Browsing by Author "Diniz, Ana Marta"
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- Challenges in teaching organic chemistry remotelyPublication . Crucho, Carina; Avó, João; Diniz, Ana Marta; Gomes, MárioThe coronavirus disease (COVID-19) pandemic has changed not only people’s daily lives but also the education system. The rise of e-learning all across the world has challenged both students and teachers to adapt to digital technologies and a novel learning experience on both sides. As if COVID-19 was not enough, many students were facing the alien territory of organic chemistry for the first time. There is no denying that organic chemistry is a tough subject, and several students may also have preconceived misconceptions. In addition, organic chemistry can be challenging to teach remotely. It is very abstract in nature; it involves many concepts, and the teacher typically uses molecular models of one kind or another to depict molecules in three dimensions. Nonetheless, challenges provide an opportunity to implement new strategies to increase students’ interest, motivation, and understanding. However, most educators only had a few days to put everything they do in class onto an online platform. In this study, we evaluated the effect of these changes in the teaching and learning of organic chemistry at a first-year undergraduate level. Our results show that student success depends on the digital resources used for the different subjects. Students that received weekly quizzes performed better than those who did not, and a positive correlation exists between quiz scores and final exam marks. Based on the student's feedback, the implementation of quizzes was a successful didactic tool that helped them review the topics. In addition, the incorporation of open-access web-based tools led to a dynamic online classroom experience.
- A photoelectrochemical study of bioinspired 2-styryl-1-benzopyrylium cations on TiO2 nanoparticle layer for application in dye-sensitized solar cellsPublication . Calogero, Giuseppe; Citro, Ilaria; Sebastianella, Gioacchino Calandra; Di Marco, Gaetano; Diniz, Ana Marta; Parola, A. Jorge; Pina, FernandoIn the present work, five 2-styryl-1-benzopyrylium salts and their relative self-assembly processes towards TiO2 nanocrystalline layers were evaluated as photosensitizers in dye-sensitized solar cells (DSSCs). Integration of these 2-styryl-1-benzopyrylium salts with the semiconductor allow for the performance of highly specific functions suitable for smart applications in material science. Spectroscopic and photoelectrochemical measurements conducted on these five bio-inspired dyes, in solution and upon adsorption onto titanium dioxide films, allowed detailed discussion of the anchoring ability of the different donor groups decorating the 2-styryl-1-benzopyrylium core and have demonstrated their ability as photosensitizers. Our results suggest that the introduction of a dimethylamino group in position 4' of the 2-styryl-1-benzopyrylium skeleton can alter the conjugation of the molecule leading to larger absorption in the visible region and a stronger electron injection of the dye into the conduction band of TiO2. Moreover, our experimental data have been supported by theoretical calculations with the aim to study the energy of the excited states of the five compounds. In this specific case, the simulations reported contributed to better describe the properties of the compounds used and to help create the necessary basis for the design of new and targeted bio-inspired molecules.
- A pseudorotaxane formed from a cucurbit[7]uril wheel and a bioinspired molecular axle with pH, light and redox-responsive propertiesPublication . Seco, André; Diniz, Ana Marta; Sarrato, João; Mourão, Henrique; Cruz, Hugo; Parola, A. Jorge; Basílio, NunoA pH-, light- and redox-responsive flavylium-bipyridinium molecular dyad (bioinspired in natural anthocyanins) were synthesized and employed to devise a pseudorotaxane with the macrocycle cucurbit[7]uril (CB7) in aqueous solution. The inclusion complex was characterized by UV-Vis absorption, fluorescence emission, NMR, and electrochemical techniques which demonstrate the formation of a stable binary complex between the dyad and CB7 both under acidic and neutral conditions. It is noteworthy that the flavylium-bipyridinium tricationic dyad is only stable in highly acidic media, undergoing a reversible hydration reaction at slightly acidic or neutral pH to give a trans-chalcone-bipyridinium dication. 1H NMR experiments showed that in this last species the CB7 binds to the bipyridinium unit while in the tricationic species the macrocycle is positioned between the flavylium and the bipyridinium moieties. The different location of the CB7 wheel in the two dyad states allows control of the shuttling movement using light and pH stimuli that trigger the interconversion between these two species.
- Spatiotemporal control over the co-conformational switching in pH-responsive flavylium-based multistate pseudorotaxanesPublication . Diniz, Ana Marta; Basílio, Nuno; Cruz, Hugo; Pina, Fernando; Parola, A JorgeA multistate molecular dyad containing flavylium and viologen units was synthesized and the pH dependent thermodynamics of the network completely characterized by a variety of spectroscopic techniques such as NMR, UV-vis and stopped-flow. The flavylium cation is only stable at acidic pH values. Above pH ≈ 5 the hydration of the flavylium leads to the formation of the hemiketal followed by ring-opening tautomerization to give the cis-chalcone. Finally, this last species isomerizes to give the trans-chalcone. For the present system only the flavylium cation and the trans-chalcone species could be detected as being thermodynamically stable. The hemiketal and the cis-chalcone are kinetic intermediates with negligible concentrations at the equilibrium. All stable species of the network were found to form 1 : 1 and 2 : 1 host : guest complexes with cucurbit[7]uril (CB7) with association constants in the ranges 10(5)-10(8) M(-1) and 10(3)-10(4) M(-1), respectively. The 1 : 1 complexes were particularly interesting to devise pH responsive bistable pseudorotaxanes: at basic pH values (≈12) the flavylium cation interconverts into the deprotonated trans-chalcone in a few minutes and under these conditions the CB7 wheel was found to be located around the viologen unit. A decrease in pH to values around 1 regenerates the flavylium cation in seconds and the macrocycle is translocated to the middle of the axle. On the other hand, if the pH is decreased to 6, the deprotonated trans-chalcone is neutralized to give a metastable species that evolves to the thermodynamically stable flavylium cation in ca. 20 hours. By taking advantage of the pH-dependent kinetics of the trans-chalcone/flavylium interconversion, spatiotemporal control of the molecular organization in pseudorotaxane systems can be achieved.