Nanostructured binuclear Fe(III) and Mn(III) porphyrin materials: Tuning the mimics of catalase and peroxidase activity

Abstract

Tuning of the structures and electronic effects of nanocrystals is of great relevance to the preparation of specialized materials such as artificial enzymes.In this study, binary porphyrin materials have been prepared by ionic self-assembly of oppositely charged Fe(III) and Mn(III) porphyrins. The materials have been characterized by SEM, XPS and UV–vis spectroscopy and tested as biomimetic models of catalase. The heterometallic material [Mn/Fe], prepared by association of MnTHPyP and FeTSPP, showed the highest activity for H2O2 dismutation reaction, 89–95 U·mg−1, over a pH range of 4–7. An enhancement in activity of one to two orders of magnitude can be observed relatively to the individual Fe(III) or Mn(III) porphyrins and to the mono-metallic materials that were prepared by association of a metalloporphyrin (MP) and a metal free porphyrin (H2P). These results support the occurrence of cooperative mechanisms between two metal ion centers within the structure. The materials with the highest catalase-like activity were also tested as peroxidase mimetics in ABTS oxidation. Best activity was observed for the [Mn/Fe] material at pH 4, while at pH 6 the activity decreases by 97%. EPR studies at pH 6 demonstrate the absence of free hydroxyl or superoxide radicals in the mechanism and thus support the activity of the [Mn/Fe] material as a catalytic antioxidant under these conditions.