Origin of Non-Conservative Circular Dichroism of the CP29 Antenna Complex of Photosystem II
Sprache des Vortragstitels:
Light Harvesting Processes 2017
Sprache des Tagungstitel:
A structure-based simulation of optical spectra of the minor light harvesting complex CP29 of photosystem II is presented to give an explanation of the experimental circular dichroism (CD) signal in the Qy part of the spectrum. The latter shows strong non-conservativity, meaning that the integral over this particular area of the spectrum is non-zero. The Hamiltonian of coupled Qy transitions determined previously  is extended by including higher excited states of the chlorophylls (Chl) and the S0-S2 transition of carotenoids. Excitonic couplings are calculated with the Poisson-TrESP method that includes a description of screening and local field corrections to the Coulomb couplings between transition densities. The latter are rescaled such as to reveal the right dipole strength that is estimated from experimental data on isolated pigments in solution. Dynamic localization effects of the exciton wavefunctions due to exciton-vibrational coupling are implicitly taken into account by introducing exciton domains and by treating the mixing of high-energy transitions with Qy transitions in first-order perturbation theory. We find that the major part (75%) of the non-conservativity of the CD spectrum is due to this coupling, with large contributions from the Bx transitions of Chl. The remaining 25% are explained by non-excitonic intrinsic CD of Chls, that is estimated from experiments on isolated Chl in solution.