at T = 298.15 K, of 2-acetyl-5-nitrothiophene and 5-nitro-2-thiophenecarboxaldehyde as −(48.8 ± 1.6) and (4.4 ± 1.3) kJ mol−1, respectively. These values were derived from experimental thermodynamic parameters, namely, the standard (po = 0.1 MPa) molar enthalpies of formation, in the crystalline phase,
measured by rotating bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method.
The results are interpreted in terms of enthalpic increments and the enthalpic contribution of the nitro group in the substituted
thiophene ring is compared with the same contribution in other structurally similar compounds.
The present work is part of a broader research program on the energetics of formation of heterocycles, aiming the study of
the enthalpic effects of the introduction of different substituents into heterocycles. In this work we present the results
of the thermochemical research on sulphur heterocycles of the type substituted thiophenes with different kind of substituents,
mainly alkyl, ester, acetyl, carboxamide, acetamide, carbonitrile and carboxaldehyde.
The standard (po=0.1 MPa) molar enthalpies of formation, in the condensed phase, at T=298.15 K, of a large number of substituted thiophenes, were derived from their standard massic energies of combustion, measured
by rotating-bomb combustion calorimetry, while the standard molar enthalpies of vaporization or sublimation of those compounds
were obtained either by high temperature Calvet Microcalorimetry, or by the temperature dependence of their vapour pressures
determined by the Knudsen effusion technique. The standard molar enthalpies of formation, of the studied sulphur heterocycles
in the gaseous phase, were then derived. The results are interpreted in terms of structural contributions to the energetics
of the substituted thiophenes, the internal consistency of the results is discussed and, whenever appropriate and possible,
empirical correlations are suggested for the estimation of standard molar enthalpies of formation, at T=298.15 K, of substituted thiophenes. A Table of enthalpic increments for different group substituents in positions 2 or 3
of the thiophene ring has been established.
The standard (p0=0.1
MPa) molar enthalpies of formation, in the condensed phase, of nine linear-alkyl
substituted thiophenes, six in position 2- and three in position 3-, at T=298.15 K, were derived from the standard massic
energies of combustion, in oxygen, to yield CO2(g)
measured by rotating-bomb combustion calorimetry. The standard molar enthalpies
of vaporization of these compounds were measured by high temperature Calvet
Microcalorimetry, so their standard molar enthalpies of formation, in the
gaseous phase, were derived.
The results are discussed in terms
of structural contributions to the energetics of the alkyl-substituted thiophenes,
and empirical correlations are suggested for the estimation of the standard
molar enthalpies of formation, at T=298.15
K, for 2- and 3-alkyl-substituted thiophenes, both in the condensed and in
the gaseous phases.
Authors:Manuel Ribeiro da Silva, Luís Santos, Ana Faria, and Filipa Sistelo
The molar heat capacity and the standard (p0 = 0.1 MPa) molar enthalpies of formation of the crystalline of bis(glycinate)lead(II), Pb(gly)2; bis(dl-alaninate)lead(II), Pb(dl-ala)2; bis(dl-valinate)lead(II), Pb(dl-val)2; bis(dl-valinate)cadmium(II), Cd(dl-val)2 and bis(dl-valinate)zinc(II), Zn(dl-val)2, were determined, at T = 298.15 K, by differential scanning calorimetry, and high precision solution-reaction calorimetry, respectively. The standard
molar enthalpies of formation of the complexes in the gaseous state, the mean molar metal–ligand dissociation enthalpies,
Authors:Ana Santos, I. Basílio, F. de Souza, A. Medeiros, Márcia Pinto, D. de Santana, and R. Macêdo
Thermal analysis is an essential analytical tool in development of new formulations as well as to study the interaction between
drugs and excipients. This work aims to investigate the possible interactions between metformin and excipients as microcrystalline
cellulose (Microcel MC101®), starch sodium glycolate (Explosol®), sodium croscarmellose (Explosel®), PVP K30, magnesium stearate,
starch and lactose, usually employed in pharmaceutical products. TG, DSC and DTA techniques were used for the thermal characterization
to track if the thermal properties of the drug substance were modified in the mixture. Disregard of the starch and lactose
systems, no changes in thermal behavior of mixtures were found. Thermogravimetric studies (TG) of metformin and its binary
mixtures showed different thermal behavior.
Authors:Antonilêni Medeiros, Ana Santos, F. de Souza, J. Procópio, Márcia Pinto, and R. Macêdo
Stability of drugs
and products has a great practical interest, which is facing to strict regulation.
Thermal studies, besides the determination of the thermal properties of the
investigated product allow the verification of possible interactions between
the drug substances and excipients. The objective of this work was to obtain
solid pre-formulates of paracetamol (PC) by spray drying (SPDR), as well as
to investigate their thermal behavior. Dynamic and isotherm TG, conventional
DSC and DSC-photovisual coupled methods were used to characterize the conventional
and pre-formulated mixtures obtained by SPDR. The results of both DSC investigations
showed slight alterations in melting temperatures, which suggests incompatibilities.
The TG decomposition data of the mixtures evidenced that the dry process via
SPDR leads to stability enhancement of the pre-formulated mixtures.
Authors:Edjane F. B. Silva, Marcílio P. Ribeiro, Ana C. F. Coriolano, Ana C. R. Melo, Anne G. D. Santos, Valter J. Fernandes Jr., and Antonio S. Araujo
Thermogravimetry was applied in order to investigate the catalytic degradation of heavy oil (15.4oAPI) over silica-based MCM-41 mesoporous molecular sieve. This material was synthesised by the hydrothermal method, using cetyltrimethylammonium bromide as organic template. The physicochemical characterization by nitrogen adsorption, X-ray diffraction, and thermogravimetry, showed that the obtained material presents well-defined structure, with a uniform hexagonal arrangement. The thermal and catalytic degradation of heavy oil was performed by thermogravimetric measurements, in the temperature range from 30 to 900 °C, at heating rates of 5, 10, and 20 °C min−1. By using the model-free kinetics, proposed by Vyazovkin, it was determined that the activation energy to degrade the heavy oil was ca. 128 kJ mol−1, and for degradation of oil in presence of MCM-41, this value decreased to 69 kJ mol−1, indicating the performance of the mesoporores catalyst for the degradation process.
Authors:Antonilêni Medeiros, Ana Santos, F. de Souza, I. Júnior, J. Valdilânio, J. Procópio, D. de Santana, and R. Macêdo
Compatibility studies between active drugs and excipients are substantial in the pharmaceutical technology. The objective
of the present work was to develop pre-formulated mixtures of metronidazole (MT) obtained by spray drying (SPDR) and their
thermoanalytical characterization. Dynamic and isothermal TG, conventional DSC and DSC coupled to a photovisual system were
used. DSC experiments with both techniques confirmed the homogeneity of the conventional and pre-formulated mixtures. The
TG data made possible the comparison the thermal stability of the different mixtures. Similar thermal stabilities were found
of the conventional and pre-formulated mixtures, with slower particles sizes of MT.
Authors:Amanda Fernandes de Medeiros, Maria Gabriela Ferreira Rocha, Alexandre Coelho Serquiz, Richele Janaína Araújo Machado, Vanessa Cristina Oliveira Lima, Fabiana Maria Coimbra de Carvalho, Izael de Sousa Costa, Bruna Leal Lima Maciel, Elizeu Antunes dos Santos, and Ana Heloneida de Araújo Morais
Trypsin inhibitors have been described in peanuts and their derived industrialized foods, demonstrating diversity and thermoresistance. Given their most varied applications, these enzymatic protease inhibitors have been isolated and characterized for their potential use as bioinsecticides, herbal medicines, or medicines, but it is not simple. There are still no reports in the literature of the isolation and characterization of trypsin inhibitors in cultivar cavalo rosa (CCR) peanut, a common variety in Brazil. However, there are biological activities related to trypsin inhibitors from peanut-derived products. In this study, we isolated and characterized a novel trypsin inhibitor in CCR peanuts (Arachis hypogaea L.) under different processing conditions using a simple improved isolation. Raw and toasted peanut inhibitor was isolated by ammonium sulfate fractionation and trypsin-cyanogen bromide-activated Sepharose® 4B (CNBr-Sepharose® 4B) chromatography. The inhibitors from raw and toasted peanut were called AhTI1 and AhTI2, respectively, with potent anti-trypsin activity. Activity at different temperatures and pH was evaluated, and both samples were similarly stable under tested conditions. Minimum concentration for inhibition to occur (IC50) was 2.78 × 10−10 M and 2.39 × 10−10 M for AhTI1 and AhTI2, and inhibition constant (Ki) was 3.26 × 10−10 M and 1.54 × 10−10 M, respectively, showing non-competitive reversible kinetics. We concluded that AhTI1 and AhTI2 presented highly specific to trypsin and stable to toasting, different temperatures, and pH ranging. These are important characteristics in the process of developing bioinsecticides or biopharmaceuticals. Thus, this may be an interesting molecule, aiming at its biotechnological application, and it was obtained using a simple and easy isolation process.