Tuning the MnII2/MnIII2 redox cycle of a phenoxo-bridged diMn catalase mimic with terminal carboxylate donors.

Tuning the MnII2/MnIII2 redox cycle of a phenoxo-bridged diMn catalase mimic with terminal carboxylate donors.
J Inorg Biochem. 2018 Feb 02;182:29-36
Authors: Solís V, Palopoli C, Daier V, Rivière E, Collin F, Moreno DM, Hureau C, Signorella S
Abstract
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 the complex 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 MnIII2/MnII2 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.
PMID: 29407867 [PubMed - as supplied by publisher]

Source: Journal of Inorganic Biochemistry - February 2, 2018 Category: Biochemistry Authors: Solís V, Palopoli C, Daier V, Rivière E, Collin F, Moreno DM, Hureau C, Signorella S Tags: J Inorg Biochem Source Type: research