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121.
Hong‐Juan Deng Yu‐Jing Fang Gao‐Wei Chen Miao‐Chang Liu Hua‐Yue Wu Jiu‐Xi Chen 《应用有机金属化学》2012,26(4):164-167
An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
122.
Styrene–norbornene (S‐N) copolymerizations were carried out using β‐diketiminato nickel complexes CH{C(CF3)NAr}2NiBr (Ar = 2,6‐iPr2C6H3, 1 ; Ar = 2,6‐Me2C6H3, 2 ) in the presence of methylaluminoxane. The influence of the comonomer feed content and polymerization temperature on the conversion and composition of the copolymers with the catalytic system was investigated. An increase in the feed ratio of S/N led to an increase in the incorporated styrene content of the resulting copolymer. NMR characterization of the copolymers generated with the catalytic systems showed that the random S‐N copolymers are produced. Differential scanning calorimetric determination of the copolymers shows higher Tg values than polystyrene, and gel permeation chromatographic measurements have shown that the copolymers possess rather narrow molecular weight distributions, suggesting that the copolymerization take place at a single active site. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
123.
淡水蚌类发育过程中的钩介幼虫需要寄生在鱼鳃或鳍上,由于幼虫体型微小,依据其形态鉴定蚌种较困难,因此难以准确确定蚌类寄主鱼种类。通过提取寄生在黄颡鱼鳃上的已知蚌种三角帆蚌钩介幼虫DNA,扩增线粒体COI基因并测序,构建系统发育树,并计算种内、种间遗传距离。结果表明:寄生的三角帆蚌钩介幼虫和三角帆蚌聚为一支,置信度为100%,且种内分支明显小于种间分支长度。种内遗传距离为0.003,种间平均遗传距离为0.238,种间遗传距离为种内遗传距离的79.3倍。说明基于线粒体COI基因的分子标记,能够正确鉴定寄生钩介幼虫蚌种,为确定淡水蚌类寄主鱼提供了一种有效的方法。 更多还原 相似文献
124.
薄膜吸收是降低膜层激光损伤阈值的重要原因,为了研究薄膜吸收对激光损伤阈值的影响,对HfO2单层膜在1 064 nm处的吸收及其在不同波长激光辐照下的损伤阈值进行了测试和分析。研究结果表明:薄膜的激光损伤阈值由薄膜吸收平均值(决定于薄膜中缺陷的种类和数量)和吸收均匀性(决定于薄膜中缺陷的分布)共同决定;根据HfO2单层膜在1064 nm波长处的吸收值,不但可以定性判断薄膜在1 064 nm波长,而且还可以判断在其它波长激光辐照下的抗激光损伤能力。 相似文献
125.
映射法是一种非常经典、有效和成熟的求解非线性演化方程的方法,其最大的特点是可以有多种不同形式的设解,使得最终求得的解丰富多彩. 利用改进的 Riccati 方程映射法和变量分离法,得到了(2+1)维非对称 Nizhnik-Novikov-Veselov 系统的新显式精确解.根据得到的孤波解,构造出该系统的峰孤子和分形孤子等局域结构,研究了两个孤立波的“追碰”现象.
关键词:
改进的映射法
(2+1)维非对称 Nizhnik-Novikov-Veselov 系统
局域结构
“追碰”现象 相似文献
126.
利用同步辐射x射线衍射和 DAC 高压技术在室温下测量了钙钛矿CaTiO3在压力0—44.53 GPa下的结构变化.结果表明,随着压力的增加CaTiO3的三个晶轴都受到不同程度的压缩,a,b的压缩率相近且相对比较大,c的压缩率最小,但没有证据表明有相变的发生.在压力范围内CaTiO3的P-V关系用Murnaghan状态方程表示,设定K′0=4,得到V0=0.2245(6)nm3和K0=222(9) GPa.应用赝立方角γpc与压力的关系,初
关键词:
3')" href="#">CaTiO3
结构
超高压
状态方程 相似文献
127.
Shipeng Wu Yinghao Wang Prof. Qiue Cao Prof. Qihua Zhao Dr. Wenhao Fang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(9):3019-3028
High-surface-area mesoporous CeO2 (hsmCeO2) was prepared by a facile organic-template-induced homogeneous precipitation process and showed excellent catalytic activity in imine synthesis in the absence of base from primary alcohols and amines in air atmosphere at low temperature. For comparison, ordinary CeO2 and hsmCeO2 after different thermal treatments were also investigated. XRD, N2 physisorption, UV-Raman, H2 temperature-programmed reduction, O2 temperature-programmed desorption, EPR spectroscopy, and X-ray photoelectron spectroscopy were used to unravel the structural and redox properties. The hsmCeO2 calcined at 400 °C shows the highest specific surface area (158 m2 g−1), the highest fraction of surface coordinatively unsaturated Ce3+ ions (18.2 %), and the highest concentration of reactive oxygen vacancies (2.4×1015 spins g−1). In the model reaction of oxidative coupling of benzyl alcohol and aniline, such an exceptional redox property of the hsmCeO2 catalyst can boost benzylideneaniline formation (2.75 and 5.55 mmol h−1 based on >99 % yield at 60 and 80 °C, respectively) in air with no base additives. It can also work effectively at a temperature of 30 °C and in gram-scale synthesis. These are among the best results for all benchmark ceria catalysts in the literature. Moreover, the hsmCeO2 catalyst shows a wide scope towards primary alcohols and amines with good to excellent yield of imines. The influence of reaction parameters, the reusability of the catalyst, and the reaction mechanism were investigated. 相似文献
128.
We study “large” nonnegative solutions for a class of quasilinear equations model of which is We give a sufficient condition on the exponents and for the removability of isolated singularities. 相似文献
129.
Shuidong Zhang Fang Liu Huaqiao Peang 《Journal of Macromolecular Science: Physics》2015,54(7):836-850
Dialdehyde sweet potato starch (DASS) with various aldehyde contents was prepared and the properties analyzed in terms of solubility, intrinsic viscosity, scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results demonstrated that when the aldehyede content of DASS was increased from 20% to 95%, the solubility, molecular weight, crystallizability, and thermal stability decreased. Thermoplastic DASS (TPDASS) was prepared by adding glycerol as a plasticizer; the thermal, rheological, hydrophobic, and tensile properties of TPDASS were investigated. The results indicated that, for the same glycerol content, with the increase of aldehyde content, the moisture adsorption decreased, while the shear viscosity, glass transition temperature, and tensile properties of TPDASS increased significantly. The effects were attributed to the introduction of aldehyde groups reducing the hydrogen bonds and decreasing the hydrophility of the starch. Moreover, the aldehyde and hydroxyl groups of DASS favored a semi-acetal formation with higher aldehyde content and cross-linking of DASS occurred with the increase of aldehyde content. In summary, compared to starch, the thermoplastic properties and hydrophobicity of DASS was improved. In the presence of water (10 wt%), the tensile strength of TPDASS with 95% aldehyde content (TPDASS95) moderately decreased, from 16.7 MPa to 14.0 MPa, when the glycerol content increased from 10% to 30%. The TPDASS with improved properties will find their applications in preparing biodegradable plastics. 相似文献
130.
Conjugated polymers (CPs) have long been recognized as an important class of materials. The highly conjugated backbone of the CPs will facilitate the rapid exciton migration and result in amplification of fluorescence signals. However, CPs are likely to aggregate and form excimers in solid states, directly leading to the fluorescence quenching, namely aggregation-caused quenching (ACQ), hence inhibiting their prospective utilizations in a large degree. Since the effect of aggregation-induced emission (AIE) is opposite to that of notorious ACQ, the AIE has raised great attention from scientists. CPs with AIE or aggregation-enhanced emission (AEE) features may help to solve the ACQ problem and meanwhile impart polymers with new properties and practical applications. In this review, we summarize the recent progress on the preparation of CPs with AIE or AEE characteristics, where AIE-active luminogens are located at polymer backbones or pendants. Their potential applications including fluorescent sensors, biological probes, and active layers for the fabrication of light-emitting diodes are also described. 相似文献