Showing papers on "Oxygen published in 1984"
5,223 citations
TL;DR: New experiments in vitro show that beta-carotene belongs to a previously unknown class of biological antioxidants, and exhibits good radical-trapping antioxidant behavior only at partial pressures of oxygen significantly less than 150 torr, the pressure of oxygen in normal air.
Abstract: The mechanism of lipid peroxidation and the manner in which antioxidants function is reviewed. beta-Carotene is a purported anticancer agent, which is believed by some to have antioxidant action of a radical-trapping type. However, definitive experimental support for such action has been lacking. New experiments in vitro show that beta-carotene belongs to a previously unknown class of biological antioxidants. Specifically, it exhibits good radical-trapping antioxidant behavior only at partial pressures of oxygen significantly less than 150 torr, the pressure of oxygen in normal air. Such low oxygen partial pressures are found in most tissues under physiological conditions. At higher oxygen pressures, beta-carotene loses its antioxidant activity and shows an autocatalytic, prooxidant effect, particularly at relatively high concentrations. Similar oxygen-pressure-dependent behavior may be shown by other compounds containing many conjugated double bonds.
2,139 citations
TL;DR: In this article, the authors measured the oxygen removal at various temperatures using TPR traces of unsupported or alumina-supported ceria and showed that the reduction of surface capping oxygen and bulk oxygen anions is associated with reduction of the shared oxygen anion at the interface.
1,726 citations
TL;DR: In this paper, sulfate and water from experiments in which pyrite was oxidized at a pH of 2.0 were analyzed for sulfur and oxygen stable isotopes, and experiments were conducted under both aerobic and anaerobic sterile conditions, as well as under aerobic conditions in the presence of Thiobacillus ferrooxidans to elucidate the pathways of oxidation.
342 citations
TL;DR: In this paper, the defect structure of these materials and the resulting transport properties (electrical conductivity, diffusion and transference number) are discussed as a function of temperature, oxygen partial pressure and composition.
278 citations
TL;DR: Results indicate that in cardiac muscle oxygen derived free radicals are important byproducts of abnormal oxidative metabolism present during the post hypoxic period and the 'oxygen paradox' phenomenon is related to the formation of lipid hydroperoxides leading to the cellular membrane disruption and to the irreversible alteration of cardiac integrity.
274 citations
TL;DR: In this article, the interactions and reactions of O2, CO and CO2 with Ag(110) have been studied with AES, XPS, TDS and LEED.
274 citations
TL;DR: In this article, a polycrystalline SnO films prepared by evaporation were studied by Raman scattering, IR reflection and X-ray diffraction, and all the allowed Raman-active and IR-active phonon modes were observed.
267 citations
TL;DR: In this article, the oxygen isotope composition of sulphate in acid mine drainage shows a large variation due to differing proportions of atmospheric- and water-derived oxygen from both chemical and bacterially-mediated oxidation.
Abstract: The formation of acid waters by oxidation of pyrite-bearing ore deposits, mine tailing piles, and coal measures is a complex biogeochemical process and is a serious environmental problem. We have studied the oxygen and sulphur isotope geochemistry of sulphides, sulphur, sulphate and water in the field and in experiments to identify sources of oxygen and reaction mechanisms of sulphate formation. Here we report that the oxygen isotope composition of sulphate in acid mine drainage shows a large variation due to differing proportions of atmospheric- and water-derived oxygen from both chemical and bacterially-mediated oxidation. 18O-enrichment of sulphate results from pyrite oxidation facilitated by Thiobacillus ferrooxidans in aerated environments. Oxygen isotope analysis may therefore be useful in monitoring the effectiveness of abatement programmes designed to inhibit bacterial oxidation. Sulphur isotopes show no significant fractionation between pyrite and sulphate, indicating the quantitative insignificance of intermediate oxidation states of sulphur under acid conditions.
228 citations
01 Mar 1984
TL;DR: Oxygen and carbon isotope measurements have been made in picked planktonic and benthonic foraminifers from the five sites drilled on Leg 74, covering the whole Cenozoic.
Abstract: Oxygen and carbon isotope measurements have been made in picked planktonic and benthonic foraminifers from the five sites drilled on Leg 74, covering the whole Cenozoic. For the Neogene, the coverage gives good information on the development of the vertical temperature structure of Atlantic deep water. For the Paleogene, vertical gradients were weak and it is possible to combine data from different sites to obtain a very detailed record of both the temperature and carbon isotope history of Atlantic deep waters.
TL;DR: Gold oxide is produced by oxygen DC reactive sputtering in a UHV compatible chamber and is subsequently characterized by High Resolution Electron Energy Loss, Auger and X-ray Photoelectron Spectroscopies as discussed by the authors.
TL;DR: This work considers the threat posed by oxygen and the defenses which make aerobic life possible and the compounds which increase the conversion of oxygen to its more reactive derivatives.
Abstract: Molecular oxygen, itself not very reactive, can be converted by photosensitization to electronically excited singlet states, and by partial reduction to the superoxide and hydroxyl free radicals and to hydrogen peroxide. The very considerable toxicity of oxygen, which is due primarily to the properties of these derivatives, is ordinarily overlooked because aerobes have evolved an elaborate system of defenses which is reasonably adequate under ambient conditions. This toxicity becomes all too apparent when these defenses are overwhelmed at elevated pO2 or through the action of compounds which increase the conversion of oxygen to its more reactive derivatives. We will here consider the threat posed by oxygen and the defenses which make aerobic life possible.
TL;DR: In this paper, temperature-programmed reaction spectroscopy (TPRS), low-energy electron diffraction (LEED), and high resolution electron energy loss spectrograph (EELS) was used to study oxygen adsorption and co-adoption with CO.
TL;DR: In this article, the authors studied the mechanism of the selective oxidation of ethylene to ethylene epoxide on a well-characterized Ag(110) surface by combining high-pressure kinetic measurements with ultrahigh vacuum surface analysis in a single apparatus.
TL;DR: In this article, the activation energy for desorption of this oxygen state was estimated from the thermal de-noising spectra to be about 163 kJ mol−1, and the chemisorbed oxygen atoms and the oxygen associated with silicon were distinguished by different binding energies (529.2 and 532.3 eV respectively).
TL;DR: The light-induced EPR multiline signal is studied in O2-evolving PS II membranes and its amplitude is shown to oscillate with a period of 4, with respect to the number of flashes given at room temperature and Glycerol enhances the signal intensity.
TL;DR: It is believed that the dose-dependent OER is a true radiobiological phenomenon and not an artifact of the experimental method used in the low dose survival assay.
Abstract: A decreased oxygen enhancement ratio (OER) at lower radiation doses has been previously reported (B. Palcic, J. W. Brosing, and L. D. Skarsgard, Br. J. Cancer 46, 980-984 (1984)). The question remained whether or not this effect is due to a possible oxygen contamination at low doses, which was not the case at high doses. To ensure a sufficient degree of hypoxia prior to the start of irradiation, Chinese hamster cells (CHO) were made hypoxic by gas exchange combined with metabolic consumption of oxygen at 37°C. At the same time oxygen levels in cell suspension were measured using a Clark electrode. It was found that under experimental conditions used in this laboratory for hypoxic irradiations, the oxygen levels before the start of irradiation are always below the levels which could give any significant enhancement to radiation inactivation by X rays. Full survival curves were determined in the dose range 0-30 Gy using the conventional survival assay and in the dose range 0-3 Gy using the low dose survival...
TL;DR: A five-compartment model for the liquid flow and the oxygen transfer into the liquid phase of a large-scale bioreactor is presented to predict the following reactor operating variables: the overall oxygen transfer capacity, the local liquid dissolved oxygen concentrations and the gas-phase exhaustion.
Abstract: A five-compartment model for the liquid flow and the oxygen transfer into the liquid phase of a large-scale bioreactor is presented The aim of the model is to predict the following reactor operating variables: 1) the overall oxygen transfer capacity of the reactor; 2) the local liquid dissolved oxygen concentrations, for estimation of bad aerated zones which can introduce negative effects for the microorganisms and as a base for reliable scaledown experiments to estimate those effects; 3) the gas-phase exhaustion
TL;DR: The diffusivity of oxygen was determined in melts of Jadeite and diopside (CaMgSi2O6) compositions using diffusion couples with 18O as a tracer as mentioned in this paper.
TL;DR: In this paper, the interaction of oxygen with Ag(111) has been studied over the pressure range 10 −2 −1.0 Torr, and the maximum dioxygen population is found to be markedly sensitive to gas dosing pressure; a model is proposed which accounts for these observations and for related observations on alkali-doped Ag.
TL;DR: The first quantitative measurements of the wavelength dependence of oxygen consumption in systems containing eumelanin and synthetic DOPA melanin are reported, indicating that the major chromophore responsible for oxygen consumption is the same for both kinds of material.
Abstract: — The first quantitative measurements of the wavelength dependence of oxygen consumption in systems containing eumelanin (from bovine eyes) and synthetic DOPA melanin are reported. Consumption of oxygen (considered to be a requirement for immediate pigment darkening) during irradiation of melanins with either visible or ultraviolet light was monitored using a spin probe nitroxide-electron spin resonance spectroscopic approach. From initial rates of oxygen removal, quantum yields have been obtained over a wavelength range from 230 to 600 nm. Eumelanins are moderately effective in promoting oxygen consumption; quantum yields are low for irradiation with visible light, but increase sharply with light of shorter wavelengths. The absolute quantum yield for oxygen consumption is about 0.1% for natural melanin at 320 nm. The action spectrum is similar for both natural and synthetic melanins, indicating that the major chromophore responsible for oxygen consumption is the same for both kinds of material. This chromophore is not the major melanin chromophore responsible for absorption of visible light. The action spectrum also clearly differs from published action spectra for melanogenesis; however, the weak wavelength dependence for visible light is similar to that found for immediate pigment darkening. Catalase decreases the rate of oxygen consumption by 50%, confirming that hydrogen peroxide is the major molecular product of oxygen reduction. A Type I (free-radical) mechanism evidently predominates: D2O and azide are shown to have only minor effects, ruling out any major contribution from a Type II (singlet-oxygen) process to the overall oxygen consumption.
TL;DR: In this paper, the reactivity of coadsorbed hydrogen and hydroxyl yields new information on the catalytic oxidation of hydrogen on Pd(100) and the following reaction path could be inferred: Oad+Had→OHad, 2OHad→Oad+H2Oad +Oad−H2OG→OAD+Og.
Abstract: Water adsorption on clean and oxygen covered Pd(100) has been studied by electron energy loss spectroscopy and low energy electron diffraction. On the clean surface water is associatively adsorbed and reveals hydrogen bonding. Hydroxyl is produced upon water adsorption on oxygen precovered Pd(100). The hydroxyl molecule is adsorbed with its molecular axis significantly tilted away from the surface normal. A study of the reactivity of coadsorbed hydrogen and hydroxyl yields new information on the catalytic oxidation of hydrogen on Pd(100). The following reaction path could be inferred: Oad+Had→OHad, 2OHad→Oad+H2Oad→Oad+H2Og.
TL;DR: In this paper, the nature of two types of oxygen desorption, α and β, from perovskite-type oxides was studied by TPD and TG experiments.
Abstract: The nature of two types of oxygen desorption, α and β, from perovskite-type oxides was studied by TPD and TG experiments. The results show that α oxygen is accomodated in the oxygen vacancies formed by the partial substitution of A site cations, while the desorption of β oxygen corresponds to the reduction of B site cations to lower valencies.
TL;DR: In this paper, the structural change of an atomically smooth Pt (111) surface induced by oxidation has been followed by an electrochemical method in a sulfuric acid solution, and a sample cleaned by cycles of ion bombardment and annealing for LEED observation could also give atomically clean surfaces if the sample was not exposed to a vacuum for too long and was appropriately protected against contamination from filling pure gas.
TL;DR: In this paper, the reaction mechanisms of NO x and SO 2 were studied under irradiation with electron beams in various systems ranging from a simple system (NO-nitrogen) to the complex of NO-SO 2 -water vapour-oxygennitrogen, which was close to the composition of an flue gas.
TL;DR: The predicted best compound is a potent inhibitor, at low oxygen pressure, of the sickling of erythrocytes from patients homozygous for sickle cell disease, and may prove to be a clinically useful anti‐sickling agent.
Abstract: Substituted benzaldehydes have been designed to bind preferentially to the oxy conformation of human haemoglobin at a site between the amino terminal residues of the alpha-subunits. Such compounds should stabilize the oxygenated form of haemoglobin and thereby increase its oxygen affinity. The compounds produce the expected effect, left-shifting the oxygen saturation curve of dilute haemoglobin solutions and of whole blood, although the binding pattern to haemoglobin is more complex than envisaged by the design hypothesis. The predicted best compound is also a potent inhibitor, at low oxygen pressure, of the sickling of erythrocytes from patients homozygous for sickle cell disease, and may prove to be a clinically useful anti-sickling agent.
TL;DR: The surface of a platinum electrode was anodically polarized at 3 V vs standard hydrogen electrode in 1 N H2SO4 at 300 K for 16 h so that a thick uniform oxidation layer was formed as discussed by the authors.
TL;DR: In this paper, the electrical properties of the solid solutions between stabilized zirconia and ceria, (0.9-y)ZrO/sub 2/-yCeO/ sub 2/-0.1y, with 0 less than or equal to y less than and equal to 0.9, were investigated, between 1273 and 1673 K.
Abstract: The electrical properties of the solid solutions between stabilized zirconia and ceria, (0.9-y)ZrO/sub 2/-yCeO/sub 2/-0.1Y/sub 2/O/sub 3/ with 0 less than or equal to y less than or equal to 0.9, have been investigated, between 1273 and 1673 K, in a large range of oxygen partial pressures. The total electrical conductivity and the concentrations of the various charge carriers, determined through thermogravimetry and measurement of magnetic susceptibility at high temperature as a function of oxygen partial pressure, makes it possible to develop a model accounting for the transport properties as a function of temperature and oxygen partial pressure. On the basis of the present results, the materials in question appear to be suitable as membranes semipermeable to oxygen.