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991.
The anisotropic effects of the phenyl, α- and β-naphthyl moieties in four series of 1,3-oxazino[4,3-a]isoquinolines on the 1H chemical shifts of the isoquinoline protons were calculated by employing the Nucleus Independent Chemical Shift (NICS) concept and visualized as anisotropic cones by a through-space NMR shielding grid. The signs and extents of these spatial effects on the 1H chemical shifts of the isoquinoline protons were compared with the experimental 1H NMR spectra. The differences between the experimental δ (1H)/ppm values and the calculated anisotropic effects of the aromatic moieties are discussed in terms of the steric compression that occurs in the compounds studied. 相似文献
992.
The dynamical behavior of ethylene and ethane confined inside single-walled carbon nanotubes has been studied using Molecular
Dynamics and a fully atomistic force field. Simulations were conducted at 300 K in a broad range of molecular densities, 0.026 mol⋅L−1<ρ<15.751 mol⋅L−1(C2H4) and 0.011 mol⋅L−1<ρ<14.055 mol⋅L−1(C2H6), and were oriented towards the determination of bulk and confined phase self-diffusion coefficients. In the infinite time
limit, Fickian self-diffusion is the dominant mode of transport for the bulk fluids. Upon confinement, there is a density
threshold (ρ=5.5 mol⋅L−1) below which we observe a mixed mode of transport, with contributions from Fickian and ballistic diffusion. Nanotube topology
seems to have only a small influence on the confined fluids’ dynamical properties; instead density (loading capacity) assumes
the dominant role. In all cases studied and at a given density, the diffusivities of ethylene are larger than those of ethane,
although the difference is relatively minor. We note the collapse of self-diffusivities obtained from the bulk fluids and
confined phases into a unique single trend. These results suggest that it might be possible to infer dynamical properties
of confined fluids from the knowledge of their bulk phase densities.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
993.
Gerhard Quinkert Erna Kleiner Bernd-Jürgen Freitag Jürgen Glenneberg Uta-Maria Billhardt Franz Cech Klaus R. Schmieder Clemens Schudok Hans-Christian Steinmetzer Jan W. Bats Gottfried Zimmermann Gerd Dürner Dieter Rehm Erich F. Paulus 《Helvetica chimica acta》1986,69(3):469-537
On Dien-Ketenes from o-Quinol-Acetates A detailed picture of the photochemistry of o-quinol-acetates is presented. (RS)-6-Acetoxy-6-methyl-, (RS)-6-acetoxy-2,6-dimethyl-, (RS)-6-acetoxy-5,6-dimethyl-, (RS)-6-acetoxy-2,4,6-trimethyl-, (RS)-6-acetoxy-2,3,4,6-tetramethyl-, and (RS)-6-acetoxy-2,3,4,5,6-pentamethyl-2,4-cyclohexadien-1-ones serve as representative educts. There are two separate main photochemical routes conveniently designated as 1(π*, n) or 3(π*, π) tracks. The latter may also be attained by sensitization and leads to phenols. The former, by α-cleavage furnishes dienketens as indispensable phototransients. Photolysis of dien-ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat-induced monocyclization affords 2,4-cyclohexadien-1-ones, heat-induced bicyclization stereoselectively furnishes bicyclo[3.1.0]hex-3-en-2-ones, and multi-step addition of protic nucleophiles stereoselectively gives 1,4-, 1,6- and/or 1,2-adducts. By X-ray analysis or NOE studies, the structure of isolated photoproducts is established. Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the formation and decay of kinetically unstable intermediates. Photoproduct composition depends on the pattern of substitution of the educts, on the solvents, and on the nucleophiles that might be present. Substituents primarily exert an influence upon the population of the various conformers of the dien-keten. Solvents affect the rate of the divers reaction paths competing for the phototransient. Nucleophiles play more than a trivial role when adducts are formed. With the detailed view of a dien-keten's role on hand, the photoproduct from a given o-quinol-acetate or more general from a linear conjugated cyclohexadienone is now predictable. 相似文献
994.
Erich Ziegler Helga Wittmann Otto S. Wolfbeis Heinz Sterk 《Monatshefte für Chemie / Chemical Monthly》1984,115(10):1165-1170
When quinoline is treated with ethyl bromoacetate in ethanol at a molar ratio of 1.5:1, a highly fluorescent pyrrolodiquinolinium ion (2a) is formed along with quarternized quinoline (1a). The structure of2a has been established by infrared, proton magnetic resonance and mass spectroscopy as well as by its characteristic ultraviolet absorption spectrum.
Herrn Prof. Dr.K. Schlögl, Universität Wien, zur Vollendung des 60. Lebensjahres mit besten Wünschen gewidmet. 相似文献
995.
Erich Lamprecht 《Archiv der Mathematik》1991,57(3):254-266
Ohne Zusammenfassung 相似文献
996.
997.
Dr. Erich Glock 《Mathematische Zeitschrift》1969,110(4):257-296
Ohne ZusammenfassungHerrn Friedrich Bachmann zum 60. Geburtstag gewidmetDiese Arbeit wurde durch ein Stipendium der Deutschen Forschungsgemeinschaft ermöglicht. 相似文献
998.
The purpose of this study was to validate a method for measuring vitamin K isomers in rat tissues by liquid chromatography (LC) with fluorescence detection after simple solvent extraction. This method uses separation on a C30 column, followed by zinc reduction and fluorescence measurement (243 nm, excitation; 430 nm, emission) to detect and quantitate vitamin K isomers. We were able to separate cis- and trans-vitamin K1 in methylene chloride extracts of homogenized rat livers and in hexane extracts of rat plasma. Tissue extracts were evaporated and rediluted with tetrahydrofuran-methanol (1 + 1) or methanol before being injected under isocratic conditions onto the LC column. Liver tissue of Fischer 344 rats fed a vitamin K1-containing diet ad libitum contained approximately 20 and 60 ng/g cis- and trans-vitamin K1, respectively. Mean recoveries of vitamin K1 isomers from spiked liver were 92 +/- 11% for cis-vitamin K1 and 106 +/- 5% for trans-vitamin K1. We recovered 96 +/- 8% of trans-vitamin K1 added at 1, 3, and 6 ng/mL to plasma (containing an endogenous level of 4 ng/g) from the same rats; we recovered 112 +/- 5% when trans-vitamin K1 was added to human serum (National Institute of Standards and Technology Standard Reference Material 968C). This direct method shows significant potential for the selective measurement of vitamin K1 isomers in tissues. 相似文献
999.
1000.
Adhesion promotion of Cu on C by Cr intermediate layers investigated by the SIMS method 总被引:1,自引:0,他引:1
Mayerhofer KE Neubauer E Eisenmenger-Sittner C Hutter H 《Analytical and bioanalytical chemistry》2002,374(4):602-607
Copper-carbon composites are candidate materials for heat sinks for high speed/high-performance electronic components. They combine high thermal conductivity with low density and a tailorable coefficient of thermal expansion (CTE). Because of the low wettability of carbon by copper, a thin layer of chromium can be deposited to promote both the adhesion and the thermal contact of copper with the carbon fibers. Therefore, in a first step layers of Cr and Cu were deposited by magnetron sputtering on plane vitreous carbon substrates (Sigradur G), which serve as a model for carbon fibers. From pull-off-adhesion measurements an interlayer thickness of Cr in the range of 2-10 nm was found to provide the optimal adhesion for 1 micro m thick copper overlayers. To model the later serial fabrication of the composite that involves a hot pressing step following the deposition, the C/Cr/Cu samples were heat treated at 800 degrees C under vacuum for 1 h. Adhesion on the heat-treated samples was superior in comparison to the untreated ones. To obtain information about the adhesion mechanism secondary ion mass spectrometry (SIMS) investigations were done on the depth distribution of the main elements copper, chromium, and carbon. Two samples, one as deposited and one subjected to heat treatment after deposition, were compared in this investigation. We found that heat treatment mainly modifies the distribution of Cr in the C/Cr/Cu system. 相似文献