1,721,060 research outputs found
Identificazione di nuovi biomarcatori di stress radicalico nel plasma umano mediante spettroscopia Raman
No full textIn natura, i lipidi insaturi hanno esclusivamente il doppio legame in configurazione cis; di conseguenza, gli isomeri mono-trans degli acidi grassi poli-insaturi (PUFA) possono esclusivamente derivare o da una fonte esogena, ossia dalla dieta, o da un processo endogeno di isomerizzazione della configurazione cis a quella trans in seguito ad un insulto radicalico (stress da radicali liberi). In quest’ultimo caso, l’isomerizzazione avviene tramite un’addizione/eliminazione del tiil radicale al doppio legame cis con generazione della geometria trans (isomeri geometrici). Questi isomeri mono-trans PUFA possono essere considerati dei biomarcatori di stress radicalico nell’analisis di campioni biologici ottenuti da cellule di coltura, da animali e dall’uomo.
Il plasma umano è un campione biologico ad elevato interesse lipidomico a causa del suo alto contenuto lipidico. In particolare, la frazione dei colesteril esteri (CE) è di grande importanza nell’analisi lipidomica in quanto la loro biosintesi è strettamente correlata con quella delle lipoproteine e di conseguenza può essere bersaglio dello stress radicalico. I CE sono particolarmente ricchi in PUFA, in prevalenza acido linoleico e arachidonico. Per questo motivo è stato progettato un approccio combinato di chemical biology per la sintesi e l’identificazione di isomeri mono-trans di CE nel plasma umano. Sono stati quindi sintetizzati gli isomeri mono-trans del colesteril linoleato (due C=C) e colesteril arachidonato (quattro C=C) tramite isomerizzazione fotolitica. Una volta caratterizzati tramite varie tecniche analitiche (GC, MS, NMR, IR, Raman), questi composti sono stati utilizzati come riferimento per la loro individuazione nel plasma umano. A tale scopo la spettroscopia Raman è risultata essere estremamente appropriata poiché la banda C=C dei colesteril esteri si trova in posizione differente a seconda della geometria del doppio legame.
Sono stati quindi registrati gli spettri dei composti cis e mono-trans sintetizzati e di alcuni campioni di plasma. Negli spettri Raman degli isomeri cis furono visibili due bande dovute ai legami cis del doppio legame nella catena alchilica e dell’anello del colesterolo, mentre in quelli degli isomeri mono-trans apparve anche una nuova componente a 1671 cm-1, attribuibile alla geometria trans del doppio legame. Queste tre componenti furono individuate anche nei colesteril esteri estratti dai campioni di plasma. In conclusione, grazie ad un approccio combinato di sintesi e spettroscopia siamo riusciti ad identificare per la prima volta nel plasma umano gli isomeri mono-trans di CE, che possono essere utilizzati come indicatori di stati di stress radicalico, con promettenti sviluppi sia in medicina sia in biologia
Thermal decomposition of the tert-butyl perester of thymidine-5'-carboxylic acid. Formation and fate of the pseudo-C4'-radical
No full textThermal decomposition of the tert-butyl perester of thymidine-5'-carboxylic acid carried out at 85 °C in different solvents affords the tert-butylacetal, deriving from in cage decomposition, and pseudo C4'-radicals. These latter can be reduced to by hydrogen
atom abstraction from thiol (thiophenol or glutathione) or THF, or can be oxidized to cations by dioxygen or perester itself. Cations are stereoselectively trapped by the nucleophilic solvent (tert-butanol, methanol, water) to give acetals the corresponding acetals
Regioselective cis-trans isomerization of arachidonic double bonds by thiyl radicals: the influence of phospholipid supramulecular organization
No full textCIS/TRANS ISOMERIZATION OF UNSATURATED PHOSPHOLIPIDS BY GAMMA−IRRADIATION OF LIPOSOME VESICLES IN THE PRESENCE OF SULFUR-CONTAINING PROTEINS.
No full textabstract P-1
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
Radical cyclization approach to cyclonucleosides
No full textEfficient methodologies based on consecutive radical ractions for the preparation of cyclonucleosides are reported. The reactions were performed on modified thymidine and 2'-deoxyadenosine substrates using (TMS)3SiH as the reducing agent. The rate constants for the 6-exo-trig radical cyclization have been estimated
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
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