Cleaving arene rings for acyclic alkenylnitrile synthesis.

Synthetic chemistry is built around the formation of carbon-carbon bonds. However, the development of methods for selective carbon-carbon bond cleavage is a largely unmet challenge1-6. Such methods will have promising applications in synthesis, coal liquefaction, petroleum cracking, polymer degradation and biomass conversion. For example, aromatic rings are ubiquitous skeletal features in inert chemical feedstocks, but are inert to many reaction conditions owing to their aromaticity and low polarity. Over the past century, only a few methods under harsh conditions have achieved direct arene-ring modifications involving the cleavage of inert aromatic carbon-carbon bonds7,8, and arene-ring-cleavage reactions using stoichiometric transition-metal complexes or enzymes in bacteria are still limited9-11. Here we report a copper-catalysed selective arene-ring-opening reaction strategy. Our aerobic oxidative copper catalyst converts anilines, arylboronic acids, aryl azides, aryl halides, aryl triflates, aryl trimethylsiloxanes, aryl hydroxamic acids and aryl diazonium salts into alkenyl nitriles through selective carbon-carbon bond cleavage of arene rings. This chemistry was applied to the modification of polycyclic aromatics and the preparation of industrially important hexamethylenediamine and adipic acid derivatives. Several examples of the late-stage modification of complex molecules and fused ring compounds further support the potential broad utility of this methodology.

Influence mechanism of industrial agglomeration on carbon emission intensity-a perspective on borrowing performance.

Under the background of urban connectivity, whether there are similarities and differences in the impacts of local industrial agglomeration and inter-city industrial agglomeration borrowing performance on carbon emission intensity(CI), and how cities can fully utilize the external force-borrowing performance to reduce local CI, these issues are of great significance for the cost saving and efficiency enhancement in the process of carbon emission (CE) reduction. Based on panel data of 280 prefecture-level cities in China from 2003 to 2020, the panel dual fixed-effect model, instrumental variable method, and adjustment effect model were used to analyze the impacts of the manufacturing agglomeration (MA), producer service agglomeration (PA), and the collaborative agglomeration (CA) on the CI from the perspective of individual cities and the urban system. The results showed that the influence of MA on CI presents a significant inverted U-shaped relationship, PA significantly reduces CI, and the CA of the two industries increases CI. Further analysis showed that the borrowing MA performance improves CI, especially in newer industrial-based cities, non-resource-based cities, and medium and big cities; the borrowing PA performance reduces CI, especially in old industrial-based cities, non-resource-based cities, and large cities; and the borrowing CA performance has no significant effect on CI. In addition, the development of the Internet strengthens the influence of borrowing performance in MA and PA on CI.

X-ray and NMR crystallography in an enzyme active site: the indoline quinonoid intermediate in tryptophan synthase.

Chemical-level details such as protonation and hybridization state are critical for understanding enzyme mechanism and function. Even at high resolution, these details are difficult to determine by X-ray crystallography alone. The chemical shift in NMR spectroscopy, however, is an extremely sensitive probe of the chemical environment, making solid-state NMR spectroscopy and X-ray crystallography a powerful combination for defining chemically detailed three-dimensional structures. Here we adopted this combined approach to determine the chemically rich crystal structure of the indoline quinonoid intermediate in the pyridoxal-5'-phosphate-dependent enzyme tryptophan synthase under conditions of active catalysis. Models of the active site were developed using a synergistic approach in which the structure of this reactive substrate analogue was optimized using ab initio computational chemistry in the presence of side-chain residues fixed at their crystallographically determined coordinates. Various models of charge and protonation state for the substrate and nearby catalytic residues could be uniquely distinguished by their calculated effects on the chemical shifts measured at specifically (13)C- and (15)N-labeled positions on the substrate. Our model suggests the importance of an equilibrium between tautomeric forms of the substrate, with the protonation state of the major isomer directing the next catalytic step.

Long-observation-window band-selective homonuclear decoupling: increased sensitivity and resolution in solid-state NMR spectroscopy of proteins.

Sensitivity and resolution are the two fundamental obstacles to extending solid-state nuclear magnetic resonance to even larger protein systems. Here, a novel long-observation-window band-selective homonuclear decoupling (LOW BASHD) scheme is introduced that increases resolution up to a factor of 3 and sensitivity up to 1.8 by decoupling backbone alpha-carbon (C(α)) and carbonyl (C') nuclei in U-(13)C-labeled proteins during direct (13)C acquisition. This approach introduces short (<200 µs) pulse breaks into much longer (~8 ms) sampling windows to efficiently refocus the J-coupling interaction during detection while avoiding the deleterious effects on sensitivity inherent in rapid stroboscopic band-selective homonuclear decoupling techniques. A significant advantage of LOW-BASHD detection is that it can be directly incorporated into existing correlation methods, as illustrated here for 2D CACO, NCO, and NCA correlation spectroscopy applied to the ß1 immunoglobulin binding domain of protein G and 3D CBCACO correlation spectroscopy applied to the α-subunit of tryptophan synthase.

[An experimental study on repairing horn-shaped root canal orifice by different materials].

OBJECTIVE: To study the fracture resistance and the failure pattern of horn-shaped root canal orifice restored by different materials. METHODS: Fifteen human maxillary central incisors were selected. After schedule root canal therapy, the residual dental roots with horn-shape root canal orifice were prepared. The specimens were assigned to three groups randomly. A group was rehabilitated by casting metal post-core crown. B group was rehabilitated by prefabricated fiber post and composite core crown. C group was rehabilitated by shapeable fiber-reinforced composite resin post and core crown. Loads were applied on the samples at 130 degree to the long axis of the root and measured with universal testing machine. The failing patterns were recorded. RESULTS: There were no difference in fracture resistance among three groups (P>0.05). But the failing patterns were different. A group manifested root fracture and separation between cement and root dentin. B group mainly manifested separation between cement and post. C group manifested separation between cement and root dentin. CONCLUSION: For restoration of residual dental root with horn-shaped orifice, fiber composite post-core crown has advantages in residual root protection and once more restoration.