Modeling of Optical Spectra and Light Harvesting in Photosystem I

Abstract

In this chapter, structure-based modeling of excitation energy transfer and trapping in Photosystem I (PS I) core complexes will be addressed. The prerequisite for modeling is the knowledge of the spatial arrangement of the pigments (distances between pigments, orientation of their transition dipole moments) and the understanding of the spectral properties of the core antenna and the reaction center. The former is provided by the X-ray structure of trimeric photosystem I core complexes from Thermosynechococcus elongatus (formerly Synechococcus elongatus) at 2.5 Å resolution (Jordan et al., 2001). The spectral properties are determined by the local transition energies of the pigments, the pigment–pigment interactions and the coupling of the electronic pigment transitions with pigment and protein vibrations. The simultaneous description of the dynamics of excitation energy transfer and of the spectral properties of PS I is a major challenge for the theory. In this chapter, recent theoretical attempts in the literature and our own work are described. The focus is put on the question of how the different approaches relate to experimental data.