Effect of coordination dissymmetry on the catalytic activity of manganese catalase mimics

Ripul Mehrotra (1) , Micaela Richezzi (1) , Claudia Palopoli (1) , Christelle Hureau (2) , Sandra Signorella (1)

1 IQUIR - Instituto de Química Rosario
2 LCC - Laboratoire de chimie de coordination

Two mixed-valence Mn(II)Mn(III) complexes, [Mn2L1(OAc)2(H2O)]BPh4·2.5H2O and [Mn2L2(OAc)2]·4H2O, obtained with unsymmetrical N4O2-hexadentate L1(2−) (H2L1 = 2-(N,N-bis(2-(pyridylmethyl)aminomethyl)-6-(N-(2-hydroxybenzyl)benzylaminomethyl)-4-methylphenol) and N4O3-heptadentate L2(3−) (NaH2L2 = 2-(N,N-bis(2-(pyridylmethyl)aminomethyl)-6-(N′-(2-hydroxybenzyl)(carboxymethyl)aminomethyl)-4-methylphenol sodium salt) ligands, have been prepared and characterized. Both complexes share a μ-phenolate-bis(μ-acetate)Mn(II)Mn(III) core and N3O3-coordination sphere around the Mn(II) ion, but differ in the donor groups surrounding Mn(III) (NO4(solvent) and NO5). In non-protic solvents, these two complexes are able to disproportionate at least 3600 equiv. of H2O2 without significant decomposition, with first-order dependence on catalyst and saturation kinetics on [H2O2]. Spectroscopic monitoring of the reaction mixtures revealed the two complexes disproportionate H2O2 employing a different redox cycle, with retention of dinuclearity. The higher catalytic efficiency of [Mn2L2(OAc)2] was rationalized in terms of the larger labilizing effect of the heptadentate ligand that favors the acetate-shift and the replacement of the non-coordinating benzyl arm of L1 by a carboxylate arm in L2 which facilitates the formation of the catalyst-H2O2 adduct, placing [Mn2L2(OAc)2] as the most efficient among the phenolate-bridged diMn catalysts based on the kcat/KM criterion.

Mots clés: Biomimics; diMn complexes; Unsymmetrical ligands; CAT activity; Mechanism; Spectroscopy

Domaines: Chimie de coordination

Ripul Mehrotra, Micaela Richezzi, Claudia Palopoli, Christelle Hureau, Sandra Signorella. Effect of coordination dissymmetry on the catalytic activity of manganese catalase mimics. Journal of Inorganic Biochemistry, 2020, 213, pp.111264. ⟨10.1016/j.jinorgbio.2020.111264⟩. ⟨hal-03025390⟩