AQUEOUS CHEMISTRY OF INORGANIC FREE RADICALS.1V. THE USE OF CARBON MONOXIDE AS A SCAVENGER FOR HYDROXYL RADICALS GENERATED BY THE PHOTOLYSIS OF HYDROGEN PEROXIDE

1963 ◽  
Vol 67 (12) ◽  
pp. 2835-2841 ◽  
Author(s):  
George Buxton ◽  
W. K. Wilmarth
Keyword(s):  
Hydrogen Peroxide ◽  
Carbon Monoxide ◽  
Free Radicals ◽  
Hydroxyl Radicals ◽  
Aqueous Chemistry

The gaseous oxidation of aliphatic alcohols. III. n - and iso -propyl alcohols

1960 ◽  
Vol 257 (1290) ◽  
pp. 402-412 ◽  
Keyword(s):  
Hydrogen Peroxide ◽  
Carbon Monoxide ◽  
Free Radicals ◽  
Induction Period ◽  
Isopropyl Alcohol ◽  
Side Reactions ◽  
Chain Mechanism ◽  
Complete Elimination ◽  
Chain Branching ◽  
A Chain

A study of the gaseous oxidation of n -propyl alcohol (1-propanol) at 264°C shows that, after an induction period during which higher aldehydes and hydrogen peroxide are apparently the only products formed, the pressure starts to rise autocatalytically and methanol, formaldehyde and carbon monoxide become detectable. Additions of higher aldehydes reduce the induction period but the amounts required for its complete elimination are considerably greater than those normally present at the end of the induction period. A chain mechanism is proposed which involves initially abstraction of hydrogen from 1-propanol by HO 2 radicals followed by interaction of the resulting hydroxypropyl radicals with oxygen to yield propionaldehyde. Further reactions of this aldehyde are believed to be responsible for chain-branching and for the formation of the various C 1 products. Isopropyl alcohol (2-propanol) is much less readily oxidized than 1-propanol. At 330°C the main oxidation product is acetone which is formed together with hydrogen peroxide in somewhat smaller quantities. Minor products include methanol, acetaldehyde and formaldehyde. The course of the oxidation of 2-propanol is little affected by additions of acetone or formaldehyde but the induction period is markedly reduced by added acetaldehyde. The chain cycle suggested for the initial stages of oxidation involves attack by HO 2 radicals at the tertiary C─H bond of the alcohol followed by reaction of the resulting free radicals with oxygen to give acetone. The intermediate responsible for chain-branching is believed to be acetaldehyde which is produced by side reactions. C 1 compounds are formed partly by oxidation of this aldehyde and partly by further reactions of acetone.

Studies of the reactions of hydroxyl radicals. II

1966 ◽  
Vol 291 (1424) ◽  
pp. 85-93 ◽  
Keyword(s):  
Hydrogen Peroxide ◽  
Carbon Monoxide ◽  
Hydroxyl Radicals ◽  
Room Temperature ◽  
Order Reaction ◽  
Methyl Radicals ◽  
Third Order ◽  
Experimental Conditions ◽  
Homogeneous Decomposition ◽  
Methane Carbon

The homogeneous decomposition of hydrogen peroxide has been used as a source of hydroxyl radicals. In part I values were reported for the relative rates of reaction of hydroxyl radicals with methane, carbon monoxide, formaldehyde and hydrogen peroxide. In this paper these values are confirmed for different experimental conditions and more consideration is given to details of subsequent reactions. The reaction of methyl radicals with oxygen has previously been shown to occur by a third order reaction both at 200 °C (Hoare & Walsh 1957) and at room temperature (Christie 1958). Present results show that the reaction is second order at 525 °C as suggested by Barnard & Honeyman (1964). In the absence of added oxygen, methyl radicals combine to give ethane which in turn reacts with hydroxyl radicals twelve times more rapidly than does methane.

scholarly journals Catalase Expression Is Modulated by Vancomycin and Ciprofloxacin and Influences the Formation of Free Radicals in Staphylococcus aureus Cultures

2015 ◽  
Vol 81 (18) ◽  
pp. 6393-6398 ◽  
Author(s):  
Ying Wang ◽  
Anni B. Hougaard ◽  
Wilhelm Paulander ◽  
Leif H. Skibsted ◽  
Hanne Ingmer ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Staphylococcus Aureus ◽  
Free Radicals ◽  
Hydroxyl Radical ◽  
Hydroxyl Radicals ◽  
Bacterial Species ◽  
Iron Chelation ◽  
Radical Formation ◽  
Bacterial Cells ◽  
Content Type

ABSTRACTDetection of free radicals in biological systems is challenging due to their short half-lives. We have applied electron spin resonance (ESR) spectroscopy combined with spin traps using the probes PBN (N-tert-butyl-α-phenylnitrone) and DMPO (5,5-dimethyl-1-pyrrolineN-oxide) to assess free radical formation in the human pathogenStaphylococcus aureustreated with a bactericidal antibiotic, vancomycin or ciprofloxacin. While we were unable to detect ESR signals in bacterial cells, hydroxyl radicals were observed in the supernatant of bacterial cell cultures. Surprisingly, the strongest signal was detected in broth medium without bacterial cells present and it was mitigated by iron chelation or by addition of catalase, which catalyzes the decomposition of hydrogen peroxide to water and oxygen. This suggests that the signal originates from hydroxyl radicals formed by the Fenton reaction, in which iron is oxidized by hydrogen peroxide. Previously, hydroxyl radicals have been proposed to be generated within bacterial cells in response to bactericidal antibiotics. We found that whenS. aureuswas exposed to vancomycin or ciprofloxacin, hydroxyl radical formation in the broth was indeed increased compared to the level seen with untreated bacterial cells. However,S. aureuscells express catalase, and the antibiotic-mediated increase in hydroxyl radical formation was correlated with reducedkatAexpression and catalase activity in the presence of either antibiotic. Therefore, our results show that inS. aureus, bactericidal antibiotics modulate catalase expression, which in turn influences the formation of free radicals in the surrounding broth medium. If similar regulation is found in other bacterial species, it might explain why bactericidal antibiotics are perceived as inducing formation of free radicals.

Studies of the reactions of hydroxyl radicals. I

1966 ◽  
Vol 291 (1424) ◽  
pp. 73-84 ◽  
Keyword(s):  
Hydrogen Peroxide ◽  
Carbon Monoxide ◽  
Kinetic Study ◽  
Hydroxyl Radicals ◽  
Rate Constants ◽  
The Other ◽  
General Applicability ◽  
Preliminary Account ◽  
Homogeneous Decomposition ◽  
Methane Carbon

This paper describes how the homogeneous decomposition of hydrogen peroxide vapour has been successfully used as a source of hydroxyl radicals in a kinetic study of the relative rates of reaction of hydroxyl radicals with methane, carbon monoxide, formaldehyde and hydrogen peroxide. It has been found that the method is of general applicability provided subsequent reactions of radicals formed can be controlled. With hydroxyl radicals so produced from the decomposition of hydrogen peroxide, surprisingly consistent values were obtained for the relative rates of reaction of methane and carbon monoxide with hydroxyl radicals. Thus, within an accuracy of 10%, the ratios of rate constants for reaction of hydroxyl radicals with methane and carbon monoxide were found to be 3.6 at 650 °C, 2.1 at 525 °C and 0.85 at 400 °C. The rates of reaction of hydroxyl radicals with formaldehyde and hydrogen peroxide were less accurately determined because of expected additional reactions. Within an accuracy of about 50% it was estimated that hydroxyl radicals reacted ten times as fast with hydrogen peroxide as with carbon monoxide at 525 °C. At the same temperature hydroxyl radicals reacted 33 ± 6 times as fast with formaldehyde as with methane. Data were obtainable at temperatures as low as 400 °C even though heterogeneous decomposition of hydrogen peroxide was relatively more important at these temperatures. This was because heterogeneous decomposition of hydrogen peroxide did not cause oxida­tion of the other gases which were also present. A preliminary account (Hoare 1962) of this work has previously been published.

The effect of cation concentration on the nitrogen splitting constant of nitroxide free radicals

1990 ◽  
Vol 55 (10) ◽  
pp. 2377-2380
Author(s):  
Hamza A. Hussain
Keyword(s):  
Hydrogen Peroxide ◽  
Hydrogen Bonding ◽  
Free Radicals ◽  
Esr Spectroscopy ◽  
The Other ◽  
Tetraethylammonium Bromide ◽  
Splitting Constant ◽  
The One ◽  
Positively Charged ◽  
Two Equilibria

Nitroxide free radicals prepared from diethylamine, piperidine and pyrrolidine by oxidation with hydrogen peroxide were studied by ESR spectroscopy. The changes in the 14N splitting constant (aN) caused by the addition of KBr or tetraethylammonium bromide were measured in dependence on the concentration of the ions. For diethylamine nitroxide and piperidine nitroxide, the results are discussed in terms of two equilibria: the one, involving the anion, is associated with a gain or loss of hydrogen bonds to the nitroxide oxygen atom, the other is associated with the formation of solvent shared units involving the cation, which results in changes in the hydrogen bonding strenght. The large increase in the aN value in the case of pyrrolidine nitroxide is explained in terms of an interaction from one side of the positively charged N atom; the increase in aN in the case of diethylamine and piperidine nitroxides is explained in terms of interactions with both sides of the positively charged N atom.

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