Publications

Abstract Combustion energies of the 5-fluoro-2-nitrophenol, 4-fluoro-2-nitrophenol, 3-fluoro-4-nitrophenol and 2-fluoro-4-nitrophenol isomers were obtained by means of a rotating-bomb combustion calorimeter. From these de-terminations, standard molar combustion enthalpies and standard molar formation enthalpies, at T = 298.15 K, in the crystalline state, were derived. The Knudsen mass-loss effusion technique was used to determine the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the studied com-pounds. The standard molar enthalpies of sublimation of the four isomers were also measured by Calvet microcalorimetry. The gas-phase standard molar enthalpies of formation were derived from the experimental measurements, at T = 298.15 K, for the fluoronitrophenols studied.Additionally, the standard molar enthalpies of formation were estimated by means of computational meth-odology at the G3(MP2)//B3LYP level. The estimated values are in very good agreement with experimental data, giving us support to estimate the gas-phase enthalpies of formation of the remaining isomers whose values have not been determined experimentally.A simple group additivity scheme was successfully applied for prediction of molar enthalpies of formation. The computational study was also extended to the determination of O-H bond dissociation enthalpies for all the isomers.

Abstract The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES.

Abstract An experimental and theoretical study of solution and solvation of mono-and divalent alkali metal cations in the protic ionic liquid (IL) ethylammonium nitrate (EAN) is reported. High precision solution-reaction calorimetry was used to obtain the heat of solvation, which was used for the analysis of the thermodynamics. A close relation between the structure of the salts in the crystalline phase and its enthalpy of solvation in the IL is reported. A detailed picture of the molecular environments in the solvation shells around the metal cations is provided by means of molecular dynamics simulations. The analysis of the energetics and structure of solvation confirms the well-known water-like solvation properties of EAN, with the solvation shell around the metal cations in both media being very similar. On the other hand, the results show that it is energetically more favourable to solvate smaller cations with higher valence. Indeed, the simulations show that the long-range electrostatic interactions are the main contribution to solvation interaction, with the electric field at the surface of the alkali metal cations as the basic magnitude controlling it.

Abstract The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.

Abstract This work reports the thermodynamic and morphological study and characterization of four salts consisting of a divalent/trivalent cobalt complex with pyrazole-pyridine ligands (FK 102 and FK 209 samples) and bis(trifluoromethylsulfonyl)imide (TFSI) moieties as counter anions. The oxidation state of the central metal (Co(II) or Co(III)) and the presence of tert-butyl (t-Bu) groups in the ligand structure were found to have a strong impact on the thermal behavior, phase stability, heat capacities, and thin-film morphology of each salt. The Co(II) complexes exhibited good thermal stability up to 600 K. Lower thermal stability was observed for the Co(III) congeners. The FK 209 Co(III) displayed a higher melting temperature but a partial decomposition during or above melting was detected. The higher melting temperatures observed for the Co(III) complexes were found to be entropically driven. However, the addition of t-Bu in the ligand (FK 209) leads to an increase in the melting temperature, which is driven by the enthalpy of fusion. The four compounds studied evidenced a large glass-forming ability. Moreover, the thermal stability of the glassy state was clearly increased when the ligands comprised t-Bu groups. The contribution of the t-Bu group for the molar heat capacity in the solid phase, at T = 298.15 K, was found to be (110 ± 3) J·K−1·mol−1 and (98 ± 4) J·K−1·mol−1 for the Co(II) and Co(III) complexes, respectively. These results are in good agreement with the contribution of the t-Bu group observed for both solid and liquid phases in other materials, indicating that the t-Bu groups are relatively unhindered in the crystalline phase of the salts. The morphological behavior of the thin films of FK 102 samples was found to be quite similar to the observed for typical ionic liquids, with the formation of micro- and nanodroplets onto different substrates. The introduction of t-Bu substituents in the ligand structure was found to have a strong impact on the formation of homogeneous and compact nanofilms for the FK 209 salts. © 2022 Elsevier Ltd

Abstract This work reports the experimental determination of relevant thermodynamic properties of four benzaldehydes. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of syringaldehyde, 3,4,5-trimethoxybenzaldehyde, 4-(dimethylamino)benzaldehyde and of the liquid phase of veratraldehyde were determined using a static method based on capacitance diaphragm manometers. Additionally, the sublimation vapor pressures of the four compounds were also determined at different temperatures, using the Knudsen mass -loss effusion method. The experimental results allowed accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization for the benzaldehydes studied, at reference temperatures, allowing phase diagram representations of the (p,T) results, in the neighborhood of the triple point of the four compounds. Their temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the ones obtained indirectly through vapor pressure measure-ments. Using high-precision drop calorimetry, the standard isobaric molar heat capacities of the four crystalline benzaldehydes were determined at 298.15 K. The enthalpy of the intermolecular hydrogen bond O-H...O in the crystalline phase of syringaldehyde was estimated.

Abstract This work presents the effect of methylation in the C2 position of the imidazolium in the cohesive interaction of trifluoromethanesulfonate ionic liquids (ILs). The effect of C2 methylation was evaluated and analyzed by comparison between the C2-methylated and C2-protonated analogues. It was found that the nature of the anion has a strong impact on the differentiation of the effect of the C2-methylation. While strong-coordinating and smaller anions promote the hydrogen bonding interaction with the acidic hydrogen at the C2 position of the imidazolium ring, for the case of a weak-coordinating and larger anions, the C2-methylation is expected to have a dominant contribution in the decrease of the liquid entropy, associated with the decrease of the anion-around-cation dynamics due to the presence of the bulkier methyl group (-CH3) in the position 2. The volatility, heat capacities, thermal stability, and phase behavior are presented for two ionic liquids methylated at the C2 position of imidazolium ring [(1)C(2)(2)C(1)(3)C(1)im][OTf] and [(1)C(4)(2)C(1)(3)C(1)im][OTf], and their. C2-protonated analogues [(1)C(2)(3)C(1)im][OTf] and [(1)C(4)(3)C(1)im][OTf]. It was found that the C2 methylation has a quite low impact on the volatility, due to an enthalpic - entropic compensation effect. However, the derived thermodynamic properties indicate a decrease of enthalpy and entropy of vaporization with the methylation at the C2 position, which is consistent with the existence of hydrogen bond interactions in the. C2-protonated [OTf]-based ILs. The methylation at position 2 of the imidazolium leads to an increase in the melting temperature. This effect is especially significant between [(1)C(2)(3)C(1)im][OTf] and [(1)C(2)(2)C(1)(3)C(1)im] [OTf] with an increase of 125 K in melting temperature. The experimental results suggest that this behavior is associated with an increase of enthalpy of fusion due to the substitution of the hydrogen at the C2 position by the bulkier methyl group (-CH3).

Abstract The importance of choline chloride (ChCl) is recognized due to its widespread use in the formulation of deep eutectic solvents. The controlled addition of water in deep eutectic solvents has been proposed to overcome some of the major drawbacks of these solvents, namely their high hygroscopicities and viscosities. Recently, aqueous solutions of ChCl at specific mole ratios have been presented as a novel, low viscous deep eutectic solvent. Nevertheless, these proposals are suggested without any information about the solid-liquid phase diagram of this system or the deviations from the thermodynamic ideality of its precursors. This work contributes significantly to this matter as the phase behavior of pure ChCl and (ChCl + H2O) binary mixtures was investigated by calorimetric and analytical techniques. The thermal behavior and stability of ChCl were studied by polarized light optical microscopy and differential scanning calorimetry, confirming the existence of a solid-solid transition at 352.2 +/- 0.6 K. Additionally, heat capacity measurements of pure ChCl (covering both ChCl solid phases) and aqueous solutions of ChCl (x(ChCl) < 0.4) were performed using a heat-flow differential scanning microcalorimeter or a high-precision heat capacity drop calorimeter, allowing the estimation of a heat capacity change of (ChCl) approximate to 39.3 +/- 10 J K-1 mol(-1), between the hypothetical liquid and the observed crystalline phase at 298.15 K. The solid-liquid phase diagram of the ChCl + water mixture was investigated in the whole concentration range by differential scanning calorimetry and the analytical shake-flask method. The phase diagram obtained for the mixture shows an eutectic temperature of 204 K, at a mole fraction of choline chloride close to x(ChCl) = 0.2, and a shift of the solid-solid transition of ChCl-water mixtures of 10 K below the value observed for pure choline chloride, suggesting the appearance of a new crystalline structure of ChCl in the presence of water, as confirmed by X-ray diffraction. The liquid phase presents significant negative deviations to ideality for water while COSMO-RS predicts a near ideal behaviour for ChCl.

Abstract Chlorins are highly interesting compounds due to their spectroscopic properties in both UV-Vis and NIR regions. Upon coordination to a metal ion, the corresponding metallochlorins exhibit more valuable physicochemical properties that enable a broader range of applications, such as in photodynamic therapy (PDT), water splitting catalysis, optical sensor devices and dye-sensitized solar cells. Synthetic chemistry has been in a continuous quest to fulfil most green chemistry requirements through the development of efficient reactions. Being a heating process that does not depend on heat transfer to the reaction medium, ohmic heating accomplishes the mentioned requirements and allows a fast and uniform heating regime thanks to the ionic conductivity of the reaction medium. Herein, we report the metallation of pyrrolidine- and isoxazolidine-fused chlorins with Zn(ii), Cu(ii) and Pd(ii) salts by ohmic heating, using non-toxic aqueous solutions, and their corresponding physico-chemical characterization. All pyrrolidine-fused chlorins showed higher yields, when compared with isoxazolidine ones. From the thermogravimetric analysis performed it is possible to infer that the metal enhances the steadiness of the macrocycle, making it easier to cause the thermal decomposition of the pyrrolidine- and isoxazolidine-fused chlorins. The Zn(ii) complexes showed high absorption in the NIR spectral region, a low fluorescence quantum yield and a short excited singlet state, which indicate the high efficiency of intersystem crossing to the triplet state, making them very promising candidates as photosensitizers for PDT.

Abstract The study of the phase behaviour of binary mixtures of fatty acid methyl esters (FAME) and alkanes are here studied to understand the behaviour of the mineral diesel/biodiesel blends. Six binary mixtures of the most common saturated methyl esters (methyl stearate or methyl palmitate) with a saturated alkane (hexadecane, octadecane or eicosane) were evaluated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and optical microscopy. The binary mixtures studied show a more complex phase behaviour than previously reported, which it is shown to be dependent of the size difference between the alkyl chain length of the esters and the alkanes. It was found that in mixtures with equal alkyl chain length a co-crystal is formed, and when the alkane chain length is larger than in the FAME by two methylene groups the formation of a solid-solution increasing significantly the solid phase stability is observed. The results and conclusions derived from the phase behaviour of this set of binary mixtures, between alkanes and methyl esters, can be used as a model for the interpretation of the cloud and pour points increase in biodiesel blends (in special the ones with a rich fraction of methyl palmitate or methyl stearate when combined with mineral diesel with high content of octadecane or eicosane respectively).