Publications

Abstract A novel, straightforward, and environmentally friendly direct coupling procedure to immobilize carbohydrates on solid supports is presented. A characterization study showed that all amino groups on solid supports participated in the linkage with a carbohydrate unit, implicating that the surface load can be easily adjusted by tuning the amination coverage of the surface. Most importantly, the integrity of the cyclic conformation of the linked sugar unit was demonstrated, a feature that is critical for most of the possible applications of carbohydrate-functionalized surfaces. Furthermore, carbohydrate-immobilized submicron particles synthesized by the direct coupling method, on which lectin profiling experiments were conducted, validated the successfulness of our simplistic approach.

Abstract The objective of this work was the exploration of low calcination temperature ranges (< 350 degrees C) to obtain molecularly imprinted microspheres (MIM) with a high crystallinity as anatase, in cooperation of an acidic pretreatment aiming at the preservation of the hollow shape and also of the selective binding sites. It was confirmed the possibility of obtaining bilirubin-imprinted crystalline TiO2 microspheres (highly crystalline anatase, as confirmed by XRD) exhibiting higher photocatalytic efficiency associated especially with the hollow shape and calcination at lower temperatures (200 degrees C or 250 degrees C). It was with the calcination temperature of 250 degrees C that the highest photocatalytic efficiency was obtained, under UV irradiation, associated with the highest adsorption selectivity (alpha(K) = 19) and degradation selectivity (alpha(k) = 2.7) observed for the degradation of the template against a closely related analogue compound.

Abstract The possibility of generating organically modified hollow TiO2 microspheres via a simple sol-gel synthesis was demonstrated for the first time in this work. A mixture of titania precursors, including an organically modified precursor, was used to obtain methyl-modified hollow TiO2 microspheres selective for bilirubin by the molecular imprinting technique (Methyl-HTM-MIM). Methyl-HTM-MIM were prepared by a sol-gel method using titanium (IV) isopropoxide (TTIP), and methyltitanium triisopropoxide (MTTIP) as precursors. Two ratios of titania precursors were tested (1/6 and 1/30 mol(MTTIP)/mol(TTIP)). With the characterization results obtained by the SEM and ATR-FTIR techniques, it was possible to establish that only the 1/30 mol(MTTIP)/mol(TTIP) ratio allowed for the preparation of hollow spheres with a reasonably homogeneous methylated-TiO2 shell. It was possible to obtain a certain degree of organization of the hybrid network, which increased with calcination temperatures. By adjusting isothermal adsorption models, imprinting parameters were determined, indicating that the new methylated microspheres presented greater selectivity for bilirubin than the totally inorganic hollow TiO2 microspheres. The effectiveness of the molecular imprinting technique was proven for the first time in an organically modified titania material, with imprinting factor values greater than 1.4, corresponding to a significant increase in the maximum adsorption capacity of the template represented by the molecularly imprinted microspheres. In summary, the results obtained with the new methyl-HTM-MIM open the possibility of exploring the application of these microspheres for selective sorption (separation or sensing, for example) or perhaps even for selective photocatalysis, particularly for the degradation of organic compounds.

Abstract A suitable dispersion of carbon materials (e.g., carbon nanotubes (CNTs)) in an appropriate dispersant media, is a prerequisite for many technological applications (e.g., additive purposes, functionalization, mechanical reinforced materials for electrolytes and electrodes for energy storage applications, etc.). Deep eutectic solvents (DES) have been considered as a promising "green" alternative, providing a versatile replacement to volatile organic solvents due to their unique physical-chemical properties, being recognized as low-volatility fluids with great dispersant ability. The present work aims to contribute to appraise the effect of the presence of MWCNTs and Ag-functionalized MWCNTs on the physicochemical properties (viscosity, density, conductivity, surface tension and refractive index) of glyceline (choline chloride and glycerol, 1:2), a Type III DES. To benefit from possible synergetic effects, AgMWCNTs were prepared through pulse reverse electrodeposition of Ag nanoparticles into MWCNTs. Pristine MWCNTs were used as reference material and water as reference dispersant media for comparison purposes. The effect of temperature (20 to 60 degrees C) and concentration on the physicochemical properties of the carbon dispersions (0.2-1.0 mg cm(-3)) were assessed. In all assessed physicochemical properties, AgMWCNTs outperformed pristine MWCNTs dispersions. A paradoxical effect was found in the viscosity trend in glyceline media, in which a marked decrease in the viscosity was found for the MWCNTs and AgMWCNTs materials at lower temperatures. All physicochemical parameters were statistically analyzed using a two-way analysis of variance (ANOVA), at a 5% level of significance.

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.