Antonio S. Mangrich

Lessons from the Terra Preta de Índios of the Amazon region for the utilisation of charcoal for soil amendment

Neste trabalho faz-se a divulgacao do potencial de carvoes e residuos orgânicos parcialmente carbonizados visando obter materiais que mimetizam a materia orgânica do solo das Terras Pretas de Indio da Amazonia, e que sirvam como condicionadores de solo e sequestrem carbono de forma recalcitrante e reativa. Pesquisas desenvolvidas por grupos brasileiros e estrangeiros tem contribuido para o entendimento do surgimento e utilizacao das Terras Pretas de Indio da Amazonia. Aqui sao divulgados resultados de estudos quimicos no sentido do desenvolvimento do conhecimento cientifico e tecnologico e de inovacao no aproveitamento de subprodutos orgânicos, principalmente de industrias de biocombustiveis, carvao vegetal metalurgico e outros, buscando imitar a excelente performance da chamada Terras Pretas de Indio da Amazonia.

Dehydrated halloysite intercalated mechanochemically with urea: thermal behavior and structural aspects.

Urea has been intercalated mechanochemically into dehydrated halloysite and analyzed by X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance ultraviolet/visible spectroscopy (DRUV-VIS), thermal analysis (TGA/DTA), transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR). The basal distance expands from 7.4 to 10.7 A and the interaction of urea to adjacent layers of halloysite through hydrogen bonds increases the structural order of the matrix. After heat treatment in air at different temperatures, decomposition products begin to appear starting from 100 degrees C. Although the basal distance remains constant up to 160 degrees C and collapses to the original value at 200 degrees C, urea and the decomposition products are still present in the sample. Starting from 125 degrees C, urea decomposition products reduce halloysite structural Fe3+ centers to Fe2+, as indicated by DRUV-VIS and EPR spectroscopy.

N(4)-tolyl-2-benzoylpyridine thiosemicarbazones and their copper(II) complexes with significant antifungal activity: crystal structure of N(4)-para-tolyl-2-benzoylpyridine thiosemicarbazone

) para os complexos. Nossos resultados sugerem que a coordenacao ao cobre constitui estrategia interessante de reducao da dose necessaria a atividade. Three new copper complexes of general formula [Cu(HL)Cl 2 ] have been obtained with N(4)-ortho (H2Bz4oT, HL1), N(4)-meta (H2Bz4mT, HL2) and N(4)-para-tolyl-2-benzoylpyridine thiosemicarbazone (H2Bz4pT, HL3), in which the thiosemicarbazone attaches to the metal through the N py -N-S chelating system. H2Bz4pT (HL3) crystallizes in the P1 – space group, with a = 9.509(3) A, b = 9.807(4) A, c = 11.564(4) A; α = 100.76(2)°, β = 105.99(2)°, γ = 114.59(2)°. The thiosemicarbazones and their copper(II) complexes exhibit high antifungal activities against Candida albicans with low values of minimum inhibitory concentration (MIC), in the 8-0.3 μg mL -1 (23 – 0.7 μmol L -1 ) range for the free bases and in the 1-0.1 μg mL -1 (2 – 0.3 μmol L -1 ) range for the complexes. Our results suggest that coordination to copper(II) could be an interesting strategy for dose reduction.

Chemical modification of zinc hydroxide nitrate and Zn–Al-layered double hydroxide with dicarboxylic acids

A zinc hydroxide nitrate (ZHN), Zn5(OH)8(NO3)2.2H2O, and a layered double hydroxide (LDH), Zn/Al-NO3 were doped with 0.2 mol% of Cu2+ during alkaline chemical precipitation. Both compounds were intercalated with adipate ((-)OOC(CH2)4COO(-)), azelate ((-)OOC(CH2)7COO(-)), and benzoate (C6H5COO(-)) ions through ion exchange reactions. Solid state 13C nuclear magnetic resonance spectroscopy showed only one signal of carboxylic carbon for adipate and azelate intercalated into LDH, indicating that the carboxylic ends of both acids were equivalent, whereas the signal split when the intercalation was into the ZHN matrix. The electron paramagnetic resonance (EPR) spectrum of copper in octahedral cation sites of LDH layers showed a Hamiltonian parameter ratio g ||/A ||=170 cm and, after intercalation of adipate, the change was not significant: g ||/A ||=174 cm. This result indicates that the carboxylate ions did not coordinate with copper centers. Nonetheless, the intercalation of azelate increased the ratio to g ||/A ||=194 cm, similar to the spectra of ZHN modified with adipate, g ||/A ||=199 cm, and azelate, g ||/A ||=183 and 190 cm, which are associated with the coordination of copper by weak carboxylate anion ligands. Copper occupies octahedral or tetrahedral sites in ZHN layers, and the EPR spectra indicate that the dicarboxylate anions reacted preferentially with octahedral sites, whereas benzoate reacted with both sites.

Antioxidant and pro-oxidant properties of some di-Schiff base copper(II) complexes

Abstract The di-Schiff base complexes, [ N , N ′-bis(2-pyridyl)methylene-1,2-diaminoethane]- ( N , N ′, N ″, N ′′′)-copper(II) ( 1 ), and [ N , N ′-bis(2-acetylpyrazyl)methylene-1,3-diaminopropane]-( N , N ′, N ″, N ′′′)-copper(II) ( 2 ), were prepared in the perchlorate form, and characterized using elemental analysis, UV/Vis, infrared (IR) and electronic paramagnetic resonance (EPR) spectroscopies. The relative thermodynamic stabilities of these complexes were estimated by circular dichroism (CD), using bovine albumin as the competitive ligand. Their antioxidant properties were verified by their catalytic activities in the dismutation of superoxide radicals (SOD activity), and in the disproportionation of hydrogen peroxide (catalase activity). The determined SOD-activities were comparable to that of known SOD mimics, with IC 50 =0.447 for ( 1 ) and 0.0902 μM for ( 2 ), in comparison to 0.0054 μM for the native Cu 2 Zn 2 -SOD. The determined rate constants for the catalase activity were k =0.098 mol −1 dm 3 s −1 , and 1.10 mol −1 dm 3 s −1 to compounds ( 1 ) and ( 2 ), respectively.

Cu2+ ions as a paramagnetic probe to study the surface chemical modification process of layered double hydroxides and hydroxide salts with nitrate and carboxylate anions

A layered zinc hydroxide nitrate (Zn5(OH)8(NO3)2.2H2O) and a layered double hydroxide (Zn/Al-NO3) were synthesized by coprecipitation and doped with different amounts of Cu2+ (0.2, 1, and 10 mol%), as paramagnetic probe. Although the literature reports that the nitrate ion is free (with D3h symmetry) between the layers of these two structures, the FTIR spectra of two zinc hydroxide nitrate samples show the C2v symmetry for the nitrate ion, whereas the g ||/A || value in the EPR spectra of Cu2+ is high. This fact suggests bonding of some nitrate ions to the layers of the zinc hydroxide nitrate. The zinc hydroxide nitrate was used as matrix in the intercalation reaction with benzoate, o-chlorobenzoate, and o-iodobenzoate ions. FTIR spectra confirm the ionic exchange reaction and the EPR spectroscopy reveals bonding of the organic ions to the inorganic layers of the zinc hydroxide nitrate, while the layered double hydroxides show only exchange reactions.

Novel Aminonaphthoquinone Mannich Bases Derived from Lawsone and their Copper(II) Complexes: Synthesis, Characterization and Antibacterial Activity

A series of novel Mannich bases (HL1-HL13) derived from 2-hydroxy-1,4-naphthoquinone (lawsone), substituted benzaldehydes [C6H2R1R2R3C(O)H] and various primary amines (NH2R4, R4 = n-butyl, benzyl, allyl, 2-furfuryl), and their Cu2+ complexes, [Cu(L1)2]-[Cu(L13)2], have been synthesized and fully characterized by analytical and spectroscopic methods. The structures of complexes 1(R1 = R2 = R3 = H; R4 = Bu), 2(R1 = R3 = H; R2 = NO2; R4= Bu) and 7 (R1 = OH; R2 = R3 = H; R4= Bu) were determined by single crystal X-ray diffraction studies. All complexes crystallize in centrosymmetric space groups, with a copper atom in the inversion centre. Two L- coordinate through the naphthalen-2-olate oxygen and secondary amine-N atoms, forming six-membered chelate rings around the copper atom in a trans-N2O2 environment; spectroscopic data confirm that the other complexes exhibit similar molecular arrangement. The antimicrobial activity of all compounds has been tested on seven different strains of bacteria: Bacillus cereus, Bacillus subtilis, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Pseudomonas aeruginosaand Staphylococcus aureus. In general, Mannich bases were more active than complexes, HL11(R1 = OH; R2 =H; R3 = Me; R4= Bn) and HL13(R1 = OH; R2 = H; R3 = Br; R4= Bn) being the most potent inhibitors. The MIC for the most active compound HL11against S. Coliwas 20 µmol L-1 (8 µg mL-1), better than Chloramphenicol (90 µmol L-1) and well below most values reported for other naphthoquinones.

Photochemical weathering study of Brazilian petroleum by EPR spectroscopy

Abstract The EPR spectrum of the petroleum of the Campos Basin, Rio de Janeiro, Brazil shows signals characteristic of free radical, vanadyl (VO 2+ ) and iron III ion (Fe 3+ ). The value of g =2.0045±0.0001 corresponds to free radical species with a peak-to-peak line width Δ H =4.64±0.03 G. The g spectroscopic factor suggests the presence of free radicals in aromatic systems containing carbon, nitrogen and oxygen. Δ g o (chemical shift)=21.6±0.1 determined for the VO 2+ species characterizes porphyrin and non-porphyrin (with sulfur) complexes in asphaltenes of the crude oil. The species observed with g =2.16±0.01 corresponds to Fe 3+ in Fe 2 O 3 , and therefore is not part of the molecular structure of the oil under study. The photochemical weathering of Brazilian oil as a film over seawater was monitored by EPR. After 100 h of solar irradiation the line width of the radical decreased by 10.6%, indicating rearrangement among radicals. The Δ g o value for VO 2+ in the irradiated oil decreased to 19.5±0.1, characterizing degradation of porphyrin systems. Solar irradiation promotes the partial destruction of the asphaltenic fraction of the oil.

Copper(II) complexes with (2-hydroxybenzyl-2-pyridylmethyl)amine–Hbpa: syntheses, characterization and crystal structures of the ligand and [Cu(II)(Hbpa)2](ClO4)2·2H2O

Abstract Copper(II) complexes were synthesized and characterized by means of elemental analysis, IR and visible spectroscopies, EPR and electrochemistry, as well as X-ray structure crystallography. The group consists of discrete mononuclear units with the general formula [Cu(II)(Hbpa) 2 ](A) 2 · n H 2 O, where Hbpa=(2-hydroxybenzyl-2-pyridylmethyl)amine and A=ClO 4  − , n =2 ( 1 ), CH 3 COO − , n =3 ( 2 ), NO 3  − , n =2 ( 3 ) and SO 4  2− , n =3 ( 4 ). The structures of the ligand Hbpa and complex 1 have been determined by X-ray crystallography. Complexes 1 – 4 have had their UV–Vis spectra measured in both MeCN and DMF. It was observed that the compounds interact with basic solvents, such that molecules coordinate to the metal in axial positions in which phenol oxygen atoms are coordinated in the protonated forms. The e values were all less than 1000 M −1 cm −1 . EPR measurements on powdered samples of 1 – 3 gave g ∣∣ / A ∣∣ values between 105 and 135 cm −1 , typical for square planar coordination environments. Complex 4 ·3H 2 O exhibits a behaviour typical for tetrahedral coordination. The electrochemical behaviour for complexes 1 and 2 was studied showing irreversible redox waves for both compounds.

Synthesis, structure and properties of the first dinuclear copper(II) complex as a structural model for the phenolic intermediate in tyrosinase–cresolase activity

Abstract The synthesis, X-ray crystal structure and spectroscopic and electrochemical properties of the new dinuclear copper(II) complex [Cu2(Hbtppnol)CH3COO](ClO4)2 (1), employing the novel unsymmetric dinucleating ligand N-(2-hydroxybenzyl)-N,N′,N′-tris(2-pyridylmethyl)-1,3-diaminopropan-2-ol (H2btppnol), are presented. This complex could be a relevant model for the axial interaction of a phenolic substrate to tyrosinase during cresolase activity.