1,721,176 research outputs found
Zirconocene mediated synthesis of nitrogen heterocycles
No full text4-Aza-1,7-octa-dienes, -enynes, ynenes and -diynes have been cyclised using Cp2Ar-(1-butene). The resultant 3-aza-8-zirconabicyclo[4.3.0]non-anes,-6-enes, -9-enes and -6,9-dienes were quenched with either MeOH, I2 or CO to generate a range of products containing a 3,4-disubstituted piperidine structure. Where the bicyclisation resulted in a mixture of diastereomers, the effects of temperature on the ratio of the two zirconabicycles was studied. The conjugated exocyclic dienes formed from 4-aza-1,7-octadiynes were reacted with activated dienophiles to yield reduced isoquinolines.New methods have been developed for the bicyclisation of substrates containing hindered alkene and terminal alkyne groups using Cp2Zr(DMAP)2 and Cp2Zr-(C2H4) respectively. The latter reagent was employed in the reductive coupling of but-2-enyl-methyl-(2-methyl-but-3-ynyl)-amine, the key step in our synthesis of (+/-)-tecomanine.2-Aza-7-zirconabicyclo[3.3.0]oct-anes, -5-enes, -8-enes and -5,8-dienes have been prepared by the unprecedented bicyclisation of substrates containing enamine and ynamine functionalities. The latter three complexes have been isolated and characterised using NMR techniques. 'Work-up' of these zirconabicycles with MeOH, Br2, Co and xylylisocyanide generated a range of 2,3-disubstituted pyrrolidines, with the occasional formation of 2o amine by-products.The novel Cp2Zr-(1-butene) mediated bicyclisation of 3-oxo-1,6-heptynenes has been exemplified using two substrates. The resultant complexes were protonated to form 2-alkylidene-3-methyl-tetrahydrofurans in good yield.</p
Biosynthesis, properties and structure of phytochrome photoreceptors from cyanobacteria
No full textRecombinant cyanobacterial phytochrome CphA from Tolypothrix sp. PCC 7601 (formerly Calothrix) was shown to bind the linear tetrapyrroles phytochromobilin (PΦB), phycocyanobilin (PCB) and phycoerythrobilin (PEB). PCB- and PΦB adducts formed photochromic species displaying U.V./visible spectral properties characteristic of cyanobacterial and higher plant phytochromes, with the non-photochromic PEB-CphA adduct displaying the expected fluorescence spectrum. Kinetic analyses for the binding of linear tetrapyrroles to CphA has revealed dissociation and catalytic rate constants that are similar to those determined for higher plant phytochromes (for binding of PEB to CphA Kd = 3.22 μM, kcat = 3.4x10-4 s-1). Circular dichroism studies suggest that a change in the secondary structure of holo-CphA may be occurring during photoisomerisation from the red light-absorbing (Pr) form to the far-red absorbing (Pfr) form. Purified PCB-CphA appears to exist as a multimer of approximately 2 MDa. This is contrary to other known phytochromes that exist as dimers of approximately 170 kDa in cyanobacteria or approximately 250kDa in higher plants. Crystallographic trials were performed with recombinant PCB-CphA from Tolypothrix sp. PCC 7601.Haem oxygenases, HO1 from Synechocystis sp. PCC 6803 and HO1 from Arabidopsis thaliana, were recombinantly expressed for use in structural studies. Synechocystis HO1 was shown to be irreversibly inhibited in the presence of divalent transition metal ions. Crystallographic trials were performed with HO1 from Synechocystis sp. PCC 6803 and with HO1 from Arabidopsis thaliana.</p
The role of the human leptomeninges in the inflammatory response to bacterial pathogens
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
Do possible worlds compromise God’s beauty? A reply to Mark Ian Thomas Robson
Get PDFIn a recent article Mark Ian Thomas Robson argues that there is a clear contradiction between the view that possible worlds are a part of God's nature and the theologically pivotal, but philosophically neglected, claim that God is perfectly beautiful. In this article I show that Robson's argument depends on several key assumptions that he fails to justify and as such that there is reason to doubt the soundness of his argument. I also demonstrate that if Robson's argument were sound then this would be a problem for all classical theists and not just those who hold the possible worlds view
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
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
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