Formation of electronically excited states during the interaction of <i>p</i>‐benzoquinone with hydrogen peroxide

Brunmark, Anders

doi:10.1002/bio.1170040131

Cited by 16 publications

(9 citation statements)

References 22 publications

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“…Hydrogen peroxide has been shown to react with benzoquinone ( 46 ) and chlorinated benzoquinone ( 47 ). Experiments 6−10 of Table 2 examine the possible reaction of H 2 O 2 with a typical PCB-quinone, 2′-Cl-2,5-Q.…”

Section: Resultsmentioning

confidence: 99%

Semiquinone Radicals from Oxygenated Polychlorinated Biphenyls: Electron Paramagnetic Resonance Studies

Song

Wagner

Lehmler

et al. 2008

Chem. Res. Toxicol.

126

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Polychlorinated biphenyls (PCBs) can be oxygenated to form very reactive hydroquinone and quinone products. A guiding hypothesis in the PCB research community is that some of the detrimental health effects of some PCBs are a consequence of these oxygenated forms undergoing one-electron oxidation or reduction, generating semiquinone radicals (SQ•−). These radicals can enter into a futile redox cycle resulting in the formation of reactive oxygen species, that is, superoxide and hydrogen peroxide. Here, we examine some of the properties and chemistry of these semiquinone free radicals. Using electron paramagnetic resonance (EPR) to detect SQ•− formation, we observed that (i) xanthine oxidase can reduce quinone PCBs to the corresponding SQ•−; (ii) the heme-containing peroxidases (horseradish and lactoperoxidase) can oxidize hydroquinone PCBs to the corresponding SQ•−; (iii) tyrosinase acting on PCB ortho-hydroquinones leads to the formation of SQ•−; (iv) mixtures of PCB quinone and hydroquinone form SQ•− via a comproportionation reaction; (v) SQ•− are formed when hydroquinone-PCBs undergo autoxidation in high pH buffer (≈>pH 8); and, surprisingly, (vi) quinone-PCBs in high pH buffer can also form SQ•−; (vii) these observations along with EPR suggest that hydroxide anion can add to the quinone ring; (viii) H2O2 in basic solution reacts rapidly with PCB-quinones; and (ix) at near-neutral pH SOD can catalyze the oxidization of PCB-hydroquinone to quinone, yielding H2O2. However, using 5,5-dimethylpyrroline-1-oxide (DMPO) as a spin-trapping agent, we did not trap superoxide, indicating that generation of superoxide from SQ•− is not kinetically favorable. These observations demonstrate multiple routes for the formation of SQ•− from PCB-quinones and hydroquinones. Our data also point to futile redox cycling as being one mechanism by which oxygenated PCBs can lead to the formation of reactive oxygen species, but this is most efficient in the presence of SOD.

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Section: Resultsmentioning

confidence: 99%

Semiquinone Radicals from Oxygenated Polychlorinated Biphenyls: Electron Paramagnetic Resonance Studies

Song

Wagner

Lehmler

et al. 2008

Chem. Res. Toxicol.

126

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“…Hydrogen peroxide is a nucleophile and has been shown to react with benzoquinone [24,49,84,85] as well as chlorinated benzoquinone [86]. Reductive addition can occur at higher pH environments because peroxide anion (HOO − ) is a powerful nucleophile, much more reactive than hydroxide anion (p K a1 for H 2 O 2 is 11.7 [87]).…”

Section: Thiols/gsh Addition Of Nucleophiles To Quinone Compoundsmentioning

confidence: 99%

Thermodynamic and kinetic considerations for the reaction of semiquinone radicals to form superoxide and hydrogen peroxide

Song

Buettner

2010

Free Radical Biology and Medicine

304

291

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The quinone/semiquinone/hydroquinone triad (Q/SQ •− /H 2 Q) represents a class of compounds that has great importance in a wide range of biological processes. The half-cell reduction potentials of these redox couples in aqueous solutions at neutral pH, E°′, provide a window to understanding the thermodynamic and kinetic characteristics of this triad and their associated chemistry and biochemistry in vivo. Substituents on the quinone ring can significantly influence the electron density "on the ring" and thus modify E°′ dramatically. E°′ of the quinone governs the reaction of semiquinone with dioxygen to form superoxide. At near-neutral pH the pK a 's of the hydroquinone are outstanding indicators of the electron density in the aromatic ring of the members of these triads (electrophilicity) and thus are excellent tools to predict half-cell reduction potentials for both the one-electron and two-electron couples, which in turn allow estimates of rate constants for the reactions of these triads. For example, the higher the pK a 's of H 2 Q, the lower the reduction potentials and the higher the rate constants for the reaction of SQ •− with dioxygen to form superoxide. However, hydroquinone autoxidation is controlled by the concentration of di-ionized hydroquinone; thus, the lower the pK a 's the less stable H 2 Q to autoxidation. Catalysts, e.g., metals and quinone, can accelerate oxidation processes; by removing superoxide and increasing the rate of formation of quinone, superoxide dismutase can accelerate oxidation of hydroquinones and thereby increase the flux of hydrogen peroxide. The principal reactions of quinones are with nucleophiles via Michael addition, for example, with thiols and amines. The rate constants for these addition reactions are also related to E°′. Thus, pK a 's of a hydroquinone and E°′ are central to the chemistry of these triads.

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“…An ultraweak CL (Φ CL ≈ 10 −8 , λ = 485-530 nm) was observed by Brunmark and Cadenas (16,17) for pbenzoquinone oxidized by H 2 O 2 in slightly alkaline aqueous solution, which was described as the reaction between hydroxy-1,4-benzosemiquinone and OH· radical. The OH· radical in our system may originate from a Fenton-like reaction between H 2 O 2 and Co(II) present in the reaction mixture, or from an 'organic Fenton reaction' (18,19), which is the reaction between H 2 O 2 and 1,2-benzosemiquinone or other semiquinone intermediates.…”

Section: Ms Spectramentioning

confidence: 78%

Oxidation and chemiluminescence of catechol by hydrogen peroxide in the presence of Co(II) ions and CTAB micelles

Lasovský¹,

Hrbáč²,

Sichertova³

et al. 2007

Luminescence

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The oxidation of catechol in neutral and slightly alkaline aqueous solutions (pH 7-9.6) by excess hydrogen peroxide (0.002-0.09 mol/L) in the presence of Co(II) (2.10(-7)-2.10(-5) mol/L) is accompanied by abrupt formation of red purple colouration, which is subsequently decolourized within 1 h. The electron spectra of the reaction mixture are characterized by a broad band covering the whole visible range (400-700 nm), with maximum at 485 nm. The reaction is initiated by catechol oxidation to its semiquinone radical and further to 1,2-benzoquinone. By nucleophilic addition of hydrogen peroxide into the p-position of benzoquinone C=O groups, hydroperoxide intermediates are formed, which decompose to hydroxylated 1,4-benzoquinones. It was confirmed by MS spectroscopy that monohydroxy-, dihydroxy- and tetrahydroxy-1,4-benzoquinone are formed as intermediate products. As final products of catechol decomposition, muconic acid, its hydroxy- and dihydroxy-derivatives and crotonic acid were identified. In the micellar environment of hexadecyltrimethylammonium bromide the decomposition rate of catechol is three times faster, due to micellar catalysis, and is accompanied by chemiluminescence (CL) emission, with maxima at 500 and 640 nm and a quantum yield of 1 x 10(-4). The CL of catechol can be further sensitized by a factor of 8 (maximum) with the aid of intramicellar energy transfer to fluorescein.

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Formation of electronically excited states during the interaction of p‐benzoquinone with hydrogen peroxide

Cited by 16 publications

References 22 publications

Semiquinone Radicals from Oxygenated Polychlorinated Biphenyls: Electron Paramagnetic Resonance Studies

Semiquinone Radicals from Oxygenated Polychlorinated Biphenyls: Electron Paramagnetic Resonance Studies

Thermodynamic and kinetic considerations for the reaction of semiquinone radicals to form superoxide and hydrogen peroxide

Oxidation and chemiluminescence of catechol by hydrogen peroxide in the presence of Co(II) ions and CTAB micelles

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