Equilibrium and detailed spectroscopic characterization of zinc(ii) complexes with NiSOD binding loop and their related model fragments are reported in the whole investigated pH-range. The zinc(ii) complexes of L1 (HCDLPCGVY-NH2), L2 (Ac-HCDLPCGVY-NH2) and L3 (HCDLACGVY-NH2) and the nickel(ii) and zinc(ii) complexes of L4 (HCDLPCG-NH2) were studied by pH-potentiometric and several spectroscopic methods. The results indicated that the macrochelate coordinated zinc(ii) complexes are dominant in a whole pH-range and the side chain donors of the peptides are involved in the metal binding. Therefore, the deprotonation and coordination of the peptide backbone occur only in a strongly alkaline solution. The acetylation of the peptide amino terminus (L2) significantly enhances the zinc(ii) binding ability compared to the corresponding nickel(ii) complexes. L2 complexes of zinc(ii) are 2 or 3 orders of magnitude more stable than the corresponding nickel(ii) complexes. This effect clearly shows the crucial role of the terminal amino group in the nickel binding for the NiSOD enzyme.