Publications

Abstract The thermodynamic study of the phase transition (fusion and sublimation) of 2,2':5',2 ''-terthiophene and 3,2':5',3 ''-terthiophene is presented. The obtained data is used to evaluate the (solid + liquid) and (solid + gas) phase equilibrium, and draw the phase diagrams of the pure compounds near the triple point coordinates. For each compound the vapour pressures at different temperatures were measured by a combined Knudsen effusion method with a vacuum quartz crystal microbalance. Based on the previous results, the standard molar enthalpies, entropies and Gibbs energies of sublimation were derived at T = 298.15 K. For the two terthiophenes and for 3,3'-bithiophene, the temperature, and the molar enthalpies of fusion were measured in a power compensated differential scanning calorimetry. The relationship between structure and energetics is discussed based on the experimental results, ab initio calculations and previous literature data for 2,2'-bithiophene and 3,3'-bithiophene. The 3,2':5',3 ''-terthiophene shows a higher solid phase stability than the 2,2':5',2 ''-terthiophene isomer arising from the higher cohesive energy due to positioning of the sulphur atom in the thiophene ring. The higher phase stability of 3,3'-bithiophene relative to 2,2'-bithiophene isomer is also related to its higher absolute entropy in the solid phase associated with the ring positional degeneracy observed in the crystal structure of this isomer. A significant differentiation in the crystal phase stability between isomers was found.

Abstract A new Knudsen effusion apparatus, enabling simultaneous gravimetric and quartz crystal microbalance mass loss detection, is described. This device allows the measurement of vapour pressures of small sample mass (50 to 100) mg over a wide temperature range (350 to 650) K using very short effusion time intervals. The performance of the apparatus was checked by measuring the vapour pressures of anthracene, benzanthrone, and 1,3,5-triphenylbenzene, between (0.1 and 1) Pa, over temperature intervals of 20 K. The derived standard molar enthalpies of sublimation and vapour pressures are in excellent agreement with the mean of the available literature values and with the recommended values. The new working methodology and design of this apparatus allows the measurement of high quality vapour pressure data due to: accurate temperature measurement and control; improvement in vacuum thermal contact between the effusion cell and the oven metal block; optimisation of the quartz crystal sensor head microbalance position; efficient temperature control of the quartz crystal microbalance head; accurate measurement of the resonance crystal frequency using an impedance circuit analyser methodology.

Abstract A set of three N-(diethylaminothiocarbonyl)benzimido derivatives was structurally characterized by solid state single crystal X-ray diffractometry. The temperature, standard molar enthalpies, and entropies of fusion were measured and derived using differential scanning calorimetry, including two more derivatives, whose structures have been published before. The compounds were further analysed by solid state FIR spectroscopy and the experimental FTIR spectra were compared with the calculated gas phase spectra at the B3LYP/6-311+G(d) level of theory. The structural results for the set were further used in the interpretation of thermophysical phase transition properties of the title compounds. A detailed molecular picture of N-(diethylaminothiocarbonyl)benzimido derivatives was obtained from Natural Bond Order (NBO) analysis. The combination of the applied methods reveals a deeper insight into the structures of this type of compound.

Abstract A series of 1-arylnaphthalenes and 1,8-diarylnaphthalenes were synthesized by the Suzuki-Miyaura cross-coupling methodology showing significant differentiation in the yields and selectivity between aryl rings with electron donating (higher yields), and electron withdrawing substituents (lower yields). These results strongly support the relation between the nucleophilicity of the boronate complex and its reactivity, and emphasize the importance of the transmetalation step in the overall efficiency of this cross-coupling reaction. The results obtained with non-symmetric 1,8-diarylnaphthalenes indicate preference for arylation of an already arylated species (the 1-aryl-8-bromonaphthalene intermediate) over mono-arylation of 1,8-dibromonaphthalene. Evidences for the existence of intramolecular Pd center dot center dot center dot pi and aromatic interactions in some Pd(II) complexes were found.

Abstract Nanobiotechnology refers to the ability to create and manipulate biological and bio-chemical materials, devices, and systems at atomic and molecular levels. Nano delivery systems hold great potential to overcome some of the obstacles in bio-pharmaceutical production, such as water soluble/insoluble pharmaceutical drugs and cosmetic ingredients, risks of toxicity, increasing bio-active efficacy, specificity, tolerability and its therapeutic index. Within nanoparticulate carriers, polymeric and lipid nanoparticles have risen to the forefront of bio-technology, having diverse applications in several fields of pharmaceuticals for oral, topical, ocular and intravenous administration, as well as in dermo-cosmetic products.

Abstract For s-triphenetriazine, at T = 298.15 K, were measured the standard (p(0) = 10(5) Pa) molar enthalpy of combustion, by static bomb combustion calorimetry, and the standard molar enthalpy, entropy, and Gibbs energy of sublimation by Knudsen/Quartz crystal effusion. A comparison between the entropies of sublimation of s-triphenyltriazine and the isosteric 1,3,5-triphenylbenzene gave a good indication that the higher symmetry of the former contributes significantly to the decrease of its volatility. A computational study at the MP2/cc-pVDZ and B3LYP/6-311++g(d,p) levels of theory was carried out in order to obtain the gas phase geometry, enthalpy, and barriers to internal rotation about the phenyl-triazine bonds. Making use of homodesmotic reaction schemes, a marked stabilization was observed in the molecule of s-triphenyltriazine relative to analogous systems. This result is supported both experimentally and computationally and, combined with a detailed analysis of the literature data concerning the energetics and structure of related compounds, pointed to a significant enthalpic stabilization associated with the exchange of an intramolecular Ar-H center dot center dot center dot H-Ar close contact by an Ar-H center dot center dot center dot N(Ar) one. An inspection of the ring-ring torsional profiles in azabenzenes and biphenyls, obtained computationally at the SCS-MP2/cc-pVDZ level, showed that the ring-ring torsions are the dimensions of the potential energy surface (PES) that chiefly determine the energetic differentiation in this class of compounds.

Abstract This work reports a thermodynamic study and structural analysis of a series of linear alpha-oligothiophenes to explore the effect of the successive increase of the number of thiophene rings on the thermodynamic properties related to solid liquid and solid gas equilibria. The compounds studied were alpha-quaterthiophene (alpha-4T), alpha-quinquethiophene (alpha-ST), and alpha-sexithiophene (alpha-6T). For each compound, the vapor pressures at different temperatures were measured using the Knudsen effusion method combined with a quartz crystal microbalance (KMI3Q). From the obtained results, the standard molar enthalpies, entropies and Gibbs energies of sublimation were determined. For alpha-4T and alpha-ST (alpha-6T decomposes), the fusion temperatures and the standard molar enthalpies of fusion were determined in a power compensated differential scanning calorimeter (DSC). Standard molar entropies of fusion were derived accordingly. The obtained results for sublimation and fusion were compared with available data for the analogous thiophene (T), 2,2'-bitiophene (alpha-2T) and 2,2':5',2 ''-terthiophene (alpha-3T) compounds. To support the energetic study, a structural analysis was performed, based on the available X-ray crystallographic data for solid phase, and computational chemistry calculations, using density functional theory (DFT) with the hybrid exchange correlation functional (B3LYP) at the 6-311++G(d,p) level of theory, for gas phase. Entropic and enthalpic differentiations along the linear a oligothiophenes series were observed, suggesting a subtle odd-even effect and also a trend change in the series, centered at alpha-4T, which is probably related with the change in the supramolecular structure.

Abstract For the first time, two distinct trends are clearly evidenced for the enthalpies and entropies of vaporization along the [C(n)mim][Ntf(2)] ILs series. The trend shifts observed for Delta H-g(1)m degrees and Delta S-g(1)m degrees, which occur at [C(6)mim] [Ntf(2)], are related to structural modifications. The thermodynamic results reported in the present article constitute the first quantitative experimental evidence of the structural percolation phenomenon and make a significant contribution to better understanding of the relationship among cohesive energies, volatilities, and liquid structures of ionic liquids. A new Knudsen effusion apparatus, combined with a quartz crystal microbalance, was used for the high-accuracy volatility study of the 1-alkyl-3-methylirnidazolium bis(trifluoromethylsulfonyl)imide series ([C(n)mim][Ntf(2)], where n = 2, 3, 4, 5, 6, 7, 8, 10, 12). Vapor pressures in the (450-500) K temperature range were measured, and the molar standard enthalpies, entropies, and Gibbs energies of vaporization were derived. The thermodynamic parameters of vaporization were reported, along with molecular dynamic simulations of the liquid phase structure, allowing the establishment of a link between the thermodynamic properties and the percolation phenomenon in ILs.

Abstract The thermodynamic and structural study of a series of polyphenylbenzenes, from benzene, n(Ph) = 0, to hexaphenylbenzene, n(Ph) = 6, is presented. The available literature data for this group of compounds was extended by the determination of the relevant thermodynamic properties for 1,2,4-triphenylbenzene, 1,2,4,5-tetraphenylbenzene, and hexaphenylbenzene, as well as structural determination by X-ray crystallography for some of the studied compounds. Gas phase energetics in this class of compounds was analyzed from the derived standard molar enthalpies of formation in the gaseous phase. The torsional profiles relative to the phenyl-phenyl hindered rotations in some selected polyphenylbenzenes, as well as the gas phase structures and energetics, were derived from quantum chemical calculations. In the ideal gas phase, a significant enthalpic destabilization was observed in hexaphenylbenzene relative to the other polyphenylbenzenes, due to steric crowding between the six phenyl substituents. A relatively low enthalpy of sublimation was observed for hexaphenylbenzene, in agreement with the decreased surface area able to establish intermolecular interactions. The apparently anomalous low entropy of sublimation observed for hexaphenylbenzene is explained by its high molecular symmetry and the six highly hindered phenyl internal rotations. For the series of polyphenylbenzenes considered, it was shown that the differentiation in the entropy of sublimation can be chiefly ascribed to the torsional freedom of the phenyl substituents in the gas phase and the entropy terms related with molecular symmetry.

Abstract The aqueous solubility of hexafluorobenzene has been determined, at 298.15 K, using a shake-flask method with a spectrophotometric quantification technique. Furthermore, the solubility of hexafluorobenzene in saline aqueous solutions, at distinct salt concentrations, has been measured. Both salting-in and salting-out effects were observed and found to be dependent on the nature of the cationic/anionic composition of the salt. COSMO-RS, the Conductor-like Screening Model for Real Solvents, has been used to predict the corresponding aqueous solubilities at conditions similar to those used experimentally. The prediction results showed that the COSMO-RS approach is suitable for the prediction of salting-in/-out effects. The salting-in/-out phenomena have been rationalized with the support of COSMO-RS sigma-profiles. The prediction potential of COSMO-RS regarding aqueous solubilities and octanol-water partition coefficients has been compared with typically used QSPR-based methods. Up to now, the absence of accurate solubility data for hexafluorobenzene hampered the calculation of the respective partition coefficients. Combining available accurate vapor pressure data with the experimentally determined water solubility, a novel air-water partition coefficient has been derived.