Structures of the nearest surroundings of the K<Superscript>+</Superscript>, Rb<Superscript>+</Superscript>, and Cs<Superscript>+</Superscript> ions in aqueous solutions of their salts

Published data on structural characteristics of hydration of K⁺, Rb⁺, and Cs⁺ ions in aqueous solutions of their salts under standard conditions, including authors’ X-ray diffraction data, are summarized and correlated. The structural parameters of the nearest surrounding of the K⁺, Rb⁺, and Cs⁺ ions, such as the coordination numbers, interparticle distances, and types of ionic association, are discussed. It is noted that, because of weak tendency of these cations to hydration, the parameters of their coordination spheres strongly depend on the concentration and chemical nature of counterions.     

Structure of the nearest surrounding of the Li+ ion in aqueous solutions of its salts

Structural characteristics of hydration of lithium ion in aqueous solutions of its salts are studied by X-ray diffraction. The results are summarized and correlated with relevant published data obtained by various methods. The structural parameters of the nearest surrounding of the Li⁺ ion, such as the coordination number, interparticle distances, and types of ionic association, are discussed.     

An NMR study of comenic acid and its salts with Li<Superscript>+</Superscript> and Na<Superscript>+</Superscript> in aqueous solution and solid state

The forms and structure of comenic acid and its salts with Na⁺ and Li⁺ in solution and solid state are studied by multinuclear NMR spectroscopy. The formation of dimeric structures of comenic acid in the solid state is shown. It is found that disubstituted sodium and lithium salts have different structures.     

Selective ion-exchange sorption of K<Superscript>+</Superscript> from aqueous solutions containing Na<Superscript>+</Superscript>-K<Superscript>+</Superscript> mixture on Sn(IV) hydrophosphate

Ion-exchange sorption of K⁺ and Na⁺ from their mixture on X-ray-amorphous and crystalline Sn(IV) hydrophosphates was studied. These sorbents exhibit a high selectivity for K⁺. Amorphous Sn(IV) hydrophosphate can be used for efficient purification of aqueous sodium salt solutions to remove potassium impurity.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1275–1278.Original Russian Text Copyright © 2004 by Smirnov, Dimova, Redchenko.     

Structural parameters of Ca<Superscript>2+</Superscript> ion nearest neighbors in aqueous solution of its salts

Published data on structural parameters of the environment of calcium(II) ions in aqueous solutions of the corresponding salts under standard conditions, obtained by different methods, as well as authors’ X-ray diffraction data, were summarized. Such parameters of the nearest neighborhood of Ca²⁺ ion as coordination number, interatomic distances, parameters of the second coordination shell, and ion association modes are discussed.     

Kinetics of H<Superscript>+</Superscript>/Na<Superscript>+</Superscript> solid-phase ion exchange on iron(III) hydrogen sulfate

The kinetics of solid-phase reaction between iron(III) hydrogen sulfate and sodium chloride was studied by thermal analysis followed by analysis of leaving gases. The exchange kinetics are described by the soft cylinder model. The hydrogen and sodium ion interdiffusion coefficients were determined for various temperatures, as well as the activation energy of interdiffusion. Sodium ion diffusion through the product layer is the rate-controlling stage of the reaction.     

Hydration numbers of Na<Superscript>+</Superscript> and Cl<Superscript>−</Superscript> ions in an aqueous urea solution

The relations for the calculation of the partial molar volumes of NaCl, NaBPh₄, and Ph₄AsCl in an aqueous urea solution are obtained. The salt characteristics are divided into ionic components. Different methods of the division are discussed. It is shown that the hydration numbers of Na⁺ and Cl⁻ ions decrease with increasing urea concentration; therewith, the dehydration of Cl⁻ ion occurs relatively faster.     

Na<Superscript>+</Superscript>-stimulated ATPase of alkaliphilic halotolerant cyanobacterium <Emphasis Type="Italic">Aphanothece halophytica</Emphasis> translocates Na<Superscript>+</Superscript> into proteoliposomes via Na<Superscript>+</Superscript> uniport mechanism

Background  

When cells are exposed to high salinity conditions, they develop a mechanism to extrude excess Na⁺ from cells to maintain the cytoplasmic Na⁺ concentration. Until now, the ATPase involved in Na⁺ transport in cyanobacteria has not been characterized. Here, the characterization of ATPase and its role in Na⁺ transport of alkaliphilic halotolerant Aphanothece halophytica were investigated to understand the survival mechanism of A. halophytica under high salinity conditions.     

The solvation dynamics of Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> ions in liquid methanol

The structure of the solvation shell of Na⁺ and K⁺ in fully deuterated liquid methanol has been studied by ab initio Car-Parrinello molecular dynamics simulations. The solvent cage has been found relatively stable and this property has been explained by means of charge transfer and electrostatic interactions as was previously done for Li⁺ in the same solvent. The differences with Li⁺ such as the increase of the coordination number going from Li⁺ to K⁺ and the reduced stability of the cage have been ascribed to the increase in the ionic radius.     

Crisis of stability of hydration shell of Na<Superscript>+</Superscript> ion in condensing water vapor

The Gibbs energy and equilibrium work of the formation of nuclei of the condensed phase on sodium ions are calculated on the molecular level by a Monte Carlo simulation using a detailed interaction model. The stationary rate of nucleation is estimated based on the data obtained. The presence of ionic impurities only substantially affects the rate of nucleation at strong vapor supersaturation. The nucleus losses its thermodynamic stability with an increase in the size of the nucleus and the barrier is formed depending on the work of formation on the size of the nucleus. An abrupt loss of stability is accompanied by pushing the ion off of the microdroplet surface and the restoration of the network of hydrogen bonds. The effect of pushing an ion to the surface of a cluster greatly depends on many-particle polarization interactions.     

Interaction energies of histidine with cations (H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>)

The imidazol side group of histidine has two nitrogen atoms capable of being protonated or participating in metal binding. Hence, histidine can take on various metal-bound and protonated forms in proteins. Because of its variable structural state, histidine often functions as a key amino acid residue in enzymatic reactions. Ab initio (HF and MP2) calculations were done in modeling the cation (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺) interaction with side chain of histidine. The region selectivity of metal ion complexation is controlled by the affinity of the side of attack. In the imidazol unite of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity. The complexation energies with the model systems decrease in the following order: Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.     

Hydration of the H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, and Cs<Superscript>+</Superscript> ions in MF-4SK perfluorinated sulfonic acid cation-exchange membranes modified with inorganic dopants

The hydration, state, and mobility of protons and Li⁺, Na⁺, and Cs⁺ ions in MF-4SK perfluorinated sulfonic acid cation-exchange membranes doped with silicon dioxide and phosphotungstic acid have been investigated by NMR and impedance spectroscopy. The dopants increase the moisture content of the membrane and change the system of pores and channels in which ion transport takes place. At low humidities, the dopant particles are involved in ion transport. The greatest effect is observed for the membranes doped with both SiO₂ and phosphotungstic acid. The water molecules sorbed by dopant particles as a material participate in the hydration of alkali metal cations in the membrane.     

Kinetics of solid-phase H<Superscript>+</Superscript>/M<Superscript>+</Superscript> ion exchange on hafnium hydrogen phosphate

The kinetics of solid-phase reactions between hafnium hydrogen phosphate and alkali metal chlorides were studied by thermogravimetry with subsequent analysis of leaving gases. For sodium and potassium chlorides, the reaction occurs in two stages; the first stages produces MHHf(PO₄)₂, and the second yields the MHf₂(PO₄)₃ NASICON phosphate. For rubidium chloride, the reaction is one stage and produces Rb₂Hf(PO₄)₂. For cesium chloride, the reaction is an analogue of the reaction for rubidium chloride, but has two stages. Kinetic data were used to determine interdiffusion coefficients for hydrogen and alkali-metal ions at various temperatures and the activation energies of interdiffusion.     

Structural parameters of Cu<Superscript>2+</Superscript> aqua complexes in aqueous solutions of its salts

Published data of various research techniques and own experimental results obtained by the X-ray structural analysis concerning structural characteristics of copper(II) aqua complexes in aqueous solutions of its salts under standard conditions have been generalized. Structural parameters of the nearest environment of this ion, such as coordination number, interparticle distances, and ionic association types, were considered. The possibility of the Jahn-Teller effect realization in aqueous solutions of Cu²⁺ salts was examined.     

Structure of a Na<Superscript>+</Superscript> cation hydration shell on heating in a planar nanopore

Resistance to heating above the boiling point of water of the molecular structure of a single-charged sodium cation hydration shell growing under the conditions of a model planar nanopore with a width of 5 Å is studied by computer simulation. Monte Carlo calculations of spatial correlation functions are performed in a detailed model with regard to many-body interactions between the ion and water molecules. The system demonstrates an increased resistance to thermal fluctuations along the pore plane and a decreased one in the transverse direction. The heating is accompanied by an enhanced coating effect of molecules around the ion and a diminished effect of extruding the ion out of its own hydration shell. The orientational molecular order due to strong spatial anisotropy inside the nanopore is much more stable than the hydrogen bonds between the molecules.     

Time-dependent inhibition of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase induced by single and simultaneous exposure to lead and cadmium

Time-dependent interactions of Na⁺/K⁺-ATPase, isolated from rat brain synaptic plasma membranes (SPMs), with Cd²⁺ and Pb²⁺ ions in a single exposure and in a mixture were investigated in vitro. The interference of the enzyme with these metal ions was studied as a function of different protein concentrations and exposure time. The aim of the work was to investigate the possibility of selective recognition of Cd²⁺ and Pb²⁺ ions in a mixture, on the basis of the different rates of their protein-ligand interactions. Decreasing protein concentration increased the sensitivity of Na⁺/K⁺-ATPase toward both metals. The selectivity in protein-ligand interactions was obtained by variation of preincubation time (incubation before starting the enzymatic reaction). The text was submitted by the authors in English.     

Kinetic aspects of the ion-exchange reactions of Cs<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, Sr<Superscript>2+</Superscript>and Eu<Superscript>2+</Superscript> ions on the H<Superscript>+</Superscript> form of chromium hexacyanoferrate(II)

Summary This paper reports the radiochemical study of the ion-exchange of Cs⁺, Na⁺, Sr²⁺ and Eu³⁺ ions with H⁺ by chromium hexacyanoferrate(II) which was prepared in a granular form using a gel method. The slow steps which determine the rate of exchange of these ions are directly proportional to the particle diameter and this is confirmed from the linearity test of Bt vs. t plots at different particle diameters. Boyed’s equation and Reichenberg’s tables were used for evaluating all the kinetic parameters. The results reveal that the effective particle radii are unchanged for both chromium hexacyanoferrate(II) dried at 60 and 120 °C. The obtained data were analyzed using McKay plots and Arrhenius equation and the kinetic and thermodynamic parameters, e.g., effective diffusion coefficient, activation energies and entropies of activation have been evaluated. The mobility of these ions inside the particles of chromium hexacyanoferrate(II) decrease in the order of Eu³⁺>Sr²⁺>Na⁺⊃Cs⁺.     

Dynamics of the Na<Superscript>+</Superscript>-Ca<Superscript>2+</Superscript> exchange on a carboxy cation exchanger

Nonequilibrium dynamics of the Na⁺-Ca²⁺ exchange in water softening on a Lewatit CNP 80 carboxylic cation-exchanger was studied at a widely varying linear velocity of water filtration. The kinetic coefficient of the pore-diffusion mass-transfer was determined at various flow rates of the model solution.     

Thermodynamics of ion exchange of H<Superscript>+</Superscript> by Na<Superscript>+</Superscript> or NH<Subscript>4</Subscript><Superscript>+</Superscript> on ion-exchange resins based on <Emphasis Type="Italic">C</Emphasis>-tetramethylcalix[4]resorcinarene

The corrected selectivity coefficients of the ion exchange H⁺-Na⁺ and H⁺-NH₄ ⁺ on ion-exchange resins based on C-tetramethylcalix[4]resorcinarene were calculated from the experimental data obtained from studying ion-exchange equilibria. The preference of the ion-exchange resins for cations increases in the sequence: Na⁺ < NH₄ ⁺ < < H⁺, and the ion-exchange resin based on (2-furyl)hydroxymethyltetramethylcalix[4]resorcinarene has a higher preference for ammonium cations. According to the results of microcalorimetric measurements, the exchange H⁺-Na⁺ on this ion-exchange resin is accompanied by the highest change in the differential enthalpy. It follows from the quantum-chemical calculations that the introduction of a (2-furyl)hydroxymethyl group into the structure of the polymer induces additional electrostatic interactions between an ammonium cation and an elementary unit of the ion-exchange resin.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2560–2563, December, 2004.     

Ion-exchange selectivity of a network calixarene-containing polymer obtained by the template synthesis on Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, and Ba<Superscript>2+</Superscript> matrices

The ion-exchange equilibrium in network polymers obtained from cis-2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene by template synthesis on cations Na⁺, K⁺, and Ba²⁺ as matrices was studied. The selectivity coefficients of ion exchanges Ba²⁺-H⁺, Na⁺-H⁺, K⁺-H⁺, Na⁺-K⁺, and Na⁺-NH₄ ⁺ were determined. The template synthesis enhanced the affinity of the polymers to matrix-forming cations by 6–8 kJ mol⁻¹. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1919–1922, August, 2005.