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排序方式: 共有599条查询结果,搜索用时 15 毫秒
91.
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93.
Frank Seela Georg Becher Helmut Rosemeyer Hans Reuter Guido Kastner Igor A. Mikhailopulo 《Helvetica chimica acta》1999,82(1):105-124
The conformation of the 7-bromo- and 7-iodo-substituted 8-aza-7-deazapurine nucleosides 1 and 2 in the solid state and in aqueous solution was studied by single-crystal X-ray analyses and by 1H-NMR spectroscopy. In the solid state, both compounds display a high-anti conformation around the glycosylic bond, and their 2′-deoxy-β-D -ribofuranose moieties adopt an N-type sugar puckering. The orientation of the exocyclic C(4′)−C(5′) bond was found to be ap in both cases. In D2O solution, both compounds display i) an 8 – 10% higher N-conformer population than 2′-deoxyguanosine and ii) a preference of the −sc conformation about the C(4′)−C(5′) bond. A comparative study on the influence of modified bases on the sugar structure of nucleosides is made. 相似文献
94.
95.
Uta Neubauer 《Nachrichten aus der Chemie》2009,57(6):722-724
96.
F. Casetti W. Jung U. Wlfle J. Reuter K. Neumann B. Gilb A. Whling S. Wagner I. Merfort C.M. Schempp 《Journal of photochemistry and photobiology. B, Biology》2009,96(3):260-265
We investigated the skin tolerance and anti-inflammatory potential of a nanoparticular solubilisate of a luteolin-rich Reseda extract (s-RE) in two independent studies in vivo. Reseda luteola extract containing 40% flavonoids was solubilized with polysorbate, resulting in product micelles with a diameter of 10 (±1.5) nm. Standardized inflammation was induced by irradiating test areas on the back of healthy volunteers with defined doses of ultraviolet B (UVB). In the first study different concentrations of s-RE were tested in 10 volunteers to evaluate dose-dependency of anti-inflammatory effects of s-RE. In the second randomized, double-blind, placebo-controlled study a defined concentration of s-RE (2.5% w/w) was tested in 40 volunteers in comparison to the vehicle (glycerol) and hydrocortisone (1% w/w). s-RE dose-dependently reduced UVB-induced erythema when applied 30 min before irradiation. To a lesser extent, topical application of s-RE after irradiation also reduced UVB-induced erythema. s-RE was as effective as hydrocortisone, whereas the vehicle had no effect. Occlusive application of s-RE on non-irradiated test sites did not cause any skin irritation. Due to excellent skin tolerance combined with potent anti-inflammatory properties s-RE bears potential especially for the prevention but also for the treatment of inflammatory skin conditions such as UV-induced erythema. 相似文献
97.
Computational study on the 1,2-rearrangement in beta-(nitroxy)vinyl and beta-(acetoxy)vinyl radicals
Wille U 《The Journal of organic chemistry》2006,71(11):4040-4048
The 1,2-nitroxyl and 1,2-acetoxyl rearrangement in beta-(nitroxy)vinyl and beta-(acetoxy)vinyl radicals 13a and 13b, respectively, has been studied for the gas phase with various ab initio and density functional methods. The energetically most favorable pathway for 13a is calculated to proceed via reversible fragmentation/radical addition through transition state I-19a. In the case of 13b, rearrangement through a five-membered ring transition state III-16b and the fragmentation/radical addition pathway via transition state I-19b are competing processes. Mulliken and natural population analysis reveal a certain degree of charge separation in III-16a/b that may indicate a potential solvent effect on the rearrangement rate. A stepwise group migration through a cyclic radical intermediate V-18a/b or rearrangement through a three-membered ring transition state II-15a/b can be ruled out for both vinyl radicals. A comparison of the results of the calculations with experimental findings provides important insights into the kinetics of "self-terminating radical oxygenations". A significant method dependence on the outcome of the calculations was observed, which revealed the unsuitability of the UHF, MP2, B3LYP, and mPW1PW91 methods for computing these radical rearrangement processes. The results from BHandHLYP/cc-pVDZ calculations showed the best agreement with single-point energy calculations performed at the QCISD and CCSD(T) levels of theory. 相似文献
98.
Harry Podlesak Uta Faust Bernhard Wielage Michael Quast Peter Mayr Heinz-Rolf Stock 《Mikrochimica acta》2000,133(1-4):285-288
Detailed examinations were made by AES depth profiling, SEM, TEM and electron diffraction to get information about the relation
between treatment conditions and the state of plasma-nitrided aluminium. The chemical composition and the elemental depth
distribution were proofed to be depending on gas phase mixture, pressure and temperature during plasma treatment. The admixture
of hydrogen during presputtering for surface cleaning and during nitriding results both in an improved nitriding behaviour
and in a reduction of the formation of conical-shaped particles at the surface. The microstructure of the nitride layer isn’t
depending on tested process conditions significantly. Surface and interface between layer and substrate are roughly in a scale
of a few ten nanometers owing to sputtering effects. The main phase inside the layer is nanocrystalline AlN of the known hexagonal
modification. In addition, some crystallites of remaining aluminium are present as a second phase. In contrast to nitrogen-implanted
aluminium no preferred lattice orientation of the AlN phase was evident. 相似文献
99.
D. Fliegner M. Reuter M. G. Schmidt C. Schubert 《Theoretical and Mathematical Physics》1997,113(2):1442-1451
By calculating the two-loop QED Euler-Heisenberg Lagrangian in dimensional regularization, we clarify a discrepancy between
two previous calculations of this quantity performed in proper-time regularization.
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 113, No. 2, pp. 289–300, November, 1997. 相似文献
100.