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61.
考察了晶种尺寸形貌及晶化温度对T型沸石膜的形成演化过程以及分离性能的影响,调查表明采用小尺寸的晶种可制备出致密的沸石膜,且膜的生长速率受晶化温度影响,低温下合成同性能的膜需更长的晶化时间。当晶种尺寸分别为0.4和0.6μm时,423 K晶化4 h可制得高性能的T型沸石膜,348 K分离90%(w/w)异丙醇/水混合物体系,其通量分别高达6.21和5.98 kg·m~(-2)·h~(-1),分离因子均10 000。实验发现,膜的形成过程受外延生长机理控制,与晶种形貌尺寸和晶化温度无关,且所制得的高性能T型沸石膜具有很好的水热稳定性及耐酸性。 相似文献
62.
63.
A new palladium-catalyzed C-H amination of aryl enamines for the synthesis of trifluoromethylated indoles is established. The attractive features of this transformation are the use of atom-economical O2 as the oxidant and easily prepared enamines as substrates. A variety of pharmaceutically important 2-trifluoromethyl indoles can be targeted in moderate to good yields with good functional compatibility. 相似文献
64.
Shao-Yuan Chen Jing-Jing Nie Jin-Zhong You Duan-Jun Xu Yao-Zu Chen 《Journal of chemical crystallography》2001,31(6):339-343
The title compound including a stable nitroxide radical was synthesized by a reaction of N,N-diisopropylcarbondiimide (DIC) with 2,2,5,5-tetramethyl-1-oxo-3-pyrroline-3-carboxylic acid (TPCO) in an EtOAc solution under nitrogen atmosphere. From 1:1 EtOAc/hexane the compound crystallizes in triclinic space group P
with a = 11.078(2), b = 11.970(2), c = 15.746(3) Å, = 105.41(3), = 103.47(3), = 106.52(3)°, and Z = 4. In an asymmetric unit two molecules assemble with each other in similar bond distances and angles but show crystallographically independent conformation. A normal single C–N bond is observed in the title compound, other than the partial double C=N bond shown in the parent urea. A longer N–O distance of 1.26 Å implies the existence of a single electron bond between N and O atoms, which stabilizes the radical molecule. 相似文献
65.
A novel on-column sequential preconcentration method based on the combination of field-amplified sample injection induced
by acetonitrile and pseudo isotachophoresis (ITP)–acid stacking is developed for simply but efficiently concentrating alkaloid
cations in a high-salt sample matrix in capillary electrophoresis. Acetonitrile (70%) added to a sample solution with a high-salt
sample matrix not only induces field-amplified sample stacking by decreasing conductivity but also acts as a termination reagent
in the succeeding pseudo ITP. After sample injection had been completed, a plug of H+ was injected electrokinetically and a neutralization reaction between H+ and tartrate from the buffer solution produced a low conductivity zone, in which the injected analyte cations were further
concentrated. With the sequential preconcentration method, a 3 orders of magnitude detection sensitivity (1,400-fold) increase
could be observed compared with the conventional electrokinetic injection method, without compromising separation efficiency
and peak shape, and detection limits of 0.1 ng/mL for myosmine and 0.3 ng/mL for anabasine with the conditions selected were
achieved. The calibration curves demonstrated good linearity in the concentration ranges 1.3–600 ng/mL for myosmine and 4.9–900 ng/mL
for anabasine, respectively. The proposed method has been used to analyze successfully trace alkaloids in cigarette samples.
Figure Sequential preconcentration processes: a sample injection; b introduction of HCl; c capillary zone electrophoresis separation. A
−
tartrate, white circles acetonitrile, black circles Na+, sample zone, myosmine, anabasine 相似文献
66.
Jia-Ni Lu Jing-Jing Liu Long-Zhang Dong Prof. Jiao-Min Lin Prof. Fei Yu Prof. Jiang Liu Prof. Ya-Qian Lan 《Angewandte Chemie (International ed. in English)》2023,62(36):e202308505
Photocatalytic synthesis of hydrogen peroxide (H2O2) is a potential clean method, but the long distance between the oxidation and reduction sites in photocatalysts hinders the rapid transfer of photogenerated charges, limiting the improvement of its performance. Here, a metal-organic cage photocatalyst, Co14(L−CH3)24 , is constructed by directly coordinating metal sites (Co sites) used for the O2 reduction reaction (ORR) with non-metallic sites (imidazole sites of ligands) used for the H2O oxidation reaction (WOR), which shortens the transport path of photogenerated electrons and holes, and improves the transport efficiency of charges and activity of the photocatalyst. Therefore, it can be used as an efficient photocatalyst with a rate of as high as 146.6 μmol g−1 h−1 for H2O2 production under O2-saturated pure water without sacrificial agents. Significantly, the combination of photocatalytic experiments and theoretical calculations proves that the functionalized modification of ligands is more conducive to adsorbing key intermediates (*OH for WOR and *HOOH for ORR), resulting in better performance. This work proposed a new catalytic strategy for the first time; i.e., to build a synergistic metal-nonmetal active site in the crystalline catalyst and use the host–guest chemistry inherent in the metal-organic cage (MOC)to increase the contact between the substrate and the catalytically active site, and finally achieve efficient photocatalytic H2O2 synthesis. 相似文献
67.
Yang-Rong Xu Jing-Jing Yang Juan Liu Gui-Ge Hou Qing-Guo Meng 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(6):498-503
Ocotillol‐type saponins have a wide spectrum of biological activities. Previous studies indicated that the configuration at the C24 position may be responsible for their stereoselectivity in pharmacological action and pharmacokinetics. Natural ocotillol‐type saponins share a 20(S)‐form but it has been found that the 20(R)‐stereoisomers have different pharmacological effects. The semisynthesis of 20(R)‐ocotillol‐type saponins has not been reported and it is therefore worthwhile clarifying their crystal structures. Two C24 epimeric 20(R)‐ocotillol‐type saponins, namely (20R,24S)‐20,24‐epoxydammarane‐3β,12β,25‐triol, C30H52O4, (III), and (20R,24R)‐20,24‐epoxydammarane‐3β,12β,25‐triol monohydrate, C30H52O4·H2O, (IV), were synthesized, and their structures were elucidated by spectral studies and finally confirmed by single‐crystal X‐ray diffraction. The (Me)C—O—C—C(OH) torsion angle of (III) is 146.41 (14)°, whereas the corresponding torsion angle of (IV) is −146.4 (7)°, indicating a different conformation at the C24 position. The crystal stacking in (III) generates an R44(8) motif, through which the molecules are linked into a one‐dimensional double chain. The chains are linked via nonclassical C—H…O hydrogen bonds into a two‐dimensional network, and further stacked into a three‐dimensional structure. In contrast to (III), epimer (IV) crystallizes as a hydrate, in which the water molecules act as hydrogen‐bond donors linking one‐dimensional chains into a two‐dimensional network through intermolecular O—H…O hydrogen bonds. The hydrogen‐bonded chains extend helically along the crystallographic a axis and generate a C44(8) motif. 相似文献
68.
The one-pot reaction of aromatic aldehydes, ethylenediamine and Oxone (2 KHSO5 x KHSO4 x K2SO4) in pure water was found to unexpectedly afford aldoximes in excellent yields. 相似文献
69.
70.
A highly efficient numerical algorithm using the multigrid method (MGM) is introduced to solve a three-dimensional (3-D)field distribution. Taking advantage of the restriction and prolongation in MGM computation, a more accurate field distribution can be acquired rapidly. According to the MGM algorithm, a 3-D program is accomplished, which can solve the field distributions in electron optical systems for various electrostatic lenses. The 3-D field distribution in an electrostatic concentric spherical model is tested with the MGM algorithm and with an algorithm based on the finite difference method (FDM). Comparing these two results in terms of computational efficiency and computational accuracy, it appears that MGM is superior to FDM, which is now used the most in field computations. This paper shows that the 3-D field computation using MGM greatly improves the computational efficiency of field distributions in electron optical systems and shortens the computational time. 相似文献