Publications

Abstract The interaction between glucose oxidase (GOx) and phospholipid monolayers is studied at the 1, 2-dichloroethane/water interface by electrochemical impedance spectroscopy. Electrochemical experiments show that the presence of GOx induces changes in the capacitance curves at both negative and positive potentials, which are successfully explained by a theoretical model based on the solution of the Poisson-Boltzmann equation. These changes ore ascribed to a reduced partition coefficient of GOx and on increase of the permittivity of the lipid hydrocarbon domain. Our results show that the presence of lipid molecules enhances the adsorption of GOx molecules at the liquid/liquid interface. At low lipid concentrations, the adsorption of GOx is probably the first step preceding its penetration into the lipid monolayer. The experimental results indicate that GOx penetrates better and forms more stable monolayers for lipids with longer hydrophobic toils. At high GOx concentrations, the formation of multilayers is observed. The phenomenon described here is strongly dependent on 1) the GOx and lipid concentrations, 2) the nature of the lipid, and 3) the potential drop across the interface.

Abstract The present work reports the values of the gaseous standard (p degrees = 0.1 MPa) molar enthalpies of formation of the three acetylpyridine isomers, at T = 298.15 K. For each isomer, that value was derived from measurements of the standard molar energy of combustion of the corresponding liquid, using a static bomb calorimeter, together with measurements of the standard molar enthalpy of vaporization, measure by Calvet microcalorimetry. [GRAPHICS]

Abstract The protection from ultraviolet radiation were demonstrated by four simple experiments provided by different systems that constitutes a simple simulation of the protection provided by the ozone layer. The four protection systems that were studied include: the plexiglass plates obtained from a plastic materials store, sunscreens, cotton cloths of different colors and natural organic matter. This experiment may be used either in a directed or more flexible manner by using the proposal of the problem and a list of material.

Abstract The present work reports the values of the standard (p degrees = 0.1 MPa) molar energies of combustion for the liquid isomers methyl picolinate and methyl isonicotinate and for the crystalline isomer methyl nicotinate measured by static bomb calorimetry. The molar enthalpies of vaporization of the three isomers at T = 298.15 K as well as the molar enthalpies of sublimation of two of them (methyl picolinate and methyl nicotinate) were derived from vapor pressure measurements at different temperatures using a static method. The molar enthalpies of vaporization at T = 298.15 K of methyl picolinate and methyl isonicotinate were also measured using Calvet microcalorimetry. The thermal behavior of the compounds was studied by differential scanning calorimetry, and the temperatures and the molar enthalpies of fusion were determined using this technique. The experimental results were used to derive the gaseous standard molar enthalpies of formation, at 298.15 K, of the three pyridinecarboxylic acid methyl ester isomers and the triple points of the ortho and meta isomers.

Abstract For the first time, the partition coefficients of the ionized forms of several opioids, amphetamine-like drugs, and their metabolites were determined by studying their ionic transfer process across the bare interface water/organic solvent. The ionic partition coefficients of the monocationic forms of 12 compounds heroin, 6-monoacetylmorphine (6-MAM), morphine, acetylcodeine, codeine, dihydrocodeine, methamphetamine, amphetamine, 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy"), 3,4-methylenedioxyamphetamine (MDA), 3-methoxy-alpha-methyldopamine (3-OMe-alpha-MeDA), and alpha-methyldopamine (alpha-MeDA)-were attained using electrochemical measurements, by cyclic voltammetry, at the interface between two immiscible electrolyte solutions (ITIES). Then the acquired lipophilicity values were correlated to the chemical structure of the compounds and with the metabolic pathways central to each class of drugs. Although the mechanisms of biotoxicity of this type of drugs are still unclear, the data obtained evidence that the lipophilicity of metabolites may be a contributing factor for the qualitative differences found in their activity. In addition, the partition coefficients of the ionic drugs were calculated using three available software packages: ModesLab, Dragon, and HyperChem. As shown by cross-comparison of the experimental and calculated values, HyperChem was the most reliable software for achieving the main goal. The data obtained so far seem to be correlated to the proposed metabolic pathways of the drugs and could be of great value in understanding their pharmacological and/or toxicological profiles at the molecular level. This study may also contribute to gaining an insight into the mechanisms of biotransportation of this type of compounds given that the ionic partition coefficients reflect their ability to cross the membrane barriers.

Abstract Malaria is nowadays a worldwide and serious problem with a significant social, economic, and human cost, mainly in developing countries. In addition, the emergence and spread of resistance to existing antimalarial therapies deteriorate the global malaria situation, and lead thus to an urgent need toward the design and discovery of new antimalarial drugs. In this work, a QSAR predictive model based on GETAWAY descriptors was developed which is able to explain with, only three variables, more than 77% of the variance in antimalarial potency and displays a good internal predictive ability (of 73.3% and 72.9% from leave-one-out cross-validation and bootstrapping analyses, respectively). The performance of the proposed model was judged against other five methodologies providing evidence of the superiority of GETAWAY descriptors in predicting the antimalarial potency of the bisbenzamidine family. Moreover, a desirability analysis based on the final QSAR model showed that to be a useful way of selecting the predictive variable level necessary to obtain potent bisbenzamidines. From the proposed model it is also possible to infer that elevated high atomic masses/polarizabilities/van der Waals volumes could play a negative/positive/positive role in the molecular interactions responsible for the desired drug conformation, which is required for the optimal binding to the macromolecular target. The results obtained point out that our final QSAR model is statistically significant and robust as well as possessing a high predictive effectiveness. Thus, the model provides a feasible and practical tool for looking for new and potent antimalarial bisbenzamidines.

Abstract A Diltiazem kinetic spectrophotornetric UV-Vis method, based on a reaction of the Diltiazem with hidroxylamine and a ferric salt, was used for the quantification of Diltiazem in different pharmaceutical formulations. This method is based on the acquisition of three-way data structures [wavelength (nm) x time (s) x concentration (mg/L)] followed by chemometric analysis by an appropriate PARAFAC2 or MCR-ALS second-order calibration model. The results obtained are compared with those obtained by direct determination, at maximum wavelength, and by the United States Pharmacopeia (USP) standard chromatographic method. For all the pharmaceutical formulations analysed good quantification results were found with PARAFAC2 and MCR-ALS second-order calibration models. For bulk drug analysis, detection limits of 6 and 2 mg/L, and for pharmaceutical formulations analysis, an average detection limit of 41 and 39 mg/L were found, respectively with PARAFAC2 and MCR-ALS.

Abstract The adsorption behaviour of a series of phosphatidylcholines (PCs) with saturated carbon chains of different length (DLPC, DPPC, DSPC, DAPC, and DBPC) at the electrified 1,2-dichloroethane/water interface was studied by measuring electrochemical impedance spectroscopy at the polarized interface. Two different trends in the interfacial capacitance were observed for any of the PCs the capacity dependence on the applied potential: strong adsorption occurs at negative potential with a marked decrease of C(E); increase of capacity is observed at positive potentials. It is demonstrated that the interfacial lipid adsorption was dependent on phospholipid concentration, applied potential, and phospholipid chain length. The potential and concentration dependence of the interfacial capacitance in the presence of these phospholipids were successfully described by a model based on the solution of the Poisson-Boltzmann equation in the interfacial region.

Abstract An electrochemical approach for the improved electrochemical sensing of DNA was developed in this study based on the oxidation signals of silver and DNA base, guanine by using disposable pencil graphite electrode (PGE) electrodes. The easy surface modification of disposable electrodes PGEs with nucleic acids was performed by passive adsorption using amino linked DNA oligonucleotide attached onto the surface of silver nanoparticles (Ag-NPs). Firstly, the microscopic characterization of silver nanoparticles was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and the electrochemical behaviour of these NPs was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Then, the overall performance of this novel electrochemical DNA sensing method based on these nanoparticles is studied and discussed in terms of optimum analytical conditions, such as; the effect of DNA concentration, NPs concentration and different buffer solutions, etc. in order to obtain silver and guanine oxidation signals in higher sensitivity and selectivity. The main features related with this electrochemical assay based on silver nanoparticles are discussed and compared with other assays reported in the literatures.

Abstract We present a proposal for research, development and construction of international communities in Portuguese using digital platforms. The idea was born following an international conference on distance teaching and learning, in which a meeting on 'E-learning and Portuguese-language culture' was promoted. The established contacts gave place to a new project to stimulate learning communities via the internet. Currently, the countries involved are Portugal, Brazil and Mozambique, but in a near future other Portuguese-speaking communities will be able to participate. The theoretical framework is provided by Vigotsky's ideas on learning contexts. Copyright © 2007 Inderscience Enterprises Ltd.