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Comparison of the chemical properties of iron and cobalt porphyrins and corrins.

Jensen, Kasper LU and Ryde, Ulf LU (2003) In ChemBioChem 4(5). p.413-424
Abstract
Density functional calculations have been used to compare various geometric, electronic and functional properties of iron and cobalt porphyrin (Por) and corrin (Cor) species. The investigation is focussed on octahedral MII/III complexes (where M is the metal) with two axial imidazole ligands (as a model of b and c type cytochromes) or with one imidazole and one methyl ligand (as a model of methylcobalamin). However, we have also studied some five-coordinate MII complexes with an imidazole ligand and four-coordinate MI/II complexes without any axial ligands as models of other intermediates in the reaction cycle of coenzyme B12. The central cavity of the corrin ring is smaller than that of porphine. We show that the cavity of corrin is close... (More)
Density functional calculations have been used to compare various geometric, electronic and functional properties of iron and cobalt porphyrin (Por) and corrin (Cor) species. The investigation is focussed on octahedral MII/III complexes (where M is the metal) with two axial imidazole ligands (as a model of b and c type cytochromes) or with one imidazole and one methyl ligand (as a model of methylcobalamin). However, we have also studied some five-coordinate MII complexes with an imidazole ligand and four-coordinate MI/II complexes without any axial ligands as models of other intermediates in the reaction cycle of coenzyme B12. The central cavity of the corrin ring is smaller than that of porphine. We show that the cavity of corrin is close to ideal for low-spin CoIII, CoII, and CoI with the axial ligands encountered in biology, whereas the cavity in porphine is better suited for intermediate-spin states. Therefore, the low-spin state of Co is strongly favoured in complexes with corrins, whereas there is a small energy difference between the various spin states in iron porphyrin species. There are no clear differences for the reduction potentials of the octahedral complexes, but [CoICor] is more easily formed (by at least 40 kJ mole-1) than [FeIPor]. Cobalt and corrin form a strong CoC bond that is more stable against hydrolysis than iron and porphine. Finally, FeII/III gives a much lower reorganisation energy than CoII/III; this is owing to the occupied dz2 orbital in CoII. Altogether, these results give some clues about how nature has chosen the tetrapyrrole rings and their central metal ion. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
ChemBioChem
volume
4
issue
5
pages
413 - 424
publisher
John Wiley & Sons
external identifiers
  • pmid:12740813
  • wos:000182962700006
  • scopus:0038702224
ISSN
1439-4227
DOI
10.1002/cbic.200200449
language
English
LU publication?
yes
id
d4901b40-44d9-418f-869e-91e2e80009ca (old id 128717)
date added to LUP
2007-07-17 10:56:34
date last changed
2018-05-29 10:30:13
@article{d4901b40-44d9-418f-869e-91e2e80009ca,
  abstract     = {Density functional calculations have been used to compare various geometric, electronic and functional properties of iron and cobalt porphyrin (Por) and corrin (Cor) species. The investigation is focussed on octahedral MII/III complexes (where M is the metal) with two axial imidazole ligands (as a model of b and c type cytochromes) or with one imidazole and one methyl ligand (as a model of methylcobalamin). However, we have also studied some five-coordinate MII complexes with an imidazole ligand and four-coordinate MI/II complexes without any axial ligands as models of other intermediates in the reaction cycle of coenzyme B12. The central cavity of the corrin ring is smaller than that of porphine. We show that the cavity of corrin is close to ideal for low-spin CoIII, CoII, and CoI with the axial ligands encountered in biology, whereas the cavity in porphine is better suited for intermediate-spin states. Therefore, the low-spin state of Co is strongly favoured in complexes with corrins, whereas there is a small energy difference between the various spin states in iron porphyrin species. There are no clear differences for the reduction potentials of the octahedral complexes, but [CoICor] is more easily formed (by at least 40 kJ mole-1) than [FeIPor]. Cobalt and corrin form a strong CoC bond that is more stable against hydrolysis than iron and porphine. Finally, FeII/III gives a much lower reorganisation energy than CoII/III; this is owing to the occupied dz2 orbital in CoII. Altogether, these results give some clues about how nature has chosen the tetrapyrrole rings and their central metal ion.},
  author       = {Jensen, Kasper and Ryde, Ulf},
  issn         = {1439-4227},
  language     = {eng},
  number       = {5},
  pages        = {413--424},
  publisher    = {John Wiley & Sons},
  series       = {ChemBioChem},
  title        = {Comparison of the chemical properties of iron and cobalt porphyrins and corrins.},
  url          = {http://dx.doi.org/10.1002/cbic.200200449},
  volume       = {4},
  year         = {2003},
}