Publications

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.

Abstract Cortical function has been suggested to be highly compromised by repeated heroin self-administration. We have previously shown that street heroin induces apoptosis in neuronal-like PC12 cells. Thus, we analysed the apoptotic pathways involved in street heroin neurotoxicity using primary cultures of rat cortical neurons. Our street heroin sample was shown to be mainly composed by heroin, 6-monoacetylmorphine and morphine. Exposure of cortical neurons to street heroin induced a slight decrease in metabolic viability, without loss of neuronal integrity. Early activation of caspases involved in the mitochondrial apoptotic pathway was observed, culminating in caspase 3 activation, Poly-ADP Ribose Polymerase (PARP) cleavage and DNA fragmentation. Apoptotic morphology was completely prevented by the non-selective caspase inhibitor z-VAD-fmk, indicating an important role for caspases in neurodegeneration induced by street heroin. Ionotropic glutamate receptors, opioid receptors and oxidative stress were not involved in caspase 3 activation. Interestingly, street heroin cytotoxicity was shown to be independent of a functional mitochondrial respiratory chain, as determined using NT-2 rho(0) cells. Nonetheless, in street heroin-treated cortical neurons, cytochrome c was released, accompanied by a decrease in mitochondrial potential and Bcl-2/Bax. Pure heroin hydrochloride similarly decreased metabolic viability but only slightly activated caspase 3. Altogether, our data suggest an important role for mitochondria in mediating street heroin neurotoxic effects.

Abstract Aqueous mixtures containing a homopolymer, poly(vinylpyrrolidone) (PVP), or a hydrophobically modified graft copolymer, HM-pullulan, (PULAU(9), where 9 stands for the nominal substitution degree), and different Gemini surfactants have been investigated at 25.0 degrees C. A wide variety of experimental conditions were addressed by changing the amount of polymer and of surfactant. The Gemini surfactants were synthesized, purified, and characterized by routine methods. They differ from each other in polar head groups (two sulfonate-, two quaternary ammonium-, or two arginine-based groups), in alkyl chain length (11 or 12 carbon atoms), and in the distance between the polar head groups. The spacers consist of 2, 3, and 6 methylene units or 3 oxyethylene units. Surface activity and solution calorimetry measurements yield some physicochemical features inherent to micelle formation and polymer-surfactant interactions. The data are supported by ionic conductivity, detecting the critical thresholds and quantifying the modifications in binding associated with critical association (CAC) and micelle formation (CMC*). The Gibbs energy of transfer from the micelles to a polymer-binding site, Delta G(trans), was evaluated from the CAC/CMC* ratios versus the amount of added polymer. A similar procedure determined the enthalpy of transfer, Delta H-trans. Delta G(trans) decreases with added polymer, whereas Delta H-trans becomes more negative on increasing the amount of polymer in the medium. According to the selected data presented here, cationic Geminis do not interact with PVP, while significant interactions have been observed in other surfactants. In mixtures with PULAU(9), the interaction is significant for all Geminis. This effect is due to interactions between the surfactants and the hydrophobic alkyl groups on the main polymer chain. The pendent groups facing away from the polysaccharide chain act as binding sites for aggregates onto such polymers.