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Spanning Four Mecha...
Spanning Four Mechanistic Regions of Intramolecular Proton-Coupled Electron Transfer in a Ru(bpy)32+-Tyrosine Complex
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- Irebo, Tania, 1980- (författare)
- Uppsala universitet,Fysikalisk kemi
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- Zhang, Ming-Tian (författare)
- Uppsala universitet,Fysikalisk kemi
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- Markle, Todd F. (författare)
- Uppsala universitet,Fysikalisk kemi
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- Scott, Amy (författare)
- Uppsala universitet,Fysikalisk kemi
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- Hammarström, Leif (författare)
- Uppsala universitet,Fysikalisk kemi
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(creator_code:org_t)
- 2012-09-24
- 2012
- Engelska.
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 134:39, s. 16247-16254
- Relaterad länk:
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https://urn.kb.se/re...
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https://doi.org/10.1...
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Abstract
Ämnesord
Stäng
- Proton-coupled electron transfer (PCET) from tyrosine (TyrOH) to a covalently linked [Ru(bpy)(3)](2+) photosensitizer in aqueous media has been systematically reinvestigated by laser flash-quench kinetics as a model system for PCET in radical enzymes and in photochemical energy conversion. Previous kinetic studies on Ru-TyrOH molecules (Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932; Irebo et al. J. Am. Chem. Soc. 2007, 129, 15462) have established two mechanisms. Concerted electron-proton (CEP) transfer has been observed when pH < pK(a)(TyrOH), which is pH-dependent but not first-order in [OH-] and not dependent on the buffer concentration when it is sufficiently low (less than ca. 5 mM). In addition, the pH-independent rate constant for electron transfer from tyrosine phenolate (TyrO(-)) was reported at pH >10. Here we compare the PCET rates and kinetic isotope effects (k(H)/k(D)) of four Ru-TyrOH molecules with varying Ru-III/II oxidant strengths over a pH range of 1-12.5. On the basis of these data, two additional mechanistic regimes were observed and identified through analysis of kinetic competition and kinetic isotope effects (KIE): (i) a mechanism dominating at low pH assigned to a stepwise electron-first PCET and (ii) a stepwise proton-first PCET with OH- as proton acceptor that dominates around pH = 10. The effect of solution pH and electrochemical potential of the Ru-III/II oxidant on the competition between the different mechanisms is discussed. The systems investigated may serve as models for the mechanistic diversity of PCET reactions in general with water (H2O, OH-) as primary proton acceptor.
Ämnesord
- NATURVETENSKAP -- Kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences (hsv//eng)
Nyckelord
- proton-coupled electron transfer
- phenol oxidation
- artificial photosynthesis
- Fysikalisk kemi
- Physical Chemistry
Publikations- och innehållstyp
- ref (ämneskategori)
- art (ämneskategori)
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