Electrochemical oxidation and superoxide radical scavenging activity of 2-hydroxy/methoxy-phenylbenzothiazole derivatives

Abstract

Electrochemical characterisation and antioxidant activity against superoxide radical anion of four 2-hydroxy/methoxy-phenylbenzothiazole derivatives (1–4) are reported.The electrochemical oxidation was studied at a glassy carbon electrode using square-wave voltammetry in an aqueous buffer solution (pH = 1–12). In 1 (2-(2-methoxyphenyl)benzothiazole-6-ammonium chloride) and 2 (2-(2-hidroxyphenyl)benzothiazole-6-ammonium chloride), the benzothiazole C6-amino group was the main electroactive centre, undergoing a complex, pH-dependent process, coupled to the follow-up chemical reaction. The initial electrode reaction of 3 (6-(4,5-dihydro-1H-imidazol-3-ium-2-yl)-2-(2,3,4-trihydroxyphenyl)benzothiazole chloride) and 4 (6-amidinium-2-(2,3,4-trihydroxyphenyl)benzothiazole chloride) is a quasireversible, two-electrons, two-protons oxidation of the pyrogallol group.Superoxide radical scavenging activity was evaluated by means of cyclic voltammetry and computational analysis, which was revealed to rely on their ability to undergo the hydrogen atom transfer. In 1 and 2, H• donation from the benzothiazole C6-amino group is favoured, while a considerable improvement in the antioxidant activity was achieved in systems with the pyrogallol moiety 3 and 4, where it is realized from the middle 2-hydroxyl group, which allows for the formation of a stable OH∙∙∙O•∙∙∙HO fragment following the H• liberation.