BIOINORGANIC CHEMISTRY A Short Course Second Edition

CYTOCHROME P450 : A MONOOXYGENASE 377

Figure 7.21 (A) Formation of the [Fe IV = O(TMP + • )] + complex using the TMP ligand.
(B) Molecular orbital diagram describing bonding in the [Fe IV = O(TMP + • )] + complex.
(Adapted with permission from Scheme 4 and Figure 2 of reference 68. Copyright 1997,
Society of Biological Inorganic Chemistry.)

H 3 C

H 3 C

CH 3

H

H

meta-proton

meta-proton

mesityl substituent on porphyrin

N

N

N

N

Mes

Mes

Mes

Mes FeIII

[FeIII(TMP)]+

N

N N

N

Mes

Mes

Mes

FeIV

O

X

Mes

[FeIV(TMP+.)(O)(X)]

Fe4+ O2-

pz px py

dxy

non-bonding

dxz dyz

d-x 2

dz 2

y^2

O 3 N 2

A

B

1 -X in Gross, Z., Nimri, S., Barzilay,

C.M., Simkhovich, L. J. Biol. Inorg.

Chem. 1997, 2, 492-506.

• 78o C

one 2c-2e σ-bond (pz-dz 2 ) and two 2c-3e π-bonds (px-dxz, py-dyz), bond order = 2

EXAFS data indicated an Fe = O bond length of 1.65 ± 0.05 Å , similar to that
found for compound I intermediates in several enzymes such as catalases,
horseradish peroxidase, cytochrome c peroxidase, and chloroperoxidases.
Studies by other researchers showed that substituents on the porphyrin
ligand affected formation of the [Fe IV = O(P + • )] + radical. Electron - defi cient