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941.
Reactivity of Oxygen Radical Anions Bound to Scandia Nanoparticles in the Gas Phase: CH Bond Activation
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Li‐Hua Tian Jing‐Heng Meng Dr. Xiao‐Nan Wu Dr. Yan‐Xia Zhao Dr. Xun‐Lei Ding Prof. Dr. Sheng‐Gui He Dr. Tong‐Mei Ma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):1167-1175
The activation of C?H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O?.) is an important species in C?H activation. The mechanistic details of C?H activation by O?. radicals can be well understood by studying the reactions between O?. containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n‐butane was studied by using a high‐resolution time‐of‐flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n‐butane by (Sc2O3)NO? (N=1–18) clusters was observed. The reactivity of (Sc2O3)NO? (N=1–18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13?) and 12 (Sc24O37?). Larger (Sc2O3)NO? clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)NO? (N=1–5) clusters, which were found to contain the O?. radicals as the active sites. The local charge environment around the O?. radicals was demonstrated to control the experimentally observed size‐dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O?. containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C?H bond activation. 相似文献
942.
Zi‐Yu Li Zhen Yuan Dr. Yan‐Xia Zhao Prof. Dr. Sheng‐Gui He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):4163-4169
Metal carbide species have been proposed as a new type of chemical entity to activate methane in both gas‐phase and condensed‐phase studies. Herein, methane activation by the diatomic cation MoC+ is presented. MoC+ ions have been prepared and mass‐selected by a quadrupole mass filter and then allowed to interact with methane in a hexapole reaction cell. The reactant and product ions have been detected by a reflectron time‐of‐flight mass spectrometer. Bare metal Mo+ and MoC2H2+ ions have been observed as products, suggesting the occurrence of ethylene elimination and dehydrogenation reactions. The branching ratio of the C2H4 elimination channel is much larger than that of the dehydrogenation channel. Density functional theory calculations have been performed to explore in detail the mechanism of the reaction of MoC+ with CH4. The computed results indicate that the ethylene elimination process involves the occurrence of spin conversions in the C?C coupling (doublet→quartet) and hydrogen atom transfer (quartet→sextet) steps. The carbon atom in MoC+ plays a key role in methane activation because it becomes sp3 hybridized in the initial stages of the ethylene elimination reaction, which leads to much lower energy barriers and more stable intermediates. This study provides insights into the C?H bond activation and C?C coupling involved in methane transformation over molybdenum carbide‐based catalysts. 相似文献
943.
Highly Enantioselective Catalytic System for Asymmetric Copolymerization of Carbon Dioxide and Cyclohexene Oxide
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Yuan‐Zhao Hua Liu‐Jie Lu Pei‐Jin Huang Dong‐Hui Wei Prof. Ming‐Sheng Tang Prof. Dr. Min‐Can Wang Prof. Dr. Jun‐Biao Chang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12394-12398
A new ligand can be easily prepared, and its intramolecular dinuclear zinc complexes act as a high performance catalyst for the asymmetric alternating copolymerization of cyclohexene oxide and CO2 under very mild conditions (1 atm CO2, room temperature), affording completely alternating polycarbonates with up to 93.8 % enantiomeric excess (ee) and 98 % yield. A high Mn value of 28 600 and a relatively narrow polydispersity (Mw/Mn ratio) of 1.43 were also achieved. 相似文献
944.
采用圆二色光谱法(CD)研究了Cu2+存在下葛根素(PUE)对牛血清白蛋白(BSA)二级结构的影响。结果表明,在pH 7.4的条件下,BSA的各种二级结构分别为56.3%α-螺旋,26.1%β-折叠,17.6%转角和无规则卷曲。葛根素和Cu2+-葛根素都能诱导BSA二级结构发生改变。葛根素使BSA的α-螺旋含量增加,β-折叠含量减少,这表明葛根素与BSA的相互作用,可使蛋白质分子的疏水作用增强,导致BSA的肽链结构收缩。Cu2+-葛根素使BSA的α-螺旋含量大幅度降低,β-折叠含量略有增加,这表明Cu2+-葛根素与BSA的相互作用以配位作用为主,使得BSA的肽链结构伸展,蛋白质的构象发生变化。 相似文献
945.
Wei‐Li Li Dr. Ya‐Fan Zhao Dr. Han‐Shi Hu Prof. Dr. Jun Li Prof. Dr. Lai‐Sheng Wang 《Angewandte Chemie (International ed. in English)》2014,53(22):5540-5545
Chirality is vital in chemistry. Its importance in atomic clusters has been recognized since the discovery of the first chiral fullerene, the D2 symmetric C76. 1 A number of gold clusters have been found to be chiral, 2 raising the possibility to use them as asymmetric catalysts. The discovery of clusters with enantiomeric structures is essential to design new chiral materials with tailored chemical and physical properties. 3 Herein we report the first inherently chiral boron cluster of [B30]? in a joint photoelectron spectroscopy and theoretical study. The most stable structure of [B30]? is found to be quasiplanar with a hexagonal hole. Interestingly, a pair of enantiomers arising from different positions of the hexagonal hole are found to be degenerate in our global minimum searches and both should co‐exist experimentally because they have identical electronic structures and give rise to identical simulated photoelectron spectra. 相似文献
946.
Highly Enantioselective Kinetic Resolution of Axially Chiral BINAM Derivatives Catalyzed by a Brønsted Acid
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Dr. Dao‐Juan Cheng Liang Yan Prof. Dr. Shi‐Kai Tian Ming‐Yue Wu Lu‐Xin Wang Zi‐Li Fan Dr. Sheng‐Cai Zheng Prof. Dr. Xin‐Yuan Liu Prof. Dr. Bin Tan 《Angewandte Chemie (International ed. in English)》2014,53(14):3684-3687
A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid‐catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities. 相似文献
947.
Simultaneous In Situ Quantification of Two Cellular Lipid Pools Using Orthogonal Fluorescent Sensors
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Dr. Shu‐Lin Liu Dr. Ren Sheng Matthew J. O'Connor Yang Cui Dr. Youngdae Yoon Svetlana Kurilova Dr. Daesung Lee Dr. Wonhwa Cho 《Angewandte Chemie (International ed. in English)》2014,53(52):14387-14391
Lipids regulate a wide range of biological activities. Since their local concentrations are tightly controlled in a spatiotemporally specific manner, the simultaneous quantification of multiple lipids is essential for elucidation of the complex mechanisms of biological regulation. Here, we report a new method for the simultaneous in situ quantification of two lipid pools in mammalian cells using orthogonal fluorescent sensors. The sensors were prepared by incorporating two environmentally sensitive fluorophores with minimal spectral overlap separately into engineered lipid‐binding proteins. Dual ratiometric analysis of imaging data allowed accurate, spatiotemporally resolved quantification of two different lipids on the same leaflet of the plasma membrane or a single lipid on two opposite leaflets of the plasma membrane of live mammalian cells. This new imaging technology should serve as a powerful tool for systems‐level investigation of lipid‐mediated cell signaling and regulation. 相似文献
948.
Optoelectronic and Self‐assembly Properties of Porphyrin Derivatives with Click Chemistry Modification
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Liang Pengxia Zhengcai Du Dr. Dong Wang Prof. Dr. Zhou Yang Huiyun Sheng Shuqiong Liang Hui Cao Wanli He Prof. Dr. Huai Yang 《Chemphyschem》2014,15(16):3523-3529
A series of functionalized porphyrin molecules containing electron‐rich alkynes, synthesized by means of the Sonogashira coupling reaction were further modified by reacting the ethynyl groups with click reagent through a formal [2+2] click reaction. The photophysical and electrochemical properties of the porphyrin derivatives were studied by UV/Vis spectroscopy and cyclic voltammetry. We show that the optoelectronic properties are affected by the click reagent groups and central metal ions. The functionalized porphyrin molecules show strong charge‐transfer (CT) bands in the visible region (near‐IR region) and potent redox activities. Through a phase‐exchange self‐assembly method, the highly organized morphologies were observed by scanning electron microscopy (SEM). The functionalized porphyrin molecules represent an interesting set of candidates for optoelectronic device components. The effect of the metal ions or click reagent groups on the self‐assembly properties were also studied by the UV/Vis spectroscopic titration experiments. 相似文献
949.
950.
Ultrasound/microwave‐assisted extraction and comparative analysis of bioactive/toxic indole alkaloids in different medicinal parts of Gelsemium elegans Benth by ultra‐high performance liquid chromatography with MS/MS
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Indole alkaloids are the main bioactive/toxic components in Gelsemium elegans Benth. To determine the distribution and contents of indole alkaloids in its different medicinal parts, a novel and rapid method using ultra‐high performance LC (UPLC) with MS/MS has been established and validated with an optimized ultrasound/microwave‐assisted extraction method. Four constituents, namely, humantenidine, humantenmine, gelsemine, and koumine, were simultaneously determined in 6 min. Chromatographic separation was achieved on an ultra‐high performance LC BEH C18 column with a gradient mobile phase consisting of methanol and water (containing 0.1% formic acid both in methanol and water) at a flow rate of 0.3 mL/min. The detection was performed on a triple quadrupole electrospray MS/MS by positive ion multiple‐reaction monitoring mode. All the analytes showed good linearity (r ≥ 0.9934) within a concentration range from 0.1–25 μg/mL with a LOQ of 25–50 ng/mL. The overall intra‐ and intervariations of four components were <4.7% with an accuracy of 97.3–101.3%. The analysis results showed that there were remarkable differences in the distribution and contents of four chemical markers in the roots, stems, and leaves of G. elegans Benth. The findings can provide necessary and meaningful information for the rational utilization of its resources. 相似文献