Browsing by Author "Elvas-Leitao, Ruben"
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- Composition and in vitro antioxidants activity of Chamaerops Humilis L.Publication . Coelho, Jose P.; Veiga, Jerson G.; Elvas-Leitao, Ruben; Brigas, Amadeu; Dias, Ana M.; Oliveira, Maria C.; Morgado, M.; Bernardes, R.; Amador, M.; Afonso, P. M.The aim of this work is to evaluate the polyphenols composition and the antioxidant activity of methanol extracts of Chamaerops humilis L. Methanol extracts from dried leaves of Chamaerops humilis were prepared using Soxhlet extraction and examined as potential sources of phenolic compounds. Different methods were used to evaluate antioxidant activity of the extracts, including colored (ABTS*+), DPPH radical scavenging assay and reducing power. Total phenolic and flavonoid contents of the extracts were evaluated by Folin-Ciocalteu and aluminum chloride (AlCl3) methods, respectively. Phenolic compositions of the methanol extracts were elucidated by high performance liquid chromatography coupled on-line with tandem mass spectrometry (HPLC-MS/MS). The extract was mainly composed of C-and O-flavones and its O-methylated derivatives. The results suggest that methanol extracts have good potential as sources of bioactive compounds and presents an important antioxidants capacity, which can ensures its potential recommendation for application in the pharmaceutical and nutraceutical sectors.
- Kinetic study of Friedel-Crafts acylation reactions over hierarchical MCM-22 zeolitesPublication . Aleixo, Rodrigo; Elvas-Leitao, Ruben; Martins, Filomena; Carvalho, Ana P.; Brigas, Amadeu; Martins, Angela; Nunes, NelsonFriedel-Crafts acylation was studied under mild conditions using hierarchical MCM-22 zeolites prepared by desilication and by desilication + acid treatment, using furan, pyrrole and anisole as substrates, and acetic anhydride as acylating agent. Enhanced catalysis was observed for furan and anisole, especially at short reaction times. Kinetic results modelling using non-linear regressions applied to a simplified Langmuir-Hinshelwood equation showed that desilication treatment followed by acid treatment improved kinetics (higher k and TOF). A QSPR methodology using nine substrate and zeolite descriptors was applied to model kinetics and adsorption. For both processes, the best QSPR model equations lead to the same descriptors, namely, Bronsted acidity, as zeolite's feature, and both van der Waals volume and Dimroth-Reichardt E-T(N) parameter (related to dipolarity and Lewis acidity) as substrates' characteristics. Normalization of descriptors allowed quantification of each descriptor's relative importance leading to a better understanding of the catalytic and adsorption processes. (C) 2017 Elsevier B.V. All rights reserved.
- Zooming in with QSPR on Friedel-Crafts acylation reactions over modified BEA zeolitesPublication . Aleixo, Odrigo; Elvas-Leitao, Ruben; Martins, Filomena; Carvalho, Ana P.; Brigas, Amadeu; Nunes, Ricardo; Fernandes, Auguste; Rocha, Joao; Martins, Angela; Nunes, NelsonThe catalytic behaviour of hierarchical BEA zeolites with Si/Al ratio of 12.5 and 32 was studied in Friedel-Crafts acylation reactions using furan, anisole and pyrrole as substrates and acetic anhydride as acylating agent. Hierarchical BEA samples were submitted to alkaline and alkaline + acid treatments. Kinetic modelling using nonlinear regressions applied to a simplified Langmuir-Hinshelwood equation showed that the Si/Al ratio of the parent materials strongly influenced the catalytic behaviour. Catalytic results were correlated with physicochemical properties using a Quantitative Structure-Property Relationship (QSPR) methodology. This approach provided detailed information about the role of key properties on the catalytic behaviour, and pointed out which properties should be modified through direct synthesis and/or post-synthesis treatments to obtain materials with optimized catalytic performance.