Biomimetic Mn-catalases based on dimeric manganese complexes in mesoporous silica for potential antioxidant agent

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 for 2, 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

The dynamics of water in nanoporous silica studied by dielectric spectroscopy

International audienceBroad-band dielectric spectroscopy is used to investigate the dynamics of hydration water on the surface of the cylindrical pores of a nanostructured silica material (MCM-41, with pore diameter of 3.2 nm) at various hydrations, in the temperature range 250-150 K. We focus our attention on orientational relaxations that shift from 0.5 MHz at 250 K to less than 1 Hz at 150 K. The measurements distinguish the relaxation of the hydroxyl groups at the surface of silica from the orientational dynamics of hydration water which strongly depends on the degree of hydration. Although it is significantly faster than the dynamics of water in ice, the orientational relaxation of “non-freezing” water has an activation energy comparable to that in ice when the hydration layer is complete and approximately two-molecule thick

Si-O-Si Angle Distribution in Amorphous Silica Characterized by EXAFS Multiple Scattering Calculations

EXAFS-Multiple Scattering (MS) calculations has been performed to characterize the second shell of neighbours around silicon in amorphous silica. To render the large Si-O-Si angle distribution, a combination of three regular [(Si(OSi)4] structural models covering the 130 to 160° angle range is used in the calculations

Minute-made and low carbon fingerprint microwave synthesis of high quality templated mesoporous silica

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Contrôle des étapes d’adsorption électrostatique et de greffage du complexe bis (éthylénediamine) cuivre(II) sur un gel de silice

L’évolution de la symétrie, de la force du champ cristallin et du nombre d’atomes voisins des ions Cu(II) complexés par l’éthylènediamine lorsqu’ils sont déposés à la surface d’une silice est étudiée par spectroscopie électronique, EXAFS et XANES. Différents modes de déposition de ces ions sont mis en évidence. L’imprégnation, consistant en un remplissage de pores par la solution cuivrique, conduit lors du séchage à la recristallisation du complexe bis(éthylènediamine) Cu(II) dans la porosité du support. L’échange ionique mettant en jeu l’acidité des groupements silanols de surface génère des "paires d’ions de surface" formées par les groupements SiO- et le complexe cuivrique. Le greffage s’opère progressivement sur le complexe échangé, lors du séchage à 100°C, par substitution dans la sphère de coordination du cuivre d’une molécule d’éthylènediamine par deux groupements SiO-, la silice jouant le rôle de ligand bidentate

MCM-41 "LUS": Alumina Tubular Membranes for Metal Separation in Aqueous Solution

1 Lam, K. F. Kassab, H. Pera-Titus, M. Yeung, K. L. Albela, B. Bonneviot, L.Heavy metals are discharged to the environment through industrial effluents in which certain amounts of valuable metal ions such as gold and silver are present. Current technologies remove metal ions nonspecifically, which constitutes a serious difficulty for metal recovery and reuse. The present article describes the synthesis of MCM-41 (LUS-type) membranes and their further surface functionalization with aminopropyl and sulfonate groups to separate valuable and/or toxic metal ions species in aqueous medium. A feasibility test for metal-ion separation is demonstrated using two model systems: (1) toxic metal removal by separating anionic chromate from cationic copper ions and (2) precious metal recovery by separating gold from copper ions. The results reveal that aminopropyl functionalized LUS membranes might show high selectivity to Cu(II) for the Cu(II)/Au(III) system, approaching virtually infinite selectivity depending on the pH values of both the feed and stripping solutions and the concentration of chloride counteranions. We provide a critical discussion about the relative role of cation diffusion and migration to gain insight into the metal-ion separation mechanisms