Publications

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 The volatility, heat capacity, and thermal behavior were used to explore the effect of alkyl size and anion nature in the thermodynamic properties of ionic liquids (ILs) by measuring the 1-alkyl-3-methylimidazolium trifluoromethanesulfonate series ([C(n)C(1)im][OTf], with n = 2, 4, 6, 8, 10, 12). The volatility of the ILs, assessed through the Knudsen effusion method coupled with quartz crystal microbalance (KEQCM), indicates that molar enthalpy and entropy of vaporization present a quasi-linear dependence with the alkyl chain length, while the molar Gibbs energy of vaporization is nearly constant until n = 6 and increases with alkyl chain length for n > 6. The [C(n)C(1)im][OTf] series was found to be less volatile than the [C(n)C(1)im][NTf2] series. Their phase behavior was studied by means of DSC and a non-monotonous trend was found for the melting point, as well as for the standard molar enthalpy and entropy of fusion, along the number of carbon atoms on the alkyl side chain of the cation. The typical trendshift associated with the intensification of the nanostructuration of the ILs was clearly observed in the volumetric heat capacity, where it reaches a minimum at n approximate to 6 and becomes nearly constant for ILs with a longer alkyl chain. The high resolution and accurate measurement of thermodynamic properties can be used as a robust strategy for the analysis and interpretation of nanostructuration in the liquid phase, which is essential for the tuning of properties/functionalities, as well as for the deep molecular understanding of the ionic fluid behavior.

Abstract Syngas fermentation is a promising carbon capture and utilization (CCU) technology for producing carboxylic acids while transforming low-cost waste gas into high-value products. This study evaluates the two bioreactor feeding strategies for synthesis gas (syngas) fermentation by Eubacterium callanderi (formerly Butyribacterium methylotrophicum) strain Marburg-on-demand feeding (ODF) and continuous feeding (CF)-with a synthetic syngas mixture of 23 vol% CO2, 29 vol% CO, 32 vol% H2, and 16 vol% CH4, mimicking the syngas from lignocellulosic gasification. The ODF assay achieved a maximum syngas consumption rate of 112 mL/h, yielding 24.1 g/L acids, namely 22.9 g/L acetate and 1.3 g/L butyrate. CF of syngas at 223 mL/h required more gas (62.9 L) to produce 22.7 g/L total acids, from which 19.0 g/L acetate and 3.7 g/L butyrate were achieved. The CF-specific production rate (gproduct/gdry_cell_weight/hour) reached 0.5 g/gDCW/h (acetate) and 0.17 g/gDCW/h (butyrate), outperforming ODF with 0.3 and 0.02 g/gDCW/h, respectively. ODF minimized gas wastage and enabled CH4 accumulation inside the bioreactor up to approximately 78 vol%, while CF led to CO2 accumulation, indicating a need for more efficient CO2 utilization strategies, such as sequential fermentations. This work highlights the critical impact of the two feeding options studied with regard to scaling up the carbon-efficient production of carboxylic acids, and indicates that both strategies can have potential applications. ODF is ideal for increasing carbon fixation and achieving, simultaneously, gas cleaning, while CF fermentations are better suited to maximizing the acid production rate.

Abstract Mentoring within affinity spaces holds an invaluable potential for informal learning. It promotes continuous learning through reflective practices and ongoing feedback, which are vital for developing expertise and for fostering lifelong learning. However, ensuring active engagement in these spaces can be challenging. Understanding the mechanisms of curiosity, interest and engagement appears as key to comprehending the conscious and unconscious negotiations that occur in participation, collaboration, and their subsequent outcomes in this setting. This paper examines the curiosity, interest and engagement (CIE) development throughout the informal learning processes that underpin the development of digital and cultural literacy through intergenerational digital storytelling within the project Narratives of Our Age (NOOA). The project facilitated intergenerational digital storytelling, focusing on local myths, crafts, and traditions, based on the creation of a hybrid affinity space. Drawing from the collaborative and participatory potential of web 2.0 applications, the project fostered in-person intergenerational exchanges to develop digital stories that raise acknowledgment and have the potential to preserve and to disseminate regional cultural identity, while contributing to participants' cultural and digital literacy. In parallel, the project also developed a cross media online space to disseminate the digital stories that were produced by the intergenerational groups, and to expand the discussions around the topic of cultural identity. With an action-research methodology and drawing from qualitative data obtained through interviews and participative observation, we investigated how the CIE construct manifested within both in-person and digital affinity spaces of the project. Findings indicate that in-person interactions were particularly effective in fostering all levels of the CIE construct, promoting deeper engagement and sustained interest. Conversely, online spaces primarily stimulated initial curiosity and interest but encountered challenges in maintaining prolonged engagement. These results underscore the value of an integrated, hybrid approach that combines face-to-face and digital interactions to effectively support informal learning and cultural and digital literacy development in an intergenerational setting. The study contributes to the understanding of the opportunities and challenges of hybrid affinity spaces for enhancing community-based digital storytelling initiatives, and of how innovative informal educational approaches can leverage technology and cultural practices to create engaging, culturally responsive learning environments that bridge generational gaps and promote lifelong learning. © 2025 IADIS Press All rights reserved.

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.

Abstract An extensive thermochemical study of gamma-undecanolactone and delta-undecanolactone has been developed using two complementary calorimetric techniques. The combustion energy of each compound was determined by static-bomb combustion calorimetry, and the corresponding enthalpy of vaporization was determined by high-temperature Calvet microcalorimetry, in which both properties of each compound are reported at T = 298.15 K. The standard molar enthalpy of formation in the gas phase of each lactone was derived by the combination of the experimental results. Additionally, high-level computational calculations were carried out, using composite ab initio G4 and G4(MP2) methods, as well as DFT M06-2X/6-311++G(d,p) approach, to estimate the corresponding enthalpy of formation in the gas phase. The experimental and computational results are in good agreement. The G4 and G4(MP2) methods show the best accordance with experimentally determined gas phase enthalpies of formation. The experimental results are discussed in terms of structural contributions to the energetic properties of the lactones studied, as well as to other alkylated gamma- and delta-lactones, and empirical correlations are suggested for the estimation of the standard molar enthalpies of formation, at T = 298.15 K, for other alkylated gamma- and delta-lactones, both in the liquid and gaseous phases, as well as for the respective enthalpies of vaporization. Finally, the thermochemistry of individual steps of lactone ring opening and successive decarboxylation mechanism, including the identification of transition states, was studied using the M06-2X/6-311++G(d,p) approach.

Abstract Borophene, a monolayer of boron atoms, belongs to intensively studied two-dimensional beyond-graphene materials. The B36 borophene nanoflake is a finite size model system, containing a hexagonal vacancy similar to the ones present in (312 and chi 3 borophene sheets. The hydrogen binding performance of B36 decorated with various transition metal atoms is investigated using density functional theory and quantum theory of atoms in molecules. Hydrogen is considered to become one of the crucial energy sources in future, hence, a search for effective hydrogen storage materials is of urge importance. Obtained results suggest that B36 decorated with Co, Ni, Fe, and Cu possess strong affinity to bind the H2 molecule via formation of eta 2-dihydrogen bonds. Among them, the strongest H2 binding is found for Co- and Ni-decorated B36. Furthermore, B36 decorated with Sc and Ti behave like H-H bond breakers while B36 decorated with Zn possess only negligible affinity to bind H2 molecule. The stability of the B36 decorated with Co and Ni is verified by ab initio molecular dynamics. The presented data may also serve as a basis for reference in future large-scale computational studies of borophene-based materials.

Abstract Heat capacity, a crucial physical property for chemical processes, is often understudied in Deep Eutectic Solvents (DESs), which in turn are promising green alternatives to environmentally hazardous conventional solvents. This work addresses this gap by developing a machine learning model to predict DES heat capacity and identify key structural features influencing it. We employed a dataset of 530 DESs with corresponding experimental heat capacity values. Quantum-chemical COSMO-RS-based descriptors, capturing detailed information about DES structures, were calculated for each data point. Various machine learning algorithms, namely k-Nearest Neighbours (kNN), Random Forests (RF), Neural Network Multilayer Perceptron (MLP), and Support Vector Machines (SVM) were explored alongside a linear model (Multiple Linear Regression, MLR). Hyperparameter optimisation ensured all models were fine-tuned for optimal performance. The most successful model, based on the MLP technique, achieved remarkably low Average Absolute Relative Deviation (AARD) values of 0.500 % and 3.999 % for the training and test sets, respectively. This signifies a significant improvement in prediction accuracy compared to traditional methods. Furthermore, by applying a SHapley Additive exPlanations (SHAP) analysis, we identified the most crucial structural factors within DES components that govern their heat capacity. This comprehensive investigation offers valuable insights that can pave the way for an efficient design of novel DESs in the future. © 2024 The Author(s)