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A comparison of the inner-sphere reorganization energies of cytochromes, iron-sulphur clusters, and blue copper proteins

Sigfridsson, Emma; Olsson, Mats H. M. and Ryde, Ulf LU (2001) In The Journal of Physical Chemistry Part B 105(23). p.5546-5552
Abstract
Inner-sphere reorganization energies have been calculated for a number of models of six-coordinate iron porphyrins (with varying axial ligands), using the density functional B3LYP method. If the axial ligands are uncharged, the reorganization energy is very low, 5-9 kJ/mol. If one of the axial ligands is charged, the reorganization energy is higher, 20-47 kJ/mol, but such sites are normally not used in electron carriers. The former reorganization energies are appreciably smaller than what was found for blue copper proteins (62-90 kJ/mol), the dimeric CuA site in cytochrome c oxidase and nitrous oxide reductase (43 kJ/mol), and six different types of iron-sulfur clusters with one, two, or four iron atoms (40-75 kJ/mol), even if these vacuum... (More)
Inner-sphere reorganization energies have been calculated for a number of models of six-coordinate iron porphyrins (with varying axial ligands), using the density functional B3LYP method. If the axial ligands are uncharged, the reorganization energy is very low, 5-9 kJ/mol. If one of the axial ligands is charged, the reorganization energy is higher, 20-47 kJ/mol, but such sites are normally not used in electron carriers. The former reorganization energies are appreciably smaller than what was found for blue copper proteins (62-90 kJ/mol), the dimeric CuA site in cytochrome c oxidase and nitrous oxide reductase (43 kJ/mol), and six different types of iron-sulfur clusters with one, two, or four iron atoms (40-75 kJ/mol), even if these vacuum energies are typically halved inside the protein (as a result of hydrogen bonds and solvation effects). Therefore, the cytochromes seem to have the inherently lowest inner-sphere reorganization energy of the three commonly used electron carriers. All three types of sites have reduced the reorganization energy by using a delocalized charge and N- and S-donors (rather than O-donors) as metal ligands. Moreover, iron is a more appropriate metal for electron transfer than copper because Fe(II) and Fe(III) prefer the same coordination number and geometry and give bonds weaker than those of copper. The low-spin state of the cytochrome has a ∼20 kJ/mol lower reorganization energy than that of the corresponding high-spin site. Moreover, ring strain in the porphyrin reduce the changes in the Fe-NPor distances by 5 pm and therefore the reorganization energy by 8 kJ/mol. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part B
volume
105
issue
23
pages
5546 - 5552
publisher
The American Chemical Society
external identifiers
  • scopus:0035859440
ISSN
1520-5207
DOI
10.1021/jp0037403
language
English
LU publication?
yes
id
e6eb49bb-d36a-4e85-b517-325c62af34fc (old id 2275877)
date added to LUP
2012-01-04 11:11:24
date last changed
2018-05-29 09:27:21
@article{e6eb49bb-d36a-4e85-b517-325c62af34fc,
  abstract     = {Inner-sphere reorganization energies have been calculated for a number of models of six-coordinate iron porphyrins (with varying axial ligands), using the density functional B3LYP method. If the axial ligands are uncharged, the reorganization energy is very low, 5-9 kJ/mol. If one of the axial ligands is charged, the reorganization energy is higher, 20-47 kJ/mol, but such sites are normally not used in electron carriers. The former reorganization energies are appreciably smaller than what was found for blue copper proteins (62-90 kJ/mol), the dimeric CuA site in cytochrome c oxidase and nitrous oxide reductase (43 kJ/mol), and six different types of iron-sulfur clusters with one, two, or four iron atoms (40-75 kJ/mol), even if these vacuum energies are typically halved inside the protein (as a result of hydrogen bonds and solvation effects). Therefore, the cytochromes seem to have the inherently lowest inner-sphere reorganization energy of the three commonly used electron carriers. All three types of sites have reduced the reorganization energy by using a delocalized charge and N- and S-donors (rather than O-donors) as metal ligands. Moreover, iron is a more appropriate metal for electron transfer than copper because Fe(II) and Fe(III) prefer the same coordination number and geometry and give bonds weaker than those of copper. The low-spin state of the cytochrome has a ∼20 kJ/mol lower reorganization energy than that of the corresponding high-spin site. Moreover, ring strain in the porphyrin reduce the changes in the Fe-NPor distances by 5 pm and therefore the reorganization energy by 8 kJ/mol.},
  author       = {Sigfridsson, Emma and Olsson, Mats H. M. and Ryde, Ulf},
  issn         = {1520-5207},
  language     = {eng},
  number       = {23},
  pages        = {5546--5552},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {A comparison of the inner-sphere reorganization energies of cytochromes, iron-sulphur clusters, and blue copper proteins},
  url          = {http://dx.doi.org/10.1021/jp0037403},
  volume       = {105},
  year         = {2001},
}