Ion Association In Solutions Research Articles

Machine-guided path sampling to discover mechanisms of molecular self-organization

Molecular self-organization driven by concerted many-body interactions produces the ordered structures that define both inanimate and living matter. Here we present an autonomous path sampling algorithm that integrates deep learning and transition path theory to discover the mechanism of molecular self-organization phenomena. The algorithm uses the outcome of newly initiated trajectories to construct, validate and—if needed—update quantitative mechanistic models. Closing the learning cycle, the models guide the sampling to enhance the sampling of rare assembly events. Symbolic regression condenses the learned mechanism into a human-interpretable form in terms of relevant physical observables. Applied to ion association in solution, gas-hydrate crystal formation, polymer folding and membrane-protein assembly, we capture the many-body solvent motions governing the assembly process, identify the variables of classical nucleation theory, uncover the folding mechanism at different levels of resolution and reveal competing assembly pathways. The mechanistic descriptions are transferable across thermodynamic states and chemical space.

Dielectric Characteristics, Electrical Conductivity and Solvation of Ions in Electrolyte Solutions

Solvation and association of ions in solutions largely depend on the dielectric properties of the solvent, the distance between ions in solutions, and temperature. This paper considers the effect of temperature on static dielectric constant (DC), dipole dielectric relaxation (DR) time, and limiting (ultimate) high frequency (HF) electrical conductivity (EC) of water and some polar solvents. In the investigated temperature range (0–370 °C), the static DC and DR time of water decrease, and limiting HF EC passes through a maximum at 250–300 °C with temperature growth. The dielectric characteristics of methanol, ethanol, and propanol behave in a similar way. It is shown that the existence of an HF EC temperature maximum is due to the different nature of the temperature dependences of DC and DR time. It is suggested that the same dependences are responsible for the presence of a maximum in the temperature dependences of the dissociation degree and the ionic product of water. The influence of non-electrolytes concentration as well as metal salts on the dielectric properties of their aqueous solutions is considered. The limiting HF EC of water determines the specific EC value of aqueous electrolyte solutions. Analysis of the absorption of microwave energy by polar solvents, as well as aqueous solutions of non-electrolytes and electrolytes, at a frequency of 2455 MHz is carried out. The optimal conditions for high-frequency heating of solutions have been established. The distance between ions in aqueous solutions of inorganic salts and in non-aqueous solutions of ionic liquids is calculated. It is shown that the maximum on the concentration dependence of the specific EC can be related to ions association.

Quantum-Chemical and IR Spectroscopic Study of Ionic Association in Solutions of LiCF3SO3 in Acetonitrile

The association of ions in solutions of lithium trifluoromethanesulfonate in acetonitrile is studied via quantum chemistry and Fourier-transform infrared spectroscopy (FT-IR). Quantum-chemical calculations are performed using the attached-molecule approach, allowing for the influence of a polarized solvent medium for {Li+CF3SO$$_{3}^{ - }$$}m(CH3CN)n solvated neutral ionic associates (where m = 1 (ion pair) and 2 (ion quadrupole)). Vibrational spectra calculated at the RHF + MP2/6-311G** + SMD level of theory are used to identify ionic associates in IR spectroscopic studies of LiCF3SO3 acetonitrile solutions (25°C and 0.05–1.28 mol/kg range of concentrations). {Li+CF3SO$$_{3}^{ - }$$}(CH3CN)3 ion pairs are found in all solutions; {Li+CF3SO$$_{3}^{ - }$$}2(CH3CN)2 ionic quadrupoles appeared at concentrations of ≥0.55 mol/kg. Characteristic changes in spectra of a CF3SO$$_{3}^{ - }$$ polyatomic anion, due to different solvated ionic associates (ion pairs and quadrupoles), are observed.

Predicting Ion Association in Sodium Electrolytes: A Transferrable Model for Investigating Glymes

Given the prior success in developing lithium batteries for similar purposes, many of the same types of solvent molecules and salt pairings have been investigated as electrolytes in sodium-ion and sodium–oxygen systems. Of these candidates, ether-containing electrolytes have emerged as a promising material as a result of their electrochemical stability and utility in tuning the pertinent electrochemistry. The ability for ethers to chelate metal ions provides a unique feature to ion solvation structure; however its role in changing the association of ions in solution has not been fully explored. By using computational simulations validated by FTIR and NMR spectroscopy, detailed descriptions of the changes to solvation structure as a result of chelation and concentration were investigated for a series of ethers (monoglyme to tetraglyme). From these simulations it can clearly be seen that with increasing chelation, ion association is diminished in a nonlinear fashion. For a monoglyme solvent, sodiums are ent...

Probing Crystallization Pathways in Group V Polyoxometalate Solutions

Structure elucidation is extremely important to understand and control processes in synthetic chemistry, in drug design, and in biomolecular function; and the most important step of structure elucidation is crystallization. Preceding crystallization of ionic compounds is usually ion-association in solution, which can be induced by a variety of ways. Here we study ion-association of hexaniobate and hexatantalate polyoxometalate salts in mixed water-alcohol solutions. These hexametalate clusters have the unusual characteristic of increased solubility with increased ion-association, which makes them ideal candidates to understand the fundamentals of ion-pairing. We utilize direct (X-ray scattering) and indirect (ion-conductivity) methods to document the ion-association as a function of alkali, concentration, alcohol:water ratio, and Nb versus Ta. The conductivity data coupled with X-ray scattering shows that decreasing solvent polarity increases cluster-alkali association; but decreases any interaction between the alkali-cluster aggregates. Conductivity data show the trend of increasing alkali-cluster association with increasing alkali size as is expected for hexaniobate, but has some discrepancies with hexatantalate. We attribute this to the concomitant effects of protonation of the clusters, with hexaniobate being a stronger base. These studies provide insight into aqueous behaviour of these clusters that exhibit the anomalous behaviour of high solubility with maximum ion-association.

Ion Association in Aprotic Solvents for Lithium Ion Batteries Requires Discrete–Continuum Approach: Lithium Bis(oxalato)borate in Ethylene Carbonate Based Mixtures

Ion association in solutions of lithium salts in mixtures of alkyl carbonates carries significant impact on the performance of lithium ion batteries. Focusing on lithium bis(oxalato)borate, LiBOB, in binary solvents based on ethylene carbonate, EC, we show that neither continuum nor discrete solvation approaches are capable of predicting physically meaningful results. So-called mixed or the discrete–continuum solvation approach, based on explicit consideration of an ion solvatocomplex combined with estimation of the medium polarization effect, is required in order to characterize the ion association at the quantitative level. The calculated changes of the Gibbs free energy are overestimated by nearly an order of magnitude by the purely continuum and purely discrete approaches, with the values having the opposite signs. The physically balanced discrete–continuum description predicts weak ion association. The numerical data obtained with density functional theory are validated using coupled-cluster calculations and experimental X-ray data. The study contributes to resolution of the challenge in solvation modeling in general, and develops a reliable, practical method that can be used to screen ion association in a broad range of ion–molecular mixtures for lithium ion batteries, especially for the solutions of LiBOB in EC based mixtures.

ChemInform Abstract: Cesium Salts of Niobo‐Tungstate Isopolyanions with Intermediate Group V—Group VI Character.

AbstractCs4Na2 [Nb4W2O19]·12H2O (I) and Cs3Na [Nb2W4O19]·10H2O (II) are prepared by acidification of an aq.

Conductivity Measurements of 4-Amino Salicylic Acid and with some Transition Metal Chlorides in Different Solvents and at Different Temperatures

In the first part of this work we have measured the electrical conductivity of 4-amino salicylic acid (4-ASA) solution in water, methanol and ethanol at different temperatures (293.16-313.16 K). The experimental results were analyzed using Lee-Wheaton equation (LW) for symmetrical electrolytes (1:1). The conductivity parameters were calculated: the equivalent conductivity at infinite dilution (Λo), the association constant (KA) and the mean distance values between ions (R) at the best standard deviation σs(Λ). It is found that by increasing the temperature, the values of Λo increased, in contrast of that the values of KA decreased in ethanol only, R are found to be between (2-29 )Ao which indicates the formation of solvent separated ion pairs in solution. By Vant Hoff equation we have calculated the thermodynamic parameters (ΔG, ΔH and ΔS) of ion association in solution. The second part of this work is the measurement of electrical conductivity of (4-ASA) in water with chlorides of each of nickel, cobalt and manganese at different temperatures (293.16-313.16 K) and calculation of conductivity parameters by Lee-Wheaton equation for unsymmetrical electrolytes (2:1), besides the thermodynamic parameters were also performed. The Walden-product (Λoη) was also determined and discussed.

A Conductance Study of Guanidinium Chloride, Thiocyanate, Sulfate, and Carbonate in Dilute Aqueous Solutions: Ion-Association and Carbonate Hydrolysis Effects

We study the conductance of dilute aqueous solutions for a series of guandinium salts at 298.15 K. The experimental molar conductivities were analyzed within the framework of the Quint-Viallard theory in combination with Debye-Hückel activity coefficients. From this analysis, we find no evidence for significant ion association in aqueous solutions of guanidinium chloride (GdmCl) and guanidinium thiocyanate (GdmSCN), and the molar conductivity of these electrolytes can be modeled assuming a complete dissociation. The limiting ionic conductivity of the guanidinium ion (Gdm(+)) is accurately determined to λ(Gdm(+)) = 51.45 ± 0.10 S cm(2) mol(-1). For the bivalent salts guanidinium sulfate (Gdm(2)SO(4)) and guanidinium carbonate (Gdm(2)CO(3)), the molar conductivities show small deviations from ideal (fully dissociated electrolyte) behavior, which are related to weak ion association in solution. Furthermore, for solutions of Gdm(2)CO(3), the hydrolysis of the carbonate anion leads to distinctively increased molar conductivities at high dilutions. The observed ion association is rather weak for all studied electrolytes and cannot explain the different protein denaturing activities of the studied guanidinium salts, as has been proposed previously.

Ion transport in the polyamide layer of RO membranes: Composite membranes and free-standing films

The permeability of the composite ESPA1 membrane to ferro- and ferricyanide ions without and with an excess of supporting buffer was analyzed by three different methods: filtration followed by phenomenological analysis, and electrochemical impedance spectroscopy and chronoamperometry using free polyamide films isolated from the membrane. Appropriate relations were developed that relate the observed permeability to actual permeability of the trace redox ions and correct for concentration polarization of the trace ion in presence of a more concentrated (dominant) electrolyte. Within the uncertainties associated with polarization correction, coupling of ionic fluxes, and ion association in solution and within the membrane, consistent values of permeabilities, of about 0.03–0.05 μm/s, were obtained by all methods. The results validate that (a) the contribution of convection to salt permeation through the active layer of thin-film composite membranes is small; (b) the procedures used to isolate the active polyamide layer from commercial membranes has a minimal impact on the transport properties of the polyamide films; the isolated free films may then adequately represent the properties of the original active layer in characterization studies. This information may have important implications for studying transport, modeling and characterization of thin-film composite membranes.

Effect of temperature and pressure on structural self-organization of aqueous sodium chloride solutions

The features of self-organization of aqueous NaCl solution structure are studied by the extended RISM integral equation method over a wide range of temperature ( T = 313–633 K, p = 25 МPа), pressure ( p = 0.1–1000 МPа, T = 298 K) and concentration (1.11–5.55 molal). Effects of external parameters ( T, p) on the structural state of bulk water, ion hydration and ion association in solutions are analyzed. According to the obtained results, temperature and pressure exert the same destructive influence on bulk water structure but have opposite impact on ion hydration and ion association. The pressure-induced structure transformations discussed here are largest at p > 150 МPа and specific to moderate salt concentrations of NaCl(aq).

Vibrational Spectroscopic Study on Ion Solvation and Association of Lithium Perchlorate in 4‐Methoxymethyl‐ethylene Carbonate

AbstractSolvation interaction and ion association in solutions of lithium perchlorate/4‐methoxymethyl‐ethylene carbonate (MEC) have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li+ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li+ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO−4 band revealed the presence of contact ion pair, and free ClO−4 anion in the concentrated solutions.

Association of ions in solutions of lithium and sodium chlorides

The critical distances for the formation of ion pairs were calculated by a nonempirical quantum-chemical method. The results were in agreement with the Bjerrum theory. Ion pair formation in aqueous solutions of lithium and sodium chlorides was visualized, and the energies of ion pair formation calculated.

Ion solvation and association in LiClO 4/sulfolane solution: a vibrational spectroscopic and molecular orbital study

Solvation interaction and ion association in solutions of lithium perchlorate/sulfolane have been studied by using infrared and Raman spectra as a function of concentration of lithium perchlorate. The band changes of antisymmetric OSO stretch, antisymmetric CSC stretch, −SO 2 wag and twist suggest that there is an interaction between Li + and sulfolane molecules, and the site of solvation is the oxygen atom of –SO 2 group. The molecular orbital calculation supports this suggestion. On the other hand, the apparent solvation number was calculated, and the band fitting for the ClO 4 − band reveals the presence of contact ion pair, solvent separated ion pair and free ClO 4 − anion in the concentrated solutions.

Solvation and ion association in solutions containing oxyanions

Ion solvation and association behaviour has been studied for solutions of lithium perchlorate and lithium nitrate in N,N-dimethylformamide (DMF) methanol and ethanol. The techniques of Raman spectroscopy and multinuclear n.m.r. have been employed, and in some studies the cation has been caged in the cryptand Kryptofix 221. Solvation in DMF was examined through quantitative analysis of the OCN bending vibrational band of the DMF in the Raman spectra. A range of univalent and divalent cations was employed and solvation numbers and some information on solvation geometries were obtained. In alcohol solutions determination of solvation numbers was not possible but the involvement of Li+ and NO–3 produced observable spectroscopic changes, while the ClO–4 anion appeared to have only a weak solvation. Evidence for at least two associated species was obtained for both salts in DMF and ethanol and the concentration dependence of the species was determined. In methanol association was much less with the behaviour approaching that observed in aqueous solution.

Nuclear magnetic relaxation by quadrupolar interaction of ionic nuclei in non-aqueous solvents. Part 2.—Ion association in solutions of RbI in formamide and N-methylformamide

87 Rb, 127I and 14N magnetic relaxation rates are reported for solutions of RbI dissolved in formamide and N-methylformamide. The mean-square electric-field gradients at the cationic and anionic nuclei indicate the presence of higher ion associates.

A computer method for the calculation of enthalpy changes for ion association in solution from calorimetric data

A general method for the determination of enthalpy changes in solution for systems containing an unlimited number of components, that can give rise to mononuclear, polynuclear, protonated, hydroxo and mixed species was set up. A computer program, DOEC, able to elaborate data on a calorimetric titration such as concentrations, changes to the mole number of the various species, solution ionic strength and reaction enthalpy was written. The program can also correct the ionic strength changes, that can occur during a titration. Thanks to the analogy of the mathematical expressions, the program can also be used for the treatment of spectrophotometric data.

Ion association in solutions of HCl in DMSO–water mixtures: ultrasonic absorption studies

Ultrasonic absorption measurements are reported for the System HCl–dimethylsulfoxide (DMSO)–water in the frequency range 3.5 to 140 MHz. For ail solutions studied, the excess absorption due to the presence of HCl can be fitted well with a single relaxation equation. For 0.10 mol ℓ−1 solutions of HCl in DMSO–water mixtures, no further relaxations at higher frequencies are likely. Reasonable results are obtained when the ultrasonic results are analyzed assuming the process responsible for the excess absorption to be the dissociation–association equilibrium of HCl, and using equilibrium constants determined from conductivity (C. Cooke etal. Electrochim. Acta, 20, 591 (1975)). The value of |ΔVeff| is 20–25 cm3 mol−1 and Kass is approximately 3 × 109ℓ mol−1 s−1, as compared to a value of 10 × 109ℓ mol−1 s−1 calculated from limiting conductivities assuming diffusion-controlled rate theory.

Ion association in solutions of dimethylthallium(III) hydroxide

From studies of the specific hydroxide ion catalyzed decomposition of diacetone alcohol by dimethylthallium(III) hydroxide at 25°C, it is concluded that both ion pairs (dissociation constantK=0.090 mole-dm−3) and dimers (dimerization constantKd=1.5 dm3-mole−1) exist in aqueous solution.

Study of Hydration and Association of Ions in Solution. II. Complete Resolution of Tris(ethylenediamine)Cobalt(III), Chromium(III), and Rhodium(III) Complexes by Means of Paper Electrophoresis

Abstract Complete resolution of racemic [M en3]3+ (M=CoIII, CrIII, and RhIII) by means of electrophoresis was achieved in a background solution of sodium d-tartrate and aluminum chloride. Electrophoretic data obtained under various conditions (various compositions, concentrations, and pH values of supporting electrolyte solutions) indicated that the separation of the enantiomers of [M en3]3+ complexes was accomplished not by the d-tartrate anion but by some aluminum d-tartrate complex anion.