1,720,969 research outputs found
Combined powder X-ray diffraction data and quantum-chemical calculations in EXPO2014
No full textThis paper describes new features implemented in the EXPO2014 software and aimed at assisting crystallographers in the use of quantum-chemistry calculations in combination with experimental powder diffraction data. The implemented tools are useful in particular in two important steps of the process of crystal structure determination from powder diffraction data: (1) preparing accurate structural model suitable for crystal structure determination by real-space methods; (2) validating structure determination. The combination of experimental/quantum-chemical methods in EXPO2014 is now managed easily thanks to the following capabilities: (a) converting crystallographic data in input files and reading molecular geometry from output files of a wide variety of computational chemistry packages (GAMESS-US, NWChem, Gaussian, CRYSTAL, ABINIT, QUANTUM ESPRESSO); (b) optimizing the geometry of a molecule using Open Babel's force fields; (c) a graphical interface to run semi-empirical quantum calculation by MOPAC (Molecular Orbital PACkage); (d) producing input file for dispersion-corrected density functional theory
Functionalization of four-membered cyclic sulfoximines by a convenient lithiation/trapping sequence
No full textThe functionalization of four-membered cyclic sulfoximine, based on a lithiation/electrophile trapping sequence, led to unprecedented
C(2)-substituted N-Boc-1-imino-16-thietane 1-oxide in moderate to good yields. Interestingly, the reaction proceeded with high
stereocontrol showing a preferential bias for an introduction of the electrophile syn to the oxygen on the sulfur. Starting from thietan-
1-one, by a combination of lithiation/electrophile trapping followed by N-transfer, it is possible to obtain the stereoisomer bearing the
electrophile syn to the nitrogen on the sulfur. Thus, all stereoisomers can be accessible for medicinal chemistry studies
Stereoselective synthesis of α-alkylidene β-oxo amides by palladium-catalyzed carbonylation
No full textA direct method to obtain α-alkylidene β-oxo amides by the palladium-catalyzed carbonylation of α-chloro ketones in the presence of aromatic imines has been described. The methodology can be applied to a variety of C-aryl imines bearing N-aryl or N-alkyl substituents. The entire process is highly stereoselective and affords the α-alkylidene β-oxo amides only as (Z) isomers. A mechanistic hypothesis involving an acyl-β-lactam intermediate has also been proposed
Artificial Photosynthesis: Capture and Valorization of CO2 via Surface Decoration of MWCNT with amines”.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Preparation of polysubstituted isochromanes by addition of ortho-lithiated aryloxiranes to enaminones
No full textThe reaction of ortho-lithiated aryloxiranes with various enaminones straightforwardly affords new functionalized isochromanes as mixtures of two epimeric stereoisomers in reasonable to very good yields (50–90%). The two diastereomers, which show a high structural variability, can be easily separated by column chromatography
Direct observation of a lithiated oxirane: a synergistic study using spectroscopic, crystallographic, and theoretical methods on the structure and stereodynamics of lithiated ortho-trifluoromethyl styrene oxide
No full textalpha-Lithiated epoxides, long considered "fleeting" intermediates in the reactions of epoxides with strong bases, have nowadays proven to be key synthons for asymmetric synthesis. In this study, the solution and the solid state structure of an alpha-lithiated aryloxirane, namely a-lithiated ortho-trifluoromethyl styrene oxide (1-Li), were determined. Single crystal X-ray diffraction analysis of 1-Li performed at 100 K applying the X-TEMP-2 device revealed a self-assembled heterochiral dimeric structure with a rare central six-membered (O-Li-C)(2) planar core, which is unprecedented in Li/oxygen carbenoids. Multinuclear magnetic resonance (H-1, C-13, F-19, Li-7) studies suggested that 1-Li exists in THF solution as a mixture of two interconverting diastereomeric dimeric aggregates, each one featuring a single s-contact between lithium and a carbon atom. Line shape analysis provided activation parameters for both the dynamic interconversion of the two dimers and the enantiomerisation of 1-Li, which proved to be mostly entropy controlled. The structural assignment in solution was supported by density functional theory computations through the investigation of conformers of monomeric and dimeric complexes of 1-Li featuring different degrees of specific solvation. A mechanism based on the equilibration of six-membered homo-and heterochiral dimers was proposed to explain the configurational instability exhibited by 1-Li in THF
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
1,3‐Dipolar Cycloaddition of Alkanone Enolates with Azides in Deep Eutectic Solvents for the Metal‐Free Regioselective Synthesis of Densely Functionalized 1,2,3‐Triazoles
Full text linkThe 1,3-dipolar cycloaddition reaction between alkanone enolates and azides proceeds smoothly and regioselectively in eco-friendly eutectic mixtures to yield densely functionalized 1,2,3-triazoles. Pharmacologically active triazoles have also been targeted directly in DESs via telescoped, one-pot cycloaddition/reduction processes
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