Photostimulatory and bioinhibitory effects of a quinone derived from phenanthrene

Phenanthrene (1) is a typical and abundant PAH commonly found in petroleum distillates and coal-derived products such as creosote. In both polar and nonpolar environments, it is converted by sunlight to more polar products such as 9,10-phenanthrene-quinone (2) and further oxidation products such as the corresponding ring-opened dicarboxylic acid product. The photostimulatory and bioinhibitory effects of 2 from 1 were studied. The oxygen-dependent photolysis mechanism for 1 involved photoionization, with the released electron scavenged by molecular O₂, and subsequent recombination of the radical cation of 1 with •O₂^-. Slow rearrangement of the resulting peroxyl radical could lead to formation of 2, which would then induce a faster photolysis reaction. For biological experiments, PAH-degrading enrichment cultures were created, using soil near a source of creosote; both 1 and the quinone were subjected to microbial attack. The experiment was repeated using HPLC with diode-array absorbance detection. In this case, the effects of phenanthrene on naphthalene biodegradation were investigated. Though the quinone inhibited biodegradation of naphthalene, phenanthrene did not. The observation of the inhibition of naphthalene biodegradation by phenanthrene photoproducts corresponded with a recent observation that quinones derived from the bacterial transformation of another PAH, fluoranthene, also inhibited the degradation (mineralization) of other PAH by several bacterial strains. This is an abstract of a paper presented at the 22nd ACS National Meeting (Chicago, IL 8/26-30/2001).