1,720,976 research outputs found
NMR spectroscopy: a versatile tool for the investigation of organic reaction mechanisms and metabolomics analyses
Full text linkOlefin metathesis has become a powerful tool for the formation of carbon-carbon bonds and, therefore, for the synthesis of a number of molecules. This progress was recognized in 2005 with the award of NOBEL Prize in Chemistry to Yves Chauvin, Robert Grubbs and Richard Schrock for their work in this area. While the series of [2+2]cycloadditions and retro[2+2]cycloadditions that make up the pathways of ruthenium-catalysed metathesis reactions is wellestablished, the exploration of mechanistic aspects of alkene metathesis is going on. At first, we reported the tetramerization of (E)-2,4-dimethoxycinnamic acid ω-undecenyl ester with ethereal BF3. The reaction gave three stereoisomers 1a, 1b, and 1c, which were assigned as the chair, cone, and 1,2-alternate conformations, respectively. Undecenyl resorc[4]arene 1a, which featured the simplest pattern of substituent, was submitted to olefin metathesis using the second generation Grubbs complex as the catalyst. Depending on the reaction conditions, different products were isolated: a bicyclic alkene 2a, a linear dimer 3a, and a cross-linked homopolymer P1a. Moreover, we detected for the first time the formation of a ruthenium-carbene resorc[4]arene complex during the metathesis reaction of resorc[4]arene olefin 2a with the first generation Grubbs catalyst in CDCl3. We developed an NMR analytical protocol which proved capable of yielding both qualitative and quantitative information. In the first case, we were able to identify the complex 3a[Ru] as a key intermediate in the ROM-CM sequence of reactions, giving us a definitive proof of the previously hypothesized mechanism. As a further feedback of the pathway, we performed a quantitative analysis using benzene in the place of CDCl3, due to the poor stability of the catalyst in such a solvent. The reaction allowed the isolation of decomposition products of the ruthenium-carbene-resorc[4]arene complex 2a[Ru] such as compound 4a, which, due to the presence of still reactive alkene functions, proved to behave as propagating alkylidene species leading to further decomposition products.Metabolomics provides a direct measure of the state of the cell or biological system, where changes in the metabolome capture how the system responds to environmental or genetic stress. Specifically, a drug or an active chemical lead would be expected to perturb the
metabolome of a cell or tissue upon treatment. The two leading analytical approaches to metabolomics are mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. In particular, NMR technique accounts for high reproducibility, quantitative determination of a wide dynamic range, and the capability to determine the structure of unknown metabolites. Cells of high-grade tumors, including medulloblastoma (MB) and glioblastoma (GBM), must similarly balance energy metabolism with the need to synthesize the macromolecules essential for tumor growth. Cells with large ATP requirements are likely to be disadvantaged by aerobic glycolysis because glycolysis generates less ATP per molecule of glucose than oxidative phosphorylation. Proliferating cells, however, may use aerobic glycolysis to satisfy the competing needs for both energy generation and the accumulation of biomass. Recently, it has been demonstrated that Sonic Hedgehog (SHH) pathway activation in granule cell progenitors (GCPs), responsible of MB development, induces transcription of hexokinase 2 (HK2) and pyruvate kinase M2 (PKM2), two key gatekeepers of glycolysis. The process is mediated by the canonical activation of the GLI transcription factors and causes a robust increase of extracellular lactate concentration.
Glabrescione B (GlaB), an isoflavone naturally found in the seeds of Derris glabrescens (Leguminosae), turned out to be an efficient inhibitor of the growth of HH/GLI-dependent tumors and cancer stem cells in vitro and in vivo. Here, we reported the GlaB activity on
both human MB DAOY and murine glioma GL261 cell models in vitro and in vivo. In order to evaluate how the GlaB-treatment affects cell metabolism as a consequence of GLI1 inhibition, untargeted NMR metabolomics analyses of cellular lysates and conditioned media were performed in both cell lines. For this purpose, a simple, fast, and reproducible sample preparation protocol was developed. To reduce bias in the interpretation of the experiments, it was decided to produce from five to seven biological replicates for each treated and untreated group. The 1D 1H NMR spectra were acquired to determine the metabolic fingerprints of the treated and untreated cancer cells. Notably, the NMR metabolomics approach revealed a typical endo-metabolic phenotype of the cells under investigation. Both the exo- and endo-metabolome of the DAOY and GL261 cell lines resulted to be completely changed after 24 h and 48 h of GlaB administration, respectively. The levels of most metabolites decreased after treatment, consistently with possible apoptosis phenomenon
Validation of paramagnetic cross correlation rates for solution structure determination of high spin iron(III) heme proteins
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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
Zn2+-linked dimerization of UreG from Helicobacter pylori, a chaperone involved in nickel trafficking and urease activation
No full textDispelling 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
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