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871.
溴代二噁英(PBDD/Fs)属于潜在的持久性有机污染物,是一种平面三环芳香化合物,具有致畸、致癌、致突变等特性。目前,国际上对PBDD/Fs分析检测的研究是一大热点,但国内对PBDD/Fs的研究却较少。因此,探究PBDD/Fs的分析检测方法,对进一步控制PBDD/Fs污染具有重要科学意义。本文介绍了PBDD/Fs的特性及其分析方法,着重探讨了PBDD/Fs的提取、净化、仪器分析以及质量控制这四个方面,通过对PBDD/Fs的研究能够更好地了解我国当前对PBDD/Fs的分析检测能力,为后续开展PBDD/Fs的分析检测提供科学有效的方法参考。 相似文献
872.
Linwen Zhang Ran Long Yaoming Zhang Delong Duan Yujie Xiong Yajun Zhang Yingpu Bi 《Angewandte Chemie (International ed. in English)》2020,59(15):6224-6229
Single‐atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single‐atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single‐atom Pt/C3N4 catalyst in photocatalytic water splitting by synchronous illumination X‐ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt?N bond cleavage to form a Pt0 species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum‐decorated C3N4 catalyst. As expected, H2 production activity (14.7 mmol h?1 g?1) was enhanced significantly with the single‐atom Pt/C3N4 catalyst as compared to metallic Pt‐C3N4 (0.74 mmol h?1 g?1). 相似文献
873.
Xu Deng Jinju Xu Chaoying Tong Fangying Shi Shuyun Shi 《Journal of separation science》2020,43(8):1406-1414
Roots of Ophiopogon japonicus have been used as a functional food ingredient and traditional Chinese medicine for a long time in China. Homoisoflavonoids are one of the major kinds of bioactive compounds in O. japonicus; however, literature data about its homoisoflavonoids profile are scarce because of the complex ingredients with low abundance. Here, homoisoflavonoid fraction was prepared by petroleum ether extraction. Then, a high‐speed countercurrent chromatography off‐line coupling with high‐performance liquid chromatography–diode array detector?quadrupole time‐of‐flight tandem mass spectrometry was developed for systematic identification of homoisoflavonoids. After that, 39 homoisoflavonoids, including 29 homoisoflavanone and 10 homoisoflavone, were unambiguously or tentatively identified, while 12 of them were reported in O. japonicus for the first time. Finally, eight available homoisoflavonoids were sensitively, precisely, and accurately determined by standard calibration curves, with limit of detection and limit of quantification in the range of 0.05–0.30 μg/mL and 0.12–0.66 μg/mL, relative standard deviation less than 7.3% for intra‐ and interday variations, and recovery at 94.5–105.2%. Collectively, our developed method is efficient, reliable, and valuable to profile chemical components of complex natural products. 相似文献
874.
Qinggong Zhu Dexin Yang Huizhen Liu Xiaofu Sun Chunjun Chen Jiahui Bi Jiyuan Liu Haihong Wu Buxing Han 《Angewandte Chemie (International ed. in English)》2020,59(23):8896-8901
Electrocatalytic reduction of CO2 to a single product at high current densities and efficiencies remains a challenge. However, the conventional electrode preparation methods, such as drop‐casting, usually suffer from low intrinsic activity. Herein, we report a synthesis strategy for preparing heterogeneous electrocatalyst composed of 3D hierarchical Cu dendrites that derived from an in situ electrosynthesized hollow copper metal–organic framework (MOF), for which the preparation of the Cu‐MOF film took only 5 min. The synthesis strategy preferentially exposes active sites, which favor's the reduction of CO2 to formate. The current density could be as high as 102.1 mA cm?2 with a selectivity of 98.2 % in ionic‐liquid‐based electrolyte and a commonly used H‐type cell. 相似文献
875.
[3+2] Cycloaddition of Propargylic Alcohols and α‐Oxo Ketene Dithioacetals: Synthesis of Functionalized Cyclopentadienes and Further Application in a Diels–Alder Reaction 下载免费PDF全文
Zhongxue Fang Jianquan Liu Prof. Qun Liu Prof. Xihe Bi 《Angewandte Chemie (International ed. in English)》2014,53(28):7209-7213
Cyclopentadienes are valuable intermediates in organic synthesis and also ubiquitous as the Cp ligands in organometallic chemistry. As part of ongoing efforts to develop novel organic reactions that employ functionalized alkynes, a [3+2] cycloaddition of propargylic alcohols and ketene dithioacetals has been developed, which leads to fully substituted 2,5‐dialkylthio cyclopentadienes in good to excellent yields. In an unusual dethiolating Diels–Alder reaction, the cyclopentadienes were further reacted with maleimides to afford a family of novel fluorescent polycyclic compounds. 相似文献
876.
An Aqueous Rechargeable Formate‐Based Hydrogen Battery Driven by Heterogeneous Pd Catalysis 下载免费PDF全文
Dr. Qing‐Yuan Bi Jian‐Dong Lin Dr. Yong‐Mei Liu Dr. Xian‐Long Du Prof. Dr. Jian‐Qiang Wang Prof. Dr. He‐Yong He Prof. Dr. Yong Cao 《Angewandte Chemie (International ed. in English)》2014,53(49):13583-13587
The formate‐based rechargeable hydrogen battery (RHB) promises high reversible capacity to meet the need for safe, reliable, and sustainable H2 storage used in fuel cell applications. Described herein is an additive‐free RHB which is based on repetitive cycles operated between aqueous formate dehydrogenation (discharging) and bicarbonate hydrogenation (charging). Key to this truly efficient and durable H2 handling system is the use of highly strained Pd nanoparticles anchored on graphite oxide nanosheets as a robust and efficient solid catalyst, which can facilitate both the discharging and charging processes in a reversible and highly facile manner. Up to six repeated discharging/charging cycles can be performed without noticeable degradation in the storage capacity. 相似文献
877.
Dr. Jia‐Bi Ma Zhen Yuan Jing‐Heng Meng Qing‐Yu Liu Prof. Dr. Sheng‐Gui He 《Chemphyschem》2014,15(18):4117-4125
The reactivity of metal oxide clusters toward hydrocarbon molecules can be changed, tuned, or controlled by doping. Cerium‐doped vanadium cluster cations CeV2O7+ are generated by laser ablation, mass‐selected by a quadrupole mass filter, and then reacted with C2H4 in a linear ion trap reactor. The reaction is characterized by a reflectron time‐of‐flight mass spectrometer. Three types of reaction channels are observed: 1) single oxygen‐atom transfer , 2) double oxygen‐atom transfer , and 3) C?C bond cleavage. This study provides the first bimetallic oxide cluster ion, CeV2O7+, which gives rise to C?C bond cleavage of ethene. Neither CexOy± nor VxOy± alone possess the necessary topological and electronic properties to bring about such a reaction. 相似文献
878.
879.
880.
Poly(amidoamine) (PAMAM) dendrimer-based nanodevices are of recent interest in targeted cancer therapy. Characterization of mono- and multifunctional PAMAM-based nanodevices remains a great challenge because of their molecular complexity. In this work, various mono- and multifunctional nanodevices based on PAMAM G5 (generation 5) dendrimer were characterized by UV-Vis spectrometry, (1)H NMR, size exclusion chromatography (SEC), and capillary electrophoresis (CE). CE was extensively utilized to measure the molecular heterogeneity of these PAMAM-based nanodevices. G5-FA (FA denotes folic acid) conjugates (synthesized from amine-terminated G5.NH(2) dendrimer, approach 1) with acetamide and amine termini exhibit bimodal or multi-modal distributions. In contrast, G5-FA and bifunctional G5-FA-MTX (MTX denotes methotrexate) conjugates with hydroxyl termini display a single modal distribution. Multifunctional G5.Ac(n)-FI-FA, G5.Ac(n)-FA-OH-MTX, and G5.Ac(n)-FI-FA-OH-MTX (Ac denotes acetamide; FI denotes fluorescein) nanodevices (synthesized from partially acetylated G5 dendrimer, approach 2) exhibit a monodisperse distribution. It indicates that the molecular distribution of PAMAM conjugates largely depends on the homogeneity of starting materials, the synthetic approaches, and the final functionalization steps. Hydroxylation functionalization of dendrimers masks the dispersity of the final PAMAM nanodevices in both synthetic approaches. The applied CE analysis of mono- and multifunctional PAMAM-based nanodevices provides a powerful tool to evaluate the molecular heterogeneity of complex dendrimer conjugate nanodevices for targeted cancer therapeutics. 相似文献