Chemistry Reference
In-Depth Information
Cyt has no p
K
a
in the basic pH range below 12 (Table 10.1). A number of transfor-
mations at pH <11 were observed by pulse radiolysis (Hissung and von Sonntag
1978). In Cyt and 5MeCyt, there is an OH
−
-induced reaction (
k
= 1.4
10
8
dm
3
mol
−1
s
−1
) that is not observed with dCyd, indicating that the
N
(1)-H must be
involved in this reaction, but the rate of reaction is somewhat too slow for a de-
protonation at a heteroatom. EPR and product data that could shed some light
on these reactions are missing. It is, hence, premature to suggest mechanistic
details.
The
C
(4)-
•
OH-adduct of dGuo
has oxidizing properties (note the mesomer-
ic form with spin density at
O
(6)). It eliminates water yielding the even more
strongly oxidizing G
•
[reaction (77);
k
= 6
×
10
3
s
−1
in the absence of buffer; Can-
×
deias and Steenken 2000].
A similar reaction has been suggested for the of dAdo that gives rise to A
•
[reac-
tion (78);
k
= 1.9
10
4
s
−1
]. Again, the
C
(4)-
•
OH-adduct is less oxidizing than
A
•
and reacts with TMPD with 2.3
×
10
7
dm
3
mol
−1
s
−1
, while A
•
reacts with 2
×
×
10
9
dm
3
mol
−1
s
−1
(Vieira and Steenken 1990).
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