Browsing by Author "Freire, Cristina"
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- Antioxidant activity of Agaricus sp mushrooms by chemical, biochemical and electrochemical assaysPublication . Barros, Lillian; Falcão, Soraia; Baptista, Paula; Freire, Cristina; Vilas-Boas, Miguel; Ferreira, Isabel C.F.R.The antioxidant activity of five Agaricus sp. mushrooms was screened through chemical, biochemical and electrochemical techniques. The chemical assays allowed an evaluation of their reducing power and radical scavenging activity, while biochemical assays evaluated the lipid peroxidation inhibition capacity, using erythrocytes and brain cells as models; the electrochemical characterization of the mushrooms extracts were performed by cyclic voltammetry and differential pulse voltammetry. All the species proved to have antioxidant activity and particularly, by the electrochemical techniques, it has been shown that mushroom extracts revealed similar electrochemical responses, suggesting similar electroactive chemical composition, and oxidation potentials more positive than those of the standards (ascorbic and gallic acids). Agaricus silvaticus was the most efficient species presenting the lowest EC50 values in the chemical and biochemical assays, and the highest "antioxidant power" in the electrochemical assays.
- Characterization of new phenolic derivatives in Portuguese propolis by electrospray mass spectroscopyPublication . Falcão, Soraia; Vilas-Boas, Miguel; Freire, Cristina; Domingues, Maria R.M.; Cardoso, Susana M.Propolis is a resinous substance collected by honeybees from tree buds, comprising plant exudates, secreted substances from bee metabolism, pollen and waxes. This product is widely used in traditional medicine [I] and it has recently gained popularity as a health food supplement. Currently, it is extensively used in foods and beverages, and it is claimed to improve health and prevent diseases such as inflammation, heart disease, diabetes and cancer.
- Characterization of new phenolic derivatives in Portuguese propolis by electrospray mass spectroscopyPublication . Falcão, Soraia; Vilas-Boas, Miguel; Freire, Cristina; Domingues, Maria R.M.; Cardoso, Susana M.This research outlines an extensive characterization of the phenolic composition of a propolis sample from the northeast of Porto gal. For that, ao ethanolic extract was prepared, fractionated by HPLC and the identification of the phenolic compounds was done by electro spray mass spectrometry in the negative mode. This technical approach allowed the identification of 37 phenolic compounds in the Portoguese propolis sample, including seven that were described for the first time. Two of these new compounds had [M-Hr ions at mlz 403, aod the others had [M-Hr ions at mlz 433, mlz 461, mlz 417, mlz 475, and mlz 565. In general, the molecular weight of these compounds was higher thao the common phenolic compounds of propolis aod their fragmentation pattern suggested that they belong to the flavonoid family probably lioked with a phenylpropanoic acid moiety in the position C5 (mlz 403, 433, 461, 475) and C3 (mlz 403, 417), corresponding to pinocembrio and pinobaoksin derivatives. The ion at mlz 565 seems to be a p-counlaric ester derivative dimer.
- A combined electrochemical quartz-crystal microbalance probe beam deflection (EQCM-PBD) study of solvent and ion transfers at a poly[Ni(saltMe)]: modified elecrode during redox switchingPublication . Vilas-Boas, Miguel; Henderson, Mark J.; Freire, Cristina; Hillman, A. Robert; Vieil, EricThe oxidative polymerization of the complex2,3-dimelhyl-N,N-bis( salicylidene)butane-2,3-diaminatonickel( n), [Ni(saltMe)], was monitored by the electrochemical quartz microbalance (EQCM) and crystal impedance techniques. Polymerisation efficiency was maintained throughout deposition of a film, which behaved rigidly, on the electrode.
- Development of natural sporopollenin microcapsules: from bee pollen to versatile biomaterialsPublication . Aylanc, Volkan; Ertosun, Seymanur; Peixoto, Andreia F.; Santamaria-Echart, Arantzazu; Russo-Almeida, Paulo; Vale, Nuno; Freire, Cristina; Vilas-Boas, MiguelThe outer layer of the pollen grain, which plays a crucial role in the continuity of terrestrial plant life, has received significant attention due to its robustness, chemical inertness, and biocompatible structure made of sporopollenin. Herein, we present a straightforward method for producing high-purity (up to 97%) polymeric sporopollenin biocapsules (S-BioCaps) from bee pollen, exploring new plant sources for S-BioCaps, and diversifying the available morphologies to broaden the applications of pollen-based microcapsules. Following a purification process involving defatting, acidolysis, and several washing steps, we removed the inner components of the pollen grains and reduced the protein content to 2%. Confocal laser scanning and scanning electron microscopy images showed that the hollow and 3D S-BioCaps microstructure were preserved, while laser diffraction particle size analysis validated their monodisperse distribution across each pollen type within the size range of 15 to 24 μm. S-BioCaps tended to exhibit hydrophobic behavior when assessed through water dispersion and water marble analysis. Moreover, we sought to figure out the chemical changes occurring in specimens through Fourier-transform infrared analysis, and findings were consistent with simultaneous thermal analysis, where the thermal decomposition of sporopollenin biopolymer reached up to 457 °C. Overall, this work demonstrates a straightforward approach for utilizing pollen grains from Echium sp., Jasione sp., Papaver sp., Amaranthaceae, and Helianthemum sp., collected with the assistance of honeybees, to produce stable S-BioCaps with diverse morphologies, thereby broadening their potential applications as drug delivery microcarriers.
- Electrochemical and structural studies of nickel (II) Schiff base complexes derived from salicylaldehyde. Structural effects of bridge substituents on the stabilisation of the +3 oxidation statePublication . Santos, Isabel C.; Vilas-Boas, Miguel; Piedade, M.F.M.; Freire, Cristina; Duarte, M.T.; Castro, Baltazar deThe oxidative chemistry of three Ni(II) complexes with Schiff base ligands derived from salicylaldehyde and diamines with different steric demands, N,N9-2-methylpropane-2,3-diyl-bis(salicylideneiminate)nickel(II) (1), N,N9-1,2-cyclohexyl-1,2-dyil-bis(salicylideneiminate)- nickel(II) (2) and N,N9-2,3-dimethylbutane-2,3-diyl-bis(salicylideneiminate)nickel(II) (3), was studied by cyclic voltammetry and chronoamperometry in N,N9-dimethylformamide and (CH3)2SO.
- Electrochemical behavior of a new precursor for the design of poly[Ni(salen)]-based modified electrodesPublication . Vilas-Boas, Miguel; Santos, Isabel C.; Henderson, Mark J.; Freire, Cristina; Hillman, A. Robert; Vieil, EricWedescribe the potentiodynamic preparation and subsequent characterization of poly[Ni(3-MeOsaltMe)] films (surface concentration, 3 < ¡/nmol cm-2 < 350) in acetonitrile media. Coulometric and gravimetric (electrochemical quartz crystal microbalance, EQCM) data allow one to monitor the deposition process and show that the resultant films are physically and chemically stable.
- Electrochemical characterization of a novel salen type modified electrodePublication . Vilas-Boas, Miguel; Freire, Cristina; Castro, Baltazar de; Hillman, A. RobertThe nickel(II) complex with H2saltMe, a N2O2 Schiff base ligand derived from salicylaldehyde, was oxidatively electropolymerized on Pt electrodes in CH3CN/0.1 mol dm-3 tetraethylammonium perchlorate (TEAP) to generate polymer films that exhibit reversible oxidative electrochemical behavior in a wide potential range (0.0-1.3 V), high conductivity, and stability/durability.
- Evaluation of the antioxidant capacity of edible wild mushrooms by cyclic voltammetryPublication . Falcão, Soraia; Barros, Lillian; Ferreira, Isabel C.F.R.; Freire, Cristina; Vilas-Boas, MiguelThe problems of oxygen metabolism in humans constantly attract the attention. especially now that is obvious that the excess of oxygen and its reactive species cause radical-chain oxidation processes in cellular tissues, resulting in fast aging, cell destruction and incurable diseases. Cells are equipped with several defense systems which act through a variety of mechanisms, one of those is the protection through low-molecular weight antioxidants. like phenolic compounds
- In vitro evaluation of portuguese propolis and floral sources for antiprotozoal, antibacterial and antifungal activityPublication . Falcão, Soraia; Vale, Nuno; Cos, Paul; Gomes, Paula; Freire, Cristina; Maes, Louis; Vilas-Boas, MiguelPropolis is a beehive product with a very complex chemical composition, used since ancient times in several therapeutic treatments. As a contribution to the improvement of drugs against several tropical diseases caused by protozoa, we screened Portuguese propolis and its potential floral sources Populus x Canadensis and Cistus ladanifer against Plasmodium falciparum, Leishmania infantum, Trypanosoma brucei and Trypanosoma cruzi. The toxicity against MRC-5 fibroblast cells was evaluated to assess selectivity. The in vitro assays were performed following the recommendations of WHO Special Programme for Research and Training in Tropical Diseases (TDR) and revealed moderate activity, with the propolis extracts presenting the relatively highest inhibitory effect against T. brucei. Additionally, the antimicrobial activity against Staphylococcus aureus, Candida albicans, Trichophyton rubrum and Aspergillus fumigatus was also verified with the better results observed against T. rubrum. The quality of the extracts was controlled by evaluating the phenolic content and antioxidant activity. The observed biological activity variations are associated with the variable chemical composition of the propolis and the potential floral sources under study.
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