Publications

Abstract In the past decade, clinical evidence has increasingly shown that the liver is a target organ for 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") toxicity. The aims of the present in vitro study were: (1) to evaluate and compare the hepatotoxic effects of MDMA and one of its main metabolites, N-methyl-alpha-methyldopamine (N-Me-alpha-MeDA) and (2) to investigate the ability of antioxidants, namely ascorbic acid and N-acetyl-L-cysteine (NAC), to prevent N-Me-alpha-MeDA-induced toxic injury, using freshly isolated rat hepatocytes. Cell suspensions were incubated with MDMA or N-Me-alpha-MeDA in the final concentrations of 0.1, 0.2, 0.4, 0.8, and 1.6 mM for 3 It. To evaluate the potential protective effects of antioxidants, cells were preincubated with ascorbic acid in the final concentrations of 0.1 and 0.5 mM, or NAC in the final concentrations of 0.1 and I mM for 15 min before treatment with 1.6 mM N-Me-alpha-MeDA for 3 In (throughout this incubation period the cells were exposed to both compounds). The toxic effects were evaluated by measuring the cell viability, glutathione (GSH) and glutathione disulfide (GSSG), ATP and the cellular activities of GSH peroxidase (GPX), GSSG reductase (GR), and GSH S-transferase (GST). MDMA induced a concentration- and time-dependent GSH depletion, but had a negligible effect on cell viability, ATP levels, or on the activities of GR, GPX, and GST. In contrast, N-Me-alpha-MeDA was shown to induce not only a concentration- and time-dependent depletion of GSH, but also a depletion of ATP levels accompanied by a loss in cell viability, and decreases in the antioxidant enzyme activities. For both compounds, GSH depletion was not accompanied by increases in GSSG levels, which seems to indicate GSH depletion by adduct formation. Importantly, the presence of ascorbic acid (0.5 mM) or NAC (1 mM) prevented cell death and GSH depletion induced by N-Me-alpha-MeDA. The results provide evidence that MDMA and its metabolite N-Me-alpha-MeDA induce toxicity to freshly isolated rat hepatocytes. Oxidative stress may play a major role in N-Me-alpha-MeDA-induced hepatic toxicity since antioxidant defense systems are impaired and administration of antioxidants prevented N-Me-alpha-MeDA toxicity.

Abstract In nonequimolar solutions of a cationic and an anionic surfactant, vesicles bearing a net charge can be spontaneously formed and apparently exist as thermodynamically stable aggregates. These vesicles can associate strongly with polymers in solution by means of hydrophobic and/or electrostatic interactions. In the current work, we have investigated the rheological and microstructural properties of mixtures of cationic polyelectrolytes and net anionic sodium dodecyl sulfate/didodecyldimethylammonium bromide vesicles. The polyelectrolytes consist of two cationic cellulose derivatives with different charge densities; the lowest charge density polymer contains also hydrophobic grafts, with the number of charges equal to the number of grafts. For both systems, polymer-vesicle association leads to a major increase in viscosity and to gel-like behavior, but the viscosity effects are more pronounced for the less charged, hydrophobically modified polymer. Evaluation of the frequency dependence of the storage and loss moduli for the two systems shows further differences in behavior: while the more long-lived cross-links occur for the more highly charged hydrophilic polymer, the number of cross-links is higher for the hydrophobically modified polymer. Microstructure studies by cryogenic transmission electron microscopy indicate that the two polymers affect the vesicle stability in different ways. With the hydrophobically modified polymer, the aggregates remain largely in the form of globular vesicles and faceted vesicles (polygon-shaped vesicles with largely planar regions). For the hydrophilic polycation, on the other hand, the surfactant aggregate structure is more extensively modified: first, the vesicles change from a globular to a faceted shape; second, there is opening of the bilayers leading to holey vesicles and ultimately to considerable vesicle disruption leading to planar bilayer, disklike aggregates. The faceted shape is tentatively attributed to a crystallization of the surfactant film in the vesicles. It is inferred that a hydrophobically modified polyion with relatively low charge density can better stabilize vesicles due to formation of molecularly mixed aggregates, while a hydrophilic polyion with relatively high charge density associates so strongly to the surfactant films, due to strong electrostatic interactions, that the vesicles are more perturbed and even disrupted.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following 4-n-alkylbenzoic acids: 4-methylbenzoic acid, between 319.68 K and 337.33 K, 4-ethylbenzoic acid, between 321.17 K and 335.25 K, 4-propylbenzoic acid, between 331.16 K and 347.16 K, 4-butylbenzoic acid, between 333.16 K and 349.15 K, 4-pentylbenzoic acid, between 341.16 K and 357.16 K, 4-hexylbenzoic acid, between 347.08 K and 363.14 K, 4-heptylbenzoic acid, between 353.16 K and 369.20 K and 4-octylbenzoic acid, between 356.67 K and 371.86 K. From the temperature dependence of the vapour pressure of the crystalline compounds, the standard, pdegrees = 10(5) pa, molar enthalpies, entropies and Gibbs energies of sublimation at T = 298.15 K, were derived. A d.s.c. study of the crystalline polymorphic transitions, fusion and isotropization of liquid crystals is also presented.

Abstract The standard molar enthalpies of combustion and sublimation of 2- and 4-biphenylcarboxylic acid, 2,2'- and 4,4'-biphenyldicarboxylic acid were measured and the gas-phase enthalpies of formation, at T = 298.15 K, were determined. Ab initio calculations were performed and a theoretical study on molecular structure of all the biphenyl acid isomers has been carried out. Calculated enthalpies of formation using appropriate isodesmic reactions are compared with experimental values, and a good agreement is observed. Estimates of enthalpies of formation for the isomers, which were not studied experimentally, are presented. All the acids containing at least one ortho COOH are comparatively less stable than their isomers having just meta or para COOH group(s).

Abstract Cardiovascular complications associated with 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) abuse have increasingly been reported. The indirect effect of MDMA mediated by a sustained high level of circulating biogenic amines may contribute to the cardiotoxic effects, but other factors, like the direct toxic effects of MDMA and its metabolites in cardiac cells, remain to be investigated. Thus, the objective of the present in vitro study was to evaluate the potential cardiotoxic effects of MDMA and its major metabolites 3,4-methylenedioxyamphetamine (MDA), N-methyl-alpha-methyldopamine (N-Me-alpha-MeDA), and alpha-methyldopamine (alpha-MeDA) using freshly isolated adult rat cardiomyocytes. The cell suspensions were incubated with these compounds in the final concentrations of 0.1, 0.2, 0.4, 0.8, and 1.6 mM for 4 h. alpha-MeDA, N-Me-alpha-MeDA, and their respective aminochromes (oxidation products) were quantified in cell suspensions by HPLC-DAD. The toxic effects were evaluated at hourly intervals for 4 h by measuring the percentage of cells with normal morphology, glutathione (GSH), and glutathione disulfide (GSSG); intracellular Ca2+, ATP, and ADP; and the cellular activities of glutathione peroxidase, glutathione reductase, and glutathione-S-transferase. No toxic effects were found after exposure of rat cardiomyocytes to MDMA or MDA at any of the tested concentrations for 4 h. In contrast, their catechol metabolites N-Me-alpha-MeDA and alpha-MeDA induced significant toxicity in rat cardiomyocytes. The toxic effects were characterized by a loss of normal cell morphology, which was preceded by a loss of GSH homeostasis due to conjugation of GSH with N-Me-alpha-MeDA and alpha-MeDA, sustained increase of intracellular Ca2+ levels, ATP depletion, and decreases in the antioxidant enzyme activities. The oxidation of N-Me-alpha-MeDA and alpha-MeDA into the toxic compounds N-methyl-alpha-methyldopaminochrome and alpha-methyldopaminochrome, respectively, was also verified in cell suspensions incubated with these MDMA metabolites. The results obtained in this study provide evidence that the metabolism of MDMA into N-Me-alpha-MeDA and alpha-MeDA is required for the expression of MDMA-induced cardiotoxicity in vitro, being N-Me-alpha-MeDA the most toxic of the studied metabolites.

Abstract The present work reports a vibrational spectroscopic study of several beta-methyl-beta-nitrostyrene derivatives, which are important intermediates in the synthesis of illicit amphetamine-like drugs, such as 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA), p-methoxyamphetamine (PMA) and 4-methylthioamphetamine (4-MTA). A complete conformational analysis of 3,4-methylenedioxy-beta-methyl-beta-nitrostyrene (3,4-MD-MeNS), 4-methoxy-beta-methyl-beta-nitrostyrene (4-MeO-MeNS), 4-methylthio-beta-methyl-beta-nitrostyrene (4-MeS-MeNS), was carried out by Raman spectroscopy coupled to ab initio MO calculations - both complete geometry optimisation and harmonic frequency calculation. The Raman spectra show characteristic features of these precursors, which allow their ready differentiation and identification. It was verified that the conformational behaviour of these systems is mainly determined by the stabilising effect of pi-electron delocalisation.

Abstract The standard (pdegrees = 0.1 MPa) molar enthalpy of formation of crystalline 2-hydroxypyridine N-oxide was measured, at T = 298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T = 298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation of 2-hydroxypyridine N-oxide in gaseous phase, and to evaluate the dissociation enthalpy of the N-O bond. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for the three isomers of hydroxypyridine N-oxide in order to confirm the experimental trend for the dissociation enthalpy of the (N-O) bond.

Abstract The standard (p(o) = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of four 1,3-benzodioxole derivatives ( sesamol, piperonyl alcohol, piperonylic acid and homopiperonylic acid) were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation, at T = 298.15 K, were derived from vapour pressure - temperature measurements using the Knudsen effusion technique. Combining these results the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, have been calculated: sesamol (- 325.7 +/- 1.9) kJ mol(-1); piperonyl alcohol (- 329.0 +/- 2.0) kJ mol(-1); piperonylic acid ( - 528.9 +/- 2.6) kJ mol(-1) and homopiperonylic acid (- 544.5 +/- 2.9) kJ mol(-1). The most stable geometries of all the compounds were obtained using the density functional theory with the B3LYP functional and two basis sets: 6-31G** and 6-311G**. The nonplanarity of the molecules was analyzed in terms of the anomeric effect, which is believed to arise from the interaction between a nonbonded oxygen p orbital and the empty orbital sigma*(co) involving the other oxygen atom. Calculations were performed to obtain estimates of the enthalpies of formation of all the benzodioxoles using appropriate isodesmic reactions. There is a perfect agreement between theoretical and experimental results.

Abstract In this work, the gas-phase homolytic N-H bond dissociation enthalpy (BDE) was investigated for a large series of molecules containing at least one N-H bond by means of accurate density-functional theory calculations. The molecules studied belong to different classes of compounds, namely, amines, amides and anilines, amino acids, phenoxazines, indolamines, and other compounds of general interest, such as anti-inflammatory drugs. To achieve these purposes, the (RO)B3LYP/6-311+G(2d,2p)//(U)B3LYP/6-31G* level of theory was used. The calculated gas-phase N-H BDEs, at T = 298.15 K, are in the range 499.6-203.9 kJ/mol, for purine and HNO, respectively. Further, the calculated BDEs are in excellent agreement with a significant number of available experimental BDEs. Solvent effects were also taken in account, and rather significant differences are found among N-H BDEs computed in the gas phase and in heptane, DMSO, or water.

Abstract The standard (pdegrees = 0.1 MPa) molar enthalpies of formation of the crystalline complexes bis[N-(N",N"-diethylaminothiocarbonyl)benzamidinato]nickel(II), {Ni(datb)(2)}, and bis[N-(N",N"-diethylaminothiocarbonyl)-N'-phenylbenzamidinato]nickel(II), {Ni(datpb)(2)}, were determined, at T = 298.15 K, by high precision solution-reaction calorimetry. [GRAPHICS] From the obtained results, the metal-ligand exchange enthalpies in the crystalline phase were derived. The enthalpy of a hypothetical metal-ligand exchange reaction in the crystalline phase was derived, thus allowing a discussion of the energetics of complexation in comparison with known crystal-structural parameters.