Showing papers by "Juan A. Squella published in 2000"

Electrochemical, UV-Visible and EPR studies on nitrofurantoin: Nitro radical anion generation and its interaction with glutathione

Abstract: This paper deals with the reactivity of the nitro radical anion electrochemically generated from nitrofurantoin with glutathione. Cyclic voltammetry (CV) and controlled potential electrolysis were used to generate the nitro radical anion in situ and in bulk solution, respectively and cyclic voltammetry, UV--Visible and EPR spectroscopy were used to characterize the electrochemically formed radical and to study its interaction with GSH. By cyclic voltammetry on a hanging mercury drop electrode, the formation of the nitro radical anion was possible in mixed media (0.015M aqueous citrate/DMF, 40/60, pH 9) and in aprotic media. A second order decay of the radicals was determined, with a k2 value of 201 and 111 M(-1) s(-1), respectively. Controlled potential electrolysis generated the radical and its detection by cyclic voltammetry, UV--Visible and EPR spectroscopy was possible. When glutathione (GSH) was added to the solution, an unambiguous decay in the signals corresponding to a nitro radical anion were observed and using a spin trapping technique, a thiyl radical was detected. Electrochemical and spectroscopic data indicated that it is possible to generate the nitro radical anion from nitrofurantoin in solution and that GSH scavenged this reactive species, in contrast with other authors, which previously reported no interaction between them.

Electroreduction of Nitroaryl‐1,4‐dihydropyridines on a Mercury Pool Electrode in Mixed Media Analysis of the Reaction Products and Their Reactivity with Biomolecules

Abstract: The electroreduction of a series of nitroaryl-1,4-dihydropyridines has been studied in mixed media. Controlled potential electrolyses using a mercury pool electrode at three different reduction potentials were carried out. Voltammetric (polarography and cyclic voltammetry) and chromatographic studies, showed that these nitro compounds were transformed into their corresponding hydroxylamine derivatives at the end of the electrolysis. On the other hand, early in the electrolysis it was possible to detect the formation of the nitro radical anion in the bulk solution which through a dismutation reaction produces the nitroso compound which is reduced to the final product, a hydroxylamine derivative. When different biomolecules like glutathione, cysteamine, adenine, and uracil were added, a direct reaction with the nitro radical anion derivative was detected. The parent nitro compound and the final product, the hydroxylamine derivative, did not react with the biomolecules.

Voltammetric behaviour of clonixin and its differential pulse polarographic determination in tablets

Abstract: Clonixin, a non-steroid analgesic, can be both reduced at the mercury electrode and oxidised at the glassy carbon electrode. The anodic response shows well-defined waves in a pH range between pH 2-12. The polarographic response shows two irreversible waves or peaks in the range between pH 1-6 shifting cathodically when pH increases. Above pH 7.0 all the signals disappeared. The first signal in the dpp mode at pH 1.8 was selected for analytical use. The polarographic

Electrochemical Characterization of Tacrine, an Antialzheimer's Disease Drug, and Its Determination in Pharmaceuticals

Abstract: Tacrine, 9-amino-1,2,3,4-tetrahydroacridine, an antialzheimer's disease agent was electrochemically studied and a polarographic method for its quantitative determination in pharmaceuticals was developed. Tacrine was electrochemically reduced and oxidized in aqueous medium, but for analytical purposes the cathodic behavior was prefered. According to the linear relation between the peak current and the tacrine concentration a differential pulse polarographic method was developed. Precision and accuracy of the developed method was checked by recovery studies. The proposed method was applied to the individual capsule assay (ICA) of the commercial capsules, showing that the uniformity content requirements were fulfilled. Alternatively a UV spectroscopic characterization was conducted, from the pH dependence of the absorbance bands an apparent pKa of 10.44 was obtained. For comparative purposes a spectrophotometric determination also was developed.

Nitroradical anion formation from nitrofurantoin in carbon electrodes

Abstract: La formacion electroquimica del nitro anion radicalde nitrofurantoina ha sido estudiada sobre electrodos de carbonovitreo y pasta de carbono. Se encontro que sobre ambos tipos de electrodos, existe un proceso monoelectronico reversible correspondientea la cupla redox ArNO2/ArNO2.-, seguido de un pico irreversible correspodiente a la reduccion viatres electrones del anion radical a la correspondiente hidroxilamina.De acuerdo a los resultados obtenidos, el proceso de reduccion ocurrea traves de un mecanismo EC, donde los valores de k2 encontrados, indican que el anion radical nitro es mejor estabilizadosobre electrodos de pasta de carbono

Cytochrome C reductase immobilized on carbon paste electrode and its electrocatalytic effect on the reduction of cytochrome C

Abstract: El electrodo de pasta de carbono fue modificado con la enzima Citocromo C reductasa. El comportamiento de los electrodos fue caracterizado por voltametria ciclica. La reduccion de citocromo C fue investigada tanto sobre la enzima como en un sistema homogeneo. En el primer caso, un significante efecto electrocatalitico sobre la reduccion de Citocromo C fue observado. El efecto concuerda con un aumento de 4.3 veces de la corriente de pico y por un desplazamiento del potencial de pico a valores menos catodicos. Tambien, valores para la constante de Michaelis aparente fueron calculados. Los resultados de este trabajo muestran que el electrodo de pasta de carbono modificado por la enzima Citocromo C reductasa representa una nueva interfase que permitira el estudio de reacciones de transferencia electronica involucradas en procesos de biodegradacion