Enzymatic reduction of 2,4.6-trinitrotoluene and related nitroarenes: Kinetics linked to one-electron redox potentials

At military bases a nd munitions factories, 2,4,6-trinitrotoluene (TNT) is a common soil and groundwater contaminant. Although the reduction of nitro groups in TNT and related nitroarenes has been extensively investigated, few researchers have studied the link between reduction rates and the electrochemical properties of these compounds. In this work, the standard one-electron redox potentials at pH 7 (E(1)(o')) for six important nitroarenes have been measured by pulse radiolysis. The internally consistent values were -0.253 V for TNT, -0.417 V for 2-amino-4,6-dinitrotoluene, -0.449 V for 4-amino-2,6-dinitrotoluene, -0.397 V for 2-4-dinitrotoluene, -0.402 V for 2,6-dinitrotoluene, and -0.502 V for 2,4-diaminoB-nitrotoluene. The reduction kinetics of these nitroarenes was investigated using a bacterial nitroreductase, NAD(P)H:FMN oxidoreductase that uses NADH . H(+) as a cosubstrate. A log-linear relationship was observed between the E(1)(o') values and the enzymatic reduction rates for five nitroarenes, suggesting that transfer of the first electron is the rate-limiting step in nitro reduction.