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排序方式: 共有871条查询结果,搜索用时 15 毫秒
101.
102.
Dr. Dominique T. Thielemann Anna T. Wagner Dr. Yanhua Lan Dr. Pascual Oña‐Burgos Prof. Dr. Ignacio Fernández Prof. Dr. Esther S. Rösch Dr. Dominik K. Kölmel Prof. Dr. Annie K. Powell Prof. Dr. Stefan Bräse Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):2813-2820
A new family of pentadecanuclear coordination cluster compounds (from now on simply referred to as clusters) [{Ln15(OH)20(PepCO2)10(DBM)10Cl}Cl4] (PepCO2=2‐[{3‐(((tert‐butoxycarbonyl)amino)methyl)benzyl}amino]acetate, DBM=dibenzoylmethanide) with Ln=Y and Dy was obtained by using the cell‐penetrating peptoid (CPPo) monomer PepCO2H and dibenzoylmethane (DBMH) as supporting ligands. The combination of an inorganic cluster core with an organic cell‐penetrating peptoid in the coordination sphere resulted in a core component {Ln15(μ3‐OH)20Cl}24+ (Ln=Y, Dy), which consists of five vertex‐sharing heterocubane {Ln4(μ3‐OH)4}8+ units that assemble to give a pentagonal cyclic structure with one Cl atom located in the middle of the pentagon. The solid‐state structures of both clusters were established by single‐crystal X‐ray crystallography. MS (ESI) experiments suggest that the cluster core is robust and maintained in solution. Pulsed gradient spin echo (PGSE) NMR diffusion measurements were carried out on the diamagnetic yttrium compound and confirmed the stability of the cluster in its dicationic form [{Y15(μ3‐OH)20(PepCO2)10(DBM)10Cl}Cl2]2+. The investigation of both static (dc) and dynamic (ac) magnetic properties in the dysprosium cluster revealed a slow relaxation of magnetization, indicative of single‐molecule magnet (SMM) behavior below 8 K. Furthermore, the χT product as a function of temperature for the dysprosium cluster gave evidence that this is a ferromagnetically coupled compound below 11 K. 相似文献
103.
Ayari Faouzi Mannei Emna Asedegbega-Nieto Esther Mhamdi Mourad Guerrero-Ruiz Antonio Ricardo Delahay Gérard Ghorbel Abdelhamid 《Journal of Thermal Analysis and Calorimetry》2018,131(2):1295-1306
Journal of Thermal Analysis and Calorimetry - Thermal decomposition (2 K min?1) of ammonium heptamolybdate tetrahydrate, performed between room temperature and... 相似文献
104.
Esther Beneish 《Transactions of the American Mathematical Society》1998,350(9):3571-3585
Following Procesi and Formanek, the center of the division ring of generic matrices over the complex numbers is stably equivalent to the fixed field under the action of , of the function field of the group algebra of a -lattice, denoted by . We study the question of the stable rationality of the center over the complex numbers when is a prime, in this module theoretic setting. Let be the normalizer of an -sylow subgroup of . Let be a -lattice. We show that under certain conditions on , induction-restriction from to does not affect the stable type of the corresponding field. In particular, and are stably isomorphic and the isomorphism preserves the -action. We further reduce the problem to the study of the localization of at the prime ; all other primes behave well. We also present new simple proofs for the stable rationality of over , in the cases and .
105.
Kilian Muñiz Prof. Dr. Claas H. Hövelmann Esther Campos‐Gómez José Barluenga Prof. Dr. José M. González Prof. Dr. Jan Streuff Martin Nieger Dr. 《化学:亚洲杂志》2008,3(4):776-788
The oxidative intramolecular diamination of alkenes with tethered ureas and related groups as the nitrogen source has been investigated both with the iodonium reagent IPy2BF4 (Py=pyridine) and under palladium catalysis in the presence of copper(II) bromide as a reoxidant. For terminal alkenes, the two procedures enable selective and high‐yielding transformations. Studies with deuterated material led to the conclusion that the reactions proceed through different stereochemical pathways. An advanced protocol for palladium‐catalyzed diamination through six‐membered‐ring annulation was also developed, and the first examples of the intramolecular diamination of internal alkenes are described. In this case, the same stereochemical outcome was observed for the iodonium‐promoted and palladium‐catalyzed transformations. On this basis, it was possible to determine the importance of aminohalogenated intermediates in both diamination reactions. Overall, the disclosed procedures broaden significantly the synthetic applicability of the oxidative intramolecular diamination of alkenes. 相似文献
106.
Sánchez A Millán S Sampedro MC Unceta N Rodríguez E Goicolea MA Barrio RJ 《Journal of chromatography. A》2008,1177(1):170-174
A sensitive and specific method for determining fenitrothion and its main metabolites, 3-methyl-4-nitrophenol and fenitrooxon, in poplar leaves using deuterated isotopes as the internal standard is described. The analytes and the labeled isotopes were extracted from leaves by solid-phase microextraction and subsequently analysed by gas chromatography coupled with mass spectrometry. The method had a chromatographic run time of 17.0 min and good linearity over the range 0.01-10 mg kg(-1). The detection limits ranged between 2.5 and 0.6 microg kg(-1). The isotopic dilution technique allowed improving significantly the repetitivity even using different fibers with the same coating (RSD<5.1%). The method was applied successfully to study the persistence of fenitrothion in forestal matrices in a poplar forest after cannon spray application of the insecticide. 相似文献
107.
Molecularly imprinted capillary electrochromatography for selective determination of thiabendazole in citrus samples 总被引:3,自引:0,他引:3
In this work, the suitability of the combination of molecular imprinting and capillary electrochromatography (MIP-CEC) to be used as powerful tool in environmental or food analysis has been for the first time studied and successfully demonstrated. A molecularly imprinted monolith (MIM) has been synthesised and evaluated as stationary phase for the selective determination of the fungicide thiabendazole (TBZ) in citrus samples by non-aqueous capillary electrochromatography. The influence of the mobile phase composition, the voltage of the power supply and the separation temperature on the recognition of TBZ by the imprinted polymer has been evaluated, and the imprint effect in the MIM was clearly demonstrated. Once optimum recognition conditions were established, other variables affecting mechanical properties and chromatographic performance of MIM were adjusted using computational approach. The high selectivity achieved by the MIP-CEC developed procedure allowed unambiguous detection and quantification of TBZ in citrus samples by direct injection of the crude sample extracts, without any previous clean-up, in less than 6 min. The developed method was properly validated and the calculated detection limits were below the established maximum residue limits (MRLs), clearly demonstrating the suitability of the method to be used for the control of the selected fungicide. 相似文献
108.
Natalia Quici Marta I. Litter Andr M. Braun Esther Oliveros 《Journal of photochemistry and photobiology. A, Chemistry》2008,197(2-3):306-312
The vacuum-UV- (VUV-) photolysis of water is one of the advanced oxidation processes (AOP) based on the production of hydroxyl radicals (HO) that can be applied to the degradation of organic pollutants in aqueous systems. The kinetics of the VUV-photolyses of aqueous solutions of citric acid (1) or gallic acid (2) were investigated in the presence or absence of dissolved molecular oxygen (O2) and under different pH conditions. In the case of 1, the rate of consumption of the substrate was faster at pH 3.4 than in alkaline solution (pH 11), whereas, in the case of 2, the variation of pH (2.5–7.5) did not affect the course of the reaction. Unexpectedly, the rates of depletion of both 1 and 2 decreased in the absence of O2, this effect being much more pronounced in the case of 2. In order to explain these results, possible reaction pathways for the degradation of 1 and 2 are proposed, and the roles of the oxidizing (HO) and reducing (H and eaq−) species produced by the VUV-photolysis of water are discussed. 相似文献
109.
We study worst-case complexities of visibility and distance structures on terrains under realistic assumptions on edge length ratios and the angles of the triangles, and a more general low-density assumption. We show that the visibility map of a point for a realistic terrain with n triangles has complexity . We also prove that the shortest path between two points p and q on a realistic terrain passes through triangles, and that the bisector of p and q has complexity . We use these results to show that the shortest path map for any point on a realistic terrain has complexity , and that the Voronoi diagram for any set of m points on a realistic terrain has complexity and . Our results immediately imply more efficient algorithms for computing the various structures on realistic terrains. 相似文献
110.