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981.
Reinforced self-assembly of hexa-peri-hexabenzocoronenes by hydrogen bonds: from microscopic aggregates to macroscopic fluorescent organogels 总被引:1,自引:0,他引:1
Dou X Pisula W Wu J Bodwell GJ Müllen K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):240-249
Hexa-peri-hexabenzocoronene derivatives (HBCs) that have hydrogen-bonding functionalities (either amido or ureido groups) adjacent to the aromatic cores have been synthesized to study the effects of intracolumnar hydrogen bonds on the self-assembly behavior of HBCs. The hydrogen bonds effectively increased the aggregation tendency of these compounds in solution. In the bulk state, the typical columnar supramolecular arrangement of HBCs was either stabilized substantially (1 a, 1 b, 2 a, and 2 b), or suppressed by dominant hydrogen-bonding interactions (3). For some of the compounds (1 a, 2 a, and 2 b), the supramolecular arrangement adopted in the liquid-crystalline state was even retained after annealing, presumably owing to the reinforcement of the pi-stacking interactions by the hydrogen bonds. Additionally, the combined effect of the hydrogen bonds and pi-stacking of the aromatic moieties led to the formation of fluorescent organogels, whereby some derivatives were further investigated as novel low molecular-mass organic gelators (LMOGs). 相似文献
982.
An approach to the synthesis of hydroxyl-terminated polymethylphenylsiloxane (PMPS-OH) was proposed and the synthesized PMPS-OH was successfully applied as a precursor to prepare a novel coating for solid-phase microextraction (SPME) via the sol-gel process. The thickness and length of the prepared coating was 70 μm and 1.5 cm, respectively. The extraction efficiency of the PMPS-coated fiber for selected pesticides was higher than that of commercial fibers including 100 μm polydimethylsiloxane (PDMS), 85 μm polyacrylate (PA) and 65 μm polydimethylsiloxane/divinylbenzene (PDMS/DVB). The influence of the extraction process, extraction temperature, extraction time, stirring rate, ionic strength, GC inlet conditions, desorption temperature and time for PMPS-coated fiber application was studied and optimized. Several experiments were carried out to evaluate the analytical characteristics of the proposed SPME-GC-ECD method under optimized conditions. The linearity was from 0.5 to 100 ng g−1 for p,p′-DDE, p,p′-DDD and bifenthrin, and from 2 to 100 ng g−1 for o,p′-DDT, p,p′-DDT, fenpropathrin, beta-cyfluthrin and cyhalothrin. The detection limits of these pesticides were between 0.13 and 1.45 ng g−1. The recovery of the pesticides spiked in various vegetables at 4 ng g−1 ranged from 42.9% to 105.3%, and the relative standard deviations were less than 16.2%. 相似文献
983.
A thorough phytochemical investigation of the whole plant of Saxifraga montana H. afforded a new glucoside, methyl 6″‐O‐(E)‐p‐hydroxycinnamoxyl‐glucosyringate ( 1 ), and seventeen known natural products, 3‐methyl‐6‐methoxy‐3,4‐dihydroisocoumarin‐8‐O‐β‐D‐glucospyranoside ( 2 ), gallic acid ( 3 ), glucosyringic acid ( 4 ), daphnoretin ( 5 ), chamaejasmoside ( 6 ), myricetin ( 7 ), quercetin ( 8 ), quercetin‐3‐O‐β‐D‐galactopyranoside ( 9 ), quercetin‐3‐O‐α‐L‐arabinoside ( 10 ), quercetin‐3‐O‐β‐D‐glucospyranoside ( 11 ), rutin ( 12 ), quercetin‐3‐O‐β‐D‐glucopyranosyl (6‐1) glucopyranoside ( 13 ), ursolic acid ( 14 ), 5,28‐stigmastadien‐3β‐ol ( 15 ), β‐sitosterol ( 16 ), β‐daucosterin ( 17 ), 6′‐palmitoxyl‐β‐daucosterin ( 18 ). On the basis of various spectroscopic methods, especially intensive 2D‐NMR (COSY, HMQC and HMBC), FAB‐MS and HR‐ESI‐MS techniques, their structures were elucidated. 相似文献
984.
Xi Lu Huayang Wang Zhengting Cai Dacheng Feng 《International journal of quantum chemistry》2008,108(2):334-338
In the course of an extensive investigation aimed at understanding the detailed mechanism of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The concerned system is HO + CH4 → H2O + CH3, of which the partial potential energy surface is constructed by the coupling between vibrational models and reactive coordinates. Then we explain the formation mechanism of the reactive resonance state by the partial potential energy surface. Finally, we estimated the lifetime of the resonance state, and it is about 45fs. The study of the reactive resonance in a polyatomic reaction is more than just an extension from a typical atom + diatom reaction. As shown here, it holds great promise to disentangle the elusive intramolecular vibrational dynamics of the transient collision complex in the critical transition‐state region. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
985.
Multifunctional Antioxidants: Regenerable Radical‐Trapping and Hydroperoxide‐Decomposing Ebselenols
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Shailesh Kumar Jiajie Yan Jia‐fei Poon Dr. Vijay P. Singh Dr. Xi Lu Dr. Marjam Karlsson Ott Prof. Dr. Lars Engman Prof. Dr. Sangit Kumar 《Angewandte Chemie (International ed. in English)》2016,55(11):3729-3733
Regenerable, multifunctional ebselenol antioxidants were prepared that could quench peroxyl radicals more efficiently than α‐tocopherol. These compounds act as better mimics of the glutathione peroxidase enzymes than ebselen. Production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in human mononuclear cells was considerably decreased upon exposure to the organoselenium compounds. At a concentration of 25 μm , the ebselenol derivatives showed minimal toxicity in pre‐osteoblast MC3T3 cells. 相似文献
986.
Yang Jiao Wan‐Lu Li Dr. Jiang‐Fei Xu Dr. Guangtong Wang Prof. Jun Li Prof. Zhiqiang Wang Prof. Xi Zhang 《Angewandte Chemie (International ed. in English)》2016,55(31):8933-8937
Tuning the activity of radicals is crucial for radical reactions and radical‐based materials. Herein, we report a supramolecular strategy to accelerate the Fenton reaction through the construction of supramolecularly activated radical cations. As a proof of the concept, cucurbit[7]uril (CB[7]) was introduced, through host–guest interactions, onto each side of a derivative of 1,4‐diketopyrrolo[3,4‐c]pyrrole (DPP), a model dye for Fenton oxidation. The DPP radical cation, the key intermediate in the oxidation process, was activated by the electrostatically negative carbonyl groups of CB[7]. The activation induced a drastic decrease in the apparent activation energy and greatly increased the reaction rate. This facile supramolecular strategy is a promising method for promoting radical reactions. It may also open up a new route for the catalytic oxidation of organic pollutants for water purification and widen the realm of supramolecular catalysis. 相似文献
987.
Lina Ma Wenjuan Li Hui Xi Xiaohui Bai Enlu Ma Dr. Xiaoyu Yan Prof. Dr. Zhiping Li 《Angewandte Chemie (International ed. in English)》2016,55(35):10410-10413
Exploiting catalytic carbonyl–olefin metathesis is an ongoing challenge in organic synthesis. Reported herein is an FeCl3‐catalyzed ring‐closing carbonyl–olefin metathesis. The protocol allows access to a range of carbo‐/heterocyclic alkenes with good efficiency and excellent trans diastereoselectivity. The methodology presents one of the rare examples of catalytic ring‐closing carbonyl–olefin metathesis. This process is proposed to take place by FeCl3‐catalyzed oxetane formation followed by retro‐ring‐opening to deliver metathesis products. 相似文献
988.
Prof. YuCheng Huang Danmei Zhou Xi Chen Hai Liu Chan Wang Prof. Sufan Wang 《Chemphyschem》2016,17(3):375-379
Doping is a vitally important technique that can be used to modulate the properties of two‐dimensional materials. In this work, by using first‐principles density functional calculations, we investigated the electrical properties of SnSe2 monolayers by p‐type/n‐type and isoelectronic doping. Substitution at Sn/Se sites was found to be easy if the monolayer was grown under Sn‐/Se‐poor conditions. Substitutions at Sn sites with metallic atoms (e.g. Ga, Ge, In, Bi, Sb, Pb) resulted in positive substitution energies, which indicated that they were not effective doping candidates. For substitutions at Se sites with nonmetallic atoms, no promising candidates were found for p‐type doping (e.g., N, P, As). Among these, N and As showed positive substitution energies. Although P had a negative substitution energy under Sn‐rich conditions, it introduced trap states within the band gap. For n‐type doping (e.g., F, Cl, Br), all the calculated substitution energies were negative under both Sn‐ and Se‐rich conditions. Br was proven to be a promising candidate, because the impurity introduced a shallow donor level. Finally, for isoelectronic doping (e.g., O, S, Te), the intrinsic semiconducting features of the SnSe2 monolayer did not change, and the contribution from the impurity to the states near the band edge increased with the atomic number. 相似文献
989.
Bimetallic Au2Cu6 Nanoclusters: Strong Luminescence Induced by the Aggregation of Copper(I) Complexes with Gold(0) Species
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Xi Kang Shuxin Wang Yongbo Song Shan Jin Guodong Sun Prof. Haizhu Yu Prof. Manzhou Zhu 《Angewandte Chemie (International ed. in English)》2016,55(11):3611-3614
The concept of aggregation‐induced emission (AIE) has been exploited to render non‐luminescent CuISR complexes strongly luminescent. The CuISR complexes underwent controlled aggregation with Au0. Unlike previous AIE methods, our strategy does not require insoluble solutions or cations. X‐ray crystallography validated the structure of this highly fluorescent nanocluster: Six thiolated Cu atoms are aggregated by two Au atoms (Au2Cu6 nanoclusters). The quantum yield of this nanocluster is 11.7 %. DFT calculations imply that the fluorescence originates from ligand (aryl groups on the phosphine) to metal (CuI) charge transfer (LMCT). Furthermore, the aggregation is affected by the restriction of intramolecular rotation (RIR), and the high rigidity of the outer ligands enhances the fluorescence of the Au2Cu6 nanoclusters. This study thus presents a novel strategy for enhancing the luminescence of metal nanoclusters (by the aggregation of active metal complexes with inert metal atoms), and also provides fundamental insights into the controllable synthesis of highly luminescent metal nanoclusters. 相似文献
990.
H∞ stochastic synchronization for master–slave semi‐Markovian switching system via sliding mode control
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In this article, synchronization problem of master–slave system with phase‐type semi‐Markovian switching is investigated via sliding mode control scheme. By utilizing a supplementary variable technique and a plant transformation, the master–slave semi‐Markovian switching system can be equivalently expressed as its associated Markovian switching system. Then an integral sliding surface is constructed to guarantee stochastic synchronization of master–slave semi‐Markovian switching system, and the suitable controller is synthesized to ensure that the trajectory of the closed‐loop error system can be driven onto the prescribed sliding mode surface. Finally, numerical simulations are presented to show the effectiveness of the proposed sliding‐mode design scheme. © 2015 Wiley Periodicals, Inc. Complexity 21: 430–441, 2016 相似文献