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The π-Cation Radical of Chlorophyll a*

By Donald C. Borg, Jack Fajer, Ronald H. Felton and David Dolphin


Chlorophyll a undergoes reversible one-electron oxidation in dichloromethane and butyronitrile. Removal of the electron by controlled potential electrolysis or by stoichiometric charge transfer to a known cation radical yields a radical (epr line width = 9 gauss, g = 2.0025 ± 0.0001) whose optical spectrum is bleached relative to that of chlorophyll. Upon electrophoresis this bleached species behaves as a cation. By comparison with the known properties of π-cation radicals of porphyrins and chlorins, the chlorophyll radical is also identified as a π-cation. Further correlation of optical and epr properties with published studies on photosynthesis leads to the conclusion that oxidized P700, the first photochemical product of photosystem I in green plants, contains a π-cation radical of the chlorin component of chlorophyll a. This radical is the likely source of the rapidly-decaying, narrow epr signal of photosynthesis

Topics: Biological Sciences: Biochemistry
Year: 1970
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Provided by: PubMed Central
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