Publications

Abstract The knowledge of the thermodynamic properties of heterocyclic compounds, particularly the corresponding enthalpies of formation in condensed and gaseous states, enables a better understanding of their chemical behavior and, consequently, leads to an important background for the future development of their practical applications. Following our particular interest along the last decade on the establishment of energetic and structural relationships for heterocycle compounds with one or two benzene rings fused to a five- or six-membered ring containing oxygen or sulfur heteroatoms, we review the thermochemical data for derivatives of the following main structures: benzoxazole/benzothiazole, dibenzofuran/dibenzothiophene, xanthene/thioxanthene, and phenoxazine/phenothiazine. The experimental results, obtained by calorimetric and effusion techniques, namely static and rotating bomb combustion calorimetry, vacuum sublimation/vaporization drop microcalorimetry, and Knudsen effusion methods, were used to derive reliable thermodynamic values for the compounds studied. A complementary analysis of computational results for these molecules is presented. The agreement between the calculated and the experimental gas-phase enthalpies of formation represents a reinforcement on the validation of the established predictive schemes, supporting their use for related compounds whose energetic study is not available.

Abstract Vesicles based on mixed cationic and anionic surfactants (catanionic vesicles) offer a number of advantageous colloidal features over conventional lipid-based vesicles, namely spontaneity in formation, long-term stability, and easy modulation of size and charge. If biocompatibility is added through rational design of the chemical components, the potential for biorelated applications further emerges. Here, we report for the first time on two catanionic vesicle systems in which both ionic amphiphiles are derivatized from the same amino acid-serine-with the goal of enhancing aggregate biocompatibility. Phase behavior maps for a mixture with chain length symmetry, 12Ser/12-12Ser, and another with asymmetry, 16Ser/8-8Ser, are presented, for which regions of vesicles, micelles, and coexisting aggregates are identified. For the asymmetric mixture, detailed phase behavior and microstructure characterization have been carried out based on surface tension, light microscopy, cryo-SEM, cryo-TEM, and dynamic light scattering analysis. Vesicles are found with tunable mean size, pH, and zeta potential. Changes in aggregate shape with varying composition and the effect of preparation methods and aging on vesicle features and stability have been investigated in detail. The results are discussed in the light of self-assembly models and related catanionic systems reported before. A versatile system of robust vesicles is thus presented for potential applications.

Abstract A computational study has been performed for protonated oxygen- or nitrogen-containing heterocyclic derivatives of cyclopropane and cyclopropanone. We have searched for the most stable conformations of the protonated species using density functional theory with the B3LYP functional and the 6-31G(2df,p) basis set. More accurate enthalpy values were obtained from G4 calculations. Proton affinities and gas-phase basicities were accordingly derived.

Abstract Fluorescent carbon dots (CDs) and its nitrogen doped (N-CDs) nanoparticles have been synthesized from lactose as precursor using a bottom-up hydrothermal methodology. The synthesized nanoparticles have been characterized by elemental analysis, FUR, Raman, TEM, DLS, XPS, and steady-state and life-time fluorescence. The synthesized carbon nanoparticles, CDs and N-CDs, have a size at about 7.7 +/- 2.4 and 50 +/- 15 nm, respectively, and quantum yields of 8% (CDs) and 11% (N-CDs). These techniques demonstrated the effectiveness of the synthesis procedure and the functionalization of the CDs surface with amine and amide groups in the presence of NH3 in aqueous media. The effect of excitation wavelength and pH on the luminescent properties was studied. Under the optimal conditions, the nitrogen doped nanoparticles can be used as pyridine sensor in aqueous media because they show an enhancement of its fluorescence with a good linear relationship. The analytical method is simple, reproducible and very sensitive for pyridine determination.

Abstract Highly luminescent nanoparticles based in Silicon quantum dots, coated by hydroxyl PAMAM dendrimer (PAMAM-OH) of 5th generation, were obtained by one step process by hydrothermal treatment of 3-Aminopropyl)triethoxysilane (APTES) in aqueous solution. Previous to the optimization of the synthesis procedure, different dendritic molecules of 5th generation were tested to obtain the most intense fluorescence signal. The influence of different parameters such ratio APTES/PAMAM-OH, pH and ionic strength on the fluorescence intensity was studied. The fluorescence spectra showed maximum excitation and emission wavelengths at 370 and 446 nm, respectively. The obtained silicon nanoparticles (SiQDs@PAMAM-OH) were characterized by TEM, DLS and XPS, and were found to detect selectively Cr (VI) in aqueous solutions at 2.7 mu M level of detection, sensitivity of 0.2 mu M with a RSD of 0.16% (n=10). To study the feasibility of the proposed system for Cr(VI) detection, it was tested in real electrochemical solution bath and a tanning effluent obtained from electrochemical industry and with two certified waters, demonstrating promising outcomes as nano-sensor.

Abstract This work presents the synthesis, volatility study and electrospray ionization mass spectrometry with energy-variable collision induced dissociation of the isolated [(cation)(2)(anion)](+) of a novel series of 2-alkyl-1-ethyl pyridinium based ionic liquids, [(CN-2C2Py)-C-2-C-1][NTf2]. Compared to the imidazolium based ionic liquids, the new ionic liquid series presents a higher thermal stability and lower volatility. The [(cation)(2)(anion)](+) collision induced dissociation energies of both [(CN-2C2Py)-C-2-C-1][NTf2] and [CNPy][NTf2] pyridinium series show an identical trend with a pronounced decrease of the relative cation-anion interaction energy towards an almost constant value for N = 6. It was found that the lower volatility of [(CN-2C2Py)-C-2-C-1][NTf2] with a shorter alkyl chain length is due to its higher enthalpy of vaporization. Starting from [(C3C2Py)-C-2-C-1][NTf2], the lower volatility is governed by the combination of slightly lower entropies and higher enthalpies of vaporization, an indication of a higher structural disorder of the pyridinium based ionic liquids than the imidazolium based ionic liquids. Dissociation energies and volatility trends support the cohesive energy interpretation model based on the overlapping of the electrostatic and van der Waals functional interaction potentials.

Abstract The in vivo NO sensing is of outstanding relevance for the comprehension of the diverse physiological and pathological process in which this species is involved. Nevertheless, in vivo NO sensing is a complex challenge due to its own physicochemical properties, antioxidant mechanisms and possible interferences. Some electrochemical and optical sensors have already been developed for in vivo NO sensing. Most of the electrochemical sensors are amperometric and most of the optical sensors are based on fluorescence. New materials are being developed for new NO electrochemical or optical sensors. Due to their intrinsic properties, the nanomaterials are one of the most promising emergent materials. This chapter review the most promising nanomaterials for the development of electrochemically or optical sensors for in vivo NO sensing. © 2015 Nova Science Publishers, Inc.

Abstract This work presents and highlights the differentiation of the physicochemical properties of the [C(1)Him][NTf2], [C(2)Him][NTf2], [(1)C(1)(2)C(1)Him][NTf2], and [(1)C(4)(2)C(1)(3)C(1)im][NTf2] that is related with the strong bulk interaction potential, which highlights the differentiation on the physicochemical arising from the presence of the acidic group (NH) as well as the methylation in position 2, C(2), of the imidazolium ring. Densities, viscosities, refractive indices, and surface tensions in a wide range of temperatures, as well as isobaric heat capacities at 298.15 K, for this IL series are presented and discussed. It was found that the volumetric properties are barely affected by the geometric and structural isomerization, following a quite regular trend. A linear correlation between the glass transition temperature, T-g, and the alkyl chain size was found; however, ILs with the acidic NH group present a significant higher Tg than the [(1)C(N-1)(3)C(1)im][NTf2] and [(1)C(N)(3)C(N)im][NTf2] series. It was found that the most viscous ILs, ([(1)C(1)Him][NTf2], [(1)C(2)Him][NTf2], and [(1)C(1)(2)C(1)Him][NTf2]) have an acidic NH group in the imidazolium ring in agreement with the observed increase of energy barrier of flow. The methylation in position 2, C(2), as well as the NH acidic group in the imidazolium ring contribute to a significant variation in the cationanion interactions and their dynamics, which is reflected in their charge distribution and polarizability leading to a significant differentiation of the refractive indices, surface tension, and heat capacities. The observed differentiation of the physicochemical properties of the [(1)C(1)Him][NTf2], [(1)C(2)Him][NTf2], [(1)C(1)(2)C(1)Him][NTf2], and [(1)C(4)(2)C(1)(3)C(1)im][NTf2] are an indication of the stronger bulk interaction potential, which highlights the effect that arises from the presence of the acidic group (NH) as well as the methylation in position 2 of the imidazolium ring.

Abstract Isobaric vapor-liquid equilibria of 1-butyl-3-methylimidazolium thiocyanate ([C(4)C(1)im][SCN]), 1-butyl-3-methylimidazolium dicyanamide ([C(4)C(1)im][N(CN)(2)]), 1-butyl-3-methylimidazolium tricyanomethanide ([C(4)C(1)im] [C-(CN)(3)]), and 1-ethyl-3-methylimidazolium tetracyanoborate ([C(2)C(1)im][B(CN)(4)]), with water and ethanol were measured over the whole concentration range at 0.1, 0.07, and 0.05 MPa. Activity coefficients were estimated from the boiling temperatures of the binary systems, and the data were used to evaluate the ability of COSMO-RS for describing these molecular systems. Aiming at further understanding the molecular interactions on these systems, molecular dynamics (MD) simulations were performed. On the basis of the interpretation of the radial and spatial distribution functions along with coordination numbers obtained through MD simulations, the effect of the increase of CN-groups in the IL anion in its capability to establish hydrogen bonds with water and ethanol was evaluated. The results obtained suggest that, for both water and ethanol systems, the anion [N(CN)(2)](-) presents the higher ability to establish favorable interactions due to its charge, and that the ability of the anions to interact with the solvent, decreases with further increasing of the number of cyano groups in the anion. The ordering of the partial charges in the nitrogen atoms from the CN-groups in the anions agrees with the ordering obtained for VLE and activity coefficient data.

Abstract Exploring chemistry through its presence in the literature in general, and poetry in particular, may increase students' curiosity, may enhance several basic skills, such as writing, reading comprehension and argumentative skills, as well as may improve the understanding of the chemistry topics covered. Nevertheless, the pedagogical potential of the link between poetry and chemistry has not yet been fully explored in school. This article describes a study during which a teaching strategy was used with pre-university students of introductory chemistry in order to explore the topics atomic radius and ionization energy by resorting to a poem about alkali metals. The study resulted in new poems and cartoons of chemical elements created by the students, which, together with the results of a questionnaire survey, were positive indicators of the impact of poetry in the motivation and learning of the chemistry topics explored. While the students showed some difficulties interpreting the poem, they considered that teaching chemistry with poetry is a motivating strategy that should be used more often, and that it enhances the students' engagement in the construction of significant learning.