Mechanism of energy transfer from carotenoids to bacteriochlorophyll: Light-harvesting by carotenoids having different extents of π-electron conjugation incorporated into the B850 antenna complex from the carotenoidless bacterium Rhodobacter sphaeroides R-26.1

Ruel Z B Desamero, Veeradej Chynwat, Ineke Van Der Hoef, Frans Jos Jansen, Johan Lugtenburg, David Gosztola, Michael R Wasielewski, Agnes Cua, David F. Bocian, Harry A. Frank

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Spheroidene and a series of spheroidene analogues with extents of π-electron conjugation ranging from 7 to 13 carbon-carbon double bonds were incorporated into the B850 light-harvesting complex of Rhodobacter sphaeroides R-26.1. The structures and spectroscopic properties of the carotenoids and the dynamics of energy transfer from the carotenoid to bacteriochlorophyll (BChl) in the B850 complex were studied by using steady-state absorption, fluorescence, fluorescence excitation, resonance Raman, and time-resolved absorption spectroscopy. The spheroidene analogues used in this study were 5′,6′-dihydro-7′,8′-didehydrospheroidene, 7′,8′-didehydrospheroidene, and 1′,2′-dihydro-3′,4′,7′,8′- tetradehydrospheroidene. These data, taken together with results from 3,4,7,8-tetrahydrospheroidene, 3,4,5,6-tetrahydrospheroidene, 3,4-dihydrospheroidene, and spheroidene already published (Frank, H. A.; Farhoosh, R.; Aldema, M. L.; DeCoster, B.; Christensen, R. L.; Gebhard, R.; Lugtenburg, J. Photochem. Photobiol. 1993, 57, 49. Farhoosh, R.; Chynwat, V.; Gebhard, R.; Lugtenburg, J.; Frank, H. A. Photosynth. Res. 1994, 42, 157), provide a systematic series of molecules for understanding the molecular features that determine the mechanism of energy transfer from carotenoids to BChl in photosynthetic bacterial light-harvesting complexes. The data support the hypothesis that only carotenoids having 10 or less carbon-carbon double bonds transfer energy via their 21Ag (S1) states to BChl to any significant degree. Energy transfer via the 11Bu (S2) state of the carotenoid becomes more important than the S1 route as the number of conjugated carbon-carbon double bonds increases. The results also suggest that the S2 state associated with the Qx transition of the B850 BChl is the most likely acceptor state for energy transfer originating from both the 21Ag (S1) and 11Bu (S2) states of all carotenoids.

Original languageEnglish
Pages (from-to)8151-8162
Number of pages12
JournalJournal of Physical Chemistry B
Issue number42
Publication statusPublished - Oct 15 1998


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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