Effect of alkali ions (Na+, K+) on the solvent extraction of uranium(VI) with a di-carboxylated calix[4] arene

The solvent extraction of uranium(VI) with a di-carboxylated calix[4]arne (LH₂) in chloroform and 1,2-dichloroethane has been studied in the presence or absence of alkali ions (M=Na⁺,K⁺). For UO ₂ ²⁺ when studied alone, a 12 (metal: ligand) extracted species is evidenced, with a rather low associated extraction equilibrium constant. The efficiency of extraction increases drastically in the presence of alkali ions, due to the formation of heteronuclear complexes. In all cases, the extracted species are found to be both 122 and 112 (UO ₂ ²⁺ MLH₂) mixed complexes, except in chloroform with K⁺, where only the latter is formed. In the case of Na⁺, mass spectrometry spectra confirm the existence of both homo and heteronuclear complexes as determined in the extraction studies.     

Homodimerization of spiro{bicyclo[2.2.1]Hepta-2,5-Diene-7,1′-cyclopropane}, catalyzed by group VIII transition metal complexes

Conclusions The homodimerization of spiro{bicyclo[2.2.1]hepta-2,5-diene-7,1-cyclopropane} (I) has been investigated in the presence of Ni-, Fe-, Co-, Rh-, and Ir-based metal complex catalysts. Depending on the nature of the metal and its ligand environment cyclodimerization of (I) can take place via [2+2]-, [2+2+2]-, and [4+4]-cycloaddition schemes, to give high yields of hepta-, octa-, and nonacyclic strained hydrocarbons.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2592–2599, November, 1988.     

Multielement standards in routine reactor neutron activation analysis

The application of multielement standards (MES) in routine neutron activation analysis brings a whole range of advantages. This paper deals with the experience obtained during many years of application of these MES. Nine of these MES contain a total of 50 elements in suitable combinations and concentrations; thus, the determination of most of the common elements by NAA can be carried out simultaneously. This refers to the following elements: Na, Mg, Al, Cl, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Mo, Ag, Cd, In, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Re, Au, Hg, Th and U. For the determination of the remaining elements such as Zr, Ta, Ir etc., single element standards (SES) are used.     

Diastereotopic effect in some N-substituted-3-methyl-4,1-benzoxazepine-2,5-diones

1H NMR assignment of seven differently N-substituted-3-methyl-4,1-benzoxazepine-2,5-diones (I) revealed that with the exception of allyl, N-methylene protons of the substituents exhibit diastereotopy due to presence of a chiral centre in the heterocyclic ring at C-3. The significant finding is that the methylenes at C-2' in the substituents n-propyl and n-butyl (Id, Ie) also show diastereotopy. However, the one closer to the chiral centre (at C-1') exhibits greater non-equivalence of its protons. The diastereotopic methylene groups reported in this study correspond to the simplest system AB on one hand and as complex as ABMM'X2 or ABMM'X3 on the other. Calculated spectra obtained from assigned set of data for most of the coupled protons were in good agreement with the observed ones.     

Measurement of the electron distribution function in flowing afterglow plasma by means of Langmuir probe

Conclusion In the present report an attempt has been made to use the second derivative method for measurements of the electron distribution function in flowing afterglow plasma. It has been shown that using the cross-correlation technique, this method seems to be a useful tool for flowing afterglow plasma investigation.     

Optical properties of ZnO and ZnO:In nanorods assembled by sol-gel method

Self-assembled zinc oxide (ZnO) and indium-doping zinc oxide (ZnO:In) nanorod thin films were synthesized on quartz substrates without catalyst in aqueous solution by sol-gel method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), Raman-scattering spectroscopy, room-temperature photoluminescence (PL) spectra, and temperature-dependent PL spectra measurements. XRD and Raman spectra illustrated that there were no single In2O3 phase in ZnO lattice after indium doping. The PL spectra of ZnO showed a strong UV emission band located at 394 nm and a very weak visible emission associated with deep-level defects. Indium incorporation induced the shift of optical band gap, quenching of the near-band-edge photoluminescence and enhanced LO mode multiphonon resonant Raman scattering in ZnO crystals at different temperatures. Abnormal temperature dependence of UV emission integrated intensity of ZnO and ZnO:In samples is observed. The local state emission peak of ZnO:In samples at 3.37 eV is observed in low-temperature PL spectra. The near-band-edge emission peak at room temperature was a mixture of excitons and impurity-related transitions for both of two samples.     

Tight‐binding molecular dynamics simulation of Si?H bond dissociation in silicon clusters

New model of Si? H bond dissociation is proposed and tested in the cluster Si₁₀H₁₆ by the simulation approach that combines classic molecular dynamics method and the self‐consistent tight‐binding electronic and total energy calculation one. It is shown that the monohydride Si? H bond is unstable with respect to silicon dangling bond and bend‐bridge Si? H? Si bond formation when this cluster traps the single positive charge and that hydrogen migrates through a path involving rather rotation around the Si? Si bond than the center of this bond (the bond‐centered position). These results can be useful for understanding hydrogen‐related phenomena at surfaces, interfaces, and internal voids of various hydrogenated silicon systems: electronic devices, silicon solar cells, and nanocrystalline and porous silicon. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 351–359, 2003     

The dietary intake of238U,234U,230Th,232Th,228Th and226Ra from food and drinking water by inhabitants of the Walbrzych region

Intake with food and water of the natural radionuclides of the uranium and thorium series was determined for adult population of the south-western region in Poland, where in the 1950-ies an exploration of uranium ore was conducted. Concentration of the radionuclides was determined in food products and drinking water and their annual intake was estimated on the basis of the average annual consumption. The intake of²³⁸U,²³⁴U and²³⁰Th occurred mainly with water (33% to 68%), whereas the intake of²³²Th,²²⁸Th and²²⁶Ra was mainly with vegetables, potatoes, milk and flour. From the intake and dose coefficients the annual effective doses from the ingested radionuclides were calculated. The total dose was 5.6 Sv, of which 74% originated from²²⁶Ra.     

Über das Kriechen kristallisierender Salze, 2. Mitt.

Zusammenfassung Versuchsergebnisse über die Verteilung des bivariant gebundenen Wassers und von Wasserstoff- bzw. Hydroxylionen in den Kristallen bei kriechender Kristallisation, wie auch die hydrolytische Spaltung dieser Kristalle, werden dargelegt. Sie zeigen, daß der Gehalt an Wasser und die damit verbundene hydrolytische Spaltung bei den Kristallen in der Kristallkruste größer ist als bei den auf dem Boden des Gefäßes ausgeschiedenen Kristallen. Die Wasserstoff- bzw. Hydroxylionen verteilen sich so, daß, in Zusammenhang mit dem pH-Wert der Ausgangslösung, die Lösungen, bereitet aus den Kristallen der Kristallkruste, einen niedereren bzw. höheren pH-Wert besitzen, als die Lösungen, bereitet aus den Kristallen am Boden des Gefäßes.