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991.
Summary The effects of pH, gas flow rate and collector concentration on the rate of thorium removal by foaming with sodium lauryl sulphate have been investigated. The obtained data indicate that only aged hydrated thorium oxide is removed by a flotation mechanism. All the other colloidal and condensed thorium species as well as the colloidal sublates which are formed between the dissolved thorium species and the collector anions appear to be removed by partition and their removal rates could be described by a reversible first-order rate equation. The obtained results are discussed in terms of thorium hydrolysis.
With 7 figures 相似文献
Zusammenfassung Der Einfluß der pH-Werte, Gasdurchflußmengen und Kollektor-Konzentration auf die Geschwindigkeit der Entfernung des Thoriums durch Schaumbildung mit Natrium-Lauryl-Sulfat wurde untersucht. Die Ergebnisse zeigen, daß das gealterte, wässerige Thoriumoxid durch Flotations-Mechanismen entfernt wird. Die anderen kolloidalen und kondensierten Thorium-Spezien und auch die Kolloidalprodukte, die durch Reaktionen zwischen den gelösten Thoriumspezien und den Kollektor-Anionen formiert sind, sind durch die Verteilung entfernt worden. Die Entfernungsgeschwindigkeit kann beschrieben werden durch eine reversible 1. Ordnungs-Gleichung. Die Ergebnisse werden in Abhängigkeit einer ThoriumHydrolyse diskutiert.
With 7 figures 相似文献
992.
Thermal analysis supported by kinetic calculations was applied exhaustively to these compounds. Under dynamic conditions, tetrafluorometallates(III), which as intermediates, could not be isolated, for the first three compounds. In each case, the final step was the pure metal(III) fluoride. Ammonium hexafluorochromate(III) decomposed directly to the pure chromium(III) fluoride. The decomposition rate of all compounds slowed down towards the end, probably for kinetic reasons. Polymorphic transitions of ammonium hexafluorotitanate(III) were observed at 35 and 100°C. Ammoniumhexafluoroscandate(III) underwent polymorphic transition at 47°C. The decomposition patterns for all these compounds were similar. Conditions for the preparation of pure ammonium tetrafluorometallates(III) of Sc, Ti and V are described. 相似文献
993.
María Luisa Moyá Setefilla Escalera Cristina Martín Amalia Rodríguez María Mu?oz María del Mar Graciani 《Reaction Kinetics and Catalysis Letters》2006,89(1):177-182
Summary The reaction methyl 4-nitrobenzenesulfonate + Br- was studied in water-formamide tetradecyltrimethylammonium bromide micellar solutions. A pseudophase kinetic model was used
to quantitatively rationalize the kinetic micellar effects observed 相似文献
994.
995.
Aviñó A Cubero E González C Eritja R Orozco M 《Journal of the American Chemical Society》2003,125(51):16127-16138
The structural, dynamical, and recognition properties of antiparallel DNA triplexes formed by the antiparallel d(G#G.C), d(A#A.T), and d(T#A.T) motifs (the pound sign and dot mean reverse-Hoogsteen and Watson-Crick hydrogen bonds, respectively) are studied by means of "state of the art" molecular dynamics simulations. Once the characteristics of the helix are defined, molecular dynamics and thermodynamic integration calculations are used to determine the expected stabilization of the antiparallel triplex caused by the introduction of 8-aminopurines. Finally, oligonucleotides containing 8-aminopurine derivatives are synthesized and tested experimentally using several approaches in a variety of systems. A very large stabilization of the triplex is found experimentally, as predicted by simulations. These results open the possibility for the use of oligonucleotides carrying 8-aminopurines to bind single-stranded nucleic acids by formation of antiparallel triplexes. 相似文献
996.
Franco FernándezXerardo Garc?&#x;a-Mera José Enrique Rodr?&#x;guez-BorgesMar?&#x;a Luisa C. Vale 《Tetrahedron letters》2003,44(3):431-433
The recently reported compound (+)-(1R,endo)-2-benzonorbornenol (2) proved to be an efficient chiral auxiliary in the asymmetric aza-Diels-Alder reaction between cyclopentadiene and the N-benzyl imine of its glyoxylate, which afforded a virtually all-exo mixture of cycloaducts with a 1S:1R diastereomeric ratio of 63:37. 相似文献
997.
Katarzyna Samson Anna Klisiska Irena Gressel Barbara Grzybowska 《Reaction Kinetics and Catalysis Letters》2002,77(2):309-315
VOx/TiO2 and MoOx/TiO2 catalysts with the addition of Re (Re/V or Mo = 0.5) were synthetized and tested in oxidative dehydrogenation of propane and in reduction by propane. XPS measurements showed depletion of the surface in Re. The Re additive does not affect the total conversion of propane, but increases the selectivity to propene. The effect is more pronounced for the MoOx/TiO2 catalyst. The increase in the selectivity to propene is accompanied with the increase in the reducibility of the catalysts. 相似文献
998.
The mer‐octahedral complexes(2‐carbonyl)(4‐Me)(6‐tBu)phenolato[C,O]hydridotris(trimethylphosphine)cobalt(III) ( 1 ) or ‐(1‐carbonyl)(2‐oxo)(1,2‐diphenylethene)[C,O]hydridotris(trimethylphosphine)cobalt(III) ( 2 ) via formal insertion of propynoic acid ethyl ester into Co‐H functions afford pentacoordinate vinylcobalt(III) 3 and 4 , respectively, that are diamagnetic and attain a square pyramidal structure as exemplified by an X‐ray diffraction analysis of 3 . 相似文献
999.
Vivekananda S Sadílek M Chen X Turecek F 《Journal of the American Society for Mass Spectrometry》2004,15(7):1055-1067
Collisional neutralization of several isomeric C(4)H(7)O(2) cations is used to generate radicals that share some structural features with transient species that are thought to be produced by radiolysis of 2-deoxyribose. The title 2-hydroxyoxolan-2-yl radical (1) undergoes nearly complete dissociation when produced by femtosecond electron transfer from thermal organic electron donors dimethyl disulfide and N,N-dimethylaniline in the gas phase. Product analysis, isotope labeling ((2)H and (18)O), and potential energy surface mapping by ab initio calculations at the G2(MP2) and B3-PMP2 levels of theory and in combination with Rice-Ramsperger-Kassel-Marcus (RRKM) kinetic calculations are used to assign the major and some minor pathways for 1 dissociations. The major (approximately 90%) pathway is initiated by cleavage of the ring C-5[bond]O bond in 1 and proceeds to form ethylene and *CH(2)COOH as main products, whereas loss of a hydrogen atom forms 4-hexenoic acid as a minor product. Loss of the OH hydrogen atom forming butyrolactone (2, approximately 9%) and cleavage of the C-3[bond]C-4 bonds (<1%) in 1 are other minor pathways. The major source of excitation in 1 is by Franck-Condon effects that cause substantial differences between the adiabatic and vertical ionization of 1 (5.40 and 6.89 eV, respectively) and vertical recombination in the precursor ion 1(+) (4.46 eV). (+)NR(+) mass spectra distinguish radical 1 from isomeric radicals 2-oxo-(1H)oxolanium (3), 1,3-dioxan-2-yl (9), and 1,3-dioxan-4-yl (10) that were generated separately from their corresponding ion precursors. 相似文献
1000.
Orhan Acar A. Rehber Türker Ziya Kl? 《Fresenius' Journal of Analytical Chemistry》1998,360(6):645-649
A comparative and systematic study has been carried out of the effects of palladium and molybdenum containing chemical modifiers,
such as Pd + Rh, Pd + Pt, Pd + Ru, Pd + Rh + Pt, Pd + Rh + Ru, Mo + Pd, Mo + Rh, Mo + Ru and Mo + Pt and additionally tartaric
acid (TA) as a reducing agent together with mixed modifiers for the thermal stabilization of Bi, In and Pb in a Zeeman electrothermal
atomic absorption spectrometer (ETAAS). The effect of the mass ratios of the mixed modifier components on the maximum pretreatment
temperature for the analytes has been determined. The modifier mixtures of Pd + Rh + Pt, Mo + Pd + TA and Mo + Pt + TA were
found to be especially powerful for the determination of Bi, In and Pb. These mixed modifiers could increase the ashing temperatures
of the analytes up to 1250–1400° C. They were applied to the determination of Bi and Pb in dissolved geological reference
samples and accuracy and precision of the method were thereby enhanced. The percent relative error was decreased from 20.0
to 0.4 for Bi and from 10.5 to 0.3 for Pb, depending on the sample type.
Received: 9 May 1997 / Revised: 19 August 1997 / Accepted: 20 August 1997 相似文献