Blue-Light Harvesting in the Ocean: Theory meets Experiment

In the initial steps of photosynthesis, photons are absorbed in light-harvesting antenna complexes. Afterwards, the excitation energy is transferred towards reaction centres, in which a series of charge- and electron transfer processes initiates the metabolic function of the organism. Adaptation to environmental light conditions is crucial for photosynthetic organisms. About 40 % of the global photosynthetic solar energy conversion takes place in aquatic environments, specifically in microalgae termed diatoms and in dinoflagellates. Both types have adopted their light-harvesting apparatus to the light conditions under water and have increased their absorbance in the blue and green spectral regions by using, besides chlorophyll a (Chl a), that also occurs in plants, the new pigments Chl c and the Car fucoxanthin (Fx) in diatoms and peridinin (Per) in dinoflagellates. In particular, the Cars take over the role of the main light- harvesting pigment in marine photosynthesis, whereas in plants they mainly serve photoprotective purposes. The main goal of the present project to provide a microscopic description of the adaptation of these marine light-harvesting systems. We aim for a structure-based understanding of the energy transfer between Car Fx and Chl c to Chl a in the light-harvesting fucoxanthin-chlorophyll a/c protein and between Car Per and Chl a in the peridinin-chlorophyll protein PCP. For this purpose, we follow a combined experimentalheoretical approach. Jürgen Hauer`s team at TU Munich will characterize the excited state structure and dynamics of PCP and FCP and its constituting pigments using ultrafast spectroscopy. Samples of FCP will be prepared in the labs of Radek Litvin at the Institute of Plant Molecular Biology (University of Southern Bohemia, Czech Republic). The PCP samples will be provided by Eckhard Hofmann`s group at Bochum University. The team around Thomas Renger at JKU Linz will parameterize the Frenkel exciton Hamiltonian of FCP and PCP using quantum chemical / electrostatic methods and calculate optical spectra and energy transfer kinetics with methods from non- equilibrium quantum statistics.