Publications

Abstract Fluorescent water soluble carbon nanoparticles, in short carbon dots (CDs), was synthesized from lactose by microwave assisted hydrochloric acid method. Characterized by TEM and DLS to obtain the morphology shape (average 10 nm in size), with a higher negative surface charge supported by the composition was obtained by XPS spectroscopy. The maximum of the emission was centered at 450 nm with a lifetime of 2.1 ns. Without further functionalization of the CDs a nanosensor was obtained that responded exponentially to HAAs in the 0.35-0.45 mg L-1 concentration range by fluorescence static quenching, demonstrated by the lifetime analysis of the CDs in presence of HAAs. Some amino compounds were selected as model for interferences to evaluate the selectivity of this method, showing a notorious added value, with recoveries around 98%. The accuracy of the method was in terms of RSD about 2.5%. The results suggest their promising applications in chemical sensing.

Abstract This report presents a comprehensive experimental and computational study of the thermodynamic properties of two bromine fluorene derivatives: 2-bromofluorene and 2,7-dibromofluorene. The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the crystalline phase of these compounds were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapour pressures of the crystalline phase of the two compounds were measured using the Knudsen effusion method and a static method that has also been used to measure the liquid vapour pressures of 2-bromofluorene. From these results the standard molar enthalpies, entropies and Gibbs energies of sublimation of the two compounds studied and of vapourisation of 2-bromofluorene were derived. The enthalpies and temperatures of fusion were determined from DSC experiments. Derived results of standard enthalpies and Gibbs energies of formation, in both gaseous and crystalline phases, were compared with the ones reported in the literature for fluorene. The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates based on density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with the 6-311++ G(d,p) basis set.

Abstract This work addresses an energetic and structural study regarding hydroxy and methoxy naphthaldehyde derivatives, based both on experimental and computational research. The massic energy of combustion and vapor 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, an appropriate theoretical procedure for these kinds of compounds. The combination of experimental and computational data enabled the determination of the enthalpies, entropies, and Gibbs energies of sublimation and formation of these compounds both in the crystal and gas phase. Complementing the experimental studies, the intramolecular hydrogen bonding energetics of all three o-hydroxynaphthaldehydes and their corresponding tautomeric structures were evaluated. Additionally, the gasphase Gibbs free energy and enthalpy of formation of the radical and anion as well as the O-H homolytic bond dissociation enthalpy and gas-phase acidity were studied.

Abstract The dissemination of chemistry has been experienced as a difficult task, largely because of the negative image that the public has of this science, but also because of its inherent complexity and its own semantics and symbolism. Science centers, as informal learning environments, can contribute to a more effective dissemination of chemistry to an audience of all ages. This article describes a study that took place in "ROMULO-Centro Ciencia Viva da Universidade de Coimbra", which involved a convenience sampling of 29 students (ages 8-10) from a elementary school. The experiment included storytelling (covering concepts of chemistry) followed by hands-on activities emulating the story. After the hands-on activities, the students were asked to express, through drawing, what they felt to be the most relevant aspects of what they experienced. Students' drawings have shown that they enjoyed the whole experience, with an emphasis on the storytelling, the hands-on activities, or a combination of both. In the future, we plan to assess in a more systematic manner the impact of the storytelling on learning and development of scientific literacy, as well as the impact on the way young students perceive chemistry.

Abstract A combined experimental and computational study was performed to evaluate the energetics, stability and volatility of pyrene and 1-pyrenecarboxaldehyde. The standard (p(o) = 0.1 MPa) molar enthalpy of combustion, Delta H-c(m)o, of 1-pyrenecarboxaldehyde was measured by static bomb combustion calorimetry, from which its standard (p(o) = 0.1 MPa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived. The vapour pressures of the two compounds were measured at different temperatures using the Knudsen mass-loss effusion method enabling the determination of molar standard enthalpies and entropies of sublimation at the mean temperatures of the experiments and at 298.15 K, using estimated values of Delta C-g(cr)p,m(o) for the temperature adjustments. The temperature and the molar enthalpy of fusion of both compounds were determined using differential scanning calorimetry. From fluorescence spectroscopy measurements, their photophysical properties, in solution and in the solid state, were determined. The experimental thermodynamic and luminescence results were compared with values available in the literature. Additionally, standard ab initio molecular calculations, at the G3(MP2)//B3LYP level, were performed and the standard enthalpies of formation of these two compounds were estimated. A very good agreement between the calculated and the experimental data was obtained. Furthermore, the results were interpreted in terms of enthalpic increments. The gas-phase molar heat capacities and absolute entropies of the two compounds studied were also calculated.

Abstract This article aims to analyse if and how relevant the timing of exposure to a videotaped experiment and its stojyboard may be, both before and after the experiment is performed. 27 students of one 11th grade class took part in the experiment, subdivided in two conditions and 5 work groups per shift. Interviews were conducted and their results were analysed using the NVivo software. The results indicate that both student perception and laboratorial work perfonnance are different according to the timing of exposure to the video. Exposure before laboratory work resulted in a more controlled and guided behaviour, fewer mistakes and shorter work time to conduct the experiments. Exposure after the experiment allows a better evaluation of students performance, and a higher level of student's reflection about the way experiment was conducted. Results are thus marked by a tension between goal orientation (appraisal) and learning orientation. The teacher 's role is to manage the pros and cons of both possibilities. © Fundación Revista de Educación de las Ciencias.

Abstract This paper reports vapour pressures measured at several different temperatures using the Knudsen effusion method of ortho-acetoxybenzoic acid (aspirin) (341.1 to 361.1) K, meta-acetoxybenzoic acid (344.2 to 362.2) K, ortho-acetamidobenzoic acid (367.2 to 389.2) K, and meta-acetamidobenzoic acid (423.2 to 441.1) K. The experimental results enabled the determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the four compounds studied. DSC experiments yield results of the temperature and enthalpy of fusion. The experimental results were compared with literature ones for the para isomers of the acids acetoxybenzoic and acetamidobenzoic. Correlations involving temperature of fusion, and standard molar enthalpy and Gibbs energy of sublimation of several substituted benzoic acids were proposed. Those correlation equations allow a good estimative of volatility of benzoic acid derivatives from their enthalpies of sublimation and temperatures of fusion.

Abstract Because of the close relation between oxidative stress and a plethora of inflammatory diseases, antioxidants have received an increased attention for incorporation into dermatological products. Their use and absorption are, however, limited by their low solubility in water-rich formulations. Herein, a set of novel cholinium-based salts, namely dicholinium ellagate and cholinium caffeate, syringate, vanillate, gallate, and salicylate, were synthesized and characterized. Their melting and decomposition temperatures, water solubility, and toxicological, antioxidant, cytotoxicity and pro-/anti-inflammatory activities were addressed. These new salts, exclusively composed of ions derived from natural sources, display a high thermal stability-up to 150 degrees C. The synthesized compounds are significantly more soluble in water (on average, 3 orders of magnitude higher) than the corresponding phenolic acids. Furthermore, they present not only similar but even higher antioxidant and anti-inflammatory activities, as well as comparable cytotoxicity and lower ecotoxicity profiles than their acidic precursors. Among all the investigated salts, dicholinium ellagate is the most promising synthesized salt when considering the respective antioxidant and anti-inflammatory activities. Because all the synthesized salts are based on the cholinium cation, they can further be envisaged as essential nutrients to be used in oral drugs.