Biomimetic Mn-Catalases Based on Dimeric Manganese Complexes in Mesoporous Silica for Potential Antioxidant Agent
† Laboratoire de Chimie, ENS de Lyon, Université de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France
‡Departament de Química Inorgànica and §Crystal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, 08028 Barcelona, Spain
∥ Institut de Ciència Molecular, Universitat de València, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
Inorg. Chem., Article ASAP
DOI: 10.1021/acs.inorgchem.5b01425
Publication Date (Web): October 20, 2015
Copyright © 2015 American Chemical Society
*E-mail: luis.escrichetur@gmail.com., *E-mail: belen.albela@ens-lyon.fr.
Abstract
Two new structural and functional models of the Mn-catalase with formula [{MnIII(bpy)(H2O)}(μ-2-MeOC6H4CO2)2(μ-O){MnIII(bpy)(X)}]X, where X = NO3 (1) and ClO4 (2) and bpy = 2,2′-bipyridine, were synthesized and characterized by X-ray diffraction. In both cases, a water molecule and an X ion occupy the monodentate positions. The magnetic properties of these compounds reveal a weak antiferromagnetic behavior (2J = −2.2 cm–1 for 1 and −0.7 cm–1 for2, using the spin Hamiltonian H = −2J S1·S2) and negative zero-field splitting parameter DMn(−4.6 cm–1 and −3.0 cm–1 for 1 and 2, respectively). This fact, together with the nearly orthogonal orientation of the Jahn–Teller axes of the MnIII ions explain the unusual shape of χMT versus T plot at low temperature. Compound 1 presents a better catalase activity than 2 in CH3CN–H2O media, probably due to a beneficial interaction of the NO3− ion with the Mn complex in solution. These compounds were successfully inserted inside two-dimensional hexagonal mesoporous silica (MCM-41 type) leading to the same hybrid material ([Mn2O]@SiO2), without the X group. The manganese complex occupies approximately half of the available pore volume, keeping the silica’s hexagonal array intact. Magnetic measurements of [Mn2O]@SiO2 suggest that most of the dinuclear unit is preserved, as a non-negligible interaction between Mn ions is still observed. The X-ray photoelectron spectroscopy analysis of the Mn 3s peak confirms that Mn remains as MnIII inside the silica. The catalase activity study of material [Mn2O]@SiO2 reveals that the complex is more active inside the porous silica, probably due to the surface silanolate groups of the pore wall. Moreover, the new material shows catalase activity in water media, while the coordination compounds are not active.
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