Cooperativity between Metal Ions in the Cleavage of Phosphate Diesters and RNA by Dinuclear Zn(II) Catalysts

A survey of the potential energy surface for a 1:1 copper dioxygen complex, (C3N2H5)CuO2, reveals two distinct states in the valence region, a singlet (1A1) and a triplet (3B1). The former spans a continuum from CuIII-O2^2 to CuI-02((delta)g), while the latter spans CuII-O2 to CuI-O2(3(SIGMA)g). The point at which the potential energy curves for the two states cross marks an abrupt discontinuity in electron distribution, where the system shifts from dominant CuIII-O2^2- character to CuII-O2^1-. On this basis, we argue that there is no continuum between CuII-peroxide and CuI-superoxide: the two are represented by distinct states that differ both in symmetry and multiplicity.