Purines. Part I. Kinetics of interaction of nickel(II) with some purine bases and nucleosides

Abstract

The interaction of Ni^II with adenine, 4-aminopyrazolo[3,4-d]pyrimidine (app), adenosine, hypoxanthine, and inosine have been studied by stopped-flow techniques. Adenine and app show a complex reaction pattern with both the neutral (HL) and protonated (H₂L⁺) species attacking the nickel ion with subsequent deprotonation, the forward rate constants for adenine being 336 and 1.44 × 10³ l mol^–1 s^–1 respectively. The preference for the protonated ligand may be explained in terms of the neutral ligand hydrogen bonding with a water molecule in the metal-ion co-ordination sphere, poorly aligning the ligand for attack on Ni^II. Hypoxanthine and inosine show no pH dependence in the region pH 2–6 and give rates within the range of ‘normal’ substitution.