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排序方式: 共有162条查询结果,搜索用时 250 毫秒
21.
Dina M. Bower 《Journal of Raman spectroscopy : JRS》2011,42(8):1626-1633
Laminated sandstones from the 2.9 Ga Pongola Supergroup, South Africa, were characterized using micro‐Raman spectral imaging to elucidate the origin of the mineral components. These sandstones were formed in a paleoenvironment conducive to sustaining life and contain compelling features reminiscent of ancient microbial mat remains. Most sedimentary rocks of this age have been altered over time through metamorphism and weathering, obscuring any original biologic or mineralogic signatures. Therefore, determination of the exact formation mechanism for biologically associated features is often precluded, resulting in large gaps in our understanding of early life and Earth's early habitable environments. The results of the Raman analyses show that the parallel to bedding laminations in these rocks consist of elongated muscovite grains that are intimately associated with anatase, rutile, goethite, and graphitic carbon. The morphology, orientation, and intimate associations of the component mineral assemblage in the laminations suggest that physiochemical events, such as weathering, low‐grade metamorphism, or hydrothermal fluids, were also key in their formation and influenced their geochemical makeup. Given the complicated histories of ancient sedimentary rocks, the use of techniques such as micro‐Raman spectroscopy is crucial in determining the origins of sedimentary structures that might otherwise be misinterpreted. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
22.
Under hydrogen autotransfer conditions employing a catalyst derived from [Ir(cod)Cl]2 and BIPHEP, 1,3-cyclohexadiene (CHD) couples to benzylic alcohols 1a-9a to furnish carbonyl addition products 1c-9c, which appear as single diastereomers with variable quantities of regioisomeric adducts 1d-9d. Under related transfer hydrogenation conditions employing isopropanol as terminal reductant, identical carbonyl adducts 1c-9c are obtained from the aldehyde oxidation level. Isotopic labeling studies corroborate a mechanism involving hydrogen donation from the reactant alcohol or sacrificial alcohol (i-PrOH). 相似文献
23.
Patman RL Williams VM Bower JF Krische MJ 《Angewandte Chemie (International ed. in English)》2008,47(28):5220-5223
24.
Dr. Samuel C. Scott Dr. Jamie A. Cadge Grace K. Boden Prof. John F. Bower Dr. Christopher A. Russell 《Angewandte Chemie (International ed. in English)》2023,62(23):e202301526
We describe a AuI complex of a hemi-labile (C^N) N-heterocyclic carbene ligand that is able to mediate oxidative addition of aryl iodides. Detailed computational and experimental investigations have been undertaken to verify and rationalize the oxidative addition process. Application of this initiation mode has resulted in the first examples of “exogenous oxidant-free” AuI/AuIII catalyzed 1,2-oxyarylations of ethylene and propylene. These demanding yet powerful processes establish these commodity chemicals as nucleophilic-electrophilic building blocks in catalytic reaction design. 相似文献
25.
26.
Stereospecific construction of substituted piperidines. Synthesis of (-)-paroxetine and (+)-laccarin
Bower JF Riis-Johannessen T Szeto P Whitehead AJ Gallagher T 《Chemical communications (Cambridge, England)》2007,(7):728-730
Short and efficient enantioselective syntheses of (-)-paroxetine and (+)-laccarin are described based on the highly stereospecific cleavage of C(3)-substituted 1,3-cyclic sulfamidates. 相似文献
27.
KM Varier AM Vinodkumar NVSV Prasad PV Madhusudhana Rao DL Sastry Lagy T Baby MC Radhakrishna NG Puttaswamy JJ Das P Sugathan N Madhavan AK Sinha DO Kataria 《Pramana》1999,53(3):529-533
Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies.
Coupled channel calculations incorporating couplings to 2+ and 3− states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements
had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer
were carried out for 46,48Ti+61Ni systems. The present paper gives the results of these studies. 相似文献
28.
JohnF. Bower InSu Kim RyanL. Patman MichaelJ. Krische 《Angewandte Chemie (International ed. in English)》2009,48(1):34-46
Classical protocols for carbonyl allylation, propargylation and vinylation typically rely upon the use of preformed allyl metal, allenyl metal and vinyl metal reagents, respectively, mandating stoichiometric generation of metallic byproducts. Through transfer hydrogenative C C coupling, however, carbonyl addition may be achieved from the aldehyde or alcohol oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. Here, we review transfer hydrogenative methods for carbonyl addition, which encompass the first catalytic protocols enabling direct C H functionalization of alcohols. 相似文献
29.
30.
Wei D Grande L Chundi V White R Bower C Andrew P Ryhänen T 《Chemical communications (Cambridge, England)》2012,48(9):1239-1241
Graphite was electrochemically exfoliated in mixtures of room temperature ionic liquids and deionized water containing lithium salts to produce functionalized graphenes and such an electrochemical exfoliation technique can be directly used in making primary battery electrodes with significantly enhanced specific energy capacity. 相似文献