This study looks at how Ni(II) ions interact with a small peptide (Ac-TSKCGS-NH₂) that mimics parts of the tau protein involved in Alzheimer’s disease. It shows that specific amino acids, especially cysteine, help bind metal ions effectively at near-physiological pH. The peptide forms stable complexes with Ni(II), where the metal is held by nitrogen and sulfur atoms in a square planar structure. Experimental techniques confirmed that these complexes remain structurally stable over time. However, unlike copper, Ni(II) and its peptide complexes produce very little reactive oxygen species (ROS). In contrast, Cu(II)-peptide systems, particularly those containing cysteine, show much higher ROS activity. Overall, the type of amino acid involved plays a key role in determining both metal binding and oxidative behavior.