Single-crystal EPR of the oxygen-17-enriched dioxygen adduct of vitamin B12r: reversible oxygen bonding, electronic and geometric structure and molecular dynamics

Joerin, E.; Schweiger, A.; Guenthard, Hs. H.

doi:10.1021/ja00351a027

Cited by 34 publications

(32 citation statements)

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“…17O-substitution experiments on B, ZrOZ' [33] determined a significant spin density in the oxygen AO's of the same symmetry as the la MO in our notation and supports this case. Such a characteristic will markedly affect the 59 Co hf contributions.…”

Section: The Electronic Structure Of Co(iii)oep -Py •Oz'supporting

confidence: 79%

“…However, oxygenation is no problem since the 0 2 molecule is very small. an sp2 hybridized lone pair and may be contrasted to the axial Co-N situation found in vitamin B, Z , [ 33], where a value of 0.63 is determined. (These authors neglect to mention whether a correction for the cobalt spin-density contribution was included.)…”

Section: Ligand Nitrogen Endormentioning

confidence: 99%

“…The parameter values required to get the best overall fit to the experimental data are presented in the bottom half of Table 4 in the superoxo complex section. For comparison purposes, and to demonstrate the wider application of this approach to other superoxo Co(III) • Oz ' complexes, a complementary analysis with data for vitamin B 12r [68] and vitamin B 12rO2' [33] is presented in Table 4.…”

Section: The Electronic Structure Of Co(iii)oep -Py •Oz'mentioning

confidence: 99%

“…Although "O experiments were beyond the scope of this work, the study by Jorin et al [33], used as the second example for our analysis (see Table 4), reported the determination of the "O hf tensors for both oxygen atoms. For B I2rOz' we also estimate a positive spin density for both the ma and 7e oxygen orbitals.…”

Section: The Electronic Structure Of Co(iii)oep -Py •Oz'mentioning

confidence: 99%

“…Superhyperfine (shf) structure from the ligand nuclei can rarely be resolved, since they are usually obscured by the large linewidths met in the powder-type EPR spectra of paramagnetic metal complexes. An exception are "O hfc's in appropriately labeled dioxygen complexes [26,32,33]. In most of the other cases, cw and pulsed electron-nuclear double resonance (ENDOR) spectroscopy are the methods of choice to additionally resolve the interaction of the paramagnetic metal ion with its surrounding magnetic nuclei having nuclear spins I >_ 1/2.…”

Section: Introductionmentioning

confidence: 99%

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Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

2001

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Octaethylporphyrinato-cobalt(II), Co(II)OEP, was studied by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) in frozen solutions of methanol, tetrahydrofuran and pyridine diluted into chloroform. Oxygenation led to the respective paramagnetic superoxo complexes Co(III)OEP • py • O. The EPR spectra demonstrate strong differences in the axial ligation states ((base-on)/(base-off)) and ease of the oxygenation process. Additional ENDOR studies with partial orientation selection along the principal g tensor axes are performed for resolution of the 'H, 4115N and 59 Co hyperfine coupling constants. This allows a comparison of the electron spin density distribution of the superoxo complex and its precursor. The data are interpreted in the framework of a more rigorous and detailed theoretical configuration interaction model than previously presented in the literature. The theoretical treatment shows that the structure of the superoxo complex is best described in a three-orbital model with contributions from the cobalt 3d, 4s, and oxygen it orbitals. The analysis reproduces the experimental g and Co hyperfine data yielding the relative energies of the MO's and the MO coefficients for the description of the spin density distribution in the Co(II) complex and its superoxo complex. To demonstrate the generality of the approach and possible applications, a comparison is made with the vitamin B, 2 , system. Furthermore, it provides detailed insight into the electronic and geometric changes resulting from axial ligation and oxygenation of the Co(II)OEP complex; this information can be used for predictions of the catalytic activity.

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Section: The Electronic Structure Of Co(iii)oep -Py •Oz'supporting

confidence: 79%

Section: Ligand Nitrogen Endormentioning

confidence: 99%

Section: The Electronic Structure Of Co(iii)oep -Py •Oz'mentioning

confidence: 99%

Section: The Electronic Structure Of Co(iii)oep -Py •Oz'mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

2001

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ChemInform Abstract: SINGLE‐CRYSTAL EPR OF THE OXYGEN‐17‐ENRICHED DIOXYGEN ADDUCT OF VITAMIN B12R: REVERSIBLE OXYGEN BONDING, ELECTRONIC AND GEOMETRIC STRUCTURE AND MOLECULAR DYNAMICS

Joerin¹,

Schweiger²,

Guenthard³

1983

Chemischer Informationsdienst

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Thermodynamic trans‐Effects of the Nucleotide Base in the B₁₂ Coenzymes

Kräutler

1987

Helvetica Chimica Acta

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The thermodynamic effects of the nucleotide coordination on the Co‐C bond strengths in the B12 coenzymes were analyzed. Methyl group transfer reactions from methylcob(III)inamides to cob(II)inamides and cob(I)inamides in neutral aqueous solution were used in equilibration experiments to determine the effect fo the intramolecular coordination of the nucleotide function on the Co‐C bond dissociation energies of methylcob(III)alamin (4). In the equilibrium between 4, cob(I)inamide (11), cob(I)alamin (10) and methylcob(III)inamide 6 (Scheme 2), 4 and 11 were found to predominate (4+11⇆10+6, equilibrium constant KI/III≈0.004), while the equilibrium between 4, cob(II)inamide 9, cob(II)alamin (5), and 6 (Scheme 1) proved to be well balanced (4+9⇄5+6, equilibrium constant KII/III=0.60). These equilibrium values indicate the nucleotide coordination to stabilize the Co–C bond in 4 both against homolysis (slight effect) and against nucleophilic heterolysis (considerable effect). They reflect a stabilization of the complete corrins 4 and 5by the nucleotide coordination, which is also indicated for 4 and 5 by their (nucleotide) basicity. The latter information, where available for other organocobalamins, allows the analysis of the thermodynamicnucleotide trans effect there as well: e.g. in coenzyme B12 (1), the nucleotide coordination is found this way to weaken the Co–C bond towards homolysis by ca. 0.7 kcal/mol.

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Single-crystal EPR of the oxygen-17-enriched dioxygen adduct of vitamin B12r: reversible oxygen bonding, electronic and geometric structure and molecular dynamics

Cited by 34 publications

References 1 publication

Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

ChemInform Abstract: SINGLE‐CRYSTAL EPR OF THE OXYGEN‐17‐ENRICHED DIOXYGEN ADDUCT OF VITAMIN B12R: REVERSIBLE OXYGEN BONDING, ELECTRONIC AND GEOMETRIC STRUCTURE AND MOLECULAR DYNAMICS

Thermodynamic trans‐Effects of the Nucleotide Base in the B₁₂ Coenzymes

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Single-crystal EPR of the oxygen-17-enriched dioxygen adduct of vitamin B12r: reversible oxygen bonding, electronic and geometric structure and molecular dynamics

Cited by 34 publications

References 1 publication

Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

ChemInform Abstract: SINGLE‐CRYSTAL EPR OF THE OXYGEN‐17‐ENRICHED DIOXYGEN ADDUCT OF VITAMIN B12R: REVERSIBLE OXYGEN BONDING, ELECTRONIC AND GEOMETRIC STRUCTURE AND MOLECULAR DYNAMICS

Thermodynamic trans‐Effects of the Nucleotide Base in the B12 Coenzymes

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Thermodynamic trans‐Effects of the Nucleotide Base in the B₁₂ Coenzymes