Publications

Abstract The standard (p degrees = 0.1 MPa) molar enthalpy of formation of 4-methyldibenzothiophene, in the gaseous phase, at T = 298.15 K, was derived from the combination of the values of the standard molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, and the standard molar enthalpy of sublimation, at the same temperature. The standard molar enthalpy of formation in the crystalline phase, determined from the standard massic energy of combustion, in oxygen, is (70.9 +/- 4.8) kJ . mol(-1) and was measured by rotating-bomb combustion calorimetry. From Calvet microcalorimetry measurements, the standard molar enthalpy of sublimation obtained is (90.3 +/- 0.7) kJ . mol(-1).

Abstract The rheological behaviour of chitosan solutions in 250 mM acetate buffer was studied at different pHs (25 degrees C). The intrinsic viscosity decreased from similar to 17 dL/g to similar to 14 dL/g when the pH increased from 4.7 to 6.0. Concentrated solutions (0.5-3.0% w/w) exhibited a shear-thinning behaviour which increased with increasing chitosan concentration and decreasing pH. A good fitting of the experimental data to the Cross and Carreau flow models was obtained. The elasticity of the solutions decreased with increasing pH and decreasing chitosan concentration, as a consequence of increased chain flexibility. The interaction of chitosan with whey proteins (WPI) was studied by isothermal titration calorimetry (ITC) and turbidity measurements, at different pHs (3.0-6.0) and ionic strengths (100 and 250 mM). ITC results showed that electrostatics is the main driving force for chitosan: WPI interaction, as an increase in ionic strength lead to a smaller interaction. A pH and chitosan: WPI ratio dependence of aggregate formation was clearly observed by turbidimetry. At pH 3.0, there was no change in turbidity upon addition of chitosan, whereas at pH 4.0 and 6.0, the turbidity values varied with chitosan: WPI ratio and were smaller at 250 mM than those at 100 mM. The rheology of chitosan:WPI coacervates was studied in acetate buffer (100 and 250 mM), at pH 5.5, mixing ratios of 0.25:1 and 0.10:1. Time dependent flow behaviour, higher G' and G '' values and higher elasticity were observed for the coacervates, originating mainly from the electrostatic interactions between the protein and the polysaccharide chains.

Abstract In the crystal of the title compound, C(12)H(16)N(2)OS, inversion dimers linked by pairs of N-H center dot center dot center dot S hydrogen bonds occur, generating R(2)(2)(8) loops. The molecules are also linked by weak C-H center dot center dot center dot O hydrogen bonds. The structure is isostructural with that of N'-benzoyl-N,N-diethylselenourea [Bruce et al. (2007). New J. Chem. 31, 1647-1653].

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.