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111.
Xiaodan Yu Yihang Guo Kexin Li Xia Yang Leilei Xu Yingna Guo Jianglei Hu 《Journal of molecular catalysis. A, Chemical》2008,290(1-2):44-53
A series of insoluble cesium partly substituted Wells–Dawson type heteropolyacids, CsxH6−xP2W18O62 (x = 1.5–6.0), were synthesized and characterized using the techniques including UV–vis/DRS, FT-IR, XRD, XPS, and N2 porosimetry. As the unique and reusable solid acid catalysts, CsxH6−xP2W18O62 salts were applied to produce diphenolic acid by the condensation reaction of phenol with bio-platform molecule, levulinic acid. For comparison, cesium partly substituted Keggin type heteropolyacids (CsxH3−xPW12O40, x = 1.0–3.0), HCl, HZSM-5, and MCM-49 were also tested. Influences on the catalytic activity and selectivity were considered for factors including solvent, molar ratio of phenol to levulinic acid, amount of catalyst, reaction temperature, stirring speed, and reaction time. The experimental results demonstrated that both Cs1.5H4.5P2W18O62and Cs2.5H0.5PW12O40 exhibited excellent catalytic performance under solvent-free conditions. Furthermore, both selectivity and activity of Cs1.5H4.5P2W18O62 were higher than those of Cs2.5H0.5PW12O40. Reasons for the different catalytic behaviors between two types of cesium partly substituted heteropolyacids were investigated. 相似文献
112.
Enantioselective Trifluoromethylthiolating Lactonization Catalyzed by an Indane‐Based Chiral Sulfide
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Xiang Liu Rui An Dr. Xuelin Zhang Jie Luo Prof. Dr. Xiaodan Zhao 《Angewandte Chemie (International ed. in English)》2016,55(19):5846-5850
Enantioselective trifluoromethylthiolation, especially of alkenes, is a challenging task. In this work, we have developed an efficient approach for enantioselective trifluoromethylthiolating lactonization by designing an indane‐based bifunctional chiral sulfide catalyst and a shelf‐stable electrophilic SCF3 reagent. The desired products were formed with diastereoselectivities of >99:1 and good to excellent enantioselectivities. The transformation represents the first enantioselective trifluoromethylthiolation of alkenes and the first enantioselective trifluoromethylthiolation that is enabled by a catalyst with a Lewis basic sulfur center. 相似文献
113.
Novel and efficient Br?nsted acid (p-TsOH) catalyzed inter- and intramolecular Friedel-Crafts alkylations have been developed to synthesize selenated three-component coupling and selenation-cyclization indole derivatives. Chemical removal of the phenylseleno moiety was investigated, and the reaction mechanisms were discussed. 相似文献
114.
Prof. Dr. Xiaodan Chen Prof. Dr. Liu Leo Liu Shihua Liu Prof. Dr. Hansjörg Grützmacher Prof. Dr. Zhongshu Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(52):24038-24043
Distonic radical cations (DRCs) with spatially separated charge and radical sites have, so far, largely been observed by gas-phase mass spectrometry and/or matrix isolation spectroscopy work. Herein, we disclose the isolation of a crystalline dicarbondiphosphide-based β-distonic radical cation salt 3.+ (BARF) (BARF=[B(3,5-(CF3)2C6H3)4)]−) stable at room temperature and formed by a one-electron-oxidation-induced intramolecular skeletal rearrangement reaction. Such a species has been validated by electron paramagnetic resonance (EPR) spectroscopy, single-crystal X-ray diffraction, UV/Vis spectroscopy and density functional theory (DFT) calculations. Compound 3.+ (BARF) exhibits a large majority of spin density at a two-coordinate phosphorus atom (0.74 a.u.) and a cationic charge located predominantly at the four-coordinate phosphorus atom (1.53 a.u.), which are separated by one carbon atom. This species represents an isolable entity of a phosphorus radical cation that is the closest to a genuine phosphorus DRC to date. 相似文献
115.
This paper is concerned with the existence, nonexistence, uniqueness, and non‐uniqueness of solutions for a singular parabolic equation in one dimension case. For different cases of some constant m of the equation, we study the uniqueness of solutions for m > ? 1, the nonexistence of solutions for m ≤ ? p, and the existence and non‐uniqueness of solutions for ? p < m ≤ ? 1. The novelty of this paper lies in the study of nonexistence. Moreover, the other results of this paper extend some recent works. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
116.
Zhengqing Liu Pengfei Yin Huiping Gong Pingping Li Xiaodan Wang Youqiu He 《Journal of luminescence》2012,132(9):2484-2488
Aqueous glutathione (GSH)-capped CdTe/ZnS QDs with the diameter of 3–4 nm were synthesized. The fluorescence of CdTe/ZnS QDs at 577 nm was quenched in the presence of rifampicin (Rfp), with excitation wavelength at 350 nm. The mechanism of the interaction of CdTe/ZnS QDs with Rfp was investigated. Under the optimal conditions, the calibration plot of ln(F0/F) was linear in the range 0.83–56 μg mL?1 with concentration of Rfp, and the detection limit was 0.25 μg mL?1. The proposed method was successfully applied to the determination of Rfp in its commercial capsules, and satisfactory results were obtained. The recovery of the method was in the range 98.6–103.2%. 相似文献
117.
Multiwalled carbon nanotubes functionalized by oxidation of original multiwalled carbon nanotubes with NaClO were prepared and their application as solid phase extraction sorbent for 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated systemically, and a new method was developed for the determination of trace 2,4-D in water samples based on extraction and preconcentration of 2,4-D with solid phase extraction columns packed with NaClO-treated multiwalled carbon nanotubes prior to its determination by HPLC. The optimum experimental parameters for preconcentration of 2,4-D, including the column activating conditions, the amount of the sorbent, pH of the sample, elution composition, and elution volume, were investigated. The results indicated 2,4-D could be quantitatively retained by 100 mg NaClO-treated multiwalled carbon nanotubes at pH 5, and then eluted completely with 10 mL 3:1 (v/v) methanol-ammonium acetate solution (0.3 mol/L). The detection limit of this method for 2,4-D was 0.15 μg/L, and the relative standard deviation was 2.3% for fortified tap water samples and 2.5% for fortified riverine water sample at the 10 μg/L level. The method was validated using fortified tap water and riverine water samples with known amount of 2,4-D at the 0.4, 10, and 30 μg/L levels, respectively. 相似文献
118.
考虑时标上奇异三阶微分方程特征值问题.首先使用Krein-Rutmann定理得到正线性算子的第一特征值,再联合不动点指数定理证明了特征值问题正解的存在性,同时也给出了参数λ的取值区间. 相似文献
119.
孔道结构H3PW12O40/TiO2的制备及其可见光光催化降解水溶性染料的性能 总被引:3,自引:0,他引:3
采用溶胶-凝胶方法制备了孔道结构复合材料H3PW12O40/TiO2,采用ICP-AES,UV/DRS,31P MAS NMR,TEM和N2吸附等技术对其组成和结构进行了表征. 结果表明,催化剂中活性组分H3PW12O40的基本骨架结构未发生改变,H3PW12O40的担载量为22.29%,催化剂平均粒径为40 nm,具有双孔结构,其平均微孔和介孔孔径分别为0.61和3.06 nm. 考察了催化剂可见光光催化降解6种水溶性染料的性能. 结果表明,6种染料均可不同程度地被降解和矿化. 通过对染料中性红的光催化降解实验,比较了H3PW12O40/TiO2,Degussa P-25和锐钛矿结构TiO2的可见光光催化活性,其中,H3PW12O40/TiO2活性最高,且催化剂最易分离,可循环使用. 相似文献
120.
Lingling Xiao Lu Yu Pei Li Jiyan Chi Zhangfei Tang Jie Li Shuming Tan Xiaodan Wang 《Molecules (Basel, Switzerland)》2021,26(15)
In this study, using the botanical active component thiochromanone as the lead compound, a total of 32 new thiochromanone derivatives containing a carboxamide moiety were designed and synthesized and their in vitro antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas oryzae pv. oryzicolaby (Xoc), and Xanthomonas axonopodis pv. citri (Xac) were determined, as well as their in vitro antifungal activities against Botryosphaeria dothidea (B. dothidea), Phomopsis sp., and Botrytis cinerea (B. cinerea). Bioassay results demonstrated that some of the target compounds exhibited moderate to good in vitro antibacterial and antifungal activities. In particular, compound 4e revealed excellent in vitro antibacterial activity against Xoo, Xoc, and Xac, and its EC50 values of 15, 19, and 23 μg/mL, respectively, were superior to those of Bismerthiazol and Thiodiazole copper. Meanwhile, compound 3b revealed moderate in vitro antifungal activity against B. dothidea at 50 μg/mL, and the inhibition rate reached 88%, which was even better than that of Pyrimethanil, however, lower than that of Carbendazim. To the best of our knowledge, this is the first report on the antibacterial and antifungal activities of this series of novel thiochromanone derivatives containing a carboxamide moiety. 相似文献