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‣ Platinum catalysts supported on MWNT for catalytic wet air oxidation of nitrogen containing compounds

García, Juan; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, Joaquim
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
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Multi-walled carbon nanotubes (MWNT) activated by nitric acid oxidation were used to prepare supported platinum (1% Pt) catalysts by the excess solution impregnation method. Three different platinum precursors were used to prepare the impregnation solutions, namely diiodo dicarbonyl platinum(II) [PtI2(CO)2], dimethyl (1,5-cyclooctadiene) platinum(II) [Pt(CH3)2(C8H12)] and hydrogen hexachloroplatinate(IV) hexahydrate H2PtCl6 6H2O. The catalysts were characterized by transmission electron microscopy (TEM) analysis and H2 chemisorption. They were tested in the catalytic wet air oxidation (CWAO) of aniline aqueous solutions (200 8C and 6.9 bar of oxygen partial pressure). The Pt/MWNT catalyst prepared from H2PtCl6 6H2O showed the best performance with respect to combined activity and selectivity for aniline conversion to non-organic compounds. This catalyst was used in CWAO (150 8C and 6.9 bar of oxygen partial pressure) of aqueous solutions of various textile dyes such as the monoazo dye chromotrop 2R (C2R), the diazo dye erionyl red B (ERB) and the triazo dye solophenyl green BLE (SG) 155%. It was found that the selectivity for dye removal decreased in the order diazo > monoazo > triazo. The CWAO of a textile wastewater was also performed using the same catalyst and identical reaction conditions. Complete color removal and 51.2% TOC abatement was obtained under these conditions.

‣ Platinum nanoparticles embledded in layer-by-layer films from SnO2/polyallylamine for ethanol electrooxidation

BARRETTO, Caroline B.; PARREIRA, Renato L. T.; GONCALVES, Rogria R.; AZEVEDO, Dayse C. de; HUGUENIN, Fritz
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
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Self-assembled films from SnO2 and polyallylamine (PAH) were deposited on gold via ionic attraction by the layer-by-layer(LbL) method. The modified electrodes were immersed into a H2PtCl6 solution, a current of 100 mu A was applied, and different electrodeposition times were used. The SnO2/PAH layers served as templates to yield metallic platinum with different particle sizes. The scanning tunnel microscopy images show that the particle size increases as a function of electrodeposition time. The potentiodynamic profile of the electrodes changes as a function of the electrodeposition time in 0.5 mol L-1 H2SO4, at a sweeping rate of 50mVs(-1). Oxygen-like species are formed at less positive potentials for the Pt-SnO2/PAH film in the case of the smallest platinum particles. Electrochemical impedance spectroscopy measurements in acid medium at 0.7 V show that the charge transfer resistance normalized by the exposed platinum area is 750 times greater for platinum electrode (300 k Omega cm(2)) compared with the Pt-SnO2/PAH film with 1 min of electrodeposition (0.4 k Omega cm(2)). According to the Langmuir-Hinshelwood bifunctional mechanism, the high degree of coverage with oxygen-like species on the platinum nanoparticles is responsible for the electrocatalytic activity of the Pt-SnO2/PAH concerning ethanol electrooxidation. With these features...

‣ Estudo da adsorção e eletro-oxidação de etanol sobre platina por espectroscopia de geração de fótons de soma de frequências; On the adsorption and electro-oxidation of ethanol over platinum as probed by sum frequency generation spectroscopy

Gomes, Janaina Fernandes
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/11/2007 Português
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A possível aplicação de etanol como combustível em células a combustível de oxidação direta de álcoois continua motivando pesquisas voltadas à compreensão do mecanismo da eletro-oxidação de etanol. Notoriamente, a eletro-oxidação de etanol sobre platina ocorre por diferentes caminhos paralelos de reação que conduzem à formação de acetaldeído, ácido acético e CO2. No entanto, o mecanismo desta reação permanece incerto. Estudos prévios baseados em técnicas espectroscópicas lineares contribuíram significativamente para a elucidação da reação de eletro-oxidação de etanol sobre platina. Contudo, a desvantagem de usar este tipo de sonda espectroscópica é que não se podem discriminar os traços de espécies adsorvidas na superfície das contribuições de espécies em solução. Visto que a geração de fótons de soma de freqüências (SFG) é um processo não-linear de segunda-ordem que ocorre na interface entre dois meios centrossimétricos, onde a simetria de inversão é quebrada, a espectroscopia SFG pode ser usada como uma ferramenta poderosa para obter espectros vibracionais das espécies adsorvidas sem a contribuição do seio da solução. Neste trabalho, a interface etanol-platina em meio ácido é investigada por espectroscopia SFG infravermelho-visível. Nosso principal objetivo é documentar os intermediários adsorvidos presentes durante a eletro-oxidação do etanol. Novas evidências de intermediários adsorvidos da oxidação de etanol sobre platina...

‣ Determinação da estrutura de alguns complexos de estanho e de platina; Crystal structure of complexes of tin and platinum

Azevedo Junior, Walter Filgueira de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/09/1992 Português
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Foram determinadas as estruturas de três complexos de Platina, dois complexos de estanho e um ligante orgânico. AS intensidades das reflexões foram medidas com umdifratômetro CAD-4. As estruturas foram resolvidas por métodos diretos ou pela função de Patterson e refinadas por mínimos quadrados. Bis (fenilsulfonil) etano, C14H14(SO2)2, foi obtido durante as tentativas de sintetizar ligantes para serem usados na complexação com diversos organo-estânicos, o cristal pertence ao sistema moniclínico, P21/n, a= 8,495(3), b= 10,159(1), c= 9,072(1)Å, β= 116,23(2) °, V= 702,3(3) ޵, Z= 2, dcalc= 1,467g.cm-3. Cis-dicloro[meso-1,2-bis(n-propilsulfinil)etano]platina(II), PtCl2. (PrSO)2C2H4, o cristal pertence ao sistema ortorrômbico, P212121, a= 7,360(2), b= 9,793(2), c= 19,369(2)Å, V= 1396,1(4)޵, Z= 4, dcalc= 2,25g.cm-3. Trans-diclorol[(trietilfosfina) (2-metilsulfinil)piridina)]platina(II), Et3PPtCl 2.PySOMe, o cristal pertence ao sistema monoclínico, P21/c, a= 8,067(3), b= 8,5184(9), c= 25,592(3)Å, β= 92,000(9)°, V= 1757,6(7)޵, Z= 4, dcalç= 1,98g.cm-3. Trans-dicloro [(trietilfosfina)(2-n-propilsulfinil)piridina)]platina(II), Et3PPtCl2.PySOPr, o cristal pertence ao sistema triclínico, P-1...

‣ Eletrocatálise em regime oscilatório: eletro-oxidação de moléculas orgânicas pequenas em eletrodos bimetálicos de platina; Electrocatalysis under Oscillatory Regim: Electro-oxidation of Small Organic Molecules on Modifiers Platinum Electrodes

Perini, Nickson
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/02/2015 Português
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A auto-organização é uma das principais características de sistemas naturais. Os fenômenos auto-organizados podem emergir em sistemas suficientemente afastados do equilíbrio termodinâmico. A não-linearidade intrínseca aos sistemas eletroquímicos, permite inúmeros exemplos de comportamento complexo, sendo, grande parte, em eletrocatálise. Apesar do considerável progresso no entendimento dos aspectos mecanísticos da eletro-oxidação oscilatória de moléculas orgânicas pequenas, aparentemente não existe nenhum estudo sistemático do impacto de modificadores superficiais na dinâmica oscilatória. Nesta tese de doutorado, a eletro-oxidação oscilatória do ácido fórmico em bimetálicos de platina, com estanho ou bismuto, é comparada com aquela obtida em platina policristalina. A modificação da superfície afeta drasticamente a dinâmica oscilatória. As oscilações auto-organizadas de potencial foram usadas como sonda para a atividade eletrocatalítica dos eletrodos bimetálicos de platina. Em intermetálicos ordenados de platina e estanho, a velocidade de envenenamento diminui significativamente, o que retarda a desativação da superfície e promove oscilações de longa duração, sem precedentes, com estabilização de mais de 2200 ciclos. Isto corresponde a 30-40 vezes mais estável com relação ao eletrodo de platina. A presença de estanho na superfície do eletrodo tem grande impacto na produção de CO2...

‣ Platinum-coated nanostructured oxides for active catalytic electrodes

Bueno, Paulo R.; Joanni, Ednan; Savu, Raluca; Garcia, Lourdes M.; Goes, Marcio S.; Fabregat-Santiago, Francisco; Bisquert, Juan
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 58-61
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); In this work we propose the use of platinum-coated nanostructured oxides for improving the redox rate of active electrodes for applications in catalysts for water splitting, fuel cells, organic depollution, etc. In order to test this concept, CaCu(3)Ti(4)O(12) nanorods were grown by magnetron sputtering over Si/SiO(2)/Ti/Pt substrates and coated with a platinum layer using the same technique. The performance of this active electrode was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Other Pt films (both dense and porous) deposited on oxidized silicon, and platinum-coated FTO-glass, when tested under the same conditions, were less efficient. The charge transfer resistance and the capacitance of one dimensional platinum-coated nanostructured electrodes were at least one order of magnitude better than those measured for platinum-coated FTO-glass. (C) 2011 Elsevier B.V. All rights reserved.

‣ Botryoidal platinum, palladium and potarite from the Bom Sucesso stream, Minas Gerais, Brazil: Compositional zoning and origin

Fleet, M. E.; De Almeida, C. M.; Angeli, N.
Fonte: Mineralogical Associação Canada Publicador: Mineralogical Associação Canada
Tipo: Artigo de Revista Científica Formato: 341-355
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Platinum-Pd nuggets from the Born Sucesso stream alluvium Minas Gerais, Brazil. have been investigated by electron-probe microanalysis. The nuggets attain 1 mm in maximum dimension and have a botryoidal habit, with pronounced compositional core-to-margin zoning of internal structures, Although there is a wide variation in internal morphology and individual zones vary markedly in thickness (<1-100 mum), a typical composite arborescent nugget comprises a broad irregular core region of massive auriferous Pd-Hg alloy (potarite delta-PdHg) or cavity space + relict potarite enclosed by a narrow zone of platiniferous, palladium or alloy of near Pt50Pd50 composition, and is progressively oscillatory zoned by palladian platinum, with growth eventually enveloping the whole botryoidal colony, to a narrow rim of palladian platinum or pure platinum. Other nuggets comprise an arborescent to dendritic core of auriferous potarite, a broad internal zone of either pure platinum or palladian platinum, and a narrow rim of platinum, the mineral palladium contains up to about 65 at.% Pd; this is the first detailed modern confirmation of palladium in its type locality. Auriferous potarite ranges in composition from similar toPd(3)Hg(2) to near Pd(Hg,Au). The origin of these nuggets remains unclear...

‣ Platinum surface modification with cerium species and the effect against the methanol anodic reaction

Bonilla, S. H.; Carvalho, J. G. A.; Almeida, C. M. V. B.; Giannetti, B. F.; Zinola, C. F.
Fonte: Elsevier B.V. Sa Publicador: Elsevier B.V. Sa
Tipo: Artigo de Revista Científica Formato: 203-210
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Spontaneous deposition and electrochemical deposition by potential perturbation programs were used to place cerium-containing species on platinum surfaces in acid solution. Cyclic voltammetric profiles of cerium-modified platinum surfaces obtained after potentiostatic or potentiodynamic procedures (applied in the true hydrogen evolution region) differ from those recorded after spontaneous methods. However, the catalytic effects are nearly the same on these cerium-modified platinum surfaces for methanol electrooxidation, i.e. lower onset potential values for the anodic reaction. Besides, a different electrocatalytic effect was observed at large positive potentials on methanol oxidation due to the cerium oxide capability of oxygen storage. This effect is observed on platinum modified by a drastic potentiostatic procedure (by applying -2.0 V) in cerium(IV) acid solution. (C) 2008 Elsevier B.V. All rights reserved.

‣ The solid solution between platinum and palladium in nature

Bindi, L.; Zaccarini, F.; Garuti, G.; Angeli, N.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 269-274
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Chemical and structural data are reported for platinum-palladium intermediates from two nuggets found at Corrego Bom Sucesso, Minas Gerais, Brazil. Three grains with simple stoichiometries (i.e. PtxPd1 -x with x ∼0.67, ∼0.5 and ∼0.33, which correspond to Pt2Pd, PtPd and PtPd2, respectively) were characterized by single-crystal X-ray diffraction and electron-probe microanalysis. In the absence of single-crystal data it might be tempting to hypothesize that such simple stoichiometries represent distinct mineral species, however structural analyses show that all of the phases are cubic and crystallize in space group Fm3̄m. They are, therefore, natural intermediates in the palladium-platinum solid solution. Reflectance and micro-hardness values are reported for the samples and a comparison with the pure metallic elements made. On the basis of information gained from the chemical and structural characterization it can be concluded that there is a complete solid solution between Pt and Pd in nature. These findings corroborate results from experiments on synthetic compounds. © 2013 The Mineralogical Society.

‣ Simultaneous determination of palladium, platinum and rhodium by on-line column enrichment and HPLC with 2,4-dihydroxybenzylidenethiorhodanine as pre-column derivatization reagent

Dong,Xuechang; Han,Yong; Hu,Qiufen; Chen,Jing; Yang,Guangyu
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2006 Português
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A new method for the simultaneous determination of palladium, platinum and rhodium ions as metal-DHBTR chelates was developed. The palladium, platinum and rhodium ions were pre-column derivatized with 2,4-dihydroxybenzylidenethiorhodanine (DHBTR) to form colored chelates. The Pd-DHBTR, Pt-DHBTR and Rh-DHBTR chelates can be absorbed onto the front of the enrichment column when they were injected into the injector and sent to the enrichment column with a 0.05 mol L-1 sodium acetate-acetic acid buffer solution (pH 3.5) as mobile phase. After the enrichment had finished, by switching the six ports switching valve, the retained chelates were back-flushed by mobile phase and traveling towards the analytical column. These chelates separation on the analytical column was satisfactory with 62% (v/v) acetonitrile (containing 0.05 mol L-1 of pH 3.5 sodium acetate-acetic acid buffer salt and 0.1% (m/v) of tritonX-100) as mobile phase. The Limits of detection of palladium, platinum and rhodium are 3.6 ng L-1, 3.2 ng L-1 and 4.5 ng L-1, respectively. This method was applied to the determination of palladium, platinum and rhodium in water, urine and soil samples with good results.

‣ Novel 3-(aminomethyl)naphthoquinone mannich base-platinum(IV) complexes: synthesis, characterization, electrochemical and cytotoxic studies

Silva,Gustavo B. da; Neves,Amanda P.; Vargas,Maria D.; Alves,Wagner A.; Marinho-Filho,José D. B.; Pessoa,Cláudia; Moraes,Manoel O.; Costa-Lotufo,Letícia V.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2013 Português
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Three novel platinum(IV) complexes cis,cis,trans-[Pt(HL1-3)Cl2(OH)2] 1b-3b (HL = 2-hydroxy-3-[(R¹-amino)(pyridin-2-yl)methyl]-1,4-naphthoquinone, R¹ = n-butyl, HL1; n-heptyl, HL2 and n-decyl, HL3) have been obtained from the oxidation of the respective precursors cis-[Pt(HL1-3)Cl2] 1a-3a. Cyclic voltammetry studies of 1b-3b in MeCN showed the quasi-reversible naphthoquinonate (NQO-, i.e. , L-) redox process and irreversible process attributed to the reduction of the Pt4+/Pt2+ pair, at potentials about 400 mV less negative than for the cisplatin precursor cis,cis,trans-[Pt(NH3)2Cl2(OH)2]. Hydrogen bond interaction between the naphthoquinone 2-hydroxyl group and an axially coordinated hydroxide ligand in 1b-3b has been proposed to favor the Pt4+/Pt2+ reduction. The cytotoxicity studies against four human cancer cell lines have shown that in general the platinum(IV) and platinum(II)derivatives exhibit the same cytotoxic profile and are all more active than cisplatin. The lowest in vitro IC50 values have been observed for 2b-3b, which bear ligands with the largest R¹ groups (HL2-HL3) being the most lipophilic. Furthermore similar IC50 values for platinum(II) and platinum(IV) complexes of the same ligands have been associated with rapid in vitro reduction of the latter complexes to afford 1a-3a.

‣ Platinum uptake from chloride solutions using biosorbents

Morcali,Mehmet Hakan; Zeytuncu,Bihter; Yucel,Onuralp
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2013 Português
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Present work investigates platinum uptake from synthetically prepared, dilute platinum-bearing solutions using biomass residues, i.e. pistachio nut shell and rice husk, which are abundant in Turkey, and provides a comparison between these two biosorbents. Effects of the different uptake parameters, sorbent dosage, contact time, temperature and pH of solution on platinum uptake (%) were studied in detail on a batch sorption. Before the pistachio nut shell was activated, platinum uptake (%) was poor compared to the rice husk. However, after the pistachio nut shell was activated at 1000 °C under an argon atmosphere, the platinum uptake (%) increased two-fold. The pistachio nut shell (original and activated) and rice husk were shown to be better than commercially available activated carbon in terms of adsorption capacity. These two sorbents have also been characterized by FTIR and SEM. Adsorption equilibrium data best complied with the Langmuir isotherm model. Maximum adsorption capacities, Qmax, at 25 °C were found to be 38.31 and 42.02 mg.g- 1for the activated pistachio nut shell and rice husk, respectively. Thermodynamic calculations using the measured ∆H°, ∆S° and ∆G° values indicate that the uptake process was spontaneous and endothermic. The experimental data were shown to be fit the pseudo-second-order kinetic model.

‣ The Implementation of a Coherent Memory Abstraction on a NUMA Multiprocessor: Experiences with PLATINUM (Revised)

Cox, Alan L. ; Fowler, Robert J.
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
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PLATINUM is an operating system kernel with a novel memory management system for N on-Uniform Memory Access (NUMA) multiprocessor architectures. This memory management system implements a coherent memory abstraction. Coherent memory is uniformly accessible from all processors in the system. When used by applications coded with appropriate programming styles it appears to be nearly as fast as local physical memory and it reduces memory contention. Coherent memory makes programming NUMA multiprocessors easier for the user while attaining a level of performance comparable with hand-tuned programs. This paper describes the design of the PLATINUM memory management system with emphasis on the implementation of coherent memory and the factors that affect its performance. We measure the cost of basic operations implementing coherent memory. We also measure the performance of a set of application programs running on PLATINUM. Finally, we comment on the interaction between architecture and the coherent memory system. PLATINUM currently runs on the BBN Butterfly Plus (TM) Multiprocessor.

‣ Platinum terpyridine acetylide complexes for photo-induced charge separation and the photogeneration of hydrogen from aqueous media

Jarosz, Paul R. (1981 - ); Eisenberg, Richard Alan
Fonte: University of Rochester. Publicador: University of Rochester.
Tipo: Tese de Doutorado Formato: Number of Pages:xv, 133 leaves
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Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2008.; Platinum terpyridyl acetylides are well-studied complexes with many favorable properties for the design of molecular assemblies to achieve photo-induced charge separation. The design and synthesis of such compounds is facilitated by the directionality of charge transfer in the excited state, with the energetic electron residing in the π* of the terpyridyl ligand. This thesis describes the synthesis of several platinum terpyridyl acetylide complexes in the pursuit of efficient charge transfer dyads and triads. Also described are efforts to couple these charge transfer complexes to catalysts to drive the reduction of protons in aqueous media. The most successful of this work is a system which employs a platinized titanium dioxide catalyst which is sensitized by several of the platinum terpyridyl acetylide compounds described. Chapter 2 describes a continuation of previous efforts to make molecular triads which employ pyridinium acceptors, including the viologen moiety. These efforts required a modification of synthetic methodology to accommodate the sensitivity of these pyridinium compounds to nucleophiles. Chapter 3 illustrates subsequent efforts to design more chemically robust complexes for photo-induced charge transfer. Nitrophenyl groups were proposed as acceptors on the basis of results obtained previously for a functional platinum terpyridyl acetylide triad with a nitrostilbene acceptor. These syntheses rely on a Suzuki coupling to halogenated nitrobenzenes...

‣ Zytotoxische Effekte von Platin(IV)chloridauf Zellstämme aus Leber- und Nierengewebe; Cytotoxic effects of platinum(IV)chlorideon cell lines of liver- and kidney cells

Lenz Martin
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
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Einleitung: Durch zunehmende Verwendung von Katalysatoren steigt die weltweite Umweltbelastung durch PtCl4. Auch der verstärkte Einsatz von aktivierten Platinkomplexen in der Antitumortherapie trägt zu diesem Problem bei. Bekannte Gesundheitsrisiken sind unter anderem das Platin-Asthma, Sekundärtumore und primäre Zellschädigung bei der Behandlung mit Platinkomplexen in der Tumortherapie. Dringender Forschungsbedarf bestand jedoch auf dem Gebiet der wasserlöslichen Platinsalze und deren Akut- und Langzeittoxizität, weswegen diese Studie erstellt wurde. Methoden: Es wurden jeweils 2 etablierte Zellreihen aus Leber,(Chang Liver, Hep.G 2) und Nierengewebe,(OK, A-498) untersucht. Die Zellkulturen wurden über 24h und 72h kontinuierlich PtCl4-exponiert und die Zellvitalität daraufhin mit MTT-Test und NR-Test bestimmt. Für die Langzeittoxizität wurden zusätzlich noch die Migrationsfähigkeit und die Klonierungseffizienz bestimmt. Ergebnisse: Die Ergebnisse der Studie zeigen bei der durch den MTT-Test ermittelten 24h Zytotoxizität eine deutliche Abnahme der Zellvitalität, jedoch keine Organspezifität. Der Neutralrot-Essay kennzeichnet dagegen eine Reduktion der Zellzahl nur bei den Leberzellreihen. Bei den Nierenzellreihen ist keine Veränderung der Zellzahl nachweisbar. Bei der 72h Exposition ist für beide Testansätze eine deutliche Organspezifität nachweisbar (ED50(72h)=60µg/ml für Leberzellen...

‣ Effekte des Schwermetalls Platin auf die frühe Individualentwicklung des Zebrabärblings (Danio rerio) und der Paradies-Schnecke (Marisa cornuarietis); Effects of the heavy metal platinum on the early development of the zebrafish (Danio rerio) and the ramshorn snail (Marisa cornuarietis)

Osterauer, Raphaela
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
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Seit der Einführung des Kfz-Katalysators werden die Platingruppenelemente Platin, Palladium und Rhodium vermehrt in die Umwelt eingetragen und gelangen u.a. über Straßenabflussgewässer in aquatische Ökosysteme. Die vorliegende Arbeit untersuchte die Effekte verschiedener Konzentrationen des löslichen Platinchlorids (0, 0.1, 10, 50, 100 und 200 µg/L PtCl2) auf verschiedene Endpunkte während der frühen Individualentwicklung der beiden Süßwasserorganismen Zebrabärbling (Danio rerio) und Paradies-Schnecke (Marisa cornuarietis). Bei beiden Organismen wurden die Bioakkumulation von Platin, Effekte auf die Embryonalentwicklung, die Induktion von Stressproteinen (Hsp70) und histopathologische Gewebe- und Organveränderungen untersucht sowie gentoxische Untersuchungen durchgeführt. Es zeigte sich, dass beide Organismen Platin stark anreicherten. Bei D. rerio wurden Bioakkumulationsfaktoren (BAF) von 5-55 und bei M. cornuarietis sogar BAF von 218-714 gefunden. Die Embryotests ergaben für beide Organismen eine Verzögerung der Herzschlagrate und der Schlupfrate. Bei M. cornuarietis war weiterhin die Augenentwicklung verzögert sowie das Gewicht reduziert. Histopathologische Untersuchungen ergaben bei D. rerio Effekte von Platin auf Leber und Darm...

‣ Crystal and molecular structure of a dinuclear ortho-metalated platinum ylid complex, [Pt(u-Cl)CH3COCHP(C6H4)(C6H5)2]2*2CDCl3

Illingsworth, Marvin; Teagle, John; Burmeister, John; Fultz, William; Rheingold, Arnold
Fonte: The American Chemical Society: Organometallics Publicador: The American Chemical Society: Organometallics
Tipo: Abstract Formato: 31371 bytes; application/pdf
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The product of the reaction between PtCl2 and APPY (APPY = acetylmethylenetriphenylphosphorane, (C6H5)3PCHC(O)CH3), upon heating a 1:2 mole ratio at reflux in acetonitrile for 44 h, was originally formulated as Pt(APPY)2C12 (1) on the basis of elemental analysis and infrared and proton NMR spectral data. However, this product has now been shown by X-ray crystallography to have undergone orthometalation of an APPY ligand and dimerization to form [Pt(u-Cl)CH3COCHP(C6H4)(C6H6)2]2 (2). The APPYH+Cl- formed in the process was identified by its IR, lH, 13C, and 31P NMR spectra and removed by washing the original sample with water. Yellow monoclinic crystals of compound 2 and two molecules of deuteriochloroform, space group C62H-C2/c were obtained by slow evaporation of a deuteriochloroform solution of the original reaction product. The unit-cell parameters at 26 degrees C are a = 21.33 (1) A, b = 18.453 (3) A, c = 14.337 (6) A, beta = 122.93 (2)O, and Z = 4. The structure has been refined to an R index on F of 0.070 for 3214 observations and 263 parameters. The two platinum atoms and the two chlorine atoms of compound 2 are planar, due to a crystallographically imposed inversion center (i) located between the two platinum atoms and the two bridging chlorine atoms. The coordination about each of the platinum atoms is square planar with a platinum-to-platinum nonbonding distance of 3.599 A. The two deuteriochloroform molecules are weakly interacting with the carbonyl oxygen of the ortho-metalated APPY ligand...

‣ Kinetics and Mechanism for Reversible Chloride Transfer between Mercury(II) and Square-Planar Platinum(II) Chloro Ammine, Aqua, and Sulfoxide Complexes. Stabilities, Spectra, and Reactivities of Transient Metal-Metal Bonded Platinum-Mercury Adducts

Groning, Osten; Sargeson, Alan; Deeth, R; Elding, Lars
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Português
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The Hg2+(aq-) and HgCl+(aq-)assisted aquations of [PtCl4]2- (1), [PtCl3(H2O)]- (2), cis-[PtCl2(H2O)2] (3), trans-[PtCl2(H2O)2] (4), [PtCl(H2O)3]+ (5), [PtCl3Me2SO]- (6), trans-[PtCl2(H2O)Me2SO] (7), cis-[PtCl(H2O)2Me2-SO]+ (8), trans-[PtCl(H2O)2Me2SO]+ (9), trans-[PtCl2(NH3)2] (10), and cis-[PtCl2(NH3)2] (11) have been studied at 25.0 °C in a 1.00 M HClO4 medium buffered with chloride, using stopped-flow and conventional spectrophotometry. Saturation kinetics and instantaneous, large UV/vis spectral changes on mixing solutions of platinum complex and mercury are ascribed to formation of transient adducts between Hg2+ and several of the platinum complexes. Depending on the limiting rate constants, these adducts are observed for a few milliseconds to a few minutes. Thermodynamic and kinetics data together with the UV/vis spectral changes and DFT calculations indicate that their structures are characterized by axial coordination of Hg to Pt with remarkably short metal-metal bonds. Stability constants for the Hg2+ adducts with complexes 1-6, 10, and 11 are (2.1 ± 0.4) x 104, (8 ± 1) x 102, 94 ± 6, 13 ± 2, 5 ± 2, 60 ± 6, 387 ± 2, and 190 ± 3 M-1, respectively, whereas adduct formation with the sulfoxide complexes 7-9 is too weak to be observed. For analogous platinum(II) complexes...

‣ Evidence for a late chondritic veneer in the Earths mantle from high-pressure partitioning of palladium and platinum

Holzheid, A; Sylvester, Paul; O'Neill, Hugh; Rubie, David; Palme, Herbert
Fonte: Macmillan Publishers Ltd Publicador: Macmillan Publishers Ltd
Tipo: Artigo de Revista Científica
Português
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The high-pressure solubility in silicate liquids of moderately siderophile 'iron-loving' elements (such as nickel and cobalt) has been used to suggest that, in the early Earth, an equilibrium between core-forming metals and the silicate mantle was established at the bottom of a magma ocean. But observed concentrations of the highly siderophile elements - such as the platinum-group elements platinum, palladium, rhenium, iridium, ruthenium and osmium - in the Earth's upper mantle can be explained by such a model only if their metal-silicate partition coefficients at high pressure are orders of magnitude lower than those determined experimentally at one atmosphere (refs 3-8). Here we present an experimental determination of the solubility of palladium and platinum in silicate melts as a function of pressure to 16 GPa (corresponding to about 500 km depth in the Earth). We find that both the palladium and platinum metal-silicate partition coefficients, derived from solubility, do not decrease with pressure - that is, palladium and platinum retain a strong preference for the metal phase even at high pressures. Consequently the observed abundances of palladium and platinum in the upper mantle seem to be best explained by a 'late veneer' addition of chondritic material to the upper mantle following the cessation of core formation.

‣ Platinum promotion of Au/A1(2)0(3) catalysts for glycerol oxidation: activity, selectivity and deactivation

Royker,M.; Case,J.; van Steen,E.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 Português
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Gold has been demonstrated as a possible catalyst for oxidation reactions. Some evidence for a possible promotion effect of platinum has also been recorded. The influence of platinum as promoter for Au/y-Al2O3 prepared via anionic ion-exchange for the oxidation of glycerol was investigated in a batch reactor at 60°C. It is inferred that the addition of platinum reduces the catalytic activity and the rate of deactivation, resulting in an overall higher final conversion of glycerol with increasing platinum loading. The addition of platinum to the catalyst favours the formation of the desired product, glyceric acid.