Multireference ab initio calculations on reaction intermediates of the multicopper oxidases

The spectroscopic parameters for the intermediated of multicopper oxidases (MCOs) are calculated using multireference wave functions from the CASPT2 and MRDDC12 methods. The results have supported the suggestion that the native intermediate (NI) has an [O.sup.2-] atom in the center of the trinuclear cluster, whereas both the peroxy intermediate (PI) and the peroxy adduct (PA) have an [O.sub.2.sup.2-] ion in the center of the cluster, which agrees well with the quantum mechanical/molecular mechanical (QM/MM) results and spectroscopic measurements.