Molecular probe techniques for the identification of reductants in sediments: Evidence for reduction of 2-chloroacetophenone by hydride transfer

The reduction of 2-chloroacetophenone (2-CAP) was examined in anoxic sediment slurries from both freshwater and marine sources. The reduction of 2-CAP produces acetophenone via electron transfer and 2-chloro-1- phenylethanol (2-CPE) via hydride transfer. Experimental results demonstrate that 2-CAP is an effective probe molecule for distinguishing and quantifying reductive transformations occurring by electron transfer and hydride transfer in anaerobic sediments. These results varied among the sediments examined, with freshwater sediments generating more 2-CPE (hydride transfer product) than the marine sediments. Enantiomeric excess of (R)-2-CPE (over the (S)- enantiomer) demonstrated that reduction by hydride transfer is enantioselective, providing direct evidence that the source of hydride is a chiral reductant. Temperature studies demonstrate that increasing temperature eliminates the production of 2-CPE, further evidence for an enzyme mediated pathway.