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排序方式: 共有655条查询结果,搜索用时 312 毫秒
611.
Kyle AF Jakubec P Cockfield DM Cleator E Skidmore J Dixon DJ 《Chemical communications (Cambridge, England)》2011,47(36):10037-10039
A highly diastereoselective bifunctional organocatalyst controlled Michael addition, a nitro-Mannich/lactamization cascade, a furan N-acyliminium cyclisation, a sequential alkyne RCM/syn-reduction and an alkene RCM has allowed a 19 step, highly stereoselective synthesis of (-)-nakadomarin A. 相似文献
612.
Zhang T Zhang X Ng J Yang H Liu J Sun DD 《Chemical communications (Cambridge, England)》2011,47(6):1890-1892
Superparamagnetic Fe(3)O(4) nanoparticles were successfully grafted onto the manganese oxide OMS-2 nanowires, and the synthesized material exhibits excellent magnetic separation and adsorption properties. 相似文献
613.
Lee JH Li S Liu T Hsu S Kim C Woods VL Casteel DE 《International journal of mass spectrometry》2011,302(1-3):44-52
The type I cGMP-dependent protein kinases play critical roles in regulating vascular tone, platelet activation and synaptic plasticity. PKG I α and PKG Iβ differ in their first ~100 amino acids giving each isoform unique dimerization and autoinhibitory domains with identical cGMP-binding pockets and catalytic domains. The N-terminal leucine zipper and autoinhibitory domains have been shown to mediate isoform specific affinity for cGMP. PKG Iα has a >10 fold higher affinity for cGMP than PKG Iβ, and PKG Iβ that is missing its leucine zipper has a three-fold decreased affinity for cGMP. The exact mechanism through which the N-terminus of PKG alters cGMP-affinity is unknown. In the present study, we have used deuterium exchange mass spectrometry to study how PKG Iβ's N-terminus affects the conformation and dynamics of its cGMP-binding pockets. We found that the N-terminus increases the rate of deuterium exchange throughout the cGMP-binding domain. Our results suggest that the N-terminus shifts the conformational dynamics of the binding pockets, leading to an "open" conformation that has an increased affinity for cGMP. 相似文献
614.
采用φ振荡和φ固定两种数据采集模式的中子衍射实验结果表明较高的时效温度对消除枝晶最有效,微应变(晶粒区域间的变形不协调性)主要存在于γ'相.利用中子衍射结合扫描电子显微镜对合金的微观组织形貌进行了细致观察,给出了时效温度和时间对γ'相的影响状况,超晶格测量发现了γ'相晶粒之间出现的独特取向差.由不同晶面的中子衍射结果判断时效后合金出现了轻微的四方对称性(a < c)畸变,对这种畸变起主要作用的是基体相.实验结果同时证实了不同方向的应变差异,因而为筏化驱动模型的定量
关键词:
单晶高温合金
中子衍射
超晶格
时效处理 相似文献
615.
Hudson DD Dekker SA Mägi EC Judge AC Jackson SD Li E Sanghera JS Shaw LB Aggarwal ID Eggleton BJ 《Optics letters》2011,36(7):1122-1124
An octave spanning spectrum is generated in an As?S? taper via 77 pJ pulses from an ultrafast fiber laser. Using a previously developed tapering method, we construct a 1.3 μm taper that has a zero-dispersion wavelength around 1.4 μm. The low two-photon absorption of sulfide-based chalcogenide fiber allows for higher input powers than previous efforts in selenium-based chalcogenide tapered fibers. This higher power handling capability combined with input pulse chirp compensation allows an octave spanning spectrum to be generated directly from the taper using the unamplified laser output. 相似文献
616.
Dr. Filippo Sladojevich Ángel L. Fuentes de Arriba Dr. Irene Ortín Dr. Ting Yang Dr. Alessandro Ferrali Dr. Robert S. Paton Prof. Darren J. Dixon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(42):14286-14295
The enantioselective Conia‐ene cyclization of alkyne‐tethered β‐ketoesters is efficiently catalyzed by the combination of cinchona‐derived amino‐urea pre‐catalysts and copper(I) salts. The reaction scope is broad and a series of substrates can be efficiently cyclized with high yields and enantioselectivities. Herein, we present a detailed mechanistic study based on experimental considerations and quantum mechanical calculations. Several variables, such as the nature of the organic pre‐catalyst and the metal‐ion source, have been thoroughly investigated. Kinetic studies, as well as kinetic isotope effects and deuterium labeling experiments have been used to gain further insights into the mechanism and prove the cooperative nature of the catalytic system. Our studies suggest that the rate‐limiting step for the reaction involves the β‐ketoester deprotonation and that the active species responsible for the enantiodeterming step is monomeric in amino‐urea pre‐catalyst. Computational studies provide a quantitative understanding of the observed stereoinduction and identify hydrogen bonding from the urea group as a crucial factor in determining the observed enantioselectivity. 相似文献
617.
Hongwei Bai Dr. Zhaoyang Liu Lei Liu Prof. Darren Delai Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(9):3061-3070
We report a facile non‐hydrothermal method for the large‐scale production of hierarchical TiO2 nanorod spheres for the photocatalytic elimination of contaminants and killing bacteria. Crescent Ti/RF spheres were prepared by deliberately adding titanium trichloride (TiCl3) to the reaction of resorcinol (R) and formaldehyde (F) in an open reactor under heating and stirring. The hierarchical TiO2 nanorod spheres were obtained by calcining the crescent Ti/RF spheres in a furnace in air to burn off the RF spheres. This method has many merits, such as large‐scale production, good crystallisation of TiO2, and good reproducibility, all of which are difficult to realise by conventional hydrothermal methods. The calcination temperature plays a significant role in influencing the morphology, crystallisation, porosity, Brunauer–Emmett–Teller (BET) specific surface area, and hierarchy of the TiO2 nanorod spheres, thus resulting in different photocatalytic performances under UV light and solar light irradiation. The experimental results have demonstrated that the hierarchical TiO2 nanorod spheres obtained after calcination of the crescent Ti/RF spheres at different temperatures displayed similar photocatalytic activities under irradiation with UV light. We attribute this to a balance of opposing effects of the investigated factors. A higher calcination temperature leads to greater light absorption capability of the TiO2 nanorod spheres, thus resulting in higher photocatalytic antibacterial activity under solar light irradiation. It is also interesting to note that the hierarchical TiO2 nanorod spheres displayed intrinsic antibacterial activity in the absence of light irradiation, apparently because their sharp outward spikes can easily pierce and penetrate the walls of bacteria. In this study, the sharpest hierarchical TiO2 nanorod spheres were obtained after calcination at 500 °C, and these exhibited the highest antibacterial activity without light irradiation. A higher calcination temperature proved detrimental to the sharpness of the TiO2 nanorods, thus reducing their intrinsic antibacterial activity. 相似文献
618.
Jeroen Peters Darren Thomas Ed Boers Theo de Rijk Franz Berthiller Willem Haasnoot Michel W. F. Nielen 《Analytical and bioanalytical chemistry》2013,405(24):7783-7794
A combined (triplex) immunoassay for the simultaneous detection of three mycotoxins in grains was developed with superparamagnetic colour-encoded microbeads, in combination with two bead-dedicated flow cytometers. Monoclonal antibodies were coupled to the beads, and the amounts of bound mycotoxins were inversely related to the amounts of bound fluorescent labelled mycotoxins (inhibition immunoassay format). The selected monoclonal antibodies were tested for their target mycotoxins and for cross-reactivity with relevant metabolites and masked mycotoxins. In the triplex format, low levels of cross-interactions between the assays occurred at irrelevant high levels only. All three assays were influenced by the sample matrix of cereal extracts to some extent, and matrix-matched calibrations are recommended for quantitative screening purposes. In a preliminary in-house validation, the triplex assay was found to be reproducible, sensitive and sufficiently accurate for the quantitative screening at ML level. The triplex assay was critically compared to liquid chromatography–tandem mass spectrometry using reference materials and fortified blank material. Results for the quantification of ochratoxin A and zearalenone were in good agreement. However, the fumonisin assay was, due to overestimation, only suitable for qualitative judgements. Both flow cytometer platforms (Luminex 100 and FLEXMAP 3D) performed similar with respect to sensitivity with the advantages of a higher sample throughput and response range of the FLEXMAP 3D and lower cost of the Luminex 100.
The priciple of the direct inhibition microbead immunoassay using fluorescent mycotoxin-reporter conjugates 相似文献
619.
Novel synthesis of P‐chiral 1,3‐oxaphospholane starting from optically pure propylene oxide is described. The exact structure is confirmed by X‐ray crystallographic analysis. 相似文献
620.
Sudarat Yadnum Dr. Jérome Roche Eric Lebraud Philippe Négrier Patrick Garrigue Dr. Darren Bradshaw Dr. Chompunuch Warakulwit Prof. Jumras Limtrakul Prof. Alexander Kuhn 《Angewandte Chemie (International ed. in English)》2014,53(15):4001-4005
Herein, bipolar electrochemistry is applied in a straightforward way to the site‐selective in situ synthesis of metal–organic framework (MOF) structures, which have attracted tremendous interest in recent years because of their significant application potential, ranging from sensing to gas storage and catalysis. The novelty of the presented work is that the deposit can be intentionally confined to a defined area of a substrate without using masks or templates. The intrinsic site‐selectivity of bipolar electrochemistry makes it a method of choice to generate, in a highly controlled way, hybrid particles that may have different functionalities combined on the same particle. The wireless nature of electrodeposition allows the potential for mass production of such Janus‐type objects. 相似文献