Influence of the disposition of the anisotropy axes into the magnetic properties of Mn-III dinuclear compounds with benzoato derivative bridges

The two new Mn-III dinudear compounds [{Mn-(H2O)(phen)}(2)(mu-4-CH3C6H4COO)(2)(mu-O)](ClO4)(2)center dot 3CH(3)CN center dot H2O (1.3CH(3)CN center dot H2O) and [{Mn(H2O)(phen)}(mu-O)](mu-2-BrC6H4COO)(2){Mn(NO3)(phen)}]NO3 (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn-III ions in both compounds. The different distortions from ideal geometry incite a very different magnetic behavior, affecting both the zero-field splitting parameters of the Mn-III ions (D-Mn and E-Mn) and the magnetic interaction between them. Compound 1, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state S = 0) and local D-Mn 0. Theoretical CASSCF and DFT calculations corroborate the different magnetic anisotropy and exchange coupling found in both compounds. Moreover, with the help of theoretical calculations, some interesting magneto-structural correlations have been found between the degree of distortion of the coordination octahedra and the magnetic coupling; it becomes more antiferromagnetic when the elongation parameter, Delta, in absolute value is increased

Compostos polinuclears de manganès mimètics d'enzims redox. Inserció en suports mesoestructurats. Estudi de les propietats magnètiques i catalítiques

[cat] Els organismes aerobis, com a subproducte del metabolisme, produeixen espècies reduïdes d'oxigen (ROS) de manera incompleta com: el radical superòxid (01, el peròxid d'hidrogen (H202) o el radical hidroxil (*OH), entre d'altres. Malgrat que les ROS tenen un paper essencial en l'organisme, una sobreproducció de ROS en l'organisme pot generar estrès oxidatiu. Aquest, sol estar associat a malalties degeneratives com l'Alzheimer, el Parkinson, l'esclerosi lateral amiotròfica, l'esclerosi múltiple o el càncer i a processos d'envelliment. Tot i així, el cos té certs mecanismes de defensa per controlar la homeòstasi de les ROS. Un d'aquests mecanismes són les catalases que s'encarreguen de desproporcionar el H2O2 en O2 i H2O. En el grup de Models en Bioinorgànica es sintetitzen compostos mimètics del centre actiu de les catalases de manganès que es troben en alguns bacteris. Aquests compostos mimètics són compostos dinuclears de Mn(III) de fórmula general [{Mn(L)(NN)}2(1.1-0)(1.1-n-RC6H4C00)2]X2. Els compostos sintetitzats en aquest treball consten de NN (Iligand bidentat) = 1,1 0-fenantrolina (phen) o 2,2'-bipiridina (bpy), X = perclorat (C104-) o nitrat (NO3-), L (posició làbil) = molècules de dissolvent o contra-anió i n-R (carboxilat pont) on R = Br o Me i n = 2, 3 o 4. A part de testar l'activitat catalítica dels compostos també s'estudien les propietats magnètiques. Els compostos dinuclears de manganès(III) poden presentar acoblaments magnètics tant del tipus ferromagnètic com antiferromagnètic depenent del Iligand carboxilat pont i dels paràmetres estructurals. Aquests compostos, en general, tenen un octàedre de coordinació més aviat allargat en la direcció del Iligand làbil (o eix Jahn-Teller) i per tant a l'hora d'ajustar-los ha estat necessari introduir altres paràmetres que tenen en compte l'anisotropia de l'ió Mn(III) (DM„ i EMn). Mitjançant càlculs teòrics s'ha pogut relacionar el signe d'aquests paràmetres amb la distorsió de l'octàedre. Per altra banda, a través de les correlacions magneto-estructurals s'ha intentat buscar una tendència general entre els factors estructurals dels compostos aquí estudiats i el tipus d'acoblament magnètic. També s'ha estudiat les propietats magnètiques de sistemes de Mn(II) (carboxilats de manganès (Mn(n-RC6H4C00)2) i compostos hexanuclears de valència mixta Mn(II)- Mn(III) de formula [Mn6(1.14-0)2(1.1-n-RC6H4C00)10(L)4] on en ambdós casos on R = Br o Me i n = 2, 3 i 4). Els primers són sistemes estesos de diferent nuclearitat. Tots ells presenten interaccions febles i el caràcter magnètic dependrà dels modes de coordinació del Iligand pont. D'altra banda, tots els compostos hexanuclears presenten un acoblament magnètic de tipus antiferromagnètic fort i sembla que el fet de canviar els Iligands no afecta a la interacció magnètica.[eng] Aerobic organisms, as a by-product of the metabolism, generate some incomplete reduced oxygen species (ROS) like 02' -, H202 or the radical •0H. Increased levels of ROS can cause oxidative damage and causing some degenerative diseases like Alzheimer, Parkinson, sclerosis or cancer. Nevertheless, biological organisms have some defence mechanisms to fight against ROS. One of them are catalase that decomposes H202 in 02 and H2O. In Models en Bioinorganica group Mn(III) dinuclears compounds are synthesised with the aim to mimic the active centre of the manganese catalase that can be found in some bacteria. The general formula for these compounds is [{Mn(L)(NN)}2(.1.-0) (1.1.-n-RC6H4C00)2]X2 where NN = bpy or phen, X = solvent molecule or counter-ion and R = Br or Me and n= 2, 3 or 4. Mn(III) dinuclear compounds, also presents magnetic coupling that can be ferromagnetic or antiferromagnetic depending on the carboxilato bridge and of its structural parameters. Through theoretical calculations we try to relate these parameters with the sign of the distortion of the octahedron. Moreover, through the magneto-structural correlations it has tried to find a general tendency among the structural factors of the compounds studied here and type of magnetic coupling. Also the catalase activity of the Mn(III) dinuclear compounds was studied. Despite all compounds presents catalytic activity, has been observed that all the ligands and the counter-ion have a certain effect on the reaction rate. However, the compounds are not stables or robust. To emulate the protein pocket and confer some stability to the Mn(IIII) compound during the catalysis, some of this compounds were introduced in a mesoporous support MCM-41 type. This supports were first functionalised by a molecular stencil patterning method (MST) and after the Mn(III) compound was introduced by an ionic exchange. The catalytic activity of the new hybrid materials presents an improved catalase activity than Mn(III) dinuclear compounds

Bio-inspired manganese mesoporous silica hybrid material as a water compatible antioxidant

International audienc

Multifunctionalized Mesostructured Silica Nanoparticles Containing Mn2 Complex for Improved Catalase-Mimicking Activity in Water

International audienceWe report the synthesis of a hybrid nanocatalyst obtained through the immobilization of bio-inspired [{Mn(bpy)(H2O)}(µ-2-MeC6H4COO)2(µ-O){Mn(bpy)(NO3)}]NO3 compound into functionalized, monodispersed, mesoporous silica nanoparticles. The in situ dual functionalization sol–gel strategy adopted here leads to the synthesis of raspberry-shaped silica nanoparticles of ca. 72 nm with a large open porosity with preferential localization of 1,4-pyridine within the pores and sulfobetaine zwitterion on the nanoparticles’ periphery. These nano-objects exhibit improved catalase-mimicking activity in water thanks to the encapsulation/immobilization of the catalytic active complex and high colloidal stability in water, as demonstrated through the dismutation reaction of hydrogen peroxide

Influence of the Disposition of the Anisotropy Axes into the Magnetic Properties of Mn^III Dinuclear Compounds with Benzoato Derivative Bridges

The two new Mn^III dinuclear compounds [{Mn­(H₂O)­(phen)}₂(μ-4-CH₃C₆H₄COO)₂(μ-O)]­(ClO₄)₂·3CH₃CN·H₂O (<b>1</b>·3CH₃CN·H₂O) and [{Mn­(H₂O)­(phen)}­(μ-O)­(μ-2-BrC₆H₄COO)₂{Mn­(NO₃)­(phen)}]­NO₃ (<b>2</b>) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn^III ions in both compounds. The different distortions from ideal geometry incite a very different magnetic behavior, affecting both the zero-field splitting parameters of the Mn^III ions (<i>D</i>_Mn and <i>E</i>_Mn) and the magnetic interaction between them. Compound <b>1</b>, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state <i>S</i> = 0) and local <i>D</i>_Mn < 0, while compound <b>2</b>, with compression in the oxo bridge direction, displays a ferromagnetic interaction (ground state <i>S</i> = 4) and local <i>D</i>_Mn > 0. Theoretical CASSCF and DFT calculations corroborate the different magnetic anisotropy and exchange coupling found in both compounds. Moreover, with the help of theoretical calculations, some interesting magneto-structural correlations have been found between the degree of distortion of the coordination octahedra and the magnetic coupling; it becomes more antiferromagnetic when the elongation parameter, Δ, in absolute value is increased