Structural Forms and Transitions for the Complex of Mercury(II) with Poly(dG-dC)

Infrared spectroscopy was used to study hydrated double-helical poly(dG-dC) complexed with varying amounts of mercury(II). For one Hg(II) per ten nucleotide residues (r = 0.1), the B structure was stabilized and the B* structure was absent at high hydration. The Z structure did not form as hydration was reduced. For r = 0.2, the B and Z structures coexisted at high hydration and the transition to total Z structure was broad as hydration was reduced. Hg(II) was bound exclusively to the guanine residues probably at N3 or N7 for r less than or equal to 0.25. The cytosine residue did not protonate (at N3) as Hg(II) was bound to guanine. The addition of NaCl together with Hg(II) reduced the binding of Hg(II), stabilized the B structure at the highest hydration and caused a sharp transition between the B and Z structures as hydration was lowered. Hydration with D2O stabilized the Z structure for poly(dG-dC) complexed with HgCl2.