P. Santander

VOLTAMMETRIC DETERMINATION OF MELATONIN AND PYRIDOXINE (VITAMIN B6) IN TABLETS

Melatonina y Vitamina B6 puede ser oxidada en el electrodo de carbono vitreo produciendo picos anodicos bien resueltos mediante Voltametria de Pulso diferencial. La Vitamina B6 revela un pico de oxidacion con un potencial de pico de 650 mV vs Ag/AgCl en tampon de amoniaco pH 9, mientras que melatonina produce un pico con un potencial de pico de 840 mV vs Ag/AgCl en el tampon Britton-Robinson pH 2. Ambos picos muestran una relacion lineal entre la corriente de pico y la concentracion que es utilizada para la cuantificacion.

Electrochemical and ESR Characterization of Free Radicals from C-4 Nitroso Phenyl 1,4-Dihydropyridines in Aprotic Media

The present paper deals with the electrochemical and electron spin resonance (ESR) characterization of a number of nitroso phenyl 1,4-dihydropyridines in aprotic media on a hanging drop mercury electrode (HDME). The electrochemically generated nitroso radical anions decayed by a second-order reaction. Kinetic rate constants varied between k 2 , 4906 ± 43 (M s) -1 and 17,955 ± 159 (M s) -1 depending on the chemical structures. An increase in the bulk of the alkyl substituents from methyl-to isopropyl in 3- and 5-positions on the dihydropyridine ring stabilized the free radicals. Also, the electrochemically generated nitro radical anions from the parent nitrophenyl 1,4-dihydropyridines (1,4-DHP) derivatives were kinetically characterized and were significantly more stable than nitroso derivatives. The time-course of controlled potential electrolysis of the different compounds was followed electrochemically by differential pulse voltammetry, cyclic voltammetry, and spectroscopically by UV-visible and ESR. There is an intermolecular consecutive reaction during electrolysis, which gives the nitranion products. Formation of the one-electron reaction product, i.e., the nitroso radical anion, was confirmed by ESR experiments, and the corresponding hyperfine coupling constants were calculated for all the nitrosophenyl 1, 4-DHP derivatives studied.

1,4-Dihydropyridines: Reactivity of Nitrosoaryl and Nitroaryl Derivatives with Alkylperoxyl Radicals and ABTS Radical Cation

In the present paper, a direct quenching of radical species by a number of synthesized nitrosoaryl 1,4-dihydropyridines and their parent nitroaryl 1,4-dihydropyridines was determined in aqueous media at pH 7.4. These two series of compounds were compared with the C-4 unsubstituted 1,4-dihydropyridines derivatives and the corresponding C-4 aryl substituted 1,4-dihydropyridines derivatives. Kinetic rate constants were assessed by UV-Vis spectroscopy. Nitrosoaryl derivatives were more reactive than the parent nitroaryl 1,4-dihydropyridines. Our results strongly support the assumption that the reactivity between the synthesized 1,4-dihydropyridines derivatives with alkylperoxyl radicals involves electron transfer reactions, which is documented by the presence of pyridine as final product of reaction and the complete oxidation of the nitroso group to give rise the nitro group in the case of the nitrosoaryl 1,4-dihydropyridines derivatives.