•The cyclic voltammetry has been successfully used for the determination of SRSA of flavonoids.•Correlation between structure and SRSA has been established.•The reaction mechanism involved in ...superoxide radical scavenging by flavonoids has been proposed.
The reactivities of a set of 18 diverse flavonoids against electrochemically generated superoxide anion radical were studied by monitoring changes in O2/O2·− cyclic voltammetry response upon addition of increasing concentrations of flavonoids. In the presence of flavonoids, the O2·- anodic peak current decreased, while the cathodic peak of O2 remained almost unchanged. Concomitantly with an O2·- anodic peak current decrease, a new irreversible cathodic pre-peak before the O2 reduction peak appeared on the CVs of O2/O2·− upon adding flavonoids. This phenomenon is described in detail for the first time on the basis of experimental measurements and model calculations. Based on the changes in O2/O2·− cyclic voltammetry response upon adding flavonoids, we could draw conclusions about the mechanism of superoxide radical scavenging by flavonoids. The superoxide radical scavenging activities of flavonoids, determined by measuring the anodic current decay of the radical in the presence of increasing concentrations of flavonoids, were expressed in terms of EC60 values, i.e. the concentration of flavonoid needed to consume 40% of a superoxide radical. All of the studied flavonoids showed a more or less pronounced superoxide radical scavenging activity, depending on their structural features. The structure-activity relationship was discussed. Superoxide radical scavenging activities of flavonoids correlated well with their electrochemical oxidation potentials, implying that the scavenging activity of flavonoids is mainly governed by their redox properties.
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The electrochemical behaviour of potential antitumor benzimidazole derivatives (benzobthieno2,3-bpyrido1,2-abenzimidazoles and benzimidazo1,2-aquinolines) bearing one or two piperazine substituents ...was studied at a glassy carbon electrode (GCE) using cyclic and square-wave voltammetry in a wide range of pH values and potential scan rates. The electrochemical oxidation of the studied benzimidazoles proceeded via one or two electrode reactions assigned to the oxidation of one or two piperazine substituents, respectively. The oxidation of piperazine ring involved the transfer of two electrons and one proton in a pH-dependent, kinetically controlled electrode reaction, followed by a homogenous chemical reaction (EC mechanism). Both the reactants and the products of EC reactions were strongly adsorbed on the GCE surface. The electrochemical reduction occurred in one quasireversible, pH-dependent step, followed by a chemical transformation of the electrochemically formed product. The proposed reduction mechanism was related to the cyano moiety. The assignment of electroactive sites in molecules of interest was confirmed by theoretically calculated, using the PM6 method, differences of Net atomic charges between the cation (or anion) and neutral molecule.
Amino-substituted benzamide derivatives are very attractive compounds due to their capacity to act as powerful antioxidants by scavenging free radicals. Knowledge on electrochemical oxidation ...mechanisms plays an important role in understanding the free radical scavenging activity of antioxidants. In this paper, the electrochemical oxidation of four amino-substituted derivatives N-(4-aminophenyl)-2-hydroxybenzamide (1), N-(4-aminophenyl)-2-hydroxy-4-methoxybenzamide (2), N-(4-aminophenyl)-2-methoxybenzamide (3), N-(4-aminophenyl)-3,4,5-trihydroxybenzamide (4) in an aqueous buffer solution was studied by means of cyclic and square-wave voltammetry, and probable reaction mechanisms have been proposed. In compounds 1–3, the primary amino group was found to be the main electroactive centre undergoing a complex, pH-dependent oxidation process with the transfer of two electrons and two protons. This reaction occurs in one step or in two separate steps, depending on the pH of the medium. A possible explanation for this electrochemical behaviour is discussed. The final products of initial electrochemical oxidation of amino-substituted benzamides 1–3 are quinonediimine derivatives that undergo further chemical transformation into electroactive forms. Oxidation of compound 4 proceeds through two sequential reactions; the first anodic reaction is the oxidation of the trihydroxyphenyl group to the corresponding o-quinone, followed by the oxidation of a primary amino group. Considering the oxidation potentials, and bearing in mind that lower/less positive potential implies better radical scavenging activity, the order of antioxidant activity of the here studied amino-substituted benzamides is: 4 >2 >1 >3.
•The first report on the electrochemical behaviour of hydroxy and methoxy substituted N-arylbenzamides.•Mechanism of the oxidation was proposed.•Oxidation potentials were used to evaluate antioxidant activity.
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