Publications

Abstract In the present work, the heat capacities at T = 298.15 K of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide, [C(N/2)C(N/2)im][NTf2], were measured, for the first time, using a high-precision heat capacity drop calorimeter, with an uncertainty of less than 0.15%. Based on the obtained results, it was possible to evaluate the effect of the cation symmetry on the heat capacity data through a comparative analysis with the [C(N-1)C(1)im][NTf2] ionic liquid series. The molar heat capacities of the [C(N/2)C(N/2)im][NTf2] ionic liquids series present a less pronounced deviation from the linearity along the alkyl chain length than the asymmetric based ionic liquids series. Lower molar heat capacities for the symmetric than the asymmetric series were observed, being this difference more evident for the specific and volumic heat capacities. As observed for the [C(N-1)C(1)im][NTf2] series, a trend shift in the heat capacities at [C(6)C(6)im][NTf2] was found that reflects the impact of nonpolar region nanostructuration on the thermophysical properties of the ionic liquids. The profile of the two regions is in agreement with the expected effect arising from the nanostructuration in ionic liquids. The results obtained in the present work show a clear indication that for the symmetric series, [C(N/2)C(N/2)im][NTf2], the starting of the liquid phase nanostructuration/alkyl chain segregation occurs around [C(6)C(6)im][NTf2]. (C) 2013 AIP Publishing LLC.

Abstract Adhesion between rubber and leather is a crucial factor in the footwear industry. In the present work, three types of vulcanized styrene-butadiene rubbers (SBR) were modified using optimized atmospheric plasma jet treatment. Adhesion strength of SBR samples to leather, bonded by polyurethane (PU) adhesive, was evaluated and the ageing effect was studied. Plasma-treated rubbers were subjected to air ageing to evaluate the extent of hydrophobic recovery and the effect on the joint strength. Joint strength of the modified samples was evaluated by the T-peel test. The plasma treated surfaces were analyzed by means of contact angle measurements and scanning electron microscopy (SEM). The atmospheric plasma surface treatment significantly improves the wettability as well as adhesion of SBR. The ageing study showed a partial hydrophobic recovery of only one type of SBR, but the strength of adhesively-bonded joints between SBR surfaces and PU adhesive did not correspond with the ageing of plasma treatment.

Abstract In this work, the analytical use of facilitated ion transfer of catecholamines by dibenzo-18-crown-6 was investigated at the water/1,6-dichlorohexane interface using electrochemical methods (cyclic and square wave voltammetry). The experimental conditions for the analytical determination of noradrenaline and dopamine were established and detection limits of 1.7 and 0.35μM were obtained, respectively. The effect of excess ascorbic acid on the transfer and detection of the two catecholamines was investigated. The selectivity coefficients obtained for dopamine and noradrenaline in the presence of ascorbic acid were 3.5×10-4 and 2.5×10-3, respectively. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract The stability of the UV filters 2-ethylhexyl-4-methoxycinnamate (EHMC) and 4-tert-butyl-4'-methoxydibenzoylmethane (BDM) in chlorinated water was studied. High-performance liquid chromatography (HPLC)-UV-diode array detection (DAD) was used to follow the reaction kinetics of both UV filters and HPLC-tandem mass spectrometry (MS/MS) was used to tentatively identify the major transformation by-products. Under the experimental conditions used in this work both UV filters reacted with chlorine following pseudo-first order kinetics: rate constant k = 0.0095 +/- 0.0007 min(-1) and half-life t(1/2) = 73 +/- 4 min for EHMC and rate constant k = 0.006 +/- 0.001 min(-1) and half-life t(1/2) = 119 +/- 14 min for BDM (mean +/- standard deviation). The chemical transformation of the UV filters in chlorinated water led to the formation of chlorinated by-products that were tentatively identified as mono- and dichloro-substituted compounds that resulted from substitution of the hydrogen atoms in the benzene rings by one or two chlorine atoms. Experimental Box-Behnken designs were used to assess the effect of experimental factors: pH, temperature, chlorine concentration, dissolved organic matter and artificial sunlight irradiation on the transformation of the UV filters.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, of 2-, 3- and 4-bromobenzonitrile isomers were calculated from the combination of the following two parameters experimentally determined: the standard molar enthalpy of formation in the condensed phase, derived from the standard molar energy of combustion in oxygen at T = 298.15 K, measured by rotating-bomb combustion calorimetry, and the standard molar enthalpy of sublimation at the same reference temperature, derived from vapour pressure studies at several temperatures, as measured by mass-loss Knudsen effusion. The computational calculations complement the energetic study and analysis of the electron delocalization allows a comparison between the fluorine and bromine benzonitrile isomers. The harmonic oscillator model of aromaticity and nucleus-independent chemical shift aromaticity criteria and the natural bond orbital analysis were applied and related with the intramolecular enthalpic interactions. The intermolecular interactions in the crystal packing were analysed in terms of enthalpic and entropic contributions, using the crystallographic structures available in literature.

Abstract The interaction between biocompatible cholic acid-modified dextrans with different pendent cholic acid groups' content and phosphatidylcholine liposomes was studied by a variety of techniques including isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), turbidity measurements, microscopy imaging (transmission electron microscopy (TEM), and cryo-scanning electron microscopy (cryo-SEM)). The variation of the interaction enthalpy with polymer concentration, as obtained by ITC, highlighted the formation of different aggregates. Complete phase modification, from vesicles covered with a few polymer chains to vesicle disintegration, was observed by turbidity measurements. DSC showed the effect of polymer addition to the liposome gel to liquid-crystalline phase transition, and microscopy images gave information about the size and morphology of the aggregates. The composition, structure, and morphology of polymer/liposome aggregates were found to be strongly influenced by the cholic acid content in the polymer (degree of substitution, DS). Along with a rather monotonous change in the polymer/liposome system's properties with increasing DS, a discontinuity in behavior could also be observed at DS = 4 mol %. For DS <= 4 mol %, the polymer/liposome interaction takes place mainly between individual components, and liposome disintegration occurs in a narrow concentration range, whereas for DS > 4 mol % extended physical networks are formed, which last over a wide concentration range. A mechanism of interaction, as a function of DS, is proposed and discussed in detail.

Abstract The aim of the present work was to evaluate, at microcosm level, the capacity of constructed wetlands (CWs) to remove veterinary pharmaceutical compounds, from wastewater. Results indicated that CWs have potential to mitigate the release of veterinary drugs, namely enrofloxacin (ENR, a fluoroquinolone) and tetracycline (TET, tetracyclines family). Removal efficiencies of 94% and 98% where achieved for TET and ENR, respectively, when treating pigfarm wastewater effluent doped at 100 mu g L-1 drug level, along twelve weeks. Occurrence of adsorption of the drugs to CWs substrate may be the predominant mechanism for ENR, although for TET there are signs that degradation is also occurring.

Abstract Agars obtained by traditional hot-water (TWE) and microwave-assisted (MAE) extractions were compared in terms of their rheological and physicochemical properties and molecular self-association in solutions of low (0.05%, w/w) and high (1.5%, w/w) polymer concentrations. At low concentration, thin gelled layers were imaged by AFM. Slow or rapid cooling of the solutions influenced structure formation. In each case, TWE and MAE agar structures were different and apparently larger for MAE. At high concentration, progressive structural reinforcement was seen; while TWE agar showed a more open and irregular 3D network, MAE agar gel imaged by cryoSEM was denser and fairly uniform. The rheological (higher thermal stability and consistency) and mechanical (higher gel strength) behaviors of MAE agar seemed consistent with a positive effect of molecular mass and 3,6-anhydro-alpha-L-galactose content. MAE produced non-degraded agar comparable with commercial ones and if properly monitored, could be a promising alternative to TWE.

Abstract The present study has been aimed to assess the antibacterial effects of the glucosinolate hydrolysis product phenyl isothiocyanate (PITC) against Escherichia coli and Staphylococcus aureus. Aspects on the antibacterial mode of action of PITC have also been characterized, such as the changes on surface physicochemical characteristics and membrane damage. The minimum inhibitory concentration of PITC was 1000 g/mL, for both bacteria. The antimicrobial potential of PITC was compared with selected antibiotics (ciprofloxacin, erythromycin, streptomycin, tetracycline and spectinomycin), that reported a moderate effect. The combination of PITC with ciprofloxacin and erythromycin against S. aureus exhibited a good antimicrobial efficacy, due to an additive effect (the diameter of inhibition zones increased from 30 to 40 mm for ciprofloxacin and almost the double for erythromycin). The other combinations reported unsatisfactory results against both bacteria. The study of the physiological changes induced by PITC action demonstrated the interaction between the electrophilic compound and the bacterial cells at several points that causes changes in membrane properties (decreases negative surface charge, increases surface hydrophilicity and electron donor characteristics). PITC was also found to disturb membrane function, as manifested by phenomena such as cellular disruption and loss of membrane integrity, triggering cell death.

Abstract The increased resistance of pathogenic microorganisms is frequently attributed to the extreme and inadequate use of antibiotics and transmission of resistance within and between individuals. To counter the emergence of resistant microorganisms, considerable resources have been invested in the search for new antimicrobials. Plants synthesize a diverse array of secondary metabolites (phytochemicals) known to be involved in defense mechanisms, and in the last few years it is recognized that some of these molecules have health beneficial effects, including antimicrobial properties. In this study, the mechanism of action of gallic (GA) and ferulic (FA) acids, a hydroxybenzoic acid and a hydroxycinnamic acid, was assessed on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria monocytogenes. The targets of antimicrobial action were studied using different bacterial physiological indices: minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), membrane permeabilization, intracellular potassium release, physicochemical surface properties, and surface charge. It was found that FA and GA had antimicrobial activity against the bacteria tested with MIC of 500 mu g/mL for P. aeruginosa, 1500 mu g/mL for E. coli, 1750 mu g/mL for S. aureus, and 2000 mu g/mL for L. monocytogenes with GA; 100 mu g/mL for E. coli and P. aeruginosa, 1100 mu g/mL and 1250 mu g/mL for S. aureus and L. monocytogenes, respectively, with FA. The MBC for E. coli was 2500 mu g/mL (FA) and 5000 (GA), for S. aureus was 5000 mu g/mL (FA) and 5250 mu g/mL (GA), for L. monocytogenes was 5300 mu g/mL (FA) and 5500 mu g/mL (GA), and 500 mu g/mL for P. aeruginosa, with both phytochemicals. GA and FA led to irreversible changes in membrane properties (charge, intra and extracellular permeability, and physicochemical properties) through hydrophobicity changes, decrease of negative surface charge, and occurrence of local rupture or pore formation in the cell membranes with consequent leakage of essential intracellular constituents. The overall study emphasizes the potential of plant-derived molecules as a green and sustainable source of new broad spectrum antimicrobial products.