The solution chemical properties, superoxide dismutase and catecholase activity of the copper(II)–Ac-His-His-Gly-His-OH (hhgh) complexes were studied to identify functional and structural models of copper-containing oxidases. The solution speciation was determined in the pH range 3–11 by two independent methods (potentiometry and pH-dependent EPR measurements). The results obtained by the two methods agree very well with each other and show the formation of differently protonated CuH_xL complexes (where x = 2 ,1, 0, −1, −2, −3) in aqueous solution. The spectroscopic (UV–Vis, CD, EPR) data indicate that the coordination of the imidazole rings is a determinant factor in all these complexes. Amide coordinated complexes are dominant only above pH 8. This offers excellent possibilities for structural/functional modelling of copper(II) containing metalloenzymes. Indeed, the {3N_im} coordinated CuL species (pH = 6–7) has efficient superoxide dismutase-like activity. The {3N_im,OH⁻} coordinated CuH₋₁L possesses outstanding activity to catalyze the oxidation of 3,5-di-tert-butylcatechol (H₂dtbc) by dioxygen in 86 wt% methanol–water, providing the first example that copper(II)–peptide complexes are able to mimic copper containing oxidases.

Two histidine-rich branched peptides with one lysine as a branching unit have been designed and synthesized by solid-phase peptide synthesis. Their complex formation with Cu(II) and Zn(II) as well as their ability to attenuate the metal-ion induced amyloid aggregation has been characterized. Both peptides can keep Cu(II) and Zn(II) in complexed forms at pH 7.4 and can bind two equivalents of metal ions in solutions with excess metal. The stoichiometry, stability and structure of the complexes formed have been determined by pH potentiometry, UV-Vis spectrophotometry, circular dichroism, EPR and NMR spectroscopy and ESI-MS. Both mono- and bimetallic species have been detected over the whole pH range studied. The basic binding mode is either a tridentate {N_amino, N_amide, N_im} or a histamine-type of coordination which is complemented by the binding of far imidazole or amino groups leading to macrochelate formation. The peptides were able to prevent Cu(II)-induced Aβ(1–40) aggregation but could not effectively compete for Zn(II)in vitro. Our results suggest that branched peptides containing potential metal-binding sites may be suitable metal chelators for reducing the risk of amyloid plaque formation in Alzheimer's disease.