Publications

Abstract Surfactants have been widely employed to debundle, disperse and stabilize carbon nanotubes in aqueous solvents. Yet, a thorough understanding of the dispersing mechanisms at molecular level is still warranted. Herein, we investigated the influence of the molecular structure of gemini surfactants on the dispersibility of multiwalled carbon nanotubes (MWNTs). We used dicationic n-s-n gemini surfactants, varying n and s, the number of alkyl tail and alkyl spacer carbons, respectively; for comparisons, single-tailed surfactant homologues were also studied. Detailed curves of dispersed MWNT concentration vs. surfactant concentration were obtained through a stringently controlled experimental procedure, allowing for molecular insight. The gemini are found to be much more efficient dispersants than their single-tailed homologues, i.e. lower surfactant concentration is needed to attain the maximum dispersed MWNT concentration. In general, the spacer length has a comparatively higher influence on the dispersing efficiency than the tail length. Further, scanning electron microscopy imaging shows a sizeable degree of MWNT debundling by the gemini surfactants in the obtained dispersions. Our observations also point to an adsorption process that does not entail the formation of micelle-like aggregates on the nanotube surface, but rather coverage by individual molecules, among which the ones that seem to be able to adapt best to the nanotube surface provide the highest efficiency. These studies are relevant for the rational design and choice of optimal dispersants for carbon nanomaterials and other similarly water-insoluble materials.

Abstract In the present work, the gas-phase standard molar enthalpy of formation of 2-(1H-indol-3-yl)ethanol was derived, at T = 29B.15 K, from the enthalpy of combustion for the crystalline compound, measured by static-bomb calorimetry, and its enthalpy of sublimation obtained from Calvet microcalorimetry measurements. The standard molar enthalpies of formation of this compound and for (1H-indol-2-yl)methanol, (1H-indol-3-yl)methanol and 2-(1H-indol-2-yl)ethanol were calculated using the composite G3 method. The experimental value of the gasphase enthalpy of formation of 2-(1H-indol-3-yl)ethanol is -(48.5 +/- 3.3) kJ mol(-1), being in excellent agreement with the G3 value, thus giving confidence to the estimates. The results were analysed in terms of the enthalpic methylene increments and compared with other related systems.

Abstract Calorimetric experiments performed for ethyl 2-aminobenzoate and ethyl 3-aminobenzoate allowed the determination of their standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T= 298.15 K. The techniques used were static bomb combustion calorimetry and high temperature Calvet microcalorimetry, which enabled the determination of the standard molar enthalpies of formation in the liquid phase, and the standard molar enthalpies of vaporization, at T= 298.15 K, of the above aminobenzoates. In addition, computational calculations, through the G4 composite method, were performed to estimate the enthalpies of formation in the gas phase of the title compounds. Boltzmann weighted averages were performed over sets of stable conformers of each compound, using Gibbs energy to compute population weights. The ethyl 2-aminobenzoate presents an intramolecular hydrogen bond, which was confirmed through topological analyses of the electron density. Furthermore, the energetic effect caused from exchanging the position of the amino substituent was evaluated, and was also compared with similar compounds. (C) 2019 Published by Elsevier Ltd.

Abstract A series of piperic acid esters and amides were synthesized using a two-step strategy. Mass spectrometry and unidimensional (H-1 NMR, C-13 NMR, DEPT) and bidimensional (COSY, HSQC, HMBC) NMR methodologies were used to study the molecular structure of the final compounds, resulting in the assignment of all detected signals. Preliminary biological data of piperine and the derivatives thereof showed that piperic acid 2 and amides 3 and 4 did not display significant inhibitory activity at 10 tiM against both hMAO-A and hMAO-B. In contrast, the esters 5 and 6 displayed relevant hMAO inhibitory activities, with IC50 values for hMAO-B lower than piperine and within the nanomolar range (compound 1: IC50 = 1.05 ttM; compound 6: IC50 =169 nM; compound 5: IC50 =156 nM). Moreover, X-ray crystallographic analyses showed relevant differences between amides 3 and 4 and esters 5 and 6 constituting a valuable information to understand the ligand-target interactions. Additional studies are warranted for a systematic lead optimization process that can lead in the future to a more potent and selective hMAO-B inhibitor based on piperine scaffold.

Abstract Despite a growing number of research reports on neat room temperature ionic liquids (RTILs) and their mixtures with molecular solvents in recent years, understanding and rationalising of such systems is still a challenge. In this work, we performed a classical molecular dynamics simulation study of the pure components - 1-ethyl-3-methylimidazolium thiocyanate (C2C1 imSCN), methanol, and ethanol - and their binary mixtures at room temperature. Thermodynamic (density and heats of vaporization), transport (viscosity and self-diffusion coefficients) and structural (in terms of radial, angular and spatial distributions) properties were analysed. It was found, that with the decrease of RTIL content, the ions self-diffusion coefficients notably increase, reaching higher values in the C2C1 imSCN-MeOH system. Density and viscosity follow the opposite trend, reaching their minimum at lower RTIL mole fraction. Negative deviations of excess molar volume from ideality in the studied mixtures with minima at similar to 0.2-03 mole fraction of RTIL suggest the strongest ion-molecular interactions at this mixture composition. A careful analysis at the molecular level revealed that introducing of alcohols to both systems weakens the inter-ionic H-bonding network, particularly, at low RTIL content. The cation-cation arrangement was found to lose its characteristic above/below orientation in neat RTIL and become disordered at low RTIL content. As to the tail length of the selected alcohols, this was found to have an insignificant effect on the structural properties of the addressed systems.

Abstract In this chapter, we present and analyse the perceptions of Portuguese students about the relationship between science and religion in a Catholic cultural context. A pen and paper questionnaire was answered by 308 High School students. Results suggest that conflict, independence, and dialogue seem to be ways adopted by respondents for conceiving the relationship between science and religion. It is worth mentioning that the Bible and the theory of the evolution of species do not seem to be the reasons why science and religion are perceived as conflictual among young believers. Further research is necessary to understand the sources of conflictual perceptions, exploring the consistency of results across different levels of analysis.

Abstract The surface properties of nanoparticles have decisive influence on their interaction with biological barriers (i.e., living cells), being the concentration and type of surfactant factors to have into account. As a result of different molecular structure, charge, and degree of lipophilicity, different surfactants may interact differently with the cell membrane exhibiting different degrees of cytotoxicity. In this work, the cytotoxicity of two cationic solid lipid nanoparticles (SLNs), differing in the cationic lipids used as surfactants CTAB (cetyltrimethylammonium bromide) or DDAB (dimethyldioctadecylammonium bromide), referred as CTAB-SLNs and DDAB-SLNs, respectively, was assessed against five different human cell lines (Caco-2, HepG2, MCF-7, SV-80, and Y-79). Results showed that the cationic lipids used in SLN production highly influenced the cytotoxic profile of the particles, with CTAB-SLNs being highly cytotoxic even at low concentrations (IC50 < 10 <mu>g/mL, expressed as CTAB amount). DDAB-SLNs produced much lower cytotoxicity, even at longer exposure time (IC50 from 284.06 +/- 17.01 mu g/mL (SV-80) to 869.88 +/- 62.45 mu g/mL (MCF-7), at 48 h). To the best of our knowledge, this is the first report that compares the cytotoxic profile of CTAB-SLNs and DDAB-SLNs based on the concentration and time of exposure, using different cell lines. In conclusion, the choice of the right surfactant for biological applications influences the biocompatibility of the nanoparticles. Regardless the type of drug delivery system, not only the cytotoxicity of the drug-loaded nanoparticles should be assessed, but also the blank (non-loaded) nanoparticles as their surface properties play a decisive role both in vitro and in vivo.

Abstract The present work reports the effect of polysaccharides (chitosan and sodium alginate) on silica nanoparticles (SiNP) for hydrophilic molecules delivery taking insulin as model drug. The influence of tetraethyl orthosilicate (TEOS) and homogenization speed on SiNP properties was assessed by a 2(2) factorial design achieving as optimal parameters: 0.43 mol/L of TEOS and homogenization speed of 5000 rpm. SiNP mean particle size (Z-Ave) was of 256.6 nm and polydispersity index (PI) of 0.218. SiNP coated with chitosan (SiNP-CH) or sodium alginate (SiNP-SA) increased insulin association efficacy; reaching 84.6% (SiNP-SA) and 90.8% (SiNP-CH). However, coated SiNP released 50-60% of the peptide during the first 45 min at acidic environment, while uncoated SiNP only released similar to 30%. Similar results were obtained at pH 6.8. The low Akaike's (AIC) values indicated that drug release followed Peppas model for SiNP-SA and second order for uncoated SiNP and SiNP-CH (pH 2.0). At pH 6.8, the best fitting was Boltzmann for Ins-SiNP. However, SiNP-CH and SiNP-SA showed a first-order behavior. Cytotoxicity of nanoparticles, assessed in Caco-2 and HepG2 cells, showed that 100 to 500 mu g/mL SiNP-CH and SiNP-SA slightly decreased cell viability, comparing with SiNP. In conclusion, coating SiNP with selected polysaccharides influenced the nanoparticles physicochemical properties, the insulin release, and the effect of these nanoparticles on cell viability.