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Journal of Thermal Analysis and Calorimetry
Authors: S. Silva, M. Conceiçăo, A. Souza, S. Prasad, M. Silva, V. Fernandes, A. Araújo, and F. Sinfrônio

Abstract  

The powder and the bran of algaroba pods, submitted to drying temperatures of 55, 65, 75, 85, 95 and 105C, were studied by conventional and thermogravimetric methods. The dynamic thermogravimetric curves of the samples indicated the following thermal stability order: 105>55>65>95>85>75C. The powder and the bran of algaroba pods, dried at 55C, presented protein content higher and isothermal thermogravimetric profiles comparable. The calorimetric curves of samples, dried at 55C, indicated the gelatinization of starch.

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Acta Biologica Hungarica
Authors: Gabrielle Souza Rocha, A. Fonseca, Michelle Rodrigues, F. Dantas, A. Caldeira-de-Araujo, and R. Santos

The aim of this work was to evaluate, by comet assay, the possible inducing of DNA lesions in peripheral blood mononuclear cells of rats subjected to acute or chronic food deprivation. Wistar male rats were subjected to 72 h of partial (50%), or total acute food deprivation, and then allowed to recover for different time periods (24, 48 and 72 h). In other experiments, comet scores were determined in peripheral blood mononuclear cells of rats subjected to chronic food deprivation (25% and 50%) for 50 days. Blood aliquots were obtained before, during and after food deprivation. Comet assay was carried out, the comet units photographed and scored (class 0 up to 3). Acute and chronic food-deprived rats presented peripheral blood mononuclear cells with DNA lesions (comet classes 1, 2 and 3) and a significant increase ( p < 0.05) in the number of comet units compared with its basal level. The increase was proportional to acute food deprivation time, but after being taken off, it progressively returned to basal level after 48 h (partial group) or 72 h (total group). Chronic food-deprived rats presented a progressive increase of comet score up to 5 days, and a decrease thereafter to reach a basal level. Possible mechanisms of DNA lesions are discussed.

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Abstract  

In this work was studied the acid properties of a series of HZSM-12 zeolites with different Si/Al molar ratio. The samples of ZSM-12 were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na2O:xAl2O3:100SiO2:200H2O, where: x=2, 1, 0.67 and 0.50, respectively. After the synthesis, the samples of ZSM-12 were ion-exchanged NH4Cl solution to obtain zeolite in the acid form (HZSM-12). The acid properties were evaluated by n-butylamine thermodesorption in a TG equipment at three different heating rates. The model-free kinetic model was applied in the TG integral curves to estimate the apparent activation energy (E a) of the n-butylamine desorption process. The results obtained showed that the HZSM-12 zeolite presents two kinds main of acid sites: one with E a in the range of 115-125 kJ mol-1 classified as weak and other kind with E a varying of 230-250 kJ mol-1 classified as strong.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Santos, M. Conceiçăo, M. Trindade, A. Araújo, V. Fernandes, and A. Souza

Abstract  

The lanthanidic complexes of general formula Ln(C11H19O2)3 were synthesized and characterized by elementary analysis, infrared absorption espectroscopy, thermogravimetry (TG) and differential scanning calorimetry (DSC). The reaction of thermal decomposition of complexes has been studied by non-isothermal and isothermal TG. The thermal decomposition reaction of complexes began in the solid phase for Tb(thd)3, Tm(thd)3 and Yb(thd)3 and in the liquid phase for Er(thd)3 and Lu(thd)3, as it was observed by TG/DTG/DSC superimposed curves. The kinetic model that best adjusted the experimental isothermal thermogravimetric data was the R1 model. Through the Ozawa method it was possible to find coherent results in the kinetic parameters and according to the activation energy the following stability order was obtained: Tb(thd)3>Lu(thd)3>Yb(thd)3>Tm(thd)3>Er(thd)3

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Abstract  

The study of the incorporation of rare earth elements as additives in Y zeolites is a very interesting field of research, mainly by its potential application as additives in catalytic cracking process. In this work was studied the thermal and structural properties of cerium, holmium and samarium supported on HZSM-12 zeolite. The obtained materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), nitrogen adsorption, thermogravimetry (TG/DTG), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). TG/DSC/DTA analyses showed that the dehydration temperatures of RE/HZSM-12 zeolites (RE=Ce, Ho, Sm) increase in relation to pure HZSM-12. The acid properties were investigated by pyridine thermo desorption via TG. The results showed two events of mass loss attributed to elimination of pyridine adsorbed on the weak+medium acid sites and on the strong acid sites.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Regis Botelho, A. Duarte Gondim, I. Garcia dos Santos, P. Dunstan, A. Souza, V. Fernandes, and A. Araújo

Abstract  

The standard molar enthalpy of formation of crystalline dialkyldithiocarbamate chelates, [Pd(S2CNR2)2], with R=CH3 and i-C3H7, was determined through reaction-solution calorimetry in 1,2-dichloroethane, at 298 K. Using the standard molar enthalpies of formation of the gaseous chelates, the homolytic (52618 and 66610) and heterolytic (269318 and 295710 kJ mol-1) mean enthalpies of palladium-sulphur bond dissociation were calculated.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Frederico A. D. Araújo, Sonia V. Pereira, Deivson C. S. Sales, A. R. Schuler, and Cesar A. M. Abreu

Abstract

The free fatty acids of cotton seed oil were processed with methanol and ethanol into the corresponding alkyl fatty esters in the presence of diluted sulfuric acid. The products characterized as biodiesels presented higher mass fraction levels (43.0 wt%) of the alkyl linoleates, and 17.0 and 13.0 wt% of the alkyl esters C16:0 and C18:1, respectively. A model based on the mechanism of the acid esterification, and representing the evolutions of the fatty ester concentrations, was fitted to the experimental evolution results where the orders of magnitude of the kinetic parameters were quantified. The selectivities of the methyl and ethyl fatty esters in the biodiesel mixtures were compared, where the C18:2 ethyl linoleate selectivity (92.3 %) in the ethyl biodiesel was almost twice the methyl linoleate selectivity (57.3 %) in the methyl biodiesel.

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Abstract

Zinc oxide is a widely used white inorganic pigment. Transition metal ions are used as chromophores and originate the ceramic pigments group. In this context, ZnO particles doped with Co, Fe, and V were synthesized by the polymeric precursors method, Pechini method. Differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques were used to accurately characterize the distinct thermal events occurring during synthesis. The TG and DSC results revealed a series of decomposition temperatures due to different exothermal events, which were identified as H2O elimination, organic compounds degradation and phase formation. The samples were structurally characterized by X-Ray diffractometry revealing the formation of single phase, corresponding to the crystalline matrix of ZnO. The samples were optically characterized by diffuse reflectance measurements and colorimetric coordinates L*, a*, b* were calculated for the pigment powders. The pigment powders presented a variety of colors ranging from white (ZnO), green (Zn0.97Co0.03O), yellow (Zn0.97Fe0.03O), and beige (Zn0.97V0.03O).

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Abstract  

Oxamniquine (OXA) is a schistosomicide agent that causes some adverse effects in central nervous system. Intending to improve OXA therapeutic properties, a polymeric prodrug was designed. Currently, there is an increasing interest of thermal analytical techniques in the pharmaceutical area, so differential thermal analysis (DTA) and thermogravimetry (TG) were carried out to evaluate the thermal behavior of OXA, polymethacrylic acid (PMA), [poly(methacrylic-co-oxamniquine methacrylate)acid] (PMOXA) and physical mixture (OXA+PMA). The thermoanalytical profile of the physical mixture showed characteristic events of the thermal decomposition of OXA and PMA. Distinctly, PMOXA DTA curve did not show an endothermic peak at 148.5C indicating that the drug was incorporated into the polymeric system. These results were corroborated by the IR spectroscopy and X-ray diffraction data.

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