The Mechanism of Methyl Hydroperoxide Formation in the Photoöxidation of Azomethane at 25°

1962 ◽  
Vol 84 (7) ◽  
pp. 1113-1118 ◽  
Author(s):  
N. R. Subbaratnam ◽  
J. G. Calvert
Keyword(s):  
Hydroperoxide Formation ◽  
Methyl Hydroperoxide

Kinetic analysis of compound I formation and the catalatic activity of chloroperoxidase

1981 ◽  
Vol 59 (4) ◽  
pp. 233-236 ◽  
Author(s):  
Tsunehisa Araiso ◽  
Rick Rutter ◽  
Monica M. Palcic ◽  
Lowell P. Hager ◽  
H. Brian Dunford
Keyword(s):  
Steady State ◽  
Kinetic Analysis ◽  
Rate Constant ◽  
Peracetic Acid ◽  
Rate Constants ◽  
Compound I ◽  
Hydroperoxide Formation ◽  
Methyl Hydroperoxide

When the only substrate added to a solution of chloroperoxidase is a hydroperoxide, the reactions are: ferric enzyme + ROOH → compound I + ROH and compound I + ROOH → ferric enzyme + O2 + ROH. When H2O2 is used as substrate, the rate constants for the formation and catalatic decomposition of compound 1 are 2.4 × 106 M−1∙s−1 and 3.4 × 105 M−1∙s−1 at pH 4.7 and it is predicted that a maximum of 87% of the enzyme converts to compound I in the steady state of the catalatic reaction. With methyl hydroperoxide, formation of compound I has a rate constant of 4.7 × 105 M−1∙s−1 and its decomposition 2.9 × 104 M−1∙s−1. When peracetic acid is used, compound I is formed with a rate constant of 3.8 × 106 M−1∙s−1 and a 100% yield of compound I is obtained.

scholarly journals Quantitative and Predictive Modelling of Lipid Oxidation in Mayonnaise

Antioxidants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 287
Author(s):  
Donny W. H. Merkx ◽  
Andries Swager ◽  
Ewoud J. J. van Velzen ◽  
John P. M. van Duynhoven ◽  
Marie Hennebelle
Keyword(s):  
Lipid Oxidation ◽  
Oxidative Stability ◽  
Shelf Life ◽  
Onset Time ◽  
Predictive Modelling ◽  
Oxidation Products ◽  
Food Emulsions ◽  
Hydroperoxide Formation ◽  
Life Tests ◽  
Volatile Aldehydes

Food emulsions with high amounts of unsaturated fats, such as mayonnaise, are prone to lipid oxidation. In the food industry, typically accelerated shelf life tests are applied to assess the oxidative stability of different formulations. Here, the appearance of aldehydes at the so-called onset time, typically weeks, is considered a measure for oxidative stability of food emulsions, such as mayonnaise. To enable earlier assessment of compromised shelf-life, a predictive model for volatile off-flavor generation is developed. The model is based on the formation kinetics of hydroperoxides, which are early oxidation products and precursors of volatile aldehydes, responsible for off-flavor. Under accelerated shelf-life conditions (50 °C), hydroperoxide (LOOH) concentration over time shows a sigmoidal curvature followed by an acceleration phase that occurs at a LOOH-concentration between 38–50 mmol/kg, here interpreted as a critical LOOH concentration (CCLOOH). We hypothesize that the time at which CCLOOH was reached is related to the onset of aldehyde generation and that the characterization of the LOOH-generation curvature could be based on reaction kinetics in the first days. These hypotheses are tested using semi-empirical models to describe the autocatalytic character of hydroperoxide formation in combination with the CCLOOH. The Foubert function is selected as best describing the LOOH-curvature and is hence used to accurately predict onset of aldehyde generation, in most cases within several days of shelf-life. Furthermore, we find that the defining parameters of this model could be used to recognize antioxidant mechanisms at play.

Swelling, reductive stress, and cell death during chemical hypoxia in hepatocytes

1989 ◽  
Vol 257 (2) ◽  
pp. C347-C354 ◽  
Author(s):  
G. J. Gores ◽  
C. E. Flarsheim ◽  
T. L. Dawson ◽  
A. L. Nieminen ◽  
B. Herman ◽  
...  
Keyword(s):  
Cell Injury ◽  
Rat Hepatocytes ◽  
Iodoacetic Acid ◽  
Cell Killing ◽  
Cell Swelling ◽  
Reductive Stress ◽  
Chemical Hypoxia ◽  
Hydroperoxide Formation ◽  
Bleb Formation ◽  
The Relationship

In rat hepatocytes, we examined the relationship between cell volume, bleb formation, and loss of cell viability during chemical hypoxia with KCN plus iodoacetic acid. In hypotonic media (150-200 mosmol/kgH2O), cells swelled to a greater extent during chemical hypoxia than in isotonic media, but rates of cell killing were identical. Sucrose (300 mM) added to isotonic media prevented early cell swelling but actually accelerated cell killing. In contrast, mannitol (300 mM) improved cell survival but did not prevent cell swelling. Bleb formation occurred regardless of buffer tonicity. The antioxidants desferrioxamine and cyanidanol but not superoxide dismutase +/- catalase delayed lethal cell injury. Cell killing was greater during aerobic compared with anaerobic chemical hypoxia. Hydroperoxide formation was measured using a dichlorofluorescin assay and was accelerated during aerobic but not anaerobic chemical hypoxia. The results indicate that cell swelling is not the driving force for bleb formation or lethal cell injury. We conclude that “reductive stress” caused by respiratory inhibition favors formation of toxic oxygen species and may contribute to lethal cell injury during intermittent or incomplete oxygen deprivation.

Spectroscopic Study of Photosensitized Oxidation of Polyisoprene

1977 ◽  
Vol 50 (4) ◽  
pp. 704-713 ◽  
Author(s):  
M. A. Golub ◽  
M. L. Rosenberg ◽  
R. V. Gemmer
Keyword(s):  
Zero Order ◽  
Double Bonds ◽  
Photosensitized Oxidation ◽  
The Third ◽  
Type Process ◽  
Zero Order Kinetics ◽  
Hydroperoxide Formation ◽  
Cis And Trans ◽  
In Cis ◽  
Suitable Measure

Abstract The microstructural changes which occur in cis- and trans-1,4-polyisoprenes and in squalene during photosensitized oxidation were investigated with the aid of infrared and proton and carbon-13 NMR spectroscopy. The singlet oxygenation of these isoprenic compounds resulted in allylic hydroperoxides with shifted double bonds, according to the expected “ene”-type process. In contrast to trans-1,4-polyisoprene and squalene, which displayed the three possible double bond shifts, cis-1,4-polyisoprene showed essentially two of the shifts (to di- and trisubstituted double bonds) and very little of the third (to exomethylene groups). A suitable measure of the extent of hydroperoxidation was afforded by the absorbance ratio, A3400/A1440≡A′. Similar correlations of A′ with oxygen uptake were obtained for the three isoprenic compounds, using chlorophyll or methylene blue as sensitizer. The use of rose bengal gave erratic results indicative of some autoxidation accompanying the hydroperoxide formation. The singlet oxygenation followed zero-order kinetics, the relative rates for cis- and trans-1,4-polyisoprenes being approximately 1.0:1.5.

scholarly journals Formaldehyde and peroxide concentrations in Law Dome (Antarctica) firn and ice cores

2000 ◽  
Vol 46 (152) ◽  
pp. 15-19 ◽  
Author(s):  
R. W. Gillett ◽  
T. D. van Ommen ◽  
A.V. Jackson ◽  
G. P. Ayers
Keyword(s):  
Last Glacial Maximum ◽  
Detection Threshold ◽  
Ice Cores ◽  
Glacial Maximum ◽  
Early Holocene ◽  
Modern Times ◽  
Last Glacial ◽  
Depositional Processes ◽  
Methyl Hydroperoxide

AbstractPeroxide speciation and formaldehyde measurements have been made on ice cores retrieved from Law Dome, Antarctica. Measurements were made for ice deposited during four different periods: modern, pre-industrial Holocene, early Holocene and Last Glacial Maximum (LGM). The data show modern peroxide levels >50% above pre-industrial levels (at ∼1.6 μmol L−1) and an absence of methyl hydroperoxide (down to a detection threshold of 0.003 μmol L−1). Formaldehyde levels show a 40% increase from pre-industrial to modern times (rising from ∼0.07 μmol L−1 to ∼0.10 μmol L−1), with a further increase and possible seasonality near the surface which we associate with post-depositional processes. Peroxide levels in LGM ice are low, but formaldehyde concentrations are high (at ∼0.13 μmol L−1) relative to modern levels. Similar high levels of formaldehyde are seen in early Holocene ice (∼6900 years BP).

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