Abstract
Illumination at low temperatures of ethanol solutions of p-benzoquinone, alone or in the presence of chlorophyll or pheophytin, leads to the reversible formation of radical complexes. Based on g-value determinations and deuterium-substitution effects, the radicals are identified as a semiquinone and an ethoxy radical. In the porphyrin-sensitized system, ternary complexes are produced. Chlorophyll also forms a cation radical upon illumination, whereas pheophytin does not. The generation of this cation radical is independent of the presence of quinone, and proceeds via the chlorophyll singlet state, as opposed to quinone and ethoxy radical production, which involve triplet states. The significance of these reactions to photosynthetic energy conversion is discussed.
Keywords: photochemistry, pheophytin, semiquinone, ethoxy radical, ESR
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Borg D. C., Fajer J., Felton R. H., Dolphin D. The pi-Cation Radical of Chlorophyll a. Proc Natl Acad Sci U S A. 1970 Oct;67(2):813–820. doi: 10.1073/pnas.67.2.813. [DOI] [PMC free article] [PubMed] [Google Scholar]
- CHARNEY E., BECKER E. D. MOLECULAR VIBRATIONS OF QUINONES. II. INFRARED SPECTRA (SOLUTION AND VAPOR) OF P-BENZOQUINONE AND P-BENZOQUINONE-D4. J Chem Phys. 1965 Feb 1;42:910–913. doi: 10.1063/1.1696081. [DOI] [PubMed] [Google Scholar]
- KOK B. Partial purification and determination of oxidation reduction potential of the photosynthetic chlorophyll complex absorbing at 700 millimicrons. Biochim Biophys Acta. 1961 Apr 15;48:527–533. doi: 10.1016/0006-3002(61)90050-6. [DOI] [PubMed] [Google Scholar]
- Mukherjee D. C., Cho D. H., Tollin G. ESR studies of chlorophyll one-electron photochemistry in solution: kinetics of reversible quinone reduction and general redox mechanisms. Photochem Photobiol. 1969 Mar;9(3):273–289. doi: 10.1111/j.1751-1097.1969.tb07291.x. [DOI] [PubMed] [Google Scholar]
- Vernon L. P., Ke B., Shaw E. R. Relationship of P700, electron spin resonance signal, and photochemical activity of a small chloroplast particle obtained by the action of Triton X-100. Biochemistry. 1967 Jul;6(7):2210–2220. doi: 10.1021/bi00859a044. [DOI] [PubMed] [Google Scholar]