Polyanions, intercalated

Tris(phenanthroline) complexes of ruthenium(II), cobalt(III), and rhodium(III) are octahedral, substitutionally inert complexes, and as a result of this coordina-tive saturation the complexes bind to double-helical DNA through a mixture of noncovalent interactions. Tris(phenanthroline) metal complexes bind to the double helix both by intercalation in the major groove and through hydrophobic association in the minor groove. " " Intercalation and minor groove-binding are, in fact, the two most common modes of noncovalent association of small molecules with nucleic acids. In addition, as with other small molecules, a nonspecific electrostatic interaction between the cationic complexes and the DNA polyanion serves to stabilize association. Overall binding of the tris(phenanthroline) complexes to DNA is moderate (log K = 4)." ... 

Actnally, these redox couples have been used as central metals of the polyanionic cathodes in recent years, as shown in Table 9.2. It can be expected that the three-dimensional framework of the oxygen-closed pack framework is sufficiently stable to tolerate repeated lithium intercalation/deintercalation reaction, because it does not inclnded weak van der Waals bonding in the matrix. 

The intercalation cathode Li MyXz (X = anion) should have a low lithium chemical potential, and the intercalation anode should have a high lithium chemical potential to maximize the cell voltage. This implies that the transition metal ion should have a high oxidation slate in the cathode and a low oxidation state in the anode. The chemical potential or redox energies of the cathode and anode could also be tuned by counter cations as illustrated by an increase in voltage on going from an oxide to a polyanion cathode with the same oxidation state for the transition metal ions. 

---