Chemistry Reference
In-Depth Information
Table 2.3
Binding constants of metal ions with ctDNA (20 mM Na
+
).
Metal ions
Cr
3+
Co
2+
Ni
2+
Cu
2+
Zn
2+
Ag
+
Cd
2+
Pb
2+
Log
K
3.85
4.3
4.64
5.1
4.2
5.84
4.1
4.25
Ag
+
Pb
2+
1.0
Cu
2+
0.9
Ni
2+
Co
2+
−
Cr
3+
0.8
Zn
2+
Cd
2+
H
+
0.7
0.6
Mg
2+
0.5
ϕ
0.4
M-DNA
0.3
−
3.0
−
2.5
−
2.0
−
1.5
−
1.0
−
Log[Na(1)]
Figure 2.2
Effi cacy of Na
+
concentration on the stability constants (log
K
) for ctDNA com-
plexes with Mg
2+
43
Co
2+
, Ni
2+
, Cu
2+
, Zn
2+
, Cd
2+
, Pb
2+
, Cr
3+
, Ag
+
and
, which is the electrostatic
potential of a cylindrical polyion surface (
r
= 1 nm) obtained from the Poisson-Boltzman
equation
44
reduced to unity
ϕ
dynamics. For example, the difference in p
K
between Co
2+
and Cu
2+
binding to
ctDNA is only 0.8 (Table 2.3) compared to the much larger differences for binding
of Co
2+
and Cu
2+
to bidentate ligands like NH
2
CH
2
CO
2−
and ethylendiamine (en)
where the p
K
varies from 4.6 to 8.6 and from 6 to 11, respectively.
46
Thus, when
M
2+
ions interact with DNA, the dynamic properties of DNA connected with big
amplitude movements, e.g. unwinding the double helix and opening of base pairs,
determine to a large extent the stability constants for complex formation.
Effect of Ionic Strength
Figure 2.2 is a graphic representation showing how p
K
varies with ionic strength for
H
+
and metal ions (Cr
3+
, Co
2+
, Ni
2+
, Cu
2+
, Zn
2+
, Ag
+
, Cd
2+
, Pb
2+
) binding to DNA. An
NaCl salt solution was used for all metal ions except Ag
+
and Pb
2+
where NaNO
3
was used. For Mg
2+
the binding constants with poly(A-U) are given in reference.
47
