Center for Relativistic Laser Science

■  SPEAKER

Prof. Thomas Renger (Institute for Theoretical Physics, JKU Linz)

■    TITLE

 Light Harvesting in the Core of Green Sulfur Bacteria: From Structure to Function

■   ABSTRACT

The Fenna-Matthews-Olson (FMO) complex of green sulfur bacteria has been an important model system for the development of structure-based methods for the parametrization of the Frenkel exciton Hamiltonian of photosynthetic pigment-protein complexes. I will give a short summary of our own journey in this process introducing the Poisson-TrEsp and the charge density coupling (CDC) methods for the calculation of excitonic couplings and site energies, respectively, and a combination of these methods with a normal mode analysis for the spectral density of the exciton-vibrational coupling [1]. Using the cryoEM structural model of the FMO-RCC (reaction center complex) supercomplex [2], we have investigated light-harvesting and trapping of excitation energy by primary electron transfer in the reaction center [3]. In our calculations we take into account energy transfer from the baseplate as an initial condition and calculate the light-harvesting efficiency (LHE) of the FMO-RCC using a combination of Redfield and genaralized Förster theory. Our calculations predict a LHE of (95+/-3) % that is much larger than experimental estimates [4], indicating problems in the experimental sample preparation. The influence of different factors on the LHE, as quantum effects of nuclear motion [5,6], the site energy funnel in the FMO protein [1], the mutual orientation of FMO protein and RCC, and the timescale of primary electron transfer are investigated. We find that a fast electron transfer is most important for a high LHE. In this way the entropic penalty in the free energy difference between the RC and the core antenna, caused by the larger number of antenna states can be beaten. In the end of this seminar, if time permits, I will comment on recent theoretical and experimental progress in using circular polarized light for refining the structure of the baseplate of green sulfur bacteria [7] and artificial helices formed by squaraine chromophores [8], as well as investigating exciton dynamics in the latter by using circularly polarized pulses [8].

■   References

[1] Renger, T.; Müh, F. Understanding photosynthetic light-harvesting: a bottom up theoretical approach. Phys. Chem. Chem. Phys. 2013, 15, 3348–3371.

[2] Chen, J.-H.; Wu, H.; Xu, C.; Liu, X.-C.; Huang, Z.; Chang, S.; Wang, W.; Han, G.; Kuang, T.; Shen, J.-R.; Zhang, X. Architecture of the photosynthetic complex from a green sulfur bacterium. Science 2020, 370, eabb6350.

[3] A. Klinger, D. Lindorfer, F. Müh, T. Renger: Living on the Edge: Light-Harvesting Efficiency and Photoprotection in the Core of Green Sulfur Bacteria (submitted).

[4] Francke, C.; Otte, S.; Miller, M.; Amesz, J.; Olson, J. M. Energy transfer from carotenoid and FMO-protein in subcellular preparations from green sulfur bacteria. Spectroscopic characterization of an FMO-reaction center core complex at low temperature. Photosynth. Res. 1996, 50, 71–77.

[5] J. Cao et al., Quantum biology revisited, Sci. Adv. 6 : eaaz4888 (2020).

[6] T. Renger, Semiclassical Modified Redfield and Generalized Förster Theories of Exciton Relaxation/Transfer in Light-Harvesting Complexes: The Quest for the Principle of Detailed Balance, J. Phys. Chem. B 125, 6406−6416 (2021).

[7] D. Lindorfer and T. Renger: Theory of Anisotropic Circular Dichroism of Excitonically Coupled Systems: Application to the Baseplate of Green Sulfur Bacteria, J. Phys. Chem. B 122, 2747-2756 (2018).

[8] L. Ress, P. Malý, J. B. Landgraf, D. Lindorfer, M. Hofer, J. Selby, C. Lambert, T. Renger, T. Brixner: Time-Resolved Circular Dichroism of Excitonic Systems: Theory and Experiment on an Exemplary Squaraine Polymer (submitted).

■   DATE AND VENUE

May 9, 2023 (Tuesday, 5:00 p.m. - 6:00 p.m.) Room 116

■   LANGUAGE

English

■   INVITED BY

Director Mihaeng Cho