Linear-dichroism measurements on the LH2 antenna complex of Rhodopseudomonas acidophila strain 10050 show that the transition dipole moment of the carotenoid rhodopin glucoside is not collinear with the long molecular axis

We have applied linear-dichroism experiments to determine the orientation of the transition dipole moment, corresponding to the main absorption band of the carotenoid, rhodopin glucoside, in the light-harvesting complex LH2 from Rhodopseudomonas acidophila strain 10050. The crystal structure of this LH2 complex is known and MO calculations have been performed that indicate that the transition dipole moment is 9.1degrees off axis from the extended pi-electron conjugated chain (Dolan, P. M.; Miller, D.; Cogdell, R. J.; Birge, R. R. Frank, H. A. J. Phys. Chem. B 2001, 105, 12134-12142). Our experimental results confirm that the transition dipole moment is not oriented along the long axis of the carotenoid molecule, and they are in excellent agreement with the MO calculations. However, they disagree with the linear-dichroism results of the same authors. Possible reasons for the discrepancy are discussed

The open, the closed, and the empty: time-resolved fluorescence spectroscopy and computational analysis of RC-LH1 complexes from Rhodopseudomonas palustris

We studied the time-resolved fluorescence of isolated RC-LH1 complexes from Rhodopseudomonas palustris as a function of the photon fluence and the repetition rate of the excitation laser. Both parameters were varied systematically over 3 orders of magnitude. On the basis of a microstate description we developed a quantitative model for RC-LH1 and obtained very good agreement between experiments and elaborate simulations based on a global master equation approach. The model allows us to predict the relative population of RC-LH1 complexes with the special pair in the neutral state or in the oxidized state P+ and those complexes that lack a reaction center