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.

[1]  C. Ragan.  NADH-ubiquinone oxidoreductase. , 1976, Biochimica et biophysica acta.

[2]  G. Tollin.  Model systems for photosynthetic energy conversion , 1976 .

[3]  S. Denmark,et al.  Synthetic Analogs of the Active Sites of Iron-Sulfur Proteins. XI. Synthesis and Properties of Complexes Containing the Fe2S2 Core and the Structures of Bis[o-xylyl-α,α′-dithiolato-μ-sulfido-ferrate(III)] and Bis[p-tolylthiolato-μ-sulfido-ferrate(III)] Dianions , 1975 .

[4]  G. Tollin,et al.  CHLOROPHYLL ONE‐ELECTRON PHOTOCHEMISTRY‐II. PHOTOSENSITIZATION BY CHLOROPHYLL, PHEOPHYTIN AND BACTERIOCHLOROPHYLL OF A ONE‐ELECTRON TRANSFER REACTION BETWEEN ETHANOL AND QUINONE * , 1974 .

[5]  P. Dutton,et al.  Primary events in the photosynthetic reaction centre from Rhodopseudomonas spheroides strain R26: triplet and oxidized states of bacteriochlorophyll and the identification of the primary electron acceptor. , 1973, Biochimica et biophysica acta.

[6]  J. Bolton,et al.  Reversible photooxidation of chlorophyll. Study of the chlorophyll-benzoquinone system utilizing flash photolysis and electron spin resonance spectroscopy , 1972 .

[7]  G. Feher,et al.  Identification of an electron acceptor in reaction centers of Rhodopseudomonas spheroides by EPR spectroscopy. , 1972, Biochimica et biophysica acta.

[8]  A. Bearden,et al.  Primary reactions of photosynthesis: photoreduction of a bound chloroplast ferredoxin at low temperature as detected by EPR spectroscopy. , 1971, Proceedings of the National Academy of Sciences of the United States of America.

[9]  G. Tollin,et al.  ESR STUDIES OF CHLOROPHYLL ONE‐ELECTRON PHOTOCHEMISTRY IN SOLUTION: KINETICS OF REVERSIBLE QUINONE REDUCTION AND GENERAL REDOX MECHANISMS † , 1969, Photochemistry and photobiology.

[10]  B. Diehn,et al.  The oxidation of chlorophyll a in alcohols. , 1968, Biochimica et biophysica acta.

[11]  G. Tollin,et al.  Electron Paramagnetic Resonance Studies of the Role of Solvent in Chlorophyll-Photosensitized One-Electron-Transfer Reactions Involving Quinones and Hydroquinones , 1967 .

[12]  G. Tollin,et al.  Light-induced single electron transfer reactions between chlorophyll a and quinones in solution. I. Some general feature of kinetics and mechanism. , 1962, Biochimica et biophysica acta.