Showing: 10 from total: 420 publications
1. Junior university: fostering young minds' interest in higher education
Silva, V ; Urbano, D ; Pinto, IM ; da Silva, MDMCR ; Graça, P ; Soares, S ; Almeida, T
in FRONTIERS IN EDUCATION, 2024, ISSN: 2504-284X,  Volume: 8, 
Article,  Indexed in: crossref, scopus, wos 
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.

2. Thermochemistry of amino-1,2,4-triazole derivatives
Amaral, LMPF ; Carvalho, TMT ; da Silva, MDMCR
in JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 2024, ISSN: 1388-6150, 
Article in Press,  Indexed in: crossref, scopus, wos 
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.

3. Thermochemical study of the antioxidant activity of some hydroxycoumarins
Silva, ALR ; Lima, ACMO ; Matos, MAR ; Morais, VMF
in JOURNAL OF CHEMICAL THERMODYNAMICS, 2023, ISSN: 0021-9614,  Volume: 180, 
Article,  Indexed in: scopus, wos 
Abstract This work reports a combined thermochemical experimental and computational study on 6-hydroxycoumarin. The standard (p degrees = 0.1 MPa) molar enthalpy of formation in the condensed state of this compound was derived from the standard molar energy of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpy of sublimation. By combining these values, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K,-(339.8 +/- 2.4) kJ.mol-1 was derived.Accurate quantum chemical calculations at the composite G3 and at the DLPNO-CCSD(T) levels of theory have also been conducted in order to characterize the energetics of all the hydroxycoumarins studied and their rad-icalar related species, allowing us to further support our experimental measurements and to adequately quantify and rationalize the antioxidant activity of these systems.

4. Enthalpy of Formation of the Nitrogen-Rich Salt Guanidinium 5,5′-Azotetrazolate (GZT) and a Simple Approach for Estimating the Enthalpy of Formation of Energetic C, H, N, O Salts
Silva, LR ; León, P ; Ribeiro da Silva, DMC ; Klapötke, M ; Reinhardt, J
in Thermo, 2023, ISSN: 2673-7264,  Volume: 3, 
Article,  Indexed in: crossref, scopus 
Abstract The discrepancy between the calculated (CBS-4M/Jenkins) and experimentally determined enthalpies of formation recently reported for the 2:1 salt TKX-50 raised the important question of whether the enthalpies of formation of other 2:1 C, H, N, O salts calculated using the CBS-4M/Jenkins method are reliable values. The standard (p° = 0.1 MPa) enthalpy of formation of crystalline guanidinium 5,5′-azotetrazolate (GZT) (453.6 ± 3.2 kJ/mol) was determined experimentally using static-bomb combustion calorimetry and was found to be in good agreement with the literature’s values. However, using the CBS-4M/Jenkins method, the calculated enthalpy of formation of GZT was again in poor agreement with the experimentally determined value. The method we used recently to calculate the enthalpy of formation of TKX-50, based on the calculation of the heat of formation of the salt and of the corresponding neutral adduct, was then applied to GZT and provided excellent agreement with the experimentally determined value. Finally, in order to validate the findings, this method was also applied to predict the enthalpy of formation of a range of 1:1 and 2:1 salts (M+X− and (M+)2X2− salts, respectively), and the values obtained were comparable to experimentally determined values. The agreement using this approach was generally very good for both 1:1 and 2:1 salts; therefore, this approach provides a simple and reliable method which can be applied to calculate the enthalpy of formation of energetic C, H, N, O salts with much greater accuracy than the current, commonly used method. © 2023 by the authors.

5. Thermodynamic properties of benzotriazole derivatives: An experimental and computational study
Silva, ALR ; Lima, ACMO ; da Silva, MDMCR
in JOURNAL OF CHEMICAL THERMODYNAMICS, 2023, ISSN: 0021-9614,  Volume: 186, 
Article,  Indexed in: crossref, scopus, wos 
Abstract A thermochemical study of 5-methyl-1H-benzotriazole and 5,6-dimethyl-1H-benzotriazole was carried out experimentally using calorimetric techniques and an effusion method. Parallel to that, a computational methodology was also applied. The massic energies of combustion and the enthalpies of sublimation were determined from static bomb combustion calorimetry and Knudsen mass-loss effusion method and/or high-temperature Calvet microcalorimetry, respectively. From these experimental data, the standard molar enthalpies of formation of the two benzotriazoles in the gaseous phase were derived. Additionally, the gas-phase enthalpies of formation of these benzotriazoles and other two methylated derivatives were calculated using the G3(MP2)// B3LYP level of theory. The data obtained allowed the study of the energetic effects associated with the presence of a methyl group in the benzotriazole structure and their comparison with identical effects in homocyclic molecules, namely benzene and naphthalene. The Gibbs energies of formation of the compounds in the crystalline and gaseous phases were also determined to assess their thermodynamic stability.

6. Inside Cover: On the Enthalpy of Formation and Enthalpy of Sublimation of Dihydroxylammonium 5,5′‐bitetrazole‐1,1′‐dioxide (TKX‐50) (Prop., Explos., Pyrotech. 7/2023)
Silva, ALR ; Almeida, ARRP ; Ribeiro da Silva, MDMC ; Reinhardt, J ; Klapötke, TM
in Propellants, Explosives, Pyrotechnics, 2023, ISSN: 0721-3115,  Volume: 48, 
Article,  Indexed in: crossref, unpaywall 

7. On the Enthalpy of Formation and Enthalpy of Sublimation of Dihydroxylammonium 5,5′-bitetrazole-1,1′-dioxide (TKX-50)
Silva, ALR ; Almeida, ARRP ; da Silva, MDMCR ; Reinhardt, J ; Klapötke, TM
in PROPELLANTS EXPLOSIVES PYROTECHNICS, 2023, ISSN: 0721-3115,  Volume: 48, 
Article,  Indexed in: crossref, scopus, wos 
Abstract The thermodynamic characterization of dihydroxylammonium 5,5 '-bitetrazole-1,1 '-dioxide (TKX-50) was reinvestigated. Although TKX-50 is one of the most promising new-generation energetic materials, contradictory reports are found in the literature with regard to its solid enthalpy of formation. The standard (p degrees=10(5) Pa) molar enthalpy of formation of crystalline TKX-50, (175.3 +/- 1.9) kJ center dot mol(-1), was determined experimentally based on the measured standard massic energy of combustion, determined through static-bomb combustion calorimetry. Additionally, the standard molar enthalpy of sublimation of TKX-50, at T=298.15 K, (165.0 +/- 2.4) kJ center dot mol(-1), was derived from vapor pressure measurements determined by a Knudsen mass-loss effusion technique. Finally, different approaches were used in attempts to calculate the standard enthalpy of formation of TKX-50 in the solid state. A critical overview and assessment of the data on the enthalpy of formation of TKX-50 is also presented.

8. Energetic Effects in Methyl- and Methoxy-Substituted Indanones: A Synergistic Experimental and Computational Study
Silva, ALR ; León, GP ; da Silva, MDMCR
in APPLIED SCIENCES-BASEL, 2023, ISSN: 2076-3417,  Volume: 13, 
Article,  Indexed in: crossref, scopus, wos 
Abstract This experimental and computational study on the energetic properties of 2-methyl-, 3-methyl-, 4-methoxy- and 5-methoxy-indanones has been carried out using mostly calorimetric techniques and a suitable computational approach. The combustion and sublimation/vaporization enthalpies were determined via combustion calorimetry and Calvet microcalorimetry, respectively, allowing for the calculation of the standard molar enthalpies of formation in the gaseous phase. The enthalpy of sublimation of 5-methoxy-indanone was also derived via Knudsen effusion. Additionally, the gas-phase standard molar enthalpies of formation of these compounds were determined from high-level ab initio calculations at the G3(MP2)//B3LYP level of theory. The results obtained experimentally and through the computational approach are in good agreement. Thus, the gas-phase enthalpy of formation of 2-methylcyclopentanone was estimated with this approach. Moreover, the energetic effects associated with the presence of a methyl and methoxy group on the indanone core were analyzed, using the experimental values reported in this work. The presence of a methoxy group contributes to a decrease in the gas-phase enthalpy of formation, of about 153 kJ center dot mol(-1), whereas in the case of a methyl group, the corresponding value is c.a. 35 kJ center dot mol(-1). Finally, a quantitative analysis of the effects of delocalization of the electron density on the methyl-indanones was performed, using NBO calculations at the B3LYP/6-311+G(2df,2p) wave function.

9. Book of Abstracts of the 16th Mediterranean Conference on Calorimetry and Thermal Analysis - MEDICTA 2023
R. R. P. Almeida, A ; M. Gonçalves, J
2023,
Edited Book,  Indexed in: crossref 

10. Determination and Analysis of Thermodynamic Properties of Methyl Methylanthranilate Isomers
Silva, CAO ; Freitas, VLS ; da Silva, MDMCR
in MOLECULES, 2023, ISSN: 1420-3049,  Volume: 28, 
Article,  Indexed in: crossref, scopus, wos 
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.