Publications

Abstract The dissemination of chemistry has been experienced as a difficult task, largely because of the negative image that the public has of this science, but also because of its inherent complexity and its own semantics and symbolism. Science centers, as informal learning environments, can contribute to a more effective dissemination of chemistry to an audience of all ages. This article describes a study that took place in "ROMULO-Centro Ciencia Viva da Universidade de Coimbra", which involved a convenience sampling of 29 students (ages 8-10) from a elementary school. The experiment included storytelling (covering concepts of chemistry) followed by hands-on activities emulating the story. After the hands-on activities, the students were asked to express, through drawing, what they felt to be the most relevant aspects of what they experienced. Students' drawings have shown that they enjoyed the whole experience, with an emphasis on the storytelling, the hands-on activities, or a combination of both. In the future, we plan to assess in a more systematic manner the impact of the storytelling on learning and development of scientific literacy, as well as the impact on the way young students perceive chemistry.

Abstract A combined experimental and computational study was performed to evaluate the energetics, stability and volatility of pyrene and 1-pyrenecarboxaldehyde. The standard (p(o) = 0.1 MPa) molar enthalpy of combustion, Delta H-c(m)o, of 1-pyrenecarboxaldehyde was measured by static bomb combustion calorimetry, from which its standard (p(o) = 0.1 MPa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived. The vapour pressures of the two compounds were measured at different temperatures using the Knudsen mass-loss effusion method enabling the determination of molar standard enthalpies and entropies of sublimation at the mean temperatures of the experiments and at 298.15 K, using estimated values of Delta C-g(cr)p,m(o) for the temperature adjustments. The temperature and the molar enthalpy of fusion of both compounds were determined using differential scanning calorimetry. From fluorescence spectroscopy measurements, their photophysical properties, in solution and in the solid state, were determined. The experimental thermodynamic and luminescence results were compared with values available in the literature. Additionally, standard ab initio molecular calculations, at the G3(MP2)//B3LYP level, were performed and the standard enthalpies of formation of these two compounds were estimated. A very good agreement between the calculated and the experimental data was obtained. Furthermore, the results were interpreted in terms of enthalpic increments. The gas-phase molar heat capacities and absolute entropies of the two compounds studied were also calculated.

Abstract This article aims to analyse if and how relevant the timing of exposure to a videotaped experiment and its stojyboard may be, both before and after the experiment is performed. 27 students of one 11th grade class took part in the experiment, subdivided in two conditions and 5 work groups per shift. Interviews were conducted and their results were analysed using the NVivo software. The results indicate that both student perception and laboratorial work perfonnance are different according to the timing of exposure to the video. Exposure before laboratory work resulted in a more controlled and guided behaviour, fewer mistakes and shorter work time to conduct the experiments. Exposure after the experiment allows a better evaluation of students performance, and a higher level of student's reflection about the way experiment was conducted. Results are thus marked by a tension between goal orientation (appraisal) and learning orientation. The teacher 's role is to manage the pros and cons of both possibilities. © Fundación Revista de Educación de las Ciencias.

Abstract This paper reports vapour pressures measured at several different temperatures using the Knudsen effusion method of ortho-acetoxybenzoic acid (aspirin) (341.1 to 361.1) K, meta-acetoxybenzoic acid (344.2 to 362.2) K, ortho-acetamidobenzoic acid (367.2 to 389.2) K, and meta-acetamidobenzoic acid (423.2 to 441.1) K. The experimental results enabled the determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the four compounds studied. DSC experiments yield results of the temperature and enthalpy of fusion. The experimental results were compared with literature ones for the para isomers of the acids acetoxybenzoic and acetamidobenzoic. Correlations involving temperature of fusion, and standard molar enthalpy and Gibbs energy of sublimation of several substituted benzoic acids were proposed. Those correlation equations allow a good estimative of volatility of benzoic acid derivatives from their enthalpies of sublimation and temperatures of fusion.

Abstract Because of the close relation between oxidative stress and a plethora of inflammatory diseases, antioxidants have received an increased attention for incorporation into dermatological products. Their use and absorption are, however, limited by their low solubility in water-rich formulations. Herein, a set of novel cholinium-based salts, namely dicholinium ellagate and cholinium caffeate, syringate, vanillate, gallate, and salicylate, were synthesized and characterized. Their melting and decomposition temperatures, water solubility, and toxicological, antioxidant, cytotoxicity and pro-/anti-inflammatory activities were addressed. These new salts, exclusively composed of ions derived from natural sources, display a high thermal stability-up to 150 degrees C. The synthesized compounds are significantly more soluble in water (on average, 3 orders of magnitude higher) than the corresponding phenolic acids. Furthermore, they present not only similar but even higher antioxidant and anti-inflammatory activities, as well as comparable cytotoxicity and lower ecotoxicity profiles than their acidic precursors. Among all the investigated salts, dicholinium ellagate is the most promising synthesized salt when considering the respective antioxidant and anti-inflammatory activities. Because all the synthesized salts are based on the cholinium cation, they can further be envisaged as essential nutrients to be used in oral drugs.

Abstract Four N-(4-halophenyl)-4-oxo-4H-chromene-3-carboxamides (halo = F, Cl, Br and I), N-(4-fluorophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10FNO3, N-(4-chlorophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10ClNO3, N-(4-bromophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10BrNO3, N-(4-iodopheny1)-4-oxo-4H-chromene-3-carboxamide, C16H10INO3, have been structurally characterized. The molecules are essentially planar and each exhibits an anti conformation with respect to the C-N rotamer of the amide and a cis geometry with respect to the relative positions of the C-arom-C-arom bond of the chromone ring and the carbonyl group of the amide. The structures each exhibit an intramolecular hydrogen-bonding network comprising an N-H center dot center dot center dot O hydrogen bond between the amide N atom and the 0 atom of the carbonyl group of the pyrone ring, forming an S(6) ring, and a weak C-arom-H center dot center dot center dot O interaction with the O atom of the carbonyl group of the amide as acceptor, which forms another S(6) ring. All four compounds have the same supra molecular structure, consisting of R-2(2)(13) rings that are propagated along the a axis direction by unit translation. There is pi-pi stacking involving inversion related molecules in each structure.

Abstract The knowledge of the thermodynamic properties of heterocyclic compounds, particularly the corresponding enthalpies of formation in condensed and gaseous states, enables a better understanding of their chemical behavior and, consequently, leads to an important background for the future development of their practical applications. Following our particular interest along the last decade on the establishment of energetic and structural relationships for heterocycle compounds with one or two benzene rings fused to a five- or six-membered ring containing oxygen or sulfur heteroatoms, we review the thermochemical data for derivatives of the following main structures: benzoxazole/benzothiazole, dibenzofuran/dibenzothiophene, xanthene/thioxanthene, and phenoxazine/phenothiazine. The experimental results, obtained by calorimetric and effusion techniques, namely static and rotating bomb combustion calorimetry, vacuum sublimation/vaporization drop microcalorimetry, and Knudsen effusion methods, were used to derive reliable thermodynamic values for the compounds studied. A complementary analysis of computational results for these molecules is presented. The agreement between the calculated and the experimental gas-phase enthalpies of formation represents a reinforcement on the validation of the established predictive schemes, supporting their use for related compounds whose energetic study is not available.

Abstract The title compounds, 6-(2-hydroxybenzyl)-5H-thiazolo[3,2-a] pyrimidin-5-one, C13H8N2O3S, (1), and 6-(2-hydroxybenzyl)-3-methyl-5H-thiazolo[3,2-a] pyrimidin-5-one, C14H10N2O3S, (2), were synthesized when a chromone-3-carboxylic acid, activated with (benzotriazol-1-yloxy)tripyrrolidinylphosphonium hexafluoridophosphate (PyBOP), was reacted with a primary heteromamine. Instead of the expected amidation, the unusual title thiazolopyrimidine-5-one derivatives were obtained serendipitously and a mechanism of formation is proposed. Both compounds present an intramolecular O-H center dot center dot center dot O hydrogen bond, which generates an S(6) ring. The dihedral angles between the heterocyclic moiety and the 2-hydroxybenzoyl ring are 55.22 (5) and 46.83 (6)degrees for (1) and (2), respectively. In the crystals, the molecules are linked by weak C-H center dot center dot center dot O hydrogen bonds and pi-pi stacking interactions.

Abstract Tropical parasitic diseases, especially those produced by protozoan parasites, are a major public health problem in many countries, and their impact in the health burden is significant. Oxidative processes proved to be related to these diseases, being the antioxidant agents promising therapeutic solutions for them. Therefore, this review provides an overview of published manuscripts regarding both activities. In particular, the interest of the coumarin derivatives as antioxidant agents with application in parasitic diseases is discussed in this manuscript. The recent findings in this field are highlighted.