Chemistry Reference
In-Depth Information
ion. As an example, for the DNA- Cu
2+
complex a total electron transition of 0.2
quantum output is observed under UV irradiation.
31
Thus, H
+
, Cu
2+
, Cu
+
and Ag
+
can form inner-sphere interactions with DNA while the barrier mechanism is typical
for Mn
2+
, Co
2+
, Ni
2+
and Zn
2+
. Hence, we may conclude that ions such as Mn
2+
, Co
2+
,
Ni
2+
and Zn
2+
, as well as most of the Cu
2+
ions form outer-sphere complexes with
DNA. Experiments with Ni
2+
indicate that these ions prefer the GC/CG and CG/GC
type base pairs causing a red shift of the DNA absorption spectrum.
Infl uence of GC Composition
The infl uence of the DNA nucleotide composition on the ultraviolet difference
spectrum (UDS) of DNA-metal ion complexes has been investigated for Co
2+
, Ni
2+
,
Cu
2+
and Zn
2+
. Most attention has been paid to Ni
2+
and its interactions with DNA
of various origins:
Clostridium perfringens
(27% GC), mouse liver (C3HA line, 40%
GC), calf thymus (40% GC), salmon sperm (44% GC), herring sperm (44% GC),
E. coli
(51% GC),
Micrococcus luteus
(72% GC). In addition, interaction of
Ni
+2
with the oligonucleotides poly(dG-dC).poly(dG-dC), poly(dG).poly(dC) and
poly(dA-dT).poly(dA-dT) have been studied. These results are shown in Figure 2.6
where D
e
s
versus the GC percentage is plotted. The D
e
s
values are given for the rela-
tive concentration of 0.25 Ni
+2
per nucleotide unit. Analysis of the data for the
interaction of Ni
+2
with DNA shows preferential binding to GC pairs.
Ni
2+
-I nduced B
→
Z Transition in poly( d G - d C ) · poly( d G - d C ) Polynucleotide
Figure 2.7 presents the absorption spectra of poly(dG-dC)· poly(dG - dC) in the pres-
ence of 0.25% ethanol solution (10
− 2
M NaCl without (1) and with (2) Ni
2+
ions at
600
Ni
2+
Poly(dG-dC)Poly(dG-dC)
500
400
E.coli
Micrococus
luteus
300
Herring sperm
Salmon sperm
Calf thymus
200
Mice liver(C3HA line)
Poly(dG)poly(dC)
100
Cl.perfringers
Poly(dA-dT)Poly(dA-dT)
0
−
20
0
20
40
60
80
100
GC%
Figure 2.6
Infl uence of Ni
+2
on the UV spectra of various DNAs and polynucleotides. Graphi-
cal illustration of the dependence of the mole extinction (
∆
e
s
) on the percentage of GC pairs
present
