Publications

Abstract Herein, solubility experimental data for six monosaccharides, viz. D-(+)-glucose, D-(+)-mannose, D-(-)-fructose, D-(+)-galactose, D-(+)-xylose and L-(+)-arabinose, in four ionic liquids (ILs), at temperatures ranging from 288.2 to 348.2 K, were obtained aimed at gathering a better understanding of their solvation ability and molecular-level mechanisms which rule the dissolution process. To ascertain the chemical features that enhance the solubility of monosaccharides, ILs composed of dialkylimidazolium or tetra-alkylphosphonium cations combined with the dicyanamide, dimethylphosphate or chloride anions were investigated. It was found that the ranking of the solubility of monosaccharides depends on the IL; yet, D-(+)-xylose is always the most soluble while D-(-)-fructose is the least soluble monosaccharide. The results obtained show that both the IL cation and the anion play a major role in the solubility of monosaccharides. Finally, from the determination of the respective thermodynamic properties of solution, it was found that enthalpic contributions are dominant in the solubilization process. However, the observed differences in the solubilities of monosaccharides in 1-butyl-3-methylimidazolium dicyanamide are ruled by a change in the entropy of solution.

Abstract Structural and thermodynamic insights are reported for the series of fluorinated alcohols {oFTOH; CF3(CF2)(n)CH2OH, with n = 5-12}, with the objective of comparing the phase behaviour of perfluorinated compounds with the analogous linear alkanes and alcohols. As expected the higher vibrational contribution of the -CF2- groups contributes for the higher heat capacities of the perfluorinated compounds. Concerning the fusion/sublimation equilibria, fluorination of the alcohols decreases Delta H and Delta S of phase transitions. Compared to the regular -CH2- alkyl chain structure, the less symmetric -CF2- spiral conformation is characterized by a less efficient molecular alignment in crystal packing, thus explaining the lower Delta H. The lower internal rotational barrier associated with the -CH2- alkyl chains of n-alkanes/alcohols, when compared to -CF2- chains, contributes to the larger values of Delta S observed. Regarding the vaporization equilibria, fluorination leads to greater values of Delta S, which are explained by the larger translational entropy of the heavier perfluoroalcohols, an effect that is more important in the gas than in the liquid phase. (C) 2016 Elsevier Ltd.

Abstract This work shows how the nanostructuration of ionic liquids (ILs) governs the glass and melting transitions of the bistriflimide imidazolium-based [C(n)C(1)im][NTf2] and [C(n)C(n)im][NTf2] series, which highlights the trend shift that occurs at the critical alkyl size (CAS) of n=6. An initial increase in the glass temperature (T-g) with an increase in the alkyl side chain was observed due to the intensification of the dispersive interactions (van der Waals). Above the CAS, the -CH2- increment has the same effect in both glass and liquid states, which leads to a plateau in the glass transition after nanostructuration. The melting temperature (T-m) of the [C(n)C(1)im][NTf2] and [C(n)C(n)im][NTf2] series presents a V-shaped profile. For the short-alkyl ILs, the -CH2- increment affects the electrostatic ion pair interactions, which leads to an increase in the conformational entropy. The -CH2- increment disturbs the packing ability of the ILs and leads to a higher entropy value (Delta(s)dagger S-m degrees) and consequently a decrease in T-m. Above the CAS, the -CH2- contribution to the melting temperature becomes more regular, as a consequence of the nanostructuration of the IL into polar and nonpolar domains. The dependence of the alkyl chain on the temperature, enthalpy, and entropy of melting in the ILs above the CAS is very similar to the one observed for the alkane series, which highlights the importance of the nonpolar alkyl domains on the ILs thermal behavior.

Abstract Oxidative stress is involved in several parasitic diseases such as Chagas. Agents able to selectively modulate biochemical processes involved in the disease represent promising multifunctional agents for the delay or abolishment of the progression of this pathology. In the current work, differently substituted 3-carboxamidocoumarins exerting both antioxidant and trypanocidal activities are described. Among the compounds synthesized, compound 3 (N-(4-hydroxyphenyl)coumarin-3-carboxamide) showed the most interesting antioxidant profile, presenting 53.2% superoxide radical scavenging and the highest ORAC-FL value (ORAC-FL=1.87) of the series. In the trypanocidal study, compounds 9 (N-(quinolin-6-yl) coumarin-3-carboxamide) and 10 (N-(quinolin-3-yl)coumarin-3-carboxamide) presented high activity in epimastigote stage and low activity in trypomastigote stage, as well as low cytotoxic effects. Additionally, these compounds decreased mitochondrial transmembrane potential in epimastigote Dm28c. Based on these results, compounds 9 and 10 proved to be good candidates for further studies. Interestingly, the current study revealed that small structural changes in this scaffold allow modulating both activities, suggesting that these molecules present the desirable properties for the development of promising classes of antichagasic compounds.

Abstract In this work, rearrangement reactions subsequent to the oxidation of tertiary amines were studied in 2-(cyanoethyl)-2-azanorbornane/ene systems. [1,2]- and [2,3]-Meisenheimer rearrangements, as well as the Cope elimination reaction, were observed with virtually complete selectivity. It was found that 2-(cyanoethyl)-2-azanorbornanes afford N-hydroxylamines through Cope elimination reactions and 2-(cyanoethyl)-2-azanorbornenes are prone to Meisenheimer rearrangements. In addition, the endo/exo configuration of 2-azanorbornenes plays a key role in the Meisenheimer rearrangement outcome. All the synthesized compounds were fully characterized by NMR spectroscopy and HRMS.

Abstract Imidazopyrazinone dioxetanone is a central molecule in bioluminescence, as it is the scaffold responsible for light emission in many marine species. Herein, we have theoretically studied the thermolysis of its neutral and anionic forms. Our results allowed us to explain imidazopyrazinone bioluminescence with the Interstate Crossing-Induced Chemiexcitation (ICIC) mechanism, and explain why neutral forms emit light efficiently to the contrary of anionic ones. Both forms decompose via a step-wise-biradical pathway, but the biradical is formed either via an electron transfer (anion) or due to homolytic bond cleavage (neutral species). Absence of electron transfer leads to an entropic trap, a flat region where infinite possibilities for chemiexcitation exist. However, the resulting products can be in either triplet or singlet excited states. The triplet to singlet ratio is determined by the electron spin density distribution, which controls the rates of intersystem crossing.

Abstract We have performed a study of structural, thermochemical and thermophysical properties of the (Z)-cinnamic acid neutral molecule and its corresponding oxyanion (formed by deprotonation of the carboxylic group). The thermophysical study (heat capacities, temperature and enthalpy of fusion) was made by DSC. The following intrinsic (gas-phase) thermochemical magnitudes have been experimentally determined: (i) standard enthalpy of formation, at T = 298.15 K, of the neutral molecule, Delta H-f(m)0 (g) = (-215.5 +/- 3.2) kJ.mol(-1), by combustion calorimetry and by the Knudsen effusion technique, (ii) deprotonation enthalpy, Delta H-acid(0)(g) = (1416.4 +/- 8.8) kJ.mol(-1) and acidity, GA = (1386.7 +/- 8.8) kJ.mol(-1), by the EKM method using ESI-TQ Mass Spectrometry. From these results we have also derived the enthalpy of formation of the oxyanion, Delta H-f(m)0 (oxyanion, g) = (-303.5 +/- 9.4) kJ.mol(-1). A computational study, through density functional calculations at the B3LYP/6-311++ G(d, p) level of theory, was used to check the good consistency of the experimental results. The global results show that (Z)-cinnamic acid is significantly less stable than the corresponding (E)-isomer, which can be related to the greater acidity of the (Z)-form found in both the gas and aqueous solution phases.

Abstract In order to evaluate the impact of the alkyl side chain length and symmetry of the cation on the thermophysical properties of water-saturated ionic liquids (ILs), densities and viscosities as a function of temperature were measured at atmospheric pressure and in the (298.15-363.15) K temperature range, for systems containing two series of bis(trifluoromethylsulfonyl)imide-based compounds: the symmetric [C(n)C(n)im][NTf2] (with n = 1-8 and 10) and asymmetric [C(n)C(1)im][NTf2] (with n= 2-5, 7, 9 and 11) ILs. For water-saturated ILs, the density decreases with the increase of the alkyl side chain length while the viscosity increases with the size of the aliphatic tails. The saturation water solubility in each IL was further estimated with a reasonable agreement based on the densities of water-saturated ILs, further confirming that, for the ILs investigated, the volumetric mixing properties of ILs and water follow a near ideal behavior. The water-saturated symmetric ILs generally present lower densities and viscosities than their asymmetric counterparts. From the experimental data, the isobaric thermal expansion coefficient and energy barrier were also estimated. A close correlation between the difference in the energy barrier values between the water-saturated and pure ILs and the water content in each IL was found, supporting that the decrease in the viscosity of ILs in presence of water is directly related with the decrease of the energy barrier.

Abstract Ohmic heating offers a very efficient way to perform organic reactions in aqueous media. Potentially bioactive (E)-3-styrylquinolin-4(1H)-ones were synthesized by the Heck reaction of 3-iodo-1-methylquinolin-4(1H)-one with styrenes in water and with ohmic heating. Pd(OAc)(2) was used as catalyst, and tetrabutylammonium bromide was used as phase-transfer catalyst in the presence of an inorganic base. Comparison with other established procedures highlight the benefits of this new methodology.

Abstract In this work, the effect of the alkyl chain size in 1-ethylpyridinium cation-based ionic liquids are used to explore the nanostructuration effect. Densities and viscosities and their dependence on temperature were measured for the 2-alkyl-l-ethylpyridinium bis(trifluoromethanesulfonyl)imide, [(CN-2C2Py)-C-2-C-1] [NTf2] (N = 4,5, 6, 7, 8, 9, 10, 11,12) ionic liquid series. Molar volume, thermal expansion coefficients, VET parameters, as well as, the energy barrier related to the fluid shear at T= 298.15 K, were derived. Highly precise measurements of the heat capacities, at T = 298.15 K, were performed using a drop calorimeter. In agreement with the previously studies based on the alkylimidazolium ionic liquids series, the studied thermophysical and transport properties of the series presents an indication that in the pyridinium based ionic liquids the nanostructuration is intensified after a critical alkyl length, [(C5C2Py)-C-2-C-1][NTf2]. The observed trend shift in the viscosity and heat capacities of the pyridinium ionic liquids is more pronounced in the pyridinium than in the imidazolium ionic liquids series.