1992 Fiscal Year Final Research Report Summary
The Structure-Reactivity Relationship in Heme Complexes. An Important Role of Rotational Orientations of Axial Ligands
| Project/Area Number |
03671034
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Physical pharmacy
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| Research Institution | Teikyo University |
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Principal Investigator |
SATO Mitsuo Fac.Pharm. Sci., Prof., 薬学部, 教授 (70101714)
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| Project Period (FY) |
1991 – 1992
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| Keywords | Low-spin Fe(III) heme complexes / Direction of low- symmetry field / Principal axes of g tensor / Principal axes of hyperfine tensor / ESR of low-spin Fe(III) complexes / Rotational orientation of axial ligands / Direction of maximum unpaired spin density |
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| Research Abstract |
Electron spin resonance (ESR) data for low-spin Fe(III) heme complexes are analyzed within the framework of low-symmetry (C_2) crystal field model. In the analysis, the effect of the rotational orientation angle (phi_*) of axial ligands is taken into consideration. Equations are derived which relate phi_* with the orientation angle of the rhombic field and those of the principal axes of g and hf tensors. The direction of the maximum unpaired spin density, derived from the wave functions of the Kramers doublets, is found approximately parallel to the direction of the low-symmetry field.
With these angular relations, ESR data previously reported for myoglobin azide (MbN_3) and those recently observed for model heme complexes, such as Fe(TPP)(OMe)_2^- and Fe(TPP)(OMe)(CN), are reevaluated and analyzed, respectively. It is found that the direction of the maximun unpaired spin density in MbN_3 is different from that reported previously. In model complexes, the angular analysis has enabled us to determine the relative orientations of g and hf tensors, the sign of g tensor determinant, and the low-symmetry crystal field parameters. The structure-reactivity relationship in heme complexes is discussed in the light of the angular relations and emphasis is placed to an important role of the axial ligand orientation.
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