This Review summarizes the development of catalytic asymmetric dearomatization (CADA) reactions. The CADA reactions discussed herein include oxidative dearomatization reactions, dearomatization by ...Diels–Alder and related reactions, the alkylative dearomatization of electron‐rich arenes, transition‐metal‐catalyzed dearomatization reactions, cascade sequences involving asymmetric dearomatization as the key step, and nucleophilic dearomatization reactions of pyridinium derivatives. Asymmetric dearomatization reactions with chiral auxiliaries and catalytic asymmetric reactions of dearomatized substrates are also briefly introduced. This Review intends to provide a concept for catalytic asymmetric dearomatization.
Breaking up the party: Arenes can be transformed efficiently into enantiomerically enriched, versatile ring systems by catalytic asymmetric dearomatization reactions. Known reaction types include oxidative dearomatization, dearomatization by Diels—Alder reactions, alkylative dearomatization of electron‐rich arenes, transition‐metal‐catalyzed dearomatization reactions (see example), and cascade reaction sequences involving asymmetric dearomatization as the key step.
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Ultra‐flexible stretchable organic light‐emitting diodes (OLEDs) are emerging as a basic component of flexible electronics and human‐machine interfaces. However, the brightness and efficiency of ...stretchable OLEDs remain still far inferior to their rigid counterparts, owing to the scarcity of satisfactory stretchable electroluminescent materials. Herein, we explore a general concept based on the self‐confinement effect to dramatically improve the stretchability of elastomers, without affecting electroluminescent properties. The balanced rigid/flexible chain dynamics under self‐confinement significantly reduces the modulus of the elastomers, resulting in the maximum strain reaching 806 %. Ultra‐flexible stretchable OLEDs have been constructed based on the resulting ISEEs, achieving unprecedented high‐performance non‐blended stretchable OLEDs. The results suggest an effective molecular design strategy for highly deformable stretchable displays and flexible electronics.
Achieving high‐performance electroluminescence under large deformation remains a grand challenge. In this contribution, a general concept based on the self‐confinement effect has been proposed for the design and synthesis of non‐blended intrinsically stretchable electroluminescent elastomers (ISEEs). High‐performance non‐blended stretchable OLEDs have been constructed based on the resulting ISEEs.
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Designing and modulating the local structure of metal sites is the key to gain the unique selectivity and high activity of single metal site catalysts. Herein, we report strain engineering of curved ...single atomic iron‐nitrogen sites to boost electrocatalytic activity. First, a helical carbon structure with abundant high‐curvature surface is realized by carbonization of helical polypyrrole that is templated from self‐assembled chiral surfactants. The high‐curvature surface introduces compressive strain on the supported Fe−N4 sites. Consequently, the curved Fe−N4 sites with 1.5 % compressed Fe−N bonds exhibit downshifted d‐band center than the planar sites. Such a change can weaken the bonding strength between the oxygenated intermediates and metal sites, resulting a much smaller energy barrier for oxygen reduction. Catalytic tests further demonstrate that a kinetic current density of 7.922 mA cm−2 at 0.9 V vs. RHE is obtained in alkaline media for curved Fe−N4 sites, which is 31 times higher than that for planar ones. Our findings shed light on modulating the local three‐dimensional structure of single metal sites and boosting the catalytic activity via strain engineering.
Compressive strain engineering of curved single atomic iron‐nitrogen sites could boost the catalytic activity for electrocatalytic oxygen reduction reaction.
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Conspectus Dearomatization reactions serve as powerful methods for the synthesis of highly functionalized, three-dimensional structures starting with simple planar aromatic compounds. Among processes ...of this type, catalytic asymmetric dearomatization (CADA) reactions are attractive owing to the large number of aromatic compounds that are readily available and the fact that they enable direct access to enantiopure polycycles and spirocycles, which frequently are key structural motifs in biologically active natural products and pharmaceuticals. However, as a consequence of their high stabilities, arenes only difficultly participate in dearomatization reactions that take place with high levels of enantioselectivity. Transition-metal-catalyzed asymmetric allylic substitution reactions have been demonstrated to be powerful methods for enantioselective formation of C–C and C–X (X = O, N, S, etc.) bonds. However, the scope of these processes has been explored mainly using soft carbon nucleophiles, some hard carbon nucleophiles such as enolates and preformed organometallic reagents, and heteroatom nucleophiles. Readily accessible aromatic compounds have been only rarely used directly as nucleophiles in these reactions. In this Account, we present the results of studies we have conducted aimed at the development of transition-metal-catalyzed asymmetric allylic dearomatization reactions. By utilizing this general process, we have devised methods for direct dearomatization of indoles, pyrroles, phenols, naphthols, pyridines, and pyrazines, which produce various highly functionalized structural motifs bearing all-carbon quaternary stereogenic centers in a straightforward manner. In mechanistic investigations of the dearomatization process, we found that the five-membered spiroindolenines serve as intermediates, which readily undergo stereospecific allylic migration to form corresponding tetrahydro-1H-carbazoles upon treatment with a catalytic amount of TsOH. It is worth noting that no notable loss of the enantiomeric excess of the spiroindolenine derivatives takes place during the rearrangement process as a consequence of the intervention of a “three-center–two-electron”-type transition state, a proposal that has gained support from the results of DFT calculations. Equally intriguing, upon tuning of the electronic nature of the tethers, pyrroles or indoles undergo unprecedented Ir or Ru catalyzed intramolecular allylic alkylation promoted dearomatization/migration reactions. The operation of this novel reaction pathway provides additional information leading to a greater mechanistic understanding of the transition-metal-catalyzed enantioselective intramolecular functionalizations of pyrroles and indoles. The combined results of this effort provide not only methods for the efficient synthesis of highly enantioenriched fused and spiro polycycles but also novel strategies in the field of asymmetric catalysis.
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SUMMARY
Drought stress induces anthocyanin biosynthesis in many plant species, but the underlying molecular mechanism remains unclear. Ethylene response factors (ERFs) play key roles in plant growth ...and various stress responses, including affecting anthocyanin biosynthesis. Here, we characterized an ERF protein, MdERF38, which is involved in drought stress‐induced anthocyanin biosynthesis. Biochemical and molecular analyses showed that MdERF38 interacted with MdMYB1, a positive modulator of anthocyanin biosynthesis, and facilitated the binding of MdMYB1 to its target genes. Therefore, MdERF38 promoted anthocyanin biosynthesis in response to drought stress. Furthermore, we found that MdBT2, a negative modulator of anthocyanin biosynthesis, decreased MdERF38‐promoted anthocyanin biosynthesis by accelerating the degradation of the MdERF38 protein. In summary, our data provide a mechanism for drought stress‐induced anthocyanin biosynthesis that involves dynamic modulation of MdERF38 at both transcriptional and post‐translational levels.
Significance Statement
MdERF38 promotes anthocyanin biosynthesis by interacting with MdMYB1 and enhancing the binding of MdMYB1 to its target genes in response to drought stress. MdBT2 decreases drought‐induced anthocyanin accumulation by accelerating the degradation of MdERF38.
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Summary
Cold stress severely affects plant growth and yield. C‐repeat binding factors (CBFs) play important roles in the response to cold stress. In the present study, we identified an R2R3‐MYB ...transcription factor (TF) MdMYB23 from apple (Malus × domestic) using transcriptome analyses, which was notably induced in response to cold stress. Transgenic apple calli and Arabidopsis with overexpression of MdMYB23 exhibited increased cold tolerance. Electrophoretic mobility shift assay (EMSA) and transient expression assays indicated that MdMYB23 directly bound to the promoters of MdCBF1 and MdCBF2 and activated their expression. MdMYB23 interacted with the promoter of MdANR, a key modulator of proanthocyanidin biosynthesis, and activated its expression to promote proanthocyanidin accumulation and reactive oxygen species (ROS) scavenging. MdBT2 was identified as an MdMYB23‐interacting protein using yeast two‐hybrid (Y2H), pull‐down, and bimolecular fluorescence complementation (BiFC) assays. MdBT2 repressed cold tolerance and proanthocyanidin accumulation by promoting the degradation of MdMYB23 protein. Our findings shed light on the functions of MYB TFs and underlying mechanism in the modulation of plant cold tolerance.
Significance Statement
An apple R2R3‐MYB TF MdMYB23 increases cold tolerance and proanthocyanidin accumulation by directly activating the expression of MdCBF1/2 and MdANR. MdBT2 represses cold tolerance and proanthocyanidin accumulation by promoting the degradation of MdMYB23 protein.
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Abstract
Covalent organic frameworks (COFs) have served as a family of porous crystalline molecules for various promising applications. However, controllable synthesis of COFs with uniform morphology ...is paramount yet still remains quite challenging. Herein, we report self-templated synthesis of uniform and unique hollow spheres based on highly conjugated three-dimensional (3D) COFs with diameters of 500–700 nm. A detailed time-dependent study reveals the continuous transformation from initial nano sphere-like particles into uniform hollow spherical structures with Ostwald ripening mechanism. Particularly, the resulting 3D COF (3D-Sp-COF) is prone to transport ions more efficiently and the lithium-ion transference number (
t
+
) of 3D-Sp-COF reaches 0.7, which even overwhelms most typical PEO-based polymer electrolytes. Inspiringly, the hollow spherical structures show enhanced capacitance performance with a specific capacitance of 251 F g
−1
at 0.5 A g
−1
, which compares favorably with the vast majority of two-dimensional COFs and other porous electrode materials.
Summary
The plant hormone jasmonic acid (JA) is involved in the cold stress response, and the inducer of CBF expression 1 (ICE1)‐ C‐repeat binding factor (CBF) regulatory cascade plays a key role in ...the regulation of cold stress tolerance. In this study, we showed that a novel B‐box (BBX) protein MdBBX37 positively regulates JA‐mediated cold‐stress resistance in apple.
We found that MdBBX37 bound to the MdCBF1 and MdCBF4 promoters to activate their transcription, and also interacted with MdICE1 to enhance the transcriptional activity of MdICE1 on MdCBF1, thus promoting its cold tolerance.
Two JA signaling repressors, MdJAZ1 and MdJAZ2 (JAZ, JAZMONATE ZIM‐DOMAIN), interacted with MdBBX37 to repress the transcriptional activity of MdBBX37 on MdCBF1 and MdCBF4, and also interfered with the interaction between MdBBX37 and MdICE1, thus negatively regulating JA‐mediated cold tolerance. E3 ligase MdMIEL1 (MIEL1, MYB30‐Interacting E3 Ligase1) reduced MdBBX37‐improved cold resistance by mediating ubiquitination and degradation of the MdBBX37 protein.
The data reveal that MIEL1 and JAZ proteins co‐regulate JA‐mediated cold stress tolerance through the BBX37‐ICE1‐CBF module in apple. These results will aid further examination of the post‐translational modification of BBX proteins and the regulatory mechanism of JA‐mediated cold stress tolerance.
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An organic crystal of 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (pCBP) exhibits time‐dependent afterglow color from blue to orange over 1 s. Both experimental and computational data confirm that the color ...evolution results from well‐separated, long‐persistent thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) with different but comparable decay rates. TADF is enabled by a small S1–T1 energy gap of 0.7 kcal mol−1. The good separation of TADF and RTP is due to a 11.8 kcal mol−1 difference in the S0 energies of the S1 and T1 structures, indicating that apart from the excited‐state properties, tuning the ground state is also important for luminescence properties. This afterglow color evolution of pCBP allows its applications in anticounterfeiting and data encryption with high security levels.
Organic sunset: A time‐dependent afterglow color in a single‐component organic molecular crystal was observed. It originates from well‐separated, long‐persistent thermally activated delayed fluorescence and room‐temperature phosphorescence with different but comparable decay rates.
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The molecular mechanism of ABA‐promoted anthocyanin accumulation and fruit coloration is less known. Here, an apple bZIP transcription factor MdbZIP44 was identified to be a positive regulator in ...ABA‐promoted anthocyanin accumulation by interacting with MdMYB1 and enhancing its binding capacity to the promoters of downstream target genes. MdBT2 decreased ABA‐promoted anthocyanin accumulation by degrading MdbZIP44 protein.
Phytohormone abscisic acid (ABA) induces anthocyanin biosynthesis; however, the underlying molecular mechanism is less known. In this study, we found that the apple MYB transcription factor MdMYB1 activated anthocyanin biosynthesis in response to ABA. Using a yeast screening technique, we isolated MdbZIP44, an ABA‐induced bZIP transcription factor in apple, as a co‐partner with MdMYB1. MdbZIP44 promoted anthocyanin accumulation in response to ABA by enhancing the binding of MdMYB1 to the promoters of downstream target genes. Furthermore, we identified MdBT2, a BTB protein, as an MdbZIP44‐interacting protein. A series of molecular, biochemical, and genetic analysis suggested that MdBT2 degraded MdbZIP44 protein through the Ubiquitin‐26S proteasome system, thus inhibiting MdbZIP44‐modulated anthocyanin biosynthesis. Taken together, we reveal a novel working mechanism of MdbZIP44‐mediated anthocyanin biosynthesis in response to ABA.
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