Chemistry Reference
In-Depth Information
Table 2.4
Bathochromic shift (
u
) of UV absorption spectra of ctDNA and poly(dG-dC)·poly(dG-
dC) caused by different metal ions and H
3
O
+
∆
Ions
Bathochromic
shift of the
absorption band
(
Change of the
absorption
intensity (%)
Widening of the
absorption band
(cm
−
1
) and special
characteristics
DPT formation
energy in G-C
pair
U
(kcal mol
−
1
)
u
(cm
−
1
))
∆
d(pG) + d(pC) + H
3
O
+
∼
700
Insignifi cant
Insignifi cant
-
H
3
O
+
295
0.5
2.5
↓
Mg
2+
15
2.4
Mn
2+
65
1.4
Co
2+
110
1.1
Ni
2+
150
0.9
1.5
↓
Ni
2+
+ 40% ethanol
185
[
]
2
4
Ni
(
en
)(
H
2
)
75
Ni[(en)(NO
2
−
)(NCS
−
)]
0
35
Ni
2+
+ EtBr
180
Z-DNA poly(dG-
dC)·poly(dG-dC)
25% ethanol, 10
2
NaCl, (0.75 Ni
2+
/P)
∼
700
Cu
2+
190
140 (1/2h)
0.8
Cu
+
0
∼
700
7.4
↓
Zn
2+
85
1.3
Ag
+
500
10
1000 (2/3h)
0.2
∼
↓
taking into account absorption of adenine and thymine, the amount of which totals
60% in ctDNA, we can roughly accept that the joint effect of the shift from proto-
nation of guanine and cytosine is
∼
700 cm
− 1
per 1 mol of G - C pair.
Correlation Between
D
u
and K
e/aq
Interactions of aqua ions with the DNA double helix have a discrete nature due to
steric requirements characterized as inner-sphere, outer-sphere or double outer-
sphere interactions. The latter refers to interaction of hexa-aqua ions with the hydra-
tion layer of DNA. One may also take into account so-called ' atmospheric '
interactions which involve mobile adsorption within the effective diameter of DNA
depending on the ionic strength.
56
UV spectroscopy is a sensitive method for detec-
tion and registration of the mentioned interactions. As for thermodynamic methods,
they refl ect the integral characteristics of these interactions. That is why stability
constants (p
K
) are less dependent on G-C composition, ionic strength and the type
of ions. The soft structures of transition metal-DNA interactions are also caused by
the fact that each of the six water molecules surrounding the ions may exist in two
positions (two nonbonding pairs of electrons in the water molecule are localized on
the sp
3
hybrid orbitals of the oxygen and the distance between them is
~06Å
′
).
57
Thus, the water molecules located in a six-coordinated sphere of hydration can exist
in 2
6
different states.
