1,720,969 research outputs found
Thermal stability and long-chain fatty acid positional distribution on glycerol of argan oil
No full textThe primary aim of this study was to determine the oxidative stability of argan oils by using peroxides and conjugated diene hydroperoxides measurements as analytical indicators. Both food and cosmetic argan oils were investigated. Their oxidative stability was also determined by monitoring the relative changes of their fatty acid profiles by 1H NMR. In addition, valuable information regarding minor components as well as the acyl positional distribution, were obtained for both grades by high field 1H and 13C NMR, respectively. Given that the cosmetic and food grades have a similar profile and content of phenolic antioxidants, vitamers, and squalene, it appears that the ratio of fatty acid aliphatic to bisallylic CH2 groups, much higher in argan oils than in other vegetable oils, is responsible for their higher thermal stability
Study of intermicellar interactions and micellar sizes in ionic micelle solutions by comparing collective diffusion and self-diffusion coefficients
No full textDynamic light scattering and pulsed gradient spin-echo NMR measurements were performed on D2O solutions of sodium glycocholate (NaGC). The micelle self-diffusion and collective diffusion coefficients were measured for 0.08 M NaGC solutions at different added NaC1 molarities (0.1-0.8 M). Moreover, a study as a function of NaGC concentration at 0.1 M NaCl was performed. Both the surfactant and the NaCl concentration dependencies of the diffusion coefficients were interpreted on the basis of the DLVO theory of colloidal stability. The experimental data were analyzed by considering both the effect of micellar growth and interaction potential variation. The micelle ionization degree alpha was supposed to be constant over the range of 0.03-0.10 M NaGC and 0.1 M NaCl, whereas no restriction was imposed on its NaCl concentration dependence. The NaGC critical micelle concentrations at all of the studied NaCl molarities were inferred from surface tension measurements on NaGC H2O solutions. The best-fit micellar hydrodynamic radii and aggregation numbers point out that very slight micellar growth is induced by increasing the added electrolyte and/or the surfactant concentration. Moreover, the alpha value slightly decreases by increasing the NaCl molarity. An interpretation model of monodisperse spherical particles with a hard-core interaction shell of suitable thickness was also used to interpret the data at low ionic strength (from 0.1 to 0.4 M NaCl). Satisfactory agreement between the two interpretation models is obtained
Chiral recognition of dipeptides in a biomembrane model
No full textChiral recognition of the enantiomeric couples of ditryptophan and diphenylalanine was observed by 1H NMR spectroscopy in micelles formed by sodium N-dodecanoyl-L-prolinate. Ditryptophan showed a selective association with the Z domains of the amidic aggregates, whereas diphenylalanine did not show any selectivity in the association. Partition coefficients between water and aggregates were evaluated by diffusion NMR experiments. Intramolecular distances of ditryptophan isomers associated with chiral aggregates were obtained by ROESY experiments and were used as constraints in molecular mechanics calculations. From these calculations, information on the conformation of the peptides in the chiral aggregates was obtained
Chiral HPLC resolution of neutral pesticides
No full textThe direct HPLC resolution of two synthetic neutral pesticides, Metolachlor and Ethofumesate, was studied on silica gel coated with cellulose tris-(3,5-dimethylphenylcarbamate) derivative (Chiracel OD-H). The specific composition of the mobile phase has allowed the full separation of the four Metolachlor stereoisomers, which had not previously been resolved on other chiral stationary phases. The isomer elution sequence of both resolved pesticides was determined by H-1 NMR and polarimetric analyses. The chromatographic system, coupled with mass-spectrometric detection, was used to determine the isomeric ratio of Metolachlor stereoisomers after incubation in soil
NMR characterization of the polysaccharidic fraction from Lentinula edodes grown on olive mill waste waters
No full textA high-field NMR study of the polysaccharidic fraction extracted from Lentinula edodes mycelium grown on olive mill waste waters is reported. Diffusion-ordered NMR spectroscopy (DOSY) was applied to the polysaccharidic fraction. The results showed the presence of two polysaccharides of different sizes, whose structures were revealed using one- and two-dimensional NMR techniques. These two polysaccharides were identified as xylan and lentina
Structural elucidation of the oxidation product of aminoethylcysteine ketimine decarboxylated dimer by peroxynitrite
No full textAminoethylcysteine ketimine decarboxylated dimer (2) is a natural sulfur compound with antioxidant properties. 2 Inhibits some reactions mediated by peroxynitrite, a strong oxidizing and nitrating agent that reacts with several biomolecules. This work aims to elucidate the structure of the product resulting from the interaction of 2 with peroxynitrite using 1D and 2D NMR experiments and ion trap mass spectrometry. This product is a dimerized form of 2 and is hereafter referred to as 3. During the reactions leading to 2 and during the formation of 3, no chiral selection is operated; all optical isomers are present in D2O and have been evidenced by H-1 NMR methods in D2O plus beta- or gamma-cyclodextrin. (C) 2004 Elsevier Ltd. All rights reserved
C(6)-oxidation followed by C(5)-epimerization of guar gum studied by high field NMR
No full textGuar gum, a a-D-(1f4)-linked D-mannan with R-D galactopyranosyl units attached as side groups, was treated with R-galactosidase, an enzyme that splits off the R-D-galactosyl units to obtain a galactomannan with a low galactose content. The galactose-depleted polysaccharide was then selectively oxidized in C(6) position and epimerized using mannuronan C(5)-epimerases, namely AlgE1, AlgE4, AlgE6, and their mixtures, obtaining new pseudo-alginates. In this paper, we report a full high field 1D and 2D NMR study of guar gum as such and of the galactose-depleted, oxidized and epimerized compounds, respectively. From the 1H NMR spectra, the degree of epimerization, the distribution of mannuronic acid (M) and guluronic acid (G)residues and the average G-block length, NG>1, were obtained. By means of NMR diffusion experiments, it was also shown that no significant degradation of the polysaccharide occurs as a consequence of the epimerization reaction
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
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