| Abstract
| - Recently we demonstrated that Rhodococcus sp. strainDN22 degraded hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)(I) aerobically via initial denitration followed by ringcleavage. Using UL 14C-[RDX] and ring labeled 15N-[RDX]approximately 30% of the energetic chemical mineralized(one C atom) and 64% converted to a dead end product thatwas tentatively identified as 4-nitro-2,4-diaza-butanal(OHCHNCH2NHNO2). To have further insight into the roleof initial denitration on RDX decomposition, we photolyzedthe energetic chemical at 350 nm and pH 5.5 and monitoredthe reaction using a combination of analytical techniques. GC/MS-PCI showed a product with a [M + H] at 176 Damatching a molecular formula of C3H5N5O4 that was tentativelyidentified as the initially denitrated RDX product pentahydro-3,5-dinitro-1,3,5-triazacyclohex-1-ene (II). LC/MS (ES-)showed that the removal of RDX was accompanied bythe formation of two other key products, each showing thesame [M − H] at 192 Da matching a molecular formulaof C3H7N5O5. The two products were tentatively identifiedas the carbinol (III) of the enamine (II) and its ring cleavageproduct O2NNHCH2NNO2CH2NHCHO (IV). Interestingly,the removal of III and IV was accompanied by the formationand accumulation of OHCHNCH2NHNO2 that we detectedwith strain DN22. At the end of the experiment, which lasted16 h, we detected the following products HCHO, HCOOH,NH2CHO, N2O, NO2-, and NO3-. Most were also detectedduring RDX incubation with strain DN22. Finally, wewere unable to detect any of RDX nitroso products duringboth photolysis and incubation with the aerobic bacteria,emphasizing that initial denitration in both cases wasresponsible for ring cleavage and subsequent decompositionin water.
|
