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Nuclear wavepacket motion producing a reversible charge separation in bacterial reaction centers.
A G Yakovlev1, A Y Shkuropatov, V A Shuvalov
1Laboratory of Photobiophysics, Belozersky Institute of Chemical and Physical Biology of Moscow State University, Russia.
FEBS Letters
|February 22, 2000
Summary
In modified bacterial reaction centers, ultrafast oscillations correlate with reversible electron transfer, forming a new absorption band. This suggests wavepacket motion influences charge separation dynamics.
Area of Science:
- Photosynthesis Research
- Biophysical Chemistry
- Ultrafast Spectroscopy
Background:
- Bacterial reaction centers (RCs) are crucial for light energy conversion.
- Excitation of RCs induces nuclear wavepacket motions and ultrafast oscillations.
- Previous studies observed these oscillations in primary donor excited state (P*) and acceptor (B(A)) bands.
Purpose of the Study:
- To investigate the role of pheophytin modification in bacterial RCs.
- To understand the relationship between nuclear wavepacket motion and electron transfer dynamics.
- To characterize the spectral changes associated with ultrafast events.
Main Methods:
- Femtosecond (fs) laser spectroscopy (870 nm excitation).
- Analysis of stimulated emission from P* and Qy absorption band of B(A).
- Spectroscopic monitoring of absorption changes around 1020 nm.
Main Results:
- Pheophytin-modified RCs exhibit ~130 cm(-1) oscillations in P* emission and B(A) absorption.
- These oscillations are accompanied by reversible formation of a 1020 nm absorption band.
- The 1020 nm band is characteristic of the bacteriochlorophyll monomer radical anion (B(A)-).
Conclusions:
- A reversible electron transfer between P* and B(A) occurs in modified RCs.
- This electron transfer is driven by wavepacket motion near intersecting potential energy surfaces.
- Franck-Condon factor maximization facilitates this ultrafast charge separation process.