1,720,956 research outputs found
Development of novel bio-based building blocks and their application in organic synthesis and materials science
No full textIn the progression of modern society, the inevitable exhaustion of fossil resources becomes an increasingly concerning matter. These resources are not only the basis of the energy production of the world but also the precursor for many important platform chemicals. Therefore, development of green and renewable alternatives to the chemicals used in the current industry has become necessary. Within this context, the aim of the present thesis was the development of new efficient methodologies for obtaining high added-value products starting from biomass, a renewable source. The bio-based building blocks obtained were subsequently employed for the synthesis of polyfunctionalized chemicals and of polymers.
The first part of the thesis focuses on the utilization of a bio-based meso diol for the synthesis of sugar derived structures, through the coupling of biocatalysis and multicomponent reaction (MCRs). These two different approaches are able to satisfy the requirements of an ideal approach, regarding selectivity (stereocontrol), efficiency and sustainability and their union with renewable feedstocks in a single integrated general strategy represents a powerful tool to achieve a sustainable synthesis. In particular, the work focused on the synthetic elaboration of the chiral molecules obtained through enzymatic desymmetrization to give enantiomerically pure building blocks to be used in diastereoselective Passerini reactions. In order to establish the synthetic usefulness of this new method, we demonstrated its application to the diversity-oriented synthesis of chiral, bio-based, oxygen heterocycles and to the target-oriented synthesis of Bengamides, a wide family of natural products of marine origin.
The second part of the thesis is dedicated to the synthesis of a lactam- based monomer derived from bio-based starting materials and its subsequent polymerization. The project involved the synthesis and polymerization of 3-methylene-2-piperidone (3M2Pip) monomers, targeting the synthesis of well-defined hydroxyl end functional P(3M2Pip), i.e. HO-P(3M2Pip). Once obtained end-functionalized 3M2Pip-based polymers we will use them as a macro-initiator for the synthesis of degradable polyester second blocks, applicable in drug delivery polymer materials
Biocatalysis and MCRs: a Potential Green Strategy for the Synthesis of High-Added Value Compounds Starting from Biomass
No full textApplication of MCRs to the stereoselective synthesis of diverse heterocycles starting from chemoenzymatycally obtained chiral aldehydes
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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
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
Total Synthesis of 4-<i>epi</i>-Bengamide E
No full textBengamide E is a bioactive natural product that was isolated from Jaspidae sponges by Crews and co-workers in 1989. It displays a wide range of biological activities, including antitumor, antibiotic, and anthelmintic properties. With the aim of investigating the structural feature essential for their activity, several total syntheses of Bengamide E and its analogues have been reported in the literature. Nevertheless, no synthesis of the stereoisomer with modification of its configuration at C-4 carbon has been reported so far. Here, we report the first total synthesis of the 4-epi-Bengamide E. Key reactions in the synthesis include a chemoenzimatic desymmetrization of biobased starting materials and a diastereoselective Passerini reaction using a chiral, enantiomerically pure aldehyde, and a lysine-derived novel isocyanide
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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