Photo- and chemically-produced phylloquinone biradicals: EPR and ENDOR study

Tatyana A. Konovalova, Lowell D. Kispert, Kevin Redding

Research output: Contribution to journalArticle

Abstract

Phylloquinone biradical triplet species were generated by 300 nm irradiation of frozen (77 K) solutions or by treatment with AlCl3. The shape of the (Δms=1) electron paramagnetic resonance (EPR) signal of the triplet is axially symmetric (E=0) with D=19±0.5 mT for photo-induced and D=11.2±0.5 mT for chemically induced radicals. A half-field signal (Δms=2) in the region of g≈4 was detected in both cases, confirming its assignment as a triplet. An additional line arising at the center of the (Δms=1) signal with g=2.0048±0.0002 was assigned to the phylloquinone radical anion (PhQ•-). Electron nuclear double resonance (ENDOR) measurements of the triplet revealed the sign of the D parameter. For photo-generated radicals it appeared to be negative, which is the characteristic of radical dimers with well-separated partners (biradicals). Spin-spin distances of 5.3 and 6.3 Å, respectively, were estimated from the D parameter of photo-generated and chemically prepared phylloquinone biradicals.

Original languageEnglish
Pages (from-to)255-260
Number of pages6
JournalJournal of Photochemistry and Photobiology A: Chemistry
Volume161
Issue number2-3
DOIs
Publication statusPublished - Jan 30 2004

Keywords

  • Biradicals
  • Electron nuclear double resonance
  • Electron paramagnetic resonance
  • Electron transfer
  • Phylloquinone

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Physics and Astronomy(all)

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