磨木木素在硫酸盐法蒸煮过程中的反应

在木糖存在的条件下,采用硫酸盐法蒸煮的方法对蓝花楹磨木木素(milled wood lignin,简称MWL)进行处理,然后对处理后的产物进行红外光谱和13C-NMR分析,研究蓝花楹MWL的结构变化,探讨在硫酸盐法蒸煮过程中木素-碳水化合物复合体(lignin-carbohydrate complexes,简称LCC)的形成情况。研究发现:蓝花楹MWL结构单元之间的α-烷基芳基醚键、β-O-4型连接键很容易发生断裂,而在这些连接键发生断裂的同时,形成的木素中间体与糖产生化学键的结合,蒸煮液中有新的LCC结构形成。     

铜绿假单胞菌M19降解黄曲霉毒素B1的产物研究（网络首发、推荐阅读）

以实验室筛选保藏的黄曲霉毒素B1（Aflatoxin B1,AFB1）降解菌M19产生的降解酶PADE为对象,对其AFB1降解液进行薄层色谱及荧光光谱分析（LC-MS）,分析降解产物可能的结构变化,并利用液相质谱检测AFB1降解产物。薄层色谱检测结果：有机相和水相降解液均未检测到新的荧光吸收物质,表明降解产物没有荧光吸收;荧光光谱检测结果：AFB1降解产物的荧光明显减弱;液相质谱检测结果：发现质荷比为227.18的物质P。结果推断：AFB1降解过程中内酯键断裂,产生一个分子量为226的降解产物P,利用Xcalibur软件分析其分子式为C14H10O3,并根据AFB1降解后的LC-MS图谱分析以及AFB1降解产物的相关文献对降解途径进行假设。     

Structural characterization of metabolites after the microbial degradation of type A trichothecenes by the bacterial strain BBSH 797

Contamination of feed with trichothecenes, a group of Fusarium mycotoxins, leads to losses in performance due to their immunosupressive effects and the negative effect on the gastrointestinal system in animal production. A possible way of detoxification is microbial degradation, which was the focus of this study. A bacterial strain - BBSH 797 - which can degrade some mycotoxins of the trichothecene group, has already been isolated. It transforms deoxynivalenol (DON) into its metabolite DOM-1, the non-toxic deepoxide of DON. Analogous to the microbial degradation of DON, the transformation of six different type A trichothecenes was observed. The metabolites appearing were characterized by GC-MS after derivatization with TRI-SIL®TBT. Two metabolites were additionally identified by liquid chromatography-mass spectrometry with particle beam interface (LC-PB-MS) with electron impact (EI)-ionization mode. The major finding was that scirpentriol was completely transformed into its non-toxic metabolite deepoxy scirpentriol, while the mycotoxin T-2 triol underwent a more complicated metabolism. According to the study, T-2-triol was degraded into its non-toxic deepoxy form and into T-2 tetraol, which was then further metabolized to deepoxy T-2 tetraol. GC-MS after derivatization with TRI-SIL®TBT was suitable for the structural characterization of trichothecenes and their degradation products. Besides the mass spectra of already known degradation products, spectra of new metabolites could be recorded by LC-PB-MS.     

Mechanistic studies of the photocatalytic oxidation of microcystin-LR: an investigation of byproducts of the decomposition process

Microcystins (cyclic heptapeptides) are produced by a number of freshwater cyanobacteria and cause concern in potable water supplies due to their acute and chronic toxicity. The present study reports the structural characterization of the degradation products of the photocatalytic oxidation of microcystin-LR, so aiding the mechanistic understanding of this process. TiO2 photocatalysis is a promising technology for removal of these toxins from drinking water. However, before it can be adopted in any practical application it is necessary to have a sufficient knowledge of degradation byproducts and their potential toxicity. Liquid chromatography-mass spectrometry analysis demonstrated that the major destruction pathway of microcystin appears to be initiated via three mechanisms: UV irradiation, hydroxyl radical attack, and oxidation. UV irradiation caused geometrical isomerization of microcystin converting the (4E), (6E) of the Adda configuration to (4E), 6(Z) or 4(Z), 6(E). Hydroxyl radical attack on the conjugated diene structure of Adda moiety produced dihyroxylated products. Further oxidation cleaved the hydroxylated 4-5 and/or 6-7 bond of Adda to form aldehyde or ketone peptide residues, which then were oxidized into the corresponding carboxylic acids. Photocatalysis also hydrolyzed the peptide bond on the ring structure of microcystin to form linear structures although this appeared to be a minor pathway.     

Efficacy of chlorfenapyr against Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) adults exposed on concrete, vinyl tile, and plywood surfaces

The insecticidal pyrrole chlorfenapyr was applied to concrete, vinyl tile, and plywood surfaces, at an application rate of 1.1 g AI m⁻². Adult Tribolium castaneum (Herbst), the red flour beetle, and adult Tribolium confusum (Du Val), the confused flour beetle, were exposed for 2 and 4 h, removed, and held without food for 7 d post-exposure. All beetles survived the initial exposures, but survival of both species decreased during the 7-d holding period, with T. confusum being the more susceptible species. Survival was generally lower on concrete than on tile or plywood, and was greatly reduced on all three surfaces after 4 h of exposure compared to 2 h. Survival of T. castaneum after 2 h of exposure on concrete, tile, and plywood was 2.5±2.5%, 25.5±15.4%, and 40.0±7.1%, respectively, after 7 d. In contrast, all T. confusum exposed on concrete and tile were dead after 4 and 5 d, respectively, while survival on plywood after 7 d was 20.0±16.8%. After 4 h of exposure, all T. castaneum and T. confusum exposed on concrete and tile were dead after 2–4 d post-exposure, while survival on plywood after 7 d was 41.5±6.4% and 0 for each species, respectively. Non-linear and linear regressions were fit to the data for both species. Results show exposure to chlorfenapyr is effective against T. castaneum and T. confusum, but efficacy will vary depending on the surface substrate.     

应用液-液萃取结合GC-MS与GC-NPD技术对国井芝麻香型白酒中含氮化合物的分析

应用液-液萃取结合气相色谱-质谱（gas chromatography-mass spectrometry,GC-MS）与气相色谱-氮磷检测器（GC-nitrogen phosphorus detector,GC-NPD）技术对国井芝麻香型白酒中含氮化合物进行分析,实验中以模拟酒样为研究对象确定分析的较优条件：用4 mol/L的盐酸溶液将酒样H+浓度调至1 mol/L,浓缩后用新重蒸的乙醚萃取出酸、中性组分,再将水相pH值调至9,用新重蒸的乙醚萃取出碱性组分,浓缩后进行GC-MS与GC-NPD分析。结果表明,采用液-液萃取结合GC-MS与GC-NPD方法,从国井芝麻香型白酒中共检测出31 种含氮化合物,其中23 种通过标准品比对进行准确定性,确证为吡嗪类化合物14 种 、吡咯类化合物1 种、吡啶类化合物4 种、噻唑类化合物1 种、噁唑类化合物1 种,其他类化合物2 种。     

酸、碱溶液对脱脂蚕蛹组织结构的影响

在100℃下将脱脂蛹分别置于清水、盐酸溶液(1%wt)和氢氧化钠溶液(1%wt)中浸泡处理20min,采用电子光学显微分析技术,观察处理后脱脂蛹的解剖结构,并对浸泡液进行了定性分析。结果表明:(1)清水、盐酸溶液、氢氧化钠溶液浸泡,均引起蛋白质、甲壳素膨胀,氢氧化钠溶液对蚕蛹的蛋白层与甲壳层的层间有劈开作用;(2)盐酸溶液作用下,蛹蛋白的分解产物是氨基酸;蛹蛋白在碱溶液中溶解显著,同时,伴有部分蛋白质的分解,其分解产物是氨基酸,而氨基酸进一步分解可释放出氨。     

Air-water transfer of MTBE, its degradation products, and alternative fuel oxygenates: the role of temperature

The gasoline oxygenate methyl tert-butyl ether (MTBE) has become one of the world's mostwidespread groundwater and surface water contaminants. As a result, there has been increasing interest in the environmental behavior of MTBE and its degradation products, mainly tert-butyl formate (TBF) and tert-butyl alcohol (TBA). In contrast, the environmental behavior of the proposed alternatives to MTBE, namely ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), and diisopropyl ether (DIPE) has hardly been studied yet, although some of them are already in substantial use in various countries. A key parameter for the assessment of the fate, transport, and possible remediation of these contaminants is the air-water partitioning constant (KiH). The KiH is highly temperature dependent, and it is therefore necessary to obtain reliable experimental values at relevant temperatures. Hence, the KiH of MTBE, ETBE, TAME, and DIPE, along with the degradation products, TBF and methyl acetate, were determined from 5 degrees C-40 degrees C. The alternatives to MTBE generally had a higher KiH, which implies that, upon emission into the environment, the alternatives partition more readily into the air phase than MTBE. This may favor their use, as it is in the air phase where dilution and degradation are the most effective. The degradation products of MTBE, with the exception of TBF, have much lower KiH values at all temperatures. Hence, the degradation products will have a stronger affinity for the water phase. The temperature dependency of the kinetics of air-watertransfer is discussed using a boundary layer model. Only for TBA but not for the ethers a significant effect of temperature was found.     

Variations in 13C/12C and D/H enrichment factors of aerobic bacterial fuel oxygenate degradation

Reliable compound-specific isotope enrichment factors are needed for a quantitative assessment of in situ biodegradation in contaminated groundwater. To obtain information on the variability on carbon and hydrogen enrichment factors (epsilonC, epsilonH) the isotope fractionation of methyl tertiary (tert-) butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) upon aerobic degradation was studied with different bacterial isolates. Methylibium sp. R8 showed a carbon and hydrogen isotope enrichment upon MTBE degradation of -2.4 +/- 0.1 and -42 +/- 4 per thousand, respectively, which is in the range of previous studies with pure cultures (Methylibium petroleiphilum PM1) as well as mixed consortia. In contrast, epsilonC of the beta/-proteobacterium L108 (-0.48 +/- 0.05 per thousand) and Rhodococcus ruber IFP 2001 (-0.28 +/- 0.06 per thousand) was much lower and hydrogen isotope fractionation was negligible (epsilonH < or = -0.2 per thousand). The varying isotope fractionation pattern indicates that MTBE is degraded by different mechanisms by the strains R8 and PM1 compared to L108 and IFP 2001. The carbon and hydrogen isotope fractionation of ETBE by L108 (epsilonC = -0.68 +/- 0.06 per thousand and epsilonH = -14 +/- 2 per thousand) and IFP 2001 (epsilonC = -0.8 +/- 0.1 per thousand and epsilonH = -11 +/- 4 per thousand) was very similar and seemed slightly higher than the fractionation observed upon MTBE degradation by the same strains. The low carbon and hydrogen enrichment factors observed during MTBE and ETBE degradation by L108 and IFP 2001 suggest a hydrolysis-like reaction type of the ether bond cleavage compared to oxidation of the alkyl group as suggested for the strains PM1 and R8. The variability of carbon and hydrogen enrichment factors should be taken into account when interpreting isotope pattern of fuel oxygenates with respect to biodegradation in contamination plumes.     

Anaerobic degradation of decabromodiphenyl ether

The environmental safety of decabromodiphenyl ether (BDE-209), a widely used flame retardant, has been the topic of controversial discussions during the past several years. Degradation of BDE-209 into lower brominated diphenyl ether congeners, exhibiting a higher bioaccumulation potential, has been a critical issue. Here, we report on the degradation of BDE-209 and the formation of octa- and nonabromodiphenyl ether congeners under anaerobic conditions. Sewage sludge collected from a mesophilic digester was used as the inoculum and incubated up to 238 days with and without a set of five primers. Following Soxhlet extraction and a liquid chromatography cleanup procedure, parent compounds and debromination products were analyzed by GC/HRMS. In experiments with primers, concentrations of BDE-209 decreased by 30% within 238 days. This corresponds to a pseudo-first-order degradation rate constant of 1 x 10(-3) d(-1). Without primers, the degradation rate constant was 50% lower. Formation of two nonabromodiphenyl ether and six octabromodiphenyl ether congeners proved that BDE-209 underwent reductive debromination in these experiments. Debromination occurred at the para and the meta positions, whereas debromination at the ortho position was not statistically significant. All three nonabromodiphenyl ether congeners (BDE-206, BDE-207, and BDE-208) were found to undergo reductive debromination as well. No significant change of the BDE-209 concentration and no formation of lower brominated congeners was observed in sterile control experiments. To our knowledge, this is the first report demonstrating microbially mediated reductive debromination of BDE-209 under anaerobic conditions.     

Changes in the initial stages of a glucose-proline Maillard reaction model system influences dairy product quality during thermal processing

The Maillard reaction always occurs during the thermal processing of dairy products, which significantly influences their quality. In the present study, the initial stages of a glucose-proline model system were investigated in water and different types of buffer solutions. Results showed that phosphate buffer accelerated the reversible degradation of the initial stages of the reaction. The proposed catalysis mechanism was that hydrogenous and dihydric phosphate radical anions simultaneously accepted and donated protons for the conversion of the intermediates into N-glycosylamine. The catalysis mechanism was confirmed via testing and no reducing of hydrogenous and dihydric phosphate radical anions was observed during the reaction. Moreover, both N-(1-deoxy-D-fructos-1-yl)proline and its degradation compounds were analyzed. Results showed that degradation of N-(1-deoxy-D-fructos-1-yl)proline to form 5-hydroxymethyl-2-furaldehyde and formic acid was also accelerated by phosphate buffer. An interesting phenomenon was that citrate decreased 5-hydroxymethyl-2-furaldehyde formation, which might be because Strecker-type degradation occurred more easily than 1,2-enolization reaction in citrate buffer solution. However, this hypothesis has not been confirmed, and element label experiments should be carried out in the future.     

基于LOX-HPL途径的武夷肉桂加工中香气物质的形成与调控

武夷肉桂是以福建省级茶树良种肉桂(Camellia sinensis cv.Rougui)鲜叶为原料制成的乌龙茶,具有"岩骨花香"的品质特征,深受消费者青睐。除茶树鲜叶外,武夷肉桂的品质形成很大程度上取决于加工工艺,但生产加工过程中以绿叶挥发物(Green Leaf Volatiles,GLVs)和果酯类为代表的脂肪族类香气成分代谢机理的研究,尚未见报道。以武夷肉桂的鲜叶、晒青叶及做青过程叶为试材,采用顶空固相微萃取法(Headspace Solid-Phase Microextraction,HS-SPEM)结合气相色谱与高通量飞行时间质谱联用技术(Gas Chromatography-Time-of-Flight Mass Spectrometry,GC-TOF-MS)对加工过程样中的脂肪族类香气成分检测发现:脂肪族醛类在做青过程中显著降低,而大量的脂肪族醇类和酯类显著积累,其中叶醇酯类和己烯醇、酯类分别对静置失水和机械损伤存在响应;利用紫外/可见分光光度法检测加工过程样中LOX-HPL途径中关键酶活力,结果表明,脂肪氧合酶(Lipoxygenase,LOX)、乙醇脱氢酶(Alcohol dehydrogenase,ADH)及乙醇酰基转移酶(Alcohol acyltransferases,AAT)的活力分别在第三次摇青叶(3T)、第四次摇青后叶(4T)及第五次摇青后叶(5T)中达到最大值;实时荧光定量聚合酶链式反应(Quantitative Real-Time Polymerase Chain Reaction,qRT-PCR)结果表明,CsLOX2、CsLOX5基因主要在做青初始阶段(2T、3T)相对表达量较高,而随着工艺过程的推进,CsADH2-1、CsAAT基因在做青后期(4T、5T)开始上调表达;通过Pearson系数评估武夷肉桂加工过程中的脂肪族类香气、酶活力和基因表达量间的相关性,发现正己醇、戊酸叶醇酯、己酸己酯、丁酸甲基叶醇酯、柳酸叶醇酯等大量具有天然花果香的脂肪族醇类和酯类与CsADH2-1基因具有显著(P<0.05)或极显著(P<0.01)的正相关,CsAAT基因与CsLOX2、CsLOX5基因在加工过程中具有相似的表达模式(r=0.762,r=0.732)。LOX-HPL途径关键基因的共表达,驱动了脂肪族类香气在加工过程中的协同积累,是武夷肉桂馥郁香气形成的重要基础。     

Vinylogous Amadori rearrangement: implications in food and biological systems

The 4-hydroxy-alkenals are important lipid peroxidation products and are known to play a major role both in the development of degenerative diseases in biological systems and off-flavors, or rancidity in food systems. The 4-hydroxy-alkenals can also be formed in nonlipid systems from 2-deoxy-sugar moieties such as 2-deoxy-ribose. FTIR spectroscopic evidence was provided for such a transformation catalyzed by amino acids through monitoring the decrease in intensity of the aldehydic band centered at 1716 cm(-1) of the open form of 2-deoxy-ribose and increase in the intensity of the formed conjugated aldehydic band centered at 1672 cm(-1). Furthermore, 4-hydroxy-alkenals can react with nitrogen nucleophiles such as amino acids and proteins to form Schiff base adducts that are able to undergo vinylogous Amadori rearrangement (vARP) and subsequently cyclize to generate a pyrrole moiety. This cyclization is prevented in the case of secondary amino acids such as proline to form a stable vinylogous Amadori rearrangement product (vARP). Monitoring this reaction of proline with 4-hydroxy-2-nonenal (HNE) has indicated that within 15 min at 28 degrees C the 1685 cm(-1) band of HNE completely disappears and that at 50 degrees C, vARP is formed within 5 min, as indicated by the formation of a characteristic band at 1709 cm(-1).     

AgNO3-lnduced photocatalytic degradation of odorous methyl mercaptan in gaseous phase: mechanism of chemisorption and photocatalytic reaction

In this study, AgNO3 films prepared by a simple dip-coating method were used to remove gaseous methyl mercaptan (CH3SH) for odor control. The AgNO3 films were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy/energy-dispersive X-ray spectrometry(SEM/EDX), and X-ray photoelectron spectroscopy (XPS) before and after the reaction, and as- obtained products were identified by means of gas chromatography/mass spectrometry (GC/MS) and ion chromatography. The experiments demonstrated that the AgNO3 film can induce a quick chemisorption of gaseous CH3SH to form AgSCH3 and other intermediate products such as alpha-Ag2S, Ag4S2, and AgSH on its surface. Under UVA illumination, these sulfur products can be photocatalytically oxidized to AgSO3CH3 and Ag2SO4. Then AgSO3CH3 and Ag2SO4 will continue the chemisorption of gaseous CH3SH, similar to AgNO3, to form AgSCH3 again and release two final products, HSO3CH3 and H2SO4. Hence it is a AgNO3-induced photocatalytic reaction for odorous CH3SH degradation in gaseous phase. This fundamental research about the mechanism of chemisorption and photocatalytic reaction provides essential knowledge with potential to further develop a new process for gaseous CH3SH degradation in odor control.     

Biological Degradation of Chlorophyll in a System Using Bell Peppers (Capsicum frutescens)

SUMMARY– A degradation system was developed based on the incorporation of radioactive chlorophyll into a ripening bell pepper carpel.
Pure chlorophyll a in aqueous triton X-100 injected into green bell peppers ( Capsicum frutescens ) variety 035 was degraded up to 50% by the end of ripening, versus a control in buffer pH 5.4 not exceeding 7% loss in 2 weeks. Variety and stage of ripeness affected the amount of degradation.
Labeled chlorophyll a with a specific activity of 7 to 8 × 10⁵ dpm/mg was then prepared from young wheat plants, fed ¹⁴Cob and injected in amounts of 0.2 to 0.3 mg. The distribution of activity in pepper extracts after pigment degradation was evaluated. The acetone water extract remaining after transfer of lipid material to petroleum ether acquired activity within 2 days of injection, but the amount remains fairly constant for 12 days. The activity of the extraction residue, and of an 80% ethanol extract thereof, increased throughout the experiment. The residue containing increasing amounts of protein had the largest amount of radioactivity of the three fractions at the conclusion of the experiment.
Preliminary chromatography did not yield isolated radioactive products.
Extracts of pepper show no activity when substituted for soybean extract in a system containing chlorophyll and linoleic acid.
The degradation of chlorophyll by ripening bell peppers provides a tool for further studies for degradation in a physiological system.
Labeling facilitates isolation, identification, and establishment of origin of small amounts of breakdown products.     

反应条件对β-胡萝卜素氧化降解产物的影响

为考察反应条件对β-胡萝卜素氧化降解过程的影响,对不同反应条件下的降解产物进行了GC-MS分析。结果表明:β-胡萝卜素氧化降解产物主要香味成分有2,2,6-三甲基环己酮、异佛尔酮、β-环柠檬醛、β-紫罗兰酮、二氢猕猴桃内酯等,其中二氢猕猴桃内酯的含量最高;溶剂、体系pH与反应时间对降解产物中的主要香味成分的组成具有不同程度的影响;与乙醚、石油醚和环己烷相比,极性较大的乙醇体系更有利于氧化降解反应,而主要香味成分的总量随反应时间的延长或pH下降呈先增加后减少的趋势。在所采用的各种氧化降解条件中,以乙醇为反应溶剂,体系pH3.0,反应3h的降解产物中主要香味成分的总量最高,二氢猕猴桃内酯的含量也为最高。      

气相色谱法测定黄瓜、苹果中的虫螨腈残留量

为了对虫螨腈在黄瓜和苹果上的残留分析方法进行探讨,采用乙腈提取、Flolisil 小柱净化、GC-μECD进行检测。结果表明：黄瓜上添加标准品0.005、0.01、0.5μg/g 的回收率分别为115.6%、86.4%、82.8%,相对标准偏差分别为2.6%、7.6%、9.2%;苹果上添加标准品0.005、0.1、0.5μg/g 的回收率分别为109.2%、95.9%、94.6%,相对标准偏差为8.0%、4.2%、7.6%;田间试验得到的虫螨腈在黄瓜的消解动态方程为y ＝0.0431e － 0.1665x,半衰期为4.2d;虫螨腈在苹果上的消解动态方程为y=0.1115e － 0.0734x,半衰期为9.4d。本方法灵敏度、准确度、精密度高,能够为大规模监测蔬菜水果中虫螨腈的残留情况提供参考。     

Anthocyanin-derived phenolic acids form glucuronides following simulated gastrointestinal digestion and microsomal glucuronidation

Scope: Current research indicates that anthocyanins are primarily degraded to form phenolic acid products. However, no studies have yet demonstrated the metabolic conjugation of these anthocyanin‐derived phenolic acids in humans. Methods and results: Within the present study, a simulated gastrointestinal digestion model was used to evaluate the potential degradation of anthocyanins post‐consumption. Subsequently, cyanidin (Cy) and pelargonidin and their degradation products, protocatechuic acid and 4‐hydroxybenzoic acid, were incubated in the presence of human liver microsomes to assess their potential to form hepatic glucuronide conjugates. For structural conformation, phenolic glucuronides were chemically synthesised and compared to the microsomal metabolites. During the simulated gastric digestion, anthocyanin glycosides (200 μM) remained stable however their aglycone derivatives were significantly degraded (20% loss), while during subsequent pancreatic/intestinal digestion only pelargonidin‐3‐glucoside remained stable while cyanidin‐3‐glucoside (30% loss) and Cy and pelagonidin aglycones were significantly degraded (100% loss, respectively). Following microsomal metabolism, pelargonidin formed 4‐hydroxybenzoic acid, which was further metabolised (65%) to form two additional glucuronide conjugates, while Cy formed protocatechuic acid, which was further metabolised (43%) to form three glucuronide conjugates. Conclusions: We propose that following ingestion, anthocyanins may be found in the systemic circulation as free or conjugated phenolic acids, which should be a focus of future dietary interventions.     

Quantification of sequential chlorinated ethene degradation by use of a reactive transport model incorporating isotope fractionation

Compound-specific isotope analysis (CSIA) enables quantification of biodegradation by use of the Rayleigh equation. The Rayleigh equation fails, however, to describe the sequential degradation of chlorinated aliphatic hydrocarbons (CAHs) involving various intermediates that are controlled by simultaneous degradation and production. This paper shows how isotope fractionation during sequential degradation can be simulated in a 1D reactive transport code (PHREEQC-2). 12C and 13C isotopes of each CAH were simulated as separate species, and the ratio of the rate constants of the heavy to light isotope equaled the kinetic isotope fractionation factor for each degradation step. The developed multistep isotope fractionation reactive transport model (IF-RTM) adequately simulated reductive dechlorination of tetrachloroethene (PCE) to ethene in a microcosm experiment. Transport scenarios were performed to evaluate the effect of sorption and of different degradation rate constant ratios among CAH species on the downgradient isotope evolution. The power of the model to quantify degradation is illustrated for situations where mixed sources degrade and for situations where daughter products are removed by oxidative processes. Finally, the model was used to interpret the occurrence of reductive dechlorination at a field site. The developed methodology can easily be incorporated in 3D solute transport models to enable quantification of sequential CAH degradation in the field by CSIA.     

Biodegradation of RDX nitroso products MNX and TNX by cytochrome P450 XplA

Anaerobic transformation of the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) by microorganisms involves sequential reduction of N-NO(2) to the corresponding N-NO groups resulting in the initial formation of MNX (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine). MNX is further reduced to the dinitroso (DNX) and trinitroso (TNX) derivatives. In this paper, we describe the degradation of MNX and TNX by the unusual cytochrome P450 XplA that mediates metabolism of RDX in Rhodococcus rhodochrous strain 11Y. XplA is known to degrade RDX under aerobic and anaerobic conditions, and, in the present study, was found able to degrade MNX to give similar products distribution including NO(2)(-), NO(3)(-), N(2)O, and HCHO but with varying stoichiometric ratio, that is, 2.06, 0.33, 0.33, 1.18, and 1.52, 0.15, 1.04, 2.06, respectively. In addition, the ring cleavage product 4-nitro-2,4,-diazabutanal (NDAB) and a trace amount of another intermediate with a [M-H](-) at 102 Da, identified as ONNHCH(2)NHCHO (NO-NDAB), were detected mostly under aerobic conditions. Interestingly, degradation of TNX was observed only under anaerobic conditions in the presence of RDX and/or MNX. When we incubated RDX and its nitroso derivatives with XplA, we found that successive replacement of N-NO(2) by N-NO slowed the removal rate of the chemicals with degradation rates in the order RDX > MNX > DNX, suggesting that denitration was mainly responsible for initiating cyclic nitroamines degradation by XplA. This study revealed that XplA preferentially cleaved the N-NO(2) over the N-NO linkages, but could nevertheless degrade all three nitroso derivatives, demonstrating the potential for complete RDX removal in explosives-contaminated sites.