The use of short time-on-stream in situ spectroscopic transient kinetic isotope techniques to investigate the mechanism of hydrocarbon selective catalytic reduction (HC-SCR) of NOx at low temperatures

The problem of differentiating between active and spectator species that have similar infrared spectra has been addressed by developing short time-on-stream in situ spectroscopic transient isotope experimental techniques (STOS-SSITKA). The techniques have been used to investigate the reaction mechanism for the reduction of nitrogen oxides (NOx) by hydrocarbons under lean-burn (excess oxygen) conditions on a silver catalyst. Although a nitrate-type species tracks the formation of isotopically labeled dinitrogen, the results show that this is misleading because a nitrate-type species has the same response to an isotopic switch even under conditions where no dinitrogen is produced. In the case of cyanide and isocyanate species, the results show that it is possible to differentiate between slowly reacting spectator isocyanate species, probably adsorbed on the oxide support, and reactive isocyanate species, possibly on or close to the active silver phase. The reactive isocyanate species responds to an isotope switch at a rate that matches that of the rate of formation of the main product, dinitrogen. It is concluded that these reactive isocyanates could potentially be involved in the reduction of NOx whereas there is no evidence to support the involvement of nitrate-type species that are observable by infrared spectroscopy.

Novel UV-activated colorimetric oxygen indicator

The results of a detailed characterization study of a novel UV-activated colorimetric oxygen indicator are described. The indicator uses nanoparticles of titania to photosensitize the reduction of methylene blue by triethanolamine in a polymer encapsulation medium, using UVA light. Upon UV irradiation, the indicator bleaches and remains in this colorless state in the dark, unless and until it is exposed to oxygen, whereupon its original color is restored. The indicator is reusable and irreversible. The rate of color recovery is proportional to the level of oxygen present. A layer of PET (poly(ethylene terephthalate)), of thickness b, placed on top of the indicator film slows down its response, and the 90% recovery time is proportional to b.

OXYGEN CATALYSIS BY ANHYDROUS RUTHENIUM(IV) OXIDE

The results of a kinetic study of the oxidation of water to oxygen by Ce(IV) ions in different acid media, mediated by anhydrous ruthenium(IV) oxide are described. In an acid medium which is predominantly HClO4 the kinetics are diffusion controlled and first order with respect to both [Ce(IV)] and [RuO2] and exhibit an activation energy of 19 kJ mol-1. In 0.5 mol dm-3 H2SO4 the kinetics are much slower and complex, the rate decreasing with increasing [Ce(III)]. The kinetics of catalysis observed in all the different acid media studied are readily interpreted using an electrochemical model in which the catalyst particles are considered as acting as microelectrodes which mediate electron transfer between a Nernstian reduction reaction (Ce(IV) --> Ce(III)) and an irreversible oxidation reaction (H2O --> 2H+ + 1/2O2). This electrochemical model is used to analyse the complex kinetics observed in 0.5 mol dm-3 H2SO4 and extract mechanistic information concerning the nature of the rate determining step.

Self-potential and spectral induced polarization signals associated with microbial sulphate reduction

Self-potential and spectral induced polarization responses associated with microbial processes involved in sulphate reduction have been monitored in a Perspex Winogradsky column filled with glass beads and growth medium. Salt-bridge is utilized as an electrolytic contact between experiment and control column. Equally spaced SP electrodes are used in combination of Ag-AgCl electrodes to compare electrodic and SP signals associated with the microbial processes involved in sulphate reduction. This study reveals that magnitude of SP varies from 5 to -2 mV and Electrodic potential 0 to -20 mV at the time of domination (day 39) of sulphate reducing bacteria which are very small in comparison to those measured by fixing both measuring and reference Ag-AgCl electrodes in experiment column. We observed that real and imaginary parts of complex conductivities increase with increase in production of H2S and CO in the experiment column. Both real and imaginary parts of surface complex conductivity vary at low frequencies similar to typical growth curve of bacterial population. Sodium lactate as a carbon source, dissolved in Lagan River water was flushed into the column for biostimulation on 144th day. The dissolved oxygen in flushed fluid might have killed the anaerobes in the column and decrease in complex conductivities similar to death phase of bacteria is observed for one week. The results obtained from this experiment should contribute to further understanding the biogeophysical responses involved in complex environments.


Read More: http://library.seg.org/doi/abs/10.1190/segj092009-001.57

Age-related changes in non-receptor dependent generation of reactive oxygen species from phagocytes of healthy adults

Several authors have shown that neutrophil generation of reactive oxygen species (ROS) declines with advancing age. Similar changes have also been suggested in monocytes. In both cases alterations in second messenger activity have been implicated as the most likely explanation for these observations. The aim of this study was to investigate the effect of age on phagocyte ROS generation, stimulated by the direct activation of protein kinase C (PKC). Venous blood was drawn from normal healthy subjects, cells were separated on a double density gradient into mononuclear and polymorphonuclear (pmn) cells. Phorbol myristate acetate (PMA) was employed as a cell stimulus. Superoxide generation was measured by cytochrome c reduction and myeloperoxidase (MPO) products by measurement of peak luminol chemiluminescence (CL). Fifty-eight subjects, 25 males and 33 females, were studied, median age 49 years (range 26-88 years). Polymorphonuclear cell superoxide generation was significantly higher in males and there was a trend towards higher pmn MPO product generation in males. Using Spearman's ranked correlation coefficient, monocyte superoxide generation was negatively correlated with age (r = -0.473, P <0.001). No changes in the generation of MPO products was found. There were also trends towards a negative correlation of pmn cytochrome c reduction and peak luminol CL with age in males but not females. Since PMA directly activates protein kinase C, reduced monocyte superoxide generation with increasing age appears to be related to alterations in the ROS generating system downstream of the cell receptor. Impaired monocyte superoxide generation may have implications for non-specific defence against certain infections and early tumour growth in the elderly. Factors underlying these changes in monocyte function therefore require further study.

Reactions of nitrogen and oxygen surface groups in nanoporous carbons under inert and reducing atmospheres

The reactions of surface functional groups have an important role in controlling conversion of char nitrogen to NOx during coal combustion. This study involved an investigation of the thermal stability and reactions of nitrogen surface functional groups in nanoporous carbons. Four suites of carbons, which were used as models for coal chars, were prepared with a wide range of nitrogen and oxygen contents and types of functional groups. The porous structures of the carbons were characterized by gas adsorption methods while chemical analysis, X-ray photoelectron spectroscopy, and X-ray near edge structure spectroscopy were used to characterize the surface functional groups. Temperature programmed desorption and temperature programmed reduction methods were used to study the reactivity of the surface functional groups during heat treatment under inert and reducing conditions. Heat treatment studies show that the order of stability of the functional groups is quaternary nitrogen > pyridinic > pyrrolic > pyridine N-oxide. Pyridine N-oxide surface groups desorb NO and form N-2 via surface reactions at low temperature. Pyrrolic and pyridinic functional groups decompose and react with surface species to give NH3, HCN, and N-2 as desorption products, but most pyrrolic groups are preferentially converted to pyridinic and quaternary nitrogen. The main desorption product is N-2. Approximately 15-40 wt % of the original nitrogen was retained in the carbons mainly as quaternary nitrogen after heat treatment to 1673 K. The results are discussed in terms of decomposition ranges for surface functional groups and reaction mechanisms of surface species.

Field observation of sequestration of uranium in iron-rich sediments under sequential reduction-oxidation conditions at the DOE Oak Ridge IFRC

At the U.S. DOE Oak Ridge Integrated Field Research Challenge (ORIFRC) site, the iron content of shallow subsurface materials (i.e. weathered saprolite) is relatively high (up to 5-6% as w/w), and therefore, the forms of the iron species present plays a critical role in the long-term sequestration of uranium. A long term pilot-scale study of the bioreduction and reoxidation of uranium conducted at the ORIFRC area 3 site, adjacent to the former S-3 disposal ponds (source zone), has provided us with the opportunity to study the impact of iron species on the sequestration of U(VI). The aqueous U(VI) concentrations at the site were decreased to below the EPA MCL through the intermittent injection of ethanol as the electron donor. Previous field tests indicated that both oxygen and nitrate could oxidize the bioreduced U(IV) and cause a short-term rebound of aqueous phase uranium concentration after the oxidative agents were delivered directly to the bioreduced zone.

A field test has been conducted to examine the long-term effect of exposure of bioreduced sediments to nitrate in contaminated groundwater for more than 1,380 days at the Area 3 site. Contaminated groundwater was allowed to invade the previously bioreduced zone via the natural groundwater gradient after an extended period in which reducing conditions were maintained and the bioreduced zone was protected from the influx of upgradient contaminated groundwater. The geochemical response to the invasion of contaminated groundwater was dependent on whether the monitoring location is in the middle or the fringe of the previously bioreduced zone. In general, the nitrate concentrations in the previously bioreduced area, increased gradually from near zero to ~50-300 mM within 200 days and then stabilized. The pH declined from bioreduced levels of 6.2-6.7 to below 5.0. Uranium concentrations rebounded in all monitoring wells but at different rates. At most locations U concentrations rebounded, declined and then rebounded again. Methane gas disappeared while a significant level (20,000 to 44,000 ppmv) N2O was found in the groundwater of monitoring wells after three years of reoxidization.

The U(IV) in sediments was mainly reoxidized to U(VI) species. Based on XANES analysis, the predominate uranium in all samples after re-oxidation was similar to a uranyl nitrate form. But the U content in the sediment remained as high as that determined after bioreduction activates were completed, indicating that much of the U is still sequestrated in situ. SEM observations of surged fine sediments revealed that clusters of colloidal-sized (200-500nm) U-containing precipitates appeared to have formed in situ, regardless from sample of FW106 in non-bioactivity control area or of pre-bioreduced FW101-2 and FW102-3. Additionally, SEM-EDS and microprobe analysis, showed that the U-containing precipitates (~1% U) in FW106 are notably higher in Fe, compared to the precipitates (~1-2.5% U) from FW101-2 and FW102-3. However, XRF analysis indicated that the U content was remained as high as 2180 and 1810 mg/kg with U/Fe ratio at 0.077 and 0.055 vs 0.037 g/g, respectively in pre-bioreduced FW101-2 and FW102-3, suggesting more U sequestrated by Fe in pre-bioreduced sediments.

Atmospheric pressure, nonthermal plasma inactivation of MS2 bacteriophage: effect of oxygen concentration on virucidal activity

AimsThe main aim of this study was to determine the virucidal inactivation efficacy of an in-house-designed atmospheric pressure, nonthermal plasma jet operated at varying helium/oxygen feed gas concentrations against MS2 bacteriophage, widely employed as a convenient surrogate for human norovirus.

Methods and ResultsThe effect of variation of percentage oxygen concentration in the helium (He) carrier gas was studied and found to positively correlate with MS2 inactivation rate, indicating a role for reactive oxygen species (ROS) in viral inactivation. The inactivation rate constant increased with increasing oxygen concentrations up to 075% O-2. 3 log(10) (999%) reductions in MS2 viability were achieved after 3min of exposure to the plasma source operated in a helium/oxygen (9925%:075%) gas mixture, with >7 log(10) reduction after 9min exposure.

ConclusionsAtmospheric pressure, nonthermal plasmas may have utility in the rapid disinfection of virally contaminated surfaces for infection control applications.

Significance and Impact of StudyThe atmospheric pressure, nonthermal plasma jet employed in this study exhibits rapid virucidal activity against a norovirus surrogate virus, the MS2 bacteriophage, which is superior to previously published inactivation rates for chemical disinfectants.

Quantum yield measurements for the photocatalytic oxidation of Acid Orange 7 (AO7) and reduction of 2,6-dichloroindophenol (DCIP) on transparent TiO2 films of various thickness

This work comprises the photoactivity assessment of transparent sol–gel TiO2 coatings of various thickness using two test systems. The initial rates of both photocatalytic reactions, namely the oxidative bleaching of Acid Orange 7 (AO7) and the reductive bleaching of 2,6-dichlorindophenol (DCIP) increase linearly with increasing titania film thickness as well as with increasing absorbed light flux. The latter work revealed quantum yields (QY) of 0.19% and 92% for the AO7 and DCIP test system, respectively. The low QY for the AO7 oxidation is due to the combination of a slow irreversible reduction of oxygen and also for the oxidation of AO7, thus favouring the high efficiency for electron–hole recombination that is typical for aqueous organic pollutants. In contrast, the very high QY for the photocatalysed reduction of DCIP is due to the presence of a vast excess of glycerol which traps the photogenerated holes efficiently and so allow time for the slower reduction of dye to take place. Furthermore, the oxidation of glycerol results in the generation of highly reducing R-hydroxyalkyl radicals that are able to also reduce DCIP. As a consequence of this ‘current doubling’ effect, the observed QY (92%) is much higher than the apparent theoretical value of 50%.

Density functional theory study on the activation of molecular oxygen on a stepped gold surface in an aqueous environment: a new approach for simulating reactions in solution

The activation of oxygen molecules is an important issue in the gold-catalyzed partial oxidation of alcohols in aqueous solution. The complexity of the solution arising from a large number of solvent molecules makes it difficult to study the reaction in the system. In this work, O-2 activation on an Au catalyst is investigated using an effective approach to estimate the reaction barriers in the presence of solvent. Our calculations show that O-2 can be activated, undergoing OOH* in the presence of water molecules. The OOH* can readily be formed on Au(211) via four possible pathways with almost equivalent free energy barriers at the aqueous-solid interface: the direct or indirect activation of O-2 by surface hydrogen or the hydrolysis of O-2 following a Langmuir-Hinshelwood mechanism or an Eley-Rideal mechanism. Among them, the Eley-Rideal mechanism may be slightly more favorable due to the restriction of the low coverage of surface H on Au(211) in the other mechanisms. The results shed light on the importance of water molecules on the activation of oxygen in gold-catalyzed systems. Solvent is found to facilitate the oxygen activation process mainly by offering extra electrons and stabilizing the transition states. A correlation between the energy barrier and the negative charge of the reaction center is found. The activation barrier is substantially reduced by the aqueous environment, in which the first solvation shell plays the most important role in the barrier reduction. Our approach may be useful for estimating the reaction barriers in aqueous systems.

A Model to Understand the Oxygen Vacancy Formation in Zr-Doped CeO2:Electrostatic Interaction and Structural Relaxation

Using density functional theory with the inclusion of on-site Coulomb Correction, the O vacancy formation energies of CexZr1-xO2 solid solutions with a series of Ce/Zr ratios are calculated, and a model to understand the results is proposed. It consists of electrostatic and structural relaxation terms, and the latter is found to play a vital role in affecting the O vacancy formation energies. Using this model, several long-standing questions in the field, such as why ceria with 50% ZrO2 usually exhibit the best oxygen storage capacity, can be explained. Some implications of the new interpretation are also discussed.

Effect of cation structure on the oxygen solubility and diffusivity in a range of bis{(trifluoromethyl)sulfonyl}imide anion based ionic liquids for lithium-air battery electrolytes

This paper reports on the solubility and diffusivity of dissolved oxygen in a series of ionic liquids (ILs) based on the bis{(trifluoromethyl)sulfonyl}imide anion with a range of related alkyl and ether functionalised cyclic alkylammonium cations. Cyclic voltammetry has been used to observe the reduction of oxygen in ILs at a microdisk electrode and chronoamperometric measurements have then been applied to simultaneously determine both the concentration and the diffusion coefficient of oxygen in the different ILs. The viscosity of the ILs and the calculated molar volume and free volume is also reported. It is found that, within this class of ILs, the oxygen diffusivity generally increases with decreasing viscosity of the neat IL. An inverse relationship between oxygen solubility and IL free volume is reported for the two IL families implying oxygen is not simply occupying the available empty space. In addition, it is reported that the introduction of ether-group into the IL cation structure promotes the diffusivity of dissolved oxygen but reduces the solubility of the gas.

Oxygen and hydrogen sulfide concentration of Nootka Sound bottom water

Senior thesis written for Oceanography 445

The investigation of the reduction mechanism of the 5a-reductase enzyme of Penicillium decumbens /

The 5a-reductase of Penicillium decumbens ATCC 10436 was used as a model for the mammalian enzyme to investigate the mechanism of reduction of testosterone to 5adihydrotestosterone . The purpose of this study was to search for specific 5a-reductase inhibitors which antagonize prostate cancer . In a whole-cell biotransformation mode, this organism reduced testosterone (1) to 5a-dihydrosteroids (8) and 5aandrostane- 3, 17-dione (9) in yields of 28% and 37% respectively. Control experiments have shown that 5aandrostane- 3, 17-dione (9) can be produced from the corresponding alcohol (8) in a subsequent reaction separate from that catalysed by the 5a-reductase enzyme . Androst-4- ene-3, 17-dione (2) is reduced to give only (9) with a recovery of 80% The stereochemistry of the reduction was determined by 500 MHz ^H NMR analysis of the products resulting from the deuterium labelled substrates. The results were obtained by an analysis of the NOE difference spectra, double-quantum filtered phase sensitive COSY 2-D spectra, and ^^c-Ir 2-D shift correlation spectra of deuterium labelled products. According to the unambiguous assignment of the signals due to H-4a and H-4Ii in 5a-dihydro steroids, the NMR data show clearly that addition of hydrogen to the 4{5)K bond has occurred in a trans manner at positions 413 and 5a. To Study the reduction mechanism of this enzyme, several substrates were prepared as following; 3-methyleneandrost-4-en- 17fi-ol(3), androst-4-en-17i5-ol(5) , androst-4-en-3ii, 17fi-diol (6) and 4, 5ii-epoxyandrostane-3, 17-dione (7) . Results suggest that this enzyme system requires an oxygen atom at the 3-position of the steroid in order to bind the substrate. Furthermore, the mechanism of this 5a-reductase may proceed via direct addition of hydrogen at the 4,5 position without involvement of a carbonyl group as an intermediate.

Evaluation of mitochondrial function in a model of developmental programming of hypertension associated with transient neonatal oxygen exposure

UNE EXPOSITION NÉONATALE À L’OXYGÈNE MÈNE À DES MODIFICATIONS DE LA FONCTION MITOCHONDRIALE CHEZ LE RAT ADULTE Introduction: L’exposition à l’oxygène (O2) des ratons nouveau-nés a des conséquences à l’âge adulte dont une hypertension artérielle (HTA), une dysfonction vasculaire, une néphropénie et des indices de stress oxydant. En considérant que les reins sont encore en développement actif lors des premiers jours après la naissance chez les rats, jouent un rôle clé dans le développement de l’hypertension et qu’une dysfonction mitochondriale est associé à une augmentation du stress oxydant, nous postulons que les conditions délétères néonatales peuvent avoir un impact significatif au niveau rénal sur la modulation de l’expression de protéines clés du fonctionnement mitochondrial et une production mitochondriale excessive d’espèces réactives de l’ O2. Méthodes: Des ratons Sprague-Dawley sont exposés à 80% d’O2 (H) ou 21% O2 (Ctrl) du 3e au 10e jr de vie. En considérant que plusieurs organes des rats sont encore en développement actif à la naissance, ces rongeurs sont un modèle reconnu pour étudier les complications d’une hyperoxie néonatale, comme celles liées à une naissance prématurée chez l’homme. À 4 et à 16 semaines, les reins sont prélevés et les mitochondries sont extraites suivant une méthode d’extraction standard, avec un tampon contenant du sucrose 0.32 M et différentes centrifugations. L’expression des protéines mitochondriales a été mesurée par Western blot, tandis que la production d’ H202 et les activités des enzymes clés du cycle de Krebs ont été évaluées par spectrophotométrie. Les résultats sont exprimés par la moyenne ± SD. Résultats: Les rats mâles H de 16 semaines (n=6) présentent une activité de citrate synthase (considéré standard interne de l’expression protéique et de l’abondance mitochondriales) augmentée (12.4 ± 8.4 vs 4.1 ± 0.5 μmole/mL/min), une diminution de l’activité d’aconitase (enzyme sensible au redox mitochondrial) (0.11 ± 0.05 vs 0.20 ± 0.04 μmoles/min/mg mitochondrie), ainsi qu’une augmentation dans la production de H202 (7.0 ± 1.3 vs 5.4 ± 0.8 ρmoles/mg protéines mitochondriales) comparativement au groupe Ctrl (n=6 mâles et 4 femelles). Le groupe H (vs Ctrl) présente également une diminution dans l’expression de peroxiredoxin-3 (Prx3) (H 0.61±0.06 vs. Ctrl 0.78±0.02 unité relative, -23%; p<0.05), une protéine impliquée dans l’élimination d’ H202, de l’expression du cytochrome C oxidase (Complexe IV) (H 1.02±0.04 vs. Ctrl 1.20±0.02 unité relative, -15%; p<0.05), une protéine de la chaine de respiration mitochondriale, tandis que l’expression de la protéine de découplage (uncoupling protein)-2 (UCP2), impliquée dans la dispersion du gradient proton, est significativement augmentée (H 1.05±0.02 vs. Ctrl 0.90±0.03 unité relative, +17%; p<0.05). Les femelles H (n=6) (vs Ctrl, n=6) de 16 semaines démontrent une augmentation significative de l’activité de l’aconitase (0.33±0.03 vs 0.17±0.02 μmoles/min/mg mitochondrie), de l’expression de l’ATP synthase sous unité β (H 0.73±0.02 vs. Ctrl 0.59±0.02 unité relative, +25%; p<0.05) et de l’expression de MnSOD (H 0.89±0.02 vs. Ctrl 0.74±0.03 unité relative, +20%; p<0.05) (superoxide dismutase mitochondriale, important antioxidant), tandis que l’expression de Prx3 est significativement réduite (H 1.1±0.07 vs. Ctrl 0.85±0.01 unité relative, -24%; p<0.05). À 4 semaines, les mâles H (vs Ctrl) présentent une augmentation significative de l’expression de Prx3 (H 0.72±0.03 vs. Ctrl 0.56±0.04 unité relative, +31%; p<0.05) et les femelles présentent une augmentation significative de l’expression d’UCP2 (H 1.22±0.05 vs. Ctrl 1.03±0.04 unité relative, +18%; p<0.05) et de l’expression de MnSOD (H 1.36±0.01 vs. 1.19±0.06 unité relative, +14%; p<0.05). Conclusions: Une exposition néonatale à l’O2 chez le rat adulte mène à des indices de dysfonction mitochondriale dans les reins adultes, associée à une augmentation dans la production d’espèces réactives de l’oxygène, suggérant que ces modifications mitochondriales pourraient jouer un rôle dans l’hypertension artérielle et d’un stress oxydant, et par conséquent, être un facteur possible dans la progression vers des maladies cardiovasculaires. Mots-clés: Mitochondries, Reins, Hypertension, Oxygène, Stress Oxydant, Programmation