Tuning the Mn II 2 /Mn III 2 redox cycle of a phenoxo-bridged diMn catalase mimic with terminal carboxylate donors

PALOPOLI, CLAUDIA; COLLIN, FABRICE; SIGNORELLA, SANDRA; SOLÍS, VERÓNICA; RIVIÈRE, ERIC; HUREAU, CHRISTELLE; DAIER, VERÓNICA; MORENO, DIEGO M.

JOURNAL OF INORGANIC BIOCHEMISTRY

ELSEVIER SCIENCE INC

Año: 2017 vol. 182 p. 29 - 36

0162-0134

A new phenoxo-bridged diMnIII complex, Na[Mn2L(OH)2(H2O)2]·5H2O (1), obtained with the ligand L5− = 5‐methyl‐2‐hydroxo‐1,3‐xylene‐α,α‐diamine‐N,N,N′,N′‐tetraacetato, has been prepared and characterized. Mass spectrometry, conductivity, UV?visible, EPR and 1H NMR spectroscopic studies showed that thecomplex exists in solution as a monoanionic diMnIII complex. Complex 1 catalyzes H2O2 disproportionation with second-order rate constant kcat = 305(9) M−1 min−1 and without a time-lag phase. Based on spectroscopic results, the catalase activity of complex 1 in methanol involves a Mn(III)2 /Mn(II)2 redox cycle, which distinguishes this catalyst from other phenoxo-bridged diMn complexes that cycle between MnIIMnIII/MnIIIMnIV species. Addition of base stabilizes the catalyst, restrains demetallation during catalysis and causes moderate enhancement of catalase activity. The terminal carboxylate donors of 1 not only contribute as internal bases to assist deprotonation of H2O2 but also favor the formation of active homovalent diMn species, just as observed for the enzyme.