Chemistry Reference
In-Depth Information
Table 2 . 3.
Activation parameters for the decomposition of ONOOH and ONOO
−
. (Merényi
et al. 1999)
∆
H
#
/kcal mol
−
1
E
a
/kcal mol
−
1
A
/s
−
1
S
#
/eu
pH
∆
4
13
21.2
21.8
1
×
10
16
14
−11
21.1
21.7
8
×
10
10
1998) [for corresponding adducts to aldehydes and ketones and their reactions
see Meli et al. (1999); Merényi et al. (2002a,b)]. The peroxnitrite-CO
2
adduct is
only very short-lived [reaction (34); (lifetime <100 ns (Goldstein et al. 2002)],
and CO
3
•
−
and NO
2
•
[reaction (36)] besides CO
2
and NO
3
−
[reaction (35)] result
(Goldstein and Czapski 1999; Meli et al. 1999; Merényi et al. 1999). The activation
parameters for the decay of pernitrous acid and its anion are given in Table 2.3
(for a companison of the chemistries of peroxynitrites and peroxynitrates see
Goldstein et al. 2005).
It is worth mentioning that the reduction potential of peroxynitrite is esti-
mated at only 0.8 V, and many inorganic radicals, including CO
3
•
−
, readily oxi-
dize peroxynitrite (Goldstein et al. 1998) [reaction (43),
k
= 9.6
10
6
dm
3
mol
−
1
s
−1
]. The resulting ONOO
•
radical has been suggested to decompose into NO
•
(detected under oxidizing conditions) and O
2
[reaction (44)] (Mark et al. 1996).
×
CO
3
•
−
+ ONOO
−
CO
3
2−
+ ONOO
•
→
(43)
ONOO
•
→
NO
•
+ O
2
(44)
In the presence of tyrosine, 3,3
′
-bistyrosyl and 3-nitrotyrosine are formed [reac-
tions (45)
(51)], and the additional presence of CO
2
enhances their yield (Lymar
et al. 1999). Tyrosyl radicals are specifically formed by the CO
3
•
−
and the
•
NO
2
radicals [reaction (45); the latter reacting more slowly:
k
(
•
NO
2
) = 2.9
−
10
7
dm
3
×
mol
−1
s
−1
;
k
(CO
3
•
−
) = 2.9
10
8
dm
3
mol
−1
s
−1
] (Neta et al. 1988), and since the for
the nitration process a second
•
NO
2
radical is required [reaction (46)], the 3,3
×
-
bistyrosyl to 3-nitrotyrosine ratio strongly depends on the reaction conditions
(Lymar et al. 1999).
In analogy, the reaction of peroxynitrite with DNA results in a nitration of G
to 8-NO
2
-G and to its oxidation to 8-oxo-G (Yermilov et al. 1995, 1996). The pres-
ence of bicarbonate reduces peroxynitrite-mediated DNA strand breakage and
the formation of TBA-reactive material from Thd (Yermilov et al. 1996).
It has been suggested that the main reason for the toxicity of O
2
•
−
is its con-
version into peroxynitrite by NO
•
and the ensuing deleterious effects of this
compound as well as its CO
2
-adduct (Koppenol 1998a, 1999). This suggestion
has been challenged (Liochev and Fridovich 1999), and attention has been draw
to the ready reaction of O
2
•
−
with [4Fe-4S] clusters [
k
′
10
6
dm
3
mol
−1
s
−1
(Strohmeier Gort and Imlay 1998), which are estimated to reach concentrations
≈
3
×
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