3-(4'-Methyl-1'-naphthyl)-propionic acid, 1',4'-endoperoxide (NEPO) provides singlet state of oxygen (O-1(2), (1)Delta(g)) at 37 degrees 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 O-1(2) generated by NEPO was calculated using the following equation: [O-1(2)]= [NEPO](0)[1-exp(-kt)], where [O-1(2)], [NEPO](0) and k are the total amount of O-1(2) produced during the time t, initial concentration of NEPO and the first-order reaction rate constant, respectively, When squalene was exposed to O-1(2) which was generated thermolytically from NEPO, it,vas 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 O-1(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 O-1(2) protected E, coli against O-1(2) toxicity. (C) 1998 Federation of European Biochemical Societies.