Proton-coupled electron transfer of tyrosine oxidation: buffer dependence and parallel mechanisms
2007 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, Vol. 129, no 50, 15462-15464 p.Article in journal (Refereed) Published
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 log k vs pH, is independent of buffer and cannot be explained by reaction schemes with simple first-order dependencies on [OH-], [H3O+], or buffer species.
Place, publisher, year, edition, pages
2007. Vol. 129, no 50, 15462-15464 p.
IdentifiersURN: urn:nbn:se:uu:diva-12424DOI: 10.1021/ja073012uISI: 000251581900026PubMedID: 18027937OAI: oai:DiVA.org:uu-12424DiVA: diva2:40193