Does catalysis of reductive dechlorination of tetra- and trichloroethylenes by vitamin B12 and corrinoid-based dehalogenases follow an electron transfer mechanism?

Knowing the mechanism by which dangerous organic chloride pollutants, such as tetra- or trichloroethylene, are reductively cleaved is an important task for the establishment of remediation strategies and for a better comprehension of bacterial dehalorespiration by corrinoid-based dehalogenases. On the basis of electrochemical and thermodynamic data, application of outersphere and dissociative electron transfer theories allows the prediction of the pertinent activation/driving force relationships characterizing the electron transfer mechanism. They are validated by application of the redox catalysis method to the reaction with two typical outersphere electron donors. The kinetic gap is more than 11 and 7 orders of magnitude for the dehalogenase and for cobalamin, respectively, showing that the electron transfer mechanism is not operative. Multistep mechanisms in which the chloroethylene molecule enters the cobalt coordination sphere are preferred.