Origin of non-conservative circular dichroism of the CP29 antenna complex of photosystem II

The origin of the non-conservative nature of the circular dichroism spectrum of the CP29 light-harvesting complex in the Q(y) spectral region is investigated. A structure-based Hamiltonian of coupled Qy transitions, determined previously [Muh et al., Phys. Chem. Chem. Phys., 2014, 16, 11848] is extended by including higher excited states of the chlorophylls and the S-0 -> S-2 transition of carotenoids. Excitonic couplings are calculated with the Poisson-TrESP method, taking into account dipole strengths from experiments on isolated pigments. The coupling between Qy and higher excited states is found to be responsible for the major part of the non-conservativity of the CD spectrum. The remaining part is explained by the intrinsic CD of the chlorophylls that has been estimated from experiments on isolated pigments.