Adjacent Nitrogen Atoms Research Articles

The Effects of 3,5-Dimethylpyrazole on Soil Nitrification and Related Enzyme Activities in Brown Soil

Heterocyclic nitrogen compounds containing two adjacent nitrogen atoms generally have a significant effect on soil nitrification inhibition, and 3,5-dimethylpyrazole (DMP) is a typical representative of this structure. However, the inhibitory effect and the regulatory mechanism of DMP on soil N transformation are unclear. In this study, a microcosm with different concentrations of DMP was carried out in brown soil to detect the dynamic changes of soil NH4+–N, NO3–N and related soil enzyme activities. Results showed that DMP inhibited soil nitrification effectively and decreased soil nitrate reductase activity, while increasing nitrite reductase and dehydrogenase activities. The inhibition effects were dose dependent, and DMP at the rate of 0.025 g kg−1 dry soil showed the strongest inhibitory effect on N transformation in brown soil. The soil dehydrogenase activity was increased with an increasing DMP application rate. The changes in the soil’s chemical and biological properties caused by DMP application provided a new idea for systematically explaining how DMP participated in the soil N transformation process. This study further implied that DMP would play positive roles in alleviating environmental pressure by delaying nitrate-N formation and decreasing the activity of nitrate reductase.

Boosting capacitive performance of nitrogen-doped carbon by atomically dispersed iron

Carbon-based electrochemical capacitors are important energy storage devices owing to their high power and long life. However, their practical implementation has been restrained by low energy as a result of the limitation of double-layer capacitance. In this work, we demonstrate that the incorporation of atomically dispersed Fe into nitrogen-doped carbon (Fe−NC) can drastically boost the double-layer capacitance of carbon materials. Electrochemical tests reveal that an enhancement in the capacitance from 147.5 F g−1 to 174.8 F g−1 is realized when single Fe atoms are incorporated into nitrogen-doped carbon. In addition, symmetric supercapacitors based on Fe−NC exhibit a robust cycling performance, retaining 94.7% of the capacitance over 100,000 cycles. This improvement can be correlated to the chemical coordination of iron with adjacent nitrogen atoms to tailor the electric structure of carbon, which increases the density of states near the Fermi level and improves anion adsorption on atomic Fe sites. The single-atom engineering strategy may offer new possibilities to develop high-performance carbon materials for capacitors.

Tuning the Electronic Properties of Main-Group Species by N-Heterocyclic Vinyl (NHV) Scaffolds

ConspectusMolecules and materials with easily tunable electronic structures and properties are at the forefront of contemporary research. π-Conjugation is fundamental in organic chemistry and plays a key role in the design of molecular materials. In this Account, we showcase the applicability of N-heterocyclic vinyl (NHV) substituents based on classical N-heterocyclic carbenes (NHCs) for tuning the structure, properties, and stability of main-group species (E) via π-conjugation and/or π-donation.NHVs such as [(NHC)═CR] (R = H or aryl) are monoanionic ligands formally derived by the deprotonation of N-heterocyclic olefins (NHOs), (NHC)═CHR. Further deprotonation of [(NHC)═CR] (R = H) is viable, giving rise to N-heterocyclic vinylidene (NHVD) species such as (NHC)═C. NHVs and NHVDs feature a highly polarizable exocyclic CNHC═C bond because of the presence of adjacent π-donor nitrogen atoms. The nature of the NHC, in particular the π-acceptor property, has a direct consequence on the polarity of the CNHC═C bond and hence on the magnitude of π-conjugation in the derived molecules. Thus, the electronic structure, especially the energy and shape of frontier molecular orbitals, HOMO and LUMO, of derived species can be fine-tuned by a judicious choice of the carbene unit. For instance, the HOMO of classical diphosphenes (RP═PR) (R = alkyl or aryl) is invariably the phosphorus lone-pair orbital, while the P═P π-bond is HOMO - 1 or HOMO - 2. In strong contrast, the HOMO of divinyldiphosphenes (R = NHV) is mainly the P═P π-bond. This is owing to the π-conjugation, resulting in the lowering of the LUMO and raising of the HOMO energy. They have a remarkably small HOMO-LUMO energy gap (4.15-4.50 eV) and readily undergo 1e-oxidations, giving rise to stable radical cations and dications.By employing a similar approach, one can access divinyldiarsenes and the corresponding radical cations and dications as crystalline solids. The use of divinyldiphosphenes and divinyldiarsenes as promising ligands in the stabilization of metalloradicals has been shown. By a logical selection of singlet carbenes, stable 2-phosha-1,3-butadiene and 2-arsa-1,3-butadiene compounds, as well as related radical cations and dications, can be prepared as crystalline solids.The relevance of NHV ligands as potent π-donors has been demonstrated for the stabilization of elusive electrophilic phosphinidene and arsinidene complexes {(NHV)E}Fe(CO)4 (E = P or As). Moreover, stable singlet diradicaloid [(NHC)CP]2 and p-quinodimethane derivatives [(NHC)CP2]2 based on an NHVD framework are accessible as stable solids.In this Account, a special emphasis is given to the contributions from this laboratory. The author hopes that this Account will serve as a useful reference guide for researchers interested in studying and applying NHV and NHVD scaffolds in modern molecular chemistry and materials sciences.

Pyrazole-containing pharmaceuticals: target, pharmacological activity, and their SAR studies.

Pyrazole is a five-membered heterocycle bearing two adjacent nitrogen atoms. Both pharmaceutical agents and natural products with pyrazole as a nucleus have exhibited a broad spectrum of biological activities. In the last few decades, more than 40 pyrazole-containing drugs have been approved by the FDA for the treatment of a broad range of clinical conditions including celecoxib (anti-inflammatory), CDPPB (antipsychotic), difenamizole (analgesic), etc. Owing to the unique physicochemical properties of the pyrazole core, pyrazole-containing drugs may exert better pharmacokinetics and pharmacological effects compared with drugs containing similar heterocyclic rings. The purpose of this paper is to provide an overview of all the existing drugs bearing a pyrazole nucleus that have been approved or in clinical trials, involving their pharmacological activities and SAR studies.

The Role of the 1,2,3-Triazolyl Heterocycle in the Helical Columnar Assembly and Electric Field Response

Here, we have proven the role of the 1,2,3-triazolyl group in the helical assembly and electric field (E-field) response upon comparing liquid crystal analogs 1 and 2 based on 1,2,3-triazolyl and 1,3,4-oxadiazolyl linkers, respectively. An ordered helical column was only observed in 1, driven by the hydrogen-bonding interactions between the adjacent triazolyl nitrogen and hydrogen atoms. X-ray diffraction and energy simulations indicate that the helical column is a 112 helix and the helical axis does not coincide with the center of the molecular long axis. The key for the formation of the helical column is the tilted conformation of 1 originating from the steric repulsion between the triazolyl C-H and C-H of the aromatic core. Analysis of the dynamics in the simple hexagonal columnar phase revealed that the in-plane rotational motion of the triazolyl linker (1) is allowed, while the oxadiazolyl linker of 2 has limited conformational flexibility. A uniform alignment under an E-field only occurs in 1, demonstrating the requirement for conformational flexibility in the polar linker. This alignment enhances the electric conductance of 1 by approximately two-fold.

Nature of C[sbnd]N bond in N-heterocyclic carbene

The electronic structure and bonding in five-membered N-heterocyclic carbene (NHC) have been explored by EDA-NOCV analysis, which indicates that the CN bonds in NHC are different from conventional electron sharing covalent bonds. The interaction between the carbene carbon atom and the adjacent nitrogen atoms in NHC can be best represented as one σ-type 3c-2e electron sharing bond and one σ-type 3c-2e donor–acceptor bond. It can be considered equivalent to two localized representations viz., one electron sharing NC σ bond and one donor–acceptor N → C σ bond between the two nitrogen atoms and the carbene carbon atom.

Homocoupling Reactions of Azoles and Their Applications in Coordination Chemistry.

Pyrazole, a member of the structural class of azoles, exhibits molecular properties of interest in pharmaceuticals and materials chemistry, owing to the two adjacent nitrogen atoms in the five-membered ring system. The weakly basic nitrogen atoms of deprotonated pyrazoles have been applied in coordination chemistry, particularly to access coordination polymers and metal-organic frameworks, and homocoupling reactions can in principle provide facile access to bipyrazole ligands. In this context, we summarize recent advances in homocoupling reactions of pyrazoles and other types of azoles (imidazoles, triazoles and tetrazoles) to highlight the utility of homocoupling reactions in synthesizing symmetric bi-heteroaryl systems compared with traditional synthesis. Metal-free reactions and transition-metal catalyzed homocoupling reactions are discussed with reaction mechanisms in detail.

Biologically Active Pyridazines and Pyridazinone Derivatives: A Scaffold for the Highly Functionalized Compounds

Pyridazine and pyridazinone are heterocycles that contain two adjacent nitrogen atoms and shown wide range of pharmacological activities such as antimicrobial, antidepressant anti-hypertensive, anticancer, antiplatelet, antiulcer, herbicidal, antifeedant and various other anticipated biological activities. Pyridazine ring are present in some commercially available drugs and agrochemicals. Pyridazine based systems have been shown to have numerous practical applications.

Structure and Stability of Aromatic Nitrogen Heterocycles Used in the Field of Energetic Materials.

Understanding the stabilization of nitrogen heterocycles is critical in the field of energetic materials and calls for innovative knowledge of nitrogen aromatics. Herewith, we report for the first time that nitrogen lone pair electron (NLPE) delocalization in five-membered nitrogen heterocycles creates a second σ-aromaticity in addition to the prototypical π-aromaticity. The NLPE delocalization and the attendant dual-aromaticity are enhanced as more carbon atoms in the ring are substituted by unsaturated nitrogen atoms. The presence of adjacent nitrogen atoms in the ring can enhance the aromaticity of the nitrogen heterocycles and improve in-crystal intermolecular binding strength but will decrease the firmness of the individual molecular architecture. Notably, such σ-aromaticity is not present in six-membered nitrogen heterocycles, probably due to the longer bonds and broader regions of their rings; therefore, six-membered heterocycles present overall lower aromaticity than five-membered heterocycles. This work brings new knowledge to nitrogen aromatics and is expected to inspire broad interest in the chemistry community.

Meso-Diazacorrphycenes: Neighboring Effect of Two Nitrogen Atoms.

The neighboring effect of two adjacent heteroatoms influences the structures and properties of heterocyclic compounds. Herein, we demonstrated that the introduction of two adjacent sp2 nitrogen atoms into a porphyrinic skeleton significantly enhanced its Brønsted basicity due to the repulsive interaction between two lone pairs on the nitrogen atoms. Palladium- and copper-templated ring closure of dichlorobis(dipyrrin) with hydrazine hydrate provided meso-diazacorrphycene palladium and copper complexes in good yields. The structural, magnetic, and electrochemical properties of the diazacorrphycene complexes were investigated experimentally and theoretically to elucidate the effect of the meso-nitrogen atoms.

Design Synthesis and Evaluation of Anticancer Pyrazole Derivatives of Chalcone Scaffold

Pyrazoles are also a class of compounds that have the ring C3N2 with adjacent nitrogen atoms.[2] Notable drugs containing a pyrazole ring are celecoxib (Celebrex) and the anabolic steroid stanozolol. Chalcone is an aromatic ketone and an enone that forms the central core for a variety of important biological compounds, which are known collectively as chalcones or chalconoids. Chalcones (1, 3-diaryl propenones), a family of small molecules that are naturally abundant in edible plants, have been found to have antitumor properties for specific cancer cell lines and to interfere in each step of carcinogenesis, including apoptosis.

A Mini-Review 5-Amino-N-Substituted Pyrazoles as Building Blocks for Bioactive Molecules

In this review a five-membered heterocyclic ring having two adjacent nitrogen atoms known as Pyrazole, we have framed 5-amino-N-substituted pyrazoles in particular focusing on its substantial role as a building block and starting materials for producing enormous heterocyclic skeletons. The existence of this moiety in larger compounds renders them to expose medicinal, pharmacological and biological therapeutic activities. Enormous drugs contain 5-amino-N-substituted pyrazoles such as celecoxib anti-inflammatory, antipsychotic, anti-obesity, analgesic, and antidepressant. We reported various routes of synthesis and the use of these compounds.

Overview of recent developments of pyrazole derivatives as an anticancer agent in different cell line.

Pyrazole is a five-membered aromatic heterocyclic ring with two adjacent nitrogen atoms C3H3N2H.The presence of this nucleus in pharmacological agents of various therapeutic categories gifts a broad spectrum of biological activities and pharmaceuticals that contain pyrazole like celecoxib (anti-inflammatory), CDPPB (antipsychotic), Rimonabant (anti-obesity), Difenamizole, (Analgesic), Betazole (H2 receptor agonist), Fezolamide (Antidepressant), etc… The pharmacological potential of the pyrazole fraction is proved in many publication where they synthesized and evaluated pyrazoles against several biological agents. The aim of this article review is to survey recent works linking pyrazole structures to anticancer activities corresponding to 9 different type of cancer.

Isolation, characterization and reactivity of three-coordinate phosphorus dications isoelectronic to alanes and silylium cations.

Three-coordinate main group Lewis acids are exceedingly important reagents in chemical synthesis. In contrast to the well-established chemistries of neutral group 13 and cationic group 14 species, isoelectronic group 15 element dications are unknown. In this work, we use stabilizing N-heterocyclic imine substituents to isolate and characterize phosphorandiylium dications ([R3P]2+) and show that the electrophilicity at the phosphorus atoms is controlled by the π-electron-donating ability of these subtituents. Structural, spectroscopic and theoretical results reveal that the phosphorus dications adopt a perfectly trigonal-planar geometry with the electron-deficient phosphorus centres being well separated from the borate anions. The reactivity of the dications reveal their exceptional Lewis acidity at phosphorus; the adjacent nitrogen atoms, however, are weakly basic, resulting in transformations such as chloride ion abstraction from Me3SiCl and the selective monodefluorination of trifluoromethyl groups.

An efficient Bi/NH4I-mediated addition reaction for the highly diastereoselective synthesis of homoallylic alcohols in aqueous media

An efficient water-based bismuth-mediated addition reaction of carbonyl compound with cyclic allylic halide was developed. The reactions proceeded smoothly in aqueous DMF in the presence of ammonium iodide to afford the corresponding syn-homoallylic alcohols in moderate to good yields with excellent diastereoselectivities (>99:1 syn:anti). Reversal of product diastereoselectivity was observed when heteroaryl aldehyde possessing an adjacent chelating nitrogen atom was employed as substrate.

SYNTHESIS AND BIOLOGICAL EVALUATION OF 1-SUBSTITUTED-2-THIENYL- 5-(4-CHLOROPHENYL) PYRAZOLINE DERIVATIVES AS ANTIPROLIFERATIVE AGENTS

Cancer is not a single disease, but a large group of diseases characterized by uncontrolled, rapid and pathological proliferation of abnormally transformed cells. Pyrazoline is a five-membered heterocyclic ring having two adjacent nitrogen atoms within the ring. It has only one endocyclic double bond and is basic in nature. The present study involves synthesis of 1-substituted-2-thienyl-5-(4-chlorophenyl) pyrazoline derivatives. The synthesized compounds were subjected to anticancer screening against SK-OV-3 cells line to determine the growth inhibitory effects of the compounds. Amongst all the derivatives in series (6a-j), the pyrazoline derivatives exhibited potent anticancer activity. All synthesized compounds possessed good to moderate anticancer activity. Compounds 6b and 6c at concentration 80 μg/mL possessed % control growth inhibition comparable to standard drug andriamycin. The order for the % control growth inhibition of SK-OV-3 was found to be 6h> 6j> 6f> 6i> 6e> 6g> 6d> 6a. All the compounds inhibited 50 % of the cell growth at the conc.

Mononuclear iron-dependent electrocatalytic activity of metal-nitrogen-carbon catalysts for efficient oxygen reduction reaction

As a low-cost nonprecious metal-based catalyst, the mononuclear iron embedded in nitrogen-doped carbons has been regarded as one type of the best electrocatalytic materials for the oxygen reduction reaction (ORR). Herein, we proposed a silica-protective-layer assisted strategy for fabricating the catalysts with mononuclear iron site coordinated with adjacent nitrogen and carbon atoms, through high temperature pyrolysis of melamine, carbon black and FeCl3. At 800 °C, the fabricated catalyst features completely atomic level iron-nitrogen-carbon catalysts without Fe-based phases. In concentrated 1 M NaOH solution, this catalyst displays a remarkably improved catalytic activity with half-wave potential of 0.90 V. The mass activity of catalyst can reach 1.06 times that of commercial Pt/C (20 wt%, Pt). The correlation of the mononuclear iron composition and coordination structure with the promoted ORR kinetics was discussed in detail. The superior activity can be attributed to lots of the mononuclear iron moieties with a non-planar Fe(II)-N4 structure and increased surface area of the as-synthesized heterogeneous catalyst.

Catalyst-free, aza-Michael polymerization of hydrazides: polymerizability, kinetics, and mechanistic origin of an α-effect.

Despite the powerful nature of the aza-Michael reaction for generating C-N linkages and bioactive moieties, the bis-Michael addition of 1° amines remains ineffective for the synthesis of functional, step-growth polymers due to the drastic reduction in reactivity of the resulting 2° amine mono-addition adduct. In this study, a wide range of commercial hydrazides are shown to effectively undergo the bis-Michael reaction with divinyl sulfone (DVS) and 1,6-hexanediol diacrylate (HDA) under catalyst-free, thermal conditions to afford moderate to high molecular weight polymers with M n = 3.8-34.5 kg mol-1. The hydrazide-Michael reactions exhibit two distinctive, conversion-dependent kinetic regimes that are 2nd-order overall, in contrast to the 3rd-order nature of amines previously reported. The mono-addition rate constant was found to be 37-fold greater than that of the bis-addition at 80 °C for the reaction between benzhydrazide and DVS. A significant majority (12 of 15) of the hydrazide derivatives used here show excellent bis-Michael reactivity and achieve >97% conversions after 5 days. This behavior is consistent with calculations that show minimal variance of electron density on the N-nucleophile among the derivatives studied. Reactivity differences between hydrazides and hexylamine are also explored. Overall, the difference in reactivity between hydrazides and amines is attributed to the adjacent nitrogen atom in hydrazides that acts as an efficient hydrogen-bond donor that facilitates intramolecular proton-transfer following the formation of the zwitterion intermediate. This effect not only activates the Michael acceptor but also coordinates with additional Michael acceptors to form an intermolecular reactant complex.

NVP-BHG712: Effects of Regioisomers on the Affinity and Selectivity toward the EPHrin Family.

Erythropoietin-producing hepatocellular (EPH) receptors are transmembrane receptor tyrosine kinases. Their extracellular domains bind specifically to ephrin A/B ligands, and this binding modulates intracellular kinase activity. EPHs are key players in bidirectional intercellular signaling, controlling cell morphology, adhesion, and migration. They are increasingly recognized as cancer drug targets. We analyzed the binding of NVP-BHG712 (NVP) to EPHA2 and EPHB4. Unexpectedly, all tested commercially available NVP samples turned out to be a regioisomer (NVPiso) of the inhibitor, initially described in a Novartis patent application. They only differ by the localization of a single methyl group on either one of two adjacent nitrogen atoms. The two compounds of identical mass revealed different binding modes. Furthermore, both in vitro and in vivo experiments showed that the isomers differ in their kinase affinity and selectivity.

Molecular simulation of chlorophyll-a derivatives for biological pigment solar cells

ABSTRACTIn this study, various factors affecting the photon-to-electron conversion efficiency of chlorophyll-a derivatives were determined to improve the performance of biological pigment solar cells. By employing the density functional theory with hybrid exchange–correlation functional B3LYP, we calculated the photoelectronic properties such as energy gaps, main transmission path, electronegativity, proton affinity, spectral absorption, and electron transfer rates of chlorophyll-a derivatives, e.g. chlorin–Fe, chlorin–Mg, chlorin–Ni, and chlorin–Zn. The difference in electronegativity between the central metal and the adjacent nitrogen atoms induced changes in the distribution of electron clouds, which indirectly enhanced the absorbance in ultraviolet and long wavelength ranges; thus, the absorption spectrum can be controlled. Further, chlorin–Mg and chlorin–Ni demonstrated better electron transfer rates. The results indicate that design strategies of biopigment derivatives are an effective way to reduce the reorganisation energy, hence improving the electron mobility.