Preparation, characterization and activity of CuZn and Cu₂ superoxide dismutase mimics encapsulated in mesoporous...

Encapsulation of three superoxide dismutase (SOD) functional mimics, [CuZn(dien)₂(μ-Im)(ClO₄)₂]ClO₄ (1), [Cu₂(dien)₂(μ-Im)(ClO₄)₂]ClO₄ (2) (Im = imidazolate, dien = diethylenetriamine), and [CuZn(salpn)Cl₂] (3) (H₂salpn = 1,3-bis(salicylideneamino)propane) in mesoporous MCM-41 silica afforded three hybrid catalysts 1@MCM-41, 2@MCM-41 and 3@MCM-41. Spectroscopic and magnetic analyses of these materials confirmed the metal centers of the complexes keep the coordination sphere after insertion into the MCM-41 silica matrix. For the imidazolate-bridged complexes the silica channels restraint the relative orientation of the two metal ions. While 3@MCM-41 shows SOD activity significantly lower than the host-free complex, insertion of the imidazolate-bridged CuZn or Cu₂ complexes by ion exchange onto mesoporous MCM-41 silica affords durable and recoverable supported catalysts with much better SOD activity than the free complexes. For confined imidazolate-bridged complexes, 1@MCM-41 and 2@MCM-41, the small pore size of the silica matrix improves the SOD activity more than a host with larger pores. This high SOD activity is attributed to the close-fitting of the complexes into the nanochannels of MCM-41 silica that favors the Cu active site and HImZn(or Cu) group stay in close proximity during catalysis.