Photooxidation of alkaloids: Considerable quantum yield enhancement by rose bengal-sensitized singlet molecular oxygen generation

Helmut Görner, Zsombor Miskolczy, Mónika Megyesi, László Biczók

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Abstract

The photooxidation of sanguinarine, coralyne and berberine was studied in oxygenated alkaline methanol solutions. Rose bengal as photosensitizer significantly accelerates the process, indicating the importance of singlet molecular oxygen in the reaction mechanism. The quantum yield of sensitized oxidation was found to increase significantly with pH and reaches 0.4 for berberine at pH 13.8. The direct oxidation of alkaloids is less efficient, the quantum yield does not exceed 0.01 even in oxygen-saturated solutions. The photoinduced electron ejection does not play a role in the oxidation. The uncharged pseudobase forms, which are present in alkaline medium, are oxidized much more easily than the alkaloid cations. The quantum yield of rose bengal-sensitized photooxidation of berberine and coralyne alkaloids increases significantly with pH. Singlet molecular oxygen plays an important role in the reaction mechanism.

Original languageEnglish
Pages (from-to)1315-1320
Number of pages6
JournalPhotochemistry and photobiology
Volume87
Issue number6
DOIs
Publication statusPublished - Nov 1 2011

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ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry

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