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In a study on the mechanism of stimulated petiole elongation in submerged plants, oxygen concentrations in petioles of the flood-tolerant plant Rumex palustris were measured with micro-electrodes. Short-term submergence lowered petiole partial oxygen pressure to c. 19 kPa whereas prolonged submergence under continuous illumination depressed oxygen levels to c. 8-12 kPa after 24 h. Oxygen levels in petioles depended on the presence of the lamina, even in submerged conditions, and on available light. In darkness, petiole oxygen levels in submerged plants dropped quickly to values as low as 0.5-4 kPa. It is hypothesized that prolonged submergence in the light is accompanied by a decrease in carbon dioxide in the petiole. Submergence-enhanced petiolar elongation rate was compared with emergent plants. Peak daily elongation rates occurred at the end of the dark period in emergent plants, but in the middle of the light period in submerged plants. We suggest that this shift in daily elongation pattern is induced by dependence of growth on photosynthetically derived oxygen in submerged plants. Implications of reduced oxygen for ethylene production are raised. Levels of 1- aminocyclopropane-1-carboxylic acid synthase and 1-aminocyclopropane-1-carboxylic acid oxidase and ethylene sensitivity are cited as potential factors in hypoxia-induced ethylene release.

An approach for visualizing and measuring the mass transfer around a single bubble rising in a quiescent liquid is reported. A colorimetric technique, developed by (Dietrich et al. Chem Eng Sci 100:172-182, 2013) using an oxygen sensitive redox dye was implemented. It was based on the reduction of the colorimetric indicator in presence of oxygen, this reduction being catalysed by sodium hydroxide and glucose. In this study, resazurin was selected because it offered various reduced forms with colours ranging from transparent (without oxygen) to pink (in presence of oxygen). These advantages made it possible to visualize the spatio-temporal oxygen mass transfer around rising bubbles. Images were recorded by a CCD camera and, after post-processing, the shape, size, and velocity of the bubbles were measured and the colours around the bubbles mapped. A calibration, linking the level of colour with the dissolved oxygen concentration, enabled colour maps to be converted into oxygen concentration fields. A rheoscopic fluid was used to visualize the wake of the bubbles. A calculation method was also developed to determine the transferred oxygen fluxes around bubbles of two sizes (d = 0.82 mm and d = 2.12 mm) and the associated liquid-side mass transfer coefficients. The results compared satisfactorily with classical global measurements made by oxygen micro-sensors or from the classical models. This study thus constitutes a striking example of how this new colorimetric method could become a remarkable tool for exploring gas-liquid mass transfer in fluids.

This work seeks to understand the kinetics of O2 and SO2 consumption of air-saturated red wine as a function of its chemical composition, and to describe the chemical changes suffered during the process in relation to the kinetics. Oxygen Consumption Rates (OCRs) are faster with higher copper and epigallocatechin contents and with higher absorbance at 620 nm and slower with higher levels of gallic acid and catechin terminal units in tannins. Acetaldehyde Reactive Polyphenols (ARPs) may be key elements determining OCRs. It is confirmed that SO2 is poorly consumed in the first saturation. Phenylalanine, methionine and maybe, cysteine, seem to be consumed instead. A low SO2 consumption is favoured by low levels of SO2, by a low availability of free SO2 caused by a high anthocyanin/tannin ratio, and by a polyphenolic profile poor in epigallocatechin and rich in catechin-rich tannins. Wines consuming SO2 efficiently consume more epigallocatechin, prodelphinidins and procyanidins., This work has been funded by the Spanish MINECO (Project AGL2014-59840 and RTC-2015-3379) and partly cofunded by the European Union (FEDER). V.C. received a grant from the Spanish FPU program. Universidad de Zaragoza, Fundación Bancaria Ibercaja and Fundación CAI are acknowledged for the research stay grant CB3/15. Funding from Diputación General de Aragón (T53) and Fondo Social Europeo is acknowledged.

International audience; The auto-oxidation of trans-1,2-disiloxybenzocyclobutene was found to be very efficient, giving endoperoxide in quantitative yield. Each step of the mechanism of spin-forbidden addition of triplet oxygen O2 was studied by both EPR/spin trapping and theoretical studies.

International audience; The authors have previously shown that neonatal hyperoxic stress leads to high blood pressure, impaired endothelium-mediated vasodilatation, and increased vascular production of superoxide anion by NAD(P)H oxidase in adulthood. However, it is unknown whether changes in nitric oxide (NO) production and/or bioinactivation prevail and whether NO synthase (NOS) is also a source of superoxide. The purpose of this study was to evaluate whether adult animals exposed to neonatal hyperoxic stress have impaired vascular NO production associated with NOS uncoupling participating to vascular superoxide production and vascular dysfunction. In adult male rats exposed to 80% oxygen from day 3 to 10 of life (H, n = 6) versus room air controls (CTRL, n = 6), vascular (aorta) NO production is decreased at baseline (CTRL: 21 +/- 1 vs. H: 16 +/- 2 4,5-diaminofluorescein diacetate fluorescence intensity arbitrary units; P < 0.05) and after carbachol stimulation (acetylcholine analog; CTRL: 26 +/- 2 vs. H: 18 +/- 2; P < 0.05). Pretreatment with L-arginine (CTRL: 32 +/- 4 vs. H: 31 +/- 5) and L-sepiapterine [analog of key NOS cofactor tetrahydro-L-biopterin (BH4)] (CTRL: 30 +/- 3 vs. H: 29 +/- 3) normalizes NO production after carbachol. L-Sepiapterine also normalizes impaired vasodilatation to carbachol. Vascular endothelial NO synthase (eNOS) immunostaining is reduced, whereas total eNOS protein expression is increased in H (CTRL: 0.76 +/- 0.08 vs. H: 1.76 +/- 0.21; P < 0.01). The significantly higher superoxide generation (CTRL: 20 +/- 2 vs. H: 28 +/- 3 hydroethidine fluorescence intensity arbitrary units; P < 0.05) is prevented by pretreatment with the eNOS inhibitor N-nitro-L-arginine methyl ester (CTRL: 21 +/- 4 vs. H: 22 +/- 4). Taken together, the current data indicate a role for eNOS uncoupling in enhanced vascular superoxide, impaired endothelium-mediated vasodilatation, and decreased NO production in adult animals with programmed elevated blood pressure after a brief neonatal oxygen exposure.

In a H2 and O2 mixture, the reaction of propene switches between hydrogenation and epoxidation over Au/Ti-based oxides. Reaction pathways are strongly dependent on the size of Au particles and on the presence of alkalis. The hydrogenation prevails over Au clusters smaller than 2.0 nm (in the absence of alkalis) and over Au nanoparticles larger than 5.0 nm. Alkali contamination can switch hydrogenation to epoxidation over Au clusters and promote epoxidation over Au nanoparticles with diameters of 2.0–5.0 nm. It was also confirmed that the hydrogenation of propene is enhanced by the addition of a small amount of O2. Switching of product by alkalis and enhancement of hydrogenation by oxygen are interpreted by parallel and competitive reaction pathways.

It has been shown that rice roots grown in a stagnant medium develop a tight barrier to radial oxygen loss (ROL), whereas aerated roots do not. This study investigated whether the induction of a barrier to ROL affects water and solute permeabilities. Growth in stagnant medium markedly reduced the root growth rate relative to aerated conditions. Histochemical studies revealed an early deposition of Casparian bands (CBs) and suberin lamellae (SL) in both the endodermis (EN) and exodermis, and accelerated lignification of stagnant roots. The absolute amounts of suberin, lignin and esterified aromatics (coumaric and ferulic acid) in these barriers were significantly higher in stagnant roots. However, correlative permeability studies revealed that early deposition of barriers in stagnant roots failed to reduce hydraulic conductivity (Lp(r) ) below those of aerated roots. In contrast to Lp(r) , the NaCl permeability (P(sr) ) of stagnant roots was markedly lower than that of aerated roots, as indicated by an increased reflection coefficient (σ(sr) ). In stagnant roots, P(sr) decreased by 60%, while σ(sr) increased by 55%. The stagnant medium differentially affected the Lp(r) and P(sr) of roots, which can be explained in terms of the physical properties of the molecules used and the size of the pores in the apoplast.

The effect of temperature on the oil oxygen concentration, tested in both soybean and olive oils with no added polydimethylsiloxane (PDMS), showed that the oxygen concentration increased with temperature to approximately 100 °C. Above 100 °C, the oxygen concentration abruptly decreased. This change was attributed to the balance between the rates of oxygen uptake and consumption by oil oxidation, which favored oxygen consumption over uptake at temperatures above 100 °C. The addition of 100 ppb PDMS to soybean oil, enough to form a continuous layer over the surface of the oil, reduced the oxygen concentration when compared to a soybean oil control containing no added PDMS at temperatures ranging from 93 to 180 °C; thus suggesting an oxygen barrier effect of PDMS. The accumulation of PDMS at the air–oil interface in soybean oil held at 180 °C was determined by comparing the oil’s internal temperature and the apparent surface temperature. A decrease in the apparent surface temperature while the oil was held at a constant internal temperature was attributed to a change in the emissivity of the surface as a consequence of the accumulation of PDMS in the air–oil interface. The presence of PDMS at the air–oil interface was confirmed for 100 ppm of PDMS, a concentration greater than the concentration necessary to form a monolayer of PDMS on the oil surface.

Effects of oxygen and nitrate on fatty acid/lipid production from a highly CO2-tolerant microalgal species Chlorococcum littorale were examined under photoautotrophic conditions of 295 K, a light intensity of 170 μmol-photon m−2 s−1, a bubbling CO2 concentration of 5% (v/v) and bubbling oxygen concentrations to be volumetrically adjusted by mixing oxygen gas with inert nitrogen gas at concentrations ranging from 0% to 95% (v/v). The results showed that maximum fatty acid content reached ca. 34 wt.% under oxygen-freely bubbling conditions and this value decreased to be ca. 20 wt.% when air-like oxygen concentration of 20% was chosen. This means that degree of the accumulation strongly depended on the level of bubbling oxygen concentrations, which can be a crucial factor after nitrogen depletion in the photoautotrophic culture system. TLC-FID/FPD analyses showed that triglycerides were found to be a dominant lipid class for this accumulation.

The present work focuses on the performance of Fenton, sono-Fenton, and sono-photo-Fenton processes for the oxidation of phenol present in aqueous solution. The effects of H 2 O 2 concentration, Fe 2+ concentration, pH, and initial phenol concentration on the oxidation of phenol were studied. The optimum Fe 2+ and H 2 O 2 concentrations for the Fenton process were 45 and 800 mg/L, respectively. For the sono-Fenton process, the optimum Fe 2+ and H 2 O 2 concentrations were 30 and 800 mg/L. respectively. The optimal conditions for the sono-photo-Fenton process were found to be 20 mg/L of Fe 2+ and 700 mg/L of H 2 O 2 . The optimum pH was found to be 3 for the processes investigated in the present study. The analysis of results showed that the sono-photo-Fenton method reduced the Fe 2+ concentration by 30-50% and the H 2 O 2 concentration by 12.5%. It was found that the sono-photo-Fenton technique showed better performance than the Fenton and sono-Fenton processes for the oxidation of phenol. A lumped kinetic model was used to predict the chemical oxygen demand reduction and the model was found to fit the data.

Oxygen reduction (ORR) and hydrogen peroxide reduction (HPRR) reactions were studied on polycrystalline Pt by the rotating disc electrode technique in sulphate solutions over the entire pH range. Initial potentials for both ORR and HPRR coincide with the potential region of PtOH formation and shift negatively with the increase of the pH of the solution. For pHs lower than 3.0 and higher than 10.0, the ORR takes place through 4e-series pathways from acid and alkaline solutions, respectively. For 3.0 LT pH LT 6.0, the overall number of electrons exchanged depends on the potential and falls below 4 for ORR and below two for HPRR. This indicates that both reactions occur in a limited extent due to the changes of the local pH in the course of these reactions which gives rise to the double wave in the polarization curves (as observed for ORR for pH 3.5 and pH 4.0 and for HPRR for pH 4.0). The change of the Tafel slopes with potential indicate the change in reaction pathway from one that takes place in acid - to one that takes place in alkaline solution.

We investigated whether hydrogen sulfide (H 2 S) may be a mediator of electro-acupuncture (EA) stimulation treatment for hypoxic–ischemic brain-damage (HIBD). We studied a HIBD 7-day-old rat model with 4 types of treatments: (1) 14 sessions of EA; (2) hydroxylamine (HA), an inhibitor of cystathionine-β-synthase (CBS), the key enzyme of H 2 S generation; (3) both EA and HA; or (4) no treatment. Sham-treated rats with or without EA were also studied. Regional cerebral blood flow (rCBF) was monitored before, during and after EA at different periods of treatment (d1, 7 and 14 sessions). We evaluated motor function, H 2 S levels and CBS expression in the cerebral cortex and prepared cerebral pathomorphological images after 14 sessions of treatment. EA stimulation could increase local blood circulation and improve motor function in HIBD rats. HIBD significantly increased H 2 S levels of brain tissue as compared with sham treatment, and EA treatment could decrease the H 2 S generation. Rats with HIBD receiving both EA and HA therapy showed greatly recovered motor function and brain morphology. H 2 S might be a mediator of EA treatment of HIBD in rats.

The influence of lactate/phosphate enhancement on meat color and lipid oxidation stability, tenderness, protein degradation, and protein aggregation of early postmortem beef muscles packaged in a high oxygen modified atmosphere packaging (HiOx-MAP; 80% O2, 20% CO2) were studied. At 24 hr postmortem, three bovine muscles (longissimus, semimembranosus, and adductor; n=10, respectively) were enhanced (10% injection rate) with either lactate (2.5%)/phosphate (0.3%) solution or water, packaged in HiOx-MAP, stored 9 days at 1°C, and then displayed for 7 days at 1°C. The lactate/phosphate injection significantly improved color stability (higher a* values) of all three bovine muscles throughout display period. Accumulation of lipid oxidation determined by 2-thiobarbituric acid-reactive substances values was also decreased (P0.05) in the lactate/phosphate injection compared to the water treatment during storage and display periods. The objective tenderness values of longissimus and semimembranosus were also improved (P0.05) by the lactate/phosphate enhancement treatment compared to the water treatment based on star probe measurement. There were no significant differences found in desmin and troponin-T degradation, or oxidative cross-linking of myosin between treatments. The results suggest that lactate/phosphate enhancement has beneficial effects on color and lipid oxidation stability, and tenderness development of beef cuts under HiOx-MAP conditions.

The stripping treatment of extra virgin olive oil (EVOO) by nitrogen gas to remove dissolved oxygen (DO) was tested immediately after the oil production. Dissolved oxygen was measured before and after stripping, as well as one week later along with chemical analyses with the aim to assess the effects of the stripping treatment on EVOO quality. Stripping gave a great reduction of DO, of ca 50%. Both stripped (SO) and non-stripped (non-SO) oil samples showed a fast DO consumption up to zero in seven days. At this time, the non-SO samples showed significant higher peroxide value probably as a consequence of the initial higher DO concentration that gives a greater formation of free radicals. A slightly lower concentration of total phenols was recorded for SO samples. A slight but significant decrease was recorded for only (E)-hex-2-enal concentration within the volatile compounds.

Article history:Received 9 January 2010Accepted 14 July 2010Available online 23 July 2010Keywords:Scanning tunneling microscopyIndium arsenideSemiconducting surfacesSurface chemical reactionAtomic layer depositionOxidants The substrate reactions of three common oxygen sources for gate oxide deposition on the group III rich InAs(0 0 1)-(4×2)/c(8×2) surface are compared: water, hydrogen peroxide (HOOH), and isopropyl alcohol(IPA). Scanning tunneling microscopy reveals that surface atom displacement occurs in all cases, but viadifferent mechanisms for each oxygen precursor. The reactions are examined as a function of post-depositionannealing temperature. Water reaction shows displacement of surface As atoms, but it does not fully oxidizethe As; the reaction is reversed by high temperature (450 °C) annealing. Exposure to IPA and subsequentlow-temperature annealing (100 °C) show the preferential reaction on the row features of InAs(0 0 1)-(4×2)/c(8×2), but higher temperature anneals result in permanent surface atom displacement/etching.Etching of the substrate is observed with HOOH exposure for all annealing temperatures. While nearly alloxidation reactions on group IV semiconductors are irreversible, the group III rich surface of InAs(0 0 1)shows that oxidation displacement reactions can be reversible at low temperature, thereby providing amechanism of self-healing during oxidation reactions.© 2010 Elsevier B.V. All rights reserved.

A detailed study is presented on the synthesis and characterization of purely oxygen-filled microbubbles (OMBs) stabilized by phospholipids. Microbubbles with a diameter of less than 10 μm were generated and concentrated to >50 vol % in saline. The lipid acyl chain length had little effect on the size distribution but profoundly affected the foam stability. For example, OMBs stabilized by dipalmitoyl phosphatidylcholine (DPPC) degraded over 3 weeks, but OMBs stabilized with distearoyl phosphatidylcholine (DSPC) retained over half of their initially encapsulated gas. Interestingly, the polydisperse size distribution remained nearly constant as the foam slowly broke down. Injection into an undersaturated solution led to the immediate release of the oxygen gas core. Injectable gas delivery by OMBs may find use in a variety of medical and industrial fields.

The reactivity of cyclohexane in the catalyzed autoinitiated oxidation by cobalt naphtenate under an initial partial pressure of oxygene of 11 kg/cm2, in the presence of cumene was studied. The addition of about 5% in volume by cumene in the total volume of the mixture resulted in an increase in the rate of oxidation. In the oxidation of cyclohexane with cumene, the rate was doubled, while in the presence of cumene and a salt of cobalt, the rate of oxydation was 5 times as great. This increase in the rate of oxidation of cyclohexane by the presence of cumene corresponds to the increase in the rate at which this oxidation was initiated. This increase in the rate of initiation results from the increase in concentration of peroxydic radicals which corresponds to the disparition constant of cumyl peroxydic radicals which is about 600 times below the disparition constant of the cyclohexyl peroxydic radicals. The apparent energy of activation in the mixture is 28,5 kcal mol−1 in the temperature range of 130-60°C.

Streptococcus pyogenes is a causative agent in wide range of human diseases. To inactivate S. pyogenes by the afterglow of a dielectric barrier discharge (DBD), we prepared suspensions of the cultured bacterium in liquid (with concentrations of OD600 nm = 0.25 McFarland standard) and solid (with 7.75 × 105 spread cells per surface plate) Luria–Bertini (LB) broth media. The influence of DBD exposure on S. pyogenes was evaluated at 5, 10, and 15 min by two methods: turbidimetry analysis (for liquid solution) and determination of the number of colony-forming units (for solid media). Bacterial survival was strongly dependent upon on the working gas used. For a cultured LB liquid solution, it reached (21 ± 5)% and (70 ± 8)% at an exposure time of 15 min with O2 and CO2 working gases, respectively. Bacterial cell growth on the surface of the LB plate was 1 colony and 270 colonies for O2 and CO2 gases, respectively. The results suggest that the DBD of O2 gas could be efficient in the disinfection of S. pyogenes in liquid and surface cultured media. The processes could be attributed to ozone and the excited singlet state O2(a1Δg) as the active chemical agents.

In this study, the electrochemical behavior and the electrocatalytic properties towards the reduction of hydrogen peroxide, dioxygen and nitrate are compared for the two mixed sandwich-type complexes Ni2Fe2P4 and Ni2Fe2As4. In media of pH 3, Ni2Fe2P4 displayed two waves corresponding to the reduction of the two FeIII centers within the complex followed by four WVI based-waves. Compared to Ni2Fe2P4, Ni2Fe2As4 displayed only one Fe-based wave and three W-waves. In other words, the two FeIII waves and the first two WVI waves observed for Ni2Fe2P4 merge into one Fe-based wave and one W-wave in Ni2Fe2As4. This is probably related to a slight difference in acidity between the two complexes. In other words, Ni2Fe2P4 is slightly more basic than Ni2Fe2As4. This difference in acidity is also reflected in the position of the potentials. Compared to Ni2Fe2P4, the peak potentials of Ni2Fe2As4 are slightly shifted towards positive values, and the shift is more pronounced for the W-based waves than for the Fe-waves. The remarkable stability of the two complexes (roughly from pH 0 to 7) permitted to evaluate their catalytic behavior towards H2O2, O2 and NO 3 - . For the electrocatalytic reduction of H2O2, it is noticed that Ni2Fe2As4 is more efficient than Ni2Fe2P4. However, for O2 and NO 3 - it is observed that Ni2Fe2P4 is more efficient than Ni2Fe2As4.

This paper reports a real-time study of the codynamical changes in the release of endogenous nitric oxide (NO) and oxygen (O(2)) consumption in a rat neocortex in vivo upon electrical stimulation using an amperometric NO/O(2) dual microsensor. Electrical stimulation induced transient cerebral hypoxia due to the increased metabolic demands that were not met by the blood volume inside the stimulated cortical region. A NO/O(2) dual microsensor was successfully used to monitor the pair of real-time dynamic changes in the tissue NO and O(2) contents. At the onset of electrical stimulation, there was an immediate decrease in the cortical tissue O(2) followed by a subsequent increase in the cortical tissue NO content. The averages of the maximum normalized concentration changes induced by the stimulation were a 0.41 (±0.04)-fold decrease in the O(2) and a 3.6 (±0.9)-fold increase in the NO concentrations when compared with the corresponding normalized basal levels. The peak increase in NO was always preceded by the peak decrease in O(2) in all animals (n = 11). The delay between the maximum decrease in O(2) and the maximum increase in NO varied from 3.1 to 54.8 s. This rather wide variation in the temporal associations was presumably attributed to the sparse distribution of NOS-containing neurons and the individual animal's differences in brain vasculatures, which suggests that a sensor with fine spatial resolution is needed to measure the location-specific real-time NO and O(2) contents. In summary, the developed NO/O(2) dual microsensor is effective for measuring the NO and O(2) contents in vivo. This study provides direct support for the dynamic role of NO in regulating the cerebral hemodynamics, particularly related to the tissue oxygenation.

Various aquatic dissolved organic matter (DOM) samples produce singlet oxygen (1O2) and hydrogen peroxide (H2O2) with quantum yields of 0.59 to 4.5% (1O2 at 365 nm) and 0.017 to 0.053% (H2O2, 300-400 nm integrated). The two species' yields have opposite pH dependencies and strong, but opposite, correlations with the E2/E3 ratio (A254 divided by A365). Linear regressions allow prediction of both quantum yields from E2/E3 in natural water samples with errors ranging from -3% to 60%. Experimental evidence and kinetic calculations indicate that less than six percent of the H2O2 is produced by reaction between 1O2 and DOM. The inverse relationship between the 1O2 and H2O2 yields is thus best explained by a model in which precursors to these species are populated competitively. A model is presented, which proposes that important precursors to H2O2 may be either charge-transfer or triplet states of DOM.

Udgivelsesdato: 2009-Dec-11 In the present study, the metabolic effects of heat and anoxic stress in myotubes from the mouse cell line C2C12 were investigated by using a combination of (13)C, (1)H, and (31)P nuclear magnetic resonance (NMR) spectroscopy and enrichment with [(13)C]-glucose. Both the (13)C and the (1)H NMR spectra showed reduced levels of the amino acids alanine, glutamate, and aspartate after heat or anoxic stress. The decreases were smallest at 42 degrees C, larger at 45 degrees C, and most pronounced after anoxic conditions. In addition, in both the (1)H and the (31)P NMR spectra, decreases in the high-energy phosphate compounds adenosine triphosphate and phosphocreatine with increasing severity of stress were identified. At anoxic conditions, an increase in (13)C-labeled lactate and appearance of glycerol-3-phosphate were observed. Accumulation of lactate and glycerol-3-phosphate is in agreement with a shift to anaerobic metabolism due to inhibition of the aerobic pathway in the mitochondria. Conversely, lower levels of unlabeled ((12)C) lactate were apparent at increasing severity of stress, which indicate that lactate is released from the myotubes to the medium. In conclusion, the metabolites identified in the present study may be useful markers for identifying severity of stress in muscles.

Tyrosinase has two types of enzymatic activities: the hydroxylation of monophenols to o-diphenols (monophenolase activity) and oxidation of o-diphenols to o-quinones (diphenolase activity). The action on o-diphenols involves two substrates: oxygen and o-diphenol, while the mechanism proposed is a Uni Uni Bi Bi ping-pong. In this contribution, we demonstrate experimentally that there is a kinetically preferred pathway, which translates into the appearance of curves of initial velocity vs. initial diphenol concentration shows inhibition by an excess of substrate, while sigmoid curves are obtained when the initial velocity vs. initial oxygen concentration are graphed. However, the action mechanism of the enzyme on monophenols, which is more complex because it involves three substrates (monophenol, oxygen and o-diphenol), does behave differently from the hyperbolic behaviour as regards the initial velocity vs. initial monophenol concentration, results that can be explained if the limiting step in the action of tyrosinase is the hydroxylation of monophenol to o-diphenol.

Aim: Lowered microvascular PO 2 (PO 2 mv) during the exercise off-transient likely impairs muscle metabolic recovery and limits the capacity to perform repetitive tasks. The current investigation explored the impact of altered nitric oxide (NO) bioavailability on PO 2 mv during recovery from contractions in healthy skeletal muscle. We hypothesized that increased NO bioavailability (sodium nitroprusside: SNP) would enhance PO 2 mv and speed its recovery kinetics while decreased NO bioavailability ( L -nitro arginine methyl ester: L -NAME) would reduce PO 2 mv and slow its recovery kinetics. Methods: PO 2 mv was measured by phosphorescence quenching during transitions (rest-1 Hz twitch-contractions for 3 min-recovery) in the spinotrapezius muscle of Sprague-Dawley rats under SNP (300 μM), Krebs-Henseleit (Control) and L -NAME (1.5 mM) superfusion conditions. Results: Relative to recovery in Control, SNP resulted in greater overall microvascular oxygenation as assessed by the area under the PO 2 mv curve (PO 2 AREA; Control: 3471 ± 292 mmHg s; SNP: 4307 ± 282 mmHg s; P < 0.05) and faster off-kinetics as evidenced by the mean response time (MRToff; Control: 60.2 ± 6.9 s; SNP: 34.8 ± 5.7 s; P < 0.05), whereas L -NAME produced lower PO 2 AREA (2339 ± 444 mmHg s; P < 0.05) and slower MRToff (86.6 ± 14.5 s; P < 0.05). Conclusion: NO bioavailability plays a key role in determining the matching of O 2 delivery-to-O 2 uptake and thus the upstream O 2 pressure driving capillary-myocyte O 2 flux (i.e. PO 2 mv) following cessation of contractions in healthy skeletal muscle. Additionally, these data support a mechanistic link between reduced NO bioavailability and prolonged muscle metabolic recovery commonly observed in ageing and diseased populations.

The effects of different methods for elevating the OTR (oxygen transfer rate) during foreign gene expression and the cell growth of recombinant Escherichia coli BL21 were investigated. Two strategies were introduced to control DO (dissolved oxygen) levels in the fermentation broth: (i) increasing fermentor pressure and (ii) supplying oxygen-enriched air. These two methods were compared with the glucose feedback model, which acted as the control. By adopting a fed-batch method of cultivation, the cell yield coefficient (YX/S), accumulation of acetic acid and volumetric product yield (Yp) were measured or estimated. Adoption of these two methods led to an improvement in the OTR. The cell density and volumetric product yield in the cultivation controlled by increasing the fermentor pressure reached 77 g x l(-1) (dry cell weight) and 14 g x l(-1) respectively, which were much higher than those obtained with the strategy of supplying oxygen-enriched air (48 and 6 g x l(-1) respectively) and in the control (46 and 7 g x l(-1) respectively). The results indicate that increasing fermentor pressure is an effective way to enhance the OTR and recombinant protein (human-like collagen) productivity.

The effect of low blood flow at onset of moderate-intensity exercise on the rate of rise in muscle oxygen uptake was examined. Seven male subjects performed a 3.5-min one-legged knee-extensor exercise bout (24 ± 1 W, mean ± SD) without (Con) and with (double blockade; DB) arterial infusion of inhibitors of nitric oxide synthase ( NG-monomethyl-l-arginine) and cyclooxygenase (indomethacin) to inhibit the synthesis of nitric oxide and prostanoids, respectively. Leg blood flow and leg oxygen delivery throughout exercise was 25–50% lower ( P < 0.05) in DB compared with Con. Leg oxygen extraction (arteriovenous O2 difference) was higher ( P < 0.05) in DB than in Con (5 s: 127 ± 3 vs. 56 ± 4 ml/l), and leg oxygen uptake was not different between Con and DB during exercise. The difference between leg oxygen delivery and leg oxygen uptake was smaller ( P < 0.05) during exercise in DB than in Con (5 s: 59 ± 12 vs. 262 ± 39 ml/min). The present data demonstrate that muscle blood flow and oxygen delivery can be markedly reduced without affecting muscle oxygen uptake in the initial phase of moderate-intensity exercise, suggesting that blood flow does not limit muscle oxygen uptake at the onset of exercise. Additionally, prostanoids and/or nitric oxide appear to play important roles in elevating skeletal muscle blood flow in the initial phase of exercise.

The Pd–Co/C alloy catalysts with an atomic ratio of 3:1 were deposited at various pH values and reduced at different temperatures for oxygen reduction reaction (ORR). The structure-activity relationship of the prepared catalysts has been elucidated. The pH values and reduction temperatures during the preparation process affect the deposition and reduction rates of Pd and Co ions significantly, and thus the degrees of alloying, surface species, and ORR activities of the Pd–Co/C catalysts are also influenced. Due to the enhancement of Co surface segregation and the formation of Co oxide on the surface, a deterioration of ORR activity for the catalysts reduced at high temperatures and high pH values is observed. The catalysts deposited at pH value of 9 and reduced at a very low temperature of 390 K have well-formed Pd–Co alloy structure, Pd-rich surface, and excellent ORR activity.

Oxygen or air exposure to transition metal oxides (TMOs) was demonstrated to be essential in improving the hole injection (HI) efficiency at the contact formed by TMOs and small organic hole transporter. Current–voltage (J–V) and dark-injection space-charge-limited current (DI-SCLC) techniques were used to cross-examine the TMO/organic contacts. The hole transporter under investigation was N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′biphenyl)-4,4′diamine (NPB). The improvement was attributed to the reduction in the energy barrier at TMO/NPB interface, which was a consequence of the work function enhancement of TMO by the oxidation of oxygen in air.

The effects of different oxygen species and vacancies on the adsorption and oxidation of formaldehyde over CeO2(1 1 1) surface were systematically investigated by using density functional theory (DFT) method. On the stoichiometric CeO2(1 1 1) surface, the C–H bond rupture barriers of chemisorbed formaldehyde are much higher than that of formaldehyde desorption. On the reduced CeO2(1 1 1) surface, the energy barriers of C–H bond ruptures are less than those on the stoichiometric CeO2(1 1 1) surface. If the C–H bond rupture occurs, CO and H2 form quickly with low energy barriers. When O2 adsorbs on the reduced (1 1 1) surface (O2/Ov species), the C–H bond rupture barriers of formaldehyde are greatly reduced in comparison with those on the stoichiometric CeO2(1 1 1) surface. If O2 adsorbs on oxygen vacancy at sub-layer surface, its oxidative roles on formaldehyde are much similar to that of O2/Ov species.

The effects of temperature, scan interval and rate of oxygen (O2) decline on pulse frequency modulation (PFM)-based minimum fluorescence (Fα) and the Fα-based lower oxygen limit (LOL) were investigated using ‘Honeycrisp’ apples (Malus × domestica Borkh). The effects of temperature and hypoxic stress on pulse amplitude modulation (PAM) fluorescence parameters were also investigated. The PFM scan interval had no effect on the Fα baseline, but increases in the scan interval decreased the low-O2-induced fluorescence spike intensity (ΔFα). Temperature negatively correlated with the Fα baseline while ΔFα °C−1 was greater at lower than at higher temperatures. When using a PAM fluorometer, the minimum fluorescence (Fo), and to a lesser extent the maximum fluorescence (Fm), were similarly affected by temperature as was Fα. Temperature altered the LOL in fruit. Apples stored at 20, 10, 3.5 and 0 °C spiked at 0.72, 0.33, 0.22 and 0.08 kPa O2, respectively, under a rapid O2 decline (i.e., 20.9 to

Phthalocyanines are promising photosensitizers for use in various branches of science including nanotechnology. In the presence of visible light and diatomic oxygen, phthalocyanines can react to produce singlet oxygen ( 1 O 2 ∗ ) , which has known inhibitory effects on cellular growth and metabolic activity, although other mechanisms may be involved. The present work focuses on the properties of phthalocyanines (atom charge densities, singlet oxygen production, inhibition effects at various irradiances) contributing to toxicity against the cyanobacteria, Synechococcus nidulans. Our results indicate that positive charge densities at peripheral parts of substituents exhibit greater inhibitory effects against S. nidulans than the amount of singlet oxygen produced, potentially by binding to negatively charged membranes on the cell surface. The weak effect of 1 O 2 ∗ was further demonstrated by a 10% increase in phthalocyanine toxicity (the maximal inhibition detected) when the irradiance increased 3-fold from 1200 to 4000 lux.

The pH effect on the oxidative stability of ascorbic acid in the presence of food colorant FD&C Red Nr 3 during storage with or without light was investigated. The quenching mechanism and kinetics of ascorbic acid on the FD&C Red Nr 3 photosensitized oxidation in an aqueous system at 25 degrees C were also studied by measuring the degradation of ascorbic acid or depletion of headspace oxygen. Red Nr 3 had no influence on the oxidation of ascorbic acid under dark storage, but accelerated its oxidation rate under light storage. The oxidative stability of ascorbic acid decreased as the pH increased from 4 to 7 under light without FD&C Red Nr 3. The quenching rates of ascorbic acid on the singlet oxygen by measuring the degradation of ascorbic acid in the presence of Red Nr 3 under light storage were 1.53 +/- 0.15 x 10(8), 1.86 +/- 0.25 x 10(8), and 1.19 +/- 0.12 x 10(8) M(-1)S(-1) at pH 4, 5.6, and 7, respectively.

The decomposition of perfluoroalkylether sulfonates C 2 F 5 OC 2 F 4 SO 3 - and C 3 F 7 OC 2 F 4 SO 3 - in subcritical water was investigated, and the results were compared with those for perfluorobutanesulfonate ( C 4 F 9 SO 3 - ), which has no ether linkage. This is the first report on the use of subcritical water to decompose perfluoroalkylether sulfonates, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative perfluoroalkylsulfonates. Whereas C 4 F 9 SO 3 - showed little reactivity in subcritical water, C 2 F 5 OC 2 F 4 SO 3 - decomposed efficiently in subcritical water (∼350 °C) in the presence of oxygen gas to form F− and SO 4 2 - in the aqueous phase and CO2 in the gas phase as major products. Trifluoroacetic acid (CF3COOH, TFA) and trifluoromethane (CF3H) were also detected as minor products in the aqueous and gas phases, respectively. Similar decomposition behavior was observed for C 3 F 7 OC 2 F 4 SO 3 - , which decomposed at a rate that was somewhat higher than that of C 2 F 5 OC 2 F 4 SO 3 - . When argon was used in place of oxygen gas, the time profile of the decrease in the amount of C 2 F 5 OC 2 F 4 SO 3 - remained almost unchanged, but the product distribution changed markedly: the amounts of F−, SO 4 2 - , and CO2 dramatically decreased, the amounts of TFA and CF3H increased, and a new product, HCF 2 SO 3 - , was detected. These results clearly indicate that treatment with subcritical water in the presence of oxygen gas effectively mineralized perfluoroalkylether sulfonates to F−, SO 4 2 - , and CO2. On the basis of a product analysis, we propose a decomposition mechanism.

The influence of oxygen on the development of carbon nanotubes (CNTs) during the annealing process of the surface decomposition method on SiC(000−1) surfaces was investigated. In the case of annealing a SiC substrate under ultra-high vacuum conditions, carbon nanofibers (CNFs) form between the CNT layer and the substrate. However, CNTs form without CNFs by annealing the substrate in an oxygen atmosphere. The mean length of CNTs is longer than those formed without an oxygen atmosphere. From cross-sectional transmission electron microscopy images, it was found that oxygen plays an important role in CNT growth by the surface composition method.

Analysis of exhaled nitric oxide (NO) has become an accepted complementary tool in the management of inflammatory airway diseases. Previous studies have demonstrated reduced exhaled NO at altitude and ascribed their findings to hypoxia. We studied exhaled NO partial pressures (Pe(NO)) in eight healthy subjects at reduced ambient pressure down to 540 hPa (equivalent to 5000 m altitude) and at sea level, with equivalently hypoxic breathing gases (down to 11.3% O2 in N2). Pe(NO) readings were corrected for gas density effects on the instrument performance. Sea level control values for Pe(NO) at an exhaled flow of 50 mls(-1) averaged 2.4 mPa and were virtually unchanged with normobaric hypoxia down to an inspired P(O)(2) of 10.7 kPa. With the same degree of hypoxia, hypobaric Pe(NO) was 1.4 mPa. The reduction in hypobaric Pe(NO) of up to 33+/-16% (mean+/-SD) in comparison to normobaric Pe(NO), is likely to have been caused by enhanced axial back diffusion of NO because of the reduced gas density and an associated increased alveolar NO uptake to the blood.

We present data for H2O2 production at eight different materials tested as electrocatalysts for the oxygen reduction reaction (ORR) in 0.5 M H2SO4 (Hg, Au, Ag, Cu, Pt, Pd, Pd80Co20, and Au60Cu40) using scanning electrochemical microscopy (SECM) as an alternative to the widely used rotating ring-disk electrode (RRDE) method. The amount of H2O2 is related to the total number of electrons, n, found in the O2 reduction reaction, with n = 2 showing only H2O2 production and n = 4 showing no H2O2 formation. From the SECM study Hg shows n close to 2, whereas Pt and Pd80Co20 show n-values near 4. The other materials show intermediate n-values as a function of potential.

The primary objective of this research was to investigate how low pressure (hypobaria) and low oxygen (hypoxia) affect functional phytochemicals and the nutritional quality of ‘Red Sails’ lettuce (Lactuca sativa L.). Plants were grown under two levels of total gas pressure (reduced or ambient (25 or 101 kPa, respectively)) at three levels of O2 partial pressures (low, medium or ambient (6, 12 or 21 kPa, respectively)). Hypoxia effects on nutritional and functional phytochemicals were more pronounced than hypobaria effects. Regardless of the total pressure, hypoxia, in general, enhanced leaf anthocyanin levels, enhanced total phenolic compounds, enhanced carbohydrate concentration and enhanced free radical scavenging capacity of lettuce but reduced leaf mineral concentration. Hypoxia increased the ethylene production of plants but ethylene accumulation was not the sole reason for enhanced anthocyanin production in plants grown under hypoxia. Our results suggest that low oxygen stress induces the production of protective phytochemicals and the free radical scavenging potential in lettuce, which may in turn enhance the functional value. However, further human intervention studies are needed to confirm if enhanced phytochemicals in plants have significant impact in human body.

Methods of estimating the mesophyll conductance (g(m)) to the movement of CO(2) from the substomatal airspace to the site of fixation are expensive or rely upon numerous assumptions. It is proposed that, for C(3) species, measurement of the response of photosynthesis to [O(2)] at limiting [CO(2)], combined with a standard biochemical model of photosynthesis, can provide an estimate of g(m). This method was used to determine whether g(m) changed with [CO(2)] and with water stress in soybean leaves. The value of g(m) estimated using the O(2) response method agreed with values obtained using other methods. The g(m) was unchanged over the tested range of substomatal [CO(2)]. Water stress, which decreased stomatal conductance (g(s)) by about 80%, did not affect g(m), while the model parameter V(Cmax) was reduced by about 25%. Leaves with g(s) reduced by about 90% had g(m) values reduced by about 50%, while V(Cmax) was reduced by about 64%. It is concluded that g(m) in C(3) species can be conveniently estimated using the response of photosynthesis to [O(2)] at limiting [CO(2)], and that g(m) in soybean was much less sensitive to water stress than g(s), and was somewhat less sensitive to water stress than V(Cmax).

Frankia strain CcI3 produces 2 truncated hemoglobins, HbN and HbO. Using ion-exchange chromatography, we characterized the expression of the relative amounts of HbN and HbO in −N (nitrogen-fixing) cultures and +N (nitrogen-supplemented) cultures. The −N cultures maintained an approximately constant ratio of HbO to HbN throughout the life of the culture, with HbO constituting 80%–85% of the total hemoglobin produced. In contrast, in +N cultures, HbN was observed to increase over time and HbO decreased. Total hemoglobin as a fraction of total protein was approximately constant throughout the growth phase in −N cultures, while it decreased somewhat in +N cultures. Subjecting −N cultures to a NO generator resulted in increased production of HbN, relative to the controls. Nitrite accumulated in +N cultures, but not in −N cultures. This suggests that the greater amount of HbN in +N cultures might be due to NO produced by the reduction of nitrite. The effects of O2 concentration were determined in +N cultures. Cultures grown in 1% O2 produced about 4 times more HbO than cultures grown in 20% O2. Overall, these results provide evidence for a role of HbN in NO oxidation and for a role of HbO in adaptation to low oxygen concentrations.

The microstructural properties of Au/α-Mn2O3 catalysts moderately pretreated under different atmospheres, i.e., O2, He and H2, in relation to their activities and stabilities on CO oxidation were investigated. The highest initial activity was obtained for the He-pretreated catalyst, which, however, suffered the most severe deactivation with time on stream. Pretreatment with O2 resulted in the best stability and had the highest steady-state activity among the three catalysts. TEM results revealed that the pretreatment has a negligible effect on the gold particle size. While the formation of moderate surface oxygen vacancies before reaction was suggested to be responsible for the highest initial activity of He–Au/α-Mn2O3, overreduction of the oxide support could explain the inferior activity of the H2-pretreated catalyst. Based on the XPS and in situ DRIFTS studies, the superior performance of the O2-pretreated O2–Au/α-Mn2O3 catalyst can be attributed to the creation of a specific oxygen-enriched interface leading to an enhanced metal–support synergy.

Reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) and nitric oxide (NO), have been shown to differentially alter the Ca2+ sensitivity of the contractile apparatus of fast-twitch skeletal muscle, leading to the proposal that normal muscle function is controlled by perturbations in the amounts of these two groups of molecules ( 28 ). However, no previous studies have examined whether these opposing actions are retained when the contractile apparatus is subjected to both molecule types. Using mechanically skinned fast- and slow-twitch skeletal muscle fibers of the rat, we compared the effects of sequential addition of nitrosoglutathione (GSNO), a NO donor, and H2O2 on the Ca2+ sensitivity of the contractile apparatus. As expected from previous reports in fast-twitch fibers, when added separately, GSNO (1 mM) reduced the Ca2+ sensitivity of the contractile apparatus, whereas H2O2 (10 mM; added during contractions) increased the Ca2+ sensitivity of the contractile apparatus. When added sequentially to the same fiber, such that the oxidation by one molecule (e.g., GSNO) preceded the oxidation by the other (e.g., H2O2), and vice versa, the individual effects of both molecules on the Ca2+ sensitivity were retained. Interestingly, neither molecule had any effect on the Ca2+ sensitivity of slow-twitch skeletal muscle. The data show that H2O2 and GSNO retain the capacity to independently affect the contractile apparatus to modulate force. Furthermore, the absence of effects in slow-twitch muscle may further explain why this fiber type is relatively insensitive to fatigue.

Oxygen supply and dissolved carbon dioxide (dCO(2)) stripping are two of the most important control parameters in cell culture. In this study, we investigated the effect of scale-up on the volumetric gas transfer coefficient with bioreactors of different sizes (working volume: 80 L, 500 L, 2000 L, and 10,000 L; aspect ratio: 1.0-1.6). Sparging air into water increased the volumetric oxygen transfer coefficient (k(L)a), an index of oxygen supply efficiency, by scale-up roughly in proportion to the depth of the water. A corresponding increase in k(L)a was found in a real cell culture of Chinese hamster ovary cells. dCO(2) stripping efficiency was evaluated in water tests using changes in k(L)a(co2), an index defined in relation to k(L)a. k(L)a(co2) increased following surface aeration, but the rate of increase was reduced by scale-up, which was attributed to a decrease in the liquid surface-to-volume ratio. A similar decrease in efficiency was observed in a 2000 L bioreactor by increasing the liquid volume at constant liquid surface area. The observed scale-up effects are discussed based on a simple theoretical consideration.

The initial oxidative polymerization kinetics of 2,6-dimethylphenol (DMP) catalyzed by a Cu(II)–EDTA complex in water was studied. The initial polymerization rate of DMP (R0) increases with an increase in concentrations of DMP and catalyst. R0 firstly increases with the molar ratio of N/Cu and then decreases. The reaction order with respect to oxygen is 0.1. R0 increases with NaOH concentration and reaches its maximum value at a concentration of 0.50 mol/L. 1/R0 is in direct proportion to 1/[DMP]0, which indicates that the initial polymerization kinetics of DMP in water obeys Michaelis–Menten model. The dissociation rate constant of the intermediate complex (k2) and Michaelis–Menten constant (Km) at various temperatures are calculated. It is found that both k2 and Km increase with an increase in temperature.

The oxidative dehydrogenation of sodium lactate to sodium pyruvate in an aqueous phase proceeded favorably using Pd/C and that doped with Te at 358 K with no adjustment in solution pH under pressurized oxygen, although previous reports had stated that this reaction would not proceed using Pd/C while Pd/C doped with either Pb, Bi or Te showed the activity at atmospheric pressure, 363 K, and a pH of 8.

A simple, highly effective method for the functionalization of CNTs with HNO3 vapor is developed, thus eliminating separation by filtration. A significantly higher amount of oxygen species compared to conventional wet HNO3 treatment was detected by X-ray photoelectron spectroscopy, and the morphology and the degree of agglomeration did not deteriorate because of the treatment.

Experimental data for the solubility of the two single gases carbon monoxide and oxygen in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf2N]) are reported for temperatures between (293.25 and 413.2) K. The maximum pressure (the maximum gas molality) was 9.8 MPa (0.27 mol·kg−1) for carbon monoxide and 9.1 MPa (0.31 mol·kg−1) for oxygen. The experiments were performed using a high-pressure view-cell technique operating on the synthetic method. Oxygen shows a slightly higher solubility than carbon monoxide under all conditions investigated, but the solubility generally remains very low. Both gases become less soluble in [hmim][Tf2N] with increasing temperature; however, the effect is not very pronounced and becomes ambiguous for carbon monoxide above 373 K. An extension of Henry’s law is employed in correlating the solubility pressures. The final results for the Henry’s constant (at zero pressure) of carbon monoxide and oxygen in [hmim][Tf2N] (on the molality scale)...

In NO/CO reaction, there is a competition between NO reduction by CO and Mo2C oxidation by oxygen generated during NO dissociation. A complete equality of NO conversion and NO reduction degree can be achieved after increasing CO concentration in the system, which makes establishing a catalytic cycle on Mo2C catalyst possible.

A new approach is described to analyse the barrier properties of the outer part of rice (Oryza sativa L.) roots towards oxygen. By using a root-sleeving O(2) electrode, radial oxygen loss at different distances from the root apex was measured and related to the corresponding root structure. In addition, internal oxygen concentrations were precisely adjusted using a newly developed perfusion technique. Thus, the oxygen permeability coefficient of the outer part of the root (OPR) could be calculated, since both (i) the oxygen flow across the OPR and (ii) the oxygen concentration gradient across the OPR from inside to outside were known. On the basis of the permeability coefficient, it can be decided whether or not different rates of oxygen loss across the OPR are due to changes in the OPR structure and/or to changes in the concentration gradient. The technique was applied to rice root segments, which enabled rapid perfusion of aerenchyma. In the present study, roots of rice grown under aerobic conditions were used which should have a higher O(2) permeability compared with that of plants grown in deoxygenated solution. Both radial oxygen losses and permeability coefficients decreased along the root, reaching the lowest values at the basal positions. Values of oxygen permeability coefficients of the OPR were corrected for external unstirred layers. They decreased from (2.8+/-0.2)x10(-6) m s(-1) at 30 mm to (1.1+/-0.2)x10(-6) m s(-1) at 60 mm from the apex (n=5; +/-SE). They were similar to those measured previously for cuticles. Low diffusional oxygen permeability of the OPR suggested that the barrier to radial oxygen loss was effective. This may help to retain oxygen within the root and enhance diffusion of oxygen towards the apex in the presence of a relatively high water permeability. The results are discussed in terms of the inter-relationship between the water and oxygen permeabilities as roots develop in either aerated or deoxygenated (stagnant) media.

A series of Co-AT (attapulgite) catalysts were prepared by wetness impregnation method. Detailed characterization indicated that there indeed exists interaction between Co and the support AT, leading to the formation of spinel of CoAl2O4 and CoFe2O4. Al and Fe species of AT promote the formation of CoFe2O4 spinel with much lower temperature (400 °C). The catalytic behavior was investigated by the liquid-phase solvent-free oxidation of cyclohexane and Co-AT-1 shown better activity than CoFe2O4 and Co3O4, which was likely due to a cooperation effect between CoFe2O4 and Co3O4.