Complexes of copper(II) with spermine and non-covalent interactions in the systems including nucleosides or nucleotides

Abstract

Taking into account a change in the acid-base properties of metal-free systems of spermine (Spm) and nucleoside (Nuc) or nucleotide (NMP), appearing as a result of non-covalent interactions between the bioligands, the composition of the molecular complexes formed and their overall stability constants were determined. The centres of ion-dipole interactions were established to be protonated amine groups of Spm and the nitrogen donor atoms of nucleosides as well as the phosphate residues and the nitrogen donor atoms of nucleotides. A distinct difference was found between the behavior of adenosine monophosphate and cytidine monophosphate. The presence of at least two reaction centers in the majority of relatively stable adducts was found which emphasizes the role of spatial arrangement in the species. The assumed model of interactions is supported by the fact that molecular complex formation is observed in the pH range of nucleoside or nucleotide deprotonation and polyamine protonation. The coordination nature of spermine in the systems with Cu(II) differs from that of polyamines of shorter chains. The stability constants of the mixed-ligand complexes formed, their stochiometry and mode of co-ordination were determined (the main co- ordination sites are the nucleotide phosphate residues as well as N(1) and N(7) atoms of purine or N(3) of pyrimidine rings). The interactions in nucleoside-containing systems are, however, essentially different from those in the systems which comprise nucleotides. The formation of Cu(AMP)H(x)(Spm) and Cu(CMP)H(x)(Spm) adducts, in which copper ions were coordinated only via oxygen atoms of phosphate groups, was established. In the case of nucleoside- containing systems, it was found that Cu(Nuc)(Spm) mixed-ligand complexes with a chromophore of N5-type are formed.