Chemistry Reference
In-Depth Information
-200
-200
O
‡
ONOO
C
Diffusion
barrier
~4-8kJ/mol
-250
-250
O
-
Energy of
Homolysis
-3.3 kJ/mol
Energy of
Activation
50 kJ/mol
-300
-300
O
•
NO
2
-
CO
3
•-
•
NO
2
+ CO
3
•-
ONOO
-
+ CO
2
ONOO
C
O
-
-350
Free
radicals
-350
Cagod
radicals
Energy of
Reaction
9.7 kJ/mol
O
-400
-400
O
2
NO C
Energy of
isomerization
~179.9 kJ/mol
O
-
-450
-450
(ONOO
-
to NO
3
-
)
-500
-500
NO
3
-
+ CO
2
-550
-550
Reaction coordinate
Figure 5.14.
Standard gibbs energy diagram of the reaction of peroxynitrite with CO
2
showing the energies of reactive species (adapted from Squadrito and Pryor [185] with
the permission of the American Chemical Society).
(dTPA), and nitriloacetate (NTA) had significant reactivity with peroxynitrite
[217]. Peroxynitrite reacted with pyruvate with a second-order rate constant of
(8.8 ± 0.7) × 10
1
/M/s at pH 7.4 and 37°C [77]. Pyruvate was decarboxylated by
peroxynitrite at pH 7.4 and 5.5 through the formation of a carbon dioxide radical
anion [77]. The formation of radicals was also observed in the oxidation of thiols
by peroxynitrite [213].
In the reactions of peroxynitrite with dMS and dMSe, the rates were first
order with respect to the concentrations of both peroxynitrite and dMS (or
dMSe) [208]. The rate constants for dMS decreased from (2.1 ± 0.2) × 10
4
/M/s
to (2.3 ± 0.2) × 10
−1
/M/s in the pH range of 4.6-13.0 [208]. In the same pH
range, the rate constants for dMSe varied from (2.7 ± 0.3) × 10
4
/M/s to
(6.0 ± 0.5)/M/s. This indicates a higher reactivity of ONOOH than ONOO
−
with both dMA and dMSe. A partial replacement of water with ethanol
decreased the rate of the reaction of ONOO
−
but had no effect on the rate
of the reaction with ONOOH. Both species of peroxynitrite (ONOO
−
and
ONOOH) reacted with dMS (or dMSe) to yield
NO
−
and dMS=O (or
dMSe=O). The postulated mechanism involved the formation of a prereaction
complex, a radical pair ({(dMSOH)
•
. . .
•
(ONO)}), followed by O-O bond
cleavage in a rate-limiting step. Theoretical studies on the system also sup-
ported the postulated mechanism [218]. A recent study performed one-electron
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