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The peroxidase activity of hemin-peptide complexes remains a potential factor in oxidative damage relevant to neurodegeneration. Here, we present the effect of temperature, ionic strength, and pH relevant to pathophysiological conditions on the dynamic equilibrium between high-spin and low-spin hemin-Aβ₄₀ constructs. This influence on peroxidase activity was also demonstrated using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and dopamine (DA) oxidation rate analyses with increasing ratios of Aβ₁₆ and Aβ₄₀ (up to 100 equivalents). Interaction and reactivity studies of aggregated Aβ₄₀-hemin revealed enhanced peroxidase activity versus hemin alone. Comparison of the results obtained using Aβ₁₆ and Aβ₄₀ amyloid beta peptides revealed marked differences and provide insight into the potential effects of hemin-Aβ on neurological disease progression.