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- Electroepoxidation of natural and synthetic alkenes mediated by sodium bromidePublication . Inês, Massuquinini; Mendonça, António; Esteves, Ana P.; Mendonça, Dina; Medeiros, Maria J.Electroepoxidation of synthetic alkenes (styrene, trans-stilbene and trans-b-methylstyrene) and of some natural terpenes (limonene, terpinolene, geraniol, a-terpinene, g-terpinene and a-terpineol) mediated by sodium bromide was performed in MeCN:H2O (4:1) at platinum electrodes. The indirect electrochemical oxidation of the olefins led to the corresponding epoxides in yields ranging from 23% to 79%.
- Kolbe Electrosynthesis of 1,2-Di(bicyclo[2.2.1]heptan-2-yl)ethane and 1,2-DiphenylethanePublication . Mendonça, António; Inês, Massuquinini; Esteves, Ana P.; Mendonça, Dina; Medeiros, Maria J.Kolbe electrosynthesis, at low current densities, of 1,2-diphenylethane and 1,2-di(bicyclo[2.2.1]heptan-2-yl)ethane with 77 and 72% yields, respectively, is described.
- Activity coefficients in the evaluation of food preservativesPublication . Mendonça, António; Vaz, Margarida I. P. M.; Mendonça, DinaFood preservatives are used in very low concentrations. However, usually they are used in aqueous high ionic strength solutions. The Pitzer model allows activity coefficient determination in these cases. Without the knowledge of activity coefficients, activity or ‘correct concentration’ cannot be known. In this work, the activity coefficients of sodium chloride, potassium chloride and calcium chloride in pure solutions were calculated by the Debye H¨uckel theory and the Pitzer theory. The calculated values were compared with experimental values. Activity coefficients of pure sodium benzoate in aqueous mixed solutions with potassium chloride or calcium chloride were evaluated using the Pitzer model. The same evaluation can be done to more complex systems once all Pitzer parameters values for the ionic species are known.
- New neo-Clerodanes fromTinnea antiscorbutica WelvPublication . Borges, Cristina M. P.; Mendonça, Dina; Pinheiro, Sandra C. S.; Vieira, Liliana; Mendonça, António; Gaspar, Jorge F.; Martins, Célia; Diakanamwa, Carlos; Rueff, JoséThree new neo-clerodanes, antiscorbuticane A, antiscorbuticane B and antiscorbuticane C, and known compounds glutinol, friedelin, 5,7-dihydroxyflavanone (pinocembrin), 5-hydroxy-3,6,7,4'-tetramethoxyflavone, 5-hydroxy-3,6,7,3',4'-pentamethoxyflavone (artemetin), 5,4'-dihydroxy-3,6,7,3'-tetramethoxyflavone (penduletin) and 5,3',4'-trihydroxy-3,6,7-trimethoxyflavone (chrysosplenol D), were isolated from the methanol extract of Tinnea antiscorbutica. Antiscorbuticane B exhibited no mutagenic activity at doses of up to 250 µg per plate (Ames test) and did not induce micronucleus formation in the V79 cell line at doses of up to 100 µg /mL.
- Three New Labdanes Isolated from Eragrostis viscosaPublication . Sebastião, N'Soki; Fernandes, Nelson; Vieira, Liliana; Mendonça, António; Gaspar, Jorge; Martins, Célia; Rueff, José; Diakanamwa, Carlos; Mendonça, DinaThree new labdanes with 8α,15-epoxy ring [methyl 8α,15-epoxylabdan-16β-oate, 8α,15-epoxylabdan-16β-ol and 8α,15-epoxy-16-norlabdan-13β-ol] and five known compounds [8α,15-epoxy-16-norlabdan-13-one, 8α,15-epoxylabdan-16β-oic acid, 3β-(3'',4''-dihydroxy)(E)-cinnamoyloxylup-20(29)-ene, 3-(2',3',4',6'-tetra-O-acetyl-β-D-glucopyranosyloxy)β-sitosterol and 16-acetoxy-8α,15-epoxylabdane] were isolated from toluene and dichloromethane extracts of aerial parts of Eragrostis viscosa. The structures of all the compounds were established based on their spectroscopic data and X-ray diffraction analysis of 8α,15-epoxylabdan-16β-ol. It was also studied the genotoxicity of E. viscosa, particularly compounds 16-acetoxy-8α, 15-epoxylabdane, 8α,15-epoxy-16-norlabdan-13-one and 8α, 15-epoxilabdan-16β-ol, using a cytokinesis-block micronucleus assay and the Ames test to assess mutagenicity. Both assays were negative. Cytotoxicity was also analyzed using an MTT assay, and 8α,15-epoxy-16β-ol was shown to be the most cytotoxic of the compounds tested. E. viscosa extracts were also tested to determine their antioxidant capacities, peroxide values and total phenolic contents.