Supramolecular Chemistry of Metal – Nucleobase Complexes - Metal Complex-DNA Interactions - page 123

Figure 4.42 Preferred base-pairing schemes for M-DNA in which imino protons of T and G
are replaced by metal cations
Figure 4.43 Scheme of the proposed structure of M-DNA
terization of M-DNA is again controversial. Thus, while Rakitin et al. reported
metallic-like conduction in a 15 mm long bundle of M-DNA, 70 recent new direct
atomic force microscope measurements show that in spite of the DNA length being
greatly reduced when M-DNA is formed, the conductivity is not enhanced. 71 Prob-
ably, these results are related to the low stability of the M-DNA structure, as men-
tioned above.
In order to understand the experimental results of the electronic properties
of M-DNA, several theoretical calculations have been performed. Di Felice et al.
found that Zn(II) does not effi ciently hybridize with the HOMO orbital of the
native G-C pair, and suggested that the model proposed by Lee should be consid-
ered with caution. 72 DFT calculations carried out by Alexandre et al. on a new
M-DNA structure with the metal ions located in the major groove of DNA replacing
the imino protons, but in a pseudo-tetrahedral environment instead of the square
planar suggested by Lee, 73 indicate that the conductivity of Zn-DNA, Co-DNA
and Fe-DNA could increase signifi cantly. The improved stacking effect observed in
Zn-DNA suggested a new possible route to increase DNA conductivity. Finally,