Tandem Manner Research Articles

Atomically intimate assembly of dual metal-oxide interfaces for tandem conversion of syngas to ethanol.

Selective conversion of syngas to value-added higher alcohols (containing two or more carbon atoms), particularly to a specific alcohol, is of great interest but remains challenging. Here we show that atomically intimate assembly of FeOx-Rh-ZrO2 dual interfaces by selectively architecting highly dispersed FeOx on ultrafine raft-like Rh clusters supported on tetragonal zirconia enables highly efficient tandem conversion of syngas to ethanol. The ethanol selectivity in oxygenates reached ~90% at CO conversion up to 51%, along with a markedly high space-time yield of ethanol of 668.2 mg gcat-1 h-1. In situ spectroscopic characterization and theoretical calculations reveal that Rh-ZrO2 interface promotes dissociative CO activation into CHx through a formate pathway, while the adjacent Rh-FeOx interface accelerates subsequent C-C coupling via nondissociative CO insertion. Consequently, these dual interfaces in atomic-scale proximity with complementary functionalities synergistically boost the exclusive formation of ethanol with exceptional productivity in a tandem manner.

Physicochemical Modulations in MXenes for Carbon Dioxide Mitigation and Hydrogen Generation: Tandem Dialogue between Theoretical Anticipations and Experimental Evidences

The dawn of MXenes has fascinated researchers under their intriguing physicochemical attributes that govern their energy and environmental applications. Modifications in the physicochemical properties of MXenes pave the way for efficient energy-driven operations such as carbon capture and hydrogen generation. The physicochemical modulations such as interface engineering through van der Waals coupling with homo/hetero-junctions render the tunability of optoelectronic variables driving the photochemical and electrochemical processes. Herein, we have reviewed the recent achievements in physicochemical properties of MXenes by highlighting the role of intercalants/terminal groups, atomic defects, surface chemistry and few/mono-layer formation. Recent findings of MXenes-based materials are systematically surveyed in a tandem manner with the future outlook for constructing next-generation multi-functional catalytic systems. Theoretical modelling of MXenes surface engineering proffers the mechanistic comprehension of surface phenomena such as termination, interface formation, doping and functionalization, thereby enabling the researchers to exploit them for targeted applications. Therefore, theoretical anticipations and experimental evidences of electrochemical/photochemical carbon dioxide reduction and hydrogen evolution reactions are synergistically discussed.

Spatially Separate Center-to-Surround Radiation Structure Induced Tandem Electron Transfer Effect for Stable and Enhanced Photocatalysis.

Spatially separate anchoring redox cocatalysts on the photocatalyst to shunt the charge migration paths is an effective route to regulate the charge flow. Differently, we herein introduce an artificially synthesized Sun-planet-like spatially separated center-to-surround radiation photosensitizer-cocatalyst structure to regulate electron flow in a tandem manner. A single Au sphere acts as the Sun/photosensitizer in the center, and small Pt particles scatter around as the planets/cocatalyst, both of which are fixed inside the MOF crystal. Such a structure can not only simultaneously increase the light harvesting capacity and electron migration kinetics but also optimize the electron transfer pathway to minimize the electron migration distance, so that the hot electrons generated by Au can be quickly transferred to Pt through MOF before annihilation, leading to a significant photoactivity promotion.

Base-Promoted Tandem Pathway for Keto-Amides: Visible Light-Mediated Room-Temperature Amidation Using Molecular Oxygen as an Oxidant.

Herein, we report metal- and photocatalyst-free room-temperature amidation for α-ketoamide synthesis from feedstock phenacyl bromides and amines using molecular oxygen as an oxidant as well as a source of oxygen in the amide segment. Visible light-mediated base-promoted one-pot sequential C-N/C═N/C═O bond formation takes place in a tandem manner to afford the desired product. Functional group tolerance (benzylic alcohol, keto, cyano, nitro, halo, etc.), a broad substrate scope, and gram-scale synthesis make this synthetic methodology more attractive. We have observed that electron-rich aromatic amines, aliphatic amines, and phenacyl bromide derivatives proceeded the present transformation with marginally superior reactivity in comparison to electron-deficient aromatic amines and phenacyl bromide derivatives. Moreover, several control experiments, in situ isolation of secondary amine and imine as key intermediates, and 18O-labeling experiments provide complete insight into the mechanism of the tandem pathway.

Access to Polysubstituted Furan Derivatives via Cascade Oxy-palladation and Hydrocarbofunctionalization of Unactivated Alkenes.

The development of an expedient strategy for the synthesis of biologically relevant multisubstituted furans is a much-desired yet challenging task. Herein, we report an efficient and versatile strategy involving two different pathways for the construction of diverse polysubstituted C3- and C2-substituted γ-furanyl carboxylic acid derivatives. The synthetic approach for C3-substituted furans involves intramolecular cascade oxy-palladation of alkyne-diols followed by the regioselective coordinative insertion of unactivated alkenes. In contrast, C2-substituted furans were obtained exclusively by performing the protocol in a tandem manner.

Reaction of Nitro‐Substituted Donor‐Acceptor Cyclopropanes with Pyrazoles in DMSO: Unexpected Formation of Tandem Kornblum‐Type Ring‐Opening Oxidation/Aza‐Michael Addition Products

AbstractThe ring‐opening reaction of nitro‐substituted donor‐acceptor cyclopropanes with pyrazoles in DMSO was investigated. Unexpectedly, the cyclopropanes underwent Kornblum‐type ring‐opening oxidation with DMSO to form aroylmethylidene malonates as intermediates in the reactions. The intermediates further underwent aza‐Michael addition with pyrazoles in tandem manner to give the corresponding aza‐Michael adducts. The highlights of the methodology include the occurrence of ring‐opening/oxidation under neutral conditions with DMSO and formation of aza‐Michael adducts with pyrazoles under catalyst‐free conditions.

Zinc-mediated efficient and selective reductive aza-Claisen rearrangement of N-allyl- and N-propargylaminoanthraquinones in ionic liquid.

An efficient method is described for the first time for reductive aza-Claisen rearrangement of 1-(N-allylamino)anthraquinones to 1-amino-2-(prop-2'-enyl)anthraquinones using zinc powder in 1-methylimidazolium tetrafluoroborate ([Hmim] BF4) as an ionic liquid in good to excellent yields. Extending of this method on 1-(N-propargylamino)anthraquinones causes the production of 1,2,3,4-tetrahydronaphtho[2,3-h]quinoline-7,12-diones containing a newly synthesized six membered heterocyclic ring on anthraquinone core via performing this reductive [3,3] sigmatropic reaction followed by cyclization in a tandem manner. These rearrangements can be executed even in the presence of some other functional groups with excellent chemoselectivity.

One-Pot Synthesis of N,N-Diphenyl-2-benzothiazolamines from 1-(2-Iodophenyl)-3-phenylthioureas and Iodobenzenes.

An efficient copper-catalyzed synthesis of a variety of N,N-diphenyl-2-benzothiazolamines was developed. Starting from substituted 1-(2-iodophenyl)-3-phenylthioureas and substituted iodobenzenes, the reaction proceeded smoothly via a tandem manner in the presence of CuI to afford the corresponding N,N-diphenyl-2-benzothiazolamine derivatives with good functional group tolerance. The protocol features simple performance, easily available starting materials, a one-pot manner, and good functional group tolerance, providing a practical strategy for the preparation of poly-functionalized amines.

A self-assembled trimeric protein vaccine induces protective immunity against Omicron variant

The recently emerged Omicron (B.1.1.529) variant has rapidly surpassed Delta to become the predominant circulating SARS-CoV-2 variant, given the higher transmissibility rate and immune escape ability, resulting in breakthrough infections in vaccinated individuals. A new generation of SARS-CoV-2 vaccines targeting the Omicron variant are urgently needed. Here, we developed a subunit vaccine named RBD-HR/trimer by directly linking the sequence of RBD derived from the Delta variant (containing L452R and T478K) and HR1 and HR2 in SARS-CoV-2 S2 subunit in a tandem manner, which can self-assemble into a trimer. In multiple animal models, vaccination of RBD-HR/trimer formulated with MF59-like oil-in-water adjuvant elicited sustained humoral immune response with high levels of broad-spectrum neutralizing antibodies against Omicron variants, also inducing a strong T cell immune response in vivo. In addition, our RBD-HR/trimer vaccine showed a strong boosting effect against Omicron variants after two doses of mRNA vaccines, featuring its capacity to be used in a prime-boost regimen. In mice and non-human primates, RBD-HR/trimer vaccination could confer a complete protection against live virus challenge of Omicron and Delta variants. The results qualified RBD-HR/trimer vaccine as a promising next-generation vaccine candidate for prevention of SARS-CoV-2, which deserved further evaluation in clinical trials.

Intraspecific variation in growth‐related traits—from leaf to whole‐tree—in three provenances of Cryptomeria japonica canopy trees grown in a common garden

AbstractTo elucidate the physiological and morphological factors underlying intraspecific variation in growth rate, we examined the variation in leaf and whole‐tree traits for three geographical variations of ca. 45‐year‐old Japanese cedar (Cryptomeria japonica D. Don) with contrasting heights and radial growth in a common garden. Traits that reflect leaf‐level photosynthesis, water relations, and whole‐tree level crown structure in relation to light use and hydraulic architecture were measured. Overall, intraspecific variation in growth characteristics in field‐grown adult trees was regulated by whole‐tree properties rather than leaf properties. Most leaf traits were similar among provenances. Nevertheless, the leaf traits exhibited highest maximum net photosynthetic rate, dark respiration rate, and light compensation point in provenances whose native habitats are most similar to the common garden in the present study. Together with previous reports that this provenance has higher root nutrient acquisition capacity than the other two provenances, it can be said that organ‐level resource use strategies are coupled in a tandem manner. At the whole‐tree level, hydraulic architecture—as explained by axial variation in the hydraulically weighted tracheid diameter—can be linked to leaf distribution with respect to light use strategies as well as water transport capacity, leading to differences in growth characteristics among provenances. The study of intraspecific variation in growth characteristics in trees with a wide range of native habitats is expected to be a useful indicator for predicting changes in growth potential and forest dynamics in response to climate change in each habitat.

Olefination of 3-Diazoindolin-2-imines with Hydrazones: An Approach toward Stereoselective Synthesis of (E)-3-Arylideneindolin-2-imines.

Stereoselective synthesis of (E)-3-arylideneindolin-2-imines from 3-diazoindolin-2-imines and hydrazones was achieved using copper bromide as the catalyst. The olefination reaction proceeded via copper-catalyzed aerobic oxidation of hydrazones to diazo compounds and copper-catalyzed cross coupling of two different diazo components in a tandem manner.

Cover Feature: Acenaphthenoannulation Induced by the Dual Lewis Acidity of Alumina (Chem. Eur. J. 31/2022)

Tandem bond activation: The dual Lewis acidity of alumina has been discovered and employed to activate C−F and triple C≡C bonds in a tandem manner to provide rapid access to elusive nonplanar PAHs such as π-extended helicenes, buckybowls and fragments of geodesic nanoribbons. More information can be found in the Research Article by K. Amsharov and co-workers (DOI: 10.1002/chem.202200584).

Organic Photocathode Supported by Copper Nanosheets Array for Overall Water Splitting.

The Z-scheme overall solar water splitting is a mimic of natural photosynthesis to convert solar energy into chemical energy. Since the energy levels of most organic semiconductors match well with the hydrogen evolution potential, they have great application prospects as photocathodes in Z-scheme photoelectrochemical systems. However, due to the weak light absorption and difficult carrier separation, the photocurrent density and onset potential of organic photocathodes are still low. To solve these problems, we introduced a copper nanosheets array (Cu NSA) framework under organic layers to increase the surface reaction sites, improve the light absorption and enhance the distribution range of built-in electric field simultaneously. As a result, the photocurrent density and onset potential of poly(3-hexylthiophene) : [6,6]-phenyl-C61 -butyric acid (P3HT : PCBM) photocathode were enhanced significantly. The onset potential increased by 50 mV to 0.65 V vs. RHE, and the photocurrent density reached -1 mA cm-2 at 0 V vs. RHE, which was 18 times that of the sample without Cu NSA. The optimized photocathode was connected with titanium dioxide nanorods array photoanode in a tandem manner to realize the spontaneous overall water splitting. Without bias and co-catalyst, the photocurrent density was maintained at 110 μA cm-2 and the solar-to-fuel conversion efficiency was 0.14 % in neutral solution. These results provide a feasible method for optimizing the performance of organic photocathodes.

Experimental investigation of downstream cylinder vibrations caused by FIV in the presence of upstream stationary cylinder

The mechanism of flow induced vibrations (FIV) exists in many engineering applications and plays a significant role. In offshore engineering, the risers subjected to flow induced vibrations. In this study, two circular cylinders of different diameters are arranged in tandem manner. In cross-flow transverse direction, the upstream cylinder is fixed, while the downstream cylinder is subjected to vibrations. This study carries out experiments in wind tunnel, which focuses on significant vibration-galloping. Variable mass-damping ratio is used to achieve the critical velocity corresponding to onset galloping vibration. In the present study, the diameter ratio is 0.4 and the gap L is 1.5D, and 3.5D. In the wind tunnel experiments, by changing the mass of the vibrating cylinder, the corresponding values of damping ratio, results in variable mass damping ratio m*ζ. For each value of m*ζ, the amplitude, frequency at every reduced velocity will be obtained at first, the critical velocity and stability map will be summarized. At static area between lock-in and galloping (desynchronization branch), a uniform initial displacement was set to get the total damping ratio. This study also investigates the relationship among the total damping ratio, m*ζ and critical velocity.

Transition Metal-Catalyzed Hydroalkoxylation of Alkynes: An Overview.

Oxygen-bearing motifs, mainly the congener heterocycles are ubiquitous due to their presence in various natural products and bioactive scaffolds. Although in literature, several strategies have been developed for their synthesis, hydroalkoxylation of alkynes has come forward as a method of choice and has been used extensively. In particular, hydroalkoxylation of alkynes has gained enormous attention from the synthetic community due to the rapid access to a very useful and reactive synthetic intermediate like 'enol ether'. Furthermore, to manifold the utility of these methods, reports have been developed elaborating the generation of 'enol ether' using hydroalkoxylation and their usage in various reactions in cascade or tandem manner. This review focuses on recent development on the hydroalkoxylation of alkynes for the synthesis of oxygen-containing entities.

Deciphering the frontostriatal circuitry through the fiber dissection technique: direct structural evidence on the morphology and axonal connectivity of the fronto-caudate tract.

The authors sought to investigate the very existence and map the topography, morphology, and axonal connectivity of a thus far ill-defined subcortical pathway known as the fronto-caudate tract (FCT) since there is a paucity of direct structural evidence regarding this pathway in the relevant literature. Twenty normal adult cadaveric formalin-fixed cerebral hemispheres (10 left and 10 right) were explored through the fiber microdissection technique. Lateral to medial and medial to lateral dissections were carried out in a tandem manner in all hemispheres. Attention was focused on the prefrontal area and central core since previous diffusion tensor imaging studies have recorded the tract to reside in this territory. In all cases, the authors readily identified the FCT as a fan-shaped pathway lying in the most medial layer of the corona radiata and traveling across the subependymal plane before terminating on the superolateral margin of the head and anterior part of the body of the caudate nucleus. The FCT could be adequately differentiated from adjacent fiber tracts and was consistently recorded to terminate in Brodmann areas 8, 9, 10, and 11 (anterior pre-supplementary motor area and the dorsolateral, frontopolar, and fronto-orbital prefrontal cortices). The authors were also able to divide the tract into a ventral and a dorsal segment according to the respective topography and connectivity observed. Hemispheric asymmetries were not observed, but instead the authors disclosed asymmetry within the FCT, with the ventral segment always being thicker and bulkier than the dorsal one. By using the fiber microdissection technique, the authors provide sound structural evidence on the topography, morphology, and connectional anatomy of the FCT as a distinct part of a wider frontostriatal circuitry. The findings are in line with the tract's putative functional implications in high-order motor and behavioral processes and can potentially inform current surgical practice in the fields of neuro-oncology and functional neurosurgery.

Utilization of caffeine carbon supported cobalt catalyst in the tandem synthesis of pyrroles from nitroarenes and alkenyl diols

Employing bio-waste caffeine carbon-supported heterogeneous cobalt catalyst, synthesis of various substituted pyrrole derivatives is reported. In this methodology, pyrroles were synthesized through coupling between nitroarenes and alkenyl diols in a tandem manner. Among all the heterogeneous catalysts Co(OAc)2-CC-800 displayed the highest catalytic activity. Preparative scale synthesis of pyrroles and synthesis of anti-tubercular agent 5-(4-(1H-pyrrol-1-yl)phenyl)-1,3,4-oxadiazole-2-thiol revealed the practical applicability of this protocol. Several kinetic experiments and Hammett studies were conducted to understand the probable mechanism and electronic effects on this transformation.

Intermolecular Haloamination: Double Functionalization for Accesses to Vicinal Haloamines Involving Alkenes and Alkynes

Haloamination (or called aminohalogenation) upon the C-C unsaturated bonds is an important amino functionalization, which can introduce the halogen atoms accompanying with the amino groups into the substrate backbones in a tandem manner. Over the past two decades, it has drawn increasing attention due to its versatile applications. In this review, we will mainly focus on the synthetic strategies anchoring the intermolecular haloamination reactions achieved in the past few years. Limited by the length of the context, the intramolecular haloamination and the applications of the vicinal haloamines will not be involved.

Tandem Acceptorless Dehydrogenative Coupling-Decyanation under Nickel Catalysis.

The development of new catalytic processes based on abundantly available starting materials by cheap metals is always a fascinating task and marks an important transition in the chemical industry. Herein, a nickel-catalyzed acceptorless dehydrogenative coupling of alcohols with nitriles followed by decyanation of nitriles to access diversely substituted olefins is reported. This unprecedented C═C bond-forming methodology takes place in a tandem manner with the formation of formamide as a sole byproduct. The significant advantages of this strategy are the low-cost nickel catalyst, good functional group compatibility (ether, thioether, halo, cyano, ester, amino, N/O/S heterocycles; 43 examples), synthetic convenience, and high reaction selectivity and efficiency.

Microwave‐Assisted Tandem Kornblum Oxidation and Biginelli Reaction for the Synthesis of Dihydropyrimidones

AbstractA simple and straightforward approach for the synthesis of dihydropyrimidones via sequential Kornblum oxidation/Biginelli reaction has been developed. The protocol involves an in situ oxidation of benzyl halides which serve as a carbonyl equivalents followed by cyclocondensation with (thio) urea and ethylacetoacetate to furnish dihydropyrimidones under catalyst and base free conditions in a one‐pot tandem manner under microwave irradiation. Further, the product purification using aqueous recrystallization avoids large quantities of volatile and a toxic organic solvent usually required for work‐up and very less time required for this process makes the method environmental‐ and nature‐friendly.