Chemistry Reference
In-Depth Information
4.0
Ag
+
M-DNA 20
mM Na
+
3.5
Pb
2+
3.0
Cu
2+
Co
2+
2.5
Cd
2+
Ni
2+
2.0
y
=
−
1.31
−
0.85x;
Zn
2+
R 0.92
SD 0.05; N7; p < 0.0001;
Cr
3+
1.5
−
6.0
−
5.5
−
5.0
−
4.5
−
4.0
−
3.5
pK
2
Figure 2.4
Correlation between the covalence index
Xrand
−
log
K pK
=
for M-DNA
m
complexes
p
K
for Ni
2+
binding to different species is shown to increase with G-C content. The
empirical dependence of p
K
versus G-C content has been derived: p
K
= 1.96 + 0.07
(% G-C). The observed trend to form stronger complexes with increasing G-C
content may be due to the high probability of G-N7/Ni
2+
complex formation.
A linear correlation has been observed between log metal/poly d(GC), assessed
at the midpoint of the structural transition curve, and the covalent index
Xr
(
)
53,54
(
X
m
being the Pauling electronegativity and
r
the effective ionic radius
55
). The
authors propose that the mid-phase mole ratio is inversely proportional to the sta-
bility constant for the metal ion-polydeoxynucleotide interaction. Such dependence
between binding constants and
Xr
2
2
was also obtained in our case. The linear cor-
relation of p
K
(for complexes of metal-ctDNA) and the covalent index
Xr
2
pre-
sented in Figure 2.4 suggests that the covalent contributions to the overall interaction
energy are signifi cant and demonstrates the dynamic nature of metal- DNA interac-
tions (except in the case of Pb
2+
). These results are in good agreement with data in
references
53
and
54
.
2.2.3 UV Spectroscopic Study of Proton and Metal - DNA Interactions
Table 2.4 shows spectral changes of UV absorption spectra of ctDNA and that of
poly(dG - dC) · poly(dG-dC) caused by different ligands and macroscopic changes
of the surrounding medium. D
n in the table is calculated from the expression
D
n = D
e
s
/
K
, where D
e
s
= | D
e ( n
max
)| + | D
e ( n
min
)| is the total intensity of ultraviolet dif-
ference spectrum,
K
= | e
(1)
( n
max
)| + | e
(1)
( n
min
)|; e
(1)
is the fi rst derivative of e (
) func-
tion. D
n for d(pG) + d(pC) + H
3
O
+
(pH = 2), H
3
O
+
, Cu
+
and Ag
+
were determined
by absorption spectra of DNA complexes (more precisely this issue is observed in
reference
17
). Analyzing this acid bathochromic shift (the fi rst line in the table) and
ν
