1,720,964 research outputs found
Efficient copper catalysts for C[sbnd]H bond arylation under microwave heating: Direct access to multi-substituted pivanilides
No full textWe herein describe a parallel comparison between homogeneous and heterogeneous copper catalysts for microwave-assisted direct C[sbnd]H bond arylation. These catalytic systems feature enhanced catalytic activities, unique bulky ligand/base effects, mild conditions, and operational simplicity with reduced catalyst loadings and shortened reaction times. A wide range of synthetically challenging multi-substituted pivanilides was directly assembled. Remarkably, copper-exchanged beta-zeolite under ligand-free condition shows good recyclability demonstrating its potential as an efficient and reusable heterogeneous catalytic platform. © 2016 Elsevier B.V3
A palladium and gold catalytic system enables direct access to O- and S-linked non-natural glyco-conjugates
No full textHere we report a straightforward cross-coupling method for the synthesis of non-natural glycoamino acids from alkyne-bearing monosaccharides and p-iodophenylalanine. Pd/Au-catalyzed Sonogashira coupling is tolerant to both O-and S-glycosides without any epimerization. In addition, no racemization of the amino acid was observed allowing direct access to the homogeneous glyco-conjugate in a single step. Notably, this Pd/Au catalytic system presents enhanced catalytic activity than conventional Pd/Cu and Pd-only platforms, and it further enables the convergent synthesis of glycodipeptides. (c) The Royal Society of Chemistry 2016
An Annulative Synthetic Strategy for Building Triphenylene Frameworks by Multiple C-H Bond Activations
No full textC-H activation is a versatile tool for appending aryl groups to aromatic systems. However, heavy demands on multiple catalytic cycle operations and site-selectivity have limited its use for graphene segment synthesis. A Pd-catalyzed one-step synthesis of functionalized triphenylene frameworks is disclosed, which proceeds by 2- or 4-fold C-H arylation of unactivated benzene derivatives. A Pd-2(dibenzylideneacetone)(3) catalytic system, using cyclic diaryliodonium salts as pi-extending agents, leads to site-selective inter-and intramolecular tandem arylation sequences. Moreover, N-substituted triphenylenes are applied to a field-effect transistor sensor for rapid, sensitive, and reversible alcohol vapor detection.clos
C-H bond arylation of anilides inside copper-exchanged zeolites
No full textSyntheses of fine-chemicals using heterogeneous catalysts have tremendous industrial potentials, yet C-H functionalization studies have been largely focused on homogeneous catalysis. We report here the first meta-selective C-H bond arylation of anilides inside copper-exchanged zeolites. Mid- or large-pore zeolite frameworks are selected as supports to access large organic molecules, and atomically distributed copper catalysts exhibit high activities (84-90% conversions) toward direct arylation of anilides with diphenyliodonium salt on 0.5 mol% copper concentration. Computational studies indicate the well-fitted copper-aryl complexes inside zeolite frameworks. Electron micrographs, elemental analyses, and reusability study show no observable leaching of catalytically active copper species during the reactions tested. These results demonstrate the practical synthetic potential of copper-exchanged zeolites as promising supported molecular catalysts to afford biaryl motifs-containing compounds with high catalytic activity, chemical stability, and recyclability.clos
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
A Novel Chemotherapeutic Agent to Treat Tumors with DNA Mismatch Repair Deficiencies
Full text linkImpairing the division of cancer cells with genotoxic small molecules has been a primary goal to develop chemotherapeutic agents. However, DNA mismatch repair (MMR)-deficient cancer cells, are resistant to most conventional chemotherapeutic agents. Here we have identified baicalein as a small molecule that selectively kills MutS??-deficient cancer cells. Baicalein binds preferentially to mismatched DNA and induces a DNA damage response in a mismatch repair-dependent manner. In MutS??-proficient cells, baicalein binds to MutS?? to dissociate CHK2 from MutS?? leading to S phase arrest and cell survival. In contrast, continued replication in the presence of baicalein in MutS??-deficient cells results in a high number of DNA double-strand breaks and ultimately leads to apoptosis. Consistently, baicalein specifically shrinks MutS??-deficient xenograft tumors and inhibits the growth of AOM-DSS-induced colon tumors in colon-specific MSH2 knockout mice. Collectively, baicalein offers the potential of an improved treatment option for patients with tumors with a DNA MMR deficiency.clos
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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