A new mononuclear manganese(III) complex of an unsymmetrical hexadentate N3O3 ligand exhibiting superoxide dismutase and catalase-like activity: synthesis, characterization, properties and kinetics studies

• A neutral mononuclear Mn(III) complex was obtained with an hexadentate N3O3 ligand.
• Mononuclear MnL exhibits dual superoxide dismutase and catalase-like activity.
• MnL catalyzes dismutation of O2− efficiently, with kcat = 1.7 × 106 M− 1 s− 1.
• MnL catalyzes H2O2 disproportionation with second order kinetics on catalyst.
• MnL employs a high-valent catalytic cycle to decompose O2− and H2O2.

A mononuclear MnIII complex MnL·4H2O (H3L = 1-[N-(2-pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N′-(2-hydroxybenzyl),N′-(4-methylbenzyl)amino]propan-2-ol) has been prepared and characterized. This complex catalyzes the dismutation of superoxide efficiently, with catalytic rate constant kcat = 1.7 × 106 M− 1 s− 1 and IC50 1.26 μM, obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dismutase assay, in aqueous solution of pH 7.8. MnL is also able to disproportionate more than 300 equivalents of H2O2 in CH3CN, with initial rate of H2O2 decomposition given by ri = kcat [MnL]2 [H2O2] and kcat = 1.32(2) mM− 2 min− 1. The accessibility of the MnIV state (Ep = 0.53 V vs. saturated calomel electrode), suggests MnL employs a high-valent catalytic cycle to decompose O2− and H2O2.

Complexation of Mn(III) with an hexadentate N3O3-ligand affords a neutral mononuclear complex, MnL, with the six coordination sites of the metal occupied by the donor atoms of the ligand. The complex exhibits dual superoxide dismutase and catalase-like activity employing a high-valent catalytic cycle to decompose efficiently O2− and H2O2.Figure optionsDownload as PowerPoint slide