Quenching of porphyrin triplet and singlet oxygen by stable nitroxide radicals: Importance of steric hindrance

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To study the nature of quenching, we used stable nitroxide radicals (most of which contain piperidine or pyrrolidine rings) as quenchers of triplet hematoporphyrin as well as of singlet molecular oxygen. A characteristic feature of quenching triplet porphyrin is a near-diffusion-limited rate constant, whereas the rate constant for quenching singlet oxygen is about three orders of magnitude lower. Accessibility of the nitroxide moiety in radicals was characterized quantitatively based on semi-empirical calculations (at AM1 level), with the use of van der Waals radii of the species. While variation in the rate constant values for quenching triplet porphyrin can be fully explained by the steric hindrance of the neighbouring groups of the nitroxide radical, no such effect can be observed in quenching singlet oxygen.

Original languageEnglish
Pages (from-to)2640-2652
Number of pages13
JournalHelvetica Chimica Acta
Issue number9
Publication statusPublished - Nov 12 2001


ASJC Scopus subject areas

  • Catalysis
  • Biochemistry
  • Drug Discovery
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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