1,720,959 research outputs found
Sviluppo di strategie di riconoscimento per il rilevamento di fenoli bioattivi in olio d'oliva e caffè
No full textLo scopo del progetto di dottorato è stato lo sviluppo di elementi di riconoscimento per il rilevamento di composti fenolici del caffè – in particolare acido clorogenico (CGA) e acido caffeico - e olio d'oliva – in particolare idrossitirosolo e tirosolo - per scopi di controllo qualità. L'obiettivo è stato quello di sviluppare strategie covalenti per il monitoraggio di molecole target (TM), sfruttando tecniche ottiche (assorbanza e fluorescenza) per la trasduzione del segnale. Le tre reazioni sfruttate sono state:
-formazione di pigmenti verdi di triidrossibenzacridina (TBA);
-formazione di esteri boronici;
-reazione di diazo-coupling.
La formazione del pigmento di TBA è una reazione che coinvolge i gruppi amminici primari e gli esteri dell'acido caffeico, come il CGA, che porta alla formazione di composti verdi. La reazione è stata inizialmente studiata sull'aminoacido lisina e CGA, utilizzandola per quantificare il target sia all'endpoint della reazione (dopo 24 ore) che lavorando in modalità cinetica, monitorando i primi 15 minuti di reazione, ottenendo ottimi risultati. La reazione è stata poi applicata alla sintesi di peptidi contenenti l'aminoacido lisina: per uno di essi si è potuta ottenere una prestazione migliorata rispetto all'aminoacido di partenza. La reazione è stata applicata anche alla sintesi di film polimerici contenenti monomeri amminici in grado di formare pigmenti di TBA con CGA: dopo aver testato la reattività di diverse composizioni polimeriche, quella migliore è stata utilizzata per confrontare le prestazioni nella quantificazione CGA della strumentazione di laboratorio e di diversi dispositivi portatili, ottenendo risultati promettenti per questi ultimi. Inoltre, sono state studiate nuove proprietà di fluorescenza del pigmento TBA.
Considerando la reazione degli acidi boronici, l'obiettivo era quello di avere come target particolari composti orto-difenolici in grado di formare esteri boronici ciclici stabili. A tale scopo sono stati testati due fluorofori contenenti una funzione acido boronica e in grado di modulare la loro fluorescenza in seguito al legame delle molecole bersaglio. Dopo aver selezionato il fluoroforo più performante, le sue prestazioni sono state analizzate mediante misure di titolazioni di fluorescenza con le molecole bersaglio, ottenendo in tutti i casi un buon quenching della fluorescenza. Il fluoroforo è stato utilizzato per sintetizzare tre peptidi, testandone le prestazioni mediante titolazioni di fluorescenza e confrontandole con quelle del solo fluoroforo.
Per quanto riguarda il terzo approccio, sono stati sintetizzati due peptidi, contenenti sia una porzione fluorescente -fluoresceina in un caso, EDANS nell'altro- sia l'amminoacido non naturale para-ammino-fenilalanina, in grado di stabilire interazioni di π-π stacking con fenoli ma anche di reagire nella reazione covalente di diazo-coupling, formando derivati di diazo-coupling di colore rosso dopo la reazione con il tirosolo. I peptidi sono stati testati sia nell'approccio non covalente che in quello covalente.The aim of the PhD project has been the development of sensing elements targeting phenolic compounds from coffee – i.e. chlorogenic acid (CGA) and caffeic acid - and olive oil- i.e. hydroxytyrosol and tyrosol- for quality monitoring purposes. The focus has been that of developing covalent strategies for target molecules (TM) monitoring, exploiting optical techniques (absorbance and fluorescence) for signal transduction. The three exploited reactions have been:
-green trihydroxybenzacridine (TBA) pigments formation;
-boronic esters formation;
-diazo-coupling reaction.
TBA pigment formation is a reaction involving primary amino groups and caffeic acid esters -such as CGA-, leading to formation of green compounds. The reaction has been initially studied on the amino acid lysine and CGA, using it to quantify the TM both at the endpoint of the reaction (after 24 hours) and working in kinetic mode, monitoring the first 15 minutes of reaction, obtaining very good results. Then, the reaction has been applied to the synthesis of peptides containing the amino acid lysine: for one of them, an improved performance could be obtained with respect to the starting amino acid. The reaction has been applied also to the synthesis of polymeric films containing amino monomers capable of forming TBA pigments with CGA: after testing the reactivity of several polymeric compositions, the best performing one has been used to compare the performance in CGA quantification of laboratory instrumentation and different portable devices, obtaining promising results for the latter. Also, new fluorescence properties of the TBA pigment have been investigated.
Considering boronic acid reaction, the focus was that of targeting in particular ortho-diphenolic compounds capable of forming stable cyclic boronic esters. For this purpose, two fluorophores containing a boronic acid moiety and capable of modulating their fluorescence upon target molecules binding have been tested. After selecting the best performing fluorophore, its performance has been analyzed by fluorescence titrations measurements with the target molecules, obtaining in all cases a good fluorescence quenching. The fluorophore has been used to synthesize three peptides, testing their performance by fluorescence titrations and comparing their performance with that of the fluorophore alone.
As for the third approach, two peptides have been synthesized, containing both a fluorescent moiety -fluorescein in one case, EDANS in the other- and the non-natural amino acid para-amino phenylalanine, capable of providing both π-π stacking interactions with phenols but also of reacting in covalent diazo-coupling reaction, forming red-colored diazo-coupling derivatives upon reaction with tyrosol. The peptides have been tested in both the non-covalent and covalent approach
Biosensors and Sensing Systems for Rapid Analysis of Phenolic Compounds from Plants: A Comprehensive Review
Full text linkPhenolic compounds are secondary metabolites frequently found in plants that exhibit many different effects on human health. Because of the relevant bioactivity, their identification and quantification in agro-food matrices as well as in biological samples are a fundamental issue in the field of quality control of food and food supplements, and clinical analysis. In this review, a critical selection of sensors and biosensors for rapid and selective detection of phenolic compounds is discussed. Sensors based on electrochemistry, photoelectrochemistry, fluorescence, and colorimetry are discussed including devices with or without specific recognition elements, such as biomolecules, enzymes and molecularly imprinted materials. Systems that have been tested on real matrices are prevalently considered but also techniques that show potential development in the field
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
Novel synthesis of 1,2-diaza-1,3-dienes with potential biological activity from cinnamic acids and diazonium salts of anilines
Full text linkCinnamic acids are an important class of phenolic compounds, which have many beneficial effects on human health but are also interesting synthetic intermediates thanks to the presence of several reactive sites. While studying the reactivity of cinnamic acids with diazonium salts from aromatic amines, an unexpected reactivity has been discovered, leading to the formation of 1,2-diaza-1,3-dienes instead of traditional diazo-coupling products. The new compounds have been fully characterized by mono and bidimensional NMR spectroscopy and mass spectrometry. Preliminary studies on the biological activity of the compounds have been carried out testing both their antibacterial and antitumor activity, leading to promising results
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
Dispelling 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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