1,720,973 research outputs found
Alkylations ofN4-(4-Pyridyl)-3,5-di(2-pyridyl)-1,2,4-triazole: first observation of room-temperature rearrangement of anN4-substituted triazole to the N1 analogue
No full textAttempts to use alkylation to introduce a positive charge at the nitrogen atom of the 4-pyridyl ring in the bis(bidentate) triazole ligand N-4-(4-pyridyl)-3,5-di(2-pyridy1)-1,2,4-triazole (pydpt) were made to ascertain what effect a strongly electron-withdrawing group would have on the magnetic properties of any subsequent iron(II) complexes. Alkylation of pydpt under relatively mild conditions led in some cases to unexpected rearrangement products. Specifically, when benzyl bromide is used as the alkylating agent, and the reaction is carried out in refluxing acetonitrile, the N-4 substituent moves to the NI position. However, when the same reaction is performed in dichloromethane at room temperature, the rearrangement does not occur and the desired product containing an alkylated N4 substituent is obtained. Heating a pure sample of N-4-Bzpydpt center dot 3r to reflux in MeCN resulted in clean conversion to N-1-Bzpydpt center dot Br. This is consistent with AP-Bzpydpf Br being the kinetic product whereas N-1-Bzpydpt.Br is the thermodynamic product. When methyl iodide is used as the alkylating agent, the N-4 to N-1 rearrangement occurs even at room temperature, and at reflux pydpt is doubly alkylated. The observation of the lowest reported temperatures for an N-4 to N-1 rearrangement is due to this particular rearrangement involving nucleophilic aromatic substitution: a possible mechanism for this transformation is suggested
Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris)
No full textRichardson, Alistair T., Cho, Jung, McGhie, Tony K., Larsen, David S., Schaffer, Robert J., Espley, Richard V., Perry, Nigel B. (2020): Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris). Phytochemistry (112297) 173: 1-9, DOI: 10.1016/j.phytochem.2020.112297, URL: http://dx.doi.org/10.1016/j.phytochem.2020.11229
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
Fig. 7 in Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris)
No full textFig. 7. Acetylation of 2 under basic conditions gave the unsaturated glycoside 8, but acidic conditions led to the successful acetylation of both 2 and 2a. I. Ac2O, pyridine, 0 ̊C, overnight, 44%. II. Ac2O, HClO4, 0 ̊C, 1 h, 71% (9) and 73% (9a) yield.Published as part of Richardson, Alistair T., Cho, Jung, McGhie, Tony K., Larsen, David S., Schaffer, Robert J., Espley, Richard V. & Perry, Nigel B., 2020, Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris), pp. 1-9 in Phytochemistry (112297) 173 on page 5, DOI: 10.1016/j.phytochem.2020.112297, http://zenodo.org/record/829446
Fig. 4. 1H in Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris)
No full textFig. 4. 1H NMR spectra (400 MHz, D O) of a crab apple extract fraction (I) and sucrose (II). The circled signal was consistent with the anomeric proton of a β-AAG.Published as part of Richardson, Alistair T., Cho, Jung, McGhie, Tony K., Larsen, David S., Schaffer, Robert J., Espley, Richard V. & Perry, Nigel B., 2020, Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris), pp. 1-9 in Phytochemistry (112297) 173 on page 4, DOI: 10.1016/j.phytochem.2020.112297, http://zenodo.org/record/829446
Fig. 8 in Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris)
No full textFig. 8. The downfield regions of the 1H NMR spectra for acetylated ascorbyl glycosides (structures in Fig. 7.). I. Peracetyl galactoside 9a, II. Acetylated and purified ascorbyl glycoside from crab apples, III. Peracetyl glucoside 9.Published as part of Richardson, Alistair T., Cho, Jung, McGhie, Tony K., Larsen, David S., Schaffer, Robert J., Espley, Richard V. & Perry, Nigel B., 2020, Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris), pp. 1-9 in Phytochemistry (112297) 173 on page 6, DOI: 10.1016/j.phytochem.2020.112297, http://zenodo.org/record/829446
Fig. 1 in Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris)
No full textFig. 1. Structures of AA (1) and the only known naturally occurring derivatives in plants, 2-O-β-D-glucopyranosyl L-ascorbic acid (2) and 6-O-β-D-glucopyranosyl L-ascorbic acid (3). Synthetic 2-O-α-D-glucopyranosyl L-ascorbic acid (4) is commonly used in cosmetic products.Published as part of Richardson, Alistair T., Cho, Jung, McGhie, Tony K., Larsen, David S., Schaffer, Robert J., Espley, Richard V. & Perry, Nigel B., 2020, Discovery of a stable vitamin C glycoside in crab apples (Malus sylvestris), pp. 1-9 in Phytochemistry (112297) 173 on page 2, DOI: 10.1016/j.phytochem.2020.112297, http://zenodo.org/record/829446
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