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

Ming Tian Zhang; Johan Nilsson; Leif Hammarström

doi:10.1039/c2ee03137j

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

Ming Tian Zhang, Johan Nilsson, Leif Hammarström

Uppsala University

Research output: Contribution to journal › Article › peer-review

19 Citations (Scopus)

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 Ru^III oxidant. The CEP reaction showed a pH-dependent rate constant, with an increase in log k_CEP 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.

Original language	English
Pages (from-to)	7732-7736
Number of pages	5
Journal	Energy and Environmental Science
Volume	5
Issue number	7
DOIs	https://doi.org/10.1039/c2ee03137j
Publication status	Published - Jul 2012

ASJC Scopus subject areas

Environmental Chemistry
Renewable Energy, Sustainability and the Environment
Nuclear Energy and Engineering
Pollution

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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.",

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