M. Dulce Geraldo

The reduction of styrene at microelectrodes in toluene + N,N-dimethylformamide mixtures

The steady state voltammetry of styrene at Au microdisc electrodes has been investigated in toluene + DMF mixtures as a function of the solvent composition, electrolyte and substrate concentrations and the data compared with that for ferrocene. The experimental data for styrene reveal changes in wave shape and small shifts in half-wave potential not shown by equivalent experiments with ferrocene, and the interpretation of these differences is discussed. The results confirm that the voltammetric response for styrene is a reliable basis for electroanalytical determinations in these media.

Antimicrobial and antioxidant properties of propolis ethanol extracts from Terceira Island (Azores, Portugal)

Bees produce a resinous mixture named propolis known to have several functions in the beehive, namely structural and sanitary [1,2]. Propolis presents a rich and complex chemical composition, imparted from the several plant materials collected, and several compounds and extracts have been associated with biological activities of high interest [3]. This study focuses on the antimicrobial activity and antioxidant capacity of ethanolic extracts (EE) obtained from propolis samples collected in 2010, in five different areas of the Terceira Island (Azores Archipelago). Antimicrobial activity was evaluated by dilution assay incorporating different EE concentrations in solid media. Bacteria and yeasts of clinical and agrofood relevance were used as indicators of susceptibility. The results showed that Gram-positive bacteria displayed more resistance (best MIC value 200 μg/ml) than the Gram-negative (100 μg/ml). Extracts with higher antibacterial activity (e.g. EE4 and EE5) were generally distinct from those with greater activity against yeast (EE1), but species-specific susceptibilities and extract-specific efficacies against particular microorganisms were also observed, only EE1 was effective against S. epidermidis. A relationship between propolis macroscopic characteristics (colour, hardness and odour) and its antifungal activity was noticed. If confirmed for a broader range of samples, this relationship may constitute an important diagnostic tool. The antioxidant capacity was assessed using cyclic voltammetry [4]. EE4 and EE5 showed the highest antioxidant capacities (39.6 and 23.5 mM eq. gallic acid, respectively), in agreement with results from the antimicrobial assays. Chemical characterization of all EE are underway. Despite being collected in a somewhat confined geographic area propolis samples exhibited diverse antimicrobial activities with different efficiencies and antioxidant capacities.