Cloning, sequencing, and characterization of the hexahydro-1,3,5-trinitro-1,3,5-triazine degradation gene cluster from Rhodococcus rhodochrous

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a high explosive which presents an environmental hazard as a major land and groundwater contaminant. Rhodococcus rhodochrous strain 11Y was isolated from explosive contaminated land and is capable of degrading RDX when provided as the sole source of nitrogen for growth. Products of RDX degradation in resting-cell incubations were analyzed and found to include nitrite, formaldehyde, and formate. No ammonium was excreted into the medium, and no dead-end metabolites were observed. The gene responsible for the degradation of RDX in strain 11Y is a constitutively expressed cytochrome P450-like gene, xpLA, which is found in a gene cluster with an adrenodoxin reductase homologue, xplB. The cytochrome P450 also has a flavodoxin domain at the N terminus. This study is the first to present a gene which has been identified as being responsible for RDX biodegradation. The mechanism of action of XplA on RDX is thought to involve initial denitration followed by spontaneous ring cleavage and mineralization

Density functional theory calculations of anisotropic constitutive relationships in alpha-cyclotrimethylenetrinitramine

Constitutive relationships in the crystalline energetic material alpha-cyclotrimethylenetrinitramine (alpha-RDX) have been investigated using first-principles density functional theory. The equilibrium properties of alpha-RDX including unit cell parameters and bulk modulus, as well as the hydrostatic equation of state (EOS), have been obtained and compared with available experimental data. The isotropic EOS has been extended to include the anisotropic response of alpha-RDX by performing uniaxial compressions normal to several low-index planes, {100}, {010}, {001}, {110}, {101}, {011}, and {111}, in the Pbca space group. The uniaxial-compression data exhibit a considerable anisotropy in the principal stresses, changes in energy, band gaps, and shear stresses, which might play a role in the anisotropic behavior of alpha-RDX under shock loading

Thermal Decomposition of Energetic Materials by ReaxFF Reactive Molecular Dynamics

We report the study of thermal decomposition of 1,3,5-trinitrohexahydro-s-triazine (RDX) bonded with polyurethane (Estane) and of the bulk hydrazine by molecular dynamics (MD) simulations equipped with the reactive force field (ReaxFF). For the polymer binder explosive, the simulation results show that the thermal decomposition of RDX is affected by the presence of the polymer binder Estane. Generally, with addition of Estane the decomposition of RDX slows down. Final products including N2, H2O, CO, CO2 and intermediates NO2, NO and HONO have been identified from the thermal decomposition processes. For the bulk hydrazine, it is found that with the increase of temperature, its decomposition increases and more N2 and H2 are generated, but NH3 molecules are consumed much faster at higher temperatures. This simulation work provides us an approach to quickly test the response of various energetic materials to thermal conditions

Thermodynamic Simulation of the RDX-Aluminum Interface Using ReaxFF Molecular Dynamics

We use reactive molecular dynamics (RMD) simulations to study the interface between cyclotrimethylene trinitramine (RDX) and aluminum (Al) with different oxide layers to elucidate the effect of nanosized Al on thermal decomposition of RDX. A published ReaxFF force field for C/H/N/O elements was retrained to incorporate Al interactions and then used in RMD simulations to characterize compound energetic materials. We find that the predicted adsorption energies for RDX on the Al(111) surface and the apparent activation energies of RDX and RDX/Al are in agreement with ab initio calculations. The Al(111) surface-assisted decomposition of RDX occurs spontaneously without potential barriers, but the decomposition rate becomes slow when compared with that for RDX powder. We also find that the Al(111) surface with an oxide layer (Al oxide) slightly increases the potential barriers for decomposition of RDX molecules, while α-Al_2O_3(0001) retards thermal decomposition of RDX, due to the changes in thermal decomposition kinetics. The most likely mechanism for the thermal decomposition of RDX powder is described by the Avrami–Erofeev equation, with n = 3/4, as random nucleation and subsequent growth model. Although the decomposition mechanism of RDX molecules in the RDX/Al matrix complies with three-dimensional diffusion, Jander’s equation for RDX(210)/Al oxide and the Zhuralev–Lesokin–Tempelman (Z-L-T) equation for RDX(210)/Al_2O_3(0001) provide a more accurate description. We conclude that the origin of these differences in dynamic behavior is due to the variations in the oxide layer morphologies

Application of introduced nano-diamonds for the study of carbon condensation during detonation of high explosives

This paper describes the experimental studies of the formation of nano-diamonds during detonation of TNT/RDX 50/50 mixture with small-angle x-ray scattering (SAXS) method at a synchrotron radiation beam on VEPP-3 accelerator. A new experimental method with introduction of nano-diamonds into the explosive has been applied. Inclusion of the diamonds obtained after detonation into the TNT and RDX explosives allows modelling of the case of instant creation of nano-diamonds during detonation.Comment: Latex, 4 pages, 2 figures (proc. of SR-2008

BIODEGRADATION OF HEXAHYDRO-1,3,5-TRINITRO-1,3,5-TRIAZINE (RDX) USING PHOTOSYNTHETIC BACTERIA

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is an emerging contaminant according to the Environmental Protection Agency (EPA). RDX was introduced as a secondary explosive during World War II. It is still used in many explosive such as hand grenades. RDX enters the environment mostly through the manufacturing process or from the use of explosives. RDX is a suspected carcinogen and can also affect the nervous system of humans. Therefore, RDX has become a chemical of concern across many United States military bases and open and closed manufacturing plants. The goal of this research was to evaluate the biodegradation of RDX via two phototrophic bacteria: Rhodobacter sphaeroides ATCC® 17023™ and Synechocystis sp. PCC 6803. The ability to degrade RDX via a phototrophic bacteria could make remediation more passive. A passive remediation option could be an easier and more cost effective way to remediate RDX. Biodegradation of RDX has been successful with other bacteria, but Synechocystis sp. PCC 6803 was studied because it is robust and grows well in aerobic environments. The specific objectives for this research were to: 1. Determine if electron acceptors nitrate (1 mM), sulfate (10 mM), and perchlorate (1 mM) influence R. sphaeroides’ ability to degrade RDX under ideal conditions (growth conditions with succinate as electron donor). 2. Determine if R. sphaeroides can degrade RDX with oxygen present. The work conducted showed that: 1. Adding electron acceptors to incubations with R. sphaeroides, electron donor, and RDX while in the presence of light did not significantly change the time required to degrade RDX. After 49 hours RDX was degraded 100% in samples with no electron acceptor and with perchlorate, 99% in samples with sulfate, and 94% in samples with nitrate. 2. Exposing R. sphaeroides to air drastically inhibited the degradation of RDX. After 19 days, 40% of RDX still remained in the samples. The same samples in anaerobic conditions degraded RDX in only 49 hours. 3. BG-11 media degraded RDX significantly under a cool-white fluorescent light. 4. Synechocystis’s growth was affected when BG-11 nutrient stock concentration was degraded. 5. Synechocystis completely degraded RDX with and without an electron shuttle and in anaerobic environments and in the presence of air. 6. Synechocystis reduced RDX more efficiently when placed in incubations with growth media as opposed to being placed in incubations with HEPES buffer. RDX degradation via a bacteria, Synechocystis, in aerobic conditions has not been published. The work conducted showed that RDX can be degraded by Synechocystis and R. sphaeroides (in the presence of air and electron acceptors). However, more research needs to be conducted. Reduction of RDX by R. sphaeroides in field conditions needs to be examined. Also, the mechanisms of Synechocystis that degrade RDX need to be furthered studied. 3. Determine if Synechocystis can degrade RDX and if so, under what conditions

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 compoundswere significantly degraded after a 8-h-exposition of the wastewater/TiO2 suspension, whereas RDX and HMX were poorly affected

MicroRNA and messenger RNA profiling reveals new biomarkers and mechanisms for RDX induced neurotoxicity

Background RDX is a well-known pollutant to induce neurotoxicity. MicroRNAs (miRNA) and messenger RNA (mRNA) profiles are useful tools for toxicogenomics studies. It is worthy to integrate MiRNA and mRNA expression data to understand RDX-induced neurotoxicity. Results Rats were treated with or without RDX for 48 h. Both miRNA and mRNA profiles were conducted using brain tissues. Nine miRNAs were significantly regulated by RDX. Of these, 6 and 3 miRNAs were up- and down-regulated respectively. The putative target genes of RDX-regulated miRNAs were highly nervous system function genes and pathways enriched. Fifteen differentially genes altered by RDX from mRNA profiles were the putative targets of regulated miRNAs. The induction of miR-71, miR-27ab, miR-98, and miR-135a expression by RDX, could reduce the expression of the genes POLE4, C5ORF13, SULF1 and ROCK2, and eventually induce neurotoxicity. Over-expression of miR-27ab, or reduction of the expression of unknown miRNAs by RDX, could up-regulate HMGCR expression and contribute to neurotoxicity. RDX regulated immune and inflammation response miRNAs and genes could contribute to RDX- induced neurotoxicity and other toxicities as well as animal defending reaction response to RDX exposure. Conclusions Our results demonstrate that integrating miRNA and mRNA profiles is valuable to indentify novel biomarkers and molecular mechanisms for RDX-induced neurological disorder and neurotoxicity.published_or_final_versio

Spheroidization of RDX and Its Effect on the Pourability of RDXA'NT Slurries

A technique for spheroidization of RDX has been developed using acetone as medium. Effect of spheroidized RDX vis-a-vis ordinary crystals of RDX on the pourability of RDX/TNT slurries has been studied. It is seen that mixture of different sizes of RDX crystals andratio of coarse to fine plays very important role in increasing the pourability as well as the content of RDX in RDX/TNT charges up to75 per cent.