Single ion activity coefficients in concentrated aqueous hydrogen chloride solutions

The adsorption behaviour of the steroids: ouabagenin, ouabain, proscillaridin, digoxin, and k-strophanthine was studied by a.c. polarography and capacitance—time curves at the dropping mercury electrode. The steroids behave like strongly surface-active substances: the relative capacitance decrease ΔC/C₀ depends linearly both on the concentration of the solution and on the root of the drop age. The surface area determined for ouabagenin to be 125 Ų on the basis of adsorption kinetics corresponds roughly to the maximum crosssection of the molecule. With glycosides, the surface area increases with the number of monosaccharide molecules being attached in position 3 of the steroid. It was inferred, therefore, that the adsorbed molecule rests with its steroid and sugar moiety flat on the electrode. A capacitance minimum with sharply defined edges (pit) occurs in the a.c. polarograms of ouabain. In this potential area, the dependences Δ/₀=f(c) and ΔC/C₀=f(t) show a step-like course with two plateaus, which is discussed to be due to association of the adsorbed molecules.     

NaSO 4 − ion pairs in aqueous solutions at pressures up to 2000 atm

Electrical-conductance measurements have been made at 25° C up to concentrations of 0.06M in aqueous solutions of Na₂SO₄ at atmospheric pressure and as a function of pressure up to 2000 atm. Calculations of the change of the dissociation constant for the NaSO ₄ ^? ion pair with pressure indicate that the difference in partial molal volumes between products and reactants at infinite dilution is \(\Delta \bar V^ \circ \tilde = - 8.25{\text{ }}cm^3 /mole\) . Using the equation of Davies, Otter, and Prue, we found the average dissociation constants for five concentrations between 0.005 and 0.06 moles/liter to be 0.097, 0.131, and 0.165 at 1, 1000, and 2000 atm, respectively, with a standard deviation of ±0.003. The atmospheric-pressure value is 0.080±0.016 over the entire concentration range from 0.00005 to 0.06 moles/liter, about half that obtained by Jenkins and Monk. This is consistent with a value ofK=0.077±0.006 recalculated from the limited-concentration-conductance work of Jenkins and Monk, with a value ofK=0.073 obtained by Fisher from data of Kurtze and Tamm on ultrasonic absorption in MgSO₄?NaCl solutions, and withK=0.067 calculated by Fisher from the potentiometric data of Pytkowicz and Kester at high ionic strength. The relationship of this work to sound absorption and ion pairing in seawater is discussed. The predicted pressure dependence of the NaSO ₄ ^? ion pair in seawater from this work differs substantially from earlier work by Kester and Pytkowicz and by Millero.     

Contact ion pair between Na+ and PtCl(6)(2-) favored in methanol

Ion-pair formation between a Na+ cation and the [PtCl62-] anion in methanol is observed from195Pt NMR chemical shift trends as well as from molecular dynamics computer simulations. Free energy of association calculations reveal that contact ion pairs (CIPs) are the most favored configuration in methanol, followed by solvent shared ion pairs (SSHIPs). By contrast, such ion-pair formation is not observed for comparable solutions in water.     

Rate constants for ion pair formation and dissociation in water

The reactive flux time correlation function for an associating ion pair in water is obtained by computer simulation. The transmission coefficient is found directly from the reactive flux and also through the method of absorbing barriers. Rate constants for the transitions between the contact and solvent-separated states of the ion pair are calculated.     

Molecular dynamics studies on yttrium(III) ion diffusion in a cesium chloride melt

Molecular dynamics modeling was used to study diffusion parameters of yttrium(III) ions in cesium chloride melt at the temperature range 900–1200 K.     

Spectroscopy of UO(2)Cl(4)(2)(-) in basic aluminum chloride-1-ethyl-3-methylimidazolium chloride

The optical absorption, emission, FT Raman, one-photon excitation, two-photon excitation, and luminescence lifetime measurements are reported for UO(2)Cl(4)(2)(-) in 40:60 AlCl(3)-EMIC (where EMIC identical with 1-ethyl-3-methylimidazolium chloride), a room-temperature ionic liquid. Comparison of the spectra with previous results from single crystals containing UO(2)Cl(4)(2)(-) allowed the characterization of four ground-state vibrational frequencies, two excited-state vibrational frequencies, and the location of eight electronic excited-state energy levels. The vibrational frequencies and electronic energy levels are found to be consistent with the UO(2)Cl(4)(2)(-) ion. Comparison of the one-photon and two-photon excitation spectra, and the relative intensities of the transitions in the emission spectrum indicate that the center of symmetry is perturbed by an interaction with the solvent.     

KSO 4 − , NaSO 4 − , and MgCl+ ion pairs in aqueous solutions up to 2000 atm

Electrical conductance data at 25°C for K₂SO₄, Na₂SO₄, and MgCl₂ solutions are reported at concentrations up to 0.01 eq-liter^?1 and as a function of pressure up to 2000 atm. The molal dissociation constants are as follows: $$\begin{gathered} {\text{ }}KSO_4^ - :log K_m = ( - 1.02{\text{ }} + 1.6 \times 10^{ - 4} P - {\text{ }}2.5 \times 10^{ - 8p2} ) \pm 0.03 \hfill \\ NaSO_4^ - :log K_m = ( - 1.02 + 9.6 \times 10^{ - 5} P - {\text{ }}4.3 \times 10^{ - 9p2} ) \pm 0.03 \hfill \\ MgCl^ + :log K_m = ( - 0.64 + 1.1 \times 10^{ - 4} P - {\text{ }}1.7 \times 10^{ - 8p2} ) \pm 0.04 \hfill \\ \end{gathered} $$ withP in atmospheres. These values cannot be chosen solely on the basis of minimizing errors in fitting conductance data to theoretical equations. For the values cited above, the Bjerrum distances for 1–2 (or 2-1) and 1-1 salts were used. However, the conductance fits for KSO ₄ ^? and NaSO ₄ ^? were equally good for half-Bjerrum distances and resulted in higher dissociation constants. Ultrasonic data are used to argue in favor of the lower dissociation values derived by using Bjerrum distances. Our results for MgCl⁺ disagree with those of Havel and Högfeldt.     

Rates of oxygen exchange between the [H(x)Nb(6)O(19)](8)(-)(x)(a)(q)) Lindqvist ion and aqueous solutions

Oxygen-isotope-exchange rates were measured between sites in the Lindqvist-type [H(x)()Nb(6)O(19)](8)(-)(x)()((aq)) polyoxoanion and aqueous solution as a function of pH and temperature. The ion has a central mu(6)-O that is inert to exchange, 12 mu(2)-O(H), and 6 eta-O. The potassium salt of this ion is recrystallized in (17)O-enriched water to (17)O-label the anion, which is then redissolved into isotopically normal water so that the (17)O NMR signals from structural oxygens can be followed as a function of time. Because the central mu(6)-O retains its (17)O signal throughout the experiments, it is clear that the polyoxoanion remains intact during isotopic equilibration of the other structural oxygens. At pH conditions where the [HNb(6)O(19)](7)(-) ion predominates, the mu(2)-O(H) sites isotopically exchange with solution about an order of magnitude more rapidly than the eta-O sites. Yet, we observe that the terminal and bridging oxo sites react at nearly the same rates when the ion is coordinated to 2-3 protons and possibly when it is unprotonated. On the basis of molecular models and experimental kinetic data, we propose metastable polymorphs of the hexaniobate structure where four of the mu(2)-O(H) and eta-O sites are temporarily equivalent and bonded to a coordinatively unsaturated Nb(V). This hypothesized intermediate allows facile access to bulk water molecules for exchange but cannot fully explain the kinetic results and additional experiments on other Lindvist ions are required.     

Sequential hydration energies of the sulfate ion, from determinations of the equilibrium constants for the gas-phase reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O

Sequential hydration energies of SO4(H2O)(n)2- were obtained from determinations of the equilibrium constants of the following reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O. The SO4(2-) ions were produced by electrospray and the equilibrium constants Kn,n-1 were determined with a reaction chamber attached to a mass spectrometer. Determinations of Kn,n-1 at different temperatures were used to obtain DeltaG0n,n-1, DeltaH0 n,n-1, and DeltaS0n,n-1 for n = 7 to 19. Interference of the charge separation reaction SO4(H2O)(n)2- = HSO4(H2O)(n-k)- + OH(H2O)(k-1)- at higher temperatures prevented determinations for n < 7. The DeltaS0n,n-1 values obtained are unusually low and this indicates very loose, disordered structures for the n > or = 7 hydrates. The DeltaH0n,n-1 values are compared with theoretical values DeltaEn,n-1, obtained by Wang, Nicholas, and Wang. Rate constant determinations of the dissociation reactions n,n - 1, obtained with the BIRD method by Wong and Williams, showed relatively lower rates for n = 6 and 12, which indicate that these hydrates are more stable. No discontinuities of the DeltaG0n,n-1 values indicating an unusually stable n = 12 hydrate were observed in the present work. Rate constants evaluated from the DeltaG0n,n-1 results also fail to indicate a lower rate for n = 12. An analysis of the conditions used in the two types of experiments indicates that the different results reflect the different energy distributions expected at the dissociation threshold. Higher internal energies prevail in the equilibrium measurements and allow the participation of more disordered transition states in the reaction.     

Modulating the structure and properties of poly(sodium 4-styrenesulfonate)/poly(diallyldimethylammonium chloride) multilayers with concentrated salt solutions

Poly(sodium 4-styrenesulfonate) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) multilayers were treated with 1-5 M NaCl solutions, resulting in continuous changes in the physicochemical properties of the multilayers. Significant mass loss was observed when the salt concentration was higher than 2 M and reached as high as 72% in a 5 M NaCl solution. The disassembly occurred initially in the superficial layers and then developed in the bulk multilayers. For the multilayers with PDADMAC as the outmost layer, the molar ratio of PSS/PDADMAC was increased and the surface chemistry was changed from PDADMAC domination below 2 M NaCl to PSS domination above 3 M NaCl. Owing to the higher concentrations of uncompensated for polyelectrolytes at both lower and higher salt concentrations, the swelling ratio of the multilayers was decreased until reaching 3 M NaCl and then was increased significantly again. The salt-treated PSS/PDADMAC thin films are expected to show different behaviors in terms of the physical adsorption of various functional substances, cell adhesion and proliferation, and chemical reaction activity.     

Viscometry and light scattering on moderately concentrated solutions of poly(vinyl chloride)

Moderately concentrated solutions (0.015–0.10 g/mL) of poly(vinyl chloride) have been studied in three different solvents by light scattering and viscometry. It is concluded that intermolecular association occurs in all solutions studied, including data over the temperature interval 25–110°C. The data can be interpreted in terms of a model with loci of association holding chains together in an aggregate that has an overall configuration similar to that of a randomly branched polymer.     

New BF(-)(4) and ClO(-)(4)-selective membrane electrodes and their pharmaceutical applications

The construction and general performance characteristics of ion-selective membrane electrodes sensitive to BF(-)(4) and ClO(-)(4) anions, respectively, are described. All electrodes show near-Nernstian responses in the range 10(-2) -10(-5)M. The selectivity of the electrodes to a number of organic and inorganic anions are reported. The electrodes are useful in the potentiometric determination of a few pharmaceutical preparations. The method is simple, rapid and does not require prior sample pre-treatment.     

Reactivity of the cadmium ion in concentrated phosphoric acid solutions

The solvation transfer coefficients which characterize the changes of ion reactivity with phosphoric acid concentration have been calculated for cadmium from the constants of the successive chloride complexes, and for silver and diethyldithiophosphate from potentiometric measurements. They evidence the strong desolvation of the cadmium species in concentrated phosphoric acid media, causing a remarkable increase of its reactivity. They allow the results of liquid-liquid extraction, precipitation and flotation reactions to be correctly interpreted and their changes to be foreseen when the reagents are modified.     

Ion-vacancy coupled charge transfer model for ion transport in concentrated solutions

We present a conceptual framework for understanding and formulating ion transport in concentrated solutions, which pictures the ion transport as an ion-vacancy coupled charge transfer reaction. A key element in this picture is that the transport of an ion from an occupied to unoccupied site involves a transition state which exerts double volume exclusion. An ab initio random walk model is proposed to describe this process. Subsequent coarse-graining results in a continuum formula as a function of chemical potentials of the constituents, which are further derived from a lattice-gas model. The subtlety here is that what has been taken to be the chemical potential of the ion in the past is actually that of the ion-vacancy couple. By aid of this new concept, the driving force of ion transport is essentially the chemical affinity of the ion-vacancy coupled charge transfer reaction, which is a useful concept to unify transport and reaction, two fundamental processes in electrochemistry. This phenomenological model is parameterized for a specific material by the aid of first-principles calculations. Moreover, its extension to multiple-component systems is discussed.     

The structure around the perchlorate ion in concentrated aqueous solutions

A neutron diffraction study has been carried out on a 3.25 modal solution of NaClO₄ in heavy water, in which the first-order difference method of isotopic substitution was applied to chlorine atoms of the ClO₄⁻ ion. The results show that (a) the intramolecular separation of Cl-O is 1.43 ± 0.02 Å in good agreement with X-ray diffraction results from single-crystal studies. (b) there are between four and five nearest-neighbour deuterium atoms in the range 2.4 ⩽ r ⩽ 3.2 Å. and (c) the ClO₄⁻-water coordination is less well defined than that for Cl⁻-water, but similar to that for the NO₃⁻-water structure.     

Mechanistic studies on the reactions of PhS(-) or [MoS(4)](2)(-) with [M(4)(SPh)(10)](2)(-) (M = Fe or Co)

Kinetic studies, using stopped-flow spectrophotometry, on the reactions of [M(4)(SPh)(10)](2)(-) (M = Fe or Co) with PhS(-) to form [M(SPh)(4)](2)(-) are described, as are the reactions between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) to form [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). The kinetics of the reactions with PhS(-) are consistent with an initial associative substitution mechanism involving attack of PhS(-) at one of the tetrahedral M sites of [M(4)(SPh)(10)](2)(-) to form [M(4)(SPh)(11)](3)(-). Subsequent or concomitant cleavage of a micro-SPh ligand, at the same M, initiates a cascade of rapid reactions which result ultimately in the complete rupture of the cluster and formation of [M(SPh)(4)](2)(-). The kinetics of the reaction between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) indicate an initial dissociative substitution mechanism at low concentrations of [MoS(4)](2)(-), in which rate-limiting dissociation of a terminal thiolate from [M(4)(SPh)(10)](2)(-) produces [M(4)(SPh)(9)](-) and the coordinatively unsaturated M site is rapidly attacked by a sulfido group of [MoS(4)](2)(-). It is proposed that subsequent chelation of the MoS(4) ligand results in cleavage of an M-micro-SPh bond, initiating a cascade of reactions which lead to the ultimate break-up of the cluster and formation of the products, [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). With [Co(4)(SPh)(10)](2)(-), at higher concentrations of [MoS(4)](2)(-), a further substitution pathway is evident which exhibits a second order dependence on the concentration of [MoS(4)](2)(-). The mechanistic picture of cluster disruption which emerges from these studies rationalizes the "all or nothing" reactivity of [M(4)(SPh)(10)](2)(-).     

Synthesis of the arachno-4-CB(8)H(12)(2)(-) monocarbaborane dianion and NMR/computational studies of the fluxional processes observed in the isoelectronic nine-vertex arachno anions: arachno-4-CB(8)H(12)(2)(-), arachno-4-CB(8)H(13)(-), and arachno-4-SB(8)H(11)(-)

The new monocarbaborane dianion, arachno-4-CB(8)H(12)(2)(-) has been synthesized from the reaction of arachno-4-CB(8)H(14) with 2 equiv of NaH in polar solvents. DFT/GIAO computations at the B3LYP/6-311G//B3LYP/6-311G level, in conjunction with 1D and 2D NMR spectroscopic studies, have confirmed that the dianion results from deprotonation of both the endo-CH and one bridging hydrogen of the parent arachno-4-CB(8)H(14). While the DFT calculations indicate that a C(1) symmetric structure is lowest in energy, the experimental solution NMR data are consistent with the dianion having a C(s)() symmetric structure, thus suggesting that it is fluxional in solution. Transition state calculations located a low-energy pathway with an activation energy of only 2.7 kcal/mol that allows the migration of the bridging hydrogen between the two enantiomeric forms of the dianion. The process can occur by a single-step, simple rotation through a transition state structure containing a -BH(2) group at the B7 boron. Averaging the calculated (11)B NMR chemical shifts of the resonances for those atoms in the static enantiomeric structures that become equivalent by this fluxional process then gives excellent agreement with the solution NMR data. Transition state calculations of the fluxional behavior previously observed for the isoelectronic arachno-4-CB(8)H(13)(-) and arachno-4-SB(8)H(11)(-) monoanions have likewise revealed related low-energy (0.3 and 5.0 kcal/mol, respectively) rearrangement mechanisms involving the simultaneous rotation of three hydrogens (two bridging and one -BH(2)) through a C(s)() symmetry transition state containing three -BH(2) groups.