Key Role of Persistent Free Radicals in Hydrogen Peroxide Activation by Biochar: Implications to Organic Contaminant Degradation

Catalases employ a tyrosinate-ligated ferric heme in order to catalyze the dismutation of hydrogen peroxide to O2 and water. In the first half of the catalytic cycle, H2O2 oxidizes Fe(III) to the formally Fe(V) state commonly referred to as Compound I. The second half of the cycle entails oxidation of a second hydrogen peroxide molecule by Compound I to dioxygen. The present study employs density functional (DFT) calculations to examine the nature of this second step of the catalatic reaction. In order to account for the unusual choice of tyrosinate as an axial ligand in catalases, oxidation of hydrogen peroxide by an imidazole-ligated Compound I is also examined, bearing in mind that imidazole-ligated hemoproteins such as myoglobin or horseradish peroxidase tend to display little, if any, catalatic activity. Furthermore, in order to gauge the importance of the cation radical of Compound I in peroxide activation, the performance of Compound II (the one-electron reduced version of Compound I, formally Fe(IV) ), is also examined. It is found that hydrogen peroxide oxidation occurs in a quasi-concerted manner, with two hydrogen-atom transfer reactions, and that the tyrosinate ligand is in no way required at this stage. We propose that the role of the tyrosinate is purely thermodynamic, in avoiding accumulation of the much less peroxide-reactive ferrous form in vivo – all in line with the predominantly thermodynamic role of the cysteinate ligands in enzymes such as cytochromes P450.

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ESR spin-trapping studies of free radicals generated by hydrogen peroxide activation of metmyoglobin

Journal of Agricultural and Food Chemistry ◽

10.1021/jf00097a014 ◽

1990 ◽

Vol 38 (7) ◽

pp. 1494-1497 ◽

Cited By ~ 15

Author(s):

Yuan Xu ◽

Ali Asghar ◽

J. Ian Gray ◽

Albert M. Pearson ◽

Alfred Haug ◽

...

Keyword(s):

Hydrogen Peroxide ◽

Free Radicals ◽

Spin Trapping ◽

Esr Spin Trapping ◽

Peroxide Activation

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The role of copper ions in hydrogen peroxide bleaching: Their origin, removal, and effect on pulp quality

TAPPI Journal ◽

10.32964/tj11.7.37 ◽

2012 ◽

Vol 11 (7) ◽

pp. 37-46 ◽

Cited By ~ 1

Author(s):

PEDRO E.G. LOUREIRO ◽

SANDRINE DUARTE ◽

DMITRY V. EVTUGUIN ◽

M. GRAÇA V.S. CARVALHO

Keyword(s):

Hydrogen Peroxide ◽

Copper Ions ◽

Peroxide Bleaching ◽

Metals Removal ◽

Peroxide Decomposition ◽

Equipment Corrosion ◽

And Performance ◽

And Control ◽

Main Effects

This study puts particular emphasis on the role of copper ions in the performance of hydrogen peroxide bleaching (P-stage). Owing to their variable levels across the bleaching line due to washing filtrates, bleaching reagents, and equipment corrosion, these ions can play a major role in hydrogen peroxide decomposition and be detrimental to polysaccharide integrity. In this study, a Cu-contaminated D0(EOP)D1 prebleached pulp was subjected to an acidic washing (A-stage) or chelation (Q-stage) before the alkaline P-stage. The objective was to understand the isolated and combined role of copper ions in peroxide bleaching performance. By applying an experimental design, it was possible to identify the main effects of the pretreatment variables on the extent of metals removal and performance of the P-stage. The acid treatment was unsuccessful in terms of complete copper removal, magnesium preservation, and control of hydrogen peroxide consumption in the following P-stage. Increasing reaction temperature and time of the acidic A-stage improved the brightness stability of the D0(EOP)D1AP bleached pulp. The optimum conditions for chelation pretreatment to maximize the brightness gains obtained in the subsequent P-stage with the lowest peroxide consumption were 0.4% diethylenetriaminepentaacetic acid (DTPA), 80ºC, and 4.5 pH.

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The Role of free radicals in female unexplained subfertility

10.36295/asro.2020.2311 ◽

2020 ◽

Vol 23 (01) ◽

pp. 01-08

Author(s):

Ban Jaber Edan ◽

Huda Mahmood Shakir ◽

Naseer Jwaad Almukhtar

Keyword(s):

Free Radicals

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