1,721,089 research outputs found
Stereoselective preparation of (E)-ε-nitro-β,γ-unsaturated methyl esters: Amberlyst A 27, using microwave, as superior catalyst for the 1,6-conjugate addition of nitroalkanes to methyl 1,3-butadiene-1-carboxylate
No full text1,6-Conjugate addition of nitroalkanes to methyl 1,3-butadiene-1-carboxylate, performed with Amberlyst A 27, using microwaves and in the absence of any solvent, allows the prevalent formation of the β,γ-unsaturated adduct, over the α,β-unsaturated one. The products were exclusively obtained as (E)-isomers
Development and Validation of a GC-FID Method for the Analysis of Short Chain Fatty Acids in Rat and Human Faeces and in Fermentation Fluids
No full textShort-chain fatty acids (SCFAs) are gut microbiota metabolites recognized for their beneficial effects on the host organism. In this study, a simple and rapid sample preparation method combined to SCFAs analysis by direct injection and gas chromatography coupled with flame ionization detection (GC-FID), for the determination and quantification of eight SCFAs (acetic, propionic, i-butyric, butyric, i-valeric, valeric, i-caproic and caproic acids) in rat, mice and human faeces and in fermentation fluids samples, has been developed and validated. The method consists of extraction of the SCFAs by ethyl ether after acidification of the samples. The effect of the number of extractions has been assessed in order to optimize the procedure and to obtain a satisfactory yield for all the analyzed SCFAs. The increase of the extracted analytes quantity was significant passing from 1 to 2 and from 2 to 3 extractions (P < 0.05), while no significant differences were found performing 3, 4 or 5 extractions (P > 0.05). The SCFAs extracted are directly analyzed by GC-FID without derivatization and separated on a polyethylene glycol nitroterephthalic acid modified coated capillary column, with a chromatographic run time of 13 min. The proposed method showed good sensitivity, with limits of quantifications in the range 0.14-0.48 μM for SCFAs from propionic to caproic acids and 2.12 μM for acetic acid; recovery was between 80.8 and 108.8% and intraday and interday repeatability in the range 0.6-5.0% of precision (RSD, %) The optimized method is suitable for the quantitative analysis of SCFAs in real samples of rat, mouse and human faeces and in fermentation fluids, and it can be applied also to very small amount of faecal sample (20 mg)
Synthesis and use of nitrocyclopropane derivatives
Full text linkNitrocyclopropanes are strained-ring nitro compounds of special attraction in the field of energetic materials because of the increased performance expected from the additional energy
release upon opening the strained ring system during decomposition. Moreover, the nitrocyclopropane moiety is the key structure of important natural products or the key building
block for other important targets. Thus, the aim of this micro-report is focused on the main approaches for the synthesis of nitrocyclopropane derivatives and their chemistry
Uncatalyzedconversion of linear α-nitro ketones into amides by reaction with primary amines under solventless conditions
No full textThe reaction of linear α-nitro ketones with primary amines allows the formation of amides through the cleavage of the carbon–carbon bond between the carbonyl group and the carbon-nitro group moiety, promoted by the nucleophilic effect of the amine. The reaction is performed at room temperature, without any catalyst and/or solvent
One-Pot Synthesis of γ-Diketones, γ-Keto Esters, and Conjugated Cyclopentenones from Nitroalkanes
No full textConjugated addition of primary nitroalkanes to ,-unsaturated ketones or ,-unsaturated esters, in the presence of two equivalents of DBU, allows the one-pot prepration of -diketones or -keto esters, respectively. When 2-aryl-1-nitroethane derivatives are employed as starting nitroalkanes in the reaction with ,-unsaturated ketones, the one-pot formation of cyclopentenones is observe
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
Developing a new method to analyse volatile substances in extra virgin olive oil
No full textThe applications of gas chromatography in the field of food science are of great importance for the assessment of food quality and safety. As an example, volatile compounds are key molecules in the definition of the overall quality of extra virgin olive oil.1 New methods to analyse volatile substances in olive oil by solid-phase microextraction and gas chromatography coupled to mass spectrometry are currently under investigation in our laboratory. Interesting preliminary results show that the aqueous extract of olive oil can provide the same result as when the analysis is carried out on the oil as such, with the advantage that the oil aqueous extract is much easier to handle, the solid-phase microextraction fiber assembly used has a much longer lifetime and the use of an internal standard is allowed, while using the oil as such, the homogenization of the internal standard is practically unfeasible. The results of the study will be presented and discussed.
References:
1) Angerosa, F.; Servili, M.; Selvaggini, R.; Taticchi, A.; Esposto, S., Montedoro, G. Journal of Chromatography A 2004, 1054, 17-31
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