Reductive Transformation of Tetrachloroethene Catalyzed by Sulfide–Cobalamin in Nano-Mackinawite Suspension

Abstract

In this study, we demonstrated the reductive substitution of aquo−cobalamin(III) (Cbl(III)−H 2 O) by sulfide− cobalamin(III) (Cbl(III)−S 2− ) in the presence of S 2− . Cbl(III)−H 2 O was transformed to Cbl(III)−S 2− via ligand substitution of H 2 O by S 2− at its axial position, due to the weakness of the bond strength of cobalt with H 2 O. Cbl(III)−S 2− was reduced to sulfide−cobalamin(II) and partially further to sulfide−cobalamin(I) as the concentration of S 2− increased from 0.1 to 5.0 mM. In the presence of nanomackinawite (nFeS), Cbl(III)−S 2− species were fully adsorbed onto the nFeS surface, and its reactivity was enhanced by the reactive surface chemical species. The dechlorination kinetic rate constant of tetrachloroethene by Cbl(III)−S 2− in nFeS suspension (k nFeS−Cbl(III)−S 2− = 0.008 ± 0.001 h −1 ) was 4 times greater than that by Cbl(III)−H 2 O, showing a potential role for ≡S 2− −Cbl(II) as a more effective electron transfer mediator than ≡S n 2− −Cbl(II) and ≡OH−Cbl(II). The experimental results provide fundamental knowledge on potential biogeochemical reactions relevant to interactions between S 2− and bacterial coenzyme in nFeS suspension, which can significantly enhance reductive dechlorination of chlorinated compounds in contaminated sites.

Transformation of the recalcitrant pesticide chlordecone by Desulfovibrio sp.86 with a switch from ring-opening dechlorination to reductive sulfidation activity

“…S18). The weakness of the bond strength of cobalt with H 2 O inducing a spontaneous reductive substitution of aquo − cobalamin(III) (Cbl(III) − H 2 O) by sulfide − cobalamin(III) (Cbl(III) − S 2− ) in the presence of S 2− was reported 43 . In the case of corrinoid implication in B and C families formation, it could be assessed that the presence of H 2 S could also be inhibitory and thus favored F1 by another mechanism.…”