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On the relative stability of tetragonal and trigonal Cu(II) complexes with relevance to the blue copper proteins

Olsson, Mats H M LU ; Ryde, Ulf LU ; Roos, Björn O. LU and Pierloot, Kristine (1998) In Journal of Biological Inorganic Chemistry 3(2). p.109-125
Abstract

The role of the cysteine thiolate ligand for the unusual copper coordination geometry in the blue copper proteins has been studied by comparing the electronic structure, geometry, and energetics of a number of small Cu(II) complexes. The geometries have been optimised with the density functional B3LYP method, and energies have been calculated by multi- configurational second-order perturbation theory (the CASPT2 method). Most small inorganic Cu(II) complexes assume a tetragonal geometry, where four ligands make σ bonds to a Cu 3d orbital. If a ligand lone-pair orbital instead forms a π bond to the copper ion, it formally occupies two ligand positions in a square coordination, and the structure becomes trigonal. Large, soft, and... (More)

The role of the cysteine thiolate ligand for the unusual copper coordination geometry in the blue copper proteins has been studied by comparing the electronic structure, geometry, and energetics of a number of small Cu(II) complexes. The geometries have been optimised with the density functional B3LYP method, and energies have been calculated by multi- configurational second-order perturbation theory (the CASPT2 method). Most small inorganic Cu(II) complexes assume a tetragonal geometry, where four ligands make σ bonds to a Cu 3d orbital. If a ligand lone-pair orbital instead forms a π bond to the copper ion, it formally occupies two ligand positions in a square coordination, and the structure becomes trigonal. Large, soft, and polarisable ligands, such as SH- and SeH-, give rise to covalent copper-ligand bonds and structures close to a tetrahedron, which might be trigonal or tetragonal with approximately the same stability. On the other hand, small and hard ligands, such as NH3, OH2, and OH-, give ionic bonds and flattened tetragonal structures. It is shown that axial type 1 (blue) copper proteins have a trigonal structure with a π bond to the cysteine sulphur atom, whereas rhombic type 1 and type 2 proteins have a tetragonal structure with σ bonds to all strong ligands. The soft cysteine ligand is essential for the stabilisation of a structure that is close to a tetrahedron (either trigonal or tetragonal), which ensures a low reorganisation energy during electron transfer.

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organization
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Contribution to journal
publication status
published
subject
keywords
Blue copper proteins, Copper thiolate, Quantum chemical calculations, Rhombic type 1 copper proteins, Trigonal copper complexes
in
Journal of Biological Inorganic Chemistry
volume
3
issue
2
pages
17 pages
publisher
Springer
external identifiers
  • scopus:0031944196
ISSN
0949-8257
DOI
10.1007/s007750050212
language
English
LU publication?
yes
id
0b233a2e-eaf0-4c5c-8a37-793d67dcf874
date added to LUP
2017-02-04 11:38:18
date last changed
2017-09-10 05:15:05
@article{0b233a2e-eaf0-4c5c-8a37-793d67dcf874,
  abstract     = {<p>The role of the cysteine thiolate ligand for the unusual copper coordination geometry in the blue copper proteins has been studied by comparing the electronic structure, geometry, and energetics of a number of small Cu(II) complexes. The geometries have been optimised with the density functional B3LYP method, and energies have been calculated by multi- configurational second-order perturbation theory (the CASPT2 method). Most small inorganic Cu(II) complexes assume a tetragonal geometry, where four ligands make σ bonds to a Cu 3d orbital. If a ligand lone-pair orbital instead forms a π bond to the copper ion, it formally occupies two ligand positions in a square coordination, and the structure becomes trigonal. Large, soft, and polarisable ligands, such as SH<sup>-</sup> and SeH<sup>-</sup>, give rise to covalent copper-ligand bonds and structures close to a tetrahedron, which might be trigonal or tetragonal with approximately the same stability. On the other hand, small and hard ligands, such as NH<sub>3</sub>, OH<sub>2</sub>, and OH<sup>-</sup>, give ionic bonds and flattened tetragonal structures. It is shown that axial type 1 (blue) copper proteins have a trigonal structure with a π bond to the cysteine sulphur atom, whereas rhombic type 1 and type 2 proteins have a tetragonal structure with σ bonds to all strong ligands. The soft cysteine ligand is essential for the stabilisation of a structure that is close to a tetrahedron (either trigonal or tetragonal), which ensures a low reorganisation energy during electron transfer.</p>},
  author       = {Olsson, Mats H M and Ryde, Ulf and Roos, Björn O. and Pierloot, Kristine},
  issn         = {0949-8257},
  keyword      = {Blue copper proteins,Copper thiolate,Quantum chemical calculations,Rhombic type 1 copper proteins,Trigonal copper complexes},
  language     = {eng},
  number       = {2},
  pages        = {109--125},
  publisher    = {Springer},
  series       = {Journal of Biological Inorganic Chemistry},
  title        = {On the relative stability of tetragonal and trigonal Cu(II) complexes with relevance to the blue copper proteins},
  url          = {http://dx.doi.org/10.1007/s007750050212},
  volume       = {3},
  year         = {1998},
}