Femtosecond nuclear oscillations under charge separation in reaction centers of photosynthesis.

Abstract

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.