Noncovalent interactions and coordination reactions in the systems consisting of copper(II) ions, aspartic acid and diamines

Interactions of aspartic acid between 1,3-diaminopropane (tn) and 1,4-diaminobutane (Put) in metal-free systems as well as in the systems including copper(II) ions were studied. The composition and overall stability constants of the complexes formed were determined by the potentiometric method. The interaction centres and coordination sites were identified by spectroscopic methods. Each of the ligands has both negative and positive interaction centres. In aspartic acid such centres are carboxyl groups and amine group, while in the polyamine molecules – protonated amine groups. The centres are also the potential sites of the coordination of metal ions. Analysis of the log Ke values of the adducts in the systems with polyamines has shown that the stability of the adducts in the metal-free systems depends on a significant degree on the steric factor that is the length of the polyamine. In some species the inversion effect, hitherto not reported in literature, was found. In the ternary systems including Cu(II) ions, only protonated species are formed, including molecular complexes with intermolecular interactions and metallation through the oxygen atoms of carboxyl groups and amine groups of the amino acid. In the adducts the protonated diamine is in the outer coordination sphere and is involved in noncovalent interactions with the anchoring CuH(Asp) or Cu(Asp) complexes.