Important Reactions Research Articles

Decarboxylative 1,3-dipolar cycloadditions of l-proline.

1,3-Dipolar cycloaddition is one of the important chemical reactions between a 1,3-dipole and a dipolarophile to construct a five-membered heterocyclic compound. As an available α-amino acid reactant, l-proline is extensively used in 1,3-dipolar cycloaddition reactions. A diverse spectrum of bioactive spiro and fused N-heterocycles is obtained through this synthetic approach. In this review, we have described the use of l-proline in the synthesis of various spiro- and fused heterocyclic scaffolds.

Total synthesis of natural alkaloids Schwarzinicines A-D

Naturally occurring vasorelaxant alkaloids of 1,4-diarylbutanoidphenethylamines were synthesized successfully. Synthesis started from commercially available veratraldehyde, vanillin and piperonal. The important reactions involved in this synthesis are Corey-Fuchs, Eschweiler-Clarke, Henry reaction and lithium mediated carbon-carbon bond formation.

Remediation of phenanthrene-contaminated soil by iron oxide/carboxylate-rich porous carbon composites from vinegar residue

Conversion of solid wastes into useful remediation materials is an encouraging strategy in resource recovery. Iron oxide/carboxylate-rich porous carbon composites (IOCRPC) can be synthesized by using vinegar residue (VR) and ferrous sulfate heptahydrate (FeSO4∙7 H2O) recovered from a waste acid of a titanium dioxide factory. Characterization of FeSO4-impregnated VR exhibited a high proportion of ferricarboxylate complexes [i.e. FeII(R-COO)n2-n]. Pyrolysis temperature was the most important reaction parameter to define IOCRPC phase composition. Thermal decomposition of FeII(R-COO)n2-n produced Fe3O4 nanoparticles partly at a relatively lower pyrolysis temperature (350 ºC), while successful carbonization of VR formed the porous structures of carbon. Both Fe3O4 and ferricarboxylate complexes were the components of IOCRPC responsible for its excellent visible light absorption ability. Under visible light, phenanthrene in contaminated soil was efficiently degraded (90.1%) by IOCRPC at circumneutral pH. Phytotoxicity bioassays demonstrated significant removal of toxicity after treatment with IOCRPC, highlighting its application potential in revegetation strategies.

A Data and DFT-Driven Framework for Predicting the Microstructure of Submonolayer Inverse Metal Oxide on Metal Catalysts.

Metal oxides on metal (inverse) catalysts can selectively drive many important reactions. However, understanding the active site under experimentally relevant conditions is lacking. Herein, we introduce a computational framework for predicting atomic models of stable inverse catalysts and demonstrate it for WOx on Pt(553) and a Pt79 nanoparticle at variable WOx coverages. An evolutionary algorithm identifies a small (5%) subset of promising atomic configurations on which DFT simulations are performed. We predict a maximum coverage of ∼50% WOx on Pt(553), consisting of small clusters (tetramers and pentamers), which preferentially reside on the terrace, with their oxygen atoms interacting with the Pt step sites. Consistently, WOx does not lie on curved and undercoordinated metal sites of Pt nanoparticles. The oxide clusters prefer a partially reduced oxidation state. Theoretical EXAFS spectra for select configurations provide insights into interpreting experimental spectra of inverse catalysts. The framework applies to other catalysts.

Theoretical study of hydrogen desorption on the Ni(100) surface through simulated temperature programmed desorption spectra

Nickel has been widely used as heterogeneous catalysts in important reactions such as dehydrogenation and steam reforming, where the desorption of H2 molecules is one of the key steps. Herein, based on density functional theory calculations, we have simulated the temperature programmed desorption (TPD) spectra of hydrogen (H) on the Ni(100) surface using the mean-field approximation and a new HH dimer desorption method. Zero-point energy corrections are also considered. It is found that the centered-peaks of TPD obtained from simulations are in good agreement with the previous experimental results. However, the centered-peak position moves in an opposite direction to the experiments as atomic hydrogen coverage increases. We have systematically investigated the effects of the interaction between adsorbed H atoms and the diffusion of H atoms on the peak shifts, and found that they are not responsible for the experimentally observed leftward shift of the TPD peak. We then propose and confirm that the presence of subsurface H atoms plays a key role in the leftward peak shift. This work refines the interpretation of H2 TPD spectra and contributes to the understanding of microscopic behaviors of H atoms on the Ni(100) surface.

Terminal Copper Nitrenoid Formation and Reactivity Induced by Absorption to an Antenna Ligand.

Copper nitrenoids are key intermediates in copper-catalyzed direct C-H amination reactions. Further development of this important reaction relies on knowing the properties and reactivity of the nitrenoid intermediates. This work utilizes antenna ligands to form copper nitrenoid complexes and monitor the consecutive C-H amination reactions under well-defined single-molecule conditions in the gas phase. The [Cu(Lphoto)(Lazide)]+ precursors (Lphoto is a bidentate antenna ligand, and Lazide is an organic azide) were stored in an ion trap at 3.5 K and irradiated by visible light, which resulted in denitrogenation of the complex. Further irradiation of the copper nitrenoid led to the consecutive C-H amination of the antenna ligand. The nitrenoid complexes, as well as the products of the C-H amination, were characterized by helium tagging IRPD spectroscopy, and the mechanism was described by DFT calculations. This research demonstrates that the antenna ligands can be used to promote the denitrogenation of metal azides in the gas phase and also channel the internal energy to promote further reactivity, which opens a new way to study the reactivity of highly reactive species under well-defined conditions.

Terminal Copper Nitrenoid Formation and Reactivity Induced by Absorption to an Antenna Ligand

AbstractCopper nitrenoids are key intermediates in copper‐catalyzed direct C−H amination reactions. Further development of this important reaction relies on knowing the properties and reactivity of the nitrenoid intermediates. This work utilizes antenna ligands to form copper nitrenoid complexes and monitor the consecutive C−H amination reactions under well‐defined single‐molecule conditions in the gas phase. The [Cu(Lphoto)(Lazide)]+ precursors (Lphoto is a bidentate antenna ligand, and Lazide is an organic azide) were stored in an ion trap at 3.5 K and irradiated by visible light, which resulted in denitrogenation of the complex. Further irradiation of the copper nitrenoid led to the consecutive C−H amination of the antenna ligand. The nitrenoid complexes, as well as the products of the C−H amination, were characterized by helium tagging IRPD spectroscopy, and the mechanism was described by DFT calculations. This research demonstrates that the antenna ligands can be used to promote the denitrogenation of metal azides in the gas phase and also channel the internal energy to promote further reactivity, which opens a new way to study the reactivity of highly reactive species under well‐defined conditions.

Indigeneity, land and labour in Paraguay

This article is focused on the politics of indigeneity, which is an increasingly important concept and a central area of dispute in a globalised world. Indigeneity encapsulates the friction between ethnicity and class identities, which cannot be understood without a full consideration of differences and relationships between landowners, other economic sectors, non-indigenous workers and indigenous people. The text specifically deals with the circumstances of Paraguay, whose process of nation building is directly related to longitudinal attacks on its indigenous peoples and the unresolved problems of land, labour and rights. The case study investigates the long-term tendencies of Paraguayan society, in particular, the ongoing expansion of agribusiness and land grabbing in the northeast of the country that tragically affect the Paĩ Tavyterã indigenous people. The discussion is based on qualitative, engaged research over several years, which considered the indigenous population as co-investigators and active socio-political players. The conclusion is that, despite the fact that Paraguay is a major exporter of primary commodities, the prevailing geographical force is the accumulation of multiple forms of social, ecological and even economic degradation. Against those perverse trends, the important reaction of the Paĩ Tavyterã, as well as of other indigenous peoples, and their struggle to recover their land and socio-ecological relations greatly complicate national politics and challenge the hegemony of export-oriented agribusiness.

CO2 Reduction by an Iron(I) Porphyrinate System: Effect of Hydrogen Bonding on the Second Coordination Sphere.

Transforming CO2 into valuable materials is an important reaction in catalysis, especially because CO2 concentrations in the atmosphere have been growing steadily due to extensive fossil fuel usage. From an environmental perspective, reduction of CO2 to valuable materials should be catalyzed by an environmentally benign catalyst and avoid the use of heavy transition-metal ions. In this work, we present a computational study into a novel iron(I) porphyrin catalyst for CO2 reduction, namely, with a tetraphenylporphyrin ligand and analogues. In particular, we investigated iron(I) tetraphenylporphyrin with one of the meso-phenyl groups substituted with o-urea, p-urea, or o-2-amide groups. These substituents can provide hydrogen-bonding interactions in the second coordination sphere with bound ligands and assist with proton relay. Furthermore, our studies investigated bicarbonate and phenol as stabilizers and proton donors in the reaction mechanism. Potential energy landscapes for double protonation of iron(I) porphyrinate with bound CO2 are reported. The work shows that the bicarbonate bridges the urea/amide groups to the CO2 and iron center and provides a tight bonding pattern with strong hydrogen-bonding interactions that facilitates easy proton delivery and reduction of CO2. Specifically, bicarbonate provides a low-energy proton shuttle mechanism to form CO and water efficiently. Furthermore, the o-urea group locks bicarbonate and CO2 in a tight orientation and helps with ideal proton transfer, while there is more mobility and lesser stability with an o-amide group in that position instead. Our calculations show that the o-urea group leads to reduction in proton-transfer barriers, in line with experimental observation. We then applied electric-field-effect calculations to estimate the environmental effects on the two proton-transfer steps in the reaction. These calculations describe the perturbations that enhance the driving forces for the proton-transfer steps and have been used to make predictions about how the catalysts can be further engineered for more enhanced CO2 reduction processes.

Metal‐2D Semiconductor Hybrid Nano‐Structure Catalyst: A New Frontier of Heterogeneous Catalysis

AbstractCatalytic hydrogenation of nitroarenes is a type of important reaction to get corresponding amines, the development of catalysts with outstanding catalytic performance is in urgent need. In this review, we summarize the breakthroughs in the development of supported metal catalysts in the past few decades, including the use of different metals and supports, improved metal utilization efficiency, adjustment of the structure, and the interaction. We focus on how to develop and innovate the structure of the catalyst, aiming at the contradiction between conversion and selectivity in selective hydrogenation of nitroarenes, from the perspective of the structure and the interaction to construct a kind of catalyst with low noble metal loading and high activity, stabilize the active components, and design and fabricate hybrid nanostructured catalysts with desired activity and selectivity. The development process and the catalytic performance of metal‐2D semiconductor hybrid nano‐structure catalyst are also discussed and provide a theoretical and practical basis for the precise design of supported metal catalysts.

Formation of N‐doped Graphene and Carbon Nanoparticles Integrated Composite for Efficient Oxygen Reduction Electrocatalysis

AbstractN‐doped carbon‐based materials have been regarded as promising alternatives to Pt‐based electrocatalysts for the four‐electron (4e−) oxygen reduction reaction (ORR), which is an important electrochemical reaction for the polymer electrolyte fuel cells. Here, we report a N‐doped graphene and N‐doped carbon nanoparticles integrated composite electrocatalyst by a multi‐step acid etching plus annealing method. Despite the low N‐doping level, the material exhibits efficient 4e− ORR activity with an onset potential of 0.932 V, a half‐wave potential of 0.814 V, and a limiting current density of 5.3 mA cm−2 in 0.1 M KOH solution. We demonstrate that the promoted 4e− ORR activity is attributed to the special 2D–0D integrated structure for exposing massive active sites, the favorable porous structure facilitating the H2O transfer dynamics, and the high content of oxygen‐containing C−O−C species and the increased intrinsic carbon defects for additional active sites. A “decomposition and recrystallization” mechanism is proposed for the formation of N‐doped graphene.

Anafilaksiye Güncel Yaklaşım

Anaphylaxis is the most important acute systemic allergic reaction. The incidence of anaphylaxis has been increasing in recent years. Therefore, all healthcare providers should know the diagnosis and management of anaphylaxis. In this article, the current approach to anaphylaxis is presented, considering the criteria accepted by the World Allergy Organization (WAO) and the European Academy of Allergy and Clinical Immunology (EACCI). Intramuscular epinephrine is the first-line treatment for anaphylaxis. However, it is still not used at the desired level. Children at risk of anaphylaxis should be trained to use adrenaline autoinjectors. After anaphylaxis develops, children should be referred to an allergist to investigate the underlying causes.

Operando imaging in electrocatalysis: insights into microstructural materials design.

Electrocatalysis plays a pivotal role in renewable energy conversion and associated chemical production, enabling a variety of emerging sustainability technologies with societal impacts. Achieving marked improvement in electrocatalytic performance relies on a deep understanding of catalyst microstructures and catalytic mechanisms, with a particular emphasis on the detailed, spatiotemporally resolved characterizations of the underlying fundamental electrocatalytic processes. This fundamental need drives the development of operando imaging techniques, which improve the ability to detect dynamic structural changes in electrocatalysts and establish clear structure-performance relationships for morphologically complex, hierarchically structured catalytic materials. This review aims to highlight significant advancements in the application of operando imaging techniques to develop a deeper understanding of important heterogeneous electrocatalytic reactions critical for emerging sustainability technologies. We summarize the up-to-date key mechanistic insights regarding these reactions achieved through a range of operando imaging techniques, including electron microscopies, X-ray imaging techniques, scanning probe microscopies, and optical microscopies. We conclude by pointing out emerging directions and future prospects within the field of operando imaging in electrocatalysis.

Anion Exchange in Semiconductor Magic-Size Clusters.

Ion exchange is an effective postsynthesis strategy for the design of colloidal nanomaterials with unique structures and properties. In contrast to the rapid development of cation exchange (CE), the study of anion exchange is still in its infancy and requires an in-depth understanding. Magic-size clusters (MSCs) are important reaction intermediates in quantum dot (QD) synthesis, and studying the ion exchange processes can provide valuable insights into the transformations of QDs. Here, we achieved anion exchange in Cd-based MSCs and elucidated the reaction pathways. We demonstrated that the anion exchange was a stepwise intermolecular transition mediated by covalent inorganic complexes (CICs). We proposed that this transition involved three essential steps: the disassembly of CdE1-MSCs into CdE1-CICs (step 1), an anion exchange reaction from CdE1-CICs to CdE2-CICs (step 2), and assembly of CdE2-CICs to CdE2-MSCs (step 3). Step 3 was the rate-determining step and followed first-order reaction kinetics (kobs = 0.01 min-1; from CdSe-MSCs to CdS-MSCs). Further studies revealed that the activity of foreign anions only affected the reaction kinetics without altering the reaction pathway. The present study provides a deeper insight into the anion exchange mechanisms of MSCs and will further shed light on the synthesis of QDs.

Cypin Inhibition as a Therapeutic Approach to Treat Spinal Cord Injury-Induced Mechanical Pain.

Cypin (cytosolic postsynaptic density protein 95 interactor) is the primary guanine deaminase in the central nervous system (CNS), promoting the metabolism of guanine to xanthine, an important reaction in the purine salvage pathway. Activation of the purine salvage pathway leads to the production of uric acid (UA). UA has paradoxical effects, specifically in the context of CNS injury as it confers neuroprotection, but it also promotes pain. Since neuropathic pain is a comorbidity associated with spinal cord injury (SCI), we postulated that small molecule cypin inhibitor B9 treatment could attenuate SCI-induced neuropathic pain, potentially by interfering with UA production. However, we also considered that this treatment could hinder the neuroprotective effects of UA and, in doing so, exacerbate SCI outcomes. To address our hypothesis, we induced a moderate midthoracic contusion SCI in female mice and assessed whether transient intrathecal administration of B9, starting at 1 d postinjury (dpi) until 7 dpi, attenuates mechanical pain in hindlimbs at 3 weeks pi. We also evaluated the effects of B9 on the spontaneous recovery of locomotor function. We found that B9 alleviates mechanical pain but does not affect locomotor function. Importantly, B9 does not exacerbate lesion volume at the epicenter. In accordance with these findings, B9 does not aggravate glutamate-induced excitotoxic death of SC neurons in vitro. Moreover, SCI-induced increased astrocyte reactivity at the glial scar is not altered by B9 treatment. Our data suggest that B9 treatment reduces mechanical pain without exerting major detrimental effects following SCI.

Synthesis of New Glycosylamine Derivatives based on Carbohydrates

Background: Glycosylamine play an important role in living organisms. Most plants store their chemical resources in the form of inactive glycosides, which are broken down and con-verted into sugar in the body of herbivores by hydrolyzing enzymes. Glycosylamine are obtained from the secondary metabolism of plants and consist of two parts. One part of it contains sugar like glucose and is inactive in most substances, and has a good effect on the solubility of the glycosyla-mine derivatives and its absorption and even its transfer from one organ to another. The therapeutic effect is related to the second part, which is called aglycan (or aglucan). Glycosylamine derivatives form a large group of valuable medicinal substances, which at the same time include some of the most dangerous and toxic substances in nature. These substances are present in many groups of flowering plants. Glycosides are made in different ways in different metabolic pathways. These materials have a complex and special chemical structure and leave special effects on the human body. Glycosylamine derivatives are called O-glycosid, N-glycosid, S-glycosid in terms of atoms coupling to anomeric carbon. Carbohydrate esterification reaction to prepare new glycosylamine derivatives is one of the most important carbohydrate reactions. The anomeric position of carbohy-drates with strong leaving groups is very important for the preparation of glycosides. Preparation of glycosylamine derivatives based on acetylated carbohydrates is the main purpose of this article. Dif-ferent carbohydrates were acetylated under mild conditions and high yields. The anomeric position was deacetylated by a magnesium oxide heterogeneous catalyst in methanol solvent. In order to pre-pare new glycosides acetylated/ deacytylated carbohydrate reacted with N-Methyl-(naphtha-2-ylmethoxy)amine. The final product was identified by various spectroscopic methods. Methods: Anhydrous sodium acetate (4 g) and α-D-glucose (28 mg, 5 g) were mixed. The mixture was transferred to a 200 ml Round-bottom flask . Acetic acid (260 mg, 25 ml) was added to the reaction mixture. The reaction mixture was heated in a boiling water bath for 2 h until complete dissolution of the glucose. Then 100 ml of ice was added. After 1 hour, White crystals formed and were washed with cold water. And then 1 mol of glucose pentaacetate per 50 ml of methanol was dissolved by a magnetic stirrer. After thatMgO (0.2gr) was added to the reaction mixture. The re-action mixture was refluxed at room temperature within 4-5 hours. After 5 hours, the solvent was removed and separated by chromatography. It is then washed with hexane and crystallized by ether-hexane. And the final step reacted with N-Methyl- (naphtha-2-ylmethoxy) amine in order to prepare new glycosylamine derivatives. Results: Magnesium oxide in methanol solvent is one of the best effective catalysts in the deacetyla-tion of the anomer position of acetylated carbohydrates. It is done under ambient temperature and in very easy conditions and makes carbohydrates susceptible to extensive chemical reactions. One of these reactions is the formation of glycosides. Various carbohydrates are acetylated by acetic anhy-dride in the presence of sodium acetate, and the anomeric position is deacetylated by a heterogeneous catalyst. In order to prepare N-glycoside, the glycosides are reacted with N-alkoxy N-methylglycosyl amine. The final products are identified by various spectroscopic methods. Conclusion: Glucose, mannose, for example, were acetylated by acetic anhydride in the presence of sodium acetate. And the anomeric position of pentaacetate glucose was selectively deacetylated with magnesium oxide in a methanol solvent. Then, the reaction for the preparation of glycosylamine de-rivatives was carried out under very mild and easy conditions. The aminoglycosides synthesized in this article are used as raw materials for the synthesis of a wide range of antibacterials.

Exploring the chemical kinetic effects on the direct detonation initiation in H2-O2-Ar mixtures

Chemical kinetics plays an important role in the direct detonation initiation (DDI) of various combustible mixtures. However, its impact on detonation dynamics has rarely been studied with detailed mechanisms. This study introduces the active subspace method to systematically explore the chemical kinetics impact on the unsteady detonation dynamics in DDI of H2-O2-Ar mixture, with a 13-species detailed mechanism. The kinetic effects on the ZND structure with sub-CJ shock speed (sub-CJ ZND structure) is first investigated, where three important reactions to the sub-CJ minimum shock speed, H + O2 = O + OH, H + O + M = OH + M and H2O + H2O = H + OH + H2O are identified. Then the active subspace method is further employed to analyze the kinetics impact on the critical initiation energy ( E cr ) predicted with the critical decay rate (CDR) model and critical decay time (CDT) model. Results show that the CDT model, which utilises the sub-CJ ZND model to compute the critical parameters, can properly capture the one-dimensional detonation dynamics. All the important reactions identified with the CDT model agree well with those of one-dimensional simulations. In contrast, the CDR model shares a similar active subspace with the constant volume auto-ignition process and fails to identify the less important reactions. The consistency in the key reactions between one-dimensional simulations and the CDT model implies that it is viable to employ the CDT model as an efficient surrogate for quantifying the kinetic effects in unsteady detonation dynamics.

Theoretical study of important phenylacetylene reactions in polycyclic aromatic hydrocarbon growth

Phenylacetylene is of significance in polycyclic aromatic hydrocarbon (PAH) growth in combustion systems, especially as the key intermediate species in the hydrogen abstraction carbon addition sequence. The consumption of phenylacetylene via H-atom abstraction reactions forming ortho-C6H4C2H (o-C6H4C2H) radical and its subsequent reaction with carbon addition are important steps in PAH growth. Nevertheless, rate constants for H-atom abstraction reactions from phenylacetylene have not been explored theoretically in the literature. As regards carbon addition, besides acetylene, ethylene is also presented in large concentrations in e.g., ethylene and propene flames. However, its role in PAH growth has not been well addressed yet. In this study, the H-atom abstraction reactions from phenylacetylene aromatic ring sites (ortho-, meta-, para-) by both H atoms and OH radicals, and the subsequent C2H4 addition to o-C6H4C2H radical are accurately determined with electronic structure calculations. The main bimolecular product from the potential energy surface of the C2H4 addition to o-C6H4C2H is 2-ethynylstyrene + H, while naphthalene + H and 1-methyleneindene + H are preferred to form at high temperatures and low pressures. Rate constants are lumped with an automated master equation-based lumping approach and integrated into a recently developed chemical kinetic model. Updates of the phenylacetylene-related reactions are tested by ethylene and benzene copyrolysis in shock tube, and ethylene oxidation in laminar premixed and counterflow diffusion flames. Reaction flux analysis are additionally performed regarding the phenylacetylene consumption and naphthalene formation.

Liquid‐Liquid‐Gas Triphasic Hydrogenation of Bicarbonate to Formate in a Continuous Flow Tubular Reactor

AbstractMultiphasic reaction of bicarbonate hydrogenation to form formate using homogeneous Ru PNP pincer catalyst in a continuous flow tubular reactor is reported. The reaction system consists of three phases. Catalyst is dissolved in toluene while potassium bicarbonate is dissolved in water. The significance of efficient mixing among the organic phase, aqueous phase and gaseous hydrogen to improve hydrogenation reaction by using different inert packing materials is studied by operando visualization and also quantitatively discussed. The bicarbonate conversion of up to 67% is achieved after optimization of important reaction and reactor parameters. The designed reactor setup comprised of effective recycling system that recycles the catalyst with >99% activity.

Water Oxidation over Au-Pd/TiO2 as a Substitute for Iridium-Based Catalysts

Water oxidation is one of the most important reactions needed for a transition to a green economy. The reaction relies on extracting electrons from oxygen anions and is commonly studied using homogenous catalysts based on Ru or Ir metals. Because of Ir scarcity and its relative instability in acidic environments, metals to replace it are sought after. In this study, we have synthesized Au-Pd-based catalysts deposited on TiO2 with different ratios in order to mimic IrO2 valence orbitals (Ir5d) by the hybrid valence orbitals of Au5d and Pd4d and compared their heterogeneous catalytic activity for the evolution of O2 from water in the presence of cerium ammonium nitrate (CAN). Au-Pd-based catalysts were found to be active at a particular nominal atomic ratio. At an atomic ratio of 1 Au to 2 Pd and 1 Au to 3 Pd, the catalysts were active and stable for oxygen production from water. Long-term runs up to 20,000 min still showed the expected stoichiometry between O2 production and CAN consumption (1 to 4). However, catalysts with a reverse ratio were not active. Also, the monometallic catalysts were found to be not active for the reaction. We link the reason for the activity of Au-Pd with this specific ratio to the shape and energy position of their valence band that might be similar to those of IrO2 particles. While the turnover numbers of the Au-Pd-based catalysts were found to be lower than those of IrO2-based catalysts, on the same support in a heterogenous system, there is considerable potential upon further optimization for these two metals to replace IrO2 for a water oxidation reaction.