Single Nitrogen Atom Research Articles

Redox-Tunable Ring Expansion Enabled By A Single-Component Electrophilic Nitrogen Atom Synthon.

Controllable installation of a single nitrogen atom is central to many major goals in skeletal editing, with progress often gated by the availability of an appropriate N-atom source. Here we introduce a novel reagent, termed DNIBX, based on dibenzoazabicycloheptadiene (dbabh), which allows the electrophilic installation of dbabh to organic substrates. When indanone β-ketoesters are aminated by DNIBX, the resulting products undergo divergent ring expansions depending on the mode of activation, producing heterocycles in differing oxidation states under thermal and photochemical conditions. The mechanism of each transformation is discussed, and the different reactivity modes of the indanone-dbabh adducts are compared to other nitrogenous precursors.

Redox‐Tunable Ring Expansion Enabled By A Single‐Component Electrophilic Nitrogen Atom Synthon

Controllable installation of a single nitrogen atom is central to many major goals in skeletal editing, with progress often gated by the availability of an appropriate N‐atom source. Here we introduce a novel reagent, termed DNIBX, based on dibenzoazabicycloheptadiene (dbabh), which allows the electrophilic installation of dbabh to organic substrates. When indanone β‐ketoesters are aminated by DNIBX, the resulting products undergo divergent ring expansions depending on the mode of activation, producing heterocycles in differing oxidation states under thermal and photochemical conditions. The mechanism of each transformation is discussed, and the different reactivity modes of the indanone‐dbabh adducts are compared to other nitrogenous precursors.

Tetrapyrrolic macrocycles self-organization into floating layers and sensory properties of their Langmuir-Schaefer films

The influence of the chemical structure of the 5,10,15,20-tetraphenylporphyrin (I) and 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (II) on their supramolecular organization in floating layers at the air/water interface and sensor properties in Langmuir-Schaefer films has been investigated. It was shown that a minor change in the macrocycle structure (namely, the replacement of a single nitrogen atom from the center to the periphery of macrocycle) has a considerable effect on the surface properties and hysteresis processes of the floating layers. Using the Bruster angle microscopy, it was established that both porphyrins aggregate even before the compression of their floating layers begins. The aggregation is more pronounced in porphyrin I. The analysis of hysteresis loops showed that the formation of a floating layer by the modified porphyrin II requires approximately 100 times more energy than for the unmodified porphyrin I. Using the Langmuir-Schaefer (LS) method, the floating layers were transferred onto solid substrates and the resulting thin films were analyzed by atomic force microscopy, scanning electron microscopy, polarization optical microscopy, and spectrophotometry. The combination of these methods revealed a general tendency of the porphyrins to form 3D structures on the surface of LS-films. The study of the basic properties of the porphyrin's LS-films showed that both porphyrins are diprotonated. The protonation process in porphyrin II occurs at a concentration of HClO4 that is 1000 times lower than that observed in porphyrin I. The greater tendency to protonation of porphyrin II is caused by the availability of both nitrogen atoms (the external nitrogen atom located at the macrocycle periphery and the internal nitrogen atom, which becomes more assesible to interactions due to the distortion of the macrocycle). As for the sensor properties of LS-films for iodide ion in aqueous solutions, it was observed that the diprotonated form of porphyrin I exhibited higher sensitivity due to a more developed film surface because of the presence of a greater number of 3D aggregates. The data obtained can be used in the development of efficient pH-controlled thin-film sensor materials for halide ions.

DFT Study of High‐Curie‐Temperature Ferromagnetism in α‐borophene Nanoribbons for Spintronic Applications

AbstractThe aim is to tune the stability, as well as electronic and magnetic characteristics of zigzag α‐borophene nanoribbons (ZαBNRs) based on density functional theory. For this reason, the bare ZαBNR and its passivated edges by a single nitrogen atom (N‐ZαBNR) and also Mn‐ and Cr‐doped N‐ZαBNR is investigated. The results indicate that the nanoribbon becomes more stable by passivating the edges of the structure. Furthermore, the calculated electronic structures show that the Cr atom can remove the band gap of N‐ZαBNRs and turn it into metal. Besides, it can create magnetic properties in this structure. The Cr‐ and Mn‐doped N‐ZαBNR turn it into magnetic metal and diluted magnetic semiconductors, respectively. The results reveal a high Curie temperature of more than 700K for Cr‐ and Mn‐doped N‐ZαBNRs, indicating maybe good room‐temperature ferromagnetic material for spintronic applications in the future.

Synthesis and Antimicrobial Activity of some Ester Functionalized Isoxazoles incorporating Anthracene Moieties via Nucleophilic Substitution Reaction

Background and objective: Five-membered heterocycle compounds having single oxygen and nitrogen atom at adjacent positions are known as isoxazoles. Isoxazole compounds have a broad range of biological activities and therapeutic value. In view of a strategic design of antimicrobial compounds, several new ester-functionalized isoxazoles were synthesized and characterized. Methods: A regioselective isoxazole incorporating an anthracene moiety was adducted via an effective 1,3-dipolar cycloaddition between anthracene nitrile oxide and propargyl bromide as a dipolarophile. Results: Synthesized isoxazole 4 underwent nucleophilic substitution reaction to produce unprecedented ester-functionalized isoxazoles 6a-j, by condensation with equimolar amounts of different generated in situ sodium carboxylate upon dissolving in acetonitrile with refluxing. The chemical structure of all target compounds was proved by (FT-IR, 1H-NMR, and APT13C-NMR) techniques and their antibacterial and antifungal activities was evaluated. Conclusion: Allnewly synthesizedcompounds6 a-j have been obtained in good yields after purification by column chromatography. They showed significant antibacterial and antifungal activity after screening against two bacterial strains, Escherichia coli and Staphylococcus aureus and a fungi strain, Candida albicans, using disc diffusion method.

4,5-Dihydro-1,2,4-oxadiazole as a Single Nitrogen Transfer Reagent: Synthesis of Functionalized Isoxazoles Assisted by Sc(OTf)3 or Au(I)/Sc(OTf)3 Synergistic Catalysis.

A five-membered N-O heterocycle, 4,5-dihydro-1,2,4-oxadiazole, was found to act as a single nitrogen atom transfer reagent via elimination of a ketone/aldehyde and a nitrile. This reagent was successfully applied for the synthesis of isoxazoles from ynones promoted by Sc(OTf)3 or through Au(I)/Sc(OTf)3 synergistic catalysis. The efficiency of this protocol was also demonstrated by its application in modifications of structurally complex natural products and pharmaceuticals.

Facile synthesis of 2-aza-9,10-diphenylanthracene and the effect of precise nitrogen atom incorporation on OLED emitters performance.

Polycyclic aromatic hydrocarbons (PAHs) are important compounds in materials chemistry, particularly for optoelectronic applications. One strategy for tuning PAH properties involves the net exchange of carbon atoms for heteroatoms, such as nitrogen. We report a comparative study of the well-known fluorophore 9,10-diphenylanthracene with an aza analog. The latter compound is accessed using a short sequence involving the use of two strained cyclic alkynes, benzyne and a 3,4-piperidyne, in Diels-Alder cycloaddition sequences. Comparative studies of 9,10-diphenylanthracene and the aza-analog show how the addition of a single nitrogen atom impacts electrochemical and optical properties. Organic light-emitting diode (OLED) devices were prepared using both compounds, which showed that nitrogen substitution leads to an unexpected red shift in electroluminescence, likely due to exciplex formation between the active layer and the 4,4'-N,N'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) hole-transport layer. These studies highlight a unique approach to accessing heteroatom-containing PAHs, while underscoring the impact of heteroatoms on OLED device performance.

First-principles Study of Electronic and Magnetic Properties of Two-dimensional Hexagonal Boron Nitride Doped with Germanium and Tin Atoms

For the study of geometrical structure, stability, and electronic and magnetic properties of Germanium and tin-doped two-dimensional hexagonal boron nitride (h-BN), First-principles calculations have been carried out. Plane-wave pseudo-potential method in association with the density functional theory (DFT) framework used in Quantum ESPRESSO codes has been implemented to perform the calculations. A 3X3 supercell size substitutional doping of a single Boron or Nitrogen atom was carried out for the study. Pristine h-BN showed non-magnetic behavior with comprehensive gap material having an indirect band gap of 4.64eV. The doping effect of Ge and Sn atoms at the B-site was energetically more favorable than N-site. The defected h-BN sheet was found to be severely distorted with remarkable alteration in bond length and angles around the defected sites. Ge doped h-BN showed semiconducting properties with a reduced band gap in comparison to the insulating nature of pristine h-BN, whereas half metallicity was noticed in Sn doped h-BN system. Both the systems showed a magnetic moment of 1.0 µB.

Rapid determination of single substitutional nitrogen Ns concentration in diamond from UV-Vis spectroscopy

Single substitutional nitrogen atoms Ns0 are the prerequisite to create nitrogen-vacancy (NV) centers in diamonds. They not only serve as the electron donors to create the desired NV− center and provide charge stability against photo-ionisation but also are the main source of decoherence. Therefore, precise and quick determination of Ns0 concentration is a key advantage to a multitude of NV-related research in terms of material improvement as well as applications. Here, we present a method to determine the Ns0 concentration based on absorption spectroscopy in the UV-Visible range and fitting the 270 nm absorption band. UV-Visible spectroscopy has experimental simplicity and widespread availability that bear advantages over established methods. It allows a rapid determination of Ns0 densities, even for large numbers of samples. Our method shows further advantages in determining low concentrations as well as the ability to measure locally, which is highly relevant for diamonds with largely varying Ns0 concentrations in a single crystal. A cross-check with electron paramagnetic resonance shows high reliability of our method and yields the absorption cross section of the 270 nm absorption band σ=1.96±0.15 cm−1 ppm−1 (in common logarithm) or σe=4.51±0.35 cm−1 ppm−1 (in natural logarithm), which serves as a reference to determine Ns0 concentrations and makes our method applicable for others without the need for a known Ns0-reference sample and calibration. We provide a rapid, practical, and replicable pathway that is independent of the machine used and can be widely implemented as a standard characterization method for the determination of Ns0 concentrations.

Analysis of the adsorption characteristics of gasification pollutants (HCl, COS, H2S, NH3 and HCN) on Ti-anchored graphene substrates

The adsorption characteristics of HCl, COS, H2S, NH3 and HCN (coal gasification pollutants) on the adsorbents (single vacancy, double vacancy, and doped nitrogen atoms) formed by the graphene substrates anchored with titanium atom were analyzed by density functional theory (DFT) calculation. This paper mainly analyzed the geometric configuration of the adsorbent, the adsorption configuration of the gas, and the adsorption energy and the magnetic properties. And through the analysis of the electron density difference and the projected density of states (PDOS), the adsorption mechanism of five coal gasification pollutants on different adsorbents were deeply studied. The calculated results indicate that HCl, COS, H2S, NH3 and HCN can be adsorbed on Ti/SV-N3 graphene adsorbent, and the values of the adsorption energy were −1.07 eV, −1.73 eV, −0.28 eV, −0.41 eV, and -1.23 eV, respectively. Moreover, the introduction of nitrogen atoms significantly enhanced the interaction between single-atom graphene and gas molecules. Based on theoretical results, Ti/SV-N3 was the most suitable for simultaneous removal of these five pollutant gasses, which can guide the development of new materials for pollutant gas removal.

Recent Updates on Azido‐reductive Cyclization Approaches: Syntheses of aza‐Heterocyclic Frameworks

AbstractThe first organic azide (phenyl azide) was synthesized in 1864 and since then, its structure, syntheses, and applications have reaped extreme attention from chemists across the globe. Later, the unambiguous documentation of its linear structure and chemical reactivity led to all‐embracing research in the chemistry of azides. The unique electronic structure and chemical reactivity placed the organic azides at the interface between chemistry, biology, medicine, and material science. In this regard, the reaction of azides where a single‐nitrogen atom is retained was well implemented for the synthesis of natural products and other vital organic frameworks embedding various aza‐heterocyclic skeletons. This review emphasizes the recent applications (2015–2021) of organic azides in the synthesis of the aforementioned organic molecules employing an azido‐reductive cyclization approach with the retention of a single nitrogen atom.

Impurity Substitution Enhances Thermoelectric Figure of Merit in Zigzag Graphene Nanoribbons

The thermoelectric properties of zigzag graphene nanoribbons (ZGNRs) are sensitive to chemical modification. In this study, we employed density functional theory (DFT) combined with the nonequilibrium green’s function (NEGF) formalism to investigate the thermoelectric properties of a ZGNR system by impurity substitution of single and double nitrogen (N) atoms into the edge of the nanoribbon. N-doping changes the electronic transmission probability near the Fermi energy and suppresses the phononic transmission. This results in a modified electrical conductance, thermal conductance, and thermopower. Ultimately, simultaneous increase of the thermopower and suppression of the electron and phonon contributions to the thermal conductance leads to the significant enhancement of the figure of merit in the perturbed (i.e., doped) system compared to the unperturbed (i.e., nondoped) system. Increasing the number of dopants not only changes the nature of transport and the sign of thermopower but also further suppresses the electron and phonon contributions to the thermal conductance, resulting in an enhanced thermoelectric figure of merit. Our results may be relevant for the development of ZGNR devices with enhanced thermoelectric efficiency.

Weak Electron Irradiation Suppresses the Anomalous Magnetization of N‐Doped Diamond Crystals

Several diamond bulk crystals with a concentration of electrically neutral single substitutional nitrogen atoms of ≲80 ppm, the so‐called C or P1 centers, are irradiated with electrons at 10 MeV energy and low fluence. The results show a complete suppression of the irreversible behavior in field and temperature of the magnetization below 30 K, after a decrease in ≲40 ppm in the concentration of C centers produced by the electron irradiation. This result indicates that magnetic C centers are at the origin of the large hysteretic behavior found recently in nitrogen‐doped diamond crystals. This is remarkable because of the relatively low density of C centers, stressing the extraordinary role of the C centers in triggering those phenomena in diamond at relatively high temperatures. After annealing the samples at high temperatures in vacuum, the hysteretic behavior is partially recovered.

Unusual optical centres in fancy brown diamonds

Background. Natural brown diamonds with fancy yellow, orange, red and green tints are valuable jewelry raw materials. Their colour is associated with post-crystallisation plastic deformation occurring during transportation from the mantle to the Earth’s surface.Aim. To study point defects in plastically deformed diamonds using optical and IR spectroscopy.Materials and methods. Faceted brown diamonds with fancy tints presented on the Russian market were studied spectroscopically. Selected samples were examined using UV-visible optical absorption spectroscopy and IR spectroscopy.Results. We discovered unusual optical centres in the absorption spectra of the UV-visible region. In addition, the known continuous absorption increasing from the red to the ultraviolet region of the spectrum, as well as the N3 and H3 nitrogen centres and a band at 550 nm, were revealed. In the spectra of yellowish-brown diamonds, the bands at 512.9 nm and 519.9 nm and an accompanying broad band with a maximum of 480 nm were found. The appearance of a yellowish tint of crystals was associated with these optical centres. The bands 506.5 nm, 516.1 nm and 679.7 nm were established in the spectrum of orange-brown diamond samples. An additional absorption continuum associated with single nitrogen atoms and centres (NV)– were observed in greenish-brown diamond samples. Their simultaneous presence causes the appearance of a greenish tint in the diamond colour.Conclusion. The information obtained using IR spectroscopy indicates that an intense brown colour can occur not only in the most common Ia type crystals according to the physical classification of diamonds, but also in relatively rare Ib + IaA type diamonds.

A ß-Secretase Modulator Decreases Tau Pathology and Preserves Short-Term Memory in a Mouse Model of Neurofibrillary Degeneration.

Identifying which among several in cellulo pharmacological activities is necessary for the proper in vivo activity is essential for further drug development against Alzheimer’s disease pathophysiological processes. An in-depth structure–activity relationship–based study has been carried out, and two molecules, named MAGS02-14 and PEL24-199, that share a ß-secretase modulatory effect associated or not to a lysosomotropic activity in cellulo have been identified. In terms of chemical formulas, MAGS02-14 and PEL24-199 only differ from each other by a single nitrogen atom. The study aimed to elucidate the in vivo pharmacological effects of lysosomotropic and/or the ß-secretase modulatory activity in a tau pathology mouse model. To address this question, the THY-Tau22 transgenic model of tauopathy was treated with both compounds for 6 weeks in a curative paradigm. Short-term memory, tau burden, and inflammatory processes were analyzed using orthogonal methods, and PEL24-199, but not MAGS02-14, was shown to restore the short-term memory and reduce the neurofibrillary degenerating process. These effects were associated with a reduced phosphorylation of tau, an increased phosphatase expression, and decreased astrogliosis. Our results, therefore, suggest that the lysosomotropic activity may be nonessential for the effect on tau pathology.

Excited state dynamics of 7-deazaguanosine and guanosine 5'-monophosphate.

Minor structural modifications to the DNA and RNA nucleobases have a significant effect on their excited state dynamics and electronic relaxation pathways. In this study, the excited state dynamics of 7-deazaguanosine and guanosine 5'-monophosphate are investigated in aqueous solution and in a mixture of methanol and water using femtosecond broadband transient absorption spectroscopy following excitation at 267 nm. The transient spectra are collected using photon densities that ensure no parasitic multiphoton-induced signal from solvated electrons. The data can be fit satisfactorily using a two- or three-component kinetic model. By analyzing the results from steady-state, time-resolved, computational calculations, and the methanol-water mixture, the following general relaxation mechanism is proposed for both molecules, Lb → La → 1πσ*(ICT) → S0, where the 1πσ*(ICT) stands for an intramolecular charge transfer excited singlet state with significant πσ* character. In general, longer lifetimes for internal conversion are obtained for 7-deazaguanosine compared to guanosine 5'-monophosphate. Internal conversion of the 1πσ*(ICT) state to the ground state occurs on a similar time scale of a few picoseconds in both molecules. Collectively, the results demonstrate that substitution of a single nitrogen atom for a methine (C-H) group at position seven of the guanine moiety stabilizes the 1ππ* Lb and La states and alters the topology of their potential energy surfaces in such a way that the relaxation dynamics in 7-deazaguanosine are slowed down compared to those in guanosine 5'-monophosphate but not for the internal conversion of 1πσ*(ICT) state to the ground state.

Monitoring single-heteroatom loss during deoxygenation and denitrogenation of soluble organic matter in coal using mass spectrometric methods

The structure-reactivity relationship during catalytic reactions for coal has been extensively simulated by using model compounds. However, the direct study of structure-reactivity relationship is not sufficient for coal, the complex mixture, partially due to the challenging task of monitoring catalytic reactions in complex mixtures at the molecular level. In this study, a tandem mass spectrometry (MS) approach was designed for selective observation of catalytic single-atom denitrogenation and deoxygenation reactions of a coal. According to the tandem MS data, structure of aromatic cores, total carbon number in alkyl chains, heteroatom release efficiency and preference of heteroatom removal on aromatic cores versus alkyl chains were explored and compared to reveal the relationship between heteroatom release pattern and molecular structure. Structure-reactivity relationship was not clearly observed in deoxygenation patterns due to majorities of molecules contain multiple oxygen atoms. However, structure-reactivity relationships were revealed in denitrogenation patterns due to the presence of single nitrogen atom in most nitrogen-containing molecules.

Distribution of Nitrogen-Vacancy NV– Centers in Cubic Diamond Crystals from Anabar Placers as Revealed By ODMR and PL Tomography

Nitrogen-vacancy NV– centers, which are of considerable interest for quantum electronics, are artificially produced in the diamond structure by irradiation and subsequent annealing. In this work, these centers were revealed in natural diamonds of cubic habit (type IaA + Ib according to physical classification) from an industrial placer deposit of the Anabar River (NE Siberian platform) using the method of optically detected magnetic resonance (ODMR). Localization of the NV– centers in the dislocations slip planes {111}, separated by distances of about 5 μm, was established by means of scanning the ODMR and PL signals with a submicron resolution. In various crystals, one or two intersecting systems of such slip planes have been revealed. The largest amounts of these defects were found in the peripheral zones of crystals containing increased amounts of single isomorphic nitrogen atoms in the structure. The data obtained indicate the formation of the NV– centers in natural diamonds under post-crystallization plastic deformation, i.e., by a mechanism that differs from the widely used method of their artificial production.

Structure-Photochemical Function Relationships in the Photobasicity of Aromatic Heterocycles Containing Multiple Ring Nitrogen Atoms.

Photobases are compounds that become more basic when promoted to an excited electronic state. Previous experimental and computational studies have demonstrated that several quinoline and quinoline-derived compounds are strong photobases (pKa* > 14). Moreover, the strength of photobasicity was shown to depend strongly on the identity and position of the substituent group(s), with the strongest photobases having multiple electron-donating substituents on a fused benzene ring as opposed to the ring containing the photobasic nitrogen atom. These electron-donating substituents build up electron density on one side of the molecule that shifts onto the nitrogen-containing ring in the electronic transition. This shift in electron density produces an increase in negative charge on the ring nitrogen atom responsible for the photobasicity. In this paper, we expand on our previous investigation to study the effect of an additional ring nitrogen atom on photobasicity in aromatic heterocycles. In particular, we consider how the thermodynamic driving force for excited-state protonation can be tuned by changing the relative placement of the ring nitrogen atoms and varying the position and number of electron-donating substituents. In the set of 112 molecules screened, we identified 42 strong photobases with generally comparable pKa* but lower vertical excitation energies than the quinoline derivatives with only a single ring nitrogen atom. We additionally explored photobasicity in substituted azaindole and carboline derivatives, identifying 76 strongly photobasic compounds with pKa* as large as 22.6 out of the 155 compounds that we considered. Overall, this work provides new insights into the design principles necessary to develop next-generation photocatalysts that employ photobasicity.

Charge Anisotropy of Nitrogen: Where Chemical Intuition Fails

For more than half a century computer simulations were developed and employed to study ensemble properties of a wide variety of atomic and molecular systems with tremendous success. Nowadays, a selection of force-fields is available that describe the interactions in such systems. A key feature of force-fields is an adequate description of the electrostatic potential (ESP). Several force-fields model the ESP via point charges positioned at the atom centers. A major shortcoming of this approach, its inability to model anisotropies in the ESP, can be mitigated using additional charge sites. It has been shown that nitrogen is the most problematic element abundant in many polymers as well as large molecules of biological origin. To tackle this issue, small organic molecules containing a single nitrogen atom were studied. In performing rigorous scans of the surroundings of these nitrogen atoms, positions where a single extra charge can enhance the ESP description the most were identified. Significant improvements are found for ammonia, amines, and amides. Interestingly, the optimal location for the extra charge does not correlate with the chemically intuitive position of the nitrogen lone pair. In fact, the placement of an extra charge in the lone-pair location does not lead to significant improvements in most cases.