Publications

Abstract The development of composites from 1D and 2D nanocarbon building blocks, namely carbon nanotubes and graphene layers, with enhanced properties or novel functionalities is an emerging challenge in material science. Herein, we developed a colloid-based approach using surfactants and polymers to non-covalently functionalize multiwalled carbon nanotubes (MWNTs) and graphene nanoplatelets (GnPs), and to fabricate GnP@MWNT nanocomposites via an electrostatic-driven assembly process in aqueous solution. In the assembly process, two building methods were used and compared (bulk mixing and adapted layer-by-layer assembly), using surfactant and polymer/surfactant combinations as the dispersants for the initial nanomaterials. After their characterization by scanning electron microscopy, Raman spectroscopy and BET analysis, the nanocomposites were evaluated as electrocatalysts for the oxygen reduction reaction (ORR). Results show that the type of the dispersant (namely the presence of polymer) plays a more relevant role than the specific building method in almost all the ORR parameters. Further, the nanocomposites show selectivity toward the 2-electron pathway oxygen reduction for the electrochemical production of hydrogen peroxide. The development and optimization of further nanocomposite electrocatalysts can be pursued using this type of versatile and robust assembly method.

Abstract In this work, we explore the ability of newly synthesized threonine-derived surfactants to form robust, versatile and cytocompatible catanionic vesicles when mixed with gemini surfactants, as potential effective nanocarriers for biomolecules. The threonine surfactants consist of single-tailed amphiphiles with carboxylate headgroups and varying alkyl tail length, CnThr, where n is the (even) number of tail C atoms, varying from 8 to 16. After an initial characterization of the micellization behavior of the neat CnThr surfactants (at pH = 7 and 12), the dodecyl derivative, C12Thr, was selected as the optimal surfactant to investigate regions of formation of spontaneous catanionic vesicles. Phase behavior studies and microstructural characterization of mixtures involving both conventional bis-quat n-s-n gemini (where n and s are the tail and spacer number of C atoms) and biocompatible serine-derived gemini surfactants were carried out. Light and electron microscopy, dynamic light scattering and zeta potential measurements show spontaneous vesicles indeed form and exhibit versatile features in terms of average size, morphology, polydispersity, surface charge and pH. The toxicological profile of the neat surfactants and C12Thr/gemini vesicles based on MTT assays with a L929 cell line was also evaluated, showing good levels of in vitro cytocompatibility. Overall, the assortment of developed catanionic vesicles offers very attractive physicochemical and biological features to be explored for delivery purposes.

Abstract Drug delivery vectors based on amphiphiles have important features such as versatile physicochemical properties and stimuli-responsiveness. Amino acid-based surfactants are especially promising amphiphiles due to their enhanced biocompatibility compared to conventional surfactants. They can self-organize into micelles, vesicles and complex hierarchical structures, such as fibers, twisted and coiled ribbons, and tubules. In this work, we investigated the self-assembly and drug loading properties of a family of novel anionic double-tailed lysine-derived surfactants, with variable degree of tail length mismatch, designated as mLys10 and 10Lysn, where m and n are the number of carbon atoms in the tails. These surfactants form tubular aggregates with assorted morphologies in water that undergo gelation due to dense entanglement, as evidenced by light and electron microscopy. Lysozyme (LZM), an enzyme with antimicrobial properties, was selected as model protein for loading. After the characterization of the interfacial properties and phase behavior of the amphiphiles, the LZM-loading ability of the tubules was investigated, under varying experimental conditions, to assess the efficiency of the aggregates as pH- and temperature-sensitive nanocarriers. Further, the toxicological profile of the surfactants per se and surfactant/LZM hydrogels was obtained, using human skin fibroblasts (BJ-5ta cell line). Overall, the results show that the tubule-based hydrogels exhibit very interesting properties for the transport and controlled release of molecules of therapeutic interest.

Abstract <jats:p>As pesquisas voltadas a educação científica, especificamente, sobre o tema do Inquiry-Based Science Education (IBSE) eclodiram nos últimos anos. Investigar os principais contextos de aplicação, descobertas, dificuldades e desafios advindos do uso do IBSE na Educação Básica de Ciências. Foi realizada uma revisão de literatura, utilizando uma década de produções científicas – entre 2006 e 2016 – a partir da plataforma de busca avançada da Universidade do Porto que é fornecida pela EBSCO. O corpus de análise compreendeu 45 artigos. Os principais resultados indicam que o IBSE tem sido considerado uma abordagem muito eficaz, estimulando os estudantes a questionar e propor problemas, na construção de hipóteses e na divulgação e justificação dos resultados atingidos. A abordagem do IBSE permite que os estudantes aprendam num processo investigativo semelhante ao método científico, de modo cooperativo, construindo conexões com conceitos científicos e com questões cotidianas e preparando os estudantes para uma aprendizagem ao longo da vida. A prática do IBSE nas escolas não é uma tarefa fácil, existindo muitos desafios e dificuldades para os professores e estudantes, contudo, essas dificuldades e desafios impostos a prática do IBSE devem ser explorados e debatidos a fim de ser superados.</jats:p>

Abstract This work is part of a comprehensive study of the thermal properties of several molecules of tetradentate Schiff bases, obtained as condensation products of salicylaldehyde with alkyldiamines. Herein, we report an experimental thermochemical study of SALPN (N,N'-bis(salicylaldehydo)propylenediimine) and a computational thermochemical study of SALEN (N,N' -bis(salicylaldehydo)dimethylenediimine), SALPN and SALBUTEN (N,N'-bis(salicylaldehydo)tetramethylenediimine) ligands. The standard (p degrees =0.1 MPa) molar enthalpy of formation of crystalline SALPN, at T = 298.15 K, was determined using the static-bomb calorimetry technique. Also, the enthalpy of fusion of this ligand has been determined by differential scanning calorimetry. Additionally, using quantum chemical calculations at the CCSD(T) level of theory, we have calculated the gas-phase standard molar enthalpies of formation of three Schiff base ligands, SALEN, SALPN and SALBUTEN. Moreover, a computational study of the molecular structures of the ligands has been carried out.

Abstract The gas-phase enthalpies of formation of two fragrance compounds, methyl anthranilate and butyl anthranilate, at T = 298.15 K, were determined from the combination of the corresponding enthalpies of vaporisation and energies of combustion, obtained from Calvet microcalorimetry and combustion calorimetry measurements, respectively. Additionally, theoretical calculations were performed, using the G3(MP2)//B3LYP composite method, to estimate the gas-phase enthalpies of formation of the two fragrance compounds. The good agreement between the experimental and computational gas-phase enthalpies of formation of the methyl anthranilate and butyl anthranilate, provided the confidence for extending the theoretical study to propyl anthranilate. Furthermore, the results were interpreted in terms of enthalpic increments, aiming to evaluate and understand the energetic effect inherent to the alkyl group (methyl, ethyl, propyl or butyl) present in the ester functional group of the anthranilate derivatives. (c) 2021 Elsevier Ltd.

Abstract Combustion calorimetry is the predominant method for determination of enthalpies of formation for organic compounds. Both initial and final states of the calorimeter deviate significantly from the standard conditions. Correction of the obtained results to the standard state must be applied as accurately as pos-sible to determine the combustion energy with an acceptable uncertainty, which is typically a few hun-dredths of a percent. The correction procedures in their current form were introduced in 1956 with simplifications to allow application in a pre-computer era. In this work, the procedures have been updated with respect to both the equations and reference values. The most reliable data sources are iden-tified, and the updated algorithm is presented in the form of a Web-based tool available through the NIST TRC Web site. (c) 2021 Elsevier Ltd.

Abstract The energetic study of 2-aminobenzoxazole (ABO) and 2-methyl-6-nitrobenzoxazole (MNBO) has been developed using experimental and computational tools. The enthalpies of combustion, of fusion, and of sublimation of these compounds were measured by static-bomb combustion calorimetry, differential scanning calorimetry, and Calvet microcalorimetry drop-technique and/or the Knudsen-effusion method. Additionally, we calculated the gas-phase standard molar enthalpies of formation of these compounds, as well as of 2-methyl-6-nitrobenzothiazole (MNBT), through high level ab initio calculations, at the G3(MP2)//B3LYP level of theory. Furthermore, the energetic effects associated with the presence of the amino and nitro groups on the core of benzoxazole or benzothiazole molecules were also evaluated, as well as stabilizing electronic interactions occurring in the molecules. The latter were investigated through Natural Bonding Orbital (NBO) of the corresponding wave functions. Finally, the thermodynamic stability of the titled compounds was evaluated and a comparison with their sulfur heteroanalogs was achieved. In the gaseous phase, the oxygen derivatives exhibit the lowest tendency to decompose into their constituent elements at standard conditions.

Abstract The paper describes an analysis of the questions posed by high school students regarding relationships between science and religion in a series of debates with scientists in public high schools of the northern part of Portugal. The exploratory interpretation of 171 collected anonymous written questions allowed for the detection of fragilities in the students' ideas about the nature of science and the nature of religion, connected with a trend to reject religion using scientism arguments. The findings reinforce a need of revising the fragmented teaching of nature of science and its connections with religion towards a more contextualized approach of diversified episodes of these social endeavours, anchored in life's ‘big questions' that allow students to make cross-disciplinary connections. Our analysis also supports the need for more research on students' questions rather than on students' answers in more common research methodologies conducted to inform the development of a more meaningful curriculum.

Abstract Recent density-functional theory (DFT) calculations raised the possibility that diamond could be degenerate with graphite at very low temperatures. Through high-accuracy calorimetric experiments closing gaps in available data, we reinvestigate the relative thermodynamic stability of diamond and graphite. For T400 K, graphite is always more stable than diamond at ambient pressure. At low temperatures, the stability is enthalpically driven, and entropy terms add to the stability at higher temperatures. We also carried out DFT calculations: B86bPBE-25X-XDM//B86bPBE-XDM and PBE0-XDM//PBE-XDM results overlap with the experimental -T Delta S results and bracket the experimental values of Delta H and Delta G, displaced by only about 2x the experimental uncertainty. Revised values of the standard thermodynamic functions for diamond are Delta H-f(o)=-2150 +/- 150 J mol(-1), Delta S-f(o)=3.44 +/- 0.03 J K-1 mol(-1) and Delta(f)G(o)=-3170 +/- 150 J mol(-1).