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91.
92.
Francis Leonard Deepak Alvaro Mayoral Miguel Jose Yacaman 《Applied Physics A: Materials Science & Processing》2009,96(4):861-867
The structural transformation of MoO3 nanobelts into MoS2 nanotubes using a simple sulfur source has been reported. This transformation has been extensively investigated using electron
microscopic and spectroscopic techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM),
high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and energy-dispersive X-ray analysis
(SEM-EDAX and TEM-EDX). The method described in this report will serve as a generic route for the transformation of other
oxide nanostructures into the chalcogenide nanostructures. 相似文献
93.
John Hurtado Alvaro Muñoz-Castro Raúl Quijada René Rojas Mauricio Valderrama 《Journal of organometallic chemistry》2009,694(16):2636-223
Reactions of 2,6-bis(bromomethyl)pyridine with 3,5-dimethylpyrazole and 1H-indazole yield the terdentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (5) and 2,6-bis(indazol-2-ylmethyl)pyridine (6). The molecular structure of the new compound 6 was determined by single-crystal X-ray diffraction. These ligands react with the CrCl3(THF)3 complex in THF to form neutral complexes of general formula [CrCl3{2,6-bis(azolylmethyl)pyridine-N,N,N}] (7, 8) which are isolated in high yields as stable green solids and characterized by means of elemental analysis, magnetic moments, IR, and mass spectroscopy. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active in the polymerization of ethylene. 相似文献
94.
Let (M,ω) be a symplectic 4-manifold. A semitoric integrable system on (M,ω) is a pair of smooth functions J,H∈C ∞(M,ℝ) for which J generates a Hamiltonian S
1-action and the Poisson brackets {J,H} vanish. We shall introduce new global symplectic invariants for these systems; some of these invariants encode topological
or geometric aspects, while others encode analytical information about the singularities and how they stand with respect to
the system. Our goal is to prove that a semitoric system is completely determined by the invariants we introduce.
A. Pelayo was partially supported by an NSF Postdoctoral Fellowship. 相似文献
95.
In this paper, we give examples of elliptic curves E/K overa number field K satisfying the property that there exist P1,P2 K[t] such that the twists and are of positiverank over K(t). As a consequence of this result on twists, weshow that for those elliptic curves E/K, and for each , the rank of E over the fixed field (Kab) under is infinite, where Kab is the maximal abelian extension ofK. 相似文献
96.
The compound Ru(bpy)2(dppz-R)(PF6)2, where bpy is 2,2'-bipyridine and dppz-R is 11-(diethoxyphosphorylmethyl)dipyrido[3,2-a:2',3'-c]phenazine, was prepared and anchored to mesoporous nanocrystalline (anatase) TiO2 thin films as a probe of the effects of interfacial water on excited-state charge transfer processes at semiconductor interfaces. In nitrogen-saturated fluid acetonitrile, the Ru(bpy)2(dppz-R)(PF6)2 compound was found to be highly photoluminescent. Water was found to quench the excited state by a mechanism adequately described by the Perrin model, from which the radius of quenching was abstracted, 75 +/- 2 A. The Ru(bpy)2(dppz-R)(PF6)2 compounds were found to bind to the TiO2 thin films in high surface coverages, 5 x 10(-8) mol cm(-2). When these films were immersed in acetonitrile, long-lived excited states (tau = 825 ns) that were quenched by the addition of water were observed. About 30% of the excited states could not be quenched by water. Efficient electron injection, phi(inj) = 0.8, was observed after light excitation of Ru(bpy)2(dppz-R)/TiO2 in a 0.1 M LiClO4/acetonitrile solution. The addition of large concentrations of water, >0.5 M, was found to decrease the injection yield to phi(inj) = 0.3. 相似文献
97.
Automated microcolumn-switching system for drug analysis by direct injection of human plasma 总被引:1,自引:0,他引:1
Neto AJ Rodrigues JC Fernandes C Titato GM Alves C Lanças FM 《Journal of chromatography. A》2006,1105(1-2):71-76
This study presents the application of a system that joins the known advantages of capillary liquid chromatography (e.g., higher concentration of the analytes and lower consumption of mobile phase) with those of column-switching using restricted access material (RAM) (sample clean up and extraction) to the analysis of fluoxetine in plasma samples. Automatically, the system loads the biological sample, while a RAM-BSA-C18 column (50 mm x 520 microm) excludes the macromolecules and focuses the analytes; afterwards, a second mobile phase elutes the analytes, in backflush mode, and provides the separation in a C18 analytical column (100 mm x 520 microm). We optimized the procedure for a total analysis time of 25 min. Using this approach the calibration curve shows r=0.998 with a linearity range from 20 to 500 ng ml(-1). Precision, calculated as relative standard deviation (RSD), was<20%. The developed miniaturized system showed to be adequate and attractive, demonstrating a large potential for sample preparation. 相似文献
98.
Jaeger DA Mendoza A Apkarian RP 《Langmuir : the ACS journal of surfaces and colloids》2006,22(4):1555-1560
Surfactants 3 (tripotassium O,O'-di-[11-(carboxylato)undecyl]phosphorodithioate) and 4 (sodium 12-[dimethyl-(11-carboxylatoundecyl)ammonio]dodecanoate), which are new shamrock surfactants, were prepared and characterized. Shamrock surfactants represent a novel class of surfactants that contain a central headgroup connected to two flanking headgroups by hydrocarbon chains; they do not contain long-chain alkyl groups. Surfactants 3 and 4 were characterized in water by measurement of their Krafft temperatures and critical aggregation concentrations, and their aggregates were studied by 1H and 31P NMR spectroscopy, dynamic laser light scattering, and phase-contrast optical microscopy. Aqueous 3 and 4 were also studied by cryoetch high-resolution scanning electron microscopy, which revealed fences with interposed lacelike patterns for the former and compartments formed by irregular fences for the latter. Coacervates were likely formed upon the undisturbed hydration of 3 and 4, as determined by phase-contrast optical microscopy. 相似文献
99.
Alvaro E de la Torre MC Sierra MA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(24):6403-6411
The intermolecular Nicholas reaction of terpene-based scaffolds is an excellent access to natural product hybrid compounds. These intermolecular reactions have a low selectivity and are scarcely efficient for non-conjugated cations, but they are highly efficient to produce new terpene structures through an intramolecular reaction pathway. The use of cations derived from natural product derived [Co(2)(CO)(6)]-enyne complexes is, in contrast, a highly efficient regio- and stereoselective procedure to prepare very complex structures, incorporating diverse densely functionalized or labile moieties. Thus, beta-pinene-diterpene-alkaloid or homohybrids can be accessed in totally stereo-, regio- and siteselective fashion. This approach efficiently discriminates between different propargylic positions by selecting the nature of the alcohol, being the enyne-derived cations the most reactive. The chimera 38 with a steroid-terpene-indole skeleton was prepared in this way. 相似文献
100.
This paper describes the development of an analytical method consisting of pressurised fluid extraction (PFE) and gas chromatography-mass spectrometry (GC-MS) using experimental designs to determine two volatile compounds in naturally-tainted cork stoppers. The target analytes, 2,4,6-trichloroanisole (2,4,6-TCA) and guaiacol, are involved in the cork taint of wine. First, a Plackett-Burman experimental design was carried out in order to determine the significant experimental parameters affecting the PFE process, and then a central composite design was used to optimise these significant parameters. Once the method had been optimised, the influence of the number of extraction cycles was studied. The method was applied to determine the concentration of 2,4,6-TCA and guaiacol in three cork samples, and the results were compared with the ones obtained by multiple headspace-solid-phase microextraction (MHS-SPME) and by Soxhlet extraction. 相似文献