Interaction of metal ions with polynucleotides and related compounds. XXII. Effect of divalent metal ions on the conformational changes of polyribonucleotides

Changes in the conformation of poly(G), poly(C), poly(U), and poly(I) in the presence of divalent metal ions Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ have been measured by means of ORD and u.v. spectra. Mg²⁺ and Ca²⁺ ions stabilize helical structures of all the polynucleotides very effectively at concentrations several orders of magnitude lower than the effective concentration of Na⁺ion. Cu²⁺ and Cd²⁺ destabilize the helical structure of polynucleotides to form random coils. Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺ions do not behave in such a clear-cut manner: they selectively stabilize some ordered structures, while destabilizing others, depending on the ligand strength of the nucleotide base as well as the preferred conformation of that polynucleotide.