Photodegradation of CL-20: insights into the mechanisms of initial reactions and environmental fate

Isolation and identification of a novel bacterium, Pseudomonas sp. ZyL-01, involved in the biodegradation of CL-20

Hexanitrohexaazaisowurtzitane (CL-20) is a compound with a polycyclic cage and an N-nitro group that has been shown to play an unfavorable role in environmental fate, biosafety, and physical health. The aim of this study was to isolate the microbial community and to identify a single microbial strain that can degrade CL-20 with desirable efficiency. Metagenomic sequencing methods were performed to investigate the dynamic changes in the composition of the community diversity. The most varied genus among the microbial community was Pseudomonas, which increased from 1.46% to 44.63% during the period of incubation (MC0-MC4). Furthermore, the new strain was isolated and identified from the activated sludge by bacterial morphological and 16s rRNA sequencing analyses. The CL-20 concentrations decreased by 75.21 μg/mL and 74.02 μg/mL in 48 h by MC4 and Pseudomonas sp. ZyL-01, respectively. Moreover, ZyL-01 could decompose 98% CL-20 of the real effluent in 14 day's incubation with the glucose as carbon source. Finally, a draft genome sequence was obtained to predict possible degrading enzymes involved in the biodegradation of CL-20. Specifically, 330 genes that are involved in energy production and conversion were annotated by Gene Ontology functional enrichment analysis, and some of these candidates may encode enzymes that are responsible for CL-20 degradation. In summary, our studies indicate that microbes might be a valuable biological resource for the treatment of environmental contamination caused by CL-20 and that Pseudomonas sp. ZyL-01 might be a promising candidate for eradicating CL-20 to achieve a more biosafe environment and improve public health.

Energetic contaminants inhibit plant litter decomposition in soil

Individual effects of nitrogen-based energetic materials (EMs) 2,4-dinitrotoluene (2,4-DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), 4-amino-2,6-dinitrotoluene (4-ADNT), nitroglycerin (NG), and 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) on litter decomposition, an essential biologically-mediated soil process, were assessed using Orchard grass (Dactylis glomerata) straw in Sassafras sandy loam (SSL) soil, which has physicochemical characteristics that support "very high" qualitative relative bioavailability for organic chemicals. Batches of SSL soil were separately amended with individual EMs or acetone carrier control. To quantify the decomposition rates, one straw cluster was harvested from a set of randomly selected replicate containers from within each treatment, after 1, 2, 3, 4, 6, and 8 months of exposure. Results showed that soil amended with 2,4-DNT or NG inhibited litter decomposition rates based on the median effective concentration (EC50) values of 1122 mg/kg and 860 mg/kg, respectively. Exposure to 2-ADNT, 4-ADNT or CL-20 amended soil did not significantly affect litter decomposition in SSL soil at ≥ 10,000 mg/kg. These ecotoxicological data will be helpful in identifying concentrations of EMs in soil that present an acceptable ecological risk for biologically-mediated soil processes.

New Insights into the Photochemical Degradation of the Insensitive Munition Formulation IMX-101 in Water

This study describes photolysis of the insensitive munition formulation IMX-101 [2,4-dinitroanisole (DNAN), NQ (nitroguanidine), and 3-nitro-1,2,4-triazol-5-one (NTO)] in aqueous solutions using a solar simulating photoreactor. Due to a large variance in the water solubility of the three constituents DNAN (276 mg L^-1), NQ (5,000 mg L^-1), and NTO (16,642 mg L^-1), two solutions of IMX-101 were prepared: one with low concentration (109.3 mg L^-1) and another with high concentration (2831 mg L^-1). The degradation rate constants of DNAN, NQ, and NTO (0.137, 0.075, and 0.202 d^-1, respectively) in the low concentration solution were lower than those of the individually photolyzed components (0.262, 1.181, and 0.349 d^-1, respectively). In the high concentration solution, the molar loss of NTO was 4.3 times higher than that of NQ after 7 days of irradiation, although NQ was two times more concentrated and that NQ alone degraded faster than NTO. In addition to the known degradation products, DNAN removal in IMX-101 was accompanied by multiple productions of methoxydinitrophenols, which were not observed during photolysis of DNAN alone. One route for the formation of methoxydinitrophenols was suggested to involve photonitration of the DNAN photoproduct methoxynitrophenol during simultaneous photodenitration of NQ and NTO in IMX-101. Indeed, when DNAN was photolyzed in the presence of ¹⁵NO₂-labeled explosive CL-20, we detected methoxydinitrophenols with an increase of 1 mass unit, indicating that denitration of DNAN and renitration of products simultaneously occurred. As was the case with DNAN, we found that guanidine, a primary degradation product of NQ, also underwent renitration in the presence of NTO and the photocatalyst TiO₂. We concluded that the three constituents of IMX-101 can be photodegraded in surface water and that fate and primary degradation products of IMX-101 can be influenced by the interactions between the formulation ingredients and their degradation products.

Adsorption of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) on a soil organic matter. A DFT M05 computational study

Adsorption of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) by soil organic matter considering the Leonardite Humic Acid (LHA) model at the M05/tzvp level of Density Functional Theory (DFT) applying cluster approximation has been investigated. Different orientations of CL-20 toward LHA surface were examined. It was found that deprotonation of LHA is required to obtain stable complexes with CL-20. Hydrogen bonds between CL-20 and deprotonated LHA were analyzed applying the atoms in molecules (AIM) theory. An attachment or removal of an electron with respect to the complex does not have significant effect on mutual orientation of the adsorbent in complexes. It was shown that adsorbed CL-20 does not undergo redox transformation and, therefore, adsorption on soil organic matter may be responsible for decrease of the degradation rate of CL-20 in soil.

Application of photo degradation for remediation of cyclic nitramine and nitroaromatic explosives

Photo degradation is a rapid and safe remediation process and advances in continuous-flow photochemistry can scale-up yields of photo degradation.

Radical-based destruction of nitramines in water: kinetics and efficiencies of hydroxyl radical and hydrated electron reactions

In support of the potential use of advanced oxidation and reduction process technologies for the removal of carcinogenic nitro-containing compounds in water reaction rate constants for the hydroxyl radical and hydrated electron with a series of low molecular weight nitramines (R(1)R(2)-NNO(2)) have been determined using a combination of electron pulse radiolysis and transient absorption spectroscopy. The hydroxyl radical reaction rate constant was fast, ranging from 0.54-4.35 × 10(9) M(-1) s(-1), and seen to increase with increasing complexity of the nitramine alkyl substituents suggesting that oxidation primarily occurs by hydrogen atom abstraction from the alkyl chains. In contrast, the rate constant for hydrated electron reaction was effectively independent of compound structure, (k(av) = (1.87 ± 0.25) × 10(10) M(-1) s(-1)) indicating that the reduction predominately occurred at the common nitramine moiety. Concomitant steady-state irradiation and product measurements under aerated conditions also showed a radical reaction efficiency dependence on compound structure, with the overall radical-based degradation becoming constant for nitramines containing more than four methylene groups. The quantitative evaluation of these efficiency data suggest that some (~40%) hydrated electron reduction also results in quantitative nitramine destruction, in contrast to previously reported electron paramagnetic measurements on these compounds that proposed that this reduction only produced a transient anion adduct that would transfer its excess electron to regenerate the parent molecule.

Evaluation of the dependence of aqueous solubility of nitro compounds on temperature and salinity: a COSMO-RS simulation

The solubility in pure and saline water at various temperatures was calculated for selected nitro compounds (nitrobenzene, 1,3,5-trinitrobenzene, 2-nitrotoluene, 3-nitrotoluene, 4-nitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2,3-dinitrotoluene, 3,4-dinitrotoluene, 2,4,6-trinitrotoluene) using the Conductor-like Screening model for Real Solvents (COSMO-RS). The results obtained were compared with experimental values. The COSMO-RS predictions have shown high accuracy in reproducing the trends of aqueous solubilities for both temperature and salinity. The proposed methodology was then applied to predict the aqueous solubilities of 19 nitro compounds in the temperature range of 5-50°C in saline solutions. The salting-out parameters of the Setschenow equation were also calculated. The predicted salting-out parameters were overestimated when compared to the measured values, but these parameters can still be used for qualitative estimation of the trends.

Application of quantum chemical approximations to environmental problems: prediction of water solubility for nitro compounds

Water solubility values for 27 nitro compounds with experimentally measured values were computed using the conductor-like screening model for real solvent (COSMO-RS) based on the density functional theory and COSMO technique. We have found that the accuracy of the COSMO-RS approach for prediction of water solubility of liquid nitro compounds is impressively high (the errors are lower than 0.1 LU). However, for some solid nitro compounds, especially nitramines, there is sufficient disagreement between calculated and experimental values. In order to increase the accuracy of predictions the quantitative structure-property relationship (QSPR) part of the COSMO-RS approach has been modified. The solubility values calculated by the modified COSMO-RS method have shown much better agreement with the experimental values (the mean absolute errors are lower than 0.5 LU). Furthermore, this technique has been used for prediction of water solubility for an expanded set of 23 nitro compounds including nitroaromatic, nitramines, nitroanisoles, nitrogen rich compounds, and some their nitroso and amino derivatives with unknown experimental values. The solubility values predicted using the proposed computational technique could be useful for the determination of the environmental fate of military and industrial wastes and the development of remediation strategies for contaminated soils and waters. This predictive capability is especially important for unstable compounds and for compounds that have yet to be synthesized.

Evaluation of a TiO2 photocatalysis treatment on nitrophenols and nitramines contaminated plant wastewaters by solid-phase extraction coupled with ESI HPLC-MS

Nitration reactions of aromatic compounds are commonly involved in different industrial processes for pharmaceutical, pesticide or military uses. For many years, most of the manufacturing sites used lagooning systems to treat their process effluents. In view of a photocatalytic degradation assay, the wastewater of a lagoon was investigated by using HPLC coupled with mass spectrometry. The wastewater was highly concentrated in RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and two herbicides Dinoterb (2-tert-butyl-4,6-dinitrophenol) and Dinoseb (2-sec-butyl-4,6-dinitrophenol). First of all, an analytical method using solid-phase extraction (SPE) combined with HPLC ESI MS/MS was put in work for identification and titration of RDX, HMX and the two dinitrophenols in a complex natural matrix. Then, the UV/TiO2 treatment was investigated for pollutants removal. Dinitrophenolic compounds were significantly degraded after a 8-h-exposition of the wastewater/TiO2 suspension, whereas RDX and HMX were poorly affected.

Fate of CL-20 in sandy soils: degradation products as potential markers of natural attenuation

Hexanitrohexaazaisowurtzitane (CL-20) is an emerging explosive that may replace the currently used explosives such as RDX and HMX, but little is known about its fate in soil. The present study was conducted to determine degradation products of CL-20 in two sandy soils under abiotic and biotic anaerobic conditions. Biotic degradation was prevalent in the slightly acidic VT soil, which contained a greater organic C content, while the slightly alkaline SAC soil favored hydrolysis. CL-20 degradation was accompanied by the formation of formate, glyoxal, nitrite, ammonium, and nitrous oxide. Biotic degradation of CL-20 occurred through the formation of its denitrohydrogenated derivative (m/z 393 Da) while hydrolysis occurred through the formation of a ring cleavage product (m/z 156 Da) that was tentatively identified as CH(2)=N-C(=N-NO(2))-CH=N-CHO or its isomer N(NO(2))=CH-CH=N-CO-CH=NH. Due to their chemical specificity, these two intermediates may be considered as markers of in situ attenuation of CL-20 in soil.

Uptake of hexanitrohexaazaisowurtzitane (CL-20) by the earthworm Eisenia fetida through dermal contact

The explosive compound hexanitrohexaazaisowurtzitane (CL-20) has been shown to cause both lethal and sublethal (reproductive and neurotoxic) effects in exposed oligochaetes. However, whether worms take up CL-20 and how much CL-20 enters worm bodies leading to toxicity (e.g., lethality) remain to be determined. In the present study, we used high performance liquid chromatography (HPLC) and radiolabeled tracer methods to investigate the CL-20 uptake in the whole worm body after contact exposures. Worms (Eisenia fetida) were exposed to filter paper spiked with non-radioactive or [U-(14)C]-labeled CL-20 for 1-3 d. The radiolabeled tracer method allowed us to detect the parent compound and transformation products in worms exposed to as low as 0.04 microg CL-20 cm(-2) of filter paper. The HPLC method without radiolabeled tracer was far less sensitive with a detection limit of 2.17 microg CL-20 cm(-2). Using the radiolabeled tracer, we were able to demonstrate that the worm body concentration linearly correlated to the filter paper concentration < or =0.34 microg cm(-2) (r=0.94) if no breakdown products are assumed. At higher concentrations, the body concentration increased slowly and saturated at around 11 microg g(-1) dry mass resulting in an estimated lethal critical body burden of 10-15 microg CL-20 g(-1) dry mass. These findings demonstrate that CL-20 or potential transformation products are taken into the earthworm body through dermal contact. This information should prove valuable in assessing the bioaccumulation potential and ecological risks of CL-20.

Biodegradation kinetics of the nitramine explosive CL-20 in soil and microbial cultures

The cyclic nitramine explosive CL-20 (C(6)H(6)N(12)O(12), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12 -hexaazaisowurtzitane) is a relatively new energetic compound which could be a persistent organic pollutant. To follow its biodegradation dynamics, CL-20 was added to soil alone or together with organic co-substrates and N-source and incubated under oxic and anoxic conditions. Without co-substrates, the CL-20 degradation was detectable only under anoxic conditions. The highest degradation rate was found under aerobic conditions and with the addition of co-substrates, succinate and pyruvate being more efficient than acetate, glucose, starch or yeast extract. When added to intact soil, CL-20 degradation was not affected by the N content, but in soil serially diluted with N-free succinate-mineral medium, the process became N-limited. About 40% of randomly selected bacterial colonies grown on succinate agar medium were able to decompose CL-20. Based on 16S rDNA gene sequence and cell morphology, they were affiliated to Pseudomonas, Rhodococcus, Ochrobactrum, Mycobacterium and Ralstonia. In the pure culture of Pseudomonas sp. MS-P grown on the succinate-mineral N(+) medium, the degradation kinetics were first order with the same apparent kinetic constant throughout growth and decline phases of the batch culture. The observed kinetics agreed with the model that supposes co-metabolic transformation of CL-20 uncoupled from cell growth, which can be carried out by several constitutive cellular enzymes with wide substrate specificity.

Biodegradation of the cyclic nitramine explosives RDX, HMX, and CL-20

Cyclic nitramine explosives are synthesized globally mainly as military munitions, and their use has resulted in environmental contamination. Several biodegradation pathways have been proposed, and these are based mainly on end-product characterization because many of the metabolic intermediates are hypothetical and unstable in water. Biodegradation mechanisms for cyclic nitramines include (a) formation of a nitramine free radical and loss of nitro functional groups, (b) reduction of nitro functional groups, (c) direct enzymatic cleavage, (d) alpha-hydroxylation, or (e) hydride ion transfer. Pathway intermediates spontaneously decompose in water producing nitrite, nitrous oxide, formaldehyde, or formic acid as common end-products. In vitro enzyme and functional gene expression studies have implicated a limited number of enzymes/genes involved in cyclic nitramine catabolism. Advances in molecular biology methods such as high-throughput DNA sequencing, microarray analysis, and nucleic acid sample preparation are providing access to biochemical and genetic information on cultivable and uncultivable microorganisms. This information can provide the knowledge base for rational engineering of bioremediation strategies, biosensor development, environmental monitoring, and green biosynthesis of explosives. This paper reviews recent developments on the biodegradation of cyclic nitramines and the potential of genomics to identify novel functional genes of explosive metabolism.

Degradation of CL-20 by white-rot fungi

In previous studies, we found that the emerging energetic chemical, CL-20 (C6H6N12O12, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane), can be degraded following its initial denitration using both aerobic and anaerobic bacteria. The C and N mass balances were not determined due to the absence of labeled starting compounds. The present study describes the degradation of the emerging contaminant by Phanerochaete chrysosporium using ring-labeled [15N]-CL-20 and [14C]-CL-20. Ligninolytic cultures degraded CL-20 with the release of nitrous oxide (N2O) in amounts corresponding to 45% of the nitrogen content of CL-20. When ring-labeled [15N]-CL-20 was used, both 14N14NO and 15N14NO were observed, likely produced from -NO2 and N-NO2, respectively. The incubation of uniformly labeled [14C]-CL-20 with fungi led to the production of 14CO2 (> 80%). Another ligninolytic fungus, Irpex lacteus, was also able to degrade CL-20, but as for P. chrysosporium, no early intermediates were observed. When CL-20 was incubated with manganese peroxidase (MnP), we detected an intermediate with a [M-H]- mass ion at 345 Da (or 351 and 349 Da when using ring-labeled and nitro-labeled [15N]-CL-20, respectively) matching a molecular formula of C6H6N10O8. The intermediate was thus tentatively identified as a doubly denitrated CL-20 product. The concomitant release of nitrite ions (NO2-) with CL-20 degradation by MnP also supported the occurrence of an initial denitration prior to cleavage and decomposition.

Toxicity of emerging energetic soil contaminant CL-20 to potworm Enchytraeus crypticus in freshly amended or weathered and aged treatments

We investigated the toxicity of an emerging polynitramine energetic material hexanitrohexaazaisowurtzitane (CL-20) to the soil invertebrate species Enchytraeus crypticus by adapting then using the Enchytraeid Reproduction Test (ISO/16387:2003). Studies were designed to develop ecotoxicological benchmark values for ecological risk assessment of the potential impacts of accidental release of this compound into the environment. Tests were conducted in Sassafras Sandy Loam soil, which supports relatively high bioavailability of CL-20. Weathering and aging procedures for CL-20 amended into test soil were incorporated into the study design to produce toxicity data that better reflect soil exposure conditions in the field compared with the toxicity in freshly amended soils. Concentration-response relationships for measurement endpoints were determined using nonlinear regressions. Definitive tests showed that toxicities for E. crypticus adult survival and juvenile production were significantly increased in weathered and aged soil treatments compared with toxicity in freshly amended soil, based on 95% confidence intervals. The median effect concentration (EC50) and EC20 values for juvenile production were 0.3 and 0.1 mg kg-1, respectively, for CL-20 freshly amended into soil, and 0.1 and 0.035 mg kg-1, respectively, for weathered and aged CL-20 soil treatments. These findings of increased toxicity to E. crypticus in weathered and aged CL-20 soil treatments compared with exposures in freshly amended soils show that future investigations should include a weathering and aging component to generate toxicity data that provide more complete information on ecotoxicological effects of emerging energetic contaminants in soil.

Biotic and abiotic degradation of CL-20 and RDX in soils

The caged cyclic nitramine 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a new explosive that has the potential to replace existing military explosives, but little is known about its environmental toxicity, transport, and fate. We quantified and compared the aerobic environmental fate of CL-20 to the widely used cyclic nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in surface and subsurface soil microcosms. Soil-free controls and biologically attenuated soil controls were used to separate abiotic processes from biologically mediated processes. Both abiotic and biological processes significantly degraded CL-20 in all soils examined. Apparent abiotic, first-order degradation rates (k) for CL-20 were not significantly different between soil-free controls (0.018 < k < 0.030 d(-1)) and biologically attenuated soil controls (0.003 < k < 0.277 d(-1)). The addition of glucose to biologically active soil microcosms significantly increased CL-20 degradation rates (0.068 < k < 1.22 d(-1)). Extents of mineralization of (14)C-CL-20 to (14)CO(2) in biologically active soil microcosms were 41.1 to 55.7%, indicating that the CL-20 cage was broken, since all carbons are part of the heterocyclic cage. Under aerobic conditions, abiotic degradation rates of RDX were generally slower (0 < k < 0.032 d(-1)) than abiotic CL-20 degradation rates. In biologically active soil microcosms amended with glucose aerobic RDX degradation rates varied between 0.010 and 0.474 d(-1). Biodegradation was a key factor in determining the environmental fate of RDX, while a combination of biotic and abiotic processes was important with CL-20. Our data suggest that CL-20 should be less recalcitrant than RDX in aerobic soils.

Stereo-specificity for pro-(R) hydrogen of NAD(P)H during enzyme-catalyzed hydride transfer to CL-20

A dehydrogenase from Clostridium sp. EDB2 and a diaphorase from Clostridium kluyveri were reacted with CL-20 to gain insights into the enzyme-catalyzed hydride transfer to CL-20, and the enzyme's stereo-specificity for either pro-R or pro-S hydrogens of NAD(P)H. Both enzymes biotransformed CL-20 at rates of 18.5 and 24nmol/h/mg protein, using NADH and NADPH as hydride-source, respectively, to produce a N-denitrohydrogenated product with a molecular weight of 393Da. In enzyme kinetics studies using reduced deuterated pyridine nucleotides, we found a kinetic deuterium isotopic effect of 2-fold on CL-20 biotransformation rate using dehydrogenase enzyme against (R)NADD as a hydride-source compared to either (S)NADD or NADH. Whereas, in case of diaphorase, the kinetic deuterium isotopic effect of about 1.5-fold was observed on CL-20 biotransformation rate using (R)NADPD as hydride-source. In a comparative study with LC-MS, using deuterated and non-deuterated NAD(P)H, we found a positive mass-shift of 1Da in the N-denitrohydrogenated product suggesting the involvement of a deuteride (D(-)) transfer from NAD(P)D. The present study thus revealed that both dehydrogenase and diaphorase enzymes from the two Clostridium species catalyzed a hydride transfer to CL-20 and showed stereo-specificity for pro-R hydrogen of NAD(P)H.

Prediction of CL-20 chemical degradation pathways, theoretical and experimental evidence for dependence on competing modes of reaction

Highest occupied and lowest unoccupied molecular orbital energies, formation energies, bond lengths and FTIR spectra all suggest competing CL-20 degradation mechanisms. This second of two studies investigates recalcitrant, toxic, aromatic CL-20 intermediates that absorb from 370 to 430 nm. Our earlier study (Struct. Chem., 15, 2004) revealed that these intermediates were formed at high OH(-) concentrations via the chemically preferred pathway of breaking the C-C bond between the two cyclopentanes, thereby eliminating nitro groups, forming conjugated pi bonds, and resulting in a pyrazine three-ring aromatic intermediate. In attempting to find and make dominant a more benign CL-20 transformation pathway, this current research validates hydroxylation results from both studies and examines CL-20 transformations via photo-induced free radical reactions. This article discusses CL-20 competing modes of degradation revealed through: computational calculation; UV/VIS and SF spectroscopy following alkaline hydrolysis; and photochemical irradiation to degrade CL-20 and its byproducts at their respective wavelengths of maximum absorption.

Biotransformation of CL-20 by a dehydrogenase enzyme from Clostridium sp. EDB2

In a previous study, a marine isolate Clostridium sp. EDB2 degraded 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) under anaerobic conditions (Bhushan B, Halasz A, Thiboutot S, Ampleman G, Hawari J (2004c) Chemotaxis-mediated biodegradation of cyclic nitramine explosives RDX, HMX, and CL-20 by Clostridium sp. EDB2. Biochem Biophys Res Commun 316:816-821); however, the enzyme responsible for CL-20 degradation was not known. In the present study, we isolated and purified an enzyme, from strain EDB2, responsible for CL-20 degradation. The enzyme was membrane-associated and NADH-dependent and had a molecular weight of 56 kDa (with SDS-PAGE). N-terminal amino acid sequence of enzyme revealed that it belonged to dehydrogenase class of enzymes. The purified enzyme degraded CL-20 at a rate of 18.5 nmol/h mg protein under anaerobic conditions. Carbon and nitrogen mass balance of the products were 100 and 64%, respectively. In LC-MS-MS studies, we detected three different initial metabolites from CL-20, i.e., mono-nitroso derivative, denitrohydrogenated product, and double-denitrated isomers with molecular weight of 422, 393, and 346 Da, corresponding to presumed empirical formulas of C(6)H(6)N(12)O(11), C(6)H(7)N(11)O(10), and C(6)H(6)N(10)O(8), respectively. Identity of all the three metabolites were confirmed by using ring-labeled [(15)N]CL-20 and the nitro-group-labeled [(15)NO(2)]CL-20. Taken together, the above data suggested that the enzyme degraded CL-20 via three different routes: Route A, via two single electron transfers necessary to release two nitro-groups from CL-20 to produce two double-denitrated isomers; Route B, via a hydride transfer necessary to produce a denitrohydrogenated product; and Route C, via transfer of two redox equivalents to CL-20 necessary to produce a mono-nitroso derivative of CL-20. This is the first biochemical study which showed that CL-20 degradation can be initiated via more than one pathway.

Detection of nitroaromatic and cyclic nitramine compounds by cyclodextrin assisted capillary electrophoresis quadrupole ion trap mass spectrometry

An Agilent 3DCE capillary electrophoresis system using sulfobutylether-beta-cyclodextrin (SB-beta-CD)-ammonium acetate separation buffer pH 6.9 was coupled to a Bruker Esquire 3000+ quadrupole ion trap mass detector via a commercially available electrospray ionization interface with acetonitrile sheath flow. The CE-MS system was applied in negative ionization mode for the resolution and detection of nitroaromatic and polar cyclic or caged nitramine energetic materials including TNT [2,4,6-trinitrotoluene, formula mass (FW) 227.13], TNB (1,3,5-trinitrobenzene, FW 213.12), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine, FW 222.26) HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, FW 296.16), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, FW 438.19). The CE-MS system conformed to the high-performance liquid chromatography with ultraviolet absorbance detection (HPLC-UV) and HPLC-MS reference methods for the identification of energetic contaminants and their degradation products in soil and marine sediment samples.

Decomposition of the polycyclic nitramine explosive, CL-20, by Fe(0)

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane), C6H6N12O12, is an emerging energetic chemical that may replace RDX, but its degradation pathways are not well-known. In the present study, zerovalent iron was used to degrade CL-20 with the aim of determining its products and degradation pathways. In the absence of O2, CL-20 underwent a rapid decomposition with the concurrent formation of nitrite to ultimately produce nitrous oxide, ammonium, formate, glyoxal, and glycolate. LC/MS (ES-) showed the presence of several key products carrying important information on the initial reactions involved in the degradation of CL-20. For instance, a doubly denitrated intermediate of CL-20 was detected together with the mono- and dinitroso derivatives of the energetic chemical. Two other intermediates with [M-H]- at 392 and 376 Da, matching empirical formulas of C6H7N11O10 and C6H7N11O9, respectively, were detected. Using 15N-labeled CL-20, the two intermediates were tentatively identified as the denitrohydrogenated products of CL-20 and its mononitroso derivative, respectively. The present experimental findings suggest that CL-20 degraded via at least two initial routes: one involving denitration and the second involving sequential reduction of the N-NO2 to the corresponding nitroso (N-NO) derivatives prior to denitration and ring cleavage.