排序方式: 共有153条查询结果,搜索用时 359 毫秒
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Zhen Wang Jian WenQing-Wei Bi Xiao-Qi XuZhu-Qing Shen Xiao-Xiao LiZili Chen 《Tetrahedron letters》2014
A new method was developed to synthesize oxirane products from the reaction of diazocarbonyl substrates with aryl aldehydes by using Ag(I) N-heterocyclic carbene complex as the catalyst. A combination of N-heterocyclic carbene silver complex (IPrAgCl) with another silver salt (AgOTf) generated the catalytic active IPr-Ag+ intermediate, which then catalyzed the epoxidation reaction. 相似文献
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The Large High Altitude Air Shower Observatory (LHAASO) project is proposed to study high energy gamma ray astronomy (40 GeV--1 PeV) and cosmic ray physics (20 TeV--1 EeV). The wide field of view Cherenkov telescope array, as a component of the LHAASO project, will be used to study the energy spectrum and composition of cosmic rays by measuring the total Cherenkov light generated by air showers and the shower maximum depth. Two prototype telescopes have been in operation since 2008. The pointing accuracy of each telescope is crucial for the direction reconstruction of the primary particles. On the other hand, the primary energy reconstruction relies on the shape of the Cherenkov image on the camera and the unrecorded photons due to the imperfect connections between the photomultiplier tubes. UV bright stars are used as point-like objects to calibrate the pointing and to study the optical properties of the camera, the spot size and the fractions of unrecorded photons in the insensitive areas of the camera. 相似文献
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Numerical Algorithms - In this paper, we consider an inverse problem for determining the initial value of heat equation with inhomogeneous source on a columnar symmetric domain. The quasi-boundary... 相似文献
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One new bisbenzylisoquinoline alkaloid, neferine N-oxide(1), along with three known compounds,neferine(2), liensinine(3), and isoliensinine(4), were isolated from Plumulanelumbinis – the embryo of the seed of Nelumbonucifera. Their structures were elucidated by extensive spectroscopic analysis(MS,UV, IR, NMR), and the absolute configurations were determined by experimental circulardichroism(CD)spectra. Compound 1 is a new naturally occurring bisbenzylisoquinoline alkaloid with an N-oxide functionality, and the CD spectrum of(1R, 1'R) neferine is first reported. The antioxidant activities of compounds 1–4 were evaluated using the ORAC assay, which illustrated that all these compounds showed the different levels of oxygen radical absorbance capacity. 相似文献
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Qi LW Wen XD Cao J Li CY Li P Yi L Wang YX Cheng XL Ge XX 《Rapid communications in mass spectrometry : RCM》2008,22(16):2493-2509
A novel rapid resolution liquid chromatography (RRLC) method coupled with diode-array detection (DAD) and time-of-flight mass spectrometry (TOFMS) in both positive and negative modes has been developed for quick and sensitive identification of the major compounds in Danggui Buxue Tang (DBT) preparation. Significant advantages of the use of RRLC with 1.8-microm porous particles include the much higher speed of chromatographic separation and great enhancement in sensitivity, compared with the conventional high-performance liquid chromatography (HPLC). With dynamic adjustment of the key role as fragmentor voltage in TOFMS, an efficient transmission of the ions was achieved to obtain the best sensitivity for providing the molecular formula for each analyte, and abundant fragment ions for structural information. The structural characterization of the major compounds in DBT was elucidated with authentic standards by DAD-TOF/MS, including phenolic acids, phthalides, saponins and isoflavonoids. The targets were rapidly screened from the complicated DBT matrix using a narrow mass window of 0.01 Da to restructure extracted ion chromatograms. By accurate mass measurements within 3 ppm error for each molecular ion and subsequent fragment ions, ten phenolic acids and phthalides including three groups of isomers, thirteen major saponins with a 20,24-epoxy-9,19-cyclolanostane-3,6,16,25-tetrol skeleton, sixteen isoflavonoids, corresponding glycosides, malonylglycosides, and acetylglycosides were identified in DBT preparation. The appropriate fragmentation pathways for them were also proposed based on definite elemental composition of the fragment ions. 相似文献
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Dr. Xiao-Xiao Chen Felix Bayard Nerea Gonzalez-Sanchis Dr. Khurnia Krisna Puji Pamungkas Dr. Naomi Sakai Prof. Stefan Matile 《Angewandte Chemie (International ed. in English)》2023,62(20):e202217868
Flipper probes have been introduced as small molecule fluorophores to image physical forces, that is, membrane tension in living systems. Their emergence over one decade is described, from evolution in design and synthesis to spectroscopic properties. Responsiveness to physical compression in equilibrium at the ground state is identified as the ideal origin of mechanosensitivity to image membrane tension in living cells. A rich collection of flippers is described to deliver and release in any subcellular membrane of interest in a leaflet-specific manner. Chalcogen-bonding cascade switching and dynamic covalent flippers are developed for super-resolution imaging and dual-sensing of membrane compression and hydration. Availability and broad use in the community validate flipper probes as a fine example of the power of translational supramolecular chemistry, moving from fundamental principles to success on the market. 相似文献
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Qi LW Cao J Li P Yu QT Wen XD Wang YX Li CY Bao KD Ge XX Cheng XL 《Journal of chromatography. A》2008,1203(1):27-35
A novel fast high-performance liquid chromatography (HPLC) method coupled with diode array detection (DAD) and time-of-flight mass spectrometry (TOF/MS) was developed for qualitative and quantitative analysis of Radix Astragali products. The potential of fast HPLC on 1.8-microm particles was compared with the performance of HPLC on conventional 5-microm particles columns. Significant advantages of fast HPLC include high-speed chromatographic separation, four times faster than HPLC with conventional columns, and great enhancement in sensitivity with limits of detection low to 0.001 ng. With dynamic adjustment of fragmentor voltage in TOF/MS, an efficient transmission of the ions was achieved to obtain the best sensitivity and abundant fragmentation. By accurate mass measurements within 5 ppm error for each molecular ion and subsequent fragment ions, a reliable identification and differentiation of six major saponins including two groups of isomers and twelve main isoflavonoids was described here for the first time. For quantitative analysis by fast HPLC-TOF/MS, linearity of response over two orders of magnitude was demonstrated (r(2)>0.99) for all analytes. Intra-day reproducibility was below 3% RSD and inter-day values were below 5% RSD. A good correlation (slope=1.1108, r(2)=0.9853) was observed for accuracy test. It is concluded that the fast and sensitive HPLC-DAD-TOF/MS is powerful in qualitative and quantitative analysis of complex herbal medicines in terms of time savings, sensitivity, selectivity, precision, accuracy as well as increasing sample throughout and lowering solvent consumption. 相似文献
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The first heterolytic and homolytic N(O)-NO(2) bond dissociation energy scales of three types Y-nitro (Y = N, O) compounds and corresponding radical anions in acetonitrile were established by using titration calorimetry combined with relevant electrochemical data through proper thermodynamic cycles. 相似文献