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81.
Wu X Ding S Ding Q Gray NS Schultz PG 《Journal of the American Chemical Society》2002,124(49):14520-14521
Purmorphamine, which is a 2,6,9-trisubstituted purine compound, was discovered through cell-based high-throughput screening from a heterocycle combinatorial library. It differentiates multipotent mesenchymal progenitor cells into an osteoblast lineage. It will serve as a unique chemical tool to study the molecular mechanisms of osteogenesis of stem cells and bone development. 相似文献
82.
The NMR enhancement factor of a frozenCuMn spin glass has been measured at a temperatureT?T g /5. The measurements were performed as function of static magnetic fields of different directions. A two component model of a spin glass has been outlined. One component being a “system of single spins” and the other one being a “subsystem of clusters”. Both components were attributed to different kinds of interaction being RKKY and dipole interaction respectively. The effective anisotropy field of the single spin system consists of two unidirectional contributionsH a s andH a c , which have been measured for different conditions. A second anisotropy fieldH d binds the cluster system to the system of single spins. All anisotropy fields depend on the annealing temperature of the alloys. 相似文献
83.
H. B. Desai P. K. Padmanabhan Ch. Venkateswarlu 《Journal of Radioanalytical and Nuclear Chemistry》1976,31(2):525-527
Copper in distilled water is collected on Zeokarb 226(NH
4
+
) and irradiated with thermal neutrons. By comparison of the induced activity of 0.51 MeV photopeak of64Cu with that of a standard, irradiated under comparable conditions, copper at ppb levels is easily determined. 相似文献
84.
Ch. Engelmann 《Journal of Radioanalytical and Nuclear Chemistry》1970,6(2):399-412
The (γ, n) activation curves for 17 elements were determined as a function of energy between 25 and 42 MeV. From these are
deduced the detection sensitivities intrinsically possible for an average beam intensity of 100 μA. Our experimental results
are compared with values calculated byG. J. Lutz. The activation curves relative to certain competitive nuclear reactions on N, O and Na, liable to interfere in the measurements
of C, N and F, were also determined. It is shown that the relative importance of these competitive nuclear reactions decreases
rapidly for energies below 30 MeV and becomes practically negligible at 25 MeV.
相似文献
85.
The antibiotic roridin D (C29H38O9), a companion of roridin A, yields on base catalysed hydrolysis verrucarol ( 3 ) and the hitherto unknown 2, 3-epoxy-2-anhydrororidinic acid ( 4 ) (C14H18O7). Roridin D is a macrocyclic diester to which structure 1 is assigned. In roridin D an epoxy group replaces the hydroxyl group of roridin A. 相似文献
86.
Shabanov A. L. Gasanova M. M. Mamedov Ch. I. 《Russian Journal of Organic Chemistry》2002,38(7):1060-1063
Stereochemistry of [2+2]- and [1+1]-macrocylization of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane, 1,3-dichloro-2-propanol, and 1,5-dichloro-3-oxapentane was studied. The reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane according to the [2+2]-cyclization scheme gave a mixture of stereoisomeric macroheterocycles with cis,syn,cis- and cis,anti,cis-junction of the polyether and cyclohexene rings. In the reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,5-dichloro-3-oxapentane, a mixture of crown compounds with cis,anti,cis- and cis-junction of the polyether and cyclohexene rings was obtained. The structure of the products was established on the basis of their chemical transformations and spectral data. 相似文献
87.
Methylbis(dithicarbamato) stibanes. Synthesis and Crystal Structure . The title compounds are obtained by reaction of methyldibromostibane with the sodium dithiocarbamates in methanol at low temperature (?78°C). The crystal structure of CH3Sb(S2CNEt2)2 as elucidated by X-ray diffraction shows no special intermolecular interactions. It can be compared to that of the corresponding bismutane CH3Bi(S2CNEt2)2 and the arsane C6H5As(S2CNEt2)2. 相似文献
88.
[formula: see text] A highly diastereoselective, microwave-induced Claisen rearrangement of an appropriately substituted propargylic enol ether allows the formation of the sterically congested C8-C14 bond of azadirachtin. When combined with a radical-mediated cyclization of the corresponding allene, this sequence offers rapid entry to the framework of azadirachtin. 相似文献
89.
Gaile A. A. Zalishchevskii G. D. Semenov L. V. Khadartsev A. Ch. Varshavskii O. M. Fedyanin N. P. 《Russian Journal of Applied Chemistry》2004,77(4):566-570
Five-step countercurrent extraction of aromatic hydrocarbons from hydrofined diesel fraction with the 2-methoxyethanol-water-pentane extraction system was studied. The process was performed on a rotary-disk extractor. 相似文献
90.
U. Buck J. Kesper Ch. Lauenstein M. Tolle M. Winter 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):293-295
(CO2) n , (NO) n and (NH3) n clusters are generated in a supersonic molecular beam and size selected by scattering from an He beam. By measurements of angular dependent mass spectra, TOF distributions and the angular dependence of the scattered signal quantitative information on the fragmentation probability by electron impact is derived. The van der Waals systems (CO2) n and (NO) n appear only at masses which are simply multiples of the monomer mass. The preferred cluster ion is the monomer ion for all investigated cluster sizes withn=2 to 4. The fragment pattern for the quasi-hydrogen bonded (NH3) n -cluster shows, beside a large number of fragment masses, a preference for protonated ions. The results are explained in terms of simple models based on the structural change from the neutral to the ionized configuration and the fragmentation pattern of the monomer followed by ionmolecule reactions. 相似文献