ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
KL22. Probing the Reduced S States of Photosystem II with Mixed -Valence
Trinuclear and Tetranuclear Manganese Complexes
A. Dimitrakopoulou, V. Tangoulis, D. P. Kessissoglou
Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece
e-mail: kessisog@chem.auth.gr
The enzyme which produces oxygen is known as photosystem II (PSII). At the heart of this enzyme is a
tetrameric manganese cluster known as the oxygen evolving
complex (OEC). The manganese cluster undergoes a series of
oxidations in a reaction cycle with each different oxidation
level known as an S state. The starting state, S0, is the most
reduced and the production of oxygen occurs upon the
transition of the most oxidized states to the S0 state
(S3�S4�S0). The exact oxidation states of each manganese
ion in each S state is still highly debated. To probe the
oxidation states of the manganese ions, numerous model
complexes have been synthesized and subjected to a variety of
techniques including XAS and EPR. A synthetic challenge
arises to construct complexes of the same overall charge but with a different distribution of oxidation states, and
then to probe these complexes to see if they can be distinguished under XANES and EPR experimental
conditions. We have synthesized and studied trimeric and tetrameric manganese clusters with oxidation states
distributions of Mn(III)Mn(II)Mn(III) and Mn(II)Mn(IV)Mn(II) or Mn(II)Mn(II)Mn(III)Mn(III) and
Mn(II)Mn(II)Mn(II)Mn(IV) while recently we have isolated (figure) an hexanuclear mixed valence
[Mn(II)Mn(II)Mn(III)][[Mn(II)Mn(III)Mn(III)] compound consisting of two pseudo-cubane like cores connected
by an hydroxyl and an oxo groups.
Acknowledgment. This project is co-funded by the European Union/European Social Fund, “Pythagoras II”.
References:
[1]. A. Dimitrakopoulou, C. Dendrinou-Samara, A.A. Pantazaki, M. Alexiou, E. Nordlander, D.P. Kessissoglou,
J. Inorg. Biochem., 102, 618 (2008)
[2] C. Zaleski, T-C. Weng, C. Dendrinou-Samara, M. Alexiou, P. Kanakaraki, J. Kampf, J. E. Penner-Hahn, V.
L. Pecoraro, D. P. Kessissoglou. Inorg. Chem. 47, (2008)
[3] A. Dimitrakopoulou, V. Psycharis, C. P. Raptopoulou, A. Terzis, V. Tangoulis, D. P. Kessissoglou, Inorg.
Chem. (2008)
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