Atomic Nitrogen Source Research Articles

Direct Access to Quinazolines and Pyrimidines from Unprotected Indoles and Pyrroles through Nitrogen Atom Insertion.

Recent advances in single-atom insertion reactions have opened up new synthetic approaches for molecular diversification. Developing innovative strategies to directly transform biologically relevant molecules, without any prefunctionalization, is key to further expanding the scope and utility of such transformations. Herein, the direct access to quinazolines and pyrimidines from the corresponding unprotected 1H-indoles and 1H-pyrroles is reported, relying on the implementation of lithium bis(trimethylsilyl)amide (LiHMDS) as a novel nitrogen atom source in combination with commercially available hypervalent iodine reagents. Further application of this strategy in late-stage settings demonstrates its potential in lead structure diversification campaigns.

On the Energy-specific Photodissociation Pathways of 14N2 and 14N15N Isotopomers to N Atoms of Different Reactivity: A Quantum Dynamical Perspective

Photodissociation of the nitrogen molecule in the vacuum ultraviolet (VUV) is a major source of reactive nitrogen atoms in the upper atmosphere of Earth and throughout the solar system. Recent experimental studies have revealed strong energy dependence of the VUV photodissociation branching ratios to the N(4S3/2)+N(2D J ) and N(4S3/2)+N(2P J ) product channels, the primary dissociation pathways in the 108,000–116,000 cm−1 energy region. This produces N(2D J ) and N(2P J ) excited atoms that differ significantly in their chemical reactivity. The branching ratios oscillate with increase in the VUV excitation energy. We use high-level ab initio quantum chemistry to compute the potential curves of 17 electronic excited states and their nonadiabatic and spin–orbit couplings. The dynamics follow the sequential evolution from the optically excited but bound singlets. Spin–orbit coupling enables transfer to the dissociative triplet and quintet states. We compute the photodissociation yields through the dense manifold of electronic states leading to both exit channels. The dynamical simulations accurately capture the branching oscillations and enable a detailed look into the photodissociation mechanism. The major contribution to the dissociation is through the two lowest 3Π u states. However, for both isotopomers, at about 110,000 cm−1 there is an abnormally low dissociation rate into the N(4S3/2)+N(2P J ) channel that enables comparable participation of triplet and quintet 5Π u electronic states. This leads to the first peak in the branching ratio. At higher energies, trapping of the population in the 33Π u bound triplet state occurs. This favors dissociation to the lower-energy N(4S3/2)+N(2D J ) channel and results in the observed second switch in branching ratios.

Pathways of N2O production by marine ammonia-oxidizing archaea determined from dual-isotope labeling

The ocean is a net source of the greenhouse gas and ozone-depleting substance, nitrous oxide (N2O), to the atmosphere. Most of that N2O is produced as a trace side product during ammonia oxidation, primarily by ammonia-oxidizing archaea (AOA), which numerically dominate the ammonia-oxidizing community in most marine environments. The pathways to N2O production and their kinetics, however, are not completely understood. Here, we use 15N and 18O isotopes to determine the kinetics of N2O production and trace the source of nitrogen (N) and oxygen (O) atoms in N2O produced by a model marine AOA species, Nitrosopumilus maritimus. We find that during ammonia oxidation, the apparent half saturation constants of nitrite and N2O production are comparable, suggesting that both processes are enzymatically controlled and tightly coupled at low ammonia concentrations. The constituent atoms in N2O are derived from ammonia, nitrite, O2, and H2O via multiple pathways. Ammonia is the primary source of N atoms in N2O, but its contribution varies with ammonia to nitrite ratio. The ratio of 45N2O to 46N2O (i.e., single or double labeled N) varies with substrate ratio, leading to widely varying isotopic signatures in the N2O pool. O2 is the primary source for O atoms. In addition to the previously demonstrated hybrid formation pathway, we found a substantial contribution by hydroxylamine oxidation, while nitrite reduction is an insignificant source of N2O. Our study highlights the power of dual 15N-18O isotope labeling to disentangle N2O production pathways in microbes, with implications for interpretation of pathways and regulation of marine N2O sources.

Obtaining Niobium Nitride on n-GaN by Surface Mediated Nitridation Technique

In this work the n-GaN(1000) surface is used as a source of nitrogen atoms in order to obtain niobium nitride film by a surface-mediated nitridation technique. To this end, the physical vapor deposition of the niobium film on GaN is followed by sample annealing at 1123 K. A thermally induced decomposition of GaN and interfacial mixing phenomena lead to the formation of a niobium nitride compound, which contains Nb from thin film and N atoms from the substrate. The processes allowed the obtaining of ordered NbNx films on GaN. Structural and chemical properties of both the GaN substrate and NbNx films were studied in-situ by surface-sensitive techniques, i.e., X-ray and UV photoelectron spectroscopies (XPS/UPS) and a low-energy electron diffraction (LEED). Then, the NbNx/GaN surface morphology was investigated ex-situ by scanning tunneling microscopy (STM).

Determination of Electron Excitation Temperature in an RF-DC Hollow Cathode Nitrogen Plasma

An RF-DC nitrogen glow discharge generated inside a rectangular hollow cathode was investigated as a source of nitrogen atoms. The plasma was produced at a frequency of 2 MHz at a low-pressure condition at the range of 30 to 100 Pa. The power generator was controlled at the RF voltage of 150 V and DC bias voltage of -500 V. The atomic nitrogen species have been detected by employing an optical emission spectroscopy technique. The use of a rectangular hollow cathode proves that the increase of nitrogen atoms species at a wavelength range of 700-900 nm was produced from the dissociation process of molecular nitrogen species. The present work aims to determine the electron excitation temperature based on the OES spectra. The excitation temperature was calculated by using the Boltzmann plot method. The result is the excitation temperature determined at the range of 0.59 to 0.71 eV. The excitation temperature in the hollow cathode was decreased with the increasing pressure.

Efficient one step synthesis of green carbon quantum dots catalyzed by tin oxide

Blue fluorescent carbon quantum dots (BCQDs) have been synthesized by one-step hydrothermal method with isopropanol as carbon source. The color of BCQDs was tuned to be green by incorporating N atoms into BCQDs with m-phenylenediamine as nitrogen atom source. Strong green fluorescent carbon quantum dots (GCQDs) have been obtained, and the pyrolysis reaction time was reduced much by using SnCl5⋅5H2O as a catalyst. The quantum yield for the GCQDs reached 36 % in one hour, and the quantum yield reached 55 % in 4 h. Moreover, the fluorescence of GCQDs could be selectively quenched by NO2− ions, and the relative fluorescence intensities of I/I0 was fitted perfectly in line decay curve versus the concentration of NO2− in the range of 1.0 × 10−6 mol/l–1.6 × 10−5 mol/l (R2 = 0.9998).

Activation of Dinitrogen by Polynuclear Metal Complexes.

Activation of dinitrogen plays an important role in daily anthropogenic life, and the processes by which this fixation occurs have been a longstanding and significant research focus within the community. One of the major fields of dinitrogen activation research is the use of multimetallic compounds to reduce and/or activate N2 into a more useful nitrogen-atom source, such as ammonia. Here we report a comprehensive review of multimetallic-dinitrogen complexes and their utility toward N2 activation, beginning with the d-block metals from Group 4 to Group 11, then extending to Group 13 (which is exclusively populated by B complexes), and finally the rare-earth and actinide species. The review considers all polynuclear metal aggregates containing two or more metal centers in which dinitrogen is coordinated or activated (i.e., partial or complete cleavage of the N2 triple bond in the observed product). Our survey includes complexes in which mononuclear N2 complexes are used as building blocks to generate homo- or heteromultimetallic dinitrogen species, which allow one to evaluate the potential of heterometallic species for dinitrogen activation. We highlight some of the common trends throughout the periodic table, such as the differences between coordination modes as it relates to N2 activation and potential functionalization and the effect of polarizing the bridging N2 ligand by employing different metal ions of differing Lewis acidities. By providing this comprehensive treatment of polynuclear metal dinitrogen species, this Review aims to outline the past and provide potential future directions for continued research in this area.

Direct synthesis of nitrogen-doped mesoporous carbons from triazine-functionalized resol for CO2 uptake and highly efficient removal of dyes

In this study we synthesized a triazine–formaldehyde phenolic resin as a nitrogen-containing resol (N-resol) through the condensation of 2,4,6-tris(4-hydroxyphenyl)triazine and formaldehyde. We then used this N-resol as a carbon and nitrogen atom source, mixing it with a diblock copolymer of PEO-b-PCL as the soft template, for the direct synthesis of N-doped mesoporous carbons. Interestingly, the self-assembled N-resol/PEO-b-PCL blends underwent a mesophase transition from cylinder to gyroid and back again to cylinder structures upon increasing the N-resol concentration (i.e., cylinder at 50/50; gyroid at 60/40; cylinder at 70/30). After removing the soft template at 700 °C, the resultant N-doped mesoporous carbons possessed high N atom contents (up to 13 wt%) and displayed gyroid and cylinder nanostructures. The synthesized N-doped mesoporous carbons exhibited excellent CO2 uptake capacities (up to 72 and 150 mg g–1 at 298 and 273 K, respectively). Furthermore, the N-doped mesoporous gyroid carbon structure displayed high adsorption capacities toward organic dyes in water. The maximum adsorption capacities of rhodamine B and methylene blue in water reached as high as 204.08 and 308.64 mg g–1, respectively; furthermore, these N-doped mesoporous carbons also maintained up to 98 % of their maximum adsorption capacities within 45 min.

One-step nitrogen plasma process for bimetallic impregnation to obtain N-TiO2−X/Au/Ag composite

The main motivation of this work is to deposit two different metals (gold and silver) on titanium oxide nanoparticles surface in a one-step simple and fast physical process by applying a nitrogen plasma as the main source of nitrogen atoms to obtain nanostructured N-TiO2 − X/Au/Ag materials. The obtained nanomaterials were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy–energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy. Based on the characterization results, we found that gold and silver nanoparticles were uniformly loaded on the titanium oxide nanocomposite surface, showing a surface plasmon absorption band due to the loading of the metal nanoparticles over titania samples. The results of this work have shown that nitrogen plasma technique is a more feasible and simple alternative to obtain the N-TiO2 − X/Au/Ag nanocomposite. Moreover, this plasma technique could be used to impregnate with other kind of metals over the surface of diverse nanomaterials.

Nitrogen-Iodine Exchange of Diaryliodonium Salts: Access to Acridine and Carbazole.

A nitrogen-iodine exchange protocol of diaryliodonium salts with sodium azide salt is developed for general construction of significant functional acridines and carbazoles, in which introduction of nitrogen at a late stage was successfully established avoiding heteroatom incompatibility. Inorganic sodium azide served as the sole nitrogen atom source in this transformation. The diversiform functional acridines and carbazoles were comprehensively achieved through annulated diaryliodonium salts, respectively. Notably, Acridine orange (a fluorescent indicator for cell lysosomal dye) and Carprofen (a nonsteroidal anti-inflammatory drug) were efficiently established through this protocol.

Changes in the chemical composition of the atmosphere in the polar regions of the Earth after solar proton flares (3d modeling)

The paper presents the results of numerical photochemical simulations of the impact of the most powerful solar proton flares during the 23rd solar cycle on the ozonosphere in the polar regions of the Earth. A global 3D photochemical model, CHARM, developed at Central Aerological Observatory (CAO) was used in the simulations. The model introduces an additional source of nitrogen atoms and OH radicals. These components are formed due to the ionization effect of solar protons in the Earth’s atmosphere. The ionization rate was determined from data on proton fluxes measured by GOES satellites. The production rate of additional NO x and HО x molecules per ion pair was based on published theoretical studies. It is shown that the most intense flares in the 23rd solar cycle (2000, 2001, and 2003) destroyed ozone in the mesosphere to a great extent (sometimes completely, for example, during the July 14, 2000, event). It is found that the response of ozone to solar proton events follows a seasonal pattern. For the first time, the long-term effect of solar proton events is identified; it is approximately one year.

Shallow acceptor state in ZnO realized by ion irradiation and annealing route

Activation of shallow acceptor state has been observed in ion irradiated and subsequently air annealed polycrystalline ZnO material. Low temperature photoluminescence (PL) spectrum of the sample exhibits clear signature of acceptor bound exciton (ABX) emission at 3.360 eV. The other two samples, pristine and ion irradiated (without annealing), however, do not show acceptor related PL emission in the nearby energy region. Electron transition from shallow donor (most probable site is interstitial zinc for undoped ZnO) to such newly formed shallow acceptor state creates new donor-acceptor pair (DAP) luminescence peak ∼ 3.229 eV. ABX and DAP peak energy positions confirm that the acceptor is N related. The acceptor exciton binding energy has been estimated to be 180 ± 15 meV which is in conformity with earlier reports. The activation of shallow acceptors without any source of atomic nitrogen can only be possible through diffusion of molecular nitrogen inside the sample during annealing. The N2 molecules get trapped at bulk defect sites incorporated by ion irradiation and subsequent annealing. X-ray diffraction (XRD) and Raman spectroscopic (RS) investigation have been employed to probe the changing defective nature of the ZnO samples. Irradiation induced increased disorder has been detected (both by XRD and RS) which is partially removed/modified by annealing at 300 °C. Simultaneous activation of molecular nitrogen acceptor in purposefully defective ZnO is the key finding of this work. Results presented here provide a simple but controlled way of producing shallow acceptor state in ZnO. If optimized through suitable choice of ion, its energy and fluence as well as the annealing temperature, this methodology can trigger further scope to fabricate devices using ZnO epitaxial thin films or nanowires.

Tert-Butyl nitrite (TBN) as the N atom source for the synthesis of substituted cinnolines with 2-vinylanilines and a relevant mechanism was studied.

A green method to synthesize cinnolines by 6π electrocyclic reaction with alkenyl amines and TBN has been developed. TBN plays a dual role both as a nitrogen atom source and an oxidant in this procedure. Relevant mechanism experiments reveal that the reaction proceeds through electrocyclic reaction and with diazo hydroxide as a key intermediate.

Synthesis and characterization of aluminum Oxy nitride (AlON) from the nanosized gel precursor

The purpose of this research was the synthesis of aluminum Oxy-nitride (ALON) nanocrystals with through the alkoxide sol-gel processing method. For the synthesis of the nanosized precursor, sucrose (SU, as a source of reducing and gel agent), carbamide (CR, to adjust the pH and source of atomic nitrogen), aluminum buthylate (as the source of Al3+), and magnesium acetate (as the source of Mg2+ and the doping agent) were used. Various characterizations including X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), diffusion reflectance spectroscopy (DRS spectrum), energy dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM) were used to characterize the as-synthesized samples. Our results indicated that the precursor solution containing SU:CR with the molar ratio of 1:3M and 5% magnesium acetate led to AlON phase. This phase could be obtained after a special three-step calculation schedule of nanosized precursor consisting of 1h at 1000°C, 1h at 1300°C and 3h at 1700°C.

HIGH TEMPERATURE GAS NITRIDING TREATMENT OF AISI 430 USING LOW AND HIGH PURITY NITROGEN GAS

The properties of stainless steels can be improved by high temperature gas nitriding (HTGN) treatment. The improving of their properties are obtained from nitrogen atom which diffuse into stainless steel. Nitrogen gas is the main source of nitrogen atom on the HTGN treatment. Generally, these treatment use high purity of nitrogen gas. The aim of this research is to investigate the effect of nitrogen gas purity on the HTGN treatment for AISI 430. Stainless steel AISI 430 plate 2 mm thick was processed by HTGN treatment. The specimens was exposed at nitrogen gas atmosphere at temperature 1200oC and held for 2 hours prior quenching in water. The treatment used industrial/welding grade (99.5%) as low nitrogen gas purity and ultra high purity (UHP) grade (99.999%) as high nitrogen gas purity. The vickers micro-hardness test was conducted to evaluate the hardness distribution from surface into middle section of the specimens before and after treatment. Light optical microscope was applied to examine the microstructure of specimens after treatment. Metallographic examination shows both treatments using low and high purity gas have the same grain size. However HTGN treatment using low purity of nitrogen gas produces hardness slightly lower than the high purity. This is due the high content of impurity of the low purity gas that reduces the partial pressure of nitrogen gas. Another effect of impurity is the reaction between nitrogen gas and its impurity especially oxygen gas. These reactions reduce the amount of free nitrogen atom which diffuses on the stainless steel.

Use of chiral-pool approach into epi-thieno analogues of the scarce bioactive phenanthroquinolizidine alkaloids

The stereoselective synthesis of epi-thieno analogues of the phenanthroquinolizidine bioactive alkaloids (−)-Cryptopleurine and (−)-(15R)-Hydroxycryptopleurine was achieved in five steps starting from easily available enantiopure (S)-2-aminoadipic acid used as chiral pool and nitrogen atom source. During these investigations, both π-cationic cyclization of chiral N-thienylmethyl-6-oxopipecolinic acids into pure (S)-keto-lactams and theirs regioselective and diastereoselective reduction, considered as key steps of this sequence, were studied. Of particular interest, the Friedel–Crafts cyclization using (CF3CO)2O/BF3·Et2O show that near the expected keto-lactams, enamides and enamidones containing trifluoromethyl residue were isolated. A mechanism leading to the latter products with high synthetic potential was discussed.

Non-Noble Metal Catalysts As Oxygen Depolarized Cathodes in Chlor Alkali Electrolyzers

Chlorine is an essential element of chemical industries, and especially has paramount importance in polymer industry. A typical route for chlorine generation is electrolysis of brine solution where chlorine is generated at the anode; producing caustic soda and hydrogen at cathode. However, the relevant state of the art membrane reactors is one of the most energy intensive processes in industry. Moreover, the membrane technology is believed to have reached the theoretical limit, and energy consumption cannot be reduced further. In the present chlor-alkali technology, sodium chloride solution is electrolyzed at a constant current density, and the decomposition voltage ΔE of the overall reaction is 2.186 V as per thermodynamic calculation. If the hydrogen evolution reaction at the cathode side is replaced with oxygen reduction reaction (ORR), the decomposition voltage will be significantly reduced, and, as a consequence, the energy consumption will be reduced simultaneously. Introduction of such oxygen depolarized cathode results in the following chemical reactions: Anode: 2Cl- —— Cl2+2e- (E=1.358 V vs. NHE) Cathode: 4Na+ + 2H2O + O2 +4e- —— 4NaOH (E=0.401 V vs. NHE) Overall Reaction: 4NaCl + 2H2O + O2 —— 4NaOH + 2Cl2 (ΔE=-0.957 V) Even though the voltage requirement can be minimized by oxygen depolarized cathode, there is still significant overpotential loss from the cathodic reaction. This is due to the fact that ORR is kinetically a very sluggish reaction. Platinum is the best catalyst known for ORR in acid media. However, Pt is poisoned in concentrated NaOH solution resulting in significant shifts in onset potential and limiting current values. Early in 1970s, heating of non-noble metal along with carbon and a source of nitrogen atoms in presence of ammonia resulted in formation of electrocatalysts with ability to reduce oxygen. Since then, there has been a gradual development of such “non-PGM” catalysts, where PGM stands for Precious Group Metals. The introduction of metal organic frameworks (MOFs) as sacrificial templates has brought a revolution in electrocatalysis research. Owing to the large surface area, preferable porosity and high nitrogen content, the non-PGM catalysts obtained from MOF precursors have shown excellent ORR activity. However, most of the MOF synthesis methods are based on the traditional solution reactions, which need either excessive amount of ligand or a huge amount of solvent, or both. Thus, the low yielding synthesis route and comprehensive separation methods of MOF seriously constrain the application of the MOF based catalysts for ORR. In the presentation, we will be discussing about the new in-house synthesized MOF based catalyst using solid-state reaction. In addition to advantages like simple preparatory route and high reproducibility, this catalyst has high yield and scalability which are uncommon traits for the more conventional MOF based catalysts. This catalyst has high ORR onset potential even in extreme corrosive conditions such as concentrated alkali and acid. Herein, we propose a facile, simplified approach to obtain the MOF based catalysts for ORR with low cost and high reproducibility. The as-prepared catalysts have been tested as oxygen depolarized cathodes in chlor-alkali electrolysis cells and have been operated at significantly lower voltages compared to commercial catalysts like Pt/C and Ag/C.

Myoglobin-based non-precious metal carbon catalysts for an oxygen reduction reaction

A non-precious metal catalyst (NPMC) promoting a four-electron oxygen reduction reaction (ORR) was synthesized by heat treatment of myoglobin (Mb) containing a heme (iron protoporphyrin IX) as a source of iron, nitrogen, and carbon atoms. Samples of the mixture of Mb and carbon black (Vulcan XC72R: VC) were pyrolyzed at 740, 840, 940, 1040 or 1140°C under N2flow. The microstructures of the carbonized Mb catalysts were characterized by XRD, Raman spectroscopy, XPS, and TEM. Results indicate that the iron-containing active site is embedded within the surface structure in an amorphous domain of the carbon materials. The catalyst ink in a 0.05 wt% Nafion solution in isopropanol was coated onto a glassy carbon electrode and the ORR activity of Mb-based NPMCs was evaluated in a rotating disk electrode experiment in an O2-saturated 0.1 M HClO4solution at 25°C. The catalyst synthesized at 940°C has the highest ORR activity in terms of the onset potential and the current density. In contrast, pyrolytic temperatures above 940°C decrease the activity, suggesting that the active structure of the catalyst apparently decomposes at higher temperatures. The Koutecky–Levich plots indicate that the Mb-based catalyst prepared at 940°C catalyzes four-electron ORR (n = ca. 4). The catalysts prepared at other temperatures have n values of 3.6 at 740°C, 3.7 at 840°C, and 2.9 at 1040°C. The ORR of Mb/VC is diffusion-controlled at potentials lower than 0.3 V (vs. RHE) and the onset potential is 0.84 ± 0.01 V.

A comparison study between atomic and ionic nitrogen doped carbon films prepared by ion beam assisted cathode arc deposition at various pulse frequencies

A comparison study of microstructure and bonds composition of carbon nitride (CNx) films fabricated at atomic and ionic nitrogen source by pulse cathode arc method was presented. The relative fractions of CN/CC bonds, Nsp3C/Nsp2C and graphite-like/pyridine-like N bonding configurations in the CN films were evaluated by combining C1s and N1s X-ray photoelectron spectroscopy with the hardness and optical band gap measurement. The dependence of microstructure (quantity, size and disordering degree of Csp2 clusters) of CNx films on the nitrogen source and pulse frequency was determined by Raman spectroscopy. Films with high atomic ratio of nitrogen/carbon (0.17) and high hardness were produced at ionic nitrogen source and low pulse frequency. The results showed that ionic nitrogen source facilitated the formation of CN bonds and Nsp2C bonding configurations (mainly in graphite-like N form). Moreover presenting an optimum pulse frequency (∼10Hz) leaded to the most nitrogen coordinated with sp3-C and the highest ratio of CN/CC bonds in the CNx films. An equilibrium action mechanism might exist between the quantity and energy of carbon and nitrogen ions/atoms, giving more nitrogen-incorporated carbon materials. These allow us to obtain the high content of NCsp3 bonding and expected bonding structure by optimizing pulse frequency and nitrogen source.

ChemInform Abstract: Copper‐Mediated Transformation of Organosilanes to Nitriles with DMF and Ammonium Iodide.

Cyanation of aryl-, diaryldimethyl-, and styrylsilanes was developed for the first time under copper-mediated oxidative conditions using ammonium iodide and DMF as the combined source of nitrogen and carbon atom of the introduced cyano unit, respectively. The reaction was observed to proceed in a two-step process: initial conversion of organosilanes to their iodo intermediates and then cyanation. This method has a broad substrate scope with high functional group tolerance.