Showing papers on "Oxygen published in 1973"
TL;DR: In this article, the fluorescence of various fluorophores by molecular oxygen has been studied in aqueous and nonaqueous solutions equilibrated with oxygen pressures up to 100 atm.
Abstract: Quenching of the fluorescence of various fluorophores by molecular oxygen has been studied in aqueous and nonaqueous solutions equilibrated with oxygen pressures up to 100 atm. Temperature dependence of quenching, agreement with the Stern–Volmer equation, and fluorescence lifetime measurements indicate that essentially all the observed quenching is dynamic and close to the diffusion-controlled limits. Studies of charged polyamino acids containing tryptophan show that oxygen quenching, in contrast to I−, is completely insensitive to charge effects. Ethidium bromide, when intercalated into double helical DNA, is quenched with 1/30th of the efficiency of the free dye in solution. Three dyes bound to bovine serum albumin were also found to be relatively protected from the free diffusion of oxygen. Quenching of intrinsic or bound fluorophores by molecular oxygen is therefore an appropriate method to determine the accessibility to oxygen of regions of the macromolecule surrounding the fluorophore and indirectly the structural fluctuations in the macromolecule that permit its diffusion to the fluorophore.
2,490 citations
TL;DR: By measuring the conductivity of stannic oxide crystals as a function of oxygen partial pressure at elevated temperatures, it was shown that the dominant native defect in SnO2 is a doubly ionizable oxygen vacancy as discussed by the authors.
Abstract: By measuring the conductivity of stannic oxide crystals as a function of oxygen partial pressure at elevated temperatures, it is shown that the dominant native defect in SnO2 is a doubly ionizable oxygen vacancy. Both donor levels of this defect, the first 30 meV deep and the second 150 meV deep, are identified and a model is presented that explains previous results. The behavior in hydrogen is contrasted to that in oxygen, and preliminary results are presented indicating that hydrogen introduces a donor 50 meV deep.
357 citations
TL;DR: In this article, an investigation of the sodium-cobalt-oxygen system allows the isolation of four new bronze type phases with the formula Naχ.CoO2 (χ 1).
338 citations
TL;DR: In this paper, the crystal chemistry and the occurrence of carbides and nitrides in steels are reviewed and the characteristics of nitrogen are emphasised and are related to the behaviour of carbon.
313 citations
TL;DR: In this paper, the exchange constants for both oxygen and carbon dioxide increase approximately as the square of the wind velocity, whereas the exchange constant for water vapour increases linearly with wind velocity.
257 citations
TL;DR: The results suggest a phylogenetic trend of increasing regulation of aerobic metabolism in response to declining environmental levels as animals acquire structures that effectively insulate their respiring tissue from the habitat.
Abstract: Several models for the analysis of data relating the rate of oxygen uptake to environmental oxygen level have been evaluated. We conclude that the quadratic (or second-degree) polynomial, though hardly perfect, is the best. Data from 31 species of aquatic invertebrates are described by constants of the quadratic (or second-degree) polynomial equation. The results suggest a phylogenetic trend of increasing regulation of aerobic metabolism in response to declining environmental levels as animals acquire structures that effectively insulate their respiring tissue from the habitat. Many of these species apparently cease withdrawing oxygen from their external environment long before they have exhausted its supply. Presumably, those species with long lasting internal oxygen reservoirs, such as gas bubbles or pools of high oxygen affinity hemoglobin, continue to operate aerobic pathways, but those without substantial oxygen storage devices must switch over to anaerobic pathways, despite the availability of small residual volumes of external oxygen.
248 citations
TL;DR: In this article, the authors studied the catalytic activity of N4 complexes for the electroreduction of oxygen in acid electrolyte and found that they are not completely stable when supported by active carbon or carbon black.
230 citations
TL;DR: In this article, the concentration of nitrogen and oxygen in semiconductor silicon and their solubilities in silicon at its melting point have been measured by charged particle activation analysis and infrared spectrophotometry.
Abstract: The concentration of nitrogen and oxygen in semiconductor silicon and their solubilities in silicon at its melting point have been measured by charged particle activation analysis and infrared spectrophotometry. It has been found that: (i) commercial semiconductor silicon contains less than of nitrogen in the un‐ionized state; (ii) the solubility in solid silicon is for nitrogen and for oxygen; and (iii) the solubility in liquid silicon is about for nitrogen and for oxygen. Thus, the equilibrium distribution coefficient has been determined to be about for nitrogen and for oxygen. The solubilities of the two elements are compared with those of other elements, especially carbon, and are discussed thermochemically.
225 citations
219 citations
TL;DR: In this article, the rate constants for atomic oxygen (O 3P) with organic compounds in the gas phase are compiled and critically evaluated for a total of 107 organic reactants.
Abstract: Rate constants for the reactions of atomic oxygen (O 3P) with organic compounds in the gas phase are compiled and critically evaluated. Data are given here as originally reported in the literature for a total of 107 organic reactants. From a critical evaluation of the data, recommended values for rate constants are given over specified temperature intervals, and where possible at 298 K and 1000 K. Estimated error limits are assigned to all recommended values.
184 citations
TL;DR: In this paper, it has been shown that the presence of adsorbed water enhances the photoadsorption process, and that rutile which has been subjected to prolonged outgassing at high temperature followed by reoxidation in dry oxygen is inactive.
TL;DR: Cancer pagurus L. showed a daily rhythm of oxygen consumption and heart rate with maximum rates occurring nocturnally, suggesting that in crabs, delivery of oxygen to the tissues during activity is facilitated by an increased cardiac output brought about by increase in heart-rate and in O 2 utilization, with little change in stroke volume.
TL;DR: In this paper, the specific Cu+CO interaction was revealed by a strong infrared absorption band at 2160 cm− and a heat of adsorption of 14.7 kcal/mole.
TL;DR: In this paper, it was suggested that the change from precambrian-type iron-formations to those typical of the Phanerozoic may have been the simple consequence of a change in the transport of iron from dissolved ferrous iron to ferric iron carried in the suspended load of streams.
Abstract: The hypothesis is presented that about 3.5 billion years ago oxygen was stored chiefly in carbonate rocks, silicate rocks, and water. Sediments cycled in a reducing atmosphere. Iron cycled as ferrous iron and precipitated chemically as carbonate or silicate under the same general controls as calcium and magnesium. As time went on, and photosynthesis by procaryotic organisms occurred, ferric oxides were formed in the shallow waters of the iron-depositing basins, and sulfates were formed bacterially during weathering, even though little if any free oxygen may have been produced. Organic material in an amount equivalent to the number of moles of oxygen stored in sulfates or iron oxides accumulated, and a similar number of moles of carbonate minerals was converted to other compounds. As sediments cycled, degraded organic matter was re-eroded and redeposited; ferric oxides joined the clastic fraction of stream loads, and sulfates tended to remain as sulfates. Perhaps with the advent, some 2 billion years ago, of eucaryotic photosynthetic organisms, which release free oxygen (Cloud, 1972), and the diminution of reduced mineral reservoirs consuming oxygen or its equivalent, atmospheric oxygen began to rise. Eventually a level was reached that achieved equality between the amount of organic material weathered and oxidized and the amount of new organic material deposited as the residue of photosynthesis minus respiration, decay, and oxidation. At this stage no further accumulation of organic materials was possible, and an essentially stable cycling system was established, with no further growth of oxygen-consuming reservoirs. This condition grossly characterizes Phanerozoic time. It is suggested that a major factor in the change from "Precambrian-type iron-formations" to those typical of the Phanerozoic may have been the simple consequence of a change in the transport of iron from dissolved ferrous iron to ferric iron carried in the suspended load of streams.
TL;DR: Laser photolysis experiments of aerated solutions, in which triplet anthracene is produced and quenched by oxygen, yielding singlet oxygen which then sensitizes absorption due to triplet carotene, firmly establishes diffusion‐controlled energy transfer from singletoxy as the quenching mechanism in the case of β‐carotene.
Abstract: — Bimolecular rate constants for the quenching of singlet oxygen O*2(1Δg), have been obtained for several transition-metal complexes and for β-carotene. Laser photolysis experiments of aerated solutions, in which triplet anthracene is produced and quenched by oxygen, yielding singlet oxygen which then sensitizes absorption due to triplet carotene, firmly establishes diffusion-controlled energy transfer from singlet oxygen as the quenching mechanism in the case of β-carotene. The efficient quenching of singlet oxygen by two trans-planar Schiff-base Ni(II) complexes, which have low-lying triplet ligand-field states, most probably also occurs as a result of electronic energy transfer, since an analogous Pd(II) complex and ferrocene, which both have lowest-lying triplet states at higher energies than the O*2(1Δg), state, quench much less effectively.
TL;DR: In this paper, the decomposition of NO has been studied in a flow reactor on oxides of iron, cobalt, nickel, copper, and zirconium as well as on supported platinum at 780-960 Torr between 450 and 1000 °C.
TL;DR: 3β-Hydroxy-5α-hydroperoxy-Δ6-cholestene is produced in protoporphyrin-containing red blood cell ghosts irradiated with approximately 400-nanometer light in the presence of oxygen and incorporation into normal red blood cells leads to increased osmotic fragility and eventual hemolysis.
Abstract: 3β-Hydroxy-5α-hydroperoxy-Δ6-cholestene is produced in protoporphyrin-containing red blood cell ghosts irradiated with approximately 400-nanometer light in the presence of oxygen. Incorporation of this cholesterol photooxidation product into normal red blood cells leads to increased osmotic fragility and eventual hemolysis. These results may be relevant to photohemolysis associated with erythropoietic protoporphyria.
TL;DR: For solutions of nonmetal X in a liquid alloy A-B in this paper, the authors assume a parabolic dependence of the solvation energy on the number of atoms A and B in the Solvation shell of atoms X.
TL;DR: In this article, the authors used low energy electron diffraction (LEED), Auger electron spectroscopy (AES), mass spectroglobalization and work function measurements.
TL;DR: In this article, the electrical conductivity of sintered specimens of was measured over the temperature range 700°-1500°C and from 1 to 10−22 atm of oxygen.
Abstract: The electrical conductivity of sintered specimens of was measured over the temperature range 700°–1500°C and from 1 to 10−22 atm of oxygen. All specimens of exhibited mixed conduction. Two limiting case regions were observed. At low temperatures and high oxygen pressures, the conductivity is predominantly ionic. In this region the conductivity is independent of and between approximately 1 and 8 m/o is proportional to mole per cent . The following equation for ionic conductivity was obtained by fitting the conductivity data in this region to an expression derived on the basis of an oxygen vacancy model. An approximate expression for the diffusion coefficient for oxygen vacancies was calculated from the above expression and the Nernst‐Einstein relation. At high temperatures and low oxygen partial pressures and for lower contents the conductivity is predominantly electronic. In this region the magnitude and dependence of σ is similar to "pure" . A thermodynamic argument is also presented which favors oxygen vacancies as the nonstoichiometric defect in both pure and .
TL;DR: In this paper, it has been shown that the ionisation energy of the chromium 2p electrons is dependent primarily on the oxidation state of chromium metal ion, but that small perturbations may be attributed to changes in crystal structure and hence the Madelung potential.
Abstract: X-Ray photoelectron spectroscopy has been used to study a series of chromium–oxygen compounds. It has been shown that the ionisation energy of the chromium 2p electrons is dependent primarily on the oxidation state of the chromium metal ion, but that small perturbations may be attributed to changes in crystal structure and hence the Madelung potential. Multiplet splitting in chromium(III) compounds contributes to peak widths, and the chemisorption of water and oxygen has a marked effect on the observed peak profiles. In addition such chemisorption apparently contributes to the build up of surface charge, thereby complicating the precise determination of binding energies.
01 Dec 1973
TL;DR: In this article, the conditions leading to formation of the metastable ω-phase in Ti, Zr, and Hf alloys are described and earlier experimental observations directly related to ω -phase formation are summarized.
Abstract: The conditions leading to formation of the metastable ω-phase in Ti, Zr, and Hf alloys are described and earlier experimental observations directly related to ω -phase formation are summarized. New experimental results are presented which show that increased oxygen content suppresses athermal ω-phase formation in Ti-V alloys. A mechanism of ω-phase formation based on the formation of a linear displacement defect is described and it is shown that both the earlier and new experimental results are consistent with this mechanism. Additional experimental results on variations in electrical and physical properties in Ti alloys are also shown to be consistent with the linear displacement defect model.
TL;DR: Comparative measurements of the resistance of marine bottom invertebrates of macrofauna to oxygen deficiency and to H2S reveal correlations to the respiratory conditions of the biotopes, where the species naturally occur.
TL;DR: In this article, the authors investigated the effect of a shift of the dissociation curve to the right as reflected in the mixed venous oxygen pressure and the role of this displacement in pulmonary gas exchange with particular reference to the alveolar-arterial oxygen pressure difference and the pulmonary diffusing capacity for oxygen.
Abstract: A shift of the oxygen dissociation curve to the right is often interpreted as an adaptation to hypoxia favorable for tissue oxygen supply. However, animals native to high altitude tend to show a rather high oxygen affinity. In order to elucidate this apparent discrepancy we investigated by numerical computer studies 1. the effect of a shift of the dissociation curve to the right as reflected in the mixed venous oxygen pressure, and 2. the role of this displacement in pulmonary gas exchange with particular reference to the alveolar-arterial oxygen pressure difference and the pulmonary diffusing capacity for oxygen. A right shift had a favorable effect only in the range of moderate hypoxia (and of normoxia) whereas there was a detrimental effect with severe hypoxia. The most important criterion for this distinction was the direction of the change in steepness of the physiological dissociation curve (straight line between arterial and venous points). A favorable effect was associated with a steeper slope after the shift, an unfavorable effect with a less steep slope. There was only a minor influence of a right shift on the oxygen diffusion gradient in the lung. Comparison between man (higher affinity) and rat (lower affinity) suggests that animals of small size with high metabolic rate (high arteriovenous oxygen difference) living in normoxic or possibly exposed to moderately hypoxic condition only are better served by a relatively low oxygen affinity whereas animals native to high altitude are better adapted to severe hypoxia when having a high oxygen affinity.
TL;DR: In this article, the relative magnitude of metal and oxygen migrations can be determined using markers, and the possible results are reviewed for the ideal case of a homogeneous oxide grown to uniform thickness on a plane metal surface.
Abstract: An oxide film on a metal surface will thicken only if metal, or oxygen, or both, migrate across it. The relative magnitude of the metal and oxygen migrations can be determined using markers, and the possible results are reviewed for the ideal case of a homogeneous oxide grown to uniform thickness on a plane metal surface. Such experiments require markers that are both inert and immobile; criteria are developed to establish that these requirements have been met. Experimentally, it has been shown that the anodic oxidation of tantalum is a system close to the ideal, and that the radioisotope of a noble gas is a good approximation for the required marker. Radioactive noble gases were implanted by means of a mass separator into thin films of anodic tantalum oxide, and the transport numbers of the tantalum and oxygen measured after thickening by further anodization. The transport numbers were found to be 0.243 and 0.757, respectively, for anodizing conditions of . The noble gas concentration profiles were observed to broaden on further anodizing, and this was interpreted as being due to the simultaneous movement of tantalum and oxygen atoms during the charge transfer event.
TL;DR: Nickel-gold alloy foil surfaces were analyzed with Auger electron spectroscopy as discussed by the authors, showing that the gold atom fraction at a clean surface is higher than that in the bulk, x b.
TL;DR: The mechanism of fluorescence enhancement of lipoxygenase induced by oxygen is discussed in relation to similar observations previously described for fluorescent molecules contained in a solid polyvinyl matrix.