Publications

Abstract We present herein the synthesis, and the structural and spectroscopic analysis of a non-planar tripod-shaped p-(N,N'-dimethylamino) benzyliden-1,3-indandione (DMABI) chromophore. This novel molecule is composed of a Si core with three incorporated arms, each of them contains a 1,3-indandione derivative with an electron donating (-NMe2) group, thus providing fluorescence capabilities. We prepared a DMABI arm by coupling a p-(N,N'-dimethylamino) benzaldehyde (DMAB) tripod substituted molecule with 1,3-indandione via aldol condensation. The structures of DMAB-tripods were confirmed by spectroscopic data and studied by quantum chemical calculations. Fluorescence spectroscopy was used for optical characterization. Quantum yields and the corresponding lifetimes reveal typical characteristics of conjugated derivatives. Finally, we monitored the enhancement in fluorescence intensity of compound 1 in the presence of 4-chloro-2,6-dinitroaniline (4CDNA) in the range between 0 and 20 mg L-1. We justify this enhancement by calculated energies and the distribution of the HOMO and the LUMO for DMABI-tripod and 4CDNA.

Abstract The thermodynamics and phase behavior of mixtures of cationic gemini surfactant decanediyl-alpha, omega-bis(dodecyldimethylammonium bromide) (12-10-12) and sodium dodecylsulfate (SDS) were studied in the dilute SDS-rich region. The enthalpy of interaction between both surfactant monomers before the critical micelle concentration for the mixture (cmc(mix)) was determined by isothermal titration calorimetry (ITC). After the cmc(mix), ITC results exhibited a first process associated with a large endothermic enthalpy change followed by a second one with a very small exothermic enthalpy change. In the same regions, the conductivity curves show an increase in slope after the break, followed by a plateau region, respectively for the two processes. The combined results from the various methodologies used lead us to propose that the first process reflects the formation of non-spherical micelles and the second one the vesicle formation. The area per catanionic complex was obtained through surface pressure measurements, leading to an apparent packing parameter >= 1. The observed behavior may be rationalized on the basis of the hypothesis that both surfactants distribute asymmetrically in the vesicle bilayers and unevenly in the non-spherical micelle. In order to get structural information Cryo-TEM experiments were performed, which provided images that support this interpretation. From all the information gathered a phase diagram was mapped, including three one-phase regions of spherical micelles, non-spherical micelles and vesicles.

Abstract Biofilms are encountered on nearly all wet surfaces, with their development being often unwanted due to the serious problems they can cause in different fields, including in the food sector. They are recognized as the preferential microbial lifestyle due to the numerous advantages for the embedded cells. Biofilm cells are highly resistant to stress conditions, particularly to antimicrobials, as their complex and compact structure hampers the penetration of antimicrobials and the access to the deep positioned cells. The increased resistance to the currently employed control strategies emphasizes the urgent need of new alternative and/or complementary eradication approaches. To this direction, the use of enzymes is an interesting alternative anti-biofilm approach due to their capability to degrade crucial components of the biofilm matrix, cause cell lysis, promote biofilm disruption and interrupt the cell-to-cell signaling events governing biofilm formation and maintenance. This review provides an overview of the enzymes used for biofilm control, their targets and examples of effective applications.

Abstract Background: Virtual Screening methodologies have emerged as efficient alternatives for the discovery of new drug candidates. At the same time, ensemble methods are nowadays frequently used to overcome the limitations of employing a single model in ligand-based drug design. However, many applications of ensemble methods to this area do not consider important aspects related to both virtual screening and the modeling process. During the application of ensemble methods to virtual screening the proper validation of the models in virtual screening conditions is often neglected. No analysis of the diversity of the ensemble members is performed frequently or no considerations regarding the applicability domain of the base models are being made. Methods: In this research, we review basic concepts and definitions related to virtual screening. We comment recent applications of ensemble methods to ligand-based virtual screening and highlight their advantages and limitations. Results: Next, we propose a method based on genetic algorithms optimization for the generation of virtual screening tailored ensembles which address the previously identified problems in the current applications of ensemble methods to virtual screening. Conclusion: Finally, the proposed methodology is successfully applied to the generation of ensemble models for the ligand-based virtual screening of dual target A2A adenosine receptor antagonists and MAO-B inhibitors as potential Parkinson's disease therapeutics.

Abstract Steady-state and time-resolved fluorescence techniques, in addition to quantum mechanical calculations, were employed to study the excited-state proton transfer (ESPT) to solvent of three 7-hydroxycoumarin dyes. We found that for 7-hydroxycoumarins in water, the ESPT rate is high, about 2 X 10(10) s(-1), whereas in methanol the ESPT rate is much lower than that over the nonradiative lifetime of the excited singlet state; thus, the ESPT efficiency is very low.

Abstract The heat capacities in the temperature range (5 to 370) K and the parameters of solid-phase transitions and fusion were determined for three [C(n)mim][NTf2] (n = 10, 14, 16) ILs. The temperature-dependent vapour pressures of [C(14)mim][NTf2] and [C(16)mim][NTf2] were measured with a Knudsen effusion apparatus combined with a quartz crystal microbalance. Thermodynamic properties of these compounds in the crystal, liquid, and gas states were derived from the obtained data. The results obtained in this work were combined to those available in the literature for the short-chain homologues to discuss regularities in thermodynamic properties of the series. While some properties demonstrate simple linear dependence on the alkyl chain length, a more complicated behaviour with strong non-linearity or a break at n = 6 is observed for others. Published by Elsevier Ltd.

Abstract The thermal behavior, solid and liquid heat capacities of the 1-benzyl-3-methylimidazolium, [Bzmim](+), based ionic liquid series with Cl, PF6, BF4, CHF2CF2SO3 and NTf2 as anions were used to evaluate the effect of the insertion of an aromatic character (benzyl group) and the expected increase of the pi-pi interactions as well as the impact in the cation-anion hindrance and charge delocalization in the ionic liquid properties. It was found that the molar liquid heat capacities of [Bzmim][X] are in the same order as the 1-pentyl-3-methylimidazolium, [C(5)C(1)im][X] analogs. A good correlation between the molar (solid and liquid) heat capacity and the number of atoms of the anion was found. Two different crystalline forms for [Bzmim][BF4] differing by 10 K in the melting temperature and about 10% in the heat capacity were found. The crystallization behavior, melting temperatures, and enthalpies and entropies of fusion show that the insertion of an aromatic character (benzyl group) in the imidazolium cation leads to a significant and systematic change of the thermophysical properties of the ionic liquids associated with an increase of the glass transition and melting temperatures arising from the additional pi-pi interactions. (C) 2016 Published by Elsevier Ltd.

Abstract Aryl derivatives of ferrocene are used for the modification of graphitic surfaces. Stronger adsorption is utilized as a route to enable the electrochemically tagging of new carbon materials. Model experiments are reported on an EPPG electrode where the adsorption of 1-(biphen-4-yl)ferrocene is found to be a factor of ca. 5 times more thermodynamically favorable than the underivatised form. Two further derivatives were also studied and the voltammetric responses of this class of ferrocenes are found to be significantly influenced by ion-pairing. Finally, the successful use of these new materials for the modification and redox tagging of graphene nanoplatelets is demonstrated.

Abstract This work explores the n vs. iso isomerization effects on the physicochemical properties of different families of ionic liquids (ILs) with variable aromaticity and ring size. This study comprises the experimental measurements, in a wide temperature range, of the ILs' thermal behaviour, heat capacities, densities, refractive indices, surface tensions, and viscosities. The results here reported show that the presence of the iso-alkyl group leads to an increase of the temperature of the glass transition, T-g. The isopyrrolidinium (5 atoms ring cation core) and iso-piperidinium (6 atoms ring cation core) ILs present a strong differentiation in the enthalpy and entropy of melting. Non-aromatic ILs have higher molar heat capacities due to the increase of the atomic contribution, whereas it was not found any significant differentiation between then and iso-alkyl isomers. A small increase of the surface tension was observed for the non-aromatic Its, which could be related to their higher cohesive energy of the bulk, while the lower surface entropy observed for the iso isomers indicates a structural resemblance between the IL bulk and surface. The significant differentiation between ILs with a 5 and 6 atoms ring cation in the n-alkyl series (where 5 atoms ring cations have higher surface entropy) is an indication of a more efficient arrangement of the non-polar region at the surface in ILs with smaller cation cores. The ILs constituted by non aromatic piperidinium cation, and iso-alkyl isomers were found to be the most viscous among the studied Its due to their higher energy barriers for shear stress. (C) 2016 Published by Elsevier B.V.