Determination of saturates, aromatics and ethanol in Brazilian commercial gasoline with low olefin content using 1 H NMR spectroscopy

In this work, a Hydrogen Nuclear Magnetic Resonance (1H NMR) method has been developed to determine aromatics and ethanol in Brazilian commercial gasoline with low olefin content. The proposed method involves subdividing an 1H NMR spectrum into regions, each of which is assumed to be associated with a specific type of structural group (OH, CH, CH2 and CH3). The method is based on the assignment of overlapping regions of 1H NMR spectra due to the signals of naphthene (N), iso and normal paraffins (P) and ethanol (E). Each 1H NMR spectrum was divided into 8 regions and the integration was correlated to the percentage of the substances to be determined. The results of the analysis by 1H NMR were compared with analysis of GC-FID obtained with the PONA system. The proposed technique of 1H NMR was shown to be an appropriate method for this sample type.

Integrated X-ray crystallography, optical and computational methods in studies of structure and luminescence of new synthesized complexes of lanthanides with ligands derived from 2,6-diformylpyridine

The reaction of 2,6-diformylpyridine-bis(benzoylhydrazone) [dfpbbh] and 2,6-diformylpyridine-bis(4-phenylsemicarbazone) [dfpbpsc] with lanthanides salts yielded the new chelates complexes [Eu(dfpbpsc-H +) 2]NO 3 (1), [Dy(fbhmp) 2][Dy(dfpbbh-2H +) 2]·2EtOH·2H 2O (fbhmp = 2-formylbenzoylhydrazone-6-methoxide-pyridine; Ph = phenyl; Py = pyridine; Et = ethyl) and [Er 2(dfpbbh-2H +) 2(μ-NO 3)(H 2O) 2(OH)]·H 2O. X-ray diffraction analysis was employed for the structural characterization of the three chelate complexes. In the case of complex 1, optical, synthetic and computational methods were also exploited for ground state structure determinations and triplet energy level of the ligand and HOMO-LUMO calculations, as well as for a detailed study of its luminescence properties. © 2010 Elsevier Ltd. All rights reserved.

Sistema para realização de medidas de luminescência com excitação por raios X

In this work is presented a versatile system for X-ray excited optical luminescence (XEOL) measurements. The apparatus was assembled from a sample holder connected to an optical fiber responsibly for the acquisition of the scintillation signal. The spectrum is registered with a CCD coupled in a spectrograph provided with diffraction gratings. The system performance was analyzed by exciting GdAlO3:Eu3+ 3.0 at.% with X-rays from a diffractometer and measuring the emission spectra. The system can be used to obtain precise and reliable spectroscopic properties of samples with various conformations without the loss of the required safety when dealing with ionizing radiations.

β-lactam antibiotics epitope mapping with STD NMR spectroscopy: A study of drug-human serum albumin interaction

Molecular recognition events are key issues in many biological processes. STD NMR (saturation transfer difference nuclear magnetic resonance spectroscopy) is one of the techniques used to understand such biological interactions. Herein, we have investigated the interactions of four β-lactam antibiotics belonging to two classes (cephalosporins and penicillins) with human serum albumin (HSA) by 1H STD NMR revealing that the interaction between the aromatic moiety and HSA is responsible for the binding efficiency. Thus, the structural differences from the five to six-membered thio ring in penicillins and cephalosporins do not seem to influence antibiotic-albumin interactions. © 2012 Sociedade Brasileira de Química.

Structural refinement and photoluminescence properties of cube-like (Ca 1-xCu x)TiO 3 crystals synthesized by the microwave-hydrothermal method

In this work, (Ca 1-xCu x)TiO 3 crystals with (x = 0, 0.01 and 0.02), labeled as CTO, CCTO1 and CCTO2, were synthesized by the microwave-hydrothermal method at 140°C for 32 min. XRD patterns (Fig. 1), Rietveld refinement and FT-Raman spectroscopy indicated that these crystals present orthorhombic structure Pbnm. Micro-Raman and XANES spectra suggested that the substitution of Ca by Cu in A-site promoted a displacement of the [TiO6]-[TiO6] clusters adjacent from its symmetric center, which leads distortions on the [CaO 12] clusters neighboring and consequently cause the strains into the CaTiO3 lattice. FE-SEM images showed that these crystals have an irregular shape as cube like probably indicating an Ostwald-ripening and self-assemble as dominant mechanisms to crystals growth. The powders presented an intense PL blue-emission.

Using the electrochemical impedance spectroscopy to characterize carbon steel in biodiesel medium

Electrochemical impedance spectroscopy measurements using two carbon steel electrodes in soybean biodiesel medium, produced by methylic route, were performed in an electrochemical cell that allows positioning the two electrodes face-to-face. To retain the biodiesel between the electrodes and prevent its leakage a porous membrane soaked in biodiesel was used. The amplitude of the AC potential and the area of the electrodes were varied. The linearity between disturbance and response signals was observed for tests when the amplitude of the AC potential was lower than 1500 mV (rms). The electrical resistance of biodiesel dominates the global response and carbon steel presents low corrosion, which is observed only at low frequency, and was confirmed by chemical tests performed in the membrane. In conclusion the electrical resistance of biodiesel can be estimated using electrochemical impedance spectroscopy with two electrodes set up. ©The Electrochemical Society.

Effect of pressure-assisted thermal annealing on the optical properties of ZnO thin films

ZnO thin films were prepared by the polymeric precursor method. The films were deposited on silicon substrates using the spin-coating technique, and were annealed at 330°C for 32h under pressure-assisted thermal annealing and under ambient pressure. Their structural and optical properties were characterized, and the phases formed were identified by X-ray diffraction. No secondary phase was detected. The ZnO thin films were also characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, photoluminescence and ultraviolet emission intensity measurements. The effect of pressure on these thin films modifies the active defects that cause the recombination of deep level states located inside the band gap that emit yellow-green (575nm) and orange (645nm) photoluminescence. © 2012 John Wiley & Sons, Ltd.

Upconversion luminescence in Er3+ doped Ga10Ge 25S65 glass and glass-ceramic excited in the near-infrared

The infrared-to-visible frequency upconversion was investigated in Er 3+-doped Ga10Ge25S65 glass and in the transparent glass-ceramic obtained by heat-treatment of the glass above its glass-transition temperature. Continuous-wave and pulsed lasers operating at 980 nm and 1480 nm were used as excitation sources. The green (2H 11/2 → 4I15/2; 4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) photoluminescence (PL) signals due to the Er3+ ions were characterized. The PL decay times were influenced by energy transfer among Er3+ ions, by cross-relaxation processes and by energy transfer from the Er3+ ions to the host material. The PL from the Er3+ ions hosted in the crystalline phase was distinguished only when the glass-ceramic was excited by the 1480 nm pulsed laser. The excitation pathways responsible for the green and red PL bands are discussed to explain the differences between the spectra observed under continuous-wave and pulsed excitation. © 2013 American Institute of Physics.

Preparation and photoluminescence characteristics of In(OH) 3:xTb3+ obtained by Microwave-Assisted Hydrothermal method

Crystalline terbium-doped indium hydroxide structures were prepared by a rapid and efficient Microwave-Assisted Hydrothermal (MAH) method. Nanostructures were obtained at a low temperature. FE-SEM images confirm that these samples are composed of 3D nanostructures. XRD, optical diffuse reflectance and photoluminescence (PL) measurements were used to characterize the products. Emission spectra of terbium-doped indium hydroxide (In(OH)3:xTb 3+) samples under excitation (350.7 nm) presented broad band emission referent to the indium hydroxide matrix and 5D4 → 7F6, 5D4 → 7F 5, 5D4 → 7F4, and 5D4 → 7F3 terbium transitions at 495, 550, 590 and 627 nm, respectively. Relative intensities of the Tb 3+ emissions increased as the concentration of this ion increased from 0, 1, 2, 4 and 8 mol%, of Tb3+, but the luminescence is drastically quenched for the In(OH)3 matrix. © 2012 Elsevier B.V. All rights reserved.

Fe K-edge X-ray absorption spectroscopy study of Pb(Fe2/3W 1/3)O3-PbTiO3 multiferroic ceramics

The present paper is a comprehensive study concerning Fe K-edge X-ray absorption spectroscopy (XAS) measurements, which were performed to characterize the local structure of (1 - x)Pb(Fe2/3W1/3)O 3-xPbTiO3 samples as a function of temperature and PbTiO3 content. Results obtained by the fits of extended X-ray absorption fine structure consist with rhombohedral symmetry for Pb(Fe 2/3W1/3)O3 composition at temperatures lower than room temperature. This result is in apparent disagreement with X-ray and neutron diffraction characterization which have been reported. This apparent disagreement is related to the fact that XAS probes the short-range order, whereas X-ray diffraction provides structural information about the average structure. Moreover, as the PbTiO3 content increases, a disorder has been detected at local structure of the FeO6 octahedron. Analysis of X-ray absorption near edge structure spectra did not show modifications in intensity nor energy of transitions. © 2013 American Institute of Physics.

Luminescence Enhancement of Carboxyl-Coated CdTe Quantum Dots by Silver Nanoparticles

Metallic nanoparticles (NPs) have been used to improve the sensibility of biosensors and bioassays either by enhancing radiative emission or inducing quenching process on fluorescent probes. The aim of this research was to study the interaction of silver and silver-pectin NPs with water-dispersed carboxyl-coated cadmium telluride (CdTe) quantum dots (QDs). Metallic NPs were observed to change the emission of these fluorophores through local field effects. In a solution-base platform, an increase of 82 % was observed for the CdTe emission due to the interaction of QDs and silver-pectin NPs. QDs interaction with silver NPs without pectin was also investigated and a smaller emission enhancement of 20 % was detected. We observed that the NPs' nature and QDs' surface charge and concentration are important parameters for NPs-QDs interaction. Moreover, the presence of the pectin polymer shows to be a key component to the observed fluorescence enhancement. © 2013 Springer Science+Business Media New York.

Heavy Mesons Spectroscopy

In this paper, Lippmann-Schwinger equation is solved by using Martin and Cornel potentials to calculate bc̄ energy levels. The results for some energy levels which are not observable, such as those of tt̄ in its short half-life are also predicted. Our calculated energy levels are in good agreement with results of other groups. The stability interval for Yukawa-Linear potential is also studied by investigating the spectrum of eigenvalues. © 2013 Springer Science+Business Media New York.

Rapid determination of furosemide by combined spot test/diffuse reflectance spectroscopy to detect doping in sport

This paper describes the development and application of a simple, cheap, and clean method for the quantification of furosemide in urine samples from athletes, to detect doping, using a combined spot test/diffuse reflectance spectroscopy procedure. The method is based on the complexation reaction of furosemide (5-(aminosulfonyl)-4-chloro-2-((furanylmethyl)amino)benzoic acid, dissolved in ethanol, with FeCl3 and the surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution, yielding a colored compound on the surface of a filter paper. The reagent concentrations were optimized using a chemometric experimental design. The reflectometric measurements of the complex formed were carried out at 477nm. The linear range obtained was 1.65-9.00×10-3molL-1 of furosemide (R=0.997), and the detection and quantification limits were 4.9×10-4 and 1.62×10-3molL-1, respectively. The proposed method was successfully applied in the analysis of furosemide in spiked urine, demonstrating that it is a reliable alternative method for the detection of furosemide doping in sport. © 2012 Elsevier B.V..

Effect of yttrium doping in barium zirconium titanate ceramics: A structural, impedance, modulus spectroscopy study

In the current article, we studied the effect of yttrium [Y3+] ions' substitution on the structure and electric behavior of barium zirconate titanate (BZT) ceramics with a general formula [Ba1-x Y 2x/3](Zr0.25Ti0.75)O3 (BYZT) with [x = 0, 0.025, 0.05] which were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that these ceramics have a single phase with a perovskite-type cubic structure. Rietveld refinement data confirmed [BaO 12], [ZrO6], [TiO6], [YO6] clusters in the cubic lattice. The Y3+ ions' effects on the electric conductivity behavior of BZT ceramics as a function of temperature and frequency are described, which are based on impedance spectroscopy analyses. The complex impedance plots display a double semicircle which highlights the influences of grain and grain boundary on the ceramics. Impedance analyses showed that the resistance decreased with the increasing temperature and resulted in a negative temperature coefficient of the resistance property in all compositions. Modulus plots represent a non-Debye-type dielectric relaxation which is related to the grain and grain boundary as well as temperature-dependent electric relaxation phenomenon and an enhancement in the mobility barrier by Y3+ ions. Moreover, the electric conductivity increases with the replacement of Ba 2+ by Y3+ ions may be due to the rise in oxygen vacancies. © 2013 The Minerals, Metals & Materials Society and ASM International.

Estudo das propriedades microestruturais e ópticas do BaMoO4 processado em hidrotermal assistido por microondas

Pós-graduação em Ciência e Tecnologia de Materiais - FC