Nitroaromatic compounds, from synthesis to biodegradation

Review of cathodic electroactive bacteria: Species, properties, applications and electron transfer mechanisms

Cathodic electroactive bacteria (C-EAB) which are capable of accepting electrons from solid electrodes provide fresh avenues for pollutant removal, biosensor design, and electrosynthesis. This review systematically summarized the burgeoning applications of the C-EAB over the past decade, including 1) removal of nitrate, aromatic derivatives, and metal ions; 2) biosensing based on biocathode; 3) electrosynthesis of CH4, H2, organic carbon, NH3, and protein. In addition, the mechanisms of electron transfer by the C-EAB are also classified and summarized. Extracellular electron transfer and interspecies electron transfer have been introduced, and the electron transport mechanism of typical C-EAB, such as Shewanella oneidensis MR-1, has been combed in detail. By bringing to light this cutting-edge area of the C-EAB, this review aims to stimulate more interest and research on not only exploring great potential applications of these electron-accepting bacteria, but also developing steady and scalable processes harnessing biocathodes.

Distinct influence of model electron shuttles on anaerobic mononitrophenols reduction in aquatic environments by Shewanella oneidensis MR-1

The environmental fate and risks of mononitrophenols (mono-NPs), the simplest nitrophenols (NPs) often found in aquatic environments, are profoundly influenced by anaerobic bioreduction and co-existing electron shuttles (ESs), but little is known about the underlying mechanisms. Here, we elucidate the pathways of anaerobic mono-NPs bioreduction by Shewanella oneidensis MR-1 and assess the effect of model ESs on these processes. We found that all three mono-NPs isomers could be readily reduced to their corresponding aminophenols by S. oneidensis MR-1 under anaerobic conditions. CymA, a core component of the Mtr respiratory pathway, performs a dynamic role in these bioreduction, which is highly dependent on the bioreduction kinetics. The exogenous addition of quinones was found to accelerate the mono-NPs bioreduction through interactions with key outer-membrane proteins (e.g., OmcA and MtrC), and all these processes matched well to linear free energy relationships (LFERs). Surprisingly, adding riboflavin did not influence the bioreduction of all three mono-NPs isomers, which may be due to the contribution of OmcA and MtrC to these bioreduction processes and their downregulated expression. This study enhances our understanding of the environmental fate of mono-NPs and their bioconversion processes, providing valuable insights for the bioremediation of nitrophenol-contaminated sites.

Hemicyanine-Based Highly Water-Soluble Probe for Extracellular Nitroreductase

Nitroreductase (NTR) has long been a target of interest for its important role involved in the nitro compounds metabolism. Various probes have been reported for NTR analysis, but rarely able to distinguish the extracellular NTR from intracellular ones. Herein we reported a new NTR sensor, HCyS-NO2, which was a hemicyanine molecule with one nitro and two sulfo groups attached. The nitro group acted as the reporting group to respond NTR reduction. Direct linkage of nitro group into the hemicyanine π conjugate system facilitated the intramolecular electron transfer (IET) process and thus quenched the fluorescence of hemicyanine core. Upon reduction with NTR, the nitro group was rapidly converted into the hydroxylamino and then the amino group, eliminating IET process and thus restoring the fluorescence. The sulfo groups installed significantly increased the hydrophilicity of the molecule, and introduced negative charges at physiological pH, preventing the diffusion into bacteria. Both gram-negative and gram-positive bacteria were able to turn on the fluorescence of HCyS-NO2, without detectable diffusion into cells, providing a useful tool to probe the extracellular reduction process.

Elucidating the Role of O2 Uncoupling for the Adaptation of Bacterial Biodegradation Reactions Catalyzed by Rieske Oxygenases

Oxygenation of aromatic and aliphatic hydrocarbons by Rieske oxygenases is the initial step of various biodegradation pathways for environmental organic contaminants. Microorganisms carrying Rieske oxygenases are able to quickly adapt their substrate spectra to alternative carbon and energy sources that are structurally related to the original target substrate, yet the molecular events responsible for this rapid adaptation are not well understood. Here, we evaluated the hypothesis that reactive oxygen species (ROS) generated by unproductive activation of O2, the so-called O2 uncoupling, in the presence of the alternative substrate exert a selective pressure on the bacterium for increasing the oxygenation efficiency of Rieske oxygenases. To that end, we studied wild-type 2-nitrotoluene dioxygenase from Acidovorax sp. strain JS42 and five enzyme variants that have evolved from adaptive laboratory evolution experiments with 3- and 4-nitrotoluene as alternative growth substrates. The enzyme variants showed a substantially increased oxygenation efficiency toward the new target substrates concomitant with a reduction of ROS production, while mechanisms and kinetics of enzymatic O2 activation remained unchanged. Structural analyses and docking studies suggest that amino acid substitutions in enzyme variants occurred at residues lining both substrate and O2 transport tunnels, enabling tighter binding of the target substrates in the active site. Increased oxygenation efficiencies measured in vitro for the various enzyme (variant)-substrate combinations correlated linearly with in vivo changes in growth rates for evolved Acidovorax strains expressing the variants. Our data suggest that the selective pressure from oxidative stress toward more efficient oxygenation by Rieske oxygenases was most notable when O2 uncoupling exceeded 60%.

Bifunctional Zirconium Phosphate with Greigite for Electrochemical Detection and Simultaneous Removal of Heavy Metal Ions and Nitro Compounds

Electrochemical sensing is emerging as a method of choice for the sensing and monitoring of contaminants in water. Various sensing platforms have been designed for sensing heavy metal ions and organic pollutants in water bodies. Herein, we report a new electrochemical platform that can be used for the detection of both heavy metal ions and nitro-based organic contaminants in water bodies. The electrochemical sensor uses a modified electrode based on Fe3S4-impregnated zirconium phosphate (ZrP) nanoparticles synthesized by a simple ultrasonication method. The ZrP@Fe3S4 nanoparticles were thoroughly characterized by power X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), and ζ-potential studies. The material exhibits an excellent electrochemical performance for the detection of Pb2+, Hg2+, nitrophenol, nitroaniline, and picric acid with low limits of detection of ca. 0.93, 0.70, 0.98, 1.10, and 1.53 ppm, respectively. Since ZrP@Fe3S4 nanoparticles are magnetically recyclable, their adsorption capacity and recyclability have been thoroughly investigated for the uptake of Pb2+ and Hg2+ ions from contaminated water. We observed that the adsorption of Pb2+ and Hg2+ ions on ZrP@Fe3S4 is best described by the Langmuir isotherm and pseudo-second-order kinetic models, with adsorption capacities of 219.44 and 118.4 mg/g, respectively. Similarly, the removal efficiency of ZrP@Fe3S4 was found to be 91, 57.6, and 31.3% for nitrophenol, nitroaniline, and picric acid, respectively. Furthermore, the theoretical calculations using density functional theory (DFT) were carried out to find the adsorption energy, affinity, and point of adsorption, which are in line with the experimental results. DFT calculations further suggest that the incorporation of Fe3S4 on ZrP improves the surface charge density and promotes efficient electron transfer between the electrode and the analyte. We have shown the real-time analysis of Dal lake water as a proof of concept, and the synthesized composite exhibits good recovery and promising results for metal ion sensing. ZrP@Fe3S4 demonstrated an excellent cycling stability and long-term stability without noticeable degradation for 1 week.

Compound-Specific Carbon, Nitrogen, and Hydrogen Isotope Analysis to Characterize Aerobic Biodegradation of 2,3-Dichloroaniline by a Mixed Enrichment Culture

Compound-specific isotope analysis (CSIA) is an established tool to track the in situ transformation of organic chemicals at contaminated sites. In this work, we evaluated the potential of multi-element CSIA to assess biodegradation of 2,3-dichloroaniline (2,3-DCA), which is a major industrial feedstock. Using controlled laboratory experiments, we determined, for the first time, negligible carbon (<0.5‰) and hydrogen (<10‰) isotope fractionation and a significant inverse nitrogen isotope fractionation (>10‰) during aerobic 2,3-DCA biodegradation by a mixed enrichment culture. The tentative identification of a glutamate conjugate of 2,3-DCA as a reaction intermediate indicates that the initial multistep enzymatic reaction may be rate-limiting. The formation of the glutamate adduct would increase the bond energy at the N atom, thus likely explaining the observed inverse N isotope fractionation. The corresponding nitrogen enrichment factor was +6.8 ± 0.6‰. This value was applied to investigate the in situ 2,3-DCA biodegradation at a contaminated site where the carbon and nitrogen isotope signatures from field samples suggested similar aerobic processes by native microorganisms. Under the assumption of the applicability of the Rayleigh model in a pilot wetland treating contaminated groundwater, the extent of biodegradation was estimated to be up to 80-90%. This study proposes multi-element CSIA as a novel application to study 2,3-DCA fate in groundwater and surface water and provides insights into biodegradation pathways.

Regulating microbial redox reactions towards enhanced removal of refractory organic nitrogen from wastewater

Biotechnology for wastewater treatment is mainstream and effective depending upon microbial redox reactions to eliminate diverse contaminants and ensure aquatic ecological health. However, refractory organic nitrogen compounds (RONCs, e.g., nitro-, azo-, amide-, and N-heterocyclic compounds) with complex structures and high toxicity inhibit microbial metabolic activity and limit the transformation of organic nitrogen to inorganic nitrogen. This will eventually result in non-compliance with nitrogen discharge standards. Numerous efforts suggested that applying exogenous electron donors or acceptors, such as solid electrodes (electrostimulation) and limited oxygen (micro-aeration), could potentially regulate microbial redox reactions and catabolic pathways, and facilitate the biotransformation of RONCs. This review provides comprehensive insights into the microbial regulation mechanisms and applications of electrostimulation and micro-aeration strategies to accelerate the biotransformation of RONCs to organic amine (amination) and inorganic ammonia (ammonification), respectively. Furthermore, a promising approach involving in-situ hybrid anaerobic biological units, coupled with electrostimulation and micro-aeration, is proposed towards engineering applications. Finally, employing cutting-edge methods including multi-omics analysis, data science driven machine learning, technology-economic analysis, and life-cycle assessment would contribute to optimizing the process design and engineering implementation. This review offers a fundamental understanding and inspiration for novel research in the enhanced biotechnology towards RONCs elimination.

From Nature to Technology: Exploring the Potential of Plant-Based Materials and Modified Plants in Biomimetics, Bionics, and Green Innovations

This review explores the extensive applications of plants in areas of biomimetics and bioinspiration, highlighting their role in developing sustainable solutions across various fields such as medicine, materials science, and environmental technology. Plants not only serve essential ecological functions but also provide a rich source of inspiration for innovations in green nanotechnology, biomedicine, and architecture. In the past decade, the focus has shifted towards utilizing plant-based and vegetal waste materials in creating eco-friendly and cost-effective materials with remarkable properties. These materials are employed in making advancements in drug delivery, environmental remediation, and the production of renewable energy. Specifically, the review discusses the use of (nano)bionic plants capable of detecting explosives and environmental contaminants, underscoring their potential in improving quality of life and even in lifesaving applications. The work also refers to the architectural inspirations drawn from the plant world to develop novel design concepts that are both functional and aesthetic. It elaborates on how engineered plants and vegetal waste have been transformed into value-added materials through innovative applications, especially highlighting their roles in wastewater treatment and as electronic components. Moreover, the integration of plants in the synthesis of biocompatible materials for medical applications such as tissue engineering scaffolds and artificial muscles demonstrates their versatility and capacity to replace more traditional synthetic materials, aligning with global sustainability goals. This paper provides a comprehensive overview of the current and potential uses of living plants in technological advancements, advocating for a deeper exploration of vegetal materials to address pressing environmental and technological challenges.

Semi-rational design of nitroarene dioxygenase for catalytic ability toward 2,4-dichloronitrobenzene

Rieske non-heme dioxygenase family enzymes play an important role in the aerobic biodegradation of nitroaromatic pollutants, but no active dioxygenases are available in nature for initial reactions in the degradation of many refractory pollutants like 2,4-dichloronitrobenzene (24DCNB). Here, we report the engineering of hotspots in 2,3-dichloronitrobenzene dioxygenase from Diaphorobacter sp. strain JS3051, achieved through molecular dynamic simulation analysis and site-directed mutagenesis, with the aim of enhancing its catalytic activity toward 24DCNB. The computationally predicted activity scores were largely consistent with the detected activities in wet experiments. Among them, the two most beneficial mutations (E204M and M248I) were obtained, and the combined mutant reached up to a 62-fold increase in activity toward 24DCNB, generating a single product, 3,5-dichlorocatechol, which is a naturally occurring compound. In silico analysis confirmed that residue 204 affected the substrate preference for meta-substituted nitroarenes, while residue 248 may influence substrate preference by interaction with residue 295. Overall, this study provides a framework for manipulating nitroarene dioxygenases using computational methods to address various nitroarene contamination problems.IMPORTANCEAs a result of human activities, various nitroaromatic pollutants continue to enter the biosphere with poor degradability, and dioxygenation is an important kickoff step to remove toxic nitro-groups and convert them into degradable products. The biodegradation of many nitroarenes has been reported over the decades; however, many others still lack corresponding enzymes to initiate their degradation. Although rieske non-heme dioxygenase family enzymes play extraordinarily important roles in the aerobic biodegradation of various nitroaromatic pollutants, prediction of their substrate specificity is difficult. This work greatly improved the catalytic activity of dioxygenase against 2,4-dichloronitrobenzene by computer-aided semi-rational design, paving a new way for the evolution strategy of nitroarene dioxygenase. This study highlights the potential for using enzyme structure-function information with computational pre-screening methods to rapidly tailor the catalytic functions of enzymes toward poorly biodegradable contaminants.

First report of betalain production from endolichenic Bacillus sp. LDAB-1 from Dirinaria aegilita: Insights from novel quantification methodology of image processing

Pigments are widely used in food supplements envisaging attractive colors along with health benefits. The desired advancements in the nutraceutical and antioxidant properties of pigments utilized in food products necessitate the search for novel additives. The present study is the first in the field to report the pigment-producing endolichenic bacteria, Bacillus sp. LDAB-1 from Dirinaria aegilita. Morphological, biochemical, and molecular characterization of the bacterium emphasizes that ideal pigment production occurs when utilizing sucrose and sodium nitrate. The pigment was salted out and dialyzed for further qualitative characterization using ultraviolet-visible, fluorescence, and Fourier transform infrared spectra and the results corroborated the presence of betalains. The antioxidant activity of betalain is closer to the efficiency of α-tocopherol, which confers the pigment properties for antioxidant and nutraceutical significance. An optimal methodology for pigment affirmation is an issue when using an alternative methodology. Hence, the present assessment employs a comparative analysis of findings from both a spectrophotometric method and image processing technology encompassing RGB, CMYK, YCbCr, and L*a*b* color space models. Amongst these, the L*a*b* model potentially provides an effective modality for determining the pigment concentration. Bland-Altman plot analysis indicates similar consistency levels in betalain quantification by both methods at 95% confidence intervals, affirming the integrity and consistency of color image processing technology. Consequently, the present study represents novelty and innovativeness in reporting endolichenic Bacillus sp. LDAB-1 from D. aegilita and a rational image optimization protocol for pigment elucidation characteristics.

Aromaticity of six-membered nitro energetic compounds through molecular electrostatic potential, magnetic, electronic delocalization and reactivity-based indices

The electron density depletion associated with π-hole at the ring center typical of energetic compounds was clearly revealed by the molecular electrostatic potential (ESP). In addition, the spatial arrangement of NO2 groups appears to affect the ESP value in the ring center, and therefore sensitivity to detonation. Indeed, for monocyclic nitrobenzene compounds with the same number of NO2 groups, the ESP value in the ring center decreases as the NO2 groups are more closely spaced. As expected, the central rings become less aromatic as NO2 groups are added. The MCI, PDI, PLR, NICSzz(1), FLU indices are all strongly correlated with the ESP values observed in the ring center of the set of nitrobenzenes. Aromaticity indices based on electron delocalization criteria appear to be very sensitive to small variations in aromaticity. Among magnetic-based indices, only NICSzz(1) is capable to predict small changes in aromaticity. The PLR index derived from conceptual DFT is quite relevant for predicting small variations in aromaticity. According to our results, the most suitable aromaticity index is not based on a single criterion, and that selecting it is more subtle. Therefore, it is important to combine information from several criteria to obtain a more complete description of the aromaticity of the studied compounds.

Formation of nitrated naphthalene in the sulfate radical oxidation process in the presence of nitrite

Polycyclic aromatic hydrocarbons (PAHs) have become a global environmental concern due to their potential hazardous implication for human health. In this study, we found that sulfate radical (SO4•-) could effectively degrade naphthalene (NAP), a representative PAH in groundwaters, generating 1-naphthol. This intermediate underwent further degradation, yielding ring-opening products including phthalic acid and salicylic acid. However, the presence of nitrite (NO2-), a prevalent ion in subsurface environments, was observed to compete with NAP for SO4•-, thus slowing down the NAP degradation. The reaction between NO2- and SO4•- generated a nitrogen dioxide radical (NO2•). Concurrently, in-situ formed 1-naphthol underwent further oxidization to the 1-naphthoxyl radical by SO4•-. The coupling of 1-naphthoxyl radicals with NO2• gave rise to a series of nitrated NAP, namely 2-nitro-1-naphthol, 4-nitro-1-naphthol, and 2,4-dinitro-1-naphthol. In addition, the in-situ formed phthalic acid and salicylic acid also underwent nitration, generating nitrophenolic products, although this pathway appeared less prominent than the nitration of 1-naphthol. When 10 μΜ NAP was subjected to heat activated peroxydisulfate oxidation in the presence of 10 μΜ NO2-, the total yield of nitrated products reached 0.730 μΜ in 120 min. Overall, the presence of NO2- dramatically altered the behavior of NAP degradation by SO4•- oxidation and contributed to the formation of toxic nitrated products. These findings raise awareness of the potential environmental risks associated with the application of SO4•--based oxidation processes for the remediation of PAHs-polluted sites in presence of NO2-.

Ectopic expression of an Old Yellow Enzyme (OYE3) gene from Saccharomyces cerevisiae increases the tolerance and phytoremediation of 2-nitroaniline in rice

2-nitroaniline (2-NA) is an environmental pollutant and has been extensively used as intermediates in organic synthesis. The presence of 2-NA in the environment is not only harmful for aquatic life but also mutagenic for human beings. In this study, we constructed transgenic rice expressing an Old Yellow Enzyme gene, ScOYE3, from Saccharomyces cerevisiae. The ScOYE3 transgenic plants were comprehensively investigated for their biochemical responses to 2-NA treatment and their 2-NA phytoremediation capabilities. Our results showed that the rice seedlings exposed to 2-NA stress, showed growth inhibition and biomass reduction. However, the transgenic plants exhibited strong tolerance to 2-NA stress compared to wild-type plants. Ectopic expression of ScOYE3 could effectively protect transgenic plants against 2-NA damage, which resulted in less reactive oxygen species accumulation in transgenic plants than that in wild-type plants. Our phytoremediation assay revealed that transgenic plants could eliminate more 2-NA from the medium than wild-type plants. Moreover, omics analysis was performed in order to get a deeper insight into the mechanism of ScOYE3-mediated 2-NA transformation in rice. Altogether, the function of ScOYE3 during 2-NA detoxification was characterized for the first time, which serves as strong theoretical support for the phytoremediation potential of 2-NA by Old Yellow Enzyme genes.

Characteristics and source apportionment of water-soluble organic nitrogen (WSON) in PM2.5 in Hong Kong: With focus on amines, urea, and nitroaromatic compounds

Water-soluble organic nitrogen (WSON) is ubiquitous in fine particulate matter (PM2.5) and poses health and environmental risks. However, there is limited knowledge regarding its comprehensive speciation and source-specific contributions. Here, we conducted chemical characterization and source apportionment of WSON in 65 PM2.5 samples collected in Hong Kong during a 1-yr period. Using various mass-spectrometry-based techniques, we quantified 22 nitrogen-containing organic compounds (NOCs), including 17 nitroaromatics (NACs), four amines, and urea. The most abundant amine and NACs were dimethylamine and 4-nitrocatechol, respectively. Two secondary (i.e., secondary formation and secondary nitrate) and five primary sources (i.e., sea salt, fugitive dust, marine vessels, vehicle exhaust, and biomass burning) of WSON and these three categories of NOCs were identified. Throughout the year, secondary sources dominated WSON formation (69.0%), while primary emissions had significant contributions to NACs (77.1%), amines (75.9%), and urea (83.7%). Fugitive dust was the leading source of amines and urea, while biomass burning was the main source of NACs. Our multi-linear regression analysis revealed the significant role of sulfate, NO3, nitrate, liquid water content, and particle pH on WSON formation, highlighting the importance of nighttime NO3 processing and heterogeneous and aqueous-phase formation of NOCs in the Hong Kong atmosphere.

Phenyliodine bis(trifluoroacetate) as a sustainable reagent: exploring its significance in organic synthesis

Iodine-containing molecules, especially hypervalent iodine compounds, have gained significant attention in organic synthesis. They are valuable and sustainable reagents, leading to a remarkable surge in their use for chemical transformations. One such hypervalent iodine compound, phenyliodine bis(trifluoroacetate)/bis(trifluoroacetoxy)iodobenzene, commonly referred to as PIFA, has emerged as a prominent candidate due to its attributes of facile manipulation, moderate reactivity, low toxicity, and ready availability. PIFA presents an auspicious prospect as a substitute for costly organometallic catalysts and environmentally hazardous oxidants containing heavy metals. PIFA exhibits remarkable catalytic activity, facilitating an array of consequential organic reactions, including sulfenylation, alkylarylation, oxidative coupling, cascade reactions, amination, amidation, ring-rearrangement, carboxylation, and numerous others. Over the past decade, the application of PIFA in synthetic chemistry has witnessed substantial growth, necessitating an updated exploration of this field. In this discourse, we present a concise overview of PIFA's applications as a 'green' reagent in the domain of synthetic organic chemistry. A primary objective of this article is to bring to the forefront the scientific community's awareness of the merits associated with adopting PIFA as an environmentally conscientious alternative to heavy metals.

Effect of pH on the ozonolysis degradation of p-nitrophenol in aquatic environment and the synergistic effect of hydroxy radical

Density functional theory (DFT) was employed to elucidate the mechanisms for ozonolysis reaction of p-nitrophenol (PNP) and its anion form aPNP. Thermodynamic data, coupled with Average Local Ionization Energies (ALIE) analysis, reveal that the ortho-positions of the OH/O- groups are the most favorable reaction sites. Moreover, rate constant calculations demonstrate that the O3 attack on the C2-C3 bond is the predominant process in the reaction between neutral PNP and O3. For the aPNP + O3 reaction, the most favorable pathways involve O3 attacking the C1-C2 and C6-C1 bonds. The rate constant for PNP ozonolysis positively correlates with pH, ranging from 5.47 × 108 to 2.86 × 109 M-1 s-1 in the natural aquatic environment. In addition, the formation of hydroxyl radicals in the ozonation process of PNP and the mechanisms of its synergistic reaction of PNP with ozone were investigated. Furthermore, the ozonation and hydroxylation processes involving the intermediate OH-derivatives were both thermodynamically and kinetic analyzed, which illustrate that OH radicals could promote the elimination of PNP. Finally, the toxic of PNP and the main products for fish, daphnia, green algae and rat were assessed. The findings reveal that certain intermediates possess greater toxicity than the original reactant. Consequently, the potential health risks these compounds pose to organisms warrant serious consideration.

What is the role of nitrate/nitrite in trace organic contaminants degradation and transformation during UV-based advanced oxidation processes?

The effectiveness of UV-based advanced oxidation processes (UV-AOPs) in degrading trace organic contaminants (TrOCs) can be significantly influenced by the ubiquitous presence of nitrate (NO3-) and nitrite (NO2-) in water and wastewater. Indeed, NO3-/NO2- can play multiple roles of NO3-/NO2- in UV-AOPs, leading to complexities and conflicting results observed in existing research. They can inhibit the degradation of TrOCs by scavenging reactive species and/or competitively absorbing UV light. Conversely, they can also enhance the elimination of TrOCs by generating additional •OH and reactive nitrogen species (RNS). Furthermore, the presence of NO3-/NO2- during UV-AOP treatment can affect the transformation pathways of TrOCs, potentially resulting in the nitration/nitrosation of TrOCs. The resulting nitro(so)-products are generally more toxic than the parent TrOCs and may become precursors of nitrogenous disinfection byproducts (N-DBPs) upon chlorination. Particularly, since the impact of NO3-/NO2- in UV-AOPs is largely due to the generation of RNS from NO3-/NO2- including NO•, NO2•, and peroxynitrite (ONOO-/ONOOH), this review covers the generation, properties, and detection methods of these RNS. From kinetic, mechanistic, and toxicologic perspectives, future research needs are proposed to advance the understanding of how NO3-/NO2- can be exploited to improve the performance of UV-AOPs treating TrOCs. This critical review provides a comprehensive framework outlining the multifaceted impact of NO3-/NO2- in UV-AOPs, contributing insights for basic research and practical applications of UV-AOPs containing NO3-/NO2-.

Novel quinazolines bearing 1,3,4-thiadiazole-aryl urea derivative as anticancer agents: design, synthesis, molecular docking, DFT and bioactivity evaluations

A novel series of 1-(5-((6-nitroquinazoline-4-yl)thio)-1,3,4-thiadiazol-2-yl)-3-phenylurea derivatives 8 were designed and synthesized to evaluate their cytotoxic potencies. The structures of these obtained compounds were thoroughly characterized by IR, 1H, and 13C NMR, MASS spectroscopy and elemental analysis methods. Additionally, their in vitro anticancer activities were investigated using the MTT assay against A549 (human lung cancer), MDA-MB231 (human triple-negative breast cancer), and MCF7 (human hormone-dependent breast cancer). Etoposide was used as a reference marketed drug for comparison. Among the compounds tested, compounds 8b and 8c demonstrated acceptable antiproliferative activity, particularly against MCF7 cells. Considering the potential VEGFR-2 inhibitor potency of these compounds, a molecular docking study was performed for the most potent compound, 8c, to determine its probable interactions. Furthermore, computational investigations, including molecular dynamics, frontier molecular orbital analysis, Fukui reactivity descriptor, electrostatic potential surface, and in silico ADME evaluation for all compounds were performed to illustrate the structure-activity relationship (SAR).

Merging Excited-State Copper Catalysis and Triplet Nitro(hetero)arenes for Direct Synthesis of 2-Aminophenol Derivatives

Nitro(hetero)arene derivatives are essential commodity chemicals used in various products, such as drugs, polymers, and agrochemicals. In this study, we leverage the excited-state reactivities of copper catalysts and nitro(hetero)arenes, and the Umpolung reactivity of acyl radicals to convert readily available nitro(hetero)arenes directly to valuable 2-aminophenol derivatives, which are important scaffolds in many top-selling pharmaceuticals. This reaction is applicable to a variety of nitro(hetero)arenes, acyl chlorides, and late-stage modifications of complex molecules, making it a useful tool for the discovery of new functional molecules. Mechanistic studies, including radical trapping experiments, Stern Volmer quenching studies, light ON/OFF experiments, and 18O-labeling studies, suggest a reaction mechanism involving photoexcitation of a copper complex, diradical couplings, and an in-cage contact ion pair (CIP) migration. Our findings offer a streamlined protocol for synthesizing essential pharmacophores from nitro(hetero)arenes while simultaneously advancing knowledge in excited-state and radical chemistry and stimulating new reaction design and development.

Pt(II) Tetrafacial Barrel with Aggregation-Induced Emission for Sensing

A new tetraphenylpyrazine-based tetraimidazole ligand (L) was synthesized and used for subcomponent self-assembly with cis-(tmeda)Pd(NO3)2 and cis-Pt(PEt3)2(OTf)2, leading to the formation of two tetrafacial barrels [Pd8L4(tmeda)8](NO3)16 (1) and [Pt8L4(PEt3)16](OTf)16 (2), respectively. Although ligand L is aggregation-induced emission (AIE) active, barrel 2 showed a magnificently higher AIE activity than ligand L, while 1 failed to retain the AIE properties of the ligand. Pd(II) barrel 1, undergoing an aggregation-caused quenching (ACQ) phenomenon, nullified the AIE activity of the ligand to be used in the photophysical application. The enhanced emission in the aggregated state of Pt(II) barrel 2 was used for the recognition of picric acid (PA), which is explosive in nature and one of the groundwater contaminants in landmine areas. The recognition of picric acid was found to be selective in comparison with that of other nitroaromatic compounds (NACs), which could be attributed to ground-state complex formation and resonance energy transfer between picric acid and barrel 2. The use of new AIE-active assembly 2 for selective detection of PA with a low detection limit is noteworthy.

Characterization of an efficient N-oxygenase from Saccharothrix sp. and its application in the synthesis of azomycin

BACKGROUND

The nitro group constitutes a significant functional moiety within numerous valuable substances, such as nitroimidazoles, a class of antimicrobial drugs exhibiting broad spectrum activity. Conventional chemical methods for synthesizing nitro compounds suffer from harsh conditions, multiple steps, and environmental issues. Biocatalysis has emerged as a promising alternative to overcome these drawbacks, with certain enzymes capable of catalyzing nitro group formation gradually being discovered in nature. Nevertheless, the practical application is hindered by the restricted diversity and low catalytic activity exhibited by the reported nitrifying enzymes.

RESULTS

A novel N-oxygenase SaRohS harboring higher catalytic capability of transformation 2-aminoimidazole to azomycin was characterized from Saccharothrix sp. Phylogenetic tree analysis revealed that SaRohS belongs to the heme-oxygenase-like diiron oxygenase (HDOs) family. SaRohS exhibited optimal activity at pH 5.5 and 25 ℃, respectively. The enzyme maintained relatively stable activity within the pH range of 4.5 to 6.5 and the temperature range of 20 ℃ to 35 ℃. Following sequence alignment and structural analysis, several promising amino acid residues were meticulously chosen for catalytic performance evaluation. Site-directed mutations showed that threonine 75 was essential for the catalytic activity. The dual mutant enzyme G95A/K115T exhibited the highest catalytic efficiency, which was approximately 5.8-fold higher than that of the wild-type and 22.3-fold higher than that of the reported N-oxygenase KaRohS from Kitasatospora azatica. The underlying catalytic mechanism was investigated through molecular docking and molecular dynamics. Finally, whole-cell biocatalysis was performed and 2-aminoimidazole could be effectively converted into azomycin with a reaction conversion rate of 42% within 14 h.

CONCLUSIONS

An efficient N-oxygenase that catalyzes 2-aminoimidazole to azomycin was screened form Saccharothrix sp., its phylogenetics and enzymatic properties were analyzed. Through site-directed mutation, enhancements in catalytic competence were achieved, and the molecular basis underlying the enhanced enzymatic activity of the mutants was revealed via molecular docking and dynamic simulation. Furthermore, the application potential of this enzyme was assessed through whole cell biocatalysis, demonstrating it as a promising alternative method for azomycin production.

p-Nitrobenzoate production from glucose by utilizing p-aminobenzoate N-oxygenase: AurF

Nitroaromatic compounds are widely used in industry, but their production is associated with issues such as the hazardousness of the process and low regioselectivity. Here, we successfully demonstrated the production of p-nitrobenzoate (PNBA) from glucose by constructing p-aminobenzoate N-oxygenase AurF-expressing E. coli. We generated this strain, which we named PN-1 by disrupting four genes involved in PNBA degradation: nfsA, nfsB, nemA, and azoR. We then expressed AurF from Streptomyces thioluteus in this strain, which resulted in the production of 945 mg/L PNBA in the presence of 1 g/L p-aminobenzoate. Direct production of PNBA from glucose was achieved by co-expressing the pabA, pabB, and pabC, as well as aurF, resulting in the production of 393 mg/L PNBA from 20 g/L glucose. To improve the PNBA titer, we disrupted genes involved in competing pathways: pheA, tyrA, trpE, pykA, and pykF. The resultant strain PN-4Ap produced 975 mg/L PNBA after 72 h of cultivation. These results highlight the potential of using microorganisms to produce other nitroaromatic compounds.

Biotransformation of 2,4,6-trinitrotoluene by Diaphorobacter sp. strain DS2

Diaphorobacter strain DS2 degrades 3-nitrotoluene and 2-nitrotoluene via ring oxidation with 3-nitrotoluene dioxygenase (3NTDO). In the current study, we hypothesized that 3NTDO might also be involved in the degradation of 2,4,6-trinitrotoluene (TNT), a major nitroaromatic explosive contaminant in soil and groundwater. Strain DS2 transforms TNT as a sole carbon and nitrogen source when grown on it. Ammonium chloride and succinate in the medium accelerated the TNT degradation rate. A resting cell experiment suggested that TNT does not compete with 3NT degradation (no negative impact of TNT on the reaction velocity for 3NT). Enzyme assay with 3NTDO did not exhibit TNT transformation activity. The above results confirmed that 3NTDO of DS2 is not responsible for TNT degradation. In the resting cell experiment, within 10 h, 4ADNT completely degraded. The degradation of 2ADNT was 97% at the same time. We hypothesized that 3NTDO involve in this reaction. Based on the DS2 genome, we proposed that the N-ethylmaleimide reductases (nemA) were involved in the initial reduction of the nitro group and aromatic ring of TNT. Our findings suggest that strain DS2 could be helpful for the removal of TNT from contaminated sites with or without any additional carbon and nitrogen source and with minimal accumulation of undesirable intermediates.

Efficient photocatalytic reduction of p-nitrophenol under visible light irradiation based on Ag NPs loaded brown 2D g-C3N4 / g-C3N4 QDs nanocomposite

Recently, low-cost graphitic carbon nitride (g-C3N4) revealed high photocatalytic activities and provided solutions to environmental pollution. In this study, we synthesized brown mesoporous 2D g-C3N4 by calcination dicyandiamide with pluronic P123. This is followed by loading of Ag NPs on the prepared 2D g-C3N4 by photodeposition process. After that, a ternary composite 2% Ag/ 2D g-C3N4 / g-C3N4 QDs heterojunction photocatalyst has been successfully prepared. The prepared nanomaterials were comprehensively characterized by various analysis techniques such as XRD, UV-Vis., BET, XPS, SEM, TEM. This new system exhibited a large surface area with porous structure and a wide absorption of visible light. The results verified that Ag NPs decoration enhanced the charge separation of photo-generated carriers of g-C3N4 2D and g-C3N4 QDs, promote significant enhancement in the photocatalytic activity for reduction of p-nitrophenol with a rate constant (k) value of 0.49729 / min in 6 min. This rate is about two-fold higher than that observed for pure g-C3N4 2D and g-C3N4 QDs as well as shows an improvement compared to 2% Ag/ g-C3N4 2D and g-C3N4 2D/ g-C3N4 QDs. The results open the door to design highly efficient 2D/0D nanocomposite photocatalysts for a wide variety of environmental applications.

Direct aromatic nitration by bacterial P450 enzymes

Nitro aromatics have broad applications in industry, agriculture, and pharmaceutics. However, their industrial production is faced with many challenges including poor selectivity, heavy pollution and safety concerns. Nature provides multiple strategies for aromatic nitration, which opens the door for the development of green and efficient biocatalysts. Our group's efforts focused on a unique bacterial cytochrome P450 TxtE that originates from the biosynthetic pathway of phytotoxin thaxtomins, which can install a nitro group at C4 of l-Trp indole ring. TxtE is a Class I P450 and its reaction relies on a pair of redox partners ferredoxin and ferredoxin reductase for essential electron transfer. To develop TxtE as an efficient nitration biocatalyst, we created artificial self-sufficient P450 chimeras by fusing TxtE with the reductase domain of the bacterial P450BM3 (BM3R). We evaluated the catalytic performance of the chimeras with different lengths of the linker connecting TxtE and BM3R domains and identified one with a 14-amino-acid linker (TB14) to give the best activity. In addition, we demonstrated the broad substrate scope of the engineered biocatalyst by screening diverse l-Trp analogs. In this chapter, we provide a detailed procedure for the development of aromatic nitration biocatalysts, including the construction of P450 fusion chimeras, biochemical characterization, determination of catalytic parameters, and testing of enzyme-substrate scope. These protocols can be followed to engineer other P450 enzymes and illustrate the processes of biocatalytic development for the synthesis of nitro chemicals.

Melamine-participant hydrogen-bonded organic frameworks with strong hydrogen bonds and hierarchical micropores driving extraction of nitroaromatic compounds

Enrichment and detection of trace pollutants in the real matrix are essential for evaluating water quality. In this study, benefiting from the good affinities of 1,3,6,8-tetra(4-carboxylphenyl)pyrene) (H4TBAPy) with itself and melamine (MA) respectively, the composite hydrogen-bonded organic frameworks (HOFs, MA/PFC-1), PFC-1 self-assembled by 1,3,6,8-tetra(4-carboxylphenyl)pyrene), were successfully constructed by the mild strategy of solvent evaporation at room temperature. Through a series of characterizations, such as Fourier transform infrared spectra, X-ray diffraction, thermal gravimetric analyses, and N2 adsorption-desorption, etc., the MA/PFC-1 was confirmed to be a stable and excellent material. In addition, it possessed high surface area, hierarchical micropores, strong hydrogen bonds, and rich function groups containing N and O heteroatoms, since the newly introduced MA could be another hydrogen bonding motif, as well as increased the polarity of reaction solvent. These advantages make MA/PFC-1 be an ideal coating material for solid phase microextraction (SPME). Satisfactory enrichment factors for nitroaromatic compounds (NACs) were got by the MA/PFC-1 fiber under the optimized conditions obtained by the control variables (extraction time of 60 min, extraction temperature of 80 °C, desorption time of 6 min, desorption temperature of 260 °C, pH value of 7, and stirring speed of 250 rpm). MA/PFC-1 was further used to develop an analytical method for NACs based on head-space SPME coupled with gas chromatography‒mass spectrometry (GC‒MS). The developed method with low limits of detection (4.30-20.83 ng L-1) and good reproducibility (relative standard deviations <8.6%). The excellent performance allowed the successful application of the developed method in the determinations of trace NACs in real water samples with recoveries of 80.1%-119%. This study proposed a mild approach to synthesize composite HOFs via doping MA and developed an environmentally friendly method for the precise determinations of NACs in the environment.

Catalytic ipso-Nitration of Organosilanes Enabled by Electrophilic N-Nitrosaccharin Reagent

Nitroaromatic compounds represent one of the essential classes of molecules that are widely used as feedstock for the synthesis of intermediates, the preparation of nitro-derived pharmaceuticals, agrochemicals, and materials on both laboratory and industrial scales. We herein disclose the efficient, mild, and catalytic ipso-nitration of organotrimethylsilanes, enabled by an electrophilic N-nitrosaccharin reagent and allows chemoselective nitration under mild reaction conditions, while exhibiting remarkable substrate generality and functional group compatibility. Additionally, the reaction conditions proved to be orthogonal to other common functionalities, allowing programming of molecular complexity via successive transformations or late-stage nitration. Detailed mechanistic investigation by experimental and computational approaches strongly supported a classical electrophilic aromatic substitution (SE Ar) mechanism, which was found to proceed through a highly ordered transition state.

Site-Selective Nitration of Aryl Germanes at Room Temperature

We report a site-selective ipso-nitration of aryl germanes in the presence of boronic esters, silanes, halogens, and additional functionalities. The protocol is characterized by operational simplicity, proceeds at room temperature, and is enabled by [Ru(bpy)3](PF6)2/blue light photocatalysis. Owing to the exquisite robustness of the [Ge] functionality, nitrations of alternative functional handles in the presence of the germane are also feasible, as showcased herein.

Steroids Bearing Heteroatom as Potential Drugs for Medicine

Heteroatom steroids, a diverse class of organic compounds, have attracted significant attention in the field of medicinal chemistry and drug discovery. The biological profiles of heteroatom steroids are of considerable interest to chemists, biologists, pharmacologists, and the pharmaceutical industry. These compounds have shown promise as potential therapeutic agents in the treatment of various diseases, such as cancer, infectious diseases, cardiovascular disorders, and neurodegenerative conditions. Moreover, the incorporation of heteroatoms has led to the development of targeted drug delivery systems, prodrugs, and other innovative pharmaceutical approaches. Heteroatom steroids represent a fascinating area of research, bridging the fields of organic chemistry, medicinal chemistry, and pharmacology. The exploration of their chemical diversity and biological activities holds promise for the discovery of novel drug candidates and the development of more effective and targeted treatments.

Chemo-/Regio-Selective Synthesis of Novel Functionalized Spiro[pyrrolidine-2,3'-oxindoles] under Microwave Irradiation and Their Anticancer Activity

A novel series of nitrostyrene-based spirooxindoles were synthesized via the reaction of substituted isatins 1a-b, a number of α-amino acids 2a-e and (E)-2-aryl-1-nitroethenes 3a-e in a chemo/regio-selective manner using [3+2] cycloaddition (Huisgen) reaction under microwave irradiation conditions. The structure elucidation of all the synthesized spirooxindoles were done using 1H and 13C NMR and HRMS spectral analysis. The single crystal X-ray crystallographic study of compound 4l was used to assign the stereochemical arrangements of the groups around the pyrrolidine ring in spiro[pyrrolidine-2,3'-oxindoles] skeleton. The in vitro anticancer activity of spiro[pyrrolidine-2,3'-oxindoles] analogs 4a-w against human lung (A549) and liver (HepG2) cancer cell lines along with immortalized normal lung (BEAS-2B) and liver (LO2) cell lines shows promising results. Out of the 23 synthesized spiro[pyrrolidine-2,3'-oxindoles], while five compounds (4c, 4f, 4m, 4q, 4t) (IC50 = 34.99-47.92 µM; SI = 0.96-2.43) displayed significant in vitro anticancer activity against human lung (A549) cancer cell lines, six compounds (4c, 4f, 4k, 4m, 4q, 4t) (IC50 = 41.56-86.53 µM; SI = 0.49-0.99) displayed promising in vitro anticancer activity against human liver (HepG2) cancer cell lines. In the case of lung (A549) cancer cell lines, these compounds were recognized to be more efficient and selective than standard reference artemisinin (IC50 = 100 µM) and chloroquine (IC50 = 100 µM; SI: 0.03). However, none of them were found to be active as compared to artesunic acid [IC50 = 9.85 µM; SI = 0.76 against lung (A549) cancer cell line and IC50 = 4.09 µM; SI = 2.01 against liver (HepG2) cancer cell line].

Tailored photoenzymatic systems for selective reduction of aliphatic and aromatic nitro compounds fueled by light

The selective enzymatic reduction of nitroaliphatic and nitroaromatic compounds to aliphatic amines and amino-, azoxy- and azo-aromatics, respectively, remains a persisting challenge for biocatalysis. Here we demonstrate the light-powered, selective photoenzymatic synthesis of aliphatic amines and amino-, azoxy- and azo-aromatics from the corresponding nitro compounds. The nitroreductase from Bacillus amyloliquefaciens, in synergy with a photocatalytic system based on chlorophyll, promotes selective conversions of electronically-diverse nitroarenes into a series of aromatic amino, azoxy and azo products with excellent yield (up to 97%). The exploitation of an alternative nitroreductase from Enterobacter cloacae enables the tailoring of a photoenzymatic system for the challenging synthesis of aliphatic amines from nitroalkenes and nitroalkanes (up to 90% yield). This photoenzymatic reduction overcomes the competing bio-Nef reaction, typically hindering the complete enzymatic reduction of nitroaliphatics. The results highlight the usefulness of nitroreductases to create selective photoenzymatic systems for the synthesis of precious chemicals, and the effectiveness of chlorophyll as an innocuous photocatalyst, enabling the use of sunlight to drive the photobiocatalytic reactions.

Regioselective synthesis of 3-nitroindoles under non-acidic and non-metallic conditions

An electrophilic substitution reaction, without acid and metal, of indole with ammonium tetramethylnitrate for accessing 3-nitroindole has been developed. In this protocol, trifluoroacetyl nitrate (CF3COONO2) was produced by metathesis of ammonium tetramethyl nitrate and trifluoroacetic anhydride at sub-room temperature. Trifluoroacetyl nitrate (CF3COONO2) is an electrophilic nitrating agent for a variety of indoles, aromatic and heterocyclic aromaticity. Meanwhile, this strategy could be applied to construct the skeleton structure of many kinds of bioactive molecules. Interestingly, 3-nitroindole can be further derivatived as a pyrrolo[2,3-b]indole.

Five Novel Silver-Based Coordination Polymers as Photoluminescent Sensing Platforms for the Detection of Nitrobenzene

Nitrobenzene (NB) is a highly toxic chemical and a cause for concern to human health and the environment. Hence, it is worth designing new efficient and robust sensing platforms for NB. In this study, we present three newly synthesized luminescent silver cluster-based coordination polymers, {[Ag10 (StBu)6 (CF3 COO)4 (hpbt)] (DMAc)2 (CH3 CN)2 }n (hpbt=N,N,N',N'N",N"-hexa(pyridine-4-yl)benzene-1,3,5-triamine), [Ag12 (StBu)6 (CF3 COO)6 (bpva)3 ]n (bpva=9,10-Bis(2-(pyridin-4-yl)vinyl)anthracene), and {[Ag12 (StBu)6 (CF3 COO)6 (bpb)(DMAc)2 (H2 O)2 ] (DMAc)2 }n (bpb=1,4-Bis(4-pyridyl)benzene) composed of Ag10 , Ag12 and Ag12 cluster cores, respectively, connected by multidentate pyridine linkers. In addition, two new luminescent polymorphic silver(I)-based coordination polymers, [Ag(CF3 COO)(dpa)]n (dpa=9,10-di(4-pyridyl)anthracene) referred to as Agdpa (H) and Agdpa (R), where H and R denote hexagon- and rod-like crystal shapes, respectively, have been prepared. The coordination polymers exhibit highly sensitive luminescence quenching effects to NB, attributed to the π-π stacking interactions between the polymers and NB as well as the electron-withdrawing character of NB.

Cloning of two gene clusters involved in the catabolism of 2,4-dinitrophenol by Paraburkholderia sp. strain KU-46 and characterization of the initial DnpAB enzymes and a two-component monooxygenases DnpC1C2

Little is currently known about the metabolism of the industrial pollutant 2,4-dinitrophenol (DNP), particularly among gram-negative bacteria. In this study, we identified two non-contiguous genetic loci spanning 22 kb of Paraburkholderia (formerly Burkholderia) sp. strain KU-46. Additionally, we characterized four key initial genes (dnpA, dnpB, and dnpC1C2) responsible for DNP degradation, providing molecular and biochemical evidence for the degradation of DNP via the formation of 4-nitrophenol (NP), a pathway that is unique among DNP utilizing bacteria. Reverse transcription polymerase chain reaction (PCR) analysis indicated that dnpA, which encodes the initial hydride transferase, and dnpB which encodes a nitrite-eliminating enzyme, were induced by DNP and organized in an operon. Moreover, we purified DnpA and DnpB from recombinant Escherichia coli to demonstrate their effect on the transformation of DNP to NP through the formation of a hydride-Meisenheimer complex of DNP, designated as H--DNP. The function of DnpB appears new since all homologs of the DnpB sequences in the protein database are annotated as putative nitrate ABC transporter substrate-binding proteins. The gene cluster responsible for the degradation of DNP after NP formation was designated dnpC1C2DXFER, and DnpC1 and DnpC2 were functionally characterized as the FAD reductase and oxygenase components of the two-component DNP monooxygenase, respectively. By elucidating the hqdA1A2BCD gene cluster, we are now able to delineate the final degradation pathway of hydroquinone to β-ketoadipate before it enters the tricarboxylic acid cycle.

Fluorescent Carbon Dots Derived From Soy Sauce for Picric Acid Detection and Cell Imaging

Picric acid (PA) is a powerful nitro-aromatic explosive that harms the environment and human health. Developing non-toxic and low-cost sensors for the rapid detection of PA is essential. An environment-friendly fluorescent probe for PA detection is designed based on carbon dots (CDs) directly separated from edible soy sauce by silica gel column chromatography. Neither organic reagents nor heating process was needed to prepare CDs. The obtained CDs exhibit bright blue fluorescence, good water solubility, and photostability. The fluorescent probe for PA was developed according to the CD's fluorescence can be significantly quenched via the inner filter effect between CDs and PA. The linear range was 0.2-24 µM with a limit of detection of 70 nM. This proposed method was successfully employed to detect PA in the real water samples with satisfactory recoveries between 98.0-104.0%. Moreover, the CDs were suitable for fluorescence imaging of HeLa cells owing to their low toxicity and good biocompatibility.

Thermodynamic Two-Site Surface Reaction Model for Predicting Munition Constituent Reduction Kinetics with Iron (Oxyhydr)oxides

Iron (oxyhydr)oxides comprise a significant portion of the redox-active fraction of soils and are key reductants for remediation of sites contaminated with munition constituents (MCs). Previous studies of MC reduction kinetics with iron oxides have focused on the concentration of sorbed Fe(II) as a key parameter. To build a reaction kinetic model, it is necessary to predict the concentration of sorbed Fe(II) as a function of system conditions and the redox state. A thermodynamic framework is formulated that includes a generalized double-layer model that utilizes surface acidity and surface complexation reactions to predict sorbed Fe(II) concentrations that are used for fitting MC reduction kinetics. Monodentate- and bidentate Fe(II)-binding sites are used with individual oxide sorption characteristics determined through data fitting. Results with four oxides (goethite, hematite, lepidocrocite, and ferrihydrite) and four nitro compounds (NB, CN-NB, Cl-NB, and NTO) from six separate studies have shown good agreement when comparing observed and predicted surface area-normalized rate constants. While both site types are required to reproduce the experimental redox titration, only the monodentate site concentration controls the MC reaction kinetics. This model represents a significant step toward predicting the timescales of MC degradation in the subsurface.

The Value of Different Experimental Observables: A Transient Absorption Study of the Ultraviolet Excitation Dynamics Operating in Nitrobenzene

Excess energy redistribution dynamics operating in nitrobenzene under hexane and isopropanol solvation were investigated using ultrafast transient absorption spectroscopy (TAS) with a 267 nm pump and a 340-750 nm white light continuum probe. The use of a nonpolar hexane solvent provides a proxy to the gas-phase environment, and the findings are directly compared with a recent time-resolved photoelectron imaging (TRPEI) study on nitrobenzene using the same excitation wavelength [L. Saalbach et al., J. Phys. Chem. A 2021, 125, 7174-7184]. Of note is the observation of a 1/e lifetime of 3.5-6.7 ps in the TAS data that was absent in the TRPEI measurements. This is interpreted as a dynamical signature of the T2 state in nitrobenzene─analogous to observations in the related nitronaphthalene system, and additionally supported by previous quantum chemistry calculations. The discrepancy between the TAS and TRPEI measurements is discussed, with the overall findings providing an example of how different spectroscopic techniques can exhibit varying sensitivity to specific steps along the overall reaction coordinate connecting reactants to photoproducts.

Metabolic engineering of Escherichia coli for 2,4-dinitrotoluene degradation

2,4-Dinitrotoluene (2,4-DNT) as a common industrial waste has been massively discharged into the environment with industrial wastewater. Due to its refractory degradation, high toxicity, and bioaccumulation, 2,4-DNT pollution has become increasingly serious. Compared with the currently available physical and chemical methods, in situ bioremediation is considered as an economical and environmentally friendly approach to remove toxic compounds from contaminated environment. In this study, we relocated a complete degradation pathway of 2,4-DNT into Escherichia coli to degrade 2,4-DNT completely. Eight genes from Burkholderia sp. strain were re-synthesized by PCR-based two-step DNA synthesis method and introduced into E. coli. Degradation experiments revealed that the transformant was able to degrade 2,4-DNT completely in 12 h when the 2,4-DNT concentration reached 3 mM. The organic acids in the tricarboxylic acid cycle were detected to prove the degradation of 2,4-DNT through the artificial degradation pathway. The results proved that 2,4-DNT could be completely degraded by the engineered bacteria. In this study, the complete degradation pathway of 2,4-DNT was constructed in E. coli for the first time using synthetic biology techniques. This research provides theoretical and experimental bases for the actual treatment of 2,4-DNT, and lays a technical foundation for the bioremediation of organic pollutants.

Catalytic reductions of nitroaromatic compounds over heterogeneous catalysts with rhenium sub-nanostructures

Nitroaromatic compounds (NACs) are key contaminants of anthropogenic origin and pose a severe threat to human and animal lives. Although the catalytic activities of Re nanostructures (NSs) are significantly higher than those of other heterogeneous catalysts containing NSs, few studies have been reported on the application of Re-based nanocatalysts for NAC hydrogenation. Accordingly, herein, catalytic reductions of nitrobenzene (NB), 4-nitrophenol (4-NP), 2-nitroaniline (2-NA), 4-nitroaniline (4-NA), and 2,4,6-trinitrophenol (2,4,6-TNP) over new Re-based heterogeneous catalysts were proposed. The catalytic materials were designed to enable effective syntheses and stabilisation of particularly small Re structures over them. Accordingly, catalytic hydrogenations of NACs under mild conditions were significantly enhanced by Re sub-nanostructures (Re-sub-NSs). The highest pseudo-first-order rate constants for NB, 4-NP, 2-NA, 4-NA, and 2,4,6-TNP reductions over the catalyst acquired by stabilising Re using bis(3-aminopropyl)amine (BAPA), which led to Re-sub-NSs with Re concentrations of 16.7 wt%, were 0.210, 0.130, 0.100, 0.180, and 0.090 min-1, respectively.

Structural and spectroscopic characterization of RufO indicates a new biological role in rufomycin biosynthesis

Rufomycins constitute a class of cyclic heptapeptides isolated from actinomycetes. They are secondary metabolites that show promising treatment against Mycobacterium tuberculosis infections by inhibiting a novel drug target. Several nonproteinogenic amino acids are integrated into rufomycins, including a conserved 3-nitro-tyrosine. RufO, a cytochrome P450 (CYP)-like enzyme, was proposed to catalyze the formation of 3-nitro-tyrosine in the presence of O2 and NO. To define its biological function, the interaction between RufO and the proposed substrate tyrosine is investigated using various spectroscopic methods that are sensitive to the structural change of a heme center. However, a low- to high-spin state transition and a dramatic increase in the redox potential that are commonly found in CYPs upon ligand binding have not been observed. Furthermore, a 1.89-Å crystal structure of RufO shows that the enzyme has flexible surface regions, a wide-open substrate access tunnel, and the heme center is largely exposed to solvent. Comparison with a closely related nitrating CYP reveals a spacious and hydrophobic distal pocket in RufO, which is incapable of stabilizing a free amino acid. Molecular docking validates the experimental data and proposes a possible substrate. Collectively, our results disfavor tyrosine as the substrate of RufO and point to the possibility that the nitration occurs during or after the assembly of the peptides. This study indicates a new function of the unique nitrating enzyme and provides insights into the biosynthesis of nonribosomal peptides.

Trifluoromethanesulfonic Acid Promoted Controllable Electrophilic Aromatic Nitration

In this work, we developed a facile and controllable electrophilic aromatic nitration method with commercially available 68% HNO₃ as the nitrating reagent and trifluoromethanesulfonic acid (HOTf) as the catalyst in hexafluoroisopropanol or under solvent-free conditions. The electrophilic nitration products of different arenes can be obtained in almost quantitative yields by tuning the loading of HOTf. The strong acidity and water absorbing property of HOTf allowed this transformation to reach completion in a short time at room temperature.

APDB: a database on air pollutant characterization and similarity prediction

The World Health Organization estimates that 9 out of 10 people worldwide breathe air containing high levels of pollutants. Long-term and chronic exposure to high concentrations of air pollutants is associated with deleterious effects on vital organs, including increased inflammation in the lungs, oxidative stress in the heart and disruption of the blood-brain barrier. For this reason, in an effort to find an association between exposure to pollutants and the toxicological effects observable on human health, an online resource collecting and characterizing in detail pollutant molecules could be helpful to investigate their properties and mechanisms of action. We developed a database, APDB, collecting air-pollutant-related data from different online resources, in particular, molecules from the US Environmental Protection Agency, their associated targets and bioassays found in the PubChem chemical repository and their computed molecular descriptors and quantum mechanics properties. A web interface allows (i) to browse data by category, (ii) to navigate the database by querying molecules and targets and (iii) to visualize and download molecule and target structures as well as computed descriptors and similarities. The desired data can be freely exported in textual/tabular format and the whole database in SQL format. Database URL http://apdb.di.univr.it.

Dinitro-5,5-Dimethylhydantoin: An Arene Nitration Reagent

The development of a new N-nitro type compound, dinitro-5,5-dimethylhydantoin (DNDMH), has been reported as an arene nitration reagent. The exploration demonstrated that arene nitration with DNDMH exhibited good tolerance with diverse functional groups. It is notable that, among the two N-nitro units of DNDMH, only the N-nitro unit on N1 was delivered to the nitroarene products. The N-nitro type compound with a single N-nitro unit on N2 cannot promote the arene nitration.

Realizing the Continuous Chemoenzymatic Synthesis of Anilines Using an Immobilized Nitroreductase

The use of biocatalysis for classically synthetic transformations has seen an increase in recent years, driven by the sustainability credentials bio-based approaches can offer the chemical industry. Despite this, the biocatalytic reduction of aromatic nitro compounds using nitroreductase biocatalysts has not received significant attention in the context of synthetic chemistry. Herein, a nitroreductase (NR-55) is demonstrated to complete aromatic nitro reduction in a continuous packed-bed reactor for the first time. Immobilization on an amino-functionalized resin with a glucose dehydrogenase (GDH-101) permits extended reuse of the immobilized system, all operating at room temperature and pressure in aqueous buffer. By transferring into flow, a continuous extraction module is incorporated, allowing the reaction and workup to be continuously undertaken in a single operation. This is extended to showcase a closed-loop aqueous phase, permitting reuse of the contained cofactors, with a productivity of >10 g_product g_NR-55^-1 and milligram isolated yields >50% for the product anilines. This facile method removes the need for high-pressure hydrogen gas and precious-metal catalysts and proceeds with high chemoselectivity in the presence of hydrogenation-labile halides. Application of this continuous biocatalytic methodology to panels of aryl nitro compounds could offer a sustainable approach to its energy and resource-intensive precious-metal-catalyzed counterpart.

Sequentially modified carbon felt for enhanced p-nitrophenol biodegradation through direct interspecific electron transfer

The widely applied aromatic nitration in modern industry leads to toxic p-nitrophenol (PNP) in environment. Exploring its efficient degradation routes is of great interests. In this study, a novel four-step sequential modification procedure was developed to increase the specific surface area, functional group, hydrophilicity, and conductivity of carbon felt (CF). The implementation of the modified CF promoted reductive PNP biodegradation, attaining 95.2 ± 0.8% of removal efficiency with less accumulation of highly toxic organic intermediates (e.g., p-aminophenol), compared to carrier-free and CF-packed biosystems. The constructed anaerobic-aerobic process with modified CF in 219-d continuous operation achieved further removal of carbon and nitrogen containing intermediates and partial mineralization of PNP. The modified CF promoted the secretion of extracellular polymeric substances (EPS) and cytochrome c (Cyt c), which were essential components to facilitate direct interspecies electron transfer (DIET). Synergistic relationship was deduced that glucose was converted into volatile fatty acids by fermenters (e.g., Longilinea and Syntrophobacter), which donated electrons to the PNP degraders (e.g., Bacteroidetes_vadinHA17) through DIET channels (CF, Cyt c, EPS) to complete PNP removal. This study proposes a novel strategy using engineered conductive material to enhance the DIET process for efficient and sustainable PNP bioremediation.

Reduction of Nitroaromatics by Gold Nanoparticles on Porous Silicon Fabricated Using Metal-Assisted Chemical Etching

In this study, we investigated the use of porous silicon (PSi) fabricated using metal-assisted chemical etching (MACE) as a substrate for the deposition of Au nanoparticles (NPs) for the reduction of nitroaromatic compounds. PSi provides a high surface area for the deposition of Au NPs, and MACE allows for the fabrication of a well-defined porous structure in a single step. We used the reduction of p-nitroaniline as a model reaction to evaluate the catalytic activity of Au NPs on PSi. The results indicate that the Au NPs on the PSi exhibited excellent catalytic activity, which was affected by the etching time. Overall, our results highlighted the potential of PSi fabricated using MACE as a substrate for the deposition of metal NPs for catalytic applications.

Sustainable magnetically recoverable Iridium-coated Fe3O4 nanoparticles for enhanced catalytic reduction of organic pollutants in water

The reduction of nitroarenes to aromatic amines is one of the potential pathways to remediate the hazardous impact of toxic nitroarenes on the aquatic environment. Aromatic amines obtained from the reduction of nitroaromatics are not only less toxic than nitroaromatics but also act as important intermediates in the synthesis of dyes, drugs, pigments, herbicides, and polymers. There is a huge demand for the development of cost-effective, and eco-friendly catalysts for the efficient reduction of nitroarenes. In the present study, Fe₃O₄@trp@Ir nanoparticles were explored as efficient catalysts for the reduction of nitroarenes. Fe₃O₄@trp@Ir magnetic nanoparticles were fabricated by surface coating of Fe₃O₄ with tryptophan and iridium by co-precipitation method. As-prepared Fe₃O₄@trp@Ir nanoparticles are environmentally benign efficient catalysts for reducing organic pollutants such as 4-nitrophenol (4-NP), 4-nitroaniline (4-NA), and 1-bromo-4-nitrobenzene (1-B-4-NB). The key parameters that affect the catalytic activity like temperature, catalyst loading, and the concentration of reducing agent NaBH₄ were optimized. The obtained results proved that Fe₃O₄@trp@Ir is an efficient catalyst for reducing nitroaromatics at ambient temperature with a minimal catalyst loading of 0.0025%. The complete conversion of 4-nitrophenol to 4-aminophenol took only 20 s with a minimal catalyst loading of 0.0025% and a rate constant of 0.0522 s^-1. The high catalytic activity factor (1.040 s^-1 mg^-1) and high turnover frequency (9 min^-1) obtained for Fe₃O₄@trp@Ir nanocatalyst highlight the possible synergistic effect of the two metals (Fe and Ir). The visible-light photocatalytic degradation of 4-NP was also investigated in the presence of Fe₃O₄@trp@Ir. The photocatalytic degradation of 4-NP by Fe₃O₄@trp@Ir is completed in 20 min with 95.15% efficiency, and the rate of photodegradation of 4-NP (0.1507 min^-1) is about twice the degradation rate of 4-NP in the dark (0.0755 min^-1). The catalyst was recycled and reused for five cycles without significant reduction in the conversion efficiency of the catalyst.

The Crystal Structure of Engineered Nitroreductase NTR 2.0 and Impact of F70A and F108Y Substitutions on Substrate Specificity

Bacterial nitroreductase enzymes that convert prodrugs to cytotoxins are valuable tools for creating transgenic targeted ablation models to study cellular function and cell-specific regeneration paradigms. We recently engineered a nitroreductase (“NTR 2.0”) for substantially enhanced reduction of the prodrug metronidazole, which permits faster cell ablation kinetics, cleaner interrogations of cell function, ablation of previously recalcitrant cell types, and extended ablation paradigms useful for modelling chronic diseases. To provide insight into the enhanced enzymatic mechanism of NTR 2.0, we have solved the X-ray crystal structure at 1.85 Angstroms resolution and compared it to the parental enzyme, NfsB from Vibrio vulnificus. We additionally present a survey of reductive activity with eight alternative nitroaromatic substrates, to provide access to alternative ablation prodrugs, and explore applications such as remediation of dinitrotoluene pollutants. The predicted binding modes of four key substrates were investigated using molecular modelling.

Nitration of Pyrrolo[2,1-a]isoquinolines

We have successfully modified a series of pyrrolo[2,1-a]isoquinolines via direct nitration under mild reaction conditions. Easily accessible nitrates including CAN, Cu(NO₃)₂·H₂O, and Fe(NO₃)₃·9H₂O all can serve as effective nitrating reagents for functionalizing pyrrolo[2,1-a]isoquinolines. Various nitro-bearing pyrrolo[2,1-a]isoquinolines have been efficiently prepared in acceptable to good yields.

Engineering Cytochrome P450BM3 Enzymes for Direct Nitration of Unsaturated Hydrocarbons

Applications of the peroxidase activity of cytochrome P450 enzymes in synthetic chemistry remain largely unexplored. We present herein a protein engineering strategy to increase cytochrome P450BM3 peroxidase activity for the direct nitration of aromatic compounds and terminal aryl-substituted olefins in the presence of a dual-functional small molecule (DFSM). Site-directed mutations of key active-site residues allowed the efficient regulation of steric effects to limit substrate access and, thus, a significant decrease in monooxygenation activity and increase in peroxidase activity. Nitration of several phenol and aniline compounds also yielded ortho- and para-nitration products with moderate-to-high total turnover numbers. Besides direct aromatic nitration by P450 variants using nitrite as a nitrating agent, we also demonstrated the use of the DFSM-facilitated P450 peroxidase system for the nitration of the vinyl group of styrene and its derivatives.