Bonding of copper(II) ions by proctolin analogues modified in fifth position of the peptide chain

The amine group of the 2,4-diamminobutyric acid (Dab) residue of the proctolin analogue RYLP-Dab, in whole pH range (2.5-10.5) is coordinated to the copper(II) ions, and the deprotonation and coordination of the second amide nitrogen atom to the metal ion is prevented. In solution in wide pH range (5-10.5) the CuL complex with 3N {NH2, Namide-, CO, NH2Dab} bonding mode is present.