The role of oxygen in the interaction of emeraldine base polyaniline with Cu(II) or Fe(III) ions in NMP solution

The influence of molecular oxygen in the interactions of emeraldine base form of polyaniline (EB-PANI) with Fe(III) or Cu(II) ions in 1-methyl-2-pyrrolidinone (NMP) solutions has been investigated by UV-vis-NIR, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies. Through the set of spectroscopic results it was possible to rationalize the role Of O(2) and to construct a scheme of preferential routes occurring in the interaction of EB-PANI with Fe(III) or Cu(II). Solutions of 4.0 mmol L(-1) EB-PANI with 0.8, 2.0 and 20 mmol L(-1) Fe(III) or Cu(II) ions in NMP were investigated and the main observed reactions were EB-PANI oxidation to pernigraniline (PB-PANI) and EB-PANI doping process by pseudo-protonation, or by a two-step redox process. In the presence Of O(2), PB-PANI is observed in all Fe(III)/EB solutions and EB-PANI doping only occurs in solutions with high Fe(III) concentrations through pseudo-protonation. On the other hand, emeraldine salt (ES-PANI) is formed in all Fe(III)/EB solutions under N(2) atmosphere and, in this case, doping occurs both by the pseudo-protonation and two-step redox mechanisms. In all Cu(II)/EB solutions PB-PANI is formed both in the presence and absence of O(2), and only for solutions with high Cu(II) concentrations doping process occurs in a very low degree. The most important result from EPR spectra was providing evidence for redox steps. The determined Cu(II) signal areas under oxygen are higher than under N(2) and, further. the initial metal proportions (1:2:20) are maintained in these spectra, indicating that Cu(I) formed are re-oxidized by O(2) and. so, Cu(II) ions are being recycled. Consistently, for the solutions prepared under nitrogen, the corresponding areas and proportions in the spectra are much lower, confirming that a partial reduction of Cu(II) ions actually occurs. (C) 2009 Elsevier B.V. All rights reserved.

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential (E(1/2)(ox)) = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v = 20 mV s(-1)). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 x 10(-4) to 4.0 x 10(-3) mol L(-1) for the determination of nitrite, with a detection limit of 2.1 x 10(-4) mol L(-1) and the amperometric sensitivity of 8.04 mA/mol L(-1). (C) 2010 Elsevier Ltd. All rights reserved.

Nitric oxide release using natural rubber latex as matrix

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

eNOS T-786C polymorphism affects atorvastatin-induced changes in erythrocyte membrane fluidity

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hyperfine interaction in Zn-Al layered double hydroxides intercalated with conducting polymers

Organic-inorganic hybrid materials based on the assembly between inorganic 2D host structure and polymer have received considerable attention in the last few years. This emerging class of materials presents several applications according to their structural and functional properties. Particularly, among others, layered double hydroxides (LDHs) provide the opportunity of preparing new organically modified 2D nanocomposites. Pyrrole carboxylic acid derivatives, namely 4-(lH-pyrrol-1-yl)benzoate, 3-(pyrrol-i-yl)-propanoate,7-(pyrrol-1-yl)-heptanoate, and aniline carboxylic acid derivative, namely 3-aminobenzoic acid, have been intercalated in LDHs of intralamellar composition Zn2Al(OH)(6). The LDHs were synthesized by the co-precipitation method at constant pH followed by hydrothermal treatment for 72 h. The materials were characterized by powder X-ray diffraction patterns (PXRD), transmission electron microscopy (TEM) thermogravimetric analysis (TGA), and electron spin resonance (ESR). The basal spacing found by the PXRD technique gives evidence of the formation of bilayers of the intercalated anions. ESR spectra present a typical signal with a superhyperfine structure with 6 + 1 lines (g = 2.005 +/- 0.0004), which is assigned to the interaction between a carboxylate radical from the guest molecules and a nearby aluminium nucleus (I = 5/2) from the host structure. Additionally, the ESR data suggest that the monomers are connected to each other in limited number after thermal treatment. (c) 2007 Elsevier Ltd. All rights reserved.

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigation about the copper adsorption on the chloropropylsilica gel surface modified with a nanostructured dendrimer DAB-Am-16: an analytical application for determination of copper in different samples

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Tracing source and evolution of suspended particles in the Rio Negro Basin (Brazil) using chemical species of iron

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Spectroscopic characterization of the reduction and removal of chromium (VI) by tropical peat and humin

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural XANES characterization of Ca0.99Sm0.01TiO3 perovskite and correlation with photoluminescence emission

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

On the photoluminescence behavior of samarium-doped strontium titanate nanostructures under UV light. A structural and electronic understanding

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

New layered double hydroxides intercalated with substituted pyrroles. 1. In situ polymerization of 4-(1H-pyrrol-1-yl)benzoate

The two-dimensional hybrid organic-inorganic materials Zn-2-Cr and Zn-2-Al-LDHs (Layered Double Hydroxides) containing 4-(1H-pyrrol-1yl)benzoate anions as the interlayer anions were synthesized by the co-precipitation method at constant pH followed by subsequent hydrothermal treatment for 72 h. The materials were characterized by PXRD, C-13 CP-MAS NMR, ESR, TGA, and TEM. The basal spacing found by the X-ray diffraction technique is coincident with the formation of bilayers of the intercalated anions. Solid-state C-13 NMR and ESR data strongly suggest the partial in situ polymerization of the 4-(1H-pyrrol-1yl)benzoate anions during coprecipitation. (c) 2006 Elsevier Ltd. All rights reserved.

Multimethod study of the degree of humification of humic substances extracted from different tropical soil profiles in Brazil's Amazonian region

This work consisted of determining the degree of humification of humic substances (HS) extracted from six different Amazonian soils collected from flooded and unflooded regions at different depths (0-10, 10-20, 20-40, and 60 cm). The humic substances were extracted according to procedures recommended by the International Humic Substances Society and characterized using elemental analysis, electron paramagnetic resonance (EPR), and fluorescence spectroscopy. The findings on semiquinone-type free radical concentrations in HS showed variations of 0.10-7.55x10(18) spins g(-1) of carbon (g C)(-1), indicating considerable differences between the humification levels of HS extracted from Amazonian soils. The results showed an average of 1.71 +/- 0.04 x 10(18) spins (g C)(-1), which is congruent with other data reported in the literature on Tropical soils. It was found that, on average, HS extracted from flooded soil contained higher semiquinone-type free radical concentrations than HS extracted from unflooded soils, indicating the influence of humidity in the humification process of organic matter. The humification process varies according to the profile, and the 10-20- and 0-10-cm profiles generally showed more humified HS. The degree of humification of the HS studied here displayed a similar behavior when exposed to fluorescence (excitation at 465 nm) and EPR (R=0.85). However, the low correlation between the C/H, C/O, and C/N atomic ratios and the semiquinone-type free radical concentration/fluorescence intensities indicated that data obtained by these techniques with regard to the degree of humification of HS may lead to different conclusions. (c) 2004 Elsevier B.V. All rights reserved.

New layered double hydroxides intercalated with substituted pyrroles. 2. 3-(Pyrrol-1-yl)-propanoate and 7-(pyrrol-1-yl)-heptanoate LDHs

We report the synthesis and characterization of organic-inorganic hybrid materials: Zn-2-Al-LDHs (layered double hydroxides) containing 3-(1H-pyrrol-1-yl)-propanoate and 7-(1H-pyrrol-l-yl)-heptanoate as the interlayer anions. The LDHs were synthesized by the co-precipitation method at constant pH followed by hydrothermal treatment for 72 h. The materials were characterized by PXRD, C-13 CP-MAS NMR, TGA, and ESR. The basal spacing found by PXRD technique is coincident with the formation of bilayers of the intercalated anions. The solid state C-13 NMR showed that the interlayered anions remain identical after intercalation. ESR data suggest that the monomers connect each other in a limited number of guests when a thermal treatment is applied. The inorganic LDH sheets delay the temperature of degradation of the monomers. (c) 2006 Elsevier Ltd. All rights reserved.

Correlation between the mobility of spin-labeled peptide chains and resin solvation: An approach to optimize the synthesis of aggregating sequences

Resin solvation properties affect the efficiency of the coupling reactions in solid-phase peptide synthesis. Here we report a novel approach to evaluate resin solvation properties, making use of spin label electron paramagnetic resonance (EPR) spectroscopy. The aggregating VVLGAAIV and ING sequences were assembled in benzhydrylamine-resin with different amino group contents (up to 2.6 mmol/g) to examine the extent of chain association within the beads. These model peptidyl-resins were first labeled at their N-terminus with the amino acid spin label 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (Toac). Their solvation properties in different solvents were estimated, either by bead swelling measurement or by assessing the dynamics of their polymeric matrixes through the analysis of Toac EPR spectra, and were correlated with the yield of the acylation reaction. In most cases the coupling rate was found to depend on bead swelling. Comparatively, the EPR approach was more effective. Line shape analysis allowed the detection of more than one peptide chain population, which influenced the reaction. The results demonstrated the unique potential of EPR spectroscopy not only for improving the yield of peptide synthesis, even in challenging conditions, but also for other relevant polymer-supported methodologies in chemistry and biology.