Publications

Abstract Differential capacity-potential curves, C(E), were obtained from electrochemical impedance spectra (12 kHz-2 Hz) for the interfaces between Hg and a series of alkyl imidazolium-based room temperature ionic liquids having the same anion, bis(trifluoromethanesulfonyl) imide: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide [EMIM][Tf(2)N], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide [BMIM][Tf(2)N], 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide [HMIM][Tf(2)N]. The electrocapillary curves were obtained from drop time measurements and the values of the pzc were calculated. The pzc apparently becomes more negative as the imidazolium alkyl chain length increases. A small effect of the cation is seen on the C(E) curves at negative potentials. The effect of the aromatic nature of the cation is assessed by comparing 1-butyl-1-methylimidazolium bis(trifluoromethanesulfonyl) imide, with 1-butyl-3-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide [BMPyr][Tf(2)N]. The effects of temperature on the capacitance, drop time electrocapillary curve and on the pzc were also obtained. The capacity was found to increase with increasing temperature in the whole range of accessible potentials.

Abstract Mixtures of ionic surfactants of opposite charge ("catanionic" mixtures) show strongly nonideal behaviors, for example, in terms of evolution of surface tension, critical micelle concentration, or morphology with respect to composition in each surfactant. In several catanionic systems, it has been proposed that the interaction between both surfactants is so strong that lateral phase segregation occurs within bilayers, with crystallites of preferential composition demixing from the excess of the other surfactant. Here, we investigate the temperature-composition phase diagram of the myristic acid/cetyltrimethylammonium mixtures. Combining microcalorimetry, X-ray diffusion, and solid-state deuterium NMR, we demonstrate that no separation is observed in the gel (L(beta)) state. The catanionic mixtures therefore behave like two-dimensional solid solutions with a negative azeotrope: the existence of a composition at which a maximum in melting temperature is observed does not imply the existence of a preferential crystal of this composition, but results from the preferential attraction between unlike amphiphilic molecules. Additionally, this study reveals the presence of a so-called intermediate phase, that is, a phase that shows dynamic properties intermediate between that of the L(beta) and the L(alpha) phases.

Abstract Cocaine and heroin are frequently co-abused by humans, in a combination known as speedball. Recently. chemical interactions between heroin (Her) or its metabolite morphine (Mor) and cocaine (Coc) were described, resulting in the formation of strong adducts. In this work, we evaluated whether combinations of Coc and Her affect the neurotoxicity of these drugs, using rat cortical neurons incubated with Coc, Her, Her followed by Coc (Her + Coc) and Her plus Coc (Her:Coc, 1:1). Neurons exposed to Her, Her + Coc and Her:Coc exhibited a decrease in cell viability, which was more pronounced in neurons exposed to Her and Her + Coc, in comparison with neurons exposed to the mixture (Her:Coc). Cells exposed to the mixture showed increased intracellular calcium and mitochondrial dysfunction, as determined by a decrease in intracellular ATP levels and in mitochondrial membrane potential, displaying both apoptotic and necrotic characteristics. Conversely, a major increase in cytochrome c release, caspase 3-dependent apoptosis, and decreased metabolic neuronal viability were observed upon sequential exposure to Her and Coc. The data show that drug combinations potentiate cortical neurotoxicity and that the mode of co-exposure changes cellular death pathways activated by the drugs, strongly suggesting that chemical interactions occurring in Her:Coc, such as adduct formation, shift cell death mechanisms towards necrosis. Since impairment of the prefrontal cortex is involved in the loss of impulse control observed in drug addicts, the data presented here may contribute to explain the increase in treatment failure observed in speedball abusers.

Abstract Although a great variety of classical force fields (FFs) for room-temperature ionic liquids (RTTLs) have been recently suggested, no systematically derived non-polarizable model is able to reproduce their transport properties, i.e. diffusion constants, conductivities and viscosities. In the present paper, we show that modern FFs greatly overestimate pairwise electrostatic interaction energies in the RTILs systems leading to extremely hindered ionic motions. Based on the results of our ab initio molecular dynamics calculations using explicit ionic environment, we modified the electrostatic interaction potential of 1-ethyl-3-methylimidazolium tetrafluoroborate. Starting from FF, originally derived by Liu et al., we further refined it, so that it reproduces experimental transport properties without compromizing either structure or thermodynamics. The main advantages of the suggested phenomenological account for electronic polarization are its consistency, clearness, simplicity and the possibility to improve functionality of the existing FFs by modifying exclusively atomic partial electrostatic charges. ©The Electrochemical Society.

Abstract The action of sinapic acid and its alkyl esters as potential antioxidants has been investigated. For this purpose, a series of sinapic acid ester derivatives was synthesized and their antioxidant activities were evaluated using distinctive analytical methods, namely, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and FRAP UV-vis methods and differential scanning calorimetry. The electron-donating activity and lipophilicity of these phenolic compounds were also evaluated. From the overall results it was concluded that alkyl ester sinapates (linear alkyl esters) present almost the same antioxidant activity, albeit slightly lower, exhibited by the parent compound (sinapic acid). Furthermore, the addition of an alkyl ester side chain has a positive effect on the partition coefficient of sinapic acid, improving its utility as an antioxidant in a more lipophilic medium. The data on the antioxidant activity obtained by different analytical methods correlated well with each other and have revealed interesting antioxidant data of alkyl esters of sinapic acid.

Abstract Chromone carboxylic acids were evaluated as human monoamine oxidase A and B (hMAO-A and hMAO-B) inhibitors. The biological data indicated that only chromone-3-carboxylic acid is a potent hMAO-B inhibitor, with a high degree of selectivity for hMAO-B compared to hMAO-A. Conversely the chromone-2-carboxylic acid resulted almost inactive against both MAO isoforms. Docking experiments were performed to elucidate the reasons of the different MAO IC(50) data and to explain the absence of activity versus selectivity, respectively.

Abstract In recent years flavonoids have attracted a great interest as potential therapeutic drugs against a wide range of diseases. While the antioxidant activity of these natural polyphenolic compounds is well known, their binding to DNA characteristics is not fully understood despite the fact that many of them exert their biological effects by reversibly binding to nucleic acids. The present study aims to investigate the interaction of flavone and four hydroxyflavone isomers with double stranded DNA, occurring in bulk solution. A combination of micro-DSC and UV spectroscopy has been used to study the effect of these compounds and of their structure on the structure and stability of the DNA molecule. The characteristics of DNA thermal denaturation have been used as a measure of the effect of the compounds on the stability of the double helix. Micro-DSC has been used to determine the temperature dependence of the heat capacity of the process of thermal denaturation of DNA in solutions containing flavone and the following hydroxyflavones: 3-hydroxyflavone, 5-hydroxyflavone, 6-hydroxyflavone and 7-hydroxyflavone. The observed enthalpy of transition and the transition temperature of DNA thermal denaturation were determined for each compound. UV thermal denaturation curves were also recorded, under the same experimental conditions as the DSC measurements. The transition temperature values and the thermodynamic parameters of thermal denaturation were determined. Differential scanning calorimetry and ultraviolet spectroscopy measurements have evidenced an interaction between the studied flavones and DNA, showing a stabilization of DNA structure, due mainly to intercalation of the flavones. The results also show a noteworthy effect of the structure of the hydroxyflavone isomers on this stabilization.

Abstract A static method was used to measure the vapor pressures of crystalline and liquid phases of benzamide, N-methylbenzamide, and N,N-dimethylbenzamide, in the temperature ranges (344.8 to 438.2) K, (322.9 to 388.4) K, and (297.0 to 361.7) K, respectively. The vapor pressures of the crystalline phase of benzamide were also measured using the Knudsen effusion method in the temperature range (324.1 to 344.2) K. From the experimental results, the standard molar Gibbs energies and enthalpies of sublimation and of vaporization, at T = 298.15 K, and the triple points coordinates (p,T) for the three compounds were derived. The temperatures and molar enthalpies of fusion were also determined using differential scanning calorimetry and were compared with the values derived from the vapor pressure measurements. The results enabled the determination of the hydrogen bond enthalpies in the studied compounds.