Publications

Abstract The importance of choline chloride (ChCl) is recognized due to its widespread use in the formulation of deep eutectic solvents. The controlled addition of water in deep eutectic solvents has been proposed to overcome some of the major drawbacks of these solvents, namely their high hygroscopicities and viscosities. Recently, aqueous solutions of ChCl at specific mole ratios have been presented as a novel, low viscous deep eutectic solvent. Nevertheless, these proposals are suggested without any information about the solid-liquid phase diagram of this system or the deviations from the thermodynamic ideality of its precursors. This work contributes significantly to this matter as the phase behavior of pure ChCl and (ChCl + H2O) binary mixtures was investigated by calorimetric and analytical techniques. The thermal behavior and stability of ChCl were studied by polarized light optical microscopy and differential scanning calorimetry, confirming the existence of a solid-solid transition at 352.2 +/- 0.6 K. Additionally, heat capacity measurements of pure ChCl (covering both ChCl solid phases) and aqueous solutions of ChCl (x(ChCl) < 0.4) were performed using a heat-flow differential scanning microcalorimeter or a high-precision heat capacity drop calorimeter, allowing the estimation of a heat capacity change of (ChCl) approximate to 39.3 +/- 10 J K-1 mol(-1), between the hypothetical liquid and the observed crystalline phase at 298.15 K. The solid-liquid phase diagram of the ChCl + water mixture was investigated in the whole concentration range by differential scanning calorimetry and the analytical shake-flask method. The phase diagram obtained for the mixture shows an eutectic temperature of 204 K, at a mole fraction of choline chloride close to x(ChCl) = 0.2, and a shift of the solid-solid transition of ChCl-water mixtures of 10 K below the value observed for pure choline chloride, suggesting the appearance of a new crystalline structure of ChCl in the presence of water, as confirmed by X-ray diffraction. The liquid phase presents significant negative deviations to ideality for water while COSMO-RS predicts a near ideal behaviour for ChCl.

Abstract Chlorins are highly interesting compounds due to their spectroscopic properties in both UV-Vis and NIR regions. Upon coordination to a metal ion, the corresponding metallochlorins exhibit more valuable physicochemical properties that enable a broader range of applications, such as in photodynamic therapy (PDT), water splitting catalysis, optical sensor devices and dye-sensitized solar cells. Synthetic chemistry has been in a continuous quest to fulfil most green chemistry requirements through the development of efficient reactions. Being a heating process that does not depend on heat transfer to the reaction medium, ohmic heating accomplishes the mentioned requirements and allows a fast and uniform heating regime thanks to the ionic conductivity of the reaction medium. Herein, we report the metallation of pyrrolidine- and isoxazolidine-fused chlorins with Zn(ii), Cu(ii) and Pd(ii) salts by ohmic heating, using non-toxic aqueous solutions, and their corresponding physico-chemical characterization. All pyrrolidine-fused chlorins showed higher yields, when compared with isoxazolidine ones. From the thermogravimetric analysis performed it is possible to infer that the metal enhances the steadiness of the macrocycle, making it easier to cause the thermal decomposition of the pyrrolidine- and isoxazolidine-fused chlorins. The Zn(ii) complexes showed high absorption in the NIR spectral region, a low fluorescence quantum yield and a short excited singlet state, which indicate the high efficiency of intersystem crossing to the triplet state, making them very promising candidates as photosensitizers for PDT.

Abstract The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES.

Abstract An experimental and theoretical study of solution and solvation of mono-and divalent alkali metal cations in the protic ionic liquid (IL) ethylammonium nitrate (EAN) is reported. High precision solution-reaction calorimetry was used to obtain the heat of solvation, which was used for the analysis of the thermodynamics. A close relation between the structure of the salts in the crystalline phase and its enthalpy of solvation in the IL is reported. A detailed picture of the molecular environments in the solvation shells around the metal cations is provided by means of molecular dynamics simulations. The analysis of the energetics and structure of solvation confirms the well-known water-like solvation properties of EAN, with the solvation shell around the metal cations in both media being very similar. On the other hand, the results show that it is energetically more favourable to solvate smaller cations with higher valence. Indeed, the simulations show that the long-range electrostatic interactions are the main contribution to solvation interaction, with the electric field at the surface of the alkali metal cations as the basic magnitude controlling it.

Abstract The expansion of mcr-carrying bacteria is a well-recognized public health problem. Measures to contain mcr spread have mainly been focused on the food-animal production sector. Nevertheless, the spread of MCR producers at the environmental interface particularly driven by the increasing population of gulls in coastal cities has been less explored. Occurrence of mcr-carrying Escherichia coli in gull's colonies faeces on a Portuguese beach was screened over 7 months. Cultural, molecular and genomic approaches were used to characterize their diversity, mcr plasmids and adaptive features. Multidrug-resistant mcr-1-carrying E. coli were detected for 3 consecutive months. Over time, multiple strains were recovered, including zoonotic-related pathogenic E. coli clones (e.g. B2-ST131-H22, A-ST10 and B1-ST162). Diverse mcr-1 genetic environments were mainly associated with ST2/ST4-HI2 (ST10, ST131, ST162, ST354 and ST4204) but also IncI2 (ST12990) plasmids or in the chromosome (ST656). Whole-genome sequencing revealed enrichment of these strains on antibiotic resistance, virulence and metal tolerance genes. Our results underscore gulls as important spreaders of high-priority bacteria and genes that may affect the environment, food-animals and/or humans, potentially undermining One-Health strategies to reduce colistin resistance.

Abstract While surfactants and polymers have been independently investigated as agents to separate, disperse and stabilize carbon nanotubes (CNTs) in water, mixed polymer/surfactant (P/S) systems have been far less studied for those ends. In this work, we investigated the ability of various types of P/S mixtures to effectively separate multiwalled carbon nanotubes (MWNTs) in water, using rigorously controlled processing conditions. Two types of mixtures were explored: i) nonionic polymer (PVP, polyvinylpyrrolidone) and ionic surfactant (sodium dodecylbenzene sulfonate, SDBS, or cetyltrimethylammonium bromide, CTAB); and ii) ionic polymer (poly(diallyl dimethyl ammonium chloride), PDDA, and sodium polyacrylate, PAS) and nonionic surfactant (TX-100). Detailed, high precision dispersibility curves (concentration of dispersed nanotubes vs. total P/S concentration, at fixed S concentration) are presented for four P/S mixtures (PVP/SDBS, PVP/CTAB, PDDA/TX-100 and PAS/TX-100) and their respective individual components. Quantitative metrics extracted from the dispersibility curves allow for reliable comparisons between the systems. In all P/S mixtures, beneficial (synergistic) effects in nanotube dispersibility are observed compared to the individual components, with the exception of the PDDA/TX-100 one for which a detrimental (antagonistic) effect occurs. Morphological characterization of the as-obtained dispersions by scanning electron microscopy (SEM) shows a significant degree of nanotube separation by the P/S systems. Surface tension and zeta potential measurements provide further information on the interactions at play between the MWNTs and the P/S mixtures, allowing to conceive plausible mechanisms for the synergistic effects observed. P/S association may not only offer conditions for an enhanced dispersibility of CNTs but also expand the types of noncovalent, reversible functionalization required in many applications, such as the development of nanocomposite particles, films and coatings.

Abstract The development of functional materials with uniquely advanced properties lies at the core of nanoscience and nanotechnology. From the myriad possible combinations of organic and/or inorganic blocks, hybrids combining metal nanoclusters and carbon nanomaterials have emerged as highly attractive colloidal materials for imaging, sensing (optical and electrochemical) and catalysis, among other applications. While the metal nanoclusters provide extraordinary luminescent and electronic properties, the carbon nanomaterials (of zero, one or two dimensions) convey versatility, as well as unique interfacial, electronic, thermal, optical, and mechanical properties, which altogether can be put to use for the desired application. Herein, we present an overview of the field, for experts and non-experts, encompassing the basic properties of the building blocks, a systematic view of the chemical preparation routes and physicochemical properties of the hybrids, and a critical analysis of their ongoing and emerging applications. Challenges and opportunities, including directions towards green chemistry approaches, are also discussed.

Abstract Inspired by previous disclosure of room-temperature ionic liquids derived from primaquine and cinnamic acids, which displayed slightly enhanced blood-stage activity compared to the parent drug, we have now combined this emblematic antimalarial with natural fatty acids. This affords surface-active ionic liquids whose liver-stage antiplasmodial activity is either retained or slightly enhanced, while revealing blood-stage antiplasmodial activity at least one order of magnitude higher than that of the parent compound. These findings open new perspectives towards the cost-effective recycling of classical drugs that are either shelved or in decline, and which is not limited to antimalarial agents.

Abstract Transition metal dichalcogenides (TMDs), like other two-dimensional layered materials beyond graphene, have gained enormous interest in recent years owing to their distinct electronic and optical properties, and potential applicability in areas such as sensing, nanoelectronics and catalysis. Surfactant -assisted exfoliation is commonly used to prepare aqueous dispersions of TMD nanosheets, but a clear picture of the TMD and surfactant features that influence the dispersion process is still lacking. In this work, we present a systematic study of the dispersibility of MoS2, WS2 and MoSe2 in aqueous medium using a cationic (cetyltrimethylammonium bromide, CTAB) and an anionic (sodium cholate, SC) dispersant, in a wide concentration range (seven orders of magnitude) and resorting to a carefully controlled sonication-centrifugation procedure. We present detailed, high precision dispersibility curves (concentration of dis-persed TMD versus concentration of surfactant used), together with zeta potential and pH measurements, allowing insight on the influence of the type of metal and chalcogen, surfactant charge and surfactant concentration, on the effectiveness of the exfoliation and stabilization. The metal (Mo vs. W) influences the dispersibility at low surfactant concentrations, while the chalcogen (S vs. Se) plays a more significant role as the surfactant concentration is increased, alongside the surfactant charge. Structural characterization by scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM) shows that the methodology applied yields well-exfoliated nanosheets with controlled mean lateral dimension (asymptotic to 100 nm) and thickness (<= 5 layers). Finally, the type of ionic surfactant (cationic vs. anionic) and its concentration play a pivotal role in the profile of the dispersibility curves, leading us to propose two types of master curves with distinct regions of phase behavior.