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21.
Yonggui Liu Dr. Guoyong Luo Dr. Xing Yang Shichun Jiang Prof. Dr. Wei Xue Prof. Dr. Yonggui Robin Chi Prof. Dr. Zhichao Jin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(1):450-456
The aromatic nitrogen atoms of heteroarylaldehydes are activated by carbene catalysts to react with ketone electrophiles. Multi-functionalized cyclic N,O-acetal products are afforded in good to excellent yields and optical purities. Our reaction involves the formation of an unprecedented aza-fulvene-type acylazolium intermediate. A broad range of N-heteroaromatic aldehydes and electron-deficient ketone substrates works effectively in this transformation. Several of the chiral N,O-acetal products afforded through this protocol exhibit excellent antibacterial activities against Ralstonia solanacearum (Rs) and are valuable in the development of novel agrichemicals for plant protection. 相似文献
22.
Self-assembled supramolecular networks are promising spacer layer for electronic decoupling from the metal substrate.However,the mechanism behind of how the intrinsic electronic structure of spacer layers affects the adsorbate is still unclear.Here a hydrogen bonded network composed of n-type semiconducting molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride(PTCDA)is prepared under ultra-high vacuum to serve as a spacer layer for functional organics C60 on Au(111).The geometric and electronic information of C60 was investigated by scanning tunneling microscopy and scanning tunneling spectroscopy(STM/STS)at 5 K.Effective decoupling from the metal surface yields an energy gap of 3.67 eV for C602nd,merely considering the HOMO-LUMO peak separation.The broadening of resonance peaks in STS measurements however indicates unneglected interlayer interactions in this hetero-organic system.Moreover,we scrutinize the nucleation sites of C60 on PTCDA layer and attribute this to the decreased diffusion capability on a less dense molecular arrangement possessing inhomogeneous spatial distribution of unoccupied molecular orbitals. 相似文献
23.
Xingbin Ma Xukun Zhang Hongling Lin A. M. Abd El‐Aty Tsdan Rabah Xiaoxi Liu Zhichao Yu Yanhong Yong Xianghong Ju Yongxin She 《Journal of separation science》2020,43(12):2301-2310
The naturally occurring quercetin flavonoid, dihydroquercetin, is widely distributed in plant tissues and has a variety of biological activities. Herein, a magnetic molecularly imprinted solid‐phase extraction was tailor made for selective determination of dihydroquercetin in Larix griffithiana using high‐performance liquid chromatography. Amino‐functionalized core‐shell magnetic nanoparticles were prepared and characterized using scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, and infrared spectroscopy. The polymer had an average diameter of 250 ± 2.56 nm and exhibited good stability and adsorption for template molecule, which is enriched by hydrogen bonding interaction. Multiple factors for extraction, including loading, washing, elution solvents, and extraction time, were optimized. The limit of detection was 1.23 μg/g. The precision determined at various concentration of dihydroquercetin was less than 4% and the mean recovery was between 74.64 and 101.80%. It has therefore been shown that this protocol can be used as an alternative extraction to quantify dihydroquercetin in L. griffithiana and purify quercetin flavonoid from other complex matrices. 相似文献
24.
SO2-4对铁基催化剂上费托合成反应的影响 总被引:1,自引:1,他引:0
以FeCuK/SiO2为母体催化剂,用不同浓度的NH4HSO4水溶液进行等体积浸渍,制备了不同SO2-4含量的费托合成(FTS)铁基催化剂.采用原子发射光谱、低温N2吸附、 X射线光电子能谱、程序升温还原和穆斯堡尔谱等技术对催化剂进行了表征,并在H2/CO摩尔比0.67,WHSV=2 000 h-1,压力1.5 MPa和温度250 ℃条件下进行了浆态床FTS反应.结果表明,少量SO2-4能促进催化剂在H2中的还原;在合成气还原过程中,少量SO2-4对催化剂的碳化程度影响不大,但大量SO2-4严重抑制催化剂的碳化.在约500 h的运行实验中,各催化剂样品表现出的催化活性有所差异,但均呈现较好的稳定性.SO2-4可抑制水煤气变换反应活性,且随着SO2-4含量的增加,抑制作用愈加明显;同时,催化剂上浸渍少量SO2-4可有效抑制CH4的生成,提高低碳烯烃的选择性. 相似文献
25.
Liejin Zhou Xingxing Wu Xing Yang Chengli Mou Runjiang Song Shuyan Yu Huifang Chai Lutai Pan Zhichao Jin Yonggui Robin Chi 《Angewandte Chemie (International ed. in English)》2020,59(4):1557-1561
The combined use of gold as transition metal catalyst and N‐heterocyclic carbene (NHC) as organic catalyst in the same solution for relay catalytic reactions was disclosed. The ynamide substrate was activated by gold catalyst to form unsaturated ketimine intermediate that subsequently reacted with the enals (via azolium enolate intermediate generated with NHC) effectively to form bicyclic lactam products with excellent diastereo‐ and enantio‐selectivities. The gold and NHC coordination and dissociation can be dynamic and tunable events, and thus allow the co‐existence of both active metal and carbene organic catalysts in appreciable concentrations, for the dual catalytic reaction to proceed. 相似文献
26.
超导量子干涉仪、 超导光子探测器等深空探测器需要液氦温区制冷技术提供极低温温度, 固体界面接触热阻的存在会增大耦合界面温度差, 进而增加制冷机系统冷损. 为定量探究4~20 K 深低温区固体接触热阻, 采用GM 作为冷源, 设计了一台可同时调节压力和低温温度的固体界面接触热阻测试实验台. 利用感压纸进行接触界面压力校核, 并对温度重复性进行验证. 实验测试了不同导热介质填充情况下, 温度和压力变化时固体接触热阻的变化规律. 基于最小二乘法对实验数据进行半经验公式拟合, 获得4 ~20 K 温区不同压力加载条件下的接触热阻的定量参考. 相似文献
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28.
研究了偶联剂改性的廉价填料级γ-Al_2O_3直接催化偏三甲苯(TMB)氧化为2,3,5-三甲基苯醌(TMBQ)性能的影响。结果表明,γ-(2,3-环氧丙基)丙基三甲氧基硅烷(KH560)改性后的填料γ-Al_2O_3催化氧化活性较高。考察了KH560用量、水解时间、吸附时间及吸附温度对催化效果的影响。在优化条件下(2mL KH560/Et OH溶液(体积比1∶25),水解1h,吸附4h,吸附温度50℃),偶联剂对填料γ-Al_2O_3表面产生一定的包覆,在催化氧化TMB时较温和,副反应较少,TMB转化率和TMBQ选择性分别为14.3%和72.4%。 相似文献
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