Reaction Mechanism Research Articles

Co(III)-catalyzed regioselective benzannulation of substituted pyridones with 1,6-diynes via dual C-H bond activation.

A Co(III)-catalyzed site-selective C5 and C6 benzannulation of substituted pyridones with 1,6-diynes via dual C-H bond activation has been reported. The scope of the benzannulation reaction was examined with various substituted 2-pyridyl pyridones and 1,6-diynes. The combination of cuprous acetate and silver carbonate plays a crucial role in the success of the reaction. A plausible reaction mechanism was proposed and supported by deuterium labelling studies and radical trapping experiments.

A novel approach for recovery of iron from copper slag using calcium salts.

Copper slag is not only a waste but it has many valuable and recoverable metals present in it such as iron. Therefore,this study focuses on the utilization of waste materials i.e.,copper slag and tire char for iron recovery. Four calcium salts, i.e., CaCO3, Ca(OH)2, CaCl2, and CaSO4, with different dosages, reduction temperature, reduction time, and atmospheric conditions were investigated in order to find best reaction mechanism for iron recovery. Among these salts, the optimum conditions were determined: using CaCO3 under 0.384 of CaO/SiO2 molar ratio in a 60-min reduction period at 1473.15K temperature, that gives 91.14% iron recovery. Both FESEM-EDS data and chemical titration showed more than 70% of the highest iron grade in the recovered product. The analysis results indicate that main impurity in the whole procedure was carbon from coal char that reduces the iron grade. This research not only provides a novel way to recover iron from copper slag, but also provides a future direction to handle copper slag and tire char waste materials.

Reaction Mechanism of Pyrolysis and Combustion of Methyl Oleate: A ReaxFF-MD Analysis

Reaction Mechanism of Pyrolysis and Combustion of Methyl Oleate: A ReaxFF-MD Analysis

Synthesis, characterization and antioxidant screening of a 1,10-phenanthroline-based tetraza-macrocyclic ligand and its nickel complex with therapeutic potential and catalytic significance

Abstract In this study, we present a synthetic route for the preparation of a novel 1,10- phenanthroline-based tetraza-macrocyclic ligand, 5,12,25,28-tetraazaheptacyclo [14.8.4.2⁴,⁷.210,13.0⁶,11.019,27.022,26]dotriaconta-1 (25),4,6,8,10,12,16(28),17,19(27),20,22(26),23,29, 31-tetradecaene, 3 and its corresponding nickel complex, (28Z)-1,3,6,31-tetraaza-2-nickelaoctacyclo [17.9.3.2⁷,28.0³,16.0⁴,13.0⁵, 10.022,30.025,29]tritriaconta-4(13),5(10),6,8,11,14,16,19(31),20,22(30), 23,25(29),26,28(32)-tetradecaene, 8. The ligand was synthesized via a condensation reaction involving 2,9-dimethyl-1,10-phenanthroline and 2,9-dicarbaldehyde-1,10 phenanthroline, followed by nickel metal complexation. Fourier-transformed infrared (FT-IR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and thermal analyses were employed to characterize the ligand and its Ni complex. Their ADMET parameters and potential macromolecular targets calculations showed they have therapeutic potentials. The antioxidant assay shows that Ni-complex is approximately 9 times more potent than the ligand with IC50 values of 0.045 mg/ml and 0.404 mg/ml, respectively. Their microspecies distribution which was predicted using ChemAxon Predictor revealed their catalytic potentials The reaction mechanisms involved are discussed. The 1,10-phenanthroline-based macrocyclic ligand and its nickel complex significantly expand the structural diversity within the tetraza-macrocyclic ligand system and serve as base ligands for the development of possible derivatives, with concomitant applicability in drug development and catalysis.

Polymer and micellar catalysis in d-fructose oxidation by imidazolium fluorochromate: A kinetic and mechanistic study

This work investigated the oxidation of d-fructose using imidazolium fluorochromate (IFC) as an oxidant and analyzed how sodium dodecyl sulfate (SDS) and polyethylene glycol (PEG-400) affected the reaction kinetics. The process exhibited a unit-order dependence on IFC, d-fructose, and perchloric acid concentration. Perchloric acid was the primary source of hydrogen ions in the reaction mixture. The stoichiometry of the reaction indicated that 3 mol of d-fructose requires 4 mol of IFC. Acrylonitrile, a radical-generating species, did not impact the reaction rate, indicating the absence of a free radical intermediate. The reaction rate decreases as the Mn (II) ions concentration increases, suggesting the involvement of Cr (IV) species in the reaction. The dielectric value of the reaction medium (D) had an inverse effect on the rate, and the outcomes were consistent with the Amis (log k1 and 1/D) and Kirkwood plots (log k1 and (D-1/2D+1)), indicating the presence of dipole-dipole interactions in the process. SDS and PEG-400 catalyzed the reaction. The reaction showed significant catalysis before reaching the critical micelle concentration (CMC). However, the observed rate constants stabilized at higher SDS concentrations exceeding the CMC. Piszkiewicz's cooperativity model was employed to describe the surfactant catalysis, while the Benesi-Hildebrand equation was utilized to explain polymer catalysis. The activation parameters are ΔH† = 44.3 ± 1.3 kJ mol−1, and ΔS† = −133.4 ± 4.3 J K−1 mol−1. The products of the reaction have been identified by spectral analysis as d-arabinoniclactone and formic acid. The formation of an ester complex followed by its decomposition was proposed as the rate-limiting step in the proposed mechanistic reaction pathway.

Unveiling the Nature of Chemical Bonds in Real Space.

Recent advent of diverse chemical entities necessitates a re-evaluation of chemical bond concepts, underscoring the importance of experimental evidence. Our prior study introduced a general methodology, termed Core Differential Fourier Synthesis (CDFS), for mapping the distribution of valence electron density (VED) in crystalline substances within real space. In this study, we directly compare the VED distributions obtained through CDFS with those derived from high-accuracy theoretical calculation using long-range corrected density functional theory, which quantitatively reproduces accurate orbital energies. This comparison serves to demonstrate the precision of the CDFS in replicating complex details. The VED patterns observed experimentally exhibited detailed structures and phases of wave functions indicative of sp3 hybrid orbitals, closely aligning with theoretical predictions. This alignment underscores the utility of our approach in gathering quantum chemical data experimentally, a crucial step for discussing the chemical properties, such as reaction mechanisms.

The Subtle Mechanism of Nickel-Photocatalyzed C(sp3)-H Cross-Coupling.

This computational study revises and reformulates the mechanism for the cross-coupling reaction between chlorobenzene and tetrahydrofuran catalyzed by a Ni complex with the assistance of an Ir photocatalyst. This is a representative process of transition-metal photocatalysis, and variations of it have been reported by different experimental authors. It has been also the subject of previous computational studies, which we revise and extend. Density functional theory (DFT) calculations and microkinetic modeling indicate that the most efficient mechanism takes place through an energy-transfer step and involves a NiIII complex.

Theoretical investigation of the reaction mechanism of THP oxidative rearrangement catalysed by BBOX.

γ-Butyrobetaine hydroxylase (BBOX) is a non-heme FeII/2OG dependent enzyme that is able to perform two different kinds of catalytic reactions on 3-(2,2,2-trimethylhydrazinium) propionate (THP) to produce distinct catalytic products. Although the structure of BBOX complexed with THP has been resolved, the details of its catalytic mechanism are still elusive. In this study, by employing molecular dynamics (MD) simulations and density functional theory (DFT) calculations, the mechanism of the THP oxidative rearrangement reactions catalysed by BBOX was investigated. Our calculations revealed how the enzyme undergoes a conformational conversion to initiate the catalytic reactions. In the first catalytic step, BBOX performs hydrogen abstraction from the substrate THP as a common non-heme iron enzyme. Due to the structure of the substrate stabilizing the radical species and polarizing the adjacent N-N bond, in the next step, THP takes the pathway for N-N bond homolysis but not regular hydroxyl rebounding. The cleaved ammonium radical could either react with the hydroxyl group on the iron centre of the enzyme or recombine with the other cleaved fragment of the substrate to generate the rearranged product. This study revealed the catalytic mechanism of BBOX, detailing how the enzyme and the substrate regulated the hydroxyl rebound process to generate various products.

Interference with PLA2G16 promotes cell cycle arrest and apoptosis and inhibits the reprogramming of glucose metabolism in multiple myeloma cells by modulating the Hippo/YAP signaling pathway.

Multiple myeloma, which is a clonal plasma cell tumor, derives from a postmitotic lymphoid B-cell lineage and remains untreatable. Group XVI phospholipase A2 (PLA2G16) can either be a tumor suppressor or an oncogene in different types of cancer. This study was intended to explore the role of PLA2G16 in multiple myeloma and to reveal the reaction mechanism. The mRNA and protein expressions of PLA2G16 in human bone marrow stromal cell line HS-5 and multiple myeloma cells were assessed using reverse transcription-quantitative PCR and western blot. The transfection efficacy of sh-PLA2G16 and oe-YAP was examined using reverse transcription-quantitative PCR and western blot. Through cell counting kit-8 assay and 5-ethynyl-2'- deoxyuridine staining, multiple myeloma cell viability and proliferation were detected. Flow cytometry was used to measure cell apoptosis and cell cycle distribution. Oxygen consumption rate, the activities of mitochondrial respiratory chain complexes I-V, and the activity of caspase-3 were estimated with Seahorse XF24 analyzer, oxidative phosphorylation activity assay kit, and caspase-3 assay kit, respectively. Lactate production and glucose consumption were evaluated usingcorresponding assay kits. Western blot was employed to meaure proteins associated with cell cycle, glycolysis, pentose phosphate pathway as well as Hippo/YAP signaling pathway. In this study, PLA2G16 expression was greatly increased in multiple myeloma cells and PLA2G16 silence inhibited cell proliferation, promoted cell apoptosis, facilitated cell cycle arrest, and suppressed the reprogramming of glucose metabolism in multiple myeloma. It was also identified that PLA2G16 depletion inhibited the Hippo/YAP signaling pathway. Further experiments revealed that the overexpression of YAP partially reversed the inhibitory effects of PLA2G16 silence on multiple myeloma cell malignant development and the reprogramming of glucose metabolism. Collectively, PLA2G16 silence impeded multiple myeloma progression and inhibited glucose metabolism reprogramming by blocking the Hippo/YAP signaling pathway.

Post-Synthetic Modification of Calix[4]arene Framework by Iridium-Mediated Alkyne Insertion into an Inert C-C Bond: A Novel Strategy for Unsymmetrical Macrocycles.

As a novel synthetic method for unsymmetrical macrocycles, we herein developed a post-synthetic modification of calix[4]arenes by insertion of a terminal alkyne into an inert C(methylene)-C(aryl) bond of the macrocyclic framework. In this transformation, C-iridated calix[4]arenes, readily synthesized through C-H bond activation of the parent calix[4]arene, undergoes C(methylene)-C(aryl) bond cleavage followed by insertion of an alkyne to provide a ring-expanded calix[4]arene complex. Removal of the iridium metal from the resulting complex was readily accomplished by a simple treatment with an acid. The developed sequential method affords novel unsymmetrical, monofunctionalized macrocyclic compounds via 3 steps from the parent calix[4]arene in good yield. The unique unsymmetrical structures of the alkyne-inserted macrocycles were evaluated by X-ray single crystal analyses. On the basis of theoretical calculations, we propose a reaction mechanism involving an uncommon C-C bond cleavage step through δ-carbon elimination for the ring enlargement process.

Kinetic analysis of reversible solid-gas reactions in films: application to the decomposition of CaCO$$_3$$ and BaCO$$_3$$ carbonates

AbstractTo determine the decomposition conditions of carbonates in the form of films, we investigated the dependence of the kinetics on carbon dioxide partial pressure, temperature and film thickness. Three different analyses allow us to determine the functional dependence of the decomposition onset temperature on the CO$$_2$$ 2 partial pressure, of the reaction rate on the temperature and of the kinetics on the film thickness. The latter analysis also reveals geometrical aspects of the reaction mechanism. Experiments have been carried out with CaCO$$_3$$ 3 and BaCO$$_3$$ 3 films. The simple geometry of the films and their relatively fast heat and gas transport allow the reaction kinetics to be easily explored.

Roles of Ferric Peroxide Anion Intermediates (Fe3+O2 -, Compound 0) in Cytochrome P450 19A1 Steroid Aromatization and a Cytochrome P450 2B4 Secosteroid Oxidation Model.

Cytochrome P450 (P450, CYP) 19A1 is the steroid aromatase, the enzyme responsible for the 3-step conversion of androgens (androstenedione or testosterone) to estrogens. The final step is C-C bond scission (removing the 19-oxo group as formic acid) that proceeds via a historically controversial reaction mechanism. The two competing mechanistic possibilities involve a ferric peroxide anion (Fe3+O2 -, Compound 0) and a perferryl oxy species (FeO3+, Compound I). One approach to discern the role of each species in the reaction is with the use of oxygen-18 labeling, i.e., from 18O2 and H2 18O of the reaction product formic acid. We applied this approach, using several technical improvements, to study the deformylation of 19-oxo-androstenedione by human P450 19A1 and of a model secosteroid, 3-oxodecaline-4-ene-10-carboxaldehyde (ODEC), by rabbit P450 2B4. Both aldehyde substrates were sensitive to non-enzymatic acid-catalyzed deformylation, yielding 19-norsteroids, and conditions were established to avoid issues with artifactual generation of formic acid. The Compound 0 reaction pathway predominated (i.e., Fe3+O2 -) in both P450 19A1 oxidation of 19-oxo-androstenedione and P450 2B4 oxidation of ODEC. The P450 19A1 results contrast with our prior conclusions (J. Am. Chem. Soc. 2014, 136, 15016-16025), attributed to several technical modifications.

Study of the Dynamic Reaction Mechanism of the Cable-Stayed Tube Bridge under Earthquake Action

In order to explore the failure mode of the cable-stayed pipe bridge under earthquake action, taking the structural system of an oil and gas pipeline–cable-stayed pipe bridge as the research object, the full-scale finite element calculation model of the cable-stayed pipe bridge–oil and gas pipeline structural system as well as the finite element calculation model considering the additional mass of the oil and gas medium and the fluid–structure interaction effect were established by using ANSYS Workbench finite element software. The stress and displacement of the cable under the earthquake action were analyzed in the time history, as were the response characteristics of the cable when subjected to both methods. The calculation results show that the overall failure of the pipeline is basically the same under the two methods. Compared with the additional mass method, the solution for the fluid–structure coupling method can be derived through a comprehensive analysis of the flow field and structure, respectively, avoiding the sudden change caused by model simplification or calculation error so that the analysis results can better simulate the actual situation. In summary, the fluid–structure interaction method enables a more precise prediction of the dynamic response of the structure, and the findings of this research can provide a theoretical foundation and technical guidance for optimizing the seismic performance of cable-stayed pipe bridges.

Selective nitrogen insertion into aryl alkanes

Molecular structure-editing through nitrogen insertion offers more efficient and ingenious pathways for the synthesis of nitrogen-containing compounds, which could benefit the development of synthetic chemistry, pharmaceutical research, and materials science. Substituted amines, especially nitrogen-containing alkyl heterocyclic compounds, are widely found in nature products and drugs. Generally, accessing these compounds requires multiple steps, which could result in low efficiency. In this work, a molecular editing strategy is used to realize the synthesis of nitrogen-containing compounds using aryl alkanes as starting materials. Using derivatives of O-tosylhydroxylamine as the nitrogen source, this method enables precise nitrogen insertion into the Csp2-Csp3 bond of aryl alkanes. Notably, further synthetic applications demonstrate that this method could be used to prepare bioactive molecules with good efficiency and modify the molecular skeleton of drugs. Furthermore, a plausible reaction mechanism involving the transformation of carbocation and imine intermediates has been proposed based on the results of control experiments.

Roles of Ferric Peroxide Anion Intermediates (Fe3+O2−, Compound 0) in Cytochrome P450 19A1 Steroid Aromatization and a Cytochrome P450 2B4 Secosteroid Oxidation Model

AbstractCytochrome P450 (P450, CYP) 19A1 is the steroid aromatase, the enzyme responsible for the 3‐step conversion of androgens (androstenedione or testosterone) to estrogens. The final step is C−C bond scission (removing the 19‐oxo group as formic acid) that proceeds via a historically controversial reaction mechanism. The two competing mechanistic possibilities involve a ferric peroxide anion (Fe3+O2−, Compound 0) and a perferryl oxy species (FeO3+, Compound I). One approach to discern the role of each species in the reaction is with the use of oxygen‐18 labeling, i.e., from 18O2 and H218O of the reaction product formic acid. We applied this approach, using several technical improvements, to study the deformylation of 19‐oxo‐androstenedione by human P450 19A1 and of a model secosteroid, 3‐oxodecaline‐4‐ene‐10‐carboxaldehyde (ODEC), by rabbit P450 2B4. Both aldehyde substrates were sensitive to non‐enzymatic acid‐catalyzed deformylation, yielding 19‐norsteroids, and conditions were established to avoid issues with artifactual generation of formic acid. The Compound 0 reaction pathway predominated (i.e., Fe3+O2−) in both P450 19A1 oxidation of 19‐oxo‐androstenedione and P450 2B4 oxidation of ODEC. The P450 19A1 results contrast with our prior conclusions (J. Am. Chem. Soc. 2014, 136, 15016–16025), attributed to several technical modifications.

Reaction Dynamics of CO2 Hydrogenation on Iron Catalysts Using ReaxFF Molecular Dynamics Simulation.

The conversion of CO2 to hydrocarbons using catalysts is a promising route to utilize CO2 and produce more valuable chemicals in a sustainable manner. Recent studies have shown that iron-based catalysts perform well for the hydrogenation of CO2. While the hydrogenation reaction mechanism in the gas phase is straightforward, when catalyzed by iron it has been demonstrated to involve various chemical transformations, and the selectivity and conversion are strongly dependent on the particle size. To further investigate the dependence of the reactivity of iron catalysts on cluster size, we performed reactive molecular dynamics simulations using the ReaxFF force field (ReaxFF-MD) for iron nanoclusters of various sizes in a CO2 and H2-rich environment. We demonstrated that the homogeneous hydrogenation of CO2 was correctly described by this ReaxFF model. The dissociation mechanism of CO2 on the Fe4, Fe16 clusters, and the bcc(100) Fe slab agrees with previous DFT results. The ReaxFF-MD simulations suggest a strong dependence of reactivity on the cluster size, with the Fe4 cluster having the highest reactivity. We show that ReaxFF-MD provides a route to understand reaction mechanisms in these nonequilibrium reactive processes where fast processes and local minima are important.

Fluctuating Flame from Suspending Ferrimagnetic Core/Shell Al@Fe3O4 Nanoparticles in a Magnetic Field

AbstractCore–shell fuel@oxidizer nanocomposite can combust in oxygen‐starved environment. A ferrimagnetic reactive particle, being successfully engineered, allows for manipulation using an external magnetic field and facilitates target heat or gas production. This research reports on interesting flame dynamics of newly synthesized core–shell Al@Fe3O4 nanoparticles under the influence of a magnetic field. Serving as an oxidizer and a functional ferrimagnetic component, iron oxide nanoparticles (IONPs) are grown in situ on nano‐sized Al (n‐Al) particles. Electron microscopic images demonstrate nearly monodispersed IONPs ≈7 nm decorating the surface of n‐Al. X‐ray diffractogram and X‐ray photoelectron spectroscopy confirm the formation of Fe3O4. Thermal analysis suggests the as‐prepared core–shell particles predominantly go through a solid‐state reaction mechanism that exhibits 30% lower activation energy compared to physically‐mixed nanocomposite (215.0 vs 310.8 kJ mol−1). The core/shell particles can be ignited and combust under laser irradiation with or without the effect of a magnetic field. When suspended in the middle of the tube by the magnetic field, an interesting combustion process is observed, highlighting a grow‐shrink‐grow flame resulted from the interactions between the combustion products and the external magnetic field, as well as backfiring at the bottom of the sample without major changes in burning rate and ignition delay.

Mechanism of Methyl Transfer Reaction between CH3Co(dmgBF2)2py and PPh3Ni(Triphos).

DFT calculations were performed for the methyl group transfer reaction between CH3Co (dmgBF2)py and PPh3Ni(Triphos). The reaction mechanism and its energetics were investigated. This reaction is relevant to the catalytic mechanism of the enzyme acetyl coenzyme A synthase. BP86 and PBE functionals and dispersion corrections were used. It was found that intermolecular interactions are very important for this reaction. The influence of the solvent on the reaction was studied.

Structure Function Studies of Photosystem II Using X-Ray Free Electron Lasers.

The structure and mechanism of the water-oxidation chemistry that occurs in photosystem II have been subjects of great interest. The advent of X-ray free electron lasers allowed the determination of structures of the stable intermediate states and of steps in the transitions between these intermediate states, bringing a new perspective to this field. The room-temperature structures collected as the photosynthetic water oxidation reaction proceeds in real time have provided important novel insights into the structural changes and the mechanism of the water oxidation reaction. The time-resolved measurements have also given us a view of how this reaction-which involves multielectron, multiproton processes-is facilitated by the interaction of the ligands and the protein residues in the oxygen-evolving complex. These structures have also provided a picture of the dynamics occurring in the channels within photosystem II that are involved in the transport of the substrate water to the catalytic center and protons to the bulk.

Highly Efficient Carbonylation of Propylene Oxide into β‐Butyrolactone Catalyzed over Co‐Al Bimetallic Species

Rational designation of the catalyst for efficient atom‐economic conversion of propylene oxide (PO) and carbon monoxide (CO) into β‐butyrolactone is of current significance. By employing the O,N,O‐tridentate ligands R1,R2LH2 (1‐4), the aluminium compounds (R1,R2LAlCl)2 (R1,R2 = H,H (5), tBu,tBu (6), Cl,Cl (7), Br,Br (8)) and the derived anion‐cation pairs [H,HLAl(THF)3]+[Co(CO)4]ˉ (9) and [(R1,R2LAl)2Cl(THF)2]+[Co(CO)4]ˉ (R1,R2 = tBu,tBu (10), Cl,Cl (11), Br,Br (12)) as well as the aluminium‐cobalt bimetallic cluster compounds [(R1,R2LAl)2Cl(THF)][Co3(CO)10] (R1,R2 = tBu,tBu (13), Cl,Cl (14), Br,Br (15)) were prepared. Compounds 9‐12 efficiently catalyzed the PO carbonylation into β‐butyrolactone to achieve up 93.4‐98.9% yields while 13‐15 gained 95.2‐99.0% yields all at 25 °C and 0.1 MPa CO pressure. The Lewis acidic property of the aluminium compounds 5‐8 was investigated. The kinetic of the catalytic reaction using compound 10 was studied. The cooperatively catalytic reaction mechanism by the Co‐Al bimetallic species is proposed.