Nitrosoruthenium nitrite-nitrate complexes in aqueous and nitric acid solutions as probed by 15N NMR

Aqueous and nitric acid solutions of Na₂[Ru¹⁵NO(¹⁵NO₂)₄OH] in the concentration range $c_{H^{15} NO_3 }$ = 0–3.3 mol/L have been studied by ¹⁵N NMR, dominating complex species have been identified, and the equilibrium constants for the nitrate ion incorporation into the inner coordination sphere of nitrosoruthenium have been estimated. The equilibration time for such equilibria is no more than 2 h at room temperature. In addition to the nitro complexes, isomeric nitritonitronitrosoruthenium compounds have been identified in solutions. In weak acidic solutions at $c_{HNO_3 }$ < 0.25 mol/L, nitro and nitritonitro complexes containing four and three coordinated nitrite ions predominate. At the HNO₃ concentration 0.4–1.7 mol/L, the vast majority of ruthenium presents in solution as fac-dinitronitrosoruthenium complexes containing coordinated water molecules and nitrate ions. In solutions with $c_{HNO_3 }$ > 1.5 mol/L, the fractions of dinitro- and mononitronitrosoruthenium complexes are comparable. In strong nitric acid solutions ( $c_{H^{15} NO_3 }$ = 10 mol/L) kept for three years in contact with air, nitro complexes are absent, and mononitrato- and dinitratoaquanitrosoruthenium complexes are dominating.     

Behaviours of trinitratonitrosyl complexes of ruthenium in dilute nitric acid solutions (author's transl)

This study aimed to elucidate the protolysis and condensation processes of the Ru complexes in relation to the concentration of nitric acid. The compositions of the dissociated and undissociated complexes were determined by the extraction with tributyl phosphate (TBP) and absorption spectroscopy in order to follow the rather rapid protolysis reaction of the complexes. The test solutions were prepared by dissolving the freshly obtained complexes into 0.50-0.001 M nitric acid solutions. The amounts of the undissociated complexes were determined at different elapses of time in the test solutions. The protolysis became significant when the concentration was below 0.15 M, and the dissociation rate suddenly increased at this concentration. At the concentrations above 0.2 M, the absorption peak of the complexes at 480 nm survived even after 144 hours. But below 0.15 M, the formation of dissociation products by protolysis was observed after the disappearance of the absorption peak. The amount of dissociation products rapidly increased after the preparation of the test solution as the concentration decreased below 0.15 M.     

The role of water molecules in a resorcinarene capsule as probed by NMR diffusion measurements

[structure: see text] NMR diffusion measurements were used to probe the role of water molecules in a resorcinarene capsule in a CDCl(3) solution. It was found that the water/resorcinarene ratio affects both the chemical shift and the diffusion coefficient of the water molecules. From the NMR diffusion measurements we could conclude that the major species in the chloroform solution is the hexamer having eight water molecules that are in fast exchange, on the NMR time scale, with the bulk water.     

Hexameric capsules of lipophilic pyrogallolarene and resorcinarene in solutions as probed by diffusion NMR: one hydroxyl makes the difference

[reaction: see text] NMR diffusion measurements were used to characterize the self-assembled molecular capsule of pyrogallolarene 2c in CDCl(3) solutions. The results were compared with the characteristics of the hexameric capsule of 1b. Although both 2c and 1b self-assemble into hexameric capsules, the role of water in these capsules is rather different. It was also found that the capsule of 2c is more stable in polar media than that of 1b.     

Chemical forms of iron(III) in solutions of orthophosphoric acid as probed by electronic absorption spectroscopy

It has been demonstrated that a combination of H₂O and H₂PO ₄ ^? groups in the coordination sphere of iron(III) complexes leads to the bathochromic shift and changes the shapes of the ⁶ A _1g ⁶ S-⁴ A _1g , ⁴ E _g transition band and charge transfer bands, whereas the substitution of phosphate ligands for all water molecules does not lead to such changes. The stabilization energies of aquaphosphate complexes have been calculated from the low-energy shifts. Spectrochemical parameters of iron(III) phosphate complexes have been determined.     

Diffusion processes in mesoporous adsorbents probed by NMR

In this contribution, we review the results of our experimental studies on diffusion of guest molecules in mesoporous solids using pulsed field gradient (PFG) NMR technique. Having unique potentials to non-invasively probe the microscopic diffusion processes in pores, this method may provide quintessential information on the character of molecular propagation for different pore morphologies and fluid phase state. In particular, different modes of molecular diffusion in partially filled pores may be separately probed and the overall diffusion process could be analyzed taking account of the details of the inter-phase coexistence. In addition to the dynamic properties, some information concerning the distribution of guest molecules within the porous matrix may also be obtained.     

The sorption of molybdenum from solutions of nitric acid

The sorption of molybdenum(VI) on KU-2 × 8 and AV-17 × 8 ionites from 6 n solutions of nitric acid was studied. The sorption of molybdenum(VI) on the cationite and anionite changed depending on solution composition and nitric acid concentration. The sorption and electromigration data were used to determine the isoelectric point of molybdenum in solutions of nitric acid.     

Reversed phase extraction chromatography using solutions of nitric acid as eluants

Approximately 40 ions have been chromatographed on thin layers of silica gel impregnated with Alamine 336-S, Alamine 336-S oxide, tri-n-octylarsine oxide, tri-n-octylphosphine oxide or tri-n-butyl phosphate, and on non-impregnated silica gel. Solutions of 0.2–15 N HNO₃ are used as eluants. R_F spectra and a number of separations are reported. The ions are classified into four groups according to their chromatographic behaviour, which is explained on the basis of anion exchange, solvation, hydrolysis and interaction with the support.Data on the extraction of HNO₃ and the co-extraction of water are reported. The behaviour of Alamine oxide and tri-n-octylarsine oxide parallels that of high-molecular-weight amines: extraction proceeds through anion exchange. Nitric acid taken up in excess of the stoichiometric amount is mainly present in the organic phase as part of the ion [O₂NO…HONO₂]⁻. On the other hand, with tri-n-octyl-phosphine oxide (TOPO) and tri-n-butyl phosphate (TBP), extraction proceeds through solvation; TOPO·HNO₃, TOPO·2HNO₃ and TBP·HNO₃ are the species present in the organic extracts.     

Dynamics in nanoporous materials probed by 2H solid state NMR: estimation of self-diffusion coefficients

Adsorption - 2H solid-state NMR represents a reliable method for probing the dynamics of the molecules in confined geometries, including microporous and mesoporous materials such as zeolites or...     

Separation of traces of silver in nitric acid solutions using mercury as collector

Summary Microgram quantities of silver are quantitatively deposited into mercury globules from nitric acid solutions (ca. 1N acidity), leaving large amounts of base metals (e. g., copper, lead, and bismuth) in solution. This separation method has been applied to the atomic absorption spectrometric determination of a few ppm of silver in copper or lead.

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Zusammenfassung Mikrogrammengen Silber werden aus salpetersaurer Lösung (ca. 1-n) quantitativ auf Quecksilbertröpfchen niedergeschlagen, wobei große Mengen unedle Metalle (z. B. Cu, Pb und Bi) in Lösung bleiben. Diese Trennmethode wurde bei der Bestimmung weniger ppm Silber in Kupfer oder Blei durch Atomarabsorption angewendet.

     

Kinetics of reduction of hexavalent neptunium by nitrous acid in solutions of nitric acid

Nitrous acid is a key redox controlling factor, affecting the speciation of neptunium in the reprocessing of used nuclear fuel by solvent extraction. The kinetics of the reduction of neptunium(VI) by nitrous acid in solutions of nitric acid was investigated spectrophotometrically by the method of initial rates. The reaction is of first order with respect to Np(VI) while the order with respect to HNO₂ is 1.20 ± 0.04. The reaction rate is almost inversely proportional to the hydrogen ion concentration (reaction order −0.92 ± 0.06), indicating that the reaction proceeds primarily through the reaction of neptunium(VI) with the nitrate anion. The experimental value of the rate constant k for the rate law −d[Np(VI)]/dt = k·[Np(VI)]·[HNO₂]^1.2/[H⁺] is of (0.159 ± 0.014) M^−0.2 s⁻¹ in I = 4 M and at 20 °C. The activation energy is (−57.3 ± 1.6) kJ/mol, which is in agreement with previous data on this reaction in perchloric acid.     

Extraction behavior of cerium by tetraoctyldiglycolamide from nitric acid solutions

The diamide N,N,N′,N′-tetraoctyldiglycolamide (TODGA) was synthesized and characterized. The prepared TODGA was applied for extraction of Ce(III) from nitric acid solutions. The equilibrium studies included the dependencies of cerium distribution ratio on nitric acid, TODGA, nitrate ion, hydrogen ion and cerous ion concentrations. Analysis of the results indicates that the main extracted species is Ce(TODGA)₂(NO₃)₃HNO₃. The capacity of Ce loading is approximately 45 mmol/L for 0.1 M solution of TODGA in n-hexane. Finally, the thermodynamic parameters were calculated: K (25 °C) = 3.8 × 10³, ΔH = −36.7 ± 1.0 kJ/mol, ΔS = −54.6 ± 3.0 J/K mol, and ΔG = −20.4 ± 0.1 kJ/mol.     

Hydrogen generation in nitric acid solutions of plutonium

Summary Literature data on the radiolytic generation of hydrogen in nitric acid solutions of plutonium are used to construct a model that predicts G(H₂) as a function of the nitric acid and plutonium concentrations. The model indicates that G(H₂) decreases with increasing concentration of nitric acid, in agreement with most experimental observations. The effect of the plutonium concentration on G(H₂) is secondary to the effect of the acid concentration. An equation for interpolating Gvalues for total gas is included.     

Actinide and lanthanide extraction from nitric acid solutions by flotation

Flotation of thorium, plutonium (IV), uranium(VI) and gadolinium from aqueous nitric acid solutions (HNO₃ concentration from 0.01 to 5.0M) was investigated using lauryl phosphoric acid (LPA) as a SAS-collector. It is established that the extent of removal of the metal ions increases with the amount of LPA introduced, regardless of the solution acidity. At a fixed mole LPA to metal ratio the extent of uranium(VI) and gadolinium removal is reduced with increasing acidity, while in case of plutonium(IV) and thorium this parameter remains constant. It is shown that in principle 100% extraction of plutonium(IV) and thorium by flotation is possible regardless of the acidity of aqueous solutions. Ca(NO₃)₂ added to the system in the amount of 0.5M does not significantly affect the flotation extraction of thorium.     

The sodium ions inside a lipophilic G-quadruplex channel as probed by solid-state (23)Na NMR

We report solid-state 23Na NMR and X-ray crystallographic results for a self-assembled G-quadruplex channel formed by a guanine nucleoside, 5'-tert-butyl-dimethylsilyl-2',3'-O-isopropylidene guanosine (G 1). The study provides an unambiguous 23Na NMR identification for the Na+ ions inside a lipophilic G-quadruplex channel. The crystalline nature of the sample yields a remarkably high resolution in the 23Na multiple-quantum magic-angle spinning (MQMAS) spectrum, making it possible to extract very accurate 23Na NMR parameters for each of the three crystallographically distinct Na sites. The observation of a single Na+ ion from a 9-kDa system demonstrates the potential of solid-state 23Na NMR as a complementary technique to X-ray for detecting Na+ ions in biological structures.     

The extraction of hexavalent uranium from nitric acid solutions by tetrabutylpyrophosphate (TBPP)

The mechanism of extraction of nitric acid and uranyl ions by tetrabutylpyrophosphate (TBPP) solutions in carbon tetrachloride, has been investigated. The solvation number for the uranyl ion, determined by both extraction and the spectrophotometric method, was one. A reaction of aggregates of the extractant species with the TBPP-uranium complex is suggested. Kinetic investigations of this reaction were carried out recording the absorbance in the PO stretch band at different times after reaching thermodynamic equilibrium for the primary extraction. The postulated reaction follows a zero order equation when the molar ratio of TBPP and uranium nitrate was 10:1.