Molecular mechanism of the metal-independent production of hydroxyl radicals by thiourea dioxide and H2O2.
Proc Natl Acad Sci U S A
; 121(14): e2302967120, 2024 Apr 02.
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| ID: mdl-38547063
ABSTRACT
It is well-known that highly reactive hydroxyl radicals (HOâ¢) 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 HOâ¢. 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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2024
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