ИСТИНА

LHCII is the primary light-harvesting complex in higher plants photosystem II. These complexes are widely studied both experimentally and theoretically. In particular, the phenomenon called non-photochemical quenching of fluorescence (NPQ) is of great interest since this is one of the photoprotecting mechanisms of higher plants. The process of NPQ appears at high intensity of light. The essence of this phenomenon is that the efficiency of energy transfer from chlorophylls to the dark state of the carotenoids increases. As a result, excitation energy can disappear only through dissipation and quantum yield of fluorescence decreases. Non-empirical all-pigment model was proposed to describe the excited states of the LHCII by means of the excitonic Hamiltonian approach. Linear adsorption and circular dichroism spectra which are in a good agreement with the experimental data were obtained. It was shown that the most effective transition takes place between chlorophyll a and lutein (CLA612 and LUT620 according to 1rwt PDB structure). Six vibrational normal modes for LUT620 were singled out for which locations of PES minima of the ground and excited states differs significantly. The vibrational structure of lutein adsorption spectra was modeled using excitation energies scans along these modes and excitation energy gradients. For lutein geometries displaced along these normal modes rate constants of energy transfer to lutein molecule were calculated. It was shown that such displacements has a great impact on the energy transfer rate and thus it should be taken into account when modeling of NPQ is performed.