Determination of stability constants of ternary copper(II) complexes formed with 2,6-pyridinedicarboxylic acid and several amino acids

In this work, the formation of ternary complexes with their respective formation constants in the systems formed by copper (II), 2,6-pyridinedicarboxylic acid (H₂Dipi) and the amino acids = histidine (His), aspartic acid (H₂Asp), glutamic acid (H₂Glu), glycine (HGly), proline (HPro), α-alanine (HαAla), β-alanine (HβAla), serine (HSer), threonine (HThr), phenylalanine (HPhe) and methionine (HMet)). The analysis used potentiometric data analysed with the least-squares program LETAGROP in aqueous solution at 25°C in 1.0 mol.dm⁻³ KNO₃ solution. The relative stability of the ternary complexes is compared with the binary ones using the values of Δlog K and log χ. Subsequently, by using the formation constants, the species distribution diagrams were generated and are briefly discussed here. The Cu (II) -dipicolinic acid-glutamic acid, Cu (II) -dipicolinic acid-glycine and Cu (II) – dipicolinic acid-histidine systems were characterised by UV-Vis molecular absorption spectroscopy and cyclic voltammetry, confirming the formation of ternary complexes with octahedral geometry.