Synthesis of novel binary and ternary Zn2+ complexes with putrescine and phosphocreatine and the metal complexes study in aqueous solution

Binary and ternary systems of Zn2+ complexes with phosphocreatine (PCr) and putrescine (Put) were investigated in aqueous solution using potentiometric titrations, Raman spectroscopy, Nuclear Magnetic Resonance (1H NMR) and molecular modeling. The stability constants of the complexes and molecular adducts, determined by potentiometry (T = 25.0 °C, I = 0.100 mol L−1, KNO3), are for some of the calculated complexes log KZnPCr = 10.63 ± 0.03, log KZnPut = 5.22 ± 0.08 and for log KZnPCrPut = 16.56 ± 0.02. PCr acts as a bidentate ligand and Put as a monodentate ligand until around pH 11. The Raman and 1H NMR spectra and minimum total molecular energies calculations confirm the coordination modes of all systems. The ternary species are suggested by the values of the stability constants found as, when compared to those of the binary complexes with each ligand, they are neither the sum of the two or a value less than each one separately complexed with Zn2+. An intermolecular interaction was suggested for the ZnPCrPut species. However, for ZnPCrPutH species it was not possible to establish the same kind of interaction due to the long distance between the carboxylate group of phosphocreatine and the NH3+ group of Put.