Anelastic spectroscopy in Al2O3

Engineering ceramics have found use in many applications, such as engine parts, ball bearings, artificial bone and hip replacements and gyroscopes, because of their good chemical inertness, hardness, high temperature stability and excellent wear resistance. Oxide ceramic may meet these demands. Alumina (Al2O3) ceramics offer a high potential for many engineering applications, such as wear- and/or corrosion-resistant components, and as material for substrates or housings in microelectronic devices. Alumina is used among other things for seal ring, draw-cones, guides, water mixing tapes, bearing parts, medical prostheses and cutting tools. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occurs in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in Al2O3 samples using commercial starch. These measurements were carried out in a torsion pendulum operating in frequencies around 40 Hz. The results shown strongly influence of the type of forming in the elastic modulus obtained by anelastic relaxation measurements.

Anelastic spectroscopy in superconducting oxides

Since the discovery of the high Tc superconductors, several works have been made about the different properties of these materials. Anelastic spectroscopy experiments are sensitive tools to the study of defects in solids and phase transitions. By this technique, we can distinguish the different types of atomic jumps that happen to different temperatures. The intensity of the peaks in the anelastic spectrum and the step in the torsional modulus are related with the concentration of the relaxing entities, and the position of the peaks is determined by its mobility. In this paper, the study on Bi and Sm based superconducting oxides was made by anelastic relaxation measurements using a torsion pendulum. The samples were submitted to successive thermal treatments in high vacuum, in the temperature range between 100 K and 650 K, heating rate about 1 K/min. For Bi based superconducting oxides the results shown two peaks, that were associated to interstitial oxygen mobility and to orthorhombic to monoclinic phase transition. For Sm based superconducting oxides the results shown a relaxation peak that was attributed to the jumps of the oxygen atoms in the inter-chains O1 and 05 of the lattice.

Determination of methyldopa in pharmaceutical formulations by combined spot test-diffuse reflectance spectroscopy

This paper describes a very simple and rapid quantitative reflectance spot test procedure for the determination of methyldopa in pharmaceutical formulations. This method is based on the complexation reaction of methyldopa with molybdate ions yielding a yellow stable complex on filter paper. Reflectance measurements were carried out at 410 nm. Under optimal conditions, the calibration graphs obtained for methyldopa by plotting the optical density of the reflectance signal (A R) vs. the log of the concentration were linear from 6.30 × 10 -3 to 1.89 × 10 -2 mol L -1, with a correlation coefficient of 0.998. The detection limit was 2.74 × 10 -3 mol L -1 (R.S.D. = 1.02%) for methyldopa. The common excipients used as additives in pharmaceuticals do not interfere in the proposed method. The method was applied to determine metyldopa in commercial pharmaceutical formulations. The results obtained by the proposed method compare favorably with those obtained by an official procedure at 95% confidence level. ©2006 Sociedade Brasileira de Química.

Anelastic spectroscopy in potassium aluminum metaphosphate glasses

Anelastic spectroscopy (internal friction and the dynamic modulus) was measured by means of a torsion pendulum at 3-12 Hz, in the range of 100-300 K, for a KAP metaphosphate glass. Two thermally activated internal friction peaks appeared at ∼190 and ∼250 K. These peaks were attributed to the behavior of potassium ions (high temperature) and to hydrogen (low temperature). Dynamic modulus showed a gradual decrease with increasing temperature in the range studied for all compositions. © 2006 Elsevier B.V. All rights reserved.

Lead-cadmium fluorogermanate glasses and transparent glassceramics. Spectroscopy and structure

In Lead-cadmium fluorogermanate glasses (PbF2-CdF 2-PbGeO3) the addition of metal fluorides to the base PbGeO3 glass leads to a decrease of the glass transition temperature (Tg) and to an enhancement of the ionic conductivity properties. Based on different spectroscopic techniques (19F NMR, Ge K-edge X-ryas absorption and Raman scattering) an heterogeneous glass structure is proposed at the molecular scale, which can be described by fluoride rich regions permeating the metagermanate chains. The temperature dependence of the 19F NMR lineshapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluoride mobility in these systems. Eu 3+ emission and vibronic spectra are used to follow the crystallization process leading to transparent glass ceramics.

Orphan nuclear receptor NGFI-B forms dimers with nonclassical interface

The orphan receptor nerve growth factor-induced B (NGFI-B) is a member of the nuclear receptor's subfamily 4A (Nr4a). NGFI-B was shown to be capable of binding both as a monomer to an extended half-site containing a single AAAGGTCA motif and also as a homodimer to a widely separated everted repeat, as opposed to a large number of nuclear receptors that recognize and bind specific DNA sequences predominantly as homo- and/or heterodimers. To unveil the structural organization of NGFI-B in solution, we determined the quaternary structure of the NGFI-B LBD by a combination of ab initio procedures from small-angle X-ray scattering (SAXS) data and hydrogen-deuterium exchange followed by mass spectrometry. Here we report that the protein forms dimers in solution with a radius of gyration of 2.9 nm and maximum dimension of 9.0 nm. We also show that the NGFI-B LBD dimer is V-shaped, with the opening angle significantly larger than that of classical dimer's exemplified by estrogen receptor (ER) or retinoid X receptor (RXR). Surprisingly, NGFI-B dimers formation does not occur via the classical nuclear receptor dimerization interface exemplified by ER and RXR, but instead, involves an extended surface area composed of the loop between helices 3 and 4 and C-terminal fraction of the helix 3. Remarkably, the NGFI-B dimer interface is similar to the dimerization interface earlier revealed for glucocorticoid nuclear receptor (GR), which might be relevant to the recognition of cognate DNA response elements by NGFI-B and to antagonism of NGFI-B-dependent transcription exercised by GR in cells. Published by Cold Spring Harbor Laboratory Press. Copyright © 2007 The Protein Society.

Colorimetric evaluation of composite materials with different thickness by reflectance spectroscopy

Selection of the proper shade and color matching of restorations to natural dentition continues to be one of the most frustrating problems in dentistry and currently available shade guide presents a limited selection of colors compared to those found in natural dentition. This investigation evaluation if the composites resins shade B2 are equivalent to the Vita shade guide B2. Twelve composite resins (Renamel Microfill Super Brite- Cosmedent USA, Renamel Universal Brite- Cosmedent USA, Renamel Microfill Body- Cosmedent USA, Renamel Universal Body- Cosmedent USA, Opallis EB2-FGM, Opallis DB2-FGM, Filtek Supreme XT-3M/ESPE, Filtek Z250-3M/ESPE, Filtek Z350-3M/ESPE, Z100-3M/ESPE, 4 Seasons Dentin - Ivoclar/Vivadent, Tetric Ceram - Ivoclar/Vivadent) shade B2 were used. From each composite, two specimens were made in a steel matrix with 8.0 mm diameter and 10.0 mm different predetermined thickness (0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0 mm). The specimens were 40 seconds light polymerized by LED Ultrablue (DMC). The specimens were measured 10 times each to determine the shade using a reflectance spectrophotometer (Pocket Spec). According to results was verified that not any of composites resins shade B2 evaluated in this study presented values of color difference (ΔE) equivalent to the Vita shade guide B2 and the 2 mm thickness showed the closer match to the Vita shade guide B2.

Structure and properties of Brazilian peat: Analysis by spectroscopy and microscopy

Peat was taken from the Sergipe State, Brazil and characterized by several techniques: elemental and thermal analyses; Fourier infrared (FTIR) and solid state 13C nuclear magnetic resonance (NMR) spectroscopies; scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM) and X-ray diffractometry (XRD). Also, the Sergipe State peat samples were compared with other peat sample from later from Sao Paulo State, Brazil. The lowest O/C and E 4/E 6 ratios and differential thermal analysis (DTA) curves of the Santo Amaro (SAO) sample indicated that this sample had the highest degree of decomposition. FTIR results showed that Itabaiana (ITA) and São Paulo (SAP) samples presented more prominent peak at 1086 cm -1 attributed the presence of Si-O than SAO sample spectra. The SAO sample showed two more intense peaks at 2920 cm -1 and 2850 cm -1. These results were corroborated by 13C NMR and thermal gravimetric (TG) where the relative abundance of the alkyl-C groups was greater in the SAO sample. The X-ray diffractometry (XRD) of SAO sample is characteristic of amorphous matter however, the SAP and ITA samples revealed the large presence of quartz mineral. The scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM) showed that the surface of peat samples have porous granules of organic material. The ITA and SAP peat samples are alike while SAO peat sample is richer in organic material. Only the SAO sample has truthful characteristics of peat. The results of this study showed that the samples are very different due to variable inorganic and organic material contents. ©2007 Sociedade Brasileira de Química.

Determination of atenolol in pharmaceutical formulations by diffuse reflectance spectroscopy

A simple analytical method for quantification of atenolol in pharmaceutical formulations by diffuse reflectance spectroscopy is described. The method is based on the reaction, on the filter paper surface, between the drug and p-chloranil producing a colored compound. The best reaction conditions were obtained with 20 μL of atenolol solution and 20 μL of p-chloranil. All reflectance measurements were carried out at 550 nm and the linear range was from 1.13×10-2 to 7.88×10-2 mol L-1 (r = 0.9992). The limit of detection was 2.80 × 10-3 mol L-1. The proposed method was successfully applied to analysis of different commercial brands of pharmaceutical formulations and the results obtained by the proposed method were in good agreement with those obtained using the British Pharmacopoeia method.

Diffusion phenomena of the oxygen and nitrogen in niobium by mechanical spectroscopy

The short-range diffusion phenomenon (Snoek Effect) was investigated by mechanical spectroscopy measurements between 300 K and 650 K, in a polycrystalline niobium sample, containing oxygen and nitrogen, using a torsion pendulum. Experimental spectra of anelastic relaxation were obtained under three conditions: as-received sample; annealed sample and subsequently annealed in an oxygen atmosphere for three hours at 1170 K in partial pressure of 5°10 -5mbar. The experimental spectra obtained were decomposed in elementary Debye peaks and the anelastic relaxation processes were identified. With anelastic relaxation parameters and the lattice parameters, the interstitial diffusion coefficients of the oxygen and nitrogen in niobium were calculated for each kind of preferential occupation (octahedral and tetrahedral). The results were compared with the literature data, and confirmed that the best adjustment is for the preferential occupation octahedral model for low concentrations of interstitial solutes, but at higher concentration of oxygen were observed deviations of experimental data for the interstitial diffusion coefficients of oxygen in niobium when compared with the literature data, this could be related to the possible occurrence of a double occupation of interstitial sites in the niobium lattice by oxygen interstitials. © (2010) Trans Tech Publications.

Impedance spectroscopy study of solid-state dye-sensitized solar cells with varying Spiro-OMeTAD concentration

This work reports on the changes of performance of solid-state cells dye-sensitized solar cells with the variation of concentration of spiro-OMeTAD between 5% and 25% in the fabrication of the cell. Variations of charge recombination and capacitance correlate with the improvement of current-potential characteristics at increasing spiro-OMeTAD content, which is explained by reduction of transport resistance for hole transport, the increase of charge separation in the dye molecules, and importantly, with the increase of the β-factor in the recombination resistance, that causes a reduction of the diode ideality factor. © 2010 Materials Research Society.

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.

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.

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.

Thermal denaturation and aggregation of hemoglobin of Glossoscolex paulistus in acid and neutral media

The thermal denaturation and aggregation of the HbGp, in the oxy- and cyanomet-forms, was investigated by DSC, AUC, DLS, optical absorption and CD, in the pH range from 5.0 to 7.0. Oxy-HbGp has a denaturation process partially reversible and dependent on the temperature. DSC melting curve is characterized by a single peak with Tc value of 333.4±0.2K for oxy-HbGp, while two peaks with Tc values of 332.2±0.1 and 338.4±0.2K are observed for cyanomet-HbGp, at pH 7.0. In acidic pH oxy- and cyanomet-HbGp are more stable showing higher Tc values and aggregation. AUC data show that, HbGp, at pH 7.0, upon denaturation, remains undissociated at 323K, presenting oligomeric dissociation at 333 (12±3% of tetramer and 88±5% of whole HbGp) and 343K (70±5% of monomer and 30±2% of trimer). DLS data show that the lag period before aggregation is dependent on the temperature and HbGp concentration. Optical absorption and CD results show that the increase of temperature leads to the oxy-HbGp oxidation and aggregation, above 331K, in acidic pH. CD data, for HbGp, present a greater thermal stability in acid medium than at neutral pH, with similar Tc values for both oxidation forms. Our data are consistent with previous studies and represents an advance in understanding the thermal stability of oligomeric HbGp structure. © 2012 Elsevier B.V.