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991.
Winfried Hartl Dipl.-Phys. J. Wolfgang Hammer 《Zeitschrift für Physik A Hadrons and Nuclei》1976,278(2):183-188
TheK-Shell Electron-Capture ProbabilityP K for the Electron Capture of139Ce has been measured using the coincidence method. The detectors used have been a NaJ(Tl)-detector with Be-window for the Lanthan-X-ray, a Ge(Li)- and a 76.2 mm Ø×76.2 mm-NaJ(Tl)-detector for the 166 keV-γ-ray. The escape-effect of the Lanthan-X-ray in the NaJ(Tl)-detector was investigated. The experimental results areP K ΩK= 0.726±0.010 andP K =0.801±0.034 using ΩK=0.906±0.026. 相似文献
992.
Andrew McGlashon Weimin Zhang Detlef M. Smilgies Maxim Shkunov Kristijonas Genevicius Katherine S. Whitehead Aram Amassian George G. Malliaras Donal D.C. Bradley Martin Heeney Alasdair J. Campbell 《Current Applied Physics》2012
3′-methyl-(5,5′′-bis[3-ethyl-3-(6-phenyl-hexyloxymethyl)-oxetane])-2,2′:5′,2′′-terthiophene (5T(Me)Ox) is a solution processable small molecule semiconductor displaying smectic-C and nematic liquid crystal phases. The pendant oxetane group can be polymerized in situ in the presence of a suitable photoacid at concentrations ≥1% by weight. Spin-coated films of pure 5T(Me)Ox and 5T(Me)Ox doped with the soluble photoacid were characterized by absorption and photoluminescent spectroscopy. Thick pristine films showed absorption and emission from a crystalline phase. Thin monolayer (<5 nm) films, as well as thicker photoacid doped films, instead showed absorption from an H-aggregate phase and emission from an excimer. Optical microscopy showed a significant change in film structure upon addition of the photoacid; large and well-orientated crystals being replaced by much smaller domains which appear to vary in thickness. Grazing Incidence Wide Angle X-Ray Scattering (GIWAXS) was used to characterize the packing and orientation of molecules in the crystalline and doped samples. The results are consistent with the photoacid doped samples forming layers of H-aggregate phase monolayer sheets parallel to the substrate where the photoacid inhibits the transition into the three-dimensionally ordered crystalline phase. Field-effect transistors and light emitting diodes were constructed incorporating 5T(Me)Ox as the active layer. Pure 5T(Me)Ox field-effect transistors showed good, p-type device characteristics, but the morphological changes upon doping result in a loss of transistor action. In the diodes, curing through melting and exposure to UV light followed by photoacid removal resulted in an increase in current density but a decrease in light emission. These results indicate that the presence of the photoacid (≥1% by weight) can have a dramatic effect on the structure, morphology and device performance of ordered, photopatternable materials for organic electronics. 相似文献
993.
994.
Deporter SM Jacobsen AC Partridge KM Williamson KS Yoon TP 《Tetrahedron letters》2010,51(40):5223-5225
We report that N-4-nosyl-3-phenyloxaziridine is an effective terminal oxidant for copper(II)-catalyzed oxyamination recently developed in our labs. This oxaziridine can be prepared on multi-gram scale and is easily purified by recrystallization. The products of oxyamination using this oxaziridine bear protecting groups that can be readily removed in high yields under mild conditions. 相似文献
995.
996.
997.
Singh SB Jayasuriya H Ondeyka JG Herath KB Zhang C Zink DL Tsou NN Ball RG Basilio A Genilloud O Diez MT Vicente F Pelaez F Young K Wang J 《Journal of the American Chemical Society》2006,128(36):11916-11920
Fatty acids are essential for survival of bacteria and are synthesized by a series of enzymes including the elongation enzymes, beta-ketoacyl acyl carrier protein synthase I/II (FabF/B). Inhibition of fatty acid synthesis is one of the new targets for the discovery and development of antibacterial agents. Platensimycin (1a) is a novel broad spectrum Gram-positive antibiotic produced by Streptomyces platensis. It was discovered by target-based whole-cell screening strategy using antisense differential sensitivity assay. It inhibits bacterial growth by selectively inhibiting condensing enzyme FabF of the fatty acid synthesis pathway and was isolated by a two-step process, a capture step followed by reversed-phase HPLC. The structure was elucidated by 2D NMR methods and confirmed by X-ray crystallographic analysis of a bromo derivative. It was determined that potential reactivity of the enone moiety does not play a key role in the biological activity of platensimycin. However, cyclohexenone ring conformation renders for the stronger binding interaction with the enzyme. The isolation, structure elucidation, derivatization, and biological activity of 6,7-dihydroplatensimycin are described. 相似文献
998.
McGilvray KL Decan MR Wang D Scaiano JC 《Journal of the American Chemical Society》2006,128(50):15980-15981
Aqueous, unprotected gold nanoparticles were prepared from HAuCl4 using a water-soluble benzoin (Irgacure-2959) as a photochemical source of strongly reducing ketyl radicals. This rapid method provides spatiotemporal control of nanoparticle generation, while light intensity can be used to control particle size. The particles are stable for months and do not require any of the conventional (S, N, or P) stabilizing ligands, although these can be readily incorporated if required. 相似文献
999.
Mikolasch A Niedermeyer TH Lalk M Witt S Seefeldt S Hammer E Schauer F Gesell M Hessel S Jülich WD Lindequist U 《Chemical & pharmaceutical bulletin》2006,54(5):632-638
Eight novel penicillins were synthesized by heteromolecular reaction of ampicillin or amoxicillin with 2,5-dihydroxybenzoic acid derivatives using a laccase from Trametes spec. All products inhibited the growth of several gram positive bacterial strains in the agar diffusion assay, among them methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci. The products protected mice against an infection with Staphylococcus aureus lethal to the untreated animals. Cytotoxicity and acute toxicity of the new compounds were neglectable. The results show the usefulness of laccase for the synthesis of potential new antibiotics. The biological activity of the new compounds stimulates intensified pharmacological tests. 相似文献
1000.
A new cysteinyldopa model ligand Cydo {3-[(2-aminoethyl)sulfanyl]-4,6-di-tert-butylbenzene-1,2-diol} was prepared and its reactivity with Cu(II) explored. Under anaerobic conditions, tetranuclear [Cu4(Cydo)4] is isolated, but in the presence of O2, a benzothiazine intermediate accumulates that is trapped as the Cu(II) complex [Cu(zine)2]. Under slightly different reaction conditions, the benzothiazine further oxidizes to benzothiazole (zole). All three compounds were characterized by X-ray crystallography, and the reactions were monitored spectrophotometrically. 相似文献