943 resultados para Reactive species of oxygen


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The insoluble species of Gd (III) in human blood plasma were investigated by computer simulation. The distribution of the Gd (I) species was obtained. It was found that most of the Gd (III) ions were bound to phosphate to form precipitate GdPO4 at the concentration of 1. 000 x 10(-7) mol/L and when the concentration of the Gd (III) increased to 3. 750 x 10(-4) mol/L, in excess of the concentration of phosphate, the Gd (III) ions were bound to carbonate to form another kind of precipitate, Gd-2 (CO3)(3).

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The effect of PMR-polyimide(POI) as the interfacial agent on the interface characteristics, morphology features and crystallization of poly (ether sulfone) /poly (phenylene sulfide) (PES/PPS) and poly(ether ether ketone)/poly (ether sulfone) (PEEK/PES) partly miscible blends were investigated by means of the scanning electron microscopy, WAXD and XPS surface analysis. It is found that the interfacial adhesion was enhanced remarkably, the size of the dispersed phase particles was reduced significantly and the miscibility was improved by the addition of POI. During melt blending cross-link and/or grafting reaction of POI with PES, PEEK and PPS homopolymers was detected, however the reaction activity of POI with PPS was much higher than that of PES and PEEK. It was also found that POI was an effective nucleation agent of the crystallization of PPS.

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In this paper, blends of Nylon 6,6 with the liquid crystal polymer Vectra A950 are considered; specifically we focused our attention on Nylon 6,6 modifications by interchange reactions that can occur in the melt, as a function of mixing conditions and blend compositions. Two matrix samples have been used, characterised by a slightly different relative amount of amine and carboxylic end groups, being the latter predominant in both cases. The dried polymers Nylon 6,6/Vectra, combined in weight ratios between 95/5 and 50/50, were subjected to reactive blending with different methods (single-screw extruder, Brabender, pyrex reactor). Pure Nylon samples have been also investigated as reference materials. The soluble Nylon 6,6-rich fraction of each blend was separated from the insoluble Vectra-rich one and used for molecular and spectroscopic characterisations. Thermal and morphological analyses, as well as testing of tensile properties, were carried out on the blends. Evidences of the occurrence of interchange reactions are given and the most probable ones are suggested. (C) 2001 Elsevier Science Ltd. All rights reserved.

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Rare earth (III)-Asp-Arg and Ca(II)-Asp-Arg systems were studied by potentiometric titration under physiological conditon. The species of each system were determined. The distribution of Tb (III) and Ca(II) species was discussed, as well as in the quaternary system of Tb(III)-Ca(II)-Asp-Arg.

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Composite membrane modified electrodes were prepared by electrochemical deposition of platinum particles in a poly(o-phenylenediamine) (PPD) him coated on glassy carbon (GC) electrodes. The modified electrodes showed high catalytic activity towards the reduction of oxygen and hydrogen peroxide. A four-electron transfer process predominated the reduction process. The pH dependence and the stability of the electrodes were also studied.

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It was found that vitamin B-12 could be strongly adsorpted on the anodized glassy carbon electrode to form a vitamin Thy-modified glassy carbon electrode. The modified electrode is stable in a wide pH range. The electrochemical characteristics of the modified electrode were studied in details. In addition, it was found that the reduction of oxygen could be catalyzed by the modified electrode to form H2O2. An EC mechanism was suggested for the process, and the follow up chemical reaction might he the rate determined step.

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Two systems of La2-xSrxCuO4+/-lambda and La2-xThxCuO4+/-lambda, mixed oxides with K2NiF4 structure were synthesized. The compositions and structures of the catalysts were characterized by means of XRD, XPS, chemical analysis and so on. The catalytic behavior for the direct decomposition of NO has been investigated. The results show that the catalytic activity is closely related to the oxygen vacancy and lower valence metallic ion in the direct decomposition of NO. The presence of oxygen vacancy is necessary for mixed oxide to have steady activity in NO decomposition.

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The mechanism of oxygen reduction on polycobaltprotoporphyrin IX dimethyl ester (PolyCoPP) film has been studied by using the rotating ring(Au)-disk(pyrolytic graphite, PG) electrode (RRDE) technique. The PolyCoPP/PG electrode promotes the oxygen reduction via two-electron process which produces peroxide as a main product in O-2-saturated 0.1 mol.dm(-3) NaOH. Once HO2- has been formed, no further reduction to OH- takes place at the disk. When the disk potential shifts to more negative, either the direct reduction of O-2 to OH- or the further reduction of HO2- to OH- occurs.

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The oxygen permselectivity of a poly[1-(trimethylsilyl)-1-propyne) (PTMSP) membrane was drastically improved by plasma polymerization of fluorine-containing monomers. The effects of such plasma polymerization conditions as deposition time, plasma power an

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Karyotype and chromosomal location of the major ribosomal RNA genes (rDNA) were studied using fluorescence in situ hybridization (FISH) in five species of Crassostrea: three Asian-Pacific species (C. gigas, C. plicatula, and C. ariakensis) and two Atlantic species (C. virginica and C. rhizophorae). FISH probes were made by PCR amplification of the intergenic transcribed spacer between the 18S and 5.8S rRNA genes, and labeled with digoxigenin-11-dUTP. All five species had a haploid number of 10 chromosomes. The Atlantic species had 1-2 submetacentric chromosomes, while the three Pacific species had none. FISH with metaphase chromosomes detected a single telomeric locus for rDNA in all five species without any variation. In all three Pacific species, rDNA was located on the long arm of Chromosome 10 (10q)-the smallest chromosome. In the two Atlantic species, rDNA was located on the short arm of Chromosome 2 (2p)-the second longest chromosome. A review of other studies reveals the same distribution of NOR sites (putative rDNA loci) in three other species: on 10q in C. sikamea and C. angulata from the Pacific Ocean and on 2p in C. gasar from the western Atlantic. All data support the conclusion that differences in size and shape of the rDNA-bearing chromosome represent a major divide between Asian-Pacific and Atlantic species of Crassostrea. This finding suggests that chromosomal divergence can occur under seemingly conserved karyotypes and may play a role in reproductive isolation and speciation.

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A molecular phylogeny is presented for the subfamily Dorippinae (including 9 individuals, representing 5 species and 4 genera), based on the sequence data from 16S rRNA gene. Two-cluster test between lineages in these phylogenetic trees has been performed. On the basis of rate constancy, the rate of nucleotide substitutions of 16S rDNA sequence data is estimated as 0.27% per million years. The analysis strongly supports the recognition of the Dorippinae as a monophyletic subfamily. Phylogenetic tree indicates that the subfamily Dorippinae is divided into two main clades, and genus Dorippe appears basal in the subfamily, diverging from other species 36.6 Ma ago. It is also clear that the Heikea is closely related to the genus Neodorippe. The divergence time between them is 15.8 Ma.

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The distribution of iodine in various biological macromolecules in Sargassum kjellmanianum was studied using neutron activation analysis combined with chemical and biochemical separation techniques. The results indicate that iodine is mainly bound with protein, part of iodine with pigment and polyphenol, and little with polysaccharides, such as algin, fucoidan and cellulose. This result is significant for the mechanism of enriching iodine of algae and utilization of alga iodine.

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The concentrations of five major and 28 trace elements in 35 marine algae collected along the coast of China were determined by instrumental neutron activation analysis. The concentrations of halogens, rare earth elements and many transition metal elements in marine algae are remarkably higher than those in terrestrial plants. The concentration factors for 31 elements in all collected algae were calculated, those for tri- and tetra-valent elements were higher than those of the mono- and di-valent elements in marine algae. The biogeochemical characteristics of inorganic elements in marine algae were investigated. In addition, the seasonal variation of inorganic elements in Sargassum kjellmanianum was also studied. (C) 1998 Elsevier Science B.V. All rights reserved.

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Members of Chrysochromulina are important components of marine phytoplankton. Four species in this genus are reported in China for the first time, namely Chrysochromulina cymbium Leadbeater & Manton, C hirta Manton, C. megacylindra Leadbeater, C. pringsheimii Parke & Manton. Their ultrastructures were studied under electron microscope.