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排序方式: 共有157条查询结果,搜索用时 353 毫秒
31.
Annett Kreimeyer Franois Andr Catherine Gouyette Tam Huynh-Dinh 《Angewandte Chemie (International ed. in English)》1998,37(20):2853-2855
The uptake of ATP in liposomes was achieved by using the lipophilic derivative cholesteryloxycarbonyl-ATP ( 1 ). Its hydrolysis leading to the release of ATP inside the vesicules (see scheme) was observed with the help of a pH gradient and monitored by 31P NMR spectroscopy. This is the first successful transfer of a nucleoside 5′-triphosphate across a membrane. 相似文献
32.
33.
Wolf D. Habicher Ingmar Bauer Kerstin Scheim Claudia Rautenberg Annett Loßack Kazuo Yamaguchi 《Macromolecular Symposia》1997,115(1):93-125
The antioxidative action of mixtures of phenols, phosphites, HALS, a) and some of their transformation products in various compositions has been studied in the thermo- and photo-oxidation of hydrocarbons and polypropylene under different conditions. In the AIBN-initiated oxidation of hydrocarbons at low temperatures (< 80°C), hindered phenols, hindered aryl phosphites and the nitroxyl derivatives of HALS act antioxidatively when used individually in appropriate concentrations. Secondary HALS do not show any induction period, but a certain retardation of the oxidation process after some reaction time. The inhibiting efficiency of nitroxyls observed cannot be explained completely by the currently accepted action mechanisms of HALS, but is also related to the reaction of the nitroxyls with alkylperoxyl radicals. In mixtures with hindered phenols, HALS have almost no influence on the rate of thermooxidation at low temperatures. Their nitroxyl derivatives, however, always exhibit synergism, most pronounced when both stabilizers are used in equimolar ratios. During the photooxidation phenols lower the efficiency of HALS. The influence of mixtures of stabilizers on the oxidative stability of polypropylene is rather different and depends on the oxidation conditions, the structure, the concentration and the ratio of the stabilizers. Synergistic as well as antagonistic effects are observed. Both aliphatic and aromatic phosphites studied act synergistically when used together and with phenols. This demonstrates that for acting as synergist for phenols, the hydrogen peroxide decomposing capability of the phosphites, but not their chain breaking activity is important. HALS-phosphites and phosphonites, containing amine and phosphorus units in one molecule, are highly effective inhibitors of photo- and thermooxidation and exhibit lower critical antioxidant concentrations and longer induction periods than phosphites alone. They even exceed the efficiency of phenols in many cases. Transformation products of phenolic antioxidants investigated act differently and in many cases contrarily under photo- and thermooxidative conditions. Therefore, they influence the efficiency of stabilizer mixtures also in a different way. 相似文献
34.
We present an analysis of the Hall conductivity σ(xy)(ω,T) in time reversal symmetry breaking states of exotic superconductors. We find that the dichroic signal is nonzero in systems with interband order parameters. This new intrinsic mechanism may explain the Kerr effect observed in strontium ruthenate and possibly other superconductors. We predict coherence factor effects in the temperature dependence of the imaginary part of the ac Hall conductivity Imσ(xy)(ω,T), which can be tested experimentally. 相似文献
35.
36.
B. Gawlik Martine Druges Michele Bianchi Angelo Bortoli Antonius Kettrup Herbert Muntau 《Fresenius' Journal of Analytical Chemistry》1997,358(3):441-445
The quality of the aquatic and marine environment can be monitored by the determination of pollutants in organisms living
in this environment. Certified reference materials and well-organised proficiency tests are powerful means of ensuring a constant
level of quality and verifying the correct application of standardised methods. The preparation of a tuna fish proficiency
testing material for the evaluation of quality of As and Hg monitoring in seafood is described. Preparation and characterisation
of the material as well as studies on its homogeneity and stability are described. Concentrations of 3.4 ± 0.2 mg/kg total
arsenic and 2.91 ± 0.09 mg/kg total mercury have been determined as target values. Moreover indicative values for some trace
elements (Cd, Cu, Ni, Pb, Sr) and some major constituents (Al, Br, C, Ca, Cl, Fe, H, K, Mg, N, Na, P, S, Si, Zn) have also
been measured.
Received: 29 November 1996 / Revised: 17 February 1997 / Accepted: 22 February 1997 相似文献
37.
F. Chisela D. Gawlik P. Brätter 《Journal of Radioanalytical and Nuclear Chemistry》1986,102(2):347-357
The suitability of graphite of spectral quality as a sample container in short irradiations for neutron activation analysis has been investigated. The material is found to be a viable alternative to polyethylene containers especially in high flux irradiation positions where the properties of the latter deteriorate as a result of high neutron and gamma dose rates. Examples of application are demonstrated in epithermal neutron irradiations of biological materials and the accuracy and precision of the determinations were assessed. 相似文献
38.
39.
Stuart Clough John Gupton Adepeju Ligali Matthew Roberts David Driscoll Scott Annett Alisa Hewitt Matthew Hudson Edward Jackson Robert Miller Bradley Norwood Rene Kanters Hadley Wyre Heather Petruzzi 《Tetrahedron》2005,61(31):7554-7561
The highly stereoselective conversions of (Z)-3-aryl-3-chloropropenals to (E)-3-alkoxy-3-arylpropenals, to (E)-3-aryl-3-morphorlinopropenals, and to vinamidinium salts are reported. The stereochemical assignments were based on 2D-NMR experiments. 相似文献
40.
Klaus Burger Lothar Hennig Annett Fuchs Dieter Greif Jan Spengler Fernando Albericio 《Monatshefte für Chemie / Chemical Monthly》2005,136(10):1763-1779
Summary. A new approach to trifluoromethyl substituted butenolides and their thioanalogues is described starting from 2-fluoro-3-trifluoromethylfurans
and -thiophenes, respectively. The reaction sequence includes three steps – nucleophilic displacement reaction, Claisen, and finally Cope rearrangement – which can be run as domino reaction. A modification of the domino reaction (transesterification instead of
Cope rearrangement) provides a concise access to α-trifluoromethyl-γ-ketoacids. 相似文献