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Determinazione delle concentrazioni di dipeptidi imidazolici, l-istidina e 3 metil-l-istidina nel latte e sangue di capra
No full textDeterminazioni delle concentrazioni di dipeptidi imidazolici, l-istidina e 3 metil-l-istidina nel seme fresco di verro
No full textEffetto della variazione di temperatura sulla reazione di derivatizzazione post colonna con ortoftalaldeide dei dipeptidi istidinici e loro componenti
No full textRIASSUNTO Scopo della ricerca è stato quello di effettuare la derivatizzazione post colonna con ortoftalaldeide (OPA) dei dipeptidi istidinici (carnosina e anserina) e dei loro componenti (listidina e 3-metil-l-istidina) a varie temperature in modo da determinare quella alla quale tali sostanze producono la massima risposta in termini quantitativi. Per quanto riguarda i dipeptidi istidinici la temperatura ottimale per la reazione di derivatizzazione con OPA va dai 35°C per la carnosina ai 45°C - 50°C per l’anserina con un aumento rispettivo della superficie dei picchi di circa il 4% e 9% rispetto alla temperatura di 30°C. L’interpolazione dei dati della temperatura e della superficie dei picchi dei due dipeptidi, visto l’andamento non lineare, è stata effettuata rispettivamente con equazione polinomiale di terzo grado (R2= 0,990) e quarto grado (R2=0,992). Per la l-istidina e 3-metil-l-istidina la temperatura ottimale risulta quella compresa tra i 55°C e i 60°C ma in questo caso si osserva un incremento costante della superficie del picco con l’aumentare della temperatura (R2=0,998 per la l-istidina e un R2=0,999 per la 3- metil-l-istidina). Per questi ultimi due componenti l’aumento della superficie dei picchi rispetto alla temperatura di 30°C risulta essere molto elevato (?70%). La riproducibilità dei valori delle superfici dei picchi sia dei dipeptidi istidinici che dei loro componenti risulta elevata, con un bassissimo coefficiente di variazione a tutte le temperature utilizzate, mostrando come la reazione di derivatizzazione sia altamente stabile. Questi dati mostrano come l’incremento di sensibilità e quindi della superficie del picco al variare della temperatura di derivatizzazione ed a parità di concentrazione sia ridotto per i dipeptidi istidinici mentre sia notevolmente elevato per i loro componenti. In conclusione questa ricerca mostra come con l’aumentare della temperatura sia possibile aumentare l’efficienza, la sensibilità e l’accuratezza della metodica HPLC usata per la determinazione di questi composti che risultano presenti in molti compartimenti dell’organismo in concentrazioni ampiamente variabili in quanto specie specifiche ed anche quantitativamente molto ridotte specialmente per quanto riguarda la 3-metil-l-istidina. SUMMARY The aim of this research was to make the o-phthalaldehyde (OPA) post-column derivatisation at different temperatures of histidine dipeptides (carnosine, anserine), L-histidine and 3-methyl-L-histidine to establish which temperature is the best to obtain highest sensibility of detection of this compounds. As regard anserine and carnosine, results showed that the best temperature of derivatisation reaction was between 45°C - 50°C for anserine and between 35-45 °C for carnosine with an increase of peak area of 9% respect to temperature of 30 °C. For L-histidine and 3-methyl-Lhistidine this research showed that the optimal temperature was between 55°C - 60°C with an increase of peak area at every temperature of derivatisation reaction (R2=0,998 for L-histidine and R2=0,999 for 3-methyl-L-histidine). For this latter the increase of peak area respect to temperature of 30 °C was more of 70 %. The reproducibility of the method (for histidine dipeptides, L-histidine and 3-methyl-Lhistidine) was very high with a very low coefficient of variation at all temperatures of derivatisation; it showed that the derivatisation reaction was very stable. Therefore all data showed that the increase of sensibility (associated to growing of temperature) was very high for histidine and 3-methyl-L-histidine while it was reduced for histidine dipeptides. In conclusion this research showed that the increase of derivatisation. temperature permitted to obtain an higher sensibility efficiency of HPLC method used for detection of histidine dipeptides that are present in animal tissues at different and very low concentrations
Confronto tra diverse fasi mobili per la determinazione in hplc di carnosina, anserina, l-istidina, 3-metil-l-istidina
No full textRIASSUNTO Scopo della ricerca è stato quello di determinare la miglior fase mobile che in condizioni isocratiche ed alla temperatura di derivatizzazione post colonna di 50°C consentisse la separazione dei picchi della carnosina, anserina e dei loro componenti. Partendo da una fase mobile costituita da 20% acetonitrile e 80% di soluzione 6 mM HCl + 0,48 moli/litro di NaCl, sono state preparate fasi mobili con % di acetonitrile a decrescere (15-10-5) fino al raggiungimento della separazione completa dei picchi. La fase mobile che ha permesso la totale separazione delle molecole è stata quella costituita dal 5% di acetonitrile. Le rette di regressione di ciascuna molecola hanno mostrato R2 di correlazione estremamente elevati (∼1) per un intervallo di concentrazione compreso tra 62.5 – 0.5 ng/20μl evidenziando una elevata accuratezza (∼100%) ed un aumento della sensibilità per ogni composto a tutte le concentrazioni utilizzate. Quindi, se l’aumento della temperatura della reazione di derivatizzazione post colonna con o-ftalaldeide (OPA) ha prodotto un forte incremento della sensibilità di rilevazione di questi composti ed in particolare modo della l-istidina e della 3-metil-l–istidina (∼70%), l’utilizzazione di una diversa fase mobile ha consentito la separazione di tutti i composti e principalmente la carnosina dalla 3-metil-l-istidina che in condizioni isocratiche mostrano tempi di ritenzione molto ravvicinati. In conclusione la possibilità di poter determinare esigue concentrazioni di questi composti con una adeguata sensibilità ed un’elevata accuratezza può consentire di rilevarli anche in quei compartimenti dell’organismo dove la loro presenza appare molto ridotta. SUMMARY This research proposes an high-performance-liquid-chromatography (HPLC) method for a quantitative detection of carnosina, anserine, l-histidine and 3-methyl-l-histidine, with ophthalaldehyde (OPA) post column derivatisation by isocratic elution. For this purpose some mobile-phases were prepared with scalar acetonitrile concentrations. The best mobile phase for a complete separation of all molecules was composed of Acetonitrile and 6mM Hydrochloric acid with 0,48 M sodium chloride solution (5%:95% v/v). The regression lines, obtained by a range of concentration between 62.5 – 0.5 ng/20μl for all substances showed a very high values of R2 (∼1) indicating a very high sensibility and accuracy (∼100%) of this new mobile phase in isocratic conditions. Temperature increase of post column derivatisation (50°C) with (OPA) showed a greater sensibility for l-histidine and 3-methyl-l-histidine detection (∼70%) and the new mobile phase in isocratic conditions produced a complete separation for all compound and in particular way between carnosine and 3-methyl-l-histidine. The high sensibility of this HPLC method can detect histidine dipeptides and correlated compounds l-histidine and 3-methyl-l-histidine in animal tissues where can be present in different and very low concentrations. In addition this very simple and fast method could be used to histidine dipeptides detection in biological compartments were their concentrations could be very low
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
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
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