Publications

Abstract The title compound, C(8)H(6)S(2), is disordered [occupancy ratio = 0.839 (2):0.161 (2)] and sits across a centre of symmetry. In the crystal, the molecules are linked by a weak C-H center dot center dot center dot pi interaction.

Abstract Although many studies have pointed out the promising role of antimicrobial peptides (AMPs) as therapeutical agents, their translation into clinical research is being slow due to the limitations intrinsic to their peptide nature. A number of structural modifications to overcome this problem have been proposed, leading to enhanced AMP biological lifetimes and therapeutic index. In this work, the interaction between liposomes of different lipidic composition and a set of lysine N-epsilon-trimethylated analogs of the cecropin A and melittin hybrid peptide, CA(1-7)M(2-9) [H-KWKLFKKIGAVLKVL-amide], was studied by differential scanning calorimetry (DSC) and fluorescence spectroscopy. The study was carried out using membrane models for mammalian erythrocytes (zwitterionic lipids) and for bacteria (mixture of zwitterionic and negatively charged lipids). The results show that trimethylated peptides interact strongly with negatively charged (bacterial cell model) but not with zwitterionic (erythrocyte model) liposomes. These results arc in agreement with the reduction of cytotoxicity and ensuing improvement in therapeutic index vs parental CA(1-7)M(2-9) found in a related study. Moreover, the modified peptides act differently depending on the model membrane used, providing further evidence that the lipid membrane composition has important implications on AMP membrane activity.

Abstract The interaction between hydrophobically modified cationic polysaccharides based on dextran and a flavonoid drug (Rutin) was studied by isothermal titration calorimetry (ITC) and fluorescence spectroscopy, in order to assess the factors responsible for the interaction and characterize its energetics, as well as for evaluating their encapsulation capacity, for possible applicability of these polymers as drug delivery vectors. To address the importance of the hydrophobic pendant groups in the solution behavior of these polymer/drug systems, we also studied the interaction of Rutin with a cationic surfactant, cetyltrimethylammonium chloride (CTAC). The interaction enthalpies and drug binding constants for D40R30/Rutin systems were derived from ITC through a simple binding model. The binding constants were independently derived from fluorescence results, with fair agreement between the parameters obtained from both methods. By changing the Rutin concentration, we were able to get evidence for a solubility enhancement induced by the presence of the polymers, a promising effect regarding its use to improve bioavailability.

Abstract Amphetamine and amphetamine-like drugs are popular recreational drugs of abuse because they are powerful stimulants of the central nervous system. Due to a dramatic increase in the abuse of methylenedioxylated derivatives, individually and/or in a mixture, and to the incoherent and contradictory interpretation of the electrochemical data available on this subject, a comprehensive study of the redox properties of amphetamine-like drugs was accomplished. The oxidative behaviour of amphetamine (A), methamphetamine (MA), methylenedioxyamphetamine (MDA) and methylenedioxymethamphetamine (MDMA) was studied in different buffer systems by cyclic, differential pulse and square-wave voltammetry using a glassy carbon electrode. A quantitative electroanalytical method was developed and successfully applied to the determination of MDMA in seized samples and in human serum. Validation parameters, such as sensitivity, precision and accuracy, were evaluated. The results found using the developed electroanalytical methodology enabled to gather some information about the content and amount of MDMA present in ecstasy tablets found in Portugal. Moreover, the data found in this study outlook the possibility of using the voltammetric methods to investigate the potential harmful effects of interaction between drugs such as MDMA and methamphetamine and other substances often used together in ecstasy tablets.

Abstract Lipophilic compounds structurally based on caffeic, hydrocaffeic, ferulic and hydroferulic acids were synthesized. Subsequently, their antioxidant activity was evaluated as well as their partition coefficients and redox potentials. The structure-property-activity relationship (SPAR) results revealed the existence of a clear correlation between the redox potentials and the antioxidant activity. In addition, some compounds showed a proper lipophilicity to cross the blood-brain barrier. Their predicted ADME properties are also in accordance with the general requirements for potential CNS drugs. Accordingly, one can propose these phenolic compounds as potential antioxidants for tackling the oxidative status linked to the neurodegenerative processes.

Abstract Research oil the volatility of aprotic ionic liquids is reviewed. This topic is limited to aprotic liquids since measurements have led to a generalization that this class of substances possesses extremely low vapor pressures. For research related to this topic, the period covered is 2003 to 2008. The review begins with a discussion of the earliest successful study of thermal vaporization of aprotic ionic liquids, the earliest indirect measurements of their vapor pressure, the first proof of conventional distillation of ionic liquids, and competition of vaporization with thermal decomposition seen at moderately high temperatures of (200 to 300) degrees C. The review then briefly discusses the nature of the vapor phase and proceeds to analyze the various approaches used to measure or predict the vapor-liquid equilibrium properties of ionic liquids, including their normal boiling point, vapor pressure, and enthalpy of vaporization. It is proposed that the most reliable thermodynamic data exist solely For the enthalpy of vaporization, and thus this property would be file best target for predictive approaches. Predictive approaches to calculate the enthalpy of vaporization are discussed in light or their ability to predict the experimentally observed trends with molar mass. The review concludes with a forward look at the following: expected effect of gas-phase ion clusters; anticipated trade-off between the energetic gain and the entropic penalty for cluster formation; and the possibility of a Trouton rule for the vaporization of ionic liquids.

Abstract The methodology for the prediction of aqueous solubilities of solid organic compounds, and their temperature dependence, based on the Conductor-like Screening Model for Real Solvents (COSMO-RS/COSMOtherm) procedure, is presented and evaluated. The predictive capability of the quantum chemistry based program and the applied methodology was tested on the most common solid carboxylic acids. From the temperature dependence of the solubilities, the mean apparent enthalpies of solution were derived. The results obtained for a set of 27 carboxylic acids, consisting of aromatic carboxylic acids, dicarboxylic acids, as well as hydroxycarboxylic acids, are in good agreement with the experimental solubility data and their dependence with the temperature. The mean apparent enthalpies of solution, although of the same order of magnitude of the experimentally values. seem to be systematically underestimated. The good response of the applied methodology based on CCSMOtherm/CCSMO-RS on the prediction of non-ideal aqueous solubilities demonstrate the capability of this approach to predict and distinguish the solubility trends and magnitude, resulting from the substituent effects on the non-ideality of the aqueous solution.

Abstract The present work reports the standard (p degrees = 0.1 MPa) molar enthalpies of formation in the gaseous phase of thioxanthone, (91.9 +/- 2.4) kJ.mol(-1), and tetrahydrothio-gamma-pyrone, (-164.6 +/- 2.0) kJ.mol(-1), at T = 298.15 K, derived from their standard molar energies of combustion and standard molar enthalpies of sublimation, measured by rotating-bomb combustion calorimetry and by the vacuum drop microcalorimetric technique, respectively. For comparison purposes, we performed additional standard ab initio molecular orbital calculations, using the G3(MP2)//B3LYP composite procedure, which were used for the calculation of the enthalpies of several homodesmotic reactions, allowing us to extract the standard molar enthalpies of formation, in the gaseous phase, of the two heterocycles considered in this work. The calculated results are in excellent agreement with the experimental data. The three-dimensional structure of the crystal tetrahydrothio-gamma-pyrone was also determined by X-ray crystallography.

Abstract The esterification of hydrophilic phenolic antioxidants is an efficient approach to enhance their solubility in apolar media. Herein, structure property studies on the antiradical activity of a series of protocatechuic acid alkyl esters have been accomplished. The increase of the lipophilicity was shown to significantly improve the antioxidant activity of protocatechuic esters. Their efficiency as radical scavengers was evaluated using distinctive analytical methods, namely, 2,2-diphenyl-1-picrylhydrazyl (DPPH) UV/visible method, electrochemistry, and differential scanning calorimetry. All the new alkyl protocatechuate antioxidants studied possessed better radical-scavenging capacity than the natural antioxidant protocatechuic acid. This work has shown that the alkyl ester side chain markedly influences the lipophilicity of this type of phenolic system without disturbing the core of the molecule responsible for antioxidant activity. The data on the antioxidant activity obtained using the different analytical methods correlated well with each other and have revealed the interesting antioxidant potential of alkyl esters of protocatechuic acid.