Spectroscopic study of the interaction of poly(ε-N-methacryloyl-L-lysine) with copper(II)

The complexes formed between copper(II) and a polymeric ligand derived from L -lysine, poly(ε-N-methacryloyl-L -lysine) have been investigated by electronic absorption, circular dichroïsm, and EPR spectroscopy. The model molecule, ε-N-isobutyroyl-L -lysine was also studied with the purpose to distinguish between the effects due to the polymeric nature of the ligand and its intrinsic complexing properties. All experiment results are consistent with the existence of two CuL and CuL₂ complexes for both model and polymer Cu systems with no deprotonation of the amide group. The two complexes involve only the carboxyl and amino groups. With the polymer, the CuL₂ complex is the main species, even at low pH and low ligand]/metal] ratio. This is attributed to the high local concentration of ligand in the vicinity of the polymer chain. With the model molecule, on the contrary, the distribution of the two complexes is strongly dependent on the pH and the ligand]/metal] ratio.