Publications

Abstract The Universidade Junior (U.Jr.) program, initiated by the University of Porto (U.Porto), Portugal, is a comprehensive educational initiative conducted during the summer months, primarily targeting the 10-18 age group. The program aims to promote science, technology, arts, humanities, and sports knowledge among elementary and secondary-level students and to influence their vocational choices and higher education aspirations. The study analyses the relationship between participation in the U.Jr. program and subsequent enrollment in higher education at U.Porto. It utilises data collected from 2006 to 2022, comparing U.Jr. participants with students who enrolled as freshmen at U.Porto. A Pearson correlation coefficient was applied to establish the connection between these datasets. Data analysis reveals a significant positive relationship between participation in U.Jr. and the choice of U.Porto for higher education. The study shows that 22 out of 100 first-year students at U.Porto in 2021 had previously attended U.Jr. Moreover, the geographical provenance of participants and U.Porto first-year students showed a robust correlation. The findings suggest that U.Jr. has a substantial impact on attracting students to U.Porto and influencing their academic choices. The program's diverse activities, coupled with its inclusive approach, have been instrumental in increasing the university's attractiveness and helping mitigate the country's low higher education rates. The study underscores the importance of such initiatives in shaping students' educational trajectories and choices for higher education.

Abstract The present work is focused on determining the enthalpy of formation of several derivatives of amino-1,2,4-triazoles. Experimentally, the enthalpies of formation of the crystalline phase and the enthalpies of sublimation of 3-amino- and 3,5-diamino-1H-1,2,4-triazole were derived, respectively, from static-bomb combustion calorimetry and Calvet microcalorimetry or Knudsen effusion measurements. For 4-amino-4H-1,2,4-triazole, only the enthalpy of sublimation was measured. Gas-phase standard molar enthalpies of formation were also estimated using theoretical calculations performed with the G3(MP2) composite approach. The very good agreement of these estimates with the experimental results, support the extension of this study to the estimate of this property for the remaining compounds not studied experimentally. The results obtained are interpreted in terms of structural contributions.

Abstract The thermal behaviour of bathophenanthroline and bathocuproine has been studied using several techniques, namely, differential scanning calorimetry and thermogravimetry. To determine their respective enthalpies of sublimation, vapor pressure measurements were carried out using different methods, such as Knudsen effusion mass loss/mass spectrometry, isothermal thermogravimetry, and a quartz crystal microbalance technique. Furthermore, the enthalpies of sublimation were determined by measuring the heat change of the sublimation process using high-temperature Calvet microcalorimetry. The results obtained in this work allowed the determination of the standard molar enthalpies of sublimation at 298.15 K, for bathophenanthroline and bathocuproine. The values obtained were (183.8 +/- 2.2) kJ & sdot;mol- 1 and (206.2 +/- 2.8) kJ & sdot;mol- 1, respectively. Additionally, the standard molar enthalpies of fusion were determined to be (30.4 +/- 0.4) kJ & sdot;mol- 1 and (26.5 +/- 1.6) kJ & sdot;mol- 1 for bathophenanthroline and bathocuproine, respectively. The analysis of the results allows a deeper understanding of the phase transition behavior for these compounds from the condensed to the gaseous phases, elucidating molecular decomposition and the inherent intermolecular forces governing the species.

Abstract This study presents the first investigation of the sublimation behavior of tin tetraiodide, SnI4, 4 , using effusion- based techniques, within a low temperature range (313-340) K. The temperature range covered in the experiments was lower than in previously reported studies based on static methods. Knudsen Effusion Mass Loss (KEML) measurements were performed in the range of (317.1-339.6) K using effusion cells with different orifice sizes. The vapor pressures were measured in the range (0.13-1.13) Pa and were found to be independent of the orifice size. The standard molar enthalpy and Gibbs energy of sublimation at 298.15 K obtained by the Clarke and Glew fit of experimental data are (88.1 +/- 0.9) kJ & sdot;mol-1 & sdot; mol- 1 and (38.96 +/- 0.08) kJ & sdot;mol-1, & sdot; mol- 1 , respectively. Knudsen Effusion Mass Spectrometry (KEMS) experiments were also performed in the range (313.3-331.7) K, resulting in a sublimation enthalpy value in good agreement with the KEML values and not negligibly higher vapor pressure values. KEMS vapor pressure data were also analyzed by the third-law method. A comparison of our experimental results with the literature data available for both sublimation and evaporation properties of SnI4 4 is reported. Additionally, ancillary DFT and ab initio calculations were performed to estimate the molecular properties of SnI4(g) 4 (g) and the extent of the gas-phase dissociation to SnI2 2 and I2. 2 .

Abstract <jats:p>The standard molar enthalpies of formation in the liquid phase for ethyl (E)-cinnamate and ethyl hydrocinnamate, two cinnamate derivatives with notable flavor and fragrance characteristics, were determined experimentally using combustion calorimetry in an oxygen atmosphere. To derive the gas-phase enthalpies of formation for these derivatives, their enthalpies of vaporization were measured using a high-temperature Calvet microcalorimeter and the vacuum drop microcalorimetric technique. Additionally, a computational analysis employing the G3(MP2)//B3LYP composite method was conducted to calculate the gas-phase standard enthalpies of formation at T = 298.15 K for both compounds. These findings enabled a detailed assessment and analysis of the structural and energetic effects of the vinyl and ethane moieties between the phenyl and carboxylic groups in the studied compounds. Considering the structural features of ethyl (E)-cinnamate and ethyl hydrocinnamate, a gas-phase enthalpy of hydrogenation analysis was conducted to explore their energetic profiles more thoroughly.</jats:p>

Abstract A thermochemical study of 2-amino-1,3,4-thiadiazole, 2-amino-5-methyl-1,3,4-thiadiazole and 2-amino-5-ethyl-1,3,4-thiadiazole has been performed, aiming to establish possible correlations between energetic properties and structural characteristics of these compounds, as well as to assess to their thermodynamic stability. Calorimetric techniques (rotating bomb combustion calorimetry and Calvet microcalorimetry) complemented with a mass loss effusion method and computational calculations were used to determine the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of the three thiadiazole derivatives. Theoretical calculations at the G3(MP2)//B3LYP level of theory were also performed to obtain the enthalpies of hypothetical reactions in the gaseous phase, as well as to calculate the gas-phase enthalpy of formation for the three thiadiazoles. From the two sets of results, it is possible to make a comparison between the experimental and computational values of the gas-phase enthalpy of formation. The standard Gibbs energies of formation in the crystalline and gaseous phases were also calculated, in order to evaluate the relative thermodynamic stability of the compounds. Additionally, a tautomeric analysis of the structure of each compound was performed, resulting in the establishment of a relationship between energy versus structure of the respective tautomeric forms.

Abstract The enthalpies of formation in the gaseous phase of methyl 3-methylanthranilate and methyl 5-methylanthranilate were determined from experimental measurements of the corresponding standard energies of combustion, obtained from combustion calorimetry, and the standard enthalpies of vaporization and sublimation, obtained from Calvet microcalorimetry and Knudsen mass-loss effusion. A computational study, using the G3(MP2)//B3LYP composite method, has also been performed for the calculation of the gas-phase standard enthalpies of formation of those two molecules at T = 298.15 K, as well as for the remaining isomers, methyl 4-methylanthranilate and methyl 6-methylanthranilate. The results have been used to evaluate and analyze the energetic effect of the methyl substituent in different positions of the ring.

Abstract An experimental study based on the thermal analysis of 5-methyl-1H-benzotriazole and 5,6-dimethyl-1H-benzotriazole was developed, by using differential scanning calorimetry. Additionally, a summary of the experimental techniques and computational methodology being performed, in order to complement the energetic study of both compounds, is described. The knowledge of the thermochemical, thermophysical and structural properties of functionalized benzotriazoles is relevant for the evaluation of their chemical behaviour, as well as in the prediction of the reactivity of similar compounds that have not been thermodynamically characterized. © 2022, Universidade do Porto - Faculdade de Engenharia. All rights reserved.

Abstract The focus of this work is the establishment of energetic-structural correlations of compounds containing a pentagonal heterocyclic ring with different substituents, and consequent contribution on the assessment of their thermodynamic stability and a thorough insight on the thiol-thione tautomeric equilibrium. In this work we report an experimental and computational thermochemical study of three mercaptothiadiazoles: 2-mercapto-1,3,4-thiadiazole, 2-mercapto-5-methyl-1,3,4-thiadiazole and 2,5-dimethyl1,3,4-thiadiazole. The experimental data were determined mainly from calorimetric techniques and from effusion method. Thermochemical properties such as the enthalpies of formation, both in crystalline and gaseous phases, the enthalpies of fusion and of sublimation of each compound, as well as the Gibbs energies of formation were derived. Thus, the methyl-substituted thiadiazole is the more stable species in both gaseous and crystalline phases. In addition, quantum chemical calculations were carried out for those isolated molecules. This approach confirms the thione form as the predominant tautomer for the mercaptothiadiazoles. Finally, the activation energies of the tautomeric equilibrium of the mercaptothiadiazoles were calculated in the gas-phase, aqueous and dimethylsulfoxide solutions, showing that the thiol ? thione single hydrogen transfers are quite unfavourable reactions in gas phase and in a presence of polar solvents. (c) 2021 Elsevier Ltd.