1,721,047 research outputs found
Unprecedented copper-catalyzed asymmetric conjugate addition of organometallic reagents to a,ß-unsaturated lactams
No full textFor the first time, an excellent enantioselectivity has been obtained in the conjugate addition of hard organometallic reagents to α,β-unsaturated lactams bearing appropriate protecting-activating groups on the nitrogen
A Multigram, Catalytic and Enantioselective Synthesis of Opitically Active 4-Methyl-2-ciyclohexen-1-one: a Useful Chiral Building Block
No full textAn insoluble polymer-bound phosphoramidite for the copper-catalysed enantioselective 1,4-addition of ZnEt2 to 2-cyclohexenone
Full text linkThe preparation of a chiral phosphoramidite ligand anchored to a Merrifield resin has been studied and its use in the copper-catalysed heterogeneous enantioselective conjugate addition of ZnEt2 to 2-cyclohexenone investigated. The insoluble polymer bound ligand could be recovered quantitatively by filtration, affording e.e. values in the range 65–84% in the course of successive recycle runs
Effect of charge-transfer enhancement on the efficiency and rotary mechanism of an oxindole-based molecular motor
No full textHarvesting energy and converting it into mechanical motion forms the basis for both natural and artificial molecular motors. Overcrowded alkene-based light-driven rotary motors are powered through sequential photochemical and thermal steps. The thermal helix inversion steps are well characterised and can be manipulated through adjustment of the chemical structure, however, the insights into the photochemical isomerisation steps still remain elusive. Here we report a novel oxindole-based molecular motor featuring pronounced electronic push-pull character and a four-fold increase of the photoisomerization quantum yield in comparison to previous motors of its class. A multidisciplinary approach including synthesis, steady-state and transient absorption spectroscopies, and electronic structure modelling was implemented to elucidate the excited state dynamics and rotary mechanism. We conclude that the charge-transfer character of the excited state diminishes the degree of pyramidalisation at the alkene bond during isomerisation, such that the rotational properties of this oxindole-based motor stand in between the precessional motion of fluorene-based molecular motors and the axial motion of biomimetic photoswitches
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
Intermolecular Repulsion through Interfacial Attraction: Toward Engineering of Polymorphs
No full textOptoelectronic Molecular Switches Based on Dihydroazulene- Vinylheptafulvene (DHA-VHF)
Full text linkVariations 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
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