Publications

Abstract Diels-Alder cycloaddition is a common synthetic approach to functionalize fullerenes. However, the stability of such fullerene adducts is hampered by the existence of the Retro Diels-Alder (RDA) reaction. Herein, the RDA reactions in the solid phase of the mono and bisadducts of C60 with indene, IC60MA and IC60BA, were studied by differential scanning calorimetry and thermogravimetric analysis. The RDA reaction in solid IC60MA occurs at a higher temperature than in IC60BA. IC60MA decomposition follows a first-order rate law and in IC60BA it is described by two consecutive first-order reaction steps. The decomposition of both adducts yields a metastable C60 solid. The higher decomposition temperature of IC60MA is due to higher activation energy, Ea, and lower preexponential factor, A. The values of Ea for the RDA reactions differ due to crystal packing efficiency in the solids. The measured A values were found to reflect the statistical weight of C60-Indene bonds that can be broken. A reaction mechanism was proposed for the decomposition of the fullerene adducts. The enthalpies of sublimation of IC60MA and IC60BA were estimated based on the enthalpies of their respective RDA reactions. Additionally, the heat capacities of the solid fullerenes (C60, IC60MA, and IC60BA), at T = 298.15 K, were measured by highprecision heat capacity drop calorimetry, indicating that the rotational motion of C60 in the crystal increases its expected heat capacity.

Abstract A systematic synthetic study was performed to explain the usual trend in selectivity towards multi-coupling, over mono-coupling, in Suzuki-Miyaura reactions. This preference was observed under different reaction conditions: for various halobenzenes, using substituents on the boronic acid, and changing the catalyst and temperature. Moreover, this reaction selectivity was found to increase for more reactive systems towards oxidative addition and more diluted media. The results constitute experimental evidence that the formation of the totally substituted coupling product is kinetically favoured by a reaction path location-the proximity between the regenerated catalyst and the newly formed coupling intermediate promotes the subsequent reaction.

Abstract Decaphenylbiphenyl (1) and 2,2',4,4',6,6'-hexaphenylbiphenyl (2) are bulky molecules expected to be greatly destabilized by steric crowding. Herein, through a combined experimental and computational approach, we evaluate the molecular energetics of crowded biphenyls. This is complemented by the study of phase equilibria for 1 and 2. Compound 1 shows a rich phase behavior, displaying an unusual interconversion between two polymorphs. Surprisingly, the polymorph with distorted molecules of C-1 symmetry is found to have the highest melting point and to be the one that is preferentially formed. The thermodynamic results also indicate that the polymorph displaying the more regular D-2 molecular geometry has larger heat capacity and is probably the more stable at lower temperatures. The melting and sublimation data clearly reveal the weakening of cohesive forces in crowded biphenyls due to the lower molecular surface area. The experimental quantification of the intramolecular interactions in 1 and 2 indicated, using homodesmotic reactions, a molecular stabilization of about 30 kJ mol(-1). We attribute the origin of this stabilization in both compounds to the existence of two parallel-displaced pMIDLINE HORIZONTAL ELLIPSISp interactions between the ortho-phenyl substituents on each side of the central biphenyl. Computational calculations with dispersion-corrected DFT methods underestimate the stabilization in 1, unless the steric crowding is well balanced in a homodesmotic scheme. This work demonstrates that London dispersion forces are important in crowded aromatic systems, making these molecules considerably more stable than previously thought.

Abstract Perovskite solar cells (PSCs) have emerged as a promising technology for renewable energy generation due to their low cost and low carbon footprint compared to traditional silicon-based solar cells. However, some main challenges associated with PSCs lie ahead, namely their toxicity and lack of stability, particularly under factors such as light, temperature, oxygen, and humidity. This review focuses on the lack of stability of PSCs and the various ways it can be mitigated. We explore different methodologies, solution and vapor based, and different strategies for PSC production and enhancing. Furthermore, the potential of ionic liquids (ILs) as promising materials for improving the stability and performance of PSCs is highlighted. ILs have advantageous physicochemical properties that make them suitable as an additive or interfacial layer in PSCs. They optimize the interface contact, improve energy level matching, suppress ion migration, and increase hydrophobicity, which inhibits the decomposition of the device in humid environments. ILs have also been used as precursors in the solution-based fabrication of perovskite thin films for PSC applications, assisting in the perovskite crystallization. Several studies have shown that the incorporation of ILs in PSCs can increase stability, lifetime, and efficiency. The existing research indicates that ILs hold great promise as materials for improving the stability and performance of PSCs, which could have significant implications for the development of low-cost, renewable energy technologies. © 2023, Universidade do Porto - Faculdade de Engenharia. All rights reserved.

Abstract Shake flask cultivation is a routine technique in microbiology and biotechnology laboratories where cell growth can be affected by the hydrodynamic conditions, which depend on the agitation velocity, shaking diameter, and shake flask size. Liquid agitation is implemented inherently to increase aeration, substrate transfer to the cells, and prevent sedimentation, disregarding the role of hydrodynamics in microbial growth and metabolism. Here, we present a simple approach to help standardize the hydrodynamic forces in orbital shakers to increase the experimental accuracy and reproducibility and give students a better knowledge of the significance of the agitation process in microbial growth.

Abstract Evaluationof the sustainability of using vineyard pruningwaste extracts as natural additives for biodiesel production is discussed,along with comparative impacts with butylated hydroxytoluene. The control of the oxidative stability of biodiesel andblendsof biodiesel with diesel is one of the major concerns of the biofuelindustry. The oxidative degradation of biodiesel can be acceleratedby several factors, and this is most critical in the so-called secondgeneration biodiesel, which is produced from low-cost raw materialswith lower environmental impacts. The addition of antioxidants isimperative to ensure the oxidative stability of biodiesel, and theseare considered products of high commercial value. The antioxidantscurrently available on the market are from synthetic origin, so theexistence/availability of alternative antioxidants of natural origin(less dependent on fossil sources) at a competitive price presentsitself as a strong business opportunity. This work describes and characterizesa sustainable alternative to synthetic antioxidants used in the biodieselmarket developed from extracts of vineyard pruning waste (VPW), whichare naturally rich in phenolic compounds with antioxidant properties.A hydrothermal extraction process was applied as a more efficientand sustainable technology than the conventional one with the potentialof the extracts as antioxidant additives in biodiesel evaluated inRancitech equipment. The VPW extract showed comparable antioxidantactivity as the commercial antioxidant butylated hydroxytoluene (BHT)typically used in biodiesel. The stability of the biodiesel is dependentfrom the amount of the extract added. Further, for the first time,the assessment of the environmental impacts of using natural extractsto control the oxidative stability of biodiesel in the productionprocess is also discussed as a key factor of the process environmentalsustainability.

Abstract Microdroplets and thin films of imidazolium-based ionic liquids (ILs) of different sizes and shapes were used as confining agents for the formation of high-quality perylene crystals by vapor deposition. The role of ILs to control the nucleation and subsequent crystal growth of perylene was investigated by sequential and simultaneous depositions of both materials using indium tin oxide (ITO) as the underlying substrate. The deposition of ILs onto the perylene film surface led to the formation of a complete 2D wetting layer, followed by island growth. Higher adhesion and affinity were found for longer-chain ILs. Inverting the deposition order, the perylene microcrystals were found to grow via the ILs droplets. Additionally, the nucleation and growth of perylene monocrystals enhanced the coalescence mechanisms of the ILs droplets. This wetting process was especially evident for longer-chain ILs. The deposition of perylene onto ITO surfaces fully covered with coalesced ionic liquid films led to the formation of a perylene film with the highest homogeneity as the result of a decrease in surface mobility. The co-deposition of perylene and ILs emphasized the potential application of ILs as crystallization solvents for the formation of thin organic films with improved crystalline quality without compromising the optoelectronic properties.

Abstract Currently, copper is approved as an active substance among plant protection products and is considered effective against more than 50 different diseases in different crops, conventional and organic. Tomato has been cultivated for centuries, but many fungal diseases still affect it, making it necessary to control them through antifungal agents, such as copper, making it the primary form of fungal control in organic farming systems (OFS). The objective of this work was to determine whether exogenous copper applications can affect AOX mechanisms and nitrogen use efficiency in tomato plant grown in OFS. For this purpose, plants were sprayed with 'Bordeaux' mixture (SP). In addition, two sets of plants were each treated with 8 mg/L copper in the root substrate (S). Subsequently, one of these groups was also sprayed with a solution of 'Bordeaux' mixture (SSP). Leaves and roots were used to determine NR, GS and GDH activities, as well as proline, H2O2 and AsA levels. The data gathered show that even small amounts of copper in the rhizosphere and copper spraying can lead to stress responses in tomato, with increases in total ascorbate of up to 70% and a decrease in GS activity down to 49%, suggesting that excess copper application could be potentially harmful in horticultural production by OFS.

Abstract In the last 60 years, auxinic herbicides like 2,4-dichlorophenoxyacetic acid (2,4-D) have been among the widest and successful herbicides used in agriculture because it is a selective herbicide that kills dicots and mimics the natural plant phytohormone indol-3-acetic acid (IAA) at the molecular level. In spite of industry attempts to reformulate 2,4-D-based herbicides and reduce their off-target movement, damage has been reported on sensitive plants, like tomato, at low ratesdi. Therefore, it is important to study the responses of such species to such conditions so that yield losses can be avoided or, at least, reduced. It is known that ethylene, abscisic acid (ABA) and reactive oxygen species (ROS) play a central role in 2,4-D toxicity, leading to numerous unbeneficial changes in plant tissues. Yet, how glutathione-related defense-and/or stress-related genes' expressions are affected needs to be more studied. In this study, tomato plants (Solanum lycopersicum L.) were used to determine the expression and participation of the different GST phi class gene family members, plus the plans' antioxidant system, in response to 2,4-D. When tomato plants were root-treated with 2.26 mM 2,4-D for 48 h, H2O2 and O2 & BULL; levels increased in shoots. Contrarily, in roots, 2,4-D did not provoke clear symptoms of oxidative stress, as lipid peroxidation, H2O2 and O2 & BULL; levels decreased. Despite the difference in ROS levels observed in both organs, the exposure of tomato plants to 2,4-D lead to the activation of key antioxidant enzymes in both organs, apart from superoxide dismutase (SOD), whose activity increased only in roots, while ascorbate peroxidase (APX) and catalase (CAT) activities increased in both. Also, tomato plants responded to 2.26 mM 2,4-D by increasing Ascorbate (AsA) levels in both organs while an increase in Glutathione (GSH) was only observed in shoots. The herbicide increased both the synthesis and the regeneration of GSH, as well as its usage to conjugate 2,4-D, as shoot & gamma;-glutamyl-cysteinyl synthetase (& gamma;-ECS), glutathione reductase (GR) and glutathione S-transferase (GST) activities increased. Shoot GST increased activity was due to an increased expression of SlGSTF4 and SlGSTF5, while no SlGSTFs increased their expression in roots. Shoots and roots of tomato plants were differentially affected by 2.26 mM 2,4-D, with 2,4-D detoxification occurring predominantly in leaves, with the specific participation of the GST phi class members SlGSTF4 and SlGSTF5. Also, this study reinforces the notion that the cultivation of tomato in 2,4-D-contaminated soils may result in yield reduction.

Abstract Isothermal titration calorimetry (ITC) has become the gold standard for studying molecular interactions in solution. Although it is increasingly being used in the soft matter and synthetic chemistry fields, ITC is most widely used for characterizing molecular interactions between ligands and macromolecules. This Primer starts by presenting the technique's foundations and instrumentation, including a brief description of the standard assay, followed by a review of common applications. Further extensions and modifications of the technique are explored. These adaptations enable key features to be studied, such as cooperative effects associated with complex biological interactions and their regulation, alongside applications to other fields, including partition to membranes, kinetics and soft matter. Advantages and caveats in ITC are discussed, with a focus on best practices, instrument calibration, experimental design, data analysis and data reporting, as well as recent and future developments.