Influence of copper(II) ions on the noncovalent interactions between cytidine-5′-diphosphate or cytidine-5′-triphosphate and biogenic amines putrescine or spermidine

Abstract

Potentiometric and NMR spectroscopic studies of the nucleotide (NucP)/polyamine (PA) system (where NucP = CDP, CTP, PA = putrescine or spermidine) revealed the formation of molecular complexes (NucP)(Hx+y)(PA) (where Hx+y = number of protons; x - from NucP and y - from PA). Their thermodynamic parameters were determined and the modes of their interactions were proposed. The main reaction centers were found to be the protonated amine groups of polyamine (positive centers) and phosphate groups of nucleotide (negative centers). The pH ranges in which the complex occurs correspond to those of amine protonation and -PO3x- group deprotonation, which unambiguously confirms the dipole-dipole type of interaction. In the pH range of total deprotonation of NHx+ groups from the polyamine, the molecular complexes disappear. The equilibrium and spectroscopic studies of the ternary systems Cu(II)/NucP/PA evidenced the formation of Cu(NucP)Hx+y(PA) type coordination compounds and Cu(NucP)⋯(PA)(Hx) type molecular complexes with polyamine in the outer coordination sphere. The main sites of metal ion bonding in the latter species are the phosphate groups of the nucleotide, while in the coordination compounds – besides the phosphate groups – also the donor nitrogen atoms from the polyamines. In this paper we have also quantitatively calculated the effect of metal ions on the formation of the molecular complexes.