CD studies on the conformation of oligonucleotides complexed with divalent metal ions: interaction of Zn2+ with guanine favours syn conformation.

The interaction of the divalent metal ions Mg2+, Mn2+, Zn2+ and Cu2+ with GpG and several other dinucleoside monophosphates were investigated by means of circular dichroism. The spectra of the complexes of GpG, GpU analogues and ApGpG caused in the presence of Zn2+ and other transition metals show a close similarity in the spectral CD shape to that previously reported in the literature for GpG and GpU at low pH and for m7GpG. From the results it may be concluded that transition metal ions-particularly considered for Zn2+/- tends to favour the degree of stacking with Guo in syn conformation in GpG or GpU due to the coordination of the metal ion at N-7 of the 3'-bound position while shielding of the phosphate site by Mg2+ does not influence the sugar-base torsional angle under comparable conditions. Stereochemical aspects and selectivity of the Zn2+ mediated conformation of the dinucleoside phosphates are discussed.