Nitroaromatic compounds: Environmental toxicity, carcinogenicity, mutagenicity, therapy and mechanism

Collective absorption of 2,4,6-trinitrotoluene into lipid membranes and its effects on bilayer properties. A computational study

The widely used explosive, 2,4,6-trinitrotoluene (TNT), is a highly toxic chemical, which can cause hepatitis, cataracts, jaundice and so on, in humans. The interaction between TNT and biological membranes is crucial for understanding its toxic effects. Here, we mainly focused on molecular-level mechanisms for the collective adsorption of TNT into lipid membranes and the corresponding effects on bilayer properties by all-atom molecular dynamics simulations. We revealed that TNT can readily form an aggregate in the aqueous phase and quickly approach the surface of the membrane. At low concentrations of TNT (7 mol%), the aggregate is unstable and breaks up after several nanoseconds, and then the dispersed TNT molecules enter the membrane alone. At high concentrations (14 mol%), the aggregate is adsorbed as a whole and remains stable inside the membrane. After some of the TNT is absorbed by the membrane, the remaining TNT across the membrane would have greater permeability, i.e., the calculated permeability coefficient (P) is increased from 1.7 × 10^-2 to 18.3 cm s^-1. Correspondingly, a higher bioconcentration factor (BCF) was also observed. The increased level is more pronounced in the presence of TNT aggregates (i.e., high concentrations). This phenomenon is closely related to the strong interaction between TNT molecules. The results suggested that TNT molecules that have entered into the membrane can facilitate the membrane uptake, permeation and bioaccumulation of subsequent TNT molecules, exhibiting a synergistic effect. This work has a certain significance for understanding the toxicity of TNT.

Prediction of toxicity of secondary metabolites

The prediction of toxicological endpoints has gained broad acceptance; it is widely applied in early stages of drug discovery as well as for impurities obtained in the production of generic or equivalent products. In this work, we describe methodologies for the prediction of toxicological endpoints compounds, with a particular focus on secondary metabolites. Case studies include toxicity prediction of natural compound databases with anti-diabetic, anti-malaria and anti-HIV properties.

Copper(II), Zinc(II), and Cadmium(II) Formylbenzoate Complexes: Reactivity and Emission Properties

Synthesis, characterization, reactivity, and sensing properties of 4-formylbenzoate complexes of copper(II), zinc(II), and cadmium(II) possessing the 1,10-phenanthroline ancillary ligand are studied. The crystal structures of the (1,10-phenanthroline)bis(4-formylbenzoate)(aqua)copper(II) and (1,10-phenanthroline)bis(4-formylbenzo-ate)zinc(II) and a novel molecular complex comprising an assembly of mononuclear and dinuclear species of (1,10-phenanthroline)bis(4-formylbenzoate)cadmium(II) are reported. These zinc and cadmium complexes are fluorescent; they show differentiable sensitivity to detect three positional isomers of nitroaniline. The mechanism of sensing of nitroanilines by 1,10-phenanthroline and the complexes are studied by fluorescence titrations, photoluminescence decay, and dynamic light scattering. A plausible mechanism showing that 1,10-phenanthroline ligand-based emission quenched by electron transfer from the excited state of 1,10-phenanthroline to nitroaniline is supported by density functional theory calculations. In an anticipation to generate a fluorescent d¹⁰-copper(I) formylbenzoate complex by a mild reducing agent such as hydroxylamine hydrochloride for similar sensing of nitroaromatics as that of the d¹⁰-zinc and cadmium 4-formylbenzoate complexes, reactivity of d⁹-copper(II) with hydroxylamine hydrochloride in the presence of 4-formylbenzoic acid and 1,10-phenanthroline is studied. It did not provide the expected copper(I) complex but resulted in stoichiometry-dependent reactions of 4-formylbenzoic acid with hydroxylamine hydrochloride in the presence of copper(II) acetate and 1,10-phenanthroline. Depending on the stoichiometry of reactants, an inclusion complex of bis(1,10-phenanthroline)(chloro)copper(II) chloride with in situ-formed 4-((hydroxyimino)methyl)benzoic acid or copper(II) 4-(hydroxycarbamoyl)benzoate complex was formed. The self-assembly of the inclusion complex has the bis(1,10-phenanthroline)(chloro)copper(II) cation encapsulated in hydrogen-bonded chloride-hydrate assembly with 4-((hydroxyimino)methyl)benzoic acid.

Environmental persistence, hazard, and mitigation challenges of nitroaromatic compounds

Nitroaromatic compounds (NACs) are extensively used in different industries and are synthesized in large quantity due to their heavy demand worldwide. The broad use of NACs poses a serious pollution threat. The treatment processes used for the removal of NACs are not effective and sustainable, leading to their release into the environment. The nitro group attached to benzene ring makes the compounds recalcitrant due to which they persist in the environment. Being hazardous to human as well as other living organisms, NACs are listed in the USEPA's priority pollutant group. This review provides updated information on the sources of NACs, prevalence in different environmental matrices, and recent developments in methods of their detection, with emphasis on current trends as well as future prospects. The harmful effects of NACs due to exposure through different routes are also highlighted. Further, the technologies reported for the treatment of NACs, including physico-chemical and biological methods, and the challenges faced for their effective implementation are discussed. Thus, the review discusses relevant issues in detail making suitable recommendations, which can be helpful in guiding further research in this subject.

Pyrenyl-Functionalized Polysiloxane Based on Synergistic Effect for Highly Selective and Highly Sensitive Detection of 4-Nitrotoluene

4-Nitrotoluene (NT) is an important intermediate for the manufacture of dyes, agricultural chemicals, medicaments, and synthetic fibers. But its wide use has resulted in a series of ecological problems and health issues due to high toxicity, mutagenicity, and carcinogenicity. However, no fluorescent probes with high selectivity and high sensitivity to NT has been reported yet, and the current probes usually prefer to detect multi-nitrosubstituted nitroaromatic compounds (NACs) including 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol. Herein, we report a series of pyrene-functionalized polysiloxanes with high selectivity and high sensitivity to NT. Pyrene was introduced into polysiloxane through a carbon-carbon double bond, and the formed rigid side-chain fluorophore and flexible backbone structure of polysiloxane provide an ideal platform for the highly selective detection of NT. We further explored the possible response mechanism and speculated that the high selectivity and high sensitivity were derived from the synergistic effect between steric hindrance and dipolar interaction. In addition, paper sensors based on the obtained fluorescent materials were fabricated and change in their high sensitivity and visible fluorescence indicated that the paper sensor is a simple testing tool for portable and visual detection of NT. Furthermore, the design strategy in this work provides a novel synthetic route to synthesize other fluorescent probes with unique selectivity to NACs detection.

The Role of Reactive Nitrogen Species in Sensitized Photolysis of Wastewater-Derived Trace Organic Contaminants

Under conditions typically encountered in the aquatic environment, the absorption of sunlight by nitrite and nitrate leads to the transformation of trace organic contaminants. In addition to the well understood mechanism through which hydroxyl radical (·OH) produced by nitrate and nitrite photolysis oxidizes contaminants, absorption of light also results in the formation of reactive nitrogen species that transform organic contaminants. To assess the importance of this process on the fate of trace organic contaminants, radical quenchers and transformation product analysis were used to discriminate among potential reaction pathways. For sulfamethoxazole, an antibiotic that is frequently detected in municipal wastewater effluent, nitrate and nitrite-sensitized photolysis pathways resulted in production of transformation products that were not detected during direct photolysis or reaction with ·OH. The reactivity of sulfamethoxazole with the reactive species produced when nitrite absorbed sunlight was affected by the presence of hydroxyl radical scavengers, indicating the likely involvement of nitrogen dioxide, which forms when nitrite reacts with hydroxyl radical. Reactive nitrogen species also reacted with emtricitabine, propranolol, and other trace organic contaminants commonly detected in wastewater effluent, indicating the potential importance of this process to the fate of other trace organic contaminants. A kinetic model indicated that reactive nitrogen species could be important to the phototransformation of trace organic contaminants when relatively high concentrations of nitrite are present (e.g., in surface waters receiving reverse osmosis concentrate from potable water reuse projects or in agricultural runoff).

Recyclable nanographene-based micromachines for the on-the-fly capture of nitroaromatic explosives

It has been more than a decade since nano/micromachines (NMMs) have received the particular attention of scientists in different research fields. They are able to convert chemical energy into mechanical motion in their surrounding environment. Herein, a powerful, efficient and fast strategy of using nanosized reduced graphene oxide flake (n-rGO)-based self-propelled tubular micromachines for the removal of nitroaromatic compounds (NACs) is described. This method relies on the integration of the rGO as a well-known adsorbent of aromatic compounds with chemically powered engines for the removal of explosive compounds such as 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol (TNP) and 2,4-dinitrotoluene (DNT). Nanographene oxide reduced electrochemically inside the pores of the polycarbonate membrane to form an outer layer (n-rGO, adsorbent layer) of the micromachines. Subsequent electrodeposition of nickel (Ni, magnetic layer) and platinum (Pt, catalytic layer) resulted in the formation of n-rGO/Ni/Pt micromachines. Notably, the bubble-propelled micromachines were able to remove nitroaromatic compounds with high efficiency (∼90-92%) compared to the efficiency of magnetic-guided (22-42%) and static (2.5-7%) micromachines. Most importantly, the micromachines were regenerated and reused several times. The regeneration is based on an electrochemical method in which electron injection into the machine causes the expulsion of contaminants from the outer layer of the micromachines within a few seconds. The integration of the powerful self-propulsion, high adsorbent capacity of rGO and the introduced ultrafast regeneration procedure are beneficial for the realization of an active platform for water remediation.

Hazardous ecotoxicological impact of two commonly used nitrofuran-derived antibacterial drugs: Furazolidone and nitrofurantoin

This paper discusses the impact of two nitrofuran-derived drugs, namely furazolidone and nitrofurantoin on growth of oat and common radish as well as their impact on bacteria Allivibrio fischeri and crustaceans Heterocypris incongruens. Results indicated that both compounds were highly phytotoxic for radish (R. sativus) being simultaneously nearly not harmful for oat (A. sativa). Growing inhibition of shoots, roots, fresh matter and photosynthetic pigments is correlated with growing concentration of drugs in soil. Ecotoxicological impact of both compounds on model luminescence bacteria Aliivibrio fischeri and freshwater crustaceans Heterocypris incongruens as a representative organisms of two different level of food chain, is also reported herein, and the obtained data show significant toxicity against these two organisms. Basing on obtained results, it was concluded that both nitrofuran drugs in case of distribution through environment, by improper utilisation after use or unplanned environmental intoxication with unused drugs may cause serious environmental problems and therefore both should be handled with a reasonable care at any step of their production or utilisation.

Coupling reactions between reduced intermediates of insensitive munitions compound analog 4-nitroanisole

Explosives, pesticides, and pharmaceuticals contain toxic nitroaromatic compounds that may form even more toxic azo compounds if they encounter reducing conditions in the environment. We investigated the mechanism by which 4,4'-dimethoxyazobenzene forms in anaerobic sludge incubations of 4-nitroanisole, an analog for the insensitive munitions compound 2,4-dinitroanisole (DNAN). Because studies have reported the mechanism to involve the coupling of reduced nitroaromatic intermediates, specifically aromatic amines and nitrosoaromatics, by nucleophilic processes, we abiotically paired 10 mM 4-aminoanisole with 2 mM 4-nitrosoanisole in nitrogen-flushed microcosms. However, only 7 μM of 4,4'-dimethoxyazobenzene had formed after 24 h. We identified the major product to be 4-methoxy-4'-nitrosodiphenylamine. Repeating this experiment in phosphate buffer at pH 5.1, 7.1, and 8.6 demonstrated that the formation of this unexpected product is acid catalyzed. We found that 4-methoxy-4'-nitrosodiphenylamine is more toxic than 4,4'-dimethoxyazobenzene to the bioluminescent bacterium Aliivibrio fischeri, with IC₅₀ values of 0.1 μM and 0.5 μM, respectively. Both products are several orders of magnitude more toxic than reduced 4-nitroanisole intermediates 4-aminoanisole and 4-nitrosoanisole, as well as DNAN and its aromatic amine metabolites. Six-fold more 4,4'-dimethoxyazobenzene formed when we incubated 4-nitrosoanisole with ascorbic acid, a reducing agent, than when we incubated 4-nitrosoanisole with 4-aminoanisole in the absence of ascorbic acid. We therefore suspect that 4-hydroxylaminoanisole, the first reduction product of 4-nitrosoanisole, is a better nucleophile than 4-aminoanisole and couples more readily with 4-nitrosoanisole. Slightly basic and reducing conditions can prevent the formation and persistence of toxic coupling products on sites contaminated with nitroaromatics, i.e. DNAN-contaminated firing ranges.

Formation of Nitrophenolic Byproducts during Heat-Activated Peroxydisulfate Oxidation in the Presence of Natural Organic Matter and Nitrite

Sulfate radical (SO₄^•-)-based advanced oxidation is a viable in situ remediation technology for degrading organic contaminants in the subsurface. In this study, we demonstrated that SO₄^•- could induce the activation of nitrite, an anion commonly present in the subsurface environment, leading to the formation of nitrophenolic byproducts. Fourier-transform infrared spectroscope and ¹⁵N nuclear magnetic resonance analysis revealed that the inorganic nitrite was incorporated into natural organic matter (NOM) to form organic nitrogen upon SO₄^•- oxidation. Nitrophenolic byproducts, including 2-hydroxy-5-nitrobenzoic acid, 4-nitrophenol, and 2,4-dinitrophenol, were identified using high-resolution mass spectrometry in combination with a ¹⁵N labeling technique. Formation of nitrated byproducts was ascribed to the scavenging of SO₄^•- by nitrite, which not only generated the nitrating agent NO₂^• but also inhibited the degradation of organic compounds, making them more available to the reactions with NO₂^•. The phenolic moieties in NOM served as the main reactive sites for NO₂^• attack. The nitration begins with H abstraction on the phenoxy oxygen, followed by the addition of another NO₂^• to its ortho or para site. Decarboxylation followed by NO₂^• addition can also generate nitrophenolic byproducts. To the best of our knowledge, this is the first study reporting the nitration of NOM and formation of toxic nitrophenolic byproducts during SO₄^•--based oxidation. It sheds light on the potential risks of this technology in subsurface remediation practices.

Mechanism-based structure-activity relationship (SAR) analysis of aromatic amines and nitroaromatics carcinogenicity via statistical analyses based on CPDB

Cancer is a leading cause of human mortality around the globe. In this study, mechanism-based SAR (Structure-Activity Relationship) was employed to investigate the carcinogenicity of aromatic amines and nitroaromatics based on CPDB. Principal component analysis and cluster analysis were used to construct the SAR model. Principle component analysis generated three principal components from 12 mechanism-based descriptors. The extracted principal components were later used for cluster analysis, which divided the selected 55 chemicals into six clusters. The three principal components were proposed to describe the "transport", "reactivity" and "electrophilicity" properties of the chemicals. Cluster analysis indicated that the relevant "transport" properties positively correlated with the carcinogenic potential and were contributing factors in determining the carcinogenicity of the studied chemicals. The mechanism-based SAR analysis suggested the electron donating groups, electron withdrawing groups and planarity are significant factors in determining the carcinogenic potency for studied aromatic compounds. The present study may provide insights into the relationship between the three proposed properties and the carcinogenesis of aromatic amines and nitroaromatics.

A theoretical insight into the reaction mechanisms of a 2,4,6-trinitrotoluene nitroso metabolite with thiols for toxic effects

2,4,6-Trinitrotoluene (TNT) is a class C carcinogen as rated by the Environmental Protection Agency. One of the toxicity mechanisms of TNT is the covalent binding of its metabolites to critical proteins. However, knowledge about their molecular reaction mechanisms is scarce. Herein, we have provided density functional theory (DFT) simulation evidences for the reaction mechanisms of the nitroso metabolite of TNT with the sulfhydryl group of model thiols for the first time. The results show that the solvent-mediated proton-transfer mechanism plays a significant role in the entire process. For the formation of semimercaptal, the mechanism is slightly different from the previous one where the thiolate anion attacks the nitroso group. The rearrangement of semimercaptal needs to be triggered by an acid or hydrated ion (H3O+), which is consistent with the previous assumption. The other pathway, the conversion of semimercaptal to hydroxylamine, has to overcome a higher barrier, although it does not need the participation of an acid or a hydrated ion. In addition, the details on transition states, intermediates and free energy surfaces for three reactions are given, which make up for the lack of experimental knowledge. These conclusions can help to deeply understand the toxic effects of TNT and other nitroaromatic explosives.

Free nitrous acid (FNA) induced transformation of sulfamethoxazole in the enriched nitrifying culture

The sulfonamide antibiotics sulfamethoxazole (SMX) has been frequently detected in the wastewater. It has been reported that part of SMX can be transformed by the co-metabolism of ammonia oxidizing bacteria (AOB) during nitrifying process. However, previous studies reported inconsistent or even contradictory results in terms of SMX degradation and/or transformation. Literature study revealed that nitrite may play certain role in SMX transformation, which has been neglected previously. In this study, the transformation behavior of SMX was investigated with and without the presence of nitrite in an enriched nitrifying culture. The results clearly show that the elimination of SMX occurred with the presence/accumulation of nitrite, and a linear regression was observed between SMX elimination efficiency and free nitrous acid (FNA) concentration, indicating that FNA was the major factor responsible for the SMX transformation. By reacting with FNA, SMX transformation products, such as 4-nitro-SMX, desamino-SMX and hydroxylated SMX, were detected. However, when FNA concentration decreased, these intermediates may be retransformed back to SMX. These findings improved our understanding on SMX transformation in a biological system and highlighted the role of nitrite/FNA in the sulfonamide antibiotics degradation.

Purine derivatives with heterocyclic moieties and related analogs as new antitumor agents

AIM

Identification of new antiproliferative compounds.

METHODOLOGY

Four series of compounds were synthesized by the Mitsunobu reaction. Their antiproliferative activity was studied against several cancer cells and a noncancerous fibroblast cell line. Their apoptotic activity was analyzed using a caspase 3/7 fluorescence assay.

RESULTS & CONCLUSION

9-alkylated-6-halogenated and 2,6-dihalogenated purines show remarkable inhibition of tumor cell proliferation, with the dichloro derivatives being the most potent of all the series. The most promising compound, tetrahydroquinoline 4c, exhibits significant antiproliferative activity against the cancer cells tested, while displaying a 19-fold lower potency against noncancerous fibroblasts, a key feature that indicates potential selectivity against cancer cells. This compound produces a high percentage of apoptosis (58%) after 24 h treatment in human breast cancer MCF-7 cells.

A Two-Step Multicomponent Synthetic Approach and Anti-inflammatory Evaluation of N-Substituted 2-Oxopyrazines

Inflammation is widely reported as a main factor for the development of chronic diseases such as cancer, diabetes, and even metabolic syndrome. Thus, the search for novel anti-inflammatory compounds is required. Herein we describe the synthesis of a collection of peptidic pyrazinones by a convenient approach involving a multicomponent isocyanide-based reaction followed by a tandem deprotection/oxidative cyclization step. This series of compounds were tested for their potential anti-inflammatory capacity in an in vivo murine model, and four compounds were identified to inhibit tetradecanoylphorbol acetate (TPA)-induced edema by more than 75 %. The two most active compounds, N-benzyl-2-(4-hydroxy-3,5-dimethoxyphenyl)-2-[2-oxopyrazin-1(2H)-yl]acetamide (10 o) and N-cyclohexyl-2-[2-oxopyrazin-1(2H)-yl]-2-[4-(trifluoromethyl)phenyl]acetamide (10 x), with methyl and trifluoromethyl groups, were also able to decrease myeloperoxidase activity and leukocyte infiltration. Moreover, 10 x decreased the thickness of TPA-treated mouse ears, as observed in histological analysis of the tissues.

Rethinking sulfate radical-based oxidation of nitrophenols: Formation of toxic polynitrophenols, nitrated biphenyls and diphenyl ethers

Sulfate radical (SO₄^-)-based oxidation of nitrophenols (NPs) have been widely studied; however, formation of potentially more toxic polynitroaromatic intermediates has been overlooked. In this contribution, we systematically investigated the degradation of four NPs by a SO₄^--based oxidation process. Degradation efficiency of NPs followed the order: 2-nitrophenol (2-NP) > 4-nitrophenol (4-NP) > 2,4-dinitrophenol (2,4-DNP) > 2,6-dinitrophenol (2,6-DNP). HPLC and LC-MS/MS analysis confirmed the formation of 2,4-DNP, 2,6-DNP and 2,4,6-trinitrophenol (2,4,6-TNP) during NPs transformation by SO₄^-, suggesting that both denitration and renitration processes occurred. Nitrogen dioxide radicals (NO₂) and phenoxy radicals are responsible for the formation of polynitrophenols. Coupling products including nitrated biphenyls and diphenyl ethers were also detected, which were proposed to be formed by combinations of resonance-stabilized radicals. Electron spin density and charge density calculation showed that ortho C-ortho C and ortho C-phenolic O were the most likely combination ways responsible for coupling products formation. ECOSAR program predicted that polynitrated diphenyl ethers and biphenyls had higher ecotoxicological effects on aquatic species such as fish and daphnia. Therefore, the formation of toxic polynitroaromatic intermediates in SO₄^--based advanced oxidation processes should be scrutinized before this technology can be safely utilized for water and wastewater treatment.

Iron-loaded amine/thiol functionalized polyester fibers with high catalytic activities: a comparative study

Dispersion of iron nanoparticles (Fe-NPs) was achieved on polyester fabrics (PET) by diverse stabilizing agents.

Structure-Based Drug Design Studies Toward the Discovery of Novel Chalcone Derivatives as Potential Epidermal Growth Factor Receptor (EGFR) Inhibitors

Human Epidermal Growth Factor Receptor-1 (EGFR), a transmembrane tyrosine kinase receptor (RTK), has been associated with several types of cancer, including breast, lung, ovarian, and anal cancers. Thus, the receptor was targeted by a variety of therapeutic approaches for cancer treatments. A series of chalcone derivatives are among the most highly potent and selective inhibitors of EGFR described to date. A series of chalcone derivatives were proposed in this study to investigate the intermolecular interactions in the active site utilizing molecular docking and molecular dynamics simulations. After a careful analysis of docking results, compounds 1a and 1d were chosen for molecular dynamics simulation study. Extensive hydrogen bond analysis throughout 7 ns molecular dynamics simulation revealed the ability of compounds 1a and 1d to retain the essential interactions needed for the inhibition, especially MET 93. Finally, MM-GBSA calculations highlight on the capability of the ligands to bind strongly within the active site with binding energies of −44.04 and −56.6 kcal/mol for compounds 1a and 1d, respectively. Compound 1d showed to have a close binding energy with TAK-285 (−66.17 kcal/mol), which indicates a high chance for compound 1d to exhibit inhibitory activity, thus recommending to synthesis it to test its biological activity. It is anticipated that the findings reported here may provide very useful information for designing effective drugs for the treatment of EGFR-related cancer disease.

Underappreciated and Complex Role of Nitrous Acid in Aromatic Nitration under Mild Environmental Conditions: The Case of Activated Methoxyphenols

Many ambiguities surround the possible mechanisms of colored and toxic nitrophenols formation in natural systems. Nitration of a biologically and environmentally relevant aromatic compound, guaiacol (2-methoxyphenol), under mild aqueous-phase conditions (ambient temperatures, pH 4.5) was investigated by a temperature-dependent experimental modeling coupled to extensive ab initio calculations to obtain the activation energies of the modeled reaction pathways. The importance of dark nonradical reactions is emphasized, involving nitrous (HNO₂) and peroxynitrous (HOONO) acids. Oxidation by HOONO is shown to proceed via a nonradical pathway, possibly involving the nitronium ion (NO₂⁺) formation. Using quantum chemical calculations at the MP2/6-31++g(d,p) level, NO₂^• is shown capable of abstracting a hydrogen atom from the phenolic group on the aromatic ring. In a protic solvent, the corresponding aryl radical can combine with HNO₂ to yield OH^• and, after a subsequent oxidation step, nitrated aromatic products. The demonstrated chemistry is especially important for understanding the aging of nighttime atmospheric deliquesced aerosol. The relevance should be further investigated in the atmospheric gaseous phase. The results of this study have direct implications for accurate modeling of the burden of toxic nitroaromatic pollutants, and the formation of atmospheric brown carbon and its associated influence on Earth's albedo and climate forcing.

Photoelectrocatalytic reduction of nitrobenzene on Bi-doped CuGaS2 films

Nitrobenzene, a toxic nitroaromatic, a feedstock compound to the production of many commercially relevant chemicals were photoelectrocatalytically reduced into aniline on a photoelectrode comprised by a bismuth-doped CuGaS₂ nanocrystallyne thin films on molybdenum. The activity of the photoelectrodes were compared to the reaction performed on undoped-CuGaS₂ films, and they were carried out under illumination with an applied bias potential at 0.9 V. Aniline was highly selectively obtained with 83% of conversion for reaction times of 100 min when using Bi-doped CuGaS₂, representing higher conversion of nitrobenzene and yield to aniline than the undoped photoelectrode. The catalytic performance of the doped films remained stable for a set of 5 consecutive experiments. These results indicate Bi-doped CuGaS₂ as a promising material to be applied in the photoelectrocatalytic reduction of nitrobenzene into aniline through the direct pathway mechanism, using solar light illumination.

Diaminocyclohexane-Functionalized/Thioglycolic Acid-Modified Gold Nanoparticle-Based Colorimetric Sensing of Trinitrotoluene and Tetryl

Detection of explosive residues in soil and postblast debris is an important issue in sensor design for environmental and criminological purposes. An easy-to-use and low-cost gold nanoparticle (AuNP)-based colorimetric sensor was developed for the determination of nitroaromatic explosives, i.e., trinitrotoluene (TNT) and tetryl, capable of analyte detection at picomolar (pM) levels. The sensor nanoparticles were synthesized by functionalizing the negatively charged thioglycolic acid (TGA)-modified AuNPs with positively charged (±)- trans-1,2-diaminocyclohexane (DACH) at a carefully calculated pH. The working principle of the sensor is charge-transfer (CT) interaction between the electron-rich free amino (-NH₂) group of DACH and the electron-deficient -NO₂ groups of TNT/tetryl, added to possible nanoparticle agglomerization via electrostatic interaction of TNT-Meisenheimer anions with more than one cationic DACH-modified AuNP. The limit of detection (LOD) and limit of quantification (LOQ) of the sensor were 1.76 pM and 5.87 pM for TNT and 1.74 pM and 5.80 pM for tetryl, respectively. TNT, tetryl, and tetrytol, extracted from a nitroaromatic explosive-contaminated soil sample, were determined with the proposed sensor, yielding good recoveries. The sensor could be selectively applied to various mixtures of TNT with common energetic materials such as RDX, HMX, and PETN. Additionally, common soil ions (Cl^-, NO₃^-, SO₄^2-, K⁺, Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺, Fe³⁺, and Al³⁺) as well as detergents, sugar, sweeteners, acetylsalicylic acid (aspirin), caffeine, and paracetamol-based painkiller drugs, which may be used as camouflage materials for explosives, either had no adverse effects or removable interferences on the detection method. The developed method was statistically validated against a GC-MS literature method.

Bioaugmented soil aquifer treatment for P-nitrophenol removal in wastewater unique for cold regions

P-nitrophenol (PNP) is a toxic and recalcitrant organic pollutant and a usual intermediate in the production of fine chemicals, which has posed a significant threat to subsurface environment safety. Soil aquifer treatment (SAT) is a promising method to remove and remediate contamination in vadose zone with low cost and high efficiency. However, there are still research gaps for the treatment of recalcitrant contaminants by SAT in cold regions, such as un-robust indigenous microbes and low temperature constraint in vadose zone. The bioaugmentation technology was first introduced into SAT in order to enhance the removal ability of PNP by SAT operated in cold regions in this study. A high-efficiency PNP-degrading bacterium was successfully isolated, which can efficiently degrade PNP below 200 mg L^-1 with a degradation rate above 99% at 15 °C close to the real subsurface temperature in cold regions, and added into SAT for bioaugmentation. The feasibility of bioaugmented SAT and associated PNP removal process were investigated by laboratory sand columns, along with effects of the SAT operative parameters (namely PNP loading concentration, flow rate and soil saturation level of SAT). Within the range of PNP loading stresses tested (1-200 mg L^-1), PNP removal efficiency was optimal at constant flow rate of 219 mL d^-1 in unsaturated operating condition of SAT under 15 °C among all the investigated experimental conditions. Longer hydraulic residence time increased the PNP removal rate, although the accumulated mass removed reduced and the removal efficiencies remained constant in unsaturated operating condition of SAT. It is found from the comparison between the PNP removals via both unsaturated and saturated columns that slight difference only in the removal rate of PNP was observed and the highly efficient bioaugmented SAT can completely degrade PNP of 10 mg L^-1 within 5 wetting/drying cycles under both scenarios.

Oxidative dehalogenation and denitration by a flavin-dependent monooxygenase is controlled by substrate deprotonation

Enzymes that are capable of detoxifying halogenated phenols (HPs) and nitrophenols (NPs) are valuable for bioremediation and waste biorefining. HadA monooxygenase was found to perform dual functions of oxidative dehalogenation (hydroxylation plus halide elimination) and denitration (hydroxylation plus nitro elimination). Rate constants associated with individual steps of HadA reactions with phenol, halogenated phenols and nitrophenols were measured using combined transient kinetic approaches of stopped-flow absorbance/fluorescence and rapid-quench flow techniques. Density functional theory was used to calculate the thermodynamic and electronic parameters associated with hydroxylation and group elimination steps. These parameters were correlated with the rate constants of hydroxylation, group elimination, and overall product formation to identify factors controlling individual steps. The results indicated that the hydroxylation rate constant is higher when the pK a of the phenolic group is lower, i.e. it is more easily deprotonated, but not higher when the energy gap between the E LUMO of the C4a-hydroperoxy-FAD intermediate and the E HOMO of the phenolate substrate is lower. These data suggest that the substrate deprotonation has a higher energy barrier than the -OH transfer, and thus controls the hydroxylation step. For the group elimination, the process is controlled by the ability of the C-X bond to break. For the overall product formation (hydroxylation and group elimination combined), this analysis showed that the rate constant of product formation is dependent on the pK a value of the substrate, indicating that the overall reaction is controlled by substrate deprotonation. This step also likely has the highest energy barrier and thus controls the overall process of oxidative dehalogenation and denitration by HadA. This report is the first to identify a key mechanistic factor controlling the enzymatic processes of oxidative dehalogenation and denitration.

Transformation of antimicrobial agent sulfamethazine by peroxymonosulfate: Radical vs. nonradical mechanisms

Peroxymonosulfate (PMS) is increasingly used as an oxidant for in situ remediation of organic contaminants in soil and groundwater. In this study we demonstrated that sulfamethazine (SMZ) could be transformed by PMS in the absence of any activators. Such transformation was ascribed to the oxidation by PMS per se, rather than free radicals (SO₄^- or HO), superoxide (O₂^-), or singlet oxygen (¹O₂). The aniline moiety of SMZ molecule was the reactive site for PMS oxidation, leading to the formation of nitrated products. This nitration pathway in fact played a significant role in the removal of SMZ in activated PMS oxidation processes. For instance, it contributed 26% of the total SMZ transformation, while SO₄^- contributed the other 74% during the removal of SMZ, in Co(II)/PMS oxidation process with initial PMS and Co(II) concentrations of 1.0 mM and 0.1 μM, respectively. Similar nitration reaction also occurred to other sulfonamide antibiotics bearing an aniline moiety upon the reaction with PMS. Since nitrated sulfonamide antibiotics appear more persistent than the parent compounds and may cause other environmental problems, such a pathway should not be desired. Therefore, PMS might not be an ideal oxidant for the treatment of sulfonamide antibiotics and other compounds having aniline moieties, especially in subsurface remediation practices where efficient activation of PMS represents a major challenge.

Phylogenomics Reveal the Dynamic Evolution of Fungal Nitric Oxide Reductases and Their Relationship to Secondary Metabolism

Fungi expressing P450nor, an unconventional nitric oxide (NO) reducing cytochrome P450, are considered significant contributors to environmental nitrous oxide (N₂O) emissions. Despite extensive efforts, fungal contributions to N₂O emissions remain uncertain. For example, the majority of N₂O emitted from antibiotic-amended soil microcosms is attributed to fungal activity, yet axenic fungal cultures do not couple N-oxyanion respiration to growth and these fungi produce only minor quantities of N₂O. To assist in reconciling these conflicting observations and produce a benchmark genomic analysis of fungal denitrifiers, genes underlying denitrification were examined in >700 fungal genomes. Of 167 p450nor—containing genomes identified, 0, 30, and 48 also harbored the denitrification genes narG, napA, or nirK, respectively. Compared with napA and nirK, p450nor was twice as abundant and exhibited 2–5-fold more gene duplications, losses, and transfers, indicating a disconnect between p450nor presence and denitrification potential. Furthermore, cooccurrence of p450nor with genes encoding NO-detoxifying flavohemoglobins (Spearman r = 0.87, p = 1.6e⁻¹⁰) confounds hypotheses regarding P450nor’s primary role in NO detoxification. Instead, ancestral state reconstruction united P450nor with actinobacterial cytochrome P450s (CYP105) involved in secondary metabolism (SM) and 19 (11%) p450nor-containing genomic regions were predicted to be SM clusters. Another 40 (24%) genomes harbored genes nearby p450nor predicted to encode hallmark SM functions, providing additional contextual evidence linking p450nor to SM. These findings underscore the potential physiological implications of widespread p450nor gene transfer, support the undiscovered affiliation of p450nor with fungal SM, and challenge the hypothesis of p450nor’s primary role in denitrification.

Quinones and nitroaromatic compounds as subversive substrates of Staphylococcus aureus flavohemoglobin

In microorganisms, flavohemoglobins (FHbs) containing FAD and heme (Fe³⁺, metHb) convert NO. into nitrate at the expense of NADH and O₂. FHbs contribute to bacterial resistance to nitrosative stress. Therefore, inhibition of FHbs functions may decrease the pathogen virulence. We report here a kinetic study of the reduction of quinones and nitroaromatic compounds by S. aureus FHb. We show that this enzyme rapidly reduces quinones and nitroaromatic compounds in a mixed single- and two-electron pathway. The reactivity of nitroaromatics increased upon an increase in their single-electron reduction potential (E¹₇), whereas the reactivity of quinones poorly depended on their E¹₇ with a strong preference for a 2-hydroxy-1,4-naphthoquinone structure. The reaction followed a 'ping-pong' mechanism. In general, the maximal reaction rates were found lower than the maximal presteady-state rate of FAD reduction by NADH and/or of oxyhemoglobin (HbFe²⁺O₂) formation (~130 s^-1, pH 7.0, 25 °C), indicating that the enzyme turnover is limited by the oxidative half-reaction. The turnover studies showed that quinones prefreqently accept electrons from reduced FAD, and not from HbFe²⁺O₂. These results suggest that quinones and nitroaromatics act as 'subversive substrates' for FHb, and may enhance the cytotoxicity of NO. by formation of superoxide and by diverting the electron flux coming from reduced FAD. Because quinone reduction rate was increased by FHb inhibitors such as econazole, ketoconazole, and miconazole, their combined use may represent a novel chemotherapeutical approach.

Organocatalytic Asymmetric Cascade Reactions Based on Gamma-Nitro Carbonyl Compound

The significant advancements in asymmetric organocascade reactions have been accomplished during the past decades, paving the way to the efficient and stereoselective construction of structurally complex scaffolds from simple and readily available starting materials. Nitro-containing cyclic compounds have become a privileged molecular library given their broad and promising activities in various therapeutic areas. In various approaches to build these valuable scaffolds, the utility of γ-nitrocarbonyl intermediates is one of the most efficient approaches due to its high efficiency, reliability and versatility. The strategies and catalyst systems described here highlight recent advances in the enantioselective synthesis of nitro-containing cyclic molecules via organocascade strategies based on γ-nitrocarbonyl intermediates. Various organocatalysts with distinct activation modes have found application in providing these sophisticated compounds. This review is organized according to the types of organocatalyst. These methods are of importance for the construction of complex chiral cyclic frameworks and the design of new pharmaceutical compounds. We believe that compounds based on nitro-containing cyclic skeletons have the potential to provide novel therapeutic agents and useful biological tools.

Design, synthesis and biological evaluation of some novel quinazolinone derivatives as potent apoptotic inducers

Aim: Novel quinazolinone and triazinoquinazolinone derivatives were designed and synthesized as apoptotic inducers. Methodology/results: Most of the synthesized compounds showed excellent antiproliferative activity against MCF-7 and HCT-116 cell lines, respectively. Compounds 7a, 8a, 8d, 14a and 14d were superior to doxorubicin as activators of caspases 3, 8 and 9 in HCT-116 cell line. The most potent caspase inducers, 8d and 14a showed cell cycle arrest mainly in G1 and S phase, respectively and increased the levels of p53, Bax and the Bax/Bcl-2 ratio compared with doxorubicin in HCT-116 cells with excellent selectivity against CCD-18Co human colon normal cell line. Conclusion: The synthesized compounds can be considered as potent apoptotic inducers interfering with extrinsic and intrinsic apoptotic pathways.

Development of a 2-Nitrobenzoate-Sensing Bioreporter Based on an Inducible Gene Cluster

Based on the sole information of structural genes of the 2-nitrobenzoate (2NBA) utilizing catabolic gene cluster (onbX1X2FCAR1EHJIGDBX3), 2NBA-sensing bioreporters were constructed by incorporating egfp into the onb gene cluster of Cupriavidus sp. strain ST-14. Incorporation of reporter gene in proximal to the hypothesized promoter region in conjunction with the disruption of the gene encoding inducer-metabolizing enzyme was turned out to be advantageous in reporter gene expression at low inducer concentration. The bioreporter strain was capable of expressing EGFP from the very 1st hour of induction and could detect 2NBA at (sub) nanomolar level exhibiting a strict specificity toward 2NBA, displaying no response to EGFP expression from its meta- and para-isomers as well as from a number of structurally related compounds. The present study is a successful demonstration of the development of a 2NBA-sensing bioreporter with respect to ease of construction, inducer specificity, and sensitivity, without prior knowledge of the associated inducer-responsive promoter-regulator elements. The present approach can be used as a model for the development of bioreporters for other environmental pollutants.

Evidence of anaerobic coupling reactions between reduced intermediates of 4-nitroanisole

Nitroaromatic compounds are widely used in agricultural pesticides, pharmaceuticals, military explosives, and other applications. They enter the environment via manufacturing and municipal wastewater discharges and releases from agricultural and military operations. Because of their ubiquity and toxicity, they are considered an important class of environmental contaminants. Nitroaromatics are known to undergo reductive transformation to aromatic amines, and under aerobic conditions they are susceptible to coupling reactions which may lead to their irreversible incorporation into soil organic matter. However, there is also evidence of coupling reactions in the absence of oxygen between reduced intermediates of the insensitive munitions compound 2,4-dinitroanisole, leading to the formation of azo dimers. The formation of such products is a concern since they may be more toxic than the original nitroaromatic compounds. The objective of this research is to provide evidence of the anaerobic formation of azo coupling products. 4-Nitroanisole was used as a model compound and was spiked into incubations containing anaerobic granular sludge with H₂ as the electron donor. Using liquid chromatography, UV-Vis spectroscopy, and mass spectrometry, the formation of the azo dimer 4,4'-dimethoxyazobenzene was confirmed. However, due to the instability of the azo bond under the reducing conditions of our incubations, the azo dimer did not accumulate. Consequently, 4-aminoanisole was the major product formed in our experiment. Other minor suspected coupling products were also detected in our incubations. The results provide clear evidence for the temporal formation of at least one azo dimer in the anaerobic reduction of a model nitroaromatic compound.

Sensing and capture of toxic and hazardous gases and vapors by metal–organic frameworks

This review summaries recent progress in the luminescent detection and adsorptive removal of harmful gases and vapors by metal–organic frameworks, as well as the principles and strategies guiding the design of these materials.

Fluorescence-based detection of nitroaromatics using a luminescent second sphere adduct self-assembled by charge-assisted hydrogen bonds

Photo-luminescent metal organic materials self-assembled via second sphere coordination using luminescent ligands show good selectivity to detect trace amounts of nitroaromatics.

Luminescent metal–organic frameworks as chemical sensors: common pitfalls and proposed best practices

In this review we approach the emerging field of sensors based on luminescent metal–organic frameworks from the perspective of the most commonly encountered pitfalls and we suggest best practices so that they can be avoided.

The role of nitrite in sulfate radical-based degradation of phenolic compounds: An unexpected nitration process relevant to groundwater remediation by in-situ chemical oxidation (ISCO)

As promising in-situ chemical oxidation (ISCO) technologies, sulfate radical-based advanced oxidation processes (SR-AOPs) are applied in wastewater treatment and groundwater remediation in recent years. In this contribution, we report for the first time that, thermally activated persulfate oxidation of phenol in the presence of nitrite (NO₂^-), an anion widely present in natural waters, could lead to the formation of nitrated by-products including 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP), and 2,6-dinitrophenol (2,6-DNP). Nitrogen dioxide radical (NO₂^•), arising from SO₄^•- scavenging by NO₂^-, was proposed to be involved in the formation of nitrophenols as a nitrating agent. It was observed that nitrophenols accounted for approximately 70% of the phenol transformed under reaction conditions of [NO₂^-] = 200 μM, [PS] = 2 mM and temperature of 50 °C. Increasing the concentration of NO₂^- remarkably enhanced the formation of nitrophenols but did not affect the transformation rate of phenol significantly. The degradation of phenol and the formation of nitrophenols were significantly influenced by persulfate dosage, solution pH and natural organic matter (NOM). Further studies on the degradation of other phenolic compounds, including 4-chlorophenol (4-CP), 4-hydroxybenzoic acid (4-HBA), and acetaminophen (ATP), verified the formation of their corresponding nitrated by-products as well. Therefore, formation of nitrated by-products is probably a common but overlooked phenomenon during SO₄^•--based oxidation of phenolic compounds in the presence of NO₂^-. Nitroaromatic compounds are well known for their carcinogenicity, mutagenicity and genotoxicity, and are potentially persistent in the environment. The formation of nitrated organic by-products in SR-AOPs should be carefully scrutinized, and risk assessment should be carried out to assess possible health and ecological impacts.