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41.
42.
Peter Schwendt Alena Oravcová Jarmila Tyršelová František Pavel?ík Jaromír Marek 《Polyhedron》1996,15(24):4507-4511
The vanadium(V) peroxo phosphato complex K7[V4O4(O2)8(PO4)]·9H2O has been obtained from the KVO3---KH2PO4---KOH---H2O2---H2O---C2H5OH system. The X-ray structural analysis revealed a tetranuclear anionic structure in which two dinuclear [V2O2(O)2)2(μ-η1 : η2-O2)2] units are connected by the μ4-PO4 group. 相似文献
43.
The accuracy, precision, and reproducibility of a rapid method for determination of fluoride in wine, using a fluoride selective ion electrode, were established by a collaborative study involving 12 laboratories, 5 in Europe and 7 in the United States. The laboratories assayed 6 Youden pairs of fluoride-fortified, red and white wine samples with fluoride concentrations ranging from 0.2 to 3.0 mg/L. The relative standard deviations of repeatability ranged from 1.94 to 4.88%; relative standard deviations of reproducibility ranged from 4.15 to 18.40%. HORRAT values ranged from 0.30 to 0.97. The average recovery was 99.97%. Based on the statistical results of this collaborative study, the Study Director recommends that this method be adopted First Action. 相似文献
44.
W. H. S. Brandão A. L. Aguiar L. A. Ribeiro D. S. Galvão J. M. De Sousa 《Chemphyschem》2021,22(7):701-707
Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( and ) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( ). Moreover, it was obtained that Young's modulus (YMod) (750–900 GPa) and ultimate strength (σUS) (120–150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. YMod values obtained for PopNTs are not significantly temperature-dependent. While the σUS values for the showed a quasi-linear dependence with the temperature, the exhibited no clear trends. 相似文献
45.
Alena N. Maratkanova Rishat G. ValeevAlexander V. Syugaev 《Journal of Physics and Chemistry of Solids》2014
Surfactant-assisted ball milling of the Fe powder in paraffin has been used for fabrication of core–shell nanocrystalline particles. The local atomic structure of the bulk and surface layers of the mechanically milled particles has been studied using X-ray absorption spectroscopic techniques with synchrotron radiation from the DORIS storage ring at DESY, Hamburg. Regardless of milling environment composition, the as-prepared powders were shown to be characterized by a significant drop in the EXAFS signal intensity and coordination numbers of the Fe–Fe pairs due to the formation of nanocrystalline state in the particles. It has been shown that an addition of perfluorononanoic acid as a surfactant has a more prominent effect on the structure of the shell layers. The effect is revealed as an appearance of light element atoms (O, F, C) in the local atomic environment of the Fe atoms due to formation of oxide, carbide and adsorbed structures of different types in the particle shell. 相似文献
46.
Ultra‐high pressure LC for astaxanthin determination in shrimp by‐products and active food packaging
A. Sanches‐Silva T. Ribeiro T. G. Albuquerque P. Paseiro R. Sendón A. Bernaldo de Quirós J. López‐Cervantes D. I. Sánchez‐Machado H. Soto Valdez I. Angulo G. P. Aurrekoetxea H. S. Costa 《Biomedical chromatography : BMC》2013,27(6):757-764
Nowadays, there is increasing interest in natural antioxidants from food by‐products. Astaxanthin is a potent antioxidant and one of the major carotenoids in crustaceans and salmonids. An ultra‐high pressure liquid chromatographic method was developed and validated for the determination of astaxanthin in shrimp by‐products, and its migration from new packaging materials to food simulants was also studied. The method uses an UPLC® BEH guard‐column (2.1 × 5 mm, 1.7 µm particle size) and an UPLC® BEH analytical column (2.1 × 50 mm, 1.7 µm particle size). Chromatographic separation was achieved using a programmed gradient mobile phase consisting of (A) acetonitrile–methanol (containing 0.05 m ammonium acetate)–dichloromethane (75:20:5, v/v/v) and (B) ultrapure water. This method was evaluated with respect to validation parameters such as linearity, precision, limit of detection, limit of quantification and recovery. Low‐density polyethylene films were prepared with different amounts of the lipid fraction of fermented shrimp waste by extrusion, and migration was evaluated into food simulants (isooctane and ethanol 95%, v/v). Migration was not detected under the tested conditions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
47.
Dayana Borges Bittar Tiago Augusto Catelani Karina Nigoghossian Hernane da Silva Barud Sidney José Lima Ribeiro Leonardo Pezza 《Analytical letters》2017,50(5):829-841
A colorimetric method based on silver nanoparticles was developed for the determination of melamine in milk. Silver nanoparticles were synthesized without any stabilizer, using sodium borohydride as the reducing agent. Optimization of the variables for the formation of the nanoparticles was performed by factorial design, resulting in stable colloidal silver nanoparticles with a mean diameter of 14.0?±?2.7?nm. Spectrophotometric measurements performed at 475?nm showed a linear range from 0.033 to 1.50?mg?L?1 of melamine with limits of detection and quantification of 0.009 and 0.031?mg?L?1, respectively. The method provided highly sensitive determination of melamine in milk. 相似文献
48.
Expanding the Scope of Hypervalent Iodine Reagents for Perfluoroalkylation: From Trifluoromethyl to Functionalized Perfluoroethyl
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Dr. Václav Matoušek Jiří Václavík Peter Hájek Julie Charpentier Zsófia E. Blastik Ewa Pietrasiak Alena Budinská Prof. Dr. Antonio Togni Dr. Petr Beier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(1):417-424
A series of new hypervalent iodine reagents based on the 1,3‐dihydro‐3,3‐dimethyl‐1,2‐benziodoxole and 1,2‐benziodoxol‐3‐(1H)‐one scaffolds, which contain a functionalized tetrafluoroethyl group, have been prepared, characterized, and used in synthetic applications. Their corresponding electrophilic fluoroalkylation reactions with various sulfur, oxygen, phosphorus, and carbon‐centered nucleophiles afford products that feature a tetrafluoroethylene unit, which connects two functional moieties. A related λ3‐iodane that contains a fluorophore was shown to react with a cysteine derivative under mild conditions to give a thiol‐tagged product that is stable in the presence of excess thiol. Therefore, these new reagents show a significant potential for applications in chemical biology as tools for fast, irreversible, and selective thiol bioconjugation. 相似文献
49.
dos Santos Poli Anne Karoline Hilário Rodrigo Barbosa Gama Adriana Medeiros Baldan Mauricio Ribeiro Gonçalves Emerson Sarmento 《Journal of Solid State Electrochemistry》2019,23(1):33-52
Journal of Solid State Electrochemistry - Polyaniline was electrosynthesized using three voltammetric cycles on carbon fiber felts annealed at 1400, 1600, 2000, and 2300 K. Felts and... 相似文献
50.