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排序方式: 共有173条查询结果,搜索用时 18 毫秒
1.
Elisabeth Seguin Michel Koch Evelyne Chenu Marcel Hayat 《Helvetica chimica acta》1980,63(5):1335-1346
Partial Synthesis and Oncostatic Properties of Pseudotubulosines, Analogues of Emetine and Tubulosine Pseudotubulosines, structural analogues of emetine and tubulosine, have been synthesized by either Pictet-Spengler or Bischler-Napieralski condensation from dihydrocorynantheal or corynantheidal. Spectral data, cytotoxic and oncostatic properties of these new alkaloids are described. 相似文献
2.
Dr. Christoph Kieninger Dr. Klaus Wurst Dr. Maren Podewitz Dr. Maria Stanley Dr. Evelyne Deery Dr. Andrew D. Lawrence Prof. Dr. Klaus R. Liedl Prof. Dr. Martin J. Warren Prof. Dr. Bernhard Kräutler 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20304-20311
The (formal) replacement of Co in cobalamin ( Cbl ) by NiII generates nibalamin ( Nibl ), a new transition-metal analogue of vitamin B12. Described here is Nibl , synthesized by incorporation of a NiII ion into the metal-free B12 ligand hydrogenobalamin ( Hbl ), itself prepared from hydrogenobyric acid ( Hby ). The related NiII corrin nibyric acid ( Niby ) was similarly synthesized from Hby , the metal-free cobyric acid ligand. The solution structures of Hbl , and Niby and Nibl , were characterized by spectroscopic studies. Hbl features two inner protons bound at N2 and N4 of the corrin ligand, as discovered in Hby . X-ray analysis of Niby shows the structural adaptation of the corrin ligand to NiII ions and the coordination behavior of NiII. The diamagnetic Niby and Nibl , and corresponding isoelectronic CoI corrins, were deduced to be isostructural. Nibl is a structural mimic of four-coordinate base-off Cbls , as verified by its ability to act as a strong inhibitor of bacterial adenosyltransferase. 相似文献
3.
Nathalie Poulain Evelyne Nakache Annabelle Pina Guy Levesque 《Journal of polymer science. Part A, Polymer chemistry》1996,34(5):729-737
The polymerization of isodecyl acrylate (ISODAC) in vesicles made from an anionic surfactant—sodium di-2-ethylhexyl phosphate (SEHP)—and from water is studied by 1H-NMR, transmission electron microscopy, and quasielastic light scattering. High polymerization rates and high conversion rates are achieved with both water-soluble initiator, K2S2O8 (potassium persulfate), and oil-soluble initiator, AIBN (azoisobisbutyronitrile). ISODAC is probably located inside the vesicle bilayer(s) because of its high hydrophobicity. Particles stable at room temperature with a mean diameter of about 50 nm are obtained. Kinetic orders of ISODAC polymerization are determined and the characterization of the resulting particles during and after polymerization are studied. © 1996 John Wiley & Sons, Inc. 相似文献
4.
Experimental and theoretical waveforms of Rayleigh waves generated by a thermoelastic laser line source 总被引:5,自引:0,他引:5
An analytical model has been developed for the generation of surface acoustic (Rayleigh) waves in an isotropic solid by a thermoelastic laser line source. For a Gaussian light intensity profile, this model leads to an expression in closed form for the normal surface displacement of the Rayleigh wave either in the near field or in the far field domain. Quantitative agreement has been found for experiments carried out with an interferometric optical probe on a duraluminum plate. 相似文献
5.
P. Feautrier J. Blondel M. Hanus J. Y. Chenu P. Encrenaz M. Carter 《International Journal of Infrared and Millimeter Waves》1990,11(2):189-200
Millimeter-wave characterization of a heterodyne receiver using (2 m2) Nb/Al-Ox/Nb Superconducting-Insulator-Superconducting (SIS) junctions arrays is reported. The fabrication of the Nb/Al-Ox/Nb SIS junction arrays as a heterodyne mixer is described. The leakage current of these junctions is below 2A at 4.2K and unmeasurable at 2.5K. The receiver gave a noise temperature Double Side Band (DSB) between 63K and 187K over the frequency range 80 to 115 GHz at the first conversion peak. The results are comparable to those obtained with SIS receivers using well researched lead junctions. Contrary to the lead junctions, our mixer using all Nb junctions have proven remarkably stable with respect to thermal cycling, characteristics which are required for space applications. To our knowledge, this is the most reliable low noise receiver operating in this frequency range. 相似文献
6.
Heckenroth M Kluser E Neels A Albrecht M 《Dalton transactions (Cambridge, England : 2003)》2008,(44):6242-6249
Palladation of C2-protected diimidazolium salts with Pd(OAc)2 afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF4, AgOAc) and Br?nsted acids (H2SO4, H3PO4, HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2 bonding. Despite its formal +2 charge, the palladium center in these complexes is best described as a Lewis base. The abnormal carbene bonding mode induces new reaction patterns such as the formation of a Pd-Ag adduct. Based on metallation studies including the palladation of a dissymmetric diimidazolium salt, a rationale for the selective activation of the C4-H bond in the diimidazolium precursor salts is proposed. 相似文献
7.
Clean Donor Oxidation Enhances the H2 Evolution Activity of a Carbon Quantum Dot–Molecular Catalyst Photosystem 下载免费PDF全文
Benjamin C. M. Martindale Evelyne Joliat Dr. Cyril Bachmann Prof. Dr. Roger Alberto Dr. Erwin Reisner 《Angewandte Chemie (International ed. in English)》2016,55(32):9402-9406
Carbon quantum dots (CQDs) are new‐generation light absorbers for photocatalytic H2 evolution in aqueous solution, but the performance of CQD‐molecular catalyst systems is currently limited by the decomposition of the molecular component. Clean oxidation of the electron donor by donor recycling prevents the formation of destructive radical species and non‐innocent oxidation products. This approach allowed a CQD‐molecular nickel bis(diphosphine) photocatalyst system to reach a benchmark lifetime of more than 5 days and a record turnover number of 1094±61 molH2 (molNi)?1 for a defined synthetic molecular nickel catalyst in purely aqueous solution under AM1.5G solar irradiation. 相似文献
8.
Christoph Kieninger Joseph A. Baker Maren Podewitz Klaus Wurst Steffen Jockusch Andrew D. Lawrence Evelyne Deery Karl Gruber Klaus R. Liedl Martin J. Warren Bernhard Krutler 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14710-14714
Replacing the central cobalt ion of vitamin B12 by other metals has been a long‐held aspiration within the B12‐field. Herein, we describe the synthesis from hydrogenobyric acid of zincobyric acid ( Znby ) and zincobalamin ( Znbl ), the Zn‐analogues of the natural cobalt‐corrins cobyric acid and vitamin B12, respectively. The solution structures of Znby and Znbl were studied by NMR‐spectroscopy. Single crystals of Znby were produced, providing the first X‐ray crystallographic structure of a zinc corrin. The structures of Znby and of computationally generated Znbl were found to resemble the corresponding CoII‐corrins, making such Zn‐corrins potentially useful for investigations of B12‐dependent processes. The singlet excited state of Znby had a short life‐time, limited by rapid intersystem crossing to the triplet state. Znby allowed the unprecedented observation of a corrin triplet (ET=190 kJ mol?1) and was found to be an excellent photo‐sensitizer for 1O2 (ΦΔ=0.70). 相似文献
9.
Kinetic isotope measurements using [4,4-2H2]NADH and [4-1H, 4-2H]NADH have been used to investigate the mechanism of the electrochemical oxidation of NADH at poly(aniline)-poly(vinyl sulfonate)-modified electrodes. The experiments show a primary kinetic isotope effect for the reaction of 4.2. This is consistent with literature values for the corresponding isotope effect for the oxidation of NADH by two-electron oxidants in homogeneous solution. The result demonstrates that transfer of H from NADH to the modified electrode occurs in the rate-limiting step within the reaction complex. 相似文献
10.
Budai M Reynaud-Angelin A Szabó Z Tóth S Rontó G Sage E Gróf P 《Journal of photochemistry and photobiology. B, Biology》2004,77(1-3):27-38
The ultraviolet A (UVA) radiation component of sunlight (320-400 nm) has been shown to be a source of oxidative stress to cells via generation of reactive oxygen species. We report here some consequences of the UVA irradiation on cell membranes detected by electron paramagnetic resonance (EPR) spectroscopy. Paramagnetic nitroxide derivatives of stearic acid bearing the monitoring group at different depths in the hydrocarbon chain were incorporated into human fibroblasts membranes to analyze two main characteristics: kinetics of the nitroxide reduction and membrane fluidity. These two characteristics were compared for control and UVA-irradiated (0-250 kJ/m(2)) cells. The term relative redox capacity (RRC) was introduced to characterize and to compare free radical reduction measured by EPR with some well-known viability/clonogenicity tests. Our results showed that UVA-irradiation produces a more rigid membrane structure, especially at higher doses. Furthermore, we found that trends agree in survival measured by neutral red (NR), trypan blue (TB), and clonogenic efficiency compared with RRC values measured by EPR for low and medium exposure doses. Above 100 kJ/m(2), differences between these tests were observed. Antioxidant effect was modeled by alpha-tocopherol-acetate treatment of the cells before UVA irradiation. While NR, TB and clonogenicity tests showed protection at the highest UVA doses (>100 kJ/m(2)), results obtained with EPR measurements, both membrane fluidity and kinetics, or using MTT test did not exhibit this protective effect. 相似文献