H2O and D2O spin-isomers as a mediator of the electron transfer in the reaction center of purple bacteria

The dynamics of charge separation states has been numerically simulated in order to calculate the polarization (in the third order of the perturbation theory) and its evolution in a pulsed optical field. Time evolution of the rotational states of the ortho-D₂O isomer with a nonzero magnetic momentum and mixed ortho/para-D₂O states have been calculated on the basis of the Liouville equation for the density matrix and the Redfield relaxation model for molecular aggregates. Frequencies similar to the known experimental frequencies of the modulation of the kinetics (electron transfer) of the reaction centers special pair in purple bacteria are selected from the set of calculated rotational-resonance frequencies. This semiquantitative coincidence of frequencies (within the experimental error) confirms the previously stated hypothesis, according to which the ortho-H₂O (D₂O) spin isomer can play a role of mediator during electron transfer in the reaction centers of purple bacteria.