Showing papers on "Oxygen published in 1973"

Quenching of fluorescence by oxygen. A probe for structural fluctuations in macromolecules.

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.

Defect structure and electronic donor levels in stannic oxide crystals

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.

Responses of Aquatic Invertebrates to Declining Oxygen Conditions

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.

Concentration, Solubility, and Equilibrium Distribution Coefficient of Nitrogen and Oxygen in Semiconductor Silicon

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.

Rate Constants for the Reactions of Atomic Oxygen (O 3P) with Organic Compounds in the Gas Phase

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.

Genesis of Precambrian Iron-Formations and the Development of Atmospheric Oxygen

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.

On the mechanism of quenching of singlet oxygen in solution.

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.

The Electrical Conductivity of CaO ‐ Doped Nonstoichiometric Cerium Dioxide from 700° to 1500°C

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 .

Advantage or disadvantage of a decrease of blood oxygen affinity for tissue oxygen supply at hypoxia. A theoretical study comparing man and rat.

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.

Transport Numbers of Metal and Oxygen during the Anodic Oxidation of Tantalum

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.

A Posteffect of Oxygen in Irradiated Bacteria: A Submillisecond Fast Mixing Study

Abstract: time scale of the oxygen effect in irradiated Serratia marcescens. The bacteria were held on a Millipore filter inside a chamber which was usually flushed with humidified nitrogen and were exposed to an explosion of oxygen released into the chamber through a fastacting solenoid-operated valve. The bacteria were irradiated with a single 2-psec pulse of 1.8 MeV electrons from a linear accelerator. The arrival of oxygen at the bacteria was timed to occur at a preset interval before or after the electron pulse. The time resolution was 100 ,sec. After fixed doses of 10, 19, and 28 krads per pulse, the bacterial survival was measured as a function of the oxygen contact time. It was found that, when oxygen contact occurred at any instant before or up to the time of the electron pulse, full sensitization was obtained. However, bacteria exposed to oxygen at times after the electron pulse showed decreasing sensitization as the time interval increased, the survival approaching the anoxic control value at times greater than 2 msec. The data show that, in Serratia marcescens irradiated under anoxic conditions, oxygen-dependent damage decays approximately exponentially with a half-life of about 500 ,usec.

Relative contributions of anaerobic and aerobic energy production during activity in amphibia

Abstract: 1. Measurements of oxygen consumption and lactate production during activity were made in three species of amphibians. Oxygen debts and rates of lactate removal were also studied. 2. Maximal values of oxygen consumption are 200 and 500% above resting levels in the plethodontid salamanderBatrachoseps attenuatus and the frogHyla regilla, respectively (Kg. 1). However, these values are not attained until 5–15 min after the cessation of activity. 3. Batrachoseps, a lungless animal, derives 25 times more energy during 2 min of activity from lactate production than from oxygen consumption.Hyla is also predominantly anaerobic during activity butBufo boreas is mainly aerobic. 4. An inverse relationship exists between aerobic and anaerobic scopes in amphibians, such that total energetic output during activity is similar even though the component factors may differ by ten-fold. 5. Oxygen debts inHyla andBatrachoseps after 2-min activity are repayed in approximately one hour but rates of lactate removal are much lower (Fig. 2); large amounts of lactate persist long after oxygen consumption has returned to resting levels. Oxygen debt, therefore, cannot be used as an estimate of energetic expenditure during activity.

The Solubility of Sulfur in Na2O–SiO2 Melts under Various Oxygen Partial Pressures at 1100 °C, 1250 °C, and 1300 °C

Abstract: The solubility of sulfur in Na2O–SiO2 melts with the Na2O/SiO2 molar ratios of 1/3, 1/2, and 1/1 was investigated by varying the oxygen partial pressure at 1100, 1250, and 1300 °C The results at 1100 °C are complicated, for the equilibrium state within the gas phase is not established From the experiments at 1250 and 1300 °C, the following conclusions are reached: (1) When the temperature and the Na2O/SiO2 ratio in the melt are constant, the solubility of sulfur increases with an increase of the total amount of sulfur in the gas phase (2) When the temperature, the Na2O/SiO2 ratio, and the total amount of sulfur in the gas phase are constant, the solubility of sulfur shows its minimum at a specific oxygen partial pressure; at higher oxygen partial pressures, the sulfur dissolves in the melts mostly as sulfate, while at lower oxygen partial pressures, the sulfur dissolves mostly as sulfide (3) When the temperature and the total amount of sulfur in the gas phase are constant, the solubility rises greatly

Yeast growth in relation to the dissolved oxygen and sterol content of wort

Abstract: The extent of the requirement for oxygen in cells of brewing yeast is determined by the availability of oxygen during propagation. Cells with no oxygen requirement ferment satisfactorily when added to either air-saturated or de-aerated wort. Cells produced during fermentation develop an oxygen-requirement and ferment poorly when added to de-aerated wort because of restriction of both rate and extent of exponential growth. The quantity of dissolved oxygen needed to ensure satisfactory growth varies greatly with yeast strain. In all cases examined, the oxygen requirement can be eliminated by addition to the growth medium of ergosterol and Tween 80 However Tween 80 alone is without effect. It seems likely that oxygen is required because it is essential for biosynthesis of sterols.