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Showing papers on "Oxygen published in 1977"



Journal ArticleDOI
01 Jun 1977-Nature
TL;DR: In this article, the authors present evidence that rapid photochemical generation of singlet oxygen occurs in inland and coastal water bodies of the south-eastern United States of the country.
Abstract: MANY studies have shown that singlet molecular oxygen can oxidise a variety of organic substances1–7. These studies have included biologically important compounds present in the aquatic environment such as amino acids4,7 and pollutants like polycyclic aromatic hydrocarbons5 and pesticides6. No data, however, have been obtained to demonstrate that reactions involving singlet oxygen (often called oxygenations) are sufficiently rapid to be significant in natural waters. The most likely mechanism for oxygenation in the environment was originally proposed by Kautsky8 by which light energy absorbed by a sensitiser is transferred to ground-state oxygen to form singlet oxygen, which in turn reacts with the organic substance, or ‘acceptor’ (A), to form a peroxide. Here we present evidence that rapid photochemical generation of singlet oxygen occurs in inland and coastal water bodies of the south-eastern United States.

337 citations


Journal ArticleDOI
TL;DR: In this paper, photoelectron spectroscopic studies of Ni(111), Ni(100) and Ni(110) surfaces were conducted to investigate the oxidation process of NiO.

292 citations


Journal ArticleDOI
TL;DR: The surface region of Pd(111) is characterized by three different types of oxygen atoms, which may be distinguished by their thermal, chemical, structural and electronic properties as discussed by the authors.

280 citations


Journal ArticleDOI
TL;DR: It is concluded that limited oxygen supply affects cellular metabolism at much higher concentrations than the P50 value for the oxygen dependence of respiration, but the respiratory rate remains relatively unchanged due to compensatory changes in the [ATP]/[ADP] X [Pi] and progressive reduction of cytochrome c.
Abstract: Simultaneous measurements of the mitochondrial [NAD+]/[NADH], the cytoplasmic [ATP]/[ADP] x [Pi], and the respiratory rate were carried out in suspensions of cultured kidney cells in a range of defined oxygen tensions. The results show that as the extracellular oxygen concentration falls there is a decrease in the respiratory rate, which is accompanied by a decrease in the [ATP]/[ADP] and a progressive reduction of cytochrome c. Even at low O2 tensions the mitochondrial respiratory chain between the NAD couple and cytochrome c remains at near equilibrium with the ATP synthesizing reactions. It is concluded that limited oxygen supply affects cellular metabolism at much higher concentrations than the P50 value for the oxygen dependence of respiration, but the respiratory rate remains relatively unchanged due to compensatory changes in the [ATP]/[ADP] X [Pi] and progressive reduction of cytochrome c. These metabolic changes may form a basis for the phenomenon of tissue oxygen sensing at near physiological oxygen tensions.

209 citations


Journal ArticleDOI
TL;DR: In this article, the role of the metal/metal oxide or the lower metal oxide/higher metal oxide couple in determining the minimum voltage required for the evolution of oxygen is emphasized, together with other essential requirements such as electrical resistivity, electrode microstructure, corrosion resistance and catalytic properties.

207 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the extent to which the excited state molecular oxygen species, singlet oxygen 1 O 2, participates in milk lipid oxidation and found that it is the immediate source of the hydroperoxides that initiate lipid oxidation catalyzed by three agents.

192 citations


Journal ArticleDOI
TL;DR: In this paper, a thermal decomposition of manganese nitrate solution on a titanium or a platinum substrate was investigated mainly in 1N H2SO4 and 1N KOH.

184 citations


Journal ArticleDOI
TL;DR: The oxygen kinetics of purified beef heart cytochrome c oxidase were investigated and the effect of addition of various fixed concentrations of the inhibitors CO, HN3, HCOOH, HCN and H2S on the double reciprocal plot of respiration rate against oxygen concentration was studied.

174 citations


Journal ArticleDOI
TL;DR: The data demonstrate that tissue oxygen gradients are very steep in the hypoxic state, so that ischemia and hypoxia result in discrete heterogeneous areas of anoxic tissue bounded by sharp areas where the oxygen supply is sufficient to maintain normal mitochondrial oxidative function.
Abstract: Tissue oxygen gradients were examined in the saline-perfused rat heart by NADH fluorescence photography. In high flow hypoxia, where the coronary flow was maintained and the arterial oxygen tension was gradually reduced, oxygen extraction was virtually complete before oxygen consumption was significantly diminished. Inadequate oxygen delivery resulted in a well defined pattern of anoxic zones. The anoxic zones were several hundred microns in width, an order of magnitude greater than intercapillary distances. In low flow hypoxia (ischemia), where the arterial oxygen tension remained at its control value and the coronary flow was diminished, anoxic zones also developed, following the same pattern as in high flow hypoxia. However, in ischemia, the anoxic areas developed while the effluent oxygen tesion was significantly greater than zero. Whereas respiratory acidosis between pH 7.3 and 6.9 resulted in vasodilation, below PH 6.8 there was a marked increase in vascular resistance. Anoxic zones appeared despite only a slight change in effluent oxygen tension from the control. In high flow hypoxia, ischemia, and acidosis-induced ischemia, the anoxic zones disappeared when control perfusion conditions were restored. The data demonstrate that tissue oxygen gradients are very steep in the hypoxic state, so that ischemia and hypoxia result in discrete heterogeneous areas of anoxic tissue bounded by sharp areas where the oxygen supply is sufficient to maintain normal mitochondrial oxidative function. In these states in which oxygen delivery is less than oxygen demand, coronary perfusion appears to be regulated at the level of the arterioles rather than the capillaries.

170 citations



Journal ArticleDOI
TL;DR: In this article, surfaces of polymers [polyethylene, polystyrene, poly(ethylene terephthalate), poly(oxymethylene), cellulose acetate, polyacrylonitrile, nylon 6, polytetrafluoroethylene] treated with argon (inert) and nitrogen (reactive) plasma were examined by ESCA (electron spectroscopy for chemical analysis).
Abstract: Surfaces of polymers [polyethylene, polystyrene, poly(ethylene terephthalate), poly(oxymethylene), cellulose acetate, polyacrylonitrile, nylon 6, and polytetrafluoroethylene] treated with argon (inert) and nitrogen (reactive) plasma were examined by ESCA (electron spectroscopy for chemical analysis). Argon plasma treatment generally introduces oxygen functionalities into the polymer surface. Nitrogen treatment generally incorporates nitrogen and oxygen functionalities into the treated surface. The extent of oxygen incorporation is typically less than that produced by argon plasma. When nitrogen and oxygen functional groups are already in a polymer structure, the extent of additional incorporation of these two elements as a result of plasma treatment is very much less than with other polymers. Polymers which contain only one of the elements tend to incorporate the other element to much the same degree as polymers without either element initially present.

Journal ArticleDOI
TL;DR: In this article, an independent iron-titanium oxide geothermometer and oxygen barometer from the experimental data of Buddington and Lindsley (1964) are presented graphically for coexisting ilmenite solid solutions and magnetite solid solution in the system FeO-Fe2O3-TiO2.
Abstract: Equilibrium thermodynamic methods are used to develop an independent iron-titanium oxide geothermometer and oxygen barometer from the experimental data of Buddington and Lindsley (1964). The geothermometer and oxygen barometer are presented graphically for coexisting ilmenite solid solution and magnetite solid solution in the system FeO-Fe2O3-TiO2. Equations are also given for calculating temperature and oxygen activity for natural coexisting iron-titanium oxides containing other components. Large departures in composition from the system FeO-Fe2O3-TiO3 result in large uncertainties in the calculated temperature and activity of oxygen.

Journal ArticleDOI
TL;DR: In this paper, the role of oxygen in the reaction between nitric oxide and ammonia on a V2O5 catalyst was examined by means of ir, XPS, mass spectrometry, and kinetic studies under reaction conditions.

Journal ArticleDOI
TL;DR: It appears that this highly reactive species of oxygen can be produced in several biochemical systems without the use of light and its reactions may account for some types of cell damage.

Journal ArticleDOI
TL;DR: A technique is described by which both oxygen and nitrate (or nitrate or chlorate) levels were continuously monitored during bacterial respiration to suggest that the nitrate reductase is orientated on the plasma membrane so that nitrate gains access from the inner (cytosolic) face.
Abstract: SUMMARY: A technique is described by which both oxygen and nitrate (or nitrite or chlorate) levels were continuously monitored during bacterial respiration. Paracoccus (Micrococcus) denitrificans and Escherichia coli oxidizing succinate rapidly ceased to reduce nitrate when oxygen was available, and equally rapidly commenced nitrate reduction when all the oxygen had been consumed. By contrast, membrane vesicles isolated from P. denitrificans reduced oxygen and nitrate simultaneously. The respiratory nitrate reductase in intact cells of P. denitrificans appeared to be inaccessible to chlorate present in the reaction medium, and it is suggested that the nitrate reductase is orientated on the plasma membrane so that nitrate gains access from the inner (cytosolic) face.

Journal ArticleDOI
TL;DR: In this paper, the reaction of carbon monoxide with oxygen chemisorbcd on polycrystalline platinum has been studied using Auger spectroscopy, and two types of chemisorbed oxygen are distinguished on the basis of Auger electron chemical shifts and reactivity towards carbon dioxide.

Journal ArticleDOI
TL;DR: In this paper, it was found that high temperature discharges are not only ineffective in reducing the oxygen on the wall, and hence in the plasma, but may even induce trapping.
Abstract: Various discharge cleaning techniques have been studied in Microtor. It was found that high temperature discharges are not only ineffective in reducing the oxygen on the wall, and hence in the plasma, but may even induce trapping. Oxygen can be removed from the wall by a low-temperature, partially ionized hydrogen plasma by conversion to water vapour. The amount of loosely bound oxygen on the surface is thus reduced below 1% of a monolayer. The residual amount of the oxygen in the plasma is near 1010 atom cm−3, and represents a significant improvement over previous tokamak results.

Journal ArticleDOI
TL;DR: In this paper, the results for oxygen evolution are discussed in terms of electrochemically generated unstable surface oxides whose decomposition is catalysed by protons in acid, and hydroxide ions in base.
Abstract: The electrocatalytic behaviour of Ti-supported RuO2, prepared by thermal decomposition of RuCl3, as substrate for oxygen evolution was investigated by a variety of techniques. B.E.T. adsorption experiments showed that the RuO2 layers are highly porous with large surface area values which, however, decrease rapidly as the annealing temperature increases above ∼ 300°C. Both the charge involved in the cyclic voltammograms and the oxygen evolution rates are dependent on the true (rather than apparent) area of these electrode surfaces, and also on the pH of the solution. The results for oxygen evolution are discussed in terms of electrochemically generated unstable surface oxides whose decomposition is catalysed by protons in acid, and hydroxide ions in base. The lower reactivity of the oxide at intermediate pH value is attributed on the one hand to loss of protons by OH groups, resulting in oxygen bridging, and on the other to lack of enhanced coordination of surface ruthenium species by OH– ions, which in this pH region are present only at low activity. The charge associated with voltammetric sweeps is accounted for in terms of surface redox processes rather than bulk penetration of protons into the oxide. The need for surface area measurements as a guide to the interpretation of the electrochemical data in the case of these oxide systems is stressed.

Journal ArticleDOI
TL;DR: In this paper, it was shown that at both ∼300 and ∼100 K the adsorption of oxygen on evaporated Mg slows dramatically when oxide layers ∼7 A thick have formed on the surface.

Journal ArticleDOI
TL;DR: In this paper, the growth kinetics of SiO2 films grown on silicon at 950 to 1100°C in an O2/N2 mixture was empirically studied, and it was found that a linear-parabolic law is in excellent agreement with the oxidation data under the oxygen partial pressure PO2 of 1 or 10−1 atm.
Abstract: Oxide growth kinetics of SiO2 films grown on silicon at 950 to 1100 °C in an O2/N2 mixture is empirically studied. It is found that a linear‐parabolic law is in excellent agreement with the oxidation data under the oxygen partial pressure PO2 of 1 or 10−1 atm. However, a parabolic law is obtained at 10−2 atm, and an inverse‐logarithmic law at 10−3 atm. The Mott‐Cabrera oxidation rate equation is adapted to the thermal oxidation of silicon in the case of PO2≲10−2 atm. Finally, 43.9 kcal/mole is derived as the activation energy value of silicon atoms entering into the oxide.

Journal ArticleDOI
TL;DR: By purchasing content from the publisher through the Service you agree to abide by the Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp.
Abstract: By purchasing content from the publisher through the Service you agree to abide by the Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. These Terms and Conditions of Use provide, in part, that this Service is intended to enable your noncommercial use of the content. For other uses, please contact the publisher of the journal. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=oup.

Journal ArticleDOI
TL;DR: In this article, a compilation and an analysis of data relating to oxygen diffusion in alpha-zirconium is presented, which spans the temperature range 290 to 1500°C and fourteen orders of magnitude in the diffusion coefficient.

Journal Article
TL;DR: In this paper, the reactions of lignins upon treatment with oxygen and hydrogen peroxide in alkaline media are summarized on the basis of the results from studies with appropriate model compounds, and two types of initial oxidation reactions may be distinguished: (1) Electrophilic attack on carbanions by molecular oxygen (oxygenations) (2) Nucleophilic addition of hydroperoxide anions to carbonyl and conjugated carbonyls structures.
Abstract: The reactions of lignins upon treatment with oxygen and hydrogen peroxide in alkaline media are summarized on the basis of the results from studies with appropriate model compounds. Two types of initial oxidation reactions may be distinguished: (1) Electrophilic attack on carbanions by molecular oxygen (oxygenations) (2) Nucleophilic addition of hydroperoxide anions to carbonyl and conjugated carbonyl structures. These two oxidants attack in phenolic and enolic lignin structures centres having alternately high (oxygen) and low (hydrogen peroxide) electron density. Both the reactions with oxygen and those with hydrogen peroxide result in the formation of intermediates of the hydroperoxide type. Subsequently, the intermediates undergo rearrangements, resulting in the cleavage of carbon-carbon bonds or in the formation of epoxide intermediates, or alternatively are converted into ortho-or para-quinoid structures. The products of the cleavage of carbon-carbon bonds and the quinoid and epoxide intermediates undergo alkaline-oxidative degradation ultimately yielding simple acids and hydrophilic polymerization products. The two types of initial oxidation (1 and 2) may take place simultaneously or sequentially, both during treatment with oxygen in alkali (oxygen pulping and bleaching). In the former process, hydrogen peroxide is generated by the autoxidation of enediol structures while, in the latter process, oxygen is originally present in the atmosphere and/or is formed by the decomposition of hydrogen peroxide. Although intimately connected with each other during both processes, these two types of oxidation reactions should be considered separately. By doing so, known observations from technical treatments of wood, pulps and lignins with oxygen or hydrogen peroxide can be interpreted in chemical terms.

Journal ArticleDOI
TL;DR: The results support the proposal that the primary oxygen adducts formed with these flavoproteins on reaction of the reduced enzymes with oxygen are flavin C(4a) peroxides.
Abstract: During the catalytic reactions of flavoprotein hydroxylases and bacterial luciferase, flavin peroxides are formed as intermediates [see Massey, V. and Hemmerich, P. (1976) in The Enzymes, 3rd edn (P. Boyer, ed.) pp. 421 - 505, Academic Press, New York]. These intermediates have been postulated to be C(4a) derivatives of the flavin coenzyme. To test this hypothesis, modified flavin coenzymes carrying an oxygen substituent at position C (4a) of the isoalloxazine ring were synthesized. They are tightly bound by the apoenzymes of D-amino acid oxidase, p-hydroxybenzoate hydroxylase and lactate oxidase ; the resulting complexes show spectral properties closely similar to those of the transient oxygen adducts of the hydroxylases. The optical spectra of the lumiflavin model compounds were found to be highly dependent on the solvent environment and nature of the substituents. Under appropriate conditions they simulate satisfactorily the spectra of the transient enzymatic oxygen adducts. The results support the proposal that the primary oxygen adducts formed with these flavoproteins on reaction of the reduced enzymes with oxygen are flavin C(4a) peroxides. Flavoprotein oxidases and monooxygenases are redox enzymes which catalyze the reaction of molecular oxygen with a variety of substrates [l - 31. Characteristic of this catalysis is the reaction with oxygen of the reduced flavoenzyme in the presence of substrate or product. It is the reduced flavin which is involved in the activation of oxygen. With monooxygenases the result is the incorporation of one atom of the molecule of oxygen in the substrate, and the reduction of the other one to water. First insights into the mechanism of the rapid reaction of reduced flavin with 02 [4,5] were obtained from its kinetics, which indicated the reversible formation of a Flred-02 complex prior to the actual electron transfer [6,7]. Direct spectral evidence for the transient occurrence of a covalent flavin-oxygen adduct was obtained later in studies with the enzymes meliotate hydroxylase [8], p-hydroxybenzoate hydroxylase [9], phenol hydroxylase [2] and very recently with salicylate hydroxylase [ 101. In the case of p-hydroxybenzoate hydroxylase a detailed kinetic investigation lead to the discovery of at least three sequential intermediates arising from the reaction of the reduced enzyme with oxygen [ll] Abbreviations. NMR, Nuclear magnetic resonance; 4a-OHFAD and 4a-OH-FMN for 5-ethyl-4a-hydroxy-4a,S-dihydro-FAD and the corresponding FMN derivative. Enzymes. D-Amino acid oxidase (EC 1.4.3.3); p-hydroxybenzoate hydroxylase (EC 1.14.13.2); lactate oxidase (EC 1.13.12.4); phenol hydroxylase (EC 1.14.13.7); melilotate hydroxylase (EC 1.14.

Journal ArticleDOI
TL;DR: In this article, it was shown that the conductivity of a SnO2 gas sensor depends on the concentration of CO and H2O in the atmosphere n which it is placed.
Abstract: It is shown that the conductivity of a SnO2 gas sensor depends on the concentration of CO and H2O in the atmosphere n which it is placed The experimental data can be explained in a consistent manner by hypothesizing that 1) adsorbed oxygen depletes the surface electron concentration and therefore decreases the conductivity; 2) adsorbed water causes electrons to accumulate at the surface and therefore increases the conductivity; 3) CO increases the conductivity by removing adsorbed oxygen by reacting with it to form CO2; and 4) adsorbed water catalyzes the CO to CO2 reaction

Journal ArticleDOI
TL;DR: A predicted relation between depth and oxygen consumption by this species off California, USA, is presented, which shows a higher oxygen-consumption rate at the nighttime depths and a much lower, partially anaerobic metabolism at the daytime depths.
Abstract: Gaussia princeps is shown to be a diurnal vertical migrator which spends its days below 400 m in the oxygen minimum layer and migrates to shallower depths (200 to 300 m) at night. This species consumption was measured at 3.5°, 7° and 10°C and 1, 14, 28, 61, 121 and 181 atm of hydrostatic pressure (1 atm corresponds to approximately 10 m of depth). The Q10 of the oxygen consumption is shown to be higher at lower temperatures and higher pressures. Hydrostatic pressure is shown to have significant effects on the oxygen-consumption rate at pressures as low as 28 atm. At all temperature and pressure combinations, G. princeps displays a very low metabolic rate compared to shallow-living copepods. The critical oxygen partial pressure for this species is shown to be about 10 to 13 mm Hg O2 at 10°, 7° and 5.5°C. Based on these data, a predicted relation between depth and oxygen consumption by this species off California, USA, is presented. This shows a higher oxygen-consumption rate at the nighttime depths and a much lower, partially anaerobic metabolism at the daytime depths.

Journal ArticleDOI
TL;DR: Azotobacter beijerinckii synthesized up to 70% of its dry weight as poly-β-hydroxybutyrate when grown in batch or oxygen-limited chemostat cultures on a glucose/ammonium salts medium, while nitrogen-grown organisms displayed a steady decrease in polymer content with increasing oxygen concentration.
Abstract: Summary: Azotobacter beijerinckii synthesized up to 70% of its dry weight as poly-β-hydroxybutyrate when grown in batch or oxygen-limited chemostat cultures on a glucose/ammonium salts medium. In a series of steady states during transition from oxygen to ammonium limitation and at different dilution rates in the chemostat, the poly-β-hydroxybutyrate content of the organism decreased to a minimum of 5 to 10% of the dry weight at an oxygen inflow rate of 1.25% (v/v) in 400 ml argon min−1. At higher dissolved oxygen tensions the polymer content increased to a new maximum of 20 to 40% of the dry weight, depending upon the dilution rate, before declining to a negligible value. In contrast, nitrogen-grown organisms displayed a steady decrease in polymer content with increasing oxygen concentration. This difference in behaviour is attributed to the greater demand for reducing power and ATP by nitrogen-fixing cultures preventing the operation of respiratory control which, it is suggested, occurs in ammonium-grown cultures over a limited range of oxygen supply rates until respiratory protection and uncoupled electron transport intervene.

Journal ArticleDOI
TL;DR: In this article, the anodic evolution of oxygen and anodic dissolution of ruthenium have been investigated by means of polarization measurements and product analyses, and the overall current for oxygen evolution is expressed by i = nFka−2H exp (2FE/RT).

Journal ArticleDOI
TL;DR: To detect changes in the oxygen concentration during biochemical reactions, the exchange broadening in the ESR spectra of nitroxide radicals caused by the dissolved oxygen, has been used.