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(ii) The dynamic properties of DNA connected with big amplitude movements like
unwinding of the double helix and opening of base pairs determine the values
of the stability constants of DNA complexes with transition metal ions, as well
as the ranges of their variations.
(iii) UV spectroscopic manifestation of double proton transfer (DPT) in GC pairs
induced by H
+
ions and transition metal ions, and the mechanisms of this phe-
nomenon can be considered using a phenomenological quantum-mechanical
approach to assess the effect of environment change on electron confi guration
of atoms in molecules participating in H-bonds. This consideration takes into
account the specifi c energy of double-level H-bonds, and self-congruent transi-
tion of protons in cyclic structures. These structures form unifi ed electronic-
proton complementary molecular complexes between proton-donor and
proton-acceptor groups. The latter is an indispensable and satisfactory condi-
tion for keto-enol and amino-imino tautomeric transformations in solutions
of polar organic molecules.
(iv) A comparison of the Scatchard plot and the Klorz method for determining
stability constants, using, for example, the Pb
2+
/DNA interaction, shows that
the former method gives the best results.
The use of UV spectroscopy has demonstrated that Ni
2+
ions under relatively
mild conditions (25% ethanol, 0.75 Ni
2+
/DNA(P), 10
− 2
M NaCl) induce B
(v)
↔
Z
transitions in double-helical DNA.
(vi) A mechanism for point defect formation induced by metal ions, leading to
mutations of transition or deletion types in DNA, has been presented, using as
an example the interaction of Cu
2+
ions with DNA. It was shown that formation
of metal-induced wrong Watson-Crick base pairs via DPT in water solutions
requires energy within the range 0 (for Cu
+
) to 2.4 kcal mol
− 1
(for Mg
2+
) .
Acknowledgements
The authors express their gratitude to Prof. J. Monaselidze for useful discussions;
Dr M. Kharatishvili for providing the CD spectra of DNA; Dr I. Khutsishvili, Dr
E. Mchedlishvili and Dr Kh. Sologashvili for their active assistance in this work.
The work was partly supported by the grant number 2.29.04 of the Georgian
Academy of Sciences.
Abbreviations
ctDNA
Calf thymus DNA
CD
Circular dichroism
DPT
Double proton transfer
e
Molar extinction coeffi cient
D
e
s
= | D
e ( n
max
)| + | D
e ( n
min
)|
