Effect of gleysation on remobilization of radionuclides in waterlogged soils

Joint leaching of iron and other macro- and microelements including radionuclides from radioactively contaminated floodplain soil of the Yenisei River is studied on miniecosystems. In developing anaerobic conditions, the redox potential E_h decreased to +140 mV, causing partial reduction of iron and solubilisation of iron hydrous oxide and organomineral films of the soil. Leaching of stable elements and radionuclides with water proceeds parallel to that of iron. To accelerate reductive mobilization of iron, 0.4% aqueous ascorbic acid was used instead of water as the leaching liquid phase. In this case, E_h approached –60 mV, and the leaching of stable and radioactive elements considerably increased, the effect being most pronounced for plutonium. To cite this article: E.K. Legin et al., C. R. Chimie 7 (2004).

Résumé

Effet du passage en milieu anaérobie sur la mobilisation des radionucléides dans les sols humides. La lixiviation simultanée du fer et d’autres éléments de sols contaminés de la vallée de la rivière Yénései a été étudiée. En imposant des conditions anaérobies, le potentiel redox chute à 140 mV, causant une réduction partielle du fer trivalent et la solubilisation de l’hydroxyde de fer et du film organominéral du sol. Les lixiviations du fer, des autres éléments et, par conséquent, des radionucléides contaminant le sol vont de pair. Pour accélérer la mobilisation réductive du fer, une solution d’acide ascorbique à 0,4% a été utilisée à la place de l’eau. Dans ces conditions, la valeur de E_h approche –60 mV et la lixiviation des éléments augmente considérablement, cet effet étant plus prononcé pour le plutonium. Pour citer cet article : E.K. Legin et al., C. R. Chimie 7 (2004).     

Spectroscopic determination of dipole-dipole interaction in solutions of trioctylammonium halides

Dimerization energies of trioctylammonium halides in carbon tetrachloride solution, associated as a result of dipole-dipole interaction, were calculated from the infrared absorption spectra. The values obtained were 5, 4, and 1.5 kcal/mole for the chloride, bromide, and iodide, respectively. The calculation showed that the dimers of these salts are contact dimers.     

Technetium(I) carbonyl dithiocarbamates and xanthates

Technetium(I) tetracarbonyl complexes with diethyldithiocarbamate and methylxanthate ligands [TcL(CO)(4)] (L = S(2)CNEt(2) and S(2)COMe) were prepared. Conditions required for the formation of these complexes were found. The crystal and molecular structure of the xanthate complex was determined by single-crystal X-ray diffraction. [Tc(S(2)CNEt(2))(CO)(4)] undergoes decarbonylation both in solution and in the course of vacuum sublimation with the formation of a dimer [Tc(S(2)CNEt(2))(CO)(3)](2) whose structure was determined by single-crystal X-ray diffraction. In donor solvents, [Tc(S(2)CNEt(2))(CO)(4)] and [Tc(S(2)COMe)(CO)(4)] undergo decarbonylation with the formation of tricarbonyl solvates [TcL(CO)(3)(Sol)]. The crystal structure of the pyridine solvate [Tc(S(2)CNEt(2))(CO)(3)(py)], chosen as an example, was determined by single-crystal X-ray diffraction. The possibility of using bidentate S-donor acidic ligands for tethering the tetracarbonyltechnetium fragment to biomolecules was examined.     

A secretory phospholipase A2-mediated neuroprotection and anti-apoptosis

Background  

Phospholipase A₂ liberates free fatty acids and lysophospholipids upon hydrolysis of phospholipids and these products are often associated with detrimental effects such as inflammation and cerebral ischemia. The neuroprotective effect of neutral phospholipase from snake venom has been investigated.     

Stoichiometry of uranyl hydrolysis reaction in acidic aqueous solutions from the evidence of oxygen exchange kinetics

The kinetics of uranyl oxygen exchange with water molecules in aqueous solutions was studied in the pH range 1–4 and uranium concentration range 10^–4–0.1 M. It was confirmed that the exchange is stimulated by hydrolyzed uranyl species. From the evidence of data on the kinetics of uranyl oxygen exchange the reaction stoichiometry of uranyl hydrolysis was determined. The scheme of uranyl hydrolysis involving formation of (UO₂)₂(OH)₂²⁺, (UO₂)₂(OH)₃⁺, and other hydrolyzed species was proposed. To cite this article: L.G. Mashirov et al., C. R. Chimie 336 (2004).

Résumé

Étude de l'hydrolyse de l'uranium hexavalent en milieu acide par échange isotopique de l'oxygène. L'échange isotopique de l'oxygène de l'ion uranyle avec les molécules d'eau a été étudié dans le domaine de pH de 1 à 4 et de concentration en uranium de 10^–4 à 0,1 M. Cet échange a lieu par l'intermédiaire d'espèces hydrolysées de U(VI). La stoechiométrie des formes hydrolysées de U(VI) est déduite des vitesses d'échange isotopique. En particulier, les espèces (UO₂)₂(OH)₂²⁺ et (UO₂)₂(OH)₃⁺ ont été clairement identifiées. Un schéma d'hydrolyse est proposé. Pour citer cet article : L.G. Mashirov et al., C. R. Chimie 336 (2004).     

Photoluminescence of a-Si:H films grown by plasma-enhanced chemical vapor deposition and doped with erbium from the metallorganic compound Er(HFA)3·DME

Using standard low-temperature (<300 °C) plasma-enhanced chemical vapor deposition (PE CVD) technology, films of a Si(Er): H were obtained that emitted light in the neighborhood of 1.54 μm at room temperature. The Er source was the specially synthesized fluorine-containing metallorganic complex Er(HFA)₃·DME where HFA=CF₃C(O)CHC(O)CF₃ and DME=CH₃OCH₂CH₂OCH₃, which possesses a low transition temperature to the gas phase (of order 100 °C) at working pressures (0.1–0.5 Torr) for the PE CVD method. Distinctive features of the photoluminescence spectrum of a-Si(Er):H were investigated in the range 0.5–1.7 μm for T=77 and 300 K. The presence of photoconductivity in the synthesized films is evidence of their satisfactory electronic quality. Fiz. Tverd. Tela (St. Petersburg) 40, 1433–1436 (August 1998)