Donatas Zigmantas - Revealing lowest functional states and excitation dynamics in bacterial photosynthetic reaction centers

MPSD ARD Seminar

  • Datum: 29.05.2018
  • Uhrzeit: 14:00 - 15:00
  • Vortragende(r): Donatas Zigmantas
  • Chemical Physics, Lund University, Sweden
  • Ort: CFEL (Bldg. 99)
  • Raum: Seminar Room IV, O1.111
  • Gastgeber: R. J. Dwayne Miller

Light-harvesting complexes in photosynthetic organisms absorb sunlight and
transfer energy to reaction centers (RCs), where the primary charge separation
takes places. Notably the general structural arrangement of RCs is preserved
throughout photosynthetic organisms and therefore many functional features
of RCs are expected to be similar. In all of the RCs the primary electron
donor is a special pair of chlorophyll-type molecules. It is tentatively assumed
that the lowestenergy state in RCs is the special pair exciton state often coupled
to a putative charge transfer state. However, despite the numerous spectroscopic
RC studies carried out over the decades, uncertainties remain regarding the lowest
functional states in photosynthetic RCs.

Absorptive 2D spectrum of the purple bacteria RC at 77K

To study the lowest states in bacterial RCs we used two-dimensional
electronic spectroscopy (2DES) at cryogenic temperatures, which
provides high spectral and time resolution. Mapping the spectral
signatures on two frequency dimensions and following their evolution
in time enables unraveling otherwise congested transitions and
excitation dynamics.
I will discuss the lowest states and their dynamics of the Q- type RC
from purple non-sulfur bacteria [1] and the FeS-type RC from green
sulfur bacteria [2,3]. The picture that we uncover is more complex
than what was thought before, as we observe functional involvement
of the additional low-energy states.
[1] A. Vermeglio, G. Paillotin, BBA 681, 32 (1982).
[2] G. Hauska, T. Schoedl, H. Remigy, G. Tsiotis, BBA 1507, 260 (2001).
[3] J. Dostal, J. Psencik, D. Zigmantas, Nat. Chem. 8, 705 (2016).

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