Determination of the interaction of ADP and dADP with copper(II), manganese(II) and lanthanide(III) ions by nuclear-magnetic-resonance spectroscopy.

The aqueous solution conformation of the 1:1 complexes of ADP and dADP bound to a lanthanide ion have been determined by examination of the dipolar shifts and induced relaxation at pH 6.4. Apparent inconsistencies in the observed data are interpreted in terms of a gradually changing lanthanide-oxygen bond length from Pr3+ to Yb3+. The conformations of ADP and dADP are very similar showing an extended diphosphate, a 2E ribose conformation and with the adenine base displaying a small syn contribution. Relaxation data obtained from Mn(II) titrations are readily interpreted in terms of bidentate coordination to alpha and beta phosphates with the nucleotides retaining the same overall conformation found from the lanthanide study. No evidence to support an intramolecular water-bridged backbound structure is observed. The interaction with Cu(II) is more complex, coordination is observed not only at the diphosphate but also at two sites on the base, N-1, and the chelate formed between N-7 and the amino group. The relative importance of these sites is different for ADP and dADP and is also pH-dependent for ADP.