Distribution Of Oxidation Products Research Articles

Occurrence and distribution of ladderane oxidation products in different oceanic regimes

Abstract. Ladderane fatty acids are commonly used as biomarkers for bacteria involved in anaerobic ammonium oxidation (anammox). These lipids have been experimentally shown to undergo aerobic microbial degradation to form short chain ladderane fatty acids. However, nothing is known of the production or the distribution of these oxic biodegradation products in the natural environment. In this study, we analysed marine water column particulate matter and sediment from three different oceanic regimes for the presence of ladderane oxidation products (C14 ladderane fatty acids) and of original ladderane fatty acids (C18 and C20 ladderane fatty acids). We found that ladderane oxidation products, i.e. C14 ladderane fatty acids, are already produced within the water column of the Arabian Sea oxygen minimum zone (OMZ) and thus only low amounts of oxygen (< 3 μM) are needed for the β-oxidation of original ladderane fatty acids to proceed. However, no short chain ladderane fatty acids were detected in the Cariaco Basin water column, where oxygen concentrations were below detection limit, suggesting that the β-oxidation pathway is inhibited by the absence of molecular oxygen, or that the microbes performing the degradation are not proliferating under these conditions. Comparison of distributions of ladderane fatty acids indicates that short chain ladderane fatty acids are mostly produced in the water column and at the sediment surface, before being preserved deeper in the sediments. Short chain ladderane fatty acids were abundant in Arabian Sea and Peru Margin sediments (ODP Leg 201), often in higher concentrations than the original ladderane fatty acids. In a sediment core taken from within the Arabian Sea OMZ, short chain ladderanes made up more than 90% of the total ladderanes at depths greater than 5 cm below sea floor. We also found short chain ladderanes in higher concentrations in hydrolysed sediment residues compared to those freely occurring in lipid extracts, suggesting that they had become bound to the sediment matrix. Furthermore, these matrix-bound short chain ladderanes were found at greater sediment depths than short chain ladderanes in the lipid extract, suggesting that binding to the sediment matrix aids the preservation of these lipids. Though sedimentary degradation of short chain ladderane fatty acids did occur, it appeared to be at a slower rate than that of the original ladderane fatty acids, and short chain ladderane fatty acids were found in sediments from the Late Pleistocene (~ 100 kyr). Together these results suggest that the oxic degradation products of ladderane fatty acids may be suitable biomarkers for past anammox activity in OMZs.

Electrocatalytic oxidation of glycerol on Pt/C in anion-exchange membrane fuel cell: Cogeneration of electricity and valuable chemicals

Electrocatalytic oxidation of glycerol for cogenerating electricity and higher-valued chemicals on a Pt/C anode catalyst (2.4nm) in an anion-exchange membrane fuel cell (AEMFC) was investigated. The peak power density of an anion-exchange membrane – direct glycerol fuel cell (AEM-DGFC) with 1.0mgPtcm−2 anode and non-PGM catalyst cathode can reach 124.5mWcm−2 at 80°C and 58.6mWcm−2 at 50°C, while the highest selectivity of C3 acids (glyceric acid+tartronic acid) can reach 91%. The study found that higher pH reaction media could enhance fuel cell output power density (electricity generation) and selectivity of C3 acids, while lower glycerol concentration could improve the selectivity of deeper-oxidized products (mesoxalic acid and oxalic acid). The fuel cell reactor with the Pt/C anode catalyst demonstrated an excellent reusability, and successfully obtained tartronic acid with a selectivity of 50% and mesoxalic acid with a selectivity of 7%, which are high compared to heterogeneous catalytic glycerol oxidation in batch reactors. It is found that the anode overpotential can regulate the oxidation product distribution, and that higher anode overpotentials favor CC bond breaking, thus lowering the C3 acids selectivity. The reaction sequence of glycerol electro-oxidation detected in an electrolysis half cell with an on-line sample collection and off-line HPLC analysis agrees with the results obtained from single fuel cell tests. However, inconsistencies between the two systems still exist and are possibly due to different reaction environments, such as electrode structure, glycerol:catalyst ratio, and residence time of reactants.

Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies

Abstract. Progress has been made over the past decade in predicting secondary organic aerosol (SOA) mass in the atmosphere using vapor pressure-driven partitioning, which implies that SOA compounds are formed in the gas phase and then partition to an organic phase (gasSOA). However, discrepancies in predicting organic aerosol oxidation state, size and product (molecular mass) distribution, relative humidity (RH) dependence, color, and vertical profile suggest that additional SOA sources and aging processes may be important. The formation of SOA in cloud and aerosol water (aqSOA) is not considered in these models even though water is an abundant medium for atmospheric chemistry and such chemistry can form dicarboxylic acids and "humic-like substances" (oligomers, high-molecular-weight compounds), i.e. compounds that do not have any gas phase sources but comprise a significant fraction of the total SOA mass. There is direct evidence from field observations and laboratory studies that organic aerosol is formed in cloud and aerosol water, contributing substantial mass to the droplet mode. This review summarizes the current knowledge on aqueous phase organic reactions and combines evidence that points to a significant role of aqSOA formation in the atmosphere. Model studies are discussed that explore the importance of aqSOA formation and suggestions for model improvements are made based on the comprehensive set of laboratory data presented here. A first comparison is made between aqSOA and gasSOA yields and mass predictions for selected conditions. These simulations suggest that aqSOA might contribute almost as much mass as gasSOA to the SOA budget, with highest contributions from biogenic emissions of volatile organic compounds (VOC) in the presence of anthropogenic pollutants (i.e. NOx) at high relative humidity and cloudiness. Gaps in the current understanding of aqSOA processes are discussed and further studies (laboratory, field, model) are outlined to complement current data sets.

Hydrogen production by photocatalytic steam reforming of methanol on noble metal-modified TiO 2

The photocatalytic production of hydrogen by methanol steam reforming was studied over a series of pristine or noble metal (Ag, Au, Au–Ag alloy and Pt) – modified TiO 2 photocatalysts, synthesised by flame spray pyrolysis or by the deposition of preformed noble metal nanoparticles on TiO 2. A closed recirculation apparatus was employed, with the photocatalyst bed continuously fed with methanol/water vapours. Methanol underwent oxidation up to CO 2 through the formation of formaldehyde and formic acid. Carbon monoxide, methane, methyl formate, acetaldehyde and dimethyl ether were identified as side products. Hydrogen evolved at constant rate, which significantly increased upon noble metal addition, Pt being the most effective co-catalyst, followed by gold and silver, according to their work function values. A systematic investigation into the effects of the inlet gas composition gave valuable information on the prevailing reaction paths and on the conditions of process optimisation, also in terms of distribution of CH 3OH oxidation products.

Hydrocarbon oxidation by homogeneous and heterogeneous non-heme iron (III) catalysts with H 2O 2

Homogeneous ( LFe III) and heterogeneous ( LFe III·SiO 2) [ L = 3-{2-[2-(3-hydroxy-1,3-diphenyl-allylideneamino)-ethylamino]-ethylimino}-1,3-diphenyl-propen-1-ol] catalysts have been synthesized and evaluated catalytically. In CH 3CN, both the homogeneous and heterogeneous catalysts were efficient in alkene oxidations. Cyclohexane oxidation provides total yield of 12.1% and 7.3% with an alcohol/ketone (A/K) ratio of 1.75 and 1.60 by the LFe III and the LFe III·SiO 2 catalysts respectively. UV–vis kinetic data suggest formation of LFe III–OOH species. EPR data show that in the presence of CH 3CN, low-spin Fe III ( S = 1/2) centers are formed, which are responsible for the catalytic activity. The heterogeneous LFe·SiO 2 catalyst, tested up to 5 re-uses, shows a total yield loss ∼4% per use, providing the same distribution of oxidation products.

Emissions and ambient distributions of Biogenic Volatile Organic Compounds (BVOC) in a ponderosa pine ecosystem: interpretation of PTR-MS mass spectra

Abstract. Two proton-transfer-reaction mass spectrometry systems were deployed at the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen-Southern Rocky Mountain 2008 field campaign (BEACHON-SRM08; July to September, 2008) at the Manitou Forest Observatory in a ponderosa pine woodland near Woodland Park, Colorado USA. The two PTR-MS systems simultaneously measured BVOC emissions and ambient distributions of their oxidation products. Here, we present mass spectral analysis in a wide range of masses (m/z 40+ to 210+) to assess our understanding of BVOC emissions and their photochemical processing inside of the forest canopy. The biogenic terpenoids, 2-methyl-3-butene-2-ol (MBO, 50.2%) and several monoterpenes (MT, 33.5%) were identified as the dominant BVOC emissions from a transmission corrected mass spectrum (PTR-MS), averaged over the daytime (11 a.m. to 3 p.m., local time) of three days. To assess contributions of oxidation products of local BVOC, we calculate an oxidation product spectrum with the OH- and ozone-initiated oxidation product distribution mass spectra of two major BVOC emissions at the ecosystem (MBO and β-pinene) that were observed from laboratory oxidation experiments. The majority (~76%) of the total signal in the transmission corrected PTR-MS spectra could be explained by identified compounds. The remainder are attributed to oxidation products of BVOC emitted from nearby ecosystems and transported to the site, and oxidation products of unidentified BVOC emitted from the ponderosa pine ecosystem.

Crossover Effects on Product Distribution of Ethanol Oxidation at Various Anode Catalysts

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Oxidation pathways of natural dye hematoxylin in aqueous solution

The oxidation mechanism of hematoxylin was studied in phosphate buffers and 0.1 M KCl by cyclic voltammetry and UV-Vis spectroscopy under deaerated conditions. The redox potential of hematoxylin in buffered solution strongly depends on pH. A two electron oxidation is preceded by deprotonation. The homogeneous rate of deprotonation process of hematoxylin in 0.1 M phosphate buffer is kd = (2.5 ± 0.1) × 104 s–1. The cyclic voltammetry under unbuffered conditions shows the distribution of various dissociation forms of hematoxylin. The dissociation constants pK1 = 4.7 ± 0.2 and pK2 = 9.6 ± 0.1 were determined using UV-Vis spectroscopy. The final oxidation product was identified by gas chromatography with mass spectrometry detection as hemathein. The distribution of oxidation products differs under buffered and unbuffered conditions. The dye degradation in natural unbuffered environment yields hemathein and hydroxyhematoxylin, which is absent in buffered solution.

Towards a Non Empirical Kinetic Model for the Lifetime Prediction of Polyethylene Pipes Transporting Drinking Water

AbstractA kinetic model has been elaborated to predict the lifetime of polyethylene pipes transporting slightly pressurized (3–12 bars) drinking water disinfected by free radical reagents. This model is composed of three levels: i) A system of differential equations, derived from a mechanistic scheme for radical chain oxidation in the presence of free radical reagents, giving access to the spatial distribution (in the pipe wall) of oxidation products and stabilizer concentration; ii) Equations allowing to predict the profiles of average molar masses from the spatial distribution of chain scissions and crosslinking events; iii) An empirical creep equation and a failure criterion derived from regression curves obtained in pure water (without disinfectant). It is assumed that the chemical degradation modifies only the time to transition between ductile and brittle regimes of failure, and that this time is linked to the weight average molar mass according to the classical power law. By superimposing these three levels, it is possible to predict the time to failure under the coupled effects of pressure and chemical degradation. This model is successfully applied to the case of chlorine dioxide.

Solvent Effects on the AIBN Forced Degradation of Cumene: Implications for Forced Degradation Practices

Solvent effects on the AIBN and ACVA forced degradation of cumene are explored. The degradant formation rates of the three cumene oxidative degradants, cumene hydroperoxide, acetophenone, and 2-phenyl-2-propanol are reported. The relative abundance and ratios of these three degradants provide insight into the fate of the peroxy radical oxidants generated by the forced stress system, and suggest that alkoxy radicals are actually a significant source of the observed reactivity. The presence of even 1% methanol in the forced stress solvent significantly quenches this alkoxy radical reactivity, dramatically reducing the overall degradation rate and leaving cumene hydroperoxide as the major product of the oxidation reaction. The origin of this significant solvent effect on the oxidation product distribution is shown to be related to the preferential H-atom abstraction from methanol and its trace impurities by any alkoxy radicals present in the reaction solution. The implications for these observations are explored with the intent of producing more predictive oxidative forced stress experiments.

Hydrocarbon oxidation with hydrogen peroxide and pentafluoroiodosylbenzene catalyzed by unusually distorted macrocycle manganese complexes

The highly distorted aza macrocycle manganese complexes as the oxidation catalyst were synthesized newly to achieve more green hydrocarbon oxidation; macrocycle 1 ringed by two bipyridine moieties and macrocycle 3 with two bipyridine and two amide bonds in the ring were prepared, and the catalytic abilities of these macrocycle manganese complexes 2 and 4 were examined. A remarkable result is that the unusually distorted manganese complex 4 coordinated by two nitrogen and two oxygen atoms of the macrocyclic ring is capable of catalyzing efficient oxidation of various alkanes and aromatic compounds with hydrogen peroxide. Catalyzed by this complex 4, a variety of alkenes can be oxidized by hydrogen peroxide and their epoxides are formed in high yields. In contrast, complex 2 shows the failure to catalyze efficient oxidation of hydrocarbons with hydrogen peroxide. To evaluate the catalytic abilities of new complexes 2 and 4 strictly, the alkene oxidation was conducted by employing 2 and 4 as the catalyst and pentafluoroiodosylbenzene as the terminal oxidant, and as a result, these complexes 2 and 4 were capable of converting various types of alkenes to their oxidation products with high yields. Moreover, the following new results were found. (A) Norbornene oxidation catalyzed by complexes 2 with different length of side chains indicates that the yield and exo/endo of epoxide depend on the side chains, suggesting that the side chain could control the catalytic ability. (B) The product distribution of styrene oxidation catalyzed by complex 2 differs greatly from that by complex 4, suggesting that the macrocyclic structure and coordinated atom affect the alkene oxidation.

Kinetic modelling of the thermal oxidation of polyisoprene elastomers. Part 2: Effect of sulfur vulcanization on mass changes and thickness distribution of oxidation products during thermal oxidation

Thermal oxidation of sulfur vulcanized polyisoprene samples was studied by gravimetry and IR mapping of carbonyl groups (to determine the oxidized layer thickness (TOL)) at temperatures ranging from 60 to 150 °C in air. Oxidation appears noticeably lower than that for the starting non-vulcanized polyisoprene, revealing a stabilizing effect of sulfur-containing species. After a short period where mass loss presumably due to water evaporation predominates, the sample mass increases until a plateau corresponding to 6.3% (at 60 °C) to 0.5% (at 140 °C) mass gain. Practically no weight gain (∼0.1%) was observed at 150 °C. The mass uptake is due to oxygen grafting to the chains. TOL varies from about 4.6 mm (70 °C) to about 1 mm (150 °C). A kinetic model, derived from a mechanistic scheme of radical chain oxidation including stabilizing events due to hydroperoxide reduction by sulfur-containing groups and taking into account the diffusion–reaction coupling, was established and numerically resolved. The model predictions for mass changes and TOL values are in good agreement with experimental data.

Determination of spatial distribution of oxidation products in ultra-high molecular weight polyethylene by staining with sulphur dioxide or hydrochloric acid

Treating a sample of oxidised ultra-high molecular weight polyethylene (UHMWPE) with SO 2 will cause a reaction between SO 2 and hydroperoxides in the sample, forming a hydrosulphate group. During subsequent heat treatment the hydrosulphate group will leave as sulphuric acid, and a double bond will form in the polymer chain. During this step the sample turns brown. This browning has previously been used to determine the spatial distribution of oxidation in PP. The aim of this work was to apply this also to UHMWPE and to determine what causes the browning and how well it corresponds to the true distribution and concentration of hydroperoxides. The possible future use of the technique to determine the spatial distribution of oxidation in UHMWPE has also been evaluated. The true nature of the browning has been difficult to establish, but it seems to originate from a charge transfer complex between the double bonds and the sulphuric acid. A similar type of coloration develops in oxidised UHMWPE, when it is treated with hot hydrochloric acid. However, in that case the coloration is proportional to the carbonyl concentration and has been concluded to originate from the oxonium ion formed by protonation of ketones. The coloration of both SO 2/heat-treated samples and samples treated with hot hydrochloric acid can be used to give a qualitative picture of the spatial distribution of oxidation in UHMWPE. The techniques have been applied to study the heterogeneous oxidation in badly consolidated UHMWPE. It was found that the very good spatial resolution gave information about the heterogeneous oxidation that is not possible to obtain when using other techniques, such as FTIR mapping and imaging chemiluminescence.

In Vivo and in Vitro Lipid Peroxidation of Arachidonate Esters: The Effect of Fish Oil ω-3 Lipids on Product Distribution

The effect of lipid composition on the distribution of free radical oxidation products derived from arachidonic acid (20:4) esters has been studied in vitro and in vivo. Pro-inflammatory prostaglandin (PG) F2-like compounds, termed F2-isoprostanes (IsoPs), are produced in vivo and in vitro by the free radical-catalyzed peroxidation of arachidonic acid. Controlled free radical oxidation of mixtures of fatty acid esters in vitro showed that the formation of IsoPs from arachidonate is dramatically influenced by the presence of other fatty acid esters in the reaction mixture. Thus, three lipid mixtures containing the same arachidonate concentration but different amounts of other fatty esters (16:0; 18:1; 18:2; 20:5, and 22:6) were oxidized, and the product yields were determined by GC and LC/MS/MS analysis. The yield of F2-IsoP formed after 1 h of oxidation was 18% (based on arachidonate consumed) for mixtures containing arachidonate as the only oxidizable PUFA, but yields of these biologically active compounds dropped to 6% in polyunsaturated fatty acid (PUFA) mixtures typical of those found in tissues of fish oil-fed animals. F2-IsoP levels were also monitored in the livers of mice on diets supplemented with eicosapentaenoic acid (C20:5 omega-3; EPA), the PUFA most abundant in fish oil. While the level of arachidonic acid present in livers was not significantly different from that in control animals, levels of IsoPs in the liver were reduced in the EPA-fed mice compared to those in controls under conditions of oxidative stress (60 +/- 25% reduction, n = 5) or at baseline (48 +/- 14% reduction, n = 5). These results suggest that dietary omega-3 PUFAs may influence the formation of bio-active peroxidation products derived from omega-6 PUFAs by channeling the free radical pathway away from the F2-IsoPs.

Study of the Effect of Gas Space Time on the Combination of Methane Gas-Phase Oxidation and Catalytic Oxidative Coupling over Mn/Na2WO4/SiO2 Catalyst

The effects of gas space time on the product distribution in noncatalytic gas-phase methane oxidation and in the combination reaction of noncatalytic and catalytic oxidative coupling of methane (OCM) over Mn/Na2WO4/SiO2 catalyst were studied. For the gas-phase reaction, methane and oxygen conversions and syngas selectivity increase drastically with increasing gas space time (tg) from 6.2 to 7.7 s; however, the selectivity of C2 hydrocarbons decreases sharply in this range and the concentration of C2H4 in the producing mixture is much lower than that of CO and H2. For the combination reaction, there is a minimum of methane conversion and C2 hydrocarbon selectivity with tg increasing from 3 to 5 s resulting from the variation of the mixture composition reaching the catalyst bed. The dilution of the catalyst bed with silica chips in the combination reaction partially restricts the sequential oxidation of products and raises the selectivities of ethylene and hydrogen. Surface enrichment of Na, W, and Mn speci...

Solid-State 13C NMR Investigation of the Oxidative Degradation of Selectively Labeled Polypropylene by Thermal Aging and γ-Irradiation

Unstabilized polypropylene (PP) films having selective 13C isotopic labeling were subjected to thermal aging at 50, 80, and 109 °C and to γ-irradiation at 24 and 80 °C. The oxidized films were examined using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Dramatic differences were found in the type and distribution of oxidation products originating from the three carbon atom sites within the PP macromolecule (tertiary carbon, secondary carbon, and methyl side group). Most of the oxidation products that formed on the polymer chain originated through chemical reactions at the PP tertiary carbons. Under all of the aging conditions examined, tertiary peroxides (from the PP tertiary site) were the most abundant functional group produced. Also originating from the PP tertiary carbon were significant amounts of tertiary alcohols, together with several more minor products that included “chain-end” methyl ketones. No significant amount of peroxides or alcohols associated with the PP secondary carbon sites was detected. A substantial yield of carboxylate groups was identified (acids, esters, etc.). The majority of these originated from the PP secondary carbon site, from which other minor products also formed, including in-chain ketones. We found no measurable yield of oxidation products originating from reaction at the PP methyl group. Remarkably similar distributions of the major oxidation products were obtained for thermal aging at different temperatures, whereas the product distributions obtained for irradiation at the different temperatures exhibited significant differences. Time-dependent concentration plots have been obtained, which show the amounts of the various oxidation products originating at the different PP sites, as a function of the extent of material oxidation.

Selective oxidation of ammonia to nitrogen on transition metal containing mixed metal oxides

The selective catalytic oxidation of ammonia to nitrogen (NH3-SCO) has been studied over hydrotalcite derived mixed metal oxides containing Cu, Co, Fe or Ni. XRD, BET, NH3-TPD and TPR techniques were used for catalysts characterization. Results of NH3-SCO were compared with those of selective catalytic reduction of NO with NH3 (NO-SCR). Reaction mechanism was studied by temperature-programmed surface reaction (TPSR) and activity tests with a various contact time. Catalytic performance of the studied samples depends on both kind and loading of transition metals in the mixed metal oxide system. The Cu-containing samples have been found to be the most active catalysts of the NH3-SCO process. Transition metal loading strongly influences distribution of ammonia oxidation products. The highest selectivity to N2 was measured for the catalysts with the lowest transition metal content.

C1 oxidative coupling via bromine activation and tandem catalytic condensation and neutralization over CaO/zeolite compositesII. Product distribution variation and full bromine confinement

We describe a three-step bromine-mediated process for oxidative coupling of methane using O2 as oxidant. In the first step, a supported metal bromide solid is treated with O2 to generate Br2 and supported metal oxide. The Br2 thus formed reacts with excess CH4, giving a mixture of CH4, bromomethanes, and HBr. This mixture is passed over a CaO/zeolite composite which condenses bromocarbons with 100% conversion to products, and neutralizes HBr to reform the metal bromide. The resulting product contains higher hydrocarbons, excess CH4, and water. Once the HBr neutralizing capacity of the CaO is spent, the supported CaBr2/ZSM-5 may also serve as catalyst for methyl bromide coupling. The effect of temperature, pressure, and reaction time on the intermediate methane bromination as well as on the overall partial oxidation product distribution is discussed. Incorporation of this scheme into a reactor into which only methane and O2 are fed is described.

C 1 oxidative coupling via bromine activation and tandem catalytic condensation and neutralization over CaO/zeolite composites : II. Product distribution variation and full bromine confinement

We describe a three-step bromine-mediated process for oxidative coupling of methane using O 2 as oxidant. In the first step, a supported metal bromide solid is treated with O 2 to generate Br 2 and supported metal oxide. The Br 2 thus formed reacts with excess CH 4, giving a mixture of CH 4, bromomethanes, and HBr. This mixture is passed over a CaO/zeolite composite which condenses bromocarbons with 100% conversion to products, and neutralizes HBr to reform the metal bromide. The resulting product contains higher hydrocarbons, excess CH 4, and water. Once the HBr neutralizing capacity of the CaO is spent, the supported CaBr 2/ZSM-5 may also serve as catalyst for methyl bromide coupling. The effect of temperature, pressure, and reaction time on the intermediate methane bromination as well as on the overall partial oxidation product distribution is discussed. Incorporation of this scheme into a reactor into which only methane and O 2 are fed is described.

Distribution and significance of chlorophyll derivatives and oxidation products during the spring phytoplankton bloom in the Celtic Sea April 2002

The abundances and distributions of chlorophyll a and its common transformation products have been profiled by high performance liquid chromatography during the disruption, re-establishment, growth and senescence of a phytoplankton bloom in the Celtic Sea during April 2002. Transformation products of chlorophyll a indicative of herbivory of the phytoplankton bloom have been identified using atmospheric pressure chemical ionisation liquid chromatography-multistage mass spectrometry and chlorophyll oxidation products, formed by autoxidation, are present in increasing abundance in samples collected during the later stages of bloom development. The formation of oxidation products during the earliest stages in the chlorophyll transformation pathway identifies water column processes as sources of these early intermediates in the formation of geologic aetioporphyrins and/or cycloalkanoporphyrins.