Chemical Journal of Chinese Universities, 2016, 37(8): 1442-1450.
1H NMR spectra of the reaction product in deuterated dimethyl sulfoxide (DMSO-d6) always showed formation of a second product which was generated at the expense of the first one immediately after dissolution in DMSO. Repeated recording of the UV visible spectra confirmed a uniform slow transformation (within minutes) of one substance into the other by exhibiting four isosbestic points at λ = 325, 375, 432, and 473 nm (). The 1H and 13C NMR spectra in DMSO-d6 revealed resonances which are in accordance with the two systems (I) and (II) shown in Fig. . The final assignments of the signals to the hydride complex of picric acid (I) and its protonated form (II) are summarized in Table . It is important to mention here that these assignments were possible only after further spectroscopic investigations in deuterated acetonitrile (CD3CN) as described below.
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The widespread use of nitrophenols as intermediate chemicals of large-scale syntheses of N-substituted aromatic compounds has led and still leads to considerable environmental problems (, , ). 2,4,6-Trinitrophenol (picric acid) was used as an explosive and is consequently found as a contaminant in ground water at certain military sites and former production facilities (). It is also a major byproduct of large-scale nitration of benzene and is therefore found in waste streams (, ). Thus, biodegradation of picric acid is of great industrial concern. This is documented by a recent patent on the degradation of picric acid and other nitrophenols by single bacterial isolates ().
During growth studies with R. erythropolis HLPM-1, originally isolated as a mutant of a 2,4-dinitrophenol-degrading organism (), we were able to cultivate this strain with picric acid as the sole nitrogen, carbon, and energy source. The initial transient color change of the culture medium to orange-red corresponded to observations in cultures containing picric acid as the sole nitrogen source (). It indicated the potential key function of this metabolite in the catabolic pathway of picric acid. In contrast to these findings, a color change was not () or was only occasionally () reported in recent publications on aerobic degradation of picric acid as the sole carbon, nitrogen, and energy source by different isolates. With respect to toxicity, it is important to mention that picric acid was utilized by R. erythropolis HLPM-1 at concentrations up to 3.4 mM. Under batch conditions, the organism tolerated picric acid at concentrations up to 14 mM ().
Search results for 2,4,6-Trinitrophenol at Sigma-Aldrich
This strain was originally isolated with picric acid as the sole nitrogen source (). In order to demonstrate that the organism could also use picric acid as the sole carbon and energy source, we used a culture that was cultivated for several months with 2,4-dinitrophenol (>2 mM) as the sole carbon, nitrogen, and energy source in mineral medium (). To prevent any carryover of residual organic carbon, cells from the stationary-growth phase were resuspended in phosphate buffer and served as inoculum (optical density, 0.1) for a mineral medium containing 3 mM picric acid (Fig. ). Initially, the cells formed strong conglomerates and thus prevented the monitoring of the optical density. Therefore, the cultures were sonified for 30 to 60 s prior to each measurement.
2,4,6-Trinitrophenol - Craig's Area
All chemicals used were of the highest purity commercially available. Picric acid and 2,4-dinitrophenol were obtained from Fluka (Neu-Ulm, Germany) as moistened preparation. The water was removed through high-vacuum evaporation. 2-Amino-4,6-dinitrophenol (picramic acid) from Tokyo Casei (Tokyo, Japan) and (CH3)4NB3H8 (tetramethylammonium octahydridotriborate) from Alfa Johnson Matthey (Karlsruhe, Germany) were used.
Preparation of 2,4,6-TRINITROTOLUENE
Reversed-phase high-performance liquid chromatography (HPLC) analyses of picric acid (tR = 7.1 min), 2,4-dinitrophenol (tR = 12.5 min), nitrite (tR = 2.4 min), and other metabolites were performed on a 125- by 4.6-mm RP 8 column (particle size, 5 μm) equipped with a precolumn (20 by 4.6 mm) by using a mobile phase of 20% (vol/vol) acetonitrile and 0.26% H3PO4 in water. Separation of the hydride complex of picric acid (tR = 3.1 min) was performed by ion pair chromatography on a column of the same size and material as described above with an isocratic eluent consisting of 30% methanol–water and 5 mM tetrabutylammonium hydrogen sulfate (PicA; Waters, Milford, Mass.). The compounds were detected by UV absorption at 210 nm. Metabolites were identified through in situ recording of the absorption spectra (200 to 600 nm).