Copper(II) complexes with L-lysine and L-ornithine: Is the side-chain involved in the coordination? A thermodynamic and spectroscopic study

The involvement of the o-NH2 terminal group of L-lysine and L-ornithine in the complexation of Cu(II) was investigated by means of potentiometry, calorimetry, UV±Vis and ESR. The thermodynamic parameters (DG0, deltaH0 and deltaS0) obtained by combining the potentiometric and calorimetric data show that the two ligands complex copper(II) in a different manner, indicating that the o-NH2 terminal group is involved in ornithine complexes only. UV±Vis and ESR spectra further support the involvement of ornithine o-NH2 and provide details on the complexation geometries of the complexes of the two amino acids.