Electrochemical behavior of dopamine at a 3,3 '-dithiodipropionic acid self-assembled monolayers

Monolayers of 3,3'-dithiodipropionic acid (DTDPA) were prepared on a polycrystalline gold electrode through a self-assembly procedure to produce a gold 3,3'-dithiodipropionic acid self-assembled monolayer (AuDTDPA) modified electrode. The characterization of the AuDTDPA electrode was investigated by cyclic voltammetry and ac impedance using the [Fe(CN)(6)](3-/4-) redox couple. The electrochemical behavior of DA on the modified electrode AuDTDPA was studied by cyclic and square-wave voltammetries, using phosphate buffer as supporting electrolyte. The oxidation peak current for DA increases linearly with concentration in the range of 0.35 x 10(-5) to 3.4 x 10(-5) mol L-1. The performance of the AuDTDPA modified electrode was evaluated for the electroanalytical determination of dopamine (DA) in a pharmaceutical formulation. The AuDTDPA modified electrode showed a stable behavior and the presence of surface-COOH groups avoided the passivation of the electrode surface during the dopamine oxidation. (c) 2006 Elsevier B.V. All rights reserved.72242743

Electrochemical behavior of nicotine studied by voltammetric techniques at boron-doped diamond electrodes

The electrochemical behavior of nicotine in alkaline media was studied using a boron doped diamond (BDD) surface as the working electrode. In order to establish the pH dependence and to gain information about the mass transport of the species, cyclic voltammetry studies were carried out in a 0.1 mol L-1 BR (Britton-Robinson) buffer in the presence of 1.0 x 10(-3) mol L-1 nicotine. The optimum pH value was 8 and the mass transport was controlled by diffusion of the species. The square wave voltammetry technique was used to determine the electroanalytical parameters such as frequency, amplitude, and scan increment. After optimization, an analytical curve was constructed. The limits of detection and quantification were 0.50 and 1.66 mg L-1, respectively. Theoretical calculations indicate that the probable oxidation site on the nicotine molecule was the nitrogen atom denoted "11N" and a speculation about the reaction mechanism was proposed. Finally, an experiment using a real sample (cigarette tobacco) was carried out and a recovery study revealed a value of about 4.3 mg L-1 in 0.1 g of tobacco.38101587159

Antiprotozoal and molluscicidal activities of five Brazilian plants

Leishmaniasis, Chagas' disease and schistosomiasis (bilharzia) are parasitic diseases with wide distribution on the American continent, affecting millions of people. In the present study, biological assays for antiprotozoal and molluscicidal activities were carried out with ethanolic extracts of plant species from the Brazilian part of the Upper Paraná River. Crude extracts were obtained by percolation with absolute ethanol from the leaves of Cayaponia podantha Cogn., Nectandra falcifolia (Nees) Castiglioni and Paullinia elegans Cambess., as well as from the aerial parts of Helicteres gardneriana St. Hil. & Naud. and Melochia arenosa Benth., all belonging to genera used in folk medicine. Trypanocidal activity of plants was assayed on epimastigote cultures in liver infusion tryptose. Anti-leishmanial activity was determined over cultures of promastigote forms of the parasite in Schneider's Drosophila medium. Microscopic countings of parasites, after their incubation in the presence of different concentrations of the crude extracts, were made in order to determine the percentage of growth inhibition. C. podantha and M. arenosa, at a concentration of 10 µg/mL, showed 90.4 ± 11.52 and 88.9 ± 2.20% growth inhibition, respectively, of epimastigote forms of Trypanosoma cruzi, whereas N. falcifolia demonstrated an LD50 of 138.5 µg/mL against promastigote forms of Leishmania (Viannia) braziliensis. Regarding molluscicidal activity, the acute toxicity of the extracts on Biomphalaria glabrata was evaluated by a rapid screening procedure. M. arenosa was 100% lethal to snails at 200 µg/mL and showed an LD50 of 143 µg/mL. Screening of plant extracts represents a continuous effort to find new antiparasitic drugs