1,720,954 research outputs found
Diphosphate formation using cyanuric chloride or triisopropylbenzenesulfonyl chloride as the activating agents
No full textStudy of Sugar Diphosphate Formation via New Monophosphate Coupling Reactions
No full text雙磷酸在生物體內扮演不可或缺的角色，以寡糖的生合成為例:生物體利用醣基轉移酶催化核苷酸醣和醣基受體形成一個新的醣苷鍵。在細菌細胞壁的生合成中，雙磷酸亦為構成Lipid I及Lipid II的重要部分。現今已知建構雙磷酸的步驟往往繁瑣且反應時間冗長，而偏低的產率更為阻礙合成核苷酸糖以及Lipid II衍生物的主要原因，因此，研究發展更有效率的雙磷酸合成方法是勢在必行。
我們發現2,4,6-三異丙基苯磺醯氯(2,4,6-triisopropylbenzenesulfonyl chloride)以及 2,4,6-三氯-1,3,5-三氮代苯(2,4,6-trichloro-1,3,5-triazine, cyanuric chloride)為合適建構雙磷酸之試劑，同時藉由添加溴化鎂作為螯合試劑以拉近兩單磷酸之距離進而增加了反應的效率。在我們模型反應中反應時間為5–48小時，轉換效率則為20–70%不等。另外我們也利用2,4,6-三異丙基苯磺醯氯合成了GDP-pyrrolidine類似物，並經由比較發現使用 2,4,6-三異丙基苯磺醯氯較傳統使用預先製備之morpholidate來的更有效率，這樣的策略為合成雙磷酸化合物提供了另一種選擇。Diphosphate is an indispensible starting material in organism. For example, oligosaccharides are synthesized from a sugar nucleoside diphosphate and a glycosyl acceptor by glycosyltransferases. Diphosphate moiety is also an important part in the structures of Lipid I and Lipid II in the process of bacterial cell wall formation. The approaches to the sugar nucleoside diphosphate and analogues of Lipid II are impeded by the diphosphate bond formation, which often requires tedious procedure and long reaction time, albeit in low yield. So, exploration of efficient methods to get diphosphate compounds is needed.
We found that 2,4,6-triisopropylbenzenesulfonyl chloride and 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride) were proper condensation reagents for diphosphate bond construction. By using MgBr2 as the chelating agent of the two monophosphate substrates, the coupling reactions proceeded efficiently. The reaction times are 5–48 hours to give conversion yields of 20–70% in our model reactions. We synthesized the GDP-pyrrolidine analogue, and found that using 2,4,6-triisopropylbenzenesulfonyl chloride is more efficient than the conventional method using morpholidate. This approach provides an alternative choice for diophosphate formation
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
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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