1,720,960 research outputs found
Photoinduced hydrothiolation and hydrophosphonylation of alkenes and alkynes
No full textHydrofunctionalization of terminal double or triple bonds have become classical ligation tools for facile assembly of building blocks into larger molecules especially because comply Sharpless’ prerequisite to be considered “click-chemistry” reactions. In particular the free-metal photoinduced radical thiol-ene (TEC) and thiol-yne (TYC) couplings are well-known to be atom economy, high-efficient, catalyzed only by light and completely regioselective. If both TEC and TYC have already been studied on simple substrates as linear terminal alkenes or alkynes, only few researches have been carried out about particular molecules as protein, peptides and endo-glycals. Hydrothiolation of protein, peptides and aminoacids has been studied to obtain a double different substitution of the peptidic scaffold with one carbohydrate and one marker (fluoresceine or biotine) using TYC. A new technique to synthesize S-disaccharides has been developed starting from different glycals and thio-glucose, demonstrating the efficiency of TEC on internal internal double bonds.
The successful work about hydrothiolation of different substrates has pushed us to study both hydrophosphonylation of alkenes and alkynes starting from the same conditions of TEC and TYC reactions. The different reactivity of the functionalization agent (thiol or H-phosphonate) has resulted in different conditions for the addition to double bonds, but not in a loss of efficiency o regioselectivity. On the other hand the addition on a triple bond has resulted to be ineffective and to stop at the internal double bond intermediate. A thiol-ene coupling on this intermediate, formally a vinyl phosphonate, gives equilibration to E form of the alkene without traces of hydrothiolation adducts.
It is well known that multivalent effect is a key factor in supramolecular chemistry and it governs many biological interactions, in particular in the relationship between pathogenic microorganisms and their host that involves protein–glycan recognition. The affinity of a multivalent cluster is highly dependent on the combination of the carbohydrate head with the cluster core and the spacer between them; several families of multivalent bioactive molecules have been developed by a large numbers of groups all around the world using disparate synthetic techniques. Thiol-Ene (TEC) and Thiol-Yne (TYC) couplings have been chosen as ligation tool for the synthesis of a variety of multivalent biomolecules containing carbohydrates or peptidic termini supported on different bio-inactive clusters as dendrimers and the rigid silica cube known as POSS (polyhedral oligomeric silsesquioxane). Both TEC and TYC are highly efficient, regioselective and atom economy reactions that, moreover, permit us to avoid purification problems due to metal catalysis or to use large excess of reagents to have a complete substitution on the central core. In fact all the reactions have been carried out with success, high yield and without by-products of any kind. Affinity toward specific target of this large library of compounds has been tested by Enzyme-Linked Lectin Assay (ELLA) and results from good to excellent have been found in all classes of compounds
Free-radical hydrothiolation of glycals: a thiol-ene-based synthesis of S-disaccharides
No full textA method for the synthesis of a new family of 1-deoxy S-disaccharides has been established via free-radical hydrothiolation of glycals by sugar thiols (thiol-ene coupling). The photoinduced coupling between four tri-O-acetyl-D-glycals and three different sugar thiols reveals that the reaction efficiency and stereoselectivity are highly dependent on the stereochemistry of the OAc groups at C3 and C4 of the glycal. (C) 2011 Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Multi-molecule reaction of serum albumin can occur through thiol-yne coupling.
No full textThe free-radical hydrothiolation of alkynes (thiol-yne coupling, TYC) unites two thiol fragments across the carbon-carbon triple bond to give a dithioether derivative with exclusive 1,2-addition; this reaction can be used for modification of peptides and proteins allowing glycoconjugation and fluorescent labeling. These results have implications not only as a flexible strategy for attaching two modifications at a single site in proteins but also for unanticipated side-reactions of reagents (such as cycloalkynes) used in other protein coupling reactions
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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