Useful 1O 2 ( 1Δ g) generator, 3-(4′-methyl-1′-naphthyl)-propionic acid, 1′,4′-endoperoxide (NEPO), for dioxygenation of squalene (a skin surface lipid) in an organic solvent and bacterial killing in aqueous medium

Abstract

3-(4′-Methyl-1′-naphthyl)-propionic acid, 1′,4′-endoperoxide (NEPO) provides singlet state of oxygen ( 1O 2, 1Δ g) at 37°C in sodium phosphate buffer (pH 7.2), acetate buffer (pH 4.5), methanol or chloroform, through the retro-Diels-Alder reaction. The total amount of 1O 2 generated by NEPO was calculated using the following equation: [ 1O 2]=[NEPO] 0[1−exp −kt], where [ 1O 2], [NEPO] 0 and k are the total amount of 1O 2 produced during the time t, initial concentration of NEPO and the first-order reaction rate constant, respectively. When squalene was exposed to 1O 2 which was generated thermolytically from NEPO, it was oxidized to three hydroperoxides, mono-, di- and tri-hydroperoxides, in amounts proportional to the dose of NEPO. The oxidizability of squalene was much more extensive compared with unsaturated phospholipids. Additionally, when wild-type E. coli and lycopene-producing mutant E. coli were exposed to NEPO-derived 1O 2, there was significant loss of viability of wild-type E. coli but no significant loss of viability in lycopene-producing strain, suggesting that lycopene by scavenging 1O 2 protected E. coli against 1O 2 toxicity.