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Projeto de investigação
Coimbra Chemistry Center
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Acenaphthylene-Based Chromophores for Dye-Sensitized Solar Cells
Publication . Malta, Gabriela; Pina, João; Lima, J. Carlos; Parola, A. Jorge; Branco, Paula S.; DQ - Departamento de Química; LAQV@REQUIMTE; ACS - American Chemical Society
A set of acenaphthylene dyes with arylethynyl π-bridges was tested for dye-sensitized solar cells (DSSCs). Crucial steps for the extension of the conjugated system from the acenaphylene core involved Sonogashira coupling reactions. Phenyl, thiophene, benzotriazole, and thieno-[3,2-b]thiophene moieties were employed to extend the conjugation of the π-bridges. The systems were characterized by cyclic voltammetry and by UV-vis absorption and emission. The spectroscopic characterization showed that the last three bridges resulted in red-shifted absorption and emission spectra relative to the parent phenyl-bridged compound, in accordance with TD-DFT calculations. The phenylethynyl derivative 6a achieved a conversion efficiency of 2.51% with Voc, Jsc, and FF values of 0.365 V, 13.32 mA/cm2, and 0.52, respectively. The efficiency of this compound improved to 3.15% with the addition of CDCA (10 mM), representing the best efficiency result in this study.
Elucidating the concentration-dependent effects of thiocyanate binding to carbonic anhydrase
Publication . Silva, José Malanho; Cerofolini, Linda; Carvalho, Ana Luísa; Ravera, Enrico; Fragai, Marco; Parigi, Giacomo; Macedo, Anjos L.; Geraldes, Carlos F. G. C.; Luchinat, Claudio; UCIBIO - Applied Molecular Biosciences Unit; DQ - Departamento de Química; Elsevier
Many proteins naturally carry metal centers, with a large share of them being in the active sites of several enzymes. Paramagnetic effects are a powerful source of structural information and, therefore, if the native metal is paramagnetic, or it can be functionally substituted with a paramagnetic one, paramagnetic effects can be used to study the metal sites, as well as the overall structure of the protein. One notable example is cobalt(II) substitution for zinc(II) in carbonic anhydrase. In this manuscript we investigate the effects of sodium thiocyanate on the chemical environment of the metal ion of the human carbonic anhydrase II. The electron paramagnetic resonance (EPR) titration of the cobalt(II) protein with thiocyanate shows that the EPR spectrum changes from A-type to C-type on passing from 1:1 to 1:1000-fold ligand excess. This indicates the occurrence of a change in the electronic structure, which may reflect a sizable change in the metal coordination environment in turn caused by a modification of the frozen solvent glass. However, paramagnetic nuclear magnetic resonance (NMR) data indicate that the metal coordination cage remains unperturbed even in 1:1000-fold ligand excess. This result proves that the C-type EPR spectrum observed at large ligand concentration should be ascribed to the low temperature at which EPR measurements are performed, which impacts on the structure of the protein when it is destabilized by a high concentration of a chaotropic agent.
Novel organotin-PTA complexes supported on mesoporous carbon materials as recyclable catalysts for solvent-free cyanosilylation of aldehydes
Publication . Mahmoud, Abdallah G.; Librando, Ivy L.; Paul, Anup; Carabineiro, Sónia A. C.; Ferraria, Ana Maria; Botelho do Rego, Ana Maria; Guedes da Silva, M. Fátima C.; Geraldes, Carlos F. G. C.; Pombeiro, Armando J. L.; LAQV@REQUIMTE; DQ - Departamento de Química; Elsevier
New organotin compounds with general formula [(PTA-CH2-C6H4-p-COO)SnR3]Br (where R is Me for 3 and Ph for 4; PTA = 1,3,5-triaza-7-phosphaadamantane), bearing the methylene benzoate PTA derivative, were synthesized through a mild two-step process. The compounds were characterized by Fourier transform infrared spectroscopy, electrospray ionization mass spectrometry, elemental analysis and nuclear magnetic resonance spectroscopy (NMR). They were heterogenized on commercially available activated carbon (AC) and multi-walled carbon nanotubes (CNT), as well as on their chemically modified analogues. The obtained materials were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Complex 3 supported on activated carbon (3-AC) was found to be an active and recyclable catalyst for the cyanosilylation of several aromatic and aliphatic aldehydes. Using 3-AC with a low loading of 0.1 mol% several substrates were quantitatively converted, within just 5 min at 50 °C and under microwave irradiation in solvent-free conditions. Multinuclear NMR analysis suggested a mechanism that potentially involves a double activation process, where the nucleophilic phosphorus at the PTA derivative acts as a Lewis base and the Sn(IV) metal centre as a Lewis acid.
Triazaphosphaadamantane-functionalized terpyridine metal complexes
Publication . Librando, Ivy L.; Paul, Anup; Mahmoud, Abdallah G.; Gurbanov, Atash V.; Carabineiro, Sónia A. C.; Silva, M. Fátima C. Guedes da; Geraldes, Carlos F. G. C.; Pombeiro, Armando J. L.; LAQV@REQUIMTE; DQ - Departamento de Química; RSC - Royal Society of Chemistry
In accordance with UN's Sustainable Development Goal (UN's SDG) 12 which encompasses the sustainable use of chemical products and a sound circular economy, this work is focused on the synthesis of Co(II), Ni(II) and Mn(II) complexes bearing combined 1,3,5-triaza-7-phosphaadamantane and benzyl terpyridine core moieties (PTA–Bztpy) as ligand, followed by their evaluation as catalysts for the microwave-assisted cyclohexane oxidation using tert-butyl hydroperoxide (TBHP) as oxidant. The most active catalyst, with a manganese metal center, was heterogenized on six different carbon materials. The results disclosed the influence of several reaction parameters, such as catalyst loading, temperature, reaction time and solvent, on the catalytic activity and selectivity of the homogeneous and carbon-supported catalysts. Recyclability of the carbon-supported catalyst allowed facile separations, recovery and reuse for five consecutive cycles.
Exploring the impact of structural rigidification of amino-substituted bio-inspired flavylium dyes in DSSCs
Publication . Pinto, Ana Lúcia; Máximo, Patrícia; Pina, João; Calogero, Giuseppe; Laia, César A. T.; Parola, A. Jorge; Lima, J. Carlos; LAQV@REQUIMTE; DQ - Departamento de Química; Elsevier
Sharing with anthocyanins the 2-phenyl-1-benzopyrylium structural motif, flavylium derivatives are strongly colored bio-inspired dyes that have been explored in dye-sensitized solar cells (DSSCs). Following on the fact that the most efficient flavylium-based dyes for DSSCs require amine electron-donating groups, a diethylamino group and the corresponding rigidified julolidine group were introduced in the benzopyrylium core. This structural variation was combined with another structural parameter – increased planarization of the flavylium ring system – to yield four flavylium derivatives all with a catechol anchoring group. The several pKa values of the new dyes and the UV–vis absorption data at different pH values and upon adsorption to TiO2 (corroborated by TD-DFT calculations) demonstrate a stronger delocalization of the nitrogen lone pair in the julolidine systems when compared to the diethylamino ones, reflecting the stronger electron-donating ability of the former. However, the julolidine-based dyes resulted in a decrease in all DSSC parameters, with efficiencies of 0.6% vs. 2.3% for the diethylamino devices. Discarding eventual increased self-aggregation processes of the more planar julolidine derivatives through studies with a de-aggregating agent (CDCA), and determining comparable dye loadings for all dyes, the presence of increased back-electron transfer processes for the julolidine-based compounds is advanced to explain their lower efficiencies. Rigidification of the flavylium dyes by bridging the benzopyrylium and the phenyl rings is demonstrated by higher fluorescence quantum yields and by electrochemical data and leads to a slight increase in the efficiency of the respective DSSCs. The results contribute to consolidate the potential of flavylium dyes as sensitizers for DSSCs.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UIDB/00313/2020