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Mao L, Quan Z, Liu ZS, Huang CH, Wang ZH, Tang TS, Li PL, Shao J, Liu YJ, Zhu BZ. Molecular mechanism of the metal-independent production of hydroxyl radicals by thiourea dioxide and H 2O 2. Proc Natl Acad Sci U S A 2024; 121:e2302967120. [PMID: 38547063 PMCID: PMC10998598 DOI: 10.1073/pnas.2302967120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 05/12/2023] [Indexed: 04/08/2024] Open
Abstract
It is well-known that highly reactive hydroxyl radicals (HO•) can be produced by the classic Fenton system and our recently discovered haloquinone/H2O2 system, but rarely from thiol-derivatives. Here, we found, unexpectedly, that HO• can be generated from H2O2 and thiourea dioxide (TUO2), a widely used and environmentally friendly bleaching agent. A carbon-centered radical and sulfite were detected and identified as the transient intermediates, and urea and sulfate as the final products, with the complementary application of electron spin-trapping, oxygen-18 isotope labeling coupled with HPLC/MS analysis. Density functional theory calculations were conducted to further elucidate the detailed pathways for HO• production. Taken together, we proposed that the molecular mechanism for HO• generation by TUO2/H2O2: TUO2 tautomerizes from sulfinic acid into ketone isomer (TUO2-K) through proton transfer, then a nucleophilic addition of H2O2 on the S atom of TUO2-K, forming a S-hydroperoxide intermediate TUO2-OOH, which dissociates homolytically to produce HO•. Our findings represent the first experimental and computational study on an unprecedented new molecular mechanism of HO• production from simple thiol-derived sulfinic acids, which may have broad chemical, environmental, and biomedical significance for future research on the application of the well-known bleaching agent and its analogs.
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Affiliation(s)
- Li Mao
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
| | - Zhuo Quan
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing100875, China
| | - Zhi-Sheng Liu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
| | - Chun-Hua Huang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
| | - Zi-Han Wang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
| | - Tian-Shu Tang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
| | - Pei-Lin Li
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
| | - Jie Shao
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
| | - Ya-Jun Liu
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing100875, China
- Center for Advanced Materials Research, College of Chemistry, Beijing Normal University, Zhuhai519087, China
| | - Ben-Zhan Zhu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China
- College of Resources and Environment, University of the Chinese Academy of Sciences, Beijing100049, China
- State Key Laboratory of Chemical Resource Engineering, Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing100029, China
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