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

The supramolecular assembly [Ga4 L6 ]12- acts as a nanoscale flask to mediate the reactivity of encapsulated reactive guests and also functions as a catalyst to carry out enzyme-like chemical transformations. The guest binding to the interior cavity and exterior of this host is difficult to untangle because multiple equilibria occur in solution, and only when refining simultaneously data obtained from different techniques, such as NMR, UV/Vis, and calorimetry, can the accurate solution thermodynamics of these host-guest systems be determined. This study reports the driving forces for the inclusion and stepwise exterior guest binding of different aliphatic quaternary ammonium guests to the [Ga4 L6 ]12- assembly. Encapsulation into the host cavity was found to be an entropy-driven process, whereas exterior ion association is driven either by enthalpically favorable attractive forces or by the entropy gain due to desolvation, depending on guest size and character. The analysis of the energetics of reaction may help predicting and understanding the intimate role and contribution of the transition state in those rate-accelerated reactions involving this supramolecular assembly as an enzyme-like molecular flask.

Molecular dynamics simulations unravel the association of citrate to (10–10) and (000–1) growth fronts of zinc oxide and demonstrate an unexpected mobility of the surfactant. Citrate association to perfectly planar (10–10) and (000–1) ZnO-ethanol interfaces was found to be favored over dissociation by 1.5–2 eV hence suggesting strongly bound, immobilized surfactants. However, intramolecular stress prevents binding of all three carboxyl groups to planar surfaces and the typical arrangement is that of two carboxyl-Zn contacts (including two salt bridges each) whilst the remaining carboxyl group is dangling into the solvent. As a consequence, the surfactant exhibits a “walking” mechanism to move along the surface by exchanging the role of its carboxyl groups. This finding has strong implications for the role of citrate during crystal growth as illustrated by a recently developed simulation scheme based on hundreds of individual Zn2+ and OH– ion association steps. In particular, for the (10–10) surface – which grows via formation of ridges embedded by {10–10} faces – these simulations show how citrate ions move towards steps and bind to the growth front by additional 4 eV per surfactant molecule.

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

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

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

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 construction and electrochemical response characteristics of a screen-printed electrode (SPE) for the determination of dodecyltrimethylammonium bromide (DTAB) are described. The sensor was based on the use of DTA-tetraphenylborate ion association complex as an electroactive material in screen-printed electrode with dioctylsebacate (DOS) as a solvent mediator. In aqueous solution of pH 3, the sensor displayed a stable response for six months with reproducible potential and linear response for surfactant over the concentration range 1.20 × 10(-2) -5.6 × 10(-7) mol L(-1) at 25 °C with Nernstian slope of 55.95 ± 0.58 mV decade(-1) for detection limit of 6.8 x 10(-6) mol L(-1) . The response time was 6-10 s. The selectivity coefficients indicate excellent selectivity for DTAB over many common cations (e.g. Mg(2+), Na(+), K+, Co(2+), Ni(2+), Ca(2+), Cl(-), I(-), SO(4)(-2) and cetylpyridinium chloride (CPC). The sensor was used successfully for the determining of DTAB in pure form and water samples with average recoveries of 99.98, 98.78, and 99.99%.

A novel method for the sensitive determination of bismuth(III) in pharmaceutical products using phosphoric acid as a molecular probe by resonance light scattering (RLS) is discussed. In 0.5 mol/L phosphoric acid (H3PO4) medium, bismuth(III) reacted with PO43− to form an ion association compound, which resulted in the significant enhancement of RLS intensity and the appearance of the corresponding RLS spectral characteristics. The maximum scattering peak of the system existed at 364 nm. Under optimal conditions, there was linear relationship between the relative intensity of RLS and concentration of bismuth(III) in the range of 0.06–10.0 µg/mL for the system. A low detection limit for bismuth(III) of 3.22 ng/mL was achieved. The relative standard deviations (RSD) for the determination of 0.40 and 0.80 µg/mL bismuth(III) were 2.1% and 1.1%, respectively, for five determinations. Based on this fact, a simple, rapid, and sensitive method was developed for the determination of bismuth(III) at nanogram level by RLS technique with a common spectrofluorimeter. This analytical system was successfully applied to determine the trace amounts of bismuth(III) in pharmaceutical products, which was in good agreement with the results obtained by atomic absorption spectrometry (AAS). Copyright © 2011 John Wiley & Sons, Ltd.

A method for the determination of Cd by AAS in foodstuffs is presented. The determination is carried out after low temperature ashing and extraction with a high molecular weight amine. Of the several extractions investigated, Aliquat 336 3% and Alamine 336 3% in Methylisobutylketone allowed the best results. The former was chosen. The analysis of international standards shows that the method yields accurate results.

A family of cationic heavy alkaline earth-metal complexes based on the weakly coordinating tetraphenylborate anion [BPh4]– provides unique insight into ion association trends within this family of compounds. The compounds were prepared by protonolysis of the respective alkaline earth-metal bis[bis(trimethylsilyl)]amides M[N(SiMe3)2]2(thf)2 (M = Ca, Sr, Ba) with ammonium tetraphenylborates [R3NH][BPh4] (R = Me, Et) in various stoichiometric ratios, resulting in the separated ions [M(donor)n][BPh4]2 (M = Ca, Sr, Ba; n = number of donors). All compounds but [Ba(hmpa)6][BPh4]2 (3c) were characterized using single-crystal X-ray diffraction, 1H and 13C NMR, IR spectroscopy and melting point.

An algorithm is developed to compute the conductivity of lake and dilute ocean water from measured chem- ical composition at arbitrary temperature and pressure. The complex mixed electrolyte is considered as a sum of binary electrolytes rather than a sum of ions. Effects of ion association are included, and it is found that pair- ing effects are important in natural freshwaters. Bounds on the accuracy of the algorithm for specific classes of binary electrolytes are assessed and it is estimated that the algorithm has an overall accuracy of better than 2% for salinities less than about 4 g L -1 . Comparison with seawater conductivities is much better than 1%, but pre- dicted conductivities of some published analyses of river waters are about 3% too high. Some of this difference may be due to a lack of data on ion pairing effects between bivalent metals and bicarbonate, but also may result from uncertainties in the measured chemical composition and measured conductivity. An iterative procedure incorporating this algorithm is used to compute reference conductivity at 25°C and salinity from in situ mea- surements of conductivity in waters where only relative amounts of ions are known. It is found that the con- version to reference conductivity is reasonably independent (to within about 1%) of the ionic composition for most world river waters, but is somewhat different than that for KCl solutions. However, derived salinities are quite sensitive to the composition, and the ratio of ionic salinity to reference conductivity varies between 0.6 and 0.9 mg L -1 (μS cm -1 ) -1 .

Schiff base VO2V and VOV complexes with long 4-substituted alkoxy chains have been synthesised from the corresponding VOIV complexes, [VO{(4-CnH2n+1O)xsalen}] [x = 1, 2, n = 3–16 and salen = N,N′-ethylenebis(salicylideneiminato)], in solutions in the absence or presence of HClO4 under aerobic conditions. The green single-crystals of the VOIV complexes (x = 2, n = 3, 4, 6) coexisting with solutions without HClO4 turned slowly to the yellow single-crystals of the species with n = 3 (1) and 4 (2), a process which took several months. An X-ray crystallographic analysis revealed that the VOIV complexes are transformed into the dimeric VO2V complexes with the tridentate sal-en (sal-en = N-salicylideneethylenediamine) ligand from the tetradentate salen moieties. However, the single crystals of the VOIV complexes with longer alkoxy chains of n ≥ 8 did not yield the corresponding yellow crystals of the VO2V complexes. This crystal-to-crystal transformation is discussed in relation to the crystal packing structures of the VOIV complexes. In contrast, addition of HClO4 solution to two series with one and two alkoxy chains in the 4-positions immediately afforded the corresponding blue VOV perchlorate complexes, [VO{(4-CnH2n+1O)xsalen}]ClO4 (x = 1, 2) without transformation of the salen moieties. The structure of 8·MeOH·0.5H2O determined from an X-ray crystallographic analysis was a unique dimeric structure supported by electrostatic stacking and CH–π interactions in an octahedral environment. The DFT calculations were studied to obtain the stabilisation energy for the dimerisation. Furthermore, in methanol solution, the effects of the alkoxy chain lengths on the ion association were investigated by conductivity measurements. The ion-association state in methanol solution is discussed with the solid-state structure.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Solvation and association interactions in solutions of lithium tetrafluoroborate/4-ethoxymethyl-ethylene carbonate (EEC) have been studied as a function of concentration of lithium tetrafluoroborate by infrared and Raman spectroscopy. Strong interactions between Li(+) and solvent molecules or BF(4)(-) anions were observed. Splitting of the ring symmetric angle deformation band, the carbonyl stretching band and the skeletal ring vibrational band suggests that the interaction between Li(+) ions and EEC molecules take place via the oxygen atom on the carbonyl group. The apparent solvation numbers of Li(+), varying from 4.32 to 1.26 with increasing the solution concentrations, were deduced. Band-fitting to the B-F stretching band of BF(4)(-) anion permits detailed assess of ion pairing. The spectroscopically free BF(4)(-) anion, contact ion pair and contact ion dimmers coexist in concentrated solutions.

In search of new synthetic precursors for the preparation of alkaline earth organometallic compounds, we investigated the application of a powerful desilylation reaction to cleanly afford a variety of contact and charge-separated alkali metal derivatives without the difficulties commonly encountered in other methods. The resulting diphenylmethanides display both contact molecules and separated ion pairs. Analysis of the structural data demonstrates that simple electrostatic models are insufficient for predicting and explaining the solid-state structures of these complexes. Detailed computational investigations were performed to probe the nature of the metal-anion and metal-donor interactions and determine the contributions of each to the observed solid-state structures.

The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1 x 10(-2) to 6 x 10(-5) M and 1 x 10(-2) to 1 x 10(-5) M for PA-TPB and PA-TTC respectively at 25 degrees C over the pH range of 3-5.0 with a cationic slope of approximately 56.5 +/- 0.5 mV/decade for both sensors respectively. The lower detection limit is 4 x 10(-5) and 8 x 10(-6) M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0- 3000.0 microg/ml of PA in aqueous solutions shows an average recovery of 99.1% and a mean relative standard deviation of 1.4 at 100microg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out.

Conductances of sodium alginate, sodium carboxymethylcellulose and sodium carboxymethyl dextran solutions have been measured in the presence of sodium chloride. It has been found that the sum of the specific conductances of the components measured separately is always greater than the specific conductance of the mixture. The difference in specific conductance between the sum and the mixture, Δ, has been studied as a function of the polyelectrolyte concentration, concentration of sodium chloride and also temperature. An attempt has been made to interpret the results in terms of both electrostatic effects and the Donnan theory of membrane equilibrium. The latter approach does not seem satisfactory.

Solvation 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.

The anion polymerization process is affected by the solvent and the counterion. A study has been made of the quantitative aspects of this effect using as a model reaction the formation of aromatic anion radicals in various ethers. The solvating capacity of the ethers with respect to alkali metal cations has been compared. The stability of the solvate complexes is due more to steric factors than to the electron donor and dielectric properties of the solvent or the polarity of its molecules. The heat of solvation of the cation contributes considerably to the energetics of anion-radical formation. Therefore the structure of the solvent molecules strongly affects the thermodynamic parameters of the reaction. The solvation mechanism and its role in the ion association are discussed.

In the ternary system CCl4-PMMA-benzene, benzene is preferentially adsorbed in the solvation shell of the polymer. One solvation equilibrium constant allows a satisfactory description of the preferential solvation for a large range of solvent compositions. The nuclear magnetic relaxation time T1 of benzene protons was measured for different values of the polymer concentration. The measurements are compared with analogous measurements in the system C6D6-PMMA-C6H6 where no preferential solvation is to be expected. For the system CCl4-PMMA-benzene the resulting dimensionless solvation equilibrium constant is K = c32c10/c12c30 = 2.5 ± 0.5 where c10 is the CCl4 concentration in the “free” solvent; c30 is the benzene concentration in the free solvent; c12 and c32 are the concentrations of CCl4 and benzene in contact with the polymer chain, respectively.

A detailed investigation of aqueous solutions of magnesium sulfate has been made by dielectric relaxation spectroscopy (DRS) over a wide range of frequencies (0.2or=nu/GHzor=89), concentrations (0.02or=m/mol kg(-1)or=2.3) and temperatures (5or=theta/ degrees Cor=65). Consistent with literature data from other techniques, the spectra show clear evidence at all temperatures for the simultaneous existence of double solvent-separated (2SIP), solvent-shared (SIP) and contact (CIP) ion pairs and a triple ion (TI), Mg(2)SO(4) (2+)(aq). Increased formation of CIPs and especially TIs occurs with increasing temperature. The overall standard ion-association constant, K(A) degrees , corresponding to the equilibrium: Mg(2+)(aq)+SO(4) (2) (-)(aq)==MgSO(4) (0)(aq) is in good agreement with literature data at lower temperatures but is overestimated at higher temperatures due to processing difficulties. Despite the limited precision of the spectra, analysis of the individual steps in the ion-association process is possible for the first time. The 2SIPs are formed with little disturbance to their hydration shells, the (partial) destruction of which appears to occur mostly during the formation of SIPs. Effective hydration numbers derived from the DRS spectra indicate that both Mg(2+) and SO(4) (2-) influence solvent water molecules beyond their first hydration spheres but that MgSO(4)(aq) is less strongly hydrated than the previously studied CuSO(4)(aq).

The ionization constants of 2,7-dichlorofluorescein were determined and the molecular structures of the equilibrium forms were established in the ternary solvent system benzene-ethanol-water (mass ratio 47:47:6) by using visible spectroscopy. In this solvent mixture with relative dielectric constant e r =12.8 and normalized Reichardt's parameter E N T = 0.587, an inversion of the stepwise ionization constants of the dye, K α1 and K α2 , occurs. The K α1 /K α2 ratio changes from 16 in water and 4.8 in 50 mass % aqueous ethanol to 0.1 in the ternary solvent system with ionic strength of 0.002 mol dm -3 , where pK α1 =9.23 ±0.08 and pK α2 = 8.22 ± 0.08 (25 °C). Such an extraordinary interrelation between the K a constants is in line with the molecular structure of ionic and nonionic species of 2,7-dichlorofluorescein deduced from their vis absorption spectra, as well as with the expressed salt effects and the probable ion association. The dianion R 2- (5 in Scheme 1) possesses a band with λ max =512nm and a molar absorptivity of E=84.3 × 10 3 cm -1 mol -1 dm 3 . The tautomeric equilibrium of the neutral form, H 2 R, is strongly shifted toward the colorless lactone (2 in Scheme 1). The (very intensive) absorption band of the HR - species singled out from the vis spectra at different acidity, is red-shifted by Δλ ≈ 20 nm against the band of the dianion R 2- . Hence, the monoanion HR - is found to be completely converted into the 'phenolate' tautomer 4 with groups -COOH and -O - , while in aqueous solutions the 'carboxylate' tautomer 3 with groups -COO - and -OH predominates. In 50 mass % aqueous ethanol, the two tautomers 3 and 4 exist in commensurable concentrations. Emission and fluorescence excitation spectra and fluorescence quantum yield of the dianion R 2- in the ternary solvent mixture were determined.

Raman spectroscopic studies of the ion association of Mg2+ and SO42− with H2O molecules in solutions of different crystallization fields of the quaternary system Na+, Mg2+/Cl−, SO42−/H2O were carried out in the wavenumber ranges 100–1700 and 2700–4000 cm−1. The water activity of the examined solutions was calculated at 25 °C using the Pitzer method. Direct correlation between the SO42− ion associations and the water activity in these saturated solutions was established. The ν1(SO42−) Raman band was found to be symmetrical in saturated solutions with a high water activity and low concentration of Mg2+ ions. With increasing Mg2+ concentration, asymmetry of the ν1(SO42−) band appeared. Band components at 980, 990, 1003 and 1021 cm−1 were found. We assume that the ν1(SO42−) band components at 980 cm−1 correspond to non-associated SO42− ions. At 990 cm−1 they are associated with solvent-separated ionic pairs (Mg2+H2OSO42−), at 1003 cm−1 with the direct ionic pair Mg2+–OSO32− and at 1021 cm−1 with more strongly deformed SO42− groups. The differences observed in the crystallization kinetics of the salts in this quaternary system are explained by the different associations of the SO42− and Mg2+ ions and the H2O molecules in these saturated solutions. Copyright © 2005 John Wiley & Sons, Ltd.

Raman spectra of sodium chlorate in N,N-dimethylformamide (DMF) solution were obtained. The band at 926 cm−1 that has been previously assigned to the vibrational mode of the associated chlorate with Cs symmetry is, in fact, due to the non-associated chlorate vibration with C3v symmetry. In the ν2 region of the chlorate anion, a new feature at 600 cm−1 was observed and the results show that it also belongs to the non-associated chlorate. Both bands at 926 and 600 cm−1 are assigned to the vibrations involving O37ClO, in full agreement with the results of normal coordinate analysis reported by others workers. Quantitative measurements performed in the range 590–630 cm−1, allowed the determination of the extent of contact ion pair formation. The results show that the ion association in the NaClO3–DMF system is significantly greater than in the NaClO4–DMF system and this is due the higher charge density and lower symmetry of the chlorate anion. Similar conclusions were reached by others who used different experimental techniques. Copyright © 2004 John Wiley & Sons, Ltd.

The electrode oxidation of 11-ferrocenyltrimethylundecylammonium (FeTMUA) at carbon paste electrode (CPE) was investigated by cyclic voltammetry in order to reveal the adsorption nature of FeTMUA ion-paired with anion. The voltammograms of FeTMUA were classified by the counter anion; hydrophilic and hydrophobic ions. The electric charge reflecting the adsorption isotherm increased gently with the FeTMUA concentration until a critical point (CP), which was independent of the sort of hydrophilic anion and comparable with the amount of the maximum surface coverage of FeTMUA at the air-water interface. The voltammogram for hydrophobic anion had two oxidation waves. The electric charge for the first wave monotonously increased with the FeTMUA concentration without indicating CP. The second wave was not observed on the voltammogram at the glassy carbon electrode, thus the second wave was made from the pasting liquid. These results suggested that CPE adsorbed FeTMUA with hydrophilic anion behaved like serving a liquid surface, however, CPE adsorbed FeTMUA with hydrophobic anion was disordered and represented the heterogeneity.

Using a molal conductance method, ion solvation and ion association in polytriethylene glycol dimethacrylate (PTREGD)-LiClO4 gel electrolytes with amorphous ethylene oxide-co-propylene oxide (EO-co-PO, , = 1750) as the plasticizer were investigated. It was found that the fraction of solute existing as single ions (alpha(i)) and ion pairs (alpha(p)) decreases, while that of triple ions (alpha(t)) increases linearly with increasing salt concentration. The dependence of these fractions on molecular weight of plasticizer was also examined. It was shown that alpha(i) and alpha(t) increase and alpha(p) decreases with increasing molecular weight. The result of temperature dependence of these fractions was very interesting: when the temperature is lower than 55 degrees C, alpha(i) increases while alpha(p) and alpha(t) decrease with increasing temperature; however, when the temperature is higher than 55 degrees C, the reverse is true.

Solutions of sodium tetrafluorobrate (NaBF4) in N,N-dimethylformamide were investigated by Fourier transform Raman spectroscopy up to 4.30 mol kg−1 salt concentration. The new band in the N—CO deformation region arising from the bound solvent was examined in detail and a mean solvation number of 3.3 was obtained. The changes in the ν1 band of the BF4− anion indicate the presence of the contact ion pair Na+BF4−. The geometry of the contact ion pair is suggested from density functional theory calculations. Copyright © 2003 John Wiley & Sons, Ltd.

Separation of the positional isomers of chlorobenzoates and naphthalenesulfonates by capillary electrophoresis was investigated. A quaternized porphyrazine ion was synthesized and used as an additive in aqueous electrolytic solution. The positively charged macromolecule dynamically coated the surface of the fused silica capillary and reversed the direction of electroosmotic flow. The positional isomers of aromatic anions were well separated by the ion association reaction and possibly by π-π interaction between macrocyclic cation and aromatic anions.

The conductivity of some transition metal perchlorates, M(ClO 4 ) 2 (M 2 + = Mn, Co, Ni, Cu and Zn) has been measured in urea-water mixtures at 288-318 K. The limiting molar conductivities and the ion association constantsof these electrolytes were calculated by the Shedlovsky extrapolation method. The ion association constants decreased in the order Co > Ni > Zn with increasing the atomic number, whereas Cu >Mn in the ionic association constants as a result of the maximum temperature dependencies of Cu 2 + , The thermodynamic functions, ΔH \ and ΔS \ , for the formation of that ion pair have also been obtained. Both ΔH \ and ΔS \ for all the salts under study are positive values. On the other hand, the Walden products, Λ o η, of the salts increase with an increase in temperature at 288-318 K, which indicate that these electrolytes behave as structure-makers or promotors. Also, the activation energies, E, have been calculated and discussed.

The synthesis and structural characterization of a family of calcium thiolates and selenolates is described. In the solid state the compounds adopt either contact pairs, as observed in Ca(THF)4(SMes*)2 (1), (Mes* 2,4,6-tBu3C6H2), and Ca(THF)4(SeMes*)2, (2), or separated ions as shown in [Ca(18-crown-6)(HMPA)2][SeMes*]2 (3). The two different ion association modes are induced by addition of specific donors. The compounds were prepared by metalation involving the reaction of elemental calcium dissolved in dry liquid ammonia with either HSMes* or Mes*SeSeMes*. All compounds were characterized by X-ray crystallography, NMR and IR spectroscopy. Calciumthiolate und -selenolate: Synthese und Kristallstruktur Die Synthese und Kristallstruktur einiger Calciumthiolate und -selenolate wird beschrieben. Im Festkorper werden entweder Kontakt-Ionenpaare wie in Ca(THF)4(SMes*)2 (1), (Mes* 2,4,6-tBu3C6H2), und Ca(THF)4(SeMes*)2 (2), beobachtet, oder separierte Ionenpaare wie in [Ca(18-crown-6)(HMPA)2][SeMes*]2 (3) erhalten. Die verschiedenen Verbindungstypen konnen durch die Zugabe von spezifischen Donatoren erhalten werden. Die Titelverbindungen werden durch die Reaktion von in trockenem, flussigem Ammoniak gelostem elementaren Calcium mit HSMes* oder Mes*SeSeMes* erhalten. Alle Verbindungen wurden durch Rontgenstrukturanalyse, IR- und NMR-Spektrokopie charakterisiert.

Thermodynamic parameters for complexation of polyvalent cyclodextrin (CD) cation and anion with oppositely charged guests have been determined in D2O containing 0.02 M NaCl by means of 1H-NMR spectroscopy. Protonated heptakis(6-amino-6-deoxy)-beta-CD (per-NH3+-beta-CD) forms stable inclusion complexes with monovalent guest anions. The enthalpy (deltaH) and entropy changes (deltaS) for complexation of per-NH3+-beta-CD with p-methylbenzoate anion (p-CH3-Ph-CO2-) are 3.8 +/- 0.7 kJ mol(-1) and 88.6 +/- 2.2 J mol(-1) K(-1), respectively. The deltaH and deltaS values for the native beta-CD-p-CH3-Ph-CO2- system are -8.6 +/- 0.1 kJ mol(-1) and 15.3 +/- 0.7 J mol(-1) K(-1), respectively. The thermodynamic parameters clearly indicate that dehydration from both the host and guest ions accounts for the entropic gain in inclusion process of p-CH3-Ph-CO2- into the per-NH3+-beta-CD cavity. The fact that the neutral guests such as 2,6-dihydroxynaphthalene and p-methylbenzyl alcohol hardly form the complexes with per-NH3+-beta-CD exhibits that van der Waals and/or hydrophobic interactions do not cause the complexation of the polyvalent CD cation with the monovalent anion. The acetate anion is not included into the per-NH3+-beta-CD cavity, while the butanoate and hexanoate anions form the inclusion complexes. The complexation of the alkanoate anions is entropically dominated. Judging from these results, it may be concluded that Coulomb interactions cooperated with inclusion are required for realizing the large entropic gain due to extended dehydration. Entropically favorable complexation was also observed for the anionic CD-cationic guest system. The present study might present a general mechanism for ion pairing in water.

Complex formation reaction of some crown ethers with alkali metal ions was analyzed by measuring the electrophoretic mobility of analytes in capillary zone electrophoresis. For UV-absorbing crown ethers, the crown ethers were used as the analytes, whereas for less UV-absorbing crown ether, alkali metal ions were used as the analytes and detected indirectly. The apparent electrophoretic mobility of the analytes changed with increasing the concentrations of reacting agents in the migrating solution. The complex formation constants were obtained by analyzing the mobility change by a nonlinear least-squared method. Also ion association reaction of the metal complexes with some hydrophobic anions were analyzed. ©2000 John Wiley & Sons, Inc. J Micro Sep 12: 113–119, 2000

Adsorption stripping voltammetry (AdSV) for anionic surfactants was examined, based on ion association with an electroactive ferrocenyl cationic surfactant. The ion association complex between an anionic surfactant and a ferrocenyl cationic surfactant accumulated on the carbon paste electrode (CPE) in the absence of an applied potential. The concentration of anionic surfactant was indirectly evaluated from the oxidation wave of the ferrocenyl cationic surfactant. By means of AdSV, levels of anionic surfactants of 10−7 mol dm−3 could be measured with good selectivity. The role of pasting liquids on the accumulation behavior of ferrocenyl TMA were examined by a comparison of two pasting liquids. The first, 2-nitrophenyl octyl ether (NPOE) was capable of extracting the ferrocenyl TMA salt, while the other, di-n-octylphthalate (DOP) was not. The voltammograms of ferrocenyl TMA varied considerably with the pasting liquids. In particular, the peak potentials at NPOE-CPE gradually shifted with time, as a result of the extraction of the ferrocenyl TMA salt into the CPE. However, the peak potential at DOP-CPE remained constant.

A Raman spectroscopic study of aqueous solutions of MgSO4 as function of concentration and temperature was performed. From the analysis of the band profile of the internal vibrations of the sulphate ion, the spectroscopic ionic association constant was calculated at different temperatures. It was found that the association is solvent separated in the ranges of concentration and temperature studied. The large differences observed between the values obtained for the spectroscopic association constant and those obtained from macroscopic measurements were interpreted on the basis of a four-step solvent-separated dehydration mechanism. It is, assumed that the Raman spectra reflect only the short-distance force acting on the sulphate anions. The contribution of the long-range forces for the consecutive steps were calculated using the Bjerrum equation. Good agreement between the overall association constant thus calculated and the macroscopic value was found in the concentration and temperature ranges studied.

The temperature dependence of ionic mobility for a silver ion conducting borate glass with composition 55.5 AgI-22.25 Ag 2 0-22.25 B 2 O 3 (in mol%) is reported along with conductivity. Subsequently the value of mobile carriers n is calculated. The value of n is found to decrease with increase in temperature. Two types of ion association mechanisms viz., (i) self association and (ii) network association are proposed to explain the results. The proposed ion associations are checked by optical microscopy and temperature dependent IR spectral studies

Ion–polymer and ion–ion interactions in polymer electrolytes have been investigated at different temperatures and pressures, and for different polymer molecular weights. Salt–polymer complexes of various triflate salts, M(CF3SO3)x (M = Li+, Na+, Ca2+, Cu2+ and Nd3+), in low molecular weight polyethers (PEO and PPO) have been studied using Raman and Brillouin scattering. It is found that anions coordinated to the OH end groups of the polyethers are more stable than cations forming crosslinks between oxygens of adjacent chains, which in turn are more stable than cations coordinated to single chains. We have observed that the number of ion pairs increases as the polymer molecular weight increases. Furthermore, the ion–ion interaction is strongly temperature-dependent and shows widely different behavior in different systems. In the case of Li+-, Na+- and Ca2+-containing polyether complexes the ion association increases with increasing T. It is constant in Cu2+–triflate complexes, while it decreases for complexes containing trivalent Nd3+ cations. Pressure observations in LiCF3SO3–PPO complexes reveal increasing solubility and fewer ion pairs as pressure increases. It is shown that theories which consider volume changes in the salt dissociation process can qualitatively explain the effects of molecular weight, temperature and pressure using entropy considerations. The entropy effect includes contributions due to free-volume dissimilarities between the solvated ions and the macromolecules, structural ordering induced via cationic crosslinking of adjacent chains and electrostriction. Comparing the spectroscopic data with conductivity data, it is found that differences in the “free” solvated ion concentration can account for differences in conductivity.

The formation of adducts with 1 :2 and 1:3 stoichiometry by methoxide addition to nitro-activated anisoles has been examined spectrophotometrically. For these equilibria the ‘basicity’ of sodium methoxide solutions in methanol is appreciably greater than that of corresponding potassium methoxide solutions. This is in contrast with other measures of basicity and is attributed to the association of the multi-charged adducts with cations which is stronger with sodium than with potassium ions.

EPR analysis shows that the anion radical of 2,6-dinitrotoluene (DNT) in liquid ammonia exists with the counterion (either K+ or Na+) associated with one of the two nitro groups. This tight association (−NO2•-M+) persists after solvent removal, and it renders the anion radical very susceptible to loss of metal nitrite. The slightest agitation of the solid potassium salt of DNT•- leads to detonation, and formation of KNO2 and polymer (in the solid phase) and CH4, HCN, H2, and N2O (in the gas phase). Trapping experiments suggest that the methane comes from carbenes, and it is suggested that the HCN comes from an anthranil radical intermediate. The potassium anion radical salts of 1,3-dinitrobenzene, 2,6-dinitrotoluene, 1,3,5-trinitrobenzene, and 2,4,6-trinitrotoluene all readily lose KNO2, and the ease of C−NO2•-M+ bond rupture increases with the degree of nitration. In the cases of the two trinitrated systems dissociation takes place immediately upon anion radical formation in liquid ammonia. This observat...

Highly sensitive and selective methods for the determination of trace elements in waters and solutions are made possible by the combination of flotation and spectrophotometry (flotation spectrophotometry). The basis for it are multiply charged anion complexes of the analyte, which form sparingly soluble ion association complexes with singly charged basic dye cations in aqueous solution. Intense shaking of the aqueous solution with an organic solvent (having a low dielectric constant) results in the accumulation of these ion association complexes at the interface or on the vessel walls (flotation step). After separating the ion association complexes from the liquid phases, they are dissolved and dissociated in a polar organic solvent and the absorbance of the basic dye ions is measured as a function of the concentration of the analyte. By the example of the trace determination of arsenic in natural water, the possibilities of analytical chemistry by combination of flotation steps and spectrophotometry are demonstrated. According to the arsenic content, its determination can be performed by flotation spectrophotometry with crystal violet (detection limit 50 ng/ml As), by an indirect determination of arsenic via flotation spectrophotometry of molybdenum in the dodecamolybdoarsenic acid (detection limit 1 ng/ml As) or by the combination of collector precipitation of arsenic with zirconium hydroxide followed by froth flotation and flotation spectrophotometry as the determination technique (detection limit 0.05 ng/ml As). The reproducibilities of these variants are indicated and their accuracy is checked by comparison of methods.

Solution behavior of Na sulfonated polystyrene (NaSPS) ionomers with different percentages of sulfonate was studied by viscosity and dipole moment measurements. Two solvents of different character were chosen, i.e. dioxane (ϵ = 2.22) and dimethyl formamide (DMF, ϵ = 36) and their mixtures. The reduced viscosity as a function of concentration in polar solvents reflects the ‘polyelectrolyte’ behaviour of the ionomers. Mean-squared dipole moment ( /x) values were calculated over a temperature range of 20–100°C, in dioxane and in a mixture of 4% DMF in dioxane. The results confirm the ‘polyelectrolyte’ behavior of ionomers by the addition of a small amount of polar cosolvent. The effect of increasing temperature on /x in the DMF-dioxane mixture is attributed to the formation of a coordination complex.

The electrical conductivities of aqueous solutions of Na2SO4, H2SO4, and their mixtures have been measured at 373−673 K at 12−28 MPa in dilute solutions for molalities up to 10-2 mol kg-1. These conductivities have been fit to the conductance equation of Turq et al.1 with a consensus mixing rule and mean spherical approximation activity coefficients. Provided the concentration is not too high, all of the data can be fitted by a solution model that includes ion association to form NaSO4-, Na2SO40, HSO4-, H2SO40, and NaHSO40. The adjustable parameters of this model are the dissociation constants of the SO4- species and the H+, SO4-2, and HSO4- conductances (ion mobilities) at infinite dilution. For the 673 K and 230 kg m-3 state point with the lowest dielectric constant, e = 3.5, where the Coulomb interactions are the strongest, this model does not fit the experimental data above a solution molality of 0.016. Including the species H9(SO4)5- gave satisfactory fits to the conductance data at the higher concen...

The possibility that ion clusters of different species are formed during dissolution of LiAsF6 in a low- or high-molecular-weight solvent has been studied. The Hessian matrix of clusters has been calculated by the numerical and analytical differentiation of their full energy in the MO LCAO approximation using the Roothaan−Hartree−Fock method and the PC GAMESS software package. It was found that stable ion clusters are represented by ion pairs Li+[AsF6]- with the bi- or tridentate coordination of the cation relative to the octahedral anion, triple ions [AsF6]-Li+[AsF6]- and Li+[AsF6]-Li+ with the bi- or tridentate coordination, ion dimers {Li+[AsF6]-}2 with the bidentate coordination, and also ion trimers {Li+[AsF6]-}3 and ion tetramers {Li+[AsF6]-}4 shaped as symmetric ring structures with the unidentate coordination. The frequencies and intensities of IR absorption bands of different species of ion clusters in the gaseous phase and nonaqueous solutions (acetone, ethanol, nitromethane, and tetrahydrofuran...