Objective
The aim of this project is to understand excitation energy transfer and exciton-state relaxation (dephasing) processes in a structurally and biochemically well characterized photosynthetic light-harvesting system, the phycobiliproteins. C-phycocyanin (PC), allophycocyanin (APC) and phycoerythrocyanin (PEC) in different states of aggregation, will be studied by femtosecond time-resolved polarized absorption laser spectroscopy.
Photoinduced difference spectra will be measured, along with ultrafast kinetics and corresponding anisotropy, with 50 fs resolution in 400-800 nm spectral region. In PC and APC, specific spectral features will be used as criteria for exciton interaction between neighbouring chromophores in the trimers, viz. the theoretically predicted two-component anisotropy decay (due to dephasing and Förster processes), and excited state absorption to the doubly excited exciton state. The same processes will be studied in PEC, which has nearly the same geometry as PC but changed energies of the respective chromophores. Complementary investigations are forseen: biliprotein monomers in which rapid processes are inhibited, and synthetic model systems of higher symmetry (tetrapyrole dimers).
The objective is to understand the absorption spectrum of APC trimer and its dramatic difference from the spectra of APC monomer and PC trimer. One has to consider three possibilities: the strong interaction between a-80 and b-81 chromophores, the weak (intermediate) interaction between spectrally similar chromophores acquired vibronic bands upon trimer formation, and the very different absorption specta of a-80 and b-81 chromophores in the trimer. The estimetion os the distance between chromophores and their orientations will be of permanent importance. The X-ray structure of trimeric APC is not available now, but is expected in the near future. No structures are presently known for the complexes of APC (and other) with linker polypeptides; it is therefore hoped to provide functional and structural information on the changes induced by the linker.
Topic(s)
Call for proposal
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80638 München
Germany