Self-assembled biomimetic catalysts: studies of the catalase and peroxidase activities of Mn(III)-Schiff base complexes

Abstract

Five Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases obtained by the condensation of 3-ethoxy-2-hydroxybenzaldehyde with different diamines. The complexes have been characterized by elemental analysis, ESI mass spectrometry, IR and 1H NMR spectroscopy, r. t. magnetic, and molar conductivity measurements. Parallel-mode EPR spectroscopy of 1 is also reported. Ligand H2L3 and complexes [MnL1(H2O)2](NO3)(CH3OH) (1), [MnL3(H2O)2]2(NO3)2(CH3OH)(H2O) (3), and [MnL4(H2O)2](NO3)(H2O)2 (4) were crystallographically characterized. The X-ray structures show the self-assembly of the Mn(III)–Schiff base complexes through µ-aquo bridges between neighboring axial water molecules and also by π–π stacking interactions, establishing dimeric and polymeric structures. The peroxidase and catalase activities of the complexes have been studied. Complexes with the shorter spacer between the imine groups (1–2) behave as better peroxidase and catalase mimics, probably due to their ability to coordinate the hydrogen peroxide substrate to manganese.