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

Abstract

The sodium salt of poly(dG---dC) is known to exhibit a B → 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 → 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 → 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.