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Proton-Coupled Electron Transfer from Tyrosine in a Tyrosine-Ruthenium-tris-Bipyridine Complex: Comparison with TyrosineZ Oxidation in Photosystem II

Sjödin, Martin; Styring, Stenbjörn LU ; Åkermark, Björn; Sun, Licheng and Hammarström, Leif (2000) In Journal of the American Chemical Society 122(16). p.3932-3936
Abstract
The pH- and the temperature dependence of the rate constant for electron transfer from tyrosine to ruthenium in Ru(II)(bpy)2(4-Me-4'CONH-L-tyrosine etyl ester-2,2'-bpy) 2PF6 was investigated using flash photolysis. At a pH below the tyrosine pKa 10 the rate constant increased monotonically with pH. This increase was consistent with a concerted electron transfer/deprotonation mechanism. Also indicative of a concerted reaction was the unusually high reorganization energy, 2 eV, extracted from temperature-dependent measurements. Deprotonation of the tyrosine group, at pH > pKa, resulted in a 100-fold increase in rate constant due to a decreased reorganization energy, λ = 0.9 eV. Also, the rate constant became independent of pH. In... (More)
The pH- and the temperature dependence of the rate constant for electron transfer from tyrosine to ruthenium in Ru(II)(bpy)2(4-Me-4'CONH-L-tyrosine etyl ester-2,2'-bpy) 2PF6 was investigated using flash photolysis. At a pH below the tyrosine pKa 10 the rate constant increased monotonically with pH. This increase was consistent with a concerted electron transfer/deprotonation mechanism. Also indicative of a concerted reaction was the unusually high reorganization energy, 2 eV, extracted from temperature-dependent measurements. Deprotonation of the tyrosine group, at pH > pKa, resulted in a 100-fold increase in rate constant due to a decreased reorganization energy, λ = 0.9 eV. Also, the rate constant became independent of pH. In Mn-depleted photosystem II a similar pH dependence has been found for electron transfer from tyrosineZ (TyrZ) to the oxidized primary donor P680+. On the basis of the kinetic similarities we propose that the mechanisms in the two systems are the same, that is, the electron transfer occurs as a concerted proton-coupled electron-transfer reaction, and at pH < 7 the TyrZ proton is released directly to the bulk water. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of the American Chemical Society
volume
122
issue
16
pages
3932 - 3936
publisher
The American Chemical Society
external identifiers
  • scopus:0038025025
ISSN
1520-5126
DOI
10.1021/ja993044k
language
English
LU publication?
yes
id
c923ac7f-3a26-4ad1-89dd-3a4715db4b85 (old id 125170)
date added to LUP
2007-07-06 15:25:02
date last changed
2017-07-23 04:50:11
@article{c923ac7f-3a26-4ad1-89dd-3a4715db4b85,
  abstract     = {The pH- and the temperature dependence of the rate constant for electron transfer from tyrosine to ruthenium in Ru(II)(bpy)2(4-Me-4'CONH-L-tyrosine etyl ester-2,2'-bpy) 2PF6 was investigated using flash photolysis. At a pH below the tyrosine pKa 10 the rate constant increased monotonically with pH. This increase was consistent with a concerted electron transfer/deprotonation mechanism. Also indicative of a concerted reaction was the unusually high reorganization energy, 2 eV, extracted from temperature-dependent measurements. Deprotonation of the tyrosine group, at pH &gt; pKa, resulted in a 100-fold increase in rate constant due to a decreased reorganization energy, λ = 0.9 eV. Also, the rate constant became independent of pH. In Mn-depleted photosystem II a similar pH dependence has been found for electron transfer from tyrosineZ (TyrZ) to the oxidized primary donor P680+. On the basis of the kinetic similarities we propose that the mechanisms in the two systems are the same, that is, the electron transfer occurs as a concerted proton-coupled electron-transfer reaction, and at pH &lt; 7 the TyrZ proton is released directly to the bulk water.},
  author       = {Sjödin, Martin and Styring, Stenbjörn and Åkermark, Björn and Sun, Licheng and Hammarström, Leif},
  issn         = {1520-5126},
  language     = {eng},
  number       = {16},
  pages        = {3932--3936},
  publisher    = {The American Chemical Society},
  series       = {Journal of the American Chemical Society},
  title        = {Proton-Coupled Electron Transfer from Tyrosine in a Tyrosine-Ruthenium-tris-Bipyridine Complex: Comparison with TyrosineZ Oxidation in Photosystem II},
  url          = {http://dx.doi.org/10.1021/ja993044k},
  volume       = {122},
  year         = {2000},
}