional theory (DFT). Adaptive‐bias MD simulations show that the mechanisms for ion pairing change from dissociative to associative exchange depending upon cation size. Thermodynamics of association reveal that whereas ion pairing is favourable, the equilibrium distribution of species at low concentration is dominated by weakly bound solvent‐shared and solvent‐separated ion pairs, rather than contact ion pairs, reconciling a number of contrasting observations of LnIII–Cl association in the literature. In addition, we show that the thermodynamic stabilities of a range of inner sphere and outer sphere LnClx(3-x)+ coordination complexes are comparable and that the kinetics of anion binding to cations may control solution speciation distributions beyond ion pairs. The techniques adopted in this work provide a framework with which to investigate more complex solution chemistries of cations in water.

Experimental results of the osmotic coefficients of aqueous solutions of 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4], 1-ethyl-3-methylimidazolium methylsulfate [EMIM][MeSO4], 1-ethyl-3-methylimidazolium tosylate [EMIM][Tos], 1,3-dimethylimidazolium methylsulfate [MMIM][MeSO4], tributylmethylphosphonium methylsulfate [TBMP][MeSO4] and triisobutylmethylphosphonium tosylate [(iBu)3MP][Tos] obtained by vapor pressure osmometry (VPO) at 298.15 K and at atmospheric pressure are reported in this work. From this data water activity (aw), vapor pressure (p), mean molal activity coefficients (γ±), Gibbs free energy due to mixing (ΔGmix) and excess Gibbs free energy change (ΔGE) are calculated. The activity coefficient data obtained are correlated with McMillan-Mayer theory and Pitzer model. The results obtained are elucidated in terms of ion association and structural characteristics of ILs.

Label-free biosensing based on the nanoporous anodic alumina (NAA) membrane emerged as a versatile biosensing platform in the recent decade. In the present work, we developed a new immunosensing strategy based on the nanochannels of NAA and the ion pair interaction mediated by electrochemistry of C60. The NAA served as the matrix for the immobilization of the capture antibodies. The incubation of target antigens resulted in the formation of the immunocomplexes and thus an increase of the steric hindrance of the nanochannels. Therefore, the concentration of the redox probe transported through the nanochannels decreases, which can be detected at the working electrode modified with C60. Herein, we initially found that the cathodic peak ascribed to the reduction of C60 to C60– was obviously enhanced by the presence of the redox probe K3[Fe(CN)6] and which was contributed to the formation of a ternary ion association complex among C60, tetraoctylammonium bromide, and K3[Fe(CN)6]. Therefore, the transportation ...

The effect of 1‑octyl‑3‑methylimidazolium salicylate, [OMIm][Sal] and 1‑octyl‑3‑methylimidazolium ibuprofenate, [OMIm][Ibu] as active pharmaceutical ingredient ionic liquids (API-ILs) on the solvation properties of l -alanine in aqueous media have been investigated by thermophysical properties determination. The partial molar volume of transfer (ΔtraVϕ0), partial molar isentropic compressibility of transfer (Δtraκϕ0), viscosity B-coefficient of transfer (∆traB), ion association constant (KA) and molar refraction (RD) quantities have been calculated using the measured density, speed of sound, viscosity, electrical conductance and refractive index data. The results showed that the ion-polar and polar-polar interactions between API-ILs and l -alanine are dominant.

In this study, the ion association characteristics and the hydration dynamics of Mg2+ ions in MgSO4 aqueous solution at various concentrations were systematically investigated using density functional theory and classical molecular dynamics simulations. The results show that contact associated (CA) and solvent separated (SS) structures of Mg2+ and SO42− ions are the dominant species and play different roles in the crystallization and gelation processes of MgSO4 aqueous solution due to their distinctive association trend and the distinctive dynamics of their second hydration shells. The CA structures are more stable and the further aggregation of these clusters is sluggish in MgSO4 aqueous solution. The supersaturation or the formation of gel state can be partially attributed to the abundance of CA structures in supersaturated MgSO4 aqueous solution. In contrast, although the ion exchange in SS structures occurs frequently, the aggregation of SS structures is active and can be greatly promoted by increasing of the concentration. The dynamics of the second hydration shells around Mg2+ ions of SS structures also becomes more active as the concentration increases. The dynamic evolution characteristics of SS structures demonstrate their aggregation tendency for nucleation in the oversaturated MgSO4 aqueous solution, which helps to understand the nucleation mechanism in MgSO4 aqueous solution and the role of ion hydration dynamics in the nucleation process.

The extraction behavior and mechanism of uranium(VI) from aqueous solution with the multidentate ligand N,N,N″′,N″′-tetraoctyl-N″,N″-ethidene diglycolamide (TOE-BisDGA) as extractant were investigated. The extraction percentages of uranium(VI) were found to increase with increasing aqueous nitric acid solution. The extraction process was deduced to proceed by neutral extraction mechanism or ion association extraction mechanism, and the TOE-BisDGA extractant formed a major 1:1 complex with uranium(VI) in xylene system. The possible molecular structure of extracted pieces were presumed to be [UO2(NO3)2(TOE-BisDGA)] or [UO2(TOE-BisDGA)](NO3)2 or [UO2(NO3)TOE-BisDGA)](NO3) by ESI–MS and extraction mechanism.

The current study assembles liquid-microextraction, surface enhanced Raman spectroscopy (SERS) and chemometric algorithms in one platform for chromium speciation using octahedral Cu2O@Ag nanocomposites (Cu2O@AgNCs) as a SERS substrate. The reaction between cationic dye rhodamine 6G (RG+) and the chlorochromate anion (CrO3Cl−) at pH < 1.0 has been exploited for chromium determination by the phenomenon of ion association. The conditions of microextraction were carefully established, followed by depositing the sediment organic phase on the ethanolic octahedral Cu2O@AgNCs suspension. The SERS intensity was recorded for the complex ion associate (RG+·CrO3Cl−) versus a reagent blank. Chemometric algorithms such as partial least squares (PLS) and variable selection competitive adaptive reweighted sampling (CARS)-PLS were applied for masking redundancy in the SERS spectra of the complex ion associate (RG+·CrO3Cl−) formed in the sediment phase extract. Substrate characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), stoichiometry, analytical applications, selectivity and standard method validation was performed. The designed octahedral Cu2O@AgNCs/RG+/HCl probe displayed a detection limit of 0.028 μg L−1 for chromium(VI) under optimized chemometric modeling and microextraction conditions.