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

Abstract

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 N 3 orN7forr < 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 D,0 stabilized the Z structure for poly(dG-dC) complexed with HgCl₂.