Critical cation balance in B leads to Z transition: role of Li+

The sodium salt of poly(dG-dC) is known to exhibit a B leads to Z transition in the presence of various cations and 60% alcohol. We here show that the lithium salt of poly(dG-dC) does not undergo B leads to Z transition in the presence of 60% alcohol since Li+ with its large hydration shell cannot stabilize the Z-form. On the other hand, high concentrations of Mg2+ or micromolar concentrations of the cobalt hexamine complex which are known to stabilize the Z-form can compete with Li+ for charge neutralization and hence bring about a B leads to Z transition in the same polymer. From the model building studies the mode of action of the cobalt-hexamine complex in stabilizing the Z-form is postulated.