1994 Fiscal Year Final Research Report Summary
ESR Studies of Low-Spin Fe (III) Heme Complexes with Hydrogen-Bonded Axial Ligands. Deuterium Isotope Effect on the Principal g values
| Project/Area Number |
05671791
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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 Biophys.Div., Fac.Pharm.Sci., Teikyo University Prof., 薬学部, 教授 (70101714)
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| Co-Investigator(Kenkyū-buntansha) |
SATO Mitsuo Biophys.Div., Fac.Pharm.Sci., Teikyo University Prof. (70101714)
SATO Mitsuo Biophys.Div., Fac.Pharm.Sci., Teikyo University Prof. (70101714)
SATO Mitsuo Biophys.Div., Fac.Pharm.Sci., Teikyo University Prof. (70101714)
SATO Mitsuo Biophys.Div., Fac.Pharm.Sci., Teikyo University Prof. (70101714)
SATO Mitsuo Biophys.Div., Fac.Pharm.Sci., Teikyo University Prof. (70101714)
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| Project Period (FY) |
1993 – 1994
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| Keywords | ESR / Low-spin heme complex / ESR of low-spin heme complex / Deuterium isotope effect / Isotope effect on g value / Hydrogen-bonded axial ligand |
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| Research Abstract |
The deuterium isotope effect on ESR g values has been determined for the first time for low-spin Fe (III) heme complexes with hydrogen-bonded axial ligands. The ESR observations have been made on frozen solutions of Fe (TPP) (OMe-LOMe) _2^-in CH_2Cl_2-MeOL,where TPP is tetraphenylporphyrin dianion and L=H or D.The principal g avlues (g_X=1.9134, g_Y=2.1654, g_Z=2.4949 for L=H and g_X=1.9146, g_Y=2.1643, g_Z=2.4917 for L=D) are analyzed based on the low-symmetry crystal field model to show that both the d orbital energy splittings and the energies to the excited Kramers doublets are increased from the complex with L=H to the one with L=D by 10-30cm^<-1>. On the other hand, a quantum mechanical calculation using double-minimum potentials for O-L-o vibration has shown that the d orbital energy splittings as well as the excitation energies for L=D become greater in comparison with those for L=H in the case of a weaker L-bond in the electronic ground state than in the excited state, and vice versa. It is thus demonstrated that the L-bonding in Fe (TPP) (OMe-LOMe) _2^- is stronger in the excited states than in the ground state. Qualitatively, this finding is explained in terms of an increased electron density at the iron-bound oxygen atoms on electronic excitation. Such a change in the electron density is consistent with the prediction from the electronic structure generally accepted for low-spin Fe (III) heme complexes.
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