Publications

Abstract Soil acts as a natural 'filter', playing a crucial role in the transfer of geogenic and anthropogenic pollutants from abandoned coal mine sites to surrounding water bodies. Key indicators of soil contamination, such as pH, electrical conductivity (EC), and organic matter (OM), expressed as loss-on-ignition (LOI), can signal contamination risks when they deviate from optimal ranges. To enable sustainable risk assessment through monitoring of pH, EC, and LOI, streamlined spectroscopic techniques Fourier transform infrared (FTIR), near-infrared (NIR), Raman, and X-ray fluorescence (XRF) were applied in combination with multivariate analysis (MVA), to soil samples from two abandoned coal mines in NW Portugal. Partial least squares (PLS) regression models demonstrated that XRF spectroscopic data provided the most accurate assessment of soil pH, EC, and LOI at the local scale (R2 = 0.92-0.99). The most significant spectroscopic signatures, identified through weighted regression coefficients (Bw), enabled robust predictions of these key soil parameters. These findings highlight that these geochemical variables outperform molecular spectroscopy techniques for efficient and environmentally relevant risk monitoring of contamination in abandoned coal mine sites.

Abstract Due to the high quantities of solid waste with high concentrations of chromium that the footwear industry produces and its disposal sites, it is vital to understand whether leather residue itself is harmful to the ecosystem. Thus, a microcosm test with multispecies (Brassica oleracea and Eisenia fetida) was carried out using an agricultural soil contaminated with two different leather residues (Wet Blue and Finished Leather) from the footwear industry. After the stabilization period, Brassica oleracea seedlings and Eisenia fetida adults were exposed to these treatments. At the end of the experiment, a series of parameters were analysed in the B. oleracea leaves (leaf chlorophyl content, gas exchange measurements and photosynthetic parameters), in the E. fetida organisms (alkaline comet assay and biomarkers such as acetylcholinesterase and lipid peroxidation) and in the soils (total chromium content, enzymes activity and nitrogen mineralization and potential nitrification). In the case of soil’s enzymatic activity, even though some were significantly altered, no negative effects could be attributed to the leather residues. Moreover, the addition of residues to the soil did not significantly affect the plant species; however, the same was not observed for the earthworm E. fetida when in contact with Finished Leather. Overall, Finished Leather residue was the one that caused more effects on the parameters analysed and therefore its disposal should be carefully examined.

Abstract An interaction between the hydrogen molecules and circumcoronenes (CCs) decorated with light transition metals, namely Sc, Ti, and V, is investigated using density functional theory and ab initio molecular dynamics. The systems under study show affinity to bind H<inf>2</inf> molecules in two distinct ways: formation of η2-coordination, also called Kubas interaction, and dissociation of H<inf>2</inf> molecule leading to so-called dihydride coordination. When considering the interaction of Sc-, Ti-, and V-decorated CCs with one H<inf>2</inf> molecule only, the dihydride coordination is energetically preferred over the Kubas interaction by 114, 73, and 74 kJ mol−1, respectively. However, when considering the interaction of Sc-, Ti-, and V-decorated CCs with a larger number of H<inf>2</inf> molecules, the energy difference between these two types of systems decreases significantly (up to 1 kJ mol−1). This finding points on the dynamic co-existence of these systems which is confirmed also by molecular dynamics simulations. The strongest H<inf>2</inf> binding is found for V-decorated CC, followed by Ti-decorated CC and Sc-decorated CC. Calculated H<inf>2</inf> binding energies of these Kubas interactions are in the interval of −40 to −80 kJ mol−1, which is suitable for H<inf>2</inf> storage applications. It is shown that Sc-, and Ti-decorated CCs are able to chemisorb four H<inf>2</inf> molecules per one metal atom while V-decorated CC is able to chemisorb only three H<inf>2</inf> molecules per one V atom. However, formed V–H bonds are significantly stronger than Ti–H and Sc–H ones. The hydrogen storage capacity of fully saturated Sc-decorated CC is sixteen H<inf>2</inf> molecules, corresponding to a gravimetric density of 4.5 wt%. © 2025 Elsevier B.V., All rights reserved.

Abstract Due to their distinctive combination of ionic liquid (IL) characteristics and magnetic susceptibility, magnetic ionic liquids (MILs) have emerged as promising materials for gas capture and separation. In this study, molecular dynamics (MD) simulations were employed to investigate the thermodynamic, transport, and structural properties of selected MILs and their interactions with environmentally relevant gases, including methane (CH4), ammonia (NH3), carbon dioxide (CO2) and sulfur dioxide (SO2). The study focused on both imidazolium-based ([C4C1im]+) and phosphonium-based ([P66614]+) cations paired with various anions, including [FeCl4]- , [FeBr4]-, [MnCl4]2- and [GdCl6]3-. Fixed-charge force field parameters were established and validated for phosphonium-based MILs for the first time in the area. Free energy calculations demonstrated that phosphoniumbased MILs with multivalent anions exhibit favorable solvation energies for CO2 and SO2 gases, indicating a high potential for selective gas capture. A reduction in gas mobility is observed in these multivalent-based MILs/gas systems. The molecular-level insights provided by radial distribution functions (RDFs) elucidate the critical role of anions in determining solvation behavior. This observation underscores the importance of these paramagnetic elements in the interactions between the gases and MILs. This study advances the understanding of gas-MIL interactions and offers a foundation for the rational design of advanced materials for industrial gas capture and environmental remediation processes.

Abstract The multifaceted nature of the neurodegenerative diseases, as Alzheimer's disease (AD) and Parkinson's disease (PD) with several interconnected etiologies, and the absence of effective drugs, led herein to the development and study of a series of multi-target directed ligands (MTDLs). The developed RIV-IND hybrids, derived from the conjugation of an approved anti-AD drug, rivastigmine (RIV), with melatonin analogues, namely indole (IND) derivatives, revealed multifunctional properties, by associating the cholinesterase inhibition of the RIV drug with antioxidant activity, biometal (Cu(II), Zn(II), Fe(III)) chelation properties, inhibition of amyloid-/3 (A/3) aggregation (self- and Cu-induced) and of monoamine oxidases (MAOs), as well as neuroprotection capacity in cell models of AD and PD. In particular, two hybrids with hydroxyl-substituted indoles ( 5a2 and 5a3) ) could be promising multifunctional compounds that inspire further development of novel anti-neurodegenerative drugs.

Abstract An experimental and computational thermochemical study is reported focus on the relationship between the energetic properties, the structural characteristics and the inherent reactivity of three thiothiadiazoles: 2-amino5-(methylthio-)-1,3,4-thiadiazole, 2-amino-5-(ethylthio-)-1,3,4-thiadiazole and 2-mercapto-5-methylthio-1,3,4thiadiazole. From the DSC measurements, the enthalpies of fusion and the respective onset temperatures were determined. The standard molar energies of combustion of the (alkylthio)-1,3,4-thiadiazoles were determined by rotating bomb combustion calorimetry. The corresponding standard molar enthalpies of sublimation, at T = 298.15 K, were derived from high-temperature Calvet microcalorimetry measurements and the study of the dependence of the compound's vapour pressures with the temperature, using the Knudsen-effusion technique. The combination of these experimental results enables the calculation of the standard molar enthalpies of formation in the gaseous state, at T = 298.15 K, which are discussed in terms of structural contributions. The latter property was also determined from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. The computed values are in good agreement with the experimental ones. In addition, a conformational and tautomeric study was conducted using the same approach, in order to provide insight on the amino/imino and thiol/thione tautomerism of the compounds studied. The amino form predominates in aminothiadiazoles, while the thione form prevails in mercaptothiadiazole. Moreover, the relative thermodynamic stability of each compound was also evaluated showing that in both solid and gas phases, the most stable species is the mercaptothiadiazole (in its thione form). The thermochemical results of the (alkylthio)-1,3,4-thiadiazoles show a good agreement with the NBO (natural bond orbitals) analysis results.

Abstract Given the challenges associated with understanding electrochemistry content by engaging in prediction, observation, and explanation, laboratory activities can foster active participation and critical thinking, enabling individuals to proactively confront and revise their understanding. Since pre-service teachers should gain firsthand experience with predict-observe-based on a predict-observe-explain strategy, we propose a laboratory activity presented as a mystery box related to concentration cells coupled with an Arduino-based electronic data measurement system to identify how pre-service chemistry teachers move from observations to inferences in a qualitative research. Data was collected by written records and oral explanations during the practical interactions. Results suggest that the proposed laboratory activity allows pre-service chemistry teachers to access data and correct inferences related to electrochemistry content, promoting critical thinking. Data also showed a connection between the macroscopic and symbolic domains, and pre-service teachers recognized concepts associated with the activity, such as solution conductivity and the potential difference in chemical reactions, interpreting the system with prior knowledge, like electron flow direction and concentration cell components. However, additional strategies are needed for detailed and consistent observation and inference recording, enhancing the potential of such activities in favoring electrochemistry education in high schools.

Abstract The subject of chemical bonding is formal in nature and prone to the development of errors among students. This research was carried out at the beginning of the instruction on this subject in secondary education. It employed representations of the three types of chemical bonds to help students define and differentiate them. The participants were 27 students, from a 10th grade class in a school in Portugal, who faced conceptual and representational difficulties related to this topic. A pedagogical intervention, incorporating digital resources, was implemented to help them overcome these difficulties. Data collection instruments included a questionnaire (administered as both a pre-test and post-test), a post-class question, and an interview to gather students' opinions on the digital resources used, as well as the difficulties they experienced before and after learning this topic. The results show significant improvements in the second questionnaire compared to the first, although not all difficulties were overcome. Overall, students found the digital resources beneficial to their learning and offered suggestions for further improvement. This study underscores the importance of these resources in enhancing the teaching and learning of chemical bond representations and presents student feedback through interviews, providing firsthand insights into the effectiveness of these tools.

Abstract Iron is essential for the formation, maturation and dispersal of bacterial biofilms, playing a crucial role in the physiological and metabolic functions of bacteria as well as in the regulation of virulence. Limited availability of iron can impair the formation of robust biofilms by altering cellular motility, hydrophobicity and protein composition of the bacterial surface. In this study, the antibiofilm activity of two natural iron chelating agents, kojic acid (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one) and maltol (3-hydroxy-2-methyl-4-pyrone), were investigated against Staphylococcus aureus and Pseudomonas aeruginosa. In addition, the ability of these 2-hydroxy-4-pyrone derivatives in preventing and eradicating S. aureus and P. aeruginosa biofilms through the enhancement of the efficacy of two antibiotics (tobramycin and ciprofloxacin) was explored. The iron binding capacity of the kojic acid and maltol was confirmed by their affinity for iron (III) which was found to be about 90 %, comparable to the regular chelating agent ethylenediaminetetraacetic acid (EDTA, 89 %). The antibiofilm efficacy of 2-hydroxy-4-pyrone derivatives, alone and in combination with antibiotics, was evaluated by measuring the total biomass, metabolic activity, and culturability of biofilm cells. Furthermore, their impact on the membrane integrity of S. aureus biofilm cells was investigated using flow cytometry and epifluorescence microscopy with propidium iodide staining. It was also examined the ability of 2-hydroxy-4-pyrone derivatives and 2-hydroxy-4-pyrone derivate-antibiotic dual-combinations in inhibiting the production of virulence factors (total proteases, lipases, gelatinases and siderophores) by S. aureus. Regarding biofilm formation, the results showed that 2-hydroxy-4-pyrone derivatives alone reduced the metabolic activity of S. aureus biofilm cells by over 40 %. When combined with tobramycin, a 2-log (CFU cm-2) reduction in S. aureus biofilm cells was observed. Moreover, the combination of maltol and kojic acid with ciprofloxacin prevented P. aeruginosa biomass production by 60 %, compared to 36 % with ciprofloxacin alone. In pre-established S. aureus and P. aeruginosa biofilms, selected compounds reduced the metabolic activity by over 75 %, and a 3-log (CFU cm-2) reduction in the culturability of biofilm cells was noted when kojic acid and maltol were combined with antibiotics. Moreover, 2-hydroxy-4-pyrone derivatives alone and in combination with tobramycin, damaged the cell membranes of pre-established biofilms and completely inhibited total proteases production. Despite the increasing of reactive oxygen species production caused by the cellular treatment of maltol, both 2-hydroxy-4-pyrone derivatives showed good safe profile when tested in human hepatocarcinoma (HepG2) cells. The pre-treatment of HepG2 cells with both compounds was crucial to prevent the cellular damage caused by iron (III). This study demonstrates for the first time that the selected 2-hydroxy-4-pyrone derivatives significantly enhance the antibiofilm activity of tested antibiotics against S. aureus and P. aeruginosa, highlighting their potential as antibiotic adjuvants in preventing and eradicating biofilm-related infections.