On the influence of aromatic residues on the interaction of copper (II) with small peptides containing aromatic amino acids: ESR and optical studies.

The complexation behaviour of Cu(II) with di- and tripeptides containing the aromatic amino acids phenylalanine or typtophan has been investigated at different pH-values and compared with results obtained with di- and triglycine. The results obtained by means of ESR and optical absorption spectroscopy show an influence of the two different aromatic entities on the magnetic and optical parameters. A significant decrease of the g11-value and, concomittantly, an increase of the energy of the d-d transition was measured when an aromatic entity is present in the peptide. A possible explanation for this observation is given.