Showing papers on "Oxygen published in 1981"

Toxic drug effects associated with oxygen metabolism: Redox cycling and lipid peroxidation

Abstract: Various endogenous and exogenous compounds exert cytotoxic effects via oxygen reduction. In general, these are reduced by intracellular enzymes (reductases of various kinds) in one-electron transfer reactions, before they in turn reduce O2 to O2, the superoxide anion radical. Thus, a cycle is formed of O2 uptake at the expense of cellular reducing equivalents, notably NADPH, generating further active oxygen species (figs 1,2). Structures capable of 'redox cycling' include catechols and other quinone compounds, iron chelates, and aromatic nitro compounds. Several anticancer agents, and also some mutagens, operate on this principle, and their toxic effects may be explained by redox cycling. The particular importance of hypoxic conditions for deleterious O2 effects is given by the concomitant flux through reductive as well as oxidative pathways. Toxic effects include membrane damage resulting from peroxidative reactions of polyunsaturated fatty acids (lipid peroxidation), as well as the attack of reactive oxygen species on proteins (enzymes) and nucleic acids; thus O2 metabolism is linked to carcinogenicity and mutagenicity. Lipid peroxidation is also induced by various halogenated compounds such as carbon tetrachloride. Again, hypoxic conditions are particularly critical because, on the one hand, metabolic activation leading to the free radical is enhanced and, on the other hand, oxygen required for the maintenance of lipid peroxidation is still available. - Powerful antioxidant systems of the cell maintain low steady state concentrations of oxygen metabolites, and toxic effects may, in part, also be explained by the constant drain of reducing equivalents resulting from redox cycling.

Rate constants for the decay and reactions of the lowest electronically excited singlet state of molecular oxygen in solution

Abstract: The available rate data on the reactivity and physical deactivation of molecular oxygen in its first electronic excited state (1Δg) in liquid solution have been critically compiled. Where possible, relative rates reported in the literature have been normalized to standard values selected by a statistical analysis of the experimental data. Second order rate constants for the deactivation and chemical reaction of singlet oxygen are reported for 670 compounds. Additionally, psuedo first order rate constants (kd) for solvent deactivation of singlet oxygen are reported for 50 different solvents.

Nutrition of the intervertebral disc: solute transport and metabolism.

Abstract: The metabolism of the canine nucleus pulposus was investigated at different oxygen tensions. It was found that even at high oxygen tensions the metabolism is mainly anaerobic, only approximately 1.5% of the glucose being converted to carbon dioxide. The concentration dependence of oxygen consumption is limited to very low oxygen tensions. Values of oxygen consumption and lactic acid production were used to calculate the concentration profiles of these substances within the nucleus pulposus, using a diffusion theory. The predicted concentration profiles were compared with the experimental measurements of concentration at various positions in the disc. The good agreement in these values found in the nucleus confirms that the main mechanism of metabolite transport is diffusion, and the main route of nutrient supply into the nucleus is via the endplate.

Nonstoichiometry in SrTiO3

Abstract: The defect chemistry of polycrystalline has been studied by means of the equilibrium electrical conductivity as a function of temperature, oxygen activity, Sr/Ti ratio, and impurity additions. Reduction, excess , and acceptor impurities all contribute to the oxygen vacancy content and their effects are therefore highly interdependent. The effect of added donor‐impurities,e.g., 500 ppm Nb, is highly dependent on the presence and amount of excess .

Implantable glucose sensor

Abstract: A method and apparatus for more accurate measurements of the glucose content in body fuids by sensing the absolute level of oxygen concentration in the fluid and correcting the output differential measurement indicative of the glucose content in the fluid according to the absolute level of oxygen. In the two electrode systems known to the art, the unaltered oxygen electrode of the electrode pair may be employed to read the absolute level of oxygen concentration and in addition, function to establish the difference in oxygen concentration caused by glucose oxidation. In view of the fact that temperature may vary, a thermistor may be included in the electrode system to make temperature corrections for reason that the absolute oxygen reading from either a polarographic or galvanic oxygen electrode is extremely sensitive to temperature and the rate of glucose oxidation is temperature sensitive.

Nonstoichiometry in Undoped BaTiO3

Abstract: Equilibrium electrical conductivity data for large-grained, poly crystalline, undoped BaTiO3, as a function of temperature, 750° to 1000°C, and oxygen partial pressure, 10−20

Primary production of microalgae in sediments measured by oxygen microprofile, H14CO3 ‐ fixation, and oxygen exchange methods1

Abstract: A platinum microelectrode was used to measure changes in dissolved oxygen profiles in surface sediment exposed to light and darkness. Estimates of production by microalgae thus derived were compared with those derived from conventional methods of measuring changes in dissolved oxygen and H14C0,- uptake. For each particular depth in the sediment, the primary production can be determined within a few seconds by the new method. Undisturbed sediment cores were used for the H14C0,- fixation assay of benthic photosynthesis. Measurements of the specific activity of HC03- within the photic zone showed a steep gradient of IP”CO,- at the sediment surface. Calculations of benthic photosynthesis taking the actual specific activity into account yielded 2-5 times higher estimates than calculations using the specific activity in the overlying water. In a highly oxidized sediment, the three methods yielded almost identical results at low light intensities (200 pEinst*m-2*s-1). The oxygen methods grossly underestimated the primary productivity at higher light intensities, due to bubble formation. The conventional oxygen method grossly underestimated the primary productivity in sulfuretm~r-type sediments as compared to the two other methods. In addition to photosynthesis, the oxygen consumption by the sediment was determined by oxygen microprofiles.

In-situ combustion method for recovery of heavy oil utilizing oxygen and carbon dioxide as initial oxidant

Abstract: An in-situ combustion method for recovering viscous oil from a subterranean, viscous oil-containing formation comprising injecting a mixture of essentially pure oxygen and carbon dioxide into the formation to initiate an in-situ combustion operation followed by injecting essentially pure oxygen.

TPD AND XPS STUDY ON THERMAL BEHAVIOR OF ABSORBED OXYGEN IN La1−xSrxCoO3

Abstract: Two types of oxygen desorption from La1−xSrxCoO3 were revealed by the appearance of a broad desorption peak(α) below ca. 800°C and a sharp one(β) around 820°C. The binding energy of O ls level for absorbed oxygen was clearly different from that for lattice oxygen. Close examination shows that α is ascribable to the desorption of the absorbed oxygen while β may be the desorption of a part of lattice oxygen.

Limits on oxygen concentration in the prebiological atmosphere and the rate of abiotic fixation of nitrogen

Abstract: Two possible scenarios in early terrestrial atmospheric evolution are examined using a one-dimensional chemistry and flow model of the atmosphere. In each case the production of oxygen results from photolysis of H2O followed by the escape of hydrogen to space. In case 1 the rate of release of reduced volcanic gases is assumed to be greater than the oxygen production rate. This leads to ground-level oxygen concentrations on the order of 10−13 PAL (present atmospheric level). In case 2 the volcanic reduced gas source is omitted, as might have been the case during an extended period of decreased tectonic activity. The oxygen concentration would then have been limited to ∼4 × 10−8 PAL by reaction with dissolved ferrous iron in the early oceans. The case 1 atmosphere is shown to be reducing, and the case 2 atmosphere oxidizing, based on the relative concentrations of reduced versus oxidized radical species present in the troposphere. Redbeds should have been able to form under case 2 conditions, but not under case 1. The NO produced by lightning discharges is converted primarily to HNO in case 1 and to HNO3 in case 2. In either case, fixed nitrogen was probably sufficiently scarce to be a limiting nutrient for marine organisms.

Hyperbaric oxygen therapy.

Abstract: Hyperbaric oxygen therapy is the use of oxygen at increased atmospheric pressure. The history of hyperbaric oxygen therapy can be traced back to the late seventeenth century, when Henshaw treated patients in a pressurized chamber. Initially, patients were treated with pressurized air. In 1955, the modern era of hyperbaric oxygen therapy was born. Today, patients are treated in either monoplace chambers or multiplace chambers. The pressurized oxygen exerts its effects by several different mechanisms, including creating a diffusion gradient for inert gases, oxygenating ischemic tissues, limiting reperfusion injuries, inactivating certain toxins, and supporting angiogenesis and leukocyte function. There are 13 indications for which scientific evidence supports the use of hyperbaric oxygen therapy: arterial gas embolism; decompression sickness; carbon monoxide poisoning; clostridial myonecrosis; crush injuries, compartment syndrome, and other acute ischemias; enhancement of healing in selected problem wounds; exceptional blood loss anemia; intracranial abscess; necrotizing soft tissue infections; refractory osteomyelitis; delayed radiation injury; preservation of skin grafts and flaps; and thermal burns.

AN ACTIVE INTERMEDIATE FORMED IN THE REACTION OF BLEOMYCIN-Fe(II) COMPLEX WITH OXYGEN

Abstract: The base-release activity of oxygen adduct of bleomycin-Fe(II) complex [BLM-Fe(II)] from DNA decreased with a half-life of 5.2 minutes, when incubated at 0°C in 0.05 M Tris-HCl buffer at pH 7.8 in the absence of DNA. Under the same condition, however, visible and ESR spectra showed that the adduct was immediately converted into the ferric complex. The ESR study further indicated the simultaneous formation of two kinds of the low-spin BLM-Fe(III) complex. One of them disappeared in parallel with the decrease of the base-release activity and transformed into the other. The latter Fe(III) complex was stable but inactive. However, by addition of hydrogen peroxide to the latter, the former was regenerated and the base-release activity appeared. Oxygen concentration measurements by oxygraph showed that one mole of BLM-Fe(II) consumed approximately 0.5 mole of molecular oxygen instantly, but did not any more thereafter in the absence of a reducing agent. While in the presence of 2-mercaptoethanol, the oxygen consumption proceeded biphasically, and equimolar oxygen was consumed by BLM-Fe(II) in the first rapid reaction. These results suggest that oxygen adduct of BLM-Fe (II) is reduced by one electron transfer from an external electron donor and the resulting BLM-Fe(III)-O2H- [or its deprotonated form: BLM-Fe(III)-O22-] shows the activity to break DNA accompanying the base-release.

Method of and apparatus for control of reactive sputtering deposition

Abstract: A method and apparatus for the control of reactive sputtering deposition of oxide-containing films, including the monitoring of and maintaining the constancy of the deposition rate and total pressure of the system by adjustment of the oxygen and argon input flow rates. Deposition rate is monitored by an activated quartz crystal, and behaves as a sensitive function of actual oxygen partial pressure. Stoichiometry, optical and electrical properties of the oxide-containing films are therefore controllable by maintaining constant oxygen partial pressure.

Ruthenium‐Based Mixed Oxides as Electrocatalysts for Oxygen Evolution in Acid Electrolytes

Abstract: Ruthenium oxide, prepared by the thermal decomposition method, has the highest known initial electrocatalytic activity for oxygen evolution in acid electrolyte. However, this material is not stable in the electrolyte and at the same time exhibits a significant increase of oxygen overpotential with time, probably due to a chemical transformation of the oxide from a lower to a higher valence state. Efforts were made to stabilize ruthenium by preparing mixed oxides with Ir and/or Ta using the thermal decomposition method. The electrocatalytic activities for oxygen evolution on these oxides in were determined using the potentiostatic method. The surface areas of these oxides were estimated using cyclic voltammetry. Dual Tafel slopes (approximately 30 and 40 mV) were found on most of these oxides. The ternary oxide exhibited a single Tafel slope of 30 mV, had the lowest overpotential, and showed minimum variation of overpotential with time.

Rate constants for deactivation of N2(A 3Σ+u, v′ = 0,1) by O

Abstract: The removal of N2(A 3Σ+u, v′ = 0,1) by O has been studied in a room temperature discharge–flow apparatus by monitoring the temporal decay of the 0,6 and 1,10 bands of the Vegard–Kaplan system. The measured rate constants are (2.8±0.4) and (3.4±0.6)×10−11 cm3 molecule−1 s−1 for v′ = 0 and 1, respectively.

Blood Function in the Hydrothermal Vent Vestimentiferan Tube Worm

Abstract: Extracellular hemoglobin in the whole blood of Riftia pachyptila has a high oxygen affinity (P50 = 1.8 millimeters of mercury at 3 degrees C), a moderate decrease in oxygen affinity at higher temperatures (P50 = 2.7 millimeters of mercury at 14 degrees C), a small effect of carbon dioxide on oxygen affinity (Delta log P50/Delta pH =-0.12), and a high oxygen carrying capacity (up to 11 milliliters of oxygen per 100 milliliters of blood). These characteristics are compatible with the high oxygen demand of chemoautotrophic metabolism in the variable vent environment.