Chemistry Reference
In-Depth Information
MbFe O
II
+
•
NO
→
MbFe OONO
III
(5.28)
2
2
2
III
V
−
(5.29)
MbFe OONO
→
MbFe
=
O NO
+
2
3
MbFe
V
= →
O MbFe
•
IV
=
O
(5.30)
•
IV
II
IV
III
2
(5.31)
MbFe
=
O MbFe O H O MbFe
+
+
→
=
O MbFe OH O
+
+
2
2
2
MbFe
IV
=
O MbFe O H O H
+
II
+
+
2
+
→
2
MbFe OH O
III
+
.
(5.32)
2
2
2
2
The reaction of MbFe
II
O
2
with
•
NO
2
yielded MbFe
III
OONO
2
(
k
28
=
4.5 ± 0.3 × 10
7
/M/s; pH 7.4), which rapidly transformed to perferryl species
(MbFe
V
=O) and
NO
−
through heterolysis along the O-O bond (reaction 5.29).
The perferryl species converted rapidly to the ferryl species with a radical site
on the globin (reaction 5.30), which oxidizes another oxymyoglobin to form
equal amounts of ferrylmyoglobin and metmyoglobin (reaction 5.31;
10
4
/M/s <
k
31
< 10
7
/M/s). At a longer timescale of minutes, a slow buildup of
ferrylmyoglobin from the comproportionation of ferryl species with oxymyo-
globin occurred (reaction 5.32;
k
32
= (2.13 ± 0.53) × 10
1
/M/s). Overall, three
oxymyoglobin molecules converted to metmyoglobin, consumed by each
•
NO
2
radical.
The intermediate, MbFe
III
OONO
2
species, produced in reaction (5.28),
was also observed in the reaction of peroxynitrite with metmyoglobin
(
k
= (4.6 ± 0.3) × 10
4
/M/s). The chemistry and reactions of peroxynitrite with
biological molecules are discussed in the next section. The ferryl species could
also be reduced by
•
NO
2
to yield transient species, MbFe
III
ONO
2
(
k
33
= (1.2 ± 0.2) × 10
7
/M/s), which dissociated into metmyoglobin and nitrate
(
k
34
= (1.9 ± 0.2) × 10
2
/M/s) [125]:
IV
•
III
2
(5.33)
MbFe
=
O NO
+
→
MbFe ONO
2
III
−
III
−
.
MbFe ONO OH
+
→
MbFe OH NO
+
(5.34)
2
3
5.2.3 Peroxynitrite
5.2.3.1 Generation.
Numerous studies have been performed to suggest the
formation of ONOO
−
through photochemical and biological systems [131-
134]. Photolysis of the aqueous nitrate ion in the UV region produces ONOO
−
(Eq. 5.35) [131, 135-139]. A spectrum of
NO
−
exhibits peaks at 200 nm
(ε = 9900/M/cm) (Fig. 5.12) [131]. With the excitation of the π → π* band, the
nitrate ion can isomerize to peroxynitrite (Eq. 5.35) [140-143]:
−
−
NO
+ →
h
ν
ONOO
.
(5.35)
3
The spectra of other nitrogen and oxygen species involved in the photody-
namics are also depicted in Figure 5.12. Absorption of
•
NO is weak, while its
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