Density Functional Theory Mechanistic Study Research Articles

Synthesis, Characterization, DFT mechanistic study, Antibacterial Activity, Molecular modeling, and ADMET properties of novel chromone-isoxazole hybrids

A series of novel hybrid heterocycles incorporating isoxazole rings have been successfully synthesized, characterized, and evaluated for their antibacterial responses. The synthesized compounds were obtained by a subsequent N-alkylation and 1,3-dipolar cycloaddition reactions, their structures were identified by spectroscopy techniques (1H NMR, 13C NMR and 2D HSQC), and confirmed by mass spectrometry (HRMS). The spectroscopic data also show that the 1,3-dipolar cycloaddition (1,3-DC) reactions proceed in a regiospecific manner to give only one cycloadduct. The observed regioselectivity and the mechanistic study of the 1,3-DC reaction were further highlighted and explained using Density Functional Theory (DFT) calculations with the B3LYP/6–31G(d,p) basis set and Electron Localization Function (ELF) analysis. Moreover, the antibacterial screening shows that some compounds exhibit good efficacy against the tested bacterial strains. In addition, molecular docking studies were carried out to highlight the modes of interaction between the most active molecule 5d and receptors of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus strains. The results show that the studied compound was effectively docked to the active sites of each responsible protein with high protein-binding energies in kcal/mol. Finally, the prediction of ADMET properties suggests that almost all the hybrid compounds have good pharmacokinetic profiles, with no observed signs of toxicity, except for compounds 5e, 5f and 5g.

DFT mechanistic study of the chemical fixation of CO2 by aziridine derivatives.

Using density functional theory (DFT), we treat the reaction of coupling of CO2 with aziridine in gas phase, in the presence of water and of a green catalyst (NaBr). Computations show that, in gas phase, this ring-opening conversions to oxazolidinones initiates by coordinating a CO2 molecule to the nitrogen atom of the aziridine. Then, a nucleophilic interaction between one oxygen atom of the coordinated CO2 and the carbon atom of the aziridine occurs. For methyl substituted aziridine, two pathways are proposed leading either to 4-oxazolidinone or to 5-oxazolidinone. Besides, we show that the activation energy of this reaction reduces in aqueous solution, in the presence of a water molecule explicitly or NaBr catalyst. In addition, the corresponding reaction mechanisms and regioselectivity associated with this ring-opening conversions to oxazolidinones, in the presence of carbon dioxide are found to be influenced by solvent and catalyst. The present findings should allow better designing regioisomer oxazolidinones relevant for organic chemistry, medicinal and pharmacological applications.

A DFT Mechanistic Study of the Regio-, Chemo-, and Stereo- Selectivities of the (3 + 2) Cycloaddition of Diarylnitrone Derivatives with 1-(4-Nitrophenyl)-5H-Pyrrolin-2-One

Heterocyclic compounds are vital in rational drug design by providing convenient means for the optimization of drugs or drug candidates. Isoxazolidine (a heterocyclic compound) derived from the (3 + 2) cycloaddition reaction is reported to possess anticancer, antiviral, antibacterial, and anti-inflammatory properties. The mechanistic study of the chemo-, regio-, and stereo-selectivities of the (3 + 2) cycloaddition reaction (32CA) of diarylnitrones (A1) to 1-(4-nitrophenyl)-5H-pyrrolin-2-one (A2) has been conducted using the density functional theory (DFT) method at the M06/6-311G (d,p) computational level. The 32CA reaction of A1 and A2 proceeds through a chemo-selective addition of A1 across the C=C olefinic bond of A2 to furnish both kinetically and thermodynamically favored reaction routes. The effect of substitution on the 32CA reaction has been studied using a representative set of electron-acceptor and electron-releasing groups on both A1 and A2. The chemo-, regio-, and stereo-selectivities observed in the 32CA reaction remained unchanged irrespective of the substituents used on both reactants, but a change in kinetics and thermodynamics was observed based on the substituents. In the 32CA reaction of A1 and A2, the “exo” cycloadduct formation was favored over the “endo” cycloadducts in all instances.

Organic additive for the selective C2-product formation on Cu(100): a density functional theory mechanistic study

Electrochemical CO2 reduction is a promising approach to increase the chemical feedstock of energetically valuable products, especially ethylene and ethanol.

Novel Quinazolinone–Isoxazoline Hybrids: Synthesis, Spectroscopic Characterization, and DFT Mechanistic Study

Quinazolinone and isoxazoline systems have attracted much attention due to their interesting pharmacological properties. The association of these two pharmacophores in a single hybrid structure can boost the biological activity or bring a new one. Inspired by this new paradigm, in the present work we report the synthesis and spectroscopic characterization of new quinazolinone–isoxazoline hybrids. The target compounds were obtained via 1,3-dipolar cycloaddition reactions of arylnitriloxides and N-allylquinazolinone. The synthesized compounds were characterized using spectroscopic techniques such as IR, 1D NMR (1H and 13C), 2D NMR (COSY and HSQC), and high-resolution mass spectrometry (HRMS). The spectral data show that this reaction leads only to the 3,5-disubstituted isoxazoline regioisomer, and that the observed regiochemistry is not affected by the nature of the substituents in the phenyl ring of the dipole. In addition, a theoretical study was performed using density functional theory (DFT) to support the experimental results in regard to the regiochemistry of the studied reactions. The computational mechanistic study was in good agreement with the experimental data.

Neutral Phosphine-Sulfonate Pd Complex-Catalyzed Copolymerization of 2-Methoxystyrene and Ethylene Polar Monomers: A DFT Mechanistic Study

The density functional theory (DFT) method was employed to investigate the nature of the copolymerization reaction of ethylene monomers and 2-methoxystyrene catalyzed by a palladium phosphine-sulfonate complex. The calculated results indicate that (1) the ethylene molecules prefer to coordinate with neutral phosphine-sulfonate Pd catalyst along the Pd–P side to generate an intermediate owning a cis-configuration, which indicate that the chain transfer proceeds from cis-3 but not trans-5. (2) Subsequently, the insertion of polar monomers in the chain propagation is easier than that of the ethylene monomer and adopts the 2,1 insertion pathway; meanwhile, the R-configuration pathway is more favorable than the S-configuration pathway in stage II. (3) After the polar monomer insertion, the β-H elimination pathway is easier than the ethylene insertion, which makes polar monomer insertion into the in-chain easier. This work revealed the mechanism of the copolymerization reaction of ethylene and 2-methoxystyrene catalyzed by a palladium phosphine-sulfonate complex, which could provide theoretical insights into the development of new transition-metal complexes for the copolymerization reaction.

DFT Mechanistic Study of the Cyclopropanation of Styrene and Aryldiazodiacetate Catalyzed by Tris(pentafluorophenyl)borane.

Metal-free boron Lewis acids, tris(pentafluorophenyl)borane B(C6F5)3, have the advantages of low toxicity and low cost and are a promising catalyst. A density functional theory (DFT) calculation was used to clarify the mechanism and the origin of the diastereoselective cyclopropanation of aryldiazodiacetate and styrene derivatives catalyzed by B(C6F5)3. Four pathways were calculated: B(C6F5)3-catalyzed N-, C-, and O-bound boron-activated aryldiazodiacetate and without B(C6F5)3 catalysis. By calculating and comparing the energy barriers, the most possible reaction mechanism was proposed, that is, first, B(C6F5)3 catalyzed O-bound boron to activate aryldiazodiacetate, followed by the removal of a N2 molecule, and finally, styrene nucleophilic attack occurred to produce [2+1] cyclopropane products. N2 removal is the rate-limiting step, and this step determines the preference of a given mechanism. The calculated results are in agreement with experimental observations. The origin of diastereoselectivity is further explained on the basis of the favorable mechanism. The steric hindrance interference between the styrene aryl group and the large tri(pentafluorophenyl)borane B(C6F5)3 and the favorable π–π stacking interaction between the benzene rings combined to cause the high diastereoselectivity, which resulted in lower energy of the transition state (TS) corresponding to the reaction mechanism. The calculated results not only provide a more detailed explanation of the mechanism for the experimental study but also have certain reference and guiding significance for other catalytic cyclopropanation reactions.

The Role of AQ in the Regioselectivity of Strong Alkyl C-O Bond Activation Catalyzed by Pd(OAc)2: A Density Functional Theory Mechanistic Study.

A density functional theory method was employed to investigate the mechanism of C-O bond activation of butanoic acid substrates bearing the 8-aminoquinoline (AQ) group catalyzed by Pd(OAc)2. The whole reaction consists of five fundamental steps: the chelation of substrate A1, the C-H activation step, the C-N coupling step, the protodepalladation step, and the release of the final product. The calculated results indicated that the protodepalladation step is the rate-determining step with a free energy barrier of 24.3 kcal/mol. This theoretical study pointed out that the energy barriers of C-H activation in the presence and absence of AQ are 11.3 and 26.6 kcal/mol, respectively. This is to say that the installation of the AQ directing group is critical to the regioselectivity of C-H activation and the β-O elimination steps, and this reason enables selective activation of the γ C-O bond. Furthermore, this chelating functionality facilitated the protodepalladation step because the energy barrier of the protodepalladation step was decreased with the coordination of the AQ directing group with a Pd center, and that was 39.3 kcal/mol in the absence of AQ. This also explains why no product formation was observed in the experiment upon changing the directing AQ group to a phenylamino group. Finally, other substrates bearing the phenol leaving group at the β- and δ-positions of carbonyl were investigated in order to expand the applicability of the AQ directing strategy. This work could provide new theoretical insights into the activation of strong alkyl C(sp3) covalent bonds via the AQ directing strategy.

Boron-Catalyzed Hydroarylation of 1,3-Dienes with Arylamines.

Catalytic hydroarylation reactions of conjugated dienes are achieved using tris(pentafluorophenyl)borane as a Lewis acid catalyst under mild reaction conditions. This new protocol shows a broad substrate scope for the highly regioselective functionalization of sterically hindered aniline derivatives. Experimental and extensive density functional theory mechanistic studies show that the complex of residual water and B(C6F5)3 plays a crucial role in the aryl-assisted protonation of conjugated dienes, forming allyl cation intermediates that induce the facile electrophilic aromatic substitution of aniline substrates.

Investigating the site-, regio-, and stereo-selectivities of the reactions between organic azide and 7-heteronorbornadiene: a DFT mechanistic study.

The site-, regio-, and stereo-selectivities of the title reactions have been studied using density functional theory (DFT) at the M06/6-311G(d,p) level of theory. The effects of substituents on both the three-atom component (TAC) and norbornadiene derivatives have been investigated with a focus on the site-selectivity. The reaction of benzylazide with (1S,4R)-2-tosyl-7-oxabicyclo[2.2.1]hepta-2,5-diene and (1R,4S)-2-bromo-3-tosyl-7-oxabicyclo[2.2.1]hepta-2,5-diene proceeds via addition across the substituted olefinic bond of the two norbornadiene derivatives. Substituents on the TAC do not affect the selectivity of the reaction while substituents on the norbornadiene significantly affect the selectivity of the reaction. Benzylazide preferentially adds across the substituted olefinic bond of the norbornadiene derivative when strong electron-withdrawing group (EWGs) and electron-releasing group (ERGs) substituents are on the norbornadiene while weak ERGs and EWGs on the norbornadiene significantly decreases the site-selectivity such that addition across either double is no longer favored over the other. The formation of exo-cycloadducts is generally favored over the endo-cycloadducts. The reaction of benzylazide and norbornadiene derivatives is a highly irreversible exergonic reaction. The direction of electron density flux is dependent on the nature of the substituent on the reactants. Global reactivity indices and Parr function calculations are in good agreement with the activation barriers and the selectivity of the reactions.

DFT mechanistic study on the formation of 8-oxoguanine and spiroiminodihydantoin mediated by iron Fenton reactions.

Fenton reactions unavoidably take place in the human body and have been demonstrated to cause oxidative DNA damage. However, the molecular-level understanding of DNA damage mediated by Fenton reactions is limited. Herein, density functional theory (DFT) calculations were made to investigate the counterion effects on aqueous Fenton reactions and the detailed mechanisms of chemical modifications to guanine induced by Fenton reactions. Our calculations show that the activation energy of the Fenton reaction catalyzed by a pure aquo complex [FeII(H2O)6]2+ is too high to agree with experiments, whereas complexation with counteranions reduces the activation energy to a reasonable range. This result suggests that FeII-counteranion complexes are the real catalyst for fast aqueous Fenton reactions. In addition, we found that the Fenton oxidation mediated by FeII bonded to the N7 atom of guanine can result in the formation of 8-oxoguanine and spiroiminodihydantoin through multiple reaction pathways, including the electrophilic addition of ˙OH, H-abstraction by ˙OH, and oxygen atom transfer of oxoiron(iv) species. The activation of hydrogen peroxide by ferrous iron is the rate-determining step. The guanine N7-bound iron ion and the coordinated counteranion were found to play an important role in the Fenton oxidation of guanine.

Remarkable N2-selectivity enhancement of practical NH3-SCR over Co0.5Mn1Fe0.25Al0.75Ox-LDO: The role of Co investigated by transient kinetic and DFT mechanistic studies

A Co0.5Mn1Fe0.25Al0.75Ox-LDO catalyst was developed which showed excellent performance for the low-temperature NH3-SCR. NOx conversions ∼100% were achieved in the whole 100-250 °C range, while after 10-h operation at 150 °C with 100 ppm SO2/5 vol% H2O in the feed, the NOx conversion was maintained at 80%. This catalyst provided a much better N2-selectivity than the Mn1Fe0.25Al0.75Ox-LDO and Mn1Al1Ox-LDO, especially at 150-300 °C. It was found that Co0.5Mn1Fe0.25Al0.75Ox possessed higher surface acidity and reducibility, while XPS analyses indicated an electron transfer between Co3+/Co2+ and Mn4+/Mn3+ redox cycles, leading to a much lower N2O formation, supported by Density Functional Theory (DFT) calculations. Detailed analysis of gas responses obtained upon various step-gas switches was performed, which allowed to measure the surface concentration and reactivity of preadsorbed NOx-s and NHx-s leading to N2 and N2O. Transient kinetic and DFT studies strongly suggested likely mechanisms of NH3-SCR and the critical role of Co for N2-selectivity enhancement.

Density Functional Theory Mechanistic Study of Ni-Catalyzed Reductive Alkyne-Alkyne Cyclodimerization: Oxidative Cyclization versus Outer-Sphere Proton Transfer.

Density functional theory mechanistic study of the nickel-catalyzed reductive alkyne-alkyne cyclodimerization with CH3OH/BEt3 unveils that, after forming a nickel-alkyne π complex, the reaction prefers outer-sphere proton transfer rather than the common alkyne-alkyne oxidative cyclization. The outperformance of aminophosphine ligand (L1) is attributed to its bidentate coordination that favors the proton transfer, the labile -NH2 and strong electron-donating -PPh2 arms and adequate Ni-P distance that allow the hydrogen transfer of the ethyl group of MeO-BEt3-.

Selective Oxidation of H2 and CO by NiIr Catalyst in Aqueous Solution: A DFT Mechanistic Study.

One of the challenges in utilizing hydrogen gas (H2) as a sustainable fossil fuel alternative is the inhibition of H2 oxidation by carbon monoxide (CO), which is involved in the industrial production of H2 sources. To solve this problem, a catalyst that selectively oxidizes either CO or H2 or one that co-oxidizes H2 and CO is needed. Recently, a NiIr catalyst [NiIICl(X)IrIIICl(η5-C5Me5)], (X = N,N'-dimethyl-3,7-diazanonane-1,9-dithiolate), which efficiently and selectively oxidizes either H2 or CO depending on the pH, has been developed (Angew. Chem. Int. Ed. 2017, 56, 9723-9726). In the present work, density functional theory (DFT) calculations are employed to elucidate the pH-dependent reaction mechanisms of H2 and CO oxidation catalyzed by this NiIr catalyst. During H2 oxidation, our calculations suggest that dihydrogen binds to the Ir center and generates an Ir(III)-dihydrogen complex, followed by subsequent isomerization to an Ir(V)-dihydride species. Then, a proton is abstracted by a buffer base, CH3COO-, resulting in the formation of a hydride complex. The catalytic cycle completes with electron transfer from the hydride complex to a protonated 2,6-dichlorobenzeneindophenol (DCIP) and a proton transfer from the oxidized hydride complex to a buffer base. The CO oxidation mechanism involves three distinct steps, i.e., (1) formation of a metal carbonyl complex, (2) formation of a metallocarboxylic acid, and (3) conversion of the metallocarboxylic acid to a hydride complex. The formation of the metallocarboxylic acid involves nucleophilic attack of OH- to the carbonyl-C followed by a large structural change with concomitant cleavage of the Ir-S bond and rotation of the COOH group along the NiIr axis. During the conversion of the metallocarboxylic acid to the hydride complex, intramolecular proton transfer followed by removal of CO2 leads to the formation of the hydride complexes. In addition, the barrier heights for the binding of small molecules (H2, OH-, H2O, and CO) to Ir were calculated, and the results indicated that dissociation from Ir is a faster process than the binding of H2O and H2. These calculations indicate that H2 oxidation is inhibited by CO and OH- and thus prefers acidic conditions. In contrast, the CO oxidation reactions occur more favorably under basic conditions, as the formation of the metallocarboxylic acid involves OH- attack to a carbonyl-C and the binding of OH- to Ni largely stabilizes the triplet spin state of the complex. Taken together, these calculations provide a rationale for the experimentally observed pH-dependent, selective oxidations of H2 and CO.

Density Functional Theory Mechanistic Insight into the Base-Free Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling of Acid Fluoride: Concerted versus Stepwise Transmetalation.

Density functional theory mechanistic study has been carried out to account for the base-free nickel-catalyzed Suzuki-Miyaura coupling of acid fluorides (ArC(O)F) with boronic acids (Ar'B(OH)2). After oxidative addition to break the C-F bond of acid fluoride, the resultant ArC(O)[Ni]F species undergoes transmetalation with Ar'B(OH)2 to give ArC(O)[Ni]Ar'. Subsequently, ArC(O)[Ni]Ar' can either undergo decarbonylation, finally leading to the coupling product (ArAr'), or reductive elimination to give ketone byproduct ArC(O)Ar'. The kinetic competition between the two pathways controls the chemoselectivity of the reaction, and transmetalation is the rate-determining step of the coupling. Importantly, it was found that transmetalation prefers a stepwise mechanism over a conventional concerted one. Detailed analyses indicate that the strong fluorophilicity of boron facilitates the base-free transmetalation and the coordination interaction between an oxygen atom of boronic acid and nickel gears the base-free transmetalation to undergo the stepwise pathway. The stepwise transmetalation mechanism also involves the nickel-catalyzed Suzuki-Miyaura coupling of aldehydes with ketone (PhC(O)CF3) as the transmetalation promoter.

DFT mechanistic study on tandem sequential [4 + 2]/[3 + 2] addition reaction of cyclooctatetraene with functionalized acetylenes and nitrile imines

AbstractThe mechanistic pathways for the tandem sequential [4 + 2] / [3 + 2] and [3 + 2]/[4 + 2] cycloaddition reaction of functionalized‐acetylenes with cyclooctatetraene (COTE) and nitrile imines for the formation of the biologically‐active tricyclic cyclobutane‐condensed pyrazoline systems, and the subsequent cycloreversion/thermolysis of these adducts, have been studied using density functional theory (DFT) at the M06‐2X/6‐31G(d) and 6‐311G(d,p) levels with the aim of providing mechanistic rationale for the regioselectivities and stereoselectivities. Along the [4 + 2] / [3 + 2] addition sequence, it has been found that the initial 6π‐electrocyclic ring‐closure of the COTE is the rate‐determining step irrespective of the type of substituent on the parent acetylene or the nitrile imine. The mechanistic channels along the [4 + 2] / [3 + 2] addition sequence show that the addition of the dipole across the unsubstituted olefinic bond in the cyclohexadiene moiety in the endo fashion is the most favored, which is in agreement with experimentally observed selectivity. The results show that the thermolysis proceeds with relatively high activation barriers toward formation of the monocyclic pyrazolines among other products. The decomposition of the tandem adducts has been found to be controlled solely by kinetic factors. An exploration of a [3 + 2] / [4 + 2] addition sequence as a mechanistic possibility reveals that in contrast to the [4 + 2] / [3 + 2] addition sequence, the Diels‐Alder addition step is the rate‐determining. The [3 + 2] / [4 + 2] addition order is found as an approach with better selectivity as it leads to formation of only tandem adducts where the nitrile imines are attached to the substituted olefinic bond in the cyclohexadiene subunit. The results show that the monocyclic pyrazolines obtained from the thermolysis of the [4 + 2] / [3 + 2] tandem adducts could easily be obtained from a direct 1,3‐dipolar addition of the alkynes with the dipoles which has been found to proceed rapidly with low activation barriers. The results are rationalized with perturbation molecular orbital theory.

A DFT mechanistic study of the ODH of n-hexane over isolated H3VO4

Catalytic (H3VO4) oxidative dehydrogenation (ODH) mechanistic studies of the activation of n-hexane have been conducted by means of Density Functional Theory (DFT).Catalytic oxidative dehydrogenation is an important strategy for the conversion of alkanes to alkenes to provide useful chemical feedstocks from saturated hydrocarbons. Transition metal oxide catalysts based on vanadium provide an important class of catalysts for this reaction. The catalyst is usually prepared with vanadium in a high oxidation state prepared as an over layer supported on a relatively inert main group oxide (silica, alumina, etc.). Activation of the hydrocarbon is then energetically possible through the reduction of vanadium cations which can be subsequently re-oxidised using molecular O2 to complete the catalytic cycle.The aim of this study was to use density functional theory to explore the catalytic mechanism of this type of reaction using the conversion of n-hexane to 1- and 2-hexene as an illustrative example. Calculations are performed for the 1- and 2-hexene radical pathways and the results extrapolated to discuss the expected selectivity under laboratory experimental conditions (573, 673 and 773 K). Consideration of 3-hexene is excluded as in our earlier experimental studies and in the general literature this product is not reported. The stationary points on the potential energy surfaces were characterized and the associated geometries and relative energies (ΔE#, ΔE, ΔG# and ΔG) were determined. The relative energies of all intermediates and transition states identified are used to lend insight on the mechanistic pathways for the reaction.We have concentrated on the role of the transition metal in this chemistry and so the catalyst model chosen is an isolated, tetrahedral H3VO4 cluster containing one vanadyl bond, V(V)O. The calculated rate-limiting step is the CH bond activation (β-hydrogen abstraction) from the C6H14 chain by the vanadyl O, with a calculated ΔE# = +27.4 kcal/mol. This produces a C6H13HOH3VO3 complex as an intermediate with vanadium reduced to V(IV). There are then two possible routes for the propagation step that leads to 2-hexene. Firstly, the abstraction of the second γ-hydrogen on the radical intermediate fragment (C6H13) can take place on a different active V(V) = O site. Secondly this step may involve reaction with gas-phase molecular O2. These alternatives are compared computationally and results used to discuss some existing experimental data.

Density Functional Theory Mechanistic Study of Boron-Catalyzed N-Alkylation of Amines with Formic Acid: Formic Acid Activation by Silylation Reaction.

New methodology for the alkylation of amines is an intriguing issue in both academia and industry. Recently, several groups reported the metal-free B(C6 F5 )3 -catalyzed N-alkylation of amines, but the mechanistic details of these important reactions are unclear. Herein, a computational study was performed to elucidate the mechanism of the N-alkylation of amines with formic acid catalyzed by the Lewis acid B(C6 F5 )3 in the presence of hydrosilane. We found that the reaction started with the activation of formic acid through a novel model. Then, the high electrophilicity of the C center of the formic acid unit and the nucleophilic character of the amine resulted in a C-N coupling reaction. Finally, two sequential silyl-group and H- transfer steps occurred to generate the final product. Upon comparing the reaction barrier and the hydrogenation of indole, our mechanism is more favorable than that proposed by the group of Yu and Fu.

Carbon-doped boron nitride nanosheet as a promising metal-free catalyst for NO reduction: DFT mechanistic study

Currently, metal-based catalysts are commonly used to convert highly toxic gases like NO molecules into less toxic gases, such as N2O molecules through the process of reduction reaction that has a low activation energy (Ea) and high efficiency. Due to the high cost, environmental hazards and limited supply of metal-based catalysts, development of metal-free catalysts that are low cost and environmentally friendly has increased. For this research, NO reduction mechanism using the carbon-doped boron nitride nanosheets (CBNs) as a metal-free catalyst was investigated by density functional theory (DFT). For the NO reduction mechanism, the dimer mechanism pathway was investigated using the following equation: 2NO → N2O + Oad. In addition, the catalytic activity of carbon atom substitution onto BNs for NO reduction was studied. The results showed that the trans-(NO)2 structure of CNBNs (D5) is a potentially crucial intermediate with thermodynamically and kinetically favorable, in which the calculated rate-determining step along the most energetically favorable pathway is 0.62 eV. Hence, our results presented here suggest that CNBNs can be a highly active metal-free material in NO removal, which will reduce NO into environmentally friendly gases.

A combined experimental and DFT mechanistic study for the unexpected nitrosolysis of N-hydroxymethyldialkylamines in fuming nitric acid.

The reaction of dimorpholinomethane in fuming HNO3 was investigated. Interestingly, the major product was identified as N-nitrosomorpholine and a key intermediate N-hydroxymethylmorpholine was detected during the reaction by 1H-NMR tracking which indicates that the reaction proceeds via an unexpected nitrosolysis process. A plausible nitrosolysis mechanism for N-hydroxymethyldialkylamine in fuming nitric acid involving a HNO3 redox reaction is proposed, which is supported by both experimental results and density functional theory (DFT) calculations. The effects of ammonium nitrate and water on the nitrosolysis were studied using different ammonium salts as additives and varying water content, respectively. Observations show the key role of ammonium ions and a small amount of water in promoting the nitrosolysis reaction. Furthermore, DFT calculations reveal an essential point that ammonia, merged from the decomposition of the ammonium salts, acts as a Lewis base catalyst, and the hydroxymethyl group of the substrate participates in a hydrogen-bonding interaction with the NH3 and H2O molecules.