Complexes of Cu(II) Ions and Noncovalent Interactions in Systems with L-Aspartic Acid and Cytidine-5'-Monophosphate

Interactions between aspartic acid (Asp) and cytidine-5-monophosphate (CMP) in metal-free systems as well as the coordination of Cu(II) ions with the above ligands were studied. The composition and overall stability constants of the species formed in those systems were determined by the potentiometric method, and the interaction centres in the ligands were identified by the spectral methods UV-Vis, EPR, NMR, and IR. In metal-free systems, the formation of adducts, in which each ligand has both positive and negative reaction centres, was established. The main reaction centres in Asp are the oxygen atoms of carboxyl groups and the nitrogen atom of the amine group, while the main reaction centre in CMP at low pH is the N(3) atom. With increasing pH, the efficiency of the phosphate group of the nucleotide in the interactions significantly increases, and the efficiency of carboxyl groups in Asp decreases. The noncovalent reaction centres in the ligands are simultaneously the potential sites of metal-ion coordination. The mode of coordination in the complexes formed in the ternary systems was established. The sites of coordination depend clearly on the solution pH. In the molecular complexes ML⋯L, metallation involves the oxygen atoms of the carboxyl groups of the amino acid, while the protonated nucleotide is in the outer coordination sphere and interacts noncovalently with the anchoring CuHx(Asp) species. The influence of the metal ions on the weak interactions between the biomolecules was established

Stability and mode of coordination complexes formed in the silver(i)/nucleoside systems

Complexes of silver(i) with nucleosides (adenosine, cytidine, uridine and thymidine) have been studied using potentiometric, spectral and theoretical methods. Stability constants of the complexes as well as their coordination modes have been determined. Results of the equilibrium studies have provided evidence for the formation of only ML and ML(OH) type complexes. The basicity of nucleosides was found to substantially influence the stability constant of the ML type complexes. Spectral data have allowed us to identify the sites of silver attachment to the nucleoside. Additionally a new silver-adenosine complex of stoichiometry Ag(Ado)(OH) was prepared from aqueous solution at pH close to 6. Its characterization and comparison with complexes formed in solution are described. The structures of complexes formed in solution and in solid state were confirmed through computational calculations (DFT/B3LYP: lanL2DZ theoretical procedure). © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique