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A Biomimetic Model System for the Water Oxidizing Triad in Photosystem II
Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
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1999 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 121, no 1, 89-96 p.Article in journal (Refereed) Published
Abstract [en]

In plants, solar energy is used to extract electrons from water, producing atmospheric oxygen. This is conducted by Photosystem II, where a redox ”triad” consisting of chlorophyll, a tyrosine, and a manganese cluster, governs an essential part of the process. Photooxidation of the chlorophylls produces electron transfer from the tyrosine, which forms a radical. The radical and the manganese cluster together extract electrons from water, providing the biosphere with an unlimited electron source. As a partial model for this system we constructed a ruthenium(II) complex with a covalently attached tyrosine, where the photooxidized ruthenium was rereduced by the tyrosine. In this study we show that the tyrosyl radical, which gives a transient EPR signal under illumination, can oxidize a manganese complex. The dinuclear manganese complex, which initially is in the Mn(III)/(III) state, is oxidized by the photogenerated tyrosyl radical to the Mn(III)/(IV) state. The redox potentials in our system are comparable to those in Photosystem II. Thus, our synthetic redox “triad” mimics important elements in the electron donor ”triad” in Photosystem II, significantly advancing the development of systems for artificial photosynthesis based on ruthenium−manganese complexes.

Place, publisher, year, edition, pages
1999. Vol. 121, no 1, 89-96 p.
Keyword [en]
Electron-Transfer, Y-Z, Photosynthesis, Mechanism, Complexes, Tyrosine, Oxygen, Light
National Category
Physical Chemistry
URN: urn:nbn:se:uu:diva-89492DOI: 10.1021/ja981494rOAI: oai:DiVA.org:uu-89492DiVA: diva2:161006
Available from: 2001-10-19 Created: 2001-10-19 Last updated: 2013-07-05
In thesis
1. Electron Transfer in Ruthenium-Manganese Complexes for Artificial Photosynthesis: Studies in Solution and on Electrode Surfaces
Open this publication in new window or tab >>Electron Transfer in Ruthenium-Manganese Complexes for Artificial Photosynthesis: Studies in Solution and on Electrode Surfaces
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In today’s society there is an increasing need for energy, an increase which for the most part is supplied by the use of fossil fuels. Fossil fuel resources are limited and their use has harmful effects on the environment, therefore the development of technologies that produce clean energy sources is very appealing. Natural photosynthesis is capable of converting solar energy into chemical energy through a series of efficient energy and electron transfer reactions with water as the only electron source. Thus, constructing an artificial system that uses the same principles to convert sunlight into electricity or storable fuels like hydrogen is one of the major forces driving artificial photosynthesis research.

This thesis describes supramolecular complexes with the intention of mimicking the electron transfer reactions of the donor side in Photosystem II, where a manganese cluster together with a tyrosine catalyses the oxidation of water. All complexes are based on Ru(II)-trisbipyridine as a photosensitizer that is covalently linked to electron donors like tyrosine or manganese. Photochemical reactions are studied with time-resolved transient absorption and emission measurements. Electrochemical techniques are used to study the electrochemical behavior, and different photoelectrochemical techniques are used to investigate the complexes adsorbed onto titanium dioxide surfaces. In all complexes, intramolecular electron transfer occurs from the linked donor to photo-oxidized Ru(III). It is also observed that coordinated Mn(II) quenches the excited state of Ru(II), a reaction that is found to be distance dependent. However, by modifying one of the complexes, its excited state properties can be tuned in a way that decreases the quenching and keeps the electron transfer properties. The obtained results are of significance for the development of multinuclear Ru-Mn complexes that are capable of multi-electron transfer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2001. 69 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 669
Physics, Artificial photosynthesis, electron transfer, energy transfer, ruthenium, manganese, titanium dioxide, Fysik
National Category
Physical Sciences
Research subject
Physical Chemistry
urn:nbn:se:uu:diva-1468 (URN)91-554-5154-3 (ISBN)
Public defence
2001-11-09, The Svedberg Lecture Hall, Institute of Chemistry, Uppsala University, Uppsala, 10:15
Available from: 2001-10-19 Created: 2001-10-19Bibliographically approved

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Magnuson, AnnHammarström, LeifStyring, Stenbjörn
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