Theoretical insight into the role of urea in the hydrolysis reaction of NO2 as a source of HONO and aerosols

2018 ◽  
Vol 15 (6) ◽  
pp. 372 ◽  
Author(s):  
Shuang Lv ◽  
Feng-Yang Bai ◽  
Xiu-Mei Pan ◽  
Liang Zhao
Keyword(s):  
Nitric Acid ◽  
Energy Barrier ◽  
Computational Study ◽  
Theoretical Calculations ◽  
Nbo Analysis ◽  
Hydrolysis Reaction ◽  
Hydrogen Bond Interaction ◽  
Distribution Maps ◽  
Urea Nitrate

Environmental contextUrea is an important component of dissolved organic nitrogen in rainfall and aerosols, but the sources and the mechanisms of its production are not well understood. This computational study explores the effects of urea and water on the hydrolysis of NO2 and urea nitrate production. The results will aid our interpretation of the role of urea in the formation of atmospheric secondary nitrogen contaminants and aerosols. AbstractThe effects of urea on the hydrolysis reaction 2NO2 + mH2O (m = 1–3) have been investigated by theoretical calculations. The energy barrier (−2.67 kcal mol−1) of the urea-promoted reaction is lower than the naked reaction by 14.37 kcal mol−1. Urea also has a better catalytic effect on the reaction than methylamine and ammonia. Urea acts as a catalyst and proton transfer medium in this process, and the produced HONO may serve as a source of atmospheric nitrous acid. In addition, the subsequent reactions include clusters of nitrite, urea, and nitric acid. Then urea nitrate (UN), which is a typical HNO3 aerosol, can be formed in the subsequent reactions. The production of the acid-base complex (UN-2) is more favourable with an energy barrier of 0.10 kcal mol−1, which is 3.88 kcal mol−1 lower than that of the zwitterions NH2CONH3+NO3− (UN-1). The formation of zwitterions and the hydrolysis reaction are affected by humidity. The multi water-promoted hydrolysis reactions exhibit better thermodynamic stability when the humidity is increased. The extra water molecules act as solvent molecules to reduce the energy barrier. The natural bond orbital (NBO) analysis is employed to describe the donor-acceptor interactions of the complexes. The hydrogen bond interaction between the urea carbonyl and nitric acid of UN-2 is the strongest. The potential distribution maps of the urea nitrate and hydrate are examined, and the result shows that they tend to form zwitterions.

scholarly journals The Activating Effect of Strong Acid for Pd-Catalyzed Directed C–H Activation by Concerted Metalation-Deprotonation Mechanism

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4083
Author(s):  
Heming Jiang ◽  
Tian-Yu Sun
Keyword(s):  
Activation Energy ◽  
Dft Calculations ◽  
Energy Barrier ◽  
Computational Study ◽  
Strong Acid ◽  
Activation Energy Barrier ◽  
Pd Catalysts ◽  
Acid Ligand ◽  
Strong Acids

A computational study on the origin of the activating effect for Pd-catalyzed directed C–H activation by the concerted metalation-deprotonation (CMD) mechanism is conducted. DFT calculations indicate that strong acids can make Pd catalysts coordinate with directing groups (DGs) of the substrates more strongly and lower the C–H activation energy barrier. For the CMD mechanism, the electrophilicity of the Pd center and the basicity of the corresponding acid ligand for deprotonating the C–H bond are vital to the overall C–H activation energy barrier. Furthermore, this rule might disclose the role of some additives for C–H activation.

scholarly journals Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

2020 ◽  
Vol 16 ◽  
pp. 3059-3068
Author(s):  
Giovanna Zanella ◽  
Martina Petrović ◽  
Dina Scarpi ◽  
Ernesto G Occhiato ◽  
Enrique Gómez-Bengoa
Keyword(s):  
Double Bond ◽  
Nitrogen Atom ◽  
Deleterious Effect ◽  
Computational Study ◽  
Theoretical Calculations ◽  
Piperidine Ring ◽  
Nazarov Reaction ◽  
Activation Barriers ◽  
Propargyl Ester

The tandem gold(I)-catalyzed rearrangement/Nazarov reaction of enynyl acetates in which the double bond is embedded in a piperidine ring was computationally and experimentally studied. The theoretical calculations predict that the position of the propargylic acetate substituent has a great impact on the reactivity. In contrast to our previous successful cyclization of the 2-substituted substrates, where the nitrogen favors the formation of the cyclized final product, the substitution at position 3 was computed to have a deleterious effect on the electronic properties of the molecules, increasing the activation barriers of the Nazarov reaction. The sluggish reactivity of 3-substituted piperidines predicted by the calculations was further confirmed by the results obtained with some designed substrates.

Theoretical study of the gaseous hydrolysis of NO2 in the presence of NH3 as a source of atmospheric HONO

2016 ◽  
Vol 13 (4) ◽  
pp. 611 ◽  
Author(s):  
Xu Wang ◽  
Feng-Yang Bai ◽  
Yan-Qiu Sun ◽  
Rong-Shun Wang ◽  
Xiu-Mei Pan ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
Nitrous Acid ◽  
Energy Barrier ◽  
Theoretical Calculations ◽  
Hydrolysis Reaction ◽  
Phase Reaction ◽  
Chemical Mechanisms ◽  
Decomposition Processes ◽  
Additional Water ◽  
Hydrolysis Of

Environmental context Nitrous acid is an important atmospheric trace gas, but the sources and the chemical mechanisms of its production are not well understood. This study explores the effects of ammonia and water on the hydrolysis of nitrogen dioxide and nitrous acid production. The calculated results show that ammonia is more effective than water in promoting the hydrolysis reaction of nitrogen dioxide. Abstract The effects of ammonia and water molecules on the hydrolysis of nitrogen dioxide as well as product accumulation are investigated by theoretical calculations of three series of the molecular clusters 2NO2–mH2O (m=1–3), 2NO2–mH2O–NH3 (m=1, 2) and 2NO2–mH2O–2NH3 (m=1, 2). The gas-phase reaction 2NO2 + H2O → HONO + HNO3 is thermodynamically unfavourable. The additional water or ammonia in the clusters can not only stabilise the products by forming stable complexes, but also reduce the energy barrier for the reaction. There is a considerable energy barrier for the reaction at the reactant cluster 2NO2–H2O: 11.7kcalmol–1 (1kcalmol–1=4.18kJmol–1). With ammonia and an additional water in the cluster, 2NO2–H2O–NH3, the thermodynamically stable products t-HONO + NH4NO3–H2O can be formed without an energy barrier. With two ammonia molecules, as in the cluster 2NO2–mH2O–2NH3 (m=1, 2), the reaction is barrierless and the product complex NH4NO2–NH4NO3 is further stabilised. The present study, including natural bond orbital analysis on a series of species, shows that ammonia is more effective than water in promoting the hydrolysis reaction of NO2. The product cluster NH4NO2–NH4NO3 resembles an alternating layered structure containing the ion units NH4+NO2– and NH4+NO3–. The decomposition processes of NH4NO2–NH4NO3 and its monohydrate are all spontaneous and endothermic.

Investigating the Resonance in Nitric Acid and the Nitrate Anion Based on a Modern Bonding Analysis

2018 ◽  
Vol 71 (4) ◽  
pp. 227 ◽  
Author(s):  
Malte Fugel ◽  
Florian Kleemiss ◽  
Lorraine A. Malaspina ◽  
Rumpa Pal ◽  
Peter R. Spackman ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Double Bond ◽  
Theoretical Calculations ◽  
Valence Bond ◽  
Nbo Analysis ◽  
Nitrate Anion ◽  
Resonance Structures ◽  
Bonding Analysis ◽  
Experimental Electron Density ◽  
Bond Character

The nitrate anion, NO3−, is often regarded as a textbook example for the very fundamental concept of resonance. Usually, three equivalent resonance structures with one N–O double bond and two N–O single bonds are considered. Consequently, each of the three N–O bonds should have a partial double bond character. In this study, we analyse the resonance in NO3− in comparison with the related species HNO3 and FNO3 by applying a combination of the Quantum Theory of Atoms in Molecules (QTAIM), a natural bond orbital (NBO) analysis, the electron localizability indicator (ELI), and valence bond (VB) calculations. Despite the fundamental importance of nitrate salts and nitric acid for the environment, chemistry, and industry, a bonding analysis is absent from the literature so far. The classical resonance structures are clearly reflected by the bond analysis tools, but are not the only contributions to the bonding situation. The resonance in HNO3 and FNO3 is greatly perturbed by the hydrogen and fluorine atoms. In addition to theoretical calculations, experimental electron density and wave function refinements were carried out on a KNO3 crystal.

scholarly journals Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO2 to methane

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yanming Cai ◽  
Jiaju Fu ◽  
Yang Zhou ◽  
Yu-Chung Chang ◽  
Qianhao Min ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Active Sites ◽  
Theoretical Calculations ◽  
High Energy ◽  
Single Atom ◽  
Faradaic Efficiency ◽  
High Energy Barrier ◽  
Catalytic Sites ◽  
Electron Reduction ◽  
First Time

AbstractSingle-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN2O2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO2 to CH4 with current density of 40 mA·cm-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN2O2 active sites are due to the proper elevated CH4 and H2 energy barrier and fine-tuned electronic structure of Cu active sites.

scholarly journals Improvements in the profiles and distributions of nitric acid and nitrogen dioxide with the LIMS version 6 dataset

2010 ◽  
Vol 10 (10) ◽  
pp. 4741-4756 ◽  
Author(s):  
E. Remsberg ◽  
M. Natarajan ◽  
B. T. Marshall ◽  
L. L. Gordley ◽  
R. E. Thompson ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Nitrogen Dioxide ◽  
Theoretical Calculations ◽  
Spin Splitting ◽  
Oxides Of Nitrogen ◽  
Polar Night ◽  
Chemical Effects ◽  
Satellite Sensors ◽  
Precision And Accuracy

Abstract. The quality of the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) nitric acid (HNO3) and nitrogen dioxide (NO2) profiles and distributions of 1978/1979 are described after their processing with an updated, Version 6 (V6) algorithm and subsequent archival in 2002. Estimates of the precision and accuracy of both of those species are developed and provided herein. The character of the V6 HNO3 profiles is relatively unchanged from that of the earlier LIMS Version 5 (V5) profiles, except in the upper stratosphere where the interfering effects of CO2 are accounted for better with V6. The accuracy of the retrieved V6 NO2 is also significantly better in the middle and upper stratosphere, due to improvements in its spectral line parameters and in the reduced biases for the accompanying V6 temperature and water vapor profiles. As a result of these important updates, there is better agreement with theoretical calculations for profiles of the HNO3/NO2 ratio, day-to-night NO2 ratio, and with estimates of the production of NO2 in the mesosphere and its descent to the upper stratosphere during polar night. In particular, the findings for middle and upper stratospheric NO2 should also be more compatible with those obtained from more recent satellite sensors because the effects of the spin-splitting of the NO2 lines are accounted for now with the LIMS V6 algorithm. The improved precisions and more frequent retrievals of the LIMS profiles along their orbit tracks provide for better continuity and detail in map analyses of these two species on pressure surfaces. It is judged that the chemical effects of the oxides of nitrogen on ozone can be studied quantitatively throughout the stratosphere with the LIMS V6 data.

scholarly journals Theoretical Study on the Photo-Oxidation and Photoreduction of an Azetidine Derivative as a Model of DNA Repair

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2911
Author(s):  
Miriam Navarrete-Miguel ◽  
Antonio Francés-Monerris ◽  
Miguel A. Miranda ◽  
Virginie Lhiaubet-Vallet ◽  
Daniel Roca-Sanjuán
Keyword(s):  
Electron Transfer ◽  
Energy Barrier ◽  
Ring Opening ◽  
Dna Lesions ◽  
Barrier Heights ◽  
Dna Lesion ◽  
Electron Reduction ◽  
The Stability ◽  
Electron Transfer Processes

Photocycloreversion plays a central role in the study of the repair of DNA lesions, reverting them into the original pyrimidine nucleobases. Particularly, among the proposed mechanisms for the repair of DNA (6-4) photoproducts by photolyases, it has been suggested that it takes place through an intermediate characterized by a four-membered heterocyclic oxetane or azetidine ring, whose opening requires the reduction of the fused nucleobases. The specific role of this electron transfer step and its impact on the ring opening energetics remain to be understood. These processes are studied herein by means of quantum-chemical calculations on the two azetidine stereoisomers obtained from photocycloaddition between 6-azauracil and cyclohexene. First, we analyze the efficiency of the electron-transfer processes by computing the redox properties of the azetidine isomers as well as those of a series of aromatic photosensitizers acting as photoreductants and photo-oxidants. We find certain stereodifferentiation favoring oxidation of the cis-isomer, in agreement with previous experimental data. Second, we determine the reaction profiles of the ring-opening mechanism of the cationic, neutral, and anionic systems and assess their feasibility based on their energy barrier heights and the stability of the reactants and products. Results show that oxidation largely decreases the ring-opening energy barrier for both stereoisomers, even though the process is forecast as too slow to be competitive. Conversely, one-electron reduction dramatically facilitates the ring opening of the azetidine heterocycle. Considering the overall quantum-chemistry findings, N,N-dimethylaniline is proposed as an efficient photosensitizer to trigger the photoinduced cycloreversion of the DNA lesion model.

scholarly journals Antioxidant Properties of Ergosterol and Its Role in Yeast Resistance to Oxidation

Antioxidants ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1024
Author(s):  
Sebastien Dupont ◽  
Paul Fleurat-Lessard ◽  
Richtier Gonçalves Cruz ◽  
Céline Lafarge ◽  
Cédric Grangeteau ◽  
...  
Keyword(s):  
Computational Study ◽  
Antioxidant Properties ◽  
Beneficial Effects ◽  
Tert Butyl Hydroperoxide ◽  
Resistance To Oxidation ◽  
Specific Accumulation ◽  
The Subject

Although the functions and structural roles of sterols have been the subject of numerous studies, the reasons for the diversity of sterols in the different eukaryotic kingdoms remain unclear. It is thought that the specificity of sterols is linked to unidentified supplementary functions that could enable organisms to be better adapted to their environment. Ergosterol is accumulated by late branching fungi that encounter oxidative perturbations in their interfacial habitats. Here, we investigated the antioxidant properties of ergosterol using in vivo, in vitro, and in silico approaches. The results showed that ergosterol is involved in yeast resistance to tert-butyl hydroperoxide and protects lipids against oxidation in liposomes. A computational study based on quantum chemistry revealed that this protection could be related to its antioxidant properties operating through an electron transfer followed by a proton transfer mechanism. This study demonstrates the antioxidant role of ergosterol and proposes knowledge elements to explain the specific accumulation of this sterol in late branching fungi. Ergosterol, as a natural antioxidant molecule, could also play a role in the incompletely understood beneficial effects of some mushrooms on health.

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