title: Cob(II)alamin: Relativistic DFT Analysis of the EPR Parameters.
abstract: Relativistic density functional theory (DFT) has been applied to explore electron paramagnetic resonance (EPR) parameters as well as ground-state spin properties of cob(II)alamin. Cob(II)alamin is an intermediate which participates in many reactions catalyzed by derivatives of vitamin B12 and that can be detected by EPR spectroscopy due to the presence of the paramagnetic Co(II)(d(7)) center. The full structure of cob(II)alamin and its truncated analogues were examined. Three different DFT functionals, B3LYP, BP86, and PBE, have been applied to obtain the g- and A-tensors. Both tensors are axially symmetric and can provide useful insight into specific axial ligand interactions. Of the functionals tested, the hybrid B3LYP functional, was found to overestimate the axial bond length, whereas the GGA-type functionals, BP86 and PBE, produced geometries consistent with experimental data. The reliability of nonrelativistic and approximate relativistic methods for the calculation of EPR parameters has also been tested against a fully relativistic four-component approach. Since the EPR parameters are very sensitive to the local environment surrounding Co(II), a theoretical (DFT-BP86) estimate of the dependence of the g- and A-tensors on the metal-to-axial ligand interatomic distance can be directly correlated with EPR measurements. The usefulness of such an approach has been demonstrated for the methionine synthase enzyme where the reduction of cob(II)alamin takes place during the reactivation cycle.
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, UiT The Arctic University of Norway , 9037 Tromsø, Norway.|Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Taye B
authors.initials: TB
authors.lastname: Demissie
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, UiT The Arctic University of Norway , 9037 Tromsø, Norway.
authors.forename: Michal
authors.initials: M
authors.lastname: Repisky
authors.affiliation: Department of Chemistry, University of Louisville , 2320 South Brook Street, Louisville, Kentucky 40292, United States.
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, UiT The Arctic University of Norway , 9037 Tromsø, Norway.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Ruud
authors.affiliation: Department of Chemistry, University of Louisville , 2320 South Brook Street, Louisville, Kentucky 40292, United States.
authors.forename: Pawel M
authors.initials: PM
authors.lastname: Kozlowski