Showing papers on "Hydrogen peroxide published in 2008"

Catalytic Oxidation of Organic Substrates by Molecular Oxygen and Hydrogen Peroxide by Multistep Electron Transfer : A Biomimetic Approach

Abstract: Oxidation reactions are of fundamental importance in nature, and are key transformations in organic synthesis. The development of new processes that employ transition metals as substrate-selective catalysts and stoichiometric environmentally friendly oxidants, such as molecular oxygen or hydrogen peroxide, is one of the most important goals in oxidation chemistry. Direct oxidation of the catalyst by molecular oxygen or hydrogen peroxide is often kinetically unfavored. The use of coupled catalytic systems with electron-transfer mediators (ETMs) usually facilitates the procedures by transporting the electrons from the catalyst to the oxidant along a low-energy pathway, thereby increasing the efficiency of the oxidation and thus complementing the direct oxidation reactions. As a result of the similarities with biological systems, this can be dubbed a biomimetic approach.

Bactericidal Effect of Zero-Valent Iron Nanoparticles on Escherichia coli

Abstract: Zero-valent iron nanoparticles (nano-Fe0) in aqueous solution rapidly inactivated Escherichia coli. A strong bactericidal effect of nano-Fe0 was found under deaerated conditions, with a linear correlation between log inactivation and nano-Fe0 dose (0.82 log inactivation/mg/L nano-Fe0·h). The inactivation of E. coli under air saturation required much higher nano-Fe0 doses due to the corrosion and surface oxidation of nano-Fe0 by dissolved oxygen. Significant physical disruption of the cell membranes was observed in E. coli exposed to nano-Fe0, which may have caused the inactivation or enhanced the biocidal effects of dissolved iron. The reaction of Fe(II) with intracellular oxygen or hydrogen peroxide also may have induced oxidative stress by producing reactive oxygen species. The bactericidal effect of nano-Fe0 was a unique property of nano-Fe0, which was not observed in other types of iron-based compounds.

Factors affecting the yield of oxidants from the reaction of nanoparticulate zero-valent iron and oxygen.

Abstract: The corrosion of zero-valent iron (Fe0(s)) by oxygen (O2) can lead to the oxidation of organic compounds. To gain insight into the reaction mechanism and to assess the nature of the oxidant, the oxidation of methanol, ethanol, 2-propanol, and benzoic acid by the reaction of nanoparticulate zero-valent iron (nZVI) or ferrous iron (Fe[II]) with O2 in the absence of ligands was studied. At pH values below 5, Fe0(s) nanoparticles were oxidized by O2 within 30 min with a stoichiometry of approximately two Fe0(s) oxidized per O2 consumed. The yield of methanol and ethanol oxidation products increased from 1% at acidic pH to 6% at pH 7, relative to nZVI added. Product yields from 2-propanol and benzoic acid were highest under acidic conditions, with little oxidation observed at neutral pH. At pH values below 5, product formation was attributable to hydroxyl radical (OH·) production through the Fenton reaction, involving hydrogen peroxide and Fe(II) produced during nZVI oxidation. At higher pH values, the oxidati...

A Targetable Fluorescent Probe for Imaging Hydrogen Peroxide in the Mitochondria of Living Cells

Abstract: We present the design, synthesis, and biological applications of mitochondria peroxy yellow 1 (MitoPY1), a new type of bifunctional fluorescent probe for imaging hydrogen peroxide levels within the mitochondria of living cells. MitoPY1 combines a chemoselective boronate-based switch and a mitochondrial-targeting phosphonium moiety for detection of hydrogen peroxide localized to cellular mitochondria. Confocal microscopy and flow cytometry experiments in a variety of mammalian cell types show that MitoPY1 can visualize localized changes in mitochondrial hydrogen peroxide concentrations generated by situations of oxidative stress.

An ICT-Based Approach to Ratiometric Fluorescence Imaging of Hydrogen Peroxide Produced in Living Cells

Abstract: We present the synthesis, properties, and biological applications of Peroxy Lucifer 1 (PL1), a new fluorescent probe for imaging hydrogen peroxide produced in living cells by a ratiometric response PL1 utilizes a chemoselective boronate-based switch to detect hydrogen peroxide by modulation of internal charge transfer (ICT) within a 1,8-naphthalimide dye PL1 features high selectivity for hydrogen peroxide over similar reactive oxygen species, including superoxide, and nitric oxide, and a 65 nm shift in emission from blue-colored fluorescence to green-colored fluorescence upon reaction with peroxide Two-photon confocal microscopy experiments in live macrophages show that PL1 can ratiometrically visualize localized hydrogen peroxide bursts generated in living cells at immune response levels

Oxidative stress: the vulnerable β-cell

Abstract: Antioxidative defence mechanisms of pancreatic β-cells are particularly weak and can be overwhelmed by redox imbalance arising from overproduction of reactive oxygen and reactive nitrogen species. The consequences of this redox imbalance are lipid peroxidation, oxidation of proteins, DNA damage and interference of reactive species with signal transduction pathways, which contribute significantly to β-cell dysfunction and death in Type 1 and Type 2 diabetes mellitus. Reactive oxygen species, superoxide radicals (O 2 •− ), hydrogen peroxide (H 2 O 2 ) and, in a final iron-catalysed reaction step, the most reactive and toxic hydroxyl radicals (OH • ) are produced during both pro-inflammatory cytokine-mediated β-cell attack in Type 1 diabetes and glucolipotoxicity-mediated β-cell dysfunction in Type 2 diabetes. In combination with NO • , which is toxic in itself, as well as through its reaction with the O 2 •− and subsequent formation of peroxynitrite, reactive species play a central role in β-cell death during the deterioration of glucose tolerance in the development of diabetes.

Electrocatalytic Oxygen Reduction Reaction

Abstract: Oxygen (O2) is the most abundant element in the Earth’s crust. The oxygen reduction reaction (ORR) is also the most important reaction in life processes such as biological respiration, and in energy converting systems such as fuel cells. ORR in aqueous solutions occurs mainly by two pathways: the direct 4-electron reduction pathway from O2 to H2O, and the 2-electron reduction pathway from O2 to hydrogen peroxide (H2O2). In non-aqueous aprotic solvents and/or in alkaline solutions, the 1-electron reduction pathway from O2 to superoxide (O2 -) can also occur.

N-Doped TiO2 Nanoparticle Based Visible Light Photocatalyst by Modified Peroxide Sol−Gel Method

Abstract: The peroxide gel route is employed to synthesize N-doped TiO2 nanoparticles (NP) at low temperature using titanium tetraisopropoxide, ethylmethylamine, and hydrogen peroxide as precursors. Structural studies show anatase phase in the undoped titania NPs as well as at 5 at. % N-doped titania NPs, although with a degree of matrix disorder in the latter case. The annealing of N-doped titania NPs at different temperatures shows that above 400 °C nitrogen escapes the O−Ti−O matrix and at 500 °C the sample becomes crystalline. Transmission electron microscopy reveals that the particle size is in the range of 20−30 nm for the undoped TiO2 but only 5−10 nm for N-doped TiO2. At higher nitrogen concentration (10 at. %) bubble-like agglomerates form. FTIR and photoluminescence quenching also confirm the incorporation of nitrogen in anatase TiO2. Optical properties reveal an extended tailing of the absorption edge toward the visible region upon nitrogen doping. X-ray photoelectron spectroscopy is used to examine the ...

Ruthenium-catalyzed oxidative cyanation of tertiary amines with molecular oxygen or hydrogen peroxide and sodium cyanide: sp3 C-H bond activation and carbon-carbon bond formation.

Abstract: Ruthenium-catalyzed oxidative cyanation of tertiary amines with molecular oxygen in the presence of sodium cyanide and acetic acid gives the corresponding α-aminonitriles, which are highly useful intermediates for organic synthesis. The reaction is the first demonstration of direct sp3 C−H bond activation α to nitrogen followed by carbon−carbon bond formation under aerobic oxidation conditions. The catalytic oxidation seems to proceed by (i) α-C−H activation of tertiary amines by the ruthenium catalyst to give an iminium ion/ruthenium hydride intermediate, (ii) reaction with molecular oxygen to give an iminium ion/ruthenium hydroperoxide, (iii) reaction with HCN to give the α-aminonitrile product, H2O2, and Ru species, (iv) generation of oxoruthenium species from the reaction of Ru species with H2O2, and (v) reaction of oxoruthenium species with tertiary amines to give α-aminonitriles. On the basis of the last two pathways, a new type of ruthenium-catalyzed oxidative cyanation of tertiary amines with H2O2...

Palladium and gold-palladium catalysts for the direct synthesis of hydrogen peroxide.

Abstract: Today hydrogen peroxide is produced by an indirect process in which an alkyl anthraquinone is sequentially hydrogenated and oxidized. In this way hydrogen and oxygen are kept separate during the manufacturing process. A process where molecular oxygen is directly hydrogenated could be preferred if control of the sequential hydrogenation can be achieved, particularly if high rates can be attained under intrinsically safe, non-explosive conditions. Herein we describe recent progress in the direct synthesis of hydrogen peroxide using supported palladium and gold-palladium alloy catalysts and consider some of the problems that have to be overcome.

Ligand-enhanced reactive oxidant generation by nanoparticulate zero-valent iron and oxygen.

Abstract: The reaction of zero-valent iron or ferrous iron with oxygen produces reactive oxidants capable of oxidizing organic compounds. However, the oxidant yield in the absence of ligands is too low for practical applications. The addition of oxalate, nitrilotriacetic acid (NTA), or ethylenediaminetetraacetic acid (EDTA) to oxygen-containing solutions of nanoparticulate zero-valent iron (nZVI) significantly increases oxidant yield, with yields approaching their theoretical maxima near neutral pH. These ligands improve oxidant production by limiting iron precipitation and by accelerating the rates of key reactions, including ferrous iron oxidation by oxygen and hydrogen peroxide. Product yields indicate that the oxic nZVI system produces hydroxyl radical (OH·) over the entire pH range in the presence of oxalate and NTA. In the presence of EDTA, probe compound oxidation is attributed to OH· under acidic conditions and a mixture of OH· and ferryl ion (Fe[IV]) at circumneutral pH.

Fenton-like reaction catalyzed by the rare earth inner transition metal cerium.

Abstract: Cerium (Ce) is a rare earth metal that is not known to have any biological role. Cerium oxide materials of several sizes and shapes have been developed in recent years as a scaffold for catalysts. Indeed even cerium oxide nanoparticles themselves have displayed catalytic activities and antioxidant properties in tissue culture and animal models. Because of ceria's ability to cycle between the +3 and +4 states at oxygen vacancy sites, we investigated whether cerium metal would catalyze a Fenton-like reaction with hydrogen peroxide. Indeed, cerium chloride did exhibit radical production in the presence of hydrogen peroxide, as assessed by relaxation of supercoiled plasmid DNA. Radical production in this reaction was also followed by production of radical cation of 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS). Radical scavengers and spin traps were capable of competing with ABTS for radicals produced in this cerium dependent Fenton-like reaction. Electron paramagnetic resonance experiments reveal both hydroxyl radical and superoxide anion in a reaction containing cerium and hydrogen peroxide. Based on these results we propose that cerium is capable of redox-cycling with peroxide to generate damaging oxygen radicals.

Evidence for hole participation during the photocatalytic oxidation of the antibiotic flumequine

Abstract: Photocatalytic degradation of the antibiotic flumequine (FQ) was carried out on TiO2 aqueous suspension assisted by simulated solar light. Using multivariate analysis, it was determined that the most important variable for FQ degradation is pH, where the optimal value is around 6. Hydrogen peroxide addition does not alter oxidation efficiency. Under optimised conditions, the time required to completely eliminate FQ antibiotics was 30 min. Mineralization after 60 min irradiation was around 80%. The role of hydroxyl and superoxide anion radicals was monitored by using the radical scavengers isopropanol and benzoquinone, respectively. On the other hand, the participation of oxidative holes in the reaction mechanism was evaluated by adding iodine anions (hole scavenger) to the reaction system. Isopropanol's slight influence on degradation indicated that FQ oxidation was slightly influenced by OH radicals. The presence of the iodide anion significantly inhibited degradation, thus suggesting that holes played a major role. Experiments carried out in acetonitrile, in absence of water, confirmed the significant role of holes in FQ oxidation. The inhibition of the reaction profile in the presence of benzoquinone confirms the participation of the superoxide anion in the FQ oxidation. The analysis of the reaction products suggests that photo-Kolbe decarboxylation mechanism and hydroxylation of aromatic ring are the reaction's primary steps. The Langmuir–Hinshelwood kinetic model was fitted for FQ photodegradation.

Catalytic Asymmetric Epoxidation of Cyclic Enones

Abstract: A highly enantioselective epoxidation of cyclic enones with hydrogen peroxide has been developed that is catalyzed by chiral primary amine salts.

Ultra-deep oxidative desulfurization of diesel fuel by the Mo/Al2O3-H2O2 system: The effect of system parameters on catalytic activity

Abstract: This work presents the results obtained in the development of Mo/γ-Al2O3 catalysts and their evaluation in the oxidative desulfurization (OD) process of diesel fuel using hydrogen peroxide as the oxidizing reagent. The catalysts were prepared by equilibrium adsorption using several molybdenum precursors and aluminas with different acidity values. They were characterized by Raman spectroscopy. The effect of the reaction time, reaction temperature, nature of solvent, concentration of solvent and hydrogen peroxide, content of molybdenum and phosphate in the catalysts were investigated. The results showed that the activity for sulfur elimination depends mainly on the presence of hepta- and octamolybdates species on the catalyst support and the use of a polar aprotic solvent. Likewise, the presence of phosphate markedly increases the sulfur elimination. In this way, it is possible to reduce sulfur level in diesel fuel from about 320 to less than 10 ppmw at 333 K and atmospheric pressure. Additionally, on the basis of the results obtained a mechanistic proposal for this reaction is described, as an oxidation mechanism by nucleophilic attack of the sulfur atom on peroxo species of hepta- and octamolybdates, but a mechanism involving the singlet oxygen presence can be discarded.

Ag nanoparticle-catalyzed chemiluminescent reaction between luminol and hydrogen peroxide

Abstract: Ag colloid was found to enhance intensely the chemiluminescence (CL) from the reaction between luminol and hydrogen peroxide. Ag nanoparticles exhibited the better CL catalysis activity than gold and platinum nanoparticles. The superoxide anion scavenger nitro blue tetrazolium and superoxide dismutase was added to the hydrogen peroxide–Ag colloid and the luminol–hydrogen peroxide–Ag colloid systems, respectively, showing that the decomposition of hydrogen peroxide by catalysis of silver nanoparticles formed superoxide anion and superoxide anion was involved in luminol–hydrogen peroxide–Ag colloid CL reaction. The Ag nanoparticle-enhanced CL was ascribed to that Ag nanoparticles could catalyze the decomposition of H2O2 to produce some reactive intermediates such as hydroxyl radical, superoxide anion. Hydroxyl radical reacted with luminol to form luminol radical and diazaquinone, followed by the reaction with superoxide anion or monodissociated hydrogen peroxide, giving rising to light emission. Halide ions (X−) were found to quench the CL in the following order: I− > Br− > Cl−, due to the formation of AgX shell on Ag nanoparticles surface which poisoned the Ag catalyst. An obvious turning point was observed in the curve of CL intensity versus iodine ion concentration, which corresponded to the I− concentration needed for mono-layer saturation adsorption on the Ag nanoparticles. A chemical adsorption model for iodine ions on the surface of Ag colloids has been proposed. Among 20 natural amino acids, cysteine, histidine, methionine, tyrosine and tryptophan were found to inhibit the CL due to their adsorption on the Ag nanoparticles and their competitive consumption for the reactive intermediates. The most intense inhibition of cysteine may be of potential for selective determination of cysteine.

Direct synthesis of hydrogen peroxide from H2 and O2 using supported Au–Pd catalysts

Abstract: The direct synthesis of H2O2 at low temperature (2 °C) from H2 and O2 using carbon-supported Au, Pd and Au–Pd catalysts is described and contrasted with data for TiO2, Al2O3 and Fe2O3 as supports. The Au–Pd catalysts all perform significantly better than the pure Pd/TiO2 and Au/TiO2 materials. The Au–Pd/carbon catalysts gave the highest rate of H2O2 production, and the order of reactivity observed is: carbon > TiO2 > Al2O3. Catalysts were prepared by co-impregnation of the supports using incipient wetness with aqueous solutions of PdCl2 and HAuCl4, and following calcination at 400 °C the catalysts were stable and could be re-used several time without loss of metal. The method of preparation is critical, however, to achieve stable catalysts. No promoters are required (e.g. halides) to achieve the high rates of hydrogen peroxide synthesis. The surface and bulk composition of the gold palladium nanoparticles was investigated by STEM-XEDS spectrum imaging. For TiO2 and Al2O3 as supports the Au–Pd particles were found to exhibit a core-shell structure, Pd being concentrated on the surface. In contrast, the Au–Pd/carbon catalyst exhibited Au–Pd nanoparticles which were homogeneous alloys and X-ray photoelectron studies were consistent with these observations. The origin of the enhanced activity for the carbon supported catalysts is a result of higher H2 selectivity for the formation of hydrogen peroxide which is due to the surface composition and size distribution of the nanoparticles. The key problem remaining is the sequential hydrogenation of hydrogen peroxide which limits the utilisation of the direct synthesis methodology and this is discussed in detail.

Mechanism of Interaction of Polyphenols, Oxygen, and Sulfur Dioxide in Model Wine and Wine

Abstract: The interaction of oxygen, sulfur dioxide, and 4-methylcatechol (4-MeC) was studied in a model wine containing catalytic concentrations of iron and copper in order to provide further evidence that when a catechol and oxygen interact, hydrogen peroxide and a quinone are formed, both of which react with SO2. The aerial oxidation of the catechol in the presence of benzenesulfinic acid (BSA) slowly produced the BSA-quinone adduct in high yield. It was also quickly prepared by adding ferric chloride, demonstrating that the quinone is cleanly produced in this model wine and that the catechol is rapidly oxidized by Fe(III) ions. This reaction is important in the catalytic function of the metal. The oxygen and SO2 molar reaction ratio was 1:2, which is consistent with one mole equivalent of SO2 reacting with hydrogen peroxide and a second with the quinone. When BSA was added to the system to trap the quinone the ratio was reduced to 1:1. The rate of reaction of oxygen and SO2 increased with catechol concentration. However, the rate of reaction of oxygen was also markedly accelerated by SO2 and by BSA, and it is proposed that substances that react with quinones accelerate catechol autoxidation. When 4-MeC was oxidized in the presence of SO2, ~38% of the quinone that was formed reacted with bisulfite to produce the sulfonic acid adduct and most of the remainder was reduced back to the catechol. The O2/SO2 molar reaction ratio in two red wines was 1:~1.7, suggesting that some nucleophilic substances may be competing with bisulfite for quinones. The rate of reaction of oxygen was also accelerated by SO2 in red wine.