Evidence for a Radical Mechanism of the Dechlorination of Chlorinated Propenes Mediated by the Tetrachloroethene Reductive Dehalogenase of Sulfurospirillum multivorans

Abstract

The reductive dehalogenation of chlorinated propenes was studied with the tetrachloroethene reductive dehalogenase purified from Sulfurospirillum multivorans to obtain indications for a radical mechanism of this reaction. When reduced methyl viologen (MV), which is a radical cation, was applied as electron donor for the reduction of different chloropropenes, a significant part of MV could not be rereduced with Ti(III) citrate, indicating that a part of the MV was consumed in a side reaction. Mass spectrometric analysis of assays with MV as electron donor revealed the formation of side products, the masses of which might account for the formation of adducts from a chloropropenyl radical and reduced methyl viologen. With Ti(III) citrate as sole electron donor, 2,3-dichloropropene was reduced and as a side product, 2,5-dichloro-1,5-hexadiene was formed demonstrating that the reductive dechlorination of 2,3-dichloropropene proceeds via a radical reaction mechanism. The results support different dehalogenation mechanisms forthe reductive dechlorination of chloropropenes and halogenated ethenes.