The Initial Binding of Cu(II) to Some Amino Acids and Dipeptides: A 13 C Nuclear‐Magnetic‐Resonance Study

The initial binding of Cu 2+ to l ‐lysine, l ‐histidine, glycyl‐histidine and histidyl‐glycine in aqueous solutions was examined by 13 C nuclear magnetic resonance spectroscopy. The measurements were carried out in a substantially improved way employing the pulse Fourier transform technique. Spectra of both high quality and resolution were obtained. Cu 2+ complex formation with l ‐lysine occurred with the α‐amino and carboxyl group attributable to the well expressed broadening effect of the 13 C signals of the α‐carbon atom and the carboxyl atom. The ɛ‐amino group was not involved. Measurements of the Cu chelates using l ‐histidine and glycyl‐histidine and histidyl‐glycine confirmed the ambidentate nature of the histidine residue. It was concluded that an equilibrium exists between two Cu‐complex species designated as histamine‐like and histamine‐like/glycine‐like species. In the homogeneous histamine‐like Cu complex, the Cu 2+ is exclusively bound with 4 nitrogens, while in the other species one oxygen of the glycyl carboxyl group is involved in the Cu 2+ binding. Blocking of this carboxyl group by peptide bonding as found in histidyl‐glycine favoured the formation of a Cu complex where the imidazole carbons of the histidyl residue were the most influenced species.