1,721,035 research outputs found
A promising Raman spectroscopy technique for the investigation of trans and cis cholesteryl ester isomers in biological samples
No full textLipid geometry is an important issue in biology and medicine. The cis-trans geometry conversion of double bonds in lipids is an endogenous process that can be mediated by sulfur-centered free radicals. Trans isomers of polyunsaturated fatty acids can be used as biological markers of free radical stress, and their presence in biological samples can be determined by synthesis and characterization of appropriate reference compounds. Fractions of plasma lipids, such as cholesteryl linoleate and arachidonate esters, are interesting targets because of their connection with membrane phospholipid turnover and their roles in cardiovascular health. In this context, Raman spectroscopy can provide a useful contribution, since Raman analysis can be performed directly on the lipid extracts without any derivatization reaction, is nondestructive, and can rapidly supply biochemical information. This study focused on the build up of Raman spectral libraries of different cis and trans isomers of cholesteryl esters to be used as references for the examination of complex biological samples and to facilitate isomer recognition. Unsaturated cholesteryl esters obtained by chemical synthesis and with different alkyl chain lengths, double bond numbers, or both, were analyzed. The potential of Raman analysis for trans isomer detection in biological samples was successfully tested on some cholesteryl ester lipid fractions from human serum. The data suggest promising applications of Raman spectroscopy in metabolomics and lipidomics
Free-radical-mediated formation of trans-cardiolipin isomers, analytical approaches for lipidomics and consequences of the structural organization of membranes
Full text linkFree-radical-mediated processes, such as peroxidation, isomerization and hydrogenation affecting fatty acid integrity and biological functions, have a trans-disciplinary relevance. Cardiolipins (CL, (1,3-diphosphatidyl-sn-glycerol)) and tetra-linoleoyl-CL are complex phospholipids, exclusively present in the Inner Mitochondrial Membrane (IMM) lipids, where they maintain membrane integrity and regulate enzyme functionalities. Peroxidation pathways and fatty acid remodeling are known causes of mitochondrial disfunctions and pathologies, including cancer. Free-radical-mediated isomerization with the change of the cis CL into geometrical trans isomers is an unknown process with possible consequences on the supramolecular membrane lipid organization. Here, the formation of mono-trans CL (MT-CL) and other trans CL isomers (T-CL) is reported using CL from bovine heart mitochondria and thiyl radicals generated by UV-photolysis from 2-mercaptoethanol. Analytical approaches for CL isomer separation and identification via 1H/13C NMR are provided, together with the chemical study of CL derivatization to fatty acid methyl esters (FAME), useful for lipidomics and metabolomics research. Kinetics information of the radical chain isomerization process was obtained using γ-irradiation conditions. The CL isomerization affected the structural organization of membranes, as tested by the reduction in unilamellar liposome diameter, and accompanied the well-known process of oxidative consumption induced by Fenton reagents. These results highlight a potential new molecular modification pathway of mitochondrial lipids with wide applications to membrane functions and biological consequences
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
Pyridine ylide formation by capture of phenylchlorocarbene and tert-butylchlorocarbene. Reaction rates of an alkylchlorocarbene by laser flash photolysis
No full textPT: J; CR: BARCUS RL, 1986, J AM CHEM SOC, V108, P3928 CHATGILIALOGLU C, 1982, J AM CHEM SOC, V104, P5124 GOULD IR, 1985, TETRAHEDRON, V41, P1587 GRILLER D, 1984, J AM CHEM SOC, V106, P2227 LIU MTH, 1985, TETRAHEDRON LETT, V26, P3071 MOSS RA, 1981, TETRAHEDRON LETT, V38, P3749 SOUNDARARAJAN N, IN PRESS J AM CHEM S SOUNDARARAJAN N, IN PRESS TETRAHEDRON SOUNDARARAJAN N, UNPUB TURRO NJ, 1985, J ORG CHEM, V50, P4417 TURRO NJ, 1987, J AM CHEM SOC, V109, P2101 ZUGRAVESCU I, 1976, N YLID CHEM; NR: 12; TC: 144; J9: J AMER CHEM SOC; PG: 2; GA: P5279Source type: Electronic(1
Occurrence of trans fatty acids in rats fed a trans-free diet: A free-radical-mediated formation ?
No full textTrans isomers of unsaturated fatty acids are absorbed from the diet, due to their presence in diary fat and hydrogenated vegetable oils, and health concern has risen due to their effects on lipid risk factors in cardiovascular diseases. On the basis of the efficiency of the thiyl-radical-catalyzed cis/trans isomerization in vitro and the presence of many sulfur-containing compounds in the cell, the aim of this study was to demonstrate that trans geometry of lipid double bonds can be endogenously generated within membrane phospholipids. The study reports trans fatty acids occurrence in tissue and erythrocyte phospholipids of young adult rats fed a diet completely free of trans isomers. Results show that tissues are differently prone to the endogenous isomerization and that, following a free radical attack, trans fatty acids can reach very high amounts. The effectiveness of this process is considerably inhibited in the presence of all-trans retinol, confirming previous data in model membranes. Our results suggest that geometrical isomerization of unsaturated fatty acids, which causes a structural modification of membrane lipids and may influence basic membrane properties and vital biochemical functions, can occur under radical stress conditions and could be efficiently prevented by vitamin A
The reaction of hydrogen atoms with methionine residues: A model of reductive radical stress causing tandem protein-lipid damage
No full textThe occurrence of tandem damage, due to reductive radical
stress involving proteins and lipids, is shown by using a biomime-
tic model. It is made of unsaturated lipid vesicle suspensions in
phosphate buffer in the presence of methionine, either as a
single amino acid or as part of a protein such as RNase A, which
contains four methionine residues. The radical process starts with
the formation of HC atoms by reaction of solvated electrons with
dihydrogen phosphate anions, which selectively attack the thioether
function of methionine. The modification of methionine to
a-aminobutyric acid is accompanied by the formation of thiyl
radicals, which in turn cause the isomerization of the cis fatty
acid residues to the trans isomers. The relationship between
methionine modification and lipid damage and some details of
the reductive radical stress obtained by proteomic analysis of
irradiated RNase A are presented
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