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排序方式: 共有607条查询结果,搜索用时 93 毫秒
601.
Louis A. Silks III David B. Kimball Duane Hatch Morgane Ollivault-Shiflett Ryszard Michalczyk Eddie Moody 《合成通讯》2013,43(4):641-653
The chiral oxazolidineselone functionality was found to be an excellent partner in the stereospecific acetate aldol reaction with aldehydes via the titanium enolates. Good stereocontrol was obtained as determined by NMR spectroscopy. The oxazolidineselone also provided a straightforward way to establish the stereopurity of the coupling reaction through 77Se NMR spectroscopy. 相似文献
602.
Determination of post-culture processing with carbohydrates by MALDI-MS and TMS derivatization GC-MS 总被引:1,自引:0,他引:1
Wunschel DS Wahl KL Melville AM Sorensen CM Colburn HA Valentine NB Stamper CL 《Talanta》2011,85(5):2352-2360
Biological materials generally require stabilization to retain activity or viability in a dry form. A number of industrial products, such as vaccines, probiotics and biopesticides have been produced as dry preparations. The same methods and materials used for stabilizing commercial microbial products may be applicable to preserving biothreat pathogens in a dry form. This is a likely step that may be encountered when looking at samples from terrorism attempts since only spores, such as those from Bacillus anthracis, are inherently stable when dried. The stabilizers for microbial preparations generally include one or more small carbohydrates. Different formulations have been reported for different industrial products and are often determined empirically. However sugar alcohols (mannitol and sorbitol) and disaccharides (lactose, sucrose and trehalose) are the common constituents of these formulations. We have developed an analytical method for sample preparation and detection of these simple carbohydrates using two complementary analytical tools, MALDI-MS and GC-MS. The native carbohydrates and other constituents of the formulation are detected by MALDI-MS as a screening tool. A longer and more detailed analysis is then used to specifically identify the carbohydrates by derivatization and GC-MS detection. Both techniques were tested against ten different types of stabilization recipes with Yersinia pestis cell mass cultured on different media types used as the biological component. A number of additional components were included in these formulations including proteins and peptides from serum or milk, polymers (e.g. poly vinyl pyrrolidone - PVP) and detergents (e.g. Tween). The combined method was characterized to determine several figures of merit. The accuracy of the method was 98% for MALDI-MS and 100% for GC-MS. The repeatability for detection of carbohydrates by MALDI-MS was determined to be 96%. The repeatability of compound identification by GC-MS was determined by monitoring variation in retention time, which is vital for identification of isomeric carbohydrates. The figures of merit illustrate an effective and accurate method for mono and disaccharide detection independent of formulation. This meets our primary goal for method development as small carbohydrates are among the most common stabilizers employed. 相似文献
603.
Ranaweera RA Sankaranarayanan J Casey L Ault BS Gudmundsdottir AD 《The Journal of organic chemistry》2011,76(20):8177-8188
Photolysis of 1 in chloroform yielded 2 as the major product and a small quantity of 3. Laser flash photolysis demonstrated that upon irradiation, the first excited triplet state of the ketone (T(1K)) of 1 is formed and decayed to form radical 4, which has a λ(max) at 380 nm (τ = 2 μs). Radical 4 expelled a nitrogen molecule to yield imine radical 5 (λ(max) at 300 nm). Density functional theory (DFT) calculations showed that the transition state barrier for the formation of 5 is approximately 4 kcal/mol. In comparison, photolysis of 1 in argon matrices resulted in triplet nitrene 6, which was further characterized with (15)N and D isotope labeling and DFT calculations. Prolonged irradiation of 6 yields triplet imine nitrene 7. 相似文献
604.
Sterile neutrinos are attractive dark matter candidates. Their parameter space of mass and mixing angle has not yet been fully tested despite intensive efforts that exploit their gravitational clustering properties and radiative decays. We use the limits on gamma-ray line emission from the Galactic center region obtained with the SPI spectrometer on the INTEGRAL satellite to set new constraints, which improve on the earlier bounds on mixing by more than 2 orders of magnitude, and thus strongly restrict a wide and interesting range of models. 相似文献
605.
Girod FX Niyazov RA Avakian H Ball J Bedlinskiy I Burkert VD De Masi R Elouadrhiri L Garçon M Guidal M Jo HS Joo K Kubarovsky V Kuleshov SV MacCormick M Niccolai S Pogorelko O Sabatié F Stepanyan S Stoler P Ungaro M Zhao B Amaryan MJ Ambrozewicz P Anghinolfi M Asryan G Bagdasaryan H Baillie N Ball JP Baltzell NA Batourine V Battaglieri M Bellis M Benmouna N Berman BL Biselli AS Blaszczyk L Bouchigny S Boiarinov S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Butuceanu C Calarco JR 《Physical review letters》2008,100(16):162002
The beam-spin asymmetries in the hard exclusive electroproduction of photons on the proton (e p-->epgamma) were measured over a wide kinematic range and with high statistical accuracy. These asymmetries result from the interference of the Bethe-Heitler process and of deeply virtual Compton scattering. Over the whole kinematic range (x(B) from 0.11 to 0.58, Q2 from 1 to 4.8 GeV2, -t from 0.09 to 1.8 GeV2), the azimuthal dependence of the asymmetries is compatible with expectations from leading-twist dominance, A approximately a sinphi/(1+c cosphi). This extensive set of data can thus be used to constrain significantly the generalized parton distributions of the nucleon in the valence quark sector. 相似文献
606.
607.