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Proton-Coupled Electron Transfer in a Series of Ruthenium-Linked Tyrosines with Internal Bases: Evaluation of a Tunneling Model for Experimental Temperature-Dependent Kinetics
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Yale Univ, Dept Chem, 225 Prospect St,POB 208107, New Haven, CT 06520 USA..
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Tsinghua Univ, Dept Chem, Beijing 100084, Peoples R China..
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Univ Messina, Dipartimento Sci Chim, Via F Stagno dAlcontres 31, Messina, Italy..
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Univ Manchester, Sch Chem Engn & Analyt Sci, Manchester M13 9PL, Lancs, England..
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2016 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 35, 9308-9321 p.Article in journal (Refereed) Published
Abstract [en]

Photoinitiated proton-coupled electron transfer (PCET) kinetics has been investigated in a series of four modified tyrosines linked to a ruthenium photosensitizer in acetonitrile, with each tyrosine bearing an internal hydrogen bond to a covalently linked pyridine or benzimidazole base. After correcting for differences in driving force, it is found that the intrinsic PCET rate constant still varies by 2 orders of magnitude. The differences in rates, as well as the magnitude of the kinetic isotope effect (KIE = k(H)/k(D)), both generally correlate with DFT calculated proton donor-acceptor distances. An Arrhenius analysis of temperature dependent data shows that the difference in reactivity arises primarily from differences in activation energies. We use this kinetic data to evaluate a commonly employed theoretical model for proton tunneling which includes a harmonic distribution of proton donor-acceptor distances due to vibrational motions of the molecule: Applying this model to the experimental data yields the conclusion that donor-acceptor compression is more facile in the Compounds with shorter PT distance; however, this is contrary to independent calculations for the same compounds. This discrepancy is likely because the assumption in the model of Morse-shaped proton potential energy surfaces is inappropriate for (strongly) hydrogen-bonded systems. These results question the general applicability of this, model. The results also suggest that a correlation of rate vs proton tunneling distance for the series of compounds is complicated by a concomitant variation of other relevant parameters.

Place, publisher, year, edition, pages
2016. Vol. 120, no 35, 9308-9321 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-305468DOI: 10.1021/acs.jpcb.6b05885ISI: 000383005200005PubMedID: 27490689OAI: oai:DiVA.org:uu-305468DiVA: diva2:1038556
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg Foundation
Available from: 2016-10-19 Created: 2016-10-18 Last updated: 2016-10-19Bibliographically approved

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