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Various kinds of roles of the water molecules in the electronic states of the complexes of metal ions (M) and deoxyribonucleic acid (DNA) are reviewed. Divalent metal ions M like Fe, Mn, Zn and so on, form Metal-DNA complexes (M-DNA) with each metal ion between the bases of a base pair of DNA. The electronic states of the complexes depend on the species of ions in M-DNA. Metal ions in Fe-DNA and Mn-DNA possess 3d magnetic moments, but those in Zn-DNA do not. Interestingly, the magnetic property of the complexes, especially the magnetic interaction between the metal ions, is dominated by water molecules in the complexes. In Fe-DNA, the water molecules play a role of ligands for the iron ions, which controls the spin states of Fe3+, whereas they govern the magnetic interaction between the Mn2+ ions in Mn-DNA. In contrast, Zn-DNA has no 3d magnetic moment, but the water molecules dominate the bonding states of the Zn ions and the magnetic states of the Zn-DNA system. [ABSTRACT FROM AUTHOR]

Magnetic behaviors in freeze dried DNA complexes with Zn ions (FD-Zn-DNA) are reported. Dehydrated Zn-DNA was prepared from pure Zn-DNA by a freeze drying procedure. Complete dehydration of Zn-DNA by the freeze drying induces an irreversible structural change and produces one π electron spin at each base pair of FD-Zn-DNA. Magnetic behaviors essential to the π electron spins are markedly changed by introducing water molecules in FD-Zn-DNA. In the dehydrated FD-Zn-DNA, the paramagnetism of the π spin system is totally suppressed because of the spin singlet ground state caused by the strong off-site Coulomb repulsion V, which is larger than the on-site Coulomb repulsion U. In contrast, the hydrated FD-Zn-DNA carries large Pauli-like temperature-independent paramagnetism, whose magnitude corresponds to the π-band width of ≈0.24 eV. A possible mechanism of the π electron spin creation is proposed. As a subsidiary effect of the freeze drying procedure, the nonlinear paramagnetism saturating below 0.1 T is observed in both DNA and Zn-DNA. The nonlinear paramagnetism disappears after the hydration of the sample. On the basis of the magnitude of the saturation magnetization, it is suggested that the origin of the nonlinear paramagnetism is the magnetic impurities in DNA. [ABSTRACT FROM AUTHOR]

Magnetic behaviors in freeze dried DNA complexes with Zn ions (FD-Zn-DNA) are reported. Dehydrated Zn-DNA was prepared from pure Zn-DNA by a freeze drying procedure. Complete dehydration of Zn-DNA by the freeze drying induces an irreversible structural change and produces one π electron spin at each base pair of FD-Zn-DNA. Magnetic behaviors essential to the π electron spins are markedly changed by introducing water molecules in FD-Zn-DNA. In the dehydrated FD-Zn-DNA, the paramagnetism of the π spin system is totally suppressed because of the spin singlet ground state caused by the strong off-site Coulomb repulsion V, which is larger than the on-site Coulomb repulsion U. In contrast, the hydrated FD-Zn-DNA carries large Pauli-like temperature-independent paramagnetism, whose magnitude corresponds to the π-band width of ≈0.24 eV. A possible mechanism of the π electron spin creation is proposed. As a subsidiary effect of the freeze drying procedure, the nonlinear paramagnetism saturating below 0.1 T is observed in both DNA and Zn-DNA. The nonlinear paramagnetism disappears after the hydration of the sample. On the basis of the magnitude of the saturation magnetization, it is suggested that the origin of the nonlinear paramagnetism is the magnetic impurities in DNA. [ABSTRACT FROM AUTHOR]