Chemistry Reference
In-Depth Information
Table 12.5.
Compilation of products and their
G
values (unit: 10
−
9
mol J
−
1
) in the radiolysis
of ss- and dsDNA in aqueous solution as determined by the GC-MS/SIM technique (Fuci-
arelli et al. 1990). For further data under air, see reference
N
2
N
2
O
N
2
O/O
2
Product
dsDNA
ssDNA
dsDNA
ssDNA
dsDNA
ssDNA
5,6-H
2
Thy
7.8
30.3
5.6
8.8
n.d.
n.d.
5OH5,6H
2
Thy
3.8
26.0
7.7
40.5
<0.1
<0.1
Tg
3.8
6.6
10.2
14.3
43.4
58.4
5OH5,6H
2
Cyt
2.0
5.4
2.6
7.4
<0.1
<0.1
Cg
2.6
13.3
10.7
16.3
25.6
32.2
FAPY-A
2.9
1. 3
8.7
3.1
5.9
4. 5
8-oxo-A
0.9
0.5
5.3
3.1
15.8
24.0
FAPY-G
6.8
1.6
12.4
4.1
3.6
4.9
8-oxo-G
<0.1
<0.1
16.2
7.5
46.7
70.5
Sum
31
87
79
105
141
195
Yield with respect to
•
OH
11%
31%
14 %
19 %
2 5 %
3 5 %
n.d., Not detectable
Under such conditions neither the Fo, 5HmU, 5ForU nor the hydantoin lesions
are formed. Thus, the fact that such compounds cannot be determined with
the given technique cannot serve as an 'excuse' for the poor material balance
of only 19% with respect to
•
OH. In model systems, dimers are major products
(Chap. 10.3). Applied to DNA, the formation of dimers would constitute either
an intra-strand or an inter-strand cross-link. This possibility has usually been
disregarded, since DNA being rod-like is not very f flexible. Radical-radical re-
combination could occur, however, at a distance, and from other polymers there
is evidence that intra-molecular reactions do occur also at a distance (Chap. 9.4).
The type of reaction that is envisaged here would form a small loop and would
not be connected with an increase in molecular weight. A DNA
DNA cross-link
that connects two DNA molecules, and thus increases the molecular weight, is a
much less likely reaction if other polymers are a good guide (Chap. 9.6).
It is noteworthy that some product yields do not change very much whether
the solutions were saturated with air or with N
2
O/O
2
, despite the fact that the
•
OH yield is halved in air-saturated solutions (cases in point are for ssDNA and
in the units of Table 12.5: Cg (37.9), Tg (43.4), 8-oxo-G (62.0); for further values
see Fuciarelli et al. 1990). Whether this means that O
2
•
−
that is an abundant and
freely diffusing radical under such conditions plays an important role in the
−
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