Resonance Raman spectroelectrochemistry of bacteriochlorophyll and bacteriochlorophyll cation radical

The newly developed technique of resonance Raman spectroelectrochemistry (RRSE) is applied to the study of the radical ion species involved in the primary photochemistry of photosynthesis. By means of controlled potential coulometry combined with resonance Raman spectroscopic detection, the vibrational spectrum of the bacteriochlorophyll a cation radical (BChl⁺·) has been obtained and compared with the corresponding spectrum of the parent molecule. The cation radical spectrum is significantly different from the neutral spectrum both in band frequencies and intensities. These results suggest that RR vibrational spectra may provide a new means of identifying and kinetically monitoring radical ion formation both in photosynthetic model systems and in vivo.