Chemistry Reference
In-Depth Information
Mg
Co
Ni
75
Mn
Zn
65
55
Cd
45
Cu
35
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
MOLES M
+2
/DNA (P)
Figure 1.1
Variation of
T
m
of solutions of DNA as a function of divalent metal ion concentra-
tion. (Reprinted with permission from
J. Am. Chem. Soc.
, 1968,
90
, 7327. Copyright 1968
American Chemical Society.)
stabilizing the double helix, whereas copper ions decrease
T
m
by binding to the bases
and destabilizing the double helix. Based on the metal-induced variation in
T
m
they
suggested that the relative metal affi nity to the phosphate backbone of DNA follows
the order Mg
2+
Cu
2+
.
This implies that the binding of an individual metal ion may involve phosphate
and base on the same molecule or form a linkage between two different nucleotides.
An example of the latter situation is the mononucleotide-metal ion binding pattern
observed for the Cu-(GMP) complex, where Cu
2+
ions are bridging the GMP ligands
through alternating N7-Cu-phosphate bonds (Figure 1.2).
4
When nucleobases are incorporated into a duplex DNA matrix, the affi nities
towards metal ions are modifi ed. It has been shown that several divalent metal ions,
like Mn
2+
, Cu
2+
and Pt
2+
prefer GC-rich regions, while Hg
2+
, for example prefer AT-
rich regions.
5,6
A more detailed picture indicates that metal binding to base residues
is sequence-dependent, i.e. not all guanines in a particular sequence show identical
affi nity towards a specifi c type of metal ion.
7 - 10
As a consequence, one may envisage
designing metal complexes that can bind selectively to chosen sequences of DNA.
>
Co
2+
>
Ni
2+
>
Mn
2+
>
Zn
2+
>
Cd
2+
>
