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Femtosecond Nuclear Oscillations under Charge Separation in Reaction Centers of Photosynthesis

A. G. Yakovlev1, A. Ya. Shkuropatov2, and V. A. Shuvalov1,2*

1Department of Photobiophysics, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia; fax: (095) 939-3181; E-mail: yakov@genebee.msu.su

2Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region 142292, Russia; fax: (277) 90532; E-mail: shuvalov@issp.serpukhov.su

* To whom correspondence should be addressed.

Received April 10, 2002; Revision received May 29, 2002
Results are presented of a study of primary processes of formation of the charge separated states P+BA- and P+HA- (where P is the primary electron donor, BA and HA the primary and secondary electron acceptors) in native and pheophytin-modified reaction centers (RCs) of Rhodobacter sphaeroides R-26 by methods of femtosecond spectroscopy of absorption changes at low temperature. Coherent oscillations were studied in the kinetics at 935 nm (P* stimulated emission band), at 1020 nm (BA- absorption band), and at 760 nm (HA absorption band). It was found that when the wavepacket created under femtosecond light excitation approaches the intersection between P* and P+BA- potential surfaces at 120- and 380-fsec delays, the formation of two electron states emitting light at 935 nm (P*) and absorbing light at 1020 nm (P+BA-) takes place. At the later time the wavepacket motion has a frequency of 32 cm-1 and is accompanied by electron transfer from P* to BA in pheophytin-modified and native RCs and further to HA in native RCs. It was shown that electron transfer processes monitored by the 1020-nm absorption band development as well as by bleaching of 760-nm absorption band have the enhanced 32 cm-1 mode in the Fourier transform spectra.
KEY WORDS: photosynthesis, reaction center, electron transfer, wavepacket, femtosecond spectroscopy