uu.seUppsala universitets publikationer
Ändra sökning
RefereraExporteraLänk till posten
Permanent länk

Direktlänk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Kinetic effects of hydrogen bonds on proton-coupled electron transfer from phenols
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap, Kemisk fysik.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap, Kemisk fysik.
Visa övriga samt affilieringar
2006 (Engelska)Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, nr 40, s. 13076-13083Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The kinetics and mechanism of proton-coupled electron transfer (PCET) from a series of phenols to a laser flash generated [Ru(bpy)(3)](3+) oxidant in aqueous solution was investigated. The reaction followed a concerted electron-proton transfer mechanism (CEP), both for the substituted phenols with an intramolecular hydrogen bond to a carboxylate group and for those where the proton was directly transferred to water. Without internal hydrogen bonds the concerted mechanism gave a characteristic pH-dependent rate for the phenol form that followed a Marcus free energy dependence, first reported for an intramolecular PCET in Sjodin, M. et al. J. Am. Chem. Soc. 2000, 122, 3932-3962 and now demonstrated also for a bimolecular oxidation of unsubstituted phenol. With internal hydrogen bonds instead, the rate was no longer pH-dependent, because the proton was transferred to the carboxylate base. The results suggest that while a concerted reaction has a relatively high reorganization energy (lambda), this may be significantly reduced by the hydrogen bonds, allowing for a lower barrier reaction path. It is further suggested that this is a general mechanism by which proton-coupled electron transfer in radical enzymes and model complexes may be promoted by hydrogen bonding. This is different from, and possibly in addition to, the generally suggested effect of hydrogen bonds on PCET in enhancing the proton vibrational wave function overlap between the reactant and donor states. In addition we demonstrate how the mechanism for phenol oxidation changes from a stepwise electron transfer-proton transfer with a stronger oxidant to a CEP with a weaker oxidant, for the same series of phenols. The hydrogen bonded CEP reaction may thus allow for a low energy barrier path that can operate efficiently at low driving forces, which is ideal for PCET reactions in biological systems.

Ort, förlag, år, upplaga, sidor
2006. Vol. 128, nr 40, s. 13076-13083
Nationell ämneskategori
Kemi
Identifikatorer
URN: urn:nbn:se:uu:diva-83646DOI: 10.1021/ja063264fISI: 000241030500024PubMedID: 17017787OAI: oai:DiVA.org:uu-83646DiVA, id: diva2:111554
Tillgänglig från: 2006-11-07 Skapad: 2006-11-07 Senast uppdaterad: 2017-12-14Bibliografiskt 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

Open Access i DiVA

Fulltext saknas i DiVA

Övriga länkar

Förlagets fulltextPubMed

Personposter BETA

Irebo, TaniaHammarström, Leif

Sök vidare i DiVA

Av författaren/redaktören
Irebo, TaniaHammarström, Leif
Av organisationen
Kemisk fysik
I samma tidskrift
Journal of the American Chemical Society
Kemi

Sök vidare utanför DiVA

GoogleGoogle Scholar

doi
pubmed
urn-nbn

Altmetricpoäng

doi
pubmed
urn-nbn
Totalt: 1150 träffar
RefereraExporteraLänk till posten
Permanent länk

Direktlänk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf