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排序方式: 共有139条查询结果,搜索用时 31 毫秒
1.
Axel Ingendoh Jan Becher Helen Clausen Helle Chris Nielsen 《Tetrahedron letters》1985,26(9):1249-1252
The high reactivity of the -1-acyloxy-1,3-pentadiene-5-ols as dienes in intramolecular Diels-Alder reactions with maleic anhydride and fumaric acid ethylester monochloride is discussed. 相似文献
2.
It has been shown, that in vitro incubation of Laminaria digitata extract (containing mainly As-sugar 1 (glycerol-arsenoribose) and As-sugar 3 (sulfonate-arsenoribose)) with liver cytosol, produced the same two arsenicals, as when L. digitata extract was treated with H(2)S. By parallel use of HPLC-ICP-MS and HPLC-ES-MS the compounds displayed mainly m/z 345 and m/z 409. A pure As-sugar 1 standard was obtained, and a standard of arsinothioyl-sugar 1 (m/z 345) was produced, by purging a solution of As-sugar 1 with gaseous H(2)S. The identity of arsinothioyl-sugar 1 was characterised by ES-MS, 1D and 2D NMR. Arsinothioyl-sugar 1 showed the same chromatographic behaviour and MS characteristics as one of the two arsenic-containing compounds (m/z 345) produced by incubation of L. digitata extracts with liver cytosol, and as the product of the incubation of As-sugar 1 with liver cytosol (HPLC-ICP-MS, HPLC-ES-MS). Assuming that As-sugar 3 reacts in a similar way to As-sugar 1 with H(2)S, it is most likely that the second unknown (m/z 409) is arsinothioyl-sugar 3. The degradation of As-sugar 1 in acidic solution (100 mM HCl) was followed by (1)H-NMR, and the relative slow degradation (t(1/2)= 17 h) suggests that arsenosugars are taken up from the stomach in their original chemical form, hence the study of arsenosugar incubation in tissue is highly relevant. The arsinothioyls are a new group of organoarsenicals, which have only recently been identified in nature. Here, arsinothioyl sugars are detected for the first time. The in vitro formation of arsinothioyl-sugars in liver cytosol suggests that arsinothioyls may be of large biochemical and toxicological importance. 相似文献
3.
On the Constitution of Silicate Anions in Tetraethylammonium Silicates and their Aqueous Solutions Investigations by paperchromatography, 29Si-NMR spectroscopy and trimethylsilylation method show that concentrated solutions of tetraethylammonium (TEA) silicates with molar TEA:Si ratios from 2.8 to 1 contain mainly double three-ring silicate anions. Besides of these small amount of mono-, di-, tri-, tetra-, cyclotri-, cyclotetra-, double four-ring- and other polycyclic silicate anions are present. From these solutions a crystalline double three-ring silicate of the formula [N(C2H5)4]6[Si6O15] · 57 H2O could be obtained by crystallization at low temperature. Concentrated solutions with TEA:Si ratios of 0.8 to 0.6 contain mainly double three-, double four-, double five- an probably double six-ring silicate anions. From such solutions always the solid TEA-double four-ring silicate is obtained by crystallization. The reasons for the prefered formation of double ring silicate anions in TEA-silicate solutions and their crystallization are discussed. 相似文献
4.
High-resolution 29Si NMR spectra of zunyite Si5Al13O20 (OH,F)18Cl have been studied by magic-angle sample spinning in combination with high-power proton decouplina and polarization transfer. The isotropic 29Si chemical shift depends mainly on the number of Si-O-Si bridges and the bond angles in these bridges connecting the different SiO4 tetrahedra. 相似文献
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T. Pehk E. Lippmaa V. V. Sevostjanova M. M. Krayuschkin A. I. Tarasova 《Magnetic resonance in chemistry : MRC》1971,3(6):783-790
The carbon-13 chemical shifts of mono- and 1,3-disubstituted adamantanes are reported. The effects caused by the substituents are compared with those met in aliphatic and alicyclic compounds. It is shown that the 1,4-interactions have only minor importance in l-substituted adamantanes. The influence of polar groups on the chemical shifts of γ- and δ-carbon atoms is a typical ‘through-the-bonds’ interaction and correlates with inductive parameters of the substituents. 相似文献
9.
Horiba K Taguchi M Chainani A Takata Y Ikenaga E Miwa D Nishino Y Tamasaku K Awaji M Takeuchi A Yabashi M Namatame H Taniguchi M Kumigashira H Oshima M Lippmaa M Kawasaki M Koinuma H Kobayashi K Ishikawa T Shin S 《Physical review letters》2004,93(23):236401
Using hard x-ray (HX; hnu=5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La(1-x)Sr(x)MnO(3) (LSMO) thin films. Comparison of Mn 2p core-levels with soft x-ray (SX; hnu approximately 1000 eV) PES shows a clear additional well-screened feature only in HX PES. Takeoff-angle dependent data indicate its bulk (> or =20 A) character. The doping and temperature dependence track the ferromagnetism and metallicity of the LSMO series. Cluster model calculations including charge transfer from doping-induced states show good agreement, confirming this picture of bulk properties reflected in Mn 2p core-levels using HX PES. 相似文献
10.
JPC – Journal of Planar Chromatography – Modern TLC - Two simple and rapid methods for early detection of the effects of herbicides using two different groups of plant biomarkers are... 相似文献