1,720,981 research outputs found
Analysis of S-adenosylmethionine and related sulfur metabolites in bacterial isolates of Pseudomonas aeruginosa (BAA-47) by liquid chromatography/electrospray ionization coupled to a LTQ hybrid linear quadrupole ion trap and Fourier transform ion cyclotron resonance mass spectrometry
No full textA comprehensive and highly selective method for detecting in bacterial supernatants a modified sulfur nucleoside, S-adenosyl-L-methionine (SAM), and its metabolites, i.e., S-adenosylhomocysteine (SAH), adenosine (Ado), 5(-deoxy-5(-methylthioadenosine (MTA), adenine (Ade), S-adenosylmethioninamine
(dcSAM), homocysteine (Hcy) and methionine (Met), was developed. The method is based on reversed-phase liquid chromatography with positive electrospray ionization (ESIR)
coupled to a hybrid linear quadrupole ion trap (LTQ) and 7-T Fourier transform ion cyclotron
resonance mass spectrometry (FTICRMS). A gradient elution was employed with a binary solvent of 0.05M ammonium formate at pH 4 and acetonitrile. The assay involves a simultaneous cleanup of cell-free bacterial broths by solid-phase extraction and trace enrichment of metabolites with a 50-fold concentration factor by using immobilized phenylboronic and anion-exchange cartridges. While the quantitative determination of SAM was performed using stable-isotope-labeled SAM-d3 as an internal standard, in the case of Met and Ade, Met-13C and Ade-15N2 were employed as isotopelabeled
internal standards, respectively. This method enabled the identification of SAM and its metabolites in cell-free culture of Pseudomonas aeruginosa grown in Davis minimal broth
(formulation without sulphur organic compounds), with routine sub-ppm mass accuracies
(0.27W0.68 ppm). The resulting contents of SCSS-SAM, SS-dcSAM, MTA, Ado and Met in the
free-cell supernatant of P. aeruginosa was 56.4W2.1 nM, 32.2W2.2 nM, 0.91W0.10 nM, 19.6W1.2nM
and 1.93W0.02mM (meanWSD, n1⁄44 extractions), respectively. We report also the baseline separation (Rs ‡1.5) of both diastereoisomeric forms of SAM (SCSS and SCRS) and dcSAM (SS and RS), which can be very useful to establish the relationship between the biologically active versus the
inactive species, SCSS/SCRS and SS/RS of SAM and dcSAM, respectively. An additional confirmation
of SAM-related metabolites was accomplished by a systematic study of their MS/MS spectra
Identification and fragmentation pathways of caffeine metabolites in urine samples via liquid chromatography with positive electrospray ionization coupled to a hybrid quadrupole linear ion trap (LTQ) and Fourier transform ion cyclotron resonance mass spectrometry and tandem mass spectrometry.
No full textLiquid chromatography (LC) with positive ion electrospray ionization (ESI+) coupled to a hybrid quadrupole linear ion trap (LTQ) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) was employed for the simultaneous determination of caffeine and its metabolites in human urine within a single chromatographic run. LC/ESI-FTICRMS led to the unambiguous determination of the molecular masses of the studied compounds without interference from other biomolecules. A systematic and comprehensive study of the mass spectral behaviour of caffeine and its fourteen metabolites by tandem mass spectrometry (MS/MS) was performed, through in-source ion trap collision-induced dissociation (CID) of the protonated molecules, [M+H](+). A retro-Diels-Alder (RDA) process along with ring-contraction reactions were the major fragmentation pathways observed during CID. The base peak of xanthine precursors originates from the loss of methyl isocyanate (CH(3)NCO, 57 Da) or isocyanic acid (HNCO, 43 Da), which in turn lose a CO unit. Also uric acid derivatives shared a RDA rearrangement as a common fragmentation process and a successive loss of CO(2) or CO. The uracil derivatives showed a loss of a ketene unit (CH(2)CO, 42 Da) from the protonated molecule along with the loss of H(2)O or CO. To assess the potential of the present method three established metabolite ratios to measure P450 CYP1A2, N-acetyltransferase and xanthine oxidase activities were evaluated by a number of identified metabolites from healthy human urine samples after caffeine intake
SURVEY ABOUT MANAGEMENT OF WASTE COOKING OIL FROM HOUSEHOLDS: A CASE STUDY
No full textThe main aim of this study was to survey the management of waste cooking oil (WCO) from households in Angri, a town of around 34,000 people (about 2,500 inhabitants/km2) in Southern Italy. About 90% of interviewed knew WCO. Around 70% knew that there was a WCO collection program, but slightly more than 50% collected WCO. Eighty-seven percent of the sample was not aware of any informative campaign. Among those not involved in the collection program: 94% claimed to know the damages of a wrong WCO disposal; 46% discharged WCO into the toilet; misinformation was the main source of non-collection. Among those involved in the collection program: slightly more than 57% delivered WCO into the street containers; approximately 50% delivered WCO every month; 65% had not a negatively evaluation of the WCO collection service; 34% stated that they were the unique dealing with the collection of WCO at their home (more than 50% of them were housewives). To overcome the problems identified, it is suggested to: organize communication programs in schools and near shopping centres; set up focus groups with citizens and stakeholders; establish a rewarding competition for housewives, giving prominence to a category that in a traditional society like Southern Italy still plays a fundamental role
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
Layered-double hydroxides and derived oxide as CRM-free highly active catalysts for the reduction of 4-nitrophenol
Full text linkThe present study investigates the possibility to abate 4-nitrophenol (4NP), a well-known persistent contaminant in wastewaters, using Layered-Double Hydroxides (LDH) based catalysts, non-noble metals-based and Critical Raw Materials-free materials used for 4NP reduction with NaBH4. It is reported the study of the effects of several parameters on the overall reaction kinetic by in situ monitoring of the 4NP reduction through UV-Vis Spec-troscopy, as: (i) LDH's trivalent and divalent cation nature, (ii) LDH thermal treatment, (iii) substrate/catalyst ratio, and (iv) stirring rate. The reasons that led to increased activity were identified and correlated with cat-alyst's structure characterization. The results pointed out that LDH enhance synergic effect of nickel and copper by increasing reducibility which is further raised when defective mixed oxide by calcination is obtained. This resulted in enhanced 4NP reduction which could be further increased by calcination providing a highly reducible mixed oxide
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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