[On the mechanism of the biological persistence of halogenated and sulfonated aromatic hydrocarbons (author's transl)]

Abstract

Aromatic compounds with unphysiological substituents like halogen or SO2H-groups are mainly degraded by cometabolism. Investigations with model compounds show, that the negative inductive effect (-I-effect) of the halogen substituents impede the electrophilic attack of the oxygenases, particularly the pyrocatechases. Although the "affinity" of the enzyme for the substrate increases with the number of halogen substituents, the rate of ring cleavage decreases by the presence of halogen substituents. Benzoate oxygenation shows that in certain positions of substitution the -I-effect can be weakened by the + M-effect of the halogen. As soon as aromaticity is lost by the action of dioxygenases, halide can be eliminated with greater ease and total mineralization is possible. When naphthalene-2-sulfonic acid is degraded by a naphthalene utilizing Pseudomonas strain the sulfonic acid group appears to be eliminated oxygenolytically and the carbon skeleton is channelled into the naphthalene pathway.