Publications

Abstract This paper reports the standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of acridone and N-methylacridone as (50.0 +/- 5.0) kJ . mol(1) and (60.6 +/- 4.3) kJ . mol(1), respectively. These data were obtained from experimental thermodynamic parameters, namely the standard molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, derived from the standard molar enthalpies of combustion measured by static-bomb combustion calorimetry, and the standard molar enthalpies of sublimation, at T = 298.15 K, determined by Calvet microcalorimetry or the Knudsen effusion techniques. Additionally, the gas-phase enthalpies of formation were estimated by G3(MP2)//B3LYP calculations, using several hypothetical gas-phase reactions, and were compared with the corresponding ones determined experimentally. The gas-phase keto-enol tautomerization chemical equilibrium of acridone M 9-acridinol was analysed using the Boltzmann's distribution, being confirmed that the equilibrium favours the formation of the keto form. The bond dissociation enthalpies (N-H) and (C-H) and the gas-phase acidities were also determined. The electrostatic potential surfaces and the frontier molecular orbitals were determined for both compounds, allowing us to infer about their reactivity properties. Other properties studied include the HOMO-LUMO energy gap and the ionization potential. (C) 2017 Elsevier Ltd.

Abstract Theoretical and experimental studies on the energetic, structural and some other relevant physicochemical properties of the antioxidant tyrosol (1), hydroxytyrosol (1OH) molecules and the corresponding radicals 1(rad)(center dot) and 1O(rad)(center dot) are reported in this work. The experimental values of the gas -phase enthalpy of formation, Delta H-f(m)0(g), in kJ.mol(-1), of 1 (-302.4 +/- 3.4) and 1OH (-486.3 +/- 4.1) have been determined. Quantum chemical calculations, at DFT (M05-2X) and composite ab initio G3 and G4 levels of theory, provided results that served to (i) confirm the excellent consistency of the experimental measurements performed, (ii) establish that the stabilizing effect of H -bond of hydroxyethyl chain and aromatic ring (OH center dot center dot center dot pi interaction) is smaller in radicals than in parent molecules, (iii) deduce-combining experimental data in isodesmic reactions-Delta H-f(m)0(g) of radicals 1(rad)(center dot) (-152.3 +/- 4.4 kJ.mol(-1)) and 1O(rad)(center dot) (-370.6 +/- 3.8 kJ.mol(-1)), (iv) estimate a reliable O-H bond dissociation enthalpy, BDE of 1 (368.1 +/- 5.6 kJ.mol(-1)) and of 1OH (333.7 +/- 5.6 kJ.mol(-1)), and (v) corroborate-using "BDE criteria"-than 1OH is a more effective antioxidant than 1.

Abstract The wealth of site-selective structural information on CO2 speciation, obtained by spectroscopic techniques, is often hampered by the lack of easy-to-control synthetic routes. Herein, an alternative experimental protocol that relies on the high sensitivity of C-13 chemical shift anisotropy (CSA) tensors to proton transfer, is presented to unambiguously distinguish between ionic/charged and neutral CO2 species, formed upon adsorption of (CO2)-C-13 in amine-modified porous materials. Control of the surface amine spacing was achieved through the use of amine protecting groups during functionalisation prior to CO2 adsorption. This approach enabled the formation of either isolated or paired carbamate/carbamic acid species, providing a first experimental NMR proof towards the identification of both aggregation states. Computer modelling of surface CO2-amine adducts assisted the solid-state NMR assignments and validated various hydrogen-bond arrangements occurring upon formation of isolated/aggregated carbamic acid and alkylammonium carbamate ion species. This work extends the understanding of chemisorbed CO2 structures formed at pore surfaces and reveals structural insight about the protonation source responsible for the proton-transfer mechanism in such aggregates.

Abstract Debundling and dispersing single-walled carbon nanotubes (SWNTs) is essential for applications, but the process is not well understood. In this work, aqueous SWNT dispersions were produced by sonicating pristine SWNT powder in the presence of an amphiphilic triblock copolymer (Pluronic F127) as dispersant. Upon centrifugation, one obtains a supernatant with suspended individual tubes and thin bundles and a precipitate with large bundles (and impurities). In the supernatant, that constitutes the final dispersion, we determined the dispersed SWNT concentration by thermogravi-metric analysis (TGA) and UV-vis spectroscopy, and the dispersant concentration by NMR The fraction of dispersant adsorbed at the SWNT surface was obtained by H-1 diffusion NMR Sigmoidal dispersion curves recording the concentration of dispersed SWNTs as a function of supernatant dispersant concentration were obtained at different SWNT loadings and sonication times. As SWNT bundles are debundled into smaller and smaller ones, the essential role of the dispersant is to sufficiently quickly cover the freshly exposed surfaces created by shear forces induced during sonication. Primarily kinetic reasons are behind the need for dispersant concentrations required to reach a substantial SWNT concentration. Centrifugation sets the size threshold below which SWNT particles are retained in the dispersion and consequently determines the SWNT concentration as a function of sonication time.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpy of formation of crystalline uridine, (C9H12N2O6), was determined from its specific energy of combustion, measured by static bomb combustion calorimetry, in oxygen, at T = 298.15 K, as - (1159.8 +/- 1.8) kJ mol(-1). Gas-phase standard molar enthalpy of formation of uridine was determined as - (992.8 +/- 3.2) kJ mol(-1) from quantum-chemical calculations using the G3(MP2) method. The enthalpy of sublimation of uridine at T = 298.15 K, determined as the difference between standard molar enthalpies of formation of uridine in crystalline and gaseous states, was found to be (167.0 +/- 3.7) kJ mol(-1). (C) 2018 Elsevier Ltd.

Abstract When using amphiphilic polymers to exfoliate and disperse carbon nanotubes in water, the balance between the hydrophobic and hydrophilic moieties is critical and nontrivial. Here, we investigate the mode of surface attachment of a triblock copolymer, Pluronics F127, composed of a central hydrophobic polypropylene oxide block flanked by hydrophilic polyethylene oxide blocks, onto single-walled carbon nanotubes (SWNTs). Crucially, we analyze the composition in dispersant of both the as-obtained dispersion (the supernatant) and the precipitate-containing undispersed materials. For this, we combine the carefully obtained data from H-1 NMR peak intensities and self-diffusion and thermogravimetric analysis. The molecular motions behind the observed NMR features are clarified. We find that the hydrophobic blocks attach to the dispersed SWNT surface and remain significantly immobilized leading to H-1 NMR signal loss. On the other hand, the hydrophilic blocks remain highly mobile and thus readily detectable by NMR. The dispersant is shown to possess significant block polydispersity that has a large effect on dispersibility. Polymers with large hydrophobic blocks adsorb on the surface of the carbonaceous particles that precipitate, indicating that although a larger hydrophobic block is good for enhancing adsorption, it may be less effective in dispersing the tubes. A model is also proposed that consistently explains our observations in SWNT dispersions and some contradicting findings obtained previously in carbon nanohorn dispersions. Overall, our findings help elucidating the molecular picture of the dispersion process for SWNTs and are of interest when looking for more effective (i.e., well-balanced) polymeric dispersants.

Abstract Approximately half the students enrolled in the many arts and design undergraduate programmes offered by Portuguese public higher education institutions will learn or have an opportunity to learn about computer programming while taking their degree. A preliminary study to assess those students' attitudes and opinions towards the subject of programming was conducted using an online survey based on Unified Theory of Acceptance and Use of Technology (UTAUT). An opportunity sample of 187 students participated, and 41.2% reported proficiency in some form of computer programming, 35.8% reported to be currently learning, and only 23% reported no knowledge of the subject. Expectations of utility, effortlessness and peer approval were found to positively correlate with students' intention to program or, in the case of students without such knowledge, an intention to learn computer programming. Students currently learning to code reported greater anxiety about the subject overall, and those reporting greater anxiety had the least intention to program in the future. Female students were also more likely to ascribe greater anxiety to the perspective of programming computers, as did younger students in general. Mitigating anxiety thus presents a challenge to educators engaged with computer programming, alongside adapting syllabi and pedagogies as to reduce the gender imbalance in programming acceptance and use.

Abstract A review of arts and design undergraduate programmes offered by Portuguese public higher education institutions found out that 50 out of the 105 programmes include at least one unit concerning computer programming in their curricula. A preliminary study partially based on the Unified Theory of Acceptance and Use of Technology (UTAUT), conducted through an online survey, sought to find out how lecturers in those programmes regard the subject of computer programming. A sample of 68 educators participated, split between 43 that reported no knowledge of computer programming and 25 that reported programming proficiency, 14 of which were engaged teaching the subject. A noticeable gender discrepancy was found concerning proficiency, raising the question of whether there's a relation to the anxieties of female students regarding programming found in a related study. Commenting on the relevance of the subject, some educators stressed that coding is both a fundamental problem-solving tool and a means to teach logical thinking, while others highlighted the creative potential of programming. Given the push to demystify computer programming, institutions can be encouraged to reduce the gender imbalance in the programming competency of educators. More research concerning educators' attitudes towards programming is welcome, both through practice characterization case-studies and through a deeper understanding of technology acceptance models applied in higher arts and design education.

Abstract An energetic study of 5-fluoro-2-methylbenzoxazole (FMBO) and of 5-fluoro-2-methylbenzothiazole (FMBT), in condensed and gaseous states, has been performed using calorimetric techniques and computational calculations. The standard (p degrees = 0.1 MPa) molar enthalpies of formation of FMBO and FMBT, in the liquid phase, at T = 298.15 K, were derived from the corresponding standard molar energies of combustion, measured by rotating-bomb combustion calorimetry. At T = 298.15 K, the standard (p degrees = 0.1 MPa) molar enthalpy of vaporization, for each compound, was determined, by a direct method, using the vacuum drop microcalorimetric technique. For each compound, from this last value and from the enthalpy of formation of the liquid compounds, the corresponding standard (p degrees = 0.1 MPa) enthalpy of formation in the gaseous phase has been calculated. Additionally, the gas-phase standard molar enthalpies of formation of these two compounds were estimated computationally at the G3(MP2)//B3LYP level of theory, as well as their gas-phase basicities and proton affinities. (C) 2018 Elsevier Ltd.

Abstract The energetic study of 2-methylnaphtho[1,2-d] oxazole (MN12O), 2-methylnaphtho-[2,3-d] oxazole (MN23O) and 2-methylnaphtho[1,2-d] thiazole (MN12T) has been performed experimental and computationally. The enthalpies of combustion and sublimation/vaporization of these compounds were determined, respectively, from static or rotating bomb combustion calorimetry and high temperature Calvet microcalorimetry and/or the Knudsen-effusion studies. These experimental data allow derivation of the corresponding gas-phase standard molar enthalpies of formation of the three compounds. Additionally, we have obtained the gas-phase standard molar enthalpies of formation of these three compounds, as well of the 2-methylnaphtho[2,3-d] thiazole (MN23T), through high level ab initio calculations, at the G3(MP2)//B3LYP and DLPNO-CCSD(T)/cc-pVTZ levels of theory. The computational study of the molecular structures of the compounds has been carried out. Furthermore, a relationship between the energetic and structural characteristics of these molecules was also evaluated. (C) 2018 Elsevier Ltd.