Study of copper(II) ternary complexes with phosphocreatine and some polyamines in aqueous solution

Abstract

Ternary systems of Cu(II) with phosphocreatine (PCr) and the polyamines (PAs), ethylenediamine (en), 1,3-diaminopropane (tn), putrescine (Put), spermidine (Spd), and spermine (Spm), were investigated in aqueous solution through potentiometry, ultraviolet–visible, EPR and Raman spectroscopy. The binary complex CuPCr was also studied by Raman spectroscopy, and the calculation of the minimum stabilization energy was done assuming this molecule in aqueous solution. The stability constants of the CuPCrPA ternary complexes were determined by potentiometry (T = 25 °C, I = 0.1 mol L − 1 , KNO 3). The stability order determined was CuPCrSpm > CuPCrSpd > CuPCren > CuPCrtn > CuPCrPut, the same order of the corresponding binary complexes of Cu(II) with these polyamines. The evaluation of intramolecular PA–PCr interactions in protonated and deprotonated species of ternary complexes was carried out using the equation Δlog K = log β CuPCrPAHq + p − (log β CuPAHq + log β CuPCrHp). All of the CuPCrPA ternary complexes have a square planar structure and are bonded to PCr through the nitrogen atom of the guanidine group and the oxygen atom of the phosphate group, and to the PAs through two nitrogen atoms of the amine groups. The structure of the complex CuPCrSpm is planar with distortion towards tetrahedral. Calculation of the minimum stabilization energy for the CuPCr and CuPCrenH complexes confirmed the proposed coordination mode.