INTERPRETATION OF CHLOROPHYLL ELECTRON SPIN RESONANCE SPECTRA

Dry, oxygen-free chlorophyll systems possess no intrinsic dark esr signal, nor can a photo-esr signal be induced in such systems by irradiation with red light. Chlorophyll-water micelles, which form in aliphatic hydrocarbon solvents, yield a narrow, reversible, photo-induced esr signal on irradiation with red light. Oxygen in either dry or water-containing systems causes extensive photodecomposition. In benzene solution, a solvent in which micelle formation is not favored, photooxidation is much more rapid than in dodecane. The line shape and isotope effects on the narrow, reversible, photo-induced esr signal are consistent with a delocalization of an electron into a large micelle. A new model for the primary light conversion act in photosynthesis is suggested in which light absorption by a chlorophyll-water micelle results in the formation of chlorophyll radical cation and anions (Chl- and Chl+), which furnish the reducing and oxidizing power for the reactions of photosynthesis.