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Catalytic conversion of carbon dioxide (CO2) into value‐added chemicals is of pivotal importance, well the cost of capturing CO2 from dilute atmosphere is super challenge. One promising strategy is combining the adsorption and transformation at one step, such as applying alkali solution that could selectively reduce carbonate (CO32−) as consequences of CO2 adsorption. Due to complexity of this system, the mechanistic details on controlling the hydrogenation have not been investigated in depth. Herein, Ru/TiO2 catalyst was applied as a probe to elucidate the mechanism of CO32− activation, in which with thermodynamic and kinetic investigations, a compact Langmuir‐Hinshelwood reaction model was established which suggests that the overall rate of CO32− hydrogenation was controlled by a specific C−O bond rupture elementary step within HCOO− and the Ru surface was mainly covered by CO32− or HCOO− at independent conditions. This assumption was further supported by negligible kinetic isotope effects (kH/kD≈1), similarity on reaction barriers of CO32− and HCOO− hydrogenation (ΔH≠hydr,Na2CO3 and ΔH≠hydr,HCOONa) and a non‐variation of entropy (ΔS≠hydr≈0). More interestingly, the alkalinity of the solution is certainly like a two sides in a sword and could facilitate the adsorption of CO2 while hold back catalysis during CO32− hydrogenation. [ABSTRACT FROM AUTHOR]

Context: The reaction of NO2 with pristine and Pt-doped SnS2 surfaces is investigated theoretically and compared with the experiment. Transition state theory formalism for gas sensors is adopted to present NO2 gas sensing. The dissociation temperature at approximately 150 °C is found to be of great importance in NO2 reactions. The adsorption and transition states of NO2 with pristine and Pt-doped SnS2 are calculated. Pt doping includes 0.5, 1, and 1.5% in accordance with available experimental results. The variation of thermodynamic quantities such as Gibbs free energy with Pt concentration and temperature is calculated. Transition state theory parameters that are suitable for the present sensor are determined. The results include the variation in response time with temperature, Pt concentration, and NO2 concentration. Response and response time as a function of temperature are rarely investigated in theoretical calculations, which is one of the advantages of the present study. Optimum response temperature and Pt concentration are found. The results agree with available experimental results. Methods: Density functional theory at the B3LYP level optimize molecular structures. 6-311G** basis set is used for all elements except Sn and Pt treated using SDD basis set. Gaussian 09 program and its facilities are used to perform present optimizations. [ABSTRACT FROM AUTHOR]

The geometrical structure, stability, electronic properties, and hydrogen storage capabilities of a titanium-doped B7 cluster was calculated using density functional theory computations. The results show that the TiB7 cluster is predicted to be stable under near-ambient conditions based on an ab initio molecular dynamic simulation. The transition state analysis found that the H2 molecule can dissociate on the TIB7 cluster surface to form a hydride cluster. The Ti atom within the TiB7 cluster demonstrates an impressive capacity to adsorb up to five H2 molecules, achieving a peak hydrogen storage mass fraction of 7.5%. It is worth noting that the average adsorption energy of H2 molecules is 0.27–0.32 eV, which shows that these configurations are suited for reversible hydrogen storage under mild temperature and pressure regimes. In addition, calculations found that both polarization and hybridization mechanisms play pivotal roles in facilitating the adsorption of H2 molecules onto the TiB7 cluster. Our research results show that the TiB7 cluster has potential for hydrogen storage applications under near-ambient conditions. [ABSTRACT FROM AUTHOR]

Hydroxylamine nitrate (HAN) is a new type of high-energy oxidant used in controllable propulsion. The present study explores the reaction mechanism of HAN using density functional theory and constructs reaction mechanism diagrams to understand the mechanism of small-molecule gas formation during the thermal decomposition of HAN. Based on transition state theory, the half-life of each reaction is calculated under standard conditions and the kinetic parameters of each reaction are scanned across the temperature range 298.15–1200 K. The research revealed a vast half-life time scale forreaction of NO generation, NO 2 generation, NO+NO 2 generation, N 2 O generation and N 2 generation process, meaning thatthese reaction can not occur. The half-life of RDS5 is very short. However, the reaction is also limited by the concentration of the reactant HNO. However, increasing the temperature rapidly decreases the reaction half-life and the reaction can easily proceed. Taking 300 s as the easily reactive boundary point, the cut-off points of the rate-determining steps of Processes 1 (NO generation), 2 (NO 2 generation), 3 (NO + NO 2 generation), 4 and 5 (N 2 O generation) and 6 (N 2 generation) are 466 K, 468 K, 576 K, 587 K and 402 K, respectively. The calculated reaction mechanism revealed two isomeric transformations of HNO 2 and H 2 N 2 O 2 and three isomeric transformations of H 2 N 2 O. Both HNO 2 and H 2 N 2 O 2 are transformed via H-atom transfer, while H 2 N 2 O is transformed either by H-atom transfer or intramolecular rotation. As the formation reaction of NO 2 does not have the lowest free energy, the NO 2 product is easily converted to other products. When NO 2 coexists with NO, it is also easily converted to the stable products N 2 O, N 2 and NH 3. [ABSTRACT FROM AUTHOR]

Hydroxylamine nitrate (HAN) is a new type of high-energy oxidant used in controllable propulsion. The present study explores the reaction mechanism of HAN using density functional theory and constructs reaction mechanism diagrams to understand the mechanism of small-molecule gas formation during the thermal decomposition of HAN. Based on transition state theory, the half-life of each reaction is calculated under standard conditions and the kinetic parameters of each reaction are scanned across the temperature range 298.15–1200 K. The research revealed a vast half-life time scale forreaction of NO generation, NO2 generation, NO+NO2 generation, N2O generation and N2 generation process, meaning thatthese reaction can not occur. The half-life of RDS5 is very short. However, the reaction is also limited by the concentration of the reactant HNO. However, increasing the temperature rapidly decreases the reaction half-life and the reaction can easily proceed. Taking 300 s as the easily reactive boundary point, the cut-off points of the rate-determining steps of Processes 1 (NO generation), 2 (NO2 generation), 3 (NO + NO2 generation), 4 and 5 (N2O generation) and 6 (N2 generation) are 466 K, 468 K, 576 K, 587 K and 402 K, respectively. The calculated reaction mechanism revealed two isomeric transformations of HNO2 and H2N2O2 and three isomeric transformations of H2N2O. Both HNO2 and H2N2O2 are transformed via H-atom transfer, while H2N2O is transformed either by H-atom transfer or intramolecular rotation. As the formation reaction of NO2 does not have the lowest free energy, the NO2 product is easily converted to other products. When NO2 coexists with NO, it is also easily converted to the stable products N2O, N2 and NH3.

Chemical reactions are dynamical processes involving the correlated reorganization of atomic configurations, driving the conversion of an initial reactant into a result product. By virtue of the metastability of both the reactants and products, chemical reactions are rare events, proceeding fleetingly. Reaction pathways can be modelled probabilistically by using the notion of reactive density in the phase space of the molecular system. Such density is related to a function known as the committor function, which describes the likelihood of a configuration evolving to one of the nearby metastable regions. In theory, the committor function can be obtained by solving the backward Kolmogorov equation (BKE), which is a partial differential equation (PDE) defined in the full dimensional phase space. However, using traditional methods to solve this problem is not practical for high dimensional systems. In this work, we propose a reinforcement learning based method to identify important configurations that connect reactant and product states along chemical reaction paths. By shooting multiple trajectories from these configurations, we can generate an ensemble of states that concentrate on the transition path ensemble. This configuration ensemble can be effectively employed in a neural network-based PDE solver to obtain an approximation solution of a restricted BKE, even when the dimension of the problem is very high. The resulting solution provides an approximation for the committor function that encodes mechanistic information for the reaction, paving a new way for understanding of complex chemical reactions and evaluation of reaction rates.

This study explores the potential mechanisms (Paths 1 and 2) involved in the regioselective dipolar cycloaddition of thioamides, selenoamides, and amides with propargyl alcohol using density functional theory (DFT). Our calculations reveal that the initial step involves the formation of a cation with catalyst. Subsequently, isomerization occurs between cations I and II via 1,3‐hydride transfer in the second step. We analyzed the global reactivity index and frontier molecular orbital (FMO) theory to gain insights into the mechanism. In the third step, chalcoamides attack cations I and II, forming an intermediate. The formation of a five‐member ring intermediate constitutes the fourth step, followed by hydrogen transfer to produce stable five‐member heterazole compounds in the final step. We demonstrated the influence of substituents in the electrophile by employing various electron‐withdrawing and donating groups. Additionally, we examined the effect of the dielectric medium on the reaction barrier using polarizable continuum model. Thus, this study provides valuable insights for the rational design of more efficient 1,3‐dipolar cycloaddition reactions yielding regioselective products. [ABSTRACT FROM AUTHOR]

In this study, the dissociation process of MgCO3and the synthesis of MgAl2O4by using the dissociation products and Al2O3were studied. From the CCSD (t) 6 - 311 + + G (D, p) and M06-2x/6-311++g (D, p) methods, the single-point energy and frequency of MgCO3were calculated and the thermal decomposition process of the reactant was also calculated to find the transition states. In the meantime, the powders of MgAl2O4were synthesized from MgCO3and Al2O3by high temperature sintering method at 1450°C in the laboratory. The experimental products were characterized by XRD and agreed with the theoretical calculation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the rapid development of high performance computers and computational methods, including software, an increasing number of experimental chemists have tried to use computational methods such as optical rotation (OR, including the matrix model), optical rotatory dispersion (ORD), electronic circular dichroism (ECD or CD), vibrational circular dichroism (VCD), and magnetic shielding constants--nuclear magnetic resonance (NMR)--to explain and/or assign absolute configuration (AC) for various compounds. Such reports in the field of natural products have increased dramatically. However, every method has its range of application. This leads, in some cases, to incorrect conclusions by researchers who are not familiar with these methods. In this review, we provide experimental chemists and researchers with more computational details and suitable suggestions, and especially hope that this experience may help readers avoid computational pitfalls. Finally, we discuss the use of simplified models to replace original complex structures with a long side chain. The fundamental basis for using models to represent complex chiral compounds, such as in OR calculations, is the existence of conformation pairs with near canceling conformer contributions that justify the use of models rather than the original compounds. Using examples, we here introduce the transition state (TS) calculation, which may benefit readers in this area for use and mastery for their AC study. This review will summarize the general concepts involved in the study of AC determinations. [ABSTRACT FROM AUTHOR]

ANSYS finite element analysis software is used to calculate the fatigue life of a certain turbine blade during the thermal shock process in this paper. The various state parameters of the turbine blades during the thermal shock process are calculated and analyzed. The changes in temperature, stress, and strain of the turbine blade at various locations during the thermal shock process are obtained. The stress and strain results obtained from various monitoring points are used to calculate the fatigue life using the local stress–strain method. A thermal shock test bench is established to conduct thermal shock fatigue tests on the blades. The full life formula is used to calculate the blade's crack propagation life. The stress and strain changes at various points near the leading edge of the blade during the thermal shock process are similar to the trend of gas temperature changes. The point of maximum stress and strain appears at the leading edge of the blade. The location of fatigue failure first appears near the leading edge of the blade, with fatigue damage traces also found at the trailing edge of the blade. Using the full life formula, the estimated crack propagation life of the blade is approximately 3500–4500 cycles. The total life is estimated to be approximately 6500–7500 cycles. The fatigue life calculation method based on transitional state parameters can significantly reduce the number of thermal shock experiments and calculate the fatigue life at each stage of the turbine blade. [ABSTRACT FROM AUTHOR]

The LiFePO4 cathode material possesses a low diffusion coefficient and exhibits poor electronic conductivity, respectively due to its uniaxial ion channel and inherent semiconductor properties. To address these limitations, Co and Nb doping emerges as a vital solution owing to their similar ionic radii and stable valence states. In this study, density functional theory (DFT) is employed to investigate the impact of Co and Nb doping on the electrochemical and mechanical properties of LiFePO4. The results reveal that the dopants lead to an expansion in the lattice constant of LiFePO4. Furthermore, doping brings about a significant reduction in the volume change rate (0.3% for Co doping and 1% for Nb doping), resulting in enhanced transmission of lithium ions. Specifically, Co and Nb doping elevate the lithium removal voltage of LiFePO4 from 3.44 to 3.96 V and 3.8 V, respectively. Furthermore, these doping processes enhance the material's mechanical properties. It is worth noting that the doping of Co and Nb reduces the migration barrier and increases the diffusion rate of lithium ions. It is observed that the proximity to the doped ion increases the energy barrier, whereas moving away from the doped ion decreases the energy barrier, emphasizing the significant influence of dopant ions on the local energy barrier. Additionally, after doping, the operating voltage of the battery experiences a significant increase. Overall, the selected elements in this study demonstrate promising potential to enhance the performance of LiFePO4 cathode materials, offering encouraging prospects for future advancements in battery technology. [ABSTRACT FROM AUTHOR]

In this work, we propose a multi-level protocol for routine theoretical studies of chemical reaction mechanisms. The initial reaction paths of our investigated systems are sampled using the Nudged Elastic Band (NEB) method driven by a cheap electronic structure method. Forces recalculated at the more accurate electronic structure theory for a set of points on the path are fitted with a machine learning technique (in our case symmetric gradient domain machine learning or sGDML) to produce a semi-local reactive potential energy surface (PES), embracing reactants, products and transition state (TS) regions. This approach has been successfully applied to a unimolecular (Bergman cyclization of enediyne) and a bimolecular (SN2 substitution) reaction. In particular, we demonstrate that with only 50 to 150 energy-force evaluations with the accurate reference methods (here complete-active-space self-consistent field, CASSCF, and coupled-cluster singles and doubles, CCSD) it is possible to construct a semi-local PES giving qualitative agreement for stationary-point geometries, intrinsic reaction coordinates and barriers. Furthermore, we find a qualitative agreement in vibrational frequencies and reaction rate coefficients. The key aspect of the method's performance is its multi-level nature, which not only saves computational effort but also allows extracting meaningful information along the reaction path, characterized by zero gradients in all but one direction. Agnostic to the nature of the TS and computationally economic, the protocol can be readily automated and routinely used for mechanistic reaction studies. [ABSTRACT FROM AUTHOR]

Context: Xylanases derived from Bacillus species hold significant importance in various large-scale production sectors, with increasing demand driven by biofuel production. However, despite their potential, the extreme environmental conditions often encountered in production settings have led to their underutilisation. To address this issue and enhance their efficacy under adverse conditions, we conducted a theoretical investigation on a group of five Bacillus species xylanases belonging to the glycoside hydrolase GH11 family. Bacillus sp. NCL 87–6-10 (sp_NCL 87–6-10) emerged as a potent candidate among the selected biocatalysts; this Bacillus strain exhibited high thermal stability and achieved a transition state with minimal energy requirements, thereby accelerating the biocatalytic reaction process. Our approach aims to provide support for experimentalists in the industrial sector, encouraging them to employ structural-based reaction modelling scrutinisation to predict the ability of targeted xylanases. Methods: Utilising crystal structure data available in the Carbohydrate-Active enzymes database, we aimed to analyse their structural capabilities in terms of thermal-stability and activity. Our investigation into identifying the most prominent Bacillus species xylanases unfolds with the help of the semi-empirical quantum mechanics MOPAC method integrated with the DRIVER program is used in calculations of reaction pathways to understand the activation energy. Additionally, we scrutinised the selected xylanases using various analyses, including constrained network analyses, intermolecular interactions of the enzyme–substrate complex and molecular orbital assessments calculated using the AM1 method with the MO-G model (MO-G AM1) to validate their reactivity. [ABSTRACT FROM AUTHOR]

The evolution of the electronic characteristics of chemical bonds formed and broken along the path of the bimolecular nucleophilic substitution reaction at a tetrahedral central atom, which is the Tt=C, Si, and Ge atom, is analyzed. For this purpose, the reaction paths of the step-by-step replacement of the chlorine atom with the phenyl fragment are modeled, and the energy characteristics of the equilibrium initial, transition, and final states are obtained within the framework of the DFT. For different reaction centers, which are atoms of the carbon group (Tt), changes in electron density distributions and shifts in the positions of the extremes of the total static and electrostatic potential for the forming C–Tt and breaking Tt–Cl bonds along the reaction path are compared. Quantitative criteria are refined that determine the region of existence of a typical noncovalent tetrel bond Tt...Cl, allowing it to be distinguished from a covalent one. Establishment of the properties of the transition state stabilizing tetrel bond may be useful for monitoring the efficient synthesis of covalent organic framework precursors. [ABSTRACT FROM AUTHOR]

Context: The performance of pristine and Pd-doped WO3 acetone gas sensors is calculated theoretically and compared with available experimental results. Temperature, humidity, and acetone concentration variation are considered in the present work. Transition state theory calculates Gibbs free energy of transition, including its components enthalpy and entropy of transition or activation. The variation of Pd doping concentration is used to obtain the maximum response and lowest response time for the optimum performance of the gas sensor. The present theory considers the reduction of acetone gas concentration as acetone reaches its autoignition temperature. Acceptable agreement between theory and experiment is obtained. The acceptance includes the decrease of Gibbs free energy with doping percentage, variation of temperature exponent to the power twelve in the considered reactions, and reduction of response time with the increase of temperature. Methods: Density functional theory at the B3LYP level is used. 6-311G** basis set (for O atoms) and SDD (for heavy Pd and W atoms) are used to optimize the structures examined in the present work. The Gaussian 09 program and accompanying software were used to perform the current tasks. [ABSTRACT FROM AUTHOR]

Based on the properties of the conjugated p-electron system in cyclic polyenes, possible steric and electronic structures of transition states in thermal isomerizations of pyridine and phosphinine in an oxygen-free atmosphere have been determined by DFT calculations using B3LYP functional and 6-31G* basis set. The degree of stabilization of the transition states depends on the level of p-electron conjugation. Schemes of the thermal isomerizations of pyridine and phosphinine have been constructed, and potential barriers to these transformations have been calculated. The study of the reactivities of pyridine and phosphinine in the thermal isomerization processes has revealed lower aromaticity of phosphinine compared to pyridine. [ABSTRACT FROM AUTHOR]

We improved our previous theoretical method for prediction of the catalytic activity of porous materials, which is based on the concept of transition state shape selectivity. This method used adsorption energy calculations for transition state (TS) with «frozen» (only the placement of TS inside the pore is optimized) structure on porous materials with molecular mechanics (MM) as a calculational method. Our improvement consists of application of semi-empirical methods with dispersion correction (e.g., PM3-D3 or PM6-D3H4) instead of MM. We found that with semi-empirical methods adsorption energy dependences on pore diameter are similar to dependences obtained by MM, and also semi-empirical methods predict the same value of the cavity diameter, at which there is a maximum of TS adsorption energy. Despite these similarities in obtained results, semi-empirical methods have the advantages that they can more accurately describe structures, intermolecular interactions and energy values. We have shown that the level of theory (PM3-D3 or RI-MP2/ma-def2-SVP) used for TS structure search, in the case of suggested method, has little effect. [ABSTRACT FROM AUTHOR]

Pi (π) interactions originating from the N-H bond of amine and ethylene moiety have been explored on the mechanism of aromatic nucleophilic substitution (ArSN) of the nitro group of 4-methylene-5,7-dinitroquinazoline with methylamine in the gas phase and solvent media within DFT framework. The free energy profiles confirmed that the amination should take place at peri-position and calculations support the one-step mechanism through a transition state with no intermediate in the reaction route. Stabilisation of peri-transition state by intramolecular weak interaction akin to hydrogen bonding N-H—CH2 = C leads to the regioselective amination at peri-position of 4-methylene-5,7-dinitroquinazoline. The intramolecular hydrogen bond interactions at N-H—CH2 = C in the peri-transition state are strongly supported by a red shift in N-H stretching vibrations in simulated IR spectra and are confirmed by studying energetics of amination of structural/electronic analogues of 4-methylene-5,7-dinitroquinazoline. The present study established that ethylene plays an important role as an efficient H-bond acceptor in fixing the regioselectivity at peri-position in the amination of 4-methylene-5,7-dinitroquinazoline. This is the first-ever report for the exploration of the role of ethylene moiety as a hydrogen bond acceptor in mediating the regioselectivity of organic reactions. [ABSTRACT FROM AUTHOR]

The reaction of ethanol with pristine and Mo-doped SnO2 is computed and compared to experimental results. The comparison includes response, response time, and the effect of humidity. Adsorption and transition states are evaluated and used to calculate the reaction rate of ethanol with pristine and Mo-doped SnO2. The modified Evans–Polanyi principle is used to evaluate Gibbs free energy of transition, including its components enthalpy and entropy at the investigated doping percentages of Mo at 3, 5, and 7 mol%. The effect of humidity on the backward reaction of ethanol burning is discussed. The impact of the autoignition temperature of ethanol at 368 °C on the reaction rate is included for the first time for Mo-doped SnO2. The theoretical results show good agreement with the experiment. Mo-doped SnO2 shows high response, short response time, and stability towards ethanol that nominate the sensor for practical applications.

The geometrical structure, stability, electronic properties, and hydrogen storage capabilities of a titanium-doped B7 cluster was calculated using density functional theory computations. The results show that the TiB7 cluster is predicted to be stable under near-ambient conditions based on an ab initio molecular dynamic simulation. The transition state analysis found that the H2 molecule can dissociate on the TIB7 cluster surface to form a hydride cluster. The Ti atom within the TiB7 cluster demonstrates an impressive capacity to adsorb up to five H2 molecules, achieving a peak hydrogen storage mass fraction of 7.5%. It is worth noting that the average adsorption energy of H2 molecules is 0.27–0.32 eV, which shows that these configurations are suited for reversible hydrogen storage under mild temperature and pressure regimes. In addition, calculations found that both polarization and hybridization mechanisms play pivotal roles in facilitating the adsorption of H2 molecules onto the TiB7 cluster. Our research results show that the TiB7 cluster has potential for hydrogen storage applications under near-ambient conditions.

This document provides a comprehensive overview of the stereochemical aspects of C-glycosylation, focusing on the synthesis of glycoside-based drugs and the development of stereoselective methods for constructing C-glycoside bonds. It explores the conformational analysis of sugars and the role of Lewis acid-mediated nucleophilic addition in glycoside bond formation. The text also discusses various methods for the synthesis of C-glycosides, including Lewis acid mediated nucleophilic addition, arylalane addition, glucal epoxide method, glycosyl leaving group substitution method, and glycosylation via transition-metal-mediated cross-coupling. Additionally, the document discusses the stereochemistry of glycoside bond formation in furanosides and the influence of substituents on the stereochemical outcome. It concludes by summarizing the stereoselective synthesis of α- and β-C-glycosides and the factors that influence stereoselectivity. [Extracted from the article]

In the present study, the mechanism of Maillard reaction was investigated using density functional theory calculations. Glucose and aminomethane were used as initial reactants in this study. The calculations show that the Amadori rearrangement reaction is the rate-controlling step with a corresponding energy potential of 402 kJ/mol, the enthalpy change is 219 kJ/mol, which is an endothermic reaction and therefore energy needs to be supplied from outside if the reaction is to proceed. The calculated results are in good agreement with the previous findings and can provide insight into the reaction mechanism of the Maillard reaction. These findings will help further research and find out the correct reaction mechanism. [ABSTRACT FROM AUTHOR]

A mechanism of the reaction between the cationic nitrosyl iron complex with thiourea ligands [Fe(SC(NH2)2)2(NO)2]+Cl− and molecular oxygen in aqueous solution is proposed. It was demonstrated that NO released as reaction product can undergo subsequent transformations in the presence of molecular oxygen and water. As a result, various oxygen-containing products including NO2, NO2−, NO3−, and ONOO− are released to the solution. A mechanism was proposed for the formation of an OH radical in the system, which makes it possible to explain the experimental data on the kinetics of NO release by the complex under study under aerobic and anaerobic conditions. [ABSTRACT FROM AUTHOR]

Tautomerization paths of β‐alanine with explicit inclusion of water molecules, (H2O)n, were investigated by DFT calculations, wB97X‐D/6‐311+G(d,p) SCRF=PCM. Structures of zwitterions of the alanine of trans (t−) and gauche (g−) conformations with seven water molecules (n=7) were examined. On the basis of those geometries, elementary processes of the tautomerization were investigated. For the t‐conformer of β‐alanine, reaction models of n=8, 10, 14, 18 and 24 were scrutinized. While reaction processes are slightly modified with different number of water molecules, n=18 and 24 models afforded three elementary reactions, t‐alanine with cis‐COOH→t‐ion pair→t‐alanine with trans‐COOH→t‐zwitterion. The (H2O)4 hydrogen‐bonded chain participates in the reactions. For the g‐conformer, models of n=7, 10, 14 and 18 were investigated, and the tautomerization was found to take place concertedly via (H2O)2. [ABSTRACT FROM AUTHOR]

Copyright of Acta Scientiarum Naturalium Universitatis Sunyatseni / Zhongshan Daxue Xuebao is the property of Sun-Yat-Sen University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on the density functional theory, the stereoselectivity of the asymmetric synthesis of tetrahydroisoquinolinopyrazole derivatives by the cycloaddition reaction of C, N‐cyclic azomethine imines with allyl alkyl ketones which was catalyzed using a chiral primary amine is studied theoretically. The results demonstrate that the four chiral transition states (TS‐1R2R, TS‐1R2S, TS‐1S2R and TS‐1S2S) are formed by the reaction of dienamine intermediate with C, N‐cyclic azomethine imine, and the reaction barrier of TS‐1R2S is in the lowest level (ΔG=6.98 kcal/mol). The consequence reveal that the 1R2S configuration product is formed by TS‐1R2S transition state. Non‐covalent interaction and electron density topology analysis show that the stereoselectivity of the chiral product is determined through van der Waals forces and hydrogen bond interaction of the transition state molecules. [ABSTRACT FROM AUTHOR]

Transition metal Mn ions are highly promising cathode dopant materials. Due to the introduction of Mn ions, as lithium ions are deintercalated, Mn2+ will be transformed into Mn3+. This situation will lead to a severe Jahn-Teller effect, causing significant local lattice distortion and greatly reducing electrochemical stability. This article utilizes first-principles calculations to investigate the doping of Mg, Co, and V to weaken Jahn-Teller effect in LiMn0.5Fe0.5PO4 cathode. The oxidation-reduction processes of three doped models were analyzed, and the electronic structure and charge transfer amount between the Mn ion and the O ion were calculated for each. It was found that, when Mg ions are doped into the crystal, Mn ions will stabilize as Mn2+, thereby weakening the Jahn-Teller effect. However, the addition of V and Co will not alter the Jahn-Teller effect. The differential charge density and partial density of states (PDOS) were also calculated. It was found that only the doping of Mg ions can enable the material to achieve the lowest energy and the smallest volume change rate, which attribute to weaken the Jahn-Teller effect. Only doping with V and Co ions can achieve the highest lithium removal voltage, increasing the average lithium removal voltage from 4.22 to 4.42 V. Mechanical performance calculations show that the structures with two types of doped Mg ion are prone to shear deformation and cannot improve the ductility of the material. Additionally, it was found that the migration barrier of the three doped models was reduced to varying degrees, which is beneficial for the transition of lithium ions. Moreover, the diffusion coefficient of lithium ions also increased by 1–4 orders of magnitude. [ABSTRACT FROM AUTHOR]

It was found for the first time that 2,3-dialkyl-substituted gem-dibromocyclopropanes react with a solution of the aluminum carbenoid Me2AlCH2I in CH2Cl2 to form substituted bromoalkenes in a good yield. The reaction is sensitive both to the nature of the organoaluminum Lewis acid and to the substitution in gem-dibromocyclopropane. A mechanism of the cyclopropyl–allyl rearrangement was proposed. The free activation energies of the cyclopropyl–allyl rearrangement were calculated by the B3LYP/6-31G(d) method for a number of gem-dibromocyclopropanes and aluminum-containing Lewis acids. [ABSTRACT FROM AUTHOR]

The one-pot three-component condensation of benzaldehyde, 1,3-indenedione, and indole was investigated at the B3LYP/6-311G level to explore the best reaction mechanism for the gas phase. All of routes were studied and structure of intermediates (IM) were optimized and all of respective transition states were found. Nine different mechanism paths were proposed and relevant calculations and investigations were performed. The calculation results proved that the proposed mechanism consists of three-step, enolic form of 1,3-indenedione, benzaldehyde and indole is more suitable than other mechanism routes. [ABSTRACT FROM AUTHOR]

Extraction of sulfur compounds from crude oil is one of the problems of industries related to crude oil. The use of ionic liquids (ILs) as a green solvent to extract these sulfur compounds, especially cyclic sulfur compounds, can be considered a potential point in this regard. A functional theory comparison was made to investigate the interaction between N-butylpyridinium tetrafluoroborate as IL and several different cyclic sulfur compounds including Thiophene, benzothiophene, dibenzothiophene, and 4,6-dibenzothiophene. The difference between the solution phase and the gas phase has been investigated. Based on the results, the proper interaction between the components of IL and the cyclic sulfur compounds, the extraction of these compounds is theoretically possible. Natural bond orbital, atoms in molecules, HOMO-LUMO overlap integral, and electron density difference were analyzed. The analysis informs on the use of ionic liquids as solvents for the removal of sulfur compounds from crude oil. The hydrogen and vander Waals bonds formed between the anion and cation of ionic liquid and the sulfur compounds have been determined. The main bonds are formed between the anion of ionic liquid and the sulfur compounds. Between the compound [C4Py][BF4] and C4H4S, the hydrogen bonds are S…H13, F29.... H38, F26…H38, has been established. The hydrogen bonds between the anion of the ionic liquid and the sulfur compound are shorter than the other hydrogen bonds formed. Due to the intermolecular bonds, the transition state with the lowest energy has been obtained. In this way, we will have a proposed mechanism for the extraction of the cyclic compounds from oil with the help of ionic liquids.

The work aims to determine the kinetic parameters of reactions for production of light olefins via catalytic cracking reactions of C4–C6 n-alkanes based on the energy characteristics of the transition state using quantum chemical calculations. Cracking reactions of C4–C6 n-alkanes proceed via protolytic mechanism on the Brønsted acid sites of zeolite-containing catalysts. For kinetic studies in this work, the thermochemical parameters of the intermediate stages, including hydrocarbon adsorption and transition state were determined, then the activation energies and rate constants were determined over the temperature range of catalytic cracking process from 773 to 903 K (500–630 °C).The results showed that DFT method in combination with B3LYP and ωB97X-D functionals, and 3–21 G basis demonstrated quite high accuracy in determining thermochemical parameters, including enthalpy, entropy and Gibbs free energy at both energetic levels of adsorption and transition state. Then, modeling continued by calculations of activation energies and rate constants of reactions. Obtained kinetic parameters made it possible to determine the reactivity of hydrocarbons with different chain length. It was obtained that the rate constants of butane cracking reactions with the formation of ethylene are 54–90 times higher than the formation of propylene. The rate constants of pentane cracking reactions with the formation of butylene are on average 5 times higher than the formation of propylene. The rate constants for hexane cracking reactions with the formation of butylene are 2.9–3.7 times higher compared to the formation of propylene.

This study explored the influence of Cr interfacial segregation on the precipitation mechanism and mechanical properties of MC carbides in high-carbon chromium bearing steels. The precipitation of Cr-doped MC carbides at different concentrations was investigated using microscopic morphological characterization (SEM, EDS and HR-TEM) alongside first principles calculations. The results indicated that both the austenite matrix and MC carbides exhibited, FCC structures, and the following orientation relationships of crystal planes in high-carbon chromium bearing steels were as follows: MC (010)//FCC-Fe (100) and MC (111)//FCC-Fe (111). Initially, Cr atoms adsorbed on the Fe-top site of the MC carbide (010) crystal plane, maintaining a distance of 2.5 Å from the Fe atom. Notably, when the Cr atom doping amount was 0.5, the Cr–Fe metallic bond exhibited a long bond length, large bond angle and low bond strength in the MC transition state (TS), resulting in a reduced, reaction barrier (908.08 kcal/mol), thus promoting the precipitation of MC carbide in bearing steel. However, at a Cr atom doping amount level of 1, the shorter bond length, small bond angle, and higher bonding strength of the Cr–Fe metallic bond in the MC TS, elevated the reaction barrier (49709.72 kcal/mol), inhibiting the precipitation of MC carbide in bearing steel. Additionally, this study quantitatively analyzed the effect of Cr atom content on the brittle plastic properties and hardness of MC carbides. At Cr atom contents of 0.23 and 1, the MC carbide hardness reached a minimum value of 3.0 GPa and a maximum value of 17.1 GPa, respectively. This investigation not only elucidated the atomic scale effects of Cr interfacial segregation on the precipitation mechanism and mechanical properties of MC carbides but also provided new ideas for controlling carbide precipitation in high-carbon chromium bearing steels.

TiO2 cluster sensitivity to acetone adsorption using transition state theory is investigated. Ti10O20 cluster is used to perform the calculations using density functional theory with dispersion corrections. Adsorption state and transition state are calculated via thermodynamic energies, i.e., Gibbs free energy of adsorption and activation. Reaction rate, response, response time, and recovery time as a function of temperature and acetone concentration are calculated. Acetone burning in the air due to autoignition is considered using a logistic function. The results of the theory are compared with available experimental findings that revealed the quality of both theoretical and experimental results. The response time decreases with respect to acetone concentration. On the other hand, the recovery time in the desorption phase increases with acetone concentration. The temperature of maximum response is 356 °C, while the maximum response value is 2.9.

Abstract Inert allyl-type monomers have been widely documented due to reduce degradation chain transfer. Recently, we and others discovered that the [3 + 2] cyclization reaction process by a photo-driven radical reaction, which can accelerate the polymerization. It was discovered that allyl ether monomers had much higher reactivity than other allyl monomers in the suspension photopolymerization initiated by Type I photoinitiator. Since the hydrogen abstraction reaction (HAR) is the initial step of cyclization, and in order to clarify the influence of solvents effect, three allyl-type monomers were employed, containing “O”, “N” and “S” atom as hydrogen donors. The benzoyl radical obtained from cleavage of photoinitiator was chosen as hydrogen acceptors. We explored the hydrogen abstraction reaction in different solvents (methanol, water and DMSO) by quantum chemistry for geometry and energy. An investigation was undertaken regarding the structural orbital by electrostatic potential (ESP) and topological analysis (ELF and LOL). The findings were also combined with the distortion model and transition state theory. We obtained the molecular interactions used independent gradient method in the Hirshfeld molecular density partition (IGMH). The Eckart’s correction allowed to examine the driving factors of the hydrogen abstraction reaction tunnels and these reactions constant rates are determined in the range of 500–2500 K depending on the modified Arrhenius form in different solvents effect. Our results can provide an answer for the different reactivities.

EFFECTS OF MULTIPLE STRUCTURES AND TORSIONAL ANHARMONICITY FOR THE HYDROGEN ABSTRACTION REACTIONS OF THE THMETHYL BUTANOATE BY H RADICAL. Thermal rate constants for the hydrogen abstraction reactions of the methyl butanoate (MB) by H radical were estimated by applying the multistructural canonical variational theory with small-curvature tunneling (CVT/SCT). The conformational search was performed at MPWB1K/6-31+G(d,p) level of theory and 68 distinguishable conformers for MB and transition state located. The multistructural and torsional anharmonicity effects were corrected through the rovibrational partition functions calculated with the multistructural method based on a coupled torsional potential, MS-T(C). The MS-CVT/SCT thermal rate constants are shown in good concordance with previous combustion models. After fitting the rate constants in a four-parameters equation, the activation energy showed a temperature dependence. The product branching ratios indicate a preference for (Rα) until 500 K. Above this temperature, the contribution of other reactions becomes relevant, especially for (Rβ).

The complex of methyltransferase-like proteins 3 and 14 (METTL3-14) is the major enzyme that deposits N6-methyladenosine (m6A) modifications on messenger RNA (mRNA) in humans. METTL3-14 plays key roles in various biological processes through its methyltransferase (MTase) activity. However, little is known about its substrate recognition and methyl transfer mechanism from its cofactor and methyl donor S-adenosylmethionine (SAM). Here, we study the MTase mechanism of METTL3-14 by a combined experimental and multiscale simulation approach using bisubstrate analogues (BAs), conjugates of a SAM-like moiety connected to the N6-atom of adenosine. Molecular dynamics simulations based on crystal structures of METTL3-14 with BAs suggest that the Y406 side chain of METTL3 is involved in the recruitment of adenosine and release of m6A. A crystal structure with a BA representing the transition state of methyl transfer shows a direct involvement of the METTL3 side chains E481 and K513 in adenosine binding which is supported by mutational analysis. Quantum mechanics/molecular mechanics (QM/MM) free energy calculations indicate that methyl transfer occurs without prior deprotonation of adenosine-N6. Furthermore, the QM/MM calculations provide further support for the role of electrostatic contributions of E481 and K513 to catalysis. The multidisciplinary approach used here sheds light on the (co)substrate binding mechanism, catalytic step, and (co)product release, and suggests that the latter step is rate-limiting for METTL3. The atomistic information on the substrate binding and methyl transfer reaction of METTL3 can be useful for understanding the mechanisms of other RNA MTases and for the design of transition state analogues as their inhibitors.

Two-dimensional material rhenium disulfide (ReS 2) has attracted much attention recently as a potential electrochemical catalyst for the Hydrogen Evolution Reaction (HER). The ReS 2 monolayer is found to be catalytically inert. The challenge lies in activating the ReS 2 monolayer to increase HER output. One of the approaches to this lies in depositing small metal clusters on the monolayer. This paper examines the formation and stability of small metal clusters on 1T distorted ReS 2 monolayer using dispersion-corrected Density Functional Theory. Four different kinds of transition metal clusters, viz. Au, Pt, Mo, and Cr are investigated for geometry and binding on the ReS 2 monolayer. HER activity of each type of ReS 2 -supported metal cluster is investigated based on computed free energy. The HER mechanism was investigated for clusters with optimal activity, and it was found that while the ReS 2 monolayer follows the Volmer-Heyrovsky route, for the transition metal cluster decorated ReS 2 , the Volmer-Tafel route is more probable. • ReS 2 basal plane is catalytically inert; therefore, surface activation is required. • ReS 2 monolayer decorated with small clusters of Au, Pt, Mo and Cr are stable. • ReS 2 supported Au, Pt and Mo clusters are HER active, especially Au3, Pt4 and Mo5, but Cr clusters are not. • The clusters on ReS 2 follow a Tafel mechanism, with lower activation barriers than pure ReS 2. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

By using the B3 LYP methods in Gaussian package and the 6-31 G** and TZVP basis sets, the potential energy curves(PECs) of OCS3+ ion in the ground electronic state is deduced, and its dissociation mechanism is explored. If fixing the C—O bond length at the equilibrium internuclear distance of OCS, which is 2.1 a.u., we found the PEC along C—S is repulsive with a very low barrier. Conversely, if the C—S is fixed at 2.9 a.u., the PEC along C—O presents a very deep minimum and a high and broad barrier. According to the Frank Condon Principle, above phenomenon suggests that the ground state OCS3+ will dissociate through the breakup of C—S bond: OCS3+→CO++S2+. The following calculation of the transition state and IRC further confirms this fragmentation pathway. Finally, the Mulliken charge distribution and molecular bond length of reactants and products are analyzed, the result is also consistent with our conclusion. [ABSTRACT FROM AUTHOR]

The interaction of 4-fluorostyrene with 4-CN-PhNO2 in the presence of various solvents has been simulated by quantum chemistry methods. The reaction mechanism and activation barriers of its stages are proposed. The software package Gaussian03 was used for calculations. The optimal geometric parameters of the structures under study were obtained by means of the DFT/WB97XD/DGDZVP2 methods, the TD-SCF/DFT/WB97XD/DGDZVP2 and TD-SCF/DFT/PBEPBE/6-311g++(3d2f,3p2d) methods were used to calculate excited singlet and triplet states, and the IEFPCM model was employed to account for the solvent effects. The transition states were calculated by the TS method using the DFT/PBEPBE/6-311g++(3d2f,3p2d) method. [ABSTRACT FROM AUTHOR]

A comparative study of the kinetic resolution of racemic 6-methoxy-, 6-nitro-, and 6-chloro-3-methyl-3,4-dihydro-2H-[1,4]benzoxazines with (S)-naproxen acyl chloride, N-phthaloyl-(S)-leucyl chloride, and O-phenyl-(R)-lactyl chloride was carried out. The selectivity factors in the kinetic resolution of racemic amines with (S)-naproxen acyl chloride and O-phenyl-(R)-lactyl chloride were higher compared to N-phthaloyl-(S)-leucyl chloride. The factors responsible for the stereodifferentiation in the kinetic resolution of racemic dihydrobenzoxazines containing groups with different electronic properties were explained based on DFT calculations. Stacking interactions between aromatic moieties in the transition state were demonstrated to play a key role in the stereodifferentiation. [ABSTRACT FROM AUTHOR]

The mechanism of Rh2(S‐NTTL)4 catalyzed carbene insertion into C(3)−H of indole is investigated using DFT methods. Since the commonly accepted enol mechanism cannot account for enantioinduction, a concerted oxocarbenium pathway was proposed in an earlier work using a model catalyst. However, after considering the full catalytic system, this study finds that akin to other reactions, here, too, the enol pathway is of lower energy, which now naturally raises a conundrum regarding the mode of chiral induction. Herein, a new water promoted mechanistic pathway involving a metal‐associated enol intermediate hydrogen bonding and stereochemical model are proposed to solve this puzzle. It is shown how the catalyst bowl‐shaped structure along with substrate‐catalyst binding is crucial for achieving high levels of enantioselectivity. A stereodetermining water‐assisted proton transfer is proposed and confirmed through deuterium‐labeling experiments. The water molecules are held together by H‐bonding interactions with the carboxylate ligands that is reminiscent of enzyme catalysis. Although several previous studies have aimed at understanding the mechanism of metal catalyzed carbene insertion reactions, the origin of high stereoinduction especially with chiral metal complexes remains unclear, and till date there is no transition state model that can explain the high enantioselectivity with such chiral Rh complexes. The metal‐associated enol pathway is currently underrepresented in catalytic cycles and may play a crucial role in catalyst design. Since the enol pathway is commonly adopted in other metal‐catalyzed X−H insertion reactions involving a diazoester, the presented results are not specific to the current reaction. Therefore, this study could provide the direction for achieving high levels of enantioselectivity which is otherwise difficult to achieve with a single metal catalyst. [ABSTRACT FROM AUTHOR]

As an organic molecule catalyst, N,N′,N″‐trihydroxyisocyanuric acid can selectively catalyze the oxidation of the methyl group of waste 2,4,6‐trinitrotoluene to generate 2,4,6‐trinitrobenzoic acid. This reaction can avoid environmental pollution by inorganic heavy metal catalysts. In this study, four reaction stages of this catalytic reaction were designed and validated computationally at the M06‐2X‐D3ZERO/6‐311G(d,p) level using the acetic acid solvent model. These validations include transition state searches, intrinsic reaction coordinate calculations, reactant and product optimizations, and frequency calculations. The final reaction network of 23 transition states shows that after N,N′,N″‐trihydroxyisocyanuric acid activation and common reaction, the network bifurcates into two stages: alcohol to carboxylic acid and aldehyde to carboxylic acid. Although the former stage releases about 155 kcal/mol of Gibbs free energy, less than the 177 kcal/mol from the latter stage, the overall reaction equation shows that the pathway including former stage does not consume the catalytically active substance IM_T2, which saves the energy required for reactivation and is thus more favorable. Furthermore, the key transition states in the reaction network include bimolecular substitution reactions and proton‐hopping transfer reactions. Analyses of their interaction region indicators and intrinsic reaction coordinate results demonstrate strong selectivity. Additionally, the energy barriers and heat releases of the latter are twice and 1.3 times greater than those of the former, respectively. In summary, this study elucidated two competitive reaction pathways and identified the more energetically favorable and selective pathway, and it provides useful insights for further optimization of industrial utilization of 2,4,6‐trinitrotoluene. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)