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Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis.

ABSTRACT: Singlet oxygen (¹O₂) plays a pivotal role in numerous catalytic oxidation processes utilized in water purification and chemical synthesis. The spin-trapping method based on electron paramagnetic resonance (EPR) analysis is commonly employed for ¹O₂ detection. However, it is often limited to time-independent acquisition. Recent studies have raised questions about the reliability of the ¹O₂ trapper, 2,2,6,6-tetramethylpiperidine (TEMP), in various systems. In this study, we introduce a comprehensive, kinetic examination to monitor the spin-trapping process in EPR analysis. The EPR intensity of the trapping product was used as a quantitative measurement to evaluate the concentration of ¹O₂ in aqueous systems. This in situ kinetic study was successfully applied to a classical photocatalytic system with exceptional accuracy. Furthermore, we demonstrated the feasibility of our approach in more intricate ¹O₂-driven catalytic oxidation processes for water decontamination and elucidated the molecular mechanism of direct TEMP oxidation. This method can avoid the false-positive results associated with the conventional 2D ¹O₂ detection techniques, and provide insights into the reaction mechanisms in ¹O₂-dominated catalytic oxidation processes. This work underscores the necessity of kinetic studies for spin-trapping EPR analysis, presenting an avenue for a comprehensive exploration of the mechanisms governing catalytic oxidation processes.

SUBMITTER: Wu JH

PROVIDER: S-EPMC10372693 | biostudies-literature | 2023 Jul

REPOSITORIES: biostudies-literature

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Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis.

Wu Jing-Hang JH Chen Fei F Chen Fei F Yang Tian-Hao TH Yu Han-Qing HQ

Proceedings of the National Academy of Sciences of the United States of America 20230717 30

Singlet oxygen (1O2) plays a pivotal role in numerous catalytic oxidation processes utilized in water purification and chemical synthesis. The spin-trapping method based on electron paramagnetic resonance (EPR) analysis is commonly employed for 1O2 detection. However, it is often limited to time-independent acquisition. Recent studies have raised questions about the reliability of the 1O2 trapper, 2,2,6,6-tetramethylpiperidine (TE ...[more]

PMID: 37459516

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Project description:Recently, we showed that peroxynitrite (ONOO(-)) reacts directly and rapidly with aromatic and aliphatic boronic acids (k ≈ 10(6) M(-1)s(-1)). Product analyses and substrate consumption data indicated that ONOO(-) reacts stoichiometrically with boronates, yielding the corresponding phenols as the major product (∼85-90%), and the remaining products (10-15%) were proposed to originate from free radical intermediates (phenyl and phenoxyl radicals). Here, we investigated in detail the minor, free radical pathway of boronate reaction with ONOO(-). The electron paramagnetic resonance (EPR) spin-trapping technique was used to characterize the free radical intermediates formed from the reaction between boronates and ONOO(-). Using 2-methyl-2-nitrosopropane (MNP) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) spin traps, phenyl radicals were trapped and detected. Although phenoxyl radicals were not detected, the positive effects of molecular oxygen, and inhibitory effects of hydrogen atom donors (acetonitrile, and 2-propanol) and general radical scavengers (GSH, NADH, ascorbic acid, and tyrosine) on the formation of phenoxyl radical-derived nitrated product, suggest that the phenoxyl radical was formed as the secondary species. We propose that the initial step of the reaction involves the addition of ONOO(-) to the boron atom in boronates. The anionic intermediate undergoes both heterolytic (major pathway) and homolytic (minor pathway) cleavage of the peroxy (O-O) bond to form phenol and nitrite as a major product (via a nonradical mechanism), or a radical pair PhB(OH)(2)O(•-)···(•)NO(2) as a minor product. It is conceivable that phenyl radicals are formed by the fragmentation of the PhB(OH)(2)O(•-) radical anion. According to the DFT quantum mechanical calculations, the energy barrier for the dissociation of PhB(OH)(2)O(•-) radical anion to form phenyl radical is only a few kcal/mol, suggesting rapid and spontaneous fragmentation of the PhB(OH)(2)O(•-) radical anion in aqueous media. Biological implications of the minor free radical pathway are discussed in the context of ONOO(-) detection, using the boronate probes.

Dataset Information

Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis.

Publications

Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis.

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