ABSTRACT
In most M-DNA systems, the charge transfer frommetal ions to DNA does not occur, except for Fe-DNA, where Fe2+ transforms into Fe3+
by releasing an electron to the bases of a base pair, as described in
Chapter 7. UV/Vis absorption spectra revealed that Fe3+ absorption typical of FeCl3 emerged in addition to that of the base π bands. The
magnetism of Fe3+ was observed as a mixture of the S = 5 2 high
spins and the S = 1 2 low spins. However, the magnetism of the π
electron spins was not observed probably because of nonmagnetic
ground state of the π spin system, in which the localized nature
of the π band is concerned. In this chapter, the other example
of the charge-transferred system, Zn-DNA, is described in detail,
which shows an interesting role of water molecules in governing
the magnetic properties of Zn-DNA. The electronic states of Zn-DNA
depend on the sample preparation procedure [28]. The conventional
ethanol precipitation procedure produces usual M-DNA systems with M2+ ions surrounded by hydrating water molecules, which prevent the metal ions from forming covalent bonds with the
nitrogen atoms of bases. In contrast, Omerzu et al. reported that a freeze-drying procedure leads to different electronic states from
that by the ethanol precipitation procedure, as shown in Figs. 9.1 and
9.2 [24]. The electronic states of the new freeze-dried Zn-DNA (FD-
Zn-DNA) system have been uncovered by the other approach than
that by Omerzu et al. in sample preparation [28]. The FD procedure removes almost all the water molecules from Zn-DNA and induces
Figure 9.1 The room-temperature ESR spectrum of Zn-DNA (black circles) fitted with an asymmetric Lorentzian (Dysonian) (solid red line) and a
Lorentzian (dashed blue line) curve. The inset shows the temperature
development of the Zn-DNA ESR resonance measured on cooling from
the room temperature (the bottom curve) down to 10 K (the top curve)
measured at every 10 K. Reprinted with permission from Ref. [24].
Copyright 2010, American Physical Society.
