Publications

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of the crystalline diaquobis(dibenzoylmethanate)nickel(II), Ni(DBM)(2)(H2O)(2), diaquobis(thenoyltrifluoroacetonate)nickel(II), Ni(TTFA)(2)(H2O)(2) bis(monothiodibenzoylmethanate)nickel(II), Ni(DBMS)(2) and bis(monothiothenoyltrifluoroacetonate)nickel(II), Ni(HTTFAS)(2) were determined, at T = 298.15 K, by high precision solution-reaction calorimetry. The standard molar enthalpy of sublimation of the monothiothenoyltrifluoroacetone (HTTFAS) complex was measured by high-temperature Calvet microcalorimetry. From the standard molar enthalpies of formation of the complexes in the gaseous state, the mean nickel(II)-ligand molar dissociation enthalpies, < D-m >(Ni-L), were derived. Delta H-f(m)degrees(cr)/(kJ . mol(-1)) Diaquobis(dibenzoylmethanate)nickel(II), Ni(DBM)(2)(H2O)(2) -993.3 +/- 3.8 Diaquobis(thenoyttrifluoroacetonate)nickel(II), Ni(TTFA)(2)(H2O)(2) -2452.0 +/- 8.3 Bis(monothiodibenzoylmethanate)nickel(II), Ni(DBMS)(2) -42.1 +/- 5.9 Bis(monothiothenoyltrifluoroacetonate)nickel(II), Ni(TTFAS)(2) -1473.5 +/- 8.1

Abstract We synthesized and characterized a series of new polymers-hydrophobically modified cationic polysaccharides-based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-alkylammonium chloride groups randomly distributed along the polymer backbone. These polymers are good candidates for studying the hydrophobic effect on polymer/surfactant association. In previous papers we reported their interactions with oppositely charged surfactants. For further insight into the relative importance of the hydrophobic interaction in the association process now we studied the thermodynamics of the interaction of these hydrophobically modified polymers with surfactants of the same charge (DMRX/C(n)TAC) by isothermal titration calorimetry (ITC). In order to try to discriminate the solution behavior of these polymer/surfactant systems, we analyzed separately the interaction of unmodified dextran with ionic surfactants and the interactions between the corresponding cationic surfactants. The interaction enthalpies for DMRX/C(n)TAC systems were derived from a proposed thermodynamic model with equations that describe the polymer-surfactant interactions. The thermodynamic parameters for the DMRX/C(n)TAC aggregation process as well as surfactant micellization in the presence of the polymer were also calculated. From all the results we were able to ascertain the effect on the interactions of changing the alkyl chain length of the polyelectrolyte pendant groups or the surfactant. The importance of the polymer aggregation state on the mechanism of interaction was also addressed.

Abstract The title complex, [Cu(C14H21N2OS2)(2)], is isostructural with the nickel analogue, forming a square-planar coordination enviroment. The Cu atom lies on a crystallographic twofold rotation axis.

Abstract Methamphetamine (METH) is a powerful psychostimulant that increases glutamate (Glu) levels in the mammalian brain and it is currently known that hippocampi are particularly susceptible to METH. Moreover, it is well established that the overactivation of N-methyl-D-aspartate (NMDA) and AMPA ionotropic Glu receptors causes excitotoxicity. In the present study, we investigated the effect of acute (30 mg/kg) versus escalating dose (ED) administration of METH on NMDA receptor 1, NMDA receptor 2 and glutamate receptor 2 (GluR2) subunit expression in the hippocampus and on memory. Adult Sprague-Dawley rats were injected s.c. during six consecutive days with saline (control and acute groups) or with a growing dose of METH (10, 15, 15, 20, 20, 25 mg/kg/day; ED group). On the 7th day, both METH groups were injected with a 'bolus' of 30 mg/kg METH whereas controls received saline. Western blot analysis showed an increase of GIuR2 and NR2A expression levels and no alterations on NR1 subunit in the acute group. On the other hand, in the ED group, GluR2 and NR2A expression levels were unaltered and there was a decrease on NR1 levels. Moreover, we did not observe neurodegeneration with both administration paradigms, as assessed by Fluoro-Jade C staining, but we did observe a strong astrogliosis in the acute administration group by using both immunohistochernistry and Western blot analysis. The impact of METH on working memory was evaluated using the Y maze test and revealed significant mnemonic deficit in the rats acutely treated with the drug. Overall, our results suggest a protection mechanism under conditions of METH administration by decreasing permeability and/or functionality of NMDA and AMPA receptors, which has implications on memory. So, the participation of the glutarnatergic system should be considered as an important pharmacological target to design new strategies to prevent or diminish the harmful effect of drug consumption.

Abstract The standard (p(0) = 0.1 MPa) molar enthalpies of combustion of six aminomethylbenzoic acids were measured at T = 298.15 K by static bomb calorimetry. With these values, the standard molar enthalpies of formation in the crystalline state were obtained. Combining these results with the standard molar enthalpies of sublimation, the standard molar enthalpies of formation in the gaseous phase were derived. For the 10 possible isomers, the obtained experimental results were compared to and correlated with the relative stability obtained by ab initio calculations at the B3LYP/6-311++G(d,p) level of theory. Seeking a better understanding of the aromatic behavior and energetics of aminomethylbenzoic acids in the gas phase, calculations of NICS values, HOMA indices, and dihedral angles between the aromatic carbon and the amino group, Phi(Ar-NHH), were also performed computationally. The significant differences observed in the energetics, as well as in the NICS values, HOMA indices, and (D(Ar-NHH) dihedral angles for these 10 isomers suggest a strong dependency on the identity and relative position of the three substituents on the benzene ring. This study points out a marked tendency for a decrease of the ring aromaticity, accompanied by an increase in the respective system stability, as the conjugation between the substituents becomes more extensive.

Abstract Molar enthalpies of vaporization, delta H-g(1)m(0)(T), of a homologous series of 1-alkyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imides, [C(n)mim][NTf2], (with 2 <= n <= 8) were directly determined for the first time. The results obtained in this study emphasize and constitute clear experimental support for the novel concept that these liquid salts are composed of polar and nonpolar domains; that is, they exhibit microphase segregation.

Abstract The ionic nature of ionic liquids (ILs) results in a unique combination of intrinsic properties that produces increasing interest in the research of these fluids as environmentally friendly "neoteric" solvents. One of the main research fields is their exploitation as solvents for liquid-liquid extractions, but although ILs cannot vaporize leading to air pollution, they present non-negligible miscibility with water that may be the cause of some environmental aquatic risks. It is thus important to know the mutual solubilities between ILs and water before their industrial applications. In this work, the mutual solubilities of hydrophobic yet hygroscopic imidazolium-, pyridinium-, pyrrolidinium-, and piperidinium-based ILs in combination with the anions bis(trifluoromethylsulfonyl)imide, hexafluorophosphate, and tricyanomethane with water were measured between 288.15 and 318.15 K. The effect of the ILs structural combinations, as well as the influence of several factors, namely cation side alkyl chain length, the number of cation substitutions, the cation family, and the anion identity in these mutual solubilities are analyzed and discussed. The hydrophobicity of the anions increases in the order [C(CN)(3)] < [PF(6)] < [Tf(2)N] while the hydrophobicity of the cations increases from [C(n)mim] < [C(n)mpy] <= [C(n)mpyr] < [C(n)mpip] and with the alkyl chain length increase. From experimental measurements of the temperature dependence of ionic liquid solubilities in water, the thermodynamic molar functions of solution, such as Gibbs energy, enthalpy, and entropy at infinite dilution were determined, showing that the solubility of these ILs in water is entropically driven and that the anion solvation at the IL-rich phase controls their solubilities in water. The COSMO-RS, a predictive method based on unimolecular quantum chemistry calculations, was also evaluated for the description of the water-IL binary systems studied, where it showed to be capable of providing an acceptable qualitative agreement with the experimental data.

Abstract Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for 1-indanone, 2-indanone, and 1,3-indandione were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of sublimation for 1-indanone and 2-indanone, at T = 298.15 K, were measured both by correlation-gas chromatography and by Calvet microcalorimetry leading to a mean value for each compound. For 1,3-indandione, the standard molar enthalpy of sublimation was derived from the vapor pressure dependence on temperature. The following enthalpies of formation in gas phase, at T= 298.15 K, were then derived: 1-indanone, -64.0 +/- 3.8kJ mol(-1); 2-indanone, -56.6 +/- 4.8 kJ mol(-1); 1,3-indandione, -165.0 +/- 2.6 kJ mol(-1). The vaporization and fusion enthalpies of the indanones studied are also reported. In addition, theoretical calculations using the density functional theory with the B3LYP and MPW1B95 energy functionals and the 6-311G** and cc-pVTZ basis sets have been performed for these molecules and the corresponding one-ring species to obtain the most stable geometries and to access their energetic stabilities.

Abstract The present work reports the values of the gaseous standard (p degrees = 0.1 MPa) molar enthalpies of formation of salicylaldehyde (2-hydroxybenzaldehyde) and salicylamide (2-hydroxybenzamide), at T= 298.15 K. For both molecules those values were derived from measurements of the standard molar energy of combustion of the condensed compounds, using a static bomb calorimeter, together with measurements of the standard molar enthalpy of vaporization or sublimation, measured by Calvet microcalorimetry. [GRAPHICS]

Abstract The interaction between glucose oxidase (GOx) and phospholipid monolayers is studied at the 1, 2-dichloroethane/water interface by electrochemical impedance spectroscopy. Electrochemical experiments show that the presence of GOx induces changes in the capacitance curves at both negative and positive potentials, which are successfully explained by a theoretical model based on the solution of the Poisson-Boltzmann equation. These changes ore ascribed to a reduced partition coefficient of GOx and on increase of the permittivity of the lipid hydrocarbon domain. Our results show that the presence of lipid molecules enhances the adsorption of GOx molecules at the liquid/liquid interface. At low lipid concentrations, the adsorption of GOx is probably the first step preceding its penetration into the lipid monolayer. The experimental results indicate that GOx penetrates better and forms more stable monolayers for lipids with longer hydrophobic toils. At high GOx concentrations, the formation of multilayers is observed. The phenomenon described here is strongly dependent on 1) the GOx and lipid concentrations, 2) the nature of the lipid, and 3) the potential drop across the interface.