1,720,968 research outputs found
A diethylpyrocarbonate-based derivatization method for the LC-MS/MS measurement of plasma arginine and its chemically related metabolites and analogs
No full textBackground: Changes in NO metabolism correlate with cardiovascular risk factors and are associated with endothelial dysfunction. NO availability is regulated by nitric oxide synthase (NOS) and arginine and some chemically related metabolites and analogs have the capacity to alter NOS activity. Hence the need for analytical methods for the simultaneous assessment of these analytes. Methods: Analytes (L-arginine (Arg), N G -monomethyl-L-arginine (MMA), L-homoarginine (hArg), asymmetric dimethyl-L-arginine (ADMA), symmetric dimethyl-L-arginine (SDMA), and L-citrulline (CIT)) were isolated from human plasma by thermal coagulation of plasma followed by a derivatization with diethylpyrocarbonate. Carbetoxy derivatives were separated on a C18 reversed-phase column in <10 min using an aqueous solution of 0.4% v/v formic acid and acetonitrile (95:5, v/v) mixture as a mobile phase. Positive electrospray ionization and tandem mass spectrometry in combination with specific multiple reaction monitoring transitions were used for detection of analytes and three deuterated forms of the analytes used as internal standards. Results: Intra- and inter-day precision %RSD values ranged between 3 and 5.5% and percentage recoveries were close to 100% for all analytes. Plasma concentrations in 20 healthy male volunteers were 58.62 ± 8.81 μmol/L for Arg, 105.08 ± 21.66 nmol/L for MMA, 1.88 ± 0.57 μmol/L for hArg, 0.612 ± 0.140 μmol/L for ADMA, 0.581 ± 0.172 μmol/L for SDMA, and 28.62 ± 11.60 μmol/L for Cit, respectively. Conclusion: This LC–MS/MS method provides the capacity to quantify the plasma concentrations of arginine and some of its chemically related metabolites. Sample preparation was simple, inexpensive and effortless. Overall, given the short sample preparation and chromatographic run time, the method may be suitable for the fast and reproducible quantitative determination of the analytes in large clinical trials and routine analysis
Hercynine content in widely consumed commercial beverages
No full textHercynine, the main biosynthetic precursor and oxidative metabolite of ergothioneine, was measured by an LC-ESI-MS/MS method in tea, coffee, beer, and wine samples. Results showed that hercynine was detectable and measurable in all beverage. Among teas, the higher concentration was in the black variety (170.45 +/- 7.84 ng/mg of dry weight) followed by the white (130.63 +/- 8.79 ng/mg of dry weight) and green ones (71.62 +/- 6.13 and 47.43 +/- 7.66 ng/mg of dry weight). Compared to teas, coffees had less amount of hercynine with more homogeneous levels that appear unlinked to the kind of mixture (100% Arabica 12.92 +/- 1.01 ng/mg of dry weight, 50/50 Arabica/Robusta 10.52 +/- 0.38 ng/mg of dry weight, and decaffeinated 8.59 +/- 0.75 ng/mg of dry weight). Overall, the red wines had the highest values of hercynine compared to the whites (379.57 +/- 238.15 vs. 575.51 +/- 62.60 nmol/L). In the latter, hercynine concentrations showed a trend toward an increase with increasing pH values. Hercynine concentrations in the beers were similar to the levels in wines, and there was no difference between traditional and gluten-free sample (679.24 +/- 0.92 vs. 570.58 +/- 0.88 nmol/L). These data highlight the potential of hercynine as a possible marker of antioxidant activity of ergothioneine in beverages and food
A liquid chromatography-mass spectrometry study on the spirocyclization of ninhydrin with the aminothiols
Full text link© 2018 Elsevier BV. This manuscript version is made available under the CC-BY-NC-ND 4.0 license:
http://creativecommons.org/licenses/by-nc-nd/4.0/
This author accepted manuscript is made available following 24 month embargo from date of publication (May 2018) in accordance with the publisher’s archiving policy.Ninhydrin reacts with some aminothiols to form spiranes adducts whose optical and
chromatographic properties have proved to be useful for chiral recognition. Liquid
chromatography-mass spectrometry data along with spectroscopic analysis reveal that under certain
conditions, in addition to the known single-spirane configuration, the spirothiazolidinic complexes
can exist also as double- and mixed double-spiranes. The reaction was exploited to check the
enantiomeric purity of two commercially available dosage form of D-penicillamine and to measure
the aminothiol concentration in the urine sample from a subject under treatment with the drug.
Separation of diastereoisomers was achieved on a C18 column in isocratic mode by using a mixture
of an aqueous solution of formic acid (30 mmol/L)/acetonitrile (90:10, v/v) as a mobile phase.
Diastereoisomers were detected by a fluorescence detector and mass spectrometer in short times
and with a good resolution. Intra- and inter-assay reproducibility were under 4% with an average
recovery of 98%. At a LOD of 0.01%, no evidence of the toxic distomer (L-enantiomer) was found
in the biological sample and drugs
Synthesis of 3,6-diazabicyclo[3.1.1]heptanes as novel ligands for neuronal nicotinic acetylcholine receptors
No full text
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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