Resonance Raman and infrared spectral studies on radical anions of model photosynthetic reaction center quinones (naphthoquinone derivatives).

Quinones play a vital role in the processes of electron transfer in bacterial photosynthetic reaction centers. It is of interest to investigate photochemical reactions involving quinones with a view to elucidate structure-function relationships in biological processes. Resonance Raman and FTIR spectra of electrochemically generated radical anions of 2-methyl-1,4-naphthoquinone, and 2-methyl-3-phytyl-1,4-naphthoquinone, also known as Vitamin K3 and Vitamin K1, respectively, (model compound for QA in Rhodopseudomonas viridis, a bacterial photosynthetic reaction center) have been reported. The same study has also been extended to 1,4-naphthoquinone for comparison. The vibrational assignments were carried out on the basis of comparison with our earlier time resolved resonance Raman studies on photochemically generated radical anions of 1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone (Balakrishnan et al., J. Phys. Chem., 100, (1996), 16472-16478). These in vitro results have been compared with the reported vibrational spectral data under in vivo conditions.