Showing papers by "Juan A. Squella published in 2008"

Oxidation of 4-(3-Indolyl)- and 4-(5-Indolyl)-1,4-dihydropyridines in Aprotic and Protic Media: Reactivity toward Alkylperoxyl Radicals

Abstract: Electrochemical oxidation of 4-(3-indolyl)- and 4-(5-indolyl)-1,4-dihydropyridines (DHPs) in aprotic and protic media is reported. Also, the reactivity of compounds toward alkylperoxyl radicals 2,2'-azobis-(2-amidinopropane) dihydrochloride-derived in aqueous media at pH 7.4 is assessed. Derivatives were electrochemically oxidized exhibiting two anodic signals in both electrolytic media. The first signal is due to oxidation of the dihydropyridine ring, and the second one is due to oxidation of the indolyl moiety. Electron spin resonance experiments proved the formation of carbon-centered dihydropyridyl radicals as intermediates in the oxidation of the dihydropyridine moiety in aprotic medium. Pyridine was identified as the final product of the oxidation in both electrolytic media by gas chromatography/mass spectrometry. The 4-substituted 1,4-DHPs were more reactive than tested commercial 1,4-DHPs toward alkylperoxyl radicals.

Voltammetric Reduction of a 4‐Nitroimidazole Derivative on a Multiwalled Carbon Nanotubes Modified Glassy Carbon Electrode

Abstract: We report the electrochemical behavior of a 4-nitroimidazole derivative, 1-methyl-4-nitro-2-hydroxymethylimidazole (4-NImMeOH), on glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNT). As dispersing agents, dimethylformamide (DMF) and water were used. The electrochemical response of the resulting electrodes was evaluated using linear sweep, cyclic and square-wave voltammetry (LSV, CV and SWV). Several parameters such as medium pH, nature and concentration of the CNTs dispersion and accumulation time were tested. The optimal conditions determined for obtain better response were: pH 2, dispersion concentration=4 mg/mL of CNT in water, accumulation time=7 min. The MWCNT-modified GCE exhibited attractive electrochemical properties producing enhanced currents with a significant reduction in the overpotential and good signal-to-noise characteristics, in comparison with the bare GCE. The modified electrode is highly repeatable for consecutive measurements, reaching a variation coefficient of 2.9% for ten consecutive runs.