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II. The Mechanism for Proton Coupled Electron Transfer from Tyrosine in a Model Complex and Comparisons with YZ oxidation in Photosystem II
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry.
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2002 In: Phil.Trans. R. Soc. Lond. B, Vol. 357, 1471-1479 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2002. Vol. 357, 1471-1479 p.
Identifiers
URN: urn:nbn:se:uu:diva-91497OAI: oai:DiVA.org:uu-91497DiVA: diva2:164256
Available from: 2004-03-31 Created: 2004-03-31Bibliographically approved
In thesis
1. Regulation of Proton Coupled Electron Transfer from Amino Acids in Artificial Model Systems: A Mechanistic Study
Open this publication in new window or tab >>Regulation of Proton Coupled Electron Transfer from Amino Acids in Artificial Model Systems: A Mechanistic Study
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
En Mekanistisk Studie rörande Reglering av Protonkopplad Elektronöverföring från Aminosyror i Artificiella Modellsystem
Abstract [en]

Amino acid radicals are key redox intermediates in several natural enzymes including Cytochrome c peroxidase, DNA photolyase, ribonucletide reductase, cytochrome c oxidase and photosystem II. Electron transfer from amino acids is often coupled to deprotonation and this thesis concerns the coupling of electron transfer from tyrosine and tryptophan to trisbipyridineruthenium(III) with deprotonation in model complexes. Specifically the mechanisms for these proton coupled electron transfer reactions have been studied and the controlling parameters have been identified, the possible mechanisms being stepwise electron transfer followed by deprotonation and deprotonation followed by electron transfer or concerted electron transfer/deprotonation.

Proton coupled electron transfer reactions have been studied using nano-second flash photolysis in water solution and the effect of pH, temperature, reaction driving force, deuteration and nature of the amino acid has been determined. I have shown that the rate constant for the concerted reaction depends intrinsically on the mixing entropy of the released proton and that the pH-dependence can be used as an experimental tool for mechanistic discrimination. Moreover I have shown that the concerted reaction inherently has a high reorganisation energy due to the coupling of the electron motion with deprotonation. Hydrogen bonding to the transferring proton however significantly reduces this reorganisation energy. The concerted reaction also has a relatively high driving force counteracting the high reorganisation energy in the competition between the concerted reaction and the stepwise electron transfer first reaction. The relative importance of the high reorganisation energy and the high driving force for the concerted reaction determines the mechanistic outcome of the reaction, the stepwise reaction being favoured by high over-all driving forces and the concerted reaction by high pH.

By comparing my results from model complexes with tyrosineZ oxidation in photosystem II, I give strong evidence for a concerted electron transfer/deprotonation mechanism.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 65 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 953
Keyword
Physical chemistry, Proton Coupled Electron Transfer, Tyrosine, Tryptophan, Electron Transfer, Hydrogen bond, Photosystem II, Proton transfer, Radical protein, Fysikalisk kemi
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-4132 (URN)91-554-5909-9 (ISBN)
Public defence
2004-04-22, B41, BMC, Husargatan 3, Uppsala, 10:00
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Available from: 2004-03-31 Created: 2004-03-31Bibliographically approved

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