Copper(II) complexes with uridine, uridine 5′-monophosphate, spermidine, or spermine in aqueous solution

Abstract

Molecular complexes of the types (Urd)H x (PA) and (UMP)H x (PA) are formed in the uridine (Urd) or uridine 5′-monophosphate (UMP) plus spermidine or spermine systems, as shown by the results of equilibrium and spectral studies. Overall stability constants of the adducts and equilibrium constants of their formation have been determined. An increase in the efficiency of the reaction between the bioligands is observed with increasing length of the polyamine. The pH range of adduct formation is found to coincide with that in which the polyamine is protonated while uridine or its monophosphate is deprotonated. The –NH x + groups from PA and the N(3) atom of the purine base as well as phosphate groups from the nucleotides have been identified as the significant centres of non-covalent interactions. Compared to cytidine, the pH range of Urd adduct formation is shifted significantly higher due to differences in the protonation constants of the endocyclic N(3) donor atoms of particular nucleosides. Overall stability constants of the Cu(II) complexes with uridine and uridine 5′-monophosphate in ternary systems with spermidine or spermine have been determined. It has been found from spectral data that in the Cu(II) ternary complexes with nucleosides and polyamines the reaction of metallation involves mainly N(3) atoms from the pyrimidine bases, as well as the amine groups of PA. This unexpected type of interaction has been evidenced in the coordination mode of the complexes forming in the Cu–UMP systems including spermidine or spermine. Results of spectral and equilibrium studies indicate that the phosphate groups taking part in metallation are at the same time involved in non-covalent interaction with the protonated polyamine.