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Hydrogen-Bond Promoted Intramolecular Electron Transfer to Photogenerated Ru(III): A Functional Mimic of TyrosineZ and Histidine 190 in Photosystem II
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 29, 6834-6842 p.Article in journal (Refereed) Published
Abstract [en]

As a model for redox components on the donor side of photosystem II (PS II) in green plants, a supramolecular complex 4 has been prepared. In this, a ruthenium(II) tris-bipyridyl complex which mimics the function of P680 in PS II, has been covalently linked to a tyrosine unit which bears two hydrogen-bonding substituents, dipicolylamine (dpa) ligands. Our aim is to mimic the interaction between tyrosineZ and a basic histidine residue, namely His190 in PSII, and also to use the dpa ligands for coordination of manganese. Two different routes for the synthesis of the compound 4 are presented. Its structure was fully characterized by 1H NMR, COSY, NOESY, 13C NMR, IR, and mass spectrometry. 1H NMR and NOESY gave evidence for the existence of intramolecular hydrogen bonding in 4. The interaction between the ruthenium and the substituted tyrosine unit was probed by steady-state and time-resolved emission measurements as well as by chemical oxidation. Flash photolysis and EPR measurements on 4 in the presence of an electron acceptor (methylviologen, MV2+, or cobalt pentaminechloride, Co3+) showed that an intermolecular electron transfer from the excited state of Ru(II) in 4 to the electron acceptor took place, forming Ru(III) and the methylviologen radical MV+ or Co2+. This was followed by intramolecular electron transfer from the substituted tyrosine moiety to the photogenerated Ru(III), regenerating Ru(II) and forming a tyrosyl radical. In water, the radical has a g value of 2.0044, indicative of a deprotonated tyrosyl radical. In acetonitrile, a radical with a g value of 2.0029 was formed, which can be assigned to the tyrosine radical cation. In both solvents the electron transfer is intramolecular with a rate constant kET > 1 × 107 s-1. This is 2 orders of magnitude greater than the one for a similar compound 3, in which no dpa arm is attached to the tyrosine unit. Therefore the hydrogen bonding between the substituted tyrosine and the dpa arms in 4 is proposed to be responsible for the fast electron transfer. This interaction mimics the proposed His190 and tyrosineZ interaction in the donor side of PS II.

Place, publisher, year, edition, pages
1999. Vol. 121, no 29, 6834-6842 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-89493DOI: 10.1021/ja984048cOAI: oai:DiVA.org:uu-89493DiVA: diva2:161007
Available from: 2001-10-19 Created: 2001-10-19 Last updated: 2016-01-07
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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