University of Coimbra

About: University of Coimbra is a education organization based out in Coimbra, Portugal. It is known for research contribution in the topics: Population & Context (language use). The organization has 14318 authors who have published 43067 publications receiving 994733 citations. The organization is also known as: UC & Universidade dos Estudos Gerais.

Designing ionic liquids: the chemical structure role in the toxicity

Abstract: Ionic liquids (ILs) are a novel class of solvents with interesting physicochemical properties. Many different applications have been reported for ILs as alternatives to organic solvents in chemical and bioprocesses. Despite the argued advantage of having low vapor pressure, even the most hydrophobic ILs show some degree of solubility in water, allowing their dispersion into aquatic systems and raising concerns on its pollutant potential. Moreover, now- adays most widespread notion concerning the ILs toxicity is that there is a direct relationship with their hydrophobicity/ lipophilicity. This work aims at enlarging the currently limited knowledge on ILs toxicity by addressing negative impacts in aquatic ecosystems and investigating the possi- bility of designing hydrophobic ILs of low ecotoxicity, by the manipulation of their chemical structures. The impact of aromaticity on the toxicity of different cations (pyri- dinium, piperidinium, pyrrolidinium and imidazolium) and hydrophobic anions (bis(trifluoromethylsulfonyl)imide (NTf2) and hexafluorophosphate (PF6)) was analysed. Concomitantly, several imidazolium-based ILs of the type (CnCmCjim)(NTf2) were also studied to evaluate the effects of the position of the alkyl chain on the ILs' toxicity. For that purpose, standard assays were performed using organisms of different trophic levels, Vibrio fischeri, Pseudokirchneriella subcapitata and Daphnia magna, allowing to evaluate the consistency of the structure-activity relationships across different biological targets. The results here reported suggest the possibility of designing ILs with an enhanced hydro- phobic character and lower toxicity, by elimination of their aromatic nature.

Metamaterial homogenization approach with application to the characterization of microstructured composites with negative parameters

Abstract: In this work, we develop a systematic and self-consistent approach to homogenize arbitrary nonmagnetic periodic metamaterials. The proposed method does not rely on the solution of an eigenvalue problem and can fully characterize the effects of frequency dispersion, magnetoelectric coupling, and spatial dispersion, even in frequency band gaps or when the materials are lossy. We formulate a homogenization problem to characterize a generic microstructured artificial material, and demonstrate that it is equivalent to an integral-differential system. We prove that this complex system can be reduced to a standard integral equation and solved using standard methods. To illustrate the application of the proposed method, we homogenize several important metamaterial configurations involving split-ring resonators and metallic wires.

Toxicity evaluation of three pesticides on non-target aquatic and soil organisms: commercial formulation versus active ingredient.

Abstract: The Ecological Risk Assessment of pesticides requires data regarding their toxicity to aquatic and terrestrial non-target species. Such requirements concern active ingredient(s), generally not considering the noxious potential of commercial formulations. This work intends to contribute with novel information on the effects of short-term exposures to two herbicides, with different modes of action (Spasor®, Stam Novel Flo 480®), and an insecticide (Lannate®), as well as to corresponding active ingredients (Glyphosate, Propanil and Methomyl, respectively). The microalga Pseudokirchneriella subcapitata (growth inhibition), the cladoceran Daphnia magna (immobilisation), and the earthworm Eisenia andrei (avoidance behaviour) were used as test species. Both herbicides were innocuous to all test organisms at environmentally realistic concentrations, except for Stam and Propanil (highly toxic for Pseudokirchneriella; moderately toxic to Daphnia). Lannate and Methomyl were highly toxic to Daphnia and caused Eisenia to significantly avoid the spiked soil at realistic application rates. The toxicity of formulations either overestimated (e.g. Stam/Propanil for P. subcapitata) or underestimated (e.g. Stam/Propanil for D. magna) that of the active ingredient.