Thermal C-C bond cleavage reactions allow the construction of structurally diverse molecular skeletons via predictable and efficient bond reorganizations. Visible light photoredox-catalyzed ...radical-mediated C-C bond cleavage reactions have recently emerged as a powerful alternative method for overcoming the thermodynamic and kinetic barrier of C-C bond cleavage in diverse molecular scaffolds. In recent years, a plethora of elegant and useful reactions have been invented, and the products are sometimes otherwise inaccessible by classic thermal reactions. Considering the great influence and synthetic potential of these reactions, we provide a summary of the state of art visible light-driven radical-mediated C-C bond cleavage/functionalization strategies with a specific emphasis on the working models. We hoped that this review will be useful for medicinal and synthetic organic chemists and will inspire further reaction development in this interesting area.
Recent urban transformations in China have led to critical reflections on the low-quality urban expansion in the previous decades and called for the making of vital and lively urban places. To date, ...limited research has been devoted to empirically testing the relationship between urban design, urban morphology, and urban vitality in Chinese cities. This paper employs new urban data and analytical methods and explores the relationship between urban morphology and urban vitality using regression models. Shenzhen, one of the largest and fastest growing cities in China, is selected as the case study. The regression analysis focuses on two morphological factors, density and typology, while controlling for the accessibility, functional mix, and size of individual blocks. The presence of small catering businesses is used as a proxy for urban vitality. The analysis suggests that both typology and density matter for urban vitality, with typology playing a more important role. More specifically, “block” and “strip” types tend to show significant positive effects on urban vitality. The implications for urban planning and design practices are discussed.
A large number of noncoding circular RNAs (circRNAs) with regulatory potency have been identified in animals, but little attention has been given to plant circRNAs.
We performed genome-wide ...identification of circRNAs in Oryza sativa and Arabidopsis thaliana using publically available RNA-Seq data, analyzed and compared features of plant and animal circRNAs.
circRNAs (12037 and 6012) were identified in Oryza sativa and Arabidopsis thaliana, respectively, with 56% (10/18) of the sampled rice exonic circRNAs validated experimentally. Parent genes of over 700 exonic circRNAs were orthologues between rice and Arabidopsis, suggesting conservation of circRNAs in plants. The introns flanking plant circRNAs were much longer than introns from linear genes, and possessed less repetitive elements and reverse complementary sequences than the flanking introns of animal circRNAs. Plant circRNAs showed diverse expression patterns, and 27 rice exonic circRNAs were found to be differentially expressed under phosphate-sufficient and -starvation conditions. A significantly positive correlation was observed for the expression profiles of some circRNAs and their parent genes.
Our results demonstrated that circRNAs are widespread in plants, revealed the common and distinct features of circRNAs between plants and animals, and suggested that circRNAs could be a critical class of noncoding regulators in plants.
A room‐temperature, visible‐light‐driven N‐centered iminyl radical‐mediated and redox‐neutral C−C single bond cleavage/radical addition cascade reaction of oxime esters and unsaturated systems has ...been accomplished. The strategy tolerates a wide range of O‐acyl oximes and unsaturated systems, such as alkenes, silyl enol ethers, alkynes, and isonitrile, enabling highly selective formation of various chemical bonds. This method thus provides an efficient approach to various diversely substituted cyano‐containing alkenes, ketones, carbocycles, and heterocycles.
A visible‐light‐driven room‐temperature N‐centered iminyl radical‐mediated and redox‐neutral C−C single bond cleavage/radical addition cascade reaction of oxime esters and unsaturated systems has been accomplished. The strategy tolerates a wide range of O‐acyl oximes and alkenes, silyl enol ethers, alkynes, and isonitrile. This method allows access to various cyano‐containing alkenes, ketones, carbocycles, and heterocycles.
A visible‐light‐driven, copper‐catalyzed three‐component radical cross‐coupling of oxime esters, styrenes, and boronic acids has been developed. Key steps of this protocol involve catalytic ...generation of an iminyl radical from a redox‐active oxime ester and subsequent C−C bond cleavage to generate a cyanoalkyl radical. Upon its addition to styrene, the newly formed benzylic radical undergoes coupling with a boronic‐acid‐derived ArCuII complex to achieve 1,1‐diarylmethane‐containing alkylnitriles.
Key steps of the visible‐light‐driven title reaction involve catalytic generation of an iminyl radical from a redox‐active oxime ester and subsequent C−C bond cleavage to give a cyanoalkyl radical. Upon its addition to styrene, a benzylic radical is formed that undergoes coupling with a boronic‐acid‐derived ArCuII complex to give 1,1‐diarylmethane‐containing alkylnitriles. The method features the use of readily available substrates and high functional‐group tolerance.
Photocatalytic CO2 reduction to CH4 requires photosensitizers and sacrificial agents to provide sufficient electrons and protons through metal‐based photocatalysts, and the separation of CH4 from ...by‐product O2 has poor applications. Herein, we successfully synthesize a metal‐free photocatalyst of a novel electron‐acceptor 4,5,9,10‐pyrenetetrone (PT), to our best knowledge, this is the first time that metal‐free catalyst achieves non‐sacrificial photocatalytic CO2 to CH4 and easily separable H2O2. This photocatalyst offers CH4 product of 10.6 μmol ⋅ g−1 ⋅ h−1 under non‐sacrificial ambient conditions (room temperature, and only water), which is two orders of magnitude higher than that of the reported metal‐free photocatalysts. Comprehensive in situ characterizations and calculations reveal a multi‐step reaction mechanism, in which the long‐lived oxygen‐centered radical in the excited PT provides as a site for CO2 activation, resulting in a stabilized cyclic carbonate intermediate with a lower formation energy. This key intermediate is thermodynamically crucial for the subsequent reduction to CH4 product with the electronic selectivity of up to 90 %. The work provides fresh insights on the economic viability of photocatalytic CO2 reduction to easily separable CH4 in non‐sacrificial and metal‐free conditions.
A metal‐free photocatalyst achieves high electronic selectivity for CH4 and facile separation of H2O2 in non‐sacrificial ambient conditions with only CO2 and H2O. This exceptional performance is attributed to a long‐lived oxygen‐centered radical in the excited electron acceptor, promoting the formation of a stabilized five‐member‐ring cyclic intermediate with lower energy, leading to an 90 % selectivity for the eight‐electron product CH4.
Localized surface plasmon resonance (LSPR) excitation of noble metal nanoparticles has been shown to accelerate and drive photochemical reactions. Here, LSPR excitation is shown to enhance the ...electrocatalysis of a fuel‐cell‐relevant reaction. The electrocatalyst consists of PdxAg alloy nanotubes (NTs), which combine the catalytic activity of Pd toward the methanol oxidation reaction (MOR) and the visible‐light plasmonic response of Ag. The alloy electrocatalyst exhibits enhanced MOR activity under LSPR excitation with significantly higher current densities and a shift to more positive potentials. The modulation of MOR activity is ascribed primarily to hot holes generated by LSPR excitation of the PdxAg NTs.
Plasmonic excitation of a palladium‐silver alloy nanotube electrocatalyst results in the enhancement of methanol oxidation reaction. Although photothermal heating of the electrochemical interface contributes to the enhancement, the primary mechanism involves hot holes generated by plasmonic excitation. Hot holes drive a methanol oxidation pathway that is complementary to electro‐oxidation.
The Friedel–Crafts acylation reaction, which belongs to the class of electrophilic aromatic substitutions is a highly valuable and versatile reaction in synthesis. Regioselectivity is predictable and ...determined by electronic as well as steric factors of the (hetero)arene substrate. Herein, a radical approach for the acylation of arenes and heteroarenes is presented. C−H acylation is achieved through mild cooperative photoredox/NHC radical catalysis with the cross‐coupling of an arene radical cation with an NHC‐bound ketyl radical as a key step. As compared to the classical Friedel–Crafts acylation, a regiodivergent outcome is observed upon switching from the ionic to the radical mode. In these divergent reactions, aroyl fluorides act as the acylation reagents in both the ionic as well as the radical process.
Regiodivergent benzoylation of 2‐methoxynaphthalene with benzoyl fluoride is presented using either Friedel–Crafts‐type chemistry to give selectively the 1‐isomer or cooperative NHC/photoredox catalysis to afford the 4‐isomer exclusively. Along with arenes, regiodivergent aroylation also works for heteroarenes.
Summary
Although starch degradation has been well studied in model systems such as Arabidopsis leaves and cereal seeds, this process in starchy fruits during ripening, especially in bananas, is ...largely unknown. In this study, 38 genes encoding starch degradation‐related proteins were identified and characterized from banana fruit. Expression analysis revealed that 27 candidate genes were significantly induced during banana fruit ripening, with concomitant conversion of starch‐to‐sugars. Furthermore, iTRAQ‐based proteomics experiments identified 18 starch degradation‐associated enzymes bound to the surface of starch granules, of which 10 were markedly up‐regulated during ripening. More importantly, a novel bHLH transcription factor, MabHLH6, was identified based on a yeast one‐hybrid screening using MaGWD1 promoter as a bait. Transcript and protein levels of MabHLH6 were also increased during fruit ripening. Electrophoretic mobility shift assays, chromatin immunoprecipitation and transient expression experiments confirmed that MabHLH6 activates the promoters of 11 starch degradation‐related genes, including MaGWD1, MaLSF2, MaBAM1, MaBAM2, MaBAM8, MaBAM10, MaAMY3, MaAMY3C, MaISA2, MaISA3 and MapGlcT2‐2 by recognizing their E‐box (CANNTG) motifs present in the promoters. Collectively, these findings suggest that starch degradation during banana fruit ripening may be attributed to the complex actions of numerous enzymes related to starch breakdown at transcriptional and translational levels, and that MabHLH6 may act as a positive regulator of this process via direct activation of a series of starch degradation‐related genes.
Removing organic micropollutants from water through photocatalysis is hindered by catalyst instability and substantial residuals from incomplete mineralization. Here, a novel water treatment ...paradigm, the unified heterogeneous self‐Fenton process (UHSFP), which achieved an impressive 32% photon utilization efficiency at 470 nm, and a significant 94% mineralization of organic micropollutants—all without the continual addition of oxidants and iron ions is presented. In UHSFP, the active species differs fundamentally from traditional photocatalytic processes. One electron acceptor unit of photocatalyst acquires only one photogenerated electron to convert into oxygen‐centered organic radical (OCOR), then spontaneously completing subsequent processes, including pollutant degradation, hydrogen peroxide generation, activation, and mineralization of organic micropollutants. By bolstering electron‐transfer capabilities and diminishing catalyst affinity for oxygen in the photocatalytic process, the generation of superoxide radicals is effectively suppressed, preventing detrimental attacks on the catalyst. This study introduces an innovative and cost‐effective strategy for the efficient and stable mineralization of organic micropollutants, eliminating the necessity for continuous chemical inputs, providing a new perspective on water treatment technologies.
This study introduces a novel active species, oxygen‐centered organic radicals, as a substitute for traditional transient active species in the photocatalytic degradation of organic micropollutants. Through integration with heterogeneous Fenton process, an impressive mineralization rate of up to 94% is attained, accompanied by exceptionally high photon utilization efficiency and stability.
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