Hydride-Meisenheimer complex

Behrend C, K Heesche-Wagner (1999) Formation of hydride-Meisenheimer complexes of picric acid (2,4,6-trinitrophenol) and 2,4-dinitrophenol during mineralization of picric acid by Nocardioides sp. strain CB 22-2. Appl Environ Microbiol 65 1372-1377. 

Rieger P-G, V Sinnwell, A Preup, W Francke, H-J Knackmuss (1999) Hydride-Meisenheimer complex formation and protonation as key reactions of 2,4,6-trinitrophenol biodegradation by Rhodococcus erythropolis. J Bacterial 181 1189-1195. 

Vorbeck C, H Lenke, P Fischer, H-J Knackmnss (1994) Identification of a hydride-Meisenheimer complex as a metabolite of 2,4,6-trinitrotoluene by a Mycobacterium strain. J Bacteriol 176 932-934. 

Like TNT, 2,4,6-trinitrophenol (picric acid, PA) is also degraded through reduction. The hydride Meisenheimer complex is recognized as a key intermediate of denitration for the microbial degradation of PA [104,105], Lenke and Knackmuss [106] described an initial reduction of PA via the intermediate formation of a hydride-Meisenheimer complex to produce 2,4-dinitrophenol by the enzymatic elimination of nitrite. Under aerobic conditions, the mono- or dinitrophenol can then be oxygenated with subsequent ring cleavage. 

Vorbeck CV et al., Identification of a hydride-Meisenheimer complex as a metabolite of... 

HL 24-2, originally isolated for its ability to degrade 2,4-dinitrophenol [14], cotild also utilize picric acid as nitrogen source. The mutant HL-PM-1 transiently accumulated an orange-red metabolite, which was identified as a hydride-Meisenheimer complex of picric acid. This complex was further converted with release of nitrite. 2,4,6- Trinitrocyclohexanone was the dead-end metabolite of the degradation of picric acid. 

For a strain of Rhodococcus erythropolis, Lenke and Knackmuss (35) described the initial reduction of the aromatic nucleus of picric acid (2,4,6-trinitrophenol) by a hydride ion (H"), yielding a hydride-Meisenheimer complex (Fig. 2). With the addition of a proton, the nitro group was subsequently released as nitrite and 2,4-dinitrophenol was produced. 

Figure 5. The hydride-Meisenheimer complex in the metabolism of trinitrotoluene by Pseudomonas sp. clone A.

Degradation of 2,4,6-trinitrophenol and 2,4-dinitrophenol involving a Meisenheimer hydride complex (Vorbeck et al. 1998 Behrend and Heesche-Wagner 1999 Fbert et al. 1999 Hofmann et al. 2004 Heiss et al. 2002). 

Details of the mechanism have revealed the role of Meisenheimer-type hydride complexes, which is consistent with the presence of the strongly electron-withdrawing nitro groups that facilitate what are formally hydride reductions involving reduced coenzyme F420 (Ebert et al. 1999). For example, 2,4,6-trinitrophenol is reduced successively by hydride transfers catalyzed by F420, followed by loss of nitrite, further reduction, and ring fission to 4,6-dinitrohexanoate (Hofmann et al. 2004). 

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