Chemistry Reference
In-Depth Information
Table 2.2.
O
−
O BDEs in some peroxides. (Brusa et al. 2000)
BDE /kJ mol
−
1
Peroxide
H
2
O
2
210
±
2.5
Most organic hydroperoxides
201
±
8.5
HC(O)OOH
201
±
8.5
CF
3
C(O)OOH
205
±
8.5
S
2
O
8
2
−
120
±
11
ONOOH
92
±
8.5
ClOOCl
74. 5
±
8.5
is quite stable under such conditions. A compilation of some O
−
O BDEs is found
in Table 2.2.
Among the reactive peroxides, peroxynitrous acid, ONOOH and its anion,
peroxynitrite [p
K
a
(ONOOH) = 6.5-6.8 (Lögager and Sehested 1993; Goldstein
and Czapski 1995; Kissner et al. 1997)] play an important role in cellular sys-
tems, and their reactions must be discussed here in some detail.
Nitric oxide (NO
•
) is generated enzymatically from glutamate by the nitric
acid synthase and is responsible for a large number of diverse biological pro-
cesses (for a review, see Nathan 1992; for spin trapping of the ensuing radicals,
see Tsai et al. 2000). It was soon realized that an excess production of NO
•
is
toxic, and a part of its toxicity was attributed to its reaction with O
2
•
−
, i.e., the
formation of peroxynitrite [reactions (30) and (31)] (Beckman et al. 1990; for a
review, see Murphy et al. 1998).
NO
•
+ O
2
•
−
ONOO
−
→
(30)
NO
•
+ HO
2
•
→
ONOOH
(31)
For studying the chemistry of peroxynitrite in vitro, it may be prepared by react-
ing nitrous acid with H
2
O
2
and subsequent rapid alkaninization (Hughes and
Nicklin 1968) but also nitrite-free by ozonation of azide (Gleu and Roell 1929;
Pryor et al. 1995) or from
S
-nitrosothiols with H
2
O
2
(Coupe and Williams 1999).
It also accumulates to substantial concentration upon the UV-photolysis of the
nitrate ion in basic solution (Barat et al. 1969; Wagner et al. 1980; Mark et al.
1996) and is a product when air-saturated water is subjected to ultrasound (Mark
et al. 2000). It may be detected by its absorption at 302 nm (Kissner et al. 1999).
The rate of reaction (30) is close to diffusion controlled [
k
= 6.7
10
9
dm
3
×
mol
−1
s
−1
(Huie Padmaja 1993); 4.3
10
9
dm
3
mol
−1
s
−1
(Goldstein and Czapski
×
10
9
dm
3
mol
−1
s
−1
(Kobayashi et al. 1995); 1.9
10
9
dm
3
mol
−1
s
−1
1995), 3.8
×
×
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