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排序方式: 共有542条查询结果,搜索用时 15 毫秒
91.
92.
K. C. Nicolaou Phil S. Baran Rolf Jautelat Yun He Kin Chiu Fong Ha‐Soon Choi Won Hyung Yoon Yong‐Li Zhong 《Angewandte Chemie (International ed. in English)》1999,38(4):549-552
A seven‐step cascade reaction —in which selective mesylation, epoxide formation, epoxide lysis, cyclization, reiterative oxidation, and nitrogen–oxygen exchange occur sequentially—facilitates the construction of the maleic anhydride moiety of CP molecules 1 and 2 (>93% yield per step). Unstable intermediates of this reaction sequence were detected, providing evidence for the proposed mechanism and resulting in the discovery of a new chemical entity. 相似文献
93.
Jen-Yang Chung Michael E. Grass Phil Ross Jr. Bongjin Simon Mun 《Surface science》2009,603(5):L35-20325
CO and O2 co-adsorption and the catalytic oxidation of CO on a Pt(1 1 0) surface under various pressures of CO and O2 (up to 250 mTorr) are studied using ambient pressure X-ray photoelectron spectroscopy (APXPS) and mass spectrometry. There is no surface oxide formation on Pt under our reaction conditions. CO oxidation in this pressure (<500 mTorr), O2 to CO ratio (<10), and temperature (150 °C) regime is consistent with the Langmuir-Hinshelwood reaction mechanism. Our findings provide in-situ surface chemical composition data of the catalytic oxidation of CO on Pt(1 1 0) at total pressures below 1 Torr. 相似文献
94.
95.
Gaber El-Enany Matthew J. Lacey Phil A. Johns John R. Owen 《Electrochemistry communications》2009,11(12):2320-2323
Polyacrylonitrile (PAN) films were grown on glassy carbon, nickel foam and MnO2 substrates by cathodic electropolymerisation of acrylonitrile in acetonitrile with tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. The electronic barrier properties of the films were confirmed by impedance spectroscopy of carbon |PAN| Hg cells while the ionic resistance of the films varied from 200 kΩ cm2 in the dry state to 1.4 Ω cm2 when plasticised with 1 M LiPF6 in propylene carbonate. A galvanic cell was prepared by successive electrodepositions of MnO2 and PAN on a carbon substrate, using liquid lithium amalgam as the top contact. The cell showed a stable open circuit potential and behaved normally under the galvanostatic intermittent titration technique (GITT). 相似文献
96.
Noah Z. Burns Phil S. Baran Prof. Dr. Reinhard W. Hoffmann Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(16):2854-2867
Stimulus package for organic synthesis : The economy of step and atom usage has been widely reviewed and acknowledged as being useful frameworks to evaluate the efficiency of synthesis. This Review brings to attention another form of economy which should be considered in the planning and evaluation of a multistep synthesis: redox economy. Several guidelines and examples are included to illustrate the logic of this approach and to stimulate the design of syntheses.
97.
Jun Shi Hiroki Shigehisa Dr. Carlos A. Guerrero Ryan A. Shenvi Chuang‐Chuang Li Dr. Phil S. Baran Prof. 《Angewandte Chemie (International ed. in English)》2009,48(24):4328-4331
One stereocenter makes all the difference : The synthesis and biological evaluation of 17‐epi‐cortistatin A is reported from a common intermediate used to procure natural cortistatin A. The synthesis features a unique stereocontrolled Raney‐Ni reduction process that can be employed to reliably produce both α‐ and β‐configured D‐ring aryl steroids. Biological evaluations of these “cortalogs” are reported for the first time.
98.
Skinner R Ineson P Jones H Sleep D Theobald M 《Rapid communications in mass spectrometry : RCM》2006,20(2):81-88
Passive and active ammonia (NH(3)) sampling devices have been tested for their nitrogen (N) capture potential and delta(15)N fractionation effects. Several sampling techniques produced significantly different delta(15)NH(3) signals when sampling the same NH(3) source released from field site fumigation campaigns. Conventional passive NH(3)-monitoring systems have shown to provide insufficient N for isotope-ratio mass spectrometry and various modified devices have been developed, based on existing diffusion tube designs, to overcome this problem. The final sampler design was then tested in a wind tunnel to verify that sampling NH(3) in different environmental conditions did not significantly fractionate the delta(15)N signal. 相似文献
99.
Yang J Bremer PJ Lamont IL McQuillan AJ 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10109-10117
The adhesion of bacteria to metal oxide and other mineral surfaces may involve bacterial siderophores, many of which contain hydroxamic acid (Ha) ligands. The adsorption behavior of the siderophore-related ligands acetohydroxamic acid, N-methylformohydroxamic acid, N-methylacetohydroxamic acid, and 1-hydroxy-2-piperidone on titanium dioxide thin films has been investigated using in situ ATR-IR spectroscopy with variation of concentration and pH. All the ligands were found to adsorb strongly on the TiO2 surface as hydroxamate ions and form bidentate surface complexes. Vibrational modes involving C=O stretching and N-O stretching of these ligands were assigned by comparing observed IR spectra with those calculated by the density functional method at the B3LYP/6-31+G(d) level. Calculated spectra of the complex [Ti(Ha)(OH)4]-, used to model the TiO2 surface, were compared with observed spectra of adsorbed hydroxamic acids. These results suggest that hydroxamic acid ligands in siderophores would be expected to bind to metal (oxide) and mineral surfaces during bacterial adhesion processes. 相似文献
100.
The first total synthesis of (+/-)-chartelline C in a concise 10-step sequence is reported. Highlights of the completion of this decades-old puzzle include (1) chemo- and position-selective installation of the heteroaromatic halogens, (2) halogen-sparing monoreduction of an alkyne linker, (3) a simple strategy for placement of the sensitive beta-chloroenamide, (4) an unusually facile thermolysis of a vinyl carboxylic acid, and (5) a powerful ring contraction whose potential utility in heterocyclic chemistry merits further investigation. 相似文献