Browsing by Author "Cruz, Hugo"
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- A Busca do Comum – Práticas Artísticas Para Outros Futuros PossíveisPublication . Cruz, Carla; Cruz, Hugo; Bezelga, Isabel; Falcão, Miguel; Aguiar, RamonEsta publicação reúne artigos selecionados – através de revisão cega por pares – decorrentes das apresentações proferidas no III EIRPAC – Encontro Internacional de Reflexão sobre Práticas Artísticas Comunitárias 2019, realizado de 16 a 18 de setembro na Faculdade de Belas Artes da Universidade do Porto, em Portugal, no contexto do MEXE – Encontro Internacional de Arte e Comunidade. Os textos, de acordo com as opções dos/as autores/as, apresentam-se escritos em Português de Portugal (com ou sem acordo ortográfico), Português do Brasil, Castelhano ou Inglês.
- 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.