Marie-Laurence Abasq

How do phenolic compounds react toward superoxide ion? A simple electrochemical method for evaluating antioxidant capacity.

The reactivities of different phenols and polyphenols versus superoxide ion (O₂(•-)) were investigated as an easy-to-handle electrochemical method for evaluating antioxidant capacities. In view of this application, the O₂/O₂(•-) couple and associated reactions between O₂(•-) and polyphenols (or phenols) were examined in an aprotic solvent [dimethylformamide (DMF)] by cyclic voltammetry. Comparisons based on simple criteria (reversibility of the O₂ reduction in the presence of the phenolic compound, electron stoichiometry, or apparent kinetic constants) allow discriminations between the possible mechanistic pathways (acid-base or radical reaction type). The results highlight that the proton-transfer and radical-transfer pathways are both present for monophenols and polyphenols, with the relative contributions of the two pathways depending on the phenol structure. In agreement with the literature, polyphenols containing an o-diphenol ring (as in flavonoids) were found to present the highest reactivities.

Validation of a new method using the reactivity of electrogenerated superoxide radical in the antioxidant capacity determination of flavonoids

This article lays out a new method to measure the antioxidant capacity of some flavonoids. The methodology developed is based on the kinetics of the reaction of the antioxidant substrate with the superoxide radical (O(2)(*-)). A cyclic voltammetric technique was used to generate O(2)(*-) by reduction of molecular oxygen in aprotic media. In the same experiment the consumption of the radical was directly measured by the anodic current decay of the superoxide radical oxidation in the presence of increasing concentrations of antioxidant substrate. The method was statistically validated on flavonoid monomers and on the standard antioxidants: trolox, ascorbic acid and phloroglucinol. The linear correlations between the anodic current of O(2)(*-) and the substrate concentration allowed the determination of antioxidant index values expressed by the substrate concentration needed to consume 30% (AI(30)) and 50% (AI(50)) of O(2)(*-) in given conditions of oxygen concentration and scanning rate. The fidelity of the method was examined intraday and interlaboratories.

Determination of Entacapone by Differential Pulse Polarography in Pharmaceutical Formulation

Abstract The electrochemical methods, sampled direct current, and differential pulse polarography, were developed successfully and applied to the routine determination of Entacapone in pharmaceutical formulation. Both methods gave rise to three reduction waves or peaks respectively. The irreversibility and the diffusion‐controlled of the first reduction were confirmed by cyclic voltammetry. The limiting currents are directly proportional to the concentration of entacapone with a correlation coefficient of 0.99. The within‐day coefficients of variation and the day‐to‐day coefficient of variation were less than 3.5% for entacapone and Comtan®. The percentage recovery for entacapone in tablets is satisfactory for both methods. The method is simple without any pretreatment.

Experimental and Theoretical Studies of Radical Intermediate Reactivity During the Electroreduction of Dithiolethiones and the Corresponding Dithiolium Cations

Abstract

Synthesis and Physicochemical Properties of Methyl 3-Mercapto Arylpropene Dithioates

1,2-dithiole-3-thiones and derivatives are endowed with several promising pharmacological properties.1 We have shown that the reduction of 3-(methylsulfanyl)-5-(phenyl)-1,2-dithiolium ion 1a1 by NaBH4 is an efficient way to prepare the corresponding reduction product: methyl3-mercapto-3-phenylpropene dithioate 2a1. We present here the generalization of this reaction to other 3-(methylsulfanyl)-1,2-dithiolium ions 1 to give methyl-3-mercapto-3-phenylpropene dithioates 2. Compounds 2a1 and 2a2 have been previously described according to other synthetic routes.3,4