Chemistry Reference
In-Depth Information
Table 2 . 4.
In vivo interception of peroxynitrite. (Arteel et al. 1999)
Reactant
In vivo
concentration
(mol dm
−
3
)
Rate constant
(dm
3
mol
−
1
s
−
1
)
Rate of dis-
appearance
(s
−
1
)
Spontaneous decay
−
−
0.4
10
−
3
3
×
10
4
Carbon dioxide
1
30
×
10
−
2
5.8
×
10
2
Glutathione
1
5.8
×
10
−
2
Ascorbate
1
50
0.5
×
10
−
4
4.8
×
10
6
Myeloperoxidase
2400
5
×
10
−
6
8
×
10
6
Glutathione peroxidase
16
2
×
10
−
3
2.5
×
10
4
Hemoglobin
125
5
×
10
−
4
10
3
Albumin
5.6
×
3.4
6
×
50 dm
3
mol
−1
cm
−1
(Mark et al. 1990)], and in
order to compete with other solutes present effectively for the incident photons,
high concentrations of peroxides have to be added. This situation may change,
when aromatic peroxides are used for the generation of the free radicals. In certain
cases, the decomposition of peroxides can also be photosensitized using carbonyl
compounds such as acetone (Behrens, private communication).
The oxyl radicals resulting from the decomposition of organic peroxides are
energy-rich intermediates and undergo a number of rapid reactions (Chap. 7).
Here, it is brief ly recalled that the tertiary oxyl radicals undergo facile
20 dm
3
mol
−1
cm
−1
,
≈
ε
(240 nm)
≈
-frag-
mentation [reaction (52)], and the primary and secondary oxyl radicals an
equally fast water-assisted 1,2-H shift [reaction (53)].
β
R
3
CO
•
→
•
R + R
2
C=O
(52)
HR
2
CO
•
→
•
C(OH)R
2
(53)
Since reactions (52) and (53) are very fast, oxyl radicals are unlikely to react with
substrates unless they are generated in their very close vicinity. For example, the
perester shown below yields tertiary butoxyl radicals upon photolysis, but their
efficiency to degrade dGuo is very low (Adam et al. 1998b). Most of the observed
degradation of dGuo is due to reactions of the ensuing methylperoxyl radicals
that are formed in the presence of O
2
(Adam et al. 2002), and in DNA only G is
oxidized (Mahler et al. 2001). DNA strand breakage, caused by a H-abstraction
from the sugar moiety (Chap. 12) is only induced by the photolysis of the per-
ester which binds electrostatically to DNA (Adam et al. 1998b).
Search WWH ::
Custom Search