Publications

Abstract The extent to which humans and wildlife are exposed to the vast array of anthropogenic chemicals and their degradation products, along with related naturally occurring compounds, is nowadays an important issue. The study of the physical-chemical properties of the compounds and/or degradation products is an important subject because some of them are intrinsically related to its resistance to degradation and/or bioaccumulation. Accordingly, the study of the electrochemical behavior of the selective serotonin reuptake inhibitor fluoxetine and its main metabolite norfluoxetine was investigated. The identification of the oxidation processes was done via two fluoxetine analogues, 1-(benzyloxy)-4-(trifluoromethyl)benzene and N-methyl-3-phenylpropan-1-amine hydrochloride. The oxidative processes occurring in fluoxetine are pH-dependent and were ascribed to the chemical moieties present in the molecule: the secondary amine group and the substituted aromatic nucleus. To perform an unequivocal ascription, the structural preferences of the drug and metabolite were also determined, by Raman spectroscopy coupled to quantum mechanical calculations (at the DFT level). The analytical data obtained in this work will allow the development of a rapid and unequivocal spectroscopic procedure suitable for fluoxetine identification, as well as to distinguish between the drug and its main metabolite.

Abstract The properties of the interface between platinum, gold and glassy carbon electrodes and a deep eutectic ionic liquid based on choline chloride and glycerol were assessed using cyclic voltammetry and electrochemical impedance spectroscopy. The double layer differential capacitance, obtained from electrochemical impedance, reveals a slight dependence of the potential but it is sensitive to the electrode material. In contrast to high temperature inorganic melts the differential capacitance increases with temperature.

Abstract In this work we describe and compare the synthesis of four new hexylamides of hydrocinnamic acids, namely hexylamide of hydrocinnamic, 3,4-dimethoxyhydrocinnamic, 4-hydroxy-3-methoxyhydrocinnamic and 3,4-dihydroxyhydrocinnamic acids via pentafluorophenyl esters (PFPEs) versus pentafluorophenyl thioesters (PFPTs) intermediates. It was found that the PRE are the best intermediates for this kind of synthesis giving reactions with less by products, easier work-up, higher overall yields and with the best reactivity towards hexylamine. The X-ray structures of two PRE are also reported.

Abstract The synthesis of some novel monomeric serine- and tyrosine-based cationic and 4-hydroxyproline-based anionic surfactants, having a long lipophilic alkyl chain directly attached to the nitrogen atom of the amino acid, is described. The most efficient synthetic methodologies were established: reductive amination of the corresponding 'fatty' aldehydes, followed by methylation and deprotection (serine and tyrosine) to obtain the cationic surfactants; or reductive amination followed by saponification (4-hydroxyproline) to obtain the anionic ones. All the compounds were obtained in good to excellent yields. An assessment of their micellization properties and surface activity by tensiometry showed fairly good performance levels.

Abstract A chemical sensor for mercury(II) (Hg(II)) was developed based on the quenching of the fluorescence of cadmium sulfide (CdS) quantum dots (QDs) coated with polypropylenimine tetrahexacontaamine dendrimer ( DAB) generation 5, CdS-DAB nanocomposites. The synthesis and characterization of CdS-DAB nanocomposites by means of EDXA, SEM and steady state luminescence is described. Macroscopic spherical structures are observed by electronic microscopy and the wavelength for the maximum fluorescence emission occurs at 535 nm (excitation at 351 nm). Stern-Volmer plots show a linear response in the range of 1 x 10(-6) to 1 x 10(-5) M with a quenching constant (K(sv)) of 1.5 x 10(5) M(-1). A parallel factor (PARAFAC) analysis model confirmed that Hg( II) alone provokes quenching of the fluorescence. Cu(II) and Pb(II) also quench the fluorescence of CdS-DAB nanocomposites, with a K(sv) = 1.9 x 10(5) M(-1) and K(sv) = 2.2 x 10(-4) M(-1), respectively, and Cd(II), Zn(II), Co(II) and Ni(II) have no effect. Ionic strength, in the range from 1.25 x 10(-3) up to 2 M, provokes a shift in the wavelength of the maximum of the emission spectra, from 482 to 677 nm.

Abstract The conformational behaviour of several biologically relevant hydroxycinnamic systems - ferulic acid and its methyl, ethyl, propyl and butyl esters - was studied by quantum mechanical calculations, at the DFT level. A full geometry optimisation was carried out, as well as a Fourier analysis of the main internal rotations within these molecules. The geometrical preferences of these compounds result from a balance between the stabilising resonance and hydrogen bonding effects and the destabilising non-bonding repulsions, the most stable conformers displaying an s-cis conformation and hydroxyl/methoxyl substituent groups coplanar to the aromatic ring. The results thus obtained allow a better understanding of the well recognised in vitro and in vivo antioxidant and growth-inhibiting properties of this type of phenolic systems. (C) 2009 Published by Elsevier B.V.

Abstract Semiconductor nanocrystals have unique optical properties that make them promising alternatives to traditional dyes in many luminescence based analytical techniques. An overview of the more relevant progresses in the application of quantum dots (QDs) as analytical probes in optical fibre sensing and imaging application will be addressed. Experimental results regarding the use of QDs as self-referenced multiplexed probes for chemical sensing and analytical imaging will be presented.

Abstract An interdisciplinary research project was developed combining the synthesis of a series of hydroxycinnamic acid derivatives and the evaluation of their physicochemical parameters (namely redox potentials and partition coefficients), along with the corresponding antioxidant activity. A structure-property-activity relationship (SPAR) approach was then applied aiming at establishing a putative relation between the physicochemical parameters of the compounds under study and their antioxidant activity. The results gathered allow concluding that the redox potentials could contribute to the understanding of the antioxidant activity and that the presence of an electron withdrawing group (EWG) of halogen type, namely a bromo atom, in an ortho position to a phenolic group of the cinnamic scaffold does not influence the antioxidant activity. On the other hand after the introduction of this type of substituent a significant increase on the lipophilicity of cinnamic derivatives was observed, which is a feature of extreme importance in the development of novel lipophilic antioxidants. The SPAR results revealed a relation between the redox potentials and the antioxidant activity of hydroxycinnamic acids and derivatives. The data obtained operate as a positive reinforce of the tendency to use redox properties as a guideline of the rational design of this type of compounds.

Abstract The solution Raman pattern of a series of structurally related hydroxycinnamic and hydroxybenzoicesters (caffeates and gallates) with potential antioxidant/anticancer activity was studied, for different biologically significant concentrations. The spectra were assigned with the help of theoretical calculations in the light of previously reported experimental data for these compounds in the solid state. Evidence of the formation of dimeric entities in solution, via (C)=O center dot center dot H(O) and/or (C)=O center dot center dot center dot H(C) intermolecular hydrogen bonds, was obtained. The dimer-to-monomer equilibrium, which influences the antioxidant activity of this kind of systems, was monitored through Raman titration experiments. Copyright (c) 2008 John Wiley & Sons, Ltd.

Abstract A three-layer feed forward neural network was constructed and tested to analyze the second order kinetics of solid-liquid adsorption process. The pseudo second order kinetics of auramine O onto activated carbon was used to train the artificial neural network (ANN) to model the sorption system for various operating conditions. The operating variables studied are the contact time, initial dye concentration, agitation speed, temperature, initial solution pH and activated carbon mass. The studied operating variables were used as the input to the constructed neural network to predict the dye uptake by pseudo second order kinetics at any time as the output or the target. The dye uptake predicted by ANN trained by pseudo second order kinetics was found to be precise in representing the experimental kinetics of auramine O uptake by activated carbon. The constructed network was also found to be precise in predicting the sorption kinetics of auramine O by activated carbon for the new input data which are kept unaware of the trained neural network showing its applicability to determine the dye uptake rate for any operating conditions under interest. The ANN was also trained using pseudo second order kinetics of sorption of divalent metal ions onto peat particles and also using the second order kinetics of cadmium ions onto tree fern particles. The ANN and pseudo second order kinetics compliment each other to model the studied sorption systems for a wide range of operating conditions.