The selective oxidation of organic molecules is a fundamentally important component of modern synthetic chemistry. In the past decades, direct oxidative C–H and C–C bond functionalization has proved ...to be one of the most efficient and straightforward methods to synthesize complex products from simple and readily available starting materials. Among these oxidative processes, the use of molecular oxygen as a green and sustainable oxidant has attracted considerable attention because of its highly atom-economical, abundant, and environmentally friendly characteristics. The development of new protocols using molecular oxygen as an ideal oxidant is highly desirable in oxidation chemistry. More importantly, the oxygenation reaction of simple molecules using molecular oxygen as the oxygen source offers one of the most ideal processes for the construction of O-containing compounds. Aerobic oxidation and oxygenation by enzymes, such as monooxygenase, tyrosinase, and dopamine β-monooxygenase, have been observed in some biological C–H bond hydroxylation processes. Encouraged by these biological transformations, transition-metal- or organocatalyst-catalyzed oxygenation through dioxygen activation has attracted academic and industrial prospects. In this Account, we describe some advances from our group in oxygenation via C–H/C–C bond activation with molecular oxygen as the oxidant and oxygen source for the synthesis of O-containing compounds. Under an atmosphere of O2 (1 atm) or air (1 atm), we have successfully incorporated one or two O atoms from O2 into simple and readily available substrates through C–H, C–C, CC, and CC bond cleavage by transition-metal catalysis, organocatalysis, and photocatalysis. Moreover, we have devised cyclization reactions with molecular oxygen to construct O-heterocycles. Most of these transformations can tolerate a broad range of functional groups. Furthermore, on the basis of isotope labeling experiments, electron paramagnetic resonance spectral analysis, and other mechanistic studies, we have demonstrated that a single electron transfer process via a carbon radical, peroxide radical, or hydroxyl radical is involved in these aerobic oxidation and oxygenation reactions. These protocols provide new approaches for the green synthesis of various α-keto amides, α-keto esters, esters, ketones, aldehydes, formamides, 2-oxoacetamidines, 2-(1H)-pyridones, phenols, tertiary α-hydroxy carbonyls, p-quinols, β-azido alcohols, benzyl alcohols, tryptophols, and oxazoles, which have potential applications in the preparation of natural products, bioactive compounds, and functional materials. In most cases, inexpensive and low-toxicity Cu, Fe, Mn, or NHPI was found to be an efficient catalyst for the transformation. The high efficiency, low cost, high oxygen atom economy, broad substrate scope, and practical operation make the developed oxygenation system very attractive and practical. Moreover, the design of new types of molecular-oxygen- or air-based oxidation and oxygenation reactions can be anticipated.
The oxygen evolution reaction (OER) is an important half reaction in many energy conversion and storage techniques. However, the development of a low‐cost easy‐prepared OER electrocatalyst with high ...mass activity and rapid kinetics is still challenging. Herein, we report the facile deposition of tannin‐NiFe (TANF) complex film on carbon fiber paper (CP) as a highly efficient OER electrocatalyst. TANF gives rapid OER reaction kinetics with a very small Tafel slope of 28 mV dec−1. The mass activity of TANF reaches 9.17×103 Ag−1 at an overpotential of 300 mV, which is nearly 200‐times larger than that of NiFe double layered hydroxide. Furthermore, tannic acid in TANF can be electrochemically extracted under anodic potential, leaving the inorganic composite NixFe1−xOyHz as the OER‐active species. This work may provide a guide to probing the electrochemical transformation and investigating the reactive species of other metal–organic complexes as heterogeneous electrocatalysts.
Get it down on paper: A tannin‐NiFe complex (TANF) ultrathin film is deposited on carbon fiber paper by coordinating tannin with Ni and Fe ions to give an efficient oxygen evolution reaction (OER) electrocatalyst with high mass activity and rapid kinetics. The inorganic species NixFe1−xOyHz is shown to be the OER‐active species.
Lattice structures, which are also known as architected cellular structures, have been applied in various industrial sectors, owing to their fascinated performances, such as low elastic modulus, high ...stiffness-to-weight ratio, low thermal expansion coefficient, and large specific surface area. The lattice structures fabricated by conventional manufacturing technologies always involve complicated process control, additional assembly steps, or other uncontrollable factors. Furthermore, limited types of unit cells can be used to construct lattice structures when using conventional processes. Fortunately, additive manufacturing technology, based on a layer-by-layer process from computer-aided design models, demonstrates the unique capability and flexibility and provides an ideal platform in manufacturing complex components like lattice structures, resulting in an effective reduction in the processing time to actual application and minimum of material waste. Therefore, additive manufacturing relieves the constraint of structure design and provides accurate fabrication for lattice structures with good quality. This work systematically presents an overview of conventional manufacturing methods and novel additive manufacturing technologies for metallic lattice structures. Afterward, the design, optimization, a variety of properties, and applications of metallic lattice structures produced by additive manufacturing are elaborated. By summarizing state-of-the-art progress of the additively manufactured metallic lattice structures, limitations and future perspectives are also discussed.
Floral homeotic transcription factors (TFs) act in a combinatorial manner to specify the organ identities in the flower. However, the architecture and the function of the gene regulatory network ...(GRN) controlling floral organ specification is still poorly understood. In particular, the interconnections of homeotic TFs, microRNAs (miRNAs) and other factors controlling organ initiation and growth have not been studied systematically so far. Here, using a combination of genome-wide TF binding, mRNA and miRNA expression data, we reconstruct the dynamic GRN controlling floral meristem development and organ differentiation. We identify prevalent feed-forward loops (FFLs) mediated by floral homeotic TFs and miRNAs that regulate common targets. Experimental validation of a coherent FFL shows that petal size is controlled by the SEPALLATA3-regulated miR319/TCP4 module. We further show that combinatorial DNA-binding of homeotic factors and selected other TFs is predictive of organ-specific patterns of gene expression. Our results provide a valuable resource for studying molecular regulatory processes underlying floral organ specification in plants.
A cationic cobalt(III)‐catalyzed direct CH amidation of unactivated (hetero)arenes and alkenes by using 1,4,2‐dioxazol‐5‐ones as the amidating reagent has been developed. This transformation ...proceeds efficiently under external oxidant‐free conditions with a broad substrate scope. Moreover, 6‐arylpurine compounds, which often exhibit high potency in antimycobacterial, cytostatic, and anti‐HCV activities, can be smoothly amidated, thus offering a mild protocol for their late stage functionalization.
Operationally simple: A cationic cobalt(III) catalyzed direct CH amidation of unactivated (hetero)arenes and alkenes has been developed (see scheme; DCE=1,2‐dichloroethane). This reaction proceeded efficiently under external oxidant‐free conditions with ample substrate scope, as well as excellent chemo‐ and regioselectivity. Moreover, 6‐arylpurine compounds, which often exhibit important biological activities, can be smoothly modified by this mild protocol.
For electrocatalytic water splitting, the sluggish anodic oxygen evolution reaction (OER) restricts the cathodic hydrogen evolution reaction (HER). Therefore, developing an alternative anodic ...reaction with accelerating kinetics to produce value‐added chemicals, especially coupled with HER, is of great importance. Now, a thermodynamically more favorable primary amine (−CH2−NH2) electrooxidation catalyzed by NiSe nanorod arrays in water is reported to replace OER for enhancing HER. The increased H2 production can be obtained at cathode; meanwhile, a variety of aromatic and aliphatic primary amines are selectively electrooxidized to nitriles with good yields at the anode. Mechanistic investigations suggest that NiII/NiIII may serve as the redox active species for the primary amines transformation. Hydrophobic nitrile products can readily escape from aqueous electrolyte/electrode interface, avoiding the deactivation of the catalyst and thus contributing to continuous gram‐scale synthesis.
Substitution, higher efficiency: Hydrogen (H2) production is achieved at lower potential by replacing the OER with the electrooxidation of primary amines in water. The hydrophilic primary amines at the NiSe anode can be converted oxidant‐free into the corresponding hydrophobic nitriles with high yields (>93 %) and selectivity. The process is easily scalable and free of organic solvent, and the product easily isolable.
Pooling plays an important role in generating a discriminative video representation. In this paper, we propose a new semantic pooling approach for challenging event analysis tasks (e.g., event ...detection, recognition, and recounting) in long untrimmed Internet videos, especially when only a few shots/segments are relevant to the event of interest while many other shots are irrelevant or even misleading. The commonly adopted pooling strategies aggregate the shots indifferently in one way or another, resulting in a great loss of information. Instead, in this work we first define a novel notion of semantic saliency that assesses the relevance of each shot with the event of interest. We then prioritize the shots according to their saliency scores since shots that are semantically more salient are expected to contribute more to the final event analysis. Next, we propose a new isotonic regularizer that is able to exploit the constructed semantic ordering information. The resulting nearly-isotonic support vector machine classifier exhibits higher discriminative power in event analysis tasks. Computationally, we develop an efficient implementation using the proximal gradient algorithm, and we prove new and closed-form proximal steps. We conduct extensive experiments on three real-world video datasets and achieve promising improvements.
β-type titanium (Ti) alloys have attracted a lot of attention as novel biomedical materials in the past decades due to their low elastic moduli and good biocompatibility. This article provides a ...broad and extensive review of β-type Ti alloys in terms of alloy design, preparation methods, mechanical properties, corrosion behavior, and biocompatibility. After briefly introducing the development of Ti and Ti alloys for biomedical applications, this article reviews the design of β-type Ti alloys from the perspective of the molybdenum equivalency (Moeq) method and DV-Xα molecular orbital method. Based on these methods, a considerable number of β-type Ti alloys are developed. Although β-type Ti alloys have lower elastic moduli compared with other types of Ti alloys, they still possess higher elastic moduli than human bones. Therefore, porous β-type Ti alloys with declined elastic modulus have been developed by some preparation methods, such as powder metallurgy, additive manufacture and so on. As reviewed, β-type Ti alloys have comparable or even better mechanical properties, corrosion behavior, and biocompatibility compared with other types of Ti alloys. Hence, β-type Ti alloys are the more suitable materials used as implant materials. However, there are still some problems with β-type Ti alloys, such as biological inertness. As such, summarizing the findings from the current literature, suggestions forβ-type Ti alloys with bioactive coatings are proposed for the future development.
Perfluorooctane sulfonate (PFOS) is a prominent perfluorinated compound commonly found in the environment, known to pose various risks to human health. However, the removal of PFOS presents ...significant challenges, primarily due to the limited discovery of bacteria capable of effectively degrading PFOS. Moreover, single degradation bacteria often encounter obstacles in individual cultivation and the breakdown of complex pollutants. In contrast, microbial consortia have shown promise in pollutant degradation. This study employed a continuous enrichment method, combined with multiple co-metabolic substrates, to investigate a microbial consortium with the potential for PFOS degradation. By employing this methodology, we effectively identified a microbial consortium that demonstrated the capacity to reduce PFOS when exposed to an optimal concentration of methanol. The consortium predominantly comprised of Hyphomicrobium species (46.7%) along with unclassified microorganisms (53.0%). Over a duration of 20 days, the PFOS concentration exhibited a notable decrease of 56.7% in comparison to the initial level, while considering the exclusion of adsorption effects. Furthermore, by comparing the predicted metabolic pathways of the microbial consortium with the genome of a known chloromethane-degrading bacterium, Hyphomicrobium sp. MC1, using the KEGG database, we observed distinct variations in the metabolic pathways, suggesting the potential role of the unclassified microorganisms. These findings underscore the potential effectiveness of a "top-down" functional microbial screening approach in the degradation of stubborn pollutants.
Investigation on the shock-induced finite-thickness fluid-layer evolution is very desirable but remains a challenge because it not only involves both the Richtmyer–Meshkov instability (RMI) and the ...Rayleigh–Taylor instability (RTI), but also strongly depends on the waves reverberated inside the layer. We experimentally and theoretically examined the evolution of a shocked $\textrm {SF}_6$ gas layer with a finite thickness surrounded by air. Specifically, three kinds of quasi-one-dimensional $\textrm {SF}_6$ gas layers with different layer thicknesses are generated to study the wave patterns and interface motions, and six types of quasi-two-dimensional $\textrm {SF}_6$ gas layers with diverse layer thicknesses and amplitude combinations are created to explore the interfacial instabilities of the layer. When the initial fluid layer is thin, the two interfaces of the layer coalesce at a late time. The present study is the first to report that except for the RMI induced by a shock wave on the two interfaces, the rarefaction waves (RW) inside the fluid layer induce the additional RTI and decompression effect on the first interface, and the compression waves (CW) inside the fluid layer cause the additional Rayleigh–Taylor stabilisation (RTS) and compression effect on the second interface. A general one-dimensional theory is established to describe the motions of the two interfaces. Linear and nonlinear models are successfully established by considering the interface-coupling effect on the RMI and the additional interfacial instabilities induced by these waves inside the heavy fluid layer. The established models predict well the perturbation growths on the two interfaces at all regimes.
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