Temperature-dependent energy gap of the primary charge separation in photosystem I: Study of delayed fluorescence at 77-268 K

Yutaka Shibata, Shinpei Akai, Takashi Kasahara, Isamu Ikegami, Shigeru Itoh

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3 Citations (Scopus)


The dynamics of fluorescence decay and charge recombination were studied in the ether-extracted photosystem I reaction center isolated from spinach with picosecond resolution over a wide time range up to 100 ns. At all temperatures from 268 to 77 K, a slow fluorescence decay component with a 30-40 ns lifetime was detected. This component was interpreted as a delayed fluorescence emitted from the singlet excited state of the primary donor P700*, which is repopulated through charge recombination that was increased by the lack of secondary acceptor phylloquinone in the sample. Analysis of the fluorescence kinetics allowed estimation of the standard free-energy difference -ΔG between P700* and the primary radical pair (P700+A o-) state over a wide temperature range. The values of -ΔG were estimated to be 160/36 meV at 268/77 K, indicating its high sensitivity to temperature. A temperature-dependent -ΔG value was also estimated in the delayed fluorescence of the isolated photosystem I in which the secondary acceptor quinone was partially prereduced by preillumination in the presence of dithionite. The results revealed that the temperature-dependent -ΔG is a universal phenomenon common with the purple bacterial reaction centers, photosystem II and photosystem I reaction centers.

Original languageEnglish
Pages (from-to)6695-6702
Number of pages8
JournalJournal of Physical Chemistry B
Issue number21
Publication statusPublished - 2008 May 29
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry


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