Study of binary and ternary complexes of copper(II) with some polyamines and adenosine 5′ triphosphate

The binary and ternary systems of Cu(II) complexes with adenosine 5′ triphosphate (ATP) and the polyamines (PA): ethylenediamine (en), 1,3-diaminopropane (tn), spermidine (Spd) and bis-[(2S)-2-pyrrolidinylmethyl]ethylenediamine (tetraamine) were investigated. The study was performed in aqueous solution using potentiometry, ultraviolet visible and EPR spectroscopies. The stability constants of the complexes were determined by potentiometry (T=25 °C, μ=0.1 mol l−1, KNO3). The order of the values of the stability constants of the ternary complexes was CutetraamineATP>CuSpdATP>CuenATP>CutnATP and it is the same of the correspondent binary complexes of Cu(II) with these polyamines. This behavior was confirmed by the increasing of the maximum wavelength of the absorption spectra and the g0 parameter of the EPR analyses and by the decreasing of the A0 parameter as the stability constants decrease. Δ log K(log βCuPAATP−(log βCuPA+log βCuATP) showed that the ternary complexes are less stable than the binary ones, suggesting that it does not occur any interaction between the ligands in the ternary complexes. When the same calculation was done for the protonated species CuHqPAATP, the stability constants of the complexes were greater. When PA=Spd or tetraamine This result showed that these protonated ligands favored more stable ternary complexes, though only CuHSpdATP exists in pH ≈7.