SOLVENT EFFECTS ON THE RESONANCE RAMAN-SPECTRA OF BACTERIOCHLOROPHYLLA CATION-RADICAL

Resonance Raman (RR) spectra were measured for the cation radical of b acteriochlorophyll a in acetone, methanol, dichloromethane and mixed s olvents of acetone and methanol. The ring-breathing (C-a-C-m stretchin g) frequency of the radical (abbreviated as nu(r)(+)) was observed at 1601 cm(-1) in acetone (forming a penta-coordinated monomer), at 1587 cm(-1) in methanol (forming a hexa-coordinated monomer) and at 1600 cm (-1) in dichloromethane (forming a penta-coordinated aggregate). The R R spectrum of the radical in dichloromethane is almost identical to th e transient RR spectrum ascribed to 'the aggregated T-1 species of Bch l a' formed in the particular solvent by Nishizawa, Limantara, Nanjou, Nagae, Kakuno and Koyama, indicating that their interpretation needs to be revised.