Nitrogen Functionalities Research Articles

Towards a cost-effective framework for estimating soil nitrogen pools using pedotransfer functions and machine learning

Globally, the strategic use of nitrogen (N) is important in optimizing economic returns and reducing soil nitrogen losses to the environment. Incorporating reliable estimates of nitrogen (N) mineralized over a growing season (GSN) into N-fertilizer rate prescriptions is critical, but may often lack a direct measurement. For this purpose, Pedotransfer functions (PTFs) of total nitrogen (TN) – representing the stable pool from which N is mineralized and biological nitrogen availability (BNA) – representing the labile pool of N mineralization were used to estimate GSN. GSN was calculated based on TN and BNA results from a soil health database (SHD), which also includes a suite of related soil health parameters (n = 2222). Using a process of recursive feature elimination (RFE) and cost-benefit feature elimination (CBFE), the best predictors of TN, BNA, and GSN were identified using a suite of machine learners (MLs) and regression analysis. For TN, RFE revealed that BNA, active carbon (AC), sand (Sa), and soil organic matter (OM) were the best predictors yielding a Lin’s concordance correlation coefficient (CCC) of 0.80 and a reduction in theoretical cost of 41 % compared to the control. CBFE resulted in AC, soil respiration (SR), clay, Sa, and OM as the most cost-effective predictors of TN with a CCC of 0.79 and a theoretical cost savings 49 % below the cost of using all appropriate soil health parameters in the SHD. With respect to BNA, the best predictors from RFE were aggregate stability (AS), AC, SR, and TN with a CCC of 0.78 and a theoretical cost reduction of 23 %. CBFE retained AC, SR, S, TN, OM and pH as predictors of BNA with a CCC of 0.78 and reduction of 29 % in theoretical cost. Finally, GSN results from RFE identified AS, AC, SR, OM and pH as the best predictors with a 0.82 CCC and 17 % reduction in theoretical cost. CBFE, on the other hand, identified AC, SR, sand, OM, and pH as the most cost-efficient predictors while maintaining a CCC of 0.82 and theoretical cost reduction of 29 %. Of the MLs used for pattern recognition (i.e., cubist, random forest, support vector machine, and stochastic gradient boosting), cubist model outperformed the others for the majority of iterations of the RFE and CBFE processes. The cost-effective framework, and the N-related PTFs developed in this study will greatly enhance our ability to predict of soil N-pool dynamics and the ability to incorporate GSN estimates into N-fertilizer recommendations for producers worldwide. Improvements in predictive strength could be achieved by incorporating climate and soil management practices into PTF development. Another area for improvement and future study would include addition of spatial and landscape variability related to N-measures via digital soil mapping applications.

Ligand-Enabled Carboamidation of Unactivated Alkenes through Enhanced Organonickel Electrophilicity.

Catalytic carboamination of alkenes is a powerful synthetic tool to access valuable amine scaffolds from abundant and readily available alkenes. Although a number of synthetic approaches have been developed to achieve the rapid buildup of molecular complexity in this realm, the installation of diverse carbon and nitrogen functionalities onto unactivated alkenes remains underdeveloped. Here we present a ligand design approach to enable nickel-catalyzed three-component carboamidation that is applicable to a wide range of alkenyl amine derivatives via a tandem process involving alkyl migratory insertion and inner-sphere metal-nitrenoid transfer. With this method, various nitrogen functionalities can be installed into both internal and terminal unactivated alkenes, leading to differentially substituted diamines that would otherwise be difficult to access. Mechanistic investigations reveal that the tailored Ni(cod)(BQiPr) precatalyst modulates the electronic properties of the presumed π-alkene-nickel intermediate via the quinone ligand, leading to enhanced carbonickelation efficiency across the unactivated C═C bond. These findings establish nickel's ability to catalyze multicomponent carboamidation with a high efficiency and exquisite selectivity.

Nitrogen and sulfur functionalized microporous carbon nanomaterial derived from waste coconut husk for the efficient detection and removal of ofloxacin

This study uses waste coconut husk to synthesize carbon quantum dots decorated graphene-like structure for sustainable detection and removal of ofloxacin. The XRD spectrum shows the carbon nanomaterial's layered structure with turbostratic carbon stacking on its surface. The FESEM and HRTEM studies claim the successful development of quantum dots decorated 2D layered structure of carbon nanomaterial. The functionalization of sulfur and nitrogen is well observed and studied through XPS, while Raman spectra have provided insight into the surface topology of the as-synthesized nanostructure. The BET surface area was found to be 1437.12 m2/g with a microporous structure (pore width 2.0 nm) which interestingly outcompete many reported carbon-based nanomaterials such as graphene oxide, reduced graphene oxide and quantum dots. The detection and removal processes are monitored through UV–visible spectroscopy and the obtained detection limit and adsorption capacity were 2.7 nM and 393.94 mg/L respectively. Additionally, 1 mg carbon nanomaterial has removed 49 % ofloxacin from water in just 1 h. In this way, this study has successfully managed the coconut husk waste after its utilization for environmental remediation purposes.

Bisbenzamidine and Bisbenzguanidine Ureas Act as Antibacterial Agents against Pseudomonas aeruginosa.

Due to the global rise in the number of antibiotic resistant bacterial infections over the past 20 years, there is a dire need for the development of small molecule antibiotics capable of overcoming resistance mechanisms in pathogenic bacteria. Antibiotic development against Gram-negative pathogens, such as Pseudomonas aeruginosa, is especially challenging due to their additional outer membrane which reduces antibiotic entry. Recently, it has been shown that a broad range of nitrogen functionality, including guanidines, amidines, primary amines, imidazolines, and imidazoles, promote antibiotic and adjuvant activity in Gram-negative bacteria, but few of these have been targeted towards Pseudomonas aeruginosa specifically despite this pathogen being deemed a critical threat by the United States Centers for Disease Control and Prevention. Herein, we examined a small series of known and unknown nitrogenous dimers, with guanidine, amidine, dimethyl amine, and pyridine functionality, for antibacterial activity against multidrug resistant Pseudomonas aeruginosa. We found that two, with bisbenzguanidine and bisbenzamidine functionality, are potent against clinical isolates of multidrug resistant and biofilm forming Pseudomonas aeruginosa.

Advancements in Doping Strategies for Enhanced Photocatalysts and Adsorbents in Environmental Remediation

Environmental pollution poses a pressing global challenge, demanding innovative solutions for effective pollutant removal. Photocatalysts, particularly titanium dioxide (TiO2), are renowned for their catalytic prowess; however, they often require ultraviolet light for activation. Researchers had turned to doping with metals and non-metals to extend their utility into the visible spectrum. While this approach shows promise, it also presents challenges such as material stability and dopant leaching. Co-doping, involving both metals and non-metals, has emerged as a viable strategy to mitigate these limitations. Inthe fieldof adsorbents, carbon-based materials doped with nitrogen are gaining attention for their improved adsorption capabilities and CO2/N2 selectivity. Nitrogen doping enhances surface area and fosters interactions between acidic CO2 molecules and basic nitrogen functionalities. The optimal combination of an ultramicroporous surface area and specific nitrogen functional groups is key to achievehigh CO2 uptake values and selectivity. The integration of photocatalysis and adsorption processes in doped materials has shown synergistic pollutant removal efficiency. Various synthesis methods, including sol–gel, co-precipitation, and hydrothermal approaches had been employed to create hybrid units of doped photocatalysts and adsorbents. While progress has been made in enhancing the performance of doped materials at the laboratory scale, challenges persist in transitioning these technologies to large-scale industrial applications. Rigorous studies are needed to investigate the impact of doping on material structure and stability, optimize process parameters, and assess performance in real-world industrial reactors. These advancements are promising foraddressing environmental pollution challenges, promoting sustainability, and paving the way for a cleaner and healthier future. This manuscript provides a comprehensive overview of recent developments in doping strategies for photocatalysts and adsorbents, offering insights into the potential of these materials to revolutionize environmental remediation technologies.

Climate and human impact together drive changes in ecosystem multifunctionality in the drylands of China

China's drylands encompass an area of approximately 6.60 × 106 km2 and are home to around 580 million people, providing crucial ecosystem services. The escalating impacts of global climate change are expected to exacerbate aridity, thereby adversely affecting ecosystem services and human well–being. Hence, there is a crucial need to prioritize the study of ecosystem multifunctionality (EMF) in drylands and investigate the underlying factors driving EMF changes. We collected field sampling and indoor analysis data, as well as raster level sampling data to obtain indices related to soil nutrients, vegetation, human footprint index (HFI), soil biodiversity index (SBI), and climate (mean annual temperature [MAT], mean annual precipitation [MAP], potential evapotranspiration [PET]), and soil characteristics (soil sand content [Sand], soil moisture [SM], soil pH). EMF was calculated using the averaging approach, and the cluster–multi–threshold approach. We employed the mantel test, mixed–effects model, random forest algorithm, piecewise structural equation model, and variation partition analysis to explore the significance of factors on EMF changes. The findings revealed significant correlations between EMF and all factors except pH and Sand. All factors collectively accounted for 52.7 %–57.4 % of the variation in mono– (the effect on each of the carbon, nitrogen and phosphorus functions separately) and multifunctionality. The combined effects of all factors had the greatest contribution (8.1 %–16.3 %) variation in EMF. HFI consistently emerged as the most important factor in controlling EMF variation and proved to be the most significant predictor of EMF changes. All factors examined were significant predictors of EMF change. Our study demonstrated that HFI played the most direct influence on EMF changes, surpassing the impact of any single variable. However, the overall contribution of climate (integrating MAP, MAT, and PET) to EMF change was also extremely important. Therefore, future assessments and predictions of ecological functions in drylands should consider not only the direct effects of climate change but also the integrated analysis of human impact.

Nitrogen sites prevail over textural properties in N-doped carbons for the oxygen reduction reaction

Nitrogen-doped carbon-based electrodes are among the most promising alternatives to platinum-based electrodes in the cathode of fuel cells and metal-air batteries, where the oxygen reduction reaction (ORR) takes place. Among the approaches for improving ORR activity, nitrogen functionalities and well-developed textural properties have proved very effective. Nonetheless, the question of which between nitrogen active sites or textural properties are more crucial in N-doped carbon materials remains unanswered. This work proposes a comparative and critical approach through the selective functionalization of four commercial activated carbons with different textural properties. This study highlights the greater importance of N-doping in relation to the textural properties of carbon materials, and provides fundamental insights for conclusively addressing the ongoing debate within the carbon community about the significance of these two factors in the context of ORR.

Toward quantification of active site density and size-dependent ORR activity of ZIF-derived carbons in alkaline electrolyte

ZIF-derived carbons (ZDCs) represent a novel category of non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR). Nevertheless, establishing the correlation between their structure and performance is challenging due to their diverse structural properties and ill-defined active site moieties. Here we investigate the effect of ZIF-67 derived carbon’s particle size and corresponding distribution of assorted nitrogen functionalities on the ORR. Our findings reveal a substantial increase in ORR activity with decreasing ZDC particle size, while the exact influence of nitrogen functionalities remains uncertain. Most importantly, the present work unveils a correlation between the ORR activity and the site density (SD) of Co-Nx within the ZDC materials, which can be attributed to the concurrently increasing SD and accessibility of Co-Nx on the ZDC particles with small sizes. The present work provides novel insights into the optimization of ZDCs as high-performance NPMCs for ORR in alkaline electrolytes.

Upcycling Waste: Citrus limon Peel-Derived Carbon Quantum Dots for Sensitive Detection of Tetracycline in the Nanomolar Range.

In this work, a sustainable method was developed for the production of water-soluble carbon quantum dots employing a green approach. The synthetic protocol was employed using the microwave pyrolysis technique, while lemon peel served as a carbon precursor. Fabrication of highly fluorescent lemon-peel-derived CQDs (LP-CQDs) having inherent nitrogen functionality was validated by X-ray photoelectron spectroscopy, FTIR, X-ray diffraction, Raman spectroscopic analysis, and TEM techniques. The average particle size of fabricated LP-CQDs was 4.46 nm. LP-CQDs yielded a remarkable quantum yield of 49.5%, which displayed excellent salinity, photostability, storage time, conditions, and pH stability. LP-CQDs displayed encouraging results for tetracycline (TC) detection using a PL turn-off approach. The sensitivity of LP-CQDs toward TC was seen in a nanomolar range having a detection limit of 50.4 nM. Method validation was comprehensively studied to ensure the precision of the nanosensor. A complete analysis of different photophysical parameters of LP-CQDs was performed with TC to gain a deeper understanding of the sensing mechanism. Fabricated LP-CQDs showed fluorescence quenching toward TC, elucidated by the inner filter effect (IFE) mechanism. The synthesized nanoprobe demonstrated a lesser detection limit with a broad linear range, enabling facile, cheap, environmentally friendly, and fast detection of TC. Practicality of the detection method was assessed through analysis of real samples, resulting in satisfactory recovery percentage and relative standard deviation with respect to the developed probes. Furthermore, LP-CQDs were used as fluorescent inks and to fabricate paper-based fluorescent strips. This study lays the door for the sensing platform of LP-CQDs toward detection of TC, which may impact the potential role of environmental sustainability.

Weighting the role of specific nitrogen and oxygen functionalities on porous carbons in formaldehyde removal: Combining surface chemistry analysis and factorial dimensionally reduction method

Two activated carbons (phosphoric acid activated, CG, and steam activated, SX) of marked differences in porosity and surface chemistry were modified by an introduction of oxygen, nitrogen or both heteroatoms and used as formaldehyde removal media at room temperature. Sorption of nitrogen, XPS, FTIR, thermal analysis and potentiometric titration were used to characterize the samples’ porosity and chemistry. Heating at 450, 600 and 950 °C affected the content and speciation of groups on the surface and led to complex porosity alterations. CG was more susceptible to changes in porosity and its surface accepted twice more nitrogen than that of SX. Pyridines and pyrroles were in majority, regardless the treatment. When in a high density in supermicropores and mesopores, they were found responsible for an increased surface activity for HCHO removal due to specific interactions. It increased up to an order of magnitude adding to the complex role of ultramicropores, and thus markedly enhanced the effective utilization of the carbon surface. CG, with more nitrogen overperformed the SX series. Even though pyridines and pyrroles were found active, the results suggested that quaternary nitrogen is an important specific center for HCHO adsorption and this finding was supported by a factorial dimensionally reduction method.

Enzymatic Oxy- and Amino-Functionalization in Biocatalytic Cascade Synthesis: Recent Advances and Future Perspectives.

Biocatalytic cascades are a powerful tool for building complex molecules containing oxygen and nitrogen functionalities. Moreover, the combination of multiple enzymes in one pot offers the possibility to minimize downstream processing and waste production. In this review, we illustrate various recent efforts in the development of multi-step syntheses involving C-O and C-N bond-forming enzymes to produce high value-added compounds, such as pharmaceuticals and polymer precursors. Both in vitro and in vivo examples are discussed, revealing the respective advantages and drawbacks. The use of engineered enzymes to boost the cascades outcome is also addressed and current co-substrate and cofactor recycling strategies are presented, highlighting the importance of atom economy. Finally, tools to overcome current challenges for multi-enzymatic oxy- and amino-functionalization reactions are discussed, including flow systems with immobilized biocatalysts and cascades in confined nanomaterials.

Enzymatic Oxy‐ and Amino‐Functionalization in Biocatalytic Cascade Synthesis: Recent Advances and Future Perspectives

AbstractBiocatalytic cascades are a powerful tool for building complex molecules containing oxygen and nitrogen functionalities. Moreover, the combination of multiple enzymes in one pot offers the possibility to minimize downstream processing and waste production. In this review, we illustrate various recent efforts in the development of multi‐step syntheses involving C−O and C−N bond‐forming enzymes to produce high value‐added compounds, such as pharmaceuticals and polymer precursors. Both in vitro and in vivo examples are discussed, revealing the respective advantages and drawbacks. The use of engineered enzymes to boost the cascades outcome is also addressed and current co‐substrate and cofactor recycling strategies are presented, highlighting the importance of atom economy. Finally, tools to overcome current challenges for multi‐enzymatic oxy‐ and amino‐functionalization reactions are discussed, including flow systems with immobilized biocatalysts and cascades in confined nanomaterials.

Porous Carbons Prepared from Polyacrylonitrile Doped with Graphitic Carbon Nitride or Melamine for Supercapacitor Applications

AbstractMelamine and graphitic carbon nitride (g‐C3N4) obtained by thermal condensation of melamine were doped in polyacrylonitrile (PAN) films. Nitrogen‐doped porous carbons were then prepared by pyrolysis of the composite films. Though all the porous carbons had a high nitrogen content of at least 10 %, g‐C3N4 was more efficient than melamine in nitrogen doping. The nitrogen content was elevated with the increase of the amount of each dopant, the highest value of 19.0 % was achieved by g‐3 (porous carbon obtained from the PAN/g‐C3N4 composite film with a mass ratio of 3). Amongst the nitrogen functionalities, pyridinic‐N and pyrrolic‐N held a percentage of at least 80 %. Compared with the carbon materials obtained from melamine doped PAN films, those from g‐C3N4 doped ones exhibited larger surface area and average pore size, and higher pore volume. The difference mainly resulted from the thermostability and size of the dopants. The g‐C3N4 doped materials thus presented more excellent electrochemical properties. The specific capacitance of g‐3 electrode was 135.3 F/g at a current density of 0.5 A/g. Rather than melamine, g‐C3N4 could improve the chemical composition and textural properties of the carbon materials, thus enhancing their supercapacitor performance.

Co3O4 nanoparticles-embedded nitrogen-doped porous carbon spheres for high-energy hybrid supercapacitor electrodes

This work synthesizes cobalt oxide (Co3O4)-embedded nitrogen-doped porous carbon spheres (Co3O4@NPCS) with inherent hierarchical structures through hydrothermal and pyrolysis processes. The synthesized material shows porous spherical carbon with nitrogen functionalities and contains Co3O4 nanoparticles on the surface of the carbon framework. The hybrid supercapacitor (HSC) is fabricated by Co3O4@NPCS and NPCS as anode and cathode, respectively, using aqueous KOH as electrolyte. The HSC displays exceptional electrochemical performance over the wide voltage window of 1.5 V with a large capacitance of 464 F g−1 at 1 A g−1, a high energy of 98.5 Wh kg−1, and power of 1500 W kg−1. Long charge-discharge cyclic stability demonstrates 87.2 % capacitance retention of the HSC over 10,000 cycles with almost 100 % coulombic efficiency. Additionally, first principles investigations show that the improved hybrid supercapacitors performance is as a consequence of the increased conductivity and the charge transfer. The proposed electrode and hybrid design show a potential for future high-energy storage.

ZIF-67 derived Co nanoparticles on ZIF-Derived carbon for hydrogen spillover and storage

Hydrogen spillover involves the dissociation of H2 on transition metal nanoparticles and further atomic hydrogen surface migration on catalyst supports. Hence, the spillover phenomenon has been reported in applications of heterogeneous catalysis in hydrogenation and room-temperature hydrogen storage. However, a proper catalyst design is requisite to initiate hydrogen spillover, considering the transition metal particle dispersion, sorbent surface modification, porosity, etc. In this report, we pyrolyzed the zeolitic imidazolate framework ZIF-67 for residual Co metal nanoparticles and N-dopant on ZIF-derived carbon (ZDC) for hydrogen adsorption via spillover effect. Catalyst optimization by proper ZIF carbonization process regarding manipulated pyrolytic temperatures, atmospheres, and ramping rates, results in different properties in ZDCs. Well-distributed Co nanoparticles can be obtained on N-rich graphitic sorbent ZDCs with retained high specific surface area. The Co on ZDC exhibits improved room-temperature hydrogen capacity of 0.77 wt% than neat ZIF-67 of 0.09 wt% at 30 bar, 300 K. The adsorption sites were examined experimentally by nitrogen hydrogenation, and possible atomic hydrogen diffusion was evaluated theoretically showing energy barrier reduced by over 0.1 eV. It demonstrates that cobalt nanoparticles can successfully initiate hydrogen spillover on ZIF-derived carbon with nitrogen functionality, even without noble metals.

Synthesis of chitosan based reduced graphene oxide-CeO2 nanocomposites for drug delivery and antibacterial applications

In this study, the unique characteristics of chitosan, reduced graphene oxide (rGO) and cerium oxide (CeO2) based hybrid bionano-composites make a carrier for various drug delivery and antimicrobial applications. The recent literatures shown that addition of biopolymers to rGO and CeO2 based nanocomposites exhibit excellent performance in design and development of biosensors, wound dressings, electrodes, microfluidic chips, drug delivery systems and energy storage applications. Chitosan (CS), reduced graphene oxide (rGO) mixed with cerium oxide (CeO2) to form CS-rGO and CS-rGO-CeO2 hybrid bionano-composites using precipitation method. The physiochemical characterization of casted nanocomposite sheet was done using FTIR, XRD, UV–Vis spectrum, SEM and TGA. The XRD results of CS-rGO-CeO2 revealed that the nanoparticle was found to be crystalline structure. FTIR revealed that nitrogen functionalities of CS interacted with rGO-CeO2 to form hybrid nanocomposites. The thermal gravimetric analysis (TGA) showed that the CS-rGO-CeO2 has better thermal stability up to 550 °C. The SEM confirms the surface morphology of CS-rGO-CeO2 has large surface area with smooth surface. Moreover, the antibacterial properties of nanocomposites exhibit excellent zone of inhibition against Staphylococcus aureus and Escherichia coli. The NIH3T3 cell line evaluations showed superior cell adhesion on hybrid nanocomposites. Hence bionano-composite based on CS, rGO and CeO2 are potential biomaterials for drug delivery and antibacterial applications.

Phosphorus-mediated succession of microbial nitrogen, carbon, and sulfur functions in rice-driven saline-alkali soil remediation

Although rice cultivation holds potential for restoring unproductive saline-alkali soils and increasing food production, the mechanisms underlying the relationship between microbial functions and soil element turnover remain unclear. To clarify this relationship, this study investigated the soil physicochemical properties and microbial functions during remediation in saline-alkali soil by rice cultivation over 2, 4, 6, 8, 11, 12, 20, and 23 years. The results indicated rice cultivation markedly improved soil nutrients, soil nutrient stoichiometry, and soil aggregate stability. Additionally, rice cultivation significantly increased the microbial functions involved in nutrient cycling, such as nitrogen fixation, carbon fixation, methanogenesis, dissimilatory sulfate reduction, and thiosulfate oxidation. However, these nitrogen (N), carbon (C), and sulfur (S) cycle-related functions exhibited a similar “increase-peak-decrease” successional pattern with the years of remediation, reaching optimal levels when rice was continuously grown for 11–16 years. Furthermore, correlation analysis demonstrated that the succession of soil microbial N, C, and S functions during saline-alkali soil restoration closely related to changes in soil properties, particularly the availability of phosphorus (P). Therefore, we propose to prioritize the management of P during saline-alkali soil remediation. In conclusion, this study provides a comprehensive understanding of the microbial N, C, and S functions and soil P in the remediation of saline-alkali soils mediated by rice crop.

Continuous Production of Functionalized Graphene Inks by Soft Solution Processing.

The continuous production of high-quality, few-layer graphene nanosheets (GNSs) functionalized with nitrogen-containing groups was achieved via a two-stage reaction method. The initial stage produces few-layer GNSs by utilizing our recently developed glycine-bisulfate ionic complex-assisted electrochemical exfoliation of graphite. The second stage, developed here, uses a radical initiator and nitrogen precursor (azobisisobutyronitrile) under microwave conditions in an aqueous solution for the efficient nitrogen functionalization of the initially formed GNSs. These nitrile radical reactions have great advantages in green chemistry and soft processing. Raman spectra confirm the insertion of nitrogen functional groups into nitrogen-functionalized graphene (N-FG), whose disorder is higher than that of GNSs. X-ray photoelectron spectra confirm the insertion of edge/surface nitrogen functional groups. The insertion of nitrogen functional groups is further confirmed by the enhanced dispersibility of N-FG in dimethyl formamide, ethylene glycol, acetonitrile, and water. Indeed, after the synthesis of N-FG in solution, it is possible to disperse N-FG in these liquid dispersants just by a simple washing-centrifugation separation-dispersion sequence. Therefore, without any drying, milling, and redispersion into liquid again, we can produce N-FG ink with only solution processing. Thus, the present work demonstrates the 'continuous solution processing' of N-FG inks without complicated post-processing conditions. Furthermore, the formation mechanism of N-FG is presented.

A preparative small-molecule mimic of liver CYP450 enzymes in the aliphatic C–H oxidation of carbocyclic N-heterocycles

An emerging trend in small-molecule pharmaceuticals, generally composed of nitrogen heterocycles (N-heterocycles), is the incorporation of aliphatic fragments. Derivatization of the aliphatic fragments to improve drug properties or identify metabolites often requires lengthy de novo syntheses. Cytochrome P450 (CYP450) enzymes are capable of direct site- and chemo-selective oxidation of a broad range of substrates but are not preparative. A chemoinformatic analysis underscored limited structural diversity of N-heterocyclic substrates oxidized using chemical methods relative to pharmaceutical chemical space. Here, we describe a preparative chemical method for direct aliphatic oxidation that tolerates a wide range of nitrogen functionality (chemoselective) and matches the site of oxidation (site-selective) of liver CYP450 enzymes. Commercial small-molecule catalyst Mn(CF3-PDP) selectively effects direct methylene oxidation in compounds bearing 25 distinct heterocycles including 14 out of 27 of the most frequent N-heterocycles found in U.S. Food and Drug Administration (FDA)-approved drugs. Mn(CF3-PDP) oxidations of carbocyclic bioisostere drug candidates (for example, HCV NS5B and COX-2 inhibitors including valdecoxib and celecoxib derivatives) and precursors of antipsychotic drugs blonanserin, buspirone, and tiospirone and the fungicide penconazole are demonstrated to match the major site of aliphatic metabolism obtained with liver microsomes. Oxidations are demonstrated at low Mn(CF3-PDP) loadings (2.5 to 5 mol%) on gram scales of substrate to furnish preparative amounts of oxidized products. A chemoinformatic analysis supports that Mn(CF3-PDP) significantly expands the pharmaceutical chemical space accessible to small-molecule C-H oxidation catalysis.

Nitrogen functionalities in mesoporous carbons and their impact on the sulfur infiltration efficiency and in the electrochemical performance of Li[sbnd]S cells

The cyclability of LiS batteries depends strongly on electrochemical cell stability, which is affected by the dilution of lithium polysulfides in the electrolyte. One of the proposed solutions is the use of porous carbonaceous materials in the cathode that trap lithium polysulfide species and prevent them from reaching the electrolyte. This is possible by using dopant heteroatoms in the carbon framework such as nitrogen to generate anchoring sites reducing the shuttle effect. To understand how the sulfur infiltration process in carbonaceous materials is affected by the inclusion of nitrogen in the carbon structure and its effect on the electrochemical performance of LiS batteries, in this study N-doped mesoporous carbons were prepared by varying the carbonization temperature, focusing on the structural and compositional variations. At the highest carbonization temperature (850 °C), a carbonaceous material with the lowest nitrogen content was obtained mainly prevailing the N-quaternary functionality over N-pyrrolic and N-pyridinic. The sulfur infiltration into the pores of the material was improved due to the moderate polarity obtained under the carbonization temperature used (850 °C). Given the distribution of nitrogen functionalities, it was possible to obtain a material with a high degree of graphitization reflected in the electrochemical performance where after 100 cycles a discharge capacity of 422.3 mA h g−1 was reached with a Coulombic efficiency of 99%.