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O2-binding to heme: electronic structure and spectrum of oxyheme, studied by multiconfigurational methods

Jensen, Kasper LU ; Roos, Björn LU and Ryde, Ulf LU (2005) In Journal of Inorganic Biochemistry 99(1). p.45-54
Abstract
We have studied the ground state of a realistic model of oxyheme with multiconfigurational second-order perturbation theory (CASPT2). Our results show that the ground-state electronic structure is strongly multiconfigurational in character. Thus, the wavefunction is a mixture of many different configurations, of which the three most important ones are approximately 1FeII–1O2 (70%), (12%) and 3FeII–3O2 (3%). Thus, the wavefunction is dominated by closed-shell configurations, as suggested by Pauling, whereas the Weiss configuration is not encountered among the 10 most important configurations. However, many other states are also important for this multiconfigurational wavefunction. Moreover, the traditional view is based on an oversimplified... (More)
We have studied the ground state of a realistic model of oxyheme with multiconfigurational second-order perturbation theory (CASPT2). Our results show that the ground-state electronic structure is strongly multiconfigurational in character. Thus, the wavefunction is a mixture of many different configurations, of which the three most important ones are approximately 1FeII–1O2 (70%), (12%) and 3FeII–3O2 (3%). Thus, the wavefunction is dominated by closed-shell configurations, as suggested by Pauling, whereas the Weiss configuration is not encountered among the 10 most important configurations. However, many other states are also important for this multiconfigurational wavefunction. Moreover, the traditional view is based on an oversimplified picture of the atomic-orbital contributions to the molecular orbitals. Thus, the population analysis indicates that all five iron orbitals are significantly occupied (by 0.5–2.0 electrons) and that the total occupation is most similar to the 3FeII–3O2 picture. The net charge on O2 is small, −0.20 e. Thus, it is quite meaningless to discuss which is the best valence-bond description of this inherently multiconfigurational system. Finally, we have calculated the eleven lowest ligand-field excited states of oxyheme and assigned the experimental spectrum of oxyhemoglobin with an average error of 0.24 eV. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Inorganic Biochemistry
volume
99
issue
1
pages
45 - 54
publisher
Elsevier
external identifiers
  • wos:000226555000005
  • pmid:15598490
  • scopus:10644293989
ISSN
1873-3344
DOI
10.1016/j.jinorgbio.2004.11.008
language
English
LU publication?
yes
id
65435948-25b7-486d-95f4-528ac154d372 (old id 141613)
date added to LUP
2007-07-17 11:04:24
date last changed
2017-09-10 04:37:25
@article{65435948-25b7-486d-95f4-528ac154d372,
  abstract     = {We have studied the ground state of a realistic model of oxyheme with multiconfigurational second-order perturbation theory (CASPT2). Our results show that the ground-state electronic structure is strongly multiconfigurational in character. Thus, the wavefunction is a mixture of many different configurations, of which the three most important ones are approximately 1FeII–1O2 (70%), (12%) and 3FeII–3O2 (3%). Thus, the wavefunction is dominated by closed-shell configurations, as suggested by Pauling, whereas the Weiss configuration is not encountered among the 10 most important configurations. However, many other states are also important for this multiconfigurational wavefunction. Moreover, the traditional view is based on an oversimplified picture of the atomic-orbital contributions to the molecular orbitals. Thus, the population analysis indicates that all five iron orbitals are significantly occupied (by 0.5–2.0 electrons) and that the total occupation is most similar to the 3FeII–3O2 picture. The net charge on O2 is small, −0.20 e. Thus, it is quite meaningless to discuss which is the best valence-bond description of this inherently multiconfigurational system. Finally, we have calculated the eleven lowest ligand-field excited states of oxyheme and assigned the experimental spectrum of oxyhemoglobin with an average error of 0.24 eV.},
  author       = {Jensen, Kasper and Roos, Björn and Ryde, Ulf},
  issn         = {1873-3344},
  language     = {eng},
  number       = {1},
  pages        = {45--54},
  publisher    = {Elsevier},
  series       = {Journal of Inorganic Biochemistry},
  title        = {O2-binding to heme: electronic structure and spectrum of oxyheme, studied by multiconfigurational methods},
  url          = {http://dx.doi.org/10.1016/j.jinorgbio.2004.11.008},
  volume       = {99},
  year         = {2005},
}