Porphyrin-mediated dehalogenation

Considerable attention has been directed to dehalogenation mediated by corrinoids and porphyrins in the presence of a chemical reductant (references in Gantzer and Wackett 1991 Glod et al. 1997 Workman et al. 1997). Illustrations are provided by the dechlorination and elimination reactions carried out by titanium(III) citrate and hydroxocobala-min (Bosma et al. 1988 Glod et al. 1997). The involvement of corrinoids and porphyrins is consistent with the occurrence of analogous mechanisms for biological reactions that... 

In a wider context, extracellular redox mediators have been implicated in a number of reductions. The specific role of reductive dehalogenation by porphyrins and corrins has been discussed in Chapter 1. 

CyP450 and other reduced iron porphyrins are also reported to mediate reductive dehalogenation of a variety of haloalkanes and -alkenes [4], and of the aliphatic portion of DDT [5], Reductive dehalogenation refers specifically to the reaction in which two electrons and a proton act as substrates along with the halogenated compound to yield a reduced product and the corresponding halide (Eq. 1). 

Under anaerobic conditions, 1,1,2-trichloroethane is reported to undergo dehalogenation. In order to establish whether this is a biologically mediated reaction and not simply an abiotic reaction catalyzed by free iron or iron porphyrin at low redox potential, Dow Chemical conducted 28-day studies in sterile solutions (Klecka and Gonsior 1983). They found that ppm concentrations of 1,1,2-trichloroethane did not undergo nonenzymatic dehalogenation in a sterile, anaerobic solution at pH 7 or when a sulfide redox buffer or hematin was added (Klecka and Gonsior 1983). 

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