Selective control of the radical-scavenging activity of poly(phenols) in aqueous media in terms of their electron-donor properties, using a stable organic radical as chemical sensor

The tri-potassium salt of tris(2,3,5,6-tetrachloro-4-hydroxysulphonylphenyl)methyl radical, 3K+ TSPTM3−, is a good chemical sensor of the radical-scavenging activity of poly(phenols) in aqueous media. Its water solubility and its stability at all pH values facilitates the study of the influence of the pH of the medium on the activity of poly(phenols). The radical-scavenging activity of three flavonoids of the catechol and pyrogallol type and the activity of catechol, pyrogallol and methyl gallate at pH values 7 and 8 which are close to physiological pH value (7.4) have been measured. This radical species reacts exclusively by an electron transfer mechanism against the reducing poly(phenols). Therefore, the experiments to determine the radical-scavenging activity of poly(phenols) with 3K+ TSPTM3− are related to their ionization potentials (IP). As IP is a function of the pH of the medium, the electron donor ability of a poly(phenol) depends on the acidity or basicity of the fluid in question. The radical-scavenging activity of poly(phenols) 1–6 is higher at pH 8 than at pH 7. 3K+ TSPTM3− is able to discriminate between catecholic and pyrogallolic moieties of poly(phenols) in water solutions by taking measurements at different pH values. By adjusting the pH of the medium 3K+ TSPTM3− will easily detect those moieties (e.g. pyrogallol) most prone to elicit prooxidant effects. ► 3K+ TSPTM3− has been prepared as a stable and water-soluble radical. ► Electron transfer reaction between (poly)phenols and 3K+ TSPTM3− has been confirmed. ► The activity of (poly)phenols against 3K+ TSPTM3− has been demonstrated to be higher at pH 8 than at pH 7. ► Catecholic and pyrogallolic moieties of (poly)phenols are discriminated by 3K+ TSPTM3−.