scholarly journals A study of the mechanism of quercetin oxygenation by 18O labelling. A comparison of the mechanism with that of haem degradation

1982 ◽  
Vol 205 (1) ◽  
pp. 239-244 ◽  
Author(s):  
S B Brown ◽  
V Rajananda ◽  
J A Holroyd ◽  
E G Evans
Keyword(s):  
Oxygen Molecule ◽  
Enzymic Reaction ◽  
Single Oxygen ◽  
Oxygen Atoms

The mechanism of quercetin oxygenation, which is formally analogous to haem degradation, was studied by using 18O labelling. In both the enzymic oxygenation (catalysed by quercetinase) and the non-enzymic reaction (base-catalysed), both oxygen atoms incorporated into product were derived from a single oxygen molecule. Quercetin oxygenation therefore occurs by a classical dioxygenase mechanism and is not an appropriate model for study of the mechanism of haem catabolism.

New Organogallium Peroxides

2009 ◽  
Vol 64 (11-12) ◽  
pp. 1369-1374 ◽  
Author(s):  
Werner Uhl ◽  
Mohammad R. Halvagar ◽  
Henrik R. Bock ◽  
Beate Jasper-Peter ◽  
Marcus Layh
Keyword(s):  
Oxygen Atom ◽  
Oxygen Molecule ◽  
Formula Unit ◽  
Methyl Substituent ◽  
Tert Butyl ◽  
The Third ◽  
Butyl Group ◽  
Tert Butyl Group ◽  
Single Oxygen Atom ◽  
Single Oxygen

Treatment of (Me3C)2Ga-CH(SiMe3)2 (1) with oxygen gave the oxidation of both quaternary carbon atoms of the tert-butyl groups, while the bis(trimethylsilyl)methyl substituent was not affected. One tert-butyl group was transferred to an alkoxide which in the dimeric formula unit of the product 2 occupies the bridging position between both gallium atoms. The second one afforded a terminally arranged tert-butylperoxo ligand by the insertion of a complete oxygen molecule into the respective Ga-C bond. Another organogallium peroxide (5) was obtained by the reaction of Li(OEt2)[H3GaCH(SiMe3)2] (3) with H-O-O-CMe2OMe (4). Two hydrido ligands of the trihydridogallanate were replaced by peroxo groups, while the third Ga-H bond gave a hydroxide (Ga-OH) by insertion of a single oxygen atom. The product, Li[Ga(OH)(OOCMe2OMe)2R] [5, R=CH(SiMe3)2], forms a singular dimeric formula unit with a complicated oligocyclic structure in which all peroxo groups are in bridging positions between lithium and gallium atoms

scholarly journals Single and double addition of oxygen atoms to propyne on surfaces at low temperatures

2014 ◽  
Vol 168 ◽  
pp. 167-184 ◽  
Author(s):  
Helen J. Kimber ◽  
Courtney P. Ennis ◽  
Stephen D. Price
Keyword(s):  
Oxygen Atom ◽  
Surface Temperature ◽  
Interstellar Dust ◽  
Addition Product ◽  
Phase Reaction ◽  
Surface Temperatures ◽  
Single Addition ◽  
Single Oxygen Atom ◽  
Single Oxygen ◽  
Oxygen Atoms

Experiments designed to simulate the low temperature surface chemistry occurring in interstellar clouds provide clear evidence of a reaction between oxygen atoms and propyne ice. The reactants are dosed onto a surface held at a fixed temperature between 14 and 100 K. After the dosing period, temperature programmed desorption (TPD), coupled with time-of-flight mass spectrometry, are used to identify two reaction products with molecular formulae C3H4O and C3H4O2. These products result from the addition of a single oxygen atom, or two oxygen atoms, to a propyne reactant. A simple model has been used to extract kinetic data from the measured yield of the single-addition (C3H4O) product at surface temperatures from 30–100 K. This modelling reveals that the barrier of the solid-state reaction between propyne and a single oxygen atom (160 ± 10 K) is an order of magnitude less than that reported for the gas-phase reaction. In addition, estimates for the desorption energy of propyne and reaction rate coefficient, as a function of temperature, are determined for the single addition process from the modelling. The yield of the single addition product falls as the surface temperature decreases from 50 K to 30K, but rises again as the surface temperature falls below 30 K. This increase in the rate of reaction at low surface temperatures is indicative of an alternative, perhaps barrierless, pathway to the single addition product which is only important at low surface temperatures. The kinetic model has been further developed to characterize the double addition reaction, which appears to involve the addition of a second oxygen atom to C3H4O. This modelling indicates that this second addition is a barrierless process. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and propyne could occur under on interstellar dust grains on an astrophysical time scale.

scholarly journals Photosynthesis: Light and Life

2013 ◽  
Vol 35 (5) ◽  
pp. 4-7
Author(s):  
James W. Murray
Keyword(s):  
Electron Acceptor ◽  
Energy Input ◽  
Oxygen Molecule ◽  
Crucial Importance ◽  
Terminal Electron Acceptor ◽  
Photosynthetic Organisms ◽  
Energy Technologies ◽  
The Earth ◽  
Life On Earth ◽  
Single Oxygen

Complex life on Earth requires oxygen as the terminal electron acceptor in the respiratory chain. However, the lifetime of a single oxygen molecule in the atmosphere is only 4500 years. Oxygen is continually being replenished by the action of photosynthetic organisms, using the only substantial energy input to the Earth, sunlight. How this light energy is harvested and used is of fundamental biological importance, and may be of crucial importance in developing sustainable energy technologies.

Imaging the Impact of Single Oxygen Atoms on Superconducting Bi2+ySr2-yCaCu2O8+x

Science ◽  
2012 ◽  
Vol 337 (6092) ◽  
pp. 320-323 ◽  
Author(s):  
I. Zeljkovic ◽  
Z. Xu ◽  
J. Wen ◽  
G. Gu ◽  
R. S. Markiewicz ◽  
...  
Keyword(s):  
Single Oxygen ◽  
The Impact ◽  
Oxygen Atoms

Observation of single oxygen atoms decomposed from water molecules on aSi(111)−7×7surface

2006 ◽  
Vol 73 (7) ◽  
Author(s):  
Rong-Li Lo ◽  
Chun-Ming Chang ◽  
Ing-Shouh Hwang ◽  
Tien T. Tsong
Keyword(s):  
Water Molecules ◽  
Single Oxygen ◽  
Oxygen Atoms

scholarly journals Role of hydrogen peroxide in the cytotoxicity of the xanthine/xanthine oxidase system

1988 ◽  
Vol 249 (2) ◽  
pp. 391-399 ◽  
Author(s):  
E M Link ◽  
P A Riley
Keyword(s):  
Hydrogen Peroxide ◽  
Xanthine Oxidase ◽  
Cytotoxic Effect ◽  
Oxidase System ◽  
H2o2 Decomposition ◽  
Enzymic Reaction ◽  
Single Oxygen ◽  
Phosphate Buffered Saline

1. The survival of mammalian epithelial cells exposed in vitro to the xanthine/xanthine oxidase system in phosphate-buffered saline (PBS) or serum-containing medium (SCMEM) was investigated. 2. The cytotoxic effect observed depended on the composition of the medium in which the enzymic reaction was carried out; a surviving fraction of 5 x 10(-5) was found for cells exposed in PBS and 5.2 x 10(-1) for those in SCMEM. 3. The cytotoxic product(s) formed by the xanthine/xanthine oxidase system was relatively stable in PBS; survival of cells incubated after completion of the enzymic reaction was always less than that found for cells exposed during the reaction in the same system. 4. Superoxide dismutase or mannitol present during the enzymic reaction did not inhibit the cytotoxic effect. 5. NaN3 (a single-oxygen quencher and a catalase inhibitor) added to the system in SCMEM caused a reduction in survival to the level observed for cells exposed to the enzymic reaction in PBS. 6. Catalase completely protected cells, but no protection was observed when both catalase and NaN3 were present in the reaction mixture. 7. A similar cytotoxic effect was produced when cells were treated with H2O2 alone. 8. The rate of H2O2 decomposition in medium was accelerated by the presence of serum, but this was completely inhibited by NaN3. 9. It is concluded that H2O2 is the major cytotoxic product formed by the xanthine/xanthine oxidase system.

Catalytic CO Oxidation on Unreconstructed Cu(110) by Reactive As-Adsorbed Oxygen Atoms below 230 K

1996 ◽  
Vol 100 (3) ◽  
pp. 1048-1054 ◽  
Author(s):  
Tsuyoshi Sueyoshi ◽  
Takehiko Sasaki ◽  
Yasuhiro Iwasawa
Keyword(s):  
Co Oxidation ◽  
Adsorbed Oxygen ◽  
Catalytic Co Oxidation ◽  
Oxygen Atoms

Modification of optical properties of PC-PBT/Cr2O3 and PC-PBT/CdS nanocomposites by gamma irradiation

2020 ◽  
Vol 92 (2) ◽  
pp. 20402
Author(s):  
Kaoutar Benthami ◽  
Mai ME. Barakat ◽  
Samir A. Nouh
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Band Gap ◽  
Color Difference ◽  
Band Gap Energy ◽  
Polybutylene Terephthalate ◽  
Γ Irradiation ◽  
Gap Energy ◽  
Vis Spectroscopy ◽  
Oxygen Atoms

Nanocomposite (NCP) films of polycarbonate-polybutylene terephthalate (PC-PBT) blend as a host material to Cr2O3 and CdS nanoparticles (NPs) were fabricated by both thermolysis and casting techniques. Samples from the PC-PBT/Cr2O3 and PC-PBT/CdS NCPs were irradiated using different doses (20–110 kGy) of γ radiation. The induced modifications in the optical properties of the γ irradiated NCPs have been studied as a function of γ dose using UV Vis spectroscopy and CIE color difference method. Optical dielectric loss and Tauc's model were used to estimate the optical band gaps of the NCP films and to identify the types of electronic transition. The value of optical band gap energy of PC-PBT/Cr2O3 NCP was reduced from 3.23 to 3.06 upon γ irradiation up to 110 kGy, while it decreased from 4.26 to 4.14 eV for PC-PBT/CdS NCP, indicating the growth of disordered phase in both NCPs. This was accompanied by a rise in the refractive index for both the PC-PBT/Cr2O3 and PC-PBT/CdS NCP films, leading to an enhancement in their isotropic nature. The Cr2O3 NPs were found to be more effective in changing the band gap energy and refractive index due to the presence of excess oxygen atoms that help with the oxygen atoms of the carbonyl group in increasing the chance of covalent bonds formation between the NPs and the PC-PBT blend. Moreover, the color intensity, ΔE has been computed; results show that both the two synthesized NCPs have a response to color alteration by γ irradiation, but the PC-PBT/Cr2O3 has a more response since the values of ΔE achieved a significant color difference >5 which is an acceptable match in commercial reproduction on printing presses. According to the resulting enhancement in the optical characteristics of the developed NCPs, they can be a suitable candidate as activate materials in optoelectronic devices, or shielding sheets for solar cells.

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