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

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

JOURNAL OF INORGANIC BIOCHEMISTRY

ELSEVIER SCIENCE INC

Año: 2018 vol. 182 p. 29 - 36

0162-0134

A new phenoxo-bridged diMn III complex, Na[Mn 2 L(OH) 2 (H 2 O) 2 ]·5H 2 O (1), obtained with the ligand L 5− = 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 1 H NMR spectroscopic studies showed that the complex exists in solution as a monoanionic diMn III complex. Complex 1 catalyzes H 2 O 2 disproportionation withsecond-order rate constant k cat = 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 2 redox cycle, which distinguishes this catalyst from other phenoxo-bridged diMn complexes that cycle between Mn II Mn III /Mn III Mn IV species. Additionof 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 H 2 O 2 but also favor the formation of active homovalent diMn species, just as observed for the enzyme.