The NoH value in EPR spin trapping: a n ew parameter for the identification of 5,5-dimethyl-1-pyrroline-N-oxide spin adducts

Li, Anson S. W.; Chignell, Colin F.

doi:10.1016/0165-022x(91)90084-a

Cited by 31 publications

(14 citation statements)

References 4 publications

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“…There are two classes of EPR peaks in Fig. 6a: one is due to DMPO-• OH, and the other is due to DMPO-• H. This is in agreement with the previous studies [27][28][29]. The systems of three different catalysts produce similar amounts of • OH (Fig.…”

Section: Epr Spectral Assayssupporting

confidence: 90%

Photodegradation of dye pollutants on one-dimensional TiO2 nanoparticles under UV and visible irradiation

Li¹,

Ma²,

Chen³

et al. 2007

Journal of Molecular Catalysis A: Chemical

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Section: Epr Spectral Assayssupporting

confidence: 90%

Photodegradation of dye pollutants on one-dimensional TiO2 nanoparticles under UV and visible irradiation

Li¹,

Ma²,

Chen³

et al. 2007

Journal of Molecular Catalysis A: Chemical

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“…Computer simulation of this EPR spectrum indicates that the spin adduct corresponds to a carbon-centered radical with hyperfine splittings a N = 16.1 G, α H = 23.6 G, NoH = 0.68, where NoH is the ratio of the nitrogen splitting constant to the hydrogen splitting constant (NoH = a N /a H ). 47 The similarity of this adduct and the previously reported 2-chlorophenyl-DMPO adduct (a N = 15.8 G, α H = 23.8 G, NoH = 0.65) 48 suggested that it was formed by reaction of the spin trap with an aryl radical generated during the photochemical reaction of 2,6-DBP. EPR spin trapping experiments with DMPO demonstrated that high levels of keto radical were produced during the irradiation of 2,6-DBP (Figure 5).…”

Section: Resultssupporting

confidence: 74%

Monohydroxylated Polybrominated Diphenyl Ethers (OH-PBDEs) and Dihydroxylated Polybrominated Biphenyls (Di-OH-PBBs): Novel Photoproducts of 2,6-Dibromophenol

Zhao

Jiang

Wang

et al. 2015

Environ. Sci. Technol.

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Hydroxylated polybromodiphenyl ethers (OH-PBDEs) are emerging aquatic pollutants, but their origins in the environment are not fully understood. There is evidence that OH-PBDEs are formed from bromophenols, but the underlying transformation processes remain unknown. Here we investigate if the photoformation of OH-PBDEs from 2,6-dibromophenol in aqueous solution involves 2,6-bromophenoxyl radicals. After UV irradiation of an aqueous 2,6-dibromophenol solution, HPLC-LTQ-Orbitrap MS and GC/MS analysis revealed the formation of a OH-PBDE and a dihydroxylated polybrominated biphenyl (di-OH-PBB). Both dimeric photoproducts were tentatively identified as 4′-OH-BDE73 and 4,4′-di-OH-PBB80. In addition, three debromination products (4-OH-BDE34, 4′-OH-BDE27, and 4,4′-di-OH-PBBs) were observed. Electron paramagnetic resonance spectroscopy revealed the presence of a 2,6-dibromophenoxyl radical with a six-line spectrum (aH (2 meta) = 3.45 G, aH (1 para) = 1.04 G, g = 2.0046) during irradiation of a 2,6-dibromophenol solution in water. The 2,6-dibromophenoxyl radical had a relatively long half-life (122 ± 5 μs) according to laser flash photolysis experiments. The para-para C-C and O-para-C couplings of these 2,6-dibromophenoxyl radicals are consistent with the observed formation of both dimeric OH-PBDE and di-OH-PBB photoproducts. These findings show that bromophenoxyl radical-mediated phototransformation of bromophenols is a source of OH-PBDEs and di-OH-PBBs in aqueous environments that requires further attention.

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“…• (9). It is reasonable to suggest that the keto form of DMPO/CBQϭO nitroxide adduct may be tautomerized to its corresponding more stable enol form DMPO/CBQ-OH (Scheme 3).…”

Section: Formation Of Cbq(oh)-o-t-bu Wasmentioning

confidence: 99%

Metal-independent decomposition of hydroperoxides by halogenated quinones: Detection and identification of a quinone ketoxy radical

Zhu

Shan

Huang

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

103

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We have shown recently that halogenated quinones could enhance the decomposition of hydroperoxides and formation of alkoxyl/ hydroxyl radicals through a metal-independent mechanism. However, neither the proposed quinone enoxy radical intermediate, nor the major reaction products were unambiguously identified. In the present study, one of the major reaction products between 2,5-dichloro-1,4-benzoquinone (DCBQ) and t-butylhydroperoxide (t-BuOOH) was isolated and purified by semipreparative HPLC, and identified as 2-hydroxy-3-t-butoxy-5-chloro-1,4-benzoquinone [CBQ(OH)-O-t-Bu], which is the rearranged isomer of the postulated quinone-peroxide reaction intermediate. The formation of CBQ(OH)-O-t-Bu was found to be inhibited by the spin trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and concurrently, a new DMPO adduct with 1-chlorine isotope peak clusters at m/z 268 was observed. Further electron spin resonance (ESR) spintrapping, 1 H-NMR and HPLC/Fourier transform ion cyclotron resonance (FTICR) mass spectrometric studies with oxygen-17-labeled and unlabeled hydrogen peroxide strongly suggest that the radical trapped by DMPO is a carbon-centered quinone ketoxy radical, which is the spin isomer of the proposed oxygen-centered quinone enoxy radical. Analogous results were observed when DCBQ was substituted by other halogenated quinones. This study represents the first detection and identification of an unusual carbon-centered quinone ketoxy radical, which provides direct experimental evidence to further support and expand our previously proposed mechanism for metal-independent decomposition of hydroperoxides by halogenated quinones.ESR spin-trapping ͉ spin isomerization ͉ carbon-centered quinone ketoxy radical ͉ oxygen-centered quinone enoxy radical ͉ keto-enol tautomerization W e have shown recently that alkoxyl radicals can be produced by organic hydroperoxides and halogenated quinones independent of transition metal ions, and a reaction mechanism was proposed (1): A nucleophilic reaction may take place between 2,5-dichloro-1,4-benzoquinone (DCBQ) and t-butylhydroperoxide (t-BuOOH), forming a quinone-peroxide reaction intermediate 2-chloro-5-t-butylperoxyl-1,4-benzoquinone (CBQ-OO-t-Bu), which can decompose homolytically to produce t-butoxyl radical (t-BuO • ) and 2-chloro-5-hydroxy-1,4-benzoquinone enoxy radical (CBQ-O • ). CBQ-O• then disproportionate to form the ionic form of 2-chloro-5-hydroxy-1,4-benzoquinone (CBQ-OH) (see scheme 1 in ref. 1). We also found that hydroxyl radicals could be produced metal-independently by hydrogen peroxide and halogenated quinones (2-4). However, neither the major reaction products, nor the proposed quinone-peroxide reaction intermediate CBQ-OO-t-Bu and quinone enoxy radical CBQ-O • were unambiguously identified in the previous studies.Therefore, in the present study, we addressed the following questions: (i) was it possible to isolate and purify the proposed quinone-peroxide reaction intermediate; (ii) could CBQ-OH or any other major reaction products be isolated, purifi...

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The NoH value in EPR spin trapping: a n ew parameter for the identification of 5,5-dimethyl-1-pyrroline-N-oxide spin adducts

Cited by 31 publications

References 4 publications

Photodegradation of dye pollutants on one-dimensional TiO2 nanoparticles under UV and visible irradiation

Photodegradation of dye pollutants on one-dimensional TiO2 nanoparticles under UV and visible irradiation

Monohydroxylated Polybrominated Diphenyl Ethers (OH-PBDEs) and Dihydroxylated Polybrominated Biphenyls (Di-OH-PBBs): Novel Photoproducts of 2,6-Dibromophenol

Metal-independent decomposition of hydroperoxides by halogenated quinones: Detection and identification of a quinone ketoxy radical

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