Tatiana López Fernández

A new oxo-vanadium complex employing an imidazole-rich tripodal ligand: a bioinspired bromide and hydrocarbon oxidation catalyst.

A vanadyl complex with the ligand (bis(1-methylimidazol-2-yl)methyl)(2-(pyridyl-2-yl)ethyl)amine was synthesized and fully characterized by X-ray crystallography, elemental analyses, cyclic voltammetry and infrared, electronic and electron paramagnetic resonance spectroscopies. This compound was designed under the so called hybrid concept. It shows to be able to promiscuously use hydrogen peroxide to oxidize bromide and to catalyze the oxidation of benzene and cyclohexane with very good selectivities.

Synthesis, characterization and catalytic activity of two novel cis-dioxovanadium(v) complexes: [VO2(L)] and [VO2(Hlox)]

respectively, in a distorted octahedral environment. The catalytic activity of these compounds towards cyclohexane oxidation was evaluated using H2O2 and t-BuOOH as oxidants. Both complexes presented > 70% selectivity for cyclohexylhydroperoxide formation. B3LYP/6-31G(d) calculations were used to confirm the geometry and to help assign the electronic spectra.

Binuclear CuII complexes as catalysts for hydrocarbon and catechol oxidation reactions with hydrogen peroxide and molecular oxygen

The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and HL2, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear CuII complexes, [Cu2(L1)2]Cl2•2H2O, complex 1, and [Cu2(L2)2](ClO4)2•1.5H2O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex 1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a Cu...Cu distance of 3.043(10) A, which is similar to the observed for catechol oxidase (2.90 A). The catalytic reactivities of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall hydrocarbon oxidation conversion values of 6.34 % and 7.15 %, respectively. However, for complex 1, only cyclohexanol (Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1% for Cy-OH. This low overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate CuICuI center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative charge when the complex is reduced from CuIICuII to CuICuI.

Simple enzymatic methods for glycerol analysis in commercial beverages

Two enzymatic methods using amperometric and colorimetric detection based on two coupled activities (glyceroquinase and glycerol-3-phosphate oxidase) were compared for the glycerol content determination. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark-type electrode and correlated with the glycerol concentration. In addition to the enzymatic-colorimetric method, there is a third enzymatic reaction that can be used to form a coloured compound; this method involves the addition of peroxidase, 4-chlorophenol and 4-aminoantipyrine. The enzymatic methods studied showed good linearity in the range of 4 to 60 μmol L−1 glycerol with a detection limit of 1 μmol L−1. Studies of glycerol recovery in fortified sugar cane liquor showed a recovery of 98 ± 2% for the enzymatic-amperometric method and of 96 ± 1% for the enzymatic-colorimetric method. These two methods were applied to the determination of glycerol in beverages and good correlations were found between these methods.

Estudo espectroscópico de compósito obtido da reação no estado sólido entre um complexo mononuclear de vanádio(IV) e caulinita

The use of probes, such as paramagnetic species diluted in diamagnetic materials in EPR spectroscopy, and mathematical tools such, as the Kubelka-Munk function in DRUV-VIS spectroscopy are strategies in the analysis of complex mixtures of solid materials. The results obtained here show that the solid state reaction between the complex, [VO(acac)(BMIMAPY)] [ClO4], BMIMAPY = [(bis(1-methylimidazole-2-yl)methyl)(2-(pyridyl-2-yl)ethyl) amine] and acac = acetilacetonate, with kaolinite turns possible to obtain anisotropic EPR spectrum of the complex with a reasonable level of resolution. The study by DRUV-VIS using the method of second derivative mode of the Kubelka-Munk function revealed new complex structural arrangements, a solid hitherto unknown.

Synthesis, structural and spectroscopic studies of BNSalanH2 and BPSalanH2

Abstract The synthesis and characterization of gauche-N,N′-bis-[(2-cyanoethyl)-(2-hydroxyphenylmethyl)]ethane diamine, BNSalanH2 and anti-N,N′-bis-[(methylpropanoate)-(2-hydroxyphenylmethyl)]ethane diamine, BPSalanH2 are reported. These BNSalanH2, O2N4, and BPSalanH2, O4N2, molecules have both acidic and basic groups. The BNSalanH2 and BPSalanH2 molecules adopt a gauche and anti conformation, respectively, and Z stereochemistries. The conformations are governed by intramolecular interactions of both classical and non classical hydrogen bond types. In addition, a 3D self-arrangement in BNSalanH2 is created by C-HNnitrile hydrogen bonds linking molecules along [100] and [010]. The X-ray data for BNSalanH2 are: tetragonal, P41212, a = 7.7030(11) Å, b = 7.7030(11) Å, c = 34.907(7) Å, V = 2071.2(6) Å3, Z = 4, R1 = 0.0483; for BPSalanH2 are: monoclinic, P21/c, a = 12.2572(5) Å, b = 7.9993(4), c = 13.4437(5) Å, β = 108.202(2)° V = 1252.18(9) Å3, Z = 2, R1 = 0.0614.