Photogenerated radical intermediates of vitamin K₁: a time-resolved resonance Raman study

Abstract

Quinones play a vital role in the process of electron transfer in bacterial photosynthetic reaction centers. It is of interest to investigate the photochemical reactions involving quinones with a view to elucidating the structure-function relationships in the biological processes. Resonance Raman spectra of radical anions and the time-resolved resonance Raman spectra of vitamin K₁ (model compound for Q_A in Rhodopseudomonas viridis, a bacterial photosynthetic reception center) are presented. The photochemical intermediates of vitamin K₁, viz. radical anion, ketyl radical and o-quinone methide have been identified. The vibrational assignments of all these intermediates are made on the basis of comparison with our earlier TR3 studies on radical anions of naphthoquinone and menaquinone.