Publications

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.

Abstract Lactoferrin is a glycoprotein with two globular lobes, each having two domains. Since the discovery of its antimicrobial properties, efforts have been made to find peptides derived from this protein showing antimicrobial properties. Most peptides initially studied were derived from Lactoferricin B, obtained from the protein by digestion with pepsin. More recently, a new family of antimicrobial peptides (AMPs) derived from Lactoferrin was discovered by Bolcher et al, and named Lactoferrampin (LFampin). The original sequence of LFampin contained residues 268 - 284 from the N1 domain of Lactoferrin. From this peptide, the Bolscher's group synthesized a collection of peptides obtained by extension and / or truncation at the C or N-terminal sides, in order to unravel the main structural features responsible for antimicrobial action. Here, we present results for three of these peptides, namely LFampin 265 - 284, LFampin 265 - 280, and LFampin 270 - 284. The peptides were tested against bacteria (E. coli and S. sanguinis), fungi (C. albicans), and model membranes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero- 3-[phospho-rac-(1-glycerol)] (DMPG), and their mixtures at a ratio of 3 : 1 (DMPC : DMPG (3 : 1)). The ability to adopt a helical conformation was followed by a circular dichroism (CD), and the perturbation of the gel to the liquid-crystalline phase transition of the membrane was characterized by differential scanning calorimetry (DSC). Distinct behavior was observed in the three peptides, both from the microbiology and model membrane studies, with the biophysical results showing excellent correlation with the microbiology activity studies. LFampin 265 - 284 was the most active peptide toward the tested microorganisms, and in the biophysical studies it showed the highest ability to form an α-helix and the strongest interaction with model membranes, followed by LFampin 265 - 280. LFampin 270 - 284 was inactive, showing marginal secondary structure and no interaction with the pathogen model membranes.

Abstract In the title molecule, C24H14N2, the exterior C-C-C angle of the naphthalene ring system involving the two phenyl-substituted C atoms is 126.06 (11)degrees and the dihedral angles between the mean plane of the naphthalene ring system and those of the benzene rings are 66.63 (5) and 67.89 (5)degrees. In the crystal, molecules are linked into a ladders by four weak C-H center dot center dot center dot pi interactions.

Abstract Three kappa/iota-hybrid carrageenan polysaccharides with distinct molecular mass and content of iota-carrageenan disaccharide units were isolated from Mastocarpus stellatus seaweeds. The viscoelastic and thermal properties of 2 wt% kappa/iota-hybrid carrageenan solutions with ionic strength tuned by the addition of NaCl salt were studied by means of theological tests and differential scanning calorimetry (DSC). All solutions form a gel upon cooling. The gel elasticity decreases with the content in iota-carrageenan disaccharide units, and does not correspond to the additive elasticity of a iota- and a kappa-carrageenan networks. The highest gel elasticity is obtained with the lowest molecular mass. In 0.1 M NaCl, two gelling processes are evidenced. The first increase in solution viscosity upon cooling coincides with a thermal transition process, which is assigned to a coil-to-helix conformational transition. The transition depends on both molecular mass distribution and chemical structure. The same dependencies are observed for the gel melting behaviour as all theological and thermal processes determined are shifted to higher temperature with decreased molecular mass or increased content in iota-carrageenan disaccharide units.

Abstract In this work, the phytoremediation potential of metalaxyl, a commonly used persistent, mobile and leachy fungicide, by Solanum nigrum L plants was studied. The study revealed that this plant species can be used as an excellent metalaxyl phytoremediation tool, thus providing a cost effective and environmentally friendly clean technology for the decontamination of sites and effluents. As it can be sowed directly in the remediation site, is able to complete its life cycle without suffering major stress. Because it accumulates high amounts of the fungicide in the aboveground tissues, enables its concentration and proper disposal by cutting off the corresponding plant part. The study also suggests that the tolerance to metalaxyl is due to a suitable antioxidant response comprising proline accumulation and guaiacol peroxidase and glutathione-S-transferase enhanced activities, that reduce oxidative damage to the plant organs.

Abstract The monocyclic nonsubstituted pyrones were studied computationally using state-of-the-art ab initio composite computational techniques Combination of the accurate energies so obtained with conveniently chosen isodesmic or homodesmotic chemical reactions lead to very confident predictions of their corresponding standard enthalpy of formation The internal consistency of the results obtained from a vast number of independent chemical schemes serves as a further support of the quality of our results which are thus proposed to establish the energetics of alpha-pyrone and gamma-pyrone

Abstract A fluorescent derivatization reaction for Diltiazem drug quantification based on the condensation reaction of citric or malonic acid with acetic anhydride, catalyzed by the tertiary amine group of Diltiazem, was developed. Excitation emission matrices (EEMs) of fluorescence of the pure solvent (ethanol), standard and sample solutions following a standard addition methodology were analysed by PARAFAC based methods (PARAFAC, PARAFAC2 and PARALIND) to obtain robust calibration methodologies. The quantification results of the sample were compared with the official US Pharmacopeia high performance liquid chromatography-ultraviolet method (USP HPLC-UV). Although the experimental sets of EEM show linearity deviations all the PARAFAC based methods allow correct robust estimation of Diltiazem concentration in pharmaceutical formulations. The closest results were: derivatization with citric acid and PARAFAC2 six components non-negativity constraint model with a detection limit of 0.088 ppm; and, derivatization with malonic acid and PARAFAC six components non-negativity constraint model with a detection limit of 0.066 ppm for the malonic acid was observed. The simultaneous utilization of the three PARAFAC methods gives further information about the intrinsic structure of the data sets under analysis, i.e., it works as an efficient diagnostic tool for the existence of non-linearity and colinearity.