Bismuthene on a SiC substrate Reis, F.; Li, G.; Dudy, L. ...
Science (American Association for the Advancement of Science),
07/2017, Letnik:
357, Številka:
6348
Journal Article
Recenzirano
Odprti dostop
Quantum spin Hall materials hold the promise of revolutionary devices with dissipationless spin currents but have required cryogenic temperatures owing to small energy gaps. Here we show ...theoretically that a room-temperature regime with a large energy gap may be achievable within a paradigm that exploits the atomic spin-orbit coupling. The concept is based on a substrate-supported monolayer of a high–atomic number element and is experimentally realized as a bismuth honeycomb lattice on top of the insulating silicon carbide substrate SiC(0001). Using scanning tunneling spectroscopy, we detect a gap of ~0.8 electron volt and conductive edge states consistent with theory. Our combined theoretical and experimental results demonstrate a concept for a quantum spin Hall wide-gap scenario, where the chemical potential resides in the global system gap, ensuring robust edge conductance.
The Bioorthogonal Isonitrile–Chlorooxime Ligation Schäfer, Rebecca J. B; Monaco, Mattia R; Li, Mao ...
Journal of the American Chemical Society,
11/2019, Letnik:
141, Številka:
47
Journal Article
Recenzirano
Odprti dostop
Bioorthogonal reactions are valuable tools for the selective labeling and imaging of natural products and proteins. Here, we present the reaction between isonitriles and chlorooximes as a ligation ...that proceeds quickly (k ≈ 1 M–1 s–1) and with high chemoselectivity in an aqueous environment. Imaging of metabolically labeled cell surface glycans underlined the tolerance of the ligation to common functional groups in cellular systems. Live-cell dual-labeling experiments revealed that the isonitrile–chlorooxime ligation is orthogonal to the strain-promoted azide–alkyne cycloaddition.
Quantum spin Hall insulators are two-dimensional materials that host conducting helical electron states strictly confined to the one-dimensional boundaries. These edge channels are protected by ...time-reversal symmetry against single-particle backscattering, opening new avenues for spin-based electronics and computation. However, the effect of the interelectronic Coulomb repulsion also has to be taken into account, as two-particle scattering is not impeded by topological protection and may strongly affect the edge state conductance. Here, we explore the impact of electronic correlations on highly localized edge states of the unique quantum spin Hall material bismuthene on SiC(0001) (ref. 1). Exploiting the advantage of having an accessible monolayer substrate system, we use STM/STS to visualize the close-to-perfect one-dimensional confinement of the edge channels and scrutinize their suppressed density of states at the Fermi level. On the basis of the observed spectral behaviour and its universal scaling with energy and temperature, we demonstrate the correspondence with a (helical) Tomonaga–Luttinger liquid. In particular, the extracted interaction parameter K is directly relevant to the fundamental question of the temperatures at which the quantized conductance (a hallmark of quantum spin Hall materials) will become obscured by correlations2.Scanning tunnelling microscopy and spectroscopy study of the conductive edge state in a two-dimensional topological insulator reveals the interplay of topology and electronic correlations.
Oils and fats of vegetable and animal origin have been the most important renewable feedstock of the chemical industry in the past and in the present. A tremendous geographical and feedstock shift of ...oleochemical production has taken place from North America and Europe to southeast Asia and from tallow to palm oil. It will be important to introduce and to cultivate more and new oil plants containing fatty acids with interesting and desired properties for chemical utilization while simultaneously increasing the agricultural biodiversity. The problem of the industrial utilization of food plant oils has become more urgent with the development of the global biodiesel production. The remarkable advances made during the last decade in organic synthesis, catalysis, and biotechnology using plant oils and the basic oleochemicals derived from them will be reported, including, for example, ω‐functionalization of fatty acids containing internal double bonds, application of the olefin metathesis reaction, and de novo synthesis of fatty acids from abundantly available renewable carbon sources.
More than just a greasy spoon: Oils and fats are the most important renewable feedstock of the chemical industry. Recent and exciting advances in chemistry and biotechnology were made within the last 10 years concerning their utilization as a chemical feedstock. This progress in organic synthesis, catalysis, and biotechnology using plant oils and their derivatives is highlighted.
DNA single-strand breaks (SSBs) are among the most common lesions in the genome, arising spontaneously and as intermediates of many DNA transactions. Nevertheless, in contrast to double-strand breaks ...(DSBs), their distribution in the genome has hardly been addressed in a meaningful way. We now present a technique based on genome-wide ligation of 3′-OH ends followed by sequencing (GLOE-Seq) and an associated computational pipeline designed for capturing SSBs but versatile enough to be applied to any lesion convertible into a free 3′-OH terminus. We demonstrate its applicability to mapping of Okazaki fragments without prior size selection and provide insight into the relative contributions of DNA ligase 1 and ligase 3 to Okazaki fragment maturation in human cells. In addition, our analysis reveals biases and asymmetries in the distribution of spontaneous SSBs in yeast and human chromatin, distinct from the patterns of DSBs.
Display omitted
•GLOE-Seq detects 3′-OH ends with nucleotide resolution in purified genomic DNA•GLOE-Seq maps single-strand breaks, lesions, and replication and repair intermediates•GLOE-Seq reveals insight into the use of ligases 1 and 3 in human cells•GLOE-Seq detects asymmetries in spontaneous nicks in yeast and human chromatin
We present a method for genome-wide, nucleotide-resolution mapping of DNA single-strand breaks in purified genomic DNA based on capture of 3′-OH ends followed by sequencing (GLOE-Seq). We validate the method and demonstrate its applicability to mapping of human and yeast Okazaki fragments, spontaneous single-strand breaks, and various other DNA lesions.
High-index surfaces of silicon with adsorbed gold can reconstruct to form highly ordered linear step arrays. These steps take the form of a narrow strip of graphitic silicon. In some ...casesspecifically, for Si(553)-Au and Si(557)-Aua large fraction of the silicon atoms at the exposed edge of this strip are known to be spin-polarized and charge-ordered along the edge. The periodicity of this charge ordering is always commensurate with the structural periodicity along the step edge and hence leads to highly ordered arrays of local magnetic moments that can be regarded as “spin chains.” Here, we demonstrate theoretically as well as experimentally that the closely related Si(775)-Au surface hasdespite its very similar overall structurezero spin polarization at its step edge. Using a combination of density-functional theory and scanning tunneling microscopy, we propose an electron-counting model that accounts for these differences. The model also predicts that unintentional defects and intentional dopants can create local spin moments at Si(hhk)-Au step edges. We analyze in detail one of these predictions and verify it experimentally. This finding opens the door to using techniques of surface chemistry and atom manipulation to create and control silicon spin chains.
Abstract
The scientific interest in two-dimensional topological insulators (2D TIs) is currently shifting from a more fundamental perspective to the exploration and design of novel functionalities. ...Key concepts for the use of 2D TIs in spintronics are based on the topological protection and spin-momentum locking of their helical edge states. In this study we present experimental evidence that topological protection can be (partially) lifted by pairwise coupling of 2D TI edges in close proximity. Using direct wave function mapping via scanning tunneling microscopy/spectroscopy (STM/STS) we compare isolated and coupled topological edges in the 2D TI bismuthene. The latter situation is realized by natural lattice line defects and reveals distinct quasi-particle interference (QPI) patterns, identified as electronic Fabry-Pérot resonator modes. In contrast, free edges show no sign of any single-particle backscattering. These results pave the way for novel device concepts based on active control of topological protection through inter-edge hybridization for, e.g., electronic Fabry-Pérot interferometry.
The current socio-economic, environmental and public health challenges that countries are facing clearly need common-defined strategies to inform and support our transition to a sustainable economy. ...Here, the technology-critical elements (which includes Ga, Ge, In, Te, Nb, Ta, Tl, the Platinum Group Elements and most of the rare-earth elements) are of great relevance in the development of emerging key technologies—including renewable energy, energy efficiency, electronics or the aerospace industry. In this context, the increasing use of technology-critical elements (TCEs) and associated environmental impacts (from mining to end-of-life waste products) is not restricted to a national level but covers most likely a global scale. Accordingly, the European COST Action TD1407: Network on Technology-Critical Elements (NOTICE)—from environmental processes to human health threats, has an overall objective for creating a network of scientists and practitioners interested in TCEs, from the evaluation of their environmental processes to understanding potential human health threats, with the aim of defining the current state of knowledge and gaps, proposing priority research lines/activities and acting as a platform for new collaborations and joint research projects. The Action is focused on three major scientific areas: (i) analytical chemistry, (ii) environmental biogeochemistry and (iii) human exposure and (eco)-toxicology.
The biosynthesis of thebaine is based on the regioselective, intramolecular, oxidative coupling of (R)‐reticuline. For decades, chemists have sought to mimic this coupling by using stoichiometric ...oxidants. However, all approaches to date have suffered from low yields or the formation of undesired regioisomers. Electrochemistry would represent a sustainable alternative in this respect but all attempts to accomplish an electrochemical synthesis of thebaine have failed so far. Herein, a regio‐ and diastereoselective anodic coupling of 3′,4′,5′‐trioxygenated laudanosine derivatives is presented, which finally enables electrochemical access to (−)‐thebaine.
Enforcement of selectivity through a combination of electrochemistry and substrate design was used as an elegant strategy to solve a long‐standing electrosynthetic challenge. A regio‐ and diastereoselective anodic coupling of 3′,4′,5′‐trioxygenated laudanosine derivatives is presented which enables biomimetic, electrochemical access to (−)‐thebaine.
PDF
