Femtosecond Nuclear Oscillations under Charge Separation in Reaction Centers of Photosynthesis

A. G. Yakovlev¹, A. Ya. Shkuropatov², and V. A. Shuvalov^1,2*

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

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Results are presented of a study of primary processes of formation of the charge separated states P⁺B_A^- and P⁺H_A^- (where P is the primary electron donor, B_A and H_A 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 (B_A^- absorption band), and at 760 nm (H_A absorption band). It was found that when the wavepacket created under femtosecond light excitation approaches the intersection between P* and P⁺B_A^- 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⁺B_A^-) 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 B_A in pheophytin-modified and native RCs and further to H_A 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.

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KEY WORDS: photosynthesis, reaction center, electron transfer, wavepacket, femtosecond spectroscopy

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