Browsing by Author "Ilharco, Laura M."
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- Covalent and noncovalent hybrids of di-amino porphyrin functionalized graphene oxide and their interaction with gold nanoparticlesPublication . Andrade, Suzana M.; Vaz Serra, Vanda; Bueno-Alejo, Carlos J.; Garcia, Ana; Carvalho, M. Fernanda N.N.; Ilharco, Laura M.; Neves, Maria Graça P.M.S.; Costa, Sílvia M.B.Porphyrin functionalization of graphene oxide (GO) influenced the plasmonic effect of gold nanoparticles (AuNP). The former was achieved by modification of GO with 5,10-bis(4-aminophenyl)-15,20-diphenylpor-phyrin, P(NH2)2,adj, by noncovalent interactions as well as by covalent association, following standard chemis-try. The success of the chemical functionalization of GO with P(NH2)2,adj, was confirmed by FTIR. Steady-state and time-resolved fluorescence showed a strong fluorescence quenching of porphyrin in the presence of GO, indicative of a photoinduced electron transfer process from porphyrin units to GO, which acts as an electron acceptor. The surface plasmon coupling effect promoted by the AuNP@GO hybrids, proved to be effective only in the case of the noncovalent hybrid, detected through the decrease of the porphyrin fluorescence lifetime and increase in the emission intensity in solution, in good agreement with FLIM results on deposited samples.
- Effects of hygrothermal, UV and SO2 accelerated ageing on the durability of ETICS in urban environmentsPublication . Parracha, João L.; Borsoi, Giovanni; Veiga, Rosário; Flores-Colen, Inês; Nunes, Lina; Garcia, Ana; Ilharco, Laura M.; Dionísio, Amélia; Faria, PaulinaExternal Thermal Insulation Composite Systems (ETICS) have been extensively used for either new constructions or building facades retrofitting in the last decades. These systems can provide improved thermal performance to the building envelope. However, their long-term durability remains a pervasive concern, with some systems presenting relevant anomalies after few years from their application. The durability assessment of ETICS is defined by the EAD 040083-00-0404 guideline, which stated an accelerated ageing procedure based on the hygrothermal and freeze-thaw behaviour. Nevertheless, further important environmental urban conditions, such as UV radiation and atmospheric pollutants, as well as bio-susceptibility, are not envisaged in the guideline. This paper presents the results of an experimental campaign with the aim of evaluating the durability of the rendering system of several commercially available ETICS exposed to an innovative accelerated ageing procedure, which consists of hygrothermal cycles, UV radiation and air pollutants (SO2) exposure. Physical and chemicalmorphological tests were carried out prior and after each ageing cycle in order to evaluate the durability of ETICS. Biological susceptibility to moulds was also assessed. The experimental results showed that both surface hardness and surface gloss decreased after the combined effect of the hygrothermal, UV, and SO2 ageing cycles, whereas an increase of surface roughness was observed. Substantial colour change for all systems after the ageing procedure was observed, confirming aesthetic alteration. Traces of biological growth were detected on the systems after ageing and the contact angle decreased after the hygrothermal cycles, indicating a lower surface hydrophobicity of the systems.
- Liquid mixtures involving hydrogenated and fluorinated alcohols: thermodynamics, spectroscopy, and simulationPublication . Morgado, Pedro; Garcia, Ana; Ilharco, Laura M.; Marcos, João; Anastácio, Martim; Martins, Luís F. G.; Filipe, Eduardo J. M.This article reports a combined thermodynamic, spectroscopic, and Computational study on the interactions and structure of binary mixtures of hydrogenated and fluorinated substances that simultaneously interact through strong hydrogen bonding. Four binary mixtures of hydrogenated and fluorinated alcohols have been studied, namely, (ethanol + 2,2,2-trifluoroethanol (TFE)), (ethanol + 2,2,3,3,4,4,4-heptafluoro-1-butanol), (1-butanol (BuOH) + TFE), and (BuOH + 2,23,4,4,4-heptafluoto-1-butanol). Excess molar volumes and vibrational spectra of all four binary mixtures have been measured as a function of composition at 298 K, and molecular dynamics simulations have been performed. The systems display a complex behavior when compared with mixtures of hydrogenated alcohols and mixtures of alkanes and perfluoroalkanes. The combined analysis of the results from different approaches indicates that this results from a balance between preferential hydrogen bonding between the hydrogenated and fluorinated alcohols and the unfavorable dispersion forces between the hydrogenated and fluorinated chains. As the chain length increases, the contribution of dispersion increases and overcomes the contribution of H-bonds. In terms of the liquid structure, the simulations suggest the possibility of segregation between the hydrogenated and fluorinated segments, a hypothesis corroborated by the spectroscopic results. Furthermore, a quantitative analysis of the infrared spectra reveals that the presence of fluorinated groups induces conformational changes in the hydrogenated chains from the usually preferred all-trans to more globular arrangements involving gauche conformations. Conformational rearrangements at the CCOH dihedral angle upon mixing are also disclosed by the spectra.
- Microplastics effects in Scrobicularia planaPublication . Ribeiro, Francisca; Garcia, Ana; Pereira, Beatriz P.; Fonseca, Maria; Mestre, Nélia; Fonseca, Tainá; Ilharco, Laura M.; Bebianno, Maria JoãoOne of the most common plastics in the marine environment is polystyrene (PS) that can be broken down to micro sized particles. Marine organisms are vulnerable to the exposure to microplastics. This study assesses the effects of PS microplastics in tissues of the clam Scrobicularia plana. Clams were exposed to 1mgL-1(20μm) for 14days, followed by 7days of depuration. A qualitative analysis by infrared spectroscopy in diffuse reflectance mode period detected the presence of microplastics in clam tissues upon exposure, which were not eliminated after depuration. The effects of microplastics were assessed by a battery of biomarkers and results revealed that microplastics induce effects on antioxidant capacity, DNA damage, neurotoxicity and oxidative damage. S. plana is a significant target to assess the environmental risk of PS microplastics.
- Spectroscopic Methods for Quantifying Gabapentin: Framing the Methods without Derivatization and Application to Different Pharmaceutical FormulationsPublication . Fonseca, Frederico; de Barros, Ricardo Brito; Ilharco, Laura M.; Garcia, AnaThis work aimed at analyzing the performance of direct spectroscopic methods for the quantification of gabapentin (GABAp), given the lack of previous studies, in comparison with the more reviewed and complex derivatization techniques, discussing their susceptibility to the pharmaceutical formulations. All of the methods analyzed showed high selectivity for this pharmaceutical analyte, with recoveries close to 100%. Absorption spectroscopy without derivatization yielded better sensitivity and lower limits of detection and quantification of gabapentin in aqueous solution (AqSol method) when compared with other solvents, such as acidic solution or ethanol/water mixture. Derivatization with sodium hypochlorite presented the highest precision, whereas derivatization with vanillin exhibited the highest accuracy. The best method for GABAp quantification in terms of highest sensitivity, lowest limits of detection, and quantification, and also with good precision and accuracy, proved to be fluorescence with derivatization by 4-chloro-7-nitrobenzofurazan. The effect of the pharmaceutical formulation (nature of excipients) was tested for the most robust and sensitive methods, with and without derivatization, on capsules of five commercial brands. Recoveries in the range of 97.9-101.5% proved that there are no matrix interfering effects. Although not presenting the best performance in all the parameters evaluated, the AqSol method, due to its simplicity, proved to be suitable for the quantification of GABAp in capsules and tables containing the molecule as the active ingredient.
- Structure and properties of cork-silica Xerogel nanocomposites: influence of the cork contentPublication . Garcia, Ana; Julio, Maria de Fatima; Ilharco, Laura M.Environmentally friendly nanocomposites were synthesized from a silica precursor and cork under mild conditions and dried at atmospheric pressure. Because of the covalent bonding between the components, these CorSil nanocomposites are homogeneous, light (apparent density in the range 360-750 kg m(-3)), machinable, with the Shore D hardness up to 67 and compressive strength up to 22.6 MPa. These properties place them as good replacements for wood, other natural products, and thermoplastic polymers, with the advantage of being flame-retardant. The influence of the cork content and grain size on the structure, porosity, and mechanical properties of the nano composites was studied using infrared spectroscopy, sorption isotherms, compressive strength, and Shore D hardness measurements.
- The infrared spectrum of solid L-alanine: influence of pH-induced structural changesPublication . Garcia, Ana; Barros, R. B. de; Lourenço, J. P.; Ilharco, Laura M.The influence of the pH on the infrared spectrum of L-alanine has been analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The amino acid was precipitated from aqueous solutions and dried at 36.5 °C, in order to stabilize cationic L-alanine or alaninium [CH3CH(NH3 +)COOH] at pH 1, the zwitterionic form [CH3CH(NH3 +)COO-] at pH 6, and anionic L-alanine or alaninate [CH3CH(NH2)COO-] at pH 13. New insight on the specific inter and intramolecular interactions in the different forms of L-alanine was reached by a novel methodological approach: an infrared technique not used before to analyze solid amino acid samples (DRIFTS), in combination with a detailed analysis based on spectral deconvolution. The frequency ranges of interest include the carbonyl/carboxyl stretching and amine deformation modes and the OH/NH stretching modes. It was shown that intermolecular hydrogen bonds between the NH3 + and COO- groups are predominant in the zwitterionic form, whereas in cationic L-alanine, H bonds between the COOH groups are responsible for the formation of dimers. In anionic L-alanine, only strong electrostatic interactions between the COOgroups and Na+ ions are proposed, evidencing the relevant role of the counterion.