EFFECT OF CHLORIDE ON CHLOROPHYLL PHOTOCHEMISTRY IN SOLUTION: ENHANCEMENT OF CATION RADICAL AND SEMIQUINONE YIELDS

Abstract—Illumination with red light at low temperatures of a degassed ethanol solution of chlorophyll and ferric chloride reversibly produces an EPR signal due to the chlorophyll cation radical (Chl+). The magnitude of this signal is about ten times larger than is obtained with chlorophyll alone. When benzoquinone is also present, an EPR signal due to Chl+ and the neutral semiquinone radical (QH.) is photoproduced. The semiquinone signal is about five times larger than in the absence of ferric chloride. Both of these systems show first order radical decay when the light is turned off, suggesting that radical complexes are being formed. These results indicate that iron is capable of serving as an electron transfer bridge between chlorophyll and quinone.