Publications

Abstract Herein we have studied, presented, and analyzed the phase equilibria thermodynamics of a bisphenols (BP-A, BP-E, BP-F, BP-AP, and BP-S) series. In particular, the heat capacities, melting temperatures, and vapor pressures at different temperatures as well as the standard enthalpies, entropies, and Gibbs energies of phase transition (fusion and sublimation) were experimentally determined. Also, we have presented the phase diagrams of each bisphenol derivative and investigated the key parameters related to the thermodynamic stability of the condensed phases. When all the bisphenol derivatives are compared at the same conditions, solids BP-AP and BP-S present lower volatilities (higher Gibbs energy of sublimation) and high melting temperatures due to the higher stability of their solid phases. Solids BP-A and BP-F present similar stabilities, whereas BP-E is more volatile. The introduction of -CH3 groups in BP-F (giving BP-E and BP-A) leads an entropic differentiation in the solid phase, whereas in the isotropic liquids the enthalpic and entropic differentiations are negligible.

Abstract The standard (p (o) = 0.1 MPa) molar energies of combustion, , for indole-2-carboxylic acid and indole-3-carboxaldehyde, in the crystalline state, were determined, at T = 298.15 K, using a static bomb combustion calorimeter. For both compounds, the vapour pressures as function of temperature were measured, by the Knudsen effusion technique, and the standard molar enthalpies of sublimation, , at T = 298.15 K, were derived by the Clausius-Clapeyron equation. From the experimental results, the standard (p (o) = 0.1 MPa) molar enthalpies of formation in the condensed and gaseous phases, at T = 298.15 K, of indole-2-carboxylic acid and indole-3-carboxaldehyde were derived. The results are analysed in terms of structural enthalpic increments.

Abstract A novel optimized coupled bioluminescent assay for nitrogen monoxide free radical (nitric oxide, (NO)-N-center dot), an important environmental and physiological molecule, is presented. The method is based on the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase (GAPDH), whose product is used as a substrate for phosphoglycerate kinase (PGK), generating adenosine 5'-triphosphate (ATP), which is an essential cofactor for the firefly luciferase bioluminescent reaction. Inhibition of GAPDH by (NO)-N-center dot hampers the coupled reactions, leading to a depletion of ATP and hence a decrease in the bioluminescent signal. Using diethylamine NONOate (DEA-NONOate) as the (NO)-N-center dot donor, the assay was optimized through statistical experimental design methodology, namely Plackett-Burman (screening) and Box-Behnken (optimization) designs. The optimized method requires 5 mu L of sample per tube in a final reaction volume of 100 mu L. It is linear in the range from 10 to 100 nM of (NO)-N-center dot, with limits of detection and quantitation of 4 and 15 nM, respectively. Limitations in its application to biological samples, together with approaches to solve them, are discussed using human whole saliva and microalgae culture medium as examples.

Abstract Aiming at providing a comprehensive study of the influence of the cation symmetry and alkyl side chain length on the surface tension and surface organization of ionic liquids (ILs), this work addresses the experimental measurements of the surface tension of two extended series of ILs, namely R,R'-dialkylimidazolium bis-Rtrifluoromethyl)sulfonyllimide ([C(n)C(n)im][NTf2]) and R-alkyl-3-methylimidazolium bis[ (trifluoromethyl)sulfonyl] imide ([C-n C(1)im]-[NTf2D, and their dependence with temperature (from 298 to 343 K). For both series of ILs the surface tension decreases with an increase in the cation side alkyl chain length up to aliphatic chains no longer than hexyl, here labeled as critical alkyl chain length (CACL). For ILs with aliphatic moieties longer than CACL the surface tension displays an almost constant value up to [C(12)C(1)im][NTf2] or [C(16)C(1)im][NTf2]. These constant values further converge to the surface tension of long chain n-alkanes, indicating that, for sufficiently long alkyl side chains, the surface ordering is strongly dominated by the aliphatic tails present in the IL. The enthalpies and entropies of surface were also derived and the critical temperatures were estimated from the experimental data. The trend of the derived thermodynamic Properties highlights the effect of the structural organization of the IL at the surface with visible trend shifts occurring at a well-defined CACL in both symmetric and asymmetric series of ILs. Finally, the structure of a long-alkyl side chain IL at the vacuum-liquid interface was also explored using Molecular Dynamics simulations. In general, it was found that for the symmetric series of ILs, at the outermost polar layers, more cations point one of their aliphatic tails outward and the other inward, relative to the surface, than cations pointing both tails outward. The number of the former, while being the preferred conformation, exceeds the latter by around 75%.

Abstract The design of ionic liquids has been focused on the cation-anion combinations but other more subtle approaches can be used. In this work the effect of the branching of the cation alkyl chain on the design of ionic liquids (ILs) is evaluated. The mutual solubilities with water and toxicities of a series of bis(trifluoromethylsulfonyl)-based ILs, combined with imidazolium, pyridinium, pyrrolidinium, and piperidinium cations with linear or branched alkyl chains, are reported. The mutual solubility measurements were carried out in the temperature range from (288.15 to 323.15) K. From the obtained experimental data, the thermodynamic properties of the solution (in the water-rich phase) were determined and discussed. The COnductor like Screening MOdel for Real Solvents (COSMO-RS) was used to predict the liquid-liquid equilibrium. Furthermore, molecular dynamic simulations were also carried out aiming to get a deeper understanding of these fluids at the molecular level. The results show that the increase in the number of atoms at the cation ring (from five to six) leads to a decrease in the mutual solubilities with water while increasing their toxicity, and as expected from the well-established relationship between toxicities and hydrophobicities of ILs. The branching of the alkyl chain was observed to decrease the water solubility in ILs, while increasing the ILs solubility in water. The inability of COSMO-RS to correctly predict the effect of branching alkyl chains toward water solubility on them was confirmed using molecular dynamic simulations to be due to the formation of nano-segregated structures of the ILs that are not taken into account by the COSMO-RS model. In addition, the impact of branched alkyl chains on the toxicity is shown to be not trivial and to depend on the aromatic nature of the ILs.

Abstract This work presents the vapor pressure at several temperatures for the 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide series, [C(N/2)C(N/2)im][NTf2] (N = 14, 16, 18, and 20), measured by a Knudsen effusion method combined with a quartz crystal microbalance. The thermodynamic properties of vaporization of the ionic liquids under study are analysed together with the results obtained previously for the shorter alkyl chain length [C(N/)2C(N/)2im][NTf2] (N = 2, 4, 6, 8, 10, and 12), in order to evaluate the effect of the alkyl side chains of the cation and to get additional insights concerning the nanostructuration of ionic liquids. The symmetry effect is explored, based on the comparison with the asymmetric imidazolium based ionic liquids, [C(N-1)C(1)im][NTf2]. A trend shift on the thermodynamic properties of vaporization along the alkyl side chains of the extended symmetric ionic liquids, around [C(6)C(6)im][NTf2], was detected. An intensification of the odd-even effect was observed starting from [C(6)C(6)im][NTf2], with higher enthalpies and entropies of vaporization for the odd numbered ionic liquids, [C(7)C(7)im][NTf2] and [C(9)C(9)im][NTf2]. Similar, but less pronounced, odd-even effect was found for the symmetric ionic liquids with lower alkyl side chains length, [C(N/2)C(N/2)im][NTf2] (with N = 4, 6, 8, 10, and 12). This effect is related with the predominant orientation of the terminal methyl group of the alkyl chain to the imidazolium ring and their influence in the cation-anion interaction. The same Critical Alkyl length at the hexyl, (C6C1 and C6C6) was found for both asymmetric and symmetric series indicating that the nanostructuration of the ionic liquids is related with alkyl chain length. (C) 2014 AIP Publishing LLC.

Abstract This work reports an experimental and computational thermochemical study for benzothiazole and two of its methyl benzothiazole derivatives, 2-methylbenzothiazole and 2,5-dimethylbenzothiazole. Values of the standard (p(o) = 0.1 MPa) molar energy of combustion of the three compounds were measured by rotating bomb combustion calorimetry. The standard molar enthalpy of the corresponding transitions from condensed to gaseous phases, at T = 298.15 K, was obtained from high temperature Calvet microcalorimetry measurements. The experimental results enable the calculation of the standard molar enthalpy of formation in the gaseous state, at T = 298.15 K, for the afore-mentioned compounds, the results being discussed in terms of structural and energetic contributions. The gas-phase enthalpies of formation were computationally estimated from high-level ab initio molecular orbital calculations at the G3//B3LYP level of theory. The computed values compare very well with the experimental results obtained in this work and show that, in terms of enthalpy, the methyl substituents lead to an increase on the stability of the compounds, in a similar way to that already described for the corresponded benzoxazole derivatives. Furthermore, this composite approach was also used to obtain information about the gas-phase basicity, proton and electron affinities and adiabatic ionization enthalpies.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, in the gaseous phase, for two nitrobenzofurazan derivatives, 4-N,N-dimethylamino-7-nitrobenzofurazan (DMANBF) and 4-N,N-diethylamino-7-nitrobenzofurazan (DEANBF), were derived from their enthalpies of combustion and sublimation, obtained by static bomb calorimetry and by the Knudsen effusion technique, respectively. The results are compared with the corresponding data calculated by the G3(MP2)//B3LYP approach. Computationally, the molecular structures of both compounds were established and the geometrical parameters were determined at the B3LYP/6-31G(d) level of theory.

Abstract This work reports an experimental and computational thermochemical study for 2-benzothiazolinone. The standard (p degrees = 0.1 MPa) molar energy of combustion of this compound was measured by rotating bomb combustion calorimetry. The standard molar enthalpy of the corresponding transition from crystalline to gaseous phases, at T = 298.15 K, was obtained from high temperature Calvet microcalorimetry measurements. The experimental results enable the calculation of the standard molar enthalpy of formation of the compound, in the gaseous state, at T = 298.15 K. The gas-phase enthalpies of formation of the title compounds, 2-benzothiazolinone and its enol form 2-hydroxybenzothiazole, were estimated computationally from high-level oh initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. The computed value for the keto form compares very well with the experimental result obtained in this work. The hydroxy <-> oxo tautomerism of the title compounds was explored in this work as it may be relevant to their ability to occur as different polymorphic forms.

Abstract The enthalpies of solution of alcohols were determined by calorimetry in HEPES and (HEPES + trehalose) at 298.15 K. The used methodology and experiment's design allowed us to extract from a single titration experiment the enthalpy of solution (Delta H-sol(m)), the limiting solubility of the alcohol in each aqueous media, and an estimation of the enthalpy of solution of water in the alcohol phase. From these values the changes in Gibbs energy (Delta(sol)G(m)) and in entropy (Delta S-sol(m)) of solution were derived. A decrease in solubility for 1-butanol and 1-pentanol in the crowded media (HEPES + trehalose) was observed which is driven by a significant decrease in the favorable enthalpy of solution. The partial molar heat capacity, C-p,2(infinity) in each media was determined in our heat capacity drop calorimeter, also at 298.15 K. A significant decrease of the partial molar heat capacity was observed for both alcohols in (HEPES + trehalose), which together with the obtained decrease in favorable Delta H-sol(m), is consistent with a decrease in hydrophobic solvation, as a result of a decrease in free solvent availability induced by the trehalose. Finally, we tentatively predict that in the aqueous media of the crowded solutions that characterize cells and biological fluids, solutes with low aqueous solubility will be more soluble, whereas the solubility of highly polar solutes will be reduced.