Chemistry Reference
In-Depth Information
M O
n
+
(
)
+
•
NO M
→
n
+
1
+
NO
−
3
(5.22)
2
M O
n
+
(
)
+
•
NO M O NOO
→
n
+
1
(
=
−
)
(5.23)
2
2
•
NO e
+
2
−
(
from metal ions
)
+
2
H
+
→
N O H O
+
.
(5.24)
2
2
An example of reaction (5.22) is the rapid formation of Fe
III
OON=O from
the reaction of oxyheme (
Fe O
•−
) with
•
NO
(g)
, which then decomposes imme-
diately to form the
NO
−
anion [92]. A study on the binding of NO in Fe(II)
and Fe(III) heme proteins using spectroscopic and density functional theory
(dFT) calculations has recently been reported [99-103]. The structure, chemi-
cal properties, and biological action of dinitrosyl iron complexes have recently
been reviewed [104].
The half-life of
•
NO is determined by the concentration of oxygen [105].
The reaction between
•
NO and O
2
is more rapid within membranes than in
the surrounding aqueous medium [106]. Half-lives of
•
NO have been esti-
mated in the range of seconds to minutes [105].
•
NO is difficult to oxidize to
NO
+
(E°(NO
+
/
•
NO) = 1.2V). However, NO
−
is more easily formed, which is of
biological importance. Recently, the reaction between thiols,
•
NO, and O
2
has
been studied in detail
in vitro
[107]. Three pathways from the reaction, given
in Figure 5.11, were proposed for the formation of S-nitrosothiols and thiol
disulfides. These pathways were based on kinetic, stoichiometric, and scaven-
ger studies [108-113]. Pathway 1 involves the reaction of
•
NO and O
2
to yield
N
2
O
3
. Pathway 2 associated with the radical-radical combination of the
•
NO
III
2
Figure 5.11.
Proposed pathways of the reaction among gSH, NO, and oxygen (adapted
from Keszler et al. [107] with the permission of Elsevier Inc.). See color insert.
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