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On the mechanism of visible-light sensitized photosulfoxidation of toluidine blue O.

Jennifer Otero-GonzálezWhitney Querini-SanguillénDaniel Torres-MendozaIkhil YevdayevSharon YunayevKamrun NaharBarney YooAlexander GreerDenis FuentealbaJosé Robinson-Duggon
Published in: Photochemistry and photobiology (2023)
We report on the formation of toluidine blue O (TBO) sulfoxide by a self-sensitized photooxidation of TBO. Here, the photosulfoxidation process was studied by mass spectrometry (MS) and discussed in the context of photodemethylation processes which both contribute to TBO consumption over time. Analysis of solvent effects with D 2 O, H 2 O, and CH 3 CN along with product yields and MS fragmentation patterns provided mechanistic insight into TBO sulfoxide's formation. The formation of TBO sulfoxide is minor and detectable up to 12% after irradiation of 3 h. The photosulfoxidation process is dependent on oxygen wherein instead of a type II (singlet oxygen, 1 O 2 ) reaction, a type I reaction involving TBO to reach the TBO sulfoxide is consistent with the results. Density functional theory results point to the formation of the TBO sulfoxide by the oxidation of TBO via transiently formed peroxyl radical or thiadioxirane intermediates. We discover that the TBO photosulfoxidation arises competitively with TBO photodemethylation with the latter leading to formaldehyde formation.
Keyphrases
  • mass spectrometry
  • density functional theory
  • ms ms
  • visible light
  • nitric oxide
  • liquid chromatography
  • ionic liquid
  • radiation therapy
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  • electron transfer