Publications

Abstract Plants contain numerous components that are important sources of new bioactive molecules with antimicrobial properties. Isothiocyanates (ITCs) are plant secondary metabolites found in cruciferous vegetables that are arising as promising antimicrobial agents in food industry. The aim of this study was to assess the antibacterial activity of two isothiocyanates (ITCs), allylisothiocyanate (AITC) and 2-phenylethylisothiocyanate (PEITC) against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. The antibacterial mode of action was also characterized by the assessment of different physiological indices: membrane integrity, intracellular potassium release, physicochemical surface properties and surface charge. The minimum inhibitory concentration (MIC) of AITC and PEITC was 100 mu g/mL for all bacteria. The minimum bactericidal concentration (MBC) of the ITCs was at least 10 times higher than the MIC. Both AITC and PEITC changed the membrane properties of the bacteria decreasing their surface charge and compromising the integrity of the cytoplasmatic membrane with consequent potassium leakage and propidium iodide uptake. The surface hydrophobicity was also non-specifically altered (E. coli and L. monocytogenes become less hydrophilic; P. aeruginosa and S. aureus become more hydrophilic). This study shows that AITC and PEITC have strong antimicrobial potential against the bacteria tested, through the disruption of the bacterial cell membranes. Moreover, phytochemicals are highlighted as a valuable sustainable source of new bioactive products.

Abstract Bacterial resistance has been increasingly reported worldwide and is one of the major causes of failure in the treatment of infectious diseases. Natural-based products, including plant secondary metabolites (phytochemicals), may be used to surpass or reduce this problem. The objective of this study was to determine the antibacterial effect and mode of action of selected essential oils (EOs) components: carveol, carvone, citronellol, and citronellal, against Escherichia coli and Staphylococcus aureus. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were assessed for the selected EOs components. Moreover, physicochemical bacterial surface characterization, bacterial surface charge, membrane integrity, and K+ leakage assays were carried out to investigate the antimicrobial mode of action of EOs components. Citronellol was the most effective molecule against both pathogens, followed by citronellal, carveol, and carvone. Changes in the hydrophobicity, surface charge, and membrane integrity with the subsequent K+ leakage from E. coli and S. aureus were observed after exposure to EOs. This study demonstrates that the selected EOs have significant antimicrobial activity against the bacteria tested, acting on the cell surface and causing the disruption of the bacterial membrane. Moreover, these molecules are interesting alternatives to conventional antimicrobials for the control of microbial infections.

Abstract The self-association equilibrium, i.e. formation of noncovalent dimers; in two triphenylamine derivative TPD (N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine) and mMTDAB (1,3,5-tri[(3-methylphenyl)phenylamino]benzene), in solution was evaluated by H-1 NMR. spectroscopy. The gas-phase energetics of the respective dimerization processes was explored by computational quantum chemistry: The results indicate that self-association is significantly more extensive in TPB than in TDAB. It is proposed that this fact helps to explain why TPB presents a stability, higher than expected in the liquid phase, which is reflected in a lower melting temperature, a less volatile liquid, and possibly a higher tendency to form a glass. These results highlight the influence of self-association on the phase equilibria and thermodynamic properties of pure organic substances.

Abstract Differential capacitance curves for the electrical double layer (EDL) of mixtures of imidazolium-based ionic liquids (ILs) with a common cation (1-ethyl-3-methylimidazolium, [C2MIM](+)) and two different anions (bis(trifuoromethylsulfonyl)imide, [Tf2N](-)) and tris(pentafluoroethyl)trifluorophosphate [FAP](-)) were obtained. Sharp peaks in the differential capacitance curves were observed for a small range of mixtures compositions at positive charge densities. The appearance and position on the potential scale of the peaks were found to be dependent on the mixture composition and temperature. The occurrence of these phenomena is interpreted as corresponding to an abrupt change in the EDL structure arrangement as a result of a complex interplay of electrostatic interactions and steric effects. The use of the non-structured mercury electrode allowed to decouple the eventual potential induced restructuring occurring at the double layer from the well-known surface reconstruction effects often reported for ionic liquids in contact with single crystal face electrodes.

Abstract In this work, we describe the reactivity of chlorodiphenylphosphine and its oxide, as well as diphenylphosphine, with some glyoxylate derivative systems: methyl glyoxylate, methyl or 8-phenylneomenthyl glyoxylate oximes, and methyl cyanoformate. By analyzing the reactions outcomes and with the aid of computational chemistry, we propose some reaction mechanisms and molecular rearrangements.

Abstract In this work the description, test, and performance of a new vacuum apparatus for thin film vapor deposition (ThinFilmVD) of organic semiconductor materials are presented. The apparatus is able to fabricate single, multilayer/composites, or hybrid thin films using four independent, organic or inorganic, vapor deposition sources (Knudsen cells type), and the vapor mass flow is condensed onto a substrate surface (temperature regulated). The same apparatus could be also used to measure vapor pressures according to the Knudsen effusion methodology. Vapor pressures and thermodynamic properties of sublimation measured by Knudsen effusion of some reference organic materials (benzoic acid, anthracene, triphenylene, benzanthrone, 1,3,5-triphenylbenzene, perylene) were used to evaluate and test the performance of the apparatus. Moreover, nanostructures of thin films and composite materials of relevant charge transport and electroluminescent materials were deposited onto an indium-tin oxide (ITO) surface, and the morphology and thin film thickness were evaluated by scanning electron microscopy (SEM), exploring the effect of different mass flow rates and deposition time. The new physical vapor deposition apparatus based in four Knudsen effusion cells with an accurate mass flow control was designed to assemble well-defined (composition, morphology, thickness) thin films of organic semiconductors based on their volatility. The described apparatus presents a high versatility to the fabrication of single/multilayer thin films, as-grown crystals, and hybrid micro- and nanostructured materials.

Abstract The influence of the electrode surface material, the ions chemical structure and the combination of both on differential capacitance curves plays an important role to a deeper understanding on the molecular level structure of electrical double layers (EDLs) involving ionic liquids (ILs). The research work focused on the structure of ionic liquids on charged surfaces is technologically-important for the development of new applications and in the upward of the existing ones, such electrodeposition or energy storage and conversion. Understanding EDL property will allow maximizing the specific capacitance, which in turn leads to higher energy and powering densities of the devices. The electronic interactions of 1-butyl-3-methylimidazolium (tris(pentafluoroethyl)trifluorophosphate) [C4MIM][FAP] ionic liquid with Hg, Au, Pt and GC were assessed in order to get a fundamental understanding of the electrical double layer microscopic structure and its intrinsic properties at electrode/IL interface. Ionic liquids containing the [FAP](-) anion exhibit a strong hydrophobic nature and wider electrochemical window than previously used ionic liquids and a good electrochemical stability. The magnitude and shape of C(E) curves revealed different orientations of the cation when the nature of the substrate is changed. The predominantly hydrophobic interactions of the imidazolium hydrocarbon chains with the Hg are traduced by the camel shape type curve. In contrast, the low and nearly constant C (E) values obtained for Au electrode point to the interfacial structure being dominated by the electrostatic pi-stacking of the imidazolium ring/electrode interaction with the aromatic ring adopting an orientation more parallel to the surface.

Abstract Waterborne diseases continue to be an important cause of illness and death with particular incidence in developing countries. Indeed, the use of contaminated drinking water (DW) has been linked with several health problems worldwide. So, the main goal of water companies is to ensure that water is microbiologically and chemically safe for consumers. Many of the problems in DW distribution systems (DWDS) are microbiological and thus the prevention of water associated problems has mainly focused on these contaminations. There are several public health relevant microorganisms that may be transmitted through contaminated DW and infect humans. Even more worrying is the fact that waterborne bacterial pathogens have the potential to become components of sessile microbial communities. Biofilms can act as environmental reservoirs of coliforms (intestinal and non-intestinal origin) and other clinically relevant pathogens, representing a potential source of water contamination. The presence of biofilms in DWDS constitutes special concern because they provide the ideal environment for pathogens to survive and persist for long time in distribution networks. As biofilms are recalcitrant to treatment, they also contribute to the reduced efficiency of disinfection programs. This chapter provides an overview about the involvement of biofilms in waterborne diseases. In addition, the impact of the presence of biofilms in DWDS and on the organoleptic quality of the distributed water will be also discussed. As Escherichia coli is an indicator of fecal contamination and some of their variants, enterotoxigenic and enterohemorrhagic, are one of the major causes of water-related outbreaks, their role will be also highlighted.

Abstract Antimicrobial resistance is one of the most serious public health problems. This is of particular concern when bacteria become resistant to various antimicrobial agents simultaneously and when they form biofilms. Consequently, therapeutic options for the treatment of infections have become limited, leading frequently to recurrent infections, treatment failure and increase of morbidity and mortality. Both, persistence and spread of antibiotic resistance, in combination with decreased effectiveness and increased toxicity of current antibiotics have emphasized the urgent need to search alternative sources of antimicrobial substances. Plants are recognized as a source of unexplored chemical structures with high therapeutic potential, including antimicrobial activity against clinically important microorganisms. Additionally, phytochemicals (plant secondary metabolites) present several advantages over synthetic molecules, including green status and different mechanisms of action from antibiotics which could help to overcome the resistance problem. In this study, an overview of the main classes of phytochemicals with antimicrobial properties and their mode of action is presented. A revision about the application of phytochemicals for biofilm prevention and control is also done. Moreover, the use of phytochemicals as scaffolds of new functional molecules to expand the antibiotics pipeline is reviewed.

Abstract In this contribution, we attempted to design novel inhibitors of the serine/threonine-protein kinase Chk1. After studying the interaction of Chk1 ATP binding site with known inhibitor C39, we created seven modified C39-based molecules in order to achieve higher binding potentials. Of those, modified molecules 2, 4, 6 and 7 (MD2, MD4, MD6 and MD7) were selected to be assembled in three new molecules, originating MD8, MD9 and MD10. When compared to C39, MD8 and MD9 showed significant improvements in the binding energy while MD10 had a smaller gain. MD9 achieved the best improvement (21%) and MD8 the second best (19%) while MD10 only reached a 6% improvement.