Preclusion of Irreversible Destruction of Dr Adhesin Structures by a High Activation Barrier for the Unfolding Stage of the Fimbrial DraE Subunit

Oxygen electrochemistry that comprises oxygen evolution and reduction reactions (OER/ORR) is vital for sustainable, clean and efficient energy generation. However, the high activation barrier due to the multi-electron transfer process...

Proton-coupled electron transfer at the Qo site: what type of mechanism can account for the high activation barrier?

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/s0005-2728(00)00184-5 ◽

2000 ◽

Vol 1459 (2-3) ◽

pp. 456-466 ◽

Cited By ~ 54

Author(s):

Antony R. Crofts ◽

Mariana Guergova-Kuras ◽

Richard Kuras ◽

Natalya Ugulava ◽

Jiyuan Li ◽

...

Keyword(s):

Electron Transfer ◽

Activation Barrier ◽

High Activation ◽

Proton Coupled Electron Transfer ◽

High Activation Barrier ◽

Qo Site

The surprisingly high activation barrier for oxygen-vacancy migration in oxygen-excess manganite perovskites

Physical Chemistry Chemical Physics ◽

10.1039/d0cp01281e ◽

2020 ◽

Vol 22 (25) ◽

pp. 14329-14339

Author(s):

Jacqueline M. Börgers ◽

Roger A. De Souza

Keyword(s):

Oxygen Vacancy ◽

Activation Enthalpy ◽

Activation Barrier ◽

Oxygen Activity ◽

High Activation ◽

Cation Vacancies ◽

Vacancy Migration ◽

High Activation Barrier ◽

Oxygen Excess ◽

Manganite Perovskites

Cation vacancies diminish the oxygen-vacancy diffusivity, raise the activation enthalpy, and cause the diffusivity to depend on oxygen activity.

Compensation effects and relation between the activation energy of spin transition and the hysteresis loop width for an iron(ii) complex

Physical Chemistry Chemical Physics ◽

10.1039/c6cp01892k ◽

2016 ◽

Vol 18 (25) ◽

pp. 16690-16699 ◽

Cited By ~ 11

Author(s):

Mark B. Bushuev ◽

Denis P. Pishchur ◽

Elena B. Nikolaenkova ◽

Viktor P. Krivopalov

Keyword(s):

Hysteresis Loop ◽

Spin Crossover ◽

Thermal Hysteresis ◽

Activation Barrier ◽

Spin Transition ◽

Hysteresis Loops ◽

High Activation ◽

Activation Barriers ◽

Spin Crossover Complexes ◽

Hysteresis Loop Width

Wide thermal hysteresis loops for iron(ii) spin crossover complexes are associated with high activation barriers: the higher the activation barrier, the wider the hysteresis loop for a series of related spin crossover systems.

Bypassing the Inertness of Aziridine/CO2 Systems to Access 5-Aryl-2-Oxazolidinones: Catalyst-Free Synthesis Under Ambient Conditions

10.26434/chemrxiv.11671419 ◽

2020 ◽

Author(s):

Giulio Bresciani ◽

Emanuele Antico ◽

Gianluca Ciancaleoni ◽

Stefano Zacchini ◽

Guido Pampaloni ◽

...

Keyword(s):

Activation Barrier ◽

Research Area ◽

Ambient Conditions ◽

Nmr Studies ◽

Co Catalyst ◽

Critical Issues ◽

High Activation Barrier ◽

Sequential Addition ◽

Synthetic Routes ◽

Active Research

The development of sustainable synthetic routes to access valuable oxazolidinones via CO<sub>2</sub> fixation is an active research area, and the aziridine/carbon dioxide coupling has aroused a considerable interest. This reaction is featured by a high activation barrier, so to require a catalytic system, and may present some other critical issues. Here, we describe the straightforward gram-scale synthesis of a series of 5-aryl-2-oxazolidinones at ambient temperature and atmospheric CO<sub>2</sub> pressure, in the absence of any catalyst/co-catalyst. The key to this innovative procedure consists in the direct transfer of the pre-formed amine/CO<sub>2</sub> adduct (carbamate) to common aziridine precursors (dimethylsulfonium salts), replacing the classical sequential addition of amine (intermediate isolation of aziridine) and then CO<sub>2</sub>. The reaction mechanism has been investigated by NMR studies and DFT calculations applied to model cases.<br>

Adsorption and Reaction Mechanisms of Direct Palladium Synthesis by ALD Using Pd(hfac)2 and Ozone on Si (100) Surface

Processes ◽

10.3390/pr9122246 ◽

2021 ◽

Vol 9 (12) ◽

pp. 2246

Author(s):

Chunyu Cheng ◽

Yiming Zou ◽

Jiahui Li ◽

Amanda Jiamin Ong ◽

Ronn Goei ◽

...

Keyword(s):

Reaction Mechanisms ◽

Palladium Nanoparticles ◽

Density Functional ◽

Noble Metals ◽

Activation Barrier ◽

Atomic Layer ◽

Activation Barriers ◽

Layer Deposition ◽

High Activation Barrier ◽

Palladium Metal

Palladium nanoparticles made by atomic layer deposition (ALD) normally involve formaldehyde or H2 as a reducing agent. Since formaldehyde is toxic and H2 is explosive, it is advantageous to remove this reducing step during the fabrication of palladium metal by ALD. In this work we have successfully used Pd(hfac)2 and ozone directly to prepare palladium nanoparticles, without the use of reducing or annealing agents. Density functional theory (DFT) was employed to explore the reaction mechanisms of palladium metal formation in this process. DFT results show that Pd(hfac)2 dissociatively chemisorbed to form Pd(hfac)* and hfac* on the Si (100) surface. Subsequently, an O atom of the ozone could cleave the C–C bond of Pd(hfac)* to form Pd* with a low activation barrier of 0.46 eV. An O atom of the ozone could also be inserted into the hfac* to form Pd(hfac-O)* with a lower activation barrier of 0.29 eV. With more ozone, the C–C bond of Pd(hfac-O)* could be broken to produce Pd* with an activation barrier of 0.42 eV. The ozone could also chemisorb on the Pd atom of Pd(hfac-O)* to form O3-Pd(hfac-O)*, which could separate into O-Pd(hfac-O)* with a high activation barrier of 0.83 eV. Besides, the activation barrier was 0.64 eV for Pd* that was directly oxidized to PdOx by ozone. Based on activation barriers from DFT calculations, it was possible to prepare palladium without reducing steps when ALD conditions were carefully controlled, especially the ozone parameters, as shown by our experimental results. The mechanisms of this approach could be used to prepare other noble metals by ALD without reducing/annealing agents.

Bypassing the Inertness of Aziridine/CO2 Systems to Access 5-Aryl-2 Oxazolidinones: Catalyst-Free Synthesis in Water Under Ambient Conditions

10.26434/chemrxiv.11671419.v1 ◽

2020 ◽

Author(s):

Giulio Bresciani ◽

Emanuele Antico ◽

Gianluca Ciancaleoni ◽

Stefano Zacchini ◽

Guido Pampaloni ◽

...

Keyword(s):

Co2 Fixation ◽

Activation Barrier ◽

Ambient Conditions ◽

Nmr Studies ◽

Co Catalyst ◽

Water As Solvent ◽

Critical Issues ◽

High Activation Barrier ◽

Sequential Addition ◽

Synthetic Routes

<div>The development of sustainable synthetic routes to access valuable oxazolidinones via CO2 fixation is </div><div>currently a hot topic of research, and the aziridine/carbon dioxide coupling has aroused a particular </div><div>interest. This reaction is featured by a high activation barrier, thus it requires a catalytic system and </div><div>often presents some other critical issues. Here, we describe the first gram-scale synthesis of a large </div><div>number of 5-aryl-2-oxazolidinones at ambient temperature and atmospheric CO2 pressure, in the </div><div>absence of any catalyst/co-catalyst and using water as solvent. The key to this innovative procedure </div><div>consists in the direct transfer of the CO2/amine adduct (carbamate) to common aziridine precursors </div><div>(dimethylsulfonium salts), replacing the classical sequential addition of amine (intermediate isolation </div><div>of aziridine) and then CO2. The reaction mechanism has been elucidated by NMR studies and DFT </div><div>calculations applied to model cases. </div>

Balancing the Activity and Selectivity of Propane Oxidative Dehydrogenation on NiOOH (001) and (010)

Transactions of Tianjin University ◽

10.1007/s12209-020-00267-3 ◽

2020 ◽

Vol 26 (5) ◽

pp. 341-351

Author(s):

Lisheng Li ◽

Hua Wang ◽

Jinyu Han ◽

Xinli Zhu ◽

Qingfeng Ge

Keyword(s):

Oxidative Dehydrogenation ◽

Density Functional ◽

Activation Barrier ◽

Propane Oxidative Dehydrogenation ◽

Functional Theory ◽

Activation Barriers ◽

Propylene Oxidation ◽

Propane Odh ◽

High Activation Barrier ◽

Allylic Radical

Abstract Propane oxidative dehydrogenation (ODH) is an energy-efficient approach to produce propylene. However, ODH suffers from low propylene selectivity due to a relatively higher activation barrier for propylene formation compared with that for further oxidation. In this work, calculations based on density functional theory were performed to map out the reaction pathways of propane ODH on the surfaces (001) and (010) of nickel oxide hydroxide (NiOOH). Results show that propane is physisorbed on both surfaces and produces propylene through a two-step radical dehydrogenation process. The relatively low activation barriers of propane dehydrogenation on the NiOOH surfaces make the NiOOH-based catalysts promising for propane ODH. By contrast, the weak interaction between the allylic radical and the surface leads to a high activation barrier for further propylene oxidation. These results suggest that the catalysts based on NiOOH can be active and selective for the ODH of propane toward propylene.

Effects of Chiral Ligands on the Asymmetric Carbonyl-Ene Reaction

Synlett ◽

10.1055/s-0037-1611875 ◽

2019 ◽

Vol 30 (15) ◽

pp. 1738-1764 ◽

Cited By ~ 1

Author(s):

Atefeh Bakhtiari ◽

Javad Safaei-Ghomi

Keyword(s):

Molecular Orbital ◽

Activation Barrier ◽

Alder Reaction ◽

Chiral Ligands ◽

Ene Reactions ◽

Ene Reaction ◽

Diels Alder Reaction ◽

Highest Occupied Molecular Orbital ◽

High Activation Barrier ◽

Lowest Unoccupied Molecular Orbital

The carbonyl-ene reaction is one of the most well-known reactions for C–C bond formation. Based on frontier molecular orbitals (FMO), carbonyl-ene reactions occur between the highest occupied molecular orbital (HOMO) of the ene compound bearing an active hydrogen atom at the allylic center and the lowest unoccupied molecular orbital (LUMO) of the electron-deficient enophile, which is a carbonyl compound. A high activation barrier enforces the concerted ene reaction rather than a Diels–Alder reaction at high temperature. Employing a catalytic system can eliminate defects in the ene reaction, and chiral catalysts promote the reaction under mild conditions to produce optically active compounds. In this account, we highlight investigations on the effects of various classes of chiral ligands on intermolecular and intramolecular carbonyl-ene reactions.1 Introduction2 Biaryl-Type Chiral Ligands3 C 1- and C 2-Symmetric Bis(oxazoline) Ligands4 Schiff Base Ligands5 N,N′-Dioxide Ligands6 Conclusions

Low potential electron generating enzymes serve different functions during aerobic nitrogen fixation in Azotobacter vinelandii

10.1101/2021.10.06.463449 ◽

2021 ◽

Author(s):

Alexander B Alleman ◽

Florence Mus ◽

John W Peters

Keyword(s):

Nitrogen Fixation ◽

Azotobacter Vinelandii ◽

Activation Barrier ◽

Redox Homeostasis ◽

Low Oxygen ◽

High Activation Barrier ◽

Biological Nitrogen ◽

Diazotrophic Growth ◽

Enzyme Complexes ◽

Fix Genes

Biological nitrogen fixation requires large amounts of energy in the form of ATP and low potential electrons to overcome the high activation barrier for cleavage of the dinitrogen triple bond. The model aerobic nitrogen-fixing bacteria, Azotobacter vinelandii, generates low potential electrons in the form of reduced ferredoxin (Fd) and flavodoxin (Fld) using two distinct mechanisms via the enzyme complexes Rnf and Fix. Both Rnf and Fix are expressed during nitrogen fixation, and deleting either rnf1 or fix genes has little effect on diazotrophic growth. However, deleting both rnf1 and fix eliminates the ability to grow diazotrophically. Rnf and Fix both use NADH as a source of electrons, but overcoming the energetics of NADH's endergonic reduction of Fd/Fld is accomplished through different mechanisms. Rnf harnesses free energy from the proton motive force, whereas Fix uses electron bifurcation to effectively couple the endergonic reduction of Fd/Fld to the exergonic reduction of quinone. Different stoichiometries and gene expression analyses indicate specific roles for the two reactions under different conditions. In this work, complementary physiological studies and thermodynamic modeling reveal how Rnf and Fix simultaneously balance redox homeostasis in various conditions. Specifically, the Fix complex is required for efficient growth under low oxygen concentrations, while Rnf sustains homeostasis and delivers sufficient reduced Fd to nitrogenase under standard conditions. This work provides a framework for understanding how the production of low potential electrons sustains robust nitrogen fixation in various conditions.