Isolating the effects of the proton tunneling distance on protoncoupled electron transfer in a series of homologous tyrosine-base model compounds

Starla D. Glover, Giovanny A. Parada, Todd F. Markle, Sascha Ott, Leif Hammarström

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

The distance dependence of concerted proton-coupled electron transfer (PCET) reactions was probed in a series of three new compounds, where a phenol is covalently bridged by a 5, 6, or 7 membered carbocycle to the quinoline. The carbocycle bridge enforces the change in distance between the phenol oxygen (proton donor) and quinoline nitrogen (proton acceptor), dO•••N, giving rise to values ranging from 2.567 to 2.8487 Å, and resulting in calculated proton tunneling distances, r0, that span 0.719 to 1.244 Å. Not only does this series significantly extend the range of distances that has been previously accessible for experimental distance dependent PCET studies of synthetic model compounds, but it also greatly improves the isolation of dO•••N as a variable compared to earlier reports. Rates of PCET were determined by time-resolved optical spectroscopy with flash-quench generated [Ru(bpy)3]3+ and [Ru(dce)3]3+, where bpy = 2,2′-bipyridyl and dce = 4,4′-dicarboxyethylester-2,2′-bipyridyl. The rates increased as dO•••N decreased, as can be expected from a static proton tunneling model. An exponential attenuation of the PCET rate constant was found: kPCET(d) = kPCETexp[-β(d-d0)], with β ∼ 10 Å-1. The observed kinetic isotope effect (KIE = kH/kD) ranged from 1.2 to 1.4, where the KIE was observed to decrease slightly with increasing dO•••N. Both β and KIE values are significantly smaller than what is predicted by a static proton tunneling model. We conclude that vibrational compression of the tunneling distances, as well as higher vibronic transitions, that contribute to concerted proton coupled electron transfer must also be considered.

Original languageEnglish
Pages (from-to)2090-2101
Number of pages12
JournalJournal of the American Chemical Society
Volume139
Issue number5
DOIs
Publication statusPublished - Feb 8 2017

Fingerprint

Tyrosine
Protons
Electrons
2,2'-Dipyridyl
Phenol
Phenols
Electron transitions
Isotopes
Rate constants
Spectrum Analysis
Nitrogen
Oxygen
Kinetics

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Isolating the effects of the proton tunneling distance on protoncoupled electron transfer in a series of homologous tyrosine-base model compounds. / Glover, Starla D.; Parada, Giovanny A.; Markle, Todd F.; Ott, Sascha; Hammarström, Leif.

In: Journal of the American Chemical Society, Vol. 139, No. 5, 08.02.2017, p. 2090-2101.

Research output: Contribution to journalArticle

@article{cd4ca3c83ab74e749823e4617aef9044,
title = "Isolating the effects of the proton tunneling distance on protoncoupled electron transfer in a series of homologous tyrosine-base model compounds",
abstract = "The distance dependence of concerted proton-coupled electron transfer (PCET) reactions was probed in a series of three new compounds, where a phenol is covalently bridged by a 5, 6, or 7 membered carbocycle to the quinoline. The carbocycle bridge enforces the change in distance between the phenol oxygen (proton donor) and quinoline nitrogen (proton acceptor), dO•••N, giving rise to values ranging from 2.567 to 2.8487 {\AA}, and resulting in calculated proton tunneling distances, r0, that span 0.719 to 1.244 {\AA}. Not only does this series significantly extend the range of distances that has been previously accessible for experimental distance dependent PCET studies of synthetic model compounds, but it also greatly improves the isolation of dO•••N as a variable compared to earlier reports. Rates of PCET were determined by time-resolved optical spectroscopy with flash-quench generated [Ru(bpy)3]3+ and [Ru(dce)3]3+, where bpy = 2,2′-bipyridyl and dce = 4,4′-dicarboxyethylester-2,2′-bipyridyl. The rates increased as dO•••N decreased, as can be expected from a static proton tunneling model. An exponential attenuation of the PCET rate constant was found: kPCET(d) = kPCETexp[-β(d-d0)], with β ∼ 10 {\AA}-1. The observed kinetic isotope effect (KIE = kH/kD) ranged from 1.2 to 1.4, where the KIE was observed to decrease slightly with increasing dO•••N. Both β and KIE values are significantly smaller than what is predicted by a static proton tunneling model. We conclude that vibrational compression of the tunneling distances, as well as higher vibronic transitions, that contribute to concerted proton coupled electron transfer must also be considered.",
author = "Glover, {Starla D.} and Parada, {Giovanny A.} and Markle, {Todd F.} and Sascha Ott and Leif Hammarstr{\"o}m",
year = "2017",
month = "2",
day = "8",
doi = "10.1021/jacs.6b12531",
language = "English",
volume = "139",
pages = "2090--2101",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "5",

}

TY - JOUR

T1 - Isolating the effects of the proton tunneling distance on protoncoupled electron transfer in a series of homologous tyrosine-base model compounds

AU - Glover, Starla D.

AU - Parada, Giovanny A.

AU - Markle, Todd F.

AU - Ott, Sascha

AU - Hammarström, Leif

PY - 2017/2/8

Y1 - 2017/2/8

N2 - The distance dependence of concerted proton-coupled electron transfer (PCET) reactions was probed in a series of three new compounds, where a phenol is covalently bridged by a 5, 6, or 7 membered carbocycle to the quinoline. The carbocycle bridge enforces the change in distance between the phenol oxygen (proton donor) and quinoline nitrogen (proton acceptor), dO•••N, giving rise to values ranging from 2.567 to 2.8487 Å, and resulting in calculated proton tunneling distances, r0, that span 0.719 to 1.244 Å. Not only does this series significantly extend the range of distances that has been previously accessible for experimental distance dependent PCET studies of synthetic model compounds, but it also greatly improves the isolation of dO•••N as a variable compared to earlier reports. Rates of PCET were determined by time-resolved optical spectroscopy with flash-quench generated [Ru(bpy)3]3+ and [Ru(dce)3]3+, where bpy = 2,2′-bipyridyl and dce = 4,4′-dicarboxyethylester-2,2′-bipyridyl. The rates increased as dO•••N decreased, as can be expected from a static proton tunneling model. An exponential attenuation of the PCET rate constant was found: kPCET(d) = kPCETexp[-β(d-d0)], with β ∼ 10 Å-1. The observed kinetic isotope effect (KIE = kH/kD) ranged from 1.2 to 1.4, where the KIE was observed to decrease slightly with increasing dO•••N. Both β and KIE values are significantly smaller than what is predicted by a static proton tunneling model. We conclude that vibrational compression of the tunneling distances, as well as higher vibronic transitions, that contribute to concerted proton coupled electron transfer must also be considered.

AB - The distance dependence of concerted proton-coupled electron transfer (PCET) reactions was probed in a series of three new compounds, where a phenol is covalently bridged by a 5, 6, or 7 membered carbocycle to the quinoline. The carbocycle bridge enforces the change in distance between the phenol oxygen (proton donor) and quinoline nitrogen (proton acceptor), dO•••N, giving rise to values ranging from 2.567 to 2.8487 Å, and resulting in calculated proton tunneling distances, r0, that span 0.719 to 1.244 Å. Not only does this series significantly extend the range of distances that has been previously accessible for experimental distance dependent PCET studies of synthetic model compounds, but it also greatly improves the isolation of dO•••N as a variable compared to earlier reports. Rates of PCET were determined by time-resolved optical spectroscopy with flash-quench generated [Ru(bpy)3]3+ and [Ru(dce)3]3+, where bpy = 2,2′-bipyridyl and dce = 4,4′-dicarboxyethylester-2,2′-bipyridyl. The rates increased as dO•••N decreased, as can be expected from a static proton tunneling model. An exponential attenuation of the PCET rate constant was found: kPCET(d) = kPCETexp[-β(d-d0)], with β ∼ 10 Å-1. The observed kinetic isotope effect (KIE = kH/kD) ranged from 1.2 to 1.4, where the KIE was observed to decrease slightly with increasing dO•••N. Both β and KIE values are significantly smaller than what is predicted by a static proton tunneling model. We conclude that vibrational compression of the tunneling distances, as well as higher vibronic transitions, that contribute to concerted proton coupled electron transfer must also be considered.

UR - http://www.scopus.com/inward/record.url?scp=85011961093&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85011961093&partnerID=8YFLogxK

U2 - 10.1021/jacs.6b12531

DO - 10.1021/jacs.6b12531

M3 - Article

AN - SCOPUS:85011961093

VL - 139

SP - 2090

EP - 2101

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 5

ER -