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51.
The complexation of chromium by different flavonoid dyes in micellar media has been studied, in particular the reaction between chromium and quercetin. Micellar effects, the reaction pathway proposed and the application of the method to the determination of Cr(VI) and Cr(VI) + Cr(III) mixtures are discussed. 相似文献
52.
Alessandra Sussulini Jerusa S. Garcia Márcia F. Mesko Diogo P. Moraes Érico M. M. Flores Carlos A. Pérez Marco A. Z. Arruda 《Mikrochimica acta》2007,158(1-2):173-180
Two methods of protein extraction for soybean seeds were evaluated in terms of preservation of the metal ions bound to proteins
after the extraction and separation procedures. The proteins were firstly separated according to their molar masses by polyacrylamide
gel electrophoresis. Then, the protein bands were mapped by synchrotron radiation X-ray fluorescence in order to establish
which metal ions were present in each one. Finally, some mapped protein bands were decomposed by microwave-assisted combustion
and Ca, Cu, K, Mg, Mn, and Zn were quantified by inductively coupled plasma mass spectrometry or inductively coupled plasma
optical emission spectrometry. The extraction methods studied were Method A (based on the treatment of ground soybean seeds with hexane and their extraction with Tris–HCl and β-mercaptoethanol) and
Method B (based on the treatment of ground soybean seeds with petroleum ether and their extraction with Tris–HCl, dithiothreitol,
phenylmethanesulfonyl fluoride, sodium dodecyl sulfate and potassium chloride). The best method was Method B, in which a 78% higher extraction efficiency was obtained when compared to Method A. Additionally, the metal-protein interactions were more appropriately preserved when Method B was applied, where the most affected ions were those that are bound weakly to proteins, such as Ca, K, and Mg. 相似文献
53.
Bernd A Simon S Ramirez Bosca A Kippenberger S Diaz Alperi J Miquel J Villalba Garcia JF Pamies Mira D Kaufmann R 《Photochemistry and photobiology》1999,69(2):218-221
Extracts of Hypericum perforatum (St. John's wort) are used in the treatment of depression. They contain the plant pigment hypericin and hypericin derivates. These compounds have light-dependent activities. In order to estimate the potential risk of phototoxic skin damage during antidepressive therapy, we investigated the phototoxic activity of hypericin extract using cultures of human keratinocytes and compared it with the effect of the well-known phototoxic agent psoralen. The absorbance spectrum of our Hypericum extract revealed maxima in the whole UV range and in parts of the visible range. We cultivated human keratinocytes in the presence of different Hypericum concentrations and irradiated the cells with 150 mJ/cm2 UVB, 1 J/cm2 UVA or 3 h with a white light of photon flux density 2.6 mumol m-2 s-1. The determination of the bromodeoxyuridine incorporation rate showed a concentration- and light-dependent decrease in DNA synthesis with high hypericin concentrations (> or = 50 micrograms/mL) combined with UVA or visible light radiation. In the case of UVB irradiation a clear phototoxic cell reaction was not detected. We found phototoxic effects even with 10 ng/mL psoralen using UVA with the same study design as in the case of the Hypericum extract. These results confirm the phototoxic activity of Hypericum extract on human keratinocytes. However, the blood levels that are to be expected during antidepressive therapy are presumably too low to induce phototoxic skin reactions. 相似文献
54.
Gallardo J. Duran A. Garcia I. Celis J.P. Arenas M.A. Conde A. 《Journal of Sol-Gel Science and Technology》2003,27(2):175-183
Sol-gel hybrid organic-inorganic and inorganic SiO2-based protective coatings with and without added 3 m glass particles were developed and tested for their corrosion and wear behavior of an stainless steel substrate (AISI316L). The corrosion resistance greatly increases by incorporating glass particles in the sols. The incorporation of particles in the coatings allows the synthesis of thicker crack-free coatings. On the other hand, the corrosion resistance increases for coatings with a higher organic content obtained at lower sintering temperature. These coatings are also highly stable in saline aqueous solutions. However, the wear resistance is badly affected by the hybrid character of the SiO2 matrix. The optimum coating process in terms of corrosion and wear resistance, appears to be a hybrid system with a dense SiO2 network achieved at intermediate sintering temperatures. 相似文献
55.
Blay G Bargues V Cardona L Collado AM Garcia B Munoz MC Pedro JR 《The Journal of organic chemistry》2000,65(7):2138-2144
Hydroxyester 2, easily obtained from santonin (1), has been transformed into 10 alpha-hydroxyguai-3-en-8,12-olide 6, a good intermediate for the synthesis of natural 8,12-guaianolides. Compound 6 was obtained from 2 by photochemical rearrangement of its acetyl derivative 7, stereoselective hydrogenation on Pd/C, reduction, regioselective elimination, hydrolysis, and lactonization. The synthesis of the natural guaianolides 3-5 was carried out in two sequences in which the regioselective elimination of a hydroxyl group at C10 with triflic anhydride or SOCl2 to afford, respectively, the endo or exo double bond on C10 and the regioselective opening of the C3-C4 alpha-epoxide were the key steps. 相似文献
56.
W. Klaus M. E. Garcia K. H. Bennemann 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,35(1):43-49
The short-time behavior of small Hg n clusters immediately after single or double ionization is studied. We calculate self-consistently the ground state electronic energyE of ionized Hg n clusters. Upon ionization changes of the potential energy surface (PES) occur, which govern the atomic motion in the cluster. These changes depend on cluster size and charge and are determined by the interplay between the localization of the holes within an ionic core and the polarization energy of the neutral rest of the cluster. In the case of single ionization of the cluster the PES results mainly from hole delocalization. In contrast, in the case of double ionization the PES is governed almost only by strong environment polarization. We use our theory to explain the physical origin of the oscillations in the ionization cross-section of singly and doubly excited Hg n clusters observed in recent pump-probe experiments. 相似文献
57.
J. V. Sinisterra F. Garcia Blanco M. Iglesias J. M. Marinas 《Reaction Kinetics and Catalysis Letters》1984,25(3-4):277-282
A general and repetitive method to determine the base strength and number of basic sites of catalysts with low surface area is reported. The nature of the titrating agent is discussed. The nature of the active sites of a Ba(OH)2 catalyst with low surface area is discussed.
. . Ba(OH)2, .相似文献
58.
Variations of densities and viscosities with temperature and composition are reported for binary liquid mixtures containing propionic acid+aniline (I),+o-toluidine (II),+o-anisidine (III), and+o-chloroaniline (IV). Entropies S
m and enthalpies H
m of activation as functions of the composition of the mixtures, as well as free energies of activation G
m at 10, 20, 30, 40, and 50°C and different compositions were calculated by means of Eyring's equation. The formation of activated complexes between the components of these binary mixtures is postulated and claimed to result from acid-base and hydrogen bonding exchange interactions. 相似文献
59.
Neutral oxorhenium(V) complexes with thiosemicarbazones derived from 2‐pyridine formamide, HL1, are formed when [ReOCl3(PPh3)2] reacts with equimolar amounts of the ligands. Reduction of the metal and the formation of rhenium(III) complexes of the composition [Re(L1)2]+ occurs when an excess of thiosemicarbazones is used and the reaction is performed in boiling toluene for a prolonged period of time. The thiosemicarbazones deprotonate and act as tridentate ligands as has been confirmed by an X‐ray structure of [ReOCl2(L1b)], where HL1b is 2‐pyridineformamide‐N(4)‐ethylthiosemicarbazone and the ligand occupies the equatorial coordination sphere of the complex together with one of the chloro ligands. 相似文献
60.