Nitroaromatic compounds, from synthesis to biodegradation

Nitrophenyl-Group-Containing Heterocycles. I. Synthesis, Characterization, Crystal Structure, Anticancer Activity, and Antioxidant Properties of Some New 5,6,7,8-Tetrahydroisoquinolines Bearing 3(4)-Nitrophenyl Group

Regioselective cyclocondensation of 2,4-diacetyl-5-hydroxy-5-methyl-3-(3-nitrophenyl/4-nitrophenyl)cyclohexanones 1a,b with cyanothioacetamide afforded the corresponding 7-acetyl-4-cyano-1,6-dimethyl-6-hydroxy-8-(3- and -4-nitrophenyl)-5,6,7,8-tetrahydrosoquinoline-3(2H)-thiones 2a,b. Reaction of compounds 2a,b with ethyl iodide, 2-chloroacetamide (4a), or its N-aryl derivatives 4b-e in the presence of sodium acetate trihydrate gave 3-ethylthio-5,6,7,8-tetrahydroisoquinoline 3 and (5,6,7,8-tetrahydroisoquinolin-3-ylthio)acetamides 5a-i, respectively. Cyclization of compounds 5b-d,f,g into their isomeric 1-amino-6,7,8,9-tetrahydrothieno[2,3-c]isoquinoline-2-carboxamides 6b-d,f,g was achieved by heating in ethanol containing a catalytic amount of sodium carbonate. Structures of all synthesized compounds were characterized on the basis of their elemental analyses and spectroscopic data. The crystal structure of 5,6,7,8-tetrahydroisoquinoline 5d was determined by X-ray diffraction analysis. In addition, the biological evaluation of some synthesized compounds as anticancer agents was performed, and only six compounds showed moderate to strong activity against PACA2 (pancreatic cancer cell line) and A549 (lung carcinoma cell line). Moreover, the antioxidant properties of most synthesized compounds were examined. The results revealed high antioxidant activity for the most tested compounds.

Potentials of N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol as novel charge transfer acceptors in pharmaceutical analysis of some quinolones and cephalosporins

Background

Quinolones and cephalosporins are antibiotic agents with activity against Gram-positive and Gram-negative bacteria. They contain chromophores and amine groups which are electron-rich centres capable of donating electrons to electron-deficient compounds. A survey of the literature revealed that 2, 4-dinitro-1-naphthol, a nitroaromatic useful in chemical synthesis, can accept electrons in charge transfer reactions. This work investigates N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol in the formation of charge transfer complexes by accepting electrons from selected quinolones and cephalosporins. Five other nitroaromatics (i.e. 4-nitro-1-naphthylamine, 2-nitro-1-naphthol, 2,4-dinitro-1-naphthylamine, 1-nitronaphthalene and 1,4-dinitronaphthalene) were screened in addition to the aforementioned and compared for charge transfer complexes formation. Spot test was used to establish charge transfer complex formation at room and elevated temperatures with determination done by visual inspection and thin layer chromatographic analysis of the reaction mixture. Ultraviolet visible absorption spectroscopy was used to estimate the extent of complexes.

Results

Only solutions of adducts of N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol gave instant and distinct colour with each drug used at room and elevated temperature. While the former gave deep golden yellow, the latter gave golden yellow against their blank reagent solutions which were, lemon and greenish yellow respectively. Visual inspections of 2-nitro-1-naphthol adduct solutions showed no colour change from the yellow colour of the blank reagent solution, even though the Ultraviolet visible absorption spectra revealed the formation of charge transfer complexes. The adducts solutions of 4-nitro-1-naphthylamine, 2,4-dinitro-1-naphthylamine, 1-nitronaphthalene and 1,4-dinitronaphthalene showed no colour change from their blank reagent solutions and their Ultraviolet visible absorption spectra revealed no formation of charge transfer complexes.

Conclusion

Ultraviolet visible absorption spectral analysis shows superiority of N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol in charge-transfer complex formation over other nitroaromatics screened. N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol are good acceptors of electrons from these drugs, hence could be useful as charge transfer reagents in ultraviolet visible spectrophotometric analysis of these drugs.

Spectrophotometric and fluorometric detection of DNA/BSA interaction, antimicrobial, anticancer, antioxidant and catalytic activities of biologically active methoxy substituted pyrimidine-ligand capped copper nanoparticles

New Schiff base ligand (DPMN) was synthesized from the condensation of 2-hydroxy-5-nitrobenzaldehyde and 2-amino-4,6-dimethoxypyrimidine which was confirmed by spectroscopic and analytical methods. Solid air stable copper nanoparticles (DPMN-CuNPs) were synthesized from its copper chloride salt and it is stabilized by the prepared Schiff base ligand by phase transfer assisted synthesis which is a modified Brust-Schiffrin technique. The formation of ligand stabilized copper nanoparticles was confirmed by UV-Visible and FT-IR spectroscopic techniques. The size, surface morphology and quality of DPMN-CuNPs were analyzed by SEM and TEM techniques. Antioxidant activities of DPMN and DPMN-CuNPs with DPPH, SOD, peroxide and nitrous oxide were analyzed by electronic absorption spectroscopy. DNA interaction between DPMN and DPMN-CuNPs with CT-DNA was carried out using electronic absorption, fluorescence, viscometric measurements and cyclic voltammetric techniques. Interaction between BSA and the synthesized compounds analyzed by electronic absorption spectroscopy, Antimicrobial studies confirmed that the synthesized DPMN-CuNPs possess significant biological activities than DPMN. Anticancer results suggest that prepared DPMN-CuNPs have significant anticancer activity against different cancer cell lines and least toxic effect against the normal (NHDF) cell line. Other than the positive response in biological evaluation, our DPMN-CuNPs possess good catalytic activity in methyl orange reduction, methylene blue degradation and nitro phenol reduction.

Metabolic Engineering of Escherichia coli for Methyl Parathion Degradation

Organophosphate compounds are widely used in pesticides to control weeds, crop diseases, and insect pests. Unfortunately, these synthetic compounds are hazardous and toxic to all types of living organisms. In the present work, Escherichia coli was bioengineered to achieve methyl parathion (MP) degradation via the introduction of six synthetic genes, namely, opdS, pnpAS, pnpBS, pnpCS, pnpDS, and pnpES, to obtain a new transformant, BL-MP. MP and its subsequent decomposition intermediates were completely degraded by this transformant to enter the metabolites of multiple anabolic pathways. The MP-degraded strain created in this study may be a promising candidate for the bioremediation of MP and potential toxic intermediates.

Exploring multifunctional behaviour of g-C3N4 decorated BiVO4/Ag2CO3 hierarchical nanocomposite for simultaneous electrochemical detection of two nitroaromatic compounds and water splitting applications

Development of multifunctional ternary nanocomposite based electrocatalysts for detection of toxic elements and generation of renewable energy describes an environmentally sustainable technique to address the dual challenges of pollution and energy. Herein, we adopted microwave-assisted synthesis to design a multifunctional graphitic carbon nitride (g-C₃N₄) decorated BiVO₄/Ag₂CO₃ (BVG@C) hierarchical ternary nanocomposite for sensing and water splitting applications. The morphological, structural and elemental characterizations demonstrate the successful decoration of carbon nitride on the composite surface. The electrochemical activity of BVG@C modified glassy carbon electrode reveals excellent redox behaviour towards simultaneous detection of 4-Nitrophenol (4-NP) and 4-Nitroaniline (PNA). The modified electrode shows rapid amperometric current response with high sensitivity of 2.368 μA mM cm^-2 and 1.534 mA mM cm^-2 and low detection limit of 0.012 μmol L^-1and 0.028 μmol L^-1, respectively for 4-NP and PNA. Moreover, the modified electrode was further investigated for hydrogen evolution and oxygen evolution reactions and the electrocatalytic results show admirable activity and good stability for oxygen evolution with very low overpotential of 136 mV in alkaline medium. It is worthwhile to mention that the excellent activity of electrocatalyst can be ascribed to the decoration and electronic interaction of g-C₃N₄ with the BiVO₄/Ag₂CO₃ nanocomposite, increasing its surface area, active sites, charge transfer and decreasing resistance.

Application of palladium nanoparticles supported organo-kaolinite for 4-chloro-2-nitroaniline catalytic reduction and electrochemical detection

Palladium nanoparticles (PdNPs) supported organo-kaolinite was used as a solid catalyst for the reduction and electrochemical detection of 4-chloro-2-nitroaniline (CNA). During the catalytic reduction in presence of NaBH4, the effects...

Biochemical and structural characterization of Haemophilus influenzae nitroreductase in metabolizing nitroimidazoles

Nitroheterocycle antibiotics, particularly 5-nitroimidazoles, are frequently used for treating anaerobic infections. The antimicrobial activities of these drugs heavily rely on the in vivo bioactivation, mainly mediated by widely distributed bacterial nitroreductases (NTRs). However, the bioactivation can also lead to severe toxicities and drug resistance. Mechanistic understanding of NTR-mediated 5-nitroimidazole metabolism can potentially aid addressing these issues. Here, we report the metabolism of structurally diverse nitroimidazole drug molecules by a NTR from a human pathogen Haemophilus influenzae (HiNfsB). Our detailed bioinformatic analysis uncovered that HiNfsB represents a group of unexplored oxygen-insensitive NTRs. Biochemical characterization of the recombinant enzyme revealed that HiNfsB effectively metabolizes ten clinically used nitroimidazoles. Furthermore, HiNfsB generated not only canonical nitroreduction metabolites but also stable, novel dimeric products from three nitroimidazoles, whose structures were proposed based on the results of high resolution MS and tandem MS analysis. X-ray structural analysis of the enzyme coupled with site-directed mutagenesis identified four active site residues important to its catalysis and broad substrate scope. Finally, transient expression of HiNfsB sensitized an E. coli mutant strain to 5-nitroimidazoles under anaerobic conditions. Together, these results advance our understanding of the metabolism of nitroimidazole antibiotics mediated by a new NTR group and reinforce the research on the natural antibiotic resistome for addressing the antibiotic resistance crisis.

The nitroreductase of Haemophilus influenzae metabolizes clinically used nitroimidazoles, generates dimeric metabolites and anaerobically sensitizes an E. coli mutant to antibiotics. We further uncover its biochemical and structural details.

Multiple roles of extracellular polymeric substance in nitrobenzene reduction by nano-sized zero-valent iron in water and their mechanism

Extracellular polymeric substance (EPS) is secreted by many organisms and makes up a significant constituent of natural organic matter in the environment. However, nothing is known about EPS's role in the reduction of pollutants by nano-sized zero-valent iron (NZVI). This research showed that the degradation kinetics of nitrobenzene (NB) by NZVI with EPS (0.0272 ± 0.006 min^-1) were 2.27 times lower than that without EPS (0.0618 ± 0.006 min^-1) in the first cycle, mainly due to competition for reactive sites on the NZVI surface and the complexation of EPS with Fe(II) and Fe(III). In the second and third cycle, the degradation kinetics of NB by NZVI alone decreased obviously, while those in the presence of EPS were preserved or accelerated. Comparative studies with a quinine model compound indicated that EPS did not function as the electron shuttle to transmit electrons effectively. X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction results suggested that EPS could prevent the oxidation of NZVI and even expose more effective sites on the NZVI surface, thus leading to the preservation or enhancement of NZVI reactivity in the second and third NB degradation cycles. Moreover, we found that EPS also provided colloidal stability to NZVI particles, either by steric mechanisms or electrostatic repulsion. These results indicate that EPS can play an important role in the prolongation of NZVI reactivity during standing application.

Solvent dielectric delimited nitro–nitrito photorearrangement in a perylenediimide derivative

The discovery of vibrant excited-state dynamics and distinctive photochemistry has established nitrated polycyclic aromatic hydrocarbons as an exhilarating class of organic compounds. Herein, we report the atypical photorearrangement of nitro-perylenediimide (NO₂-PDI) to nitrito-perylenediimide (ONO-PDI), triggered by visible-light excitation and giving rise to linkage isomers in the polar aprotic solvent acetonitrile. ONO-PDI has been isolated and unambiguously characterized using standard spectroscopic, spectrometric, and elemental composition techniques. Although nitritoaromatic compounds are conventionally considered to be crucial intermediates in the photodissociation of nitroaromatics, experimental evidence for this has not been observed heretofore. Ultrafast transient absorption spectroscopy combined with computational investigations revealed the prominence of a conformationally relaxed singlet excited-state (S^CR₁) of NO₂-PDI in the photoisomerization pathway. Theoretical transition state (TS) analysis indicated the presence of a six-membered cyclic TS, which is pivotal in connecting the S^CR₁ state to the photoproduct state. This article addresses prevailing knowledge gaps in the field of organic linkage isomers and provides a comprehensive understanding of the unprecedented photoisomerization mechanism operating in the case of NO₂-PDI.

The unprecedented photorearrangement of nitro-perylenediimide (NO₂-PDI) to nitrito-perylenediimide (ONO-PDI) is shown to occur through a cyclic six-membered transition state triggered by visible-light excitation.

Biocatalysis making waves in organic chemistry

Biocatalysis has an enormous impact on chemical synthesis. The waves in which biocatalysis has developed, and in doing so changed our perception of what organic chemistry is, were reviewed 20 and 10 years ago. Here we review the consequences of these waves of development. Nowadays, hydrolases are widely used on an industrial scale for the benign synthesis of commodity and bulk chemicals and are fully developed. In addition, further enzyme classes are gaining ever increasing interest. Particularly, enzymes catalysing selective C-C-bond formation reactions and enzymes catalysing selective oxidation and reduction reactions are solving long-standing synthetic challenges in organic chemistry. Combined efforts from molecular biology, systems biology, organic chemistry and chemical engineering will establish a whole new toolbox for chemistry. Recent developments are critically reviewed.

Hydrazone connected stable luminescent covalent-organic polymer for ultrafast detection of nitro-explosives

Developing promising luminescent probes for the selective sensing of nitro-explosives remains a challenging issue. Porous luminescent covalent–organic polymers are one of the excellent sensing probes for trace hazardous materials. Herein, fluorescent monomers 1,1,2,2-tetrakis(4-formyl-(1,1′-biphenyl))ethane (TFBE) and 1,3,5-benzenetricarboxylic acid trihydrazide (BTCH) were selected to build a novel hydrazone connected stable luminescent covalent–organic polymer (H-COP) of high stability by typical Schiff-base reaction. The N₂ sorption study, BET surface area analysis, and TGA profile indicate the porosity and stability of this H-COP material. Such properties of the H-COP material enable a unique sensing platform for nitro-explosives with great sensitivity (Ksv ∼ 10⁶ M) and selectivity up to μM. This polymer material shows attractive selectivity and sensitivity towards phenolic nitro-explosives and other common explosives among earlier reported COP-based sensors.

A novel H-COP was synthesized through Schiff-base condensation reaction, which shows high sensitivity (K_sv ∼ 10⁶ M⁻¹) and selectivity (μM level) towards nitro-explosives.

Electrochemical Nitration with Nitrite

Aromatic nitration has tremendous importance in organic chemistry as nitroaromatic compounds serve as versatile building blocks. This study represents the electrochemical aromatic nitration with NBu₄ NO₂ , which serves a dual role as supporting electrolyte and as a safe, readily available, and easy-to-handle nitro source. Stoichiometric amounts of 1,1,1-3,3,3-hexafluoroisopropan-2-ol (HFIP) in MeCN significantly increase the yield by solvent control. The reaction mechanism is based on electrochemical oxidation of nitrite to NO₂ , which initiates the nitration reaction in a divided electrolysis cell with inexpensive graphite electrodes. Overall, the reaction is demonstrated for 20 examples with yields of up to 88 %. Scalability is demonstrated by a 13-fold scale-up.

“Doing More with Less”: Ni(II)@ORMOSIL, a Novel Sol-Gel Pre-Catalyst for the Reduction of Nitrobenzene

Reduction of nitrobenzene with NaBH4 using zero-valent iron nanoparticles (ZVI-NPs) and NiCl2∙6H2O incorporated in organically modified hybrid silica matrices as ZVI@ORMOSIL and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H+ of the ORMOSIL matrix with NiII. Ni(II)@ORMOSIL is a pre-catalyst that undergoes reduction by NaBH4 by an in-situ reaction and promotes nitrobenzene reduction by the unconsumed NaBH4, leading to sparing use of the catalyst. Ni(II)@ORMOSIL undergoes color change from green to black in this process, returning to a green hue after washing and drying. Nitrobenzene reductions were examined in aqueous acetonitrile solvent mixtures, and the reduction cascade produced the reaction end-products with catalytic implications. Plausible mechanisms of ZVI@ORMOSIL and Ni(II)@ORMOSIL catalyzed reductions of nitrobenzene are discussed. This work is the first to report M(II)@ORMOSIL pre-catalysts for in-situ reduction of nitrobenzene, and expands the scope of the ORMOSIL series of catalysts for the reduction of polluting compounds. This approach enables the development of catalysts that use very low concentrations of transition metal cations.

A Rational Analysis on Key Parameters Ruling Zerovalent Iron-Based Treatment Trains: Towards the Separation of Reductive from Oxidative Phases

The development of treatment trains for pollutant degradation employing zerovalent iron has been attracting a lot of interest in the last few years. This approach consists of pre-treatment only with zerovalent iron, followed by a Fenton oxidation taking advantage of the iron ions released in the first step. In this work, the advantages/disadvantages of this strategy were studied employing commercial zerovalent iron microparticles (mZVI). The effect of the initial amount of mZVI, H₂O₂, pH, conductivity, anions and dissolved oxygen were analysed using p-nitrobenzoic acid (PNBA) as model pollutant. 83% reduction of PNBA 6 µM into p-aminobenzoic acid (PABA) was achieved in natural water at an initial pH 3.0 and 1.4 g/L of mZVI, under aerobic conditions, in 2 h. An evaluation of the convenience of removing mZVI after the reductive phase before the Fenton oxidation was investigated together with mZVI reusability. The Fenton step against the more reactive PABA required 50 mg/L of H₂O₂ to achieve more than 96% removal in 15 min at pH 7.5 (final pH from the reductive step). At least one complete reuse cycle (reduction/oxidation) was achieved with the separated mZVI. This approach might be interesting to treat wastewater containing pollutants initially resistant to hydroxyl radicals.

Characterization of microbial communities from rumen and large intestine of lactating creole goats grazing in arid plant communities

Arid plant communities provide variable diets that can affect digestive microbial communities of free-foraging ruminants. Thus, we used next-generation sequencing of 16S and 18S rDNA to characterize microbial communities in the rumen (regurgitated digesta) and large intestine (faeces) and diet composition of lactating creole goats from five flocks grazing in native plant communities in the Sonoran Desert in the rainy season. The bacterial communities in the rumen and large intestine of the five flocks had similar alpha diversity (Chao1, Shannon, and Simpson indices). However, bacterial community compositions were different: a bacterial community dominated by Proteobacteria in the rumen transitioned to a community dominated by Firmicutes in the large intestine. Bacterial communities of rumen were similar across flocks; similarly occurred with large-intestine communities. Archaea had a minimum presence in the goat digestive tract. We detected phylum Basidiomycota, Ascomycota, and Apicomplexa as the main fungi and protozoa. Analyses suggested different diet compositions; forbs and grasses composed the bulk of plants in the rumen and forbs and shrubs in faeces. Therefore, lactating goats consuming different diets in the Sonoran Desert in the rainy season share a similar core bacterial community in the rumen and another in the large intestine and present low archaeal communities.

Facile synthesis of an aggregation-induced emission (AIE) active imidazoles for sensitive detection of trifluralin

A novel imidazoles fluorescent probe (2) was synthesized from vanillin, o-phenylenediamine, and N,N-diphenylcarbamyl chloride. Its structure was characterized by fluorescence spectra, UV-Vis spectra, ¹H NMR, ¹³C NMR, and high-resolution mass spectrometry (HRMS). Moreover, its aggregation-induced emission (AIE) feature was investigated in THF/MeOH solution. Furthermore, the fluorescence quenching experimental results suggest that compound 2 is the potential fluorescent probe of small organic molecules showing high selectivity and sensitivity for nitroaromatic compounds. In addition, the probe could be applied in the determination of trifluralin with fast response and stability. The fluorescence response of the probe exhibited a good linear correlation with the concentration of trifluralin ranging from 10 to 100 μM, and the limit of detection (LOD) was as low as 5.066 μM. Finally, the probe was successfully utilized to determine the amount of trifluralin in real samples, and the recoveries were 91.1% to 111.2%, indicating the applicability and reliability of the probe.

Fluorescence quenching based detection of nitroaromatics using luminescent triphenylamine carboxylic acids

Detection of nitroaromatics employing greener techniques has been one of the most active research fields in chemistry. A series of triphenylamine (TPA) functionalized carboxylic acids were synthesized and characterized using various spectroscopic techniques including single-crystal X-ray diffraction analysis. The interaction of carboxylic acid-decorated TPAs with nitroaromatic compounds was photophysically explored using absorption and emission spectroscopy. Stern–Volmer plot accounts for the appreciable quenching constant of the TPA-acids. Density functional theory calculations were carried out to study the new compounds' frontier molecular orbital energy levels and the possible interactions with picrate anion and revealed an unusual charge transfer interaction between acids and picrate anion. The contact mode detection shows the TPA-acids can be used as dip-strip sensors for picric acid detection.

Recent Advances in the Nitration of Olefins

Nitroolefins are important synthetic intermediates in the field of organic synthesis as well as in medicinal chemistry. The high reactivity of nitroalkenes due to the polarized double bond which enables them to act as Michael acceptor in conjugate addition reactions, or as a dienophile in cycloaddition makes it an essential synthetic handle for accessing complex molecules. The classical method to prepare nitroolefins is indeed the Henry nitroaldol reaction, where a carbonyl compound and nitroalkane are condensed in presence of base. Direct nitration of olefin, on the other hand, serves as a useful alternative as olefins are abundant, have broad commercial availability and easy to manipulate. In this context, numerous methods have been developed over the last few decades, focusing on direct nitration of styrene and aliphatic olefins. Furthermore, thorough literature search revealed that implementation of this class of reactions are gaining momentum as a preferred pathway to access nitroolefins, despite the presence of a powerful technique such as Henry reaction. In this review, we aim to cover recent advances in direct olefin nitration and their importance in accessing biorelevant molecules, total synthesis targets and future outlook in this specific research area.

The low-nanomolar 4-nitrobenzoate-responsive repressor PnbX negatively regulates the actinomycete-derived 4-nitrobenzoate-degrading pnb locus

Nitroaromatic compounds pose severe threats to public health and environmental safety. Nitro group removal via ammonia release is an important strategy for bacterial detoxification of nitroaromatic compounds, such as the conversion of 4-nitrobenzoate (4-NBA) to protocatechuate by the bacterial pnb operon. In contrast to the LysR-family transcriptional regulator PnbR in proteobacteria, the actinomycete-derived pnb locus (4-NBA degradation structural genes) formed an operon with the TetR-family transcriptional regulator gene pnbX, implying that it has a distinct regulatory mechanism. Here, pnbBA from the actinomycete Nocardioides sp. strain LMS-CY was biochemically confirmed to express 4-NBA degradation enzymes, and pnbX was essential for inducible degradation of 4-NBA. Purified PnbX-6His could bind the promoter probe of the pnb locus in vitro, and 4-NBA prevented this binding. 4-NBA could bind PnbX at a 1:1 molar ratio with K_D  = 26.7 ± 4.2 nM. Low-nanomolar levels of 4-NBA induced the transcription of the pnb operon in strain LMS-CY. PnbX bound a palindromic sequence motif (5'-TTACGTTACA-N₈ -TGTAACGTAA-3') that encompasses the pnb promoter. This study identified a TetR-family repressor for the actinomycete-derived pnb operon that recognizes 10^-8  M 4-NBA as its ligand, implying that nitro group removal of nitroaromatic compounds may be especially important for actinomycetes.

Aerobic degradation of 2,4,6-trinitrophenol by Proteus sp. strain OSES2 obtained from an explosive contaminated tropical soil

A 2,4,6-trinitrophenol (TNP) degrading bacterial strain isolated from a site polluted with explosives was identified as Proteus sp. strain OSES2 via 16S rRNA gene sequencing. Metabolic investigation showed that the organism grew exponentially on 100 mg l^-1 of TNP as a source of carbon, nitrogen, and energy. In addition, the growth of the organism was sustainable on 3-nitrotoluene, 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, 4-nitrophenol, methyl-3-nitrobenzoate, 4-nitroaniline, aniline and nitrobenzene. Strain OSES2 was able to utilize TNP within a concentration range of 100 mg l^-1 to 500 mg l^-1. The specific growth rate and degradation rates on TNP were 0.01043 h^-1 and 0.01766 mg l^-1 h^-1 respectively. Effective degradation of TNP in a chemically defined medium was evident with a gradual reduction in the concentration of TNP concomitant with an increase in cell density as well as the substantial release of ammonium (NH₄⁺), nitrite (NO₂^-), and nitrate (NO₃^-) as metabolites in 96 h. Degradation competence of the organism was enhanced in the presence of starch and acetate. On starch-supplemented TNP, the highest specific growth rate and degradation rates were 0.02634 h^-1 and 0.04458 mg l^-1 h^-1, respectively, while the corresponding values on acetate were 0.02341 h^-1 and 0.02811 mg l^-1 h^-1. However, amendment with nitrogen sources yielded no substantial improvement in degradation. TNP was utilized optimally at pH 7 to 9 and within the temperature range of 30 °C to 37 °C. The enzyme hydride transferase II [HTII], encoded by the npdI gene which is the first step involved in the TNP degradation pathway, was readily expressed by the isolate thus suggesting that substrate was utilized through the classical metabolic pathway.

Transformation of ammonium to nitrophenolic byproducts by sulfate radical oxidation

Sulfate radical (SO₄^•-) based oxidation shows great promise in wastewater treatment and subsurface remediation. For the first time, we demonstrated that SO₄^•- could induce the transformation of ammonium (NH₄⁺) to nitrophenolic byproducts. Using high-resolution mass spectrometry in combination with ¹⁵N labeling, mono-nitro and di-nitro phenolic byproducts were identified in a sample containing 1 mM NH₄⁺ and 10 mg/L natural organic matter (NOM) following heat activated peroxydisulfate (PDS) oxidation. At PDS dose of 1 mM, the formation of p-nitrophenol and 5-nitrosalicylic acid reached 0.21 and 0.30 μM, respectively, in 12 h and then decreased; the formation of 2,4-dinitrophenol and 3,5-dinitrosalicylic acid increased monotonically, reaching 0.37 and 0.62 μM, respectively, in 24 h. One-electron oxidation of NH₄⁺ to form aminyl radicals (^•NH₂) was the first step of the transformation. The reaction of ^•NH₂ with oxygen was a key step in propagating radical chain reactions, leading to nitrogen dioxide radicals (NO₂^•) as a key nitrating agent. The reactive sites susceptible to nitrating in NOM molecules are not limited to phenolic moieties. We found that aromatic carboxylate moieties could be in situ transformed to phenolics by SO₄^•-, thus contributed to nitrophenolic byproducts formation as well. Considering the ubiquitous presence of NH₄⁺ in the environment, formation of nitrophenolic byproducts will be widespread when SO₄^•- is applied for onsite remediation, which should be taken into consideration when evaluating the feasibility of this technology.

Biodegradation of p-nitrophenol by engineered strain

p-Nitrophenol (PNP) is an important environmental pollutant and can causes significant environmental and health risks. Compared with the traditional methods, biodegradation is a useful one to completely remove the harmful pollutants from the environment. Here, an engineered strain was first constructed by introducing PNP biodegradation pathway via the hydroquinone (HQ) pathway into Escherichia coli. In the engineered strain BL-PNP, PNP was completely degraded to β-ketoadipate and subsequently enter the metabolites of multiple anabolic pathways. The high tolerance and rapid degradation ability to PNP enable the engineered strain to have the potential to degrade toxic substances. The engineered strain created in this study can be used as a functional strain for bioremediation of PNP and potential toxic intermediates, and the method of assembling aromatic hydrocarbons metabolic pathway can be used to eradicate nitroaromatic pollutants in the environment.

A Recently Assembled Degradation Pathway for 2,3-Dichloronitrobenzene in Diaphorobacter sp. Strain JS3051

Diaphorobacter sp. strain JS3051 utilizes 2,3-dichloronitrobenzene (23DCNB), a toxic anthropogenic compound, as the sole carbon, nitrogen, and energy source for growth, but the metabolic pathway and its origins are unknown. Here, we establish that a gene cluster (dcb), encoding a Nag-like dioxygenase, is responsible for the initial oxidation of the 23DCNB molecule. The 2,3-dichloronitrobenzene dioxygenase system (DcbAaAbAcAd) catalyzes conversion of 23DCNB to 3,4-dichlorocatechol (34DCC). Site-directed mutagenesis studies indicated that residue 204 of DcbAc is crucial for the substrate specificity of 23DCNB dioxygenase. The presence of glutamic acid at position 204 of 23DCNB dioxygenase is unique among Nag-like dioxygenases. Genetic, biochemical, and structural evidence indicate that the 23DCNB dioxygenase is more closely related to 2-nitrotoluene dioxygenase from Acidovorax sp. strain JS42 than to the 34DCNB dioxygenase from Diaphorobacter sp. strain JS3050, which was isolated from the same site as strain JS3051. A gene cluster (dcc) encoding the enzymes for 34DCC catabolism, homologous to a clc operon in Pseudomonas knackmussii strain B13, is also on the chromosome at a distance of 2.5 Mb from the dcb genes. Heterologously expressed DccA catalyzed ring cleavage of 34DCC with high affinity and catalytic efficiency. This work not only establishes the molecular mechanism for 23DCNB mineralization, but also enhances the understanding of the recent evolution of the catabolic pathways for nitroarenes.

Rapid evaluation of the substrate specificity of 3-nitrobenzoic acid dioxygenase MnbAB via colorimetric detection using Saltzman reagent

Nitroaromatic compounds are essential materials for chemical industry, but they are also potentially toxic environmental pollutants. Therefore, their sensitive detection and degradation are important concerns. The microbial degradation pathways of nitroaromatic compounds have been studied in detail, but their usefulness needs to be evaluated to understand their potential applications in bioremediation. Here, we developed a rapid and relatively sensitive assay system to evaluate the activities and substrate specificities of nitroaromatic dioxygenases involved in the oxidative biodegradation of nitroaromatic compounds. In this system, nitrous acid, which was released from the nitroaromatic compounds by the dioxygenases, was detected and quantified using the Saltzman reagent. Escherichia coli producing the 3-nitrobenzoic acid dioxygenase complex MnbAB from Comamonas sp. JS46 clearly showed the apparent substrate specificity of MnbAB as follows. MnbAB accepted not only 3-nitrobenzoic acid but also several other p- and m-nitrobenzoic acid derivatives as substrates, although it much preferred 3-nitrobenzoic acid to others. Furthermore, the presence of a hydroxy or an amino group at the ortho position of the nitro group decreased the activity of MnbAB. In addition, MnbAB accepted 2-(4-nitrophenyl)acetic acid as a substrate, which has one additional methylene group between the aromatic ring and the carboxy group of 3-nitrobenzoic acid. This is the first report about the detailed substrate specificity of MnbAB. Our system can be used for other nitroaromatic dioxygenases and contribute to their characterization.

Smart hydrogel-microsphere embedded silver nanoparticle catalyst with high activity and selectivity for the reduction of 4-nitrophenol and azo dyes

A simple method is reported for the preparation of silver nanoparticle (AgNP) embedded pH-responsive hydrogel microparticle catalyst via Michael addition gelation and in-situ silver nitrate (AgNO₃) reduction. The AgNP-hydrogel microsphere exhibited an efficient reduction of pollutants like 4-Nitrophenol (4-NP) and Congo red (CR) under acidic medium with turn over frequency (TOF) of ~170 h^-1 and ~124 h^-1 respectively. Interestingly, the activity of the catalysts was turned-OFF under a basic medium (≥ pH 12) due to the deswelling pH-responsive matrix surrounding the AgNPs. On the contrary, turning-OFF the hydrogenation of a cationic pollutant like methylene blue (MB) using high pH (≥ 12) was not possible, due to ionic interaction of MB molecules with the negatively charged catalyst at this pH. This feature was used to demonstrate selective hydrogenation of only MB from a mixture of 4-NP and MB. Finally, five recycling steps confirmed the reusability and practical application potential of the catalyst.

Substantial emissions of nitrated aromatic compounds in the particle and gas phases in the waste gases from eight industries

Nitrated aromatic compounds, the ubiquitous nitrogen-containing organic pollutants, impact the environment and organisms adversely. As industrial raw materials and intermediates, nitrated aromatic compounds and their aromatic precursors are widely employed in the industrial production activities. Nevertheless, their emission from industrial waste gases has so far not been studied extensively. In this study, the concentrations of 12 nitrated aromatic compounds in the particle and gas phases downwind of 16 factories encompassing eight industries (i.e., pharmaceutical, weaving and dyeing, herbicide, explosive, painting, phenolic resin, paper pulp and polystyrene foam industries), were determined by ultra-high-performance liquid chromatography-mass spectrometry. Their concentrations in the particle and gas phases from different factories ranged from 114.7 ± 63.5 to 296.6 ± 62.5 ng m^-3 and 148.7 ± 7.4 to 309.8 ± 26.2 ng m^-3, respectively, thus, exhibiting significantly high concentrations as compared to the background sites. Among the 12 detected species, 4-nitrophenol, 5-nitrosalicylic acid, 3-nitrosalicylic acid and 4-methyl-2,6-dinitrophenol were observed to be the predominant species, with total fractions up to 47.9-72.3% and 63.1-70.3% in the particle and gas phases, respectively. Their emission profiles with respect to the industrial activities exhibited large discrepancies as compared to the combustion sources, thus, indicating different formation mechanisms. The emission ratios of particulate nitrated aromatic compounds owing to the industrial activities were estimated between 0.5 ± 0.2 and 4.3 ± 1.5 ng μg^-1, which were higher than or comparable to those from various combustion sources. The findings from this study confirm the industrial emission to be an important source of nitrated aromatic compounds in the atmosphere. The substantial emissions of nitrated aromatic compounds from various industries reported in this study provide the fundamental basis for further emission estimation and pollution control.

Quantitative Structure-Activity Relationship (QSAR) Studies on the Toxic Effects of Nitroaromatic Compounds (NACs): A Systematic Review

Nitroaromatic compounds (NACs) are ubiquitous in the environment due to their extensive industrial applications. The recalcitrance of NACs causes their arduous degradation, subsequently bringing about potential threats to human health and environmental safety. The problem of how to effectively predict the toxicity of NACs has drawn public concern over time. Quantitative structure-activity relationship (QSAR) is introduced as a cost-effective tool to quantitatively predict the toxicity of toxicants. Both OECD (Organization for Economic Co-operation and Development) and REACH (Registration, Evaluation and Authorization of Chemicals) legislation have promoted the use of QSAR as it can significantly reduce living animal testing. Although numerous QSAR studies have been conducted to evaluate the toxicity of NACs, systematic reviews related to the QSAR modeling of NACs toxicity are less reported. The purpose of this review is to provide a thorough summary of recent QSAR studies on the toxic effects of NACs according to the corresponding classes of toxic response endpoints.

Environmental occurrence, toxicity concerns, and remediation of recalcitrant nitroaromatic compounds

Nitroaromatic compounds (NACs) are considered important groups of chemicals mainly produced by human and industrial activities. The large-scale application of these xenobiotics creates contamination of the water and soil environment. Despite applicability, NACs have been caused severe hazardous side effects in animals and human systems like different cancers, anemia, skin irritation, liver damage and mutagenic effects. The effective remediation of the NACs from the environment is a significant concern. Researchers have implemented physicochemical and biological methods for the remediation of NACs from the environment. Most of the applied methods are based on adsorption and degradation approaches. Among these methods, degradation is considered a versatile method for the subsequent removal of NACs due to its exceptional properties like simplicity, easy operation, cost-effectiveness, and availability. Most importantly, the degradation process does not generate hazardous side products and wastes compared to other methods. Hence, the importance of NACs, their remediation, and supreme attributes of the degradation method have encouraged us to review the recent progress and development for the removal of these perilous materials using degradation as a versatile method. Therefore, in this review, (i) NACs, physicochemical properties, and their hazardous side effects on humans and animals are discussed; (ii) Physicochemical methods, microbial, anaerobic bioremediation, mycoremediation, and aerobic degradation approaches for the degradation of NACs were thoroughly vetted; (iii) The possible mechanisms for degradation of NACs were investigated and discussed. (iv) The applied kinetic models for evaluation of the rate of degradation were also assessed and discussed. Finally, (vi) current challenges and future prospects of proposed methods for degradation and removal of NACs were also directed.

Biogenic Synthesis of Gold Nanoparticles on a Green Support as a Reusable Catalyst for the Hydrogenation of Nitroarene and Quinoline

Direct attachment of gold nanoparticles to a green support without the use of an external reducing agent and using it for removing toxic pollutants from wastewater, i. e., reduction of nitroarene to amine, are described. A novel approach involving the reduction of gold by the jute plant (Corchorus genus) stem-based (JPS) support itself to form nanoparticles (AuNPs) to be used as a catalytic system ('dip-catalyst') and its catalytic activity for the hydrogenation of series of nitroarenes in aqueous media are presented. AuNPs/JPS catalyst was characterized using SEM, UV-Vis, FTIR, TEM, XPS, and ICP-OES. Confined area elemental mapping exhibits uniform and homogeneous distribution of AuNPs on the support surface. TEM shows multi-faceted AuNPs in the range of 20-30 nm. The reactivity of AuNPs/JPS for the transfer hydrogenation of nitroarene as well as hydrogenation of quinoline under molecular H₂ pressure was evaluated. Sodium borohydride, when used as the hydrogen source, demonstrates a high catalytic efficiency in the transfer hydrogenation reduction of 4-nitrophenol (4-NP). Quinoline is quantitatively and chemoselectively hydrogenated to 1,2,3,4-tetrahydroquinoline (py-THQ) using molecular hydrogen. Reusability studies show that AuNPs are stable on the support surface and their selectivity is not affected.

Expanding the Substrate Scope of Nitrating Cytochrome P450 TxtE by Active Site Engineering of a Reductase Fusion

Aromatic nitration reactions are a cornerstone of organic chemistry, but are challenging to scale due to corrosive reagents and elevated temperatures. The cytochrome P450 TxtE nitrates the indole 4-position of l-tryptophan at room temperature using NO, O2 and NADPH, and has potential to be developed into a useful aromatic nitration biocatalyst. However, its narrow substrate scope (requiring both the α-amino acid and indole functionalities) have hindered this. Screening of an R59 mutant library of a TxtE-reductase fusion protein identified a variant (R59C) that nitrates tryptamine, which is not accepted by native TxtE. This variant exhibits a broader substrate scope than the wild type enzyme and is able to nitrate a range of tryptamine analogues, with significant alterations to the aromatic and aminoethyl moieties.

A review of treatment methods for insensitive high explosive contaminated wastewater

Insensitive high explosive materials (IHE) such as 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN) are increasingly being used in formulations of insensitive munitions alongside 1,3,5-trinitroperhydro-1,3,5-triazine (RDX). Load, assembly and packing (LAP) facilities that process munitions produce wastewater contaminated with IHE which must be treated before discharge. Some facilities can produce as much as 90,000 L of contaminated wastewater per day. In this review, methods of wastewater treatment are assessed in terms of their strengths, weaknesses, opportunities and threats for their use in production of IHE munitions including their limitations and how they could be applied to industrial scale LAP facilities. Adsorption is identified as a suitable treatment method, however the high solubility of NTO, up to 16.6 g.L-1 which is 180 times higher that of TNT, has the potential to exceed the adsorptive capacity of carbon adsorption systems. The key properties of the adsorptive materials along the selection of adsorption models are highlighted and recommendations on how the limitations of carbon adsorption systems for IHE wastewater can be overcome are offered, including the modification of carbons to increase adsorptive capacity or reduce costs.

Remediation of emerging environmental pollutants: A review based on advances in the uses of eco-friendly biofabricated nanomaterials

The increased environmental pollutants due to anthropogenic activities are posing an adverse effects and threat on various biotic forms on the planet. Heavy metals and certain organic pollutants by their toxic persistence in the environment are regarded as significant pollutants worldwide. In recent years, pollutants exist in various forms in the environment are difficult to eliminate by traditional technologies due to various drawbacks. This has lead to shifting of research for the development of cost-effective and efficient technologies for the remediation of environmental pollutants. The adaption of adsorption phenomenon from the traditional technologies with the modification of adsorbents at nanoscale is the trended research for mitigating the environmental pollutants with petite environmental concerns. Over the past decade, the hidden potentials of biological sources for the biofabrication of nanomaterials as bequeathed rapid research for remediating the environmental pollution in a sustainable manner. The biofabricated nanomaterials possess an inimitable phenomenon such as photo and enzymatic catalysis, electrostatic interaction, surface active site interactions, etc., contributing for the detoxification of various pollutants. With this background, the current review highlights the emerging biofabricated nano-based adsorbent materials and their underlying mechanisms addressing the environmental remediation of persistent organic pollutants, heavy metal (loid)s, phytopathogens, special attention to the reduction of pathogen-derived toxins and air pollutants. Each category is illustrated with suitable examples, fundamental mechanism, and graphical representations, along with societal applications. Finally, the future and sustainable development of eco-friendly biofabricated nanomaterial-based adsorbents is discussed.

Recent progress in the nitration of arenes and alkenes

Nitro compounds are a predominant class of synthetic intermediates and building blocks for the preparation of a wide range of nitrogen-containing compounds in the chemical industry. As such, impressive progress has been currently made in the nitration of aromatics and olefins with excellent functional group tolerance and site-selectivity. In this mini review, we intend to highlight the regiospecific nitration of arenes and alkenes in various reaction systems. The involved mechanisms are discussed as well.

Trends in Sustainable Synthesis of Organics by Gold Nanoparticles Embedded in Polymer Matrices

Gold nanoparticles (AuNPs) have emerged in recent decades as attractive and selective catalysts for sustainable organic synthesis. Nanostructured gold is indeed environmentally friendly and benign for human health; at the same time, it is active, under different morphologies, in a large variety of oxidation and reduction reactions of interest for the chemical industry. To stabilize the AuNPs and optimize the chemical environment of the catalytic sites, a wide library of natural and synthetic polymers has been proposed. This review describes the main routes for the preparation of AuNPs supported/embedded in synthetic organic polymers and compares the performances of these catalysts with those of the most popular AuNPs supported onto inorganic materials applied in hydrogenation and oxidation reactions. Some examples of cascade coupling reactions are also discussed where the polymer-supported AuNPs allow for the attainment of remarkable activity and selectivity.

Monodisperse amino-modified nanosized zero-valent iron for selective and recyclable removal of TNT: Synthesis, characterization, and removal mechanism

Nitroaromatic explosives are major pollutants produced during wars that cause serious environmental and health problems. The removal of a typical nitroaromatic explosive, 2,4,6-trinitrotoluene (TNT), from aqueous solution, was conducted using a new recyclable magnetic nano-adsorbent (Fe@SiO₂NH₂). This adsorbent was prepared by grafting amino groups onto Fe@SiO₂ particles with a well-defined core-shell structure and demonstrated monodispersity in solution. The removal performance of the nano-adsorbent towards TNT was found to be 2.57 and 4.92 times higher than that towards two analogous explosives, 2,4-dinitrotoluene (2,4-DNT) and 2-nitrotoluene (2-NT), respectively, under neutral conditions. The difference in the removal performance among the three compounds was further compared in terms of the effects of different conditions (pH value, ionic strength, humic acid concentration, adsorbent modification degree and dosage, etc.) and the electrostatic potential distributions of the three compounds. The most significant elevation is owing to modification of amino on Fe@SiO₂ which made a 20.7% increase in adsorption efficiency of TNT. The experimental data were well fit by the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model, indicating multilayer adsorption on a heterogeneous surface. The experimental results and theoretical considerations show that the interactions between Fe@SiO₂NH₂ NPs and TNT correspond to dipole-dipole and hydrophobic interactions. These interactions should be considered in the design of an adsorbent. Furthermore, the adaptability to aqueous environment and excellent regeneration capacity of Fe@SiO₂NH₂ NPs makes these remediation materials promising for applications.