The rate ladder of proton-coupled tyrosine oxidation in water: A systematic dependence on hydrogen bonds and protonation state

Tania Irebo, Olof Johansson, Leif Hammarström

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Proton coupled electron transfer (PCET) from tyrosine covalently linked to Ru(bpy)32+ has been studied with laser flash-quench techniques. Two new complexes with internal hydrogen bonding bases to the phenolic proton have been synthesized. Depending on the hydrogen bonding and protonation situation the rate constant of PCET spanned over 5 orders of magnitude and revealed a systematic dependence on pH. This resulted in a previously predicted "rate ladder" scheme: (i) pH dependent concerted electron-proton transfer (CEP) with deprotonation to bulk water, giving low PCET rates, (ii) pH independent CEP with deprotonation to the internal base, giving intermediate PCET rates, and (iii) pure electron transfer from tyrosinate, giving high rates. This behavior is reminiscent of Yz oxidation in Mn-depleted and native photosystem II. The study also revealed important differences in rates between phenols with strong and weak hydrogen bonds, and for the latter a hydrogen bond-gated PCET was observed.

Original languageEnglish
Pages (from-to)9194-9195
Number of pages2
JournalJournal of the American Chemical Society
Issue number29
Publication statusPublished - Jul 23 2008


ASJC Scopus subject areas

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

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