Micellar effect on the scavenging of singlet molecular oxygen by hydroxybenzenes

Abstract

The antioxidative effectiveness of three hydroxyaromatic derivatives (OHAD), namely phenol, resorcinol and phloroglucinol, as reflected by their scavenging ability of the photochemically generated species singlet molecular oxygen [O₂(¹Δ_g)], was studied in aqueous solution and micellar media. Kinetic results, obtained through time-resolved phosphorescence detection of O₂(¹Δ_g) emission and polarographic methods, at pH 7 and 12 in homogeneous and CTAB micellar media, were compared. Calculated photooxidation quantum efficiencies (φ_r), ranging from very low values (~0.01) to relatively high ones (~0.3), depend on the preferential solubilization sites of the hydroxyaromatic derivatives either in the micellar or homogeneous media. OHAD in water pH 7 and in CTAB 0.02 M pH 12 exhibit their highest antioxidative efficiency as O₂(¹Δ_g) scavengers. In these conditions, they present the best degree of self protection against O₂(¹Δ_g)-mediated photooxidation with relatively high values for the overall quenching rate constant and, simultaneously, the lowest φ_r.