Mono- and polynuclear copper(II) complexes with fragment of alloferons 1 and 2; combined potentiometric and spectroscopic studies.

Complex formation processes between the SGH(3)GQH(6)GVH(9)G decapeptide fragment of alloferons 1 and 2 and copper(II) ions have been studied by potentiometric, UV-vis, circular dichroism (CD) and electron paramagnetic resonance (EPR) methods. This peptide contains two histidines (H(6) and H(9)) and an N-terminal "albumin-like" Xaa-Yaa-His sequence. It was found that the decapeptide is able to bind 3 equiv of metal ions. The SGH(3) sequence is the primary metal binding site and at pH 4 irrespective of the metal-to-ligand molar ratio (1 : 1, 2 : 1, 3 : 1) the CuL species with 4 N {NH(2), 2N(-), N(Im)} binding mode is formed. For the 2 : 1 metal-to-ligand molar ratio the Cu(2)H(-2)L, Cu(2)H(-4)L and Cu(2)H(-5)L complexes, while for the 3 : 1 the Cu(3)H(-2)L, Cu(3)H(-6)L and Cu(2)H(-7)L species dominate in solution. For the metal-to-ligand 2 : 1 and 3 : 1 molar ratios the Cu(3)H(-2)L complex at 4-7 pH range is formed where the {NH(2), 2N(-), N(Im)}{N(Im)}{N(Im)} coordination mode of the decapeptide to copper(II) ions is suggested.