The catalytic redox activity of Cu(ii) bound to the motif NH2-Xxx-Zzz-His (ATCUN) with ascorbate and H2O2/O2 is very low and can be stopped via Cu(i)-chelation. This impacts its application as an artificial Cu-enzyme to degrade biomolecules via production of reactive oxygen species in a Cu(i)-chelator rich environment like the cytosol.