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

摘要

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 H_2L~3 and complexes [MnL~1(H_2O)_2](NO_3) (CH_3,OH) (1), [MnL~3(H_2O)_2]_2(NO_3)_2(CH_3OH)(H_2O) (3), and [MnL~4(H_2O)_2](NO_3)(H_2O)_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.