Chemistry Reference
In-Depth Information
10000
1600
1400
1200
1000
800
600
400
200
NO
3
-
ONOO
-
8000
NO
-
6000
NO
2
O
-
4000
0
200
250
300
350
400
450
NO
2
-
Wavelength (nm)
O
2
-
2000
ONOO
-
NO
-
NO
2
0
200
220
240
260
280
300
320
340
360
380
400
Wavelength (nm)
Figure 5.12.
Absorption spectra of the species potentially involved in oxidation by
peroxynitrite (adapted from Madsen et al. [131] with the permission of the American
Chemical Society). See color insert.
anion, NO
−
(aq), absorbs below 300 nm. Both
•
O
−
(aq) and
•
NO
2
have weak
absorptions (ε < 250/M/cm). Peroxynitrite ion has an absorption band at
302 nm (ε = 1670/M/cm). Peroxynitrous acid exhibits an absorption band at
240 nm (ε = 770/M/cm) with no significant absorption greater than 300 nm
[120, 144].
In biological systems, the diffusion-controlled reaction of
O
−
and
•
NO
has been suggested to be the most probable source of peroxynitrite (Eq. 5.36)
[143, 145]:
O
−
+
•
NO ONOO
→
−
.
(5.36)
2
Reaction (5.36) has been studied in aqueous solutions [143, 146-150].
Reported rate constants are in the range of (3.8−20.0) × 10
9
/M/s. The large
variation in rate constants was suggested to relate to the reaction studied
under irreversible conditions [150]. A study made under reversible conditions
at pH > 12 explained the dependence of the rate constant on the distance
between ONOO
−
particles (sites of generation of
O
−
and
•
NO) [150].
ONOO
−
can be synthesized by several methods [151-155]. The methods
include the reaction of ozone with azide, the reaction of hydrogen peroxide
and nitrite (or alkyl nitrite) under acidic conditions, the reaction of hydroxyl-
amine and oxygen in alkaline solution, and the mixed-phase reaction of solid
KO
2
with gaseous
•
NO. The pure peroxynitrite was synthesized by the reaction
of (Me
4
N)ONOO with
•
NO gas in liquid ammonia [155, 156].
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