Fig. 5. Established synthetic approach for heme–peroxo–copper complexes, wherein addition of dioxygen to the reduced iron and copper complexes (in a 1 : 1 stoichiometry) results in formation of the high-spin complexes, HS-^XTMPA. Addition of 1 equiv. of 1,5-dicyclohexylimidazole (DCHIm, which acts as an axial base) affords low-spin heme–peroxo–copper species (LS-^XTMPA, with X as depicted in Fig. 1). As shown in the bottom left inset (as one possible example of the present study), we are investigating the influence of H-bonding on the peroxo core.