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Proton-coupled electron transfer of tyrosine oxidation: buffer dependence and parallel mechanisms
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap.
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2007 (Engelska)Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, nr 50, s. 15462-15464Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
2007. Vol. 129, nr 50, s. 15462-15464
Nyckelord [en]
Chemistry, Multidisciplinary
Nationell ämneskategori
Kemi
Identifikatorer
URN: urn:nbn:se:uu:diva-12424DOI: 10.1021/ja073012uISI: 000251581900026PubMedID: 18027937OAI: oai:DiVA.org:uu-12424DiVA, id: diva2:40193
Tillgänglig från: 2007-12-18 Skapad: 2007-12-18 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
Ingår i avhandling
1. Proton-Coupled Electron Transfer from Hydrogen-Bonded Phenols
Öppna denna publikation i ny flik eller fönster >>Proton-Coupled Electron Transfer from Hydrogen-Bonded Phenols
2010 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Proton-coupled electron transfer (PCET) is one of the elementary reactions occurring in many chemical and biological systems, such as photosystem II where the oxidation of tyrosine (TyrZ) is coupled to deprotonation of the phenolic proton. This reaction is here modelled by the oxidation of a phenol covalently linked to a Ru(bpy)32+-moitey, which is photo-oxidized by a laser flash-quench method. This model system is unusual as mechanism of PCET is studied in a unimolecular system in water solution. Here we address the question how the nature of the proton accepting base and its hydrogen bond to phenol influence the PCET reaction.

In the first part we investigate the effect of an internal hydrogen bond PCET from. Two similar phenols are compared. For both these the proton accepting base is a carboxylate group linked to the phenol on the ortho-position directly or via a methylene group. On the basis of kinetic and thermodynamic arguments it is suggested that the PCET from these occurs via a concerted electron proton transfer (CEP). Moreover, numerical modelling of the kinetic data provides an in-depth analysis of this CEP reaction, including promoting  vibrations  along the O–H–O coordinate that are required to explain the data.

The second part describes the study on oxidation of phenol where either water or an external base the proton acceptor. The pH-dependence of the kinetics reveals four mechanistic regions for PCET within the same molecule when water is the base. It is shown that the competition between the mechanisms can be tuned by the strength of the oxidant. Moreover, these studies reveal the conditions that may favour a buffer-assisted PCET over that with deprotonation to water solution.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2010. s. 69
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 706
Nyckelord
Proton-coupled electron transfer, phenol oxidation, hydrogen bonds, artificial photosynthesis, promoting vibrations, proton transfer, laser flash-quench, transient absorption.
Nationell ämneskategori
Fysikalisk kemi
Forskningsämne
Fysikalisk kemi
Identifikatorer
urn:nbn:se:uu:diva-112060 (URN)978-91-554-7699-1 (ISBN)
Disputation
2010-02-19, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2010-01-28 Skapad: 2010-01-08 Senast uppdaterad: 2010-01-28Bibliografiskt granskad

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Irebo, TaniaSjödin, MartinHammarström, Leif

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