Bridging Nitrogen Research Articles

Molten-salt synthesis of highly condensed and nitrogen-tunable carbon nitride materials for metal-free and efficient synthesis of dimethyl carbonate

Dimethyl carbonate (DMC) is a building block in the modern chemical industry, and the transesterification of ethylene carbonate (EC) with methanol is a more sustainable strategy for the synthesis of DMC. Wherein, the design of metal-free and high-activity catalysts that can be easily prepared is a crucial research topic for clean synthesis of DMC. In this work, C3N4-T materials with non-metal components, high degrees of polycondensation, and adjustable distributions of nitrogen-containing species were successfully prepared by a facile molten-salt approach. Compared with g-C3N4 prepared by the traditional thermal polycondensation method, C3N4-T materials own larger specific surface areas and a higher degree of intralayer condensation. By simply adjusting the calcination temperatures, the fractions of bridging nitrogen species can be tuned, resulting in an improvement in alkaline strength. For the transesterification reaction of EC with methanol, the C3N4-500 materials demonstrated much higher activity than g-C3N4. Under a lower reaction temperature (100 °C) and a shorter reaction time (3 h), the maximum conversion of EC was 79.9 %. According to the characterization results of XPS and Hammett titration, the correlation between the catalytic activity of various C3N4-T materials and the alkaline properties was deliberated.

A new conjugated tripoid N4 system containing furazan and triazolofurazan cores linked by a nitrogen bridge

Two thermostable representatives of methyl-substituted triazolofurazan derivatives with zwitterionic N+N– bonds were obtained via the thermal cyclization of N,N’-bis(azidofurazanyl)-N-methyltriazene. 5-(N-Azidofurazanyl-N-methylamino)triazolofurazan was the product of known intramolecular reaction of neighboring azido and azo groups. Its isomer with methyl group in the triazolofurazan core was formed in the course of new cyclization of azido and triazene groups representing an original NN bond formation reaction giving an unusual zwitterionic heterocyclic system.

Exploring mechanistic preferences and influencing factors in acceptorless dehydrogenation reactions catalyzed by an Ir(iii)-dipyridylamine complex: A DFT study

Acceptorless dehydrogenation reactions play a pivotal role in homogeneous catalysis, with extensive applications in organic synthesis and industrial processes. Metal-ligand cooperative catalysis is crucial for enhancing reaction efficiency and selectivity. However, understanding its mechanistic pathways and identifying factors influencing catalytic performance remain challenging. In this study, density functional theory (DFT) is employed to elucidate the mechanistic selectivity of Ir(III)-bis(pyridyl)amine complexes in acceptorless dehydrogenation reactions. We specifically investigate the selectivity between pyridine nitrogen and bridging nitrogen as proton acceptor sites during the dehydrogenation process. The results indicate that the pyridine nitrogen site is preferentially chosen as the proton acceptor due to its stronger basicity and lower deformation energy. Additionally, theoretical investigations of catalytic activity across different metals in the same group reveal that early transition metals significantly influence the basicity of the pyridine nitrogen, thereby affecting catalytic activity. Our findings elucidate the unique mechanistic selectivity of bis(pyridyl)amine-based catalysts and identify critical factors influencing this selectivity, providing essential theoretical guidance for the design of more efficient catalysts in future research.

1,4-diaminophthalazine complexes of Re(CO)3

1,3-Diiminoisoindolines and substituted variants react with hydrazine to produce 1,4-diaminophthalazines. In this paper, we present the chemistry of 1,4-diaminophthalazine and two modified versions with the Re(CO)3 unit. The 1,4-diaminophthalazine ligand forms a bimetallic complex similar to that seen with unmodified phthalazine. In contrast, the semihemiporphyrazine-derived chelating ligands bind Re(CO)3 as neutral bidentate compounds; the freebase pyrazole and indazole modified 1,4-diaminophthalazines exhibit multiple tautomerization states with ionizable protons. Notably, protonation of the meso bridging nitrogen atom reduces the degree of conjugation between the two halves of the chelate, resulting in a diimine-like complex that lacks significant absorption in the visible spectrum due to the abrogation of the low energy metal to ligand charge transfer (MLCT) transition.

Structural Distortion of g-C3N4 Induced by a Schiff Base Reaction for Efficient Photocatalytic H2 Evolution.

Photocatalytic H2 evolution by water splitting is a promising approach to address the challenges of environmental pollution and energy scarcity. Graphitic carbon nitride (g-C3N4) has emerged as a star photocatalyst because of its numerous advantages. To address the limitations of traditional g-C3N4, namely its inadequate visible light response and rapid recombination of photogenerated carriers, we employed a schiff base reaction to synthesize -C=N- doped g-C3N4. The introduction of -C=N- groups at the bridging nitrogen sites induced structural distortion in g-C3N4, facilitating n-π* electronic transitions from the lone pair electrons of nitrogen atom and extending light absorption up to 600 nm. Moreover, the presence of heterogeneous π-conjugated electron distribution effectively traps photogenerated electrons and enhances charge carrier separation. Benefiting from its expanded spectral response range, unique electronic properties, increased specific surface area, the doped g-C3N4 exhibited outstanding photocatalytic H2 evolution performance of 1050.13 μmol/g/h. The value was 5.9 times greater than the pristine g-C3N4.

Triphenylamine[3]arenes: Streamlining Synthesis of a Versatile Macrocyclic Platform for Supramolecular Architectures and Functionalities.

Triphenylamine[3]arenes (TPA[3]s), featuring [16]paracyclophane backbone with alternating carbon and nitrogen bridging atoms, were synthesized through a BF3 ⋅ Et2O-catalyzed cyclization reaction using triphenylamine derivatized monomers and paraformaldehyde. This molecular design yielded a series of TPA[3] macrocycles with high efficiency, with their facile derivatizations also successfully demonstrated. On account of the strong electron-donating properties of the TPA moieties, these TPA[3]s exhibit remarkable delayed fluorescence, and possess a significant affinity for iodine. Furthermore, their inherent three-fold symmetry rendered TPA[3]s as novel building blocks for the construction of extended frameworks and molecular cages. This advancement expands the versatility of discrete macrocycles into complex architectures, enhancing their applicability across a broad spectrum of applications.

Triphenylamine[3]arenes: Streamlining Synthesis of a Versatile Macrocyclic Platform for Supramolecular Architectures and Functionalities

AbstractTriphenylamine[3]arenes (TPA[3]s), featuring [16]paracyclophane backbone with alternating carbon and nitrogen bridging atoms, were synthesized through a BF3 ⋅ Et2O‐catalyzed cyclization reaction using triphenylamine derivatized monomers and paraformaldehyde. This molecular design yielded a series of TPA[3] macrocycles with high efficiency, with their facile derivatizations also successfully demonstrated. On account of the strong electron‐donating properties of the TPA moieties, these TPA[3]s exhibit remarkable delayed fluorescence, and possess a significant affinity for iodine. Furthermore, their inherent three‐fold symmetry rendered TPA[3]s as novel building blocks for the construction of extended frameworks and molecular cages. This advancement expands the versatility of discrete macrocycles into complex architectures, enhancing their applicability across a broad spectrum of applications.

Solid-State Emissive Pillar[6]arene Derivative Having Alternate Methylene and Nitrogen Bridges.

Macrocyclic arenes show conformational adaptability, which allows host-guest complexations with the size-matched guest molecules. However, their emission properties are often poor in the solid states due to the self-absorption. Herein, we newly synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridging structures. Solvatochromic study reveals that the nitrogen-embedding into the cyclic structures can strengthen the intramolecular charge transfer (CT) nature compared to that of the linear nitrogen-bridged precursor. Owing to the large Stokes shift in the solid state, one of the nitrogen-embedded pillar[6]arenes shows high absolute photoluminescence quantum yield (ΦPL=0.36). Furthermore, it displays a turn-off sensing ability toward nitrobenzene (NB) vapor; a fluorescence quenching is observed when exposed to the NB vapor. From the structural analysis before and after the exposure of NB vapor, the amorphous nitrogen-embedded pillar[6]arene efficiently co-crystallize with NB and formed non-emissive intermolecular CT complexes with NB.

A Neutral Pyridine-Pyrazole-Based N^N*N^N Ligand as a Tetradentate Chromophore for Diverse Transition Metal Cations

Herein, the synthesis and the structural as well as the photophysical characterization of five transition metal complexes bearing a neutral pyridine-pyrazole-based N^N*N^N ligand (L) acting as a tetradentate chelator are reported. The luminophore can be synthesized via two different pathways. An alkyl chain with a terminal tert-butyl moiety was inserted on the bridging nitrogen atom to enhance the solubility of the complexes in organic solvents. Due to the neutral character of L, metal ions with different charges and electronic configurations can be chelated. Thus, complexes with Pt(II) (C1), Ag(I) (C2), Zn(II) (C3), Co(II) (C4) and Fe(II) (C5) were synthesized. Single-crystal X-ray diffraction experiments showed that complex C2 exhibits a completely different structure in the crystalline state if compared with C3 and C5, i.e., depending on the chelated cation. The UV-vis absorption and the NMR spectra showed that the complexes dissociate in liquid solutions, except for the Pt(II)-based coordination compound. Therefore, the photophysical properties of the complexes and of the ligand were studied in the solid state. For the Pt(II)-based species, a characteristic metal-perturbed ligand-centered phosphorescence was traceable, both in dilute solutions as well as in the solid state.

Role of n-DAMO in Mitigating Methane Emissions from Intertidal Wetlands Is Regulated by Saltmarsh Vegetations.

Coastal wetlands are hotspots for methane (CH4) production, reducing their potential for global warming mitigation. Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays a crucial role in bridging carbon and nitrogen cycles, contributing significantly to CH4 consumption. However, the role of n-DAMO in reducing CH4 emissions in coastal wetlands is poorly understood. Here, the ecological functions of the n-DAMO process in different saltmarsh vegetation habitats as well as bare mudflats were quantified, and the underlying microbial mechanisms were explored. Results showed that n-DAMO rates were significantly higher in vegetated habitats (Scirpus mariqueter and Spartina alterniflora) than those in bare mudflats (P < 0.05), leading to an enhanced contribution to CH4 consumption. Compared with other habitats, the contribution of n-DAMO to the total anaerobic CH4 oxidation was significantly lower in the Phragmites australis wetland (15.0%), where the anaerobic CH4 oxidation was primarily driven by ferric iron (Fe3+). Genetic and statistical analyses suggested that the different roles of n-DAMO in various saltmarsh wetlands may be related to divergent n-DAMO microbial communities as well as environmental parameters such as sediment pH and total organic carbon. This study provides an important scientific basis for a more accurate estimation of the role of coastal wetlands in mitigating climate change.

Chae-type cytochalasans from coculture of Aspergillus flavipes and Chaetomium globosum

Cocultivation of the high cytochalasan-producing fungi Aspergillus flavipes and Chaetomium globosum resulted in the isolation of 11 undescribed Chae-type cytochalasans. Their structures were determined by spectroscopic data and NMR data calculations. Asperchaetoglobin A (1) was the first Chae-type cytochalasan possessing an unprecedented nitrogen bridge between C-17 and C-20 to generate a surprising 5/6/12/5 multiple ring system; asperchaetoglobins B and C (2 and 3) displayed higher oxidation with an additional epoxide at the thirteen-member ring; asperchaetoglobin D (4) was the second Chae-type cytochalasin featuring a 5/6/12 tricyclic ring system. The cytotoxic activities against five human cancer cell lines and antibacterial activities against Staphylococcus aureus and Colon bacillus of selected compounds were evaluated in vitro.

N-doped CoO-anchored ultrafine Pt nanoparticles for acidic hydrogen evolution reaction.

An efficient hydrogen evolution reaction catalyst of ultrafine Pt nanoparticles loaded onto N-doped CoO was synthesized. This catalyst displayed high electrocatalytic activity and stability. The outstanding performance is attributed to the interactions between the active sites and support, as well as the regulation of the electronic structure through covalent nitrogen bridging.

Unveiling Amaryllidaceae alkaloids: from biosynthesis to antiviral potential - a review.

Covering: 2017 to 2023 (now)Amaryllidaceae alkaloids (AAs) are a unique class of specialized metabolites containing heterocyclic nitrogen bridging that play a distinct role in higher plants. Irrespective of their diverse structures, most AAs are biosynthesized via intramolecular oxidative coupling. The complex organization of biosynthetic pathways is constantly enlightened by new insights owing to the advancement of natural product chemistry, synthetic organic chemistry, biochemistry, systems and synthetic biology tools and applications. These promote novel compound identification, trace-level metabolite quantification, synthesis, and characterization of enzymes engaged in AA catalysis, enabling the recognition of biosynthetic pathways. A complete understanding of the pathway benefits biotechnological applications in the long run. This review emphasizes the structural diversity of the AA specialized metabolites involved in biogenesis although the process is not entirely defined yet. Moreover, this work underscores the pivotal role of synthetic and enantioselective studies in justifying biosynthetic conclusions. Their prospective candidacy as lead constituents for antiviral drug discovery has also been established. However, a complete understanding of the pathway requires further interdisciplinary efforts in which antiviral studies address the structure-activity relationship. This review presents current knowledge on the topic.

NIR-absorbing and emitting α,α-nitrogen-bridged BODIPY dimers with strong excitonic coupling.

Three new distinct NIR α,α-NH-bridged BODIPY dimers were prepared by a direct nucleophilic substitution reaction. The synergistic effects of the nitrogen bridges and strong excitonic coupling between each BODIPY unit play major roles in enhancing the delocalization of an electron spin over the entire BODIPY dimers. The in situ formed aminyl radical dimer showed an absorption maximum at 1040 nm.

Characterization of thermal decomposition mechanism and combustion performance of 4,4’‐azobis(1,2,4‐triazole)**

Abstract4,4’‐azobis(1,2,4‐triazole) (ATRZ), as a representative of high‐nitrogen compound, has attracted extensive interests. This work explores the thermal decomposition mechanism and combustion performance of ATRZ. The thermogravimetry‐differential scanning calorimetry‐fourier transform infrared spectroscopy (TG‐DSC‐FTIR) of ATRZ was carried out at heating rate of 10 °C/min in an argon atmosphere. ATRZ has two peak exothermic temperatures, 110.24 °C and 306.85 °C respectively. The exothermic peak at 110.24 °C is the decomposition of ATRZ tiny debris, and the exothermic peak at 306.85 °C is the decomposition of the main part of ATRZ. The pyrolysis‐gas chromatography mass spectrometry (PY‐GC/MS) of ATRZ was carried out at 350 °C in an argon atmosphere. By combining TG‐DSC‐FTIR and PY‐GC/MS, the thermal decomposition mechanism of ATRZ was speculated. The main reaction in the ATRZ pyrolysis process is the cleavage of two N−N single bonds in the nitrogen bridge, forming a nitrogen molecule and two triazole rings, which is the majority of the first step decomposition reaction. At the same time, a small number of triazole rings break off to form other intermediates. A small amount of nitrogen gas is generated and a large number of CN clusters are formed. Under the same testing conditions, ATRZ has a higher combustion heat (19318 J/g) than other traditional CHNO energetic materials. By comparing the laser ignition combustion of ATRZ and ATRZ+RDX, the combustion temperature of ATRZ+RDX is higher and the combustion duration is longer. The introduction of CHNO type ammonium nitrate explosives promotes the energy release of ATRZ.

Molten salt Cu(I) intercalation into the poly(triazine imide) for the electrochemical sensing of nitrite

AbstractSlight modification of the molten salt synthesis of poly(triazine imide) (PTI) with introduction of copper (I) chloride yielded a novel copper modified material. Energy‐dispersive x‐ray spectroscopy together with electron microscopy confirmed homogenous distribution of the copper within PTI lattice. X‐ray photoelectron spectroscopy suggests the copper to coordinate randomly at bridging nitrogen atoms. Thus obtained material exhibited excellent sensitivity to nitrite anions together with low limits of detection. Under previously optimized experimental conditions and pH 4 of supporting electrolyte, differential pulse voltammetric detection method showed linear response in wide range from 5 to 2200 μM with detection limit of 1.3 μM. Practical applicability for the developed method was scrutinized in wastewater and pipe water samples. Developed method of metal ion intercalation open doors to widespread introduction of metal ions in the PTI structure for practical utilization.

The Interaction of Amines with Gold Nanoparticles.

Understanding the interactions between amines and the surface of gold nanoparticles is important because of their role in the stabilization of the nanosystems, in the formation of the protein corona, and in the preparation of semisynthetic nanozymes. By using fluorescence spectroscopy, electrochemistry, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and molecular simulation,a detailed picture of these interactions is obtained. Herein, it is shown that amines interact with surface Au(0) atoms of the nanoparticles with their lone electron pair with a strength linearly correlating with their basicity corrected for steric hindrance. The kinetics of binding depends on the position of the gold atoms (flat surfaces or edges) while the mode of binding involves a single Au(0) with nitrogen sitting on top of it. A small fraction of surface Au(I) atoms, still present, is reduced by the amines yielding a much stronger Au(0)-RN.+ (RN. , after the loss of a proton) interaction. In this case, the mode of binding involves two Au(0) atoms with a bridging nitrogen placed between them. Stable Au nanoparticles, as those required for robust semisynthetic nanozymes preparation, are better obtained when the protein is involved (at least in part) in the reduction of the gold ions.

Co-modification of carbon and cyano defect in g-C3N4 for enhanced photocatalytic peroxymonosulfate activation: Combined experimental and theoretical analysis

Carbon substitution of nitrogen is considered as a non-toxic and stable way to improve the availability of π electrons in g-C3N4. In this paper, a simple one-step calcination method was adopted to prepare carbon and cyano co-doped g-C3N4 (C-CND), photocatalytic experiments, characterization and excited state calculations showed that carbon substitution of bridging nitrogen greatly improved the π-conjugated system and synergistically modulated the electronic structure of g-C3N4 with cyano, enhancing the photocatalytic activation towards peroxymonosulfate (PMS) by C-CND. Both radicals and non-radicals play an essential role in the C-CND/PMS/Vis system, where 1O2 dominates, and the activation mechanism is analyzed by combining the adsorption calculations between PMS and C-CND in different electrostatic potential regions. The results provide a valuable reference for the efficient photocatalytic activation of PMS by carbon self-doped g-C3N4.

Biochar doped carbon nitride to enhance the photocatalytic hydrogen evolution through synergy of nitrogen vacancies and bridging carbon structure: Nanoarchitectonics and first-principles calculation

Enhancing the separation and transfer of photogenerated carries is vital for improving the efficiency of photocatalytic hydrogen evolution reaction (HER) of graphitic carbon nitride (g-C3N4). Herein, a carbon-rich g-C3N4 with nitrogen vacancies (CCN4) was constructed by incorporating the biochar into g-C3N4 during a thermal polymerization in N2 atmosphere. The doped carbon atoms replaced the bridged nitrogen and increased the delocalization π states. The synergy of the enhanced π states and nitrogen vacancy favored narrowing the bandgap and accelerating the charge separation and migration in catalyst. Meanwhile, the CCN4 catalyst had favorable kinetics for HER, with simpler steps and a lower energy barrier than the PCN sample, in which H2 production from *H is prior to OH generation. The CCN4 catalyst exhibited excellent HER activity with a hydrogen evolution rate of 3342.4 μmol∙g−1∙h−1 with 0.5 wt% cocatalyst Pt, which was 5.1 times higher than that of pristine g-C3N4 (PCN). Additionally, CCN4 exhibited good resistance to salt with the concentration near that of natural seawater, showing the further improved hydrogen evolution rate of 3808.8 μmol∙g−1∙h−1. The findings reported in this work shed light on a biochar-tailored protocol to control the defects of g-C3N4 and optimize its intrinsic electronic properties and photocatalytic HER.

Probing the Role of the Bridging Nitrogen in the Signaling Mechanism of an Anthracene–Boronic Acid Sugar Sensor and a Different Version of the PET-Based Mechanism

The N-quaternized derivative 5 of the James-Shinkai anthracene-boronic acid fluorescence sugar sensor 1 was prepared to probe the role of the bridging nitrogen in the signaling mechanism of 1. Both 5 and 1 contain positively charged bridging groups NMe+ or NH+, respectively, but 5 lacks the ability to form the intramolecular ammonium-boronate doubly ionic hydrogen bond present in 1. Receptors 1 and 5 display opposite fluorescence vs pH profiles with a small turn-on effect of the sugar binding to the zwitterion of 5 in contrast to a large effect observed with 1. It is concluded that the ammonium-boronate hydrogen bond is essential for the signaling mechanism of 1. Its possible function is enabling the PET quenching effect by shifting the NH+ proton toward boronate anion inside the hydrogen bond, the degree of which is modulated by the ester formation with diols affecting the basicity of boronate anion. This mechanism agrees with observed signaling selectivity of 1 toward a series of di- and polyols of variable structures as well as with the behavior of 1 in buffered D2O and methanol solvents at controlled pH and provides an addition to the established "loose bolt" mechanism signaling mode essential for receptors with nonpolar fluorophores.