The role of solvent on the doping of polyaniline with Fe(III) ions

The products formed from the reaction of emeraldine base polyaniline (EB-PANI) with Fe(III) ions in N-methyl-pyrrolidone (NMP), dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol media have been investigated using UV-VIS-NIR and resonance Raman (lambda(0) = 632.8 and 1064 nm) spectroscopies. Through these results it was verified that the different PANI forms in solution can be formed by the suitable choice of the solvent. The behavior of Fe(III)/EB-PANI in different solvents was rationalized in terms of the interactions among Fe(III) ions, EB-PANI and solvent. In basic NMP, DMA and DMF media, the reaction of Fe(III) with EB-PANI yields EB-PANI doping giving ES-PANI and/or the EB-PANI oxidation to PB-PANI. The formation of ES-PANI is favored in DMF while PB-PANI is formed in a greater extension in NMP and DMA. In acidic m-cresol, only ES-PANI is produced in Fe(III)/EB-PANI solutions indicating the important role played by the solvent in the nature of the product. (C) 2010 Elsevier B.V. All rights reserved.

Removal of metal ions from aqueous solution by chelating polymeric hydrogel

Polysaccharide natural seed coat from the tree Magonia pubescens, in the form of hydrogel was used to remove metals in aqueous solution. Swelling tests indicate that seed coat presents hydrogel behavior, with maximum water absorption of 292 g water/g. Adsorption experiments performed using Na(+), Mg(2+), K(+), Ca(2+), Cr(3+), Fe(3+) and Zn(2+) demonstrated that the polysaccharide structure has a high capacity to extract these ions from the aqueous solution. Scanning electron microscopy revealed significant morphological changes of the material before and after water contact. Differential scanning calorimetry measurements indicate a signal shift of the water evaporation temperature in the material with adsorbed zinc. X-ray photoelectron spectroscopy analysis combined with theoretical studies by the density functional theory and on Hartree-Fock (HF) level evidence that the metallic ions were adsorbed through coordination with hydroxyl groups of polysaccharide. In the case of Zn(2+) the lowest HF energy was observed for the tetracoordination mode, where Zn(2+) is coordinated by two hydroxyl groups and two water molecules.

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.

Insights into preventive measures for dental erosion

Dental erosion is defined as the loss of tooth substance by acid exposure not involving bacteria. The etiology of erosion is related to different behavioral, biological and chemical factors. Based on an overview of the current literature, this paper presents a summary of the preventive strategies relevant for patients suffering from dental erosion. Behavioral factors, such as special drinking habits, unhealthy lifestyle factors or occupational acid exposure, might modify the extent of dental erosion. Thus, preventive strategies have to include measures to reduce the frequency and duration of acid exposure as well as adequate oral hygiene measures, as it is known that eroded surfaces are more susceptible to abrasion. Biological factors, such as saliva or acquired pellicle, act protectively against erosive demineralization. Therefore, the production of saliva should be enhanced, especially in patients with hyposalivation or xerostomia. With regard to chemical factors, the modification of acidic solutions with ions, especially calcium, was shown to reduce the demineralization, but the efficacy depends on the other chemical factors, such as the type of acid. To enhance the remineralization of eroded surfaces and to prevent further progression of dental wear, high-concentrated fluoride applications are recommended. Currently, little information is available about the efficacy of other preventive strategies, such as calcium and laser application, as well as the use of matrix metalloproteinase inhibitors. Further studies considering these factors are required. In conclusion, preventive strategies for patients suffering from erosion are mainly obtained from in vitro and in situ studies and include dietary counseling, stimulation of salivary flow, optimization of fluoride regimens, modification of erosive beverages and adequate oral hygiene measures.

Evaluation of physico-chemical properties of Portland cements and MTA

The purpose of this study was to evaluate the hydrogenionic potential and electrical conductivity of Portland cements and MTA, as well as the amount of arsenic and calcium released from these materials. In Teflon molds, samples of each material were agitated and added to plastic flasks containing distilled water for 3, 24, 72 and 168 h. The results were analyzed with a Kruskal-Wallis non-parametric test for global comparisons and a Dunn-Tukey test for pairwise comparisons. The results revealed no significant differences in the pH of the materials (p > 0.05). The electrical conductivity of the cements were not statistically different (p > 0.05). White non-structural cement and MTA BIO released the largest amount of calcium ions into solution (p < 0.05), while arsenic release was insignificant in all of the materials (p > 0.05). The results indicated that the physico-chemical properties of Portland cements and MTA were similar. Furthermore, all materials produced an alkaline environment and can be considered safe for clinical use because arsenic was not released. The electrical conductivity and the amount of calcium ions released into solution increased over time.

Dentin permeability of the apical third in different groups of teeth

This ex vivo study evaluated dentin permeability of the root canal in the apical third of different human groups of teeth. Eighty teeth were used, 8 from each dental group: maxillary and mandibular central incisors, lateral incisors and canines, maxillary first premolars (buccal and palatal roots), mandibular first premolars, and maxillary and mandibular second premolars, totalizing 88 roots that were distributed in 11 groups. The root canals were instrumented, irrigated with 1% NaOCl and 15% EDTA. Roots were immersed in 10% copper sulfate for 30 min and then in 1% rubeanic acid alcohol solution for the same period; this chemical reaction reveals dentin permeability by the formation of copper rubeanate, which is a dark-colored compound. Semi-serial 100-µm-thick cross-sections were obtained from the apical third of the roots. Five sections of each apical third were washed, dehydrated, cleared and mounted on glass slides for examination under optical microscopy. The percentage of copper ion infiltration and the amount of tubular dentin were quantified by morphometric analysis. The penetration of copper ions in the apical third ranged from 4.60 to 16.66%. The mandibular central and lateral incisors presented the highest dentin permeability (16.66%), while the maxillary canines and mandibular second and first premolars presented the lowest dentin permeability (4.60%, 4.80% and 5.71%, respectively; p<0.001). The other teeth presented intermediate permeability. In conclusion, dye penetration into dentin tubules at the apical region is strongly dependent on the group of teeth evaluated.

Avaliação de metais traços e íons majoritários em águas de chuva na cidade de São Paulo

Rainfall samples collected in the downtown area of São Paulo city, during 2003, exhibited average concentrations of cadmium, lead and copper of 1.33, 8.52 and 49.5 nmol L-1, respectively. Among the major ions, NH4+ was the predominant species followed by NO3-, SO4(2-) and Ca2+, with volume weighed mean (VWM) concentrations of 37.1, 20.1, 11.9 and 10.8 µmol L-1, respectively. All the determined species showed high inter-events variability, including free H+ ions whose VWM concentration was 4.03 µmol L-1, corresponding to a pH value of 5.39.

Enhanced response of the fricke solution doped with hematoporphyrin under X-rays irradiation

The vials filled with Fricke solutions were doped with increasing concentrations of Photogem®, used in photodynamic therapy. These vials were then irradiated with low-energy X-rays with doses ranging from 5 to 20 Gy. The conventional Fricke solution was also irradiated with the same doses. The concentration of ferric ions for the Fricke and doped-Fricke irradiated solutions were measured in a spectrophotometer at 220 to 340 nm. The results showed that there was an enhancement in the response of the doped-Fricke solution, which was proportional to the concentration of the photosensitizer. The use of such procedure for studying the radiosensitizing property of photosensitizers based on the production of free radicals is also discussed.

Técnica de bombeio e prova para medidas de absorção de estado excitado e de emissão estimulada, em materiais sólidos dopados com íons terras raras

Rare earth ion doped solid state materials are the most important active media of near-infrared and visible lasers and other photonic devices. In these ions, the occurrence of Excited State Absorptions (ESA), from long lived electronic levels, is commonplace. Since ESA can deeply affect the efficiencies of the rare earth emissions, evaluation of these transitions cross sections is of greatest importance in predicting the potential applications of a given material. In this paper a detailed description of the pump-probe technique for ESA measurements is presented, with a review of several examples of applications in Nd3+, Tm3+ and Er3+ doped materials.

EPR and magnetic studies of a carboxylate-bridged dinuclear copper(II) compound: [cu2(flu)4(dmf)2]

We report magnetic and EPR (electron paramagnetic resonance) spectroscopy studies of [Cu2(flu)4(dmf)2] (flu = flufenamate and dmf = dimethylformamide), which has CuII ions in tetracarboxylate "paddle wheel" dinuclear units. Susceptibility measurements at 10 < T < 275 K allowed the evaluation of an antiferromagnetic intradinuclear exchange coupling J0 = -294 ± 5 cm-1 between CuII ions (Hex = "J0 S1·S2). EPR experiments at 300 K in powder and single-crystals at 9.5 and 34.4 GHz indicated g// = 2.373, g⊥ = 2.073 and zero field splitting parameters D = (-0.334 ± 0.001) cm"1 and E ca. 0. EPR signal intensity measurements at X-band in the range 4 < T < 295 K indicated that J0 = "283 ± 5 cm"1. A higher limit |J´| < 5×10-3 cm-1 for the interdinuclear exchange coupling between neighbor units at ca.14.24 Å was estimated from the angular variation of the single crystal spectra around the magic angles. The results are discussed in terms of the structure of the dinuclear unit and the bridges connecting CuII ions and compared with values reported for similar compounds.

Estudo das interações entre o complexo polieletrolítico trimetilquitosana/carboximetilcelulose e Cu+2, ácido húmico e atrazina em solução aquosa

The polyelectrolyte complex (PEC) resulting from the reaction of sodium carboxymethylcellulose (CMC) and N,N,N-trimethylchitosan hydrochloride (TMQ) was prepared and then characterized by infrared spectroscopy and energy dispersive X rays analysis. The interactions involving the PEC and Cu2+ ions, humic acid and atrazine in aqueous medium were studied. From the adsorption isotherms the maximum amount adsorbed (Xmax) was determined as 61 mg Cu2+/g PEC, 171 mg humic acid/g PEC and 5 mg atrazine/g PEC. The results show that the CMC/TMQ complex has a high affinity for the studied species, indicating its potential application to remove them from aqueous media.

Preparação de membranas de acetato de celulose organomodificadas para adsorção dos íons Cu(II), Cd(II), Mn(II) e Ni(II)

Cellulose acetate polymeric membranes had been prepared by a procedure of two steps, combining the method of phase inversion and the technique of hydrolysis-deposition. The first step was the preparation of the membrane, and together was organomodified with tetraethylortosilicate and 3-aminopropyltrietoxysilane. Parameters that exert influence in the complexation of the metallic ion, as pH, time of complexation, metal concentration, had been studied in laboratory using tests of metal removal. The membranes had presented resistance mechanics and reactivity to cations, being able to be an alternative for the removal, daily pay-concentration or in the study of the lability of metals complexed.

Degradação eletroquímica do cloranfenicol em reator de fluxo

This paper reports a study of electrochemical degradation of the chloramphenicol antibiotic in aqueous medium using a flow-by reactor with DSA® anode. The process efficiency was monitored by chloramphenicol concentration analysis with liquid chromatography (HPLC) during the experiments. Analysis of Total Organic Carbon (TOC) was performed to estimate the degradation degree and Ion Chromatography (IC) was performed to determinate inorganic ions formed during the eletrochemical degradation process. In electrochemical flow-by reactor, 52% of chloramphenicol was degraded, with 12% TOC reduction. IC analysis showed the production of chloride ions (25 mg L-1), nitrate ions (6 mg L-1) and nitrite ions (4.5 mg L-1).

Gas-phase solvolysis type reactions of SiCl3+ cations

Gas-phase SiCl3+ ions undergo sequential solvolysis type reactions with water, methanol, ammonia, methylamine and propylene. Studies carried out in a Fourier Transform mass spectrometer reveal that these reactions are facile at 10-8 Torr and give rise to substituted chlorosilyl cations. Ab initio and DFT calculations reveal that these reactions proceed by addition of the silyl cation to the oxygen or nitrogen lone pair followed by a 1,3-H migration in the transition state. These transition states are calculated to lie below the energy of the reactants. By comparison, hydrolysis of gaseous CCl3+ is calculated to involve a substantial positive energy barrier.

Electronic conduction and electrocatalysis by supramolecular tetraruthenated copper porphyrazine films

A new tetraruthenated copper(II)-tetra(3,4-pyridyl)porphyrazine species, [CuTRPyPz]4+, has been synthesized and fully characterized by means of analytical, spectroscopic and electrochemical techniques. This À-conjugated system contrasts with the related meso-tetrapyridylporphyrins by exhibiting strong electronic interaction between the coordinated peripheral complexes and the central ring. Based on favorable À-stacking and electrostatic interactions, layer-by-layer assembled films were successfully generated from the appropriate combination of [CuTRPyPz]4+ with copper(II)-tetrasulfonated phtalocyanine, [CuTSPc]4-. Their conducting and electrocatalytic properties were investigated by means of impedance spectroscopy and rotating disc voltammetry, exhibiting metallic behavior near the Ru(III/II) redox potential, as well as enhanced catalytic activity for the oxidation of nitrite and sulphite ions.