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Rodent LD50 values have been used for almost a century as a measure of potential human toxicity from drugs and other chemicals. However, they have been found not, on the whole, to be good models for human toxicity. One reason for this could be the often-high variability of LD50 values. It has recently been shown that by using median LD50 values, very good correlations have been found with human lethal dosages. Bearing in mind the millions of rodent lives sacrificed, many with no good reason, it is proposed that some reparation could be made by more investigations using median values of already available rodent LD50 values.

A new chemical vapour deposition method enables transition-metal dichalcogenide (TMD) monolayers to be grown directly on insulating silicon dioxide wafers, demonstrating the possibility of wafer-scale batch fabrication of high-performance devices with TMD monolayers. Wafer-scale thin semiconducting films Monolayers of semiconducting transition-metal dichalcogenides (TMDs) — a mere three-atoms thick — show promise as materials for next-generation nanoelectronics and optoelectronics. Here Jiwoong Park and colleagues describe a new method for the fabrication of TMD monolayers by chemical vapour deposition onto insulating silicon dioxide wafers that produces large, wafer-scale areas with uniform properties. The resulting materials have a high electron mobility at room temperature which is highly constant over the whole four-inch area. Field-effect transistors can be fabricated with 99% device yield. The work demonstrates the practicability of wafer-scale batch fabrication of high-performance devices with TMD monolayers. The large-scale growth of semiconducting thin films forms the basis of modern electronics and optoelectronics. A decrease in film thickness to the ultimate limit of the atomic, sub-nanometre length scale, a difficult limit for traditional semiconductors (such as Si and GaAs), would bring wide benefits for applications in ultrathin and flexible electronics, photovoltaics and display technology 1 , 2 , 3 . For this, transition-metal dichalcogenides (TMDs), which can form stable three-atom-thick monolayers 4 , provide ideal semiconducting materials with high electrical carrier mobility 5 , 6 , 7 , 8 , 9 , 10 , and their large-scale growth on insulating substrates would enable the batch fabrication of atomically thin high-performance transistors and photodetectors on a technologically relevant scale without film transfer. In addition, their unique electronic band structures provide novel ways of enhancing the functionalities of such devices, including the large excitonic effect 11 , bandgap modulation 12 , indirect-to-direct bandgap transition 13 , piezoelectricity 14 and valleytronics 15 . However, the large-scale growth of monolayer TMD films with spatial homogeneity and high electrical performance remains an unsolved challenge. Here we report the preparation of high-mobility 4-inch wafer-scale films of monolayer molybdenum disulphide (MoS 2 ) and tungsten disulphide, grown directly on insulating SiO 2 substrates, with excellent spatial homogeneity over the entire films. They are grown with a newly developed, metal–organic chemical vapour deposition technique, and show high electrical performance, including an electron mobility of 30 cm 2 V −1 s −1 at room temperature and 114 cm 2 V −1 s −1 at 90 K for MoS 2 , with little dependence on position or channel length. With the use of these films we successfully demonstrate the wafer-scale batch fabrication of high-performance monolayer MoS 2 field-effect transistors with a 99% device yield and the multi-level fabrication of vertically stacked transistor devices for three-dimensional circuitry. Our work is a step towards the realization of atomically thin integrated circuitry.

A method for the depolymerization of oxidized lignin under mild conditions in aqueous formic acid is described that results in more than 60 wt% yield of low-molecular-mass aromatics. Useful aromatics made simply from lignin The aromatic biopolymer lignin, a major component of plant cell walls and generally obtained from wood, is a valuable and renewable source of aromatic chemicals. Considerable progress has been made in the conversion of cellulose and hemicellulose to fuels and chemicals, but lignin has proved more recalcitrant. In this manuscript, the authors report a high-yield method for conversion of lignin to low molecular mass aromatics. The C–O cleavage reaction proceeds under mild conditions in aqueous formic acid. It produces small number of well-defined aromatic products, providing raw materials well suited for targeted conversion to a variety of valuable chemicals. Lignin is a heterogeneous aromatic biopolymer that accounts for nearly 30% of the organic carbon on Earth 1 and is one of the few renewable sources of aromatic chemicals 2 . As the most recalcitrant of the three components of lignocellulosic biomass (cellulose, hemicellulose and lignin) 3 , lignin has been treated as a waste product in the pulp and paper industry, where it is burned to supply energy and recover pulping chemicals in the operation of paper mills 4 . Extraction of higher value from lignin is increasingly recognized as being crucial to the economic viability of integrated biorefineries 5 , 6 . Depolymerization is an important starting point for many lignin valorization strategies, because it could generate valuable aromatic chemicals and/or provide a source of low-molecular-mass feedstocks suitable for downstream processing 7 . Commercial precedents show that certain types of lignin (lignosulphonates) may be converted into vanillin and other marketable products 8 , 9 , but new technologies are needed to enhance the lignin value chain. The complex, irregular structure of lignin complicates chemical conversion efforts, and known depolymerization methods typically afford ill-defined products in low yields (that is, less than 10–20wt%) 2 , 10 , 11 . Here we describe a method for the depolymerization of oxidized lignin under mild conditions in aqueous formic acid that results in more than 60wt% yield of low-molecular-mass aromatics. We present the discovery of this facile C–O cleavage method, its application to aspen lignin depolymerization, and mechanistic insights into the reaction. The broader implications of these results for lignin conversion and biomass refining are also considered.

The applications of surface-emitting lasers, in particular vertical-cavity surface-emitting lasers (VCSELs), are currently being extended to various low-power fields including communications and interconnections. However, the fundamental difficulties in increasing their output power by more than several milliwatts while maintaining single-mode operation prevent their application in high-power fields such as material processing, laser medicine and nonlinear optics, despite their advantageous properties of circular beams, the absence of catastrophic optical damage, and their suitability for two-dimensional integration. Here, we demonstrate watt-class high-power, single-mode operation by a two-dimensional photonic-crystal surface-emitting laser under room-temperature, continuous-wave conditions. The two-dimensional band-edge resonant effect of a photonic crystal formed by metal–organic chemical vapour deposition enables a 1,000 times broader coherent-oscillation area, which results in a high beam quality of M 2  ≤ 1.1, narrowing the focus spot by two orders of magnitude compared to VCSELs. Our demonstration promises to realize innovative high-power applications for surface-emitting lasers. Researchers demonstrate a watt-class high-power, single-mode photonic-crystal laser operating continuously at room temperature. A beam quality of M 2  ≤ 1.1 is achieved.

Optofluidics — the synergistic integration of photonics and microfluidics — is a new analytical field that provides a number of unique characteristics for enhancing the sensing performance and simplifying the design of microsystems. This Review describes various optofluidic architectures developed over the past five years, emphasizes the mechanisms by which optofluidics enhances biological/chemical analytic capabilities, including sensing and the precise control of biological micro- and nanoparticles, and also highlights new research directions to which the field of optofluidics may lead.

A few-component network of biologically relevant, organic reactions displays bistability and oscillations, without an enzymatic catalyst. Oscillatory reactions in a simple organic system Dissipative chemical reaction networks are systems that operate away from equilibrium and exhibit features such as continuous regeneration of components and autonomous regulation. The biological cell is one such out-of-equilibrium chemical network. Until now it has not been possible to recreate this type of dynamic behavior using simple organic molecules relevant to prebiotic Earth. Now, George Whitesides and colleagues demonstrate a few-component system of interacting organic species that, combined into a reaction network, displays autocatalytic and oscillatory features. All of the organic components are relatively simple and do not require enzymatic catalysis to react. Networks of organic chemical reactions are important in life and probably played a central part in its origin 1 , 2 , 3 . Network dynamics regulate cell division 4 , 5 , 6 , circadian rhythms 7 , nerve impulses 8 and chemotaxis 9 , and guide the development of organisms 10 . Although out-of-equilibrium networks of chemical reactions have the potential to display emergent network dynamics 11 such as spontaneous pattern formation, bistability and periodic oscillations 12 , 13 , 14 , the principles that enable networks of organic reactions to develop complex behaviours are incompletely understood. Here we describe a network of biologically relevant organic reactions (amide formation, thiolate–thioester exchange, thiolate–disulfide interchange and conjugate addition) that displays bistability and oscillations in the concentrations of organic thiols and amides. Oscillations arise from the interaction between three subcomponents of the network: an autocatalytic cycle that generates thiols and amides from thioesters and dialkyl disulfides; a trigger that controls autocatalytic growth; and inhibitory processes that remove activating thiol species that are produced during the autocatalytic cycle. In contrast to previous studies that have demonstrated oscillations and bistability using highly evolved biomolecules (enzymes 15 and DNA 16 , 17 ) or inorganic molecules of questionable biochemical relevance (for example, those used in Belousov–Zhabotinskii-type reactions) 18 , 19 , the organic molecules we use are relevant to metabolism and similar to those that might have existed on the early Earth. By using small organic molecules to build a network of organic reactions with autocatalytic, bistable and oscillatory behaviour, we identify principles that explain the ways in which dynamic networks relevant to life could have developed. Modifications of this network will clarify the influence of molecular structure on the dynamics of reaction networks, and may enable the design of biomimetic networks and of synthetic self-regulating and evolving chemical systems.

Many proteins exist naturally as symmetrical homooligomers or homopolymers 1 . The emergent structural and functional properties of such protein assemblies have inspired extensive efforts in biomolecular design 2 – 5 . As synthesized by ribosomes, proteins are inherently asymmetric. Thus, they must acquire multiple surface patches that selectively associate to generate the different symmetry elements needed to form higher-order architectures 1 , 6 —a daunting task for protein design. Here we address this problem using an inorganic chemical approach, whereby multiple modes of protein–protein interactions and symmetry are simultaneously achieved by selective, ‘one-pot’ coordination of soft and hard metal ions. We show that a monomeric protein (protomer) appropriately modified with biologically inspired hydroxamate groups and zinc-binding motifs assembles through concurrent Fe 3+ and Zn 2+ coordination into discrete dodecameric and hexameric cages. Our cages closely resemble natural polyhedral protein architectures 7 , 8 and are, to our knowledge, unique among designed systems 9 – 13 in that they possess tightly packed shells devoid of large apertures. At the same time, they can assemble and disassemble in response to diverse stimuli, owing to their heterobimetallic construction on minimal interprotein-bonding footprints. With stoichiometries ranging from [2 Fe:9 Zn:6 protomers] to [8 Fe:21 Zn:12 protomers], these protein cages represent some of the compositionally most complex protein assemblies—or inorganic coordination complexes—obtained by design. An inorganic chemical approach to biomolecular design is used to generate ‘cages’ that can simultaneously promote symmetry and multiple modes of protein interactions.

Difficulties in the production of lignin from rice straw because of high silica content in the recovered lignin reduce its recovery yield and applications as bio-fuel and aromatic chemicals. Therefore, the objective of this study is to develop a novel method to reduce the silica content in lignin from rice straw more effectively and selectively. The method is established by monitoring the precipitation behavior as well as the chemical structure of precipitate by single-stage acidification at different pH values of black liquor collected from the alkaline treatment of rice straw. The result illustrates the significant influence of pH on the physical and chemical properties of the precipitate and the supernatant. The simple two-step acidification of the black liquor at pilot-scale by sulfuric acid 20w/v% is applied to recover lignin at pH 9 and pH 3 and gives a percentage of silica removal as high as 94.38%. Following the developed process, the high-quality lignin could be produced from abundant rice straw at the industrial-scale.

As some of the oldest organic chemical reactions known, the ionic additions of elemental halogens such as bromine and chlorine to alkenes are prototypical examples of stereospecific reactions, typically delivering vicinal dihalides resulting from anti -addition. Although the invention of enantioselective variants is an ongoing challenge, the ability to overturn the intrinsic anti -diastereospecificity of these transformations is also a largely unsolved problem. Here, we describe the first catalytic, syn -stereospecific dichlorination of alkenes, employing a group transfer catalyst based on a redox-active main group element (selenium). With diphenyl diselenide (PhSeSePh) (5 mol%) as the pre-catalyst, benzyltriethylammonium chloride (BnEt 3 NCl) as the chloride source and an N -fluoropyridinium salt as the oxidant, a wide variety of functionalized cyclic and acyclic 1,2-disubstituted alkenes, including simple allylic alcohols, deliver syn -dichlorides with exquisite stereocontrol. This methodology is expected to find applications in streamlining the synthesis of polychlorinated natural products such as the chlorosulfolipids. The synthetic challenge of constructing arrays of contiguous, chlorinated stereogenic centres in natural products, like the chlorosulfolipids, has sparked recent interest in new methods for stereocontrolled chlorination. Now the first catalytic, syn -stereospecific dichlorination of alkenes, employing a redox-active main group element as a group transfer catalyst is described.