22-3
Reactions of O2 with Fe(II) Porphyrin Complexes
289
Figure 22-2: Cytochrome c oxidase catalysis of
2
2
4H 4e O
2H O
  

.
A similar type of electronic mechanism can also be formulated for the cytochrome c oxidase catalysis of the reaction
2
2
4H 4e O
2H O

 

. With some
modifications, we shall follow the mechanism proposed by Reed and Landrum
9
.
On reduction of Fe(III) and Cu(II) to Fe(II) and Cu(I), the Fe(II) can bind
ground-state 2
O to form an
2
Fe(II)O complex with “increased-valence” structure
(2) of Fig. 22-2. Cu(I) with a
9
1
3d 4s configuration can then bind to the
2
Fe(II)O
complex to form the proposed “μ-peroxo dimer”
9 , with “increased-valence” structure (3) (cf. structure (a) of Fig. 22-1 for the
2
Fe(II)O Fe(II) complex). In structure
(3), the antibonding π* electrons of 2
O are spin-paired with an unpaired electron
for each of the S = 1 spin-states for Fe(II) and Cu(I). Electronic reorganization can
then proceed as is shown in structure (3) to increase the number of bonding