Proton,phosphorus and carbon nuclear magnetic relaxation studies on the interaction of poly(riboadenylic acid) with Cu2+

Interaction between poly(riboadenylic acid) (poly(A)) and Cu²⁺ in neutral aqueous (D₂O) solution has been studied by ¹H, ³¹P, and ¹³C nuclear magnetic resonance. electron-nuclear hyperfine coupling constant and apparent electron-nuclear distances were determined by measurement of T₁ and T₂ values as a function of temperature. The apparent distance from Cu²⁺ to H(2), H(8), H(1′), and phosphorus nuclei were estimated to be 4.1, 3.7, 5.1, and 3.1 Å from these results. Cu²⁺ was found to coordinate directly to the phosphate groups of poly(A) (Type I complex). Simultaneously there are bindings of Cu²⁺ directly to one of the nitrogen atoms of adenine ring, mainly to N(7) (Type II complex) and either N(1) or N(3) (Type III complex).