Proton-coupled electron transfer of tyrosine oxidation: Buffer dependence and parallel mechanisms

Tania Irebo, Steven Y. Reece, Martin Sjödin, Daniel G. Nocera, Leif Hammarstrom

Research output: Contribution to journalArticle

152 Citations (Scopus)

Abstract

The proton-coupled electron transfer (PCET) from tyrosine covalently linked to a metal complex has been studied. The reaction was induced by laser flash excitation of the metal complex, and PCET was bidirectional, with electron transfer to the excited or flash-quenched oxidized metal complex and proton transfer to water or added buffers in the solution. We found a competition between three different PCET mechanisms: (1) A concerted PCET with water as the proton acceptor, which indeed shows a pH-dependence as earlier reported (Sjödin, M.; Styring, S.; Åkermark, B.; Sun, L.; Hammarström, L. J. Am. Chem. Soc. 2000, 122, 3932); (2) a stepwise electron transfer-proton transfer (ETPT) that is pH-independent; (3) a buffer-assisted concerted PCET. The relative importance of reaction 2 increases with oxidant strength, while that of reaction 1 increases with pH. At higher buffer concentrations reaction 3 becomes important, and the rate follows the expected first-order dependence on the concentration of the buffer base. Most importantly, the pH-dependence of reaction 1, with a slope of 0.4-0.5 in a plot of logk vs pH, is independent of buffer and cannot be explained by reaction schemes with simple first-order dependencies on [OH-], [H3O+], or buffer species.

Original languageEnglish
Pages (from-to)15462-15464
Number of pages3
JournalJournal of the American Chemical Society
Volume129
Issue number50
DOIs
Publication statusPublished - 2007 Dec 19
Externally publishedYes

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Tyrosine
Protons
Buffers
Electrons
Oxidation
Coordination Complexes
Metal complexes
Proton transfer
Water
Oxidants
Sun
Solar System
Lasers

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Proton-coupled electron transfer of tyrosine oxidation : Buffer dependence and parallel mechanisms. / Irebo, Tania; Reece, Steven Y.; Sjödin, Martin; Nocera, Daniel G.; Hammarstrom, Leif.

In: Journal of the American Chemical Society, Vol. 129, No. 50, 19.12.2007, p. 15462-15464.

Research output: Contribution to journalArticle

Irebo, Tania ; Reece, Steven Y. ; Sjödin, Martin ; Nocera, Daniel G. ; Hammarstrom, Leif. / Proton-coupled electron transfer of tyrosine oxidation : Buffer dependence and parallel mechanisms. In: Journal of the American Chemical Society. 2007 ; Vol. 129, No. 50. pp. 15462-15464.
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