Reduction Of Nitroaromatics Research Articles

Photocatalytic reduction of nitroaromatics into anilines using CeO2-TiO2 nanocomposite

The reduction of nitro compounds into amines is an important approach for synthetic and pharmaceutical chemistry. The reduced compounds are used as synthetic intermediates in the synthesis of therapeutic molecules. In the present work, we have fabricated cerium dioxide decorated TiO2 nanoparticles using a sol-gel-hydrothermal method. The synthesized nanocomposite was effectively reduced various nitro-compounds, specifically aromatic nitro compounds, into amines in visible light. All the nitro compounds screened in the photoreduction reaction showed >90% conversion with >96% selectivity. Chromatographic techniques confirmed the products obtained. The nanocomposite photocatalyst has excellent stability under the experimental condition and exhibited up to five cycles with no loss of metal content. The nanomaterials were characterized using various spectroscopic techniques.

Synthesis and characterization of the ternary graphene oxide, MnFe2O4 nanoparticles, and Polyamidoamine dendrons nanocomposite decorated with palladium as a heterogeneous catalyst for nitroaromatics reduction

In this study, the divergent and magnetic separation method is employed to prepare polyamidoamine (PAMAM) dendrons functionalized magnetic graphene oxide (MGG3) using graphene oxide supported MnFe2O4 nanoparticles as the support (MG), and ethylenediamine (EDA) and methylacrylate (MA) as the precursors of PAMAM dendron. Finally, palladium ions as active catalytic sites are immobilized on the support (MGG3‐Pd). The morphology and structure of the MGG3‐Pd nanocomposite thus produced are characterized by elemental analysis, Fourier transform infrared (FT‐IR), powder X‐ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), energy dispersive X‐ray spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP‐AES), X‐ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), and Zeta potential analysis. Subsequently, the catalytic activity of the MGG3‐Pd nanocomposite is studied in the reaction of 4‐nitrophenol (4‐NP) with sodium borohydride as the reducing agent at room temperature. The MGG3‐Pd catalyst is found to exhibit an excellent catalytic activity in the reduction of 4‐NP with a high yield over a short reaction time and at a rate constant (k) of 16.82 × 10−3 s−1. Furthermore, the MGG3‐Pd catalyst thus produced can be recycled at least after 10 runs of 4‐NP reduction without any considerable loss of Pd content. The reduction of other nitroaromatic compounds is also investigated under optimal conditions to illustrate the catalyst's versatility.

CdS quantum dots-decorated InOOH: Facile synthesis and excellent photocatalytic activity under visible light

For the first time, CdS quantum dots (QDs)-decorated InOOH (CdS-In for short) was synthesized by a facile photodeposition method. The experiment results showed that CdS-In samples exhibited excellent activity and stability towards photocatalytic reduction of nitro aromatics. The conversion ratio of 4-nitroaniline (4-NA) over CdS-In sample that was prepared with photodeposition time of 120 min (CdS-In-120) reached up to 99.4% under visible light irradiation for 40 min, which was even higher than that achieved over commercial CdS (86.2%). Besides the significant enhancement of visible light absorption, quantum sized CdS were decorated evenly on the surface of InOOH, which was very beneficial for the high activity. Furthermore, the heterogeneous junction formed at the interface of CdS QDs and InOOH can significantly increase the separation efficiency of photogenerated charge carriers. Active species control experiment and electron spin resonance (ESR) technique have proved that photogenerated electrons are the main active species towards photocatalytic reduction of nitro aromatics. It is anticipated that our study would offer meaningful insights for exploring novel InOOH-based visible light photocatalysts towards efficient reduction of nitro aromatics.

Silver nanoparticles supported on P, Se-codoped g-C3N4 nanosheet as a novel heterogeneous catalyst for reduction of nitroaromatics to their corresponding amines

P, Se-codoped g-C3N4 (PSeCN) nanosheet was in situ prepared by facile thermal polymerization of melamine, phosphonitrilic chloride trimer, and selenium black powder as the precursors. It was found as a suitable support for the immobilization of silver nanoparticles (Ag NPs). The prepared nanocatalyst was fully characterized via standard analysis methods including EDX, ICP-OES, XRD, FT-IR, SEM, TEM, and BET. This PSeCN/Ag nanocatalyst with a higher specific surface area compared with CN, showed excellent catalytic activity towards the reduction of several nitroaromatic compounds using sodium borohydride (NaBH4) in short reaction times with high efficiency and good selectivity in water as a green solvent. Significantly, the above-mentioned nanocomposite could be reused six times without appreciable loss of its catalytic activity.

MOF-derived B, N co-doped porous carbons as metal-free catalysts for highly efficient nitro aromatics reduction

A convenient and rational route is designed to synthesize B, N co-doped porous carbon materials (BNPCs) via a two-step calcination method derived from adenine-based bio-MOF-1. By using the adenine from bio-MOF-1 precursor as the endogenous N source and boric acid as the exogenous B source, the N and B elements are uniformly doped in metal-free BNPCs. B has lower electronegativity than C, leading to a higher positive charge density and the enhanced activation of C atoms. Owing to the synergistic effect between B and N, the co-doped catalysts not only increase electrical conductivity of catalysts to improve electron transfer, but also produce more additional active sites to intensify the catalytic performance for the reduction of 4-NP. The as-synthesized carbon materials have abundant mesopores, graphite structure, dual heteroatoms doping and thus excellent catalytic performances. In particular, BNPC-1000, obtained by pyrolysis at 1000 °C, shows superior catalytic efficiency of 95.2% and high catalytic cycling stability for the 4-NP reduction.

Intercalating ultrathin polymer interim layer for charge transfer cascade towards solar-powered selective organic transformation

Transition metal chalcogenide quantum dots (TMCs QDs) constitute a crucial sector of semiconductors on account of large absorption coefficient for light harvesting, peculiar quantum confinement effect, and abundant active sites stemming from ultra-small size. However, elaborate and tunable modulation of anisotropic photoinduced charge carriers over TMCs QDs represents an enduring challenge in terms of sluggish charge transfer kinetic and ultra-short charge lifetime compared with nanoparticulate counterparts, thereby rendering maneuvering charge transfer of TMCs QDs a tough issue. We herein conceptually unlock the unanticipated charge transport capability of solid-state non-conductive poly(diallyl dimethylammonium chloride) (PDDA) for constructing cascade charge transfer pathway over self-assembled wide bandgap semiconductors (WBS)/PDDA/TMCs QDs multilayered heterostructures, by which unidirectional and accelerated electron transfer from TMCs QDs to WBS support mediums was spontaneously activated, markedly boosting the charge separation/migration efficiency. The integrated roles of such ultrathin insulating PDDA intermediate layer as simultaneous surface charge modifying agent and interfacial charge transfer mediator have been evidenced to be universal. The unexpected electron-withdrawing capability of ultrathin PDDA layer endows WBS (SnO2, TiO2)@PDDA@TMCs (CdSe, CdS) QDs heterostructures with significantly enhanced net efficiency of photoactivities toward selective anaerobic reduction of nitroaromatics to amino derivatives under visible light irradiation. Our work would feature a promising scope for rational design of multifarious novel insulating polymers-based photosystems for solar energy conversion.

Water-Soluble Noble Metal Nanoparticle Catalysts Capped with Small Organic Molecules for Organic Transformations in Water.

This article recaps a variety of interesting catalytic studies based on solubilized and freely movable noble metal nanoparticle catalysts employed for organic reactions in either pure water or water-organic biphasic systems. Small organic ligand-capped metal nanoparticles are fundamentally attractive materials due to their enormous potential as a well-defined system that can provide spatial control near active catalytic sites. The nanoparticle catalysts are first grouped based on the synthetic method (direct reduction, phase transfer, and redispersion) and then again based on the type of reaction such as alkene hydrogenation, arene hydrogenation, nitroaromatic reduction, carbon-carbon coupling reactions, etc. The impacts of various ligands on the catalytic activity and selectivity of semi-heterogeneous nanoparticles in water are discussed in detail. The catalytic systems using polymers, dendrimers, and ionic liquids as supporting or protecting materials are excluded from the subject of this review.

In situ integration of copper microspheres and carbon nanodots for the catalytic reduction of nitroaromatics

Herein, we report carbon dots coated over copper microspheres (CD/CuM), and its catalytic ability towards reduction of p-nitrophenol was examined. The material was synthesized by hydrothermal method utilizing eco-friendly precursors. P-XRD (powder X-ray diffraction) confirms the presence of amorphous carbon and face centred cubic copper. The morphology of CD/CuM was identified as spheres of average particle size 2.7 ± 0.6 μM by FE-SEM (field emission scanning electron microscopy), and the coated component was studied by HRTEM (high-resolution transmission electron microscopy) as nanodots with average diameter 5.6 ± 0.7 nm. EDX (energy dispersive X-ray analyser), UV-visible and infrared spectra confirm that copper formed as microspheres while the dots over microspheres are carbon dots. CD/CuM manifest high catalytic activity towards reduction of nitroaromatics with significant reusability.

Novel covalent organic polymer-supported Ag nanoparticles as a catalyst for nitroaromatics reduction

Herein, we propose a Schiff-base covalent organic polymer (COP) prepared by a condensation reaction between 2,4,6-tris-(2-methoxy-4-formyl-phenoxy)-1,3,5-triazine and p-phenylenediamine. The different amounts of silver nanoparticles were trapped by O and N atoms in the COP and synthesized Ag-COP was used as the catalyst for nitroaromatics reduction. The catalyst structure was confirmed using FTIR, XRD, BET, FESEM, ICP, and TGA analysis. The results show that Ag nanoparticles were evenly distributed on the external part or embedded in the interlayer slots of the COP. Ag-COP catalysts were selected as an efficient nanocatalyst for the reduction of nitroaromatics. The apparent rate kinetic constant (Kapp) and the activity parameter (k') were calculated to be 0.0122 s−1 and 4.06 s−1 g−1, respectively. The catalyst showed a 96.5% conversion after seven successive runs without losing its catalytic activity. The superiority of the COP nanoparticles as an effectual pattern for the elimination of industrial contaminants was confirmed by the results of this experimental research.

A Novel Carbon Support: Few‐Layered Graphdiyne‐Decorated Carbon Nanotubes Capture Metal Clusters as Effective Metal‐Supported Catalysts

Carbon-supported metal nanocatalysts have received substantial attention for heterogeneous catalysis in industry. Hunting for suitable and impactful carbon supports that have strong interactions with metal nanocatalyst is a matter of great urgency. Herein, a well-designed graphdiyne layer decorated on the carbon nanotubes sidewalls (CNT@GDY) serves as a novel carbon support. This unique hybrid structure effectively traps platinum and palladium atomic clusters (Pt/Pd-ACs) with dimensions of 0.65nm and 1.05nm uniformly and firmly, forming novel carbon-supported metal nanocatalysts (Pt(Pd)-ACs/CNT @ GDY) for efficient hydrogen generation and aromatic nitroreduction, respectively. The Pt-ACs/CNT@GDY can deliver an HER current density of 10mA cm-2 with a small overpotential of 23mV in 0.5 M H2 SO4 , showing a greatly enhanced mass activity, intrinsic activity than the commercial Pt/C catalyst. The Pd-ACs/CNT@GDY also exhibits excellent catalytic activity and a high turnover frequency of 38.0 min-1 for aromatic nitroreduction. The carbon support turns out to possess excellent conductivity, abundant and uniform reactive sites, low redox potential, more negative surface and large specific surface area as well as a strong interaction with ACs, as anticipated in ideal supports, which can be applied in other metal-supported catalysts.

Visualizing light-induced dynamic structural transformations of Au clusters-based photocatalyst via in situ TEM

Ultrasmall gold (Au) clusters have been regarded as one of the prototypes materials for solar energy conversion due to their unique strong molecular-like light absorption properties. However, the light-induced aggregation of Au clusters into nanoparticles is one of the most important factors that restricts its application in photocatalysis. Although Au clusters aggregation has been widely demonstrated, the underlying mechanism for cluster fusion is still unclear due to the lack of experimental evidence. Herein, we report the direct observation of Au clusters on TiO2 nanosheets aggregating when used as visible light photocatalysts for the reduction of nitroaromatics. Through in situ high-resolution transmission electron microscopy (TEM), the coexistence of two fusion mechanisms of Au clusters on TiO2 under ultraviolet-visible (UV-Vis) light irradiation in air is identified, i.e., the migration and coalescence (MC) and Ostwald ripening (OR). Additionally, the correlation between the photostability of Au clusters and reaction atmospheres has been investigated, among which Au clusters have higher stability in an inert N2 atmosphere or vacuum than the oxidizing atmospheres (i.e., air and O2). These results indicate the inherent stability of Au cluster during photocatalysis, and instability comes from the consuming of ligand layer. This work not only discloses the underlying mechanism of Au cluster sintering but also provides guidelines for enhancing metal clusters-based photocatalysts stability.

Modeling the Bioactivation and Subsequent Reactivity of Drugs.

Electrophilically reactive drug metabolites are implicated in many adverse drug reactions. In this mechanism-termed bioactivation-metabolic enzymes convert drugs into reactive metabolites that often conjugate to nucleophilic sites within biological macromolecules like proteins. Toxic metabolite-product adducts induce severe immune responses that can cause sometimes fatal disorders, most commonly in the form of liver injury, blood dyscrasia, or the dermatologic conditions toxic epidermal necrolysis and Stevens-Johnson syndrome. This study models four of the most common metabolic transformations that result in bioactivation: quinone formation, epoxidation, thiophene sulfur-oxidation, and nitroaromatic reduction, by synthesizing models of metabolism and reactivity. First, the metabolism models predict the formation probabilities of all possible metabolites among the pathways studied. Second, the exact structures of these metabolites are enumerated. Third, using these structures, the reactivity model predicts the reactivity of each metabolite. Finally, a feedfoward neural network converts the metabolism and reactivity predictions to a bioactivation prediction for each possible metabolite. These bioactivation predictions represent the joint probability that a metabolite forms and that this metabolite subsequently conjugates to protein or glutathione. Among molecules bioactivated by these pathways, we predicted the correct pathway with an AUC accuracy of 89.98%. Furthermore, the model predicts whether molecules will be bioactivated, distinguishing bioactivated and nonbioactivated molecules with 81.06% AUC. We applied this algorithm to withdrawn drugs. The known bioactivation pathways of alclofenac and benzbromarone were identified by the algorithm, and high probability bioactivation pathways not yet confirmed were identified for safrazine, zimelidine, and astemizole. This bioactivation model-the first of its kind that jointly considers both metabolism and reactivity-enables drug candidates to be quickly evaluated for a toxicity risk that often evades detection during preclinical trials. The XenoSite bioactivation model is available at http://swami.wustl.edu/xenosite/p/bioactivation.

Hydrothermally exfoliated P-doped g-C3N4 decorated with gold nanorods for highly efficient reduction of 4-nitrophenol

Au nanorods (AuNRs) decorated phosphorus doped graphitic carbon nitride AuNRs/g-C3N(4-x)Px-NS catalyst have been designed and prepared by a facile hydrothermal approach, which is useful for the efficient reduction of nitroaromatics in aqueous solution using NaBH4− as reductant. A series of conventional characterizations like X-ray diffraction, scanning/transmission electron microscopy, Electron dispersive scanning, elemental mapping, Fourier transform infrared FT-IR, photoluminescence, and X-ray photoelectron spectroscopy were used to identify the physicochemical properties of AuNRs/g-C3N(4-x)Px-NS. The catalytic activities of AuNRs/g-C3N(4-x)Px-NS nanohybrid were studied under different conditions, including the amount of catalyst, NaBH4 dosage, and various temperatures for reduction of 4-nitrophenol (40 mL, 3 mM). Results showed that AuNRs/g-C3N(4-x)Px-NS nanohybrid exhibited superior catalytic performance with turning over (TOF) of 967 for 4-nitrophenol reduction, which is impressively high. In addition, the catalyst exhibited the best performance in reducing the 4-nitrophenol in the shortest possible time. The recyclability and stability of AuNRs/g-C3N(4-x)Px-NS catalyst was also examined.

DNA-Chitosan Hydrogels: Formation, Properties, and Functionalization with Catalytic Nanoparticles.

DNA-chitosan (DNA-CS) hydrogels were prepared on the basis of interpolyelectrolyte complexes (IPEC) in a co-assembled regime by in situ charging of the polysaccharide in a DNA solution. In contrast to poorly controlled coacervates formed upon mixing of DNA and CS solutions, stable DNA-CS IPEC hydrogels are formed at near-stoichiometric ratios of DNA and chitosan ionogenic groups. Structure, stability, and ion absorption properties of such hydrogels depended strongly on the ratio between cationic (CS) and anionic (DNA) counterparts in hydrogels. Abundant amino- and nitrogen-containing aromatic groups of co-assembled DNA and CS make their hydrogel an efficient, multitarget absorbent toward metal ions. Such strong affinity of both DNA and CS to Au3+ cation was used to entrap Au3+ ions into the DNA-CS hydrogels. Subsequent reduction of Au3+ ion inside hydrogels resulted in the formation of ∼2-3 nm size Au nanoparticles on DNA-CS scaffolds. Metallized hydrogels demonstrated catalytic activity in reduction of various nitroaromatics that depended on the ratio between CS and DNA in the hydrogel.

N-rich MOFs derived N-doped carbon nanotubes encapsulating cobalt nanoparticles as efficient and magnetic recoverable catalysts for nitro aromatics reduction

A rational and convenient strategy was designed to synthesize high level N-doped Co@NCNTs composites derived from adenine-based AD-MOF-1 and Bio-MOF-11 via one-step pyrolysis method. Adenine can be used as an endogenous nitrogen source to apparently increase the N content of the materials. N-rich CNTs form a protecting layer for Co nanoparticles to avoid the aggregation of metal nanoparticles. The abundant nitrogen content can enhance electronic conductivity and bring additional active sites. The prepared Co@NCNTs display high catalytic efficiency for various nitro aromatics reduction in aqueous solution. The Co@NCNT-1-800 implies outstanding catalytic efficiency of 96% for the reduction of 4-NP. A mechanistic analysis revealed the abundant Co catalytic sites on the surface of catalysts to promote electron transfer efficiency and improve catalytic performance significantly. Moreover, the magnetic Co-based catalysts remained excellent catalytic activity and reusability even after five cycles.

Backbone assignment of E. coli NfsB and the effects of addition of the cofactor analogue nicotinic acid

E. coli nitroreductase NfsB (also called NfnB) has been studied extensively, largely due to its potential for cancer gene therapy. A homodimeric flavoprotein of 216 residues, it catalyses the reduction of nitroaromatics to cytotoxic hydroxylamines by NADH and NADPH and also the reduction of quinones to hydroxyquinones. Its role in vivo is not known but it is postulated to be involved in reducing oxidative stress. The crystal structures of the wild type protein and several homologues have been determined in the absence and presence of ligands, including nicotinate as a mimic of the headpiece of the nicotinamide cofactors. There is little effect on the overall structure of the protein on binding ligands, but, from the B factors, there appears to be a decrease in mobility of 2 helices near the active site. As a first step towards examining the dynamics of the protein in solution with and without ligand, we have assigned the backbone 13C, 15N, and 1HN resonances of NfsB and examined the effect of the binding of nicotinate on the amide 15N, and 1HN shifts.

Porous materials confining noble metals for the catalytic reduction of nitroaromatics: controllable synthesis and enhanced mechanism

In the field of nanocatalysis, noble metal nanoparticles (NPs) have aroused tremendous attention owing to their superb catalytic efficiency, especially in the catalytic reduction of nitroaromatics.

Photochemical Reduction of Nitroaromatics Mediated by p-Toluenethiol/PCy3

Photochemical Reduction of Nitroaromatics Mediated by<i> p</i>-Toluenethiol/PCy₃

Electrochemical evidence of nitrate release from the nitrooxy compound 4-((nitrooxy) methyl)-3-nitrobenzoic acid and its antinociceptive and anti-inflammatory activities in mice

Considering the many biological activities of nitric oxide (NO), some lines of research focused on the modulation of these activities through the provision of this mediator by designing and synthesizing compounds coupled with an NO donor group. Thus, the objectives of the present study were to carry out an electrochemical investigation of the nitrooxy compound 4-((nitrooxy) methyl)-3-nitrobenzoic acid (1) and evaluate its activities and putative mechanisms in experimental models of pain and inflammation. Voltammetric studies performed in aprotic medium (mimetic of membranes) showed important electrochemical reduction mechanisms: nitroaromatic reduction, self-protonation, and finally reductive elimination, which leads to nitrate release. Systemic administration of the nitrooxy compound (1) inhibited the nociceptive response induced by heat and the tactile hypersensitivity and paw edema induced by carrageenan in mice. The activities in the models of inflammatory pain and edema were associated with reduced neutrophil recruitment and production of inflammatory cytokines, such as interleukin (IL)-1β, IL-6, tumor necrosis factor-α and CXCL-1, and increased production of IL-10. Concluding, electrochemical analysis revealed unequivocally that electron transfer at the nitro group of the nitrooxy compound (1) results in the cleavage of the organic nitrate, potentially resulting in the generation of NO. This electrochemical mechanism may be compared to a biochemical electron-transfer mediated nitrate release that, by appropriate in vivo bioreduction (enzymatic or not) would lead to NO production. Compound (1) exhibits activities in models of inflammatory pain and edema that may be due to reduced recruitment of neutrophils and production of inflammatory cytokines and increased production of IL-10. These results reinforce the interest in the investigation of NO donor compounds as candidates for analgesic and anti-inflammatory drugs.

Copper-Based Metallogel of Bovine Serum Albumin and Its Derived Hybrid Biomaterials as Aerogel and Sheet: Comparative Study of the Adsorption and Reduction of Dyes and Nitroaromatics

This paper deals with the synthesis of a protein-inorganic hybrid hydrogel and its derived materials, including aerogel and sheet, and the demonstration of their application potentials. For this, a common and abundant protein, bovine serum albumin (BSA), and a copper salt were used in order to prepare a hydrogel by cross-linking the protein molecules using epichlorohydrin and embedding Cu2+ ions to give BSA_Cuhydrogel (1). When this material was lyophilized, it resulted in the product powder BSA_Cuaerogel (2); however, when dried under vacuum, it yielded a blue sheet material, BSA_Cusheet (3). All three of these biomaterials were characterized by spectroscopy and microscopy and further studied for three different applications, and the data were compared in order to establish the material vs property/activity relationship. The applications include (i) adsorption of organic dyes, (ii) reductive degradation of these dyes, and (iii) the reductive transformation of nitroaromatic compounds. The study revealed the efficient adsorption of the anionic and neutral dyes, while the adsorption of the cationic dye was much lower. The adsorption capacities (in mg/g) of Congo red followed the trend BSA_Cuaerogel (367 ± 6) > BSA_Cuhydrogel (274 ± 4) > BSA_Cusheet (204 ± 3). The comparison of the rate of reductive degradation of Congo red and methylene blue follows the same trend as that of the adsorption of the dyes. The reductive degradation was demonstrated for six cycles by reusing the recovered catalyst after every cycle. More than half a dozen nitroaromatics were studied for their reduction using BSA_Cuaerogel. In the case of p-nitrophenol, the rate of reduction follows the trend 2 > 1 > 3. Thus, this paper deals with a methodology to synthesize both a robust hydrogel incorporating metal ions and other derived protein-based biomaterials, viz., an aerogel and sheet, and a comparison of their activity toward the adsorption and degradation of dyes and nitroaromatics.