scholarly journals Oxygen-17 splitting of the very rapid molybdenum(V) e.p.r. signal from xanthine oxidase. Rate of exchange with water of the coupled oxygen atom

1980 ◽  
Vol 189 (3) ◽  
pp. 615-623 ◽  
Author(s):  
S Gutteridge ◽  
R C Bray
Keyword(s):  
Exchange Rate ◽  
Oxygen Atom ◽  
Xanthine Oxidase ◽  
Transient Signal ◽  
Carbonium Ion ◽  
Oxygen Ligand ◽  
Exchange Rate Constant ◽  
Single Oxygen Atom ◽  
Single Oxygen ◽  
Hydrolysis Of

Studies have been carried out of effects of 17O substitution on a Mo(V) e.p.r. signal from xanthine oxidase, known as Very Rapid. This transient signal is believed to represent an intermediate in enzymic turnover. When Very Rapid was developed from enzyme equilibrate with 17O-enriched water, strong coupling of Mo(V) to a single oxygen atom was observed, with A(17O)1,2,3 1.34, 1.40, 1.36 mT. The isotropic character of the splittings is interpreted as favouring a structure of the type Mo–O–C. The rate of exchange with water of the oxygen atom detected in the signal was studied. In oxidized enzyme, which contains a terminal oxygen ligand, the exchange rate constant was 2–4 h-1 (pH 5.9–7.8 and about 20 degrees C). However, if the exchange was allowed to take place whilst the enzyme was turning over a substrate, then the process occurred within a few seconds. The present and previous results are interpreted as favouring an enzymic mechanism in which a terminal oxygen ligand reacts, as a nucleophile, with a substrate carbonium ion. To complete the reaction, product liberation, by hydrolysis of the enzyme-bound species, occurs in such a way as to cleave the Mo–O bond, thus explaining the fast oxygen exchange in the presence of the substrate.

scholarly journals Formamide as a substrate of xanthine oxidase

1984 ◽  
Vol 220 (1) ◽  
pp. 235-242 ◽  
Author(s):  
F F Morpeth ◽  
G N George ◽  
R C Bray
Keyword(s):  
Oxygen Atom ◽  
Xanthine Oxidase ◽  
Structural Features ◽  
New Information ◽  
Single Oxygen Atom ◽  
Oxo Ligand ◽  
Single Oxygen ◽  
Do So

Formamide is a substrate of xanthine oxidase. At pH 8.2 and 1.14 mM-O2, Vmax.(app.) is 3.1 s-1 and Km (app.) is 0.7 M. Mo(V) e.p.r. signals obtained by treating the enzyme with formamide were studied, and these provide new information about the ligation of molybdenum in the enzyme and about the enzymic mechanism. The substrate is the first compound that is not a nitrogen-containing heterocycle to give a Very Rapid signal. This supports the hypothesis that the Very Rapid signal, though it is not detectable with all substrates, represents an essential intermediate in turnover. Formamide also gives the Inhibited signal and is the first non-aldehyde substrate to do so. The Rapid type 1 signal obtained in the presence of formamide was examined in H2O enriched with 2H or with 17O. The single oxygen atom detectable in the signal is shown to be strongly and anisotropically coupled. This indicates that this atom remains as an oxo ligand of molybdenum in this signal-giving species. Other structural features of this species are discussed.

scholarly journals Comparison of the molybdenum centres of native and desulpho xanthine oxidase. The nature of the cyanide-labile sulphur atom and the nature of the proton-accepting group

1978 ◽  
Vol 175 (3) ◽  
pp. 887-897 ◽  
Author(s):  
S Gutteridge ◽  
S J Tanner ◽  
R C Bray
Keyword(s):  
Exchange Rate ◽  
Xanthine Oxidase ◽  
Catalytic Reaction ◽  
Functional Form ◽  
Great Majority ◽  
Sulphur Atom ◽  
Strongly Coupled ◽  
Weakly Coupled ◽  
Exchange Rate Constant ◽  
A Site

The non-functional form of xanthine oxidase known as the desulpho enzyme was compared with the functional enzyme in various ways, to obtain information on the structure of the molybdenum centre and the mechanism of the catalytic reaction. The desulpho enzyme, like the functional one, possesses a site for the binding of anions, presumably as ligands of molybdenum. Evidence is presented that in the Mo(V) e.p.r. signal from the desulpho-enzyme, as in that from the functional enzyme, a weakly coupled proton, in addition to a strongly coupled proton, interacts with the metal. Measurements were carried out by e.p.r. on the rate at which the proton strongly coupled to molybdenum exchanged, on diluting enzyme samples with 2H2O. For the desulpho enzyme the exchange rate constant was 0.40s-1, at pH 8.2 and 12 degrees C, and for the functional enzyme it was 85 s-1. It is shown that the great majority of reported differences between the enzyme forms are consistent with functional enzyme containing an (Enzyme)-Mo=S grouping, replaced in the desulpho form by (Enzyme)-Mo=O. Protonation of these groups, with pK values of about 8 and 10 respectively, would give (Enzyme)-Mo-SH and (Enzyme)-Mo-OH, these being the forms observed by e.p.r. The accepting group in the functional enzyme, for the proton transferred from the substrate while molybdenum is reduced in the catalytic reaction [Gutteridge, Tanner & Bray (1978) Biochem J. 175 869-878], is thus taken to be Mo=S.

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.

Pushing Single-Oxygen-Atom-Bridged Bimetallic Systems to the Right: A Cryptand-Encapsulated Co–O–Co Unit

2015 ◽  
Vol 137 (49) ◽  
pp. 15354-15357 ◽  
Author(s):  
Julia M. Stauber ◽  
Eric D. Bloch ◽  
Konstantinos D. Vogiatzis ◽  
Shao-Liang Zheng ◽  
Ryan G. Hadt ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
Bimetallic Systems ◽  
Single Oxygen Atom ◽  
The Right ◽  
Single Oxygen

scholarly journals Retraction of “Pushing Single-Oxygen-Atom-Bridged Bimetallic Systems to the Right: A Cryptand-Encapsulated Co–O–Co Unit”

2020 ◽  
Vol 142 (14) ◽  
pp. 6834-6834
Author(s):  
Julia M. Stauber ◽  
Eric D. Bloch ◽  
Konstantinos D. Vogiatzis ◽  
Shao-Liang Zheng ◽  
Ryan G. Hadt ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
Bimetallic Systems ◽  
Single Oxygen Atom ◽  
The Right ◽  
Single Oxygen

Enantioselective epoxidation of olefins by single-oxygen atom donors catalyzed by managanese-glycoconjugated porphyrins

1996 ◽  
Vol 113 (1-2) ◽  
pp. 23-34 ◽  
Author(s):  
Sandrine Vilain-Deshayes ◽  
Anne Robert ◽  
Philippe Maillard ◽  
Bernard Meunier ◽  
Michel Momenteau
Keyword(s):  
Oxygen Atom ◽  
Enantioselective Epoxidation ◽  
Single Oxygen Atom ◽  
Single Oxygen ◽  
Epoxidation Of Olefins
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