Non-covalent and coordination interactions in Cu(II) systems with uridine, uridine 5′-monophosphate and triamine or tetramine as biogenic amine analogues in aqueous solutions

Abstract

Reactions of metallation and non-covalent interactions have been studied in ternary systems of Cu(II) ions with uridine, uridine 5′-monophosphate and diamines or triamines. It has been found that in metal-free systems the reaction centres of the nucleoside with the polyamine are the donor nitrogen atoms N(3) and protonated –NH x groups of the amines. In comparison to systems with adenosine or cytidine, the pH range of complex formation is shifted towards higher values. It is a consequence of significantly higher basicity of uridine and in agreement with the ion–ion, ion–dipole interaction model assumed. Formation of molecular complexes of uridine 5′-monophosphate with polyamines at a low pH is the result of activity of the phosphate group which plays the role of a negatively charged reaction site. Non-covalent interactions interfere in processes of bioligand metallation. Centres of weak interactions are simultaneously binding sites of metal ions. In protonated Cu(Urd)(PA)H x complexes, coordination has been found to involve the N(3) atom from the nucleoside and two donor nitrogen atoms from the polyamine (PA). In the heteroligand species Cu(Urd)(PA), despite deprotonation of all amine groups, one of these groups is located outside the inner coordination sphere. In complexes with uridine-5′-monophosphate, the phosphate group is active in metallation. Moreover, in certain coordination compounds this group is engaged in non-covalent interactions with PA molecules, despite binding Cu ions, as has been shown on the basis of equilibrium and spectral studies.