This manuscript describes the development of alkyne addition to the aziridine moiety of aziridinoquinoxalines using dual Ir(III)/Cu(I) catalytic system under green light‐emitting diode (LED) ...photolysis (λmax=525 nm). This mild method features high levels of chemo‐ and regioselectivity and was used to generate 30 highly functionalized substituted dihydroquinoxalines in 36–98 % yield. This transformation was also carried asymmetrically using phthalazinamine‐based chiral ligand to provide 9 chiral addition products in 96 : 4 to 86 : 14 e.r. The experimental and quantum chemical explorations of this reaction suggest a mechanism that involves Ir(III)‐catalyzed triplet energy transfer followed by a ring‐opening reaction ultimately leading to the formation of azomethine ylide intermediates. These azomethine intermediates undergo sequential protonation/copper(I) acetylide addition to provide the products.
The development of alkyne addition to the aziridine moiety of aziridinoquinoxalines using dual Ir(III)/Cu(I) catalysts under green light‐emitting diode (LED) photolysis (λmax=525 nm), is described. The experimental and quantum chemical explorations suggest a triplet energy transfer mechanism followed by a ring‐opening reaction ultimately leading to the formation of azomethine ylide intermediates that are trapped with copper(I) acetylides.
The intrinsic conflicts between mechanical performances and processability are main challenges to develop cost‐effective impact‐resistant materials from polymers and their composites. Herein, ...polyhedral oligomeric silsesquioxanes (POSSs) are integrated as side chains to the polymer backbones. The one‐dimension (1D) rigid topology imposes strong space confinements to realize synergistic interactions among POSS units, reinforcing the correlations among polymer chains. The afforded composites demonstrate unprecedented mechanical properties with ultra‐stretchability, high rate‐dependent strength, superior impact‐resistant capacity as well as feasible processability/recoverability. The hierarchical structures of the hybrid polymers enable the co‐existence of multiple dynamic relaxations that are responsible for fast energy dissipation and high mechanical strengths. The effective synergistic correlation strategy paves a new pathway for the design of advanced cluster‐based materials.
Unique physical interaction facilitated by 1D topologies of molecular cluster‐integrated polymers is applied for the design of impact‐resistant materials with exceptional energy dissipation capability and strong rate‐dependent mechanical strengths, enabling the simultaneous achievement of promising impact resistance and processability/recoverability.
The catalytic activities of sulfur sites in amorphous MoS x for the electrochemical hydrogen evolution reaction (HER) was investigated in aqueous 0.5 M H2SO4 electrolyte. Using X-ray photoelectron ...spectroscopy and linear sweep voltammetry, we found the turnover frequency for H2 production to increase linearly with the percentage of S atoms with higher electron binding energies. These S atoms could be apical S2– and/or bridging S2 2–. To distinguish the catalytic performances of these two types of atoms, we turn to quantum chemical simulations using density functional theory. The apical S2– atoms were found to adsorb H weakly with a Gibbs free energy for atomic H adsorption (ΔG H) in excess of +1 eV, and were thus ruled out as reaction sites for HER. In situ Raman spectroscopy of the model Mo3S132– cluster further demonstrate the higher catalytic reactivity of the bridging S2 2– over terminal S2 2– (which have lower electron binding energy) for proton reduction.
Exploration of the topological quantum materials with electron correlation is at the frontier of physics, as the strong interaction may give rise to new topological phases and transitions. Here we ...report that a family of kagome magnets RMn6Sn6 manifest the quantum transport properties analogical to those in the quantum-limit Chern magnet TbMn6Sn6. The topological transport in the family, including quantum oscillations with nontrivial Berry phase and large anomalous Hall effect arising from Berry curvature field, points to the existence of Chern gapped Dirac fermions. Furthermore, our observation demonstrates a close relationship between rare-earth magnetism and topological electron structure, indicating the rare-earth elements can effectively engineer the Chern quantum phase in kagome magnets.
Metal carbide catalysts are alternative nonprecious electrode materials for electrochemical energy conversion devices, such as for H2 fuel cells or electrolyzers. In this article, we report the ...experimental exchange current densities for the hydrogen evolution reaction (HER) on eight mono- and bimetallic carbide electrocatalysts and correlate the current densities to hydrogen binding energies that we have calculated via electronic structure computations. We find these materials to have activities higher than those of their parent metals and intermediate between the catalytic activities of the Pt group and early transition-metal surfaces. Increased HER activities on metal carbides relative to their parent metals can be understood with a 3-fold higher sensitivity of metal carbides to the coverage-induced weakening of hydrogen adsorption relative to metal surfaces. The trends presented here can be useful for the design of bimetallic carbide electrocatalysts.
Quantum materials hosting Weyl fermions have opened a new era of research in condensed matter physics. First proposed in 1929 in the context of particle physics, Weyl fermions have yet to be observed ...as elementary particles. In 2015, Weyl fermions were detected as collective electronic excitations in the strong spin–orbit coupled material tantalum arsenide, TaAs. This discovery was followed by a flurry of experimental and theoretical explorations of Weyl phenomena in materials. Weyl materials naturally lend themselves to the exploration of the topological index associated with Weyl fermions and their divergent Berry curvature field, as well as the topological bulk–boundary correspondence, giving rise to protected conducting surface states. Here, we review the broader class of Weyl topological phenomena in materials, starting with the observation of emergent Weyl fermions in the bulk and Fermi arc states on the surface of the TaAs family of crystals by photoemission spectroscopy. We then discuss several exotic optical and magnetic responses observed in these materials, as well as progress in developing related chiral materials. We discuss the conceptual development of high-fold chiral fermions, which generalize Weyl fermions, and we review the observation of high-fold chiral fermion phases by taking the rhodium silicide, RhSi, family of crystals as a prime example. Lastly, we discuss recent advances in Weyl line phases in magnetic topological materials. With this Review, we aim to provide an introduction to the basic concepts underlying Weyl physics in condensed matter, and to representative materials and their electronic structures and topology as revealed by spectroscopic studies. We hope this work serves as a guide for future theoretical and experimental explorations of chiral fermions and related topological quantum systems with potentially enhanced functionalities.Weyl fermions have yet to be observed as elementary particles but can be realized in topological quantum materials. This Review discusses the theoretical and experimental discovery of emergent Weyl fermions, high-fold chiral fermions, topological Weyl lines and related Dirac phases.
New chiral targets of orientational chirality have been designed and asymmetrically synthesized by taking advantage of N‐sulfinyl imine‐directed nucleophilic addition/oxidation, Suzuki‐Miyaura, and ...Sonogashira cross‐coupling reactions. Orientation of single isomers has been selectively controlled by using aryl/alkynyl levers C(sp2)‐C(sp) axis and tBuSO2‐ protecting group on nitrogen as proven by X‐ray diffraction analysis. The key structural characteristic of resulting orientational products is shown by remote through‐space blocking manner. Seventeen examples of multi‐step synthesis were obtained with modest to good chemical yields and complete orientational selectivity.
We report herein the design of the asymmetric synthesis of orientational atropisomers via Sonogashira coupling as the key step. This new category of orientational atropisomers is anticipated to have a broad impact on chemical, biomedical, and material sciences in the future.
To realize the molecular design of new functional silver(I) clusters, a new synthetic approach has been proposed, by which the weakly coordinating ligands NO3 – in a Ag20 thiolate cluster precursor ...can be substituted by carboxylic ligands while keeping its inner core intact. By rational design, novel atom-precise carboxylic or amino acid protected 20-core Ag(I)-thiolate clusters have been demonstrated for the first time. The fluorescence and electrochemical activity of the postmodified Ag20 clusters can be modulated by alrestatin or ferrocenecarboxylic acid substitution. More strikingly, when chiral amino acids were used as postmodified ligands, CD-activity was observed for the Ag20 clusters, unveiling an efficient way to obtain atom-precise chiral silver(I) clusters.
Elective single embryo transfer (eSET) has been increasingly advocated, but concerns about the lower pregnancy rate after reducing the number of embryos transferred have encouraged transfer of ...multiple embryos. Extended embryo culture combined with electively freezing all embryos and undertaking a deferred frozen embryo transfer might increase pregnancy rate after eSET. We aimed to establish whether elective frozen single blastocyst transfer improved singleton livebirth rate compared with fresh single blastocyst transfer.
This multicentre, non-blinded, randomised controlled trial was undertaken in 21 academic fertility centres in China. 1650 women with regular menstrual cycles undergoing their first cycle of in-vitro fertilisation were enrolled from Aug 1, 2016, to June 3, 2017. Eligible women were randomly assigned to either fresh or frozen single blastocyst transfer. The randomisation sequence was computer generated, with block sizes of two, four, or six, stratified by study site. For those assigned to frozen blastocyst transfer, all blastocysts were cryopreserved and a delayed frozen-thawed single blastocyst transfer was done. The primary outcome was singleton livebirth rate. Analysis was by intention to treat. This trial is registered at the Chinese Clinical Trial Registry, number ChiCTR-IOR-14005405.
825 women were assigned to each group and included in analyses. Frozen single blastocyst transfer resulted in higher rates of singleton livebirth than did fresh single blastocyst transfer (416 50% vs 329 40%; relative risk RR 1·26, 95% CI 1·14–1·41, p<0·0001). The risks of moderate or severe ovarian hyperstimulation syndrome (four of 825 0·5% in frozen single blastocyst transfer vs nine of 825 1·1% in fresh single blastocyst transfer; p=0·16), pregnancy loss (134 of 583 23·0% vs 124 of 481 25·8%; p=0·29), other obstetric complications, and neonatal morbidity were similar between the two groups. Frozen single blastocyst transfer was associated with a higher risk of pre-eclampsia (16 of 512 3·1% vs four of 401 1·0%; RR 3·13, 95% CI 1·06–9·30, p=0·029).
Frozen single blastocyst transfer resulted in a higher singleton livebirth rate than did fresh single blastocyst transfer in ovulatory women with good prognosis. The increased risk of pre-eclampsia after frozen blastocyst transfer warrants further studies.
The National Key Research and Development Program of China.
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