Publications

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the condensed phase, of the three monoiodoanisoles, were derived from the respective enthalpies of combustion, measured by rotating-bomb combustion calorimetry. Their enthalpies of sublimation/vaporization, at T = 298.15 K, were obtained by Calvet microcalorimetry using the high-temperature vacuum sublimation technique. Moreover the standard molar enthalpy, entropy and Gibbs energy of sublimation, at T = 298.15 K, of 4-iodoanisole were derived from the Knudsen mass-loss effusion technique. Combining the former sets of experimental results, the standard molar enthalpies of formation in the gas-phase, at T = 298.15 K, of 2-, 3- and 4-iodoanisole were derived, respectively, as: (15.1 +/- 2.1) kJ . mol (1); (11.8 +/- 2.2) kJ . mol (1), and (12.4 +/- 1.6) kJ . mol (1). The experimental values of the gas-phase enthalpies of formation of each iodoanisole were also estimated by means of the empirical scheme developed by Cox and by density functional theory calculations employing the B3LYP/6-311++G(d, p) approach. Estimated values are in excellent agreement with the reported experimental ones derived in the present paper.

Abstract Fluorescent silicon nanoparticles (silicon dots) are low-toxicity nanomaterials of utmost interest to analytical and bioanalytical chemistry. Silicon dots have proved to be excellent fluorescent tags for sensor development applications. This review focuses on silicon dots and their fluorescent properties and applications. Silicon dots can be produced via nine basic synthetic methods and their fluorescent properties differ considerably, according to how they are produced and functionalized. The photoluminescent mechanism depends on the particle size, surface defects and functionalization molecules. This review presents a synopsis of the most important recent analytical and bioanalytical applications, along with the toxicity assays performed with silicon dots.

Abstract It has been outlined the need of science teachers to print a more modern approach to teaching, based on effective and relevant context. Thus, the European Project PROFILES - Professional Reflection-Oriented Focus on Inquiry Learning through Science and Education - embraced by twenty participating countries, including Portugal, arises from the urgent need to invest in further continuous professional development. The aim of the project is to stimulate the skills in teaching students that may increase, through more motivating methods, their scientific literacy. In this sense, the teacher is oriented in order to experience four stages of development - the teacher as i) learner ii) teacher; iii) reflective practitioner; iv) leader - and is invited to implement with their students, new approaches based on Inquiry-Based Science Education (IBSE). Inquiry-based learning is a process where students are involved in their learning, formulate questions, investigate widely and then build new understandings, meanings and knowledge. PROFILES, and its guidelines regarding teacher training, shows great complicity with the, already completed, European Project PARSEL - Popularity And Relevance of Science Education for scientific Literacy - in which modules were developed as a set of teaching strategies for a new science approach through the discussion of social and ethical problems. The objective of the PARSEL modules is to increase the relevance and popularity of science teaching in the eyes of students, but at the same time guarantee solid student learning headed for enhancing scientific literacy. PROFILES teacher training in Portugal, lasted 50 hours and included classroom work, independent study, participation in synchronous sessions, asynchronous forums via Moodle and project implementation in their respective schools. On this last component teachers began their training by selecting and adapting a PARSEL module followed by its application with the students, bearing in mind three key stages. At the first stage, the PARSEL module was introduced to the students through relevant and interesting social issue. The relevance was achieved when the students concluded that there was a link between the title and an ordinary society situation, rather than a formal presentation of a series of scientific terms. At the moment students noted that there was a lack of scientific ideas that need to be introduced in order to elaborate a solution for the presented problem, it was the fulcral moment to start the second stage of implementation. Teachers certificated that at this stage, all the students had clearly established the relevance of the problem. Then, teachers could apply the IBSE strategy in order to guide and involve the students in the process of obtaining the formal learning. Because it was at this stage that the students acquire the so called scientific ideas, teachers took the majority of the teaching time to explore this phase. Third stage closed the circle of the learning module. This last stage was a consolidation phase of the science learning. This was made by transferring the learning achieved to the initial social issue proposed. All PARSEL modules were evaluated using the "Questionnaires for the Assessment of "motivational Learning Environment" (MoLE)" and the results pointing to an increase in student motivation.

Abstract This report presents a study of the thermodynamic properties of 9-fluorenone and 9-fluorenol. The standard enthalpies of formation of 9-fluorenone and 9-fluorenol in the crystalline phase at T = 298.15 K were determined from the energies of combustion in oxygen as -(11.4 +/- 3.8) kJ.mol(-1) and -(66.3 +/- 2.9) kJ.mol(-1), respectively. Vapor pressures of the two compounds were measured at several temperatures using two different experimental methods (Knudsen effusion for crystalline-phase vapor pressures and a static method for crystalline- and liquid-phase vapor pressures), which yielded reliable values of the enthalpies of sublimation, vaporization, and fusion. The sublimation and fusion enthalpies were also determined using calorimetric methods. The enthalpies of sublimation at T = 298.15 K were derived from the static vapor pressure measurements as (95.1 +/- 0.5) kJ.mol(-1) for 9-fluorenone and (108.3 +/- 0.5) kJ.mol(-1) for 9-fluorenol. The results enabled the determination of the standard Gibbs energy of the aerobic reactions of oxidation of fluorene to 9-fluorenol and 9-fluorenone and of the oxidation of 9-fluorenol to 9-fluorenone. Values of the standard enthalpies of formation in the gas phase were also calculated.

Abstract Vapour pressures of both crystalline and liquid (including super-cooled liquid) phases of fluoranthene were measured using a pressure gauge (capacitance diaphragm manometer) over the temperature range (348.8 to 404.3) K yielding accurate determination of enthalpies and entropies of sublimation and vaporisation. Enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapour pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluoranthene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation determined from the vapour pressure measurements. Computational results of the enthalpies of formation of fluoranthene and fluorene were also calculated at the G3 and G4 levels, and compared with the experimental values.

Abstract A phase transition study, including vapour pressure determinations of odd fluorotelomer alcohols {oFTOH; CF3(CF2)(n)CH2OH, with n = 5 to 9}, is reported in order to explore the effect of the successive introduction of -CF2- groups into the molecule on the thermodynamic properties related to (solid + liquid, solid + gas, and liquid + gas) equilibria. An odd-even effect on the thermodynamic parameters of fusion and sublimation was observed in the homologous series of odd fluorotelomer alcohols indicating an increase of the stability in the crystal packing for the members with an odd number of carbon atoms. The vaporization parameters of o-FTOH were compared with the literature data for their alkane analogues and the results showed a higher volatility of liquid fluorotelomer alcohols than their congeners. The higher molecular conformation restriction of perfluorinated alcohols and/or the higher molar mass seems to contribute to their higher entropy of vaporization which drives the volatility of the 1H,1H-perfluorinated alcohols.

Abstract High-precision heat capacities at 298.15 K of the [C(n)C(1)im][Ntf(2)] ionic liquid series were measured with an uncertainty of less than +/- 0.3%, using a drop heat capacity apparatus that was recently updated. The dependence of the c(p)(o) values on the alkyl side chain length for the extended ionic liquid series [C(n)C(1)im][Ntf(2)] (with n = 2 to 8, 10, and 12) displays a trend shift at [C(6)C(1)im][Ntf(2)], which is taken as an evidence for percolation limit. Above this limit there is an increase in the methylene group contribution to the molar heat capacity which is in agreement with the higher molar absolute entropies change observed from the (liquid + vapor) equilibrium results. The obtained experimental results support the model that the ionic liquids tend to be segregated into a polar network and non-polar domains, being followed by an increase of the entropy contribution of the non-polar domains.

Abstract The synthesis of novel cationic gemini surfactants based on serine, with long lipophilic alkyl chains and a spacer linked to the nitrogen atom of the amino acid residue by amine linkages, is described. The most efficient synthetic pathway involves introduction of the spacer into the monomeric precursors, N-alkyl derivatives, by reductive amination of dialdehydes followed by methylation and deprotection. Characterization of the basic micellization properties of the new compounds was carried out by tensiometry and conductimetry. These surfactants present enhanced interfacial properties compared to the monomeric analogues, and show improved performance, namely lower critical micelle concentration (cmc), lower surface tension at cmc and increased micellar ionization, with respect to conventional bis-quaternary ammonium salts (bis-quats).

Abstract We report within this paper the development of a fiber-optic based sensor for Hg(II) ions. Fluorescent carbon nanoparticles were synthesized by laser ablation and functionalized with PEG(200) and N-acetyl-L-cysteine so they can be anionic in nature. This characteristic facilitated their deposition by the layer-by-layer assembly method into thin alternating films along with a cationic polyelectrolyte, poly(ethyleneimine). Such films could be immobilized onto the tip of a glass optical fiber, allowing the construction of an optical fluorescence sensor. When immobilized on the fiber-optic tip, the resultant sensor was capable of selectively detecting sub,micromolar concentrations of Hg(II) with an increased sensitivity compared to carbon dot solutions. The fluorescence of the carbon dots was quenched by up to 44% by Hg(II) ions and interference from other metal ions was minimal.

Abstract Salt-free catanionic surfactants form in water binary systems, thus differing from pseudo-ternary equimolar catanionic mixtures, where salt is present. A miscibility gap, an unusual phenomenon in binary systems, is observed for the lamellar phase of the catanionic surfactant hexadecyltrimethylammonium octylsulfonate. Experimental data show the coexistence of a swollen and a collapsed lamellar phase in a wide two-phase region, while linear swelling is observed for each phase. This phase behavior is suggested to stem mainly from a concentration dependence of the charge density of catanionic bilayer, driven by the much higher solubility of the short chain ionic counterpart (octylsulfonate). Thus, a theoretical cell model based on combined DLVO and short range repulsive potentials is presented in order to provide physical insight into the miscibility gap. Furthermore, the surfactant forms at high dilution a solution phase and exhibits a very low critical micelle concentration (0.0035 wt%). The dilute lamellar phase is in equilibrium with the isotropic solution, and small vesicles can also be observed, apparently as a dispersion of the swollen lamellae in the solution. Upon temperature increase, a vesicle-to-micelle transition occurs. These unusual equilibria can also be qualitatively rationalized by the short chain solubility model.