Before investigating the possibility of H 2 O 2 formation at the active-site, we evaluate whether O • - 2 , OOH • , OOH -or H 2 O 2 could dissociate from the active-site, comparing the different dissociation reactions in light blue in Fig. . Mulliken spin densities and QM/MM and MM energies as well as point charge (ptch) contributions are reported in Tables . The dissociation of a dioxygen species from Cu turned out to be highly dependent on the micro-solvation of the resulting dioxygen species. We use the Mulliken spin density to differentiate whether the dissociation channel ends in a Cu(II) or a Cu(I) species. We generally assign the cases with a Cu spin density of 0.1 or higher as Cu(II), meaning that the species that dissociate into solution is O • - 2 , OOH • , OOH -or H 2 O 2 (cf. Figure ).