Publications

Abstract This work reports the experimental determination of relevant thermodynamic properties and the characterization of luminescence properties of the following polycyclic aromatic hydrocarbons (PAHs): 2,6-diethylnaphthalene, 2,6-diisopropylnaphthalene and 2,6-di-tert-butylnaphthalene. The standard (p(o) = 0.1 MPa) molar enthalpies of combustion, Delta H-c(m)o, of the three compounds were determined using static bomb combustion calorimetry. The vapor pressures of the crystalline phase of 2,6-diisopropylnaphthalene and 2,6-di-tert-butylnaphthalene were measured at different temperatures using the Knudsen effusion method and the vapor pressures of both liquid and crystalline phases of 2,6-diethylnaphthalene were measured by means of a static method. The temperatures and the molar enthalpies of fusion of the three compounds were determined using differential scanning calorimetry. The gas-phase molar heat capacities and absolute entropies of the three 2,6-dialkylnaphthalenes studied were determined computationally. The thermodynamic stability of the compounds in both the crystalline and gaseous phases was evaluated by the determination of the Gibbs energies of formation and compared with the ones reported in the literature for 2,6-dimethylnaphthalene. From fluorescence spectroscopy measurements, the optical properties of the compounds studied and of naphthalene were evaluated in solution and in the solid state.

Abstract This work presents a comprehensive experimental and computational study of the thermodynamic properties of 2,7-di-tert-butylfluorene. The standard (p(o) = 0.1 MPa) molar enthalpy of formation in the crystalline phase was derived from the standard molar energy of combustion, measured by static bomb combustion calorimetry. The enthalpies and temperatures of transition between condensed phases were determined from DSC experiments. The vapour pressures of the crystalline and liquid phases were measured between (349.14 and 404.04) K, using two different experimental methods. From these results the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization were derived. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The thermodynamic stability of 2,7-di-tert-butylfluorene in the crystalline and gaseous phases was evaluated by the determination of the standard Gibbs energies of formation, at the temperature 298.15 K, and compared with the ones reported in the literature for fluorene. A computational study at the G3(MP2)//B3LYP and G3 levels has been carried out. A conformational analysis has been performed and the enthalpy of formation of 2,7-di-tert-butylfluorene has been calculated, using atomization and isodesmic reactions. The calculated enthalpies of formation have been compared to the experimental values. (C) 2016 Elsevier Ltd.

Abstract The current work addresses a thermochemical study regarding the compounds N-methylphenothiazine and N-methylphenoxazine. The excellent agreement between the experimental and computational gas-phase enthalpy of formation values obtained for the N-methylphenothiazine reinforced the validation/ calibration of the computational methodology established, allowing the use of it for the homologous oxygen derivative. The computational studies were also extended to the attainment of gas-phase molar heat capacities at different temperatures, dipole moment, electrostatic potential energy maps mapped onto electron density isosurface, and frontier orbitals of N-methylphenothiazine and N-methylphenoxazine. The experimental techniques used were the Knudsen mass-loss effusion, Calvet microcalorimetry and combustion calorimetry aiming, respectively, the determination of the temperature-vapour pressures dependences, the enthalpy of sublimation and the massic energy of combustion of N-methylphenothiazine. These quantities were used to derive the corresponding enthalpy of formation in the gas phase, at T = 298.15 K, (271.3 +/- 4.1) kJ . mol(-1). The results obtained for the enthalpies of formation are discussed and compared with related compounds, providing an opportunity to evaluate the effects in the enthalpies of formation associated with the substitution of the hydrogen of the amino group by a methyl group.

Abstract In the present work the energetic properties of phthalide and phthalic anhydride are assessed experimental and computationally allowing to calculate the standard molar enthalpy of formation, in the gaseous phase, of each compound. These results enabled to analyze and interpret the enthalpic and structural molecular effects of one and two ketone groups in the main structure of phthalan. The high-temperature Calvet microcalorimetry and the static bomb combustion calorimetry were used to measure, respectively, the enthalpy of sublimation and the massic energy of combustion of the two compounds. These data were combined to derive the standard molar enthalpy of formation, in the gaseous phase, of phthalide and phthalic anhydride. The gas-phase enthalpies of formation of phthalide and phthalic anhydride compounds were estimated using the composite G3(MP2)//B3LYP approach together with adequate gas-phase working reactions. The computational study was also extended to phthalan and the reliability of the value obtained for the correspondent gas-phase enthalpy of formation, when compared with the experimental value reported in the literature, contributes to validate the computational methodology used. The good agreement verified between computational and experimental results for the other two phthalan derivatives studied gave us confidence to estimate the gas-phase enthalpy of formation of the 2,5-dihydrofuran that was not studied experimentally. Complementary, natural bond orbital (NBO) calculations were also performed, allowing an advance on the analysis of the structural and reactivity characteristics of this type of compounds.

Abstract The standard ( p degrees = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, of 6-azauracil, 6-azathymine and 6-aza-2-thiothymine at T = 298.15 K, were derived from the standard molar energies of combustion, in oxygen, measured by combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by high temperature Calvet microcalorimetry. For 6-azauracil, the standard molar enthalpy of sublimation, at T = 298.15 K, was determined from the temperature-vapour pressure dependence, obtained by the Knudsen mass-loss effusion method. From the experimental studies, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of the 6-azauracil, 6-azathymine and 6-aza-2-thiothymine were derived. The gas-phase enthalpies of formation were also estimated by G3 and G4 calculations which were further extended to the computation of the standard molar enthalpy of formation of 6-aza-2-thiouracil. We compare the values obtained computationally with the experimental data available and find a good agreement between them.

Abstract The standard (p(0) = 0.1 MPa) molar energies of combustion, Delta U-c(m)0, for the crystalline 5-isopropylbarbituric and 2-thiobarbituric acids were determined, at the temperature of 298.15 K, by static bomb or rotating bomb combustion calorimetry, respectively. For 5-isopropylbarbituric acid, the standard molar enthalpy of sublimation, Delta H-g(cr)m(0), at T=298.15 K, was derived by Calvet microcalorimetry. The standard molar enthalpy of sublimation, at T=298.15 K, was derived by the Clausius-Clapeyron equation, from the temperature-vapor pressure dependence, measured by the Knudsen mass-loss effusion method. These experiments allowed the determination of the standard molar enthalpy of formation, in the gaseous phase, at T=298.15 K for 5-isopropylbarbituric acid. For 2-thiobarbituric acid, the gas-phase enthalpy of formation was calculated combining the result derived for the crystalline phase with literature data for the enthalpy of sublimation, at T=298.15 K. These values were compared with estimates obtained from very accurate computational calculations using the G3 and G4 level theory composite methods.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, of methyl 1H-indole-3-carboxylate and ethyl 1H-indole-2-carboxylate, at T = 298.15 K, were derived from measurements of the standard massic energies of combustion using a static bomb combustion calorimeter. The Knudsen effusion technique was used to measure the vapour pressures as a function of the temperature, which allowed determining the standard molar enthalpies of sublimation of these compounds. The standard (p(o) = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, were calculated by combining, for each compound, the standard molar enthalpy of formation, in the crystalline phase, and the standard molar enthalpy of sublimation, yielding -(207.6 +/- 3.6) kJ.mol (1) and -(234.4 +/- 2.4) kJ.mol (1), for methyl 1H-indole-3-carboxylate and ethyl 1H-indole-2-carboxylate, respectively. Quantum chemical studies were also conducted, in order to complement the experimental study. The gas-phase enthalpies of formation were estimated from high level ab initio molecular orbital calculations, at the G3(MP2) level, for the compounds studied experimentally, extending the study to the methyl 1H-indole-2-carboxylate and ethyl 1H-indole-3-carboxylate. The results obtained were compared with the experimental data and were also analysed in terms of structural enthalpic group contributions.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation in the condensed phase, Delta H-f(m)0, of 2,4-dichloro-5-methylpyrimidine, 2,4-dichloro-6-methylpyrimidine, 4,6-dichloro-2-methylpyrimidine and 4,6-dichloro-5-methylpyrimidine were derived from the standard molar energies of combustion, Delta U-c(m)0, in oxygen, to yield CO2 (g), N-2 (g) and HCl center dot 600H(2)O (l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vaporization or sublimation, Delta H-g(cr, l)m(0), for these compounds, at T = 298.15 K were determined by high temperature Calvet microcalorimetry. Combining these values, the following enthalpies of formation in the gas phase, at T = 298.15 K, were then derived: 2,4-dichloro-5-methylpyrimidine, (79.6 +/- 4.1) kJ mol(-1), 2,4-dichloro-6-methylpyrimidine, (70.5 +/- 3.0) kJ mol(-1), 4,6-dichloro-2-methylpyrimidine, (68.7 +/- 3.3) kJ mol(-1), and 4,6-dichloro-5-methylpyrimidine, (78.1 +/- 2.5) kJ mol(-1). The gas-phase enthalpies of formation were also estimated by G3 theoretical calculations, which were extended to the computation of gas-phase enthalpies of formation of the other dichloromethylpyrimidine isomers, namely, 2,5-dichloro-4-methylpyrimidine, 4,5-dichloro-2-methylpyrimidine and 4,5-dichloro-6-methylpyrimidine, whose experimental study was not performed.

Abstract In this work, energetic and structural studies concerning vanillyl alcohol, based both on experimental and computational studies, were developed. The massic energy of combustion and the vapour pressures at different temperatures were measured by static bomb combustion calorimetry and Knudsen mass-loss effusion techniques, respectively. The computational studies were performed using the G3(MP2)//B3LYP method. The combination of experimental and computational data enabled the determination of the enthalpies, entropies and Gibbs energies of sublimation and formation of this compound both in the crystal and gas phase. The intramolecular hydrogen bond energy present in vanillyl alcohol was evaluated, together with the O-H homolytic bond dissociation enthalpy. The new data are very useful for process design and development in the biorefinery. (C) 2016 Elsevier Ltd.

Abstract The main purposes of the research were to know how multimedia was used to teach science and also what methods were chosen to evaluate the pedagogical designs in the Portuguese Education between 2010-2014. A systematic review of literature was conducted. The corpus of analysis consisted of Master dissertations, PhD thesis and conference papers that were retrieved from the online repositories or proceedings. The criteria to include or exclude a given document were the following: (i) the document should report actual cases of pedagogical intervention(s) based on multimedia to teach science (i. e., Biology, Natural Sciences, Physics, Geology, Mathematics and Chemistry); (ii) the interventions should be aimed at the k5-k12 levels and should necessarily include students; (iii) the Master dissertations and PhD thesis should be available at the institutional online repositories and the articles should have been published in the proceedings of the two most important Conferences on Information and Communication Technologies in Portugal. The corpus consisted of 75 works (49% Mathematics; 15% - Physics; 14% - Natural Sciences; 11% - Chemistry; 7% - Biology; 4% - Geology). A content analysis was run. Interventions were coded according to the TPACK framework and the methodological designs were coded as experimental, quasi-experimental or non-experimental. Results showed that a wide range of multimedia was used, including multimedia specifically designed to teach sciences (e.g., simulations) and non-specific multimedia (e.g., Excel). The level of interactivity and openness of the multimedia was also variable (e.g., low interactivity - videos and animations; high interactivity - games and simulations; closed environments - calculator; open environments - wikis) and the affordances of the multimedia were often not fully used. Most pedagogical designs were based on co-constructivist perspectives (43%) or dialogic perspectives (34%), while transmissive perspectives (16%) and constructivist perspectives (7%) were less used. Most research was nonexperimental (case-studies), based on small samples, using non-validated questionnaires and field notes. Mixed methods or qualitative methods were most frequently selected to gather and analyse data. The study is very significant in that it allowed us to map the trends on multimedia research in the particular case of science teaching. These trends revealed an imbalance between non-experimental, exploratory research and alternatives that increase internal validity (such as quasi-experimental or experimental designs) or that allow to explore meaning and pedagogical appropriation of technology associated with the use of multimedia to teach sciences on the long run. It also showed that it is necessary to pay more attention to emergent practices (including mobile technologies and participatory designs). At the same time, this research provides important information also for science teachers that want to improve their performance using best-practices. Current research includes monitoring an online site that gives access to the raw data of the study and allows users to suggest and upload new documents according to an open and participatory science framework.