Publications

Abstract An estimate of the digestibility and assimilability of butyltins occurring in contaminated wines (Port, red and white) was obtained by means of in vitro studies of gastrointestinal digestion. The influence of the wine matrix on the intestinal permeability was explored by studying the accumulation of butyltins in Caco-2 monolayers either when these species are dissolved in buffer only or in the dialysates of digested wines. Some important information about the fate of the butyltin compounds ingested from contaminated wines could be achieved. Only a very small fraction of the ingested DBT and TBT, the two most toxic forms, appear to be able to reach the epithelium as judged by the small dialyzable fraction found (<2%). This is probably independent from the food/drink matrix introducing these contaminants, since the influence of the involved enzymes appear to be dominant, especially for DBT and TBT. Additionally, the intestinal permeability of the three butyltins was also very low, the wine matrix possibly having a hindrance effect in a few cases.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpy of formation of 1,2,4,5-benzenetetracarboxylic dianhydride in the gaseous phase, -826.8 +/- 3.1 kJ mol(-1), was derived from the standard molar enthalpy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry and the standard molar enthalpy of sublimation, at T = 298.15 K, measured by Calvet microcalorimetry. In addition, density functional theory calculations have been performed with the B3LYP, MPW1B95, and B3PW91 density functionals and the cc-pVTZ basis set for 1,2,4,5-benzenetetracarboxylic dianhydride and 1,2,4,5-benzenetetracarboxylic diimide. Nucleus-independent chemical shifts calculations show that the aromaticity is restricted to the benzenic ring in both compounds even though they are formally 10 pi polynuclear species.

Abstract Self-assembled monolayers (SAMs) of 11-amino-1-undecanethiol (AUT) have been prepared on polycrystalline Au by immersion of the corresponding surfaces in an AUT 1 mM solution in pure ethanol. The films were studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and quartz crystal microbalance (QCM). Results of CV and EIS experiments in NaClO4 solution agree with the fast formation of a well-packed film with low current density (hundreds of nA/cm(2)) and capacitance values around 2 mu F/cm(2). The films were stable between -0.7 and 0.7 V (vs Ag/AgCl/NaCl sat.). Average values of 1.6 nm and 26 degrees were obtained for the film thickness and the tilt chain angle in the potential region under study. The kinetic analysis of the adsorption process, monitored in situ by the QCM technique, showed that it occurs in two stages: a fast Langmuir type adsorption step (k(1) = 0.1047 min(-1)), followed by a much slower process of molecular rearrangement (k(2) = 0.0020 min(-1)). AFM operated in tapping mode did not reveal any morphological changes on the surface after immersion in AUT discarding multilayer growth. The electron transfer (ET) of Fe(CN)(6)(-3) and Ru(NH3)(6)(+3) species in solution through the AUT layer was investigated by CV and EIS. A mechanism of selective permeation of the electroactive species across the monolayer, controlled by the nature of the electrostatic interactions established at the SAM-solution interface, explains the experimental data obtained and previously reported in the literature for ET processes through substituted SAMs. Analysis of the film structure according to theoretical models (commonly used for SAM characterization) to our experimental data, led to contradictory results clearly affected by the nature of the unconsidered electrostatic interactions (values of theta = 0.80 and 0.99 were obtained in the presence of Fe(CN)(6)(-3) and Ru(NH3)(6)(+3), respectively, in KCl electrolyte using the Amatore model).

Abstract Vibrational spectroscopy (both Raman and Inelastic Neutron Scattering), coupled to quantum mechanical calculations, is used in order to perform a thorough analysis of several biologically relevant molecules, such as chemotherapeutic agents, biogenic polyamines and their metal chelates, cardiovascular protectors, non-steroid anti-inflammatory drugs (NSAID's), drugs of abuse and phenolic compounds. The conjugation of these techniques yields valuable information regarding the structural preferences of the systems under investigation, which may help establish the structure-activity relationships (SAR's) ruling their biological function.

Abstract The standard ( p degrees = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of 1-naphthalenemethanol and 2-naphthalenemethanol were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by Calvet microcalorimetry. Combining these results the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, have been calculated. [GRAPHICS] Density functional theory with the B3LYP functional and two different basis sets, 6-31G( d) and 6-311G( d, p), were used to optimize the geometries of the two substituted naphthalenes. Additionally, ab initio second order Moller - Plesset calculations were also used at the MP2( FULL)/6-31G( d), MP2/ 6- 31+G( d), and MP2( FULL)/ 6-31+G( d) levels. The calculation of the energies of appropriate isodesmic reactions allowed the estimation of the standard molar enthalpies of formation in the gas phase for the compounds. The experimental measurements and both sets of quantum chemical calculations were in good agreement for both isomers.

Abstract Surgical adhesives can be applied to wound closure and to covering and protecting surface wounds. Depending on their degradability, they can then slough off or can be reabsorbed by the organism when the wound initiates the healing process. In this work, we intended to develop a new urethane-based bioadhesive that could accomplish these purposes. Urethanes are considered to be promising candidates as adhesives because of the possibility of their synthesis as prepolymers and therefore their reaction with amino groups present in the biological molecules. Some urethanes were obtained by the reaction of poly(ethylene glycol) with isophorone diisocyanate. The characterization of the various materials was accomplished with different techniques: attenuated total reflection/Fourier transform infrared, swelling-capacity determination, the evaluation of the moisture-curing kinetics, a reaction with aminated substrates (as a simulation of the living tissues), and the determination of the surface energy by contact-angle measurements. The study of the thermal properties of the urethanes was performed by dynamical mechanical thermal analysis, differential scanning calorimetry, and thermogravimetric analysis. The hemocompatibility of the urethane was also evaluated by thrombosis and hemolysis tests. (c) 2007 Wiley Periodicals, Inc.

Abstract The drugs of abuse cocaine (C), heroin (H), and morphine (M) have been studied to enable understanding of the occurrence of cocaine-opioid interactions at a molecular level. Electrochemical, Raman, and NMR studies of the free drugs and their mixtures were used to study drug-drug interactions. The results were analyzed using data obtained from quantum-mechanical calculations. For the cocaine-morphine mixture (C-MH), formation of a binary complex was detected; this involved the 3-phenolic group and the heterocyclic oxygen of morphine and the carbonyl oxygen and the methyl protons of cocaine's methyl ester group. NMR studies conducted simultaneously also revealed C-MH binding geometry consistent with theoretical predictions and with electrochemical and vibrational spectroscopy results. These results provide evidence for the occurrence of a cocaine-morphine interaction, both in the solid state and in solution, particularly for the hydrochloride form. A slight interaction, in solution, was also detected by NMR for the cocaine-heroin mixture.

Abstract A complete physicochemical characterisation of MDMA and its synthetic precursors MDA, 3,4-methylenedioxybenzaldehyde (piperonal) and 3,4-methylenedioxy-beta-methyl-beta-nitrostyrene was carried out through voltammetric assays and Raman spectroscopy combined with theoretical (DFT) calculations. The former provided important analytical redox data, concluding that the oxidative mechanism of the N-demethylation of MDMA involves the removal of an electron from the amino-nitrogen atom, leading to the formation of a primary amine and an aldehyde. The vibrational spectroscopic experiments enable to afford a rapid and reliable detection of this type of compounds, since they yield characteristic spectral patterns that lead to an unequivocal identification. Moreover, the rational synthesis of the drug of abuse 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy") from one of its most relevant precursors 3,4-methylene-dioxyamphetamine (MDA), is reported. In addition, several approaches for the N-methylation of MDA, a limiting synthetic step, were attempted and the overall yields compared.

Abstract Understanding factors responsible for the fluorescence behavior of conjugated polyelectrolytes and modulation of their behavior are important for their application as functional materials. The interaction between the anionic poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}copolymer (PBS-PFP) and cationic gemini surfactants alpha,omega-(CmH2m+1N+(CH3)(2))(2)(CH2)(s)(Br-)(2) (m-s-m; m = 12, s = 2, 3, 5, 6, 10, and 12) has been studied experimentally in aqueous solution. These surfactants are chosen to see whether molecular recognition and self-assembly occurs between the oppositely charged conjugated polyelectrolyte and gemini surfactant when the spacer length on the surfactant is similar to the intercharge separation on the polymer. Without surfactants, PBS-PFP exists as aggregates. These are broken up upon addition of gemini surfactants. However, as anticipated, the behavior strongly depends upon spacer length (s). Fluorescence measurements show three surfactant concentration regimes: At low concentrations (< 2 x 10(-6) M) quenching occurs and is most marked with the small spacer 12-2-12; at intermediate concentrations (similar to 2 x 10(-6)-10(-3) M), fluorescence intensity is constant, with a 12-carbon spacer 12-12-12 showing the strongest fluorescence; above the critical micelle concentration (CMC; similar to 10(-3) M) increases in emission intensity are seen in all cases and are largest with the intermediate spacers 12-5-12 and 12-6-12, where the spacer length most closely matches the distance between monomer units on the polymer. With longer spacer length surfactants, surface tension measurements for concentrations below the CMC reveal the presence of polymer-surfactant aggregates at the air-water interface, possibly reflecting increased hydrophobicity. Above the CMC, small-angle neutron scattering experiments for the 12-6-12 system show the presence of spherical aggregates, both for the pure surfactant and for polyelectrolyte/gemini mixtures. Molecular dynamics simulations help rationalize these observations and show that there is a very fine balance between electrostatic and hydrophobic interactions. With the shortest spacer 12-2-12, Coulombic interactions are dominant, while for the longest spacer 12-12-12 the driving force involves hydrophobic interactions. Qualitatively, with the intermediate 12-5-12 and 12-6-12 systems, the optimum balance is observed between Coulombic and hydrophobic interactions, explaining their strong fluorescence enhancement.

Abstract The coexistence of two lamellar liquid-crystalline phases in equilibrium for binary surfactant-water systems is a rare and still puzzling phenomenon. In the few binary systems where it has been demonstrated experimentally, the surfactant is invariably ionic and the miscibility gap is thought to stem from a subtle balance between attractive and repulsive interbilayer forces. In this paper, we report for the first time a miscibility gap for a catanionic lamellar phase formed by the surfactant hexadecyltrimethylammonium octylsulfonate (TASo) in water. Synchrotron small-angle X-ray scattering, polarizing light microscopy, and H-2 NMR unequivocally show the coexistence of a dilute (or swollen) lamellar phase, L-alpha', and a concentrated (or collapsed) lamellar phase, L alpha ''. Furthermore, linear swelling is observed for each of the phases, with the immiscibility region occurring for 15-54 wt % surfactant. In the dilute region, the swollen lamellar phase is in equilibrium with an isotropic micellar region. Vesicles can be observed in this two-phase region as a dispersion of L alpha' in the solution phase. A theoretical cell model based on combined DLVO and short-range repulsive potentials is presented in order to provide physical insight into the miscibility gap. The surfactant TASo is net uncharged, but it undergoes partial dissociation owing to the higher aqueous solubility of the short octylsulfonate chain. Thus, a residual positive charge in the bilayer is originated and, consequently, an electrostatic repulsive force, whose magnitude is dependent on surfactant concentration. For physically reasonable values of the solubility of the octyl chain, assumed to be constant with surfactant volume fraction, a fairly good agreement is observed between the experimental miscibility gap and the theoretical one.