Issue 7, 2012

Bimolecular proton-coupled electron transfer from tryptophan with water as the proton acceptor

Abstract

Proton-coupled electron transfer (PCET) from amino acids with water as the primary proton acceptor is a fundamental model reaction of wide relevance. We have investigated the kinetics and mechanism of PCET from tryptophan derivatives to laser flash-generated [Ru(bpy)3]3+ oxidants in aqueous solutions. The PCET reaction followed either a concerted electron–proton transfer (CEP) mechanism or a step-wise electron transfer–proton transfer (ETPT) mechanism, depending on pH and the identity of the RuIII oxidant. The CEP reaction showed a pH-dependent rate constant, with an increase in log kCEP of 0.3–0.5 per pH unit, and a significant kinetic isotope effect (KIE = 2–4), both in intramolecular and bimolecular model systems. Our results suggest that CEP with water as the proton acceptor is a general feature of amino acid oxidation, and provide further experimental observations towards a detailed understanding of the PCET process in water.

Graphical abstract: Bimolecular proton-coupled electron transfer from tryptophan with water as the proton acceptor

Supplementary files

Article information

Article type
Communication
Submitted
10 Nov 2011
Accepted
13 Jan 2012
First published
16 Jan 2012

Energy Environ. Sci., 2012,5, 7732-7736

Bimolecular proton-coupled electron transfer from tryptophan with water as the proton acceptor

M. Zhang, J. Nilsson and L. Hammarström, Energy Environ. Sci., 2012, 5, 7732 DOI: 10.1039/C2EE03137J

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