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DNA damage by sulfite autoxidation catalyzed by cobalt complexes

ALIPAZAGA, Maria V.; MORENO, Ruben G. M.; LINARES, Edlaine; MEDEIROS, Marisa H. G.; COICHEV, Nina
Fonte: ROYAL SOC CHEMISTRY Publicador: ROYAL SOC CHEMISTRY
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
396.89773%
DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 mu M) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O(2), DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO(3)(center dot)-S-, HO(center dot) and H(center dot) radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO(center dot) adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Conselho Nacional de Pesquisa e Desenvolvimento Tecnologico (CNPq); Brazilian Agencies

Estudos espectrofotométricos e por quimiluminescência da autoxidação de complexos de Ni(II) ou Cu(II)/tetraglicina induzida por S(IV). Aplicações analíticas; Spectrophotometric and chemiluminescence studies of S(IV) induced autoxidation of Ni(II) or Cu(II)/tetraglycine complexes. Analytical applications.

Bonifacio, Rodrigo Leandro
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 13/05/2004 PT
Relevância na Pesquisa
516.9284%
O presente trabalho apresenta estudos da reação de autoxidação de Ni(II)/tetraglicina ou Cu(II)/tetraglicina induzida por S(IV). Estudos espectrofotométricos enfocaram a formação do respectivo íon metálico no estado de oxidação 3+. Verificou-se que S(IV) acelera a autoxidação de Ni(II)/tetraglicina em pH=9,2 (tampão borato), com a determinação de alguns parâmetros cinéticos desta reação. A autoxidação de Cu(II)/tetraglicina induzida por S(IV), caracterizada por efeito sinérgico positivo de Ni(II), foi empregada no desenvolvimento de método analítico para S(IV) na faixa de (0-0,12) milimolar. Este método foi utilizado para estudo da autoxidação de S(IV) catalisada por traços de íons metálicos de transição, em meio não-complexante. Estudos por quimiluminescência abordaram a interação das espécies geradas na autoxidação de Ni(II)/tetraglicina e Cu(II)/tetraglicina induzida por S(IV) com o íon tris-bipiridil-2,2´-rutênio(II). Foi avaliado o efeito de intensificação da radiação emitida, causado por tensoativos ou adições sucessivas de S(IV). A interação das espécies produzidas na autoxidação de Ni(II)/tetraglicina induzida por S(IV) com luminol foi aproveitada para desenvolvimento de método quimiluminescente para determinação de sulfito. O método proposto foi aplicado para determinação de S(IV) livre em amostras de bebidas...

Desenvolvimento de métodos catalíticos para determinação de dióxido de enxofre no meio ambiente; Development of catalytic methods for determination of sulphur dioxide in the environment

Bona, Arnaldo
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 09/12/1994 PT
Relevância na Pesquisa
315.07574%
As formas SO2, HSO3- e SO32- em meio aquoso, são espécies de enxofre (IV) que coexistem; suas concentrações no equilíbrio químico dependem do pH do meio. O estudo das oxidações do S(IV) encontrado na atmosfera, resultante de fontes naturais e antropogênicas, é de fundamental importância, pois os produtos formados têm caráter ácido. Como consequência, ocorre a precipitação ácida, com seus efeitos deletérios ao ecossistema. O presente trabalho procura adicionar novas informações às já acumuladas em estudos anteriores. O estudo praticamente se restringe às condições de laboratório, levando em conta as condições ambientais. Em uma projeção futura, a metodologia poderá ser estendida e adaptada para as determinações do S(IV) na natureza. O método analítico proposto para determinar S(IV) na atmosfera, em fase aquosa, é baseado na reação catalítica onde o S(IV) induz a oxidação do Co(II) a Co(III), em tampão HN3/N3- e na presença do Mn++. O principal composto de coordenação, hexaazidocobaltato (III), é consideravelmente estável e apresenta um máximo de absorção em 365nm, com absortividade molar próxima de 3.104 mol-1cm-1L. Com o uso de uma cubeta de quartzo de 1cm de caminho ótico, a faixa de concentração de uso deste método...

Electrochemical investigation of the dimeric oxo-bridged ruthenium complex in aqueous solution and its incorporation within a cation-exchange polymeric film on the electrode surface for electrocatalytic activity of hydrogen peroxide oxidation

Teixeira, Marcos F. S.; Cincotto, Fernando H.; Raymundo-Pereira, Paulo A.
Fonte: Pergamon-Elsevier B.V. Ltd Publicador: Pergamon-Elsevier B.V. Ltd
Tipo: Artigo de Revista Científica Formato: 6804-6811
ENG
Relevância na Pesquisa
513.06734%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 05/01296-4; Processo FAPESP: 08/07298-7; Electrochemical behavior of oxo-bridged dinuclear ruthenium(III) complex ([(bpy)2(H(2)O)Ru(III)-O-Ru(III)(H(2)O)(bpy)2](4+)) has been studied in aqueous solution (KCl 0.5 mol L(-1)) by both cyclic and rotating disk electrode (ROE) voltammetry in order to identify and elucidate the reaction mechanism. Modified electrode containing the oxo-bridged ruthenium complex incorporated into a cation-exchange polymeric film deposited onto platinum electrode surface was studied. Cyclic voltammetry at the modified electrode in KCl solution showed a single-electron reduction/oxidation of the couple Ru(III)-O-Ru(III)/Ru(III)-O-Ru(IV). The modified electrode exhibited electrocatalytic property toward hydrogen peroxide oxidation in KCl solution with a decrease of the overpotential of 340 mV compared with the platinum electrode. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the hydrogen peroxide oxidation. The first at low overpotential region there is no significant change in the Tafel slope (similar to 0.130 V dec(-1)) with varying peroxide concentration. The second region at higher overpotential the slope values (0.91-0.47V dec(-1)) were depended on the peroxide concentration. The apparent reaction order for H(2)O(2) varies from 0.16 to 0.50 in function of the applied potential. The apparent reaction order (at constant potential) with respect to H. concentration of 10(-5) to 10(-1) mol L(-1) was 0.25. A plot of the anodic current vs. the H(2)O(2) concentration for chronoamperometry (potential fixed = +0.61 V) at the modified electrode was linear in the 1.0 x 10(-5) to 2.5 x 10(-4) mol L(-1) concentration range. (C) 2011 Elsevier Ltd. All rights reserved.

Thermal behaviour of Tin(II) complex with 8-hydroxyquinolinate in the solid state

Ribeiro, C. A.; Crespi, M. S.; Guinesi, L. S.; Guerreiro, CTR; Zorel, H. E.
Fonte: Kluwer Academic Publ Publicador: Kluwer Academic Publ
Tipo: Artigo de Revista Científica Formato: 1209-1215
ENG
Relevância na Pesquisa
401.15266%
Tin(II) complexes with 8-hydroxyquinolinate in solid state have been obtained by adding aqueous ammonium to a solution containing stannous chloride and 8-hydroxiquinoline in medium of HCl and acetone up to pH 5 and 9, respectively. The products obtained show the same composition, Sn(C9H6ON)(2); however there are some differences regarding both the thermal behaviour in an oxidant atmosphere and morphology. These products were characterised by elemental and complexometric analysis, TG and DTA curves, infrared and X-ray diffractometry. TG curves show, above 448 K, the partial oxidation on air atmosphere of Sn(II) complexes to Sn(IV) complexes, SnO(C9H6ON)(2). This behaviour does not depend only on pH in which the compounds were obtained but also on the heating rate in TG curves. Sn(II) complexes volatilise almost completely on nitrogen atmosphere and partially on air atmosphere depending on the oxidation degree of the compound.

Electrochemical Properties of Oxo-Manganese Complex Biomimicking Enzyme Active Sites and Its Electrocatalytic Application for Dopamine Determination

Martin, C. S.; Teixeira, M. F S
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 92-100
ENG
Relevância na Pesquisa
306.2553%
This work describes the characterization of the [Mn2 IV,IVO2(terpy)2(H2O)2]4+ complex in aqueous solution by UV-vis spectrophotometry, cyclic voltammetry, and linear sweep voltammetry with a rotating disk electrode. The pH effect, potential scan rate, effect of perfluorosulfonate polymer, and anion of supporting electrode on the electrochemical behavior of the modified electrode for better performance were investigated. The potential peak of the modified electrode was linearly dependent upon the ratio [ionic charge]/[ionic radius]. The modified electrode exerted an electrocatalytic effect on dopamine oxidation in aqueous solution with a decrease in the overpotential compared with the unmodified glassy carbon electrode. This way, the modified electrode showed an enzymatic biomimicking behavior. Tafel plot analyses were used to elucidate the kinetics and mechanism of dopamine oxidation. © 2013 Springer Science+Business Media New York.

Influence of NO2 and metal ions on oxidation of aqueous-phase S(IV) in atmospheric concentrations

Martins,Cláudia R.; Alves,Janete J.F.; Carvalho,Wanessa B.D.; Cardoso,Cristiane S.C.; Andrade,Jailson B. de
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2008 EN
Relevância na Pesquisa
1145.1145%
An investigation was made of the influence of atmospheric concentrations (15 or 130 ppbv) of NO2 on the aqueous-phase oxidation rate of S(IV) in the presence and absence of Fe(III), Mn(II) and Cr(VI) metal ions under controlled experimental conditions (pH, T, concentration of reactants, etc.). The reaction rate in the presence of the NO2 flow was slower than the reaction rate using only clean air with an initial S(IV) concentration of 10-4 mol/L. NO2 appears to react with S(IV), producing a kind of inhibitor that slows down the reaction. Conversely, tenfold lower concentrations of S(IV) ([S(IV)]º = 10-5 mol/L) caused a faster reaction in the presence of NO2 than the reaction using purified air. Under these conditions, therefore, the equilibrium shifts to sulfate formation. With the addition of Fe(III), Mn(II) or Cr(VI) in the presence of a NO2 flow, the reaction occurred faster under all the conditions in which S(IV) oxidation was investigated.

Oxidation of sulfur (IV) by oxygen in aqueous solution: role of some metal ions

Martins,Claudia R.; Cabral Neto,Clodovil A; Alves,Janete J.F.; Andrade,Jailson B. de
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/1999 EN
Relevância na Pesquisa
846.5953%
Catalytic effect of metal ions: Cr(VI), Cr(III), Cd(II), V(V) and chloride anion, on the oxidation of S(IV) in aqueous solution, at concentrations of metal ions and S(IV) usually found in urban atmospheres, were studied under controlled experimental conditions (pH (2.1 - 4,5), T (25.0 - 35.0 °C), air flow rate, concentration of reactants, etc...). The kinetic constant determined at 25.0 °C and pH range (2.1 - 4.5), using ultra pure water was 8.0 ± 0.5 x 10-4 s-1. This value was considered as a reference for the oxidation reaction rate. The kinetic constants determined in the presence of Cr(VI) revealed that the oxidation reaction of S(IV) is quite influenced by the acidity. At pH = 2.1 (K = 2.3 x 10-2 mg-1 L s-1) the reaction is carried out with a rate five times greater when compared to pH = 2.6 (K = 4.3 x 10-3 mg-1 L s-1) and thirty times greater when compared to pH = 3.4 (K= 8.0 x 10 -4 mg-1 L s-1). The following rate expression was obtained at pH = 2.6: -r(S(IV) =K [Cr(VI)] [S(IV)] and the activation energy found was: Ea =70.3KJ/mol. No catalytic effects were observed for Cd(II) or chloride ion, while inhibitory effects were observed for Cr(III) and V(V) ions.

Quinone-dependent proton transfer pathways in the photosynthetic cytochrome b6f complex

Hasan, S. Saif; Yamashita, Eiki; Baniulis, Danas; Cramer, William A.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
298.77578%
As much as two-thirds of the proton gradient used for transmembrane free energy storage in oxygenic photosynthesis is generated by the cytochrome b6f complex. The proton uptake pathway from the electrochemically negative (n) aqueous phase to the n-side quinone binding site of the complex, and a probable route for proton exit to the positive phase resulting from quinol oxidation, are defined in a 2.70-Å crystal structure and in structures with quinone analog inhibitors at 3.07 Å (tridecyl-stigmatellin) and 3.25-Å (2-nonyl-4-hydroxyquinoline N-oxide) resolution. The simplest n-side proton pathway extends from the aqueous phase via Asp20 and Arg207 (cytochrome b6 subunit) to quinone bound axially to heme cn. On the positive side, the heme-proximal Glu78 (subunit IV), which accepts protons from plastosemiquinone, defines a route for H+ transfer to the aqueous phase. These pathways provide a structure-based description of the quinone-mediated proton transfer responsible for generation of the transmembrane electrochemical potential gradient in oxygenic photosynthesis.

Constraints on superoxide mediated formation of manganese oxides

Learman, Deric R.; Voelker, Bettina M.; Madden, Andrew S.; Hansel, Colleen M.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 03/09/2013 EN
Relevância na Pesquisa
396.18875%
Manganese (Mn) oxides are among the most reactive sorbents and oxidants within the environment, where they play a central role in the cycling of nutrients, metals, and carbon. Recent discoveries have identified superoxide (O2−) both of biogenic and abiogenic origin as an effective oxidant of Mn(II) leading to the formation of Mn oxides. Here we examined the conditions under which abiotically produced superoxide led to oxidative precipitation of Mn and the solid-phases produced. Oxidized Mn, as both aqueous Mn(III) and Mn(III/IV) oxides, was only observed in the presence of active catalase, indicating that hydrogen peroxide (H2O2), a product of the reaction of O2− with Mn(II), inhibits the oxidation process presumably through the reduction of Mn(III). Citrate and pyrophosphate increased the yield of oxidized Mn but decreased the amount of Mn oxide produced via formation of Mn(III)-ligand complexes. While complexing ligands played a role in stabilizing Mn(III), they did not eliminate the inhibition of net Mn(III) formation by H2O2. The Mn oxides precipitated were highly disordered colloidal hexagonal birnessite, similar to those produced by biotically generated superoxide. Yet, in contrast to the large particulate Mn oxides formed by biogenic superoxide...

Relative Reactivity of Biogenic and Chemogenic Uraninite and Biogenic Non Crystalline U(IV)

Cerrato, José M.; Ashner, Matthew N.; Alessi, Daniel S.; Lezama-Pacheco, Juan S.; Bernier-Latmani, Rizlan; Bargar, John R.; Giammar, Daniel E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
416.02%
Aqueous chemical extractions and X-ray absorption spectroscopy (XAS) analyses were conducted to investigate the reactivity of chemogenic uraninite, nanoparticulate biogenic uraninite, and biogenic monomeric U(IV) species. The analyses were conducted in systems containing a total U concentration that ranged from 1.48 to 2.10 mM. Less than 0.02% of the total U was released to solution in extractions that targeted water soluble and ion exchangeable fractions. Less than 5% of the total U was solubilized via complexation with a 0.1 M solution of NaF. Greater than 90% of the total U was extracted from biogenic uraninite and monomeric U(IV) after 6 hours of reaction in an oxidizing solution of 50 mM K2S2O8. Additional oxidation experiments with lower concentrations (2 mM and 10 mM) of K2S2O8 and 8.2 mg L−1 dissolved oxygen suggested that monomeric U(IV) species are more labile than biogenic uraninite; chemogenic uraninite was much less susceptible to oxidation than either form of biogenic U(IV). These results suggest that non-crystalline forms of U(IV) may be more labile than uraninite in subsurface environments. This work helps fill critical gaps in our understanding of the behavior of solid-associated U(IV) species in bioremediated sites and natural uranium ore deposits.

Sulfate Formation in Sea-Salt Aerosols: Constraints from Oxygen Isotopes

Alexander, B.; Park, Rokjin J.; Jacob, Daniel J.; Li, Q. B.; Yantosca, Robert M.; Savarino, J.; Lee, C. C. W.; Thiemens, M. H.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
419.56074%
We use observations of the mass-independent oxygen isotopic composition (Δ17O) of sulfate in the marine boundary layer (MBL) to quantify the sulfate source from aqueous SO2 (S(IV)) oxidation by O3 in alkaline sea-salt aerosols. Oxidation by O3 imparts a large Δ17O signature to the resulting sulfate (8.8‰) relative to oxidation by H2O2 (0.9‰) or by OH or O2 (0‰). Ship data from two Indian Ocean Experiment (INDOEX) cruises in the Indian Ocean indicate Δ17O values usually <1‰ in the submicron sulfate aerosol but considerable variability in the supermicron sulfate with frequent occurrences above 1‰ and up to 6.7‰. The large Δ17O values are associated with high concentrations of sea-salt aerosols, providing evidence for the S(IV) + O3 pathway. We use a global chemical transport model (GEOS-CHEM) to interpret quantitatively the INDOEX observations and to assess the global importance of sulfate production in sea-salt aerosols. The model accounts for titration of sea-salt alkalinity in the MBL by uptake of acid gases (SO2, H2SO4, and HNO3), shutting down the S(IV) + O3 pathway. We find that this titration occurs rapidly over much of the oceans except at high latitudes (strong sea-salt emission) and is due to both the S(IV) + O3 reaction and HNO3 (g) condensation; that is...

Transition Metal-Catalyzed Oxidation of Atmospheric Sulfur: Global Implications for the Sulfur Budget

Alexander, Becky; Park, Rokjin J.; Jacob, Daniel J.; Gong, Sunling
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
528.19363%
We use observations of the oxygen-17 excess ((Δ^{17}O)) of sulfate in the Arctic to quantify the sulfate source from aqueous (SO_2 (S(IV))) oxidation by (O_2) catalyzed by transition metals. Due to the lack of photochemically produced OH and (H_2O_2) in high latitudes during winter, combined with high anthropogenic (SO_2) emissions in the Northern Hemisphere, oxidation by (O_3) is predicted to dominate sulfate formation during winter in this region. However, (Δ^{17}O) measurements of sulfate aerosol collected in Alert, Canada, are not consistent with (O_3) as the dominant oxidant and indicate that a S(IV) oxidant with near-zero (Δ^{17}O) values ((O_2)) is important during winter. We use a global chemical transport model to interpret quantitatively the Alert observations and assess the global importance of sulfate production by Fe(III)- and Mn(II)-catalyzed oxidation of S(IV) by (O_2). We scale anthropogenic and natural atmospheric metal concentrations to primary anthropogenic sulfate and dust concentrations, respectively. The solubility and oxidation state of these metals is determined by cloud liquid water content, source, and sunlight. By including metal-catalyzed S(IV) oxidation, the model is consistent with the (Δ^{17}O) magnitudes in the Alert data during winter. Globally...

Chemistry of OH in remote clouds and its role in the production of formic acid and peroxymonosulfate

Jacob, Daniel James
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
311.49723%
The chemistry of OH in a remote nonprecipitating tropical cloud is studied with a coupled gas-phase and aqueous-phase chemical model. The model takes into account the radial dependence of the concentrations of short-lived aqueous-phase species, in particular O3(aq) and OH(aq). The radical OH(aq) is produced rapidly by the aqueous-phase reactions O2− + O3 and H2O2 + hν and is removed primarily by oxidation of H2C(OH)2, H2O2, and HCOO−. Gas-droplet transfer of OH must be modeled as a reversible process, that is, the droplets cannot be assumed to be diffusion-limited OH(g) sinks. A strong OH(aq) concentration gradient exists between the surface and the interior of the droplets. The concentration of OH(aq) is strongly dependent on pH but is only weakly dependent on the sticking coefficient, the droplet radius, or the liquid water content of the cloud. Formic acid is rapidly produced by the aqueous-phase reaction H2C(OH)2 + OH, but HCOO− is in turn rapidly oxidized by OH(aq). The HCOOH concentration in cloud is shown to be strongly dependent on cloud water pH; clouds with pH greater than 5 are not efficient HCOOH sources. A novel mechanism is proposed for the oxidation of S(IV) by OH(aq). The main product is predicted to be HSO5− (peroxymonosulfate). Peroxymonosulfate appears to be stable in remote clouds and could contribute a large fraction of total cloud water sulfur.; Engineering and Applied Sciences

A comparison of charge-transfer mechanisms at rotated disk electrode for biomimetic binuclear and tetranuclear oxo-manganese complex in aqueous solution

Martin, Cibely S.; Teixeira, Marcos F. S.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 76-82
ENG
Relevância na Pesquisa
395.1818%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 2009/11079-1; Processo FAPESP: 2010/12524-6; Many high-valence multinuclear mu-oxo-bridged manganese complexes have been synthesized to mimic the active site of the natural enzymes. The electrochemical and kinetic parameters were determined for two mimicking complexes ([(Mn2O2)-O-IV(terpy)(2)(H2O)(2)](4+) and [(Mn4O5)-O-IV(terpy)(4)(H2O)(2)](6+)) by cyclic voltammetry and linear sweep voltammetry using a rotating disk electrode (RDE). Stability and kinetic behavior are directly related to mu-oxo bridges, where the mu-oxo-bridge provides a fast electron transition between metal centers due to stabilization of dx(2) - y(2) orbitals by the oxygen bond. On the other hand, when the dx(2) - y(2) orbitals are stabilized by aqua ligands by a coordination bond, a displacement of oxidation potential to more positive potential was observed. A shift of the potential to more negative values with increase in rotation rate was observed, which can be ascribed to a chemical step. The chemical step involves the dimerization process of the binuclear oxo-manganese complex to tetranuclear oxo-manganeses complex. (C) 2014 Elsevier B.V. All rights reserved.

Theoretical study on the reactivity of sulfate species with hydrocarbons

Ma, Qisheng; Ellis, Gregory S.; Amrani, Alon; Zhang, Tongwei
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 15/09/2008
Relevância na Pesquisa
403.76766%
The abiotic, thermochemically controlled reduction of sulfate to hydrogen sulfide coupled with the oxidation of hydrocarbons, is termed thermochemical sulfate reduction (TSR), and is an important alteration process that affects petroleum accumulations in nature. Although TSR is commonly observed in high-temperature carbonate reservoirs, it has proven difficult to simulate in the laboratory under conditions resembling nature. The present study was designed to evaluate the relative reactivities of various sulfate species in order to provide greater insight into the mechanism of TSR and potentially to fill the gap between laboratory experimental data and geological observations. Accordingly, quantum mechanics density functional theory (DFT) was used to determine the activation energy required to reach a potential transition state for various aqueous systems involving simple hydrocarbons and different sulfate species. The entire reaction process that results in the reduction of sulfate to sulfide is far too complex to be modeled entirely; therefore, we examined what is believed to be the rate limiting step, namely, the reduction of sulfate S(VI) to sulfite S(IV). The results of the study show that water-solvated sulfate anions View the MathML source are very stable due to their symmetrical molecular structure and spherical electronic distributions. Consequently...

Selective Oxidation of sp^3 C-H Bonds in Water Catalyzed by a Glycinate-Platinum(II) Complex

Chen, George S.; Labinger, Jay A.; Bercaw, John E.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 14/09/2009
Relevância na Pesquisa
397.87676%
In aqueous solution, [Pt^(II)(glycinato)Cl_2]^− catalyzes oxidation by [Pt^(IV)Cl_6]^(2−) of the methyl group of p-toluenesulfonate to the corresponding alcohol and aldehyde, with no further oxidation to the carboxylic acid. Both rate and selectivity are improved in comparison to the original Shilov system that employs [Pt^(II)Cl_n(H_2O)_(4−n)]^(2−n) as the catalyst.

A dynamic model for the production of H^+NO_3^−, and SO_4^(2−) in urban fog

Jacob, Daniel J.; Hoffmann, Michael R.
Fonte: American Geophysical Union. Publicador: American Geophysical Union.
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 20/08/1983
Relevância na Pesquisa
432.50113%
The chemical composition of nighttime urban fog has been investigated using a hybrid kinetic and equilibrium model. Extremely high acidity may be imparted to the droplets by condensation and growth on acidic condensation nuclei or by in situ S(IV) oxidation. Important oxidants of S(IV) were found to be O_2 as catalyzed by Fe(III) and Mn(II), H_2O_2, and O_3. Formation of hydroxymethanesulfonate ion (HMSA) via the nucleophilic addition of HSO_3^− to CH_2O(I) significantly increased the droplet capacity for S(IV) but did not slow down the net S(IV) oxidation rate leading to fog acidification. Gas phase nitric acid, ammonia, and hydrogen peroxide were scavenged efficiently, although aqueous phase hydrogen peroxide was depleted rapidly by reduction with S(IV). Nitrate production in the aqueous phase was found to be dominated by HNO_3 gas phase scavenging. Major aqueous phase species concentrations were controlled primarily by condensation, evaporation, and pH.

Characterization of Reactants Reaction Mechanisms and Reaction Products Leading to Extreme Acid Rain and Acid Aerosol Conditions in Southern California

Hoffmann, Michael R.; Morgan, J. J.; Jacob, D. J.; Munger, J. W.; Waldman, J. M.
Fonte: California Air Resources Board Publicador: California Air Resources Board
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em 31/03/1983
Relevância na Pesquisa
432.50113%
Analyses of fogwater collected by inertial impaction in the Los Angeles basin and the San Joaquin Valley indicated unusually high concentrations of major and minor ions. The dominant ions measured were NO_3^-, SO_4^(2-), NH_4^+ and H^+ Nitrate exceeded sulfate on an equivalent basis by a factor of 2.5 in the central and coastal regions of the Los Angeles basin, but was approximately equal in the eastern Los Angeles basin and the San Joaquin Valley. Maximum observed values for NH_4^+, NO_3^- and SO_4^(2-) were 10., 12., and 5. meq L^(-1), while the lowest pH observed was 2.2. Iron and lead concentrations over 0.1 mM and 0.01 mM, respectively, were observed. High concentrations of chemical components in fog appeared to correlate well with the occurrence of smog events. Concentrations in fogwater were also affected by the physical processes of condensation and evaporation. Light, dissipating fogs routinely showed the highest concentrations. The chemistry of urban fog has been modelled using a hybrid kinetic and equilibrium computer code. Extreme acidity found in Southern California fog may be due either to condensation and growth on acidic condensation nuclei or in situ S(IV) oxidation. Important oxidants of S(IV) were found to be O_2 as catalyzed by Fe(III) and Mn(II)...

Oxidation of telluropyrylium dyes with ozone, chlorine, and bromine. Differing regiochemical and kinetic behavior with respect to oxidations of oxygen-, sulfur-, and selenium-containing dyes

Detty, Michael; Friedman, Alan
Fonte: The American Chemical Society: Organometallics Publicador: The American Chemical Society: Organometallics
Tipo: Abstract Formato: 31371 bytes; application/pdf
EN_US
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Oxidations of telluropyrylium dyes 1-3 with ozone in water, chlorine in carbon tetrachloride, or bromine in carbon tetrachloride gave second-order rate constants of greater-than-or-equal-to 10(9) L mol-1 s-1 using stopped-flow techniques to measure rates of oxidation. Aqueous ozone gave initial oxidation of the tellurium atoms of 1-3 to produce hydroxytelluranes 4-6, respectively. Oxidative addition of chlorine or bromine across a tellurium atom of 1-3 gave the corresponding tellurium(IV) dihalides. With excess ozone, a second oxidation was observed with a second-order rate constant of (1.3 +/- 0.1) X 10(6) L mol-1 s-1. Chalcogenopyrylium dyes 7-10 which contain only oxygen, sulfur, and/or selenium heteroatoms reacted with smaller rate constants for oxidation. Chlorine and bromine gave second-order rate constants within 1 order of magnitude of those of telluropyrylium dyes for reactions with 7-10. Ozone was more than 100 000 times less reactive toward chalcogenopyrylium dyes 7-9 relative to telluropyrylium dyes 1-3 with second-order rate constants (1.1 +/- 0.1) X 10(4) L mol-1 s-1 for 7, (8.5 +/- 0.9) X 10(3) L mol-1 s-1 for 8, and (5.4 +/- 0.6) X 10(3) L mol-1 s-1 for 9. With dyes 7-10, ozone destroyed the pi-framework of the dye while chlorine and bromine gave mono- and dihalogenation of the trimethine bridge of the dye.