排序方式: 共有156条查询结果,搜索用时 15 毫秒
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The intermolecular coupling of unactivated alkenes to a range of heterocycles using a Rh(I) catalyst was investigated. A variety of functional groups were incorporated into the alkene, including esters, nitriles, acetals, and phthalimide. Furthermore, the heterocycle tolerated substitution with both electron-rich and electron-deficient groups. The intermolecular coupling became possible after it was discovered that weak acids dramatically increase the rate of both the inter- and intramolecular reactions. An extensive optimization of additives was performed, and HCl.PCy(3) (Cy = cyclohexyl) and HCl.P-t-Bu(2)Et were in general found to be the best additives for the reaction. 相似文献
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Zhang H Loh KP Sow CH Gu H Su X Huang C Chen ZK 《Langmuir : the ACS journal of surfaces and colloids》2004,20(16):6914-6920
We have synthesized edge-oriented MoS2 nanosheets by the evaporation of a single source precursor based on Mo(IV)-tetrakis(diethylaminodithiocarbomato). The surface chemistry of the MoS2 nanosheets has been studied in order to evaluate the chemical reactivities of the basal planes and edges. By irradiating the MoS2 nanosheet with a scanning infrared laser, micron-scale lithographical structures can be created due to laser-induced oxidation of MoS2 to form nanocrystalline MoO3. Preferential reactivities of the MoS2 basal edges in an electrochemical environment and during vapor phase deposition have been demonstrated. Functionalization of the basal plane with 1-pyrene acetic acid allows the immobilization of DNA and immunoglobins on the MoS2 basal plane. 相似文献
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Candy Haley Yi Xuan Lim Milos Nesladek Prof. Kian Ping Loh 《Angewandte Chemie (International ed. in English)》2014,53(1):215-219
Using IR spectroscopy, high‐pressure reactions of molecules were observed in liquids entrapped by graphene nanobubbles formed at the graphene–diamond interface. Nanobubbles formed on graphene as a result of thermally induced bonding of its edges with diamond are highly impermeable, thus providing a good sealing of solvents within. Owing to the optical transparency of graphene and diamond, high‐pressure chemical reactions within the bubbles can be probed with vibrational spectroscopy. By monitoring the conformational changes of pressure‐sensitive molecules, the pressure within the nanobubble can be calibrated as a function of temperature and it is about 1 GPa at 600 K. The polymerization of buckministerfullerene (C60), which is symmetrically forbidden under ambient conditions, is observed to proceed in well‐defined stages in the pressurized nanobubbles. 相似文献
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Kian Eang Neo Han Vinh Huynh Lip Lin Koh William Henderson T.S. Andy Hor 《Journal of organometallic chemistry》2008,693(8-9):1628-1635
Pincer PCP-Pd(II) complex [PdCl(PCP)] (1) (PCP = ?CH(CH2CH2PPh2)2) reacts with AgNO3 to give [Pd(NO3)(PCP)] (2). Similar reaction with AgBF4 gives the aqua complex [Pd(OH2)(PCP)][BF4] (3) and the dinuclear complex [{Pd(PCP)}2(μ-Cl)][BF4] (4) with singly bridging chloro ligand. All new complexes were characterized by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. Complex 1 and the triflate complex [Pd(OTf)(PCP)] (5) are active towards Suzuki–Miyaura coupling between aryl bromides and phenyl boronic acid. 相似文献
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The difference between the swiftlet white edible bird's nest from limestone caves versus house‐farmed ones, especially in response to high temperature and stewing time in water where the latter type would disintegrate readily, has been a puzzle for a long time. We show that edible bird's nests from the limestone caves have calcite deposits on the surface of the nest cement as compared to the house‐farmed nests which are built by swiftlets on timber planks. The micron and sub‐micron calcite particles are seen in SEM‐EDX and further characterized by ATR‐FTIR and Raman microspectroscopy. The calcite deposits make it possible for the cave nest to retain a gelatinous texture under the harsh retort conditions at 121 °C for 20 mins in commercial bottling. We show that house‐farmed nests can be soaked in CaCl2(aq) followed by rinsing with Na2CO3(aq) to grow the same calcite deposits on the nest cement with the same characteristic as cave nests. Therefore, there should no longer be a need to harvest cave nests, and we can better conserve the dwindling population and natural habitats of cave swiftlets. 相似文献
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Mehdi Janbazi Yavar T. Azar Farhood Ziaie Khashayar Ghandi Chérif F. Matta Muhammad Shadman Lakmehsari 《International journal of quantum chemistry》2020,120(12):e26211
Alanine is used as a transfer standard dosimeter for gamma ray and electron beam calibration. An important factor affecting its dosimetric response is humidity which can lead to errors in absorbed dose calculations. Ab initio molecular dynamics calculations were performed to determine the environmental effects on the electron paramagnetic resonance (EPR) parameters of L-α-alanine radicals in acidic and alkaline solutions. A new result, not dissimilar to the closed-shell amino acid molecule alanine, is that the non-zwitterionic form of the alanine radical is the stable form in the gas phase while the zwitterionic neutral alanine radical is not a stable structure in the gas phase. Geometric and EPR parameters of radicals in both gas and solution phases are found to be dependent on hydrogen bonding of water molecules with the polar groups and on dynamic solvation. Calculations on the optimized free radicals in the gas phase revealed that for the neutral radical, hydrogen bonding to water molecules drives a decrease in the magnitudes of g-tensor components g xx and g yy without affecting neither g zz component nor the hyperfine coupling constants (HFCCs). The transfer from the gas to solution phase of the alanine radical anion is accompanied with an increase in the spin density on the carboxylic group's oxygen atoms. However, for the neutral radical, this transfer from gas to solution phase is accompanied with the decrease in the spin density on oxygen atoms. Calculated isotropic HFCCs and g-tensor of all radicals are in good agreement with experiment in both acidic and alkaline solutions. 相似文献
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Ali Ramazani Nahid Shajari Amir Tofangchi Mahyari Mehdi Khoobi Yavar Ahmadi Ali Souldozi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2496-2502
Reactions of (N-isocyanimino)triphenylphosphorane with 1,1,1-trifluoroacetone in the presence of aromatic (or heteroaromatic) carboxylic acids (3-methylbenzoic acid, 1-naphthalenecarboxylic acid, 2-naphthalenecarboxylic acid, 2-furancarboxylic acid, and 2-thiophenecarboxylic acid) proceed smoothly at room temperature and in neutral conditions to afford sterically congested 1,1,1-trifluoro-2-(5-aryl-1,3,4-oxadiazol-2-yl)-2-propanol derivatives in high yields. The reaction proceeds smoothly and cleanly under mild conditions, and no side reactions were observed. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献