Nakédia M.F. Carvalho

Properties of (μ-Oxo)di-iron complexes and catalytic activity toward cyclohexane oxidation

We report herein the synthesis and characterization of two dinuclear μ-oxo iron compounds obtained through the reactions of FeSO4•7H2 O and FeCl3•6H2 O with 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol (L5), which resulted in the compounds [(SO4)(L5)Fe(μ-O)Fe(L5)(SO4 )]•6H2O, 1, and [Cl(L5)Fe(μ-O)Fe(L5)Cl]Cl2• 2H2O, 2. The electronic spectra of both compounds show absorption bands only in the UV range. The electrochemical analysis showed that the dinuclear unit is more stable under reduction in compound 1 than in compound 2, while the Mossbauer spectroscopy revealed that the monodentate ligands (sulfate and chloride) have a significant influence on the Mossbauer parameters determined for 1 and 2, particularly on the quadrupole splitting values. Both compounds were studied as catalysts in reactions of cyclohexane oxidation, using H2O2 and t-BuOOH as oxidants, in a substrate:oxidant:catalyst ratio of 1000:1000:1. Cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide, t-butyl cyclohexyl peroxide and adipic acid were formed during the process. The experiments revealed that compound 2 is, in general, more active than compound 1 in promoting cyclohexane oxidation.

Synthesis and Characterization of Cobalt(III), Nickel(II) and Copper(II) Mononuclear Complexes with the Ligand 1,3-bis[(2-aminoethyl)amino]-2-propanol and Their Catalase-Like Activity.

In this work, we present the synthesis and characterization of two new mononuclear complexes with the ligand 1,3-bis[(2-aminoethyl)amino]-2-propanol (HL), [Co(L)(H2O)](ClO4)2 (1), [Ni(HL)](ClO4)2 (2), as well as the known complex [Cu(HL)](ClO4)2 (3) for comparison. Their abilities to catalyze the dismutation of H2O2 and the oxidation of cyclohexane were investigated. The complexes were characterized by X-ray diffraction, elemental analysis, electronic and infrared spectroscopy, cyclic voltammetry, electrospray ionization mass spectrometry (ESI-MS) and conductivity measurements. The X-ray structures showed that the nickel (2) and copper (3) complexes are tetracoordinated, with the metal ion bound to the nitrogen atoms of the ligand. On the other hand, the cobalt complex (1) is hexacoordinated, possessing additional bonds to the alkoxo group of the ligand and to a water molecule. Neither of the complexes was able to catalyze the oxidation of cyclohexane, but all of them exhibited catalase-like activity, following Michaelis-Menten kinetics, which suggest resemblance with the catalase natural enzymes. The catalytic activity followed the order: [Ni(HL)](ClO4)2 (2) > [Cu(HL)](ClO4)2 (3) > [Co(L)(H2O)](ClO4)2 (1). As far as we know, this is the first description of a nickel complex presenting a significant catalase-like activity.

Uso de equações lineares na determinação dos parâmetros de Michaelis-Menten

The Michaelis-Menten equation is used in many biochemical and bioinorganic kinetic studies involving homogeneous catalysis. Otherwise, it is known that determination of Michaelis-Menten parameters KM, Vmax, and kcat by the well-known Lineweaver-Burk double reciprocal linear equation does not produce the best values for these parameters. In this paper we present a discussion on different linear equations which can be used to calculate these parameters and we compare their results with the values obtained by the more reliable nonlinear least-square fit.

Theoretical and Empirical Studies on the Catalytic Partial Oxidation of Methane Promoted by FeY and Fe(piperazine)Y Complexes (Y = Y-zeolite)

In this study, we synthesized and characterized zeolite-encapsulated Fe(III) complexes containing piperazine-derived ligands. The catalytic activity of these complexes was tested in the partial oxidation of methane to methanol using O2 as a low-pressure oxidant. Values for methane conversion of up to 1.2% with methanol selectivity of up to 6.7% were obtained. The experimental data were compared with thermodynamic simulation results for the reaction that takes place as a basic principle, the minimization of Gibbs free energy.

Electrochemical behaviour of mononuclear Fe(III) complexes as models for oxygenases: reactivity of Fe(II) species electrochemically formed in situ toward dioxygen

In this paper, we report the electrochemical study of a family of mononuclear Fe(III) complexes [Fe(BMPA)Cl(3)] 1, [Fe(MPBMPA)Cl(3)] 2, [Fe(PBMPA)Cl(2)]3 and [Fe(PABMPA)Cl(2)](ClO(4)) 4, where the ligand BMPA is bis-(2-pyridylmethyl)amine, and MPBMPA, PBMPA and PABMPA are the N-methylpropanoate, N-propanoate and N-propanamide BMPA-derivatives, respectively. It was possible to verify the influence of the different ligands on the redox properties of the complexes and from this to classify the complexes according to their Lewis acidity through the Fe(III)/Fe(II) redox process, resulting in the following decreasing order in CH(3)CN solution: 4> 2> 1> 3. The effect of the solvents CH(3)CN and DMSO on their electrochemical properties was also determined. Furthermore, we investigated the reactivity of the electrochemically-generated Fe(II) complexes toward dioxygen and of the Fe(III) complexes toward superoxide through cyclic voltammetry. All the complexes reacted with dioxygen and superoxide in DMSO solution. Redox processes attributed to oxygenated species were observed in a more cathodic potential than those of the original compounds. According to the data, the new species Fe(II)-O(2) converts itself to Fe(III)-O(2)(-), which presents a new redox wave attributed to the process Fe(III)-O(2)(-) + e(-) --> Fe(II)-O(2)(-). The same species Fe(III)-O(2)(-) is formed from the reaction of the Fe(III) form of the complexes and KO(2).