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  • Author or Editor: Rui Macêdo x
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Abstract  

A study was made of the thermal behavior of the starting materials, their mixtures and the resulting mebendazole tablets. The thermal curves were obtained with a Shimadzu thermobalance, model TGA-50, using an air flow of 50 mL min−1 and a heating rate of 10°C min−1 in the temperature interval 30–900°C. The reaction constant velocities for the mebendazole salt and tablets were determined isothermally, using the Arrhenius expression. The thermal stability of mebendazole tablets is lower than that of the mebendazole salt, due to the presence of starch and lactose in the composition. Analysis of the data reveals that thermogravimetry is a powerful tool in pharmaceutical technology and quality control.

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Abstract  

Nitroimidazoles are heterocycle imidazoles with a nitrogen group incorporated in its structure. The objective of this study was to develop a model to characterize possible interactions between active substances and excipients using: Thermogravimetry, Differential Thermal Analysis, Differential Scanning Calorimetry, and DSC coupled to photovisual system. It was used three nitroimidazoles (metronidazole, secnidazole, and tinidazole) and two types of microcrystalline cellulose with different particle size (Microcel and Avicel). The binary mixtures were prepared in proportion (w/w) 1:1 (nitroimidazole:excipient). Thermogravimetric data demonstrated that the tinidazole was the nitroimidazole with better uniformity. The nitroimidazoles obeyed the zero order kinetic reaction, evidencing its vaporization processes. Differential thermal analysis data showed nitroimidazoles compatibility with the different microcrystalline celluloses studied, showing that microcrystalline celluloses stabilized the active substances. Calorimetric data of secnidazole showed two melting points, characteristic of the polymorphs presented in raw material. The vaporization constants values of nitroimidazoles studied were secnidazole > metronidazole > tinidazole and for the binary mixtures these values followed the order tinidazole > metronidazole ≥ secnidazole.

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Abstract  

The objective of this work was to develop and validate a fast and reproducible method able to determine the concentration of mebendazole in raw materials and tablets. The samples were analyzed by dynamic thermogravimetry, in the heating rates of 10, 20, 40, 60 and 80C min–1, in the atmospheres of nitrogen and nitrogen with synthetic air. Obtained data were used in the equations of Antoine and Langmuir, with the purpose to get the pressure curves of those. Vapor pressure curves of drug and tablet of mebendazole were evaluated using the mathematical indexes of difference factor, f 1, and similarity factor, f 2, to compare its profiles. The data showed that there is no significant difference between the vapor pressure profiles of drug and tablet of mebendazole in both environmental conditions studied, what confirms that the process is really vaporization. The concentration of mebendazole was determined in the raw material and tablets with the drug.

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Journal of Thermal Analysis and Calorimetry
Authors: Lidiane Pinto Correia, Elisana Afonso de Moura, Hallisson Meneses Pires, and Rui Oliveira Macêdo

Abstract

Water is a fundamental element of life. Its multiple uses are indispensable for a wide spectrum of human activities. This study aims to characterize water from different salinities obtained in the Cariri region of Paraíba, Brazil. The samples were analyzed using the DSC-coupled to the Peltier system (DSC-Cooling) and physical–chemical water tests performed employing reactive kits, using the Spectroquant Merck® specific for each test. The calorimetric curves showed crystallization phase transitions with different characteristics in peak format and crystallization temperatures between the samples of different salinities. The calorimetric data obtained in the process of crystallization of water is directly correlated to the physico-chemical parameters of conductivity and total dissolved solids, showing that the analytical technology DSC-cooling/heating is suitable for characterization of different salinities water.

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Abstract  

This article had studied the thermal characterization of the raw material and different fluconazole crystals, obtained through recrystallization with different solvents using thermoanalytical techniques (TG, DTA, DSC-50, DSC Photovisual, DSC-60) and Pyr-GC/MS. The results confirmed that the fluconazole volatilizes without decomposition until 250 °C. Pyr-GC/MS showed hexachlorobenzene like impurities in fluconazole raw material.

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Journal of Thermal Analysis and Calorimetry
Authors: Ticiano do Nascimento, Irinaldo Basílio Júnior, Rui Macêdo, Elisana Moura, Camila Dornelas, Vanderson Bernardo, Vânia Rocha, and Csaba Nóvak

Abstract  

This article characterizes the stability of indinavir sulfate using different analytical techniques of quality control to evaluate important steps in the manufacturing process of indinavir, specifically involving storage and compression. Indinavir A, B, and C were obtained from different suppliers and submitted to DSC, Karl Fisher, NIR, XRPD analyses and dissolution assay. DSC curves of indinavir presented endothermic peaks of fusion at 149–150 °C for indinavir A and B (form I) and 139–143 °C for indinavir C (form II). When indinavir A and B were submitted to high Relative Humidity (RH) pseudo-polymorphic form II was formed. Indinavir C converted into an amorphous substance when submitted to compression. Near infrared and Karl Fisher assays detected high values of water for indinavir C in relation to indinavir A and B. X-ray powder diffraction of indinavir B and C showed displacement of 0.05–0.10 θ in the peaks and higher angle of diffraction in relation to indinavir A. Amorphous indinavir C demonstrated a higher intrinsic dissolution rate than indinavir A and B. Indinavir form I should be monitored during the pharmaceutical process to avoid its conversion to indinavir form II or an amorphous substance which can alter the dissolution rate.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Raquel Cristóvão, Priscilla Amaral, Ana Tavares, Maria Coelho, Magali Cammarota, José Loureiro, Rui Boaventura, Eugénia Macedo, and Fernando Pessoa

Abstract  

In this work, the laccase catalyzed degradation of reactive textile dyes was studied in supercritical carbon dioxide media. A two level Box–Behnken factorial design with two factors and response surface methodology (RSM) were performed to investigate and optimize the effects of pressure and temperature on reactive red 239 (RR239), reactive yellow 15 (RY15) and reactive black 5 (RB5) dye degradations by commercial laccase in supercritical carbon dioxide media. Mathematical models were developed for each dye showing the effect of each factor and their interactions on color removal. Pressure and the interaction between temperature and pressure were the main factors affecting the decolorization. The optimum conditions for RB5 and RY15 were found to be high pressure values (>120 bar), whilst the temperature presented a minor effect on their degradation at these pressures. For RR239, both variables influenced the decolorization and the optimum conditions appear to be at low values of pressure and high values of temperature.

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Journal of Thermal Analysis and Calorimetry
Authors: Agna Hélia de Oliveira, Elisana Afonso de Moura, Márcia Ferraz Pinto, José Valdilânio Virgulino Procópio, Valmir Gomes de Souza, Fábio Santos de Souza, and Rui Oliveira Macêdo

Abstract

This work studied the thermal characterization of the pentoxifylline raw material through thermoanalytical techniques (TG, DSC, DSC-photovisual) and analysis of degradation products by Pyr-GC/MS. The picture obtained with DSC-photovisual showed the total vaporization of pentoxifylline at 230.0 °C. The TG dynamical curve presented only one step for the loss of mass evidencing to be a kinetic process of zero order reaction. The pyrograms obtained for pentoxifylline sample in the solid state and solution in the temperatures of 250.0, 300.0, and 400.0 °C, showed only one peak identifying the pentoxifylline.

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Journal of Thermal Analysis and Calorimetry
Authors: José Valdilânio Virgulino Procópio, Valmir Gomes de Souza, Rodrigo Albuquerque da Costa, Lidiane Pinto Correia, Fábio Santos de Souza, and Rui Oliveira Macêdo

Abstract

The simvastatin (SV) is nowadays produced semi-synthetically from lovastatin. It’s one of the statins most commonly used to treat several forms of hypercholesterolemia. This study aimed to apply the thermal characterization of the SV raw material using thermoanalytical techniques and its degradation products by Pyrolysis coupled to Gas chromatography/Mass spectrometry (Pyr-GC/MS). It was studied three samples of SV (SVA, SVB, and SVC). The results showed thermal behavior differences of the samples during the melting process transition and the activation energies (E a) of the thermal decomposition, which were correlated to the thermal stability of them. The first decomposition step of Pyr-GC/MS showed two new compounds of m/z 284 and 207, in proportions dependents according to the pyrolysis temperature.

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Journal of Thermal Analysis and Calorimetry
Authors: Monica Felts de La Roca Soares, José Lamartine Soares-Sobrinho, Keyla Emanuelle Ramos de Silva, Lariza Darlene Santos Alves, Pablo Queiroz Lopes, Lidiane Pinto Correia, Fábio Santos de Souza, Rui Oliveira Macêdo, and Pedro José. Rolim-Neto

Abstract

The ornidazole drug substance presents melt at approximately 90 °C (ΔT = 85–98 °C), which is critical for its use on pharmaceutical manufacturing process. This work aimed the thermal characterization of ornidazole raw-material synthesized by three different manufacturers from India, China, and Italy, using the thermoanalytical techniques of DTA, DSC, and TG, besides the verification of its stability and compatibility as a solid pharmaceutical product by the analysis of its binary mixtures (BM) with excipients and a tablet formulation. The characterization includes the thermal decomposition kinetic investigation by Ozawa model using Arrhenius equation and drug purity determination by Van't Hoff equation. The DSC purity determination and precision were compared with results from UV–Vis spectrophotometric and liquid chromatography, showing an adequate correlation before being recommended as a general method for purity assay. The drug raw-materials presented similar quality and zero-order kinetic behavior, besides showing differences on thermal stability. The drug presented compatibility with the tested excipients since the BM studied presented melting at the same temperature range as the drug and a decomposition temperature similar to the drug for two of the BM, and at a higher temperature for the others three of the BM evaluated, which presented excipients with higher molecular structure, capable of spatial coating on the small drug molecule promoting a physical interaction pharmaceutical acceptable. The tablet was processed by wet granulation and compressed under normal conditions of pressure and temperature, maintaining the physical properties of solid drug approving the manufacturing process used. In this study, the thermal analysis was used with success as an alternative method to characterize, quantify, and perform a preformulation study.

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