Change search
ReferencesLink to record
Permanent link

Direct link
Switching the redox mechanism: Models for proton coupled electron transfer from tyrosine and tryptophan
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Show others and affiliations
2005 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 11, 3855-3863 p.Article in journal (Refereed) Published
Abstract [en]

The coupling of electron and proton transfer is an important controlling factor in radical proteins, such as photosystem II, ribinucleotide reductase, cytochrome oxidases, and DNA photolyase. This was investigated in model complexes in which a tyrosine or tryptophan residue was oxidized by a laser-flash generated trisbipyridine-Ru-III moiety in an intramolecular, proton-coupled electron transfer (PCET) reaction. The PCET was found to proceed in a competition between a stepwise reaction, in which electron transfer is followed by deprotonation of the amino acid radical (ETPT), and a concerted reaction, in which both the electron and proton are transferred in a single reaction step (CEP). Moreover, we found that we could analyze the kinetic data for PCET by Marcus' theory for electron transfer. By altering the solution pH, the strength of the Ru-III oxidant, or the identity of the amino acid, we could induce a switch between the two mechanisms and obtain quantitative data for the parameters that control which one will dominate. The characteristic pH-dependence of the CEP rate (M. Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932) reflects the pH-dependence of the driving force caused by proton release to the bulk. For the pH-independent ETPT on the other hand, the driving force of the rate-determining ET step is pH-independent and smaller. On the other hand, temperature-dependent data showed that the reorganization energy was higher for CEP, while the pre-exponential factors showed no significant difference between the mechanisms. Thus, the opposing effect of the differences in driving force and reorganization energy determines which of the mechanisms will dominate. Our results show that a concerted mechanism is in general quite likely and provides a low-barrier reaction pathway for weakly exoergonic reactions. In addition, the kinetic isotope effect was much higher for CEP (k(H)/k(D) > 10) than for ETPT (k(H)/k(D) = 2), consistent with significant changes along the proton reaction coordinate in the rate-determining step of CEP.

Place, publisher, year, edition, pages
2005. Vol. 127, no 11, 3855-3863 p.
Keyword [en]
National Category
Other Basic Medicine
URN: urn:nbn:se:su:diva-23641DOI: 10.1021/ja044395oOAI: diva2:193624
Available from: 2005-03-23 Created: 2005-03-23 Last updated: 2010-10-29Bibliographically approved
In thesis
1. Ruthenium(II) Polypyridyl Complexes in Supramolecular Systems relevant to Artificial Photosynthesis
Open this publication in new window or tab >>Ruthenium(II) Polypyridyl Complexes in Supramolecular Systems relevant to Artificial Photosynthesis
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes the synthesis and properties of ruthenium complexes relevant to artificial photosynthesis. The work includes preparation of RuIIpolypyridine complexes as well as multi component systems where RuII(bpy)3 or RuII(tpy)2 type complexes are used as photosesnsitizers.

In the first part, the synthesis and characterisation of bipyridyl(pyridyl)methane type ligands and the corresponding ruthenium(II) bistridentate polypyridyl complexes is described. The bipyridyl-pyridyl methane type ligands were designed to increase the excited state lifetime of ruthenium(II) bisterpyridine-type complexes by altering the ligand field as compared to normal terpyridine ligands.

In the second part photoinduced electron transfer and formation of charge separated states in donor-photosensitizer dyads or donor-photosensitizer-acceptor triads is studied. The first covalently linked donor-photosensitizer-acceptor triad with tyrosine as electron donor was prepared, and long lived light induced charge separation was observed. RuIIterpyridine complexes linked to carotenoid or tyrosine were also prepared, for studies of light induced charge separation on a TiO2 surface. Tryptofan was covalently linked to Ru(bpy)3 and proton coupled electron transfer from tryptophan to photogenerated ruthenium(III) was demonstrated. A pH-dependent study of the electron transfer rate gave insight into the mechanism of proton coupled electron transfer in amino acids.

Finally, the last part of the thesis presents the preparation and properties of the first complex containing a photosensitizer covalently linked to a Fe-hydrogenase active site model.

Place, publisher, year, edition, pages
Stockholm: Institutionen för organisk kemi, 2005. 54 p.
Ruthenium complexes
National Category
Organic Chemistry
urn:nbn:se:su:diva-417 (URN)91-7155-031-3 (ISBN)
Public defence
2005-04-18, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 14:00
Available from: 2005-03-23 Created: 2005-03-23 Last updated: 2014-02-24Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text
By organisation
Department of Organic Chemistry
In the same journal
Journal of the American Chemical Society
Other Basic Medicine

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 38 hits
ReferencesLink to record
Permanent link

Direct link