IR and ESR study of copper(II) complexes with 15N-labelled lysine and ornithine

[15N]-labelled lysine and ornithine amino acids together with their copper(II) complexes are investigated by IR and ESR spectroscopies. The small isotopic shifts in the vibrations frequencies of the bonds involving the N atoms were evidenced by comparing IR spectra of [15N]-labelled and [14N]-forms of these amino acids. Different monomeric species and their local symmetries were established from ESR spectra of Cu(II)–[15N]-lysine (and ornithine) complexes adsorbed on NaY and HY zeolites. The in-plane σ bond has an ionic character (α2 ≅ 0.80) while the in-plane π bond is more covalent (β2 ≅ 0.73) than that of the σ type for all these species.